Mechanism of extracellular citrate uptake and metabolism in cancer; specificity and potential use of gluconate in cancer therapy

• Applicants: Professor Dr. Jerzy Adamski; Professor Edward K. Geissler, Ph.D.
• Subject Area: General and Visceral Surgery
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411622433

To metastasize and proliferate, cancer cells need to adjust their metabolism to the increased need for energy and protein synthesis. Warburg effect, the switch from oxidative phosphorylation to anaerobic glycolysis, is considered a hallmark of cancer. Interestingly, citrate as the primary substrate in fatty acid synthesis occupies a central role in cancer cell metabolism, and therefore has been studied extensively. The source of citrate in cancer cells presents a particularly interesting and important question because mitochondria which supply citrate necessary for normal cell metabolism are known to have reduced activity in cancer. Alternatively, glutamine reductive carboxylation has been suggested as the main source of citrate in malignant cells. We have recently discovered that cancer cells unexpectedly take up extracellular citrate and use it to support their metabolism. Plasma membrane citrate transporter (pmCiC) was cloned from cancer cells and determined to be responsible for citrate import. Moreover, our studies indicate that the pmCiC is expressed in human tissues and its expression is mainly restricted to cancer cells, correlating with their stage and metastatic potential. Importantly, we have found gluconate to be an irreversible inhibitor of the pmCiC and show in pilot experiments that treatment of experimental pancreatic cancer with gluconate in vivo results in significantly decreased cancer growth and markedly changes metabolic characteristics of tumor tissues.In the present project we will: (1) study the mechanisms of citrate uptake and metabolism by cancer cells, (2) stably silence pmCiC using CRISPR-Cas9 technique, (3) determine the specificity of gluconate towards pmCiC and test effects of gluconate on cancer versus benign cells, (4) test therapeutic effects of pmCiC inhibition through stable silencing or with gluconate on cancer development in a preclinical in vivo model, (5) more precisely determine pmCiC expression in normal versus cancer cells, and (6) determine pmCiC expression as a marker of tumor progression/stage.The proposed studies will further reveal this novel mechanism supporting cancer cell metabolism that can potentially be exploited therapeutically to treat cancer. Furthermore, determination of citrate transporter expression in human tissues will be useful in establishing its potential as a molecular marker of cancer progression.

• DFG Programme: Research Grants