Abstract 1294: Sensitization of malignant melanomas to TRAIL-induced apoptosis by quercetin

Abstract Skin cancer is among the most commonly-diagnosed cancers with malignant melanoma being associated with the highest rate of metastasis and mortality. In its early stage, melanoma is easily cured, but the prognosis associated with metastatic malignant melanoma remains very poor and is one of the most treatment-refractory malignancies. We propose the application of Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL) as a potential therapeutic for malignant melanoma. TRAIL induces apoptosis in a broad range of transformed human cells while showing minimal toxicity towards non-malignant cells. However, some cancers are resistant to TRAIL, specifically certain melanomas, caused by lack of TRAIL receptors or upregulation of antiapoptotic proteins. Here we analyze the naturally-occurring flavonoid quercetin as a potential cotreatment with TRAIL to overcome the intrinsic resistance of melanoma. Found in a wide variety of sources from onions and apples to red wine, quercetin is a good candidate for TRAIL cotreatment due to its ability to upregulate TRAIL receptors and downregulate antiapoptotic proteins. We have evaluated our cotreatment of TRAIL plus quercetin on four malignant melanoma cells lines which harbor mutations in the MAPK pathway, namely A375 and WM164 (BRAF mutant), SK-Mel-2 (NRAS mutant) and MeWo (BRAF WT, NRAS WT). Numerous cell-based assays were utilized including antiproliferative SRB assay, apoptotic AnnexinV/PI assay and western blot analysis probing for key proteins of the apoptotic cascade. Out of the four melanoma cell lines evaluated, A375 and SK-Mel-2 were sensitive to TRAIL dose-dependently; whereas, MeWo and WM164 were resistant to TRAIL-induced apoptosis, even at the highest tested treatment concentration of 1μg/ml. Quercetin, as a single agent, was able to induce apoptosis in a dose-dependent manner in all four melanoma cell lines. To determine if the cotreatment, TRAIL plus quercetin, is able to sensitize melanoma cells to TRAIL-induced apoptosis, we treated resistant cell lines, MeWo and WM164 with 250 ng/ml TRAIL plus sub-cytotoxic concentrations of quercetin, 25 and 50 μM. Quercetin was able to sensitize both MeWo and WM164 to TRAIL-induced apoptosis marked by the fragmentation of PARP, a hallmark of apoptosis, and the activation of executioner caspases 3, 6 and 7. Specifically, quercetin was able to sensitize resistant melanomas to undergo TRAIL-induced apoptosis as evidenced by the cleavage of procaspase 8 to caspase 8, a marker for the initiation of TRAIL-induced apoptosis. Quercetin also promoted the TRAIL-mediated activation of the intrinsic pathway of apoptosis marked by the release of cytochrome C from the mitochondria. These preliminary data demonstrate that quercetin is a good potential cotreatment for TRAIL; however, further research is needed to reveal the mechanism of quercetin sensitization of TRAIL-resistant melanomas and its role in TRAIL receptor and antiapoptotic protein expression. Citation Format: Katherine Turner, Daniel Lindner, Michael Kalafatis. Sensitization of malignant melanomas to TRAIL-induced apoptosis by quercetin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1294.