Doxorubicin (Dox) is an effective antineoplastic drug with serious cardiotoxic side effects that persist after drug withdrawal and can lead to heart failure. Dysregulation of vascular endothelium has been linked to the development of Dox-induced cardiotoxicity, but it is unclear whether and how transient exposure to Dox leads to long-term downregulation of Endothelial Vascular Endothelial Growth Factor Receptor type2 (VEGFR2), essential for endothelial cells function. Using an in vitro model devised to study the long-lasting effects of brief endothelial cells exposure to Dox, we show that Dox leads to sustained protein synthesis inhibition and VEGFR2 downregulation. Transient Dox treatment led to the development of long-term senescence associated with a reduction in VEGFR2 levels that persisted days after drug withdrawal. By analyzing VEGFR2 turnover, we ruled out that its downregulation was depended on Dox-induced autophagy. Conversely, Dox induced p53 expression, reduced mTOR-dependent translation, and inhibited global protein synthesis. Our data contribute to a mechanistic basis to the permanent damage caused to endothelial cells by short-term Dox treatment.

SAMHD1 is the major catabolic enzyme regulating the intracellular concentrations of DNA precursors (dNTPs). The S-phase kinase CDK2-cyclinA phosphorylates SAMHD1 at Thr-592. How this modification affects SAMHD1 function is highly debated. We investigated the role of endogenous SAMHD1 phosphorylation during the cell cycle. Thr-592 phosphorylation occurs first at the G1/S border and is removed during mitotic exit parallel with Thr-phosphorylations of most CDK1 targets. Differential sensitivity to the phosphatase inhibitor okadaic acid suggested different involvement of the PP1 and PP2 families dependent upon the time of the cell cycle. SAMHD1 turn-over indicates that Thr-592 phosphorylation does not cause rapid protein degradation. Furthermore, SAMHD1 influenced the size of the four dNTP pools independently of its phosphorylation. Our findings reveal that SAMHD1 is active during the entire cell cycle and performs an important regulatory role during S-phase by contributing with ribonucleotide reductase to maintain dNTP pool balance for proper DNA replication.

Doxorubicin remains a mainstay of cancer therapy, yet its clinical use is constrained by severe cardiotoxicity, classically attributed to cardiomyocyte death. Here, we identify endothelial inflammation driven by mitochondrial DNA (mtDNA) turnover and release as a critical mediator of doxorubicin-induced cardiac injury. In vivo , a standard doxorubicin regimen activates the cGAS–STING innate immune pathway in endothelial cells before cardiomyocyte dysfunction or death occurs. Mechanistically, doxorubicin recruits the stress-inducible ribonucleotide reductase subunit RRM2B (p53R2) that normally sustains the mitochondrial deoxyribonucleotide pool, to promote aberrant mtDNA turnover and release, fuelling sterile inflammation. The FDA-approved BAX inhibitor Eltrombopag suppresses mtDNA release, attenuates endothelial inflammation, and prevents doxorubicin cardiotoxicity in vivo without compromising anticancer efficacy. These findings reveal an unrecognized proinflammatory role of RRM2B and establish endothelial inflammation as a central driver of chemotherapy-related cardiac injury, identifying the cardiac endothelium as a tractable target for cardioprotection during cancer treatment.