Single-agent Antitumor Activity Research Articles

Invention and characterization of a systemically administered, attenuated and killed bacteria-based multiple immune receptor agonist for anti-tumor immunotherapy.

Activation of immune receptors, such as Toll-like (TLR), NOD-like (NLR) and Stimulator of Interferon Genes (STING) is critical for efficient innate and adaptive immunity. Gram-negative bacteria (G-NB) contain multiple TLR, NOD and STING agonists. Potential utility of G-NB for cancer immunotherapy is supported by observations of tumor regression in the setting of infection and Coley's Toxins. Coley reported that intravenous (i.v.) administration was likely most effective but produced uncontrollable toxicity. The discovery of TLRs and their agonists, particularly the potent TLR4 agonist lipopolysaccharide (LPS)-endotoxin, comprising ~75% of the outer membrane of G-NB, suggests that LPS may be both a critical active ingredient and responsible for dose-limiting i.v. toxicity of G-NB. This communication reports the production of killed, stabilized, intact bacteria products from non-pathogenic G-NB with ~96% reduction of LPS-endotoxin activity. One resulting product candidate, Decoy10, was resistant to standard methods of cell disruption and contained TLR2,4,8,9, NOD2 and STING agonist activity. Decoy10 also exhibited reduced i.v. toxicity in mice and rabbits, and a largely uncompromised ability to induce cytokine and chemokine secretion by human immune cells in vitro, all relative to unprocessed, parental bacterial cells. Decoy10 and a closely related product, Decoy20, produced single agent anti-tumor activity or combination-mediated durable regression of established subcutaneous, metastatic or orthotopic colorectal, hepatocellular (HCC), pancreatic, and non-Hodgkin's lymphoma (NHL) tumors in mice, with induction of both innate and adaptive immunological memory (syngeneic and human tumor xenograft models). Decoy bacteria combination-mediated regressions were observed with a low-dose, oral non-steroidal anti-inflammatory drug (NSAID), anti-PD-1 checkpoint therapy, low-dose cyclophosphamide (LDC), and/or a targeted antibody (rituximab). Efficient tumor eradication was associated with plasma expression of 15-23 cytokines and chemokines, broad induction of cytokine, chemokine, innate and adaptive immune pathway genes in tumors, cold to hot tumor inflammation signature transition, and required NK, CD4+ and CD8+ T cells, collectively demonstrating a role for both innate and adaptive immune activation in the anti-tumor immune response.

Preclinical development of SGN-CD47M: Protease-activated antibody technology enables selective tumor targeting of the innate immune checkpoint receptor CD47.

CD47 is a cell surface glycoprotein that is expressed on normal human tissues and has a key role as a marker of self. Tumor cells have coopted CD47 overexpression to evade immune surveillance and thus blockade of CD47 is a highly active area of clinical exploration in oncology. However, clinical development of CD47-targeted agents has been complicated by its robust expression in normal tissues and the toxicities that arise from blocking this inhibitory signal. Further, pro-phagocytic signals are not uniformly expressed in tumors and antibody blockade alone is often not sufficient to drive antitumor activity. The inclusion of an IgG1 antibody backbone into therapeutic design has been shown to serve as an additional pro-phagocytic signal but also exacerbates toxicities in normal tissues. Therefore, a need persists for more selective therapeutic modalities targeting CD47. To address these challenges, we developed SGN-CD47M, a humanized anti-CD47 IgG1 monoclonal antibody linked to novel masking peptides through linkers designed to be cleaved by active proteases enriched in the tumor microenvironment. Masking technology has the potential to increase the amount of drug that reaches the tumor microenvironment, while concomitantly reducing systemic toxicities. We demonstrate that SGN-CD47M is well tolerated in cynomolgus monkeys and displays a 20-fold improvement in tolerability to hematologic toxicities when compared to the unmasked antibody. SGN-CD47M also displays preferential activation in the tumor microenvironment that leads to robust single-agent antitumor activity. For these reasons, SGN-CD47M may have enhanced antitumor activity and improved tolerability relative to existing therapies that target the CD47-SIRPα interaction.

Safety and efficacy of eribulin plus anlotinib in patients with advanced soft tissue sarcoma (ERAS): A multi-center phase II study.

11561 Background: Both the microtubule-dynamics inhibitor eribulin and the multi-targeted tyrosine kinase inhibitor anlotinib exhibit single-agent anti-tumor activity in previously treated soft tissue sarcoma (STS). This study aimed to evaluate the efficacy and safety of the combination treatment of eribulin and anlotinib in patients with advanced STS. Methods: In this multi-center phase II study (ERAS), patients with advanced soft tissue sarcoma who relapsed/progressed after anthracycline chemotherapy or were not candidates for such treatment were included. Patients received eribulin (1.1 mg/m² intravenously on days 1 and 8) and anlotinib (12mg orally once daily on days 1-14) every 21 days for 6-8 cycles, followed by anlotinib maintenance. The primary endpoint was progression-free survival rate at 24 weeks (PFR24w). Secondary endpoints included median progression-free survival (mPFS), median overall survival (mOS), objective response rate (ORR), disease control rate (DCR) and safety. Results: Thirty-one patients were enrolled. Twenty-eight (90.3%) patients had received anthracycline chemotherapy, and the remaining 3 (9.7%) were chemotherapy-naïve. Pathological types included L-type sarcomas (10 leiomyosarcomas and 6 dedifferentiated liposarcomas) and non-L-type sarcomas (n =15, with 8 subtypes). As of the cut-off date of Jan 28, 2024, the median follow-up time was 30.4 weeks. Response evaluation was feasible in 29 patients. The ORR, DCR and predicted PFR24w were 20.7%, 82.8% and 65.5%, respectively. The mPFS was 30.1 weeks, with no significant difference observed between patients with L-type sarcomas and non-L-type sarcomas. The mOS was not reached. Nineteen (61.3%) patients experienced at least one grade 3/4 adverse event. The most common grade 3/4 adverse events included neutropenia (35.5%), leukopenia (25.8%), hypertension (16.1%), hypertriglyceridemia (16.1%) and increased gamma-glutamyl transpeptidase (16.1%). Conclusions: The combination of eribulin and anlotinib shows promising efficacy with an acceptable toxicity profile in patients with advanced STS, irrespective of pathological type. Clinical trial information: ChiCTR2300067650.

Preliminary safety and efficacy of TQB2930, a HER2-targeted bispecific antibody in patients with advanced breast cancer: Results from a phase 1b study.

