Edwin W. Lai

Targeting GLUT1 and the Warburg effect in renal cell carcinoma by chemical synthetic lethality

A screen identifies a drug that specifically kills glycolysis-dependent cancer cells by inhibiting glucose uptake. Cancer’s Achilles’ Heel A quick tug on a fuel line can stop a car dead in its tracks. Similarly, depriving a cancer cell of its energy source can bring proliferation to a standstill. Chan et al. devised a drug discovery assay that took advantage of the fact that some kidney cancer cells depend on glucose for survival. By screening 64,000 small molecules, the authors found a class of drug that inhibits the glucose transporter and selectively impairs growth of these cancer cells in cultures and in animals. Certain kidney and other types of cancer cells lack the von Hippel–Lindau (VHL) tumor suppressor protein. This deficiency reorients carbohydrate metabolism so that the cancer cells depend on aerobic glycolysis—the conversion of glucose to lactate—rather than the more typical oxidative phosphorylation for a supply of energy. The drug identified by the authors, STF-31, was toxic to the VHL-deficient kidney tumor cells but, unlike many other cancer drugs, did not induce autophagy, apoptosis, or DNA damage. Rather, STF-31 exploited the fact that inactivation of VHL increases the activity of hypoxia-inducible factor transcription factor, which in turn stimulates the transcription of genes involved in glucose metabolism, including the glucose transporter–encoding gene GLUT1. By binding directly to the transporter, STF-31 blocked glucose uptake in VHL-deficient cancer cells but not in those with intact VHL; with their sugar delivery system stymied, the tumor suppressor–deprived cancer cells ceased glycolysis and thus adenosine 5′-triphosphate production and succumbed to necrosis. An extra benefit of the new agent is that its activity can be easily visualized, even deep inside an animal. Glucose uptake in a tumor can be monitored by fluorodeoxyglucose positron emission tomography. The reduction in glucose metabolism forced on tumors by STF-31 was detected in mice with this method—an approach that can be readily applied to humans to test the drug’s efficacy. If it can thwart the fuel supply line in human cancers, this promising drug likely will bring tumor thriving to a halt. Identifying new targeted therapies that kill tumor cells while sparing normal tissue is a major challenge of cancer research. Using a high-throughput chemical synthetic lethal screen, we sought to identify compounds that exploit the loss of the von Hippel–Lindau (VHL) tumor suppressor gene, which occurs in about 80% of renal cell carcinomas (RCCs). RCCs, like many other cancers, are dependent on aerobic glycolysis for ATP production, a phenomenon known as the Warburg effect. The dependence of RCCs on glycolysis is in part a result of induction of glucose transporter 1 (GLUT1). Here, we report the identification of a class of compounds, the 3-series, exemplified by STF-31, which selectively kills RCCs by specifically targeting glucose uptake through GLUT1 and exploiting the unique dependence of these cells on GLUT1 for survival. Treatment with these agents inhibits the growth of RCCs by binding GLUT1 directly and impeding glucose uptake in vivo without toxicity to normal tissue. Activity of STF-31 in these experimental renal tumors can be monitored by [18F]fluorodeoxyglucose uptake by micro–positron emission tomography imaging, and therefore, these agents may be readily tested clinically in human tumors. Our results show that the Warburg effect confers distinct characteristics on tumor cells that can be selectively targeted for therapy.

SAR Studies of 4-Pyridyl Heterocyclic Anilines that Selectively Induce Autophagic Cell Death in von Hippel-Lindau-Deficient Renal Cell Carcinoma Cells

We recently identified a class of pyridyl aniline thiazoles (PAT) that displayed selective cytotoxicity for von Hippel-Lindau (VHL) deficient renal cell carcinoma (RCC) cells in vitro and in vivo. Structure-activity relationship (SAR) studies were used to develop a comparative molecular field analysis (CoMFA) model that related VHL-selective potency to the three-dimensional arrangement of chemical features of the chemotype. We now report the further molecular alignment-guided exploration of the chemotype to discover potent and selective PAT analogues. The contribution of the central thiazole ring was explored using a series of five- and six-membered ring heterocyclic replacements to vary the electronic and steric interactions in the central unit. We also explored a positive steric CoMFA contour adjacent to the pyridyl ring using Pd-catalysed cross-coupling Suzuki-Miyaura, Sonogashira and nucleophilic displacement reactions to prepare of a series of aryl-, alkynyl-, alkoxy- and alkylamino-substituted pyridines, respectively. In vitro potency and selectivity were determined using paired RCC cell lines: the VHL-null cell line RCC4 and the VHL-positive cell line RCC4-VHL. Active analogues selectively induced autophagy in RCC4 cells. We have used the new SAR data to further develop the CoMFA model, and compared this to a 2D-QSAR method. Our progress towards realising the therapeutic potential of this chemotype as a targeted cytotoxic therapy for the treatment of RCC by exploiting the absence of the VHL tumour suppressor gene is reported.

Abstract 67: Selective cytotoxic targeting of von Hippel-Lindau-deficient renal cell carcinoma cells

Loss of the von Hippel-Lindau (VHL) tumor suppressor gene, an essential alteration in the development of renal cancer, can be targeted through a synthetic lethal manner. In our screen we identified a compound, STF-31536, which is selectively cytotoxic toward VHL-deficient renal cancer cells in a HIF-dependent manner. This compound did not induce apoptosis and inhibits glucose transport. These findings are significant since we have previously shown another compound STF-62247 was cytotoxic toward VHL-deficient cells and induced autophagy in a HIF-independent manner. We have also shown that STF-31536 induces cell death in vitro and in vivo, however the mechanism and target of this compound is currently unknown. In order to identify the target of STF-31536, we have coupled analogs of STF-31536 to an affinity resin. Activity of these analogs was confirmed by cytotoxicity assays. Selected affinity chromatography reagents coupled to resin were used for binding assays to determine direct drug-target interactions. The potential targets were purified and identified by gel electrophoresis after collecting fractions from the column. Renal cell carcinoma cells deficient in VHL are characterized by elevated expression of VEGF and glucose transporter 1 (Glut-1). Immunoblots for Glut-1 transporter in protein fractions eluted from the column show binding of STF-31536 to Glut-1. Therefore, we show loss of the von Hippel-Lindau (VHL) tumor suppressor gene can be targeted by this small molecule through a synthetic lethal manner by disrupting glucose transport. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 67.