Citations

Abstract The pyrimidine analog 5-fluorouracil (5-FU) was developed in the 1950s and remains one of the most widely used chemotherapy drugs in use today. A significant portion of patients who receive 5-FU suffer severe adverse toxicities, and, in extreme cases, death. Dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene) rapidly degrades 85% of administered 5-FU, and as such, limits the amount of drug available for conversion into active metabolites. Genetic variations in DPYD have been suggested to increase the risk of 5-FU toxicity. Large-scale sequencing efforts have identified nearly 100 missense and nonsense DPYD variations, however only a handful of alleles have been studied for their association with 5-FU toxicity. Most studies have focused on a single allele (DPYD*2A), which only accounts for a small fraction of DPD deficiencies. Further complicating the interpretation of DPYD alleles, many individuals carry multiple variations within the DPYD gene. The purpose of this study was to identify missense variants that affect the enzyme function of DPD using a mammalian isogenic system of expression. Expression vectors encoding missense DPYD variations were generated by site directed mutagenesis and the expressed protein assayed for enzyme activity. Cells expressing selected variants were also teasted for sensitivity to 5-FU using a novel implementation of electrical impedance based realtime cellular analysis. The results of functional studies are compared to in silico predictions used to classify variants as deleterious or benign. An appreciable fraction of DPD variants showed enzyme activity that was significantly lower than that of wildtype protein. Within the deficient group of variants, a gradient of activities was noted, prompting the grouping of variants as mildly, moderately, and severely impaired. In addition to loss-of-function variations, a few hyperactive DPYD alleles were identified. This novel class of DPYD variants may be protective against 5-FU toxicity at the cost of treatment efficacy. The further evaluation of hyperactive alleles in clinical studies will be necessary to determine their impact on patient outcomes. Overall these data will facilitate the development of predictive tests for 5-FU toxicity by allowing researchers to prioritize variations for association studies. Citation Format: Steven M. Offer, Natalie J. Wegner, Croix Fossum, Robert D. Diasio. Classification of DPYD variations using an isogenic system of expression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2202. doi:10.1158/1538-7445.AM2013-2202

Abstract Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme of the uracil catabolic pathway, being critically important for inactivation of the commonly prescribed anti-cancer drug 5-fluorouracil (5-FU). DPD impairment leads to increased exposure to 5-FU and, in turn, increased anabolism of 5-FU to cytotoxic nucleotides, resulting in more severe clinical adverse effects. Numerous variants within the gene coding for DPD, DPYD, have been described, although only a few have been demonstrated to reduce DPD enzyme activity. To identify DPYD variants that alter enzyme function, we expressed 80 protein-coding variants in an isogenic mammalian system and measured their capacities to convert 5-FU to dihydro-fluorouracil, the product of DPD catabolism. The M166V, E828K, K861R, and P1023T variants exhibited significantly higher enzyme activity than wild-type DPD (120%, P = 0.025; 116%, P = 0.049; 130%, P = 0.0077; 138%, P = 0.048, respectively). Consistent with clinical association studies of 5-FU toxicity, the D949V substitution reduced enzyme activity by 41% (P = 0.0031). Enzyme activity was also significantly reduced for 30 additional variants, 19 of which had <25% activity. None of those 30 variants have been previously reported to associate with 5-FU toxicity in clinical association studies, which have been conducted primarily in populations of European ancestry. Using publicly available genotype databases, we confirmed the rarity of these variants in European populations but showed that they are detected at appreciable frequencies in other populations. These data strongly suggest that testing for the reported deficient DPYD variations could dramatically improve predictive genetic tests for 5-FU sensitivity, especially in individuals of non-European descent. Cancer Res; 74(9); 2545–54. ©2014 AACR.

Abstract Dihydropyrimidine dehydrogenase (DPD, encoded by DPYD) is the rate-limiting enzyme in the uracil catabolic pathway and has a pivotal role in the pharmacokinetics of the commonly prescribed anticancer drug 5-fluorouracil (5-FU). Deficiency of DPD, whether due to inadequate expression or deleterious variants in DPYD, has been linked to severe toxic responses to 5-FU. Little is known about the mechanisms governing DPD expression in the liver. In this report, we show increased accumulation of RNA-induced silencing complex (RISC) proteins on DPYD mRNA in cells overexpressing the highly homologous microRNAs (miRNA) miR-27a and miR-27b. These miRNAs were shown to repress DPD expression through two conserved recognition sites in DPYD. The IC50 of 5-FU for HCT116 cells overexpressing miR-27a or miR-27b was 4.4 μmol/L (both), significantly lower than that for cells expressing a nontargeting (scramble) control miRNA (14.3 μmol/L; P = 3.3 × 10−5 and P = 1.5 × 10−7, respectively). Mouse liver DPD enzyme activity was inversely correlated with expression levels of miR-27a (R2 = 0.49; P = 0.0012) and miR-27b (R2 = 0.29; P = 0.022). A common variant in the hairpin loop region of hsa-mir-27a (rs895819) was also shown to be associated with elevated expression of the miR-27a in a panel of cell lines (P = 0.029) and in a transgenic overexpression model (P = 0.0011). Furthermore, rs895819 was associated with reduced DPD enzyme activity (P = 0.028) in a cohort of 40 healthy volunteers. Taken together, these results suggest that miR-27a and miR-27b expression may be pharmacologically relevant modulators of DPD enzyme function in the liver. Furthermore, our data suggest that rs895819 may be a potential risk allele for 5-FU sensitivity. Mol Cancer Ther; 13(3); 742–51. ©2014 AACR.

