Exploring the relationship between cancer metabolism and oncolytic adenoviruses

Tumour cells exhibiting the Warburg effect rely mostly upon aerobic glycolysis for ATP production and have a notable addiction to anaplerotic use of glutamine for macromolecular synthesis. This strategy maximises cellular biosynthetic potential and provides an attractive anabolic environment for viral infection. Here, we evaluate infection of highly permissive cells (A549 cells) and poorly permissive cells (SKOV3) with wildtype adenoviruses, and the oncolytic chimeric adenovirus enadenotucirev (EnAd) to probe the role of metabolism on the success of oncolytic virotherapy with EnAd. All adenoviruses caused an increase in glucose and glutamine uptake along with increased lactic acid secretion in their host cells, mirroring the canonical Warburg effect phenotype. Through identifying the IC50 of a panel of cancer cells, we identify a correlation showing that cells which rely upon aerobic glycolysis tend to be more permissive to EnAd oncolysis. The virus lifecycle of both wildtype adenoviruses and EnAd were critically dependent on exogenous glutamine. Virus activity in glutamine-free cells was rescued with exogenous membrane-permeable α-ketoglutarate, but not pyruvate or oxaloacetate, suggesting an essential role for reductive carboxylation in glutamine usage. We propose that this unusual glutamine metabolism is beneficial for the production of biosynthetic intermediates, particularly under conditions of hypoxia or decreased cellular respiration as is often seen during adenovirus infection. Counterintuitively, restricting glycolysis using 2-deoxyglucose or by limiting glucose supply strongly improved virus activity in both cell types. Antagonism of glycolysis also boosted EnAd replication and transgene expression within human tumour biopsies, and in xenografted tumours in vivo. We further bolstered this finding through weaning SKOV3 cells off of glucose. This process created a cell line which is highly permissive to EnAd infection and lysis. Finally, we engineered an “armed” EnAd expressing the glycolysis inhibitor TIGAR which was able to lyse cells whilst expressing TIGAR without causing acidification of the media. These findings emphasise the importance of metabolism on productive viral infections which is of particular significance for viruses restricted to replicate in tumours, that already display aberrant metabolic phenotypes.