Antiviral chemotherapy for infection with human immunodeficiency virus

Prediction of potential inhibitors for RNA-dependent RNA polymerase of SARS-CoV-2 using comprehensive drug repurposing and molecular docking approach

The pandemic prevalence of COVID-19 has become a very serious global health issue. Scientists all over the world have been seriously attempting in the discovery of a drug to combat SARS-CoV-2. It has been found that RNA-dependent RNA polymerase (RdRp) plays a crucial role in SARS-CoV-2 replication, and thus could be a potential drug target. Here, comprehensive computational approaches including drug repurposing and molecular docking were employed to predict an effective drug candidate targeting RdRp of SARS-CoV-2. This study revealed that Rifabutin, Rifapentine, Fidaxomicin, 7-methyl-guanosine-5'-triphosphate-5'-guanosine and Ivermectin have a potential inhibitory interaction with RdRp of SARS-CoV-2 and could be effective drugs for COVID-19. In addition, virtual screening of the compounds from ZINC database also allowed the prediction of two compounds (ZINC09128258 and ZINC09883305) with pharmacophore features that interact effectively with RdRp of SARS-CoV-2, indicating their potentiality as effective inhibitors of the enzyme. Furthermore, ADME analysis along with analysis of toxicity was also undertaken to check the pharmacokinetics and drug-likeness properties of the two compounds. Comparative structural analysis of protein-inhibitor complexes revealed that the amino acids Y32, K47, Y122, Y129, H133, N138, D140, T141, S709 and N781 are crucial for drug surface hotspot in the RdRp of SARS-CoV-2.

Risk factors for development of rhegmatogenous retinal detachment in patients with cytomegalovirus retinitis

We studied 259 patients to determine the time-dependent risk and risk factors for the development of retinal detachment in patients with cytomegalovirus retinitis. The six-month and one-year retinal detachment rates (by eye) were 11% and 24%, respectively. Increasing retinal surface involvement outside of the posterior pole and the presence of retinitis activity were found to be the two covariates that best predicted retinal detachment. Eyes with peripheral involvement greater than 25% had a fivefold risk for detachment, compared to eyes with 10% involvement. If there was retinitis activity and more than 25% peripheral (external to major vascular arcades) involvement, the risk increased to 24-fold. The presence of a fellow eye with retinal detachment was not an independent risk factor. These observations should help in the design of a prophylactic trial intended to prevent retinal detachment and should also help ophthalmologists counsel patients with cytomegalovirus retinitis.

Enhanced expression of alpha-type DNA polymerase genes reduces AZT cytotoxicity in hamster tr5 cells

To study the mechanism of azidothymidine (AZT) cytotoxicity, human DNA was transfected to a variant of Chinese hamster V79 fibroblasts, the tr5 line. This cell line was used for this study for its elevated sensitivity to 5 microM AZT. Primary and secondary transfectants of tr5 cells using total human DNA and pSV2neo plasmid were selected by sequential incubations in AZT (20-50 microM), G418 (400 micrograms/ml active dose), and medium containing hypoxanthine, aminopterin, and thymidine (HAT). One DNA Alu fragment was detected in transfectants using primer TC-65, specific for human Alu sequences in the polymerase chain reaction (PCR). Moreover, cDNA of Chinese hamster alpha-type DNA polymerases was detected in transfectants by reverse transcriptase PCR (RT-PCR) using specific oligo-primer from a DNA polymerase-alpha cDNA sequence and in elevated annealing temperatures. In untransfected tr5 cells, neither of these sequences was detected. The data suggested that the genetic basis for AZT sensitivity may be related to the expression of alpha-type DNA polymerase, and the result indicated that AZT cytotoxicity could be reversed by transfection of appropriate human DNA into tr5 cells. This animal cell model has applications for studies of AZT metabolism and the isolation of the human gene that modulates AZT cytotoxicity.

