Antibody-drug Conjugate Targeting Research Articles

The optimal management of relapsed and refractory Hodgkin lymphoma: post-brentuximab and checkpoint inhibitor failure.

The treatment landscape of classical Hodgkin lymphoma has changed dramatically over the past decade. Relapsed and refractory mainstay therapeutics such as brentuximab vedotin (BV) and checkpoint inhibitors (CPIs) are being moved to earlier lines of therapy. However, the treatment of patients who progress after BV and CPI remains a challenge. Allogeneic stem cell transplantation still plays an important role in this patient population as the only current treatment approach with curative potential. Unfortunately, not all patients are transplant candidates, and many will still relapse afterward. Cytotoxic chemotherapy and radiation may be used for symptom palliation or as a bridge to transplant. Targeted therapies, including the antibody drug conjugate, camidanlumab tesirine, and transcriptional agents such mammalian target of rapamycin and histone deacetylase inhibitors have shown some potential in patients with refractory disease. In addition, combination therapies with CPIs and novel agents may help overcome resistance to therapy. Clinical trials with cellular therapies, including chimeric antigen receptor T cells targeting CD30 and allogeneic natural killer cells combined with AFM13, a CD30/CD16a-bispecific antibody, have shown promising results. The availability of more therapeutic options for this patient population is eagerly awaited.

Mirvetuximab Soravtansine in FRα-Positive, Platinum-Resistant Ovarian Cancer

BackgroundMirvetuximab soravtansine-gynx (MIRV), a first-in-class antibody–drug conjugate targeting folate receptor α (FRα), is approved for the treatment of platinum-resistant ovarian cancer in the United States.MethodsWe conducted a phase 3, global, confirmatory, open-label, randomized, controlled trial to compare the efficacy and safety of MIRV with the investigator’s choice of chemotherapy in the treatment of platinum-resistant, high-grade serous ovarian cancer. Participants who had previously received one to three lines of therapy and had high FRα tumor expression (≥75% of cells with ≥2+ staining intensity) were randomly assigned in a 1:1 ratio to receive MIRV (6 mg per kilogram of adjusted ideal body weight every 3 weeks) or chemotherapy (paclitaxel, pegylated liposomal doxorubicin, or topotecan). The primary end point was investigator-assessed progression-free survival; key secondary analytic end points included objective response, overall survival, and participant-reported outcomes.ResultsA total of 453 participants underwent randomization; 227 were assigned to the MIRV group and 226 to the chemotherapy group. The median progression-free survival was 5.62 months (95% confidence interval [CI], 4.34 to 5.95) with MIRV and 3.98 months (95% CI, 2.86 to 4.47) with chemotherapy (P<0.001). An objective response occurred in 42.3% of the participants in the MIRV group and in 15.9% of those in the chemotherapy group (odds ratio, 3.81; 95% CI, 2.44 to 5.94; P<0.001). Overall survival was significantly longer with MIRV than with chemotherapy (median, 16.46 months vs. 12.75 months; hazard ratio for death, 0.67; 95% CI, 0.50 to 0.89; P=0.005). During the treatment period, fewer adverse events of grade 3 or higher occurred with MIRV than with chemotherapy (41.7% vs. 54.1%), as did serious adverse events of any grade (23.9% vs. 32.9%) and events leading to discontinuation (9.2% vs. 15.9%).ConclusionsAmong participants with platinum-resistant, FRα-positive ovarian cancer, treatment with MIRV showed a significant benefit over chemotherapy with respect to progression-free and overall survival and objective response. (Funded by ImmunoGen; MIRASOL ClinicalTrials.gov number, NCT04209855.)

A narrative review of antibody-drug conjugates in EGFR-mutated non-small cell lung cancer.

In the past 15 years, non-small cell lung cancer (NSCLC) treatment has changed with the discovery of mutations and the development of new targeted therapies and immune checkpoint inhibitors. Epidermal growth factor receptor (EGFR) was the first mutation in NSCLC to have a drug that was FDA-approved in 2013. Osimertinib, a third-generation tyrosine kinase inhibitor, is approved as first-line therapy for advanced NSCLC and in the adjuvant setting for Stage IB-IIIA resected NSCLC. However, resistance to osimertinib is inevitably an issue, and thus patterns of resistance to EGFR-mutated NSCLC have been studied, including MET amplification, EGFR C797X-acquired mutation, human epidermal growth factor 2 (HER2) amplification, and transformation to small cell and squamous cell lung cancer. Current management for EGFR-mutated NSCLC upon progression of EGFR TKI is limited at this time to chemotherapy and radiation therapy, sometimes in combination with the continuation of osimertinib. Antibody-drug conjugates (ADCs) are made up of a monoclonal antibody linked to a cytotoxic drug and are an increasingly popular class of drug being studied in NSCLC. Trastuzumab deruxtecan has received accelerated FDA approval in HER2-mutated NSCLC. ADCs offer a possible solution to finding a new treatment that could bypass the intracellular resistance mechanism. In this review article, we summarize the mechanism of ADCs and investigational ADCs for EGFR-mutated NSCLC, which include targets to MET amplification, HER3, Trop2, and EGFR, along with other ADC targets being investigated in NSCLC, and discuss future directions that may arise with ADCs in EGFR-mutated NSCLC.

Abstract B128: Preclinical characterization of ETx-22, a next-generation antibody drug conjugate (ADC) targeting nectin-4

Abstract Nectin-4 is overexpressed in a variety of cancers including urothelial, breast, cervix, lung and ovarian, with low level of expression in normal tissues. Enfortumab vedotin (EV), an anti-Nectin-4 ADC with a monomethyl auristatin (MMAE) payload, has been a significant advancement in the treatment of urothelial cancer. Yet, it is associated with important skin toxicity owing to the expression of nectin-4 in the skin, and peripheral neuropathy secondary to its toxin. We have developed a next-generation anti-nectin-4 ADC, ETx-22, which consists of a humanized IgG1, Fcg-silent antibody that is bound via maleimide-ß-glucuronide poly-sarcosine linkers to 8 molecules of the topoisomerase-I inhibitor, exatecan. Here, we describe the key pharmacological experiments, in-vivo efficacy and results from the good laboratory practice (GLP) toxicology studies. In-vitro studies have shown that the ETx-22 antibody exhibits a high affinity for tumor-expressed Nectin-4, but 10-fold lower affinity for nectin-4 expressed on skin, with significantly higher internalization in tumor cells. In-vivo efficacy was evaluated in various patient-derived xenograft models. ETx-22 was shown to be consistently superior to EV as well as chemotherapy, in a broad array of tumors, including urothelial, ovarian, cervical and triple negative breast cancer irrespective of the degree of nectin-4 expression. Antitumor activity was also observed in MMAE-resistant models. GLP studies evaluated repeated doses of ETx-22 in cynomolgus monkeys at two doses, 10 and 20 mg/kg. The treatment was administered as 30-minute intravenous infusions once every 2 weeks for a total of three cycles. The ETx-22 antibody alone was also evaluated at 20 mg/kg. Both ETx-22 doses were well tolerated and all animals survived up to scheduled euthanasia. The common observation at both doses was mild multifocal skin hyperpigmentation, which was reversible. No skin rash or pruritus was reported. Mild transient decrease in red blood cells was observed in between cycles. No gastrointestinal toxicities were observed. No signs of interstitial lung disease or eye toxicity were detected. Based on these findings, the highly non- severely toxic dose (HNSTD) is at least 20 mg/kg. The half-life of ETx-22 ranged from 3.36 – 3.6 days. In conclusion, preclinical and pharmacological shows that ETx-22 has better tolerance, longer half-life, and higher efficacy to EV. No skin rash was reported in toxicology studies. A first in human study (EXCEED) is planned to start in 2023. Citation Format: Hatem Azim, Florence Lhospice, Xavier Preville, Joanna Fares, Marc Lopez, Emerence Crompot, Emmanuelle Josselin, Remy Castellano, Maria Wehbeh, Yves Collette, Jack Elands, Daniel Olive. Preclinical characterization of ETx-22, a next-generation antibody drug conjugate (ADC) targeting nectin-4 [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B128.

