Dihydropyrimidine Dehydrogenase Inhibitor Research Articles

The upregulation of dihydropyrimidine dehydrogenase in liver is involved in acquired resistance to 5-fluorouracil

BackgroundAcquired resistance to 5-fluorouracil (5-FU) is one of the important reasons for failure in 5-FU-based chemotherapy. The upregulation of dihydropyrimidine dehydrogenase (DPD) in tumours was reported as an important factor for acquired 5-FU resistance. The aim of this study is to examine whether intra-hepatic DPD was involved in acquired 5-FU resistance. MethodsHT-29 human colorectal xenograft tumours were established in nude mice. After long-term exposure to 5-FU, some of the tumour became “resistant” and the others remained “sensitive” to 5-FU. DPD expression levels in the livers and tumours of “resistant”, “sensitive” or untreated mice were examined, and pharmacokinetics of 5-FU in rats’ plasma were investigated. Gimeracil, a DPD inhibitor, was checked whether it could reverse the reduced bioavailability of 5-FU. ResultsDPD expression was upregulated obviously in tumours of “resistant” mice as reported previously. Importantly, DPD expression was also upregulated significantly in livers of “resistant” mice, compared with those of “sensitive” or untreated mice. Furthermore, the upregulation of DPD expression in livers led to accelerated metabolism of 5-FU. Gimeracil was found to reverse the reduced serum 5-FU concentration. The cultured tumour cells from 5-FU treated mice showed relative sensitivity to higher concentration of 5-FU, even the “resistant” tumour cells. ConclusionOur study suggested that the upregulation of DPD in liver may be involved in acquired resistance to 5-FU, and DPD inhibitors or increasing 5-FU dosage may have potential application in overcoming 5-FU acquired resistance.

Factors affecting the sensitivity of human-derived esophageal carcinoma cell lines to 5-fluorouracil and cisplatin

Effective chemotherapy against esophageal carcinoma is considered achievable with a combination of 5-fluorouracil (5-FU) and cisplatin (CDDP). However, chemo-therapy remains ineffective in certain patients. The aim of this study was to clarify the factors which affect sensitivity to 5-FU and CDDP. The effects of factors known to influence sensitivity to 5-FU and CDDP, namely transporters, DNA repair enzymes and metabolic enzymes, were examined. mRNA levels of four transporters, SLC22A2, SLC23A2, ABCB1 and ABCC2, two DNA repair-related enzymes, Rad51 and MSH2, and one metabolic enzyme, dihydropyrimidine dehydrogenase (DPYD), showed a strong correlation (|r|>0.7) with IC50 values for 5-FU. In addition, the mRNA levels of ABCC2, MSH2 and DPYD showed a strong correlation (|r|>0.7) with the IC50 values for CDDP. Gimeracil, a DPYD inhibitor, enhanced the sensitivity of some cells to 5-FU but decreased the sensitivity of all the cells to CDDP. The inhibitory effects of ABCC2 with MK571 did not correspond to those observed in the correlation analysis. In conclusion, mRNA levels of SLC22A2, SLC23A2, ABCB1, ABCC2, Rad51, MSH2 and DPYD were confirmed to be strongly correlated with IC50 values for 5-FU, and mRNA levels of ABCC2, MSH2 and DPYD were confirmed to be strongly correlated with IC50 values for CDDP. In addition, the inhibition of DPYD appeared to affect the cytotoxicity of CDDP.

Standard-dose tegafur-uracil (UFT) is not a safe alternative in partial dihydropyrimidine dehydrogenase-deficient patients

