2',3'-Dideoxynucleosides (ddNS) have antiviral and cytostatic activities. ddNS are structural analogs and can be competitive inhibition or feedback regulation affect the metabolism and utilization of normal endogenous substrates. There is little or no data on their pharmacologic effects in normal tissues such as bone marrow and intestinal epithelium which are the rapidly proliferating tissues subjected to toxicity of antiproliferative agents. Our long term goals are to examine the pharmacologic effects and the biochemical basis for selectivity in these host tissues. The present proposal is focused on the pharmacology in small intestine. We recently established the methodologies to culture epithelial crypt cells isolated from rat small intestine and used them to study the pharmacology of other antiproliferative agents. These cells will be used for the following studies. 3'-Azido-3'deoxythymidine, 2',3'-dideoxycytidine and 2',3'-dideoxyinosine, which are currently tested clinically will be studied. 1. Pharmacodynamics of intestinal epithelial cell toxicity. Establish the concentration-time-effect relationship of ddNS-induced cytotoxicity. The drug concentrations which cause the 10, 50 and 90% of the maximal toxicity will be used for the metabolism and biochemical studies. 2. Kinetics of intracellular metabolism. Examine the intracellular metabolism of radiolabeled ddNS, and the kinetics of formation and degradation of the mono-, di-, and triphosphate nucleotides. 3. Effect on normal nucleosides. Examine the effects of ddNS on the levels and metabolism of endogenous pyrimidines and purines (thymidine, deoxycytidine, deoxyinosine, deoxyadenosine and adenosine), and the incorporation of DNA precursor (Deoxyguanosine) and RNA precursor (uridine). Examine whether there is a correlation between the drug- induced cytotoxicity and biochemical effects. 4. Modulation of drug toxicity by normal nucleosides. Examine the reversibility of ddNS- induced cytotoxicity by normal substrate (thymidine, deoxycytidine, deoxyinosine, deoxyadenosine and adenosine), and the effects of normal substrates on the metabolism and the biochemical effects of ddNS. 5. Potential drug interactions. ddNS are used in combination to explore therapeutic synergism, reduce drug toxicity and resistance. We will examine the interactions of ddNS when two drugs are given in combination. Examine the effect of the combination on the cytotoxicity, the metabolite kinetics, and the effect of treatment conditions (e.g., simultaneously or sequentially).
