Lineage of drug discovery research on fluorinated pyrimidines: chronicle of the achievements accomplished by Professor Setsuro Fujii.

Prof. Setsuro Fujii achieved significant results in the field of drug discovery research in Japan. He developed nine well-known drugs: FT, UFT, S-1 and FTD/TPI are anticancer drugs, while cetraxate hydrochloride, camostat mesilate, nafamostat mesilate, gabexate mesilate and pravastatin sodium are therapeutic drugs for various other diseases. He delivered hope to patients with various diseases across the world to improve their condition. Even now, drug discovery research based on Dr. Fujii's ideas is continuing.

Erratum: Trifluridine/tipiracil increases survival rates in peritoneal dissemination mouse models of human colorectal and gastric cancer.

[This corrects the article DOI: 10.3892/ol.2017.6258.].

CD44/CD133-Positive Colorectal Cancer Stem Cells are Sensitive to Trifluridine Exposure.

Cancer stem cells (CSCs) are involved in metastatic colorectal cancer recurrence, but no effective therapy targeting these cells is currently available. Because trifluridine (FTD)/tipiracil therapy is used for refractory colorectal cancer, we sought to determine whether FTD is effective against CSC-like cells. CD44+CD133+ high-expressing and other populations of human DLD-1 colon cancer cells were separately isolated through fluorescence-activated cell sorting. The sphere-forming activity of each population and the anti-sphere-forming effects of FTD and fluorouracil (5-FU) on CD44+CD133+ cells were then measured. CD44+CD133+ DLD-1 cells formed substantially more spheres than other cells. Moreover, treating CD44+CD133+ DLD-1 cells with subtoxic concentrations of FTD (1 µM) inhibited sphere formation, and this was superior to the effect of subtoxic concentrations (1 µM) of 5-FU. The associated inhibition rates for FTD and 5-FU were 58.2% and 26.1%, respectively. Further, CD44+CD133+ DLD-1 cells expressed higher levels of thymidine kinase 1, which is responsible for FTD phosphorylation, than DLD-1 cells, and FTD was incorporated into the DNA of CD44+CD133+ DLD-1 cells. Thus, our data show that FTD treatment is effective against CSC-like cells and might be applied as CSC-targeting chemotherapy for tumor subtypes with high CD44 and CD133 expression.

Estrogen Down-regulator Fulvestrant Potentiates Antitumor Activity of Fluoropyrimidine in Estrogen-responsive MCF-7 Human Breast Cancer Cells.

BACKGROUND: Endocrine therapy is clinically administered in hormone-responsive breast cancer. Combinations of fluoropyrimidine S-1 and an aromatase inhibitor or anti-estrogen are considered beneficial in Japan. Herein we assessed new combinations of S-1 and fulvestrant. PATIENTS AND METHODS: Cytotoxicity of fulvestrant and 5-fluorouracil (5-FU) was assessed in hormone-responsive (MCF-7) and non-responsive (MDA-MB-231) breast cancer cell cultures. Fulvestrant and S-1 were evaluated for antitumor activity in mice and their effects on estrogen receptor (ER)-α and progesterone receptor (PgR) levels in MCF-7 xenografts using immunohistochemical methods. RESULTS: Fulvestrant inhibited growth of MCF-7, but not of MDA-MB-231 xenografts. Combinations of 5-FU and fulvestrant were superior to monotherapy in vitro. In vivo antitumor activity of S-1/fulvestrant combination therapy was significantly (p<0.05) enhanced compared to that of both monotherapies. Fulvestrant partially down-regulated expression of ERα and PgR, but in combination with S-1, it almost completely blocked their expression. CONCLUSION: Chemo-endocrine combination therapy using S-1 and fulvestrant is beneficial in estrogen-responsive breast cancer.

ChIP-seq Analysis to Explore DNA Replication Profile in Trifluridine-treated Human Colorectal Cancer Cells In Vitro.

