Increased plasma concentration of 4-pyridone-3-carboxamide-1-ß-D-ribonucleoside (4PYR) in lung cancer. Preliminary studies

Elevated Plasma Concentration of 4-Pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) Highlights Malignancy of Renal Cell Carcinoma

Nicotinamide (NA) derivatives play crucial roles in various biological processes, such as inflammation, regulation of the cell cycle, and DNA repair. Recently, we proposed that 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR), an unusual derivative of NA, could be classified as an oncometabolite in bladder, breast, and lung cancer. In this study, we investigated the relations between NA metabolism and the progression, recurrence, metastasis, and survival of patients diagnosed with different histological subtypes of renal cell carcinoma (RCC). We identified alterations in plasma NA metabolism, particularly in the clear cell RCC (ccRCC) subtype, compared to papillary RCC, chromophobe RCC, and oncocytoma. Patients with ccRCC also exhibited larger tumor sizes and elevated levels of diagnostic serum biomarkers, such as hsCRP concentration and ALP activity, which were positively correlated with the plasma 4PYR. Notably, 4PYR levels were elevated in advanced stages of ccRCC cancer and were associated with a highly aggressive phenotype of ccRCC. Additionally, elevated concentrations of 4PYR were related to a higher likelihood of mortality, recurrence, and particularly metastasis in ccRCC. These findings are consistent with other studies, suggesting that NA metabolism is accelerated in RCC, leading to abnormal concentrations of 4PYR. This supports the concept of 4PYR as an oncometabolite and a potential prognostic factor in the ccRCC subtype.

Defining NAD(P)(H) Catabolism

Dietary vitamin B3 components, such as nicotinamide and nicotinic acid, are precursors to the ubiquitous redox cofactor nicotinamide adenine dinucleotide (NAD⁺). NAD⁺ levels are thought to decline with age and disease. While the drivers of this decline remain under intense investigation, strategies have emerged seeking to functionally maintain NAD⁺ levels through supplementation with NAD⁺ biosynthetic intermediates. These include marketed products, such as nicotinamide riboside (NR) and its phosphorylated form (NMN). More recent developments have shown that NRH (the reduced form of NR) and its phosphorylated form NMNH also increases NAD⁺ levels upon administration, although they initially generate NADH (the reduced form of NAD⁺). Other means to increase the combined levels of NAD⁺ and NADH, NAD(H), include the inhibition of NAD⁺-consuming enzymes or activation of biosynthetic pathways. Multiple studies have shown that supplementation with an NAD(H) precursor changes the profile of NAD(H) catabolism. Yet, the pharmacological significance of NAD(H) catabolites is rarely considered although the distribution and abundance of these catabolites differ depending on the NAD(H) precursor used, the species in which the study is conducted, and the tissues used for the quantification. Significantly, some of these metabolites have emerged as biomarkers in physiological disorders and might not be innocuous. Herein, we review the known and emerging catabolites of the NAD(H) metabolome and highlight their biochemical and physiological function as well as key chemical and biochemical reactions leading to their formation. Furthermore, we emphasize the need for analytical methods that inform on the full NAD(H) metabolome since the relative abundance of NAD(H) catabolites informs how NAD(H) precursors are used, recycled, and eliminated.

4-Pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR)—A Novel Oncometabolite Modulating Cancer-Endothelial Interactions in Breast Cancer Metastasis

The accumulation of specific metabolic intermediates is known to promote cancer progression. We analyzed the role of 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR), a nucleotide metabolite that accumulates in the blood of cancer patients, using the 4T1 murine in vivo breast cancer model, and cultured cancer (4T1) and endothelial cells (ECs) for in vitro studies. In vivo studies demonstrated that 4PYR facilitated lung metastasis without affecting primary tumor growth. In vitro studies demonstrated that 4PYR affected extracellular adenine nucleotide metabolism and the intracellular energy status in ECs, shifting catabolite patterns toward the accumulation of extracellular inosine, and leading to the increased permeability of lung ECs. These changes prevailed over the direct effect of 4PYR on 4T1 cells that reduced their invasive potential through 4PYR-induced modulation of the CD73-adenosine axis. We conclude that 4PYR is an oncometabolite that affects later stages of the metastatic cascade by acting specifically through the regulation of EC permeability and metabolic controls of inflammation.

The Biochemical Pathways of Nicotinamide-Derived Pyridones

As catabolites of nicotinamide possess physiological relevance, pyridones are often included in metabolomics measurements and associated with pathological outcomes in acute kidney injury (AKI). Pyridones are oxidation products of nicotinamide, its methylated form, and its ribosylated form. While they are viewed as markers of over-oxidation, they are often wrongly reported or mislabeled. To address this, we provide a comprehensive characterization of these catabolites of vitamin B3, justify their nomenclature, and differentiate between the biochemical pathways that lead to their generation. Furthermore, we identify an enzymatic and a chemical process that accounts for the formation of the ribosylated form of these pyridones, known to be cytotoxic. Finally, we demonstrate that the ribosylated form of one of the pyridones, the 4-pyridone-3-carboxamide riboside (4PYR), causes HepG3 cells to die by autophagy; a process that occurs at concentrations that are comparable to physiological concentrations of this species in the plasma in AKI patients.