Human mitochondrial peptide deformylase

Peptide deformylases (PDFs) have been investigated as potential specific targets for antibiotics, but the possible existence of a functional human PDF (HsPDF) presents a potential hurdle to the design of specific drugs. We have expression cloned an HsPDF that has deformylase activity, although it is a slower and catalytically less active enzyme than bacterial or plant PDFs. A cobalt-substituted form of HsPDF (but not nickel or zinc) is active, and the enzyme appears to be active at a pH between 6.0 and 7.2, a temperature range of 25°C to 50°C, and in a low KCl ionic strength buffer. This new human enzyme, HsPDF, localizes to the mitochondria and is capable of removing formyl groups from the N-terminal methionines of newly synthesized mitochondrial proteins, an activity previously not thought to be necessary in mammalian cells. We show that actinonin, a peptidomimetic antibiotic that inhibits HsPDF with an IC50 of 43 nM, also inhibits the proliferation of a broad variety of human cancer cell lines (n = 16). We designed and synthesized 33 chemical analogs of actinonin: all of the molecules with potent activity against HsPDF also inhibit tumor cell growth, and vice versa, confirming target specificity. siRNA inhibition of HsPDF protein expression is also anti-proliferative. Actinonin treatment of cells led to a tumor specific mitochondrial membrane depolarization in a time- and dose-dependent manner; removal of actinonin led to a recovery of the membrane potential consistent with indirect effects on the electron transport chain. In animal models, oral or parenteral actinonin is well tolerated and inhibits human prostate cancer and lung cancer growth. We conclude that HsPDF is a new human mitochondrial enzyme that may provide a novel selective target for anti-cancer therapy by use of actinonin-based antibiotics.