BACKGROUND/AIM: Trifluridine (FTD) is a key component of the novel oral antitumor drug trifluridine/tipiracil that has been approved for the treatment of metastatic colorectal cancer. In this study, a comprehensive analysis of DNA replication profile in FTD-treated colon cancer cells was performed. MATERIALS AND METHODS: HCT-116 cells were exposed to BrdU or FTD and subjected to DNA immunoprecipitation. Immunoprecipitated DNA was sequenced; the density of aligned reads along the genome was calculated. Peak finding, gene ontology, and motif analysis were performed using MACS, GREAT, and MEME, respectively. RESULTS: We identified 6,043 and 5,080 high-confidence FTD and BrdU peaks in HCT-116 cells, respectively. Of 6,043 FTD peaks, 2,911 peaks were uncommon to BrdU. We observed that FTD was preferentially incorporated into genomic regions containing simple repeats, CpG islands, and gene bodies. Conserved motifs in FTD peaks contained dinucleotide repeats such as (GT)n. CONCLUSION: Global FTD incorporation patterns delineated FTD, preferentially incorporating loci in cancer cells.

Effective Sequential Combined Chemotherapy with Trifluridine/Tipiracil and Regorafenib in Human Colorectal Cancer Cells.

Salvage chemotherapy for refractory metastatic colorectal cancer using trifluridine/tipiracil (FTD/TPI) and regorafenib has shown survival benefits. We evaluated the antitumor effects of FTD or FTD/TPI combined with regorafenib in vitro and in vivo. SW620, HCT 116, and HT-29 human colorectal cancer cell lines were treated with FTD and regorafenib simultaneously and sequentially. Cell death, incorporation of FTD into DNA, and molecules related to FTD and regorafenib-associated cell death were investigated. The antitumor effects of FTD combined with regorafenib in SW620 and COLO205 xenografts were also evaluated. Cell death was greater after sequential treatment with FTD followed by regorafenib in SW620 cells, but not in HCT 116 and HT-29 cells, than after treatment with FTD alone, which was attributable to thymidylate synthase reduction with the induction of apoptosis. In contrast, simultaneous and sequential exposure to regorafenib followed by FTD, but not FTD alone, attenuated the cell death effect. Furthermore, combined FTD/TPI treatment followed by regorafenib had greater antitumor activity than either monotherapy in SW620 and COLO205 xenograft models. Treatment results following regorafenib administration subsequent to FTD or FTD/TPI suggest that sequential therapy with FTD/TPI prior to regorafenib may be effective in a clinical setting.

Trifluridine/tipiracil overcomes the resistance of human gastric 5-fluorouracil-refractory cells with high thymidylate synthase expression.

Trifluridine/tipiracil (FTD/TPI or TFTD, also known as TAS-102) is a combination of the antineoplastic thymidine analog, FTD, and thymidine phosphorylase inhibitor, TPI (molar ratio 1:0.5). FTD/TPI was approved in Japan, the United States, and the European Union for the treatment of unresectable advanced or recurrent colorectal cancer. We evaluated the in vitro and in vivo efficacy and mechanisms of action of FTD and FTD/TPI against 5-fluorouracil (5-FU)-resistant MKN45/5FU, MKN74/5FU, and KATOIII/5FU human gastric cancer cells overexpressing thymidylate synthase (TS) and their respective parent cell lines. MKN45/5FU and KATOIII/5FU cells were not cross-resistant to FTD, whereas MKN45/5FU cells were 3.7-fold more resistant than the parental cells in vitro. FTD was also incorporated into genomic DNA in a concentration-dependent manner in 5-FU-resistant and parental cells. Additionally, deoxyuridine monophosphate levels in MKN45/5FU cells after 24-h FTD treatment were 3.0-fold higher than those in parental cells, and FTD treatment for 72 h induced G2/M arrest in MKN45/5FU cells, unlike the S phase arrest in MKN45 cells. Thus, TS-overexpressing MKN45/5FU cells, but not MKN74/5FU and KATOIII/5FU cells, showed partial cross-resistance to FTD. However, FTD/TPI (administered orally twice a day) exhibited antitumor activity to the same extent in MKN45 and MKN45/5FU xenograft mouse models, overcoming in vitro cross-resistance to FTD. DNA incorporation rather than TS inhibition seems to be the main action of FTD under these in vivo conditions. Thus, FTD/TPI is a promising chemotherapeutic agent against gastric cancers recurring following 5-FU therapy.

5-Chloro-2,4-dihydroxypyridine, CDHP, prevents lung metastasis of basal-like breast cancer cells by reducing nascent adhesion formation.

