Inhibitory effects of the mitogen-activated protein kinase kinase inhibitor CI-1040 on the proliferation and tumor growth of thyroid cancer cells with BRAF or RAS mutations.

CONTEXT

Targeting MAPK kinase (MEK) in the MAPK pathway is a potentially effective therapeutic strategy for thyroid cancer.

OBJECTIVE

The objective of the study was to investigate genotype-dependent therapeutic potential of the MEK inhibitor CI-1040 for thyroid cancer.

EXPERIMENTAL DESIGN

We examined the effects of CI-1040 on proliferation, apoptosis, transformation, thyroid gene reexpression, and xenograft tumor growth with respect to genotypes in 10 thyroid tumor cell lines.

RESULTS

Cell proliferation was potently inhibited by CI-1040 in cells harboring BRAF or RAS mutations but not in cells harboring RET/PTC rearrangement or wild-type alleles. For example, the IC50 values for BRAF mutation-harboring KAT10 cells and DRO cells and H-RAS mutation-harboring C643 cells were 0.365, 0.031, and 0.429 microm, respectively, whereas the IC50 values for RET/PTC1-harboring TPC1 cells and the wild-type MRO and WRO cells were 44, 46, and 278 microm, respectively. Proapoptotic effect of CI-1040 was seen in DRO cells, and cytostatic effect was seen in other cells. Down-regulation of cyclin D1 and reexpression of some thyroid genes were induced by CI-1040 in some BRAF mutation-harboring cells, and transformation was inhibited in all cells. CI-1040 also inhibited the growth of xenograft tumors in nude mice derived from KAT10 or C643 cells but not that derived from MRO cells.

CONCLUSIONS

We for the first time demonstrated potent inhibitory effects of a MEK inhibitor, CI-1040, on thyroid cancer cells, some of which, particularly cell proliferation and tumor growth, seemed to be BRAF mutation or RAS mutation selective. Our data encourage a clinical trial on CI-1040 in thyroid cancer patients.