Discovery of NXT-10796, an orally active, intestinally restricted EP4 agonist prodrug for the treatment of inflammatory bowel disease

A property-focused optimization strategy was employed to modify the carboxylic acid head group of a class of EP4 agonists in order to minimize its absorption upon oral administration. The resulting oxalic acid monohydrazide-derived carboxylate isostere demonstrated utility as a class of prodrug showing colon-targeted delivery of parent agonist 2, with minimal exposure observed in the plasma. Oral administration of NXT-10796 demonstrated tissue specific activation of the EP4 receptor through modulation of immune genes in the colon, without modulation of EP4 driven biomarkers in the plasma compartment. Although further in depth understanding of the conversion of NXT-10796 is required for further assessment of the developability of this series of prodrugs, using NXT-10796 as a tool molecule has allowed us to confirm that tissue-specific modulation of an EP4-modulated gene signature is possible, which allows for further evaluation of this therapeutic modality in rodent models of human disease.

RP-3500: A Novel, Potent, and Selective ATR Inhibitor that is Effective in Preclinical Models as a Monotherapy and in Combination with PARP Inhibitors

Ataxia telangiectasia and Rad3-related (ATR) kinase protects genome integrity during DNA replication. RP-3500 is a novel, orally bioavailable clinical-stage ATR kinase inhibitor (NCT04497116). RP-3500 is highly potent with IC₅₀ values of 1.0 and 0.33 nmol/L in biochemical and cell-based assays, respectively. RP-3500 is highly selective for ATR with 30-fold selectivity over mammalian target of rapamycin (mTOR) and more than 2,000-fold selectivity over ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), and phosphatidylinositol 3-kinase alpha (PI3Kα) kinases. In vivo, RP-3500 treatment results in potent single-agent efficacy and/or tumor regression in multiple xenograft models at minimum effective doses (MED) of 5 to 7 mg/kg once daily. Pharmacodynamic assessments validate target engagement, with dose-proportional tumor inhibition of phosphorylated checkpoint kinase 1 (pCHK1) (IC₈₀ = 18.6 nmol/L) and induction of phosphorylated H2A.X variant histone (γH2AX), phosphorylated DNA-PK catalytic subunit (pDNA-PKcs), and phosphorylated KRAB-associated protein 1 (pKAP1). RP-3500 exposure at MED indicates that circulating free plasma levels above the in vivo tumor IC₈₀ for 10 to 12 hours are sufficient for efficacy on a continuous schedule. However, short-duration intermittent (weekly 3 days on/4 days off) dosing schedules as monotherapy or given concomitantly with reduced doses of olaparib or niraparib, maximize tumor growth inhibition while minimizing the impact on red blood cell depletion, emphasizing the reversible nature of erythroid toxicity with RP-3500 and demonstrating superior efficacy compared with sequential treatment. These results provide a strong preclinical rationale to support ongoing clinical investigation of the novel ATR inhibitor, RP-3500, on an intermittent schedule as a monotherapy and in combination with PARP inhibitors as a potential means of maximizing clinical benefit.

Abstract P054: RP-3500: A novel, potent and selective ATR inhibitor that is effective in pre-clinical models as a monotherapy and in combination with PARP inhibitors

Background: Ataxia telangiectasia and Rad3-related (ATR) protein kinase is a key mediator of cellular DNA damage repair (DDR) and is activated in response to DNA replication stress. ATR is attractive as a drug target in tumors with loss-of-function alterations in complimentary DDR pathways, including ataxia-telangiectasia mutated (ATM) and BRCA. RESULTS: RP-3500 is a novel, orally bioavailable clinical-stage ATR kinase inhibitor. RP-3500 is highly potent with ATR kinase IC50 values of 1.0 and 0.33 nM in biochemical and cell-based assays, respectively. It is highly selective with >30-fold selectivity over mTOR and >2000-fold selectivity over ATM, DNA-PK and PI3Kα kinases. Preclinical tumor xenograft models harboring synthetic lethal (SNIPRx) gene mutations whose loss of function sensitizes to RP-3500 were selected for in vivo studies. RP-3500 treatment resulted in potent single-agent in vivo efficacy and/or tumor regression in multiple models at minimum effective doses (MED) of 5–7 mg/kg once daily. Pharmacodynamic assessments validated target engagement, with a proportional relationship between tumor pCHK1(Ser345) inhibition and circulating RP-3500 plasma levels (IC80 = 18.6 nM). Circulating free plasma levels of RP-3500 at the MED indicate that exposure above the in vivo tumor pCHK1(Ser345) IC80 for 10–12 hours is sufficient for efficacy and dose proportional phosphorylation of DNA damage markers γ-H2AX, pDNA-PKcs and pKAP1. In vitro, tumor cells with ATM loss exhibited increased susceptibility to RP-3500 and a 3-day compound exposure was sufficient to generate a sustained DNA damage response compared to cells with functional ATM expression. In ATM-deficient mouse models, short-duration intermittent (weekly 3 days on/4 days off or 5 days on/2 days off) dosing schedules maximized tumor growth inhibition while minimizing the impact on hematology parameters, including red blood cell depletion. These results emphasize the reversible nature of erythroid toxicity with RP-3500 and the advantage of intermittent dosing schedules to alleviate anemia. The 3 days on/4 days off intermittent treatment schedule also substantially improved the efficacy and tolerability of RP-3500 and PARP inhibitor combinations compared to continuous treatment schedules. Intermittent treatments of RP-3500 given concomitantly with reduced doses of olaparib or niraparib demonstrated synergistic efficacy in Granta-519 (ATM mutn) and SUM149PT (BRCA1mutn) models with minimal hematological adverse effects and superior efficacy to sequential treatment. CONCLUSIONS: These results provide a strong preclinical rationale to support clinical investigation of the novel ATR inhibitor RP-3500 on an intermittent schedule as a monotherapy and in combination with PARP inhibitors as a means of maximizing clinical benefit. RP-3500 is currently evaluated in the ongoing phase 1 TRESR (Treatment Enabled by SNIPRx) study (NCT04497116).

