Abstract 6302: Structure-based and property-based drug design of AZD9574, a CNS penetrant PARP1 selective inhibitor and trapper

PARP inhibitors exploit defects in DNA repair pathways to selectively target cancerous cells via PARP1 catalytic inhibition and PARP1 trapping onto the DNA. All known clinical PARP1 inhibitors bind at the same site at the catalytic center of the enzyme. However, despite this resemblance they show immensely different outcomes in terms of response rate in the clinic due to their varying degree of PARP trapping ability. Moreover, the first-generation PARP inhibitors were not optimized for selectivity across the PARP family potentially driving undesirable side effects, including intestinal toxicity from tankyrase inhibition or hematological toxicity from PARP2 inhibition. There has been strong rationale for the use of PARP inhibitors in neuro-oncology. However, the first-generation PARP inhibitors have limited CNS distribution as these drugs were not designed for brain penetration. Recently AstraZeneca has reported the discovery of AZD5305, a next generation PARP1 selective inhibitor and PARP1-DNA trapper which was not designed with a CNS penetrant profile. Given the unmet need of a brain penetrant PARP1 inhibitor, we set out to identify a highly potent and selective PARP1 inhibitor and trapper with CNS profile. In our next generation PARP1 inhibitor, we sought to retain the profile of AZD5305 and lower the efflux for CNS penetration. Despite the challenge of narrow SAR, we successfully used the structure- and property-based design approach to identify a brain penetrant PARP1 inhibitor and PARP1-DNA trapper. We used multiple medicinal chemistry maneuvers such as masking the hydrogen bond donors and core modifications to lower the efflux in order to achieve brain penetration. Further optimization of the nicotinamide mimetic core for potency and metabolic stability led us to the discovery of AZD9574.AZD9574 shows improved selectivity for PARP1 over PARP2 vs AZD5305 and retains its excellent selectivity over other PARP family members. It has low efflux in Caco2, MDCK-MDR1, and MDCK-MDR1-BCRP permeability assays and it also showed CNS penetration in rat and cynomolgus monkey. AZD9574 has excellent secondary pharmacology and acceptable physicochemical properties and good PK in preclinical species.In vitro, AZD9574 selectively inhibits the growth of BRCAm cell lines. Importantly, AZD9574 showed efficacy in an intracranial BRCA1m MDA-MB-436 xenograft model at doses of 3, 10 and 30 mg/kg QD, significantly extending the survival of tumor-bearing mice compared to vehicle control arm.In summary, AZD9574 is a next generation selective PARP1 inhibitor and trapper with CNS penetration. This profile makes it an ideal candidate for treating CNS malignancies or brain metastases that have a dependence on PARP inhibition either as single agent or in combination with other therapies.

Citation Format: Avipsa Ghosh, Sudhir M. Hande, Amber Balazs, Derek Barratt, Sabina Cosulich, Barry Davies, Sébastien Degorce, Kevin Embrey, Sonja Gill, Anders Gunnarsson, Giuditta Illuzzi, Peter Johnström, Jordan Lane, Carrie Larner, Rachel Lawrence, Elisabetta Leo, Andrew Madin, Elizabeth Martin, Lisa McWilliams, Lenka O’Connor, Mark O’Connor, Jonathan Orme, Fiona Pachl, Martin Packer, Andy Pike, Philip Rawlins, Marianne Schimpl, Magnus Schou, Anna Staniszewska, Wenzhan Yang, James Yates, Andrew Zhang, XiaoLa Zheng, Stephen Fawell, Petra Hamerlik, Jeffrey Johannes. Structure-based and property-based drug design of AZD9574, a CNS penetrant PARP1 selective inhibitor and trapper [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 6302.

Abstract 5076: Evaluation of the CNS penetration of a next generation PARP inhibitor, AZD9574, in cynomolgus monkey using positron emission tomography