1026 Background: TQB2930 is a HER2-targeted bispecific antibody, binding to two distinct HER2 epitopes, the same domain as trastuzumab (ECD4) and pertuzumab (ECD2). This study aims to evaluate the safety and efficacy of TQB2930 for patients with advanced breast cancer after failure of standard therapy. Methods: This phase 1b, dose-escalation and expansion trial included patients preferred HER2-expressing or HER2-amplified breast cancer who had received standard therapy. In the dose-escalation phase, TQB2930 was given weekly (10mg/kg, QW), biweekly (20mg/kg, Q2W), or triweekly (30mg/kg, Q3W). After the dose-escalation phase, eligible patients were enrolled and dosed biweekly or triweekly in the expansion cohort. The primary endpoints were safety, maximum tolerated or maximum administered dose, and the secondary endpoints were immunogenicity, pharmacokinetics, and tumor response per RECIST v1.1. Results: As of Dec 20, 2023, 34 patients(pts) have received TQB2930 weekly (n=3), biweekly (n=16), and triweekly (n=15). All pts were female, the median age was 59. 22 pts had HER2 expression of ICH3+ or ICH2+ with FISH+, and the others had ICH2+ with FISH- or ICH1+. The median prior lines of therapies were 3 (range: 0-8), with one pt intolerance to first-line treatment enrolled, and the median prior lines of HER2-targeted therapies were 2 (range: 0-8). No dose-limited toxicity was observed. The main treatment-related adverse events (TRAEs) were infusion reaction, occult blood of urine, leukopenia, and neutropenia. 3 pts were reported grade≥3 TRAEs, including neutropenia, anemia, and hypokalemia. Of 31 response-evaluable pts, the objective response rate (ORR) was 25.8% with 8 partial responses (PRs) were observed (including 5 confirmed PRs and 3 PRs awaiting confirmation). The disease control rate was 80.6%. Moreover, 5 pts achieved PR at 30mg/kg (ORR 41.7%), including one with prior exposure to trastuzumab, pyrotinib, tucatinib, ARX788, and the other one prior to trastuzumab, pertuzumab, lapatinib, MRG002. The median progression-free survival for all pts was 5.5 months (95%CI 3.58-NE). Additionally, Pharmacokinetic analysis showed exposure (Cmax and AUC0-t) of TQB2930 increased linearly with doses within 10~30mg/kg. After dosing, the mean peak concentration reached at 2.5-4.3 h, and the elimination half-life of TQB2930 was 109-161 h. Conclusions: TQB2930 is well tolerated and has demonstrated promising single-agent anti-tumor activity in HER2-positive breast cancer who have failed standard anti-HER2 therapies, including multiple lines of prior HER2 targeted agents. These early signs of activity support the further exploration of combination therapy of TQB2930 and the study is ongoing. Clinical trial information: NCT06202261 .

Abstract CT259: Results from monotherapy dose escalation of MDNA11, a long-acting IL-2 superkine, in a phase 1/2 trial show evidence of single-agent activity in advanced solid tumors

Abstract Background: MDNA11 is an albumin-fused ‘beta-enhanced not-alpha’ IL-2 agonist engineered to preferentially expand and activate CD8+ T and NK cells with minimal impact on Tregs. The ABILITY-1 (A Beta-only IL-2 ImmunoTherapY) is a global Phase 1/2 study evaluating the safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary clinical activity of MDNA11, both as single agent and in combination with a PD-1 inhibitor, in pre-treated patients with advanced solid tumors. Method: The ABILITY-1 study (NCT05086692) comprises monotherapy dose escalation/evaluation with a modified 3+3 design (enrollment complete); monotherapy dose expansion (enrolling); combination with pembrolizumab dose escalation (enrolling) followed by combination expansion. Thirty participants were enrolled in the monotherapy cohorts (3, 10, 30, 60, 90, and 120 μg/kg, IV, Q2W): 23 in dose escalation and 7 in dose evaluation. To enhance tolerability, step-up dosing with 2 or 3 priming doses was implemented starting at 60 μg/kg. Primary endpoints were incidence and severity of adverse events (AEs) and secondary endpoints included PK, PD, and tumor response (RECIST 1.1 and iRECIST). Results: As of December 22, 2023, 30 patients were enrolled in dose-escalation/evaluation, comprising 16 melanoma, 3 NSCLC, 3 PDAC, 2 RCC, 2 sarcoma, 2 ovarian cancer, 1 tonsillar squamous cell carcinoma and 1 gastro-esophageal adenocarcinoma. No dose-limiting toxicities (DLTs) were observed. Most common treatment related AEs were infusion-related reactions (53.3%), primarily grade 1-2, encompassing pyrexia (43.3%), nausea (33.3%), chills (33.3%), hypotension (30%), and fatigue (26.6%) that resolved within 48-72 hours. PK analysis showed sustained dose-dependent increase in serum concentration of MDNA11 with repeat doses. PD evaluation showed robust and durable dose-dependent increase in lymphocyte counts without eosinophilia. Immune effector cells, particularly CD8+ T cells, showed durable expansion with evidence of activation markers (CD25, ICOS and OX40) peaking at the 90 μg/kg dose. Single-agent anti-tumor activity was evident among 26 evaluable patients with confirmed partial responses (PRs) in a PDAC (MSI-H) patient (60 μg/kg cohort) and a melanoma patient (90 μg/kg cohort) as well as 8 (30.7%) stable disease (SD) including 3 melanoma patients with durable SD (>6 months, >8 months, >1.5 years). Based on the combined safety, PK, PD and preliminary anti-tumor activity, a recommended dose for expansion (RDE) of 90 μg/kg (preceded by priming doses of 30 and 60 μg/kg; Q2W) was selected for the ongoing monotherapy dose expansion of the ABILITY-1 study. Conclusions: MDNA11 was well-tolerated with no DLTs observed at all dose levels up to 120 μg/kg. With study currently ongoing, single agent clinical activity was evident with an ORR of 7.7% and Clinical Benefit Rate (CBR) of 19.2% (2 PRs + 3 SDs > 6 months) in dose escalation to date. Monotherapy dose expansion at 90 μg/kg and combination dose escalation with pembrolizumab are enrolling. Citation Format: Victoria G. Atkinson, Jesus F. Antras, Philippe Bedard, Warren Brenner, Jacqueline Brown, Charlotte R. Lemech, Peter Lloyd, Kim Margolin, Matthen Mathew, John J. Park, Sajeve Thomas, Przemyslaw Twardowski, Humphrey Gardner, Amy Prawira, Melissa Coello, Walead Ebrahimimizadeh, Minh D. To, Rosemina Merchant, Sudhir Madduri Karanam, Arash Yavari, Lillian L. Siu, Hussein A. Tawbi, Paolo A. Ascierto. Results from monotherapy dose escalation of MDNA11, a long-acting IL-2 superkine, in a phase 1/2 trial show evidence of single-agent activity in advanced solid tumors [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 CT259.

