TMC114, a next-generation protease inhibitor, has demonstrated significant antiviral activity in multiple PI-experienced HIV patients currently failing PI therapy. In the 50 patient study, the median reduction in plasma viral load was -1.35 log10 copies/ml HIV-1 RNA after 14 days treatment with TMC114 boosted with low-dose ritonavir (TMC114/r); the maximum reduction was -2.49 log10. TMC114 is being developed by Tibotec, a Belgian pharmaceutical research and development company.

The results, the first efficacy data reported for TMC114, were presented this week at the 10th Conference on Retroviruses and Opportunistic Infections by Dr Keikawus Arasteh of Vivantes Auguste-Viktoria-Klinikum, Berlin.

Antiretroviral resistance now accounts for a large proportion of HIV treatment failures and is a major concern for people living with HIV/AIDS. Cross-resistance among the currently approved PIs can render many of them ineffective.

"From the data collected so far, TMC114 seems to continue to be active in the presence of many of the strains of PI-resistant virus; these results are very encouraging," said Dr Arasteh.

The study, TMC114-C207, was a Phase IIa open label, randomized trial in 50 multiple PI-experienced HIV patients currently failing on a PI regimen. The median number of PI-resistance associated mutations at baseline was 6; all primary PI-resistance associated mutations were found among study participants. The median number of PIs previously used was 3; all patients had received at least 2 PIs and 2 NRTIs.

Patients in the study were randomised into three treatment arms (A, B, C) and one control arm, D. In arms A-C failing PIs were replaced by TMC114/r (A: 300/100 mg bid; B: 600/100 mg bid; C: 900/100 mg qd), all other antiretrovirals remained unchanged; in arm D patients continued on their failing regimen. The median change in plasma HIV-1 RNA from baseline to endpoint in arms A, B, C and D was - 1.24, - 1.50, - 1.13 and +0.02 copies/ml respectively.

Patients received TMC114/r for 14 days after which it was discontinued. None of the subjects experienced any rebound in viral load and there was no phenotypic evidence of the development of resistance to TMC114 during the two week trial. The most commonly reported AEs were GI and CNS disorders; no consistent TMC114/r related changes in blood chemistry or hematology were seen. There was one case of reversible hepatotoxicity in the TMC114/r group. TMC114 was generally well-tolerated during this study.

"These early clinical results of TMC114 in highly treatment-experienced patients are very positive," commented Wim Parys, Vice President of Clinical Development at Tibotec. "TMC114 was selected for clinical development on the basis of its novel in vitro antiviral profile and potency against PI-resistant HIV. These data, showing that TMC114 is active against PI-resistant virus, confirm previous results indicating that it is a next- generation PI that could potentially contribute to more effective HIV management in the future."

Further studies to evaluate long-term safety and efficacy and to define the optimal dose will be initiated later this year.