Abstract In the 45 years since its development, the pyrimidine analog 5-fluorouracil (5-FU) has become an integral component of many cancer treatments, most notably for the management of colorectal cancer. An appreciable fraction of patients who receive 5-FU suffer severe adverse toxicities, which in extreme cases may result in death. Dihydropyrimidine dehydrogenase (DPD, encoded by DPYD) rapidly degrades 85% of administered 5-FU, and as such, limits the amount of drug available for conversion into active metabolites. Clinical studies have suggested that genetic variations in DPYD increase the risk for 5-FU toxicity, however, there is not a clear consensus about which variations are relevant predictors. In the present study, DPYD variants were expressed in mammalian cells, and the enzymatic activity of expressed protein was determined relative to wild-type (WT). Relative sensitivity to 5-FU for cells expressing DPYD variations was also measured. The DPYD*2A variant (exon 14 deletion caused by IVS14+1G>A) was confirmed to be catalytically inactive. Compared with WT, two variants, S534N and C29R, showed significantly higher enzymatic activity. Cells expressing S534N were more resistant to 5-FU–mediated toxicity compared with cells expressing WT DPYD. These findings support the hypothesis that selected DPYD alleles are protective against severe 5-FU toxicity, and, as a consequence, may decrease the effectiveness of 5-FU an antitumor drug in carriers. In addition, this study shows a method that may be useful for phenotyping other genetic variations in pharmacologically relevant pathways. Cancer Res; 73(6); 1958–68. ©2013 AACR.

Abstract The pyrimidine analog 5-fluorouracil (5-FU) and its prodrug capecitabine are prescribed widely for the management of several common cancers, including colorectal, breast, and pancreatic cancers. 5-FU is activated by conversion to cytotoxic metabolites via the pyrimidine anabolic pathway. In the opposing catabolic pathway, dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene) initiates rapid and irreversible conversion of greater than 80% of administered 5-FU to inactive metabolites and limits the pool of 5-FU available for anabolism. Deficiency of DPD has been associated with adverse effects to 5-FU treatment, including mucositis, severe diarrhea, neurotoxicity, and life-threatening hematological toxicity, making DPD activity a potentially important predictor of 5-FU toxicity. Despite considerable study of the DPYD gene and its promoter, little is known about the post-transcriptional regulation of DPD expression at the molecular level. The objective of this study was to determine if DPD expression undergoes microRNA-mediated regulation. Computational analysis of the DPYD 3’ untranslated region (UTR) revealed an evolutionarily conserved seed-binding region for the microRNAs mir27a and mir27b. This finding prompted the hypothesis that both mir27a and mir27b are capable of modulating DPD expression. To determine if mir27a and/or mir27b bind to the DPYD 3’ UTR, HCT116 cells lines were engineered to stably express luciferase reporter constructs wherein the luciferase gene was modified to contain the 3’ UTR sequence from DPYD. As controls, stable cells lines containing mutations in the putative microRNA-binding region were generated concurrently. Two colon cancer cell lines (HT29 and HCT15) were also utilized to determine if mir27a and/or mir27b could modulate endogenous DPD expression. In cell lines expressing the luciferase gene juxtaposed to the DPYD 3’UTR, mimics of mir27a or mir27b resulted in significantly reduced luciferase activity relative to scramble control microRNA. Luciferase levels in mir27a or mir27b transfected lines were also significantly reduced compared to stable luciferase-expressing cells harboring the mutant UTR construct. Over-expression of small RNA inhibitors directed toward mir27a or mir27b led to increased luciferase activity in cells containing the wildtype UTR construct. Finally, over-expression of mir27a or mir27b significantly reduced endogenous DPD expression in both HT29 and HCT15 cells. Based on these findings, we conclude that mir27a and mir27b are capable of post-transcriptional regulation of DPD. To our knowledge this is the first report to show microRNA-mediated modulation of DPD expression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4404. doi:10.1158/1538-7445.AM2011-4404

Background and Purpose— Helicopter transportation of patients with acute stroke who have received recombinant tissue-type plasminogen activator is commonly considered the best option. We evaluated if transportation by helicopter can reduce complications and improve clinical outcomes in patients with acute stroke. Methods— We conducted a review of consecutive patients with acute ischemic stroke transferred to our hospital after intravenous thrombolysis initiated at a referral center. Results— A total of 122 patient transportations were analyzed, 94 by air and 28 by ground. Time from activation of the transport system to arrival at our hospital was significantly shorter with air transportation (53 versus 68 minutes, P =0.04). Two complications were noted in the air group and no complications were noted in the ground group ( P =1.0). All other outcome measures were not significantly different between groups. Conclusions— Air transfer of patients with acute ischemic stroke treated with thrombolysis does not seem to impart any benefit to patient outcomes when compared with ground transport. Therefore, ground transport should be considered for these patients unless they are being considered for emergency endovascular rescue therapy.

