Antigen-independent tumor targeting by CBX-12 (alphalex™-exatecan) induces long-term antitumor immunity

Aims: To determine whether antigen-independent targeting of the TOP1 inhibitor exatecan to tumor with a pH-sensitive peptide (CBX-12) produces superior synergy with immunotherapy compared with unconjugated exatecan. Materials & methods: In vitro and ex vivo functional assays were performed via FACS and ELISA assays. In vivo efficacy was evaluated in the syngeneic CT26 model. Results: CBX-12 combined with anti-PD-1 or anti-CTLA4 results in delayed tumor growth and complete response, with cured animals displaying long-term antitumor immunity. CBX-12 stimulates expression of MHC 1 and PD-L1 and is an inducer of immunogenic cell death, producing long-term immune recognition of tumor cells and resultant antitumor immunity. Conclusion: The authors' data provide the rationale for exploring immunotherapy combinations with CBX-12 in clinical trials.

TOP1-DNA Trapping by Exatecan and Combination Therapy with ATR Inhibitor

Exatecan and deruxtecan are antineoplastic camptothecin derivatives in development as tumor-targeted-delivery warheads in various formulations including peptides, liposomes, polyethylene glycol nanoparticles, and antibody-drug conjugates. Here, we report the molecular pharmacology of exatecan compared with the clinically approved topoisomerase I (TOP1) inhibitors and preclinical models for validating biomarkers and the combination of exatecan with ataxia telangiectasia and Rad3-related kinase (ATR) inhibitors. Modeling exatecan binding at the interface of a TOP1 cleavage complex suggests two novel molecular interactions with the flanking DNA base and the TOP1 residue N352, in addition to the three known interactions of camptothecins with the TOP1 residues R364, D533, and N722. Accordingly, exatecan showed much stronger TOP1 trapping, higher DNA damage, and apoptotic cell death than the classical TOP1 inhibitors used clinically. We demonstrate the value of SLFN11 expression and homologous recombination (HR) deficiency (HRD) as predictive biomarkers of response to exatecan. We also show that exatecan kills cancer cells synergistically with the clinical ATR inhibitor ceralasertib (AZD6738). To establish the translational potential of this combination, we tested CBX-12, a clinically developed pH-sensitive peptide-exatecan conjugate that selectively targets cancer cells and is currently in clinical trials. The combination of CBX-12 with ceralasertib significantly suppressed tumor growth in mouse xenografts. Collectively, our results demonstrate the potency of exatecan as a TOP1 inhibitor and its clinical potential in combination with ATR inhibitors, using SLFN11 and HRD as predictive biomarkers.

Abstract 1764: Development of an alphalex™-auristatin low pH targeting conjugate for the treatment of solid tumors

Auristatins such as monomethyl auristatin E (MMAE) are a class of high potency microtubule targeting compounds that have an extremely narrow therapeutic window. Targeting potent auristatins to the tumor is the only feasible method of unlocking the clinical potential of such toxic molecules. While there are currently four marketed antibody-drug conjugates (ADCs) featuring auristatins, these ADCs face the same fundamental issues - tumor restriction by target antigen and the potential for off target release of payload.

Alphalex࣪ is a tumor targeting technology consisting of a unique variant of a family of pH-Low Insertion Peptides (pHLIP®) that target acidic cell surfaces (references 1-2), a cleavable small molecule linker, and an anti-cancer agent warhead. Alphalex࣪ thereby allows for antigen independent targeting of the tumor and enables intracellular delivery of the warhead by leveraging the low pH microenvironment of the tumor, a universal feature common to all tumors due to the Warburg effect.

Here we report the preclinical efficacy, safety, and antigen-independent tumor-targeting properties of alphalex࣪ conjugated to MMAE. We demonstrate the ability of alphalex࣪-MMAE to display potent in vitro and in vivo efficacy in colorectal, non-small cell lung, and prostate carcinoma cell lines. We further show that alphalex࣪-MMAE efficiently and safely delivers efficacious levels of MMAE selectively to tumor and demonstrates extreme plasma stability, with 0.02% warhead release over 24h in the rat. Based on the excellent preclinical safety and efficacy profile of alphalex࣪-MMAE, Cybrexa will move forward with the goal of initiating IND-enabling studies in 2022.

References:

1. Wyatt LC, Lewis JS, Andreev OA, Reshetnyak YK, Engelman DM. Applications of pHLIP Technology for Cancer Imaging and Therapy. Trends Biotechnol. 2017 Jul;35(7):653-664.

2. Wyatt LC, Moshnikova A, Crawford T, Engelman DM, Andreev OA, Reshetnyak YK. Peptides of pHLIP family for targeted intracellular and extracellular delivery of cargo molecules to tumors. Proc Natl Acad Sci USA. 2018 Mar 20;115(12):E2811-E2818.

