Antitumor Activity In Xenograft Models Research Articles

Abstract CT110: A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in solid tumor cohorts

Abstract Background: Aberrant splicing contributes to the progression of cancer but lacks targeted drugs. CTX-712 is a potent oral CDC2-like kinase (CLK) inhibitor affecting RNA splicing, CTX-712 demonstrated potent inhibition of proliferation in human tumor cell lines and elicited robust anti-tumor activity in xenograft models. This study aimed to evaluate CTX-712’s maximum tolerated dose (MTD), dose-limiting toxicity (DLT), safety, pharmacokinetics (PK)/pharmacodynamics (PD) profiles, and preliminary efficacy in patients with advanced solid tumors. Methods: This study consisted of a dose escalation cohort (A) and three dose expansion cohorts (C, D and E) for solid tumors. The dose escalation cohort (A) was initiated with accelerated titration and then switched to a 3+3 design (10, 20, 40, 70, 105, 140 and 175 mg twice a week [TW]). The dosing regimens for dose expansion cohorts were 105 mg TW (C), 70 mg TW (D), and 105 mg once a week (QW) (E). Results: As of November 20, 2023, a total of 46 patients with solid tumors were enrolled in the dose escalation cohort (16 patients) and dose expansion cohorts (30 patients total). In the dose escalation cohort, CTX-712 was administered at a dose of 10/20/40/70 mg TW (n=1 each), 105/175 mg TW (n=3 each) and 140 mg TW (n=6). DLTs were observed in 2 patients (140 mg TW [platelet count decreased, hypokalemia], 175 mg TW [dehydration]) and MTD was determined to be 140 mg TW. Among the safety analysis population (n=46), median treatment duration was 77 days (Range 1-413+ days); 1 patient is ongoing, and 45 patients discontinued. The common any-grade related adverse events (AEs) (≥30%) were nausea (93.5%), vomiting (65.2%), diarrhea (54.3%), decreased appetite (45.7%) and blood creatinine increase (32.6%). The most common related Grade 3 or higher AE was platelet count decrease (6.5%). Among all the patients (n=46), partial responses were observed in 4 (8.7%) patients (40 (n=1)/70 (n=2)/105 (n=1) mg TW cohorts), who were all patients with ovarian cancer; the median treatment duration of ovarian cancer (n=14) was 84 days (Range 1-413+ days). In PK analysis, a dose-dependent increase in systemic exposure of CTX-712 was observed. PD response was assessed in RNA extracted from peripheral blood cells. Dose-dependent increases of exon skipping in two marker RNAs (S6K and THAP9-AS1) demonstrated mRNA splicing modification induced by CTX-712. Conclusions: CTX-712 demonstrated an acceptable safety profile in patients with solid tumors. Additionally, CTX-712 demonstrated favorable clinical efficacy for patients with ovarian cancer and further investigation is warranted. Clinical trial information: jRCT2080224127 Citation Format: Noboru Yamamoto, Takafumi Koyama, Yuki Katsuya, Jun Sato, Toshio Shimizu, Yasushi Tanoue, Maki Yamamoto, Hirokazu Tozaki, Eiji Takahara, Shingo Shoji, Akio Mizutani, Daisuke Morishita, Robert W. Oda, Hiroshi Miyake, Kan Yonemori. A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in solid tumor cohorts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT110.

Abstract B172: Potent anti-tumor activity of a selective and orally bioavailable reversible covalent CDK12 inhibitor

Abstract Cyclin-dependent kinase 12 (CDK12), in association with Cyclin K (CycK), regulates the elongation of transcription by modifying RNA polymerase II (RNAP II) through phosphorylation at Serine 2 (pS2) in the C-terminal domain, CDK12 plays an important role in maintaining genomic stability by modulating crucial cellular processes such as DNA damage response, splicing, and pre-mRNA processing. Overexpression of CDK12 has been observed in various tumor types, suggesting its potential oncogenic properties like other kinases involved in transcription. Given its significance in transcription and RNA processing, CDK12 has emerged as a promising therapeutic target for cancer treatment. We have identified a highly potent and selective reversible covalent inhibitor of CDK12, AU-22880, which exhibits significant anti-proliferative activity across various cancer cell lines. The covalent mode of action and on-target activity of AU-22880 were confirmed in a CDK12 target engagement assay and selective pS2 RNAPII inhibition respectively in a cellular context. Additionally, it has shown synergistic activity in combination with several standard-of-care agents in breast cancer, ovarian cancer, pancreatic cancer, and prostate cancer cell lines. AU-22880 shows desirable ADME-PK properties and demonstrates excellent anti-tumor activity in xenograft models. In the HCC-70 TNBC xenograft model, AU-22880 demonstrated anti-tumor efficacy at well-tolerated doses. A pharmacokinetic-pharmacodynamic (PK-PD) study revealed dose-dependent target engagement, as evidenced by the inhibition of pS2 RNAPII and DNA damage repair (DDR) genes. Furthermore, AU-22880 exhibited good tolerability in rodents, dog, and monkeys at exposure levels that demonstrated efficacy. Efficacy of AU-22880 in combination with approved SOCs targeting DDR pathway are currently being investigated. The findings reported here highlight the promising therapeutic potential of AU-22880, both as a monotherapy and in combination with existing treatments for the treatment of cancers characterized by DDR dysregulation. Citation Format: Leena Khare, Ramulu Poddutoori, Subhendu Mukherjee, Samiulla DS, Devaraja TS, Sivapriya Marappan, Shilpa Nayak, Sasirekha Sivakumar, Lakshmi Kaza, Suraj Tgore, Amit Dhudashiya, Raghavendra NR, Bhargav Gunnepalli, Aravind A B, Amith A, Charamanna KB, Thomas Antony, Kavitha Nellore, Girish Daginakatte, Shekar Chelur, Sanjeev Giri, Murali Ramachandra, Susanta Samajdar. Potent anti-tumor activity of a selective and orally bioavailable reversible covalent CDK12 inhibitor [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 B172.

