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.

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.

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.

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.

Abstract 2963: CD44+/CD133+ colorectal cancer stem cells are sensitive to trifluridine

Background: Cancer stem cells (CSCs) are involved in disease recurrence, metastases, and therapeutic resistance. However, anticancer agents that target CSCs are not currently available. Trifluridine (FTD)/tipiracil (TPI), a novel oral antitumor drug, was approved for the treatment of patients with metastatic colorectal cancer who had been previously treated with anti-vascular endothelial growth factors; anti-epidermal growth factor receptors (in patients with ras wild-type genes); or fluoropyrimidine-, oxaliplatin-, irinotecan-based chemotherapies. FTD/TPI improves overall survival, and FTD is the key component of FTD/TPI. Here, we demonstrated the efficacy of FTD against CD44 and CD133 high-expressing (CD44+CD133+) colorectal cancer cells that possess CSC-like properties.

Method: CD44+CD133+ and other populations of DLD-1, a colorectal cell line, were separated by fluorescence-activated cell sorting (FACS). The sphere-forming activity of each population, and anti- sphere-forming effects of FTD and fluorouracil (5-FU) on CD44+CD133+ cells, were measured. In addition, DLD-1 and HCT-116, two colorectal cell lines, were treated with FTD for 5 months. The CSC markers CD44 and CD133 were measured by FACS, and the cells' in vitro and in vivo tumor-initiating properties were evaluated.

Results: CD44+CD133+ DLD-1 cells formed significantly more spheres than did CD44-CD133- cells (sphere ratio CD44+CD133+/CD44-CD133- = 4.0) and CD44+CD133- cells (sphere ratio CD44+CD133+/CD44+CD133- = 1.7). In the in vitro proliferation assay, CD44+CD133+ cells had greater 5-FU resistance, but not higher FTD resistance, than did unsorted cells. In addition, treatment of CD44+CD133+ DLD-1 cells with subtoxic concentrations of FTD (1 µM) disrupted sphere formation, which was superior to the effect of treatment with 1 µM 5-FU. The inhibition rates for FTD and 5-FU were 59.5% and 14.3%, respectively. DLD-1 and HCT-116 cell lines treated with FTD for 5 months had smaller CD44+CD133+ populations and lower sphere-forming activity than did untreated cell lines; population decline rates were 93.8% and 74.7%, respectively. Furthermore, 5 months of in vitro exposure to FTD reduced in vivo tumor formation potential in both cell lines. These results suggest that FTD is effective against CSC-like cells, and that treatment with FTD might reduce CSC-like populations.

Conclusion: FTD had a direct effect on the sphere-forming activity of CSC-like CD44+CD133+ cells that was superior to that of treatment with 5-FU. Its effectiveness against CSC-like CD44+CD133+ cells suggests that FTD might be useful for CSC-targeted chemotherapy in tumors that highly express CD44 and CD133.

Citation Format: Kenta Tsunekuni, Masamitsu Konno, Jun Koseki, Ayumu Asai, Kazuaki Matsuoka, Teiji Takechi, Yuichiro Doki, Masaki Mori, Hideshi Ishii. CD44+/CD133+ colorectal cancer stem cells are sensitive to trifluridine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2963.

Abstract 2067: Trifluridine/tipiracil can overcome the resistance of gastric 5-fluorouracil-refractory cancer cells with various cancer driver-genes alterations in vitro and in vivo

Background: Trifluridine (FTD) is a key component of the antitumor drug combination trifluridine/tipiracil (FTD/TPI, also known as TAS-102), which is approved for the treatment of patients with metastatic colorectal cancer refractory to standard chemotherapies. Recently, a global phase III Trial (TAGS trial) revealed that FTD/TPI also prolongs overall survival in patients with metastatic gastric cancer. In this study, we explored the efficacy of FTD/TPI in 5-fluorouracil (5-FU)-resistant gastric cancer cell lines in vitro and in vivo, revealing their unique genomic signatures by a multi-omics profiling approach.

