Altering metabolic profiles of drugs by precision deuteration: reducing mechanism-based inhibition of CYP2D6 by paroxetine.

Selective deuterium substitution as a means of ameliorating clinically relevant pharmacokinetic drug interactions is demonstrated in this study. Carbon-deuterium bonds are more stable than corresponding carbon-hydrogen bonds. Using a precision deuteration platform, the two hydrogen atoms at the methylenedioxy carbon of paroxetine were substituted with deuterium. The new chemical entity, CTP-347 [(3S,4R)-3-((2,2-dideuterobenzo[d][1,3]dioxol-5-yloxy)methyl)-4-(4-fluorophenyl)piperidine], demonstrated similar selectivity for the serotonin receptor, as well as similar neurotransmitter uptake inhibition in an in vitro rat synaptosome model, as unmodified paroxetine. However, human liver microsomes cleared CTP-347 faster than paroxetine as a result of decreased inactivation of CYP2D6. In phase 1 studies, CTP-347 was metabolized more rapidly in humans and exhibited a lower pharmacokinetic accumulation index than paroxetine. These alterations in the metabolism profile resulted in significantly reduced drug-drug interactions between CTP-347 and two other CYP2D6-metabolized drugs: tamoxifen (in vitro) and dextromethorphan (in humans). Our results show that precision deuteration can improve the metabolism profiles of existing pharmacotherapies without affecting their intrinsic pharmacologies.

Ryanodine receptor (RYR) mutational status correlates with tumor mutational burden, age and smoking status and stratifies non-small cell lung cancer patient prognosis.

Background: The ryanodine receptors (RYRs) have been implicated in many muscular, cardiac and neurological diseases. However, there are almost no studies so far focusing on RYR genetic alterations and its roles in cancer, especially in non-small cell lung cancer (NSCLC). Methods: The whole-exome sequencing (WES) data, demographic and clinical data of 1,052 NSCLC patients was downloaded from The Cancer Genome Atlas (TCGA) database and analyzed using the corresponding packages of the R software. Mutational profile was established and its correlation with tumor mutational burden (TMB), prognosis, age and smoking status was analyzed and compared. Results: RYR mutations were found in 502 NSCLC patients, in which mutations of RYR1, RYR2 and RYR3 were found in 17.3% (182/1,052), 40.0% (421/1,052) and 21.3% (224/1,052) of patients, respectively. Random distribution of mutations without hotspot mutations were observed with all three RYR isoforms. Significant co-mutations were found between RYR1 and RYR3, while mutual exclusive mutations were found between RYR1 and RYR2, and between RYR2 and RYR3. Significant correlation was found between cumulative number of mutations and cumulative TMB for all three RYR isoforms, and patients with RYR mutations exhibited significantly higher TMB than those without RYR mutations. Significant correlation was also found between mutational status and age in RYR2 and RYR3, and between mutational status and smoking history grading in all three isoforms, and between mutational status and number of pack years in RYR3. More interestingly, significant stratification of patient survival was revealed by RYR2 mutational status, which was found to be one of the independent risk factors for patient prognosis in multivariate Cox analysis. Conclusions: The mutational profile of RYR in NSCLC has been characterized for the first time. Strong correlation was found between RYR mutational status and TMB, age and smoking status. RYR2 mutational status was an independent risk factor for NSCLC patient prognosis.

A First-in-Patient, Multicenter, Double-Blind, 2-Arm, Placebo-Controlled, Randomized Safety and Tolerability Study of a Novel Oral Drug Candidate, CTP-499, in Chronic Kidney Disease.

The prevalence of chronic kidney disease (CKD) related to type 2 diabetes is increasing worldwide. In addition to standard of care, treatment with anti-inflammatory and antifibrotic agents such as CTP-499, a novel oral, multisubtype selective inhibitor of phosphodiesterases, may be important in CKD treatment. A phase 1b randomized, double-blind, placebo-controlled clinical trial of CTP-499 in CKD patients (25 active, 8 placebo) with an estimated glomerular filtration rate of 30-59 mL/min/1.73 m(2) was conducted to assess safety and tolerability. Secondary outcomes included pharmacokinetics and exploratory effects on inflammatory and hematology markers. Patients received 600 mg CTP-499 or matching placebo tablets orally once daily for 2 weeks, then twice daily for 2 additional weeks. CTP-499 was well tolerated with no serious or severe adverse events, or adverse events leading to discontinuation. CTP-499 was rapidly absorbed and produced acceptable interpatient variability. Of the 5 metabolites (M1-M5), M5 was the most abundant in plasma and urine. Exposure to CTP-499 and metabolites was higher in CKD patients than previously reported in healthy volunteers. No statistically significant differences were detected between the CTP-499- and placebo-treated groups for any of the biomarkers tested. This study provides data supporting further evaluation of CTP-499 in CKD patients.

Quantitative analyses of CTP-499 and five major metabolites by core-structure analysis.