Abstract SY12-01: Targeting validated but un-drugged oncogenes with small molecule protein degraders

Abstract SY12-01: Targeting validated but un-drugged oncogenes with small molecule protein degraders

Abstract LB406: Synergistic antitumor effect of FRα TOP1i antibody drug conjugate, AZD5335, in combination with the PARP1 inhibitor, saruparib (AZD5305), in preclinical models of ovarian cancer

Abstract Folate receptor alpha (FRα) is a cell surface GPI-anchored protein overexpressed in several solid tumors with highest prevalence in ovarian cancer and lung adenocarcinoma but restricted expression in normal tissues. AZD5335, an FRα-targeting antibody conjugated to AZ’s proprietary topoisomerase 1 inhibitor (TOP1i) payload, AZ14170132, is currently being investigated in the FONTANA Phase 1/2 clinical trial (NCT05797168). Since homologous recombination repair deficiency (HRD) and mutations in genes involved with homologous recombination repair (HRRm+) are associated with sensitivity to DNA damaging agents, we evaluated the efficacy of AZD5335 in ovarian cancer patient-derived xenograft (PDX) models assessed for HRRm, as described1. Sixteen ovarian cancer PDX models were each treated with a single dose of AZD5335 (5 mg/kg IV). Of the HRRm- cohort, 8/11 (73%) cohort responded to treatment with a tumor regression >30% from baseline. In the HRRm+ cohort 4/5 (80%) responded to AZD5335. PARP1 can act as a positive regulator of genomic stability by counteracting TOP1-induced DNA damage (Malanga and Althaus, 2004) that led to the hypothesis that the efficacy of TOP1i drugs can be enhanced by combination with PARP inhibitors. To evaluate for potential synergy of AZD5335 with the PARP1 inhibitor, saruparib (AZD5305): Three FRα-expressing cancer cell lines, KB, IGROV-1 and OVCAR-3, were treated with AZD5335 +/- saruparib, revealing evidence of synergistic cytotoxicity. These results encouraged us to investigate this combination in pre-clinical HRRm+ in vivo xenograft models (OVCAR-3 and OV2022F). In OVCAR-3 xenograft models, single agent activity with saruparib (1 mg/kg PO QD x28) was 37% tumor growth inhibition (TGI) and with AZD5335 (0.625 mg/kg IV x1) was 50% TGI while combined administration at the same doses improved TGI to 86%. Similar combinatorial activity was seen in OV2022F with TGI 61%, 54%, and 97% for saruparib, AZD5335, and saruparib +AZD5335, respectively. In conclusion, AZD5335 exhibits a similar degree of single agent antitumor activity in both HRRm+ and HRRm- preclinical models, and the efficacy can be potentiated by combining with the PARP inhibitor, saruparib. 1. Clarke et al. 2022, NEJM Evid 2022;1(9) DOI: 10.1056/EVIDoa22000432. Malanga and Althaus 2004, JBC 2004; 279(7) DOI: 10.1074/jbc.C3004372003. Citation Format: Marco Gymnopoulos, Ravinder Tammali, Ana De Almeida, Jixin Wang, Claire Myers, Mark Albertella, Paula G. Fraenkel, Puja Sapra. Synergistic antitumor effect of FRα TOP1i antibody drug conjugate, AZD5335, in combination with the PARP1 inhibitor, saruparib (AZD5305), in preclinical models of ovarian cancer [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 LB406.

Abstract 7550: KB-0742, an oral highly selective CDK9 inhibitor, demonstrates preclinical activity in transcription factor fusion driven adenoid cystic carcinoma patient-derived models

Abstract Adenoid Cystic Carcinoma (ACC) is an aggressive rare type of cancer of the secretory glands with no approved targeted therapy and high unmet clinical need. Deregulated transcription driven by MYB-NFIB or MYBL1-NFIB transcription factor (TF) fusions are a hallmark of ACC pathogenesis. More aggressive disease and resistance to therapy has been associated with co-mutation in NOTCH. Although direct targeting of oncogenic TF fusions has remained challenging, targeting of their activity via transcriptional cofactors has emerged as an attractive and clinically actionable strategy. Cyclin-dependent kinase 9 (CDK9) is a key potentiator of TF activity via its ability to act both as an upstream regulator of TF expression and a downstream cofactor. KB-0742 is a potent, selective, and orally bioavailable inhibitor of CDK9 with a long plasma half-life. KB-0742 is being studied in an ongoing Phase 1/2 study (NCT04718675) in advanced solid tumors including ACC. KB-0742 has demonstrated on-mechanism, single agent anti-tumor activity and a manageable safety profile in heavily pre-treated patients (0-11 prior lines of therapy) with transcriptionally addicted solid tumors. Here we present the preclinical rationale for targeting of oncogenic fusion TF activity in ACC. XenoSTART Patient-Derived Xenograft (XPDX) models were established from viable human tumor tissue for in vivo and ex vivo testing. Cell viability was assessed by CellTiter GLO reagent and phase imaging. Changes in MYB-fusion transcripts were assessed by RNA-Seq. Tumor Fragments (~70 mg) from ACCx5M1, ACCx6, ACCx9, ACCx11 models were implanted into athymic nude mice. Animals were treated with either vehicle (normal saline) or 60 mg/kg KB-0742 on a Q3D/week until tumors reached 2500 mm3 or up to 60 days post start of treatment. In a retrospective analysis using real world data, ACC has a low incidence of genomic instability and high rates of MYB fusions detectable by RNA-seq, making immunotherapy challenging but creating an opportunity for targeting MYB transcription. In primary MYB-fusion positive and NOTCH co-mutated patient-derived spheroid models, KB-0742 treatment induced strong antiproliferative activity and cytotoxicity. Importantly, KB-0742 demonstrated stronger cytotoxic effects when compared to historical control agents. In XPDXs, CDK9 inhibition with KB-0742 resulted in antiproliferative activity and stronger tumor growth inhibition in MYB-fusion positive and NOTCH co-mutated tumor models compared to MYB-fusion positive only models.These data demonstrate KB-0742 is effective in preclinical models of ACC suggesting KB-0742 may be a promising therapeutic option for ACC patients. KB-0742 is currently being evaluated in a phase 1/2 dose-escalation and cohort expansion trial in patients with ACC and other transcriptionally addicted tumors (NCT04718675). Citation Format: Michael R. McKeown, Luis A. Carvajal, Tressa R. Hood, Nicole S. Burr, Jeffrey Kaufman, Adam Boynton, Kameron Mori, Tessa DesRochers, Michael Wick, Charles Y. Lin, Jorge F. DiMartino. KB-0742, an oral highly selective CDK9 inhibitor, demonstrates preclinical activity in transcription factor fusion driven adenoid cystic carcinoma patient-derived models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7550.