Method: 5-FU-resistant cell lines were established by continuously exposing the parent cell lines (MKN45, MKN74, and KATOIII) to escalating concentrations of 5-FU over a 1-year period. The sensitivities of the cell lines to FTD were evaluated by a cell growth inhibitory assay using crystal violet staining. Total RNA was purified using a silica membrane spin column-based centrifugation procedure. The extracted RNA was used to establish a cDNA library for transcriptome sequencing using a HiSeq 2500 platform. The resulting fastq files were used for mapping, gene mutation, and expression analysis. We especially focused on “pyrimidine metabolism” in Kyoto Encyclopedia of Genes and Genomes analysis.

Results: The KATOIII/5FU, MKN74/5FU, and MKN45/5FU were 2.4-fold, 4.7-fold, and 14.3-fold more resistant to 5-FU than their parent cell lines, respectively. MKN74/5FU and KATOIII/5FU did not show any cross-resistance to FTD, while TS-overexpressing MKN45/5FU showed partial cross-resistance to FTD in vitro. FTD/TPI exhibited significant antitumor activity in both MKN45/5FU and MKN74/5FU cells in vivo. As compared with corresponding parental cell lines, the transcriptome analysis revealed that ENTPD3 gene expression level changed by more than 2-fold in only MKN45/5FU, while ENTPD8 and ENPP3 gene expression changed by less than 0.5-fold in both MKN74/5FU and KATOIII/5FU. In addition, there are genes (UMPS, POLR2B, POLR2D, POLR2H, POLR2L, POLR2J2, POLR3G, PRIM1, POLE, and UPP1) that had non-synonymous mutation within their coding sequences. Interestingly, mutation status of POLR2L and PRIM1 in MKN45/5FU, of UMPS, POLR2D, and POLR2H in MKN74/5FU, of POLR2B, POLR2J2, and POLR3G in KATOIII/5FU differed from those of parental cell lines.

Conclusions: FTD/TPI was effective against 5-FU-resistant gastric cancer cells harboring various genetic alterations in vitro and in vivo. This might be a reason why FTD/TPI is expected to show significant benefits against heterogeneous metastatic gastric cancer in a clinical setting.

Citation Format: Kazuaki Matsuoka, Takashi Kobunai, Teiji Takechi. Trifluridine/tipiracil can overcome the resistance of gastric 5-fluorouracil-refractory cancer cells with various cancer driver-genes alterations in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2067.

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.

Abstract 1867: Combined and sequential chemotherapy efficacy of trifluridine/tipiracil and regorafenib in colorectal cancer cell lines

Background: Trifluridine/tipiracil (FTD/TPI or TFTD, also known as TAS-102) is recommended for treating metastatic colorectal cancers refractory to standard chemotherapies. Regorafenib is an oral multikinase inhibitor that blocks the activity of several protein kinases associated with angiogenesis, oncogenesis, and the tumor microenvironment. We evaluated the antitumor effects of FTD/TPI combined with regorafenib on a colorectal tumor xenograft mouse model. We also investigated whether cytotoxicity was enhanced when FTD was used sequentially with regorafenib in vitro.

Method: The colorectal cancer cell lines SW620 and COLO 205 were implanted into nude mice subcutaneously. FTD/TPI (150 mg/kg/day) was orally administered twice daily from days 1 to 14 and regorafenib (10 mg/kg/day) was administered once a day at approximately 2-4 h after FTD/TPI. For the in vitro cytotoxic assay, SW620 cells were treated with FTD and regorafenib as follows: (1) exposure to 0.1-4.0 µM FTD alone, (2) sequential exposure to 0.1-4.0 µM FTD for 24 h followed by 10 µM regorafenib for 24 h, or (3) sequential exposure to 10 µM regorafenib for 24 h followed by 0.1-4.0 µM FTD for 24 h. All treatments were evaluated by a colony formation assay. Molecules involved in mechanism of action of FTD and regorafenib and in apoptosis were evaluated by western blot.

Results: Tumor growth inhibition by combination therapy was 86.4% and 92.3% for SW620 and COLO 205 xenografts, respectively; this was significantly superior to the growth inhibition observed after either monotherapy for the two evaluated cancer xenografts (P &lt; 0.01). Thus, FTD/TPI combined with regorafenib is significantly more effective than either monotherapy in colorectal cancer xenografts. This combination therapy was tolerated without 20% body-weight reduction and drug-related death. FTD followed by regorafenib treatment in SW620 cells showed stronger cell killing effect than FTD alone. In contrast, regorafenib followed by FTD treatment attenuated its cell killing effect rather than that to FTD alone. In comparison with FTD alone, FTD followed by regorafenib reduced thymidine synthase (TS) and inhibited phosphorylation of ERK1/2 (pERK1/2) with the induction of proapoptotic marker, cleavage of PARP. In contrast, regorafenib followed by FTD induced TS and pERK1/2. Thus, FTD followed by regorafenib treatment is more effective than regorafenib followed by FTD treatment in vitro.

