Didanosine but Not High Doses of Hydroxyurea Rescue Pigtail Macaque from a Lethal Dose of SIV smmpbj14

It has been previously reported that hydroxyurea (HU) displays anti-HIV-1 activity and potentiates the antiviral effects of didanosine (ddI) in vitro. To assess the antiviral efficacy of HU in an animal model, the effects of HU and ddI, either individually or as combination therapy, were tested in a model using infection of pigtail macaque with the acutely fatal variant SIV_smmpbj14. At the high dosage used (100 mg/kg/day), HU monotherapy failed to protect the exposed animals from viral infection and death, which occurred within 10 days postinoculation. However, both of the ddI-treated animals (5 mg/kg/day) survived the SIV_smmpbJ14 lethal dose and displayed a reduction in viral load (undetectable SIV RNA or p27 ^gag ) in the primary phase of infection. Of the animals treated with the combination of drugs, one died at day 18 after infection and failed to seroconvert to viral antigens. These data suggest that a high dose of HU monotherapy does not protect against death induced by SIV_smmpbj14. However, lower doses of HU as monotherapy or combination therapy deserve further evaluation for their therapeutic effects.