119P Tetraspanins CD37 and CD53 immune modulators in stage IV colorectal cancer: A single-cell spatial transcriptomic study for targeted therapeutic insights

Background: The alphalex TM series of tumor targeting, antigen agnostic peptide-drug conjugates was developed to address the gaps left by antibody drug conjugates (ADCs).The alphalex TM platform is based on a unique variant of the pH Low Insertion Peptide (pHLIP ).Unlike an ADC, pH-based targeting by the alphalex TM allows for universal targeting of solid tumors and avoids the pitfalls of antigen-based restrictions and toxicities, leading to safer delivery of cytotoxics.Methods: We characterized the efficacy, safety, and immunomodulatory activities of a series of microtubule-targeting alphalex TM conjugates bearing auristatin and maytansinoid payloads in the HCT116 colorectal, B16-F10 melanoma, and Renca renal mouse tumor models and in the 13762 rat syngeneic breast tumor model.We additionally characterized the impact of conjugate treatment on T and B cell recognition of tumor in vivo and ex vivo.Results: Conjugates bearing microtubule inhibiting payloads produced complete tumor suppression in HCT116 human colorectal model as single agent and demonstrated synergy with doxorubicin and anti-PD-L1 in the B16-F10 melanoma lung metastasis model and Renca kidney syngeneic flank model, respectively.Activity was further extended to the rat 13762 syngeneic breast flank model.Ex vivo characterization demonstrated both tumor specific delivery of the payload as well as immunomodulatory activities to induce anti-tumor immune recognition through immunogenic cell death, resulting in rejection of tumor rechallenge and splenocyte release of IFN, IL-2, and tumor-binding IgG in response to exposure to tumor cells.Conclusions: These results demonstrated that the alphalex TM safely delivered efficacious levels of microtubule inhibiting payloads in a tumor-selective manner to a variety of HER2 null models.Selective delivery to tumor and avoidance of delivery to healthy immune cells led to immunogenic cell death of the tumor and subsequent Th1 and B cell anti-tumor immune responses.Antigen agnostic delivery of auristatin and maytansinoid payloads is poised to potentially serve as second-line therapy as single agent or in combination with immunotherapy post-TOP1i treatment.