RPI-1

RPI-1 is a specific, orally available 2-indolinone Ret tyrosine kinase inhibitor. RPI-1 inhibits proliferation, Ret tyrosine phosphorylation, Ret protein expression, and the activation of PLCgamma, ERKs and AKT in human medullary thyroid carcinoma TT cells. Antitumor activity^[1]. In Vitro: TPC-1 cells are sensitive to the growth inhibitory effect of RPI-1 with an IC₅₀ of 5.1 μM, following 72 hours of treatment. RPI-1 (7.5-60 µM) inhibits Ret/Ptc1 autophosphorylation in TPC-1 cells. RPI-1 inhibitory effects in the TPC-1 cell culture conditions lead to inhibition of pathways involving JNK2 and AKT^[1].
The RPI-1 IC₅₀ value for cell proliferation is 3.6 µM in NIH3T3 cells expressing the Ret mutant compared with 16 µM in non-transfected NIH3T3 cells, and that for colony formation in soft agar was 2.4 µM and 26 µM in RET mutant-transfected and H-RAS-transfected NIH3T3 cells, respectively. In NIH3T3 cells expressing the Ret mutant, Ret protein and tyrosine phosphorylation were undetectable after 24 hours of RPI-1 treatment. In TT cells, RPI-1 inhibits proliferation, Ret tyrosine phosphorylation, Ret protein expression, and the activation of PLCgamma, ERKs and AKT^[2]. In Vivo: RPI-1 (50, 100 mg/kg; p.o.; twice a day for 10 days) inhibits the tumor growth of TT xenografts by 81%^[2].