Citation Format: Sophia Gayle, Robert Aiello, Jane Bechtold, Patricia Bourassa, Johanna Csengery, Connor Hagen, Katia Howard, Kelli Jones, Lori Lopresti-Morrow, Robert Maguire, Timothy Paradis, Theresa Pasqualini, Joseph Tweed, Laurie Tylaska, Qing Zhang, Vishwas Paralkar. Development of an alphalex™-auristatin low pH targeting conjugate for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1764.

Correction to 'Tumor-selective, antigen-independent delivery of a pH sensitive peptide-topoisomerase inhibitor conjugate suppresses tumor growth without systemic toxicity'

[This corrects the article DOI: 10.1093/narcan/zcab021.].

Abstract P258: CBX-12 (alphalexTM-exatecan) sensitizes tumors to immune checkpoint blockade in an antigen agnostic manner by immune activation

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.

Abstract P047: A phase 1/2 trial of CBX-12, an alphalexTM peptide drug conjugate, in patients with advanced or metastatic refractory solid tumors

Background Tumor-targeted drug delivery technologies are urgently needed to overcome the lack of tumor selectivity, a major drawback of conventional chemotherapy. In addition, the acidic intercellular microenvironment in solid tumors traps weak acid/base chemotherapy agents, preventing necessary intracellular concentrations in tumour cells. An alphalex conjugate, which contains a low-pH insertion peptide, a linker, and a payload, is designed to overcome these limitations. Unlike antibody drug conjugates, these peptide drug conjugates target tumors in an antigen-agnostic manner. At pH ≥7.0, the peptide is unstructured. In the low-pH tumor microenvironment, the peptide forms an alpha helix, inserts directionally in the cell membrane delivering the linker and payload intracellularly where the linker is cleaved. CBX-12 consists of the pH-sensitive peptide, a self-immolating linker, and the topoisomerase 1 (TOP1) inhibitor exatecan. Methods CBX-12-101 is a first-in-human, open-label, dose-escalation, safety, pharmacokinetics (PK), and biomarker study of CBX-12 in patients with advanced or metastatic refractory solid tumors. CBX-12 is administered as a 1-hour intravenous infusion. Two dosing schedules, daily x 5 every 3 weeks (Part A) and daily x 3 every 3 weeks (Part B), are being evaluated. The starting dose in Part A is 0.25 mg/kg. Single-patient cohorts will be enrolled initially, with dose-escalations up to 100% of the prior dose, until a patient has a ≥ Grade 2 adverse event (AE) considered possibly related to CBX-12 during Cycle 1 (the DLT period), at which time 2 additional patients will be enrolled in that cohort, and a 3 + 3 design will subsequently be utilized. Further dose escalations may be no more than 50% of the prior dose. After at least 2 cohorts have been evaluated in Part A, Part B will open for accrual. Maximum tolerated doses and recommended phase 2 doses will be determined for each dosing schedule. The PK of the CBX-12 conjugate and free exatecan will be determined. The stability of the conjugate in circulation will be evaluated by the ratio of CBX-12 to free exatecan. Pre- and on-treatment tumor biopsies are required. Biomarker and pharmacodynamic evaluations including measuring intratumor exatecan levels, TOP1, gamma H2AX and schlafen-11 are planned. Antitumor activity will be assessed per RECIST v 1.1. Phase 2 expansion cohorts are planned in patients with platinum-resistant ovarian and small cell lung cancer. As of July 2021, patients are enrolling in Part A Cohort 2 at a dose of 0.50 mg/kg.

Citation Format: Anthony Tolcher, Joseph Paul Eder, David Sommerhalder, Sophia Gayle, Paul Pearson, Deb Chapman, Arthur P. DeCillis, Anish Thomas, Funda Meric-Bernstam. A phase 1/2 trial of CBX-12, an alphalexTM peptide drug conjugate, in patients with advanced or metastatic refractory solid tumors [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 P047.

Tumor-selective, antigen-independent delivery of a pH sensitive peptide-topoisomerase inhibitor conjugate suppresses tumor growth without systemic toxicity

Topoisomerase inhibitors are potent DNA damaging agents which are widely used in oncology, and they demonstrate robust synergistic tumor cell killing in combination with DNA repair inhibitors, including poly(ADP)-ribose polymerase (PARP) inhibitors. However, their use has been severely limited by the inability to achieve a favorable therapeutic index due to severe systemic toxicities. Antibody-drug conjugates address this issue via antigen-dependent targeting and delivery of their payloads, but this approach requires specific antigens and yet still suffers from off-target toxicities. There is a high unmet need for a more universal tumor targeting technology to broaden the application of cytotoxic payloads. Acidification of the extracellular milieu arises from metabolic adaptions associated with the Warburg effect in cancer. Here we report the development of a pH-sensitive peptide-drug conjugate to deliver the topoisomerase inhibitor, exatecan, selectively to tumors in an antigen-independent manner. Using this approach, we demonstrate potent in vivo cytotoxicity, complete suppression of tumor growth across multiple human tumor models, and synergistic interactions with a PARP inhibitor. These data highlight the identification of a peptide-topoisomerase inhibitor conjugate for cancer therapy that provides a high therapeutic index, and is applicable to all types of human solid tumors in an antigen-independent manner.

