Metabolism studies in breast cancer

Metabolic reprogramming has emerged as a common phenotype of cancers. Otto Warburg in 1920s observed that cancer cells consume higher amounts of glucose for their metabolism producing high levels of lactate even in normal oxygen conditions, this has been termed as the Warburg effect. In breast cancer, this seemingly wasteful metabolism of glucose is mirrored by a similarly inefficient metabolism of glutamine.
Glutamine is the most abundant amino acid in plasma and it constitutes another important source of energy besides glucose. Glutamine serves as a precursor in nucleotide, glucose and amino acid biosynthesis, glutathione metabolism, protein synthesis and lipid synthesis through the mitochondrial or cytosolic conversion into citrate. It has long been known that tumour cells metabolize glutamine at significantly greater rates than any other amino acid, and glutamine transporter.
Importantly, glutamine transporter and glutaminase expression has also been found to be upregulated in cancer versus normal tissues.
Our group has previously shown the anti-proliferative effect of metformin, which is enhanced in glutamine, deprived conditions; this has also been validated in a preclinical study. To investigate the active role of glutamine in breast cancer and the variable sensitivity in different cell lines, we worked on drugs affecting the glutamine metabolism. Breast cancer cell lines (MDA- MB 231, MDA MB-468, SKBR3, MCF 7, HCC 1806, T47D and BT474) were treated with glutamine dehydrogenase (GLUD) inhibitor bithionol (BT) and other drugs affecting glutamine metabolism including metformin and Phenylbutyrate.
The cytotoxic effects of BT against a panel of breast cancer cell lines were observed. Furthermore, apoptotic cell death was shown by expression of cPARP and confirmed by FACS. BT induced autophagy in breast cancer cell lines, which results in significant reduction in tumour growth as evidenced by LC3 B and LAMP 1 expression. Electron microscopy of the MCF 7 and MDA MB 231 cell lines (20 μM BT, 24 hour exposure) showed increased autophagosome, lysosomes and autolysosomes confirming autophagy in these treated cell lines.
Much of the interest in glutamine has stemmed from the discovery that the proto-oncogene Myc plays a role in the regulation of its metabolism. Myc transformed cells have been shown to be especially sensitive to glutamine withdrawal and subsequently it has been demonstrated that Myc induces the gene expression of several enzymes involved in glutamine metabolism. The importance of glutamine in supporting cancer cell proliferation and providing carbon for lipid synthesis has been shown to be of greater importance at times of mitochondrial stress with the reductive carboxylation pathway allowing glutamine to bypass the TCA cycle in its conversion to citrate.
Bithionol (BT) is an anthelmintic used to treat Fascioliasis (liver flukes) in humans (Bacq et al., 1991). Fascioliasis is a trematode infection caused by Fasciola hepatica, involving the liver and biliary tract. However, recently due to the advent of newer drugs, this drug is used only in veterinary medicine. Mounting evidence suggests BT inhibits tumour growth in ovarian, melanoma and breast cancer cell lines (Braddock, 2010, Saunders et al., 2008).
My DPhil focuses on the sensitivity of different breast cancer subtypes on drugs/ conditions affecting glutamine metabolism and providing a unique opportunity in developing a new approach to increase anticancer efficacy by targeting glutamine metabolism in breast cancer. Also, BT may play a key role in inhibiting growth of breast cancer cells and targeting GLUD maybe a therapeutic option in this disease. Its role will be further validated in vivo xenograft models and in human samples in my DPhil study.

Advisor: Harris, A