Abstract P258: CBX-12 (alphalexTM-exatecan) sensitizes tumors to immune checkpoint blockade in an antigen agnostic manner by immune activation
Authors: Gayle Sophia , Vasquez Juan , Paradis Timothy , Jones Kelli , Sundaram Ranjini , van Doorn Jinny , Muthusamy Viswanathan , Bindra Ranjit S. , Aiello Robert J. , Paralkar Vishwas 
Published: December 2021

Immune checkpoint blockade (ICB) in combination with chemotherapy is standard of care for several solid tumors. However, potent chemotherapies such as topoisomerase inhibitors can result in severe dose-limiting toxicities requiring dose reduction, limiting their efficacy. Moreover, leukocytopenia from chemotherapy induces immunosuppression that further limits the full potential of combinations with ICB. The use of targeted chemotherapies such as antibody-drug conjugates (ADCs) demonstrate potential synergy with ICB, however are limited to a defined subset of patients with tumors expressing the target antigen.

Cybrexa has reported the development of CBX-12, a peptide-drug conjugate consisting of alphalexTM-exatecan (1). Rather than targeting a specific antigen, alphalexTM consists of a unique variant of pH-Low Insertion Peptide (pHLIP®; 2-4) which targets the low pH environment of the tumor, a universal feature characteristic of all tumors due to the Warburg effect. The alphalexTM component of CBX-12 forms an alpha helix only in low pH conditions, allowing for directional insertion of the peptide within the cancer cell membrane, delivery of C-terminally linked exatecan across the membrane, and subsequent intracellular release of active exatecan via glutathione reduction of the linker, thereby allowing for tumor-specific intracellular delivery in an antigen-independent manner.

Here we evaluated the potential for CBX-12 to effectively synergize with PD1 and CTLA4 blockade in multiple syngeneic mouse models without requirement for tumor specific antigens. We found that CBX-12/ICB combination treatment significantly delayed tumor growth, improved survival and led to complete tumor regressions. Mice cured with combined CBX-12/ICB therapy demonstrated formation of long-term immunological memory after in vivo and ex vivo tumor rechallenge. The ability of CBX-12 to induce immunogenic cell death was confirmed by vaccinating syngeneic mice with CBX-12 treated tumor cells and subsequent tumor rechallenge, which demonstrated near total anti-tumor immunity induced by CBX-12. Together, these preclinical data demonstrate the potential for CBX-12 to enhance tumor immunogenicity and potentiate the efficacy of ICB in patients with solid tumors affording a superior, universal tumor targeting mechanism that bypasses the limitations of ADCs.

1. Gayle S et al. 2021.Tumor-selective, antigen-independent delivery of a pH sensitive peptide-topoisomerase inhibitor conjugate suppresses tumor growth without systemic toxicity. NAR Cancer.

2. Rather than targeting a specific antigen, alphalexTM includes a pHLIP® peptide. pHLIP® peptides are a family of pH-Low Insertion Peptides that target acidic cell surfaces. pHLIP® was developed at Yale University and the University of Rhode Island, and is exclusively licensed to pHLIP, Inc.

3. Wyatt LC et al. 2017. Applications of pHLIP Technology for Cancer Imaging and Therapy. Trends Biotech.

4. Wyatt LC et al. 2018. Peptides of pHLIP family for targeted intracellular and extracellular delivery of cargo molecules to tumors. PNAS.

Citation Format: Sophia Gayle, Juan Vasquez, Timothy Paradis, Kelli Jones, Ranjini Sundaram, Jinny van Doorn, Viswanathan Muthusamy, Ranjit S. Bindra, Robert J. Aiello, Vishwas Paralkar. CBX-12 (alphalexTM-exatecan) sensitizes tumors to immune checkpoint blockade in an antigen agnostic manner by immune activation [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P258.