Lead Acetate-Injected Mice is an Animal Model for Extrapolation of Calcifying Response to Humans Due to Low Involvement of Bone Resorption.

Vascular calcification affects the prognosis of patients with renal failure. Bisphosphonates are regarded as candidate anti-calcifying drugs because of their inhibitory effects on both calcium-phosphate aggregation and bone resorption. However, calcification in well-known rodent models is dependent upon bone resorption accompanied by excessive bone turnover, making it difficult to estimate accurately the anti-calcifying potential of drugs. Therefore, models with low bone resorption are required to extrapolate anti-calcifying effects to humans. Three bisphosphonates (etidronate, alendronate, and FYB-931) were characterised for their inhibitory effects on bone resorption in vivo and calcium-phosphate aggregation estimated by calciprotein particle formation in vitro. Then, their effects were examined using two models inducing ectopic calcification: the site where lead acetate was subcutaneously injected into mice and the transplanted, aorta obtained from a donor rat. The inhibitory effects of bisphosphonates on bone resorption and calcium-phosphate aggregation were alendronate > FYB-931 > etidronate and FYB-931 > alendronate = etidronate, respectively. In the lead acetate-induced model, calcification was most potently suppressed by FYB-931, followed by alendronate and etidronate. In the aorta-transplanted model, only FYB-931 suppressed calcification at a high dose. In both the models, no correlation was observed between calcification and bone resorption marker, tartrate-resistant acid phosphatase (TRACP). Results from the lead acetate-induced model showed that inhibitory potency against calcium-phosphate aggregation contributed to calcification inhibition. The two calcification models, especially the lead acetate-induced model, may be ideal for the extrapolation of calcifying response to humans because of calcium-phosphate aggregation rather than bone resorption as its mechanism.

Clinical significance of postoperative complications after pancreatic surgery in time-to-complication and length of postoperative hospital stay: a retrospective study.

PURPOSE: We retrospectively analyzed pancreatectomy patients and examined the occurrence rate and timing of postoperative complications (time-to-complication; TTC) and their impact on the length of postoperative hospital stay (POHS) to clarify their characteristics, provide appropriate postoperative management, and improve short-term outcomes in the future. METHODS: A total of 227 patients, composed of 118 pancreaticoduodenectomy (PD) and 109 distal pancreatectomy (DP) cases, were analyzed. We examined the frequency of occurrence, TTC, and POHS of each type of postoperative complication, and these were analyzed for each surgical procedure. Complications of the Clavien-Dindo (CD) classification Grade II or higher were considered clinically significant. RESULTS: Clinically significant complications were observed in 70.3% and 36.7% of the patients with PD and DP, respectively. Complications occurred at a median of 10 days in patients with PD and 6 days in patients with DP. Postoperative pancreatic fistula (POPF) occurred approximately 7 days postoperatively in both groups. For the POHS, in cases without significant postoperative complications (CD ≤ I), it was approximately 22 days for PD and 11 days for DP. In contrast, when any complications occurred, POHS increased to 30 days for PD and 19 days for DP (each with additional 8 days), respectively. In particular, POPF prolonged the hospital stay by approximately 11 days for both procedures. CONCLUSION: Each postoperative complication after pancreatectomy has its own characteristics in terms of the frequency of occurrence, TTC, and impact on POHS. A correct understanding of these factors will enable timely therapeutic intervention and improve short-term outcomes after pancreatectomy.

Uricosuric Agents Affect Plasma and Kidney Concentration of Adefovir via Inhibition of Oat1 and Mrp2 in Rats.