A Phase 1 Study of the DNA-PK Inhibitor Peposertib in Combination With Radiation Therapy With or Without Cisplatin in Patients With Advanced Head and Neck Tumors

DNA-dependent protein kinase (DNA-PK) plays a key role in the repair of DNA double strand breaks via nonhomologous end joining. Inhibition of DNA-PK can enhance the effect of DNA double strand break inducing anticancer therapies. Peposertib (formerly "M3814") is an orally administered, potent, and selective small molecule DNA-PK inhibitor that has demonstrated radiosensitizing and antitumor activity in xenograft models and was well-tolerated in monotherapy. This phase 1 trial (National Clinical Trial 02516813) investigated the maximum tolerated dose, recommended phase 2 dose (RP2D), safety, and tolerability of peposertib in combination with palliative radiation therapy (RT) in patients with thoracic or head and neck tumors (arm A) and of peposertib in combination with cisplatin and curative-intent RT in patients with squamous cell carcinoma of the head and neck (arm B). Patients received peposertib once daily in ascending dose cohorts as a tablet or capsule in combination with palliative RT (arm A) or in combination with intensity modulated curative-intent RT and cisplatin (arm B). The most frequently observed treatment-emergent adverse events were radiation skin injury, fatigue, and nausea in arm A (n=34) and stomatitis, nausea, radiation skin injury, and dysgeusia in arm B (n=11). Based on evaluations of dose-limiting toxicities, tolerability, and pharmacokinetic data, RP2D for arm A was declared as 200 mg peposertib tablet once daily in combination with RT. In arm B (n=11), 50 mg peposertib was declared tolerable in combination with curative-intent RT and cisplatin. However, enrollment was discontinued because of insufficient exposure at that dose, and the RP2D was not formally declared. Peposertib in combination with palliative RT was well-tolerated up to doses of 200 mg once daily as tablet with each RT fraction. When combined with RT and cisplatin, a tolerable peposertib dose yielded insufficient exposure.

Targeting RAF Isoforms and Tumor Microenvironments in RAS or BRAF Mutant Colorectal Cancers with SJ-C1044 for Anti-Tumor Activity.

Colorectal cancer (CRC) is a significant global health issue characterized by a high prevalence of KRAS gene mutations. The RAS/MAPK pathway, involving KRAS, plays a crucial role in CRC progression. Although some RAS inhibitors have been approved, their efficacy in CRC is limited. To overcome these limitations, pan-RAF inhibitors targeting A-Raf, B-Raf, and C-Raf have emerged as promising therapeutic strategies. However, resistance to RAF inhibition and the presence of an immunosuppressive tumor microenvironment (TME) pose additional obstacles to effective therapy. Here, we evaluated the potential of a novel pan-RAF inhibitor, SJ-C1044, for targeting mutant KRAS-mediated signaling and inhibiting CRC cell proliferation. Notably, SJ-C1044 also exhibited inhibitory effects on immunokinases, specifically, CSF1R, VEGFR2, and TIE2, which play crucial roles in immune suppression. SJ-C1044 demonstrated potent antitumor activity in xenograft models of CRC harboring KRAS or BRAF mutations. Importantly, treatment with SJ-C1044 resulted in increased infiltration of T cells and reduced presence of tumor-associated macrophages and regulatory T cells within the TME. Thus, SJ-C1044 shows immunomodulatory potential and the ability to enhance antitumor responses. The study underscores the therapeutic potential of SJ-C1044 as a novel pan-RAF inhibitor capable of targeting oncogenic signaling pathways and overcoming immune suppression in CRC.

CD47 expression is critical for CAR T-cell survival in vivo

BackgroundCD47 is an attractive immunotherapeutic target because it is highly expressed on multiple solid tumors. However, CD47 is also expressed on T cells. Limited studies have evaluated CD47-chimeric antigen receptor...

A Defucosylated Anti-EpCAM Monoclonal Antibody (EpMab-37-mG2a-f) Exerts Antitumor Activity in Xenograft Model.

The epithelial cell adhesion molecule (EpCAM) is a stem cell and carcinoma antigen, which mediates cellular adhesion and proliferative signaling by the proteolytic cleavage. In contrast to low expression in normal epithelium, EpCAM is frequently overexpressed in various carcinomas, which correlates with poor prognosis. Therefore, EpCAM has been considered as a promising target for tumor diagnosis and therapy. Using the Cell-Based Immunization and Screening (CBIS) method, we previously established an anti-EpCAM monoclonal antibody (EpMab-37; mouse IgG1, kappa). In this study, we investigated the antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and an antitumor activity by a defucosylated mouse IgG2a-type of EpMab-37 (EpMab-37-mG2a-f) against a breast cancer cell line (BT-474) and a pancreatic cancer cell line (Capan-2), both of which express EpCAM. EpMab-37-mG2a-f recognized BT-474 and Capan-2 cells with a moderate binding-affinity [apparent dissociation constant (KD): 2.9 × 10-8 M and 1.8 × 10-8 M, respectively] by flow cytometry. EpMab-37-mG2a-f exhibited ADCC and CDC for both cells by murine splenocytes and complements, respectively. Furthermore, administration of EpMab-37-mG2a-f significantly suppressed the xenograft tumor development compared with the control mouse IgG. These results indicated that EpMab-37-mG2a-f exerts antitumor activities and could provide valuable therapeutic regimen for breast and pancreatic cancers.

Elucidating the Mechanism of Action (MOA) of Navtemadlin, an MDM2 Inhibitor, and Its Synergy with Gilteritinib in Myeloid Malignancies

