Inhibition of cholesterol metabolism underlies synergy between mTOR pathway inhibition and chloroquine in bladder cancer cells

Abstract

Mutations to fibroblast growth factor receptor 3 (FGFR3) and phosphatase and tensin homologue (PTEN) signalling pathway components (for example, PTEN loss, PIK3CA, AKT1, TSC1/2) are common in bladder cancer, yet small-molecule inhibitors of these nodes (FGFR/PTENi) show only modest activity in preclinical models. As activation of autophagy is proposed to promote survival under FGFR/PTENi, we have investigated this relationship in a panel of 18 genetically diverse bladder cell lines. We found that autophagy inhibition does not sensitise bladder cell lines to FGFR/PTENi, but newly identify an autophagy-independent cell death synergy in FGFR3-mutant cell lines between mTOR (mammalian target of rapamycin) pathway inhibitors and chloroquine (CQ)—an anti-malarial drug used as a cancer therapy adjuvant in over 30 clinical trials. The mechanism of synergy is consistent with lysosomal cell death (LCD), including cathepsin-driven caspase activation, and correlates with suppression of cSREBP1 and cholesterol biosynthesis in sensitive cell lines. Remarkably, loss of viability can be rescued by saturating cellular membranes with cholesterol or recapitulated by statin-mediated inhibition, or small interfering RNA knockdown, of enzymes regulating cholesterol metabolism. Modulation of CQ-induced cell death by atorvastatin and cholesterol is reproduced across numerous cell lines, confirming a novel and fundamental role for cholesterol biosynthesis in regulating LCD. Thus, we have catalogued the molecular events underlying cell death induced by CQ in combination with an anticancer therapeutic. Moreover, by revealing a hitherto unknown aspect of lysosomal biology under stress, we propose that suppression of cholesterol metabolism in cancer cells should elicit synergy with CQ and define a novel approach to future cancer treatments.

Identification of Pharmacodynamic Transcript Biomarkers in Response toFGFRInhibition by AZD4547

“…5B). This is also in agreement with other publications suggesting an overlap in the FGFR and PI3K/ AKT pathways (3,6,21,37,38).…”

Polymeric chloroquine as an inhibitor of cancer cell migration and experimental lung metastasis

“…Upregulation of autophagy promotes tumorigenesis and tumor aggressiveness [28, 29]. CQ is among several autophagy inhibitors that have been tested in combination with other anticancer drugs [18, 19, 24, 30, 31]. Although the mechanism of action is still not fully understood, CQ is believed to inhibit autophagy in cancer cells by preventing the fusion of autophagosomes and lysosomes.…”

“…Although CQ and HCQ were initially tested in cancer treatment due to their ability to inhibit autophagy, we now know that their therapeutic effect depends on other mechanisms as well [21–23]. For example, a recent report revealed that CQ-induced cancer cell death was related to its inhibitory effects on cholesterol metabolism [24]. Taking advantage of its recently uncovered CXCR4 antagonism, CQ was able to inhibit CXCR4/CXCL12-mediated pancreatic cancer cell invasion and proliferation in vitro, to eliminate established tumors, and to improve overall survival when combined with gemcitabine in vivo [15].…”

Novel organometallic chloroquine derivative inhibits tumor growth

“…Since our in vitro cytotoxicity studies demonstrated that CMQ outperforms traditional quinolones at killing cancer cells, we sought to determine whether CMQ shared a similar mechanism of action with CQ and HCQ. CQ and HCQ accumulate in lysosomal compartments and disrupt lysosomal functions, including lysosome‐associated autophagy, although these compounds may also be inhibiting other cellular processes that are dependent upon lysosomal integrity . To determine whether differences between CMQ and CQ cytotoxic activity were due to biovailability and subsequent accumulation of these compounds in various cellular compartments, we used a cell fractionation approach coupled with high sensitivity measurement of drug analytes by HPLC‐MS/MS.…”