Uricosuric agents lower serum uric acid levels by increasing urinary excretion via inhibition of urate transporter 1 (URAT1), urate reabsorption transporter in the renal proximal tubules. Probenecid and benzbromarone have been used as uricosurics, but these drugs inhibit organic anion transporters (OATs) in addition to URAT1. In this study, we investigated whether uricosuric agents interacted with adefovir, known as a substrate for OAT1, using Sprague-Dawley (SD) rats. Furthermore, involvement of other transporters, multi-drug resistance protein 2 (MRP2) in this interaction was examined using Mrp2-deficient rats. Probenecid and lesinurad increased plasma adefovir concentrations and decreased kidney-to-plasma partition coefficient (Kp) in these rats, presumably by inhibiting Oat1. Although benzbromarone had no effect on plasma adefovir concentration, it increased the Kp to 141% in SD rats. Since this effect was abolished in Mrp2-deficient rats, together with the MRP2 inhibition study, it is suggested that benzbromarone inhibits Mrp2-mediated adefovir excretion from the kidney. In contrast, dotinurad, a novel uricosuric agent that selectively inhibits URAT1, had no effect on the plasma and kidney concentrations of adefovir. Therefore, due to the lack of interaction with adefovir, dotinurad is expected to have low drug-drug interaction risk mediated by OAT1, and also by MRP2.

Identification of a DBA/2 Mouse Sub-strain as a Model for Pseudoxanthoma Elasticum-Like Tissue Calcification.

Ectopic calcification in the cardiovascular system adversely affects life prognosis. DBA/2 mice experience calcification owing to low expression of Abcc6 as observed in pseudoxanthoma elasticum (PXE) patients; however, little is known about its characteristics as a calcification model. In this study, we explore the suitability of a DBA/2 sub-strain as a PXE-like tissue calcification model, and the effect of a bisphosphonate which prevents calcification of soft tissues in hypercalcemic models was evaluated. The incidence of calcification of the heart was compared among several sub-strains and between both sexes of DBA/2 mice. mRNA expression of calcification-related genes was compared with DBA/2 sub-strains and other mouse strains. In addition, progression of calcification and calciprotein particle formation in serum were examined. Among several sub-strains of DBA/2 mice, male DBA/2CrSlc mice showed the most remarkable cardiac calcification. In DBA/2CrSlc mice, expression of the anti-calcifying genes Abcc6, Enpp1 and Spp1 was lower than that in C57BL/6J, and expression of Enpp1 and Spp1 was lower compared with other sub-strains. Calcification was accompanied by accelerated formation of calciprotein particle, which was prevented by daily treatment with bisphosphonate. A model suitable for ectopic calcification was identified by choosing a sub-strain of DBA/2 mice, in which genetic characteristics would contribute to extended calcification.

[A Case of Delayed-Onset Acute Interstitial Nephritis following Nivolumab Treatment in a Patient with Advanced Esophagogastric Junction Cancer].

An 81-year-old man with advanced esophagogastric junction cancer with paraaortic lymph node metastasis was treated with S-1 plus oxaliplatin and nivolumab combination chemotherapy. Subsequently, conversion surgery was performed, and the patient was discharged without postoperative complications. Two months after discharge, the patient developed fever, fatigue, and anorexia. Intravenous antibiotic therapy was started; however, the symptoms did not improve. Urine biochemical tests revealed significantly elevated N-acetyl-ß-D-glucosaminidase and ß-microglobulin levels, and acute interstitial nephritis was suspected. Steroid therapy was initiated, and the patient's symptoms improved. A renal biopsy performed at the same time the nivolumab treatment was initiated led to the diagnosis of immune-related interstitial nephritis, a probable adverse event of the treatment. Although immune-related adverse events associated with immune checkpoint inhibitors are typically colitis, interstitial pneumonia, and endocrine disturbances, we observed severe interstitial nephritis in the patient. Clinicians should also consider the possible occurrence of immune-related adverse events >2 months after administering treatment.

Prognostic impact of lymph node micrometastasis in patients with gastric cancer.

PURPOSE: The clinical significance of lymph node micrometastasis (LNMM) remains controversial in gastric cancer (GC). In this study, we investigated the prognostic impact of LNMM in patients with GC. METHODS: A total of 624 patients with pathologically lymph node metastasis-negative (pN0) and N1 status (pN1) who underwent gastrectomy between 2004 and 2018 were enrolled in this retrospective study. The diameter of tumor cell clusters in metastatic lymph nodes was measured in 120 patients with pN1 GC. RESULTS: Patients with lymph node tumors < 1500 µm in diameter (LNMM) had a significantly better prognosis than those with tumors ≥ 1500 µm in diameter (p = 0.012; log-rank test). Cox's proportional hazards model revealed that LNMM (p = 0.016), several dissected lymph nodes (p = 0.049), and the provision of adjuvant chemotherapy (p = 0.002) were independent prognostic factors for the overall survival of patients with pN1 GC. There was no significant difference in the overall survival between patients with LNMM who received chemotherapy and those who did not (p = 0.332). CONCLUSIONS: LNMM is associated with a favorable prognosis and maybe an independent prognostic marker in patients with pN1 GC. LNMM in GC may be considered a factor preventing adjuvant chemotherapy.