Reprogramming tumor-associated macrophages by a dually targeted milk exosome system as a potent monotherapy for cancer

Tumor-associated macrophages (TAMs) play a key role in inducing an immunosuppressive tumor microenvironment (TME) and cancer immune escape. We previously revealed that PDL1 (a key immune checkpoint) was upregulated in TAMs and induced M2 polarization, highlighting PDL1 in TAMs as a promising cancer therapeutic target. In this study, we developed an engineered milk exosome (mExo) system decorated with M2pep (an M2 macrophage binding peptide) and 7D12 (an anti-EGFR nanobody) (7D12-mExo-M2pep-siPDL1) to specifically deliver siPDL1 into M2 TAMs. A series of in vitro and in vivo assays showed that the dually targeted engineered mExos efficiently delivered siPDL1 into M2 TAMs and repolarized them into M1 macrophages, restoring CD8+ T cell immune activity and remodeling TME. Importantly, systemically administered 7D12-mExo-M2pep-siPDL1 showed efficient single-agent antitumor activity, resulting in nearly 90% tumor growth inhibition in a mouse model of orthotopic epidermal growth factor receptor (EGFR) cancer. Collectively, our study indicates that PDL1 is a promising target for TAM-based cancer immunotherapy, and our engineered mExo-based nanomedicine represents a novel tool for specifically targeting M2 TAMs, distinguishing this novel therapeutic method from other TAM-targeting therapies and highlighting its promising clinical potential.

A highly potent anti-VISTA antibody KVA12123 -a new immune checkpoint inhibitor and a promising therapy against poorly immunogenic tumors.

Immune checkpoint therapies have led to significant breakthroughs in cancer patient treatment in recent years. However, their efficiency is variable, and resistance to immunotherapies is common. VISTA is an immune-suppressive checkpoint inhibitor of T cell response belonging to the B7 family and a promising novel therapeutic target. VISTA is expressed in the immuno-suppressive tumor microenvironment, primarily by myeloid lineage cells, and its genetic knockout or antibody blockade restores an efficient antitumor immune response. Fully human monoclonal antibodies directed against VISTA were produced after immunizing humanized Trianni mice and single B cell sequencing. Anti-VISTA antibodies were evaluated for specificity, cross-reactivity, monocyte and T cell activation, Fc-effector functions, and antitumor efficacy using in vitro and in vivo models to select the KVA12123 antibody lead candidate. The pharmacokinetics and safety profiles of KVA12123 were evaluated in cynomolgus monkeys. Here, we report the development of a clinical candidate anti-VISTA monoclonal antibody, KVA12123. KVA12123 showed high affinity binding to VISTA through a unique epitope distinct from other clinical-stage anti-VISTA monoclonal antibodies. This clinical candidate demonstrated high specificity against VISTA with no cross-reactivity detected against other members of the B7 family. KVA12123 blocked VISTA binding to its binding partners. KVA12123 induced T cell activation and demonstrated NK-mediated monocyte activation. KVA12123 treatment mediated strong single-agent antitumor activity in several syngeneic tumor models and showed enhanced efficacy in combination with anti-PD-1 treatment. This clinical candidate was engineered to improve its pharmacokinetic characteristics and reduce Fc-effector functions. It was well-tolerated in preclinical toxicology studies in cynomolgus monkeys, where hematology, clinical chemistry evaluations, and clinical observations revealed no indicators of toxicity. No cytokines associated with cytokine release syndrome were elevated. These results establish that KVA12123 is a promising drug candidate with a distinct but complementary mechanism of action of the first generation of immune checkpoint inhibitors. This antibody is currently evaluated alone and in combination with pembrolizumab in a Phase 1/2 open-label clinical trial in patients with advanced solid tumors.

Intratumoral aluminum hydroxide-anchored IL-12 drives potent antitumor activity by remodeling the tumor microenvironment.

IL-12 is a potent cytokine that can promote innate and adaptive anticancer immunity, but its clinical development has been limited by toxicity when delivered systemically. Intratumoral (i.t.) administration can expand the therapeutic window of IL-12 and other cytokines but is in turn limited by rapid drug clearance from the tumor, which reduces efficacy, necessitates frequent administration, and increases systemic accumulation. To address these limitations, we developed an anchored IL-12 designated ANK-101, composed of an engineered IL-12 variant that forms a stable complex with the FDA-approved vaccine adjuvant aluminum hydroxide (Alhydrogel). Following i.t. administration of murine ANK-101 (mANK-101) in early intervention syngeneic mouse tumors, the complex formed a depot that was locally retained for weeks as measured by IVIS or SPECT/CT imaging, while unanchored protein injected i.t. was cleared within hours. One or 2 i.t. injections of mANK-101 induced single-agent antitumor activity across a diverse range of syngeneic tumors, including models resistant to checkpoint blockade at doses where unanchored IL-12 had no efficacy. Local treatment with mANK-101 further induced regressions of noninjected lesions, especially when combined with systemic checkpoint blockade. Antitumor activity was associated with remodeling of the tumor microenvironment, including prolonged IFN-γ and chemokine expression, recruitment and activation of T and NK cells, M1 myeloid cell skewing, and increased antigen processing and presentation. Subcutaneous administration of ANK-101 in cynomolgus macaques was well tolerated. Together, these data demonstrate that ANK-101 has an enhanced efficacy and safety profile and warrants future clinical development.

