Pentamidine Is an Antiparasitic and Apoptotic Drug That Selectively Modifies Ubiquitin

We have determined the cytotoxic properties of penlamidine isethionate (2) towards the promastigotes of the protozoan parasite Leishmania infantum. The leishmanicidal activity of 2 was 60 times higher after 72 h of incubation than that of cisplatin (4). The pentamidine salt 2 induced a higher amount of programmed cell death (PCD) than cisplalin, which is associated with inhibition of DNA synthesis and cell-cycle arrest in the G2/M phase. Circular dichroism (CD) data indicate that binding of 2 to call-thymus DNA (CT-DNA) induces conformational changes in the DNA double helix, consistent with a B → A transition. Moreover, the interaction of 2 with ubiquitin led to a 6% increase in the β-sheet content of the protein as observed by CD spectroscopy. Fluoresccnce-spectroseopy studies agreed with the CD data, showing that the pentamidine portion of 2 induces a significant decrease in the fluorescence of the Ub residues Phe 4 and Phe 4 5 located on the β-cluster of the molecule, hut not of Tyr 5 9 on the α-cluster. These data indicate that pentamidine specifically modifies the β-cluster, i.e., the "basic face" of ubiquitin. Our results suggest that the biochemical mechanism of action of pentamidine may be a consequence of its dual binding to DNA and proteins.