PLK4 is a cell cycle-regulated kinase important for the biogenesis of centrioles and is known to be synthetically lethal with TRIM37 gene amplification. Previous attempts to inhibit PLK4 have been hampered by selectivity or ADME liabilities. The known inhibitor Centrinone B, while potent and selective, is metabolically unstable and lacks oral bioavailability. Assisted by structure-based drug design (SBDD), dramatic improvements in potency, selectivity and ADME properties were made to this structure, resulting in the identification of RP-1664, a potent inhibitor of PLK4 with an excellent pharmacokinetic profile in preclinical species. Kinome profiling demonstrated exquisite selectivity over related kinases, including AURKA/B and PLK1. RP-1664 disrupts centriole biogenesis in cancer cells, modulates pharmacodynamic readouts of PLK4 activity in xenograft tumor tissues, and is efficacious in multiple TRIM37-amplified xenograft models. This first-in-class clinical candidate is currently being evaluated in Phase 1 clinical trials (NCT06232408) for treatment of advanced solid tumors.

ATR is a key kinase in the DNA-damage response (DDR) that is synthetic lethal with several other DDR proteins, making it an attractive target for the treatment of genetically selected solid tumors. Herein we describe the discovery of a novel ATR inhibitor guided by a pharmacophore model to position a key hydrogen bond. Optimization was driven by potency and selectivity over the related kinase mTOR, resulting in the identification of camonsertib (RP-3500) with high potency and excellent ADME properties. Preclinical evaluation focused on the impact of camonsertib on myelosuppression, and an exploration of intermittent dosing schedules to allow recovery of the erythroid compartment and mitigate anemia. Camonsertib is currently undergoing clinical evaluation both as a single agent and in combination with talazoparib, olaparib, niraparib, lunresertib, or gemcitabine (NCT04497116, NCT04972110, NCT04855656). A preliminary recommended phase 2 dose for monotherapy was identified as 160 mg QD given 3 days/week.

A novel HIV protease inhibitor was designed using a morpholine core as the aspartate binding group. Analysis of the crystal structure of the initial lead bound to HIV protease enabled optimization of enzyme potency and antiviral activity. This afforded a series of potent orally bioavailable inhibitors of which MK-8718 was identified as a compound with a favorable overall profile.

Lipids are used as cellular building blocks and condensed energy stores and also act as signaling molecules. The glycerolipid/ fatty acid cycle, encompassing lipolysis and lipogenesis, generates many lipid signals. Reliable procedures are not available for measuring activities of several lipolytic enzymes for the purposes of drug screening, and this resulted in questionable selectivity of various known lipase inhibitors. We now describe simple assays for lipolytic enzymes, including adipose triglyceride lipase (ATGL), hormone sensitive lipase (HSL), sn-1-diacylglycerol lipase (DAGL), monoacylglycerol lipase, α/β-hydrolase domain 6, and carboxylesterase 1 (CES1) using recombinant human and mouse enzymes either in cell extracts or using purified enzymes. We observed that many of the reported inhibitors lack specificity. Thus, Cay10499 (HSL inhibitor) and RHC20867 (DAGL inhibitor) also inhibit other lipases. Marked differences in the inhibitor sensitivities of human ATGL and HSL compared with the corresponding mouse enzymes was noticed. Thus, ATGListatin inhibited mouse ATGL but not human ATGL, and the HSL inhibitors WWL11 and Compound 13f were effective against mouse enzyme but much less potent against human enzyme. Many of these lipase inhibitors also inhibited human CES1. Results describe reliable assays for measuring lipase activities that are amenable for drug screening and also caution about the specificity of the many earlier described lipase inhibitors.

A weak antagonist of the pyrimidinergic receptor P2Y14 containing a dihydropyridopyrimidine core was identified through high-throughput screening. Subsequent optimization led to potent, non-UTP competitive antagonists and represent the first reported non-nucleotide antagonists of this receptor. Compound 18q was identified as a 10nM P2Y14 antagonist with good oral bioavailability and provided sufficient exposure in mice to be used as a tool for future in vivo studies.

