Metastatic renal cell carcinoma (RCC) is incurable. IFNα or IL-2 immunotherapy has been used for RCC for more than 20 years, but response rates remain low and these cytokines can generate toxic. More recently, administration of multikinase inhibitors or anti-VEGF receptor mAb has become popular, but these agents are largely palliative and tumor regression is common. The shortcomings in current therapeutic options for patients with metastatic RCC provide the rationale for the development of novel treatment protocols. Triptolide, a diterpene triepoxide from the medicinal herb Tripterygium wilfordii, can suppress cell growth and induce apoptosis in a range of human tumor cells. Further, triptolide also sensitizes tumor cells to TNF-related apoptosis-inducing ligand (TRAIL). The objective of this study was to determine the effectiveness of combining triptolide with TRAIL receptor agonists against RCC. In vitro, the combination of triptolide and recombinant human TRAIL protein decreased cell viability in the human RCC cell line ACHN cells compared with either treatment alone. This decrease in viability correlated with increased induction of apoptosis (positive Annexin V staining) and caspase activation. The triptolide-induced sensitization was accompanied by decreased HSP70, HSP27, and HSF1 expression, as well as increased surface expression of TRAIL-R2. Similar in vitro treatment of the mouse renal cell adenocarcinoma cell line, Renca, demonstrated that triptolide enhanced the killing of these cells by membrane-bound TRAIL or agonistic anti-DR5 mAb. In vivo treatment of mice bearing orthotopic and metastatic Renca tumors showed that combination therapy consisting of minnelide (a water soluble version of triptolide) and agonistic anti-DR5 mAb resulted in significantly decreased tumor burden and increased animal survival compared to either therapy alone. Collectively, our data suggest that triptolide sensitizes RCC cells to TRAIL-induced apoptosis, which is accompanied by decreased heat shock protein expression and altered TRAIL receptor expression. These data also suggest that the combination of TRAIL receptor agonists and triptolide may prove to be an effective treatment for metastatic RCC, especially at doses that show suboptimal tumoricidal activity when used individually.
Citation Format: Thomas S. Griffith, Erik L. Brincks, Tamara A. Kucaba, Britnie R. James, Veena Sangwan, Sulagna Banerjee, Ashok Saluja. Effective therapy for advanced renal cell carcinoma using triptolide and TRAIL receptor agonists. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2271. doi:10.1158/1538-7445.AM2014-2271