Antiviral drugs for AIDS. Current status and future prospects

Screening of microbes, isolation, genetic manipulation, and physiological optimization of Brevibacterium helvolum to produce and excrete thymidine and deoxyuridine in high concentrations

Analogues of deoxypyrimidines are used in the treatment of a variety of human ailments. Azidothymidine, or AZT, is one such analogue used to treat AIDS. Thymidine is the precursor of AZT, and its cost contributes to the high price of AZT. Attempts are being made to isolate and genetically manipulate microbes that can produce and excrete this compound in high concentrations. To this end, 145 different microbial species from Zeneca and the American Type Culture Collection were screened. Moreover, soil samples were collected from 36 different sites in England, and microbes from these samples were isolated and screened. >From approximately 25,000 isolates screened as single colonies and from 4,000 in liquid cultures, a strain of Brevibacterium helvolum showed the most promising results. Pyrimidine metabolic pathways of this bacterium were worked out, the isolate was genetically manipulated, and physiological conditions were optimized to increase the production of thymidine and deoxyuridine. These mutants of B. helvolum are considered to be of commercial importance.

Use of phosphonocarboxylic acids as inhibitors of sodium-phosphate cotransport

Phosphonocarboxylic acids, initially developed as antiviral agents, are found to be specific inhibitors of phosphate (P(i)) transport across cell membranes. Foscarnet (PFA), the most potent and the most widely used compound, can induce phosphaturia both after parenteral and oral administration. Furthermore, it can inhibit intestinal phosphate absorption when administered orally. PFA absorption and bioavailability are increased in animals on phosphate-restricted diets. PFA also blunts the adaptive increase in intestinal and renal Na(+)-P(i) cotransport which accompanies dietary phosphorus restriction. Finally, PFA is shown to inhibit hydroxyapatite crystal formation and calcium-phosphate precipitation when tested in in vitro systems. These properties, and the low toxicity of PFA, point to potential new applications for PFA and some of its analogs in clinical conditions such as chronic renal insufficiency, where phosphate retention may lead to progression of renal failure and to other serious complications.

Atypical retinitis in patients with the acquired immunodeficiency syndrome

We examined three patients with AIDS who had large, sharply demarcated areas of thinned retina consistent with inactive cytomegalovirus retinitis and who were not treated with ganciclovir. These lesions appeared identical to clinically inactive areas of cytomegalovirus retinitis after effective antiviral treatment. All patients were receiving azidothymidine or ribavirin, or both, which have activity against the human immunodeficiency virus and which may improve immune function. All patients also received oral acyclovir at doses ineffective against cytomegalovirus retinitis.