To the editor, With interest we read the article by Dr Cubero and colleagues, in which they evaluated the safety of tegafur-uracil (UFT®) in five cases with partial dihydropyrimidine dehydrogenase (DPD) deficiency [Cubero et al. 2012]. Based on our previous experience [Deenen et al. 2010], however, we would like to express our concern about their conclusion that UFT is a safe alternative for the treatment of patients with partial DPD deficiency. Cubero and colleagues make the erroneous and unproven statement that the presence of uracil in UFT creates an artificial DPD deficiency, and that the DPD activity in patients with normal DPD activity would then be similarly as low as in DPD-deficient patients. This assumption, however, is incorrect. As uracil is a competitive inhibitor of DPD, it competes with 5-fluorouracil (5-FU) for DPD-mediated metabolism. This does not mean that the activity of DPD is depleted, as suggested by Cubero and colleagues, in contrast, its activity is fully utilized, as well as for the metabolism of uracil, as for the metabolism of 5-FU. We would like to caution that treating patients with partial DPD deficiency with the standard dose of UFT may unnecessarily lead to severe, potentially lethal toxicity. Unlike the cases described by Cubero and colleagues, we could previously describe four cases presenting with comparable severe toxicity profiles upon treatment with UFT as had previously occurred during treatment with capecitabine or 5-FU. In all subjects an underlying partial DPD deficiency was identified by genotype and phenotype analyses [Deenen et al. 2010]. Furthermore, there are several pharmacological lines of argument that support our clinical observation, i.e. that the standard dose of UFT is not safe in (partial) DPD-deficient patients. First, pharmacokinetic studies have shown that DPD remains essential for the metabolism of UFT, with significantly longer half-lives of 5-FU after administration of UFT compared with 5-FU administered intravenously [Ho et al. 1998]. This is due to the presence of uracil in UFT. Since DPD-deficient patients already have longer half-lives of 5-FU than other patients [Mattison et al. 2006], presence of uracil increases its half-life even further. This in turn leads to prolonged and elevated circulating levels of 5-FU, with a subsequently increased risk of 5-FU-induced severe toxicity. Another argument underscoring the importance of normal DPD function in the safe application of UFT, is the experience with S-1. S-1 is another drug combination of tegafur, consisting of tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate in a molar ratio of 1:0.4:1. CDHP inhibits DPD 200-fold more potently than does uracil [Shirasaka et al. 1996a, 1996b]. Even after administration of S-1, the primary 5-FU metabolite formed by DPD is observed in significant concentrations in plasma [Kim et al. 2007]. Thus, DPD remains an essential detoxification enzyme of 5-FU, even when its activity is strongly inhibited. The ultimate proof of theory is the occurrence of 18 treatment-related deaths in patients with cancer and herpes zoster given UFT plus the antiviral drug sorivudine [Pharmaceutical Affairs Bureau, 1994]. Subsequent studies in rats showed that a metabolite of sorivudine, (E)-5-(2-bromovinyl)uracil, instantly and irreversibly inactivates DPD by covalent binding, which has been identified as the underlying mechanism of these toxic deaths [Ogura et al. 1998; Okuda et al. 1998]. It is for these arguments that the Summary of Product Characteristics of UFT notes a known DPD deficiency as a contra-indication [Merck Serono, 2011]. The fact that the patients described by Cubero and colleagues did not develop significant toxicity might be due to patient selection, the slightly decreased dose intensity of 90%, or despite their DPYD*2A genotype a DPD enzyme activity within the (lower) range of normal. We are not aware of this, because DPD enzyme activity was not determined in these patients. In summary, we would like to state that standard-dose UFT is not a safe treatment in (partial) DPD-deficient patients. Instead, dose reductions of on average 50% of either capecitabine, 5-FU or UFT with careful monitoring of safety and further dose titration are proposed as the standard of care [Deenen et al. 2011].

O2-059 - Phase II Study of Combination Therapy with S-1 and Cetuximab in Patients with Kras Wild-Type Unresectable Colorectal Cancer, who Had Previously Received Irinotecan, Oxaliplatin, and Fluoropyrimidines (KSCC0901)

ABSTRACT Background Anti-epidermal growth factor receptor (anti-EGFR) antibodies alone or in combination with irinotecan (Iri) can be considered standard third-line therapy for KRAS wild-type (wKRAS) unresectable colorectal cancer (UNCC). However, some UNCC patients cannot tolerate Iri-containing therapy. S-1, an oral fluorouracil (FU) derivative, enhances the anti-tumor effect by inhibiting dihydropyrimidine dehydrogenase activity and reducing digestive toxicity. Combination therapy with cetuximab (C-mab) may restore 5-FU resistance in 5-FU resistant CCs. Therefore, we examined the efficacy of S-1 + C-mab therapy in wKRAS UNCC patients, who had previously received Iri, oxaliplatin (OX), and FUs. Methods The study design was multicenter, single-arm, open-label phase II study. The major inclusion criteria were written informed consent; histologically proven CC and clinically proven UNCC; presence of measurable lesions; previous therapy with Iri, OX, and 5-FU; documented progressive disease after 5-FU-based chemotherapy; wKRAS tumors; age over 20 years; performance status (PS) 0-1; and adequate organ function. The treatment protocol was as follows: weekly durable intravenous (DIV) C-mab administration at 400 mg/m2 (day 1) and 250 mg/m2/week (except day 1) and oral administration of 80 mg/m2/day S-1 on days 1–28 of each 42-day cycle. The primary end point was progression-free survival (PFS). A sample size of 39 was planned for a threshold PFS of 3.5 months and expected value of 6.0 months, with one-sided alpha of 0.05 and beta of approximately 0.2. Results One patient was ineligible; 38 patients (PS 0/1, 32/6; 1/2/over 3 prior chemotherapy regimens, 4/23/11) were enrolled. The median PFS was 5.5 months; median overall survival (OS), 13.1 months; and the best ORR, 36.8%. The most common grade 3–4 adverse events were neutrophils, hypokalemia, rash, and dry skin. Conclusion S-1 + C-mab therapy may be a promising and well-tolerated treatment choice for wKRAS UNCC patients, who have previously received extensive treatment with Iri, OX, and FUs.