Introduction: Murine double minute 2 (MDM2) is the primary negative regulator of the tumor suppressor protein, p53. Navtemadlin (KRT-232), a potent, selective, orally available MDM2 inhibitor, is being evaluated in the phase 3 BOREAS trial of patients with relapsed/refractory myelofibrosis (MF; NCT03662126) and in phase 1b/2 trials in various tumor types. In preclinical studies, navtemadlin has overcome MDM2 dysregulation and has restored p53 activity to drive apoptosis in TP53WT malignancies. The primary determinant of tumor cell sensitivity to navtemadlin is TP53 mutation status. Because MDM2 is often overexpressed and p53 mutations are less common in treatment-naïve acute myeloid leukemia (AML) and MF, navtemadlin represents a rational therapeutic candidate for these malignancies (Prokocimer et al. Blood. 2017). The present study aims to elucidate the effects of navtemadlin on proteins downstream of p53 and synergy of navtemadlin with the FLT3 inhibitor gilteritinib in myeloid malignancies. Methods: Cell viability was evaluated in three TP53WT myeloid cell lines, MOLM-13 (FLT3 AML), MV-4-11, and UKE-1, and one TP53MUT myeloid cell line, HEL-92, treated with 1-10 µM navtemadlin for 72 h. Growth inhibition was determined using the ATP-based Cell Titer Glo assay. The treatment effect on cell cycle progression, BCL-2 family proteins, and apoptosis was determined by flow cytometry. The effects of navtemadlin (0.5-1 µM) + gilteritinib (0.5-1 µM) were assessed in MOLM-13 and MV-4-11 (TP53WT and TP53MUT clones) and visualized using Combenefit. A MOLM-13 TP53WT mouse xenograft model was used to assess in vivo activity. Engrafted mice were randomly assigned to one of five treatment groups (n=10 each): vehicle control, 30 mg/kg gilteritinib, 50 mg/kg navtemadlin, 50 mg/kg navtemadlin + 30 mg/kg gilteritinib, or 100 mg/kg navtemadlin. Mice were treated orally once a day until the mice met early removal criteria or the study was terminated. Survival was measured by the percentage of mice in each group that remained alive at the end of the study. Results: Navtemadlin exposure led to dose-dependent growth inhibition in the TP53WT myeloid cell lines MOLM13, MV-4-11, and UKE-1 with an EC90 of 2-6 µM. Conversely, no growth inhibition was observed in the TP53MUT myeloid cell line HEL-92, up to 10 µM of navtemadlin. Assessment of cell cycle progression following navtemadlin exposure showed the induction of threshold-dependent apoptosis in the TP53WT myeloid cell lines, but not in the TP53MUT myeloid cell line. The threshold at which a switch from p21-mediated cell-cycle arrest to p53-directed apoptosis occurs is illustrated in Figure 1a. Navtemadlin-induced apoptosis was indicated by a release of cytochrome c and increase in processed caspase-3. Clinically, a steady-state Cmax of 2-6 µM is achieved at therapeutically active and relevant doses of navtemadlin ≥180 mg given once a day on a 5-day or 7-day schedule in clinical trials, leading to maximum tumor cell death. To gain better insight into the contribution of BCL-2 family members alterations as an MOA for navtemadlin-induced apoptosis, expression levels of BCL-2 family members were evaluated in TP53WT myeloid cell lines. Navtemadlin increased levels of the effector pro-apoptotic proteins Bak, Bax, and Bim in leukemia cells. Synergy was observed in vitro for navtemadlin + gilteritinib in TP53WT, but not TP53MUT myeloid cell lines. Treatment with 100 mg/kg navtemadlin monotherapy and 50 mg/kg navtemadlin + gilteritinib combination led to prolonged survival in mice harboring MOLM-13 TP53WT xenografts, with all mice still alive at day 113 when the study was terminated (Figure 1b). In contrast, median survival times for the vehicle, 50 mg/kg navtemadlin monotherapy, and gilteritinib monotherapy groups were 18, 53, and 65 days, respectively. Conclusion: Navtemadlin induces potent, threshold-dependent apoptosis in cell culture models of TP53WT myeloid malignancies at clinically relevant concentrations. Navtemadlin-induced p53 activity initiates apoptosis by activating the caspase cascade via cytochrome c release. Navtemadlin was shown to induce the expression of pro-apoptotic BCL-2 family proteins, key mediators in driving cell death. These pro-apoptotic effects translate to robust antitumor activity in xenograft models of TP53WT myeloid malignancies, with the navtemadlin + gilteritinib combination demonstrating synergy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

150 (PB030) - MEKi-based combination strategies for targeting KRAS-driven cancer

Background: KRAS is one of the most frequently mutated oncogenes in human cancer. Recent successes with KRAS G12C-specific inhibitors are changing the treatment paradigm in this subset of cancer patients. An alternative strategy is targeting downstream KRAS effectors, such as MEK. However, MEK inhibitors have historically proven unsuccessful as monotherapy in KRAS mutant cancers, highlighting the need for combinatory approaches. One possibility is the combination of MEK and SOS1 inhibition, which may overcome adaptive resistance to MEKi by blocking SOS1-mediated reactivation of MAPK signaling. Another promising approach is to combine MEKi with inhibitors of Bromodomain and extra-terminal (BET) proteins. While BET inhibitors exhibit broad anti-tumor activity in preclinical cancer models, BETi monotherapy demonstrated only moderate clinical activity. Resistance to BETi has been, at least partially, attributed to MAPK pathway upregulation, suggesting that a combination with MEKi may help to overcome resistance. Material and Methods: Here, we present BI 3011441, a potent and selective inhibitor of human MEK1/2. Using in vitro assays, we compare BI 3011441 to other clinical stage MEK inhibitors. We also combine BI 3011441 with BI 1701963 and BI 894999 - two potent, selective, and orally bioavailable inhibitors of SOS1 and BET, respectively. Both combinations are tested in vitro and/or in vivo across a panel of KRAS mutant pancreatic ductal adenocarcinoma (PDAC), colorectal cancer (CRC) and non-small cell lung cancer (NSCLC) models. Results: BI 3011441 efficiently inhibits ERK phosphorylation in cell-based assays and demonstrates the strongest in vitro growth inhibition in a panel of BRAF or KRAS mutant cell lines among the MEK inhibitors tested. In vivo, BI 3011441 leads to a dose-dependent modulation of MAPK pathway, which translates into anti-tumor activity in xenograft models of KRAS-driven cancer. The combination of BI 3011441 with SOS1i BI 1701963 synergistically decreases MAPK signaling resulting in enhanced efficacy in xenograft models, including NSCLC, CRC and PDAC. In NSCLC models this combination results in 10% of partial responses (PR) and 70% of stable disease (SD) as defined by modified Response Evaluation Criteria In Solid Tumors (mRECIST). In PDAC and CRC models the combination leads to 30% and 43% of SD, respectively. When combined with clinically relevant concentrations of BETi BI 894999, BI 3011441 strongly decreases in vitro proliferation and induces apoptosis in KRAS mutant cancer cells. Synergy is observed in 17 out of 44 cell lines across different indications and harboring different KRAS mutations. Conclusions: In summary, we show that combining BI 3011441 with SOS1 or BET inhibitors may lead to improved responses in KRAS mutant tumors, likely by circumventing MAPK pathway-related adaptive resistance. Conflict of interest: Other Substantive Relationships: The authors are either employees or have financial relationships with Boehringer Ingelheim.