Conclusion: FTD/TPI combined with regorafenib is significantly more effective than either monotherapy in preclinical models. Moreover, FTD followed by regorafenib is more effective than vice versa in vitro, suggesting that in patients sequential therapy with FTD/TPI prior to regorafenib may be helpful in treating colorectal cancer.

Citation Format: Kazuaki Matsuoka, Fumio Nakagawa, Junji Uchida, Teiji Takechi. Combined and sequential chemotherapy efficacy of trifluridine/tipiracil and regorafenib in colorectal cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1867.

Abstract 2886: ChIP-seq analysis to explore DNA replication profile in trifluridine-treated human colorectal cancer cells in vitro

Background: Trifluridine (FTD) is a key component of the novel oral antitumor drug trifluridine/tipiracil, which was approved for the treatment of patients with metastatic colorectal cancer refractory to standard chemotherapies. FTD, an antineoplastic thymidine analogue, is efficiently incorporated into the genomic DNA of tumor cells. However, the molecular mechanisms underlying its cytotoxic effects remain unclear. Therefore, the DNA replication profile in FTD-treated cells was comprehensively analyzed to explore the mode of FTD incorporation into the genomic DNA. Method: We generated the DNA replication profile in HCT-116 human colorectal cancer cells as follows: asynchronous cultures of HCT-116 were exposed to 5 μM 5-bromo-2′-deoxyuridine (BrdU), a non-cytotoxic control drug or FTD, for 4 h, harvested, and subjected to DNA immunoprecipitation using an anti-BrdU antibody. An input and immunoprecipitated DNA from each experiment were sequenced, and the sequence reads generated using Illumina sequencing were aligned uniquely to the human genome (hg19), allowing up to two mismatches using the BWA algorithm with default settings. The density of aligned reads along the genome was calculated and stored in a bigWig file for visualization in genome browsers. Peak finding and gene ontology analysis were performed using MACS and Genomic Regions Enrichment of Annotations Tool (GREAT). The 60-bp sequences surrounding the summits of the top 1000 peaks were analyzed for conserved motifs using the online program MEME. Results: In an antibody validation step, we observed significant FTD peaks over input DNA. We identified 6043 and 5080 high confident FTD and BrdU peaks in HCT-116 cells, respectively. Interestingly, 2911 of 6043 FTD peaks were uncommon to BrdU peaks, while 3232 peaks were common in FTD and BrdU. The FTD and BrdU peaks were not randomly distributed throughout the genome. Most FTD and BrdU peaks were ±5 kb or further away from transcription start sites. We identified the genes associated with distant peaks of FTD using GREAT. FTD peaks occurred near genes involved in extracellular matrix structural composition such as ACAN, BGN, CHAD, and COL12A1, while BrdU peaks were near genes involved in cysteine-type endopeptidase inhibitor activity such as ARRB1, BIRC7, LCN1, and CST1. Dinucleotide repeats such as TGTGTG were observed as conserved motifs in FTD-peak sequences. Conclusion: Global FTD incorporation patterns can delineate active replication loci, namely FTD preferentially incorporating loci, in human cancer cells. The DNA replication profile in FTD-treated cells differed from that in BrdU-treated cells. Thus, differences in the incorporation patterns of FTD and BrdU into the genomic DNA revealed the mechanisms of antitumor activities of FTD.

Citation Format: Takashi Kobunai, Kazuaki Matsuoka, Teiji Takechi. ChIP-seq analysis to explore DNA replication profile in trifluridine-treated human colorectal cancer cells in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2886.

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.

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.

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.