Abstract B133: Anti-tumor efficacy of GMF-1A3-MMAE, an antibody drug conjugate targeting cell surface cleaved Amphiregulin in endocrine-resistant breast cancer

Abstract The Epidermal Growth Factor Receptor ligand, Amphiregulin, is a key proliferative effector of estrogen receptor signaling in breast cancer and also plays a role in other malignancies. Amphiregulin is a single-pass transmembrane protein proteolytically processed by TACE/ADAM17 to release the soluble EGFR ligand, leaving a residual transmembrane stalk that is subsequently internalized. Here, we describe the development of an antibody drug conjugate, GMF-1A3-MMAE, targeting an AREG neo-epitope revealed following ADAM17-mediated cleavage. The antibody does not interact with uncleaved Amphiregulin, providing a novel means of targeting cells with high rates of Amphiregulin shedding. Using fluorescent dye conjugation, we demonstrated that the antibody is internalized by cancer cells in a manner dependent on the presence of cell surface cleaved Amphiregulin. Antibodies conjugated with monomethyl auristatin E (MMAE) were cytotoxic in vitro and induced rapid regression of established breast tumor xenografts in immunocompromised mice. We further demonstrate that these antibodies recognize the Amphiregulin neo-epitope in formalin fixed paraffin embedded tumor tissue, suggesting their utility as a companion diagnostic for patient selection. A pan-cancer tissue microarray analysis indicates that the target is commonly detected at high levels (&amp;gt; 50% of cases) in breast, prostate, liver and lung cancer. In normal tissue microarrays, cleaved Amphiregulin was generally detected at moderate levels in several tissues with only 7 of 93 tissue cores having levels comparable to the high levels commonly found in tumors. These data suggest therapeutic opportunities for GMF-1A3-based ADCs in multiple malignancies, however the broad off-tumor detection of cleaved Amphiregulin suggest linker/payload optimization may be necessary for an adequate therapeutic window. Citation Format: Kristopher A Lofgren, Paraic A Kenny. Anti-tumor efficacy of GMF-1A3-MMAE, an antibody drug conjugate targeting cell surface cleaved Amphiregulin in endocrine-resistant breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B133.

Abstract C112: L1CAM targeting antibody-based therapy as a novel approach for L1CAM positive lymphomas

Abstract Background. L1CAM (L1 Cell Adhesion Molecule) is a glycoprotein identified as a key mediator of the metastatic process in many different tumor types. It facilitates the detachment of tumor cells from the primary tumor and their entry into the circulation. By promoting cell-cell interactions, it also directly stimulates the colonization of distant organs by circulating tumor cells. The expression and role of L1CAM in B and T cell lymphomas is poorly explored. The aim of this project was to evaluate L1CAM expression in different subtypes of lymphoma and its role as novel therapeutic target. Methods. RNA was extracted with Monarch Total RNA Miniprep Kit and qPCR performed with QuantiFast SYBR Green RT-PCR. For flow cytometry (FACS), cells were stained either with anti-L1CAM antibody or isotype control at a dilution of 1:1000. For immunohistochemistry (IHC) samples were stained for 20 minutes at a dilution of 1:100. For direct killing assay, cells were exposed six days to compounds, followed by MTT assay. Antibody dependent cellular cytotoxicity (ADCC) was performed with ADCC Reporter Bioassay (Promega). Results. L1CAM mRNA expression was assessed in 59 lymphoma cell lines. Whereas expression in most cell lines appeared low, a subgroup of cells displayed high to very high expression of L1CAM. Surface L1CAM expression was confirmed by FACS. L1CAM mRNA and protein expression levels correlated well across the cell lines and revealed that Sezary syndrome (SS) cell lines displayed the highest expression, followed by mantle cell lymphoma (MCL) and activated B cell diffuse large B cell lymphoma (ABC DLBCL) cell lines. By IHC L1CAM expression was assessed on different tissue microarrays covering multiple lymphoma subtypes; L1CAM expression was observed especially in a subset of cutaneous T-cell lymphoma and MCL. The data confirmed the findings in lymphoma cell lines. Anti-L1CAM monoclonal antibody (mAb) and four L1CAM targeting antibody drug conjugates (ADCs) (ADC1, ADC4, ADC5, ADC6), differing for the linker and payload, were tested in L1CAM positive and negative cell lines. mAB did not show any sign of direct antitumoral activity. Among ADCs, highest activity was observed with ADC6 (SG3199 payload), followed by ADC4 (MMAE payload). ADC1 and ADC5 (also containing MMAE as payload) showed limited activity. ADC6 showed the best correlation between killing activity and L1CAM expression levels, indicating a high level of target specific activity. The in vitro activity of ADC4 and ADC6 was validated in an in vivo xenograft using the MCL cell line Z138. Finally, mAb and a bispecific anti-CD3/L1CAM antibody were tested for their ability to induce ADCC. Both induced strong intracellular signaling in the reporter cell line upon co-incubation with L1CAM expressing lymphoma cells, indicative of the induction of killing activity in effector cells. Conclusions. In summary, we have demonstrated the in vitro and in vivo activity of anti-L1CAM antibody-based therapeutic approach as novel treatment for L1CAM positive lymphomas. Citation Format: Filippo Spriano, Giulio Sartori, Luca Aresu, Luciano Cascione, Elisa Civanelli, Afua A. Mensah, Chiara Tarantelli, Stefano Pileri, Flavio Mehli, Gunther Spohn, Francesco Bertoni. L1CAM targeting antibody-based therapy as a novel approach for L1CAM positive lymphomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C112.

Abstract C120: Antitumor effect of HER3-DXd, an antibody-drug conjugate targeting HER3, in gastric cancer cell lines

Abstract Background: HER3, one of the HER family members, is expressed across various solid tumors and known to be an important oncogenic driver. HER3-DXd is an antibody-drug conjugate (ADC) that combines patritumab, an anti-HER3 antibody, and deruxtecan, a topoisomerase 1 inhibitor payload through peptide cleavable linker system. HER3-DXd has been shown to have anti-tumor effects in breast, non-small cell lung, and colorectal cancers, in vitro and in vivo, and is being evaluated in phase 2 and phase 3 clinical trials. However, the effect of HER3-DXd in gastric cancer and the mechanism of sensitivity are largely unknown. Methods: Seven gastric cancer cell lines were used (NUGC-4, NCI-N87, SNU-601, SNU-216, SNU-638, SNU-668, and MKN-45). Colony formation assay (CFA) was performed with increasing concentration of HER3-DXd (doses range: 0-100 nM) for 14 days. Cell cycle change and internalization of HER3-DXd bound to HER3 protein in the cell membrane were seen by flow cytometry analysis. Apoptotic cell death was assessed by Annexin-V assay. DNA strand breaks were examined using alkaline comet assay. DNA damage accumulation and TOP1-cleavage complexes (TOP1ccs) were identified using immunofluorescence assay. Results: Seven gastric cancer cell lines showed heterogeneous mRNA expression of HER2 and HER3, which correlated with protein expression. Three cell lines with different sensitivities to HER3-DXd were selected based on CFA. SNU-601 was sensitive to U3-1402 (IC50 value: 11.01 nM), SNU-638 was less sensitive (IC50 value: 50.04 nM), and SNU-668 was insensitive (IC50 value &amp;gt;100 nM). HER3-DXd increased the Annexin-V positive population and the sub-G1 population in SNU-601 and SNU-638 cells. Moreover, cleavage of PARP and caspase-3 were increased in SNU-601 and SNU-638 cells, but not in SNU-668 cells. HER3-DXd was efficiently internalized within 1 hour in all three cells, regardless of their sensitivities to HER3-DXd. Signal transduction through the HER2 and HER3 receptors, which mediates a PI3K-AKT signaling pathway, was inhibited in SNU-601 cells. In SNU-601 and SNU-638 cells, HER3-DXd increased the expression of γ-H2AX and length of the comet tails, which indicate DNA damage. HER3-DXd also induced topoisomerase 1 cleavage complexes (TOP1ccs) in SNU-601 and SNU-638 cells. In contrast, TOP1cc was not observed in resistant SNU-668 cells. Conclusion: HER3-DXd induced formation of TOP1ccs, subsequent DNA damage, and apoptotic cell death in sensitive cell lines, but not in an insensitive cell line. These data indicate that internalized HER3-DXd causes accumulation of DNA damage through TOP1cc formation, which leads to apoptotic cell death in gastric cancer. Citation Format: Hae Min Hwang, So Hyeon Kim, Sujin Ham, Minyoung Lee, Youlim Noh, Yu-Jin Kim, Changyun Lee, Jinyoung Kim, Dae-Won Lee, Kyung-Hun Lee, Seock-Ah Im. Antitumor effect of HER3-DXd, an antibody-drug conjugate targeting HER3, in gastric cancer cell lines [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C120.

