The Anti-HIV Drug Candidate CMDCK Pre-clinical Pharmacokinetic Study

Anti-HIV drug candidate 3-cyanomethyl-4-methyl-DCK(CMDCK)is a novel non-nucleoside reverse transcriptase inhibitor. It is designed and developed by the scientists in the Institute of Pharmacology and Toxicology. It suppresses the production of double-stranded viral DNA from a single-stranded DNA intermediate, in stark contrast to current HIV-1 RT inhibitors that block the generation of single-stranded DNA from a RNA template. The unique mechanism of action, as well as the relatively higher efficiency and lower toxicity, makes CMDCK a promising pre-clinical drug candidate.In the present study, a simple and sensitive LC-MS/MS method was developed and validated to quantify CMDCK in biological samples. The pharmacokinetic characteristics of CMDCK in experimental animals were investigated, including plasma pharmacokinetics and bioavailability of CMDCK in rat and Beagle dog after single oral or iv dose; tissue distribution of CMDCK in rat and its plasma protine binding; excretion of the parent drug from bile, urine and feces; metabolic stabilities of CMDCK in liver microsomes of different species and preliminary metabolite screening. The effects of ritonavir co-administration on the pharmacokinetics of CMDCK were also evaluated in rat.The single oral pharmacokinetics of CMDCK were studied in rat after a single dose at three dosage levels (8, 24 and 72 mg·kg^-1). The absorption of CMDCK in rat was fairly quick, and the peak plasma concentrations were reached at less of 1h with different dosages. However, the plasma concentration-time curves of high and middle-dosage groups showed double peak and absorption saturation phenomenoa. The mean elimination half life of CMDCK in rat (T_1/2) was ranged from 2.7 to 3.8 h. The oral bioavailabilities were 15.9%, 21.0% and 10.9% for low, medium and high dose groups, respectively. The plasma concentrations and the total exposure (AUC) in female rats were higher than those in male rats (p < 0.05), while the other pharmacokinetics parameters had no significant differences (p > 0.05). The gender difference in rat was mainly observed in the absorption property of CMDCK.The oral pharmacokinetics of CMDCK were also determined in Beagle dog after a single dose at three dosage levels (4, 12 and 36 mg·kg^-1). The peak time (T_max) was in between of 1² h. The double peak phenomenon was observed for all three dose groups. The mean elimination half life (T_1/2) was ranged from 7 to 9 h. The oral bioavailabilities were 20.3%, 7.8% and 3.6% for low, medium and high dose groups, respectively. Absorption saturation was significant for both medium and high dosage groups.The mean T_1/2 of CMDCK in rat after an intravenous dose of 2 mg·kg^-1 was 2.0±1.0h, while the T_1/2 for the intravenous dose at 1mg·kg^-1 in Beagle dog was 7.7±1.1 h. The elimination of the drug candidate was slower in dog than in rat for the intravenous route.CMDCK could distributed to the organs or tissues rapidly after an oral administration at 24 mg·kg^-1. The concentrations in most tissues reached the peak level at 2h post-dose. The highest concentration of CMDCK was found in gastrointestinal tract where the compound was entered first and then absorbed; the next tissues were fat and liver. The results indicated that the absorption of CMDCK in rat was fairly slow. The compound might retain in some tissues because of its liposolubility. CMDCK was highly binded with plasma proteins of human, rats and Beagle dogs. Its protein binding rates in human, dog and rat plasmas were in between of 96.00～99.52%.The excretion of the parent compound in bile, urine and feces was very low. The accumulated excretion rates for bile, urine and feces were 0.0035%, 0.0760% and 6.51%, respectively. The total excretion rate of the unchanged compound in the period of 168 h post-dose was 6.59%. The result indicated that the major excretion form of CMDCK was its metabolites.CMDCK could metabolized rapidly in rat, dog and human liver microsomes.The metabolic stability order from high to low was rat > mouse > dog > human > monkey. The major metabolic pathway of CMDCK in liver microsomes was the oxidation to form mainly mono-oxidated and di-oxidated metabolites, as well as the oxidated and dehydrogenated metabolites. The metabolites formed in human liver microsomes were also observed in the liver microsomal incubates of rat, Beagle and monkey. However, the inter-species differences were detected for formation amounts of the metabolites between the species tested.CMDCK was a CYP3A4 substrate and could be metabolically eliminated rapidly in liver and intestinal microsomes. It was also suffered a significant first-pass effect in intestine and liver of rats after an oral dose. CYP3A4 inhibitor ritonavir could significantly inhibit the hepatic and intestinal metabolism of CMDCK resulting the increased plasma concentration and AUC, when ritonavir was co-administrated orally with CMDCK. Subsequently, the oral bioavailability of the candidate was increased by 1 to 2.7 fold. However, the co-administration of ritonavir would not affect the elimination kinetics of CMDCK.