Prognostic significance of 5-fluorouracil metabolism-relating enzymes and enhanced chemosensitivity to 5-fluorouracil by 5-chloro 2,4-dihydroxy-pyridine in urothelial carcinoma

BackgroundRecently, S-1, a novel 5-fluorouracil (5-FU)-based agent containing the strong dihydropyrimidine dehydrogenase (DPD) inhibitor, 5-chloro-2,4-dihydropyrimidine (CDHP) has been clinically used to treat various non-urothelial carcinomas (UC). High levels of thymidylate synthase (TS), the target enzyme of 5-FU and DPD which degrades the majority of 5-FU, are associated with poor prognosis in some cancers. However, only a few reports have dealt with this in UC. The aim of this study was to investigate the clinical significance of TS and DPD in upper tract urothelial carcinoma (UTUC) and evaluate the role of TS and DPD on the sensitivity of 5-FU in UC cell lines and the anti-tumor effect of S-1 in UC xenograft model.MethodsFirstly, we evaluated the immunohistochemical expression of TS and DPD in 176 patients with UTUC to determine their prognostic significance. Secondly, the levels of TS and DPD in UC cell lines were measured by ELISA and real-time PCR. Furthermore, the association between their levels and the sensitivity to 5-FU was examined using the small interfering RNA (siRNA) specific for TS and DPD. Thirdly, the anti-tumor effect of S-1 was evaluated in UC xenograft model.ResultsImmunohistochemical evaluation of TS and DPD in UTUC human samples revealed that TS expression was significantly associated with stage, grade, and lymphovascular invasion and DPD expression was significantly associated with grade. Multivariate analysis revealed that high TS expression was an independent predictor of disease-specific survival in them. In in vitro study using UC cell lines, high levels of TS and DPD were associated with low response to 5-FU and these associations were confirmed with siRNA specific for TS and DPD. In in vivo study using UC xenograft model, S-1 treatment dramatically inhibited tumor growth compared to controls, tegafur, or UFT in UC tumor with a high level of DPD.ConclusionsTS plays an important role in the prognosis of UTUC and S-1 may be a key agent for UC tumor, especially with a high level of DPD.

Phase II study of combination therapy with S-1 and cetuximab in patients with KRAS wild-type unresectable colorectal cancer who had previously received irinotecan, oxaliplatin, and fluoropyrimidines (KSCC0901).

3558 Background: Anti-epidermal growth factor receptor (anti-EGFR) antibodies alone or in combination with irinotecan (Iri) can be considered standard third-line therapy for KRAS wild-type (wKRAS) unresectable colorectal cancer (UNCRC). However, some UNCRC patients (pts) cannot tolerate Iri-containing therapy. S-1, an oral fluorouracil (FU) derivative, enhances the anti-tumor effect by inhibiting dihydropyrimidine dehydrogenase activity and reducing digestive toxicity. Combination therapy with cetuximab (C-mab) may restore 5-FU resistance in 5-FU–resistant CCs. Therefore, we examined the efficacy of S-1+C-mab therapy in wKRAS UNCRC pts, who had previously received Iri, oxaliplatin (OX), and FUs. Methods: The study design was multicenter, single-arm, open-label phase II study. The major inclusion criteria were written informed consent; histologically proven CRC and clinically proven UNCRC; presence of measurable lesions; previous therapy with Iri, OX, and 5-FU; documented progressive disease after 5-FU–based chemotherapy; wKRAS tumors; age ≥ 20 years; performance status (PS) 0–1; and adequate organ function. The treatment protocol was as follows: weekly durable intravenous (DIV) C-mab administration at 400 mg/m2 (day 1) and 250 mg/m2/week (except day 1) and oral administration of 80 mg/m2/day S-1 on days 1–28 of each 42-day cycle. The primary endpoint was progression-free survival (PFS). A sample size of 39 was planned for a threshold PFS of 3.5 months and expected value of 6.0 months, with one-sided alpha of 0.05 and beta of approximately 0.2. Results: One patient was ineligible; 38 pts (PS 0/1, 32/6; 1/2/>3 prior chemotherapy regimens, 4/23/11) were enrolled from 10/2009 to 12/2010. The median PFS (central review) was 5.5 months (90% CI: 4.4 – 5.7); median overall survival (OS), 13.1 months; and the best ORR, 36.8%. The most common grade 3–4 adverse events were neutrophils, hypokalemia, rash, and dry skin. Conclusions: This study showed that S-1+C-mab may be a promising and well-tolerated treatment choice of wKRAS UNCRC, who had previously heavily treated by Iri, OX and FUs.