233 (PB113) - TNG908 is a brain-penetrant, MTA-cooperative PRMT5 inhibitor for the treatment of MTAP-deleted cancer

TNG908 is a clinical stage MTA-cooperative PRMT5 inhibitor that leverages the synthetic lethal interaction between PRMT5 inhibition and MTAP deletion. TNG908 was discovered using structure-based design following an initial high-throughput screening campaign. TNG908 is 15X selective for MTAPnull cell lines over isogenic MTAPWT cell lines and has marked selectivity for MTAP-deleted cancer cell lines independent of lineage in a large, diverse cell line panel. Oral administration of TNG908 drives dose-dependent, MTAPnull-selective antitumor activity in xenograft models, including durable tumor regressions in models representing glioblastoma, non-small cell lung cancer (adenocarcinoma and squamous), mesothelioma, cholangiocarcinoma, urothelial carcinoma, and others.

Abstract 3506: CLN-619, a clinical-stage MICA/MICB-specific IgG1 antibody, restores the MICA/MICB-NKG2D axis to promote NK-mediated tumor cell lysis

Abstract Natural killer (NK) cells play a central role in the immune surveillance of cancer. NK cells express multiple inhibitory and activating surface receptors, including the activating receptor, NKG2D. Engagement of NKG2D by the stress-induced ligands MICA/MICB stimulates NK cell activation and subsequent target cell lysis. While MICA/MICB expression is restricted in normal tissues, expression is strongly induced upon viral infection, genotoxic stress or malignant transformation. In cancer patients, the tumor microenvironment (TME) facilitates evasion of immune surveillance by NK cells. One mechanism by which tumor cells can escape NKG2D-mediated lysis is via proteolytic release of MICA/MICB from the cell surface due to proteases present in the TME. High concentrations of shed MICA have been observed in serum from patients across multiple tumor types and correlate with poor survival. In mouse models, expression of MICA on tumor cells delayed tumor growth, while the absence of NKG2D accelerated tumor growth. Given the established role of the MICA/MICB-NKG2D axis in the immune surveillance of tumor cells, a therapeutic agent that effectively restores this axis is a compelling approach to harness the immune system for treating cancer. CLN-619 is a humanized anti-MICA/MICB monoclonal IgG1 antibody being developed for the treatment of multiple cancer indications. The antibody was selected based on its high-affinity binding to MICA/MICB, potent in vitro activity and robust anti-tumor activity in xenograft models. MICA/MICB is highly polymorphic, with >150 MICA and 47 MICB alleles in humans, and expression level, binding affinity to NKG2D, and degree of MICA/MICB shedding is thought to be allele-dependent. CLN-619 demonstrated high affinity binding to all common allelic variants of MICA, including the most prevalent MICA allele, MICA*008, and the canonical allelic variant of MICB. CLN-619 was able to prevent proteolytic cleavage of MICA/MICB as evidenced by the reduction of shed MICA/MICB in cell culture supernatants and the corresponding increase in surface MICA/MICB on cancer cells. In addition to the ability to restore the MICA/MICB-NKG2D axis, CLN-619 enhanced the binding of MICA to NKG2D on NK cells. This was enabled by both FcγR engagement on NK cells as well as an intrinsic enhancement of MICA binding to NKG2D. Finally, CLN-619 was shown to elicit potent ADCC of MICA/MICB expressing tumor cells. Consistent with the multimodal mechanisms of action described above, CLN-619 treatment resulted in robust anti-tumor activity at low doses in mice bearing MICA/MICB-expressing human tumor xenografts. Given the pan-cancer expression of MICA/MICB in both solid and hematological malignancies, CLN-619 is expected to have broad anti-tumor activity. CLN-619 is currently being investigated in a Phase 1 clinical trial for the treatment of patients with advanced solid tumors. Citation Format: Kerry A. Whalen, Naveen K. Mehta, Safak Yalcin, Kristan Meetze, Neil W. Gibson, Jennifer S. Michaelson, Patrick A. Baeuerle. CLN-619, a clinical-stage MICA/MICB-specific IgG1 antibody, restores the MICA/MICB-NKG2D axis to promote NK-mediated tumor cell lysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3506.

Safety, pharmacodynamic, and clinical response evaluation of nilotinib and paclitaxel in adults with refractory solid tumors.

3026 Background: The combination of the BCR-Abl kinase inhibitor nilotinib and the anti-tubulin agent paclitaxel was identified in the NCI-ALMANAC study to have greater-than-additive activity in the NCI-60 cell line panel and greater-than-single-agent antitumor activity in xenograft models, in which this combination induces tumor epithelial-mesenchymal transition (EMT). A phase 1 study was initiated to establish the safety, tolerability, and recommended phase 2 dose (RP2D) of this combination in patients (pts) with advanced solid tumors and to examine the pharmacokinetic (PK) and pharmacodynamic (PD) effects of the combination to understand the mechanism of action (NCT02379416). The dose escalation phase established the RP2D as 300 mg oral nilotinib twice daily and 80 mg/m2 intravenous paclitaxel on days (D) 1, 8, and 15 of each 28-day cycle. Here, we report the safety, preliminary PD, and efficacy data for this combination. Methods: Nilotinib and paclitaxel were administered as noted above, with a 1-day (escalation cohort) or 2-day (expansion cohort) paclitaxel-only run-in during the first cycle to enable comparison of the PK and PD effects of the combination vs. single-agent paclitaxel. Paired biopsies to assess tumor molecular response were collected from expansion cohort pts at baseline, cycle (C) 1 D2, and C1D28, with an optional biopsy at progression; accrual continued until ≥ 12 sufficient-quality paired biopsies were obtained. Blood specimens to assess molecular responses in circulating tumor cells (CTCs) were obtained at several timepoints during C1 and longitudinally every cycle thereafter. EMT biomarkers were measured in tumor and CTC specimens using quantitative immunofluorescence microscopy assays. Results: A total of 44 pts were enrolled. Three pts had partial responses (PR), and 1 had an unconfirmed PR (9%); 23 pts (52%) had a best response of stable disease (SD), including 7 pts on study for ≥ 10 cycles. The most common grade (Gr) 3-4 treatment-related adverse events were hematologic and hypophosphatemia. No pts experienced Gr ≥ 3 peripheral neuropathy. The median time on treatment was 67 days. Two pts with granulosa cell ovarian carcinoma had durable responses, completing 74+ and 64 cycles. Multiple patient biopsies and corresponding CTC specimens exhibited treatment-induced EMT. Longitudinal analysis of CTC EMT phenotypes in the 2 pts with extended PR revealed a substantial increase in mesenchymal-like CTCs prior to progression for the pt on study for 64 cycles; such increases were not observed in the pt still on study after 74+ cycles. Further PD analyses are ongoing. Conclusions: The combination of nilotinib and paclitaxel demonstrates promising disease control with durable response in select patients. Tumor PD analyses to discover the underlying pharmacology of this active regimen are ongoing. Funded by NCI Contract No. HHSN261201500003I. Clinical trial information: NCT02379416.