[Two Cases of Carcinoma en Cuirasse, as Cutaneous Metastasis of Breast Cancer].

We present 2 cases of carcinoma en cuirasse, an uncommon clinical manifestation of metastatic cutaneous breast cancer. Case 1, a 70-year-old woman, presented with diffuse erythematous, indurated skin lesions that covered her entire anterior chest wall. Skin biopsy revealed tumor cells in the dermis which were ER and PgR positive and HER2 negative. CT showed pleural and pericardial effusion which led to a final diagnosis of cutaneous metastasis from breast cancer. Fulvestrant monotherapy was initiated and maintained a good clinical effect for 40 months. She died of multiple liver metastasis after 53 months from her first visit. Case 2 was a 71-year-old woman, with a 24 month history of a left breast tumor that gradually accompanied erythematous skin indurations and erosion, which spread to her entire left chest wall and contralateral breast. Following skin biopsy and CT, she was diagnosed to have triple negative breast cancer with multiple lymph node and cutaneous metastasis. After 4 cycles of EC, capecitabine was administrated and her skin lesions improved rapidly, including the lymph nodes. She is currently alive after 12 months since her first visit and under chemotherapy against new cutaneous metastasis.

[Long-Term Prognosis of Patients with Biliary Tract Cancer Undergoing Pancreaticoduodenectomy].

We divided the patients with biliary tract cancer who underwent pancreaticoduodenectomy(PD)at our hospital into the 5-year recurrence-free and recurrence groups and investigated the prognostic factors. Additionally, we investigated the efficacy of adjuvant chemotherapy in patients with and without lymph node (LN) metastasis. There was no significant difference between the two groups for patient characteristics and perioperative factors. However, patients with LN metastasis tended to have a higher recurrence rate. For patients without LN metastasis, the median overall survival(OS)was not significantly different between the patients who received and did not receive adjuvant chemotherapy. For patients with LN metastasis, although it was not significantly different(p=0.234), the OS of patients who received adjuvant therapy was more than 3 times than that of patients who did not(58.6 months and 18.4 months, respectively). For patients with biliary tract cancer who underwent PD, positive LN metastasis may be a poor prognostic factor, and adjuvant therapy may possibly improve prognosis.

Novel monocyclic amide-linked phenol derivatives without mitochondrial toxicity have potent uric acid-lowering activity.

Although benzbromarone (BBR) is a conventional, highly potent uricosuric drug, it is not a standard medicine because it causes rare but fatal fulminant hepatitis. We transformed the bis-aryl ketone structure of BBR to generate novel monocyclic amide-linked phenol derivatives that should possess uric acid excretion activity without adverse properties associated with BBR. The derivatives were synthesized and tested for uric acid uptake inhibition (UUI) in two assays using either urate transporter 1-expressing cells or primary human renal proximal tubule epithelial cells. We also evaluated their inhibitory activity against mitochondrial respiration as a critical mitochondrial toxicity parameter. Some derivatives with UUI activity had no mitochondrial toxicity, including compound 3f, which effectively lowered the plasma uric acid level in Cebus apella. Thus, 3f is a promising candidate for further development as a uricosuric agent.

[Pathological Complete Response of Intrapelvic Recurrence of Rectal Cancer after Chemoradiotherapy-A Case Report].

