UC-84

The carboxanilides are nonnucleoside inhibitors (NNIs) of HIV-1 reverse transcriptase (RT), of potential clinical importance. The compounds differ in potency and in their retention of potency in the face of drug resistance mutations. Whereas UC-84, the prototype compound, only weakly inhibits many RTs bearing single point resistance mutations, inhibition by UC-781 is little affected. It has been proposed that UC-38 and UC-781 may form quaternary complexes with RT at a site other than the known binding pocket of other NNIs. X-ray crystal structures of four HIV-1 RT-carboxanilide complexes (UC-10, UC-38, UC-84, and UC-781) reported here reveal that all four inhibitors bind in the usual NNI site, forming binary 1:1 complexes with RT in the absence of substrates with the amide/thioamide bond in cis conformations. For all four complexes the anilide rings of the inhibitors overlap aromatic rings of many other NNIs bound to RT. In contrast, the second rings of UC-10, UC-84, and UC-781 do not bind in equivalent positions to those of other "two-ring" NNIs such as alpha-APA or HEPT derivatives. The binding modes most closely resemble that of the structurally dissimilar NNI, Cl-TIBO, with a common hydrogen bond between each carboxanilide NH- group and the main-chain carbonyl oxygen of Lys101. The binding modes differ slightly between the UC-10/UC-781 and UC-38/UC-84 pairs of compounds, apparently related to the shorter isopropylmethanoyl substituents of the anilide rings of UC-38/UC-84, which draws these rings closer to residues Tyr181 and Tyr188. This in turn explains the differences in the effect of mutated residues on the binding of these compounds.

NSC 615985 (UC 84) has demonstrated anti-HIV activity in the NCI-AIDS antiviral screen and was under consideration as an anti-AIDS drug. The compound was subsequently shown to be a non-nucleoside reverse transcriptase inhibitor (NNRTI). An HPLC method was developed for the analysis of NSC 615985 in mouse, dog and human plasma; and was used to study its stability in plasma and blood as well as its absorption and metabolism in mice. The method involved precipitation of plasma protein with three volumes of methanol followed by HPLC analysis of the supernatant. The HPLC analysis was carried out on a reversed-phase Nova-Pak C18 column with a mobile phase of KH2PO4 (0.01 M; pH 4.8)-acetonitrile (52:48, v/v) at a flow rate of 1 ml min-1 and quantification with a UV detector set at 259 nm. The lower limit of quantitation was 0.05 microgram ml-1 in 1 ml of dog or human plasma or 0.1 microgram ml-1 in 0.5 ml of mouse plasma. NSC 615985 was more stable in dog and human plasma than in mouse plasma, and was less stable in blood than in plasma of the three species investigated. Following bolus intravenous (i.v.) administration at 10 mg kg-1 to male CDF1 mice, NSC 615985 elimination followed biexponential kinetics with half-lives of 1 and 7 min, and was extensively metabolized. NSC 615985 was very poorly absorbed following oral (PO) administration as a suspension in water or in 20% lipid emulsion (Liposyn II). Following bolus subcutaneous (s.c.) administration of [14C]NSC 615985 at 10 mg kg-1, relatively low concentrations of the parent compound were observed in three of 36 mice. One metabolite was tentatively identified in plasma of both the i.v.- and s.c.-treated animals as the sulfoxide of the parent compound. No parent compound was detected in the urine of NSC 615985 dosed mice. At least seven metabolites were present in urine; one metabolite (constituting 8-14% of urinary radioactivity) was tentatively identified as the carboxylic acid resulting from the hydrolysis of the isopropyl group from the parent compound. In summary, NSC 615985 was poorly absorbed following oral administration and extensively metabolized and eliminated following i.v. or s.c. administration. This unfavorable pharmacokinetic profile of NSC 615985 as well as its pattern of activity against NNRTI-resistant strains of HIV-1 precluded its progression to clinical trial; however, other members of the general chemical class are currently being evaluated by the NCI.