STRO-002-GM2: A phase 1, open-label, safety, pharmacokinetic, and preliminary efficacy study of STRO-002, an anti-folate receptor alpha (FolRα) antibody-drug conjugate (ADC), in combination with bevacizumab in patients with advanced epithelial ovarian cancer (EOC, including fallopian tube or primary peritoneal cancers).

TPS5622 Background: STRO-002 is a novel FolRα targeting ADC, generated using cell-free antibody production and site-specific conjugation technology. STRO-002 demonstrates potent in vitro cytotoxicity in EOC cell lines and anti-tumor activity in xenograft models, including induction of immunogenic cell death. STRO-002 is currently being studied as a single agent in ovarian and endometrial cancer (Phase 1 Study STRO-002-GM1; NCT03748186). Preliminary efficacy data in relapsed/progressive platinum resistant EOC compared favorably to standard chemotherapy (Naumann W., et al, ASCO 2021). Pre-clinical models tested with STRO-002/bevacizumab combinations demonstrated additive anti-tumor activity compared to monotherapy. This study is a first in human study of STRO-002 plus bevacizumab in patients with advanced ovarian cancer that have progressed on standard therapy. Methods: STRO-002-GM2 is a Phase 1, open-label, multicenter, dose escalation study with a standard 3+3 design with a 21-day dose-limiting toxicity (DLT) assessment period followed by dose expansion. The study will assess safety, establish recommended phase 2 dose (RP2D), and preliminary efficacy of STRO-002/bevacizumab combination in patients with recurrent high-grade EOC. Bevacizumab will be administered at the labeled dose of 15 mg/kg given with STRO-002 starting at 3.5 mg/kg, both administered IV q 3 weeks. Planned dose escalation doses of STRO-002 include 3.5, 4.3, and 5.2 mg/kg and will continue until MTD/MAD is reached. Additional intermediate dose level cohorts may be added for RP2D optimization. Once a cohort is cleared per dose escalation rules, up to 10 additional subjects may be enrolled and treated at that cleared dose level in order to obtain additional safety and efficacy data for RP2D determination and ungating of the expansion stage. Dose expansion will enroll approximately 40 patients treated at the RP2D. The patient population is relapsed high-grade EOC with up to 4 prior regimens. Subjects with primary platinum refractory disease will be enrolled in dose escalation only. Key inclusion criteria include: measurable disease, adequate bone marrow and renal function. Key exclusion criteria include: contraindication to receive bevacizumab and prior treatment with a FolRα ADC or ADC containing a tubulin inhibitor. Efficacy evaluation is per RECIST v1.1. Tumor tissue (archival or fresh biopsy) is required. Study oversight includes a Safety Evaluation Team. Samples will be collected to assess the PK and immunogenicity. No formal statistical hypothesis testing will be conducted in this study. This study is currently open for enrollment in the U.S. Clinical trial information: NCT05200364.

SOX17 and PAX8 constitute an actionable lineage-survival transcriptional complex in ovarian cancer.

Müllerian tissue-specific oncogenes, prototyped by PAX8, underlie ovarian tumorigenesis and represent unique molecular vulnerabilities. Further delineating such lineage-dependency factors and associated therapeutic implications would provide valuable insights into ovarian cancer biology and treatment. In this study, we identified SOX17 as a new lineage-survival master transcription factor, which shared co-expression pattern with PAX8 in epithelial ovarian carcinoma. Genetic disruption of SOX17 or PAX8 analogously inhibited neoplastic cell viability and downregulated a spectrum of lineage-related transcripts. Mechanistically, we showed that SOX17 physically interacted with PAX8 in cultured cell lines and clinical tumor specimens. The two nuclear proteins bound to overlapping genomic regions and regulated a common set of downstream genes, including those involved in cell cycle and tissue morphogenesis. In addition, we revealed that small-molecule inhibitors of transcriptional cyclin-dependent kinases (CDKs) effectively reduced SOX17 and PAX8 expression. ZSQ1722, a novel orally bioavailable CDK12/13 covalent antagonist, exerted potent anti-tumor activity in xenograft models. These findings shed light on an actionable lineage-survival transcriptional complex in ovarian cancer, and facilitated drug discovery by generating a serial of candidate compounds to pharmacologically target this difficult-to-treat malignancy.

Abstract 1543: Mining cancer-specific isoforms as CAR T-cell therapy targets for pediatric solid and brain tumors

Abstract Immunotherapy with T-cells expressing chimeric antigen receptors (CARs) holds the promise to improve outcomes for children with solid and brain tumors. However, at present, there is a limited array of targetable antigens. We posit here that targets generated by alternative splicing events (ASEs) in cancer cells present an untapped class of CAR targets since many of these are tumor-specific and overexpressed in malignant cells. Thus, we developed Cancer-Specific Isoform Miner (CSI-Miner), a pipeline to perform a comprehensive ASE analysis of pediatric cancers to discover CSIs as CAR T-cell therapy targets. We analyzed 1,938 solid and brain tumor samples collected from PCGP, TARGET, and St. Jude's real-time clinical sequencing data sets. In addition, 7,527 GTEx RNAseq samples across 31 human tissues were harmonized to prioritize exon candidates with minimal expression in normal tissue. Through CSI-Miner, we identified 40,748 highly expressed exons from the tumor's surfaceome and secretome, of which 185 were unannotated novel exons. Taking advantage of available mass-spectrometry proteome data from the Clinical Proteomic Tumor Analysis Consortium and St. Jude's proteomics facility, we validated the presence of peptides encoded by these novel exons for rhabdomyosarcoma, medulloblastoma, high-grade glioma, low-grade glioma, and ependymoma. Moreover, non-malignant mass-spectrometry data from muscle and brain samples were incorporated as negative controls. Several secretome targets were identified that adhered to the surface of cancer cells, including EDB, an oncofetal splice variant of fibronectin. EDB was expressed in a broad range of pediatric solid and brain tumors, including Ewing sarcoma and high-grade glioma. We generated T-cells expressing a 2nd generation EDB-CAR (EDB-CAR T-cells) by standard retroviral transduction. EDB-CAR T-cells recognized and killed EDB+ cancer cells in vitro and had potent antitumor activity in xenograft models, resulting in improved overall survival compared to control mice. Importantly, EDB-CAR T-cells did not induce ‘on target/off cancer' toxicities in mice, which is encouraging since EDB is identical in mice and humans. c-MET was also identified as a candidate surfaceome CAR target for rhabdomyosarcoma and melanoma. In summary, we developed CSI-Miner, an integrative analysis pipeline to discover CSIs as CAR T-cell therapy targets, comprised of 248 surfaceome and 51 secretome candidates, for pediatric solid and brain tumors. At present we have validated these CSIs by mass-spectrometry and successfully generated CAR T-cells for one of the candidates. Collectively, CSIs present an untapped class of immunotherapy targets that hold the promise to improve current CAR T-cell therapy approaches for a wide range of pediatric solid and brain tumors. A web portal has been developed supporting access and visualization of this data set to the research community. Citation Format: Timothy I. Shaw, Jessica Wagner, Elizabeth Wickman, Liqing Tian, Dong Li, Suresh Poudel, Elizabeth Stewart, Yuxin Li, Hong Wang, Mingming Niu, Robin Paul, Colleen Reilly, Xin Zhou, Michael Dyer, Suzanne Baker, Junmin Peng, Jiyang Yu, Paulina Velasquez, Chris DeRenzo, Giedre Krenciute, Jinghui Zhang, Stephen Gottschalk. Mining cancer-specific isoforms as CAR T-cell therapy targets for pediatric solid and brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1543.

