Inhibition of farnesyl protein-transferase in neuroblastoma cells by alpha-hydroxyfarnesylphosphonate

Oncogenic Ras is responsible for malignant transformation in a variety of t umors. Farnesylation of Ras by farnesyl-protein-transferase (FPTase) is nec cessary for membrane localization of Ras-proteins, a prerequisite for its b iological activity. Although mutations in ras genes are rare in neuroblasto ma inactivation of Ras by inhibition of the FPTase is of interest in neurob lastoma. In this tumor, amplification of N-myc is frequently observed and e xpression of N-myc is induced via Ras signaling. Farnesyl-protein-transfera se of neuroblastoma cells is inhibited by alpha-hydroxyfarnesylphosphonate. In homogenates of the cell line SK-N-AS an ID50 = 6.5 mu M is estimated, i n SK-N-SH the ID50 is 3.4 mu M. The consequences of the inhibition of FPTas e on the membrane localization was examined by immunoblots. Western blots o f membrane proteins analysed with H-ras and N-ras specific antibodies revea led that H-ms protein is more sensitive to the inhibition of FPTase than N- ras protein. After culturing neuroblastoma cells for 24 hrs in the presence of 20 mu M a-hydroxyfarnesylphosphonate H-ras protein completely dissappea red from the membrane fraction whereas N-ras protein was only affected by 5 0 %. K-ras was not detectable on Western blots of three neuroblastoma cell lines. The experiments showed that FPTase inhibitors are effective in neuro blastoma cells but for, complete inactivation of N-ras stronger conditions are required than for H-ras.