Optimization of a lead thiazole amide MF-152 led to the identification of potent bicyclic heteroaryl SCD1 inhibitors with good mouse pharmacokinetic profiles. In a view to target the liver for efficacy and to avoid SCD1 inhibition in the skin and eyes where adverse effects were previously observed in rodents, representative systemically-distributed SCD1 inhibitors were converted into liver-targeting SCD1 inhibitors.

Elevated stearoyl-CoA desaturase (SCD) activity has been linked to a number of metabolic disorders including obesity and type II diabetes. Compound 3j, a potent SCD inhibitor (human HepG2 IC(50)=1nM) was identified from the optimization of a lead thiazole compound MF-152 with over 100-fold improvement in potency. In a 4-week chronic oral dosing at 0.2mg/kg, 3j gave a robust 24% prevention of body weight gain in mice fed on a high fat diet accompanied with an improved metabolic profile on insulin and glucose levels.

Potent and orally bioavailable SCD inhibitors built on an azetidinyl pyridazine scaffold were identified. In a one-month gDIO mouse model of obesity, we demonstrated that there was no therapeutic index even at low doses; efficacy in preventing weight gain tracked closely with skin and eye adverse events. This was attributed to the local SCD inhibition in these tissues as a consequence of the broad tissue distribution observed in mice for this class of compounds. The search for new structural scaffolds which may display a different tissue distribution was initiated. In preparation for an HTS campaign, a radiolabeled azetidinyl pyridazine displaying low non-specific binding in the scintillation proximity assay was prepared.

Amino ketone warheads were explored as alternatives to the nitrile group of a potent and selective cathepsin K inhibitor. The resulting compounds were potent and selective inhibitors of cathepsin K and these nitrile replacements had a significant effect on metabolism and pharmacokinetics.

Herein, we report on the identification of nonbasic, potent, and highly selective, nitrile-containing cathepsin K (Cat K) inhibitors that are built on our previously identified cyclohexanecarboxamide core structure. Subsequent to our initial investigations, we have found that incorporation of five-membered heterocycles as P2-P3 linkers allowed for the introduction of a methyl sulfone P3-substitutent that was not tolerated in inhibitors containing a six-membered aromatic P2-P3 linker. The combination of a five-membered N-methylpyrazole linker and a methyl sulfone in P3 yielded subnanomolar Cat K inhibitors that were minimally shifted (<10-fold) in our functional bone resorption assay. Issues that arose because of metabolic demethylation of the N-methylpyrazole were addressed through introduction of a 2,2,2-trifluoroethyl substituent. This culminated in the identification of 31 (MK-1256), a potent (Cat K IC 50 = 0.62 nM) and selective (>1100-fold selectivity vs Cat B, L, S, C, H, Z, and V, 110-fold vs Cat F) inhibitor of cathepsin K that is efficacious in a monkey model of osteoporosis.

Further SAR study around the central 1,2-disubstituted phenyl of the previously disclosed Cat K inhibitor (-)-1 has demonstrated that the solvent exposed P2-P3 linker can be replaced by various 5- or 6-membered heteroaromatic rings. While some potency loss was observed in the 6-membered heteroaromatic series (IC(50)=1 nM for pyridine-linked 4 vs 0.5 nM for phenyl-linked (+/-)-1), several inhibitors showed a significantly decreased shift in the bone resorption functional assay (10-fold for pyridine 4 vs 53-fold for (-)-1). Though this shift was not reduced in the 5-membered heteroaromatic series, potency against Cat K was significantly improved for thiazole 9 (IC(50)=0.2 nM) as was the pharmacokinetic profile of N-methyl pyrazole 10 over our lead compound (-)-1.

Nitrile-based inhibitors of cathepsin K have been known for some time and mechanism-of-action studies have demonstrated that cysteinyl proteases interact with nitriles in a reversible fashion. Three main classes of nitrile-containing inhibitors have been published in the cathepsin K field: (i) cyanamides, (ii) aromatic nitriles, and (iii) aminoacetonitriles. A computational approach was used to calculate the theoretical reactivities of diverse nitriles and this was found to correlate with their extent of reactivity with free cysteine. Moreover, there is a tentative link between high reactivity with cysteine and the potential to lead to irreversible covalent binding to proteins.