EBNA1 inhibitors have potent and selective antitumor activity in xenograft models of Epstein-Barr virus-associated gastric cancer.

Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC) is the most common EBV-associated cancer and accounts for ~ 10% of all gastric cancers (GC). Epstein-Barr virus nuclear antigen 1 (EBNA1), which is critical for the replication and maintenance of the EBV latent genome, is consistently expressed in all EBVaGC tumors. We previously developed small molecule inhibitors of EBNA1. In this study, we investigated the efficacy and selectivity of an EBNA1 inhibitor in cell-based and animal xenograft models of EBV-positive and EBV-negative gastric carcinoma. We tested the potency of an EBNA1 inhibitor, VK-1727, in vitro and in xenograft studies, using EBV-positive (SNU719 and YCCEL1) and EBV-negative (AGS and MKN74) GC cell lines. After treatment, we analyzed cell viability, proliferation, and RNA expression of EBV genes by RT-qPCR. Treatment with VK-1727 selectively inhibits cell cycle progression and proliferation in vitro. In animal studies, treatment with an EBNA1 inhibitor resulted in a significant dose-dependent decrease in tumor growth in EBVaGC xenograft models, but not in EBV-negative GC xenograft studies. Gene expression analysis revealed that short term treatment in cell culture tended towards viral gene activation, while long-term treatment in animal xenografts showed a significant decrease in viral gene expression. EBNA1 inhibitors are potent and selective inhibitors of cell growth in tissue culture and animal models of EBV-positive GC. Long-term treatment with EBNA1 inhibitors may lead to loss of EBV in mouse xenografts. These results suggest that pharmacological targeting of EBNA1 may be an effective strategy to treat patients with EBVaGC.

AO-176, a Highly Differentiated Clinical Stage Anti-CD47 Antibody, Exerts Potent Anti-Tumor Activity in Preclinical Models of Multiple Myeloma As a Single Agent and in Combination with Approved Therapeutics

Upregulation of tumor CD47, the "don't eat me" signal, to evade immune surveillance is a common escape mechanism that evolves during cancer development, progression, and relapse. Previous studies have shown multiple myeloma (MM) cells leverage this mechanism through broad upregulation of CD47 compared to non-malignant plasma cells, making CD47 an attractive therapeutic target for this disease. We recently reported that AO-176, a clinical stage humanized anti-CD47 IgG2 antibody, possesses differentiated characteristics such as preferential binding of tumor cells compared to normal cells, a lack of binding to red blood cells, non-ADCC direct tumor killing and elicits immunogenic cell death with DAMP induction, all in addition to single-agent phagocytosis. In this study, AO-176's anti-tumor activity in MM was evaluated. Immunohistochemical analyses of MM patient tumors with upregulated CD47 expression showed infiltration of innate immune cells such as macrophages and dendritic cells, both previously shown to be involved in anti-CD47 antibody mechanisms of action. AO-176 binding was confirmed on human cell lines frequently used in MM xenograft models. AO-176 exerted substantial single agent in vivo anti-tumor activity in multiple MM xenograft models when dosed at 25 mg/kg, including significant tumor growth inhibition of RPMI-8226 xenografted mice, and complete responses (CRs) in (10/10) NCI-H929 xenografted mice. These CRs were durable, with treated mice tumor-free up to 120 days post antibody dosing. Immunohistochemical analysis of AO-176 treated tumors from both models showed increased numbers of macrophages and dendritic cells compared to controls. An AO-176 dose response study resulted in CRs and increases in overall survival down to 10 mg/kg, with CRs observed as low as 3 mg/kg during dosing. In addition, we found that large NCI-H929 tumors (up to 1600mm3) showed pronounced regression after AO-176 treatment. The anti-tumor activity of AO-176 was also evaluated in combination with several standard of care MM therapies. When combined with the proteasome inhibitor bortezomib, AO-176 treatment at both 10 mg/kg and 25 mg/kg resulted in profound RPMI-8226 xenograft growth inhibition, near-total CRs (19/20 mice), and extended survival at both doses. Combining AO-176 and the anti-CD38 antibody daratumumab or immunomodulatory drugs (lenalidomide/pomalidomide) both produced significant enhancement of anti-tumor activity in xenograft models. The combined regimen of AO-176 with daratumumab led to significant MM.1S tumor growth inhibition compared to AO-176 or daratumumab alone. Both lenalidomide and pomalidomide combined with AO-176 resulted in significantly increased MM.1S tumor growth inhibition and extended survival compared to AO-176 alone, with an increased number of CRs observed in the combination groups compared to monotherapy groups. In summary, the pre-clinical potent single agent activity and enhanced activity when combined with standard of care anti-MM agents, warrants further development of AO-176 in MM treatment. AO-176 is being evaluated in phase 1 clinical trials for the treatment of patients with solid tumors (NCT03834948) and with MM (NCT04445701). Disclosures Wilson: Arch Oncology: Current Employment, Current equity holder in private company. Richards:Arch Oncology: Current Employment, Current equity holder in private company. Puro:Arch Oncology: Current Employment, Current equity holder in private company. Andrejeva:Arch Oncology: Current Employment, Current equity holder in private company. Capoccia:Arch Oncology: Current Employment, Current equity holder in private company. Donio:Arch Oncology: Current Employment, Current equity holder in private company. Hiebsch:Arch Oncology: Current Employment, Current equity holder in private company. Chakraborty:Arch Oncology: Current Employment, Current equity holder in private company. Sung:Arch Oncology: Current Employment, Current equity holder in private company. Pereira:Arch Oncology: Current Employment, Current equity holder in private company.

