{"id":637517,"date":"2026-10-22T01:38:11","date_gmt":"2026-10-22T01:38:11","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/637517\/"},"modified":"2026-10-22T01:38:11","modified_gmt":"2026-10-22T01:38:11","slug":"nicotinic-acid-starvation-sensitizes-nicotinate-phosphoribosyltransferase-expressing-tumors-to-nicotinamide-phosphoribosyltransferase-inhibition","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/637517\/","title":{"rendered":"Nicotinic acid starvation sensitizes nicotinate phosphoribosyltransferase-expressing tumors to nicotinamide phosphoribosyltransferase inhibition"},"content":{"rendered":"

Nicotinamide adenine dinucleotide (NAD+) biosynthesis underlies many aspects of carcinogenesis. Inhibitors of nicotinamide phosphoribosyltransferase (NAMPT), which drives NAD+ biosynthesis from nicotinamide (NAM), are promising anticancer agents, but their activity is limited when tumors also express nicotinate phosphoribosyltransferase (NAPRT), a second NAD+-producing enzyme that uses nicotinic acid (NA) as a precursor.1<\/a>,2<\/a> The NAPRT gene is amplified and overexpressed in 25% of ovarian cancers and between 5 and 10% of breast, pancreatic, head & neck, liver, esophageal, and prostate cancers (https:\/\/www.cbioportal.org\/<\/a>, TCGA-PanCancer-Atlas studies). NAPRT-expressing tumors are addicted to its NAD+-generating activity to support oxidative phosphorylation (OXPHOS), protein synthesis and DNA repair, and to avoid NAD+ shortages in response to NAMPT inhibitors.1<\/a>,2<\/a> High NAPRT expression confers poor survival outcomes in different types of cancer, including ovarian, breast, colorectal, and pancreatic cancer (https:\/\/kmplot.com\/analysis\/<\/a>; https:\/\/www.cbioportal.org\/<\/a>), underscoring NAPRT\u2019s relevance as a therapeutic target. Given the limited potency and solubility of available NAPRT inhibitors,2<\/a> we tested whether removing NA from the diet, which is a major source of this vitamin, could be used to reduce NAPRT-mediated NAD+ production and sensitize tumors to NAMPT inhibition.<\/p>\n

In vitro, the absence of NA from culture medium sensitized NAPRT-expressing ovarian, pancreatic, breast and colorectal cancer cells to the NAMPT inhibitor FK866, whereas NA supplementation abolished FK866 activity. This NA-mediated rescue effect was on-target, as it was not detected in NAPRT-deficient cancer cells. The NAPRT inhibitor 2-hydroxynicotinic acid (2-HNA) restored sensitivity to FK866 in the presence of NA concentrations \u2264300\u2009nM (repository Fig. 1), but not at higher NA levels (not shown). Similar results were observed in NAPRT-proficient, patient-derived colorectal cancer organoids (repository Fig. 2). NAD+ measurements in cancer cells confirmed that i) FK866 reduced cellular NAD+, ii) NA supplementation restored NAD+ levels in FK866-treated NAPRT-expressing, but not NAPRT-deficient, cancer cells, and iii) NA-mediated NAD+ replenishment was abrogated by 2-HNA (repository Fig. 3). Consistent with NA causing resistance to FK866 (in NAPRT-expressing cancer cells), we verified that cell contamination with mycoplasma, which generates NA from NAM via nicotinamidase (PncA), made cells that were otherwise sensitive to FK866 resistant to it. The PncA inhibitor pyrazinecarbonitrile resensitized these tumor cells to FK866, and this effect was abolished by NA supplementation, confirming that pyrazinecarbonitrile acts by preventing NA production by mycoplasma (repository Fig. 4).<\/p>\n

In vivo, FK866 and an NA-free diet (NAFD) effectively cooperated to reduce the growth and intratumoral NAD+ levels of the NAPRT-expressing ovarian cancer, OVCAR-5 and OVCAR-8 mouse xenografts (Fig.\u00a01<\/a>; repository Fig. 5). NAFD plus FK866 (but not NAFD alone) blunted tumor and serum NA levels (repository Fig. 6). The moderate NAD+ reduction we observed in OVCAR-5 xenografts with NAFD, despite preservation of NA levels,3<\/a> suggests that NAD+ biosynthetic flux does not directly reflect the steady-state NA pool. Pharmacological NAMPT inhibition likely redirects NAD+ synthesis toward the NA-dependent pathway. Under these conditions, concomitant NA restriction renders NA supply limiting, causing depletion of both systemic and intratumoral NA and strong NAD+ collapse. FK866 and its combination with the NAFD blunted tumor and serum NAM (repository Fig. 6), likely due to the reduced NAD+ levels and, consequently, lower NAM production by NAD+-degrading enzymes. In Capan-1 pancreatic cancer xenografts, which have higher NAPRT levels (repository Fig. 1) and baseline NAD+ content compared to the ovarian cancer models, the NAFD did not suffice to sensitize tumors to FK866 despite significant NAD+ reduction, implying that residual NAD+ was still sufficient to allow tumor growth. However, 2-HNA sodium salt (2-HNANa) administration compounded the NAD+ depletion that was caused by FK866 plus NAFD, allowing slow tumor growth (repository Fig. 7). In orthotopic allografts of mouse EO771 breast cancer cells, which we transduced with NAPRT (as this cell line, similar to the other murine cancer cell lines we tested, is intrinsically NAPRT-deficient), FK866 and NAFD were ineffective by themselves, but their combination strongly reduced tumor growth and intratumoral NAD+ (repository Fig. 8), indicating that even in an immunocompetent mouse tumor model, this combined approach is effective.<\/p>\n

