The proposed application focuses on the modulation of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase (AGT) to enhance alkylating agent chemotherapy. O6-Benzylguanine is the lead compound presently in Phase I clinical trials. The objective of this application is to improve upon this agent by increasing the therapeutic index of the combination O6- benzylguanine and BCNU. This objective will be accomplished by examining the pharmacology and metabolism of two classes of AGT inactivators, esterified derivatives of O6-benzylguanine and substituted pyrimidines. The ester prodrugs are much less potent against the pure AGT protein than their deesterified counterpart requiring hydrolysis by cellular esterases for a highly potent agent. Specifically, we will compare the rate of hydrolysis of these agents with their potency as AGT-inactivators in human tumor cell lines and normal human tissues. We will assess the bioavailability of selected agents following iv and oral administration to rats. The second group of agents for evaluation are the substituted pyrimidines. Two agents in this group, 2,4-diamino-6-(benzyloxy)-5- nitrosopyrimidine and 2,4-diamino-6-(benzyloxy)-5-nitropyrimidine are much more potent inactivators of the AGT protein than O6-benzylguanine. To determine the effect of metabolism on AGT-inactivating potency of selected analogs, we will compare the ability of selected analogs to inhibit AGT activity in hepatocytes with their potency against the pure AGT protein. The metabolic pathway of selected analogs will be determined in vitro using rat and human liver microsomes and cytosol. The optimal agents will be tested in a nude mouse xenograft for their ability to increase the therapeutic index of BCNU. We anticipate that these studies will lead to a more tumor-selective compound for clinical trials.
Showing the most recent 10 out of 12 publications
