Osteosarcoma (OS) is the most common bone tumor in children and adolescents. Modern OS treatment, based on the combination of neoadjuvant chemotherapy (cisplatin + doxorubicin + methotrexate) with subsequent surgical removal of the primary tumor and metastases, has dramatically improved overall survival of OS patients. However, further research is needed to identify new therapeutic targets. Here we report that expression level of the nuclear NAD synthesis enzyme, nicotinamide mononucleotide adenylyltransferase-1 (NMNAT1), increases in U-2OS cells upon exposure to DNA damaging agents, suggesting the involvement of the enzyme in the DNA damage response. Moreover, genetic inactivation of NMNAT1 sensitizes U-2OS osteosarcoma cells to cisplatin, doxorubicin, or a combination of these two treatments. Increased cisplatin-induced cell death of NMNAT1^−/− cells showed features of both apoptosis and necroptosis, as indicated by the protective effect of the caspase-3 inhibitor z-DEVD-FMK and the necroptosis inhibitor necrostatin-1. Activation of the DNA damage sensor enzyme poly(ADP-ribose) polymerase 1 (PARP1), a major consumer of NAD⁺ in the nucleus, was fully blocked by NMNAT1 inactivation, leading to increased DNA damage (phospho-H2AX foci). The PARP inhibitor, olaparib, sensitized wild type but not NMNAT1^−/− cells to cisplatin-induced anti-clonogenic effects, suggesting that impaired PARP1 activity is important for chemosensitization. Cisplatin-induced cell death of NMNAT1^−/− cells was also characterized by a marked drop in cellular ATP levels and impaired mitochondrial respiratory reserve capacity, highlighting the central role of compromised cellular bioenergetics in chemosensitization by NMNAT1 inactivation. Moreover, NMNAT1 cells also displayed markedly higher sensitivity to cisplatin when grown as spheroids in 3D culture. In summary, our work provides the first evidence that NMNAT1 is a promising therapeutic target for osteosarcoma and possibly other tumors as well.

Background: The 2023 ESC Heart Failure (HF) Guidelines recommend the rapid up-titration of guideline-directed medical therapy (GDMT) for all patients after HF hospitalisation. Real-world data on the implementation of a rapid up-titration programme (RTP) are scarce. Methods: We aimed to summarise the primary experiences of a six-week RTP in a multicentre observational study of five cardiology centres, evaluating the GDMT applied and the target doses (TDs) achieved during the RTP. The safety of RTP in relation to exceeding the “safety indicators” used in the STRONG-HF trial and any serious adverse events were observed. Changes in the left ventricular ejection fraction (LVEF) after RTP were evaluated. Results: Among the 90 consecutive patients (age: 56 [49–63] years, HFrEF: 96%, NT-proBNP at discharge: 1390 [735–2835] pg/mL; continuous variables are presented as median and interquartile ranges, while categorical variables are shown as absolute numbers and percentages, respectively), a remarkable proportion of patients received GDMT at hospital discharge; however, target doses were rarely achieved (RASi: 100%, TD RASi: 11%; βB: 97%, TD βB: 6%; MRA: 99%, TD MRA: 82%; SGLT2i: 98%, TD SGLT2i: 98%; triple therapy [TT: RASi + βB + MRA]: 96%, TD TT: 2%, quadruple therapy [QT: RASi + βB + MRA]: 94%, TD QT: 2%). After the six-week RTP, 100% of the total cohort (TC) were receiving RASi; 99–99–99% were receiving βB, MRA, and SGLT2i medications; and altogether, 98–98% were on TT and QT. In total, 78–78% of the patients received ≥50% of the TDs of TT and QT, while 51–51% of the TC were on TDs of TT and QT. During the RTP, no serious adverse events were observed. Between two and four months after the RTP, 51% of HFrEF patients evolved to the HFimpEF category. Conclusions: The present multicentre, observational study confirms that RTP is feasible and safe in real-world clinical practice, leading to a remarkably large proportion of patients receiving GDMT by the end of the six-week RTP, resulting in a significant increase in LVEF.