50's man who have performed anterior pelvic exenteration with lateral lymph node dissection for rectal cancer with pT4bN0M0, pStage Ⅱc about 2 years ago, was admitted to our hospital for the treatment of intrapelvic recurrence of rectal cancer. No distant metastasis was found in the computed tomography examination but the tumor invaded the dorsal side of the pubis. Because radical excision was impossible with these findings, he received chemoradiotherapy(CRT). Post-CRT imaging showed that the tumor of intrapelvic recurrence region reduced the size, and invasion of pubis had disappeared and been markedly reduced. Thus, radical excision seemed possible at this point, and we decided to attempt operation after total 6 weeks of S-1(120 mg/day)regimen and radiation(40 Gy/20 Fr). We performed Miles' operation. The final pathological examination demonstrated that no viable tumor cells remained in the resected rectum specimen, confirming that a pathological complete response(pCR)had been achieved.

Pharmacological Evaluation of Dotinurad, a Selective Urate Reabsorption Inhibitor.

The effect of dotinurad [(3,5-dichloro-4-hydroxyphenyl)(1,1-dioxo-1,2-dihydro-3H-1λ 6-1,3-benzothiazol-3-yl)methanone] was compared with that of commercially available uricosuric agents-namely, benzbromarone, lesinurad, and probenecid. Its effect on urate secretion transporters was evaluated using probe substrates for respective transporters. Dotinurad, benzbromarone, lesinurad, and probenecid inhibited urate transporter 1 (URAT1) with IC50 values of 0.0372, 0.190, 30.0, and 165 µM, respectively. Dotinurad weakly inhibited ATP-binding cassette subfamily G member 2 (ABCG2), organic anion transporter 1 (OAT1), and OAT3, with IC50 values of 4.16, 4.08, and 1.32 µM, respectively, indicating higher selectivity for URAT1. The hypouricemic effects of dotinurad and benzbromarone were evaluated in Cebus monkeys. Dotinurad, at doses of 1-30 mg/kg, concomitantly decreased plasma urate levels and increased fractional excretion of urate (FEUA) in a dose-dependent manner. On the contrary, benzbromarone, at a dose of 30 mg/kg, showed a modest effect on plasma urate levels. The inhibitory effect of dotinurad on urate secretion transporters was evaluated in Sprague-Dawley rats, with sulfasalazine and adefovir as probe substrates of ABCG2 and OAT1, respectively. Drugs, including febuxostat as a reference ABCG2 inhibitor, were administered orally before sulfasalazine or adefovir administration. Dotinurad had no effect on urate secretion transporters in vivo, whereas benzbromarone, lesinurad, probenecid, and febuxostat increased the plasma concentrations of probe substrates. These results suggested dotinurad is characterized as a selective urate reabsorption inhibitor (SURI), which is defined as a potent URAT1 inhibitor with minimal effect on urate secretion transporters, including ABCG2 and OAT1/3, because of its high efficacy in decreasing plasma urate levels compared with that of other uricosuric agents. SIGNIFICANCE STATEMENT: Our study on the inhibitory effects on urate transport showed that dotinurad had higher selectivity for urate transporter 1 (URAT1) versus ATP-binding cassette subfamily G member 2 (ABCG2) and organic anion transporter (OAT) 1/3 compared to other uricosuric agents. In Cebus monkeys, dotinurad decreased plasma urate levels and increased fractional excretion of urate in a dose-dependent manner. To determine the inhibitory effect of dotinurad on urate secretion transporters, we studied the movement of substrates of ABCG2 and OAT1 in rats. Dotinurad had no effect on these transporters, whereas the other uricosuric agents increased the plasma concentrations of the substrates. These results suggested dotinurad as a potent and selective urate reabsorption inhibitor is characterized by increased efficacy with decreasing plasma urate levels.

Novel bisphosphonate compound FYB-931 preferentially inhibits aortic calcification in vitamin D3-treated rats.

