Resistance and cross-resistance to abacavir

Abacavir/lamivudine fixed-dose combination tablet for the treatment of HIV-1 infection

The fixed-dose combination tablet of the two nucleotide reverse transcriptase inhibitors abacavir (ABC) and lamivudine (3TC) was licensed in 2004. It is dosed once daily with no food restrictions and licensed for the treatment of HIV infection in treatment-naive individuals in combination with another class of antiretroviral. Its virological efficacy has been demonstrated in clinical studies with up to 96-week follow-up in combination with non-nucleoside reverse transcriptase inhibitors and protease inhibitors. Less lipodystrophy is seen with abacavir than stavudine or zidovudine. Resistance mutations selected by ABC/3TC leave options for future treatment. Abacavir hypersensitivity reaction occurs in 5% of those receiving ABC and genetic susceptibility testing is undergoing trial. ABC/3TC is a largely well-tolerated nucleoside reverse transcriptase inhibitor backbone with proven efficacy.

Differential maintenance of the M184V substitution in the reverse transcriptase of human immunodeficiency virus type 1 by various nucleoside antiretroviral agents in tissue culture

The M184V substitution in human immunodeficiency virus type 1 reverse transcriptase (RT) is rapidly selected in tissue culture following serial passage of wild-type virus in the presence of increasing concentrations of lamivudine (3TC). M184V is also associated with several alterations of RT enzymatic function in vitro that may adversely affect viral fitness or replication capacity, which creates a potential rationale for its maintenance once it has been selected by antiviral chemotherapy. However, the relative effectiveness of nucleoside RT inhibitors that are structurally unrelated to 3TC in selecting and/or maintaining M184V has not been investigated. In the present study, we have studied the abilities of a variety of drugs, i.e., zalcitabine (ddC), didanosine (ddI), abacavir (ABC), and the novel nucleoside SPD754, in addition to 3TC, to maintain the presence of M184V in tissue culture and have shown that SPD754, ABC, and 3TC are able to preserve M184V in mixed dual infections consisting of wild-type viruses and clinical isolates which contained the M184V mutation. Moreover, M184V could also be maintained in these cultures when a subtherapeutic concentration of 3TC (i.e., 0.05 microM) was used. In contrast, neither ddI nor ddC was able to maintain M184V to the same extent as the other drugs after 10 weeks of tissue culture in mixtures of wild-type viruses and isolates containing M184V in different proportions.

Imatinib mesylate in combination with other chemotherapeutic drugs: in vitro studies

Imatinib mesylate (Gleevec) (formerly STI571) has secured a definitive role in the treatment of chronic myeloid leukemia (CML) due to its specificity and efficacy. Although some patients become resistant to the drug, it may still be possible to control the leukemia with imatinib-containing regimens. Front-line treatment with such combinations may indeed minimize the risk that resistance, and hence relapse, occurs. In this review, we discuss the published data on in vitro studies that address this question in a variety of models, and attempt to predict efficacious combinations for future clinical trials. These represent regimens where imatinib is combined with conventional chemotherapeutic drugs or with inhibitors of other key signal transduction molecules that may be preferentially activated in CML cells.