Antiproliferative Effects of Tyrosine Kinase (STI 571) and Farnesyl Transferase Inhibitors (R115777 and SCH66336) on Acute Leukemia Human Tumor Cell Lines.

The inhibition of the c-Kit signal transduction pathway by imatinib mesylate (STI571) and the inhibition of the post-translational modification of the N-K Ras proteins by farnesyl transferase inhibitors (FTIs) have shown potential efficacy in treating acute myeloid leukemias. We investigated the activity of (STI571) and of two distinct FTIs, R115777 and SCH66336, on two pairs of acute leukemia (AL) human tumor cell lines, each pair consisting of the parental cell line, HL60 and CCRF-CEM, and of its drug-selected multidrug resistant (MDR) Pgp-positive subline, HL60-DNR and CEM-VLB. The effectiveness of STI571, R115777 and SCH66336 in inhibiting cell proliferation of AL cell lines have been evaluated by colorimetric MTT assay. Cell growth was evaluated after a 7-day incubation at 37°C and 5% CO₂ by using 50 microl per well of the MTT solution (5 mg/mL). The inhibition dose 50 (ID50) was defined as the drug dose that inhibited cell growth to 50% of the control. The results were correlated with the MDR phenotype and c-Kit expression. The toxic effect of STI 571 on all the acute leukemias derived cell lines was very low for both parental and MDR-Pgp+ sublines, ranging from 0.9 and more than 5 microM. STI571 activity was influenced by the c-Kit (CD117) expression and not by the MDR expression of cell lines. In fact, among these acute leukemia derived cell lines the higher toxic effect (ID50=0.9 microM) was obtained in HL60 DNR, the only cell line with a CD117 positivity. R115777 was more toxic than SCH66336 on all the tested AL cell lines. The Inhibition Dose 50 (ID50) of the two farnesyl transferase inhibitors ranged from 0.0065 to 0.21 microM for R115777 and from 0.3 to 6.5 microM for SCH66336. These results suggest that a potential synergistic effects of STI571 and R155777 combination could be explored in c-Kit positive acute myeloid leukemias.