In patients with chronic kidney disease (CKD) or those undergoing hemodialysis, pathological calcific deposition known as ectopic calcification occurs in soft tissue, resulting in a life-threatening disorder. A potent and effective inhibitor of ectopic calcification is eagerly expected. In the current study, the effects of FYB-931, a novel bisphosphonate compound synthesized for the prevention of ectopic calcification, were compared with those of etidronate using both in vitro and in vivo models. In vitro, FYB-931 inhibited calcification of human aortic smooth muscle cells induced by high phosphate medium in a concentration-dependent manner, and the effect was slightly more potent than that of etidronate. In vivo, rats were administered with three subcutaneous injections of vitamin D3 to induce vascular calcification, and were given FYB-931 (1.5, 5, or 10 mg/kg) or etidronate (9, 30, or 60 mg/kg) orally once daily for 14 days. The increased aortic phosphorus content as an index of vascular calcification was inhibited by both FYB-931 and etidronate in a dose-dependent manner; however, FYB-931 was 10 times more potent than etidronate. FYB-931 inhibited serum tartrate-resistant acid phosphatase (TRACP) activity as a bone resorption marker 5.2 times more potently than etidronate. FYB-931, but not etidronate, significantly decreased serum phosphorus levels. The preferential inhibition of aortic calcification by FYB-931 suggested that possible additional effect including a decline in serum phosphorus may lead to an advantage in terms of its efficacy.

[Effects of Preoperative Skeletal Muscle Mass on the Prognosis of Stageâ ¡ and â ¢ Colorectal Cancer].

INTRODUCTION: Some studies reported that the decrease in skeletal muscle mass worsens the immune and nutritional status and related to the poor prognosis in colorectal cancer. We examined the relationship of skeletal muscle mass, immune and nutritional index, and outcome in patients with colorectal cancer at our hospital. SUBJECTS AND METHODS: We retrospectively analyzed 196 patients of cStageⅡ andⅢ colorectal cancer who underwent curative surgery in our institution between 2007 and 2013. The cross-sectional area of the psoas muscle at the level of the third lumbar vertebra on preoperative computed tomography was assessed to calculate the psoas muscle index(PMI). Patients are divided into high PMIgroup(H-group)and low PMIgroup (L-group)with cut off value(6.36 cm / / 2/m2 for males and 3.92 cm2/m2 for females). Patient background, tumor factor, overall survival(OS), recurrence free survival(RFS)were examined retrospectively. RESULTS: There were 119 cases in H-group and 77 cases in L-group. Significant differences were recognized in gender, age, Alb value, BMI, and adjuvant chemotherapy between 2 groups. The 5-year survival rate was significantly different from 82.8% in H-group and 70.3% in L-group(p<0.01). The 5-year recurrence-free survival rate was 74.0%in the H-group, and 68.3%in the L-group (p=0.46). Univariate and multivariate analysis showed that age(OR: 1.90, p<0.01), high CEA(OR: 0.012, p<0.05), depth of invasion(OR: 2.19, p<0.05), lymph node metastasis(OR: 2.21, p<0.01), and preoperative low PMI(OR: 2.05, p<0.01), were significantly related to decrease of OS. CONCLUSION: Preoperative PMIsuggested to become prognostic factors in Stage Ⅱ and Ⅲ colorectal cancer.

[Effects of Preoperative Immune and Nutritional Indices on the Prognosis of pStage â ¡ and â ¢ Colorectal Cancer].

We examined the relationship between immune and nutritional indices and the outcome of colorectal cancer patients at our hospital. We retrospectively analyzed 196 patients with pStage Ⅱand Ⅲcolorectal cancer who underwent curative surgery in our institution between 2007 and 2013. The evaluation items were immune and nutritional indices, such as neutrophil/lym- phocyte ratio(NLR), platelet/lymphocyte ratio(PLR), lymphocyte/monocyte ratio(LMR), and the Onodera nutritional index (PNI). Moreover, we analyzed the relationship between immune and nutritional indices and outcome, overall survival(OS), and recurrence-free survival(RFS). Univariate and multivariate analyses showed that low LMR was significantly related to high mortality. Univariate analysis showed that high NLR, low LMR, and low PNIwere significantly related to a decrease in OS. Multivariate analysis showed that PNIwas an independent predictor of OS. LMR is suggested as a new predictor for postoperative complications. PNIis suggested as a new prognostic factor in pStageⅡand Ⅲcolorectal cancer.

Xanthine crystals induced by topiroxostat, a xanthine oxidoreductase inhibitor, in rats, cause transitional cell tumors.