Fig. 1\"Fig.<\/p>\n

An NA-free diet sensitizes NAPRT-expressing ovarian cancer xenografts to FK866. a\u2013d Seven- to eight-week-old female nude mice were injected subcutaneously with 5\u2009\u00d7\u2009106 OVCAR-5 or OVCAR-8 cells in both flanks. Once tumors became palpable, mice were assigned to receive an NA-free diet (NAFD) or its matched control diet (CTRD) and then treated with FK866 (20\u2009mg\/kg\/day and 30\u2009mg\/kg\/day for 5 days a week in OVCAR-5 xenograft- and in OVCAR-8 xenograft-bearing mice, respectively) or vehicle. a, c Tumor volumes were recorded twice per week (n\u2009=\u20099\u201310 OVCAR-5 xenografts per group; n\u2009=\u20094\u20135 OVCAR-8 xenografts per group). b, d At the end of the experiments that are shown in (a, c), tumors were isolated and utilized for NAD+ quantification by enzymatic cyclic assays. Tumor growth curves are shown as percentages of initial tumor volume at recruitment and are presented as the mean\u2009\u00b1\u2009SEM. Intratumoral NAD+ measurements are presented as the mean\u2009\u00b1\u2009SD. Data were analyzed by a mixed-effects model with post hoc multiple-comparison testing (a, c) or by one-way ANOVA with post hoc multiple-comparison testing (b, d). ns nonsignificant; *: P\u2009<\u20090.05; **: P\u2009<\u20090.01; ***: P\u2009<\u20090.001; ****: P\u2009<\u20090.0001<\/p>\n

We found that FK866 and NAFD cooperate to reduce OXPHOS and ATP and cause lactate dehydrogenase release by cancer cells (repository Figs. 9\u201312). Conversely, we did not detect signs of apoptosis, such as PARP or caspase-3 cleavage, or of autophagic cell death in response to these treatments in tumor models (repository Fig. 13). Therefore, these results are consistent with combined NAFD and FK866 promoting necrotic cell death in susceptible tumor cells.<\/p>\n

The effects of NA starvation phenocopied those of NAPRT silencing in the same tumor models.1<\/a>,2<\/a> Taken together with the reduction in NA that the NAFD caused in mice (when combined with FK866), these data suggest that in vivo, it directly acted at the tumor level, blunting NAPRT activity. However, we cannot exclude that the NAFD may have also worked, at least in part, indirectly, by reducing liver production of nicotinic acid riboside (NAR), another NAD+ precursor that is utilized by cancer cells through nicotinamide riboside kinase 1 (NMRK1).3<\/a> In our NAPRT-expressing tumor models, NA proved to be a more potent NAD+ precursor than NAR, and interestingly, NAPRT was found to also participate in NAD+ production from NAR (NAPRT inhibition abolished the ability of NAR to stimulate NAD+ production and prevent FK866 cytotoxicity, while NAPRT overexpression enhanced NAR-mediated cancer cell rescue from FK866; repository Fig. 14), conceivably upon NAR degradation and formation of NA,4<\/a> for subsequent NAPRT-dependent NAD+ biosynthesis. Therefore, conceded the NAFD also lowered NAR in our in vivo experiments, NAR shortage may well have contributed to lower NAD+ levels in cancer cells by affecting NAPRT-mediated NAD+ production, in addition to reducing NMRK1 activity.<\/p>\n

The NAFD showed good tolerability in mice, including a lack of significant hematologic and organ toxicities (repository Fig. 15 and repository Table 1), which may reflect the fact that NA production by intestinal bacteria and intake of tryptophan (the key precursor for NAD+ de novo production) were not prevented. Preliminary evaluations of such regimens in humans were also reported.5<\/a> Clinical studies of NAFDs plus NAMPT inhibitors in cancer should utilize NAPRT as an efficacy biomarker and also assess whether, beyond certain levels, tumor NAPRT or NAD+ content limits the benefit of this approach, as observed here in Capan-1 tumors. Finally, to minimize potential adverse events of systemic NAD+ depletion, NAFDs could be combined with NAMPT-targeting agents that selectively inhibit tumor NAMPT while sparing healthy tissues (e.g., antibody-drug conjugates) (repository Fig. 16).<\/p>\n","protected":false},"excerpt":{"rendered":"Nicotinamide adenine dinucleotide (NAD+) biosynthesis underlies many aspects of carcinogenesis. Inhibitors of nicotinamide phosphoribosyltransferase (NAMPT), which drives NAD+…\n","protected":false},"author":2,"featured_media":637518,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[120768,6472,5300,2294,298884,134,3536,14214,111,139,69,6840,6842],"class_list":["post-637517","post","type-post","status-publish","format-standard","has-post-thumbnail","category-health","tag-cancer-metabolism","tag-cancer-research","tag-cell-biology","tag-general","tag-gynaecological-cancer","tag-health","tag-internal-medicine","tag-medicine-public-health","tag-new-zealand","tag-newzealand","tag-nz","tag-oncology","tag-pathology"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/637517","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=637517"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/637517\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/637518"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=637517"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=637517"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=637517"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}