Abstract 6249: CBX-12: A low pH targeting alphalex™-exatecan conjugate for the treatment of solid tumors

Abstract

Topoisomerase inhibitors are potent DNA damaging agents with great potential as anti-cancer drugs for a wide range of solid tumors. However, dose-limiting toxicities such as myelosuppression and gastric toxicity have prevented them from reaching their full clinical potential. Targeting topoisomerase inhibitors with antibodies (i.e. antibody-drug conjugates; ADCs) may enhance the therapeutic window of these agents, but this approach typically limits applicability to a small subset of patients with tumors expressing the target antigen. We recently developed the alphalexTM tumor-targeting platform to overcome the limitations of ADC-based therapeutic strategies. Rather than targeting a specific antigen, alphalexTM consists of a unique variant of pH-Low Insertion Peptide, (pHLIP®; references 1-3) which targets the low pH environment of the tumor, a universal feature characteristic of all tumors due to the Warburg effect. These alphalexTM conjugates form an alpha helix only in low pH conditions, allowing for insertion of the peptide within the cancer cell membrane, delivery of C-terminal warheads across the membrane, and subsequent intracellular release of the agent via glutathione reduction of the linker, thereby allowing for tumor-specific intracellular delivery in an antigen-independent manner. We report the discovery and development of CBX-12, an alphalexTM conjugate of the potent topoisomerase inhibitor, exatecan. CBX-12 provides additional proof of mechanism to the alphalexTM platform by displaying remarkable tumor-targeting properties in preclinical models. CBX-12 displays enhanced stability in plasma in vivo, undergoing only 0.003% warhead release over 30 hours in circulation and demonstrating exquisite selectivity for tumor over normal tissues in mouse tumor models. Notably, CBX-12 allows for efficient delivery of exatecan into tumors due to a highly optimized cleavable linker, allowing CBX-12 to display extraordinary efficacy in a HER2-negative tumor model in an antigen-independent manner. At 10 mg/kg, CBX-12 treatment almost completely suppressed growth of human colorectal tumors in mice, with complete sparing of bone marrow. In contrast, in animals dosed with the equimolar free exatecan (1.15 mg/kg) there was substantial tumor growth accompanied by neutropenia and weight loss. This superior profile of CBX-12 allow us to greatly enhance efficacy relative to dosing equimolar amounts of unconjugated exatecan, which causes significant, dose-limiting bone marrow toxicity. We have demonstrated that CBX-12 is both safe and has potent anti-tumor activity in preclinical models, and we plan to rapidly move forward with the clinical development of CBX-12 as our lead candidate. References 1. 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. 2. Wyatt LC et al. Applications of pHLIP Technology for Cancer Imaging and Therapy. Trends Biotechnol. 2017;35(7):653-664. 3. Wyatt LC et al. Peptides of pHLIP family for targeted intracellular and extracellular delivery of cargo molecules to tumors. PNAS. 2018;115(12):E2811-E2818. Citation Format: Robert J. Aiello, Sophia Gayle, Jane Bechtold, Patricia Bourassa, Johanna Csengery, Ketaki Deshpande, Kelli Jones, Lori Lopresti-Morrow, Robert Maguire, Dan Marshall, Hunter Moore, Timothy Paradis, Laurie Tylaska, Qing Zhang, Robert Volkmann, Ranjit S. Bindra, Peter M. Glazer, Vishwas Paralkar. CBX-12: A low pH targeting alphalex™-exatecan conjugate for the treatment of solid tumors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6249.

Peptide-Based Drug Delivery Systems

“…CBX-12 is a pH-Low Insertion Peptide (pHLIP) based platform conjugated to a topoisomerase inhibitor, exatecan, which inhibits the topoisomerase enzymes preventing relieve of DNA supercoiling after its replication, transcription and chromatin remodeling [151]. At the same time, pHLIP also specifically targets the low pH environment of the tumor in an antigen-independent manner allowing the insertion of the peptide into the cancer cell membrane and subsequent release of the agent into the tumor cell through glutathione reduction of the linker [152]. Cybrexa Therapeutics is now recruiting for a phase I/II openlabel, multicenter, dose-escalation, safety study of CBX-12 on 112 patients with advanced or metastatic refractory solid tumors.…”

Targeting the Hypoxic and Acidic Tumor Microenvironment with pH-Sensitive Peptides

“…A pHLIP-based topoisomerase inhibitor has also been developed [ 64 ]. Topoisomerase inhibitors block the action of the topoisomerase enzymes that relieve DNA supercoiling caused by replication, transcription, and chromatin remodeling [ 65 ].…”

“…Alternatively, pHLIP-based approaches can target solid tumors regardless of antigen expression. Conjugation of the highly potent topoisomerase inhibitor exatecan to pHLIP conferred enhanced tumor targeting and tumor growth suppression with sparing of the bone marrow [ 64 ].…”

New horizons in early drugs development in solid cancers

“…Sting agonists, Toll-like receptor agonists) and innovative strategies to improve delivery are increasingly investigated. For example, alternative nonantibody proteins are currently engineered to bind to a variety of therapeutic targets with high affinity and have great potential utility for targeted delivery due to their small size, stability and improved penetration into tissues [42][43][44].…”