Discovery and Optimization of a Synthetic Class of Nectin-4-Targeted CD137 Agonists for Immuno-oncology

CD137 (4-1BB) is a co-stimulatory receptor on immune cells and Nectin-4 is a cell adhesion molecule that is overexpressed in multiple tumor types. Using a series of poly(ethylene glycol) (PEG)-based linkers, synthetic bicyclic peptides targeting CD137 were conjugated to Bicycles targeting Nectin-4. The resulting bispecific molecules were potent CD137 agonists that require the presence of both Nectin-4-expressing tumor cells and CD137-expressing immune cells for activity. A multipronged approach was taken to optimize these Bicycle tumor-targeted immune cell agonists by exploring the impact of chemical configuration, binding affinity, and pharmacokinetics on CD137 agonism and antitumor activity. This effort resulted in the discovery of BT7480, which elicited robust CD137 agonism and maximum antitumor activity in syngeneic mouse models. A tumor-targeted approach to CD137 agonism using low-molecular-weight, short-acting molecules with high tumor penetration is a yet unexplored path in the clinic, where emerging data suggest that persistent target engagement, characteristic of biologics, may lead to suboptimal immune response.

Abstract PO077: BT7480, a novel fully synthetic tumor-targeted immune cell agonist (TICA™) induces tumor localized 4-1BB agonism

Harnessing costimulatory molecules expressed on T and NK cells namely 4-1BB (CD137/TNFRSF9) is ideal for cancer immunotherapy. Despite promise preclinically, 4-1BB agonistic antibodies, were unable to demarcate hepatoxicity from efficacy in the clinic. Bispecific approaches promote target-mediated clustering of 4-1BB while limiting systemic and liver toxicity. Bicycles® are novel, fully synthetic, constrained bicyclic peptides with high affinity and selectivity to their targets. Their small size (~2kDa) and tunable pharmacokinetic parameters allow Bicycles to have superior tumor penetration and de-risk hepatoxicity concerns due to a renal clearance mechanism. We hypothesized that clustering and activation of 4-1BB could be attained by conjugating a 4-1BB binding Bicycle to a tumor antigen targeting Bicycle promoting a potent tumor-localized immune response. BT7480 is a tumor-targeted immune cell agonist (TICA™) targeting Nectin-4 and agonizing 4-1BB. Nectin-4 (PVRL4) is highly expressed in numerous tumor indications with unmet clinical needs. In an engineered 4-1BB reporter system, we found BT7480 induced potent 4-1BB agonism correlating to target antigen surface expression on the co-cultured tumor cells. Moreover, BT7480 induces cytokine secretion, including interleukin-2 and interferon gamma, in immune cell co-culture in the presence of tumor antigen. This activity is strictly dependent on Nectin-4 expression on tumor cells and the ability of the TICA to bind to both Nectin-4 and 4-1BB. In a MC38 (Nectin-4-expressing) syngeneic mouse model, intermittent dosing of BT7480 led to robust anti-tumor efficacy (22 out of 24 complete responders (CRs)). Importantly, a memory response was established in CR mice as resistance to a re-challenge with MC38 tumors was observed. Additionally, BT7480 led to increased intratumoral T cell infiltration without elevation of liver enzymes in a CT26 (Nectin-4-expressing) syngeneic mouse model. In non-human primates (NHPs), BT7480 exhibits dose linear exposure and is well tolerated up to 10mpk. BT7480 represents a new generation of chemically synthetic tumor antigen targeted 4-1BB agonists with potent efficacy and a favorable safety profile.

Citation Format: Elizabeth M. Repash, Punit Upadhyaya, Johanna Lahdenranta, Jessica Kublin, Jun Ma, Marianna Kleyman, Liuhong Chen, Eric Haines, Sailaja Battula, Kevin McDonnell, Kristen Hurov, Philip Brandish, Nicholas Keen. BT7480, a novel fully synthetic tumor-targeted immune cell agonist (TICA™) induces tumor localized 4-1BB agonism [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO077.

Anticancer immunity induced by a synthetic tumor-targeted CD137 agonist

Background

In contrast to immune checkpoint inhibitors, the use of antibodies as agonists of immune costimulatory receptors as cancer therapeutics has largely failed. We sought to address this problem using a new class of modular synthetic drugs, termed tumor-targeted immune cell agonists (TICAs), based on constrained bicyclic peptides (Bicycles).

Methods

Phage libraries displaying Bicycles were panned for binders against tumor necrosis factor (TNF) superfamily receptors CD137 and OX40, and tumor antigens EphA2, Nectin-4 and programmed death ligand 1. The CD137 and OX40 Bicycles were chemically conjugated to tumor antigen Bicycles with different linkers and stoichiometric ratios of binders to obtain a library of low molecular weight TICAs (MW <8 kDa). The TICAs were evaluated in a suite of in vitro and in vivo assays to characterize their pharmacology and mechanism of action.