The purpose of this work was to compare the effects of hypertension and hypercholesterolemia on carotid endothelial function, structure, and vasa vasorum density. Seventeen pigs were randomized to a 12-week normal diet without (n=5), or with renovascular hypertension (HT; n=6), or to a high cholesterol diet (HC; n=6). Carotid arteries were studied by organ chambers (endothelial function) and microcomputed tomography (vasa vasorum), and tissue was processed for Sirius red staining and immunoblotting (vascular endothelium growth factor, endostatin, matrix metalloproteinase-9, and matrix metalloproteinase-2). HC and HT showed reduced vasodilation to acetylcholine as compared with controls, but HT also had a lower response to sodium nitroprusside. In addition, HT showed a higher content of organized collagen fibers and increased intima-media thickness. Vasa vasorum density was increased in HC but not in HT. Both HT and HC showed a proangiogenetic biochemical milieu (higher vascular endothelium growth factor, matrix metalloproteinases, and lower endostatin), but this was more pronounced in HC. Both hypertension and hypercholesterolemia induce endothelial dysfunction in the carotid artery. However, hypertension is also associated with greater fibrosis and vascular wall thickening, which might impair endothelium-independent vasorelaxation and vasa vasorum growth. Hypercholesterolemia is, in turn, associated with vasa vasorum neovascularization. These data suggest that carotid atherosclerosis can evolve through different mechanisms in relation to different risk factors.

Hypercholesterolemia induces renal inflammation and neovascularization, associated with renal endothelial dysfunction and injury. Neovascularization might conceivably represent a defense mechanism to sustain renal perfusion. Therefore, the present study was designed to test the hypothesis that preventing neovascularization using thalidomide, a potent anti-inflammatory and antiangiogenic agent, would impair basal renal hemodynamics in experimental hypercholesterolemia. Single-kidney function and hemodynamic responses to endothelium-dependent challenge were assessed in pigs after 12 weeks of hypercholesterolemia, hypercholesterolemia chronically supplemented with thalidomide (4 mg/kg per day), and normal controls. Renal microvascular architecture was then studied ex vivo using 3D microcomputed tomography imaging and inflammation, angiogenesis, and oxidative stress explored in renal tissue. The density of larger microvessels (200 to 500 μm) was selectively decreased in hypercholesterolemia plus thalidomide and accompanied by a decreased fraction of angiogenic, integrin β 3 -positive microvessels (9.9%±0.9% versus 25.5%±1.7%; P <0.05 versus hypercholesterolemia), implying decreased angiogenic activity. Furthermore, thalidomide increased renal expression of endothelial NO synthase and decreased tumor necrosis factor-α and renal inflammation but did not decrease oxidative stress. Thalidomide also decreased basal renal blood flow and glomerular filtration rate but normalized the blunted renal hemodynamic responses in hypercholesterolemia. Attenuated inflammation and pathological angiogenesis achieved in hypercholesterolemia by thalidomide are accompanied by restoration of renovascular endothelial function but decreased basal renal hemodynamics. This study, therefore, suggests that neovascularization in the hypercholesterolemic kidney is a compensatory mechanism that sustains basal renal vascular function.

Experimental studies have shown the beneficial effects of antioxidant supplementation on endothelial function in the presence of increased endogenous oxidative stress, whereas limited data are available under normal conditions. The present study tested the hypothesis that in normal pigs long-term antioxidants would have deleterious effects on the cardiovascular system. Normal domestic pigs (V, n=6) were studied 12 weeks after dietary supplementation with vitamin E (100 IU/kg per day) and vitamin C (1 g/day) and compared with normal controls (C, n=7). Myocardial perfusion and permeability index were evaluated by electron beam computed tomography after intravenous adenosine and dobutamine. Coronary endothelial function was evaluated in vitro by organ chamber and coronary tissue studied by immunoblotting and staining. Myocardial perfusion response was lower in V than in C after adenosine (10.1±4.5 versus 53.4±5.2%; P <0.01) and dobutamine (V, 78.4±8.1; C, 193.0±39.0%; P <0.05). The permeability index increased in V after adenosine (48.8±5.1%) and dobutamine (59.9±13.6%) and did not change in C. Coronary vasodilation to bradykinin and substance P was lower in V than in C. Moreover, in V, coronary nitrotyrosine and superoxide content was significantly higher than in C. The groups had similar total monomer expression of endothelial nitric oxide synthase, whereas the dimerized form, reflecting coupled enzyme, was lower in V. These findings suggest that long-term experimental antioxidant vitamin supplementation in normal pigs impairs myocardial perfusion and coronary endothelial function via an increased level of oxidative stress in the arterial wall, which may be partly related to the uncoupling of endothelial nitric oxide synthase and/or the direct prooxidant effect of vitamin radicals.