Abstract 3219: Targeting lipid metabolism and ER stress in renal cell carcinoma by englerin A

Renal cell carcinoma (RCC) is among the top ten most common forms of cancer and is the leading malignancy of the kidney. Clear cell renal carcinoma (cc-RCC), the most frequent type of RCC, is one of the most refractory cancers with an incidence that is on the rise. The two-year survival rate for patients with metastatic disease is under 20% despite approved targeted therapies. Hence, there is an urgent need to investigate novel agents. Screening of plant extracts in search of new anti-cancer agents resulted in the discovery of englerin A (EA), a guaiane sesquiterpene with potent cytotoxicity against RCC and a small subset of other cancers. Although a few cellular targets have been identified for EA, in most instances, modulation of these targets required concentrations of EA much higher than that required to kill tumor cells highly sensitive to EA. Hence, it is still not clear what mechanisms account for the cytotoxicity of EA in tumor cells highly sensitive to EA. Unlike any prior study, the current study used a systems biology approach to explore the mechanism(s) of action of EA. Metabolomics analyses were conducted after treatment of human RCC A498 cells with 100 nM EA for 24 and 48 h. Pathway analysis revealed that 88% of the metabolic disturbance associated with englerin A at 24 h was due to changes in lipid metabolism. In particular, among the top metabolites, several ceramides and glucosylceramides increased up to 18- and 178-fold, respectively. On the other hand, all sphingomyelins decreased up to 5.5-fold. Furthermore, EA induced depletion in phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine phospholipids. At 48 h of englerin A treatment, the main findings from pathway analysis were the accumulation of fatty acylcarnitine derivatives, purines, pyrimidines, and phosphatidyl serine phospholipids, as well as the depletion of reduced glutathione indicating dysfunctional mitochondria and oxidative stress. Moreover, microarray analyses determined that EA (100 nM) induced ER stress signaling and an acute inflammatory response including interferon signaling, likely due to the generation of ceramides which were toxic to both A498 and UO-31 renal cancer cells. Quantitative PCR and Western Blot analyses confirmed that EA induced both the unfolded protein and acute inflammatory response. Furthermore, fluorescence confocal microscopy revealed that EA at 25 nM disrupted the morphology of the ER confirming the deleterious effect of EA on the ER. Collectively, our findings suggest that cc-RCC is highly sensitive to disruptions in lipid metabolism and ER stress and that these vulnerabilities can be targeted for the treatment of cc-RCC and possibly other lipid storing cancers. Furthermore, our results also suggest that ceramides may be a mediator of some of the actions of EA. Lastly, the acute inflammatory response induced by EA may mediate anti-tumor immunity. Note: This abstract was not presented at the meeting. Citation Format: Ayse Batova, Diego Altomare, Kim E. Creek, Robert K. Naviaux, Lin Wang, Kefeng Li, Erica Green, Richard Williams, Jane C. Naviaux, Mitchell Diccianni, Alice L. Yu. Targeting lipid metabolism and ER stress in renal cell carcinoma by englerin A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3219. doi:10.1158/1538-7445.AM2017-3219