Abstract B162: NXP900, a novel YES1/SRC kinase inhibitor demonstrates inhibition of YAP1 nuclear localization and potent single agent anti-tumor activity in esophageal squamous cancer models

Abstract Background: NXP900 (eCF506) is a novel potent and selective SRC family kinase (SFK) inhibitor, (IC50 of 0.47 nM against YES1). NXP900 locks its target into its native “closed” conformation (type 1.5 inhibitor), thereby inhibiting both kinase activity and complex formation with protein partners (Temps et al. Cancer Res. 2021, 81, 5438-5450). In contrast, multi-kinase inhibitors, including dasatinib and bosutinib, block SRC in the active “open” conformation (type 1 inhibitors) promoting the association of SFK and signaling partners via allosteric facilitation (Higuchi et al. Cell Rep 2021, 34, 108876). Crosstalk between YES1 and the Hippo pathway suggests that NXP900 may have therapeutic potential in cancers with Hippo pathway alterations. YES1 and Hippo pathway alterations are prevalent in several squamous cancers including esophageal (ESCC), lung, head and neck, and cervical. Methods: Animal strain: CD1 Nude mice (Charles River). Human ESCC cancer cell lines: KYSE70, OE21, KYSE410, KYSE30 and OE19 cells (Sigma), KYSE140 (DSMZ), TE5, and TE14 (Riken). Xenograft tumors were generated by subcutaneous implantation on the right lower flank of the thigh at a cell density of 2x106 to 1x107 cells/mouse. Experiment groups: Vehicle, NXP900 (40 mg/kg); treatment: QD for 28 days, oral gavage. Colony formation assay: 500 (KYSE70, OE21, KYSE410, KYSE30) or 1500 cells (OE19, TE5, TE14) were seeded in 24 well plates in triplicates and treated with NXP900 for 14 days followed by staining with crystal violet. KYSE70 and KYSE140 cells were treated with NXP900 for 24 hours before fixation and labelling with anti-YAP, phalloidin and hoechst. Images were analyzed using IN Carta® software. Expression and mutation status of hippo pathway modulators was determined by analysis of Dependency Map (DepMap) data. Results: NXP900 strongly inhibited cell proliferation of KYSE70, KYSE410, KYSE30, OE21, OE19, TE5 and TE14 in a colony formation assay. NXP900 significantly inhibited the activating phosphorylation of SRC in KYSE70 cells at 10 nM. Potent dose-dependent reduction in YAP1 nuclear localization was observed in ESCC lines. Oral administration of NXP900 in a KYSE70 xenograft mouse model with YES1 gene amplification, resulted in an average decrease of tumor volume of 71% while in the vehicle control group tumor volume increased by 472% (p ≤ 0.001), demonstrating significant tumor regression. Body weight measurements indicate good tolerability. Bioinformatics analysis demonstrate elevated expression and mutation of several hippo pathway modulators in ESCC cells responding to NXP900 in this study. Conclusions: NXP900 is a novel potent and selective YES1/SRC kinase inhibitor with subnanomolar IC50 against YES1. NXP900 potently inhibits YAP1 nuclear localization and cell proliferation in a panel of ESCC cell lines and induces tumor regressions in a KYSE70 xenograft model providing substantial proof of concept for targeting solid tumors with YES1 and Hippo pathway alterations. An IND for NXP900 has been cleared by the FDA and the start of the phase 1 study is pending. Citation Format: Neil O Carragher, Sweta Dash, Katherine Nyswaner, Mungo J B Harvey, Ben King, Allison Woods, Asier Unciti-Broceta, Enrique Poradosu, John Brognard. NXP900, a novel YES1/SRC kinase inhibitor demonstrates inhibition of YAP1 nuclear localization and potent single agent anti-tumor activity in esophageal squamous cancer models [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 B162.

EX103, a Novel CD20xCD3 Bispecific Antibody, Showed a Favorable Safety and Potent Single-Agent Antitumor Activity in Heavily Pretreated Relapsed/Refractory Patients with B-Cell Non-Hodgkin Lymphoma

Introduction Non-Hodgkin lymphoma (NHL) is one of the most common cancers in the United States, and relapsed or refractory (R/R) B cell NHL had a poor prognosis. In recent years, T cell engaging bispecific antibody (TCB) emerged as a promising therapy. Nevertheless, severe cytokine release syndrome (CRS) remains to be a significant challenge in TCB treatment. To overcome this issue, we designed a new CD20xCD3 bispecific antibody (EX103) with a lower affinity to CD3. In the non-human primate tox study, EX103 induced much lower IL-6 release. Preliminary data from dose escalation part of Phase I clinical study demonstrates that EX103 has an encouraging safety and robust single-agent antitumor activity trend, even at low doses, in heavily pretreated R/R B-NHL patients. Method The dose-escalation part (8 dose cohorts, ranging from 1.2 to 36 mg) of this Phase I, multicenter, single-arm, open-label clinical trial has enrolled R/R CD20+ B-cell non-Hodgkin lymphoma subjects at 4 study sites in China. Objectives include safety, dose finding (RP2D), and antitumor activity. Eligible patients in each cohort received intravenous(iv) step-up doses of EX103 (with 1 priming dose and 2 intermediate doses followed by 1 target dose of EX103) administered in a 28-day dose limiting toxicity (DLT) observation period, and then received a target dose every 2 weeks for up to 12 cycles until disease progression or unacceptable toxicity. Response rates reported are based on the Lugano criteria (2014). Results As of June 2023, 5 cohorts (target dose from 1.2 to 18 mg) of the dose-escalation were completed. Among 13 evaluable patients , 9 of them are aggressive B-NHL (5 Diffuse large B-cell lymphoma (DLBCL), 3 Follicular lymphoma (FL) grade 3B, and 1 Mantle cell lymphoma (MCL)), 2 of them are indolent B-NHL (1 FL grade 1-3A, 1 Marginal zone lymphoma (MZL)), and 2 of them are Chronic lymphocytic leukemia (CLL). No DLT was observed, and the maximum tolerated dose (MTD) was not reached. The most common adverse events (AEs) were CRS, pyrexia, neutropenia, thrombocytopenia. All CRS were grade (Gr) 1-2, no Gr 3 or higher CRS. Most CRS events occurred in first or second treatment cycle, and all CRS related clinical symptoms were resolved within 48 hours. No Immune effector cell-associated neurotoxicity syndrome (ICANS) or other clinically significant neurologic AEs were reported. Among those patients, the median age was 51 years (range 43-66) and median number of prior lines of treatment was 5 (range 2-8). The preliminary Disease Control Rate (DCR) is 84.6% (11/13). Among 9 aggressive NHL patients, the overall response rate (ORR) was 67.7 % (6/9), including 3 DLBCL patients (1 each in 6 or 12 or 18 mg cohorts) and 1 MCL patient (in 3 mg cohort) achieving CR, and 2 grade 3B FL patients achieving PR (1 each in 6 or 18 mg cohorts). Both indolent NHL patients (1 FL (Grade 1-3A) and 1 MZL in 12 mg cohort) achieved PR and the preliminary ORR for indolent NHL was 100.0 % (2/2). Of 2 CLL patients, 1 achieved SD (3mg cohort). It is worth mentioning that two of the patients who failed prior CAR-T treatment had achieved PR after received 6-14 week treatment of EX103. Both patients are still under EX103 treatment. Conclusions Although this study has a limited number of subjects so far and the findings are preliminary, the available dose-escalation data demonstrate that single-agent EX103, even at low doses (3 or 6 mg), exhibits remarkable antitumor activity and favorable safety. Furthermore, EX103 demonstrates promising efficacy in heavily pretreated patients with R/R B-NHL, including some who have previously failed CAR-T treatment. The safety and efficacy of EX103 will be further evaluated in an ongoing clinical study.