The current clinically approved PARP inhibitors have limited subtype selectivity and are to some degree restricted in their ability to penetrate the central nervous system (CNS) due to efflux transporters, potentially limiting their efficacy in treating metastatic disease or primary tumors in the brain. The current study evaluated the potential of AZD9574, a next generation, PARP1 selective inhibitor/trapper, to penetrate the CNS in cynomolgus monkey, and its occupancy of the PARP1 enzyme, using positron emission tomography (PET). In vitro bidirectional efflux assay data suggested AZD9574 showed minimal substrate potential compared to the clinically approved PARP inhibitors. This was reflected in an increased ratio of unbound brain to unbound plasma concentration (Kpuu) in the rat of ~0.31. Therefore AZD9574 was taken forward into cynomolgus monkey PET studies. Firstly, the Kpuu was determined following dosing of [11C]AZD9574, co-administered with unlabeled drug to minimize the impact of specific binding. The high specific signal observed lead to the development of [11C]AZ3391, a PARP1 selective, CNS penetrant PET tracer, which was subsequently used to directly assess the PARP1 target engagement of AZD9574 in the brain. AZD9574 was found to show a Kpuu in cynomolgus monkeys of 0.79, close to unity with unbound plasma concentrations suggesting minimal CNS restriction. Furthermore, an i.v. infusion dose response study with AZD9574, conducted to examine its ability to block target occupancy by the PET tracer [11C]AZ3391, demonstrated a reduction in [11C]AZ3391 accumulation in whole brain. The resulting calculated occupancy of AZD9574 ranged from 17% for the lowest dose (0.003 mg/kg) to 95% for the highest dose tested (0.05 mg/kg). Comparable reduction in occupancy was seen for peripheral tissue, such as bone marrow, supporting the conclusion that AZD9574 shows minimal CNS restriction. These data show that AZD9574 is the first PARP inhibitor to reach the clinic which combines PARP1 selectivity, trapping and high CNS penetration in a single molecule and supports its development as a potential therapy for the treatment of metastatic disease and primary brain tumors.

Citation Format: Andy Pike, Amber Balazs, Zsolt Cselényi, Sébastien L. Degorce, Avipsa Ghosh, Sudhir M. Hande, Jeffrey Johannes, Peter Johnström, Martin J. Packer, Magnus Schou, XiaoLan Zheng. Evaluation of the CNS penetration of a next generation PARP inhibitor, AZD9574, in cynomolgus monkey using positron emission tomography [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 5076.

Discovery of 5-{4-[(7-Ethyl-6-oxo-5,6-dihydro-1,5-naphthyridin-3-yl)methyl]piperazin-1-yl}-N-methylpyridine-2-carboxamide (AZD5305): A PARP1-DNA Trapper with High Selectivity for PARP1 over PARP2 and Other PARPs

Poly-ADP-ribose-polymerase (PARP) inhibitors have achieved regulatory approval in oncology for homologous recombination repair deficient tumors including BRCA mutation. However, some have failed in combination with first-line chemotherapies, usually due to overlapping hematological toxicities. Currently approved PARP inhibitors lack selectivity for PARP1 over PARP2 and some other 16 PARP family members, and we hypothesized that this could contribute to toxicity. Recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for driving efficacy in a BRCA mutant background. Herein, we describe the structure- and property-based design of 25 (AZD5305), a potent and selective PARP1 inhibitor and PARP1-DNA trapper with excellent in vivo efficacy in a BRCA mutant HBCx-17 PDX model. Compound 25 is highly selective for PARP1 over other PARP family members, with good secondary pharmacology and physicochemical properties and excellent pharmacokinetics in preclinical species, with reduced effects on human bone marrow progenitor cells in vitro.

α-Heteroarylation of Thioethers via Photoredox and Weak Brønsted Base Catalysis

We report the C-H activation of thioethers to α-thio alkyl radicals and their addition to N-methoxyheteroarenium salts for the redox-neutral synthesis of α-heteroaromatic thioethers. Studies are consistent with a two-step activation mechanism, where oxidation of thioethers to sulfide radical cations by a photoredox catalyst is followed by α-C-H deprotonation by a weak Brønsted base catalyst to afford α-thio alkyl radicals. Further, N-methoxyheteroarenium salts play additional roles as a source of methoxyl radical that contributes to α-thio alkyl radical generation and a sacrificial oxidant that regenerates the photoredox catalytic cycle.

Palladium-catalyzed intramolecular carboborylation of 1,3-diene and synthesis of ABCD ring of communesins

A palladium-catalyzed intramolecular carboborylation of 1,3-diene has been developed for the synthesis of iminoindolines with a quaternary carbon centre. This method was applied to a substrate bearing several functional groups to afford a complex iminoindoline, which was subsequently converted into an ABCD ring model compound of communesins via an intramolecular Friedel-Crafts-type reaction.

Estimation of phytochemical content and antioxidant activity of some selected traditional Indian medicinal plants

The powder samples and methanol extract of 11 medicinal plants were subjected to analysis of proximate composition and measurement of antioxidant activity. Different parameters studied include phenolic contents, moisture, ash, crude fiber, fats and waxes. The assays employed were ferric reducing antioxidant power, trolox equivalent antioxidant capacity and scavenging effect on the 1,1-diphenyl-2-picrylhydrazyl free radical. Results obtained indicate that the antioxidant potential varied significantly from plant to plant. The total phenolic contents were determined spectrophotometrically using Folin-Ciocalteu reagent. Significant correlation is observed between ferric reducing antioxidant power and phenolic contents (R(2) = 0.96). These findings show that the polyphenolic constituents in the extracts are responsible for free radical scavenging capacity.