Purpose: To determine whether uveal melanoma, the most common primary intraocular malignancy in adults, requires Notch activity for growth and metastasis. Experimental Design: Expression of Notch pathway members was characterized in primary tumor samples and in cell lines, along with the effects of Notch inhibition or activation on tumor growth and invasion. Results: Notch receptors, ligands, and targets were expressed in all five cell lines examined and in 30 primary uveal melanoma samples. Interestingly, the three lines with high levels of baseline pathway activity (OCM1, OCM3, and OCM8) had their growth reduced by pharmacologic Notch blockade using the γ-secretase inhibitor (GSI) MRK003. In contrast, two uveal melanoma lines (Mel285 and Mel290) with very low expression of Notch targets were insensitive to the GSI. Constitutively active forms of Notch1 and Notch2 promoted growth of uveal melanoma cultures and were able to rescue the inhibitory effects of GSI. MRK003 treatment also inhibited anchorage-independent clonogenic growth and cell invasion and reduced phosphorylation levels of STAT3 and extracellular signal-regulated kinase (Erk)1/2. Suppression of canonical Notch activity using short hairpin RNA targeting Notch2 or CBF1 was also able to reduce tumor growth and invasion. Finally, intraocular xenograft growth was significantly decreased by GSI treatment. Conclusion: Our findings suggest that Notch plays an important role in inducing proliferation and invasion in uveal melanoma and that inhibiting this pathway may be effective in preventing tumor growth and metastasis.
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