A novel human single-domain antibody-drug conjugate targeting CEACAM5 exhibits potent in vitro and in vivo antitumor activity.

Leveraging the specificity of antibody to deliver cytotoxic agent into tumor, antibody-drug conjugates (ADCs) have become one of the hotspots in the development of anticancer therapies. Although significant progress has been achieved, there remain challenges to overcome, including limited penetration into solid tumors and potential immunogenicity. Fully human single-domain antibodies (UdAbs), with their small size and human nature, represent a promising approach for addressing these challenges. Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) is a glycosylated cell surface protein that rarely expressed in normal adult tissues but overexpressed in diverse cancers, taking part in tumorigenesis, progression, and metastasis. In this study, we investigated the therapeutic potential of UdADC targeting CEACAM5. We performed biopanning in our library and obtained an antibody candidate B9, which bound potently and specifically to CEACAM5 protein (KD = 4.84 nM) and possessed excellent biophysical properties (low aggregation tendency, high homogeneity, and thermal stability). The conjugation of B9 with a potent cytotoxic agent, monomethyl auristatin E (MMAE), exhibited superior antitumor efficacy against CEACAM5-expressing human gastric cancer cell line MKN-45, human pancreatic carcinoma cell line BxPC-3 and human colorectal cancer cell line LS174T with IC50 values of 38.14, 25.60, and 101.4 nM, respectively. In BxPC-3 and MKN-45 xenograft mice, administration of UdADC B9-MMAE (5 mg/kg, i.v.) every 2 days for 4 times markedly inhibited the tumor growth without significant change in body weight. This study may have significant implications for the design of next-generation ADCs.

Debio 1562M, a Next Generation Antibody Drug Conjugate (ADC) Targeting CD37 for AML and MDS Treatment

CD37 is a trans-membrane protein specifically expressed on normal hematopoietic tissues such as B cells, neutrophils and macrophages, and has demonstrated roles in adhesion, cell migration (de Winde et al, 2018; Wee et al, 2015), survival and apoptotic signals (Lapalombella et al, 2012). Increased expression of CD37 has been observed in various hematological cancers such as lymphomas, Chronic Lymphocytic Leukemia (CLL) and Acute Myeloid Leukemia (AML) (Beckwith et al, 2014; Deckert et al, 2013; Pereira et al, 2015; Yan et al, 2021). Higher expression of CD37 was also associated with poor patient outcome in AML (Zhang et al, 2020; Larkin et al, ASH 2018). Debio 1562M is a second-generation novel ADC directed against CD37 and including Debiopharm's proprietary Multilink cleavable linker-payload technology. Multilink improves manufacturing to achieve homogenous high drug antibody ratio while retaining excellent solubility as well as favorable biologic characteristics with preserved internalization kinetics on target cells. Debio 1562M is conjugated to 8 molecules of a tubulin-binding agent and despite cleavable linker that ensure effective intracellular delivery of toxic payload, we show sustained plasma stability in vitro and in vivo with no premature extracellular release. In this work, we report Debio 1562M specificity and potent antitumor activity in multiple AML models both in vitro and in vivo. First, in our in vitro cytotoxicity assay, Debio 1562M displayed nano- to picomolar anti-proliferative activity in both AML cell lines and primary samples. Out of 30 primary samples tested, 20 were sensitive to Debio 1562M with IC50 ranging from 1 to 10nM, this regardless of their mutation status, subtype or medical history. Interestingly, we observed that AML cells have high internalization capability and therefore relatively low levels of surface CD37 is sufficient for cytotoxic activity. The specificity of Debio 1562M was demonstrated by using 3 different CD37 knock out AML cell lines which were generated by CRISPR-Cas9 technology. Parental and CD37 KO cells were treated for 72h with a dose range of Debio 1562M and viability was measured (Figure 1). While Debio 1562M has an IC50 below 1nM in all 3 parental cell lines, its activity is reduced by more than 2 log in the KO cell lines. In vivo, in 3 different AML cell line xenograft mouse models, a single injection of Debio 1562M at 5mg/kg induced complete tumor regression and all mice remained alive at study termination, more than 60 days after treatment, except one mouse in one model. In a patient derived xenograft (PDX) model, the same dose of Debio 1562M significantly reduced tumor burden in blood and bone marrow with sustained activity 42 days after treatment (37% and 98% of blasts in blood and bone marrow respectively in control animals versus 0% and 3% in treated mice, pvalue&amp;lt;0.001). Furthermore, we evaluated the activity of Debio 1562M over venetoclax and azacytidine combination in the MV4-11 Luciferase xenografted mouse model. NCG mice were inoculated with 1x10 7 cells in the tail vein and randomization in groups of 8 mice was performed 14 days later. Mice received either one administration of Debio 1562M at 5mg/kg or a combination of venetoclax (QDx14 100mg/kg) and azacitidine (QDx5 3,5mg/kg). Complete regression of the tumor was observed in all mice after Debio 1562M administration and all mice survived at study termination, 75 days after treatment while none survived after 56 days when treated with venetoclax and azacitidine combination (Figure 2). The toxicology profile of Debio 1562M in mice showed expected clinical signs related to the payload's off target toxicity but with a significant safety margin. Interestingly, no peripheral neuropathy symptoms were detected, as commonly observed for this class of payload. Additionally, Multilink TM-payload construct alone was not associated with any signs of toxicity. On-target toxicity profile couldn't be evaluated as Debio 1562M isn't cross reactive with mouse CD37, however 1 st generation CD37 ADC has already demonstrated safety and tolerability in Phase 1 and 2 clinical trials.Overall, our data confirm the relevance of CD37 targeting for AML treatment. The excellent antitumor activity and tolerability of Debio 1562M in several pre-clinical models now pave the way for upcoming clinical development.

Efficacy and Safety of Modified BV-AVD-R Regimen in Chinese Children with Previously Untreated Intermediate- and High-Risk Classical Hodgkin's Lymphoma: An Open Label, Non-Randomized, Single-Arm, Phase 2 Study from Single Center

