CLSP-5282, a first-in-class T cell engager targeting KRas G12V mutant peptide presented on HLA-A*03:01

Background: Mutant KRas is one of the most common driver oncogenes in solid tumors. Approximately 25% of pancreatic cancer, 9% of colorectal cancer (CRC), and 5% of non-small cell lung cancer (NSCLC) tumors harbor KRas G12V mutations. We describe the nonclinical characterization of CLSP-5282, a first-in-class T cell engager that selectively targets the KRas G12V [7-16] mutant peptide presented on HLA-A*03:01. Methods: Functional activity was assessed in vitro in co-culture assays of T cells and target cells expressing KRas G12V and HLA-A*03:01, including models with acquired resistance to Ras-targeted small molecule inhibitors. Since CLSP-5282 does not cross react with any preclinical toxicology species, an extensive panel of secondary pharmacology and in vitro toxicology studies was performed. A Jurkat reporter assay with a positional scanning peptide library was used to identify potential cross-reactivity to other peptides presented on HLA-A*03:01. Specificity was further assessed by T cell reactivity with a panel of normal human tissues and a panel of the most common Class I HLA alleles, and cytokine release in high density PBMC cultures was determined to evaluate CRS risk. In vivo anti-tumor activity of CLSP-5282 was investigated in PBMC engrafted mouse models. Results: CLSP-5282 induces T cell activation and target cell killing specifically against cells expressing KRas G12V and HLA-A*03:01, but not wild-type KRas. Cell lines with acquired resistance to KRas inhibitors maintain sensitivity to CLSP-5282, suggesting continued presentation of the KRas G12V neoantigen. In vitro studies did not identify potential cross-reactivity to any peptides presented on HLA-A:03:01 and showed minimal T cell reactivity or cytokine release with a panel of normal human tissues, a panel of the 50 most common Class I HLA alleles, or in high-density PBMC cultures. In vivo, CLSP-5282 induces regression of established tumors in a humanized mouse model. Conclusions: These preclinical data support clinical evaluation of CLSP-5282 in HLA-A*03:01 positive patients with solid tumors harboring the KRas G12V mutation. CLSP-5282 is expected to be the first TCE in the clinic directed against mutant KRas, providing tumor targeting without the risk of on-target, off-tumor toxicity. Our data demonstrate the potential for CLSP-5282 to be efficacious even in the context of resistance to small molecule KRas inhibitors.