Reversible cysteine protease inhibitors show promise for a Chagas disease cure.

The cysteine protease cruzipain is essential for the viability, infectivity, and virulence of Trypanosoma cruzi, the causative agent of Chagas disease. Thus, inhibitors of cruzipain are considered promising anti-T. cruzi chemotherapeutic agents. Reversible cruzipain inhibitors containing a nitrile "warhead" were prepared and demonstrated 50% inhibitory concentrations (IC50s) as potent as 1 nM in baculovirus-generated cruzipain enzyme assays. In epimastigote and intracellular amastigote in vitro assays, the most potent compounds demonstrated antiparasitic behavior in the 5 to 10 µM IC50 range; however, trypomastigote production from the amastigote form was ∼90 to 95% inhibited at 2 µM. Two key compounds, Cz007 and Cz008, with IC50s of 1.1 and 1.8 nM, respectively, against the recombinant enzyme were tested in a murine model of acute T. cruzi infection, with oral dosing in chow for 28 days at doses from 3 to 50 mg/kg of body weight. At 3 mg/kg of Cz007 and 3 mg/kg of Cz008, the blood parasitemia areas under the concentration-time curves were 16% and 25% of the untreated group, respectively. At sacrifice, 24 days after immunosuppression with cyclophosphamide, parasite presence in blood, heart, and esophagus was evaluated. Based on negative quantitative PCR results in all three tissues, cure rates in surviving animals were 90% for Cz007 at 3 mg/kg, 78% for Cz008 at 3 mg/kg, and 71% for benznidazole, the control compound, at 50 mg/kg.

Discovery of potent and liver-targeted stearoyl-CoA desaturase (SCD) inhibitors in a bispyrrolidine series.

Inhibition of stearoyl-CoA desaturase (SCD) activity represents a potential novel mechanism for the treatment of metabolic disorders including obesity and type II diabetes. To circumvent skin and eye adverse events observed in rodents with systemically-distributed SCD inhibitors, our research efforts have been focused on the search for new and structurally diverse liver-targeted SCD inhibitors. This work has led to the discovery of novel, potent and structurally diverse liver-targeted bispyrrolidine SCD inhibitors. These compounds possess suitable cellular activity and pharmacokinetic properties to inhibit liver SCD activity in a mouse pharmacodynamic model.

Nicotinic acids: liver-targeted SCD inhibitors with preclinical anti-diabetic efficacy.

An in vitro screening protocol was used to transform a systemically-distributed SCD inhibitor into a liver-targeted compound. Incorporation of a key nicotinic acid moiety enables molecular recognition by OATP transporters, as demonstrated by uptake studies in transfected cell lines, and likely serves as a critical component of the observed liver-targeted tissue distribution profile. Preclinical anti-diabetic oGTT efficacy is demonstrated with nicotinic acid-based, liver-targeting SCD inhibitor 10, and studies with a close-structural analog devoid of SCD1 activity, suggest this efficacy is a result of on-target activity.

Bicyclic heteroaryl inhibitors of stearoyl-CoA desaturase: from systemic to liver-targeting inhibitors.

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.

High-throughput scintillation proximity assay for stearoyl-CoA desaturase-1.

Stearoyl-CoA desaturase (SCD) catalyzes the synthesis of monounsaturated fatty acids and has been implicated in a number of disease states, including obesity and diabetes. To find small-molecule inhibitor leads, a high-throughput scintillation proximity assay (SPA) was developed using the hydrophobic binding characteristics of a glass microsphere scintillant bead to capture SCD1 from a crude lysate of recombinant SCD1 in Sf9 lysate coupled with the strong binding characteristics of an azetidine compound ([(3)H]AZE). The SPA assay was stable over 24 h and could detect compounds with micromolar to nanomolar potencies. A robust 1536-well high-throughput screening assay was developed with good signal-to-noise ratio (10:1) and excellent Z' factor (0.8). A screening collection of 1.6 million compounds was screened at 11 µM, and approximately 7700 compounds were identified as initial hits, exhibiting at least 35% inhibition of [(3)H]AZE binding. Further screening and confirmation with an SCD enzyme activity assay led to a number of new structural leads for inhibition of the enzyme. The SPA assay complements the enzyme activity assay for SCD1 as a tool for the discovery of novel leads in drug discovery.