A drug for metastasis prevention is necessary. The orally administered anticancer drug S-1 contributes to cancer therapy. In a mouse xenograft model of metastatic breast cancer from our previous study, the administration of S-1 inhibited lung metastasis. However, the mechanism of inhibition remains elusive. S-1 contains 5-chloro-2,4-dihydroxypyridine (CDHP), which does not have the antigrowth activity, but prevents the degradation of 5-fluorouracil, an anticancer reagent. In this study, we found that CDHP treatment shrinks cell morphology in metastatic basal-like breast cancer cell lines. Wound healing assays showed reduced cell migration in CDHP-treated cells. At the molecular level, CDHP treatment reduced the number of nascent adhesions, whereas the number of mature focal adhesions was not changed. These findings indicate that CDHP impairs focal adhesion formation, which results in a reduction in cell migration. For the in vivo metastasis assay, we used a highly lung-metastatic cell line. We xenografted them into immunodeficient mice, and administered CDHP. To determine whether CDHP prevents metastasis, we measured the weights of harvested lungs. The results showed that the lung weights of the CDHP-treated animals were not significantly different compared to the no-tumor controls, whereas the vehicle group showed a number of metastatic foci and an increase in lung weight. These observations indicate that CDHP administration prevents metastasis. This study reveals a novel effect of CDHP for lung metastasis prevention. Our findings may facilitate the establishment of future metastasis prevention therapies.

Synergistic anticancer activity of a novel oral chemotherapeutic agent containing trifluridine and tipiracil in combination with anti-PD-1 blockade in microsatellite stable-type murine colorectal cancer cells.

Trifluridine/tipiracil (FTD/TPI) is a combination of FTD, an antineoplastic thymidine-based nucleoside analog, and TPI, which acts to enhance the bioavailability of FTD in vivo. It is used to treat patients with unresectable advanced or recurrent colorectal cancer that is refractory to standard therapies. We investigated the anticancer activity of FTD/TPI combined with anti-mouse programed cell death 1 (PD-1) monoclonal antibody (mAb) against CMT-93 cells, which are microsatellite stable (MSS)-type murine colorectal cancer cells. Tumor growth inhibition (TGI) after treatment with anti-mouse PD-1 mAb monotherapy (0.1 mg, i.p., days 1, 5, 9) and FTD/TPI monotherapy (150 mg/kg/day, p.o., days 1-14) were 86.7% and 52.7%, respectively, and that of the combination was 98.4%. The TGI of the combination therapy was significantly greater than that of each monotherapy (P<0.05). The combination therapy caused complete tumor regression in four out of five mice without body-weight reduction, but neither of the monotherapies resulted in complete tumor regression. Low dose FTD/TPI (75 and 100 mg/kg) combined with anti-mouse PD-1 mAb also showed significant antitumor activity against CMT-93 tumors. Flow cytometric analysis revealed that a higher CD8+ T cell ratio among total lymphocytes and a lower regulatory T cells (Tregs) ratio in CD4+ T cells in the combination group compared with that in the control group. These results suggested that the combination therapy induced a cytotoxic response from infiltrated cytotoxic CD8+ T cells and reduced immunosuppressive activity as indicated by decreased Tregs. In this study, the combination therapy was found to have synergistically greater antitumor activity against CMT-93 cells. These preclinical findings indicated that FTD/TPI and anti-mouse PD-1 mAb combination therapy may be a promising treatment option, even for MSS-type colorectal cancer.

Improved chemoradiation treatment using trifluridine in human colorectal cancer cells in vitro.

We aimed to assess the combined effect of trifluridine (FTD) and ionizing radiation (IR) on colorectal cancer cells in vitro. Colorectal cancer cells, HT-29, HCT-15, and HCT 116, showing low, medium, and high sensitivity to IR, respectively, were treated with the combinations of FTD and IR, and evaluated by the clonogenic survival assay. The radiation dose modification factors (DMFs) were calculated as the ratio of radiation doses producing equivalent surviving fractions following the FTD/IR treatment, or IR alone. DMFs of 4 µM FTD followed by 8 Gy of IR were 2.7, 1.5, and 1.2 for HT-29, HCT-15, and HCT 116, respectively, whereas those of 8 Gy of IR followed by FTD were 1.6, 1.4, and 1.0 for these cells, respectively. Intracellular DNA double-strand break levels after IR and FTD were significantly higher than those observed following the IR treatment alone, regardless of whether the IR was applied before or after FTD. RAD51 expression levels were shown to be increased in FTD and IR treated cells. Apoptotic proteins, such as cleaved PARP and cleaved caspase-3, were detected in cells treated with the combination of FTD and IR, while their expression was not significantly induced after IR or FTD treatment alone. These findings suggest that FTD enhances the efficacy of IR and provide a rationale for designing novel combination chemoradiotherapy regimens containing FTD for patients with rectal cancer that are insensitive to the radiation treatment.

