Structural requirements for novel coenzyme-substrate derivatives to inhibit intracellular ornithine decarboxylase and cell proliferation

Creating transition-state mimics has proven to be a powerful strategy in developing inhibitors to treat malignant diseases in several cases. In the present study, structurally diverse coenzyme-substrate derivatives mimicking this type for pyridoxal 5'-phosphate-dependent human ornithine decarboxylase (hODC), a potential anticancer target, were designed, synthesized, and tested to elucidate the structural requirements for optimal inhibition of intracellular ODC as well as of tumor cell proliferation. Of 23 conjugates, phosphopyridoxyl- and pyridoxyl-L-tryptophan methyl ester (pPTME, PTME) proved significantly more potent in suppression proliferation (IC50 up to 25 mu M) of glioma cells (LN229) than alpha-DL-difluoromethylornithine (DFMO), a medically used irreversible inhibitor of ODC. In agreement with molecular modeling predictions, the inhibitory action of pPTME and PTME toward intracellular ODC of LN229 cells exceeded that of the previous designed lead compound POB. The inhibitory active compounds feature hydrophobic side chain fragments and a kind of polyamine motif (-NH-(CHX)(4)-NH-). In addition, they induce, as polyamine analogs often do, the activity of the polyamine catabolic enzymes polyamine oxidase and spermine/spermidine N-1-acetyltransferase up to 250 and 780%, respectively. The dual-action mode of these compounds in LN229 cells affects the intracellular polyamine metabolism and might underlie the more favorable cell proliferation inhibition in comparison with DFMO.-Wu, F., Gehring, H. Structural requirements for novel coenzyme-substrate derivatives to inhibit intracellular ornithine decarboxylase and cell proliferation. FASEB J.23, 565-574 (2009)