Abstract 1071: Efficacy of trifluridine/tipiracil + anti-mouse PD-1 antibody combination on mouse colorectal cancer model and related tumor immunomodulatory effects

Background: Trifluridine/tipiracil (FTD/TPI) is an oral nucleoside antitumor agent that is composed of trifluridine and tipiracil hydrochloride at a molecular ratio of 1:0.5. Checkpoint-blockade immunotherapies are particularly effective in patients with tumor T cell infiltrations. In this study, the antitumor effects of FTD/TPI + anti-mouse PD-1 antibody combination were studied in a syngeneic mouse model and the tumor-infiltrating lymphocyte (TIL) subsets were evaluated. Method: The mouse colorectal cancer cell line CMT-93 was subcutaneously implanted into C57BL/6 mice. Vehicle (0.5% Hydroxypropyl methylcellulose, 10 mL/kg, p.o.), FTD/TPI (75, 100, and 150 mg/kg/day, twice daily, days 1-14, p.o.), anti-mouse PD-1 antibody (clone RMP1-14; 0.1 mg/body; once daily, days 1, 5, and 9; i.p.), and FTD/TPI + anti-mouse PD-1 antibody combination were administered, and inhibitory activity was evaluated according to tumor-volume changes. Single-cell suspensions were prepared from collected tumors. Based on cell marker expression, CD4+ T cells, CD8+T cells, and regulatory T cells (Tregs) were identified using antibodies against CD4, CD8, CD25, and Foxp3, and subsets of TILs were evaluated by flow cytometry. Results: Both anti-mouse PD-1 antibody and FTD/TPI monotherapies were effective in vivo. Tumor-growth inhibition by anti-mouse PD-1 antibody was 81.7% at 0.1 mg/kg/day and that by FTD/TPI was 33.4%, 46.1%, and 59.5% at 75, 100, and 150 mg/kg/day, respectively. FTD/TPI + anti-mouse PD-1 antibody combination using FTD/TPI (75, 100, and 150 mg/kg/day) with anti-mouse PD-1 antibody (0.1 mg/kg/day) inhibited tumor growth at significantly higher rates (P &lt; 0.05; 91.8%, 95.7%, 98.4%, respectively) than monotherapy. Remarkably, the 150-mg/kg/day FTD/TPI + 0.1-mg/kg/day anti-mouse PD-1 antibody combination caused complete tumor regression in four/five mice without body-weight reduction or drug-related deaths; however, none of the monotherapies caused complete tumor regression. Flow cytometric analysis revealed a higher CD8+ T cell percentage among total lymphocytes and a lower Treg percentage in CD4+ T cells after combination therapy compared with the controls. Conclusion: FTD/TPI + anti-mouse PD-1 antibody combination was synergistically effective on CMT-93 mouse colon tumor. This combination increased CD8+ T cell percentages in whole lymphocyte and decreased Treg percentages in CD4+ T cell. This suggests that FTD/TPI + anti-mouse PD-1 antibody combination modulates tumor T cell populations and improves their antitumor activity.

Citation Format: Norihiko Suzuki, Hiroshi Tsukihara, Fumio Nakagawa, Takashi Kobunai, Teiji Takechi. Efficacy of trifluridine/tipiracil + anti-mouse PD-1 antibody combination on mouse colorectal cancer model and related tumor immunomodulatory effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1071. doi:10.1158/1538-7445.AM2017-1071

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.

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.

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.

Abstract 4659: Folic acid-metabolizing enzymes regulate 5-fluorouracil anticancer activity on colorectal cancer cell lines

