Unique anti-human immunodeficiency virus activities of the nonnucleoside reverse transcriptase inhibitors calanolide A, costatolide, and dihydrocostatolide.

(+)-Calanolide A (NSC 650886) has previously been reported to be a unique and specific nonnucleoside inhibitor of the reverse transcriptase (RT) of human immunodeficiency virus (HIV) type 1 (HIV-1) (M. J. Currens et al., J. Pharmacol. Exp. Ther., 279:645-651, 1996). Two isomers of calanolide A, (-)-calanolide B (NSC 661122; costatolide) and (-)-dihydrocalanolide B (NSC 661123; dihydrocostatolide), possess antiviral properties similar to those of calanolide A. Each of these three compounds possesses the phenotypic properties ascribed to the pharmacologic class of nonnucleoside RT inhibitors (NNRTIs). The calanolide analogs, however, exhibit 10-fold enhanced antiviral activity against drug-resistant viruses that bear the most prevalent NNRTI resistance that is engendered by amino acid change Y181C in the RT. Further enhancement of activity is observed with RTs that possess the Y181C change together with mutations that yield resistance to AZT. In addition, enzymatic inhibition assays have demonstrated that the compounds inhibit RT through a mechanism that affects both the K(m) for dTTP and the V(max), i.e., mixed-type inhibition. In fresh human cells, costatolide and dihydrocostatolide are highly effective inhibitors of low-passage clinical virus strains, including those representative of the various HIV-1 clade strains, syncytium-inducing and non-syncytium-inducing isolates, and T-tropic and monocyte-tropic isolates. Similar to calanolide A, decreased activities of the two isomers were observed against viruses and RTs with amino acid changes at residues L100, K103, T139, and Y188 in the RT, although costatolide exhibited a smaller loss of activity against many of these NNRTI-resistant isolates. Comparison of cross-resistance data obtained with a panel of NNRTI-resistant virus strains suggests that each of the three stereoisomers may interact differently with the RT, despite their high degree of structural similarity. Selection of viruses resistant to each of the three compounds in a variety of cell lines yielded viruses with T139I, L100I, Y188H, or L187F amino acid changes in the RT. Similarly, a variety of resistant virus strains with different amino acid changes were selected in cell culture when the calanolide analogs were used in combination with other active anti-HIV agents, including nucleoside and nonnucleoside RT and protease inhibitors. In assays with combinations of anti-HIV agents, costatolide exhibited synergy with these anti-HIV agents. The calanolide isomers represent a novel and distinct subgroup of the NNRTI family, and these data suggest that a compound of the calanolide A series, such as costatolide, should be evaluated further for therapeutic use in combination with other anti-HIV agents.

Highly potent oxathiin carboxanilide derivatives with efficacy against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus isolates.

The structure-activity relationships of a series of compounds related to the nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) oxathiin carboxanilide have been described (R. W. Buckheit, Jr., T. L. Kinjerski, V. Fliakas-Boltz, J. D. Russell, T. L. Stup, L. A. Pallansch, W. G. Brouwer, D. C. Dao, W. A. Harrison, R. J. Schultz, J. P. Bader, and S. S. Yang, Antimicrob. Agents Chemother. 39:2718-2727, 1996). From these studies, the furanyl-containing analog UC10 was identified as the most potent inhibitor of human immunodeficiency virus type 1 (HIV-1) replication and a promising candidate for further development. Three new UC analogs (UC040, UC82, and UC781) have been determined to inhibit laboratory-derived and low-passage-number, primary virus isolates at low nanomolar concentrations in both established and fresh human cells. Each of the compounds synergistically interacted with the nucleoside analogs zidovudine, dideoxyinosine, dideoxycytosine, and lamivudine to inhibit HIV-1 replication. As a group, the UC compounds were found to be less active against viruses with the L100I, K103N, and Y181C amino acid changes in the RT and, upon in vitro selection, yielded resistant virus with the Y181C mutation in the RT. The most potent of the three new compounds, UC781, contains a furanyl side chain, similar to UC10, but differs in having an extended ether side chain instead of an oxime chain. The broad therapeutic index of UC781 (>62,000) resulted in effective inhibition of NNRTI-resistant virus isolates at high nanomolar concentrations. Furthermore, UC781 and the NNRTI costatolide were able to synergistically inhibit HIV-1 replication when used in combination, suggesting that UC781 may interact with the RT differently than the other UC analogs. The favorable anti-HIV properties of the UC compounds suggest they should be considered for further clinical development.

The role of genotypic heterogeneity in wild type virus populations on the selection of nonnucleoside reverse transcriptase inhibitor-resistant viruses.

Virus populations were selected in cell culture using two widely used protocols in order to evaluate the role of selection methodology on the genotype and phenotype of nonnucleoside reverse transcriptase inhibitor resistant viruses. Selection was performed by serial passage of virus in the presence of gradually increasing concentrations of antiviral compound or passage in the presence of a constant high concentration of compound. Using the CEM-SS cell line, the IIIB strain of HIV-1, and identical nonnucleoside reverse transcriptase inhibitors, resistant viruses were obtained and their phenotypic and genotypic properties were defined. Resistant virus populations containing the Y181C amino acid change in the reverse transcriptase were predominantly selected with each of the tested compounds. Several of the compounds selected secondary amino acid changes using both methods. A comparison of the resistant viruses selected in our laboratory using each of the two protocols with viruses reported by a second laboratory employing one of the two methods suggests that genotypic differences in the selected virus isolates may most likely result from the variation in the genetic composition of the respective wild type virus pools, rather than the specific selection methodology employed. These results imply that HIV may select a wide variety of amino acid changes to avoid the inhibitory effects of the nonnucleoside reverse transcriptase inhibitors and the selection of compounds for clinical use in combination with agents possessing non-overlapping resistance phenotypes will require evaluation of the agents against virus isolates possessing each of the mutations known to confer drug resistance.

Structure-activity and cross-resistance evaluations of a series of human immunodeficiency virus type-1-specific compounds related to oxathiin carboxanilide.

A series of compounds related to the nonnucleoside reverse transcriptase (RT) inhibitor (NNRTI) oxathiin carboxanilide (UC84) were evaluated for activity against the human immunodeficiency virus (HIV) to determine structural requirements for anti-HIV activity. Twenty-seven compounds representative of the more than 400 Uniroyal Chemical Company (UC) compounds were evaluated for structure-activity relationships. Several of the compounds evaluated were highly active, with 50% effective concentrations in the nanomolar range and therapeutic indices of > 1,000. Highly synergistic anti-HIV activity was observed for each compound when used in combination with 3'-azido-3'-deoxythymidine; additive to slightly synergistic interactions were observed with the compounds used in combination with dideoxycytidine. In combination with the NNRTI costatolide, only UC38 synergistically inhibited HIV type 1. Residues in the RT which, when mutated, impart resistance to the virus isolates selected in cell culture, against virus variants with site-directed mutations, and against RTs containing defined single amino acid changes. The mutations included changes in RT amino acids 100, 101, 103, 106, 108, and 181. The results with isolates selected in cell culture indicate that the carboxanilide compounds interact with the RT at two vulnerable sites, selecting UC-resistant virus isolates with the Y-to-C mutation at position 181 (Y181C) or the L100I substitution. A resistant virus isolate containing both Y181C combination with calanolide A, an NNRTI which retains activity against virus with the single Y181C mutation, UC10 rapidly selected a virus isolate with the K103N mutation. The merits of selecting potential candidate anti-HIV agents to be used in rational combination drugs design as part of an armamentarium of highly active anti-HIV compounds are discussed.