Abstract 3526: Subcutaneous administration of PSMA/CD3-bispecific BiTE antibody MT112/BAY 2010112 leads to complete remission of human prostate cancer xenografts in mice

Blinatumomab, a CD19/CD3-bispecific BiTE antibody has shown high response rates and durable remissions in patients with relapsed or refractory acute lymphocytic leukemia and non-Hodgkin's lymphoma. For treatment of patients with prostate cancer (PCa), we have developed a novel BiTE antibody, MT112/BAY2010112, that is bispecific for prostate-specific membrane antigen (PSMA) and the CD3 epsilon subunit of the T cell receptor complex. MT112/BAY 2010112 binds PSMA and CD3 of human and macaque origin allowing for assessment of safety, pharmacodynamics and pharmacokinetics in a relevant animal species. PSMA expressing human PCa cell lines VCaP, 22Rv1, MDA PCa 2b, C4-2, PC3-PSMA and LNCaP were lysed by freshly isolated, unstimulated human T cells redirected by MT112/BAY2010112 at EC50 values ranging between 0.1 and 4 ng/ml (1.8-72 pM). Efficacy of lysis correlated with levels of surface expressed PSMA. No lysis was observed in PSMA-negative PCa cell lines PC3 and DU145, showing the target antigen-specific activity of MT112/BAY2010112. The relevance of cynomolgus monkeys for further nonclinical safety evaluation of MT112/BAY 2010112 was demonstrated by in vitro side-by-side comparison of the BiTE antibody's pharmacological characteristics in human and cynomolgus monkey assay systems. For studying the activity of MT112/BAY 2010112 after subcutaneous (s.c.) administration, human 22Rv1 PCa xenografts were grown s.c. in mice to sizes of >200 mm3 in the absence of human T cells. Three days prior to treatment with BiTE, ex-vivo expanded human T cells were intraperitoneally injected. Animals were treated s.c. at 2.5 mg/kg/d or intravenously (i.v.) at 0.5 mg/kg/d for 28 consecutive days. S.c. administration of MT112/BAY 2010112 resulted in a similar drug exposure, rapid shrinkage and complete remission of established PCa xenografts as seen upon i.v. administration of the BiTE antibody. Treatment with human T cells or vehicle alone had no effect on tumor growth. Compared to i.v. administration, the relative bioavailability of the PSMA BiTE in serum after s.c. injection in mice was approximately 18%. Initial results will be presented showing that 14C-labeled MT112/BAY 2010112 accumulates in s.c. implanted LNCaP PCa tumors of mice after tail vein injection. Based on these preclinical in vivo pharmacology results, treatment of PCa patients with s.c. administered MT112/BAY2010112 appears to be justified. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings