Ribon Therapeutics (United States)

Abstract Programmed Cell Death 1 (PD-1) signaling blockade effectively restores immune surveillance to treat melanoma. However, chronic interferon-gamma (IFNγ) -driven immune homeostatic mechanisms in melanoma cells contribute to immune evasion and acquired resistance. We previously demonstrated that poly ADP ribosyl polymerase 14 (PARP14), an IFNγ-responsive gene product, in part mediates IFNγ-driven resistance, as its inhibition prolonged PD-1 blockade responses in preclinical models. Nevertheless, PARP14 inhibition alone could not achieve full tumor clearance, indicating additional resistance mechanisms. Herein, we identify a robust PARP14 catalytic inhibitor (PARP14i) gene signature associated with improved patient survival. We elucidate immune and tumor cell adaptations to PARP14 inhibition combined with PD-1 blockade using preclinical models. This combination therapy suppressed tumor-associated macrophages while increasing pro-inflammatory memory macrophages. Notably, it preserved cytotoxic T cell function by inducing a quiescent state, mitigating terminal exhaustion. Despite enhancing immune responses, adaptive resistance mechanisms emerged in tumor cells, engaging alternative immune evasion pathways. These findings indicate that this combination therapy primes immune cells for further therapeutic intervention, providing a promising strategy to overcome resistance and optimize treatment outcomes.SummaryWhile immune checkpoint inhibitors, such as α-PD-1 therapy, provide significant clinical benefits, many tumors develop resistance and relapse. Re-treatment with α-PD-1 often fails because T cells lose their function (a process called exhaustion), and immune-suppressing cells like tumor-associated macrophages (TAMs) increase in the tumor environment, enabling tumors to evade immune attack.Recent studies have shown that a small molecule inhibitor of PARP14 can restore sensitivity to α-PD-1 therapy by remodeling the tumor environment. This includes increasing immune cell infiltration and improving antigen presentation, which helps the immune system recognize tumor cells.Using single-cell RNA sequencing, we discovered that this therapy induces a new state of T cell dormancy, where cytotoxic T cells temporarily stop attacking but retain the potential to be reactivated by additional treatments. This finding opens new opportunities to sustain immune responses and improve outcomes for patients who relapse after immunotherapy.Graphical Summary

Varoglutamstat (PQ912) is an oral, small molecule inhibitor of glutaminyl cyclase, preventing the formation of neurotoxic N3pE amyloid. A Phase 2a study (NCT02389413, Scheltens et al., 2018) reported encouraging first evidence of varoglutamstat's disease-modifying activity, most importantly with statistically significant changes from baseline in working memory after only 12 weeks of treatment. VIVIAD (NCT04498650, Vijverberg et al., 2021) is an informed multicenter, randomized, placebo-controlled, double-blind, parallel group dose-finding Phase 2b study in 250 patients with Mild Cognitive Impairment (MCI) and early Alzheimer´s disease (AD). Treatment duration varies between 48 and 96 weeks depending on the time of inclusion, with participants receiving 300mg or 600mg varoglutamstat, or placebo, twice-daily (BID). The participants' disease status at time of inclusion was confirmed by Abeta1-42 and phospho-tau CSF biomarker profiles, various cognition tests including MMSE, DSST/WAIS-IV Coding test (WAIS-IV), and A-IADL-Q. Primary outcome is a composite score of the cognitive domains attention and working memory using the Cogstate Neuropsychological Test Battery (Cogstate NTB). Enrollment has been completed, with a total of N = 259 patients randomized. The 300mg BID varoglutamstat arm was switched to 600mg BID based on positive independent Data Safety Monitoring Board review in June 2022. As of April 14, 2023, 23 patients had completed 96 weeks of treatment. The study will continue until the last patient has completed 48 weeks of treatment with the corresponding follow-up visit. While most AD trials focus on cognitive tests assessing memory deficits rather than working memory and attention, VIVIAD uses WAIS-IV to select patients with rescuable cognitive deficits in the target domains. In contrast to MMSE, WAIS-IV performance shows a reasonably good correlation with the primary outcome measures. Comparing baseline data of male and female participants showed no significant gender differences except for Abeta1-42 levels. The use of MMSE and DSST/WAIS-IV together with CSF biomarkers is a valuable tool in identifying and recruiting patients with MCI or mild AD. The strategy of recruiting individuals with evidence of baseline deficits on the WAIS-IV Coding test has successfully enriched the study cohort with respect to deficits in attention and working memory, enabling reliable assessment of potential cognitive improvement after treatment.

Abstract There are many pathways that activate the Type I interferon (IFN) response to combat tumor progression including the cytosolic nucleic acid sensing pathways. PARP7 is a monoART enzyme that was reported to negatively regulate the Type I IFN response by interacting with TBK1 during viral infection. We and others have demonstrated that PARP7 is a novel negative regulator of cytosolic nucleic acid sensing in tumor cells. RBN-2397 is the first potent and selective small molecule inhibitor of PARP7 catalytic function. We have shown that administration of RBN-2397 to CT26 tumor-bearing mice significantly decreased tumor growth and led to complete and durable regressions in a subset of mice. The antitumor effects correlated with activation of p-STAT1 and increased expression of ISGs including CXCL10, MX1, and CCL5 in tumors. A growing body of work has shown that DNA damaging agents such as chemotherapies activate the Type I IFN response by generating accumulation of nucleic acids, including DNA, in the cytosol or tumor microenvironment. These aberrant cytosolic nucleic acids are recognized by the innate immune response via cGAS leading to activation of the STING/TBK pathway and subsequent production of IFN-β and expression of ISGs (interferon induced genes). Given that PARP7 suppresses the Type I IFN response, we hypothesized that the immune-related mechanism observed with chemotherapy would be inhibited in tumors with high PARP7 expression. Combining chemo with RBN-2397 could potentiate Type I IFN response activation in PARP7 expressing tumors and enhance immune mediated anti-tumor responses. We tested the ability of platinum (cisplatin, oxaliplatin, and carboplatin) and taxane (docetaxel and paclitaxel) chemotherapy agents to activate the Type I IFN response in the CT26 mouse colon cancer cell line in vitro by gene expression analysis of several ISGs (CXCL10, CCL5, MX1, IFIT1, and IFN-β). Single agent chemo led to modest increases in the expression of ISGs. The combination of cisplatin or oxaliplatin with RBN-2397 significantly potentiated the effect of RBN-2397 and led to a synergistic increase of the ISGs in CT26 cells after 24 hours of treatment. Similar effects were obtained with the combination of docetaxel or paclitaxel with RBN-2397. To evaluate if the combinatorial effect observed in vitro translated into increased efficacy in vivo, we first identified doses of single agent cisplatin or docetaxel that increased expression of ISGs and enhanced cytosolic-DNA in CT26 tumors. Next, we verified the tolerability of validated doses in combination with RBN-2397. Finally, we performed an efficacy study in CT26 tumor bearing mice and observed that the combination of cisplatin and RBN-2397 increased tumor growth inhibition and survival relative to single agent activity. This study provides rationale for exploration of DNA damaging agents in combination with RBN-2397. Citation Format: Kaiko Kunii, Jeff J. Song, Danielle Zimmerman, Chang Liu, Kristy G. Kuplast-Barr, Jonathan J. Novak, Sunaina P. Nayak, Joseph M. Gozgit, Melissa M. Vasbinder, Kristen McEachern, Kevin W. Kuntz, Heike Keilhack, Jennifer R. Molina. Potentiation of Type I interferon signaling leads to in vivo efficacy achieved with combination of chemotherapy and the PARP7 inhibitor RBN-2397 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3260.

Abstract Adaptive resistance limits immune checkpoint blockade therapy (ICBT) response duration and magnitude. Interferon γ (IFNγ), a critical cytokine that promotes cellular immunity, also induces adaptive resistance to ICBT. Using syngeneic mouse tumour models, we confirmed that chronic IFNγ exposure confers resistance to anti-Programmed cell death protein 1 (α-PD-1) therapy. We identified consistent upregulation of poly-ADP ribosyl polymerase 14 (PARP14) in both chronic IFNγ-treated cancer cells and patient melanoma with elevatedIFNGexpression. Knockdown or pharmacological inhibition of PARP14 increased effector T cell infiltration into tumours derived from cells pre-treated with IFNγ and decreased the presence of regulatory T cells, leading to restoration of α-PD-1 sensitivity. Finally, we determined that tumours which spontaneously relapsed following α-PD-1 therapy could be re-sensitised upon receiving PARP14 inhibitor treatment, establishing PARP14 as an actionable target to reverse IFNγ-driven ICBT resistance.

Targeting metalloproteinases has been in focus of drug design for a long time. However, human proteinases of the astacin family, in particular meprin α and β emerged as potential drug targets just recently. More and more data links them to several diseases with different pathological background. Nevertheless, the validation of meprins as suitable drug targets requires highly potent and selective inhibitors as chemical probes to elucidate their role in pathophysiology. Albeit highly selective inhibitors of meprin β have already been reported, only inhibitors of meprin α with modest activity or selectivity are known. Starting from recently reported heteroaromatic scaffolds, the aim of this study was the optimization of meprin α and/or meprin β inhibition while keeping the favorable off-target inhibition profile over other metalloproteases. We now report novel potent pan-meprin inhibitors as well as highly active inhibitors of meprin α with superior selectivity over meprin β. The latter are suitable to serve as chemical probes and enable further target validation of meprin proteases.

