Comparison of potential markers of farnesyltransferase inhibition

Farnesyltransferase inhibitors (FTIs) were developed to target abnormal sig naling pathways that are commonly activated in neoplastic cells. Five FTIs have recently undergone Phase I testing; and two are currently in Phase II clinical trials. As part of the development of these agents, there has been interest in determining their cellular effects in the clinical setting. Se veral approaches have been proposed, including measurement of FT enzymatic activity, evaluation of the processing of FT polypeptide substrates, and as sessment of the accumulation of p21(waf1). In the present study, a number o f these assays have been compared in four cultured human neoplastic cell li nes of different histology (A549, HCT116, BxPC-3, and MCF-7) after treatmen t with the nonpeptidomimetic FTI SCH66336 and the peptidomimetic inhibitor FTI-277, Immunoblotting studies failed to demonstrate a mobility shift in r as proteins or increased accumulation of p21(waf1) after treatment with the se agents. In contrast, drug-induced increases in the slower migrating, unp rocessed species of the chaperone protein HDJ-2 and the intranuclear interm ediate filament protein lamin A were detected in all four cell lines after treatment with either agent. Unprocessed forms of both polypeptides accumul ated in noncycling as well as cycling cells, The precursor peptide that is present in prelamin A but absent from mature lamin A could be readily detec ted by immunohistochemistry in noncycling cells with a peptidespecific anti serum. Our results indicate that unprocessed HDJ-2 and prelamin A should be suitable markers of FT inhibition in clinical samples.