Background: In colorectal cancer chemotherapy, the current standard of care includes 5-fluorouracil (5-FU) and leucovorin (LV) combination therapy. To understand the role of folic acid-metabolizing enzymes in the LV-mediated enhancement of 5-FU's antitumor activity, we suppressed the expression of genes related to folic acid metabolism and evaluated the resultant effect on the proliferation inhibitory effect of 5-fluoro-2′-deoxyuridine (FdUrd). Method: We downregulated the expression of thymidylate synthase (TS), folate receptor 1 (FOLR1), methylenetetrahydrofolate reductase (MTHFR), methylenetetrahydrofolate dehydrogenase (MTHFD), dihydrofolate reductase (DHFR), and phosphoribosylglycinamide formyltransferase (GART) by lipofection of small interfering RNA (siRNA) in DLD-1 and HCT116 cells, and calculated the relative change in IC50 values on 48 hr exposure to FdUrd in comparison with the corresponding IC50 values in control siRNA-treated cells. In cells with TS downregulation, LV-mediated enhancement of sensitivity to FdUrd was also evaluated. Sensitivity to FdUrd was determined using the crystal violet staining method. Results: Treatment with siRNA downregulated the expression of folic acid-metabolizing enzymes. LV enhanced the sensitivity to FdUrd in control siRNA-treated cells in a dose-dependent manner. However, in cells with TS downregulation, LV did not enhance the sensitivity to FdUrd. Downregulation of folic acid-metabolizing enzymes, except TS, decreased the efficacy of FdUrd, although there was little decrease in FdUrd efficacy owing to MTHFR downregulation. Conclusion: The level of TS expression determined the LV requirement, and downregulation of folic acid-metabolizing enzymes, which impaired the folic acid cycle, decreased the efficacy of 5-FU. Comparison of the IC50 values in target siRNA-treated cells and control siRNA-treated cells.DLD-1 cellsHCT116 cellsexpression (%)*IC50 (μM)fold changeexpression (%)*IC50 (μM)fold changeNon-silencing Control siRNA100.000.671.00100.000.251.00TS10.580.010.0114.840.030.12FOLR19.148.6512.9125.122.5910.36MTHFR25.441.432.1348.750.883.52MTHFD9.662.734.0715.061.997.96DHFR8.524.146.1817.231.706.80GART18.905.388.037.102.469.84Values are means (n = 3). *: Expression (%) is the expression at the beginning of FdUrd treatment (at 48 hr after siRNA treatment).

Citation Format: Hiroshi Tsukihara, Kenta Tsunekuni, Teiji Takechi. Folic acid-metabolizing enzymes regulate 5-fluorouracil anticancer activity on colorectal cancer cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4659.

Abstract 3004: Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, with nintedanib on human colorectal cancer xenografts

Background:

TAS-102 (also named TFTD) is a novel antitumor nucleoside. This is a combination of an antineoplastic thymidine-based nucleoside analog, trifluridine (FTD), and tipiracil hydrochloride (TPI) at a molar ratio 1:0.5. FTD is the active antitumor component of TAS-102 and its triphosphate form is incorporated into DNA in tumor cells. TPI is an inhibitor of thymidine phosphorylase, which strongly inhibits the biodegradation of FTD. In a recent global, multicenter, randomized, double-blind Phase III study (RECOURSE), TAS-102 showed to significantly improve overall survival and progression-free survival and had a favorable safety profile in comparison to those achieved with placebo in patients with metastatic colorectal cancer refractory to standard chemotherapies. Nintedanib is an oral triple angiokinase inhibitor that simultaneously inhibits vascular endothelial growth factor receptors, platelet-derived growth factor receptors, and fibroblast growth factor receptors. It is currently being investigated in Phase III studies of advanced non-small cell lung cancer, colorectal cancer, and ovarian cancer. In this study, we evaluated the antitumor effects of TAS-102 in combination with nintedanib on human colorectal tumor xenografts in a nude mouse model.

Method:

Drug cytotoxicity was determined by the crystal violet staining method using DLD-1, HT-29, and HCT116 colorectal cancer cell lines. Drug interaction was evaluated by performing isobologram analysis. Furthermore, the human colorectal cancer cell lines were implanted into nude mice subcutaneously, and TAS-102 (150 mg/kg/day) and/or nintedanib (20 or 40 mg/kg/day) were orally administered twice daily from Days 1 to 14. Growth inhibitory activity was evaluated based on tumor volume.

Results:

The combination of TAS-102 and nintedanib exerted an additive effect on growth inhibition of DLD-1 and HT-29, and a sub-additive effect on HCT116 in vitro. TAS-102 and nintedanib monotherapies were both active on all of the evaluated colorectal cancers in vivo. Tumor growth inhibition by combination therapy (150 mg/kg/day TAS-102 plus 40 mg/kg/day nintedanib) was 61.5%, 67.6%, and 67.5% for DLD-1, HT-29, and HCT116 xenografts, and that was significantly superior to that of either monotherapy for all evaluated cancer xenografts (P &lt; 0.05). These results demonstrate that combination therapy with TAS-102 and nintedanib is significantly more effective than either monotherapy in colorectal cancer xenografts. This combination therapy appeared to be well tolerated because neither a reduction in body weight of more than 20% nor drug-related death was observed.