CTP-499 is a novel oral multi-subtype selective inhibitor of PDEs that is currently in clinical testing, in combination with angiotensin modulators, as a potentially first-in-class treatment for diabetic kidney disease. The compound was discovered and developed by using Concert's proprietary DCE Platform(®) in which deuterium was incorporated at select positions of 1-((S)-5-hydroxyhexyl)-3,7-dimethylxanthine (HDX). CTP-499 metabolizes to five major metabolites: C-21256, D-M2, D-M3, D-M4 and M5, of which all contains deuterium except M5. During in vivo metabolism, however, H/D exchange takes place. As a result, each analyte, except M5, has multiple molecular masses. To accurately quantify the analytes, we developed an LC-MS/MS method focusing on the core structures of the molecules, termed "core-structure analyses". The core-structure analyses method was then validated under GLP guidance in dog, rat and rabbit plasma, with a sample volume of 50 µL. Results demonstrated that this approach accurately quantifies each of the six analytes despite partial exchange of deuterium with hydrogen atoms in the in vivo samples. The validation parameters included accuracy, precision, sensitivity, stability, dilution integrity, hemolysis, matrix effect, selectivity, and recovery. Acceptable intra-run and inter-run assay precision (%CV ≤ 5.5%) and accuracy (90.1-106.7%) were achieved over a linear range of 10-5,000 ng/mL of each analyte. Various stability tests, including bench-top, freeze/thaw, stock solution, and long-term storage, were also performed. All stability results met acceptance criteria. The robustness of the methods was demonstrated by the incurred sample reproducibility (ISR) tests. After validation, the method was successfully used in support of multiple toxicological studies of CTP-499.

Revealing the metabolic sites of atazanavir in human by parallel administrations of D-atazanavir analogs.

Atazanavir (Reyataz(®)) is an important member of the HIV protease inhibitor class. Because of the complexity of its chemical structure, metabolite identification and structural elucidation face serious challenges. So far, only seven non-conjugated metabolites in human plasma have been reported, and their structural elucidation is not complete, especially for the major metabolites produced by oxidations. To probe the exact sites of metabolism and to elucidate the relationship among in vivo metabolites of atazanavir, we designed and performed two sets of experiments. The first set of experiments was to determine atazanavir metabolites in human plasma by LC-MS, from which more than a dozen metabolites were discovered, including seven new ones that have not been reported. The second set involved deuterium labeling on potential metabolic sites to generate D-atazanavir analogs. D-atazanavir analogs were dosed to human in parallel with atazanavir. Metabolites of D-atazanavir were identified by the same LC-MS method, and the results were compared with those of atazanavir. A metabolite structure can be readily elucidated by comparing the results of the analogs and the pathway by which the metabolite is formed can be proposed with confidence. Experimental results demonstrated that oxidation is the most common metabolic pathway of atazanavir, resulting in the formation of six metabolites of monooxidation (M1, M2, M7, M8, M13, and M14) and four of dioxidation (M15, M16, M17, and M18). The second metabolic pathway is hydrolysis, and the third is N-dealkylation. Metabolites produced by hydrolysis include M3, M4, and M19. Metabolites formed by N-dealkylation are M5, M6a, and M6b.

A Randomized Phase I Evaluation of CTP-499, a Novel Deuterium-Containing Drug Candidate for Diabetic Nephropathy.

To determine maximum tolerated dose and food effect for CTP-499, a novel agent being studied for the treatment of diabetic kidney disease. CTP-499 has demonstrated anti-inflammatory, anti-fibrotic and anti-oxidative activities in vitro as well as anti-inflammatory and renoprotective effects in a diabetic nephropathy (DN) model. Two studies were performed. Study 1 was a single-dose escalation study with 600, 1200, 1800, and 2400 mg doses of controlled-release (CR) CTP-499 and a 400 mg immediate release dose to aid in the development of prototype formulations of CTP-499. Study 2 was a food-effect study. Plasma concentrations of CTP-499 and its metabolites were measured to determine pharmacokinetic parameters in each study. Safety was assessed to determine tolerability. Doses up to and including 1800 mg were well tolerated. Cmax was either equivalent (CTP-499) or slightly lower (metabolites) for the fed condition, while overall exposure was equivalent (CTP-499) or slightly higher (metabolites) for the fed condition. The range of tolerated doses of CTP-499 and the effects of food on exposure were identified, contributing to selection of the dose for Phase II development.

Identification and structural elucidation of in vitro metabolites of atazanavir by HPLC and tandem mass spectrometry.

Atazanavir (marketed as Reyataz®) is an important member of the human immunodeficiency virus protease inhibitor class. LC-UV-MS(n) experiments were designed to identify metabolites of atazanavir after incubations in human hepatocytes. Five major (M1-M5) and seven minor (M7-M12) metabolites were identified. The most abundant metabolite, M1, was formed by a mono-oxidation on the t-butyl group at the non-prime side. The second most abundant metabolite, M2, was also a mono-oxidation product, which has not yet been definitively identified. Metabolites, M3 and M4, were structural isomers, which were apparently formed by oxidative carbamate hydrolysis. The structure of M5 comprises the non-prime side of atazanavir which contains a pyridinyl-benzyl group. Metabolite M6a was formed by the cleavage of the pyridinyl-benzyl side chain, as evidenced by the formation of the corresponding metabolic product, the pyridinyl-benzoic acid (M6b). Mono-oxidation also occurred on the pyridinyl-benzyl group to produce the low abundance metabolite M8. Oxidation of the terminal methyl groups produced M9 and M10, respectively, which have low chemical stability. Trace-level metabolites of di-oxidations, M11 and M12, were also detected, but the complexity of the molecule precluded identification of the second oxidation site. To our knowledge, metabolites M6b and M8 have not been reported.