The present study was performed to elucidate the underlying mechanism of transitional cell tumors found in the carcinogenicity testing of topiroxostat, a xanthine oxidoreductase inhibitor, in which topiroxostat was orally given to F344 rats at 0.3, 1, and 3 mg/kg for 2 years. In the urinary bladder, transitional cell papillomas and/or carcinomas were seen in males receiving 0.3, 1, and 3 mg/kg (1/49, 3/49, and 10/50, respectively). In the kidney, transitional cell papillomas and/or carcinomas in the pelvis were seen in 2/50 males and 1/50 females receiving 3 mg/kg. In the mechanistic study by 52-week oral treatment with topiroxostat at 3 mg/kg to F344 male rats, with and without citrate, simple and papillary transitional cell hyperplasias of the urinary bladder epithelium were observed in 5/17 in the topiroxostat-alone treatment group, along with xanthine-induced nephropathy, in contrast to neither xanthine crystals nor lesions in urinary organs by co-treatment group with citrate. As for sex differences of urinary bladder tumors, the BrdU labeling index for epithelial cells of the urinary bladder by 5-week oral treatment with topiroxostat at 10 mg/kg to F344 rats was increased in males only, showing consistency with histopathological findings. Therefore, the present study indicates that transitional cell tumors induced by topiroxostat in rats were due to physical stimulation to transitional cells of xanthine crystals/calculi and provides that other factors were not implicated in this tumorigenesis. Furthermore, the present study suggests that such tumors do not predict for humans since topiroxostat-induced xanthine deposition is a rodent-specific event.

Re-consideration of Lymph Node Metastasis in Pancreatic Cancer Patients Following Radical Resection: A Retrospective Study.

BACKGROUND/AIM: Perioperative chemotherapy has become more common in patients with pancreatic cancer (PC), and the significance of lymph node (LN) metastasis and the role of surgical resection in PC have gradually evolved. In the present study, we reconsidered the significance of LN metastasis for patients with PC. PATIENTS AND METHODS: We analyzed 142 PC patients who underwent radical resection at our hospital between September 2012 and December 2021. Patients were divided into three groups based on the performance of preoperative chemotherapy, as follows: up-front surgery (US, n=109), neoadjuvant chemotherapy (NAC, n=22), and conversion surgery (CS, n=11). The characteristics of patients with LN metastasis in the US group were clarified, and a prognostic analysis was performed. The prognostic impact of LN metastasis in the NAC/CS group was examined and compared to that in the US group. RESULTS: Multivariate analysis revealed that high CA19-9 levels, large tumor size, and positive lymphatic invasion were significantly associated with LN metastasis. LN metastasis and portal vein invasion were independent poor prognostic factors in multivariate analysis. Patients without LN metastasis in the NAC group tended to have a better prognosis than those in the US group; however, the prognosis of patients with LN metastasis was similar between the two groups. In the CS and US groups, the prognosis was comparable for patients with and without LN metastasis. CONCLUSION: LN metastasis is a notably poor prognostic factor for PC patients, even after NAC, and more aggressive perioperative treatments may be considered for these patients.

The Prognostic Implications of Perioperative Serum Cholesterol Levels in Patients With Gastric Cancer.

BACKGROUND/AIM: Although cholesterol is an important indicator of nutritional status, it is also involved in cancer progression. In this study, we investigated the clinical significance of the dynamics of perioperative total cholesterol (T-Cho) levels in patients with gastric cancer (GC). PATIENTS AND METHODS: A total of 212 patients with pathological stage II/III disease who underwent gastrectomy between 2004 and 2020 were enrolled in this retrospective study. The preoperative and postoperative serum T-Cho levels were measured in these patients. RESULTS: Increased serum T-Cho levels were significantly correlated with low preoperative serum albumin levels (p<0.001). Patients with increased serum T-Cho levels after surgery had significantly lower overall and recurrence-free survival rates (p=0.030 and p=0.013, respectively; log-rank test). Cox proportional hazards model revealed that increased serum T-Cho levels (p=0.040), advanced pathological stage (p<0.001), and the provision of adjuvant chemotherapy (p=0.006) were independent prognostic factors for recurrence-free survival in patients with GC. CONCLUSION: Increased serum T-Cho levels after gastrectomy may be an independent prognostic factor in patients with GC.

An evaluation method for uric acid uptake inhibition using primary human proximal tubule epithelial cells treated with insulin.