Abstract Targeting cytosolic nucleic acid sensing pathways and the Type I interferon (IFN) response is an emerging therapeutic strategy being explored in oncology. The PARP family consists of seventeen enzymes that regulate fundamental biological processes including response to cellular stress. In contrast to PARP1, PARP7 (TIPARP) is a monoPARP that catalyzes the transfer of single units of ADP-ribose onto substrates (MARylation) to change their function and plays a role in suppressing the Type I IFN response. RBN-2397 selectively inhibits PARP7 compared to the approved PARP1 inhibitors and demonstrates > 50-fold selectivity for inhibition of PARP7 over all PARP family members as measured by biochemical assays. The inhibition of PARP1-mediated ADP-ribosylation has been well-characterized for several PARP1 inhibitors using a cellular hydrogen peroxide-induced PARylation assay. Here, we show that RBN-2397 inhibits PARP7-dependent MARylation with an IC50 of 2 nM exhibiting a 300-fold window over PARP1-driven PARylation. Using the mouse CT26 cell line, we showed that RBN-2397, but not the PARP1 inhibitor olaparib, induced Type I IFN signaling demonstrated by STAT1 phosphorylation. The effect on pSTAT1 was phenocopied by PARP7 knockout (KO). To further demonstrate specificity, we show that simultaneous KO of PARP7 prevented any additional increase of STAT1 phosphorylation by RBN-2397; however, KO of PARP1 had no effect on the induction of Type I IFN signaling by RBN-2397. We had previously reported that RBN-2397 dosing of CT26 tumor bearing immune competent BALB/c mice led to complete and durable tumor regressions which could be reversed by interfering with tumor-derived IFN signaling (1). Here we show that in contrast, RBN-2397 showed modest activity with no tumor regressions in CT26-tumor bearing immunodeficient NOG mice. To assess which immune cell populations are involved in the antitumor effects of RBN-2397, CT26 tumor-bearing BALB/c mice were depleted of CD4 T, CD8 T or NK cells. Depletion of CD4 T or NK cells had no effect on RBN-2397 antitumor activity; however, depletion of CD8 T cells significantly reversed the effects of RBN-2397, suggesting that CD8 T cells are responsible for much of the antitumor immunity induced by RBN-2397. We have discovered and developed RBN-2397, a first-in-class, potent and selective inhibitor of PARP7. We show RBN-2397 restores Type I IFN signaling in cancer cells and that this is an on-target effect of inhibiting the catalytic activity of PARP7 and not PARP1. We further show that the adaptive immune response was required for the antitumor effects of RBN-2397. RBN-2397 is the first agent to enter clinical trials that targets this tumor-intrinsic vulnerability, and a Phase I clinical trial is underway (NCT04053673). (1) AACR Jun 22-24, 2020: Cancer Res 2020;80 (16 Suppl): Abstract nr 3405. Citation Format: Joseph M. Gozgit, Melissa M. Vasbinder, Ryan P. Abo, Kaiko Kunii, Kristy G. Kuplast-Barr, Bin Gui, Alvin Z. Lu, Jennifer R. Molina, Elena Minissale, Kerren K. Swinger, Tim J. Wigle, Danielle J. Blackwell, Christina R. Majer, Yue Ren, Mario Niepel, Ellen Bamberg, Jan-Rung Mo, David Church, Jeff Song, Luke Utley, Patricia E. Rao, Timothy J. Mitchison, Kevin W. Kuntz, Victoria M. Richon, Heike Keilhack. RBN-2397: A potent and selective small molecule inhibitor of PARP7 that induces tumor-derived antitumor immunity dependent on CD8 T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 48.