Introduction Classical Hodgkin lymphoma (cHL) accounts for about 4.8% of childhood malignant neoplasm, and the incidence of cHL in Chinese children and adolescents (0-19 years old) is about 1.78/million, which is a group of relatively low malignancy and curable tumor. With the prolonged survival of children and adolescents with cHL, the incidence of muscle and skeletal malformations, lung and cardiovascular diseases, infertility and secondary tumors increased significantly during long-term follow-up. Therefore, the goal of childhood cHL treatment is to achieve and maintain the high efficacy while reduce the treatment-related complications. Brentuximab vedotin (BV), an antibody-drug conjugates (ADC) targeting CD30, has been evaluated well in American children and some regions, but no clinical studies to explore the efficacy and safety of BV in Chinese children with cHL. Therefore, the objective of our study is to evaluate the efficacy (objective response rate, including CR and PR) and safety (short - and long-term safety) of modified BV-AVD-R regimen (Brentuximab vedotin + Rituximab + Doxorubicin + Vinblastine + Dacarbazine) in Chinese children with previously untreated intermediate- and high-risk classical HL. Methods This study is a prospective study with period from October 2022 to December 2024, and planned to enroll 44 children with newly diagnosed intermediate- and high-risk classical HL. All patients will undergo PET/CT at the time of initial diagnosis and after 2 cycles of modified BV+R+AVD regimen to determine early response. Rapid early responders (RER) defined as CR after 2 cycles of therapy. Slow early responders (SER) defined as no CR (partial response (PR) or stable disease) after 2 cycles of therapy. Intermediate-risk patients were stage IA bulk/E, IB, IIA bulk/E, IIB, and IIIA. High-risk patients were stage IIB bulk/E, IIIA bulk/E, IIIB, and IVA/B(Figure 1). The primary endpoints include ORR (CR+PR) and adverse events. The secondary endpoints include progression-free survival (PFS), event-free survival (EFS) and overall survival (OS) at 6 months and 1 year. Results From October 2022 to July 2023, a total of 14 children with newly diagnosed classical HL were enrolled, and 12 patients who had completed at least 2 cycles treatment were eligible for evaluation. 9 boys and 3 girls were enrolled, with median age of 10 years (range 7-15 years). Risk group: 9 patients in high-risk group, 3 patients in intermediate-risk group; Clinical stage: 5 patients in stage IIIA, 2 patients in stage IIIB, 4 patients in stage IVA, and 1 patient in stage IVB. Pathologic subtype: 7 patients of nodular sclerosis type and 5 patients of mixed cell type. Treatment: A total of 33 cycles of modified BV+R+AVD regimen were completed, with 66 doses of BV. The median number of treatment cycles was 3 cycles (range 2-6). 11 patients achieved CR and 1 patient achieved PR after 2 cycles, and the ORR was 100% (12/12). As of July 28, 2023, 4 children had stopped follow-up and achieved CR without sequential radiotherapy. The median follow-up was 6 months (range 2-10). 12 patients successfully received and completed BV infusions, mild nausea and vomiting (10/12), alopecia (9/12) and sensory abnormalities (3/12) were observed. Serious adverse events were mainly grade ≥3 blood cell abnormalities (10/12), none of which had an impact on the treatment flow. No patient withdrew from the study, indicating good adherence to the regimen. Conclusion The risk-adapted modified BV+R+AVD regimen for newly diagnosed Chinese children and adolescents with classical HL showed favorable treatment outcomes with good early response rate and sustained response rate. The regimen could also reduce sequential radiotherapy and demonstrated well safety and tolerability. The study is still ongoing.

Splicing Polymorphism rs12459419 Modulates Antibody-Bound Internalization of CD33 Isoforms

Background: While the standard regimen for AML has been intense chemotherapy followed by stem-cell transplantation (SCT), addition of immunotherapeutics such as gemtuzumab ozogamicin (GO) to this has shown to improve outcomes in multiple clinical trials. Since these trials, GO has been added to the National Comprehensive Cancer Network (NCCN) practice guidelines for use in AML therapy (NCCN., 2018). GO is a humanized monoclonal antibody conjugated to calicheamicin and targets the cell surface antigen CD33, observed on most AML blasts. Upon binding to GO, CD33 is internalized and the subsequent release of calicheamicin mediates cytotoxicity. CD33 contains two extracellular domains: IgV and IgC, the IgV domain is coded by CD33 exon 2 and is the binding site for GO. A splicing SNP, rs12459419 (C&amp;gt;T; A14V) in exon 2 results in a shorter isoform (CD33-D2) and has been previously associated with CD33 abundance on cell surface as well as clinical benefit from GO addition to standard chemotherapy. Patients with CC genotype (~50% of the cohort) expressed full length CD33 (CD33-FL) and benefited significantly from GO. However, heterozygous CT and homozygous TT genotype groups did not derive the same benefit. These results were perplexing as CT genotype group had intermediate levels of CD33-FL and CD33-D2 isoforms (Lamba et al., 2017). It is hypothesized that lack of IgV domain in CD33-D2 and putative CD33-FL/CD33-D2 dimerization prevents GO binding and subsequent internalization in rs12459419 CT/TT genotype cells, however this has never been tested. We have generated novel antibodies directed against the IgC domain that recognizes CD33-D2 in AML cell lines as well as primary AML cells (Gbadamosi et al., 2021) thus facilitating testing the above indicated hypothesis. Objective: In this study, we first tested the ability of antibody-bound CD33-D2 to internalize, followed by impact of the internalization status of CD33-FL and CD33-D2 in cells co-expressing both isoforms along with the concomitant impact on GO induced cytotoxicity. Methods: Using pMXs retroviral particles encoding CD33-FL or CD33-D2, we engineered CRISPR/Cas9 mediated CD33 KO in AML cell lines to overexpress either one or both CD33 isoforms to mimic cells expression varying proportions of CD33-FL/CD33-D2. Internalization of either CD33-FL or CD33-D2 over a duration of 4 hours in the presence of antibodies recognizing either of the two isoforms was performed. Cells were labeled with unconjugated mouse anti-CD33-FL P67.6 or anti-CD33-D2 HL2541 antibody on ice and incubated at 37°C for 0-4 hours, followed by staining with mouse anti-mouse IgG antibody conjugated with biotin. Surface CD33-FL or CD33-D2 was then detected using streptavidin-FITC conjugate. Percentage antibody-bound CD33-FL or CD33-D2 internalization was expressed as change in FITC MFI between each time point incubated and cells kept at 0°C post CD33 antibody labeling. Results: While P67.6-bound-CD33-FL internalized as expected in AML cell lines expressing CD33-FL only (Fig. 1A), we show for the first time that HL2541-bound-CD33-D2 also internalizes upon antibody binding in cell lines expressing CD33-D2 isoform only (Fig. 1B). In AML cell lines co-expressing both CD33-FL and CD33-D2 isoforms, a &amp;gt;2.5-3 fold decrease in this antibody-bound internalization was observed for each isoform (Figs. 1C and D). In response to GO exposure for 48 hours, cells co-expressing both CD33-FL and CD33-D2 isoforms had 7-9.5-fold higher IC50 values (233 nmol and 277 nmol) compared to cells expressing only CD33-FL (33.19 nmol and 29 nmol) (Figs. 1E and F). As expected, cells expressing CD33-D2 only did respond to GO. Discussion: Our finding that antibody-bound CD33-D2 internalizes like CD33-FL adds a novel piece of evidence in understanding the biology of this variant isoform and opens opportunities to develop antibody drug conjugate (ADC) such as GO using CD33-D2 antibody. This new CD33-D2 targeting ADC will provide a treatment option in patients with TT genotypes. Our results also provide a mechanistic insight on the previous clinical observation showing lack of benefit from GO in patients heterozygous for the splicing SNP. Our ongoing studies are focused on validating this result using live cell imaging and efforts towards design of new ADC or T cell engagers using CD33-D2 antibody. The study was supported by Leukemia Lymphoma Society, UFHealth Cancer Center, and the Frank A. Duckworth Endowment.

Trem-Cel, a CRISPR/Cas9 Gene-Edited Allograft Lacking CD33, Shows Rapid Primary Engraftment with CD33-Negative Hematopoiesis in Patients with High-Risk Acute Myeloid Leukemia (AML) and Avoids Hematopoietic Toxicity during Gemtuzumab Ozogamicin (GO) Maintenance Post-Hematopoietic Cell Transplant (HCT)