The effects of uricosuric agents have been evaluated in vitro with indices of uric acid uptake into human urate transporter 1 (URAT1)-overexpressed oocytes or cells. In the present study, we evaluated a method using primary human renal proximal tubule epithelial cells (RPTECs). Pretreatment of RPTECs with insulin significantly increased the uptake of uric acid into these cells. The uric acid uptake was inhibited in a concentration-dependent manner by the URAT1 inhibitors benzbromarone and dotinurad. Therefore, effects of uricosuric agents can be evaluated by the novel method, which is closer to the physiological system compared with previous methods.

FYX-051: a novel and potent hybrid-type inhibitor of xanthine oxidoreductase.

4-[5-(Pyridin-4-yl)-1H-1,2,4-triazol-3-yl]pyridine-2-carbonitrile (FYX-051) is a potent inhibitor of bovine milk xanthine oxidoreductase (XOR). Steady-state kinetics study showed that it initially behaved as a competitive-type inhibitor with a K(i) value of 5.7 × 10(-9) M, then after a few minutes it formed a tight complex with XOR via a Mo-oxygen-carbon atom covalent linkage, as reported previously (Proc Natl Acad Sci USA 101:7931-7936, 2004). Thus, FYX-051 is a hybrid-type inhibitor exhibiting both structure- and mechanism-based inhibition. The FYX-051-XOR complex decomposed with a half-life of 20.4 h, but the enzyme activity did not fully recover. This was found to be caused by XOR-mediated conversion of FYX-051 to 4-[5-(2-hydroxypyridin-4-yl)-1H-1,2,4-triazol-3-yl]pyridine-2-carbonitrile (2-hydroxy-FYX-051), as well as formation of 6-hydroxy-4-[5-(2-hydroxypyridin-4-yl)-1H-1,2,4-triazol-3-yl]pyridine-2-carbonitrile (dihydroxy-FYX-051) and 4-[5-(2,6-dihydroxypyridin-4-yl)-1H-1,2,4-triazol-3-yl]-6-hydroxypyridine-2-carbonitrile (trihydroxy-FYX-051) during prolonged incubation for up to 72 h. A distinct charge-transfer band was observed concomitantly with the formation of the trihydroxy-FYX-051-XOR complex. Crystallographic analysis of the charge-transfer complex indicated that a Mo-nitrogen-carbon bond was formed between molybdenum of XOR and the nitrile group of trihydroxy-FYX-051. FYX-051 showed a potent and long-lasting hypouricemic effect in a rat model of potassium oxonate-induced hyperuricemia, and it seems to be a promising candidate for the clinical treatment of hyperuricemia.

Study on species differences in nephropathy induced by FYX-051, a xanthine oxidoreductase inhibitor.

To clarify the toxicological aspects of FYX-051, a xanthine oxidoreductase inhibitor, which is currently being developed as a therapeutic agent against gout and hyperuricemia, we performed the study focused on species differences in FYX-051-induced nephropathy. In the repeated toxicology testing by oral administration, nephropathy was seen at 1 mg/kg and more in rats and at 100 mg/kg in dogs, in contrast to no toxicity even at the practical maximum dose (300 mg/kg) in monkeys. The HPLC and LC-MS/MS analyses of intrarenal deposits in dogs have proven that the entity was xanthine. The study on dose dependency of pharmacokinetics, pharmacodynamics, urinary xanthine excretion, and kidney xanthine content by oral administration at 0.3, 1, and 3 mg/kg to rats revealed the involvement of xanthine in the occurrence of nephropathy, thus suggesting that plasma concentrations of FYX-051 can contribute to species differences. Regarding the possible factors of species differences, the daily urinary excretion of total purine metabolites was 30.5- and 6.3-fold greater in rats and dogs, respectively, than in monkeys. Urinary xanthine solubility was 2.3- and 6.3-fold higher in dogs and monkeys, respectively, than in rats. Plasma concentrations of FYX-051 were fivefold higher in rats than in dogs and monkeys, without differences between the latter two species. Therefore, the present study indicated that species differences in nephropathy were produced by the combined effects of purine metabolism, urinary xanthine solubility, and plasma concentrations of FYX-051.