Results

Linking Bicycles against costimulatory receptors (e.g., CD137) to Bicycles against tumor antigens (e.g., EphA2) created potent agonists that activated the receptors selectively in the presence of tumor cells expressing these antigens. An EphA2/CD137 TICA (BCY12491) efficiently costimulated human peripheral blood mononuclear cells in vitro in the presence of EphA2 expressing tumor cell lines as measured by the increased secretion of interferon γ and interleukin-2. Treatment of C57/Bl6 mice transgenic for the human CD137 extracellular domain (huCD137) bearing EphA2-expressing MC38 tumors with BCY12491 resulted in the infiltration of CD8+ T cells, elimination of tumors and generation of immunological memory. BCY12491 was cleared quickly from the circulation (plasma t_1/2 in mice of 1–2 hr), yet intermittent dosing proved effective.

Conclusion

Tumor target-dependent CD137 agonism using a novel chemical approach (TICAs) afforded elimination of tumors with only intermittent dosing suggesting potential for a wide therapeutic index in humans. This work unlocks a new path to effective cancer immunotherapy via agonism of TNF superfamily receptors.

Abstract 6703: A fully synthetic EphA2/4-1BB tumor-targeted immune cell agonist (TICATM) induces tumor localized 4-1BB agonism

4-1BB (CD137) is a member of the TNFR superfamily involved in stimulation of several immune cell types, including T cells and NK cells. CD137 is well validated pre-clinically, as agonism with anti-CD137 antibodies is effective in vivo [1], however, clinical utility to date has been limited by dose dependent hepatotoxicity. Bicycles® are a new therapeutic modality - fully synthetic, constrained bicyclic peptides with high affinity and excellent target selectivity.

We hypothesized that Bicycle CD137 agonists that lack Fc domains and exhibit rapid renal elimination may induce CD137 mediated anti-tumor activity while avoiding liver toxicity. Initially, we identified and optimized CD137 specific Bicycle agonists which, when multimerized together, induced CD137 mediated anti-tumor activity [2]. We have built on this initial approach and developed second generation molecules to enable potent stimulation of immune cells exclusively at the tumor site. These tumor-targeted immune cell agonists (TICAsTM) comprise CD137 binding Bicycles coupled to tumor antigen binding Bicycles.

Erythropoietin-producing hepatocellular A2 receptor (EphA2) is a tumor target overexpressed in several human cancers and its overexpression correlates with poor clinical prognosis. Here, we present new preclinical data demonstrating the potent immunomodulatory activity of dual targeting EphA2/CD137 TICAs. EphA2/CD137 TICAs engage EphA2 and CD137 with high affinity resulting in picomolar potency in co-culture assays consisting of cancer cell lines endogenously expressing EphA2, and CD137 Jurkat NF-kB/luciferase reporter cells. Moreover, EphA2/CD137 TICAs potentiate cytokine secretion (e.g. IFNγ) in immune cell co-culture experiments and promote caspase activity in T cell mediated cell killing assays. In vivo, EphA2/CD137 TICA (BCY9173), when dosed at 15 mg/kg (BID) to PBMC-humanized mice bearing HT29 xenografts, increased CD8+ T cells in tumors but not in plasma, suggesting local tumor target specific stimulation of T cells without systemic CD137 agonism. Intermittent dosing with various regimens of BCY12491, an EphA2/CD137 TICA, demonstrated robust anti-tumor activity including complete responses (CR) in 10/12 animals in a syngeneic humanized CD137 MC38 mouse model. Importantly, CR mice are resistant to re-challenge with MC38 tumor cells demonstrating a memory response, a phenomenon which has been previously reported for CD137 agonists [1]. Our EphA2/CD137 TICAs have shown the potential to precisely and potently stimulate immune cells in tumors without systemic immune activation.

This provides a strong rationale to further develop first-in-class Bicycle TICAs to potentially treat EphA2 expressing cancers.

References

1. Melero I, Shuford WW, Newby SA, Aruffo A, Ledbetter JA, Hellström KE, Mittler RS, Chen L. Monoclonal antibodies against the 4-1BB T-cell activation molecule eradicate established tumors. Nat Med. 1997; 3(6): 682-5

2. K. Hurov, P. Upadhyaya, J. Kublin, M. Kleyman, X. Zhou, J. Kristensson, G. Mudd, K. Rietschoten, S. Watcham, R. Lani, W. F. An, T. Stephen, E. Haines, J. Lahdenranta, L. Chen, S. Battula, K. McDonnell, P. Park, and N. Keen. Activation of 4-1BB using multivalent and tumour targeted bicyclic peptides; Poster 2019 Annual AACR meeting, Cancer Research, DOI: 10.1158/1538-7445.AM2019-3257 Published July 2019

Citation Format: Sailaja Battula, Gemma Mudd, Punit Upadhyaya, Julia Kristensson, Marianna Kleyman, Elizabeth Repash, Jessica Kublin, Jun Ma, Eric Haines, Kristen Hurov, Liuhong Chen, Johanna Lahdenranta, Paul Beswick, Kevin McDonnell, Nicholas Keen. A fully synthetic EphA2/4-1BB tumor-targeted immune cell agonist (TICATM) induces tumor localized 4-1BB agonism [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 6703.

