Modulation of DNA Damage Response by SAM and HD Domain Containing Deoxynucleoside Triphosphate Triphosphohydrolase (SAMHD1) Determines Prognosis and Treatment Efficacy in Different Solid Tumor Types

SIMPLE SUMMARY: Ample evidence exists connecting dNTP pool dysregulation to cancer and genomic instability. SAMHD1, the unique dNTP triphosphohydrolase described in humans, has been proposed to play a key role in hematological cancers, although its value in advanced solid tumors has not yet been explored. Moreover, it has been proposed that SAMHD1 might fulfill the requirements of a driver gene in tumor development or might promote a so-called mutator phenotype. Here, we show that low SAMHD1 expression tumors show better prognosis in breast, ovarian, and lung advanced cancer. Moreover, low SAMHD1 expression is a positive predictive factor in lung and ovarian cancer treated with platin derivates and/or antimetabolites. In vitro evaluation of its underlying mechanism revealed that SAMHD1 KO cells presented enhanced susceptibility to DNA damage and subsequent induction of apoptosis of tumor cells. Our results provide strong evidence of the clinical importance of SAMHD1, becoming an interesting target for the development of personalized cancer treatments. ABSTRACT: SAMHD1 is a deoxynucleotide triphosphate (dNTP) triphosphohydrolase with important roles in the control of cell proliferation and apoptosis, either through the regulation of intracellular dNTPs levels or the modulation of the DNA damage response. However, SAMHD1′s role in cancer evolution is still unknown. We performed the first in-depth study of SAMHD1′s role in advanced solid tumors, by analyzing samples of 128 patients treated with chemotherapy agents based on platinum derivatives and/or antimetabolites, developing novel in vitro knock-out models to explore the mechanisms driving SAMHD1 function in cancer. Low (or no) expression of SAMHD1 was associated with a positive prognosis in breast, ovarian, and non-small cell lung cancer (NSCLC) cancer patients. A predictive value was associated with low-SAMHD1 expression in NSCLC and ovarian patients treated with antimetabolites in combination with platinum derivatives. In vitro, SAMHD1 knock-out cells showed increased γ-H2AX and apoptosis, suggesting that SAMHD1 depletion induces DNA damage leading to cell death. In vitro treatment with platinum-derived drugs significantly enhanced γ-H2AX and apoptotic markers expression in knock-out cells, indicating a synergic effect of SAMHD1 depletion and platinum-based treatment. SAMHD1 expression represents a new strong prognostic and predictive biomarker in solid tumors and, thus, modulation of the SAMHD1 function may constitute a promising target for the improvement of cancer therapy.