Glucose Metabolism & Radiotherapy Resistance

Clinical research performed by our group at Washington University School of Medicine has defined an essential role for pre-treatment and post-treatment 18F-fluoro-deoxy-glucose (FDG)-PET scanning for patients with cervical cancer.  We have found that cervical tumors with increased FDG uptake on pretreatment PET scans have inferior outcomes after primary radiation.  FDG uptake in human tumors decreases rapidly during the course of radiation treatments, and tumors with residual FDG uptake after treatment are likely to recur.  In the laboratory we have found that alterations in expression of genes from the PI3K pathway are associated with residual FDG uptake in human cervical tumors after radiation.

Effects of the AKT inhibitor SC-66 on glucose transport in cervical cancer cells. A) C33A cells were treated with SC-66 (35 µg/ml) for 30 minutes prior to incubation with 18F-fluorodeoxyglucose. The graph represents counts per minute values, p<0.01 for the comparison of FDG alone (cells only) versus FDG + SC-66. B) C33A cells were treated with SC-66 (0–5 µg/ml) for 3 and 24 h. Glut1 levels were analyzed by Western blot. C) C33A cells were treated with SC-66 (0, 1 and 5 µg/ml) for 24 h. Membrane and cytosol fractions were separated. Glut1 and Glut4 expression was determined by Western blot. D) Immunofluorescence was performed on C33A cells after SC-66 treatment. 

We have found that AKT inhibitors limit glucose uptake, glycolysis and tumor cell viability in preclinical models. We are currently studying how activating and inactivating mutations in genes within the PI3K pathway affect tumor glucose metabolism and the response to radiation therapy.

Recently, we have been evaluating the sensitivity of cervix cancer to inhibition of glycolysis using preclinical models both in vitro and in vivo. Similar to what we see in our patients, some cervical cancer cell lines take up large quantities of glucose, and these cell line are resistant to radiation therapy. 2-DG, similar to FDG, is taken up by glucose transporters and phosphorylated by hexokinase, but cannot transition further down the glycolytic pathway.  2-DG enhances the effects of cisplatin only minimally, and sensitizes highly glycolytic cells to irradiation.  Interestingly, when 2-DG is combined with inhibitors of glutathione (BSO) and thioredoxin metabolism (AUR), 2 key pathways necessary for maintenance of intracellular redox homeostasis, highly glycolytic cell lines are unable to form colonies in vitro and significant tumor growth delay is observed in vivo.  For cervical cancer tumor lines that display intermediate levels of glucose uptake, simultaneous treatment with 2-DG, BSO and AUR can be used to radio-sensitize cervical cancer tumor lines at clinically relevant radiation doses both in vitro and in vivo.  This drug strategy is appealing for clinical translation because all 3 drugs have been approved for human use, and demonstrate significantly less toxicity than cisplatin monotherapy in preclinical models.  We are currently optimizing our strategy for radio-sensitization in the context of standard of care chemoradiation and developing clinical trials that will test this strategy in our patients.