Vol. 304, Issue 1, 37-47, January 2003

c-myc Down-Regulation Induces Apoptosis in Human Cancer Cell Lines Exposed to RPR-115135 (C₃₁H₂₉NO₄), a Non-Peptidomimetic Farnesyltransferase Inhibitor

Patrizia Russo, Dario Arzani¹ , Sonya Trombino and Carla Falugi

Laboratory of Experimental Oncology, Molecular Pathology Section, National Institute for Research on Cancer, Genoa, Italy (P.R., D.A., S.T.) and Department of Experimental, Environmental and Applied Biology, University of Genoa, Genoa, Italy (C.F.)

A therapeutic strategy that relies on the use of c-myc antisense in combination with a farnesyltransferase inhibitor, RPR-115135 (C₃₁H₂₉NO₄), was studied in human cancer cell lines carrying different mutations (Ras, p53, myc amplification). Cell proliferation was strongly inhibited by the combination and was observed when c-myc oligo (at a concentration that down-regulates c-myc expression) was followed by RPR-115135. Cell cycle analysis demonstrated an accumulation in G₀-G₁ phase and a tendency to apoptosis (not detectable in cells treated with a single agent). Morphological examination and DNA fragmentation assays (filter binding and enzyme-linked immunosorbent assay DNA fragmentation) confirmed the induction of apoptosis. Apoptosis was not p53- and/or p21^waf-1-dependent, and the key effector was caspase activation. The combination induced Bax expression and Bcl-2 inhibition. Down-regulation of c-myc amplification carried out a specific role exclusively when Ras was mutated. Exposure of human proliferating lymphocytes to combination did not result in cytotoxicity, suggesting that mechanisms regulating c-myc gene expression during normal T cell proliferation might not be involved. Because of the high percentage of human tumors overexpressing c-myc mRNA and/or protein and, simultaneously, harboring oncogenic Ras mutants (i.e., colon cancers), interrupting the myc- and Ras-signaling pathway would be one of the major focuses on therapy of these types of tumors.