Induction of Tmolt(4) leukemia cell death by 3,3-disubstituted-6,6-pentamethylene-1,5-diazabicyclo[3.1.0]hexane-2,4-diones: Specificity for type II inosine 5 '-monophosphate dehydrogenase

Inosine 5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in the de novo pathway for synthesis of guanine nucleotides, is essential for normal cell proliferation and function. New derivatives of the 1,5-diazabi cyclo[3.1.0]hexane-2,4-diones were synthesized and examined for antiprolife rative effects and selective inhibition of human IMPDH type II activity. Th e 3,3-disubstituted-6,6-pentamethylene-1,5-diazabicyclo[3.1.0]hexane-2,4-di ones proved to be effective antiproliferative agents in tumor cell lines de rived from murine and human leukemias, lymphomas, uterine carcinoma, glioma , and breast effusion with ED50 values (concentration of compound that inhi bits 50% of cell growth) ranging from 3.3 to 16 muM. The agents acted as an timetabolites suppressing de novo purine biosynthesis at the key regulatory enzyme IMPDH, resulting in the specific suppression of dGTP pool levels by 19 to 64% and DNA synthesis by 39 to 68%. The derivatives were specific in hibitors of IMPDH type II activity as opposed to type I, acting in a compet itive manner with respect to inosine 5'-monophosphate, K-i values of 44.2 t o 62 muM. In addition, effects of agents on Tmolt(4) cell growth and DNA sy nthesis could be reversed by coincubation with guanosine. Unlike mycophenol ic acid and tiazofurin, the 6,6-pentamethylene-1,5-diazabicyclo[3.1.0]hexan e-2,4-diones specifically targeted type II IMPDH, where activity is increas ed in replicating or neoplastic cells, and did not suppress type I activity , where expression is relatively unaffected by cell proliferation or transf ormation. Agents were not inhibitors of normal human lung fibroblast cell g rowth, WI-38, most likely due to the observed isoform selectivity.