3000 Background: Targeting cytosolic nucleic acid sensing pathways and the Type I interferon (IFN) response is an emerging therapeutic strategy in oncology. PARP7 is a member of the monoPARP class of enzymes and a newly identified negative regulator of nucleic acid sensing in tumor cells. PARP7 expression is increased by cellular stress and aromatic hydrocarbons, and the PARP7 gene is amplified in multiple cancers. RBN-2397 is a potent, selective inhibitor of PARP7. In preclinical models, RBN-2397 restored Type I IFN signaling in tumors, caused complete tumor regressions, and induced adaptive immunity. Methods: Patients (pts) with advanced solid tumors were treated with RBN-2397 on either a continuous or 14-of-21-day intermittent schedule using a 3+3 dose escalation design. Primary objective: establish MTD and/or RP2D. Secondary obj.: safety, activity, PK of unmicronized/micronized tablets. Exploratory obj.: Pd. Results: As of 4 January 2021, 47 pts were treated: 25 pts in the intermittent schedule (25 to 500 mg BID) and 22 patients in the continuous schedule (100 to 400 mg BID). The most frequent RBN-2397-related AEs (all grades) were dysgeusia (26%), decreased appetite (13%), fatigue (11%), and diarrhea (11%). Gr 3/4 RBN-2397-related AEs all occurred in 7 pts (15%) at doses ≥ 200 mg: diarrhea (2 pts, 4%), increased ALT, AST, and bilirubin (1 pt, 2%), and fatigue, anemia, neutropenia, and thrombocytopenia in 1 pt (2%) each. The 2 DLTs were Gr 3 febrile neutropenia (400 mg continuous schedule) and Gr 4 increase in ALT/AST (500 mg intermittent schedule). Plasma exposures generally increased dose dependently with the majority at or above the projected efficacious range based on animal studies. All evaluable baseline tumor biopsies showed evidence of PARP7 expression as measured by mRNA in situ hybridization (n = 11; Median tumor H score: 128). In 5 evaluable tumor biopsy pairs, increases in interferon-stimulated gene expression were observed post RBN-2397, consistent with activation of Type I IFN. CXCL10 mRNA increased in all evaluable on-treatment biopsies (1.5 to 8-fold). Several on-treatment biopsies showed enrichment for immune response gene sets that was accompanied by an increase in CD8+ T cells and Granzyme B expression, evidence for induction of an adaptive immune response post RBN-2397. This increase in immune response related genes and CD8+ T cells was observed in a pt with metastatic squamous NSCLC who has been on study for 16+ months. 1 pt with HR+, HER2- breast cancer achieved a confirmed PR at 100 mg and 8 pts had SD for ≥18 weeks (RECIST 1.1). Conclusions: To date, RBN-2397 is well tolerated and demonstrates dose dependent increases in plasma exposures, evidence of target inhibition, and preliminary signs of clinical activity. Determination of MTD/RP2D is imminent and study expansion is planned to evaluate safety and efficacy in squamous NSCLC, HNSCC, HR+ breast cancer, and PARP7 amplified tumors. Clinical trial information: NCT04053673.

Abstract Neoantigens arise from somatic tumor mutations and can encode amino acid changes, generating peptides with the potential to bind to HLA molecules. Since these neoepitopes provide exquisite tumor specificity and are expected to be highly immunogenic as they are not subject to central tolerance, they were long-envisioned as highly valuable tumor antigens. Growing evidence has supported tumor neoepitopes as key antigens triggering immune-mediated tumor killing in vivo across settings of effective cancer immunotherapy, including checkpoint blockade and adoptive transfer with tumor-infiltrating lymphocytes. Vaccination is a potentially effective approach for inducing tumor-specific immune responses, but has been limited by the lack of a sufficiently potent vaccine immunogen. By leveraging next-generation sequencing technologies and new analytical pipelines to systematically identify personal tumor neoantigens, in a phase 1 trial we tested the feasibility, safety, and immunogenicity of a multi-epitope cancer vaccine targeting personal tumor neoantigens in patients with high-risk melanoma. Mutations were identified by DNA and RNA sequencing; epitopes were selected based on class I HLA binding prediction algorithms. The vaccines, comprised of up to 20 long peptides spanning mutated tumor epitopes and admixed with the Toll-Like Receptor 3 agonist poly-ICLC, were administered using a prime-boost approach. Of 12 patients enrolled, the initial 6 patients who received the full set of priming and booster vaccinations experienced only minimal adverse events, consisting of mild and transient injection site reaction, flu-like symptoms, and rash. We identified strong, polyfunctional CD4+ and CD8+ T cell responses against multiple neoepitopes in all dosed patients. Processing and presentation of neoantigens on autologous tumors was confirmed by mass spectrometry and recognition of autologous tumor by vaccine-induced neoantigen-specific T cells was verified. These studies show that a personalized neoantigen vaccine is safe, feasible, and strongly immunogenic in cancer patients. The data should reinvigorate the field of cancer vaccines, providing a rational path for the building of combinatorial approaches to extend their efficacy. Citation Format: Patrick A. Ott, Zhuting Hu, Derin B. Keskin, Sachet A. Shukla, Jing Sun, Ed Fritsch, Nir Hacohen, Catherine J. Wu. A personalized neoantigen vaccine in patients with high risk melanoma [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr PR02.