INTRODUCTION

Uveal melanoma is the highly malignant tumor of the eye and frequently leads to metastatic death. Depending on size and other parameters, traditional treatment of the primary tumor has been enucleation. However, alternative treatments to preserve the eye have been devised, including cryotherapy, radioactive therapy, transpupillary thermotherapy, surgical resection and photocoagulation. Despite these advances in treatment, mortality varies considerably, to more than 50% in high-risk patients, primarily due to metastasis to the liver. Therefore, it is critical to develop drugs that are non-toxic and can be administered for potentially extended periods to patients who have diagnosed with primary uveal melanoma. In recent years, Zeaxanthin, a naturally occurring carotenoid alcohol highly enriched in green leaves, has been used in medicine to treat various diseases. Epidemiological studies have shown that higher intake and higher blood levels of zeaxanthin appear to be associated with a lower risk of occurrence of various cancers. It has also been reported that zeaxanthin may inhibit cell growth or induce apoptosis of several tumor cell lines in vitro. The present study was designed to investigate the effect of zeaxanthin on human uveal melanoma cells.

Methods

Human uveal melanoma cells isolated from tissues of enucleated eyes were treated with zeaxanthin in a dose- and time-dependent manner. After zeaxanthin treatment, cell viability was measured using MTT assay. The proapoptotic and antiproliferative effects were evaluated by -annexin V staining and flow cytometry respectively. Mitochondrial transmembrane potential was measured as a function of drug treatment using 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-benzamidazolocarbocyanin iodide (JC-1). Immunoblotting was used to evaluate the expression of apoptosis-related proteins. Caspase-9 and -3 activities were determined by spectroflurometry.

Results

Zeaxanthin induced apoptosis in dose- and time-dependent manner. Decrease in the level of Bcl-2 and increase in the level of Bax were observed in zeaxanthin-treated in human uveal melanoma cells. Preceding cell death, zeaxanthin evoked a rapid dissipation of mitochondrial transmembrane potential. This was followed by the release of cytochrome c into the cytoplasm and a substantial increase in the activities of caspase-9 and -3.

Conclusions

These results demonstrate that zeaxanthin induces apoptosis through the regulation of Bcl-2 family protein and activation of intrinsic mitochondrial pathway. This may warrant further exploration as an adjuvant to conventional anticancer therapies for uveal melanoma.

Citation Format: Sandeep Goswami, Arpna Srivastava, Neelam Pushker, Mandeep Singh Bajaj, Seema Kashyap, Jasbir Kaur. Induction of apoptosis by zeaxanthin in human uveal melanoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3812. doi:10.1158/1538-7445.AM2015-3812