Cross-resistance analysis of human immunodeficiency virus type 1 variants individually selected for resistance to five different protease inhibitors.

Human immunodeficiency virus type 1 (HIV-1) protease inhibitor-resistant variants, isolated on passage of HIV-1HXB2 in MT-4 cells with five different protease inhibitors, have been examined for cross-resistance to five inhibitors. The protease inhibitors studied were Ro 31-8959, A-77003, XM323, L-735,524, and VX-478. Resistant variants with two to four mutations within their protease sequence and 9- to 40-fold-decreased susceptibility were selected for all five inhibitors within six to eight passes in cell culture. Passage of a zidovudine-resistant mutant in Ro 31-8959 generated a dual reverse transcriptase- and protease-resistant virus. Variants were cloned directly into a modified pHXB2-D infectious clone for cross-resistance analysis. Although the resistant variants selected possessed different combinations of protease mutations for each inhibitor, many showed cross-resistance to the other inhibitors, and one showed cross-resistance to all five inhibitors. Interestingly, some mutants showed increased susceptibility to some inhibitors. Further HIV passage studies in the combined presence of two protease inhibitors demonstrated that in vitro it was possible to delay significantly selection of mutations producing resistance to one or both inhibitors. These studies indicate that there may be some rationale for combining different protease inhibitors as well as protease and reverse transcriptase inhibitors in HIV combination therapy.

Biological and biochemical characterization of clinical isolates of herpes simplex virus type 2 resistant to acyclovir.

A series of clinical isolates of herpes simplex virus type 2 were taken from a patient with chronic lymphocytic leukemia. Acyclovir (ACV) susceptibility assays revealed that some isolates were resistant to ACV and cross-resistant to ganciclovir but not to phosphonoacetic acid. The nature of the resistance was examined further. A number of cloned variants were generated, and thymidine kinase and DNA polymerase assays were carried out. Variants that were resistant to ACV were found to be thymidine kinase deficient. Evidence for alteration in the DNA polymerase was not found when ACV triphosphate or phosphonoacetic acid was used as the inhibitor. In vivo studies with the plaque-purified viruses showed that ACV resistance was associated with a reduced neurovirulence. In a zosteriform model, virus resistant to ACV was unable to induce secondary spread in the same dermatome, to invade the peripheral nervous system or the central nervous system, or to establish latent infections.

Characterization of a DNA polymerase mutant of herpes simplex virus from a severely immunocompromised patient receiving acyclovir.

A series of herpes simplex virus isolates were recovered from a bone marrow transplant patient who received prolonged acyclovir therapy for indolent herpes simplex mouth and throat ulceration. Of 14 isolates received 10 were resistant to acyclovir and partially resistant to phosphonoacetic acid. Biochemical characterization revealed that resistance was due to an alteration in the virus DNA polymerase. DNA sequence analysis of the polymerase gene of a plaque-purified resistant virus isolate revealed a single nucleotide change when compared with the sequence of the gene of a plaque-purified sensitive isolate. This single base change resulted in a predicted amino acid substitution of Gly to Ser at residue number 841, a putative functional region of the polymerase.

Sensitivity monitoring of herpes simplex virus isolates from patients receiving acyclovir.

A simple plaque-reduction assay was used to determine the acyclovir sensitivity of herpes simplex virus isolates taken from patients enrolled int he acyclovir clinical trial programme. The resultant data revealed no reduction in acyclovir sensitivity in virus from those patients, with a normal immune status, receiving topical, oral or intravenous acyclovir for the treatment of acute disease episodes. In the treatment or prophylaxis of chronic herpes infections in immunocompromised patients reductions in sensitivity were observed but these were infrequent. Sensitive virus was later recovered from a small number of patients who had yielded resistant virus when they were followed through to the next recurrence.

Comparison of the in vitro and in vivo antiherpes virus activities of the acyclic nucleosides, acyclovir (Zovirax) and 9-[(2-hydroxy-1-hydroxymethylethoxy)methyl]guanine (BWB759U).

The antiherpes virus activities of acyclovir and its close analogue 3-[(2-hydroxy-1-hydroxymethylethoxy)methyl]guanine (BWB759U) were compared in vitro and in vivo. The activities of both compounds against herpes simplex virus and varicella-zoster virus were similar in the majority of cell lines. However, in mouse-derived and HeLa cells, BSB759U was more effective than acyclovir against herpes simplex virus. Mutants of herpes simplex virus deficient in thymidine kinase and resistant to acyclovir were found to vary in their sensitivity to BWB759U. In two mouse models of herpes simplex virus infection BWB759U was more effective than acyclovir.

Acyclovir treatment of cutaneous herpes in guinea pigs and herpes encephalitis in mice.

Animal models of cutaneous herpes simplex and herpetic encephalitis were used to demonstrate the antiviral potential of acyclovir. Of the various topical formulations of acyclovir tested against herpes simplex in guinea pigs, 5 percent acyclovir in modified aqueous cream was the most effective. Propylene glycol was included in this preparation to increase the aqueous solubility of acyclovir. Acyclovir and vidarabine were found to be equally effective against herpetic encephalitis in mice when administered either orally or subcutaneously at 100 mg/kg.

Sensitivity of herpes virus isolates from acyclovir clinical trials.

Clinical isolates of herpes simplex virus and varicella zoster virus have been examined for changes in drug sensitivity after treatment of patients with acyclovir. Some preliminary sensitivity results determined by plaque reduction assays in Vero cells for herpes simplex virus and MRC-5 cells for varicella zoster virus are presented. Where both pretreatment and posttreatment virus isolates were available, no significant changes in sensitivity to acyclovir were observed. Similarly, isolates taken after treatment was begun, without a pretreatment sample, gave IC50 values no greater than expected when compared with other pretreatment isolates.