Abstract 5552: BT7480, a novel fully synthetic tumor-targeted immune cell agonist (TICATM) induces tumor localized 4-1BB agonism

Costimulatory molecules expressed on activated T and NK cells such as 4-1BB (CD137/TNFRSF9) can be leveraged for cancer immunotherapy. Despite compelling preclinical data, 4-1BB agonistic antibodies have been hampered by failure to delineate hepatoxicity from efficacy in the clinic [1,2]. Next generation strategies are focused on bispecific approaches aimed at promoting target-mediated clustering of 4-1BB to limit systemic and liver effects [3,4]. Bicycles® are fully synthetic, constrained bicyclic peptides that have antibody-like affinity and selectivity to their targets. Unlike traditional biologic approaches, the small size (~2 kDa) and tunable pharmacokinetic (PK) parameters of Bicycles enable superior tumor penetration and allow exploration into the relationship between pulsatile dosing and 4-1BB activation while de-risking hepatoxicity concerns due to a differentiated renal elimination mechanism combined with a tumor-localized immune response. We hypothesized that clustering and activation of 4-1BB could be achieved by conjugating a 4-1BB binding Bicycle to a tumor antigen targeting Bicycle. BT7480 is a tumor-targeted immune cell agonist (TICATM) targeting Nectin-4 and agonizing 4-1BB. Nectin-4 (PVRL4) is highly expressed on numerous tumors with unmet medical need, including bladder, pancreatic, breast, ovarian, esophageal, and lung. BT7480 exhibits highly potent 4-1BB agonism in an engineered 4-1BB reporter system that correlates with Nectin-4 surface expression on the co-cultured tumor cells. In addition, BT7480 induces robust production of interleukin-2 (IL-2) and interferon gamma (IFNγ) in primary PBMC/tumor cell co-culture assays. This activity is strictly dependent on the tumor cells expressing Nectin-4 and on the ability of the TICA to bind to both Nectin-4 and 4-1BB. Nectin-4/4-1BB TICAs are also target-specific immune cell stimulators of patient-derived lung tumors with an intact immune microenvironment. Intermittent dosing of BT7480 led to robust anti-tumor efficacy with 22 out of 24 complete responders (CRs) in a MC38 (Nectin-4-expressing) syngeneic mouse model. Importantly, a memory response was established as the CR mice were resistant to re-challenge with MC38 tumors. Additionally, BT7480 led to increased intratumoral T cell infiltration without elevation of liver enzymes in a CT26 (Nectin-4-expressing) syngeneic mouse model. In non-human primates (NHPs), BT7480 exhibits dose linear exposure and is well tolerated up to 10mpk. Further dose-range finding and safety analysis in NHPs is currently ongoing. BT7480 represents a new generation of chemically synthetic tumor antigen targeted 4-1BB agonists. References 1. Segal NH, Logan TF, Hodi FS, et al. Results from an integrated safety analysis of urelumab, an agonist anti-CD137 monoclonal antibody. Clin Cancer Res. 2017;23(8):1929-1936. 2. Chester et al. Immunotherapy targeting 4-1BB: mechanistic rationale, clinical results, and future strategies. Blood 2018;131(1): 49-57. 3. Hinner et al. Tumor-localized costimulatory T-cell engagement by the 4-1BB/HER2 bispecific antibody-anticalin fusion PRS-343. Clin Cancer Res. 2019; 25(19): 5878-5889. 4. Claus C, Ferrara, C, Xu W, et al. Tumor-targeted 4-1BB agonists for combination with T cell bispecific antibodies as off-the-shelf therapy. Sci Transl Med. 2019; 11(496): eaav5989.

Citation Format: Kristen Hurov, Punit Upadhyaya, Johanna Lahdenranta, Jessica Kublin, Jun Ma, Elizabeth Repash, Marianna Kleyman, Julia Kristensson, Liuhong Chen, Eric Haines, Sailaja Battula, Kevin McDonnell, Nicholas Keen. BT7480, a novel fully synthetic tumor-targeted immune cell agonist (TICATM) induces tumor localized 4-1BB agonism [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 5552.