MALT1 Protease Inhibition Overcomes BTK Inhibitor Resistance and Shows Synergistic Activity with Venetoclax in Models of B Cell Lymphoma and Leukemia

Background Specific B cell malignancies, including the aggressive non-germinal center B cell-like (GCB) subtype of diffuse large B cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), are driven by constitutive activation of the transcription factor NF-kB. Chronic signaling resulting from mutations or antigen-induced activation of the B cell receptor (BCR) pathway drives NF-kB activity in these tumors resulting in sustained proliferation and survival pathways. Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) represents a key mediator of the BCR/NF-kB signal transduction pathway responsible for maintaining survival and driving proliferation of NF-kB-addicted B cell tumors by proteolytically cleaving NF-kB antagonists. Aims Pharmacological inhibition of MALT1 protease activity may provide an attractive treatment option for patients with these cancers. Further, as combination therapy is often required for the treatment of aggressive B cell malignancies, the identification of therapies that synergistically combine with MALT1 inhibitors could afford additional and promising treatment options. Methods A highly potent and orally bioavailable MALT1 protease inhibitor (ABBV-MALT1) was used to test the hypothesis that MALT1 inhibition will abrogate the proliferation of preclinical models of B cell malignancies in vitro and in vivo. Tumors treated with ABBV-MALT1 were subjected to transcriptomic and functional proteomic assays to elucidate molecular mechanisms of action and rational combination partners. Results ABBV-MALT1 potently inhibits MALT1 activity in vitro while showing high selectivity against a panel of proteases, kinases and other types of receptors and enzymes. Mechanistic studies reveal that ABBV-MALT1 effectively inhibits signal transduction of the BCR pathway and reduces NF-kB gene activation in non-GCB DLBCL cell lines resulting in cell cycle arrest and diminished viability. In vivo, oral administration of this compound demonstrates robust tumor growth inhibition in several models of B cell tumors, including non-GCB DLBCL models that are resistant to Bruton's tyrosine kinase (BTK) inhibitors. NF-kB target genes include the pro-survival family members BCL-XL and BCL2-A1, which aid in regulation of the intrinsic apoptosis pathway. As ABBV-MALT1-induced inhibition of the NF-kB pathway resulted in downregulation of these genes, we hypothesized that the associated tumor models would become increasingly dependent on the pro-survival family member BCL-2. To test this hypothesis, combination studies of ABBV-MALT1 and the selective BCL-2 inhibitor venetoclax were performed in both cell line and patient-derived xenograft models of DLBCL. Herein we show that concomitant administration of ABBV-MALT1 and venetoclax results in dramatic antitumor activity in all models tested in vivo. This efficacy also translates to primary patient CLL cells in vitro where the combination confers greater levels of apoptosis compared to either agent alone. Summary/Conclusion: ABBV-MALT1 demonstrates robust single agent anti-tumor activity in malignant B cell models that are resistant to BTK inhibitors. Moreover, combination of ABBV-MALT1 with the BCL-2 inhibitor venetoclax shows synergistic cell killing of B cell tumors in vitro and dramatic tumor regression in vivo. Together, these data indicate that MALT1 inhibition may overcome BTK inhibitor resistance and combine with venetoclax to effectively treat patients with DLBCL, CLL and other B cell malignancies. Disclosures All authors are employees of AbbVie. The design, study conduct, and financial support for this research were provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication.

EPCORE FL-1: Phase 3 Trial of Subcutaneous Epcoritamab with Rituximab and Lenalidomide (R 2) Vs R 2 Alone in Patients with Relapsed or Refractory Follicular Lymphoma

