Abstract B29: In vivo alteration of nucleoside pools does not lead to carcinogenesis but rather protects from fatty liver caused by anti-neoplastic agents.
Authors: Le Thuc Tim , Urasaki Yasuyo , Kirsh Robert , Pizzorno Giuseppe 
Published: May 2015

Imbalance in the concentrations of nucleotides and deoxynucleotides essential for the replication, recombination and repair of DNA has been shown extensively in vitro to induce mutations through misinsertion of incorrect dNTP, insertion-deletion errors and DNA strand misalignment, therefore reducing the fidelity of DNA synthesis. However the consequences of nucleosides-nucleotides imbalances have not been fully explored in vivo in a mammalian system.

We have recently generated murine models with altered expression of uridine phosphorylase 1 (UPP1) leading to disruption of uridine homeostasis and causing severe nucleotide pools imbalances. We generated a UPP1 knockout model where we nullified the nucleoside phosphorolytic activity in all tissues except liver that showed a residual activity below 10% due to the expression of hepatic uridine phosphorylase 2. We also developed a UPP1 transgenic model with ubiquitous overexpression of UPP1. Both models have shown altered plasma and tissue levels of uridine and changes in nucleotide deoxy-nucleotide pools, however, we did not detect abnormalities in their growth, development, sexual maturation and reproductive ability and we did not observe any neoplastic growth, possibly associated to induced mutations, even after 22 months of age. We were able to observe changes in sensitivity to fluoropyrimidines: the UPP1 knockout mice resulted to be more resistant to 5-fluorouracil (5-FU) toxicity, therefore able to tolerate a dosage 75% higher than the control C57/Bl6 mice; on the contrary the UPP1 transgenic mice were only able to stand a dose of 5-FU that was 40% less than the control mice. These effects are likely to be attributed to changes in the activation of 5-FU to 5-fluorouridine, particularly in the gastrointestinal tract.

Surprisingly, our UPP1 murine models unveiled a linkage between uridine homeostasis and liver lipid metabolism. We discovered that uridine is an effective suppressor of fatty liver induced by multiple drugs with unrelated acting mechanisms. Among others, tamoxifen, an antagonist of the estrogen receptor in breast tissue, the therapy of choice for hormone receptor-positive breast cancer in pre-menopausal women; and methotrexate, an antifolate antimetabolite used alone or in combination for the treatment of a number of cancers including: breast, head and neck, leukemia, lymphoma and osteosarcoma.

We have so far identified a number of target proteins whose expression or post-translational modifications are affected by uridine. These proteins participate in liver energy metabolism including mitochondrial respiration, peroxisomal and mitochondrial fatty acid β-oxidation, and transport of fatty acids, triacylglycerides, and lipoproteins. We are currently in the process of establishing if these changes are the result of a direct uridine effect or a defect in the rate of translation initiation and/or other steps in the translation process due to alterations in the size of nucleotide pools.

Citation Format: Thuc Tim Le, Yasuyo Urasaki, Robert Kirsh, Giuseppe Pizzorno. In vivo alteration of nucleoside pools does not lead to carcinogenesis but rather protects from fatty liver caused by anti-neoplastic agents.. [abstract]. In: Proceedings of the AACR Special Conference: The Translational Impact of Model Organisms in Cancer; Nov 5-8, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(11 Suppl):Abstract nr B29.