Background: Allogeneic HCT is the standard of care for eligible patients with AML harboring high-risk features such as adverse-risk cytogenetics or measurable residual disease (MRD), however, the majority of these patients still relapse post-HCT and have very poor outcomes. The use of maintenance therapies intended to control post-HCT relapse is often limited by hematopoietic toxicity towards normal engrafted cells. GO (tradename: Mylotarg TM) is an anti-CD33 antibody-drug conjugate targeting CD33+ AML, but its use is limited by on-target, off-tumor hematopoietic toxicity toward CD33+ myeloid and progenitor cells. Tremtelectogene empogeditemcel (trem-cel; formerly VOR33) is a hematopoietic stem and progenitor cell product, manufactured from CD34+ cells isolated from a patient-matched donor, that has been modified by CRISPR/Cas9 gene-editing to lack CD33. Trem-cel was developed to protect normal hematopoietic cells from post-HCT CD33-directed therapies and allow exclusive targeting of residual leukemia. Methods: VBP101(NCT04849910) is a first-in-human Phase 1/2 open-label multicenter trial to establish the safety of using trem-cel as a donor allograft for CD33+ AML patients who are at high risk of relapse and undergoing myeloablative HCT followed by treatment with GO. Eligible patients (18-70 y) must have CD33+ AML with high-risk features for relapse, such as adverse-risk cytogenetics or MRD, and a 10/10 human leukocyte antigen (HLA)-matched related or unrelated donor. Donors undergo mobilization with G-CSF and plerixafor prior to apheresis. Trem-cel is manufactured from isolated CD34+ cells and cryopreserved. Patients undergo either a busulfan- or TBI-based myeloablative conditioning regimen prior to transplantation with trem-cel. After engraftment and recovery of a sufficient CD33-negative neutrophil count, patients begin maintenance therapy with GO in a 3+3 dose escalation strategy starting at 0.5 mg/m 2 every 28d for 4-8 cycles. Results: To date, 6 patients between 32-68 y (median 63.5 y) have been treated with trem-cel at a median dose of 5.2 x 10 6 CD34+ cells/kg (2.6 - 7.6) and CD33 editing efficiency of 88% (80 - 91). Primary neutrophil engraftment occurred in all patients after a median of 10 days (9 - 11) and platelet recovery occurred after a median of 16 days (15-22) excluding one patient with documented anti-platelet antibody (Fig 1). At the day 28 assessment, full peripheral blood (PB) myeloid chimerism was achieved in all patients and CD33 expression by flow was absent in a median of 94% of neutrophils (86-99) and 92% of monocytes (82 - 94), respectively. Comparable CD33 edits were detected in donor cells across myeloid and lymphoid lineages. GO dosing is ongoing at 0.5 mg/m 2 dose and neutrophil and platelet counts remain stable, suggesting protection from GO-mediated hematotoxicity. Following the 0.5 mg/ m 2 dose, the exposures of GO were predictively higher in the context of CD33-negative hematopoiesis relative to GO doses of 1-2 mg/m 2 (C max) and 4-5 mg/m 2 (AUC), respectively, in CD33+ relapsed/refractory AML patients. During GO dosing, the percent of CD33-negative cells increased in the PB and bone marrow (BM) across cell lineages consistent with enrichment of edited donor cells. Patients are followed for safety, hematologic protection from GO, disease status, and persistence of CD33 editing.

Targeted Immunotherapy and Checkpoint Blockade in Children, Adolescents, and Young Adults with Lymphoma: Radical Hodgkin Cohort

Background: Significant chronic health conditions continue to increase over time among pediatric, adolescent, and young adult (CAYA) classical Hodgkin lymphoma (cHL) survivors. Targeting the tumor microenvironment (TME) and tumor-specific antigens are emerging as effective and safe treatments for cHL patients which may help reduce toxicity. Recently, we completed a phase 2 trial evaluating the use of an antibody-drug conjugate targeting CD30 (brentuximab vedotin, Bv) and an anti-CD20 antibody targeting regulatory B-cells (rituximab, RTX) added to risk-adapted chemotherapy in newly diagnosed cHL CAYA patients. The combination was safe and resulted in significant reduction to toxic chemotherapy and radiation therapy (RT), while keeping superior outcomes (5-year OS/EFS 100%) [Hochberg/Cairo, JITC 2022]. Adding the checkpoint inhibitor nivolumab to chemoimmunotherapy with RTX + Bv may allow further anthracycline dose reduction and reduce the need for RT in intermediate-/high-risk cHL in CAYA. Methods: This is a multicenter study for patients with intermediate- and high-risk cHL. Intermediate-risk cHL patients receive 2 cycles of Bv, doxorubicin, vinblastine, dacarbazine, and RTX (Bv-AVD-R). Rapid early responders (RER) or slow early responders (SER) by FDG-PET scan receive 2 or 4 cycles of Bv, vinblastine, dacarbazine, nivolumab, and RTX (Bv-NVD-R), respectively without further anthracycline. High-risk cHL patients receive 2 cycles of Bv-AVD-R. RERs by FDG-PET scan receive 4 cycles of Bv-NVD-R; SERs receive 2 cycles of Bv, nivolumab, doxorubicin, vinblastine, dacarbazine and RTX (Bv-NAVD-R), followed by 4 cycles of Bv-NVD-R. RT will only be given to patients not achieving CR at the end of therapy. Results: Nine patients have received at least one dose of nivolumab to date and are included in the safety analysis, including 4 intermediate- and 5 high-risk patients. All 9 of these patients have completed interim FDG-PET following 2 cycles of Bv-AVD-R to evaluate early response status. All intermediate-risk patients and 3 high risk patients evaluated to date have been RER, achieving a complete response (CR) at interim FDG-PET. Two high-risk patients have been SER, with a partial response (PR) at interim FDG-PET. Both SER patients achieved a CR following the 6 additional cycles of chemotherapy as detailed above. No patients have required radiation therapy. Accrual is ongoing. We have completed the planned nivolumab safety run in phase. There have been no unexpected grade III/IV adverse events secondary to nivolumab and no dose-limiting toxicities. Conclusions: Targeting the Hodgkin Reed-Sternberg cell as well as the TME (regulatory B-cells) and PD1/PD-L1 axis is a promising approach in CAYA with cHL. (NCT05253495).

Impact of Long-Term Treatment with Belantamab Mafodotin on Safety and Efficacy Outcomes in Patients with Relapsed/Refractory Multiple Myeloma in DREAMM-3

Introduction: DREAMM-3 (NCT04162210) is a randomized study comparing single-agent belantamab mafodotin, a first-in-class antibody-drug conjugate targeting B-cell maturation antigen, to a standard-of-care regimen, pomalidomide plus dexamethasone (Pd). This post-hoc analysis from the DREAMM-3 trial evaluated the safety and efficacy of long-term treatment (≥52 weeks) with belantamab mafodotin compared with Pd, as well as the effects of dose modifications, in adult patients with relapsed/refractory multiple myeloma (RRMM) at third line of therapy or later. Methods: Patients were randomized (2:1) to belantamab mafodotin 2.5 mg/kg intravenously once every 3 weeks (Q3W; 21-day cycle) or pomalidomide 4 mg orally once daily (Days 1-21) and dexamethasone 40 mg (20 mg if &amp;gt;75 years) orally once weekly (28-day cycle). Belantamab mafodotin dose reductions or delays were permitted to manage treatment-related Grade 3-4 adverse events (AEs), or Grade 2 AEs that were worsening or had symptoms lasting &amp;gt;7 days. Following AE resolution to Grade ≤1, belantamab mafodotin treatment could resume with or without dose reduction (to 1.9 mg/kg). If no dose delays occurred, patients could receive a maximum of 17 cycles in 52 weeks, hence 17 cycles was used as a threshold to assess long term safety. Ocular exams were performed prior to dosing belantamab mafodotin Q3W up to Cycle 6, then every 3 months if no significant ocular events were reported. Treatment-related ocular AEs were graded per National Cancer Institute-Common Terminology Criteria for Adverse Events (NCI-CTCAE) v5 and per the Keratopathy Visual Acuity (KVA) scale. The KVA scale incorporates corneal examination findings and changes in Snellen-equivalent best corrected visual acuity (BCVA) into a composite grade. Ocular AEs are reported as worst-case post-baseline. Efficacy responses (per 2016 International Myeloma Working Group criteria) were assessed Q3W, regardless of treatment delays. Results: As of September 12, 2022, 50/218 (23%) patients were treated with belantamab mafodotin for ≥52 weeks. AEs were reported in all patients treated with belantamab mafodotin for ≥52 weeks. Grade ≥3 AEs occurred in 82% (n=41); the most frequent were reduced visual acuity (24%), thrombocytopenia (18%), and neutropenia (16%). The majority of AEs reported occurred at or before cycle 17. For the most common (&amp;gt;40%) AEs (any grade), few additional events occurred after cycle 17 (1 new occurrence each of dry eye, reduced visual acuity, eye irritation, and thrombocytopenia after cycle 17). Few infections (any grade) occurred after cycle 17 (COVID-19, n=5; viral infection, n=1; pneumonia influenzal, n=1). No patients permanently discontinued treatment due to AEs considered related to belantamab mafodotin. Ocular AEs were reported in 94% (n=47) of patients treated with belantamab mafodotin for ≥52 weeks. The majority of ocular AEs (n=487) were of Grade 1 or 2 severity (88%) and no ocular AEs led to study treatment discontinuation. At the time of data cutoff, 95% (n=41) of patients experiencing Grade ≥2 KVA events had recovered prior to the end of study treatment exposure (defined as last dose + 20 days). Most patients had a dose modification, and no loss of efficacy was observed. The clinical benefit rate (≥minimal response) in these patients was 90% (45/50) and the median time to best response was 6.3 months (range 0.8-18.8). Median duration of response was not reached (NR; 95% CI 17.9, NR) in the subset of patients treated for ≥52 weeks. At the time of data cutoff, 94% (n=47) patients were alive. Conclusions: In patients who received long-term treatment (≥52 weeks), the safety profile of belantamab mafodotin was consistent with previous reports. Despite the need for belantamab mafodotin dose delays and reductions, no patients discontinued study treatment due to belantamab mafodotin-related AEs. During dose delays, clinical responses were maintained or deepened in most cases, demonstrating that management of AEs using dose modifications did not impact clinical activity. Together, this suggests that dose modifications are highly effective in the management of emerging AEs while allowing for sustained clinical benefit. Funding: GSK (207495). Drug linker technology licensed from Seagen Inc.; monoclonal antibody produced using POTELLIGENT Technology licensed from BioWa.

