We have studied the effects of the gag antisense phosphorothioate
oligonucleotide GEM 91 and mismatch antisense controls on the
antiviral activities of ddC and other
nucleoside analogs in HIV-infected MT-4 cells using a cytoprotection based assay. Under standard assay conditions, i.e. simultaneous incubation of drugs, HIV-1 IIIB and MT-4 cells, both
GEM 91 and mismatch controls interacted synergistically with ddC resulting in an approximate 40-fold decrease in the IC50 value of ddC; this suggests a potent but sequence non-specific effect of
GEM 91. Under post-adsorption assay conditions, i.e. pre-incubation of virus and cells and removal of excess HIV before
drug addition,
GEM 91 exhibited synergism with ddC, with an approximate 5-fold decrease in ddC IC50 value. This favorable interaction was not seen with any of the mismatch
oligonucleotides, suggesting the involvement of a sequence-specific mechanism of action. Similar results were seen with the
thymidine analogs AZT and
d4T in combination with
GEM 91. These data suggest a potential role for
GEM 91 and future sequence-specific antisense drugs in combination with
nucleoside analogs for the treatment of
HIV infection. It is essential that potential interactions between new and existing classes of
anti-HIV drugs are studied extensively as antiretroviral
drug combinations become increasingly more complex.