Our study is subject to several limitations. The results are limited to two
GNAQmt UM cell lines, which harbor the same
GNAQ Q209 mutation. This mutation site is, however, the most common mutation present in patients with primary UM (∼45%), whereas mutations affecting the
GNAQ R183 position are much less frequent (∼3%).
12 Apart from
GNAQ Q209 and R183 mutations, UM patients also harbor mutations in
GNA11 gene, which codes for the Gα
11 subunit of the GTP-binding G-protein.
40 GNA11 mutations affect the same codon positions as
GNAQ mutations, Q209 and R183, but are less frequent, present in approximately 30% and approximately 2% of patients with primary UM, respectively.
40 The close functional relationship between Gα
q and Gα
11, together with constitutive activation of PKCs in both
GNAQmt and
GNA11mt UM cells, provides rationale that UM cells harboring
GNAQ or
GNA11 mutations are selectively sensitive to PKC inhibitors. This has indeed been demonstrated in several previous studies (Poulaki V, et al.
IOVS 2012;53:ARVO E-Abstract 6871).
15–17 Recent work by Chen et al.,
17 using two different PKC inhibitors across a panel of six different UM cell lines harboring GNAQ or GNA11 mutations, as well as melanocyte cell lines stably overexpressing GNAQ or GNA11, demonstrated selective growth inhibition of these cells, whereas melanoma cell lines harboring mutations in other genes were not sensitive to PKC inhibition, regardless of whether they were derived from uveal or cutaneous melanoma. Although PKC inhibition causes selective growth inhibition in both cells carrying an activating GNAQ or GNA11 mutation, whether the combination of PKC inhibitors with IR will result in the same radiosensitization in cells harboring
GNA11 (and
GNAQ R183) mutations requires experimental validation. As our control
GNAQwt/BRAFmt OCM3 cell line was recently identified as an atypical UM cell line more likely derived from a cutaneous melanoma,
11 we cannot exclude the possibility that the observed cooperative effects of PKC inhibitors and IR are relevant to all UM cells, and not restricted to UM cells carrying
GNAQ mutations. However, this possibility would not obviate the potential therapeutic benefit of combination therapy in patients with UM.