The combination of hyperthermia or chemotherapy with gimeracil for effective radiosensitization

5-chloro-2,4-dihydroxypyridine (gimeracil) is a component of the oral fluoropyrimidine derivative S-1. Gimeracil was originally added to S-1 to yield prolonged 5-fluorouracil (5-FU) concentrations in serum and tumor tissues by inhibiting dihydropyrimidine dehydrogenase, which degrades 5-FU. We previously demonstrated that gimeracil enhances the efficacy of radiotherapy through the suppression of homologous recombination (HR) in DNA double strand repair. The goal of this paper was to examine the effects of gimeracil on the sensitivity of anticancer drugs and hyperthermia in order to obtain effective radiosensitization. Various cell lines, including DLD 1 (human colon carcinoma cells) and cells deficient in HR or nonhomologous end-joining (NHEJ), were used in clonogenic assays. The survival of these cells after various treatments (e.g., drug treatment, heat treatment, and radiation) was determined based on their colony-forming ability. Gimeracil enhanced cell-killing effects of camptothecin (CPT), 5-FU, and hydroxyurea. Gimeracil sensitized effects of CPT or 5-FU to cells deficient in HR or NHEJ to a similar extent as in other cells (DLD1 and a parent cell), indicating that its sensitizing mechanisms may be different from inhibition of HR or NHEJ. Combination of gimeracil and CPT or 5-FU sensitized radiation more effectively than each modality alone. Gimeracil also enhanced heat sensitivity at 42°C or more. The degree of heat sensitization with gimeracil increased as the temperature increased, and the combination of gimeracil and heat-sensitized radiation was more effective than each modality alone. Gimeracil enhanced sensitivity of CPT, 5-FU, and hyperthermia. Combination of these modalities sensitized radiation more efficiently than each modality alone.

Meta-analysis of randomized phase II and phase III trials of gemcitabine with/without S-1 in Asian patients with advanced pancreatic cancer.

311 Background: Advanced pancreatic cancer (PC) is a virulent disease, where gemcitabine is considered the standard-of-care. A recent phase III evaluation demonstrated superiority of FOLFIRINOX (bolus and infusional 5-fluorouracil (FU), irinotecan, oxaliplatin) in patients with an Eastern Cooperative Oncology Group performance status (ECOG PS) of ≤1. Recently, three studies were presented in abstract form, comparing gemcitabine/S-1 (GS) to gemcitabine. S-1 is a mixture of tegafur (an oral 5-FU prodrug), a dihydropyrimidine dehydrogenase inhibitor and an agent designed to reduce the gastrointestinal toxicity of 5-FU. All three trials demonstrated significant improvements in progression-free survival (PFS) while one study also showed a statistically significant improvement in overall survival (OS). Methods: We performed a meta-analysis of the three trials. Results: Seven hundred and seventy patients were randomized to receive GS vs. gemcitabine; 75% had metastatic disease and 65% had an ECOG PS of 0. GS was associated with superior RR (hazard ratio (HR) 0.348, p=3.06×10-7), PFS (HR 0.64, p=7.26×10-9) and OS (HR 0.79, p=2.47×10-2) compared to gemcitabine. Patients receiving GS were more likely to experience nausea, diarrhea, rash and stomatitis (mostly grade 1/2); neutropenic fever occurred in <2% of patients. One study demonstrated superior quality-of-life for GS. Conclusions: GS should be considered a first-line option for the treatment of advanced PC in Asian patients. This regimen should serve as the reference for future trials and comparison with FOLFIRINOX in patients with ECOG PS ≤1 is warranted.

