Abstract CT207: A phase 1 open-label, dose escalation and expansion trial to investigate the safety, pharmacokinetics and pharmacodynamics of CB307, a Trispecific Humabody® T-cell enhancer, in patients with PSMA+ advanced and/or metastatic solid tumors (POTENTIA)

Abstract Humabodies* are fully human VH antibody components that can be connected by short peptide linkers to make multi-specific therapeutics. CB307 is a tri-specific Humabody targeting prostate specific membrane antigen (PSMA/FOLH1), CD137 (4-1BB/TNFSF9) and human serum albumin (HSA). Unlike CD3 targeting bispecific compounds, stimulation of CD137 on T cells can promote T cell cytotoxicity, proliferation, survival and memory T cell formation without compromising safety, including cytokine release syndrome (CRS). In addition, HSA binding assists CB307 penetration into the tumor since albumin is enriched in the tumor microenvironment. Several cancers including prostate cancer and lung cancer are known to have PSMA expression. The objectives of the POTENTIA study are to determine the maximum tolerated dose (MTD) and pharmacokinetics of CB307 and to assess preliminary anti-tumor activity in patients with PSMA+ solid tumor. Methods: The phase 1 study consists of dose escalation (part 1) and cohort expansion (part 2) components, and the study is currently enrolling patients in part 1 without dose limiting toxicities (DLTs). The dose escalation uses an accelerated titration design (ATD) and a modified continual reassessment method (mCRM) to guide the MTD and the recommended phase 2 dose (RP2D). The key inclusion criteria are as follows: histologically confirmed advanced or metastatic PSMA expressing solid tumors determined by immunohistochemistry; not amenable to standard-of-care; RECIST measurable disease or increased serum PSA at baseline (for bone metastasis-only prostate cancer). The key exclusion criteria are patients with brain metastases; patients who have discontinued previous immunotherapy due to intolerable immune-related adverse events; patients with acute infections or autoimmune diseases. Cohort expansion uses the same eligibility criteria, however, at least 3 patients with castration-resistant prostate cancer harboring either BRCA1, BRCA2, ATM and/or CDK12 mutation(s) will be enrolled. CB307 is administered intravenously every week. PSMA-PET scan and tumor biopsy are taken to understand the mechanism of action of CB307 as well as a change of PSMA expression during CB307 treatment. NCT04839991 * “Humabody” is a registered trademark ® of Crescendo Biologics Ltd. Citation Format: Johann S. de Bono, Hendrik-Tobias Arkenau, Eelke H. Gort, Lot L. Devriese, Elisa Fontana, Daan G. Knapen, Crescens Tiu, Anja Williams, Derk Jan A. de Groot, Ulug M. Gunaydin, Phillip Bartlett, Andrew J. Pierce, Philip Bland-Ward, Kenji Hashimoto, E.G. Elisabeth de Vries. A phase 1 open-label, dose escalation and expansion trial to investigate the safety, pharmacokinetics and pharmacodynamics of CB307, a Trispecific Humabody® T-cell enhancer, in patients with PSMA+ advanced and/or metastatic solid tumors (POTENTIA) [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 CT207.