Abstract 3257: Activation of CD137 using multivalent and tumor targeted Bicyclic peptides

CD137 (4-1BB/TNFRSF9) is a costimulatory T-cell receptor belonging to the TNF receptor superfamily. Agonistic anti-CD137 antibodies have shown potent, often curative anti-tumor activity in preclinical models. Two human anti-CD137 antibodies, urelumab and utomilumab are currently undergoing clinical testing. Urelumab has shown several single-agent, partial responses, but its use has been hampered by hepatoxicity, while utomilumab has shown little or no single agent activity.

Bicycles® are a new class of drugs - fully synthetic, constrained bicyclic peptides that combine the attributes of antibodies, small molecules, and peptides by delivering high affinity, selectivity, and rapid clearance. Their small size (1.5-2 kDa) delivers advantages in tumor penetration, and renal elimination may avoid the liver and GI toxicity often associated with other drug modalities, including certain antibodies. We hypothesized that fully synthetic Bicycle CD137 agonists with rapid clearance, minimal liver exposure and no Fc receptor interaction may induce CD137 mediated anti-tumor activity while avoiding liver toxicity.

A high affinity lead BCY3814 (KD ~30 nM) that binds to the CD137 ligand-binding site was identified. CD137 activation requires receptor crosslinking, thus multivalent binding would be expected to recapitulate the action of the natural trimeric ligand. We envisioned that CD137 agonism could be achieved directly by using multimeric CD137 Bicycles or in a tumor targeted fashion with bispecific or “heterotandem” Bicycles. The synthetic simplicity and highly modular nature of the Bicycle® platform enabled us to rapidly explore both formats.

To generate a “pure” CD137 agonist we synthesized &gt;50 different multimeric variants of BCY3814 with chemical linkers of various lengths and rigidity and using different sites of attachments, while maintaining a compact size (&lt;15 kDa). Tumor targeted CD137 agonists were generated as heterotandems, whereby BCY3814 is conjugated to a tumor antigen targeting Bicycle. In this design, the CD137 Bicycle only induces CD137 agonism after the molecule binds to a tumor cell with high receptor expression.

We discovered Bicycle multimers that exhibit a range of potencies in a cell-based CD137-dependent reporter assay, activate human T cells in vitro as indicated by increased cytokine release, and show biological activity in vivo. Bicycle heterotandems targeting Nectin-4 and EphA2 exhibited highly potent and tumor cell specific activity in both the cell-based reporter assay and the human T cell assay. Selected CD137 multimers and heterotandems are being tested further in humanized mouse models for T cell activation, anti-tumor activity, and liver safety. These molecules are promising, novel cancer immunotherapy candidates and importantly, they pave the way for development of synthetic agonists of other TNF receptors that can be targeted to the local tumor microenvironment.

Citation Format: Kristen E. Hurov, Punit Upadhyaya, Jessica Kublin, Xueyuan Zhou, Julia Kristensson, Rachid Lani, Gemma Mudd, Katerine van Rietschoten, Frank An, Johanna Lahdenranta, Liuhong Chen, Gavin Bennett, Kevin McDonnell, Peter Park, Nicholas Keen. Activation of CD137 using multivalent and tumor targeted Bicyclic peptides [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3257.

Does participation in an HIV vaccine efficacy trial affect risk behaviour in South Africa?

BACKGROUND

Increased sexual risk behaviour in participants enrolled in HIV prevention trials has been a concern. The HVTN 503/Phambili study, a phase 2B study of the Merck Ad-5 multiclade HIV vaccine in South Africa, suspended enrollment and vaccinations following the results of the Step study. Participants were notified of their treatment allocation and continue to be followed. We investigated changes in risk behaviour over time and assessed the impact of study unblinding.

METHODS

801 participants were enrolled. Risk behaviours were assessed with an interviewer-administered questionnaire at 6-month intervals. We assessed change from enrolment to the first 6-month assessment pre-unblinding and between enrolment and at least 6 months post-unblinding on all participants with comparable data. A one-time unblinding risk perception questionnaire was administered post-unblinding.

RESULTS

A decrease in participants reporting unprotected sex was observed in both measured time periods for men and women, with no differences by treatment arm. At 6 months (pre-unblinding), 29.6% of men and 35.8% of women reported changing from unprotected to protected sex (p<0.0001 for each). Men (22%) were more likely than women (14%) to report behaviour change after unblinding (p=0.009). Post-enrolment, 142 (45%) of 313 previously uncircumcised men underwent medical circumcision. 663 participants completed the unblinding questionnaire. More vaccine (24.6%) as compared to placebo recipients (12.0%) agreed that they were more likely to get HIV than most people (p<0.0001), and attributed this to receiving the vaccine.

CONCLUSION

We did not find evidence of risk compensation during this clinical trial. Some risk behaviour reductions including male circumcision were noted irrespective of treatment allocation.