Background: Follicular lymphoma (FL) is the most common form of indolent non-Hodgkin lymphoma (NHL). Several treatment options are approved by the US Food and Drug Administration for second- or later-line FL therapy, including rituximab + lenalidomide (R 2). However, advanced-stage FL remains incurable and new treatment options for relapsed or refractory (R/R) disease are needed. Epcoritamab, a subcutaneously administered, bispecific antibody that binds CD3 on T lymphocytes and CD20 on B cells, induces potent and selective T-cell-mediated killing of malignant CD20 + B cells (van der Horst et al, Blood Cancer J 2021). In the first-in-human, phase 1/2 EPCORE NHL-1 trial (NCT03625037) in heavily pretreated patients with B-cell NHL (N=68), epcoritamab showed manageable safety and promising single-agent anti-tumor activity (Hutchings et al, Lancet 2021). Among 10 patients with R/R FL, objective response rate (ORR) was 90% (95% CI: 55-100) and complete response (CR) rate was 50%. In the ongoing phase 1b/2 trial evaluating epcoritamab + R 2 for R/R FL (EPCORE NHL-2 arms 2a and 2b; NCT04663347), ORR was 98% among 104 efficacy-evaluable patients, with a complete metabolic response in 87%. Most cytokine release syndrome (CRS) events were low grade (n=111; grade 1-2, 46%; grade 3, 2%) and occurred in cycle 1; all CRS events resolved with routine management. These encouraging data, and the distinct mechanisms of action of epcoritamab and R 2, support ongoing evaluation of this combination for its potential to improve clinical outcomes in patients with R/R FL. The phase 3 EPCORE FL-1 trial was designed to evaluate epcoritamab in combination with R 2 vs R 2 alone in patients with R/R FL with ≥1 prior line of anti-lymphoma therapy. We present an updated protocol, reflecting recent developments and revisions implemented in this study. Study Design and Methods: EPCORE FL-1 (NCT05409066) is a global, randomized, open-label, multicenter phase 3 trial designed to evaluate efficacy and safety of epcoritamab in combination with R 2 vs R 2 alone in patients with R/R FL. Adult patients must have histologically confirmed classic FL (previously grades 1 to 3a FL) stage II, III, or IV with a CD20 + tumor on a representative biopsy based on local pathology report and no evidence of histologic transformation. Patients must have R/R disease after ≥1 prior anti-lymphoma regimen that contained an anti-CD20 monoclonal antibody in combination with chemotherapy; patients receiving only prior anti-CD20 monoclonal antibody monotherapy and/or radiation are not eligible. Other key eligibility criteria include Eastern Cooperative Oncology Group performance status 0 to 2, fluorodeoxyglucose positron emission tomography-avid disease, and ≥1 measurable disease site per Lugano 2014 criteria. Lenalidomide-refractory FL (best response to lenalidomide of stable or progressive disease or progressive disease within 6 months of completion of lenalidomide) is excluded. Approximately 520 patients will be enrolled and randomized 1:1 to receive a full dose of epcoritamab in combination with R 2 or R 2 alone ( Figure); the trial is currently enrolling in 2 arms, Arms A & C. Based on emerging safety and efficacy data, Arm B has been closed to enrollment and the recommended dose of epcoritamab in combination with R 2 is 48 mg. Epcoritamab will be subcutaneously administered using a step-up dosing regimen to full dose in cycle 1 (28 days/cycle). Full dose of epcoritamab will be administered weekly in cycles 2-3 and monthly from cycle 4 onward for up to 12 cycles of treatment. Patients will be serially assessed for disease progression at prespecified intervals. The primary endpoint is progression-free survival assessed by independent review committee (IRC) per Lugano criteria. Key secondary efficacy endpoints include CR rate (by IRC per Lugano criteria), overall survival, and minimal residual disease negativity. Other efficacy endpoints include best overall response, duration of response, duration of complete response, time to progression, event-free survival, time to next anti-lymphoma treatment, and patient-reported outcomes. Safety endpoints include incidence and severity of treatment-emergent adverse events and adverse events of special interest. Exploratory endpoints include assessments of pharmacodynamic and pharmacokinetic data. The study opened for enrollment in 2022 in North America, South America, Europe, Africa, Asia, and Australia.

Sulindac sulfide as a non-immune suppressive γ-secretase modulator to target triple-negative breast cancer.

Triple-negative breast cancer (TNBC) comprises a heterogeneous group of clinically aggressive tumors with high risk of recurrence and metastasis. Current pharmacological treatment options remain largely limited to chemotherapy. Despite promising results, the efficacy of immunotherapy and chemo-immunotherapy in TNBC remains limited. There is strong evidence supporting the involvement of Notch signaling in TNBC progression. Expression of Notch1 and its ligand Jagged1 correlate with poor prognosis. Notch inhibitors, including g-secretase inhibitors (GSIs), are quite effective in preclinical models of TNBC. However, the success of GSIs in clinical trials has been limited by their intestinal toxicity and potential for adverse immunological effects, since Notch plays key roles in T-cell activation, including CD8 T-cells in tumors. Our overarching goal is to replace GSIs with agents that lack their systemic toxicity and ideally, do not affect tumor immunity. We identified sulindac sulfide (SS), the active metabolite of FDA-approved NSAID sulindac, as a potential candidate to replace GSIs. We investigated the pharmacological and immunotherapeutic properties of SS in TNBC models in vitro, ex-vivo and in vivo. We confirmed that SS, a known γ-secretase modulator (GSM), inhibits Notch1 cleavage in TNBC cells. SS significantly inhibited mammosphere growth in all human and murine TNBC models tested. In a transplantable mouse TNBC tumor model (C0321), SS had remarkable single-agent anti-tumor activity and eliminated Notch1 protein expression in tumors. Importantly, SS did not inhibit Notch cleavage in T- cells, and the anti-tumor effects of SS were significantly enhanced when combined with a-PD1 immunotherapy in our TNBC organoids and in vivo. Our data support further investigation of SS for the treatment of TNBC, in conjunction with chemo- or -chemo-immunotherapy. Repurposing an FDA-approved, safe agent for the treatment of TNBC may be a cost-effective, rapidly deployable therapeutic option for a patient population in need of more effective therapies.

836P EX103, a re-designed CD20xCD3 bispecific antibody, showed a favorable safety and potent single-agent antitumor activity in heavily pretreated relapsed/refractory patients with B cell non-Hodgkin lymphoma

836P EX103, a re-designed CD20xCD3 bispecific antibody, showed a favorable safety and potent single-agent antitumor activity in heavily pretreated relapsed/refractory patients with B cell non-Hodgkin lymphoma

Phase 1/2 study of ARTS-021, a potent, oral administrated, selective CDK2 inhibitor, in advanced or metastatic solid tumors.

e17546 Background: ARTS-021 is an investigational, reversible, orally available CDK2 selective inhibitor that inhibits CDK2 at nanomolar potency and with over 600-fold selectivity against CDK1 (Liang J et al. AACR 2022). ARTS-021 has shown promising preclinical data, including strong single agent antitumor activity in CCNE1 amplified patient derived xenografts (PDX). Furthermore, consistent with the hypothesis that CDK2 activity may mediate resistance to CDK4/6 inhibitors, ARTS-021 significantly enhanced Palbociclib anti-tumor activity in an estrogen positive (ER+) breast cancer xenograft model. Taken together, these data support the clinical development of ARTS-021 as a monotherapy in CCNE1-amplified cancers and in combination with CDK4/6 inhibitors in ER+ breast cancer. Methods: A first in human, open label, multicenter phase1/2 dose escalation and dose expansion study will be conducted to evaluate the safety, tolerability, PK, pharmacodynamics (PD), and anti-tumor activity of ARTS-021 1) as a single agent in advanced or metastatic solid tumors harboring CCNE-1 gene amplification; 2) in combination with carboplatin to treat refractory/resistant CCNE-1 amplified ovarian cancer that has failed standard therapies; 3) in combination with endocrine therapy and CDK4/6 inhibitor to treat ER+/HER2- breast cancer patients have failed standard therapies. The phase 1 (dose-escalation) portion of the trial will have an accelerated dose escalation followed by a Bayesian Optimal Interval (BOIN) design. After the monotherapy recommended phase 2 dose (R2PD) is identified, the combination arms will be initiated at one dose level below the monotherapy R2PD. Phase1 primary endpoints are assessment of safety, tolerability, and pharmacokinetics (PK). The secondary endpoint is preliminary efficacy. Once the RP2D is defined for both monotherapy and in combination, the trial will be advanced into three Phase 2 expansion cohorts: monotherapy cohort (basket cohort), combination with carboplatin (ovarian cohort), and combination with endocrine therapy + CDK4/6 inhibitor (ER+ breast cancer cohort). The phase 2 primary end point is to estimate the anti-tumor efficacy in CCNE1 amplified cancer patients or CDK4/6 inhibitor resistant breast cancer patients. Objective tumor response rate will be measured per RECIST v1.1. The secondary endpoint of Phase 2 study will be safety/tolerability. Archival tumor and paired fresh tumor biopsy will be collected throughout the study for exploratory pharmacodynamics (PD) and biomarker evaluation. Results: ARTS-021 clinical study is ongoing. Conclusions: ARTS-021 shows potential anti-tumor activities.