MicroRNA profiles involved in trifluridine resistance.

Trifluridine (FTD) is a key component of the novel oral antitumor drug trifluridine/tipiracil, which is approved for the treatment of patients with metastatic colorectal cancer refractory to standard chemotherapies. A microRNA analysis of three colorectal cell lines was conducted to investigate causes of FTD resistance. Drug resistant sublines of DLD-1, HCT-116, and RKO cells were developed by continuous administration of increasing doses of FTD for 5 months. The let-7d-5p gene, which maps to chromosome 9q22.32, was downregulated in the FTD-resistant DLD-1 sublines. DLD-1 cells became more resistant to FTD when let-7d-5p was knocked down and more sensitive when let-7d-5p was overexpressed. The FTD-resistant sublines were not cross-resistant to 5-fluorouracil (5-FU); 5-FU sensitivity was affected only slightly when let-7d-5p as overexpressed or knocked down. These data indicate that let-7d-5p increases sensitivity of FTD but not 5-FU and that let-7d-5p is a potential clinical marker of treatment sensitivity.

Trifluridine/tipiracil increases survival rates in peritoneal dissemination mouse models of human colorectal and gastric cancer.

A number of patients exhibit peritoneal dissemination of gastric or colorectal cancer, which is a predominant cause of cancer-associated mortality. Currently, there is no markedly effective treatment available. The present study was designed to determine the efficacy of trifluridine/tipiracil (TFTD), formerly known as TAS-102, which is used for the treatment of patients with unresectable advanced or recurrent colorectal cancer refractory to standard therapies. Four colorectal cancer cell lines and one gastric cancer cell line were intraperitoneally inoculated into nude mice, as models of peritoneal dissemination. TFTD (200 mg/kg/day) was orally administered for 5 consecutive days followed by 2 drug-free days for 6 weeks. The increase in the lifespan (ILS) of the TFTD-treated mice compared with that of the drug-free control mice was 66.7, 43.3, 106.3, 98.3 and 133.3% for DLD-1, DLD-1/5-fluorouracil [5-fluorouracil (5FU)-resistant subline of DLD-1], HT-29 and HCT116 colorectal cancer cell lines, and MKN45 gastric cancer cell line, respectively. This ILS was similar to that of the irinotecan-treated mice (ILS, 70-84%), but was significantly (P<0.05) increased compared with that of the 5FU-, tegafur, gimeracil and potassium oxonate- and cisplatin-treated mice (ILS, 1-53%, 0.8-60% and 85%, respectively). No significant increase in body weight loss was observed during the dosing periods with any of the drugs used. The increase in CEA levels with progressive peritoneal dissemination was inhibited by TFTD treatment. TFTD also exhibited marked anticancer effects against Kirsten rat sarcoma viral oncogene homolog-mutated tumors and 5FU-resistant tumors. The results of the present study indicate that TFTD may be a potential drug against peritoneal dissemination of colorectal and/or gastric cancer in humans and may be utilized for chemo-naïve tumors and recurrent tumors following 5FU treatment.

Inhibition of PI3K suppresses propagation of drug-tolerant cancer cell subpopulations enriched by 5-fluorouracil.

Drug-tolerant cancer cell subpopulations are responsible for relapse after chemotherapy. By continuously exposing the gastric cancer cell line MKN45 to 5-FU for >100 passages, we established a 5-fluorouracil (5-FU)-tolerant line, MKN45/5FU. Orthotopic xenografts of MKN45/5FU cells in the stomach of nude mice revealed that these cells had a high potential to metastasize to sites such as the liver. Levels of phosphorylated phosphatidylinositide 3-kinase (PI3K) increased both in 5-FU-tolerant subpopulations according to the 5-FU dose, and in gastric submucosal orthotopic xenografts of MKN45/5FU cells. Sequential administration of 5-FU and a PI3K inhibitor, GDC-0941, targeted the downstream ribosomal S6 kinase phosphorylation to significantly suppress 5-FU-tolerant subpopulations and tumor propagation of orthotopic MKN45/5FU xenografts. These results suggest that administration of 5-FU followed by GDC-0941 may suppress disease relapse after 5-FU-based gastric cancer chemotherapy.