Abstract 3087: FCN-098, a novel second-generation TRK inhibitor, overcomes TRK resistance mutations in vitro and in vivo

Abstract Tropomyosin receptor kinases (TRK or NTRK) are the transmembrane tyrosine kinases activated by soluble growth factors named neurotrophins (NT). TRK family includes three different members, namely TRKA, TRKB and TRKC. Extracellular recognition of NT to TRK proteins induces receptor dimerization, phosphorylation, and activation of the downstream signal transduction pathways via PI3K, RAS/MAPK/ERK, and PLC-gamma. TRKs are expressed primarily in neuronal tissues and regulate differentiation and survival of neuronal cells. Alteration of TRK pathway caused by gene fusion of TRK is frequently associated with the poor prognosis of a wide range of solid malignancies, such as neuroblastoma, breast cancer, pancreatic cancer, melanoma, thyroid cancer, glioblastoma, colorectal cancer, sarcomas, cholangiocarcinoma, and non-small cell lung cancer. The efficacy of TRK inhibition in TRK fusion-positive cancers has been demonstrated by the high response rate and lasting effect of the first-generation TRK inhibitors larotrectinib and entrectinib. However, acquired resistance mutations of TRK, such as solvent front mutations, gatekeeper mutations and DFG motif mutations, often emerge and abrogate the inhibitory effect of first-generation inhibitors. Thus, developing novel TRK inhibitors that can effectively overcome resistance mutations can provide great clinical benefits to patients. Here we introduce FCN-098, a potent second-generation TRK inhibitor. FCN-098 demonstrated marked kinase inhibition activity against wild-type (WT) and mutant TRK with IC50 at sub-nano or single nanomolar range. FCN-098 significantly and dose-dependently inhibited phosphorylation of TRK and its downstream effector ERK in TRK fusion-positive KM12 human colon cancer cells and BaF3 cells ectopically overexpressing WT or mutant TRK fusions. FCN-098 potently inhibited proliferation of KM12 cells and BaF3 cells overexpressing WT or various mutant TRK fusions while sparing TRK-negative cell lines. Consistent with in vitro results, FCN-098 showed remarkable anti-tumor activity in xenograft models driven by WT or mutant TRK fusions in a dose-dependent manner. In particular, the anti-tumor activity of FCN-098 was superior to another second-generation TRK inhibitor LOXO-195 at the same dose in xenografts driven by TPM3-TRKA G595R or ETV6-TRKC G623R mutation, and exhibited comparable potency to LOXO-195 in LMNA-TRKA G667C-driven xenografts. In non-clinical studies, FCN-098 exhibited excellent pharmacokinetic (PK) and safety properties, demonstrating longer T1/2 in both dogs and rats along with higher Cmax and larger dose-normalized AUC in dogs compared to LOXO-195. Overall, FCN-098 overcomes TRK resistance mutations in vitro and in vivo and exhibits favorable PK and safety profiles. FCN-098 has the potential to become an effective and safe therapeutic choice for a wide range of solid tumors harboring WT or mutant TRK fusions. Citation Format: Shu Lin, Tongshuang Li, Xianlong Wang, Lijun Yang, Zhifang Chen, Yue Rong, Xingdong Zhao, Yanxin Liu, Zongyao Zou, Min Lin, Yuwei Gao, Jiashu Zhou, Weibo Wang. FCN-098, a novel second-generation TRK inhibitor, overcomes TRK resistance mutations in vitro and in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3087.

Abstract 5222: Degraders targeting both IRAK4 and IMiD substrates show combinatorial effects leading to broader activity with durable and complete regressions in MYD88 mutant lymphoma xenografts in vivo

Abstract Targeted protein degraders (TPD) are heterobifunctional small molecules that employ the ubiquitin degradation system to drive the selective degradation of target proteins. In approximately one third of B-cell lymphomas, gain of function mutations in MYD88 constitutively activate the myddosome and drive proliferation and survival through NFkB and AP1 signaling. IRAK4, is a key component of the myddosome and IRAK4 TPD show potent and selective IRAK4 degradation and preferential activity in MYD88 mutated B cell lymphoma models. Notably, the activity of IRAK4 degraders is superior to kinase inhibition, supporting the essential scaffolding role of IRAK4 in Myddosome signaling. An important goal of cancer therapy is to drive to deep and durable responses in patients, and this is frequently achieved by combination therapy. It has been suggested that blocking NFkB while simultaneously inducing a Type 1 IFN response with an IMiD (e.g. Lenalidomide Yang et al. (2012) Cancer Cell 21, 6, p723) may drive additive or synergistic antitumor activity. We have developed novel degraders that utilize an IMiD as a cereblon binder. These compounds simultaneously degrade both IRAK4 and IMiD substrates, enabling a therapeutically-relevant biological combination within a single small molecule. Here we show that dual IRAK4 and IMiD based degraders have potent antiproliferative activity across MYD88 mutant, but not MYD88WT lymphoma cell lines, with increased and broader antiproliferative and apoptosis activity relative to selective IRAK4 degraders or IMiDs alone. Several lines of evidence suggest that both IRAK4 and IMiD activity contribute to the overall superior activity of the dual degraders. Proteomic analysis demonstrates degradation of both both IRAK4 and key IMiD substrates, including Ikaros and Ailolos. This activity results in an enhanced Type 1 IFN response signature compared to selective IRAK4 degraders or IMiD alone, suggesting cooperative biological activity. Degradation of both IRAK4 and IMiD substrates corelates with cell activity, consistent with a requirement for both activities to drive cell death. In xenograft models of MYD88 mutant DLBCL, daily oral dosing of lead dual - degraders demonstrates strong antitumor activity in xenograft models of MYD88 mutant lymphoma, including durable complete regressions that can be maintained for several weeks following cessation of dosing. Regressions are associated with degradation of both IRAK4 and IMiD substrates, consistent with the dual-targeting activity of these molecules. Collectively, these data support a strategy to combine IRAK4 degradation and IMiD activity in a single molecule that will have the potential benefits of enhanced therapeutic activity, increased convenience and decreased potential for drug combination challenges, such as DDI. Lead degraders based on this synergistic profile are being advanced towards IND in 2020. Citation Format: Duncan H. Walker, Michele Mayo, Christine Klaus, Haojing Rong, Scott Rusin, Kirti Sharma, Alice McDonald, Veronica Campbell, Joseph Kelleher, Jared Gollob, Nello Mainolfi, Matt Weiss. Degraders targeting both IRAK4 and IMiD substrates show combinatorial effects leading to broader activity with durable and complete regressions in MYD88 mutant lymphoma xenografts in vivo [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5222.