Effects of Depletion of Dihydropyrimidine Dehydrogenase on Focus Formation and RPA Phosphorylation

Gimeracil, an inhibitor of dihydropyrimidine dehydrogenase (DPYD), partially inhibits homologous recombination (HR) repair and has a radiosensitizing effect as well as enhanced sensitivity to Camptothecin (CPT). DPYD is the target protein for radiosensitization by Gimeracil. We investigated the mechanisms of sensitization of radiation and CPT by DPYD inhibition using DLD-1 cells treated with siRNA for DPYD. We investigated the focus formation of various kinds of proteins involved in HR and examined the phosphorylation of RPA by irradiation using Western blot analysis. DPYD depletion by siRNA significantly restrained the formation of radiation-induced foci of Rad51 and RPA, whereas it increased the number of foci of NBS1. The numbers of colocalization of NBS1 and RPA foci in DPYD-depleted cells after radiation were significantly smaller than in the control cells. These results suggest that DPYD depletion is attributable to decreased single-stranded DNA generated by the Mre11/Rad50/NBS1 complex-dependent resection of DNA double-strand break ends. The phosphorylation of RPA by irradiation was partially suppressed in DPYD-depleted cells, suggesting that DPYD depletion may partially inhibit DNA repair with HR by suppressing phosphorylation of RPA. DPYD depletion showed a radiosensitizing effect as well as enhanced sensitivity to CPT. The radiosensitizing effect of DPYD depletion plus CPT was the additive effect of DPYD depletion and CPT. DPYD depletion did not have a cell-killing effect, suggesting that DPYD depletion may not be so toxic. Considering these results, the combination of CPT and drugs that inhibit DPYD may prove useful for radiotherapy as a method of radiosensitization.

The role of S-1 in the treatment of gastric cancer

The role of S-1 in the treatment of gastric cancer Mariela A Blum, Akihiro Suzuki, Takashi Taketa, Jaffer AjaniThe University of Texas, MD Anderson Cancer Center, Division of Gastrointestinal Oncology, Houston, TX, USAAbstract: Gastric cancer is a lethal disease and continues to be the second leading cause of cancer death worldwide. Surgical resection remains the main treatment for early stages with complete resection having the potential for a cure. Recent data suggest that surgery alone is inferior to surgery plus some form of adjunctive therapy. Unfortunately, most patients with gastric cancer are diagnosed in advanced stages, rendering palliative systemic therapy as the only choice of treatment. The most common chemotherapy combination as a first-line treatment in advanced gastric cancer (AGC) includes a platinum compound, a fluoroporyrimidine and a taxane (in the United States) or an antracycline (in Europe). Fluoropyrimidines have been the backbone in the chemotherapy regimens for the treatment of gastric cancer. There has been considerable interest in oral fluoropyrimidines. S-1 is a fourth-generation oral fluoropyrimidine that combines tegafur, which is a prodrug of 5-fluorouracil (5-FU), and two biochemical modulators: (1) 5-chloro-2,4-dihydroxypyridine, a powerful but reversible inhibitor of dihydropyrimidine dehydrogenase that prevents 5-FU degradation, and (2) potassium oxonate, which reduces gastrointestinal (GI) toxicity by inhibition of 5-FU phosphorylation in the GI mucosa. S-1 has produced an advantage in the postoperative setting in a large Phase III trial and has also been evaluated as a preoperative chemotherapy in gastric cancer, but in the preoperative setting, there are no completed Phase III clinical trials. Nonetheless, S-1 is considered, as a single agent, as the standard of care in Japan for the adjuvant treatment of resected gastric cancer and in combination with cisplatin in the advanced setting based on level 1 evidence in Phase III trials. S-1 is now widely available and has been approved in 27 European countries as a first-line treatment for AGC. S-1 is generally well tolerated with a low toxicity profile. It is a novel agent that provides a convenient and safe advantage over intravenous fluoropyrimidine in AGC.Keywords: tegafur, Ftorafur, FT, 5-FU, advanced gastric cancer

Mechanisms of Radiosensitization by Gimeracil, Inhibitor of Dihydropyrimidine Dehydrogenase

Mechanisms of Radiosensitization by Gimeracil, Inhibitor of Dihydropyrimidine Dehydrogenase

Gimeracil, an inhibitor of dihydropyrimidine dehydrogenase, inhibits the early step in homologous recombination

