Abstract
Choroidal melanoma is the most common primary malignant intraocular tumor, and very few effective therapies are available to treat it. Our study aimed to understand whether pemetrexed plus cisplatin exerts a beneficial synergistic effect in human choroidal melanoma cells and to delineate the underlying molecular mechanism. To accomplish these aims, we treated choroidal melanoma cells with pemetrexed and cisplatin and assessed cell survival with SRB and MTT assays. Proteins were detected using western blotting analysis. NOXA and CHOP were knocked down with siRNA. We found that pemetrexed or cisplatin alone inhibited survival and induced apoptosis in human choroidal melanoma cells. Furthermore, the expression levels of c-FLIP, an anti-apoptotic protein in the extrinsic apoptosis pathway, and Mcl-1, an anti-apoptotic protein in the intrinsic apoptosis pathway, were decreased by pemetrexed or cisplatin respectively, while the expression of a pro-apoptotic protein in the intrinsic apoptosis pathway, NOXA, was up-regulated. Moreover, pemetrexed or cisplatin alone increased the protein expression of the endoplasmic reticulum stress markers IRE1α, Bip and CHOP. Silencing CHOP expression reduced NOXA expression. These findings suggest that the pemetrexed or cisplatin induced intrinsic apoptosis via activation of the ER stress response. Importantly, combining the two compounds more strongly induced apoptosis. Following the cotreatment, CHOP and NOXA expression increased, while c-FLIP and Mcl-1 expression decreased, and these effects were more pronounced than when using either compound alone. This result suggests that pemetrexed and cisplatin synergistically activate ER stress response-induced apoptosis in choroidal melanoma cells. To summarize, the c-FLIP and NOXA/Mcl-1 axis participated in the synergistic effect of pemetrexed plus cisplatin in human choroidal melanoma cells. Intrinsic apoptosis was induced via activation of the ER stress response. Our study provides important mechanistic insights into potential cancer treatment with pemetrexed plus cisplatin and enriches our understanding of human choroidal melanoma.
Highlights
Choroidal melanoma is the most common primary malignant tumor of the eye, accounting for approximately 70% of all primary intraocular eye tumors [1], and the second most common type of malignant melanoma affecting the body
The combination of pemetrexed plus cisplatin has been reported to have a synergistic effect in various tumor types; we examined the cytotoxicity of this combination in choroidal melanoma cells
CHOP regulates the induction of NOXA expression and apoptosis by pemetrexed and cisplatin Because NOXA is a target gene of CHOP, we examined whether CHOP has a role in inducing NOXA expression in choroidal melanoma cells after drug treatment
Summary
Choroidal melanoma is the most common primary malignant tumor of the eye, accounting for approximately 70% of all primary intraocular eye tumors [1], and the second most common type of malignant melanoma affecting the body. 50% of choroidal melanomas metastasize within 15 years of the primary diagnosis [2]. The median survival time is less than 12 months [3]. Due to this high risk for metastasis, the prognosis of choroidal melanoma is poor [4]. Choroidal melanoma is insensitive to many commonly used chemotherapeutic drugs [5], and there is currently no routinely used conventional chemotherapy for these tumors [6]. Present treatments for choroidal melanoma, such as enucleation, focal radiotherapy and transpupillary thermotherapy, offer only temporary relief and are ineffective in inhibiting tumor metastasis or improving the survival rate [2, 5, 7]. There is significant interest in developing better therapies for this condition
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