Discovery of TNG908: A Selective, Brain Penetrant, MTA-Cooperative PRMT5 Inhibitor That Is Synthetically Lethal with MTAP-Deleted Cancers

It has been shown that PRMT5 inhibition by small molecules can selectively kill cancer cells with homozygous deletion of the MTAP gene if the inhibitors can leverage the consequence of MTAP deletion, namely, accumulation of the MTAP substrate MTA. Herein, we describe the discovery of TNG908, a potent inhibitor that binds the PRMT5·MTA complex, leading to 15-fold-selective killing of MTAP-deleted (MTAP-null) cells compared to MTAPintact (MTAP WT) cells. TNG908 shows selective antitumor activity when dosed orally in mouse xenograft models, and its physicochemical properties are amenable for crossing the blood-brain barrier (BBB), supporting clinical study for the treatment of both CNS and non-CNS tumors with MTAP loss.

Abstract P214: MTAPnull-selective PRMT5 inhibitors drive regressions in MTAP-deleted xenograft models across histologies

PRMT5 is a type II arginine methyltransferase that regulates essential cellular functions via symmetric dimethylation of target proteins involved in spliceosome regulation, cell cycle progression, apoptosis, the DNA-damage response, and other functions. PRMT5 dependence in cells with MTAP deletions is a strong and prevalent synthetic lethal interaction. Due to their mechanisms of action, existing clinical PRMT5 inhibitors do not recapitulate the selectivity for MTAPnull cells demonstrated by genetic perturbation. Given that MTAP deletion occurs in approximately 10-15% of all human cancer[i],[ii],[iii], a molecule that selectively kills MTAPnull cancer cells provides an important opportunity to deliver a targeted treatment to a significant patient population. We have discovered small molecules that exhibit MTA-cooperative PRMT5 binding and selectively kill MTAPnull cancer cells. Striking MTAP-dependent viability effects are demonstrated in MTAP-isogenic cell lines representing multiple lineages, and in a multi-lineage cell line panel comprised of 200 cancer cell lines. Furthermore, oral administration of an MTAPnull-selective PRMT5 inhibitor demonstrates dose-dependent antitumor activity and strong regressions across multiple histologies in both cancer cell line and patient-derived xenografts. These data suggest the therapeutic potential of MTAPnull-selective PRMT5 inhibitors in MTAP-deleted cancers. [i] Cerami et al., 2012 [ii] Gao et al., 2013 [iii] Lee et al., 2014

Citation Format: Kimberly J. Briggs, Kevin M. Cottrell, Matthew R. Tonini, Erik Wilker, Lina Gu, Charles B. Davis, Doug Whittington, Deepali Gotur, Haris Jahic, Matthew J. Goldstein, Alan Huang, John P. Maxwell. MTAPnull-selective PRMT5 inhibitors drive regressions in MTAP-deleted xenograft models across histologies [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 P214.

Abstract P146: Loss of HS2ST1 cooperates with MAPK inhibition to impair growth of mesenchymal KRAS mutant NSCLC

Activating mutations in the KRAS oncogene occur in approximately 30% of non-small cell lung cancers (NSCLC). Hence, multiple therapeutic strategies have been explored to block RAS including inhibition of downstream effector molecules in the MAPK pathway and direct pharmacological inhibition of the KRAS G12C mutant protein. However, inhibition of the RAS-RAF-MEK-ERK cascade with MEK inhibitor monotherapy has been insufficient to induce robust clinical responses. To identify novel drug targets that are synthetic lethal with MEK inhibition, CRISPR screens were conducted in multiple KRAS mutant NSCLC cell lines with or without trametinib treatment. Consistent with previous reports, several known MAPK-pathway genes, including KRAS, MEK, ERK, and FGFR1, were identified as top sensitizers validating our functional genomics approach. Interestingly, several novel targets were ranked among these top hits, including several members of the heparan sulfate biosynthesis pathway, such as the heparan sulfate 2-O-sulfotransferase (HS2ST1). In cells, HS2ST1 is responsible for transferring a sulfate from PAPS (3-phosphoadenosine-5’-phosphosulfate) to the 2-O position of a growing heparan sulfate chain. These chains partner with receptor tyrosine kinases at the cell surface to facilitate their interactions with growth factors. In this case, the interaction of FGF2 and FGFR1 has been shown to require HS2ST1-mediated 2-O sulfation, making HS2ST1 a novel druggable target in a well-validated FGFR-MAPK adaptive signaling axis. Here, we report that HS2ST1 is required for the feedback activation of the MAPK pathway that occurs downstream and in response to MEK or KRAS G12C inhibition via genetic validations studies. Knockout of HS2ST1 results in reduced feedback activation via FGFR1 and reduced MAPK pathway signaling. This reduced signaling leads to a reduction in cell growth in the presence of a MEK inhibitor, such as trametinib or selumetinib, or a KRAS G12C inhibitor like sotorasib. Our screen results reiterate the findings of others which indicate that effective MAPK suppression is key to inhibiting KRAS-mutant NSCLC cell growth. We find that HS2ST1 blockade would aid in maintaining the suppression of MAPK pathway signaling in KRAS-mutant NSCLC, leading to reduced cell viability and growth suppression. While others have described pairing receptor tyrosine kinase inhibitors with MAPK pathway inhibitors, this would be a novel approach to reducing upstream MAPK pathway feedback that may lead to reduced toxicity in patients.

Citation Format: Leanne G. Ahronian, Silvia Fenoglio, Nikitha Das, Daniel Aird, David Guerin, Douglas Whittington, Haris Jahic, Erin Brophy, Patrick McCarren, Brian McMillan, James Tepper, Michaela Mentzer, Fang Li, Hongxiang Zhang, Xuewen Pan, John Maxwell, Jannik Andersen, Alan Huang, Robert Tjin Tham Sjin. Loss of HS2ST1 cooperates with MAPK inhibition to impair growth of mesenchymal KRAS mutant NSCLC [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 P146.

Kinetics of avibactam inhibition against Class A, C, and D β-lactamases

Avibactam is a non-β-lactam β-lactamase inhibitor with a spectrum of activity that includes β-lactamase enzymes of classes A, C, and selected D examples. In this work acylation and deacylation rates were measured against the clinically important enzymes CTX-M-15, KPC-2, Enterobacter cloacae AmpC, Pseudomonas aeruginosa AmpC, OXA-10, and OXA-48. The efficiency of acylation (k2/Ki) varied across the enzyme spectrum, from 1.1 × 10(1) m(-1)s(-1) for OXA-10 to 1.0 × 10(5) for CTX-M-15. Inhibition of OXA-10 was shown to follow the covalent reversible mechanism, and the acylated OXA-10 displayed the longest residence time for deacylation, with a half-life of greater than 5 days. Across multiple enzymes, acyl enzyme stability was assessed by mass spectrometry. These inhibited enzyme forms were stable to rearrangement or hydrolysis, with the exception of KPC-2. KPC-2 displayed a slow hydrolytic route that involved fragmentation of the acyl-avibactam complex. The identity of released degradation products was investigated, and a possible mechanism for the slow deacylation from KPC-2 is proposed.

A homogeneous, high-throughput fluorescence anisotropy-based DNA supercoiling assay

The degree of supercoiling of DNA is vital for cellular processes, such as replication and transcription. DNA topology is controlled by the action of DNA topoisomerase enzymes. Topoisomerases, because of their importance in cellular replication, are the targets of several anticancer and antibacterial drugs. In the search for new drugs targeting topoisomerases, a biochemical assay compatible with automated high-throughput screening (HTS) would be valuable. Gel electrophoresis is the standard method for measuring changes in the extent of supercoiling of plasmid DNA when acted upon by topoisomerases, but this is a low-throughput and laborious method. A medium-throughput method was described previously that quantitatively distinguishes relaxed and supercoiled plasmids by the difference in their abilities to form triplex structures with an immobilized oligonucleotide. In this article, the authors describe a homogeneous supercoiling assay based on triplex formation in which the oligonucleotide strand is labeled with a fluorescent dye and the readout is fluorescence anisotropy. The new assay requires no immobilization, filtration, or plate washing steps and is therefore well suited to HTS for inhibitors of topoisomerases. The utility of this assay is demonstrated with relaxation of supercoiled plasmid by Escherichia coli topoisomerase I, supercoiling of relaxed plasmid by E. coli DNA gyrase, and inhibition of gyrase by fluoroquinolones and nalidixic acid.

Development of an LC–MS based enzyme activity assay for MurC: application to evaluation of inhibitors and kinetic analysis

An enzyme activity assay, based on mass spectrometric (MS) detection of specific reaction product following HPLC separation, has been developed to evaluate pharmaceutical hits identified from primary high throughput screening (HTS) against target enzyme Escherichia coli UDP-N-acetyl-muramyl-L-alanine ligase (MurC), an essential enzyme in the bacterial peptidoglycan biosynthetic pathway, and to study the kinetics of the enzyme. A comparative analysis of this new liquid chromatographic-MS (LC-MS) based assay with a conventional spectrophotometric Malachite Green (MG) assay, which detects phosphate produced in the reaction, was performed. The results demonstrated that the LC-MS assay, which determines specific ligase activity of MurC, offers several advantages including a lower background (0.2% versus 26%), higher sensitivity (> or = 10 fold), lower limit of quantitation (LOQ) (0.02 microM versus 1 microM) and wider linear dynamic range (> or = 4 fold) than the MG assay. Good precision for the LC-MS assay was demonstrated by the low intraday and interday coefficient of variation (CV) values (3 and 6%, respectively). The LC-MS assay, free of the artifacts often seen in the Malachite Green assay, offers a valuable secondary assay for hit evaluation in which the false positives from the primary high throughput screening can be eliminated. In addition, the applicability of this assay to the study of enzyme kinetics has also been demonstrated.