Citation Format: Anne Roulston, Michal Zimmerman, Robert Papp, Alex Skeldon, Charles Pellerin, Émilie Dumas-Bérube, Valerie Dumais, Stephane Dorich, Sara Fournier, Li Li, Marie-Ève Leclaire, Shou Yun Yin, Amandine Chefson, Hunain Alam, William Yang, Chloe Fugère-Desjardins, Sabrina Hammond, Kathryn Skorey, Amina Mulani, Victoria Rimkunas, Artur Veloso, Martine Hamel, Rino Stocco, Yael Mamane, Zuomei Li, Jordan Young, Mike Zinda, Cameron Black. RP-3500: A novel, potent and selective ATR inhibitor that is effective in pre-clinical models as a monotherapy and in combination with PARP inhibitors [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 P054.

Dual Glycolate Oxidase/Lactate Dehydrogenase A Inhibitors for Primary Hyperoxaluria

Both glycolate oxidase (GO) and lactate dehydrogenase A (LDHA) influence the endogenous synthesis of oxalate and are clinically validated targets for treatment of primary hyperoxaluria (PH). We investigated whether dual inhibition of GO and LDHA may provide advantage over single agents in treating PH. Utilizing a structure-based drug design (SBDD) approach, we developed a series of novel, potent, dual GO/LDHA inhibitors. X-ray crystal structures of compound 15 bound to individual GO and LDHA proteins validated our SBDD strategy. Dual inhibitor 7 demonstrated an IC₅₀ of 88 nM for oxalate reduction in an Agxt-knockdown mouse hepatocyte assay. Limited by poor liver exposure, this series of dual inhibitors failed to demonstrate significant PD modulation in an in vivo mouse model. This work highlights the challenges in optimizing in vivo liver exposures for diacid containing compounds and limited benefit seen with dual GO/LDHA inhibitors over single agents alone in an in vitro setting.

Diabetes, insulin resistance, and metabolic syndrome in women at high risk for breast cancer

e12522

Background: Despite the growing body of research on diabetes (Db), insulin resistance (IR) and metabolic syndrome (MetS) in association with breast cancer, the prevalence of these metabolic conditions has yet to be explored in the high risk population. Delineating the numerous factors that contribute to these women’s risk is key in the management of this vulnerable population, especially when outlining potentially modifiable risk factors. The overall objective of this prospective study was to quantify the prevalence of Db, IR and MetS in women at high risk for breast cancer. Methods: Participants consisted of 100 Caucasian women above the age of 35 with an estimated 5yr risk of ≥1.7%. This criteria was met by (a) BRCA mutation carriers, (b) history of LCIS, (c) history of ADH, (d) history of mantle radiation, or (e) calculated 5yr risk of ≥1.7% using the Gail model. A comprehensive metabolic profile was obtained for each participant based on a questionnaire, fasting blood sample and biophysical measurements. The diagnostic criteria used for Db were those established by the Candian Practice Guidelines. The threshold for IR was a HOMA-IR value of 2.29. The MetS diagnostic criteria were those set by the IDF where 3 of 5 criteria from ↑waist circumference, ↑triglycerides, ↓HDL, HTN and hyperglycemia must be met. Results: The frequency (%) of Db (n=97), IR (n=96) and MetS (n=88) was 5(5), 17(18) and 29(33) respectively. Among the components of MetS, ↑waist circumference had the highest prevalence 60(68.2), followed by HTN 33(37.5), hyperglycemia 27(30.7), ↑triglycerides 23(26.1) and ↓HDL 22(29.7). There was a significant correlation observed between the Gail score and HDL (0.37, p<0.01), as well as systolic Bp (0.28, p<0.01). Conclusions: The prevalence of IR and MetS in this sample of women at high risk for breast cancer is considerably higher than the prevalence of these metabolic conditions in a similar population of average risk women, based on population data. This supports the significance and feasibility of an experimental study comparing the prevalence of IR and MetS in women at high risk and average risk for breast cancer. The prevalence of Db in this sample was comparable to the prevalence described in the general population.