Significance of embryo culture methods for studying the prenatal toxicity of virustatic agents

Culture methods have become important tools for elucidating the prenatal toxicity of drugs and other xenobiotics. In this paper we will review how we used in vitro as well as in vivo approaches to demonstrate the teratogenic potential of aciclovir and other related virustatic agents. In addition, some new data on this topic will be given. The teratogenic potential of the virustatic agent aciclovir was not recognized in routinely performed segment-II-studies, but the first indication came from experiments with the culture of rat embryos. Subsequently, the findings were confirmed in modified in vivo tests and it became clear that out of a group of six related drugs aciclovir exhibited the highest potential for prenatal toxicity. The effects of aciclovir on limb development were not pronounced--this has been shown with in vitro and in vivo experiments as well. In vivo experiments first indicated that the prenatal development of the thymus is disturbed by aciclovir. This effect was further studied with the culture of fetal thymuses and again the effect of aciclovir could be compared with related drugs. In summary, our work with virustatics during the last years has shown that in vivo and in vitro approaches are by no means competitive and that a combination of both approaches can provide a solid basis for a toxicologic evaluation.

Effect of six virustatic nucleoside analogues on the development of fetal rat thymus in organ culture

The effects of the virustatic agents zidovudine (azidothymidine, AZT) 2'3'-dideoxycytidine (ddC), 2'3'-dideoxyinosine (ddI), acyclovir (ACV), ganciclovir (GCV), and vidarabine phosphate (VP) on the in vitro development of thymic lobes of 17-day-old rat fetuses were tested in an organ culture system. The virustatics were added to the medium for a culture period of 7 days. All nucleoside analogues inhibited the proliferation and differentiation of lymphatic cells. However, differences were observable with respect to the potency of the six drugs to interfere with thymic development. Compared to untreated controls, reduction in the number of thymocytes was significant at concentrations of 30 microM AZT and ddI. In the case of ACV, GCV, VP, and ddC concentrations as low as 10 microM were sufficient to cause a significant reduction, ddC being the most potent derivate. Increasing concentrations of the nucleoside analogues led to a dose-dependent further inhibition of cell proliferation. At a concentration of 30 microM flow cytometry revealed a decrease in the relative number of double positive CD4+ CD8+ and single positive CD4+ CD8- cells but an increase in the relative number of CD4-CD8+ cells. At the same concentration the expression of the CD5 antigen was reduced by the antimetabolites, indicating that maturation of the thymocytes was inhibited. Distribution of the forward light scatter, a cell size-related parameter, showed that the formation of small thymocytes was reduced by the nucleoside analogues. Light and electron microscopic investigations indicated cytotoxic effects of the drugs on the thymocytes, whereas the epithelium was only slightly affected.

Nonhuman primate models for evaluation of AIDS therapy

Infection of macaque monkeys with simian immunodeficiency virus (SIV) has been established as an excellent animal model system for studying the pathogenesis of an HIV-like virus and for evaluating newly developed antiretroviral drugs and vaccines. Based on their genetic, antigenic, and biologic properties, the simian immunodeficiency viruses are the closest known relatives of the human AIDS viruses, and experimental infection of macaque monkeys results in a disease that is remarkably similar to human AIDS. Infected macaques show diarrhea, weight loss, hematologic abnormalities including lymphopenia and thrombocytopenia, lymphadenopathy/lymphoid hyperplasia that progresses to lymphoid depletion, immunosuppression with marked reduction in CD4+ cells and in the CD4+/CD8+ cell ratio, and opportunistic infections. A majority of such macaques die from an AIDS-like disease within one to three years of infection. An acutely lethal variant of SIV has been identified that results in death in susceptible macaques within 7-12 days of infection. Preliminary prophylactic treatment trials with AZT in macaque monkeys exposed to the acutely lethal SIV variant indicate that some protection is provided when AZT treatment is initiated within 24 hours of virus exposure. Other studies with the more chronic SIV infection model, however, failed to show any prophylactic efficacy of CS-87, AZT, D4T, or FDT.