Evaluation of a Novel Method for the Assessment of Ocular Adverse Events and Associated Functional Impact in Transplant Ineligible Patients with Newly Diagnosed Multiple Myeloma Treated with Belantamab Mafodotin, Lenalidomide, and Dexamethasone in the Phase 1/2 Belard Trial

Introduction Belantamab mafodotin (belamaf; GSK2857916), an antibody-drug conjugate targeting B-cell maturation antigen, has shown promising efficacy and a favorable tolerability profile in the treatment of multiple myeloma. Ocular adverse events (OAEs), manifesting as visual acuity changes, ocular symptoms, and corneal findings, are common with belamaf and the main reason for dose modifications (dose reduction, dose holds) or treatment discontinuation. Keratopathy and Visual Acuity (KVA) scale was used in most belamaf trials, including the pivotal DREAMM-2, to guide belamaf dose modifications. KVA grading is dependent on an ophthalmologist consultation prior to belamaf administration. Herein, we evaluate a novel approach to guide belamaf dosing in transplant ineligible (TI) patients (pts) with newly diagnosed multiple myeloma (NDMM), treated with an extended dosing schedule of belamaf in combination with lenalidomide and dexamethasone (Rd) in the phase 1/2 BelaRd study. Methods BelaRd (NCT04808037) is an open-label, phase 1/2 study conducted in Greece, aiming to enroll 66 TI NDMM pts. Part 1 evaluated the safety/tolerability of three belamaf doses (2.5/1.9/1.4 mg/kg) plus Rd in 36 pts and established that the recommended phase 2 dose (RP2D) is 1.9 mg/kg, initially administered q8w and, depending on toxicity, adjusted to q12w. Part 2 investigates the safety/efficacy of RP2D in Groups A and B, comprised of 15 pts each, and evaluates two different sets of guidelines for the management of OAEs. In Group A, belamaf dosing is guided by the KVA scale; in Group B, dose modifications are determined by the pts' responses on ocular symptoms and their impact on activities of daily living (ADL), captured by the Vision Related Anamnestic (VRA) tool, and by the presence of ≥Grade (Gr) 3 KVA events (BCVA reduced/corneal findings). VRA is a novel, 9-item physician administered questionnaire designed to assess the frequency of ocular symptoms and their impact on vision-related activities. Ocular exams include Snellen best corrected visual acuity (BCVA) and slit lamp corneal evaluation, while ocular symptoms are classified by CTCAE v5.0. Herein, we present the OAEs and the clinical activity of the treatment combination for both Groups of Part 2 (cut-off date 05/06/2023). Results By the cut-off date, twenty-four pts [median age: 75.5 years; male: 16 (66.7%)] had received ≥ 1 belamaf dose in Part 2 and were still on treatment. At baseline, most pts had ocular comorbidities. The median belamaf administrations and number of cycles reached were 3.0/2.0 and 6.5/5.5, for Groups A and B, respectively. A meaningful BCVA decline (BCVA &amp;lt;20/50) with at least 3 lines drop in the better seeing eye, was noted in 5/52 (9.6%) and 5/45 (11.1%) assessments, while BCVA ≤20/200 with at least 3 lines drop was noted in 1/59 (1.7%) and 2/51 (3.9%), respectively. Overall, no ≥Gr 3 ocular symptoms were observed, while the most frequent ≥Gr 2 ocular symptom was dry eye (57/110, 51.8%); also, no ≥Gr3 keratopathies were recorded. Among 66/59 VRA assessments, ocular symptoms and ADL impairment, manifesting for &amp;gt;50% of the time (substantial time) in the last 24 hours prior to belamaf administration, were noted in 2 (3.0%)/9 (15.3%) and 2 (3.0%)/7 (11.9%), respectively. Importantly, numerically similar proportions of KVA events and skipped belamaf doses were noted in both Groups (Table 1). Furthermore, although the sample size of the present analysis does not allow conclusions for the VRA test characteristics, it is notable that in all assessments where eyesight difficulties were reported for substantial time, ≥Gr2 KVA events were also recorded, suggesting a potential association between VRA responses and KVA events, that warrants further investigation. Finally, in terms of clinical activity, for the 19 response-evaluable pts (≥2 efficacy assessments), at a median follow-up of 7.4 months the ORR was 90%/100% in Groups A and B (PR/VGPR: 30%/60%; 66.7%/33.3%) with no disease progression observed. Conclusions In this preliminary descriptive analysis, the VRA tool was safe and effective in informing belamaf dose adjustments in the extended dosing schedule. Recruitment in Part 2 is ongoing and, as data accumulates, future analyses will provide further insight on the potential association of the VRA tool with KVA events, which may eliminate the need for an ophthalmic exam prior to belamaf dosing.

Gemtuzumab Ozogamicin for Patients with Newly Diagnosed CD33 Positive Acute Myeloid Leukemia: Results from a French Retrospective Observational Study

Introduction: Gemtuzumab ozogamicin (GO) is an antibody-drug conjugate targeting CD33 with a calicheamicin derivative payload. GO is approved in France in combination with daunorubicin and cytarabine for treatment-naïve patients aged ≥15 years with de novo CD33-positive acute myeloid leukemia (AML). Before the European Medicines Agency granted marketing authorization in 2018, GO was available in France with an authorization for temporary use (ATU) for specific patients since 2010, and between 2018 and 2019 as part of a “post-ATU” cohort until its reimbursement. This study aimed to describe the real-world use, effectiveness, and safety of GO in treatment-naïve patients with CD33-positive AML in France, as requested by the French Transparency Commission. Methods: This retrospective, multicenter, observational study included all patients in the French ATU and post-ATU cohorts treated between 01 December 2014 and 31 October 2022. Patient and disease characteristics, treatment (dose/combination), response outcomes, and adverse events (AEs) of interest were described. Prognostic factors for event-free survival (EFS), relapse-free survival (RFS), and overall survival (OS) were identified using Cox proportional hazard models. Results: Overall, 113 patients were included (ATU cohort, N=62; post-ATU cohort, N=51). The median age when GO was initiated was 63.0 years (range, 19-91); 54.9% (n=62) of patients were male; 81.8% (n=72/88) had an ECOG performance score 0-1, and 65.3% (n=64/98) had favorable risk according to the ELN classification 2017 ( Table). During the first induction treatment, most patients (98.1%; n=105/107) received GO in association with other agents, most commonly cytarabine and daunorubicin (60.0%; n=63/105). Most patients (78.5%, n=84/107) received 3 doses of GO during first induction. In all cases, patients received GO in second (7.1%; n=8) or subsequent (2.7%; n=3) induction courses - always in association with cytarabine and with or without daunorubicin/other agents. GO was given during the first, second, and subsequent consolidation treatment in 46.9% (n=53), 32.7% (n=37), and 2.7% (n=3) of patients, respectively, usually with cytarabine with or without daunorubicin. After a median follow-up of 44.6 months (95% CI, 33.8-69.3), 78.6% (n=88/112) of patients responded post-induction - of these, 72.3% (n=81) achieved a complete response (CR) and 6.3% (n=7) achieved a CR without platelet recovery. Minimal residual disease was evaluable in 46 patients; 52.2% (n=24) achieved a CR without minimal residual disease. Median EFS was 13.1 months (95% CI, 9.9-17.5); EFS by ELN risk group is shown in the Table. Median RFS was 17.5 months (95% CI, 12.6-35.6) and median OS was 49.8 months (95% CI, 21.8-not estimable; Figure). After a median period of 13.0 months (range, 3.0-33.0) following GO treatment, 31.5% (n=35/111) of patients received a hematopoietic stem cell transplant. Older age predicted shorter OS (hazard ratio [HR] 1.1 [95% CI, 1.0-1.1]; p&amp;lt;0.001). Having an FLT3TKD mutation (HR 4.1 [95% CI, 1.4-12.4]; p=0.013) or adverse cytogenetic classification (HR 13.0 [95% CI, 2.3-73.8]; p=0.015) predicted shorter EFS. Having ECOG-PS ≥2 (HR 6.6 [95% CI, 1.8-24.5]; p=0.005) or adverse cytogenetic classification (HR 72.7 [95% CI, 7.6-699.1]; p=0.001) predicted shorter RFS. AEs of interest were reported for 38.9% (n=44) of patients; 13.3% (n=15) were serious and 26.6% (n=30) were treatment-related (TRAE). The most common AEs were thrombocytopenia (21.2%; n=24), pyrexia (4.4%; n=5), and hepatic cytolysis (3.5%; n=4). AEs of special interest included persistent thrombocytopenia (15.9%; n=18), severe hemorrhage (5.3%; n=6), and veno-occlusive disease/sinusoidal obstruction syndrome (0.9%; n=1). Overall, 46.9% (n=53) patients died, with relapse or progressive disease accounting for 41.5% of deaths (n=22/53). Two (1.8%) patients died from TRAEs (laryngeal edema/pulmonary alveolar hemorrhage and hepatic cytolysis). Conclusions: GO was predominantly administered according to its indication. Response rates were similar to those reported in the pivotal ALFA-0701 study. Median OS was longer in this study than in ALFA-0701 (49.8 vs 27.5 months), although median RFS and EFS were reduced. No new safety signals were reported. Overall, GO appears safe and effective in real-world practice when added to induction therapy for treating patients with de novo CD33-positive AML.

Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16/NKG2D Immune Modulating TriNKET ® BMS-986357 (CC-96191)

CD33 is widely expressed by myeloid cells and is a validated drug target in acute myeloid leukemia (AML), as shown by the benefit of some patients from the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO). However, GO is often ineffective and toxic, prompting interest in more potent CD33-directed therapies. Success of T cell-engaging bispecific antibodies in lymphoid malignancies has raised enthusiasm for similar agents targeting CD33, but toxicities from activated T cells cause significant challenges for their use and provide a strong rationale to explore drugs engaging natural killer (NK) cells. Here, we investigated BMS-986357, a TriNKET ® that activates NK cells via CD16 and NKG2D receptors while targeting CD33. This format was chosen because simultaneous engagement of multiple activating NK cell receptors yields greater cytotoxic activity against neoplastic cells than engagement via a single activating receptor. Surface plasmon resonance analyses showed BMS-986357 simultaneously binds CD33, NKG2D, and CD16a, and co-engagement of NKG2D and CD16a increases the avidity. In the presence of primary human NK cells from healthy donors or a human NK cell line, the TriNKET ® demonstrated broad cytolytic anti-leukemia activity in a strictly CD33-dependent manner using a panel of CD33-expressing or CD33-deficient/deleted acute leukemia cells. Consistent with this, removing the CD33 binding domain rendered BMS-986357 ineffective against CD33+ AML cells. Drug-induced cytotoxicity was greater with BMS-986357 than with monoclonal CD33 antibodies, including lintuzumab and an afucosylated antibody with enhanced NK function, demonstrating the benefit of the TriNKET ® format. Compared to BMS-986357, substantially less cytotoxicity was observed with an Fc-mutant variant of BMS-986357 that abrogates binding to CD16a or an NKG2D dead-arm TriNKET ®, and cytolytic effects were reduced with a CD16-deficient NK cell line vs. a CD16-expressing subline, indicating maximal efficacy of BMS-986357 required co-engagement of CD16a and NKG2D. Using sublines of OCI-AML3 and KG-1 cells (both cell lines with low endogenous CD33 expression) to overexpress wild-type CD33 at increasing levels, we found low abundance of CD33 curtailed BMS-986357-induced cytotoxicity. Flow cytometric binding studies identified BMS-986357 to recognize the membrane-distal V-set domain of CD33. Unlike GO, BMS-986357-mediated cytolysis was not affected by over-expression of ABC transporter proteins by AML cells. The potency but not maximal activity of BMS-986357 was reduced by super-physiologic concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact TriNKET ® activity. In the presence of CD33+ AML cells, BMS-986357 activated NK cells but not T cells from healthy donor peripheral blood mononuclear cells and produced similar levels of maximum cytolysis as a CD33/CD3 bispecific antibody. Despite this, BMS-986357 elicited 10 to &amp;gt;100-fold lower soluble cytokine levels including IFN-γ, TNF, IL-6, and GM-CSF than a CD33/CD3 bispecific antibody, suggesting BMS-986357 has the potential for CD33/CD3 bispecific-like efficacy without the associated risk of cytokine release syndrome. Finally, in bone marrow specimens from patients with AML, BMS-986357 killed AML cells but not normal monocytes, suggesting selectivity of drug-induced cytotoxicity toward neoplastic cells, consistent with the notion NK cells are capable to differentiate between healthy and leukemic CD33+ cells. This selectivity suggests BMS-986357 may produce less myelosuppressive toxicity than what has been observed with CD33 targeting antibody-drug conjugates. In summary, our findings demonstrate that BMS-986357 TriNKET ® has potent CD33-dependent cytolytic activity in vitro against human AML cells, supporting the drug's exploration in early phase clinical trials. One such trial (NCT04789655) has opened accrual for adults with relapsed/refractory AML.

Final Results of a Multicenter Pilot Study Evaluating Brentuximab Vedotin with Cyclophosphamide, Doxorubicin, Etoposide, and Prednisone (BV-CHEP) for the Treatment of Aggressive Adult T-Cell Leukemia/Lymphoma