Combined efficacy and mechanism of trifluridine and SN-38 in a 5-FU-resistant human colorectal cancer cell lines.

Trifluridine/tipiracil (FTD/TPI or TFTD, also known as TAS-102) with a molar ratio of 1:0.5, is a novel combination of FTD, an antineoplastic thymidine analog, and TPI, an inhibitor of thymidine phosphorylase. It has been approved as a treatment for unresectable advanced or recurrent colorectal cancer. Irinotecan (CPT-11) is an active agent in colorectal cancer. The administration order of drugs is a critical issue in clinical combination therapy. In this study, we evaluated the in vitro simultaneous and sequential combination efficacy of FTD and SN-38, an active metabolite of CPT-11, against human colorectal 5-fluorouracil (5-FU) resistant cell line DLD-1/5-FU and the parental cells DLD-1. The sequential exposure to SN-38 for 24 h followed by sequential exposure to FTD for 24 h or vice versa was more effective for cell survival than the simultaneous exposure of both drugs for 24 h. Furthermore, compared with simultaneous exposure, sequential exposure induced DNA damage, G2/M cell cycle arrest with increasing sub-G1 positive cells, and apoptosis in both DLD-1 and DLD-1/5-FU cells. In particular, in DLD-1/5-FU cells, sequential exposure to SN-38 followed by FTD induced apoptosis more than FTD followed by SN-38. Thus, the sequential treatment with SN-38 followed by FTD may be useful for the combination therapy of FTD/TPI and CPT-11 against relapsed colorectal cancer after 5-FU-based chemotherapy.

Effect of a novel oral chemotherapeutic agent containing a combination of trifluridine, tipiracil and the novel triple angiokinase inhibitor nintedanib, on human colorectal cancer xenografts.

Trifluridine/tipiracil (TFTD) is a combination drug that is used for the treatment of metastatic colorectal cancer and was formerly known as TAS-102. It is a combination of two active pharmaceutical compounds, trifluridine, an antineoplastic thymidine-based nucleoside analog, and tipiracil, which enhances the bioavailability of trifluridine in vivo. TFTD is used for the treatment of patients with unresectable advanced or recurrent colorectal cancer that is resistant to standard therapies. In the present study, the anticancer effects of trifluridine in combination with nintedanib, an oral triple angiokinase inhibitor, on human colorectal cancer cell lines were investigated. The cytotoxicity against DLD-1, HT-29, and HCT116 cell lines was determined by the crystal violet staining method. The combination of trifluridine and nintedanib exerted an additive effect on the growth inhibition of DLD-1 and HT-29 cells and a sub-additive effect on HCT116 cells, as determined by isobologram analyses. Subsequently, the human colorectal cancer cell lines were implanted subcutaneously into nude mice to allow the evaluation of the in vivo tumor growth inhibitory effects of TFTD and nintedanib combination therapy. TFTD (150 mg/kg/day) and/or nintedanib (40 mg/kg/day) were orally administered to the mice twice daily from day 1 to day 14. The tumor growth inhibition with combination therapy was 61.5, 72.8, 67.6 and 67.5% for the DLD-1, DLD-1/5-FU, HT-29, and HCT116 xenografts, respectively. This was significantly (P<0.05) higher than the effects of monotherapy with either TFTD or nintedanib. These results demonstrated the effectiveness of the combination of TFTD and nintedanib in the treatment of colorectal cancer xenografts. The concentration of trifluridine incorporated into DNA in the HT-29 and HCT116 tumors was determined by liquid chromatography-tandem mass spectrometry. The incorporation levels following treatment with TFTD and nintedanib for 14 consecutive days were higher than those associated with TFTD treatment alone. The preclinical findings indicate that the combination therapy with TFTD and nintedanib is a promising treatment option for colorectal cancer.

Folic Acid-Metabolizing Enzymes Regulate the Antitumor Effect of 5-Fluoro-2'-Deoxyuridine in Colorectal Cancer Cell Lines.

