IDENTIFICATION AND CHARACTERIZATION OF AN ENDO EXONUCLEASE IN PNEUMOCYSTIS-CARINII THAT IS INHIBITED BY DICATIONIC DIARYLFURANS WITH EFFICACY AGAINST PNEUMOCYSTIS PNEUMONIA/

Dicationic diarylfurans and dicationic carbazoles are under developmen t as therapeutic agents against opportunistic infections. While their ability to bind to the minor groove of DNA has been established, the c omplete mechanism of action has not. We demonstrate here that an effec tive diarylfuran, 2,5-bis[4-(N-isopropylguanyl)phenyl]fura inhibits an endo/exonuclease activity present in Pneumocystis carinii, Cryptococc us neoformans, Candida albicans, and Saccharomyces cerevisiae. This ac tivity was purified from the particulate fraction of P. carinii. The e nzyme requires Mg++ or Mn++, and shows preferences for single-over dou ble stranded DNA and for AT-rich over CC-rich domains. A panel of 12 d icationic diarylfurans and eight dicationic carbazoles, previously syn thesized, were evaluated for inhibition of the purified nuclease and f or efficacy against Pneumocystis pneumonia in rats. Among the diarylfu rans, potency of nuclease inhibition, in vivo antimicrobial activity, and DNA binding strength were all strongly correlated (p < 0.001). The se findings suggest that one target for antimicrobial action of the di arylfurans may be a nucleolytic or other event requiring unpairing of DNA strands. Dicationic carbazoles which were strong nuclease inhibito rs all displayed anti-Pneumocystis activity in vivo, but there were al so noninhibitory carbazoles with in vivo efficacy.