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

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.

Abstract 6242: Development of alphalex™-toxin low pH targeting conjugates for the treatment of solid tumors

Maytansines and their derived maytansinoid DMx compounds are high potency microtubule targeting compounds that have an extremely narrow therapeutic window. Unacceptable dose limiting systemic toxicity has limited the therapeutic potential of these potent anti-oncogenic compounds. Targeting maytansinoids to the tumor is the only feasible method of unlocking the clinical potential of such toxic molecules. To date Trastuzumab-DM1 (Kadcyla®) remains the only approved antibody-maytansinoid conjugate on the market. Most preclinical maytansinoid conjugates to date face the same issues encountered by Kadcyla® - tumor restriction by target antigen and the potential for off target release of payload.

alphalexTM is a tumor targeting technology consisting of a unique variant of pH-Low Insertion Peptide (pHLIP®; references 1-3), cleavable small molecule linker and anti-cancer agent warhead. alphalexTM thereby allows for antigen independent targeting of the tumor and enables intracellular delivery of the warhead by leveraging the low pH microenvironment of the tumor, a universal feature common to all tumors due to the Warburg effect. Here we demonstrate the ability to conjugate the maytansinoids DM1 and DM4 to alphalexTM via both direct and linker-mediated conjugation. We have demonstrated the ability of our alphalexTM-DM4 conjugate candidates (CBX-13) to have single digit nanomolar potency in vitro as well as exquisitely potent and long-lasting anti-tumor activity in a HER2-negative xenograft model that is un-targetable by competing therapies. In particular we have demonstrated that CBX-13 safely delivers amounts of maytansinoid in vivo that otherwise result in systemic toxicity and death when dosed as free warhead. Based on the SAR of this first generation of maytansinoid conjugates we are further optimizing our alphalexTM - maytansinoid conjugation strategy with the goal of moving forward with IND-enabling studies in the near future.

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, Lewis JS, Andreev OA, Reshetnyak YK, Engelman DM. Applications of pHLIP Technology for Cancer Imaging and Therapy. Trends Biotechnol. 2017 Jul;35(7):653-664.

3. Wyatt LC, Moshnikova A, Crawford T, Engelman DM, Andreev OA, Reshetnyak YK. Peptides of pHLIP family for targeted intracellular and extracellular delivery of cargo molecules to tumors. Proc Natl Acad Sci USA. 2018 Mar 20;115(12):E2811-E2818.

Citation Format: Sophia Gayle, Robert Aiello, 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. Development of alphalex™-toxin low pH targeting conjugates 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 6242.

B-cell non-Hodgkin lymphoma: Selective vulnerability to PIKFYVE inhibition

We identified the PIKFYVE inhibitor apilimod as a potent and selective cytotoxic agent against B-cell non-Hodgkin lymphoma (B-NHL). Our data robustly establish PIKFYVE as the target through which apilimod kills B-NHL cells and show that apilimod-induced death in B-NHL is mediated by broad disruption of lysosome homeostasis characterized by lysosomal swelling, TFEB nuclear translocation, impaired maturation of lysosomal enzymes and incomplete autophagosome clearance. Furthermore, through genome-wide CRISPR knockout screening, we identified specific lysosomal genes (TFEB, CLCN7, OSTM1 and SNX10) as critical determinants of apilimod-induced cytotoxicity. Together these data highlight disruption of lysosome homeostasis through PIKFYVE inhibition as a novel anticancer mechanism in B-NHL and potentially other cancers.

piggyBac insertional mutagenesis screen identifies a role for nuclear RHOA in human ES cell differentiation

The mechanisms regulating human embryonic stem (ES) cell self-renewal and differentiation are not well defined in part due to the lack of tools for forward genetic analysis. We present a piggyBac transposon gain of function screen in human ES cells that identifies DENND2C, which genetically cooperates with NANOG to maintain self-renewal in the presence of retinoic acid. We show that DENND2C negatively regulates RHOA activity, which cooperates with NANOG to block differentiation. It has been recently shown that RHOA exists in the nucleus and is activated by DNA damage; however, its nuclear function remains unknown. We discovered that RHOA associates with DNA and that DENND2C affects nuclear RHOA localization, activity, and DNA association. Our study illustrates the power of piggyBac as a cost-effective, efficient, and easy to use tool for forward genetic screens in human ES cells and provides insight into the role of RHOA in the nucleus.

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NANOG-sensitized piggyBac screen for regulators of stem cell differentiation

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DENND2C is a negative regulator of RHOA

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Genetic cooperation exists between RHOA and NANOG

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Nuclear RHOA associates with DNA