Gimeracil (5-chloro-2, 4-dihydroxypyridine) is an inhibitor of dihydropyrimidine dehydrogenase (DPYD), which degrades pyrimidine including 5-fluorouracil in the blood. Gimeracil was originally added to an oral fluoropyrimidine derivative S-1 to yield prolonged 5-fluorouracil concentrations in serum and tumor tissues. We have already reported that gimeracil had radiosensitizing effects by partially inhibiting homologous recombination (HR) in the repair of DNA double strand breaks. We investigated the mechanisms of gimeracil radiosensitization. Comet assay and radiation-induced focus formation of various kinds of proteins involved in HR was carried out. siRNA for DPYD were transfected to HeLa cells to investigate the target protein for radiosensitization with gimeracil. SCneo assay was carried out to examine whether DPYD depletion by siRNA inhibited HR repair of DNA double strand breaks. Tail moments in neutral comet assay increased in gimeracil-treated cells. Gimeracil restrained the formation of foci of Rad51 and replication protein A (RPA), whereas it increased the number of foci of Nbs1, Mre11, Rad50, and FancD2. When HeLa cells were transfected with the DPYD siRNA before irradiation, the cells became more radiosensitive. The degree of radiosensitization by transfection of DPYD siRNA was similar to that of gimeracil. Gimeracil did not sensitize DPYD-depleted cells. Depletion of DPYD by siRNA significantly reduced the frequency of neopositive clones in SCneo assay. Gimeracil partially inhibits the early step in HR. It was found that DPYD is the target protein for radiosensitization by gimeracil. The inhibitors of DPYD, such as gimeracil, could enhance the efficacy of radiotherapy through partial suppression of HR-mediated DNA repair.

Low-dose docetaxel enhances the sensitivity of S-1 in a xenograft model of human castration resistant prostate cancer

S-1 is a recently developed dihydropyrimidine dehydrogenase inhibitor fluoropyrimidine and has demonstrated high maximum plasma 5-Fluorouracil (5-FU) levels with mild toxicity, and an oral formulation has resulted in an improvement in patient quality of life. The aims of the present study were to determine the efficacy of S-1 or S-1 combined with docetaxel (DOC) using castration resistant prostate cancer (CRPC) cells and to explore their clinical potential for treating CRPC patients. LNCaP cells, androgen dependent prostate cancer (ADPC) cells and C4-2 cells, which are a CRPC subline of LNCaP cells, were used. Specimens obtained from ADPC and CRPC patients were also evaluated. The CRPC specimens and C4-2 cells exhibited significantly lower thymidylate synthase (TS) expression, a target of 5-FU, than the ADPC specimens and LNCaP cells. In vitro, C4-2 cells exhibited higher sensitivity to 5-FU than LNCaP cells. In C4-2 xenograft model, S-1 monotherapy suppressed tumor growth and low-dose DOC enhanced the anti-tumor effect of S-1. In vitro, low-dose DOC, which did not induce G2/M arrest, increased p53 and p21 and resulted in down-regulation of TS in C4-2 cells, and down-regulation of TS is considered to be responsible for the synergistic effect of S-1 in vivo. The present findings indicate that CRPC patients with androgen ablation may be good candidates for 5-FU based chemotherapy, and these regimens have attractive therapeutic potential for clinical practice, and they may have a significant impact on therapeutic options.

Gimeracil sensitizes cells to radiation via inhibition of homologous recombination

Background and purpose 5-Chloro-2,4-dihydroxypyridine (Gimeracil) is a component of an oral fluoropyrimidine derivative S-1. Gimeracil is originally added to S-1 to yield prolonged 5-FU concentrations in tumor tissues by inhibiting dihydropyrimidine dehydrogenase, which degrades 5-FU. We found that Gimeracil by itself had the radiosensitizing effect. Methods and materials We used various cell lines deficient in non-homologous end-joining (NHEJ) or homologous recombination (HR) as well as DLD-1 and HeLa in clonogenic assay. γ-H2AX focus formation and SCneo assay was performed to examine the effects of Gimeracil on DNA double strand break (DSB) repair mechanisms. Results Results of γ-H2AX focus assay indicated that Gimeracil inhibited DNA DSB repair. It did not sensitize cells deficient in HR but sensitized those deficient in NHEJ. In SCneo assay, Gimeracil reduced the frequency of neo-positive clones. Additionally, it sensitized the cells in S-phase more than in G0/G1. Conclusions Gimeracil inhibits HR. Because HR plays key roles in the repair of DSBH caused by radiotherapy, Gimeracil may enhance the efficacy of radiotherapy through the suppression of HR-mediated DNA repair pathways.