Difluoroethylamines as an amide isostere in inhibitors of cathepsin K.

The trifluoroethylamine group found in cathepsin K inhibitors like odanacatib can be replaced by a difluoroethylamine group. This change increased the basicity of the nitrogen which positively impacted the log D. This translated into an improved oral bioavailability in pre-clinical species. Difluoroethylamine compounds exhibit a similar potency against cathepsin K and selectivity profile against other cathepsins when compared to trifluoroethylamine analogs.

Biological activity and preclinical efficacy of azetidinyl pyridazines as potent systemically-distributed stearoyl-CoA desaturase inhibitors.

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.

Identification of potent and reversible cruzipain inhibitors for the treatment of Chagas disease.

Identification of potent and reversible cruzipain inhibitors for the treatment of Chagas disease is described. The identified inhibitors bearing an amino nitrile warhead in P1 exhibit low nanomolar in vitro potency against cruzipain. Further SAR in P2 portion led to the identification of compounds, such as 26, that have a unique selectivity profile against other cysteine proteases and offering new opportunities for safer treatment of Chagas disease.

The discovery of MK-0674, an orally bioavailable cathepsin K inhibitor.

MK-0674 is a potent and selective cathepsin K inhibitor from the same structural class as odanacatib with a comparable inhibitory potency profile against Cat K. It is orally bioavailable and exhibits long half-life in pre-clinical species. In vivo studies using deuterated MK-0674 show stereoselective epimerization of the alcohol stereocenter via an oxidation/reduction cycle. From in vitro incubations, two metabolites could be identified: the hydroxyleucine and the glucuronide conjugate which were confirmed using authentic synthetic standards.

Identification of a nonbasic, nitrile-containing cathepsin K inhibitor (MK-1256) that is efficacious in a monkey model of osteoporosis.

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.

Solid-phase analogue synthesis of caspase-3 inhibitors via palladium-catalyzed amination of 3-bromopyrazinones.

Caspase-3 is a cysteinyl protease that mediates apoptotic cell death. Its inhibition may have an important impact on the treatment of several degenerative diseases. Here we report the synthesis of reversible inhibitors via a solid-support palladium-catalyzed amination of 3-bromopyrazinones and the discovery of a pan-caspase reversible inhibitor.

Lipophilic versus hydrogen-bonding effect in P3 on potency and selectivity of valine aspartyl ketones as caspase 3 inhibitors.

Caspase 3 is a cysteinyl protease that mediates apoptotic cell death. Its inhibition may have an important impact in the treatment of several degenerative diseases. The P1 aspartic acid residue is a required element of recognition for this enzyme that was maintained constant along with the adjacent natural valine as the P2 group. The thiobenzylmethylketone warhead on the aspartate was conveniently handled through solid-phase synthesis allowing modification in the P3 region that eventually led to simpler derivatives with increased potency against caspase 3. The key to such an effect is the introduction of hydroxyl group alpha to the P3 carbonyl.

Nicotinyl aspartyl ketones as inhibitors of caspase-3.

Caspase-3 is a cysteinyl protease that mediates apoptotic cell death. Its inhibition may have an important impact in the treatment of several degenerative diseases. Since P(1) aspartic acid is a required element of recognition for this enzyme, a library of capped aspartyl aldehydes was synthesized using solid-phase chemistry. The 5-bromonicotinamide derivative of the aspartic acid aldehyde was identified to be an inhibitor of caspase-3. Substitution at the 5-position of the pyridine ring and conversion of the aldehyde to ketones led to a series of potent inhibitors of caspase-3.