Abstract CT253: Preliminary safety and efficacy data of BGB-A333, an anti-PD-L1 monoclonal antibody, alone and in combination with tislelizumab in patients with advanced solid tumors

Abstract Background: Programmed cell death protein-1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1), play critical roles in the immune modulation of tumor progression. Although both pathways have overlapping elements, each has a distinct mechanism of action. Nonclinical studies have demonstrated that potential synergistic antitumor effects can result from blocking both PD-1 and PD-L1. BGB-A333 is an investigational humanized IgG1 monoclonal antibody against PD-L1 that has antitumor activity in xenograft models. Tislelizumab, a clinical-stage anti-PD-1 antibody engineered to minimize binding to FcγR on macrophages in order to abrogate antibody-dependent phagocytosis, has demonstrated clinical activity in patients with advanced solid tumors. Here we report preliminary results from the phase 1 component of an open-label phase 1/2 study (NCT03379259) of BGB-A333 alone and in combination with tislelizumab in patients with advanced solid tumors. Methods: Phase 1 of this study consisted of two parts. In Part A, patients received single-agent BGB-A333 IV Q3W at increasing doses; in Part B patients received BGB-A333 1350 mg IV Q3W + tislelizumab 200 mg IV Q3W. Eligible patients had unresectable advanced or metastatic cancer and an ECOG performance status of ≤1. Safety/tolerability profile (primary endpoint) was examined by monitoring adverse events (AEs); secondary endpoints included antitumor activity, assessed by RECIST v1.1, and the pharmacokinetic (PK) parameters of each antibody. Results: As of Oct 30, 2019, 15 patients were enrolled in Part A (450 mg, n=3; 900 mg, n=3; 1350 mg, n=6; 1800 mg, n=3) and 12 in Part B. Across both parts, patients were female (n=17/29; 63%); squamous cell carcinoma of either skin or head and neck (n=5) and ovarian cancer (n=4) were the most common tumor types. Thirteen patients (48%) had ≥2 lines of prior systemic therapy. The most common treatment-related AEs (TRAEs) were fatigue (N=5; Part A, n=3; Part B, n=2) and nausea (N=4; n=2 in A and B); the only grade ≥3 TRAE occurring in ≥1 patient was grade 3 maculo-papular rash (N=2; n=1 in A and B). One patient in Part B experienced a fatal AE (acute kidney injury) considered possibly related to study treatment. Of the 15 patients receiving BGB-A333 monotherapy in Part A, three (20%) achieved a confirmed complete response and two (13.3%) achieved a partial response (PR). Two of the 12 (16.7%) patients receiving combination therapy in Part B achieved a PR. The PK of BGB-A333 was comparable to a typical IgG1 antibody, and was similar as a single-agent or in combination with tislelizumab. The PK of tislelizumab was comparable with historical data. Conclusions: BGB-A333, alone or in combination with tislelizumab, was generally well tolerated and demonstrated antitumor activity in patients with advanced solid tumors. Based on these data, expansion cohorts have been initiated. Citation Format: Jayesh Desai, Mark Voskoboynik, Ben Markman, Sophia Frentzas, Paul Foster, Nageshwar Budha, Jing Song, Tarek Meniawy. Preliminary safety and efficacy data of BGB-A333, an anti-PD-L1 monoclonal antibody, alone and in combination with tislelizumab in patients with advanced solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT253.

A phase I/II, two-part, multicenter, first-in-human study of DS-7300a in patients with advanced solid malignant tumors.

TPS3646 Background: B7 homologue 3 (B7-H3) is a protein that is overexpressed in various cancer types, including lung, head and neck squamous cell carcinoma, prostate, esophageal, and breast. B7-H3 overexpression is associated with poor prognosis because it promotes increased invasive and metastatic potential of cancer cells (Dong P, et al. Front Oncol. 2018;8:264). Currently, no B7-H3–targeted cancer therapies are approved. DS-7300a is an antibody-drug conjugate composed of a humanized anti–B7-H3 IgG1 monoclonal antibody (MABX-9001a) conjugated to a drug linker that releases its payload upon internalization by cancer cells. The payload, DXd, is an exatecan derivative that inhibits topoisomerase I, an enzyme that relaxes supercoiled DNA for replication and transcription. DS-7300a induced apoptosis in cancer cells in vitro and showed potent antitumor activity in xenograft models of various types of solid tumors in vivo. Methods: This phase 1/2, multicenter, nonrandomized, open-label, first-in-human study of DS-7300a is ongoing in the United States and Japan in patients with selected advanced solid tumors (NCT04145622). This study has 2 parts: dose escalation (part 1) and dose expansion (part 2). Primary objectives are to evaluate the safety, tolerability, and antitumor activity of DS-7300a and to determine the maximum tolerated dose or recommended dose for the expansion part. Secondary objectives include the pharmacokinetic characterization of DS-7300a, determination of the total levels of anti–B7-H3 antibody and the drug component (DXd), and assessment of the incidence of anti-drug antibodies against DS-7300a. Key inclusion criteria are age ≥ 18 years (United States) or ≥ 20 years (Japan), an ECOG performance status of 0 or 1, ≥ 1 measurable lesion according to RECIST 1.1 as assessed by the investigator, and consent to provide pre- and on-treatment tissue samples (mandatory if clinically allowed and not contraindicated). Key exclusion criteria include prior treatment with orlotamab, enoblituzumab, other B7-H3–targeted agents, or an antibody-drug conjugate that is conjugated with a topoisomerase I inhibitor. Dose expansion will start with 3 cohorts, including patients with selected advanced solid tumors. In both parts, DS-7300a will be administered intravenously on day 1 of each 21-day cycle. During dose escalation, the starting dose of DS-7300a is 0.8 mg/kg. This trial is currently in the dose-escalation part. Clinical trial information: NCT04145622 .