Introduction: Aggressive adult T-cell leukemia/lymphoma (ATLL) is a type of non-Hodgkin lymphoma that is often fatal. ATLL is exceedingly rare in the United States (US), with most cases occurring in emigrants from human T-lymphotropic virus type 1 (HTLV-1) endemic regions. Studies focusing on ATLL in the US are sparse, and have shown poor response rates; because of this, there is no standard of care treatment approach. Brentuximab vedotin (BV) is a CD30 targeting antibody-drug conjugate that is effective in treating many types of lymphoma, including CD30+ peripheral T-cell lymphomas. Studies have shown efficacy even in lymphomas with very low CD30 expression. We developed a prospective, multicenter pilot study evaluating BV in combination with cyclophosphamide, doxorubicin, etoposide, and prednisone (BV-CHEP) for the treatment of ATLL. We report the final safety and efficacy analysis below. Methods: Adult patients (pts) from 5 centers were enrolled from October 2017 through June 2022. Newly diagnosed ATLL pts were eligible, including the acute, lymphomatous and chronic unfavorable subtypes. Pts did not have to express CD30 to be enrolled; pts were considered CD30+ if there was &amp;gt;1% expression. Frontline consolidation with allogeneic stem cell transplant (alloSCT) was permitted at any time after 2 cycles of BV-CHEP. Transplant-ineligible pts completed a total of 6 cycles of BV-CHEP and those who expressed CD30 were eligible for BV maintenance. Pts could receive prephase steroids and/or 1 cycle of CHOP-equivalent chemotherapy prior to enrollment. Prior antiviral therapy was allowed. Pts were treated with standard dosing every 21 days: BV 1.8 mg/kg on day 1, cyclophosphamide 750 mg/m2 on day 1, doxorubicin 50 mg/m2 on day 1, etoposide 100 mg/m2 days 1-3, and prednisone 100mg days 1-5. All pts received GCSF support. The primary endpoint was CR by PET-CT (and peripheral blood for leukemic types) after at least 2 cycles of therapy per adapted Lugano and ATLL criteria. Secondary endpoints were safety, overall response rate (ORR), progression free survival (PFS) and overall survival (OS). Results: 16 pts were enrolled and evaluable for the safety and efficacy analysis. All pts were HTLV-1 positive. Seven of 16 were the acute type, 8 were lymphomatous, and 1 was chronic unfavorable. Seven of 16 (43.75%) expressed CD30. The median age was 56 (range 34 to 69) and 12 of 16 (75%) were female. 14 of 16 pts identified as Black, 1 identified as Asian, and 1 was other. Countries of origin included: Antigua and Barbuda N=1, Colombia N=1, Haiti N=7, Jamaica N=2, Japan N=1, Liberia N=1, and the US N=3. All pts were advanced stage (12 of 16 stage IV; 4 stage III). Four had positive cerebrospinal fluid at baseline, which cleared with intrathecal (IT) treatments, and 10 were given IT prophylaxis. Nine pts had an ATL-PI score &amp;gt;3 (56.25%) with a median score of 3 (range 2-4). No subjects received prior antiretroviral therapy. 12 of 16 pts completed at least 4 cycles of treatment (median 4.5 cycles; range 2 to 6). Ten of 16 pts achieved a CR (62.5%) and 4 pts achieved a PR (ORR of 87.5%) after &amp;gt;2 cycles of BV-CHEP. The median duration of follow-up was 47.2 mo. The median PFS (mPFS) was 7.11 mo (3.93 to NR) and the median OS (mOS) was 12.2 mo (9.29 to NR) (Fig.1). Of pts who achieved a CR, the mPFS was 11.07 mo and the mOS was 15.7 mo. There was no significant difference in PFS or OS by CD30 status or by ATLL subtype. One pt received 3 cycles of maintenance BV. 5 pts received alloSCT consolidation and there was an OS benefit for this group ( p=0.007; Fig.2). Grade 3 or higher toxicities included neutropenia (N=13), anemia (N=11), thrombocytopenia (N=9), febrile neutropenia (N=7), mucositis (N=6), colitis (N=3), infections (N=3; COVID19, thrush, clostridium difficile), hyponatremia (N=3), and vomiting (N=2). Nine of 16 patients had peripheral neuropathy (all grade 1/2). There were 11 pt deaths, 9 of which were disease-related and 2 were due to shock (hypovolemic and septic) off-treatment. No patients had to come off study due to toxicity and there were no treatment-related deaths. Conclusions: In this final analysis, BV-CHEP was safe and effective for the treatment of aggressive ATLL. High ORR and CR rates were achieved regardless of CD30 status, and compare favorably to prior clinical trials. AlloSCT had an OS benefit with 4 of 5 pts achieving long-term remission. Toxicity was manageable and cytopenias were expected. Peripheral neuropathy was common, but low-grade.

Hdp-101, an Anti-BCMA Antibody-Drug Conjugate with a Novel Payload Amanitin in Patients with Relapsed Multiple Myeloma, Initial Findings of the First in Human Study

Introduction Several antibody-drug conjugates (ADCs) are currently being evaluated in clinical trials in a variety of malignancies. The vast majority of these are based on a few toxic compounds, largely limited to microtubule- or DNA-targeting toxins which impact proliferating cells and have limited efficacy in diseases with a low proliferative fraction such as multiple myeloma. Thus, new compounds with alternative modes of action and the ability to actively induce cell death in non-proliferating tumor cells could enhance the therapeutic potential of ADCs. We are currently developing amanitin based ADCs. Amanitin specifically inhibits RNA polymerase II thereby inhibiting the cellular transcription process at very low concentrations irrespective of the proliferation status of the target cell. Subsequently tumor cells enter apoptosis and are eliminated. HDP-101 an Amanitin based antibody drug conjugate HDP-101 is a new ADC targeting BCMA carrying a synthetic version of amanitin as a payload. In vitro cytotoxic potency of HDP-101 was demonstrated on BCMA-positive myeloma cell lines, as well as on non-proliferating primary CD138+ cells isolated from patients with refractory myeloma The cytotoxic effects of HDP-101 were seen even in non-proliferating myeloma cells with low BCMA density. Toxicity was observed neither in non-BCMA expressing control cells nor in myeloma cells exposed to an amanitin-loaded non-target control antibody. In murine xenograft models of human myeloma, HDP-101 caused dose-dependent tumor regression including complete remissions after a single dose in subcutaneous and as well as in disseminated models. Safety profiling in Cynomolgus monkeys revealed a good therapeutic index after repeated dosing. Our non-clinical studies concluded that this amanitin-based ADC is a novel promising approach in the therapy of multiple myeloma to overcome drug resistance and improve patient outcome. HDP-101-01 Clinical study HDP-101-01 is a first-in-human, open label, non-randomized, multicenter, phase 1/2a trial with HDP-101 in patients with myeloma whose disease has progressed. The aim of the Phase 1 dose escalation part is to determine the Maximum Tolerated Dose and/or establish the Recommended Phase 2 Dose. The primary objective of the phase 2 dose expansion phase is to assess the preliminary anti-tumor activity of HDP-101. An adaptive Bayesian logistic regression model with overdose control principle is used to guide the dose escalation steps. An Interim Analysis is planned after each cohort is completed. The design of the study ensures a safe and adaptive dose escalation to reach a potential clinical benefit in a patient who have limited or no therapeutic options. HDP-101-01 Study progress The study started enrollment in February, 2022. As of 10th of July, 2023, eight (2 female and 6 male) patients were dosed in 3 consecutive dose cohorts. The median age of the patients was 70 years, ranging between 50 and 80. All 8 patients were heavily pre-treated and multidrug-resistant. The median previous lines of treatment were 7 (5 to 15). Table 1 HDP-101-01 Results Seven of 8 patients were evaluable for dose limiting toxicities (DLTs) in the first 3 treatment cohorts. The initial 3 cohorts were well tolerated, without any DLTs, there were no signs of liver and kidney toxicity, no infusion reaction was detected. No reports of keratopathy or visual acuity loss were observed. Free payload was not detected in any of the available pharmacokinetic samples. Based on the limited data, the PK of HDP-101 was in line with our expectation based on the preclinical observations, exposure to HDP-101 is dose proportional. Anti-drug antibody (ADA) was not detected and there's no sign of immunogenicity. Objective responses were not reported in these initial cohorts however in Cohort #3 (60μg/Kg) there was one patient ongoing after 8 cycles of treatment with SD. This patient had a slow decrease in M-protein levels. Image 1 The initial dose cohorts showed good tolerability in late stage relapsed and/or refractory multiple myeloma patients. The study continues to enroll patients to higher dose cohorts at selected sites in the US, Germany, Poland and Hungary. Currently the study is enrolling patients in Cohort #4 at the dose of 80μg/Kg. Additional updates will be provided at the 2023 ASH Annual Meeting.

Anti-LGALS3BP antibody-drug conjugate treatment induces durable and potent antitumor response in a preclinical model of adenoid cystic carcinoma

ObjectivesAdenoid cystic carcinoma (ACC) is a rare type of cancer that typically arises from glandular tissues, most commonly in the salivary glands. Although relatively rare, it represents a serious clinical issue as the management of the disease is highly complex being the only therapeutic options represented by invasive surgery and/or radiotherapy. In the present study, we have explored the potential of galectin-3 binding protein (LGALS3BP) as a novel target for antibody-drug conjugate (ADC) therapy in ACC. Materials and methodsRNAseq was conducted on a panel of 10 ACC patient-derived xenografts (PDX)s tissues and 6 normal salivary glands to analyze LGALS3BP gene expression. Protein expression was assessed in ACC PDX and primary tumor tissues using immunohistochemistry. Anti-LGALS3BP ADC named 1959-sss/DM4, was tested in high LGALS3BP expressing ACC PDX model ST1502B. ResultsRNAseq analysis revealed that LGALS3BP expression was highly expressed in ACC PDX tissues compared to normal salivary gland tissues. As evaluated by immunohistochemical analysis, LGALS3BP protein was found to be heterogeneously expressed in 10 ACC PDX and in tumor tissues derived from a cohort of 37 ACC patients. Further, treatment with 1959-sss/DM4 ADC led to durable tumor growth inhibition (TGI) in 100% of animals without observed toxicity. ConclusionsOur study provides strong evidence that LGALS3BP is a promising therapeutic target for ACC, warranting further expedited preclinical and clinical investigation.