302   In VitroandIn VivoPre- Clinical Analyses of the Antiretroviral Drug Candidate 4- Methyl Dicamphanoyl Khellactone.

. C. T. Wild¹, N. R. Kilgore¹, S. E. Polidoro¹, L. Xie², S.-Y. Chen², K.-H. Lee², P. C. Smith², and G. P. Allaway*¹.
¹Panacos Pharmaceuticals Inc., Gaithersburg, MD and²Univ. of North Carolina, Chapel Hill.

Background:4-Methyl dicamphanoyl khellactone (4-methyl DCK) potently inhibits replication of diverse primary HIV-1 isolates from all viral clades tested. It has a novel mechanism of action compared to approved drugs and appears to act early in the viral replicative cycle. This report presents the results of pre-clinical tests to help determine the compound's potential for further development.

Methods:Potency against primary clinical isolates of HIV-1 in vitro was tested in the presence or absence of human serum. Synergy with approved drugs was analyzed by the combination index method. In vivo disposition was examined in rats following IV or oral administration at doses of 10-25 mg/kg. The plasma concentration was examined at intervals following administration, using reverse-phase HPLC measuring absorbance at 320 nm.

Results:Human plasma at 40% had little effect on the activity of 4-methyl DCK, suggesting that plasma protein binding will not reduce the efficacy of this compound in vivo . 4-methyl DCK's antiviral activity was highly synergistic with approved drugs such as AZT (combination index <0.25), supporting its potential utility in combination therapy. When administered IV to rats, peak plasma concentrations up to severalmg/ml were achieved (approximately 100× the IC₅₀against primary HIV-1 isolates in vitro ). The mean terminal half-life was 2.4 hours, which compares favorably to many approved drugs. No detectable plasma concentration of 4-methyl DCK was observed following oral administration as a suspension in 10% Tween 80/water, possibly resulting from the compound's poor solubility in this formulation. No gross toxicities were seen following IV or oral administration in these rat disposition studies.

Conclusions:4-Methyl DCK exhibits in vitro and in vivo properties that support its further development as a drug candidate for the treatment of HIV infection. It has been proposed that we should move forward with pre- clinical testing of this compound with the goal of initiating an efficacy study in HIV-1-infected individuals if the pre-clinical studies continue to be supportive.