Uridine triacetate for lethal 5-FU toxicity due to dihydropyrimidine dehydrogenase (DPD) deficiency.

e13505 Background: The enzyme dihydropyrimidine dehydrogenase (DPD) catalyzes the first step in degradation of 5-fluorouracil (5FU). Patients with complete or partial DPD deficiency (about 0.1% and 3% of the population, respectively) can experience severe or lethal toxicities after receiving standard doses of 5FU, and impaired clearance may underlie a large fraction of the ∼1,300 deaths per year due to 5FU toxicity in the US. Orally-administered uridine triacetate (vistonuridine) prevents or diminishes toxicities when administered after 5FU overexposure, and has been used successfully as an antidote in more than 28 patients to date who had received accidental overdoses of 5FU. Because DPD deficiency may alter 5FU clearance kinetics (versus 5FU overdoses in the setting of normal DPD activity), studies were conducted on reversal of 5FU toxicity in mice pretreated with the potent DPD inhibitor ethynyluracil (eniluracil; EU) to model DPD deficiency. Methods: Balb/C mice received 2 mg/kg EU i.p., followed by 1...

UFT and S-1 for treatment of primary lung cancer

UFT and S-1 are oral 5-fluorouracil (5-FU) derivative drugs containing an inhibitor of dihydropyrimidine dehydrogenase (DPD); they are defined as DPD-inhibitory fluoropyrimidine (DIF). Because DPD is the key enzyme of 5-FU degradation, 5-FU is not active in primary lung cancers with high DPD activity, which causes rapid degradation of 5-FU. Thus, theoretically, a DIF can overcome a cancer's resistance to 5-FU through inhibiting the enzyme activity of DPD, with the result that 5-FU may be active in primary lung cancer. In fact, UFT has proved to be effective in a postoperative adjuvant setting for early non-small-cell lung cancer (NSCLC) in several randomized controlled studies (RCTs). S-1, in which a more potent DPD inhibitor is combined, is active in advanced NSCLC regardless of the histological cell subtype, and its clinical efficacy in first-line therapy for unresectable advanced disease as well as in postoperative adjuvant therapy for resected disease is now being examined in a variety of RCTs. In the present review, the mechanism of action of UFT and S-1 as well as clinical evidence regarding their use in the treatment of NSCLC are summarized.

1251 Evaluation of pharmacokinetics and safety profiles between S-1 granule and S-1 capsule in patients with solid tumors

Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the pathway of uracil and thymine catabolism. DPD is also the principal enzyme involved in the degradation of 5-fluorouracil (5-FU), an anticancer chemotherapeutic agent that is used clinically to treat renal cell carcinoma (RCC). Little is known about the significance of DPD activity in human cancers. We investigated the activity of DPD in 68 RCC and the relationship between DPD activity and the sensitivity to 5-FU. The levels of DPD activity in RCC and normal kidney samples were determined by the 5-FU degradation assay. The sensitivity to 5-FU was assessed by the microculture tetrazolium dye assay. The activity of DPD was approximately 2-fold higher in normal kidney compared with RCC. DPD activity in Stage I/II RCC was approximately 2-fold higher than that in Stage III/IV RCC. The levels of DPD activity in Grade 1 and Grade 2 RCC were 3 and 2-fold higher, respectively, than that in the Grade 3 cancers. There was an inverse correlation between DPD activity in RCC cells and their sensitivity to 5-FU. Furthermore, 5-chloro-2,4-dihydroxypyridine (CDHP), a potent DPD inhibitor, enhanced the sensitivity to 5-FU. The current study is the first to demonstrate that the level of DPD activity was inversely correlated with both the progression of the disease and increased grade of RCC, and that DPD activity was inversely associated with the sensitivity of RCC to 5-FU, which was enhanced by a DPD inhibitor. These results suggest that a low DPD activity may be associated with the malignant potential of RCC. In addition, it may be possible to overcome 5-FU resistance by using DPD inhibitors in the treatment protocols of 5-FU-based chemotherapy for RCC.

Population pharmacokinetic analysis of S-1 including the CYP2A6 genotype in patients with advanced cancer

