Uveal melanoma (UM) is the most common intraocular tumor in adults. Despite local tumor control, no effective therapy has been found to prevent metastasis, resulting in a high mortality rate. In the present study, we evaluated the anti-tumor potential of non-selective ß-blockers in 3D tumor spheroids grown from UM cell lines. Of the various ß-blockers tested, carvedilol and its enantiomers were most potent in decreasing the viability of Mel270 spheroids. Carvedilol at a concentration of 10–50 µM significantly elicited cytotoxicity and induced apoptosis in spheroid cells. In result, carvedilol inhibited tumor spheroid growth and compactness, and furthermore prevented the long-term survival and repopulation of spreading spheroid cells. The drug sensitivity of the different spheroids grown from Mel270, 92-1, UPMD2, or UPMM3 cell lines was dependent on 3D morphology rather than on high-risk cytogenetic profile or adrenergic receptor expression levels. In fact, the monosomy-3-containing UPMM3 cell line was most responsive to carvedilol treatment compared to the other cell lines. The concurrent treatment of UPMM3 spheroids with carvedilol and 5 or 10 Gy irradiation revealed additive cytotoxic effects that provided tumor control. Collectively, our data demonstrate the anti-tumor properties of carvedilol and its enantiomers, which may serve as candidates for the co-adjuvant therapy of UM.

Uveal melanoma (UM) is the most common primary cancer of the eye in adults. A new systemic therapy is needed to reduce the high metastasis and mortality rate. As β-blockers are known to have anti-tumor effects on various cancer entities, this study focuses on investigating the effect of β1-selective blockers atenolol, celiprolol, bisoprolol, metoprolol, esmolol, betaxolol, and in particular, nebivolol on UM. The study was performed on 3D tumor spheroids as well as 2D cell cultures, testing tumor viability, morphological changes, long-term survival, and apoptosis. Flow cytometry revealed the presence of all three β-adrenoceptors with a dominance of β2-receptors on cell surfaces. Among the blockers tested, solely nebivolol concentration-dependently decreased viability and altered 3D tumor spheroid structure. Nebivolol blocked the repopulation of cells spreading from 3D tumor spheroids, indicating a tumor control potential at a concentration of ≥20 µM. Mechanistically, nebivolol induced ATP depletion and caspase-3/7 activity, indicating that mitochondria-dependent signaling is involved. D-nebivolol or nebivolol combined with the β2-antagonist ICI 118.551 displayed the highest anti-tumor effects, suggesting a contribution of both β1- and β2-receptors. Thus, the present study reveals the tumor control potential of nebivolol in UM, which may offer a perspective for co-adjuvant therapy to reduce recurrence or metastasis.