Epcoritamab + R2 regimen and responses in high-risk follicular lymphoma, regardless of POD24 status.

7506 Background: Follicular lymphoma (FL) is a heterogeneous disease. Early progression after initial treatment (tx) with chemoimmunotherapy (CIT), POD24, occurs in around 20% of patients (pts) and strongly predicts poor outcomes. There is no standard tx approach for high-risk, relapsed or refractory (R/R) FL (high-risk subgroups in Table). Novel options are needed to improve efficacy in pts with high unmet need. Epcoritamab, a subcutaneous (SC) T-cell–engaging bispecific antibody, demonstrated impressive single-agent antitumor activity and a manageable safety profile in R/R FL (Hutchings et al, Lancet 2021) and shows promise combined with standards of care. Here we present pooled analyses from cohorts 2a and 2b of the ongoing phase 1/2 EPCORE NHL-2 trial (NCT04663347) of epcoritamab with rituximab + lenalidomide (R2). Methods: Pts with R/R CD20+ FL received epcoritamab SC + R2 for 12 cycles (Cs; 28 d each). Epcoritamab was dosed QW in C1–3, Q2W in C4–9, and Q4W in C≥10 (2a) or QW in C1–2 and Q4W in C≥3 (2b) for ≤2 y. Results: As of Oct 31, 2022, 109 R/R FL pts had received epcoritamab 48 mg + R2 in 2a and 2b. Median age was 65 y, 56% of pts had FLIPI 3–5, 61% had stage IV disease, and 59% had only 1 prior tx. Most had received alkylating agents (92%) or anthracyclines (62%); 2 had prior CAR T. At a median follow-up of 8.8 mo (range, 1.2–18.5), 82% were still on tx. The most common tx-emergent AEs were: CRS and neutropenia, 48% each; injection-site reactions, 38%; and fatigue, 33%. CRS events were mostly low grade (G; 46% G1–2, 2% G3) and mostly occurred following the first full dose on C1D15; all resolved and none led to discontinuation. ICANS occurred in 2 pts (G1, G2) and resolved. In 101 efficacy-evaluable pts, overall response rate (ORR) was 97%, with complete metabolic response (CMR) in 86%. Notably, pts achieved higher ORR/CMR rates with epcoritamab + R2 vs their immediate prior tx line (ORR, 97% vs 85%; CMR, 86% vs 60%). Estimated 6-mo progression-free survival was 93%. In second-line (2L) pts with POD24, ORR/CMR rates were 95%/90% (additional high-risk subgroup data in Table). Additional data with longer follow-up will be presented. Conclusions: Epcoritamab + R2 showed potent antitumor activity and a manageable safety profile in a large R/R FL population. Encouraging responses were seen in pts with high-risk disease, suggesting epcoritamab SC may abrogate negative effects of high-risk features. A separate POD24 cohort is planned, and epcoritamab + R2 is being studied in the phase 3 EPCORE FL-1 trial (NCT05409066). Clinical trial information: NCT04663347 . [Table: see text]

CBX-12-101: A first-in-human study of CBX-12, an alphalex peptide drug conjugate (PDC) in patients (pts) with advanced or metastatic solid tumors.

3087 Background: Tumor-targeted drug delivery technologies are urgently needed to overcome conventional chemotherapy’s lack of tumor selectivity. Alphalex conjugates, which contain a pH-low insertion peptide (pHLIP), a linker and a payload, are designed to overcome this lack of selectivity. Unlike antibody drug conjugates, alphalex PDCs target tumors in an antigen-agnostic manner. At pH ≥7.0, the peptide is unstructured. In the low-pH tumor microenvironment the peptide forms an alpha helix and inserts directionally into the tumor cell membrane delivering the linker and payload intracellularly where the linker is cleaved releasing the payload in the cytosol. CBX-12 consists of the pH-sensitive peptide, a self-immolating linker, and the topoisomerase 1 (TOP1) inhibitor exatecan. Methods: In this Phase 1 trial, cohorts of pts were treated with escalating doses of CBX-12 in a 3 + 3 design on three dosing schedules: daily x 5 every 3 weeks, daily x 3 every 3 weeks or once weekly. The primary objectives are safety, tolerability and to determine the MTD and/or RP2D. Secondary and exploratory objectives include evaluation of plasma PK of CBX-12 and exatecan, anti-tumor activity per RECIST v1.1, and measurement of anti-drug antibodies. Results: As of 26 Jan 2023, 42 pts have been treated on three schedules. The most frequent treatment-related AEs (TRAEs) were anaemia (42.9%), nausea (38.1%), fatigue (33.3%), ANC and WBC decreased (33.3% each), vomiting (26.2%), diarrhoea (23.8%) and thrombocytopenia (19.0%). The most frequent Gr3/4 TRAEs were ANC decreased (28.6%), anemia (23.8%), WBC decrease (16.7%), thrombocytopenia (14.3%). Dose limiting toxicity was observed in 6 pts: myelosuppression (6 pts) febrile neutropenia (2 pts), and sepsis (2 pts). Responses were observed in 2 of 9 pts with ovarian cancer and 2 of 8 with breast cancer. The MTD on the daily x 3 schedule is 45mg/m2. Dose evaluation continues on the weekly schedule. Conclusions: In this FIH study of a pH-targeting alphalex PDC, CBX-12 demonstrated single-agent antitumor activity including 4 responses with the dominant toxicity of myelosuppression. Phase 2 expansion cohorts are planned in pts with platinum-resistant ovarian cancer and hormone-receptor positive, HER2 negative breast cancer. Clinical trial information: NCT04902872 .