In colorectal cancer chemotherapy, the current standard of care includes combination therapy with 5-fluorouracil (5-FU) and leucovorin (LV). However, the factors that determine the LV-mediated enhancement of 5-FU antitumor activity are not fully understood. Therefore, we investigated the roles of thymidine synthase (TYMS), folate receptor 1 (FOLR1), dihydrofolate reductase (DHFR), phosphoribosylglycinamide formyltransferase (GART), methylenetetrahydrofolate dehydrogenase (MTHFD1), and methylenetetrahydrofolate reductase (MTHFR) in LV-mediated enhancement of 5-fluoro-2'-deoxyuridine (FdUrd) cytotoxicity in vitro as a model of 5-FU antitumor activity. These genes were downregulated in DLD-1 and HCT116 human colorectal cancer cells by using small-interfering RNA. Reduced expression of TYMS mRNA significantly increased FdUrd cytotoxicity by 100- and 8.3-fold in DLD-1 and HCT116 cells, respectively. In contrast, reducing the expression of FOLR1, DHFR, GART, MTHFD1, and MTHFR decreased FdUrd cytotoxicity by 2.13- to 12.91-fold in DLD-1 cells and by 3.52- to 10.36-fold in HCT116 cells. These results demonstrate that folate metabolism is important for the efficacy of FdUrd. Overall, the results indicate that it is important to clarify the relationship between folate metabolism-related molecules and 5-FU treatment in order to improve predictions of the effectiveness of 5-FU and LV combination therapy.

Association between mRNA expression of chemotherapy-related genes and clinicopathological features in colorectal cancer: A large-scale population analysis.

To establish the individualized treatment of patients with colorectal cancer, factors associated with chemotherapeutic effects should be identified. However, to the best of our knowledge, few studies are available on this topic, although it is known that the prognosis of patients and sensitivity to chemotherapy depend on the location of the tumor and that the tumor location is important for individualized treatment. In this study, primary tumors obtained from 1,129 patients with colorectal cancer were used to measure the mRNA expression levels of the following genes associated with the effects of standard chemotherapy for colorectal cancer: 5-fluorouracil (5-FU)-related thymidylate synthase (TYMS), dihydropyrimidine dehydrogenase (DPYD) and thymidine phosphorylase (TYMP); folate-related dihydrofolate reductase (DHFR), folylpolyglutamate synthase (FPGS) and gamma-glutamyl hydrolase (GGH); irinotecan-related topoisomerase I (TOP1); oxaliplatin-related excision repair cross-complementing 1 (ERCC1); biologic agent-related vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR). Large-scale population analysis was performed to determine the association of gene expression with the clinicopathological features, in particular, the location of the colorectal cancer. From the results of our analysis of the mRNA expression of these 10 genes, we noted the strongest correlation between DPYD and TYMP, followed by TYMS and DHFR. The location of the colorectal cancer was classified into 4 regions (the right­ and left-sided colon, rectosigmoid and rectum) and was compared with gene expression. A significant difference in all genes, apart from VEGF, was noted. Of the remaining 9 genes, the highest expression of TYMS and DPYD was observed in the right­sided colon; the highest expression of GGH and EGFR was noted in the left-sided colon; the highest expression of DHFR, FPGS, TOP1 and ERCC1 was noted in the rectosigmoid, whereas TYMP expression was approximately equivalent in the right-sided colon and rectum, and higher than that in other locations. The data generated from this study may prove to be useful for the development of individualized chemotherapeutic treatments for patients with colorectal cancer, and will mean that the tumor location is taken into account.

Novel 5-fluorouracil-resistant human esophageal squamous cell carcinoma cells with dihydropyrimidine dehydrogenase overexpression.