2507 Background: S-1 is an oral anticancer agent composed of tegafur, CDHP, and potassium oxonate. Tegafur is a prodrug of fluorouracil (5-FU), and CDHP prevents degradation of 5-FU by inhibiting dihydropyrimidine dehydrogenase and enhances the anticancer activity of 5-FU. The biotransformation of tegafur to 5-FU is demonstrated to be catalyzed by CYP2A6. CYP2A6 polymorphisms are seen more frequently in Japanese people than Caucasian. Therefore, we performed a population pharmacokinetic (PPK) analysis of S-1 including the CYP2A6 genotype in Japanese patients with advanced cancer and developed a model describing the disposition kinetics of tegafur, CDHP, and 5-FU after oral administration of S-1. Methods: Fifty-eight patients with advanced cancer were eligible if they had a performance status of 0 to 3 and had adequate organ function. A dose of 80 mg/m2 of S-1 was given orally twice daily for 28 consecutive days, followed by 14 days of rest. The PPK analysis was performed with plasma concentration data for tegafur, CDHP, and 5-FU. The CYP2A6 genotype was analyzed with the polymerase chain reaction-restriction fragment length polymorphism method or an allele-specific polymerase chain reaction-based method. On the basis of the CYP2A6 genotype, all patients were classified into 1 of 3 groups: wild type, 1 variant allele, and 2 variant alleles. Results: Creatinine clearance correlated with the individual clearance of CDHP. Body surface area correlated with the individual clearance and volumes of CDHP and tegafur. In patients with 2 variant alleles of CYP2A6, tegafur clearance was 58% less than that in patients with wild type or 1 variant allele of CYP2A6. In addition, in patients with a history of gastrectomy, the absorption rate constant of tegafur was 66% higher than that in patients with no history of gastrectomy. The time-varying concentration of CDHP was the most appropriate model component describing the inhibitory effect on 5-FU catabolism. The individual Bayesian predictions of CDHP, tegafur, and 5-FU concentrations based on the present PPK model were in good agreement with the observed data. Conclusions: This is the first PPK model of S-1 including the CYP2A6 genotype. No significant financial relationships to disclose.

Retrospective Analysis of S-1 Monotherapy in Patients with Metastatic Colorectal Cancer After Failure to Fluoropyrimidine and Irinotecan or to Fluoropyrimidine, Irinotecan and Oxaliplatin

Chemotherapy with irinotecan (CPT-11) or oxaliplatin (l-OHP) in combination with infusional 5-fluorouracil (5-FU) and their cross-over as second-line therapies are standard treatments for metastatic colorectal cancer (MCRC). Molecular target agents, which are used as third-line therapies in Western countries after failure of these three drugs, have not been available in Japan. Monotherapy with S-1 [Tegafur, Oteracil potassium and 5-chloro-2,4-dihydroxypyrimidine (CDHP)] showed activity against colorectal cancer with a response rate of 35% as a first-line therapy. It is not clear whether inhibition of dihydropyrimidine dehydrogenase by CDHP can modulate the activity of 5-FU even after patients initially fail with 5-FU. This retrospective study evaluated the efficacy and safety of monotherapy with S-1 for MCRC after the failure of standard chemotherapy. The subjects of this study comprised two cohorts; the first was 27 patients with MCRC who had failed with 5-FU and CPT-11 before approval of l-OHP in Japan (cohort 1), and the second was 23 patients who had failed with 5-FU, CPT-11 and l-OHP (cohort 2). S-1 was given orally twice daily (80 mg m(2)/day) for 28 days followed by a 14-day rest. In cohorts 1 and 2, the response rates were 7% and 0%, and the median progression-free survivals were 2.8 and 2.7 months, and overall survivals after initiation of S-1 were 10.5 and 4.7 months, respectively. The common grade 3 and 4 adverse events in cohorts 1 and 2 were diarrhea 15% and 13%, anorexia 11% and 17% and anemia 26% and 30%, respectively. S-1 monotherapy did not show promising activity against MCRC after the failures with 5-FU, CPT-11 and l-OHP.

Successful treatment of advanced gallbladder cancer with an anticancer drug S-1: assessment based on intratumoral gene

While surgical resection is the most effective treatment for gallbladder cancer, most of these cancers are not resectable at the time of diagnosis, and therefore, chemotherapy serves as the primary therapy in many cases. However, to date, there is no standard chemotherapy for this cancer. We report a case of advanced gallbladder cancer for which the anticancer drug S-1 was effective. The patient was a 53-year-old woman who presented with a huge ovarian tumor. On workup, all abdominal images revealed the presence of advanced gallbladder cancer that had invaded the liver. Because the gallbladder formed a relatively hard and swollen mass involving the omentum, as revealed during exploration, the surgical resection of the gallbladder was not possible at that time, and only hysterectomy and bilateral salpingo-oophorectomy were performed. She started on the anticancer drug S-1 just after this operation. S-1 is a prodrug of 5-fluorouracil (5-FU), and contains 5-chloro-2-4-dihydroxypyridine (CDHP), an inhibitor of dihydropyrimidine dehydrogenase (DPD) that rapidly degrades 5-FU. Eight months after the first operation, radical cholecystectomy was performed. Pathologically, the tumor was diagnosed as an adenocarcinoma of the gallbladder, and no evidence of liver invasion was found. Intratumoral gene expression analysis of the resected gallbladder revealed significantly elevated DPD expression. We suggest that the rapid degradation of 5-FU mediated by this high DPD in our patient was significantly blocked by the CDHP in S-1, and that the efficacy of 5-FU was consequently maintained at the maximum level.