5-Fluorouracil (5-FU) is a key drug for the treatment of esophageal squamous cell carcinoma (ESCC); however, resistance to it remains a critical limitation to its clinical use. To clarify the mechanisms of 5-FU resistance of ESCC, we originally established 5-FU-resistant ESCC cells, TE-5R, by step-wise treatment with continuously increasing concentrations of 5-FU. The half maximal inhibitory concentration of 5-FU showed that TE-5R cells were 15.6-fold more resistant to 5-FU in comparison with parental TE-5 cells. TE-5R cells showed regional copy number amplification of chromosome 1p including the DPYD gene, as well as high mRNA and protein expressions of dihydropyrimidine dehydrogenase (DPD), an enzyme involved in 5-FU degradation. 5-FU treatment resulted in a significant decrease of the intracellular 5-FU concentration and increase of the concentration of α-fluoro-ureidopropionic acid (FUPA), a metabolite of 5-FU, in TE-5R compared with TE-5 cells in vitro. Conversely, gimeracil, a DPD inhibitor, markedly increased the intracellular 5-FU concentration, decreased the intracellular FUPA concentration, and attenuated 5-FU resistance of TE-5R cells. These results indicate that 5-FU resistance of TE-5R cells is due to the rapid degradation of 5-FU by DPD overexpression. The investigation of 5-FU-resistant ESCC with DPYD gene copy number amplification and consequent DPD overexpression may generate novel biological evidence to explore strategies against ESCC with 5-FU resistance.

Efficacy of Combination Chemotherapy Using a Novel Oral Chemotherapeutic Agent, TAS-102, with Oxaliplatin on Human Colorectal and Gastric Cancer Xenografts.

TAS-102 is a novel oral nucleoside antitumor agent consisting of trifluridine (FTD) and the thymidine phosphorylase inhibitor tipiracil hydrochloride (at a molar ratio of 1:0.5) that was approved in Japan in 2014 for the treatment of unresectable advanced or recurrent colorectal cancer. In the present study, the enhancement of therapeutic efficacy using a combination of TAS-102 and oxaliplatin was evaluated in a xenograft-bearing nude mouse model of colorectal and gastric cancer. TAS-102 was orally administered twice-a-day from day 1 to 14, and oxaliplatin was administered intravenously on days 1 and 8. The in vivo growth-inhibitory activity was evaluated based on the tumor volume and the growth-delay period, was estimated based on the period required to reach a tumor volume five-times greater than the initial volume (RTV5). The tumor growth-inhibitory activity and RTV5 in mice administered TAS-102 with oxaliplatin were significantly superior to those associated with either monotherapy in mice with colorectal (HCT 116, SW-48; p<0.001) and gastric cancer (SC-2, MKN74; p<0.001). MKN74/5FU, a 5-fluorouracil-resistant MKN74 sub-line, was sensitive to both FTD and oxaliplatin in vitro. In vivo, TAS-102 alone was effective in MKN74/5FU, and its anti-tumor activity was significantly enhanced in combination with oxaliplatin (p<0.001). No significant decrease in body weight or toxicity was observed compared to either monotherapy. The present pre-clinical findings indicate that combination of TAS-102 and oxaliplatin is a promising treatment option for colorectal or gastric cancer, and can be utilized in both chemo-naïve tumors and recurrent tumors after 5-fluorouracil treatment.

Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, together with bevacizumab, cetuximab, or panitumumab on human colorectal cancer xenografts.

TAS-102 is a novel oral nucleoside antitumor agent that consists of trifluridine (FTD) and tipiracil hydrochloride (TPI) at a molecular ratio of 1:0.5, and was approved in Japan in March 2014 for the treatment of patients with unresectable advanced or recurrent colorectal cancer that is refractory to standard therapies. In the present study, we used colorectal cancer xenografts to assess whether the efficacy of TAS-102 could be improved by combining it with bevacizumab, cetuximab or panitumumab. TAS-102 was orally administered twice a day from day 1 to 14, and bevacizumab, cetuximab and panitumumab were administered intraperitoneally twice a week for 2 weeks. Growth inhibitory activity was evaluated based on the relative tumor volume (RTV) after 2 weeks of drug administration and time taken for the relative tumor volume to increase five-fold (RTV5). Tumor growth inhibition and RTV5 with TAS-102 and bevacizumab combination treatment were significantly better than those with TAS-102 or bevacizumab alone in the SW48 and HCT116 tumor models, and the concentration of phosphorylated FTD in tumors determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was higher in the TAS-102 and bevacizumab combination group than in the TAS-102 monotherapy group. The combination of TAS-102 and cetuximab or panitumumab was also significantly more effective than either monotherapy in the SW48 tumor model. There was no significant difference in the body weight between the mice treated with TAS-102 monotherapy and any of the combination therapies on day 29. Our preclinical findings indicate that the combination therapy of TAS-102, bevacizumab and cetuximab or panitumumab is a promising treatment option for colorectal cancer.