Conclusion:

Combination therapy of TAS-102 and nintedanib is significantly more effective than either monotherapy in preclinical models and should be considered for investigation in metastatic colorectal cancer patients.

Citation Format: Norihiko Suzuki, Fumio Nakagawa, Mamoru Nukatsuka, Kazuaki Matsuoka, Hiroshi Tsukihara, Teiji Takechi. Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, with nintedanib on human colorectal cancer xenografts. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3004.

Abstract 5175: Mutational and copy number profiling of cancer-related genes in 26 human tumor xenografts and their correlations with antitumor drug sensitivities

Background: Tumor responses to antitumor drugs are variable, but predicting these responses is important when selecting effective chemotherapy treatments. Our aim was to identify variations or alterations in gene copy number that influence cancer cells’ susceptibilities to standard chemotherapeutic agents. Methods: Twenty-six human cancer cell lines representing the five main tumor types were subcutaneously implanted into nude mice and tested for sensitivity to fluorinated pyrimidines (UFT, TS-1, 5’-DFUR, and capecitabine), CDDP, CPT-11, and paclitaxel. The cell lines included lung (AOI, LC-11, Lu-99, LX-1, LC-6, Lu-134, Lu-130), colon (KM12C, KM12C/FU, HCT-15, COL-1, CO-3), pancreas (PAN-3, PAN-4, PAN-12, H-48, MIAPaCa-2, BxPC-3), gastric (SC-2, ST-40, 4-1ST, SC-4) and breast (MC-2, MX-1, MDA-MB-435SHM, MDA-MD-231). Genomic DNA was prepared from frozen tumor tissues. Mutations in 48 genes from the TruSeq Amplicon Cancer Panel were screened using the MiSeq system (Illumina, San Diego, CA). Somatic copy number alterations were analyzed by high-density SNP arrays (Affymetrix, Santa Clara, CA). Results: Of the 225 amplicons (187 non-overlapping regions) in the cancer panel, 86% achieved a minimum average sequencing depth of 1000X and the average coverage across all target regions was 5374X. In 26 tumors, sequencing detected 55 somatic mutations in 18 out of 48 cancer related genes of high prognostic or therapeutic significance, such as TP53, APC, PTEN, and SMAD4. Mutation frequencies across 26 xenografts were 73.1% (TP53), 38.5% (KRAS), 15.4% (APC), 11.5% (SMAD4 and RET), 7.7% (BRAF, GNAS, and PTEN), and 3.8% (CTNNB1, GNAQ, HNF1A, HRAS, IDH1, KIT, NOTCH1, PIK3CA, SMO, and STK11). Tumor xenografts with TP53 mutations were significantly less sensitive to CDDP and CPT-11 than wild-type cell lines (P&lt;0.05). The APC mutation conferred resistance to paclitaxel. Copy number gain was observed at 23.1% (KRAS), 15.1% (EGFR), and 11.5% (JAK2 and CDK2NA). Copy number loss was observed at 30.8% (CDK2NA), 19.2% (SMAD4), and 15.4% (PTEN). Cell lines with more copies of CDK2NA and JAK2 were more sensitive to CDDP, while cell lines with fewer copies of PTEN were more sensitive to CDDP. Similarly, copy number gain of CDH1 conferred resistance to UFT, while copy number gain of KRAS sensitized tumors to 5’-DFUR. The copy number of 48 genes determined by the GeneChip array moderately agreed with those estimated by local GC-content adjusted coverage profiles in the sequencing analysis (average Pearson's correlation coefficient = 0.66, 95%CI = 0.54-0.69). Conclusions: Integrated analysis of mutational profiling and gene copy number may be useful to elucidate candidate genes influencing susceptibility of cancer cells to antitumor drugs.

Citation Format: Takashi Kobunai, Kenta Tsunekuni, Kazuaki Matsuoka, Hiroshi Tsukihara, Teiji Takechi. Mutational and copy number profiling of cancer-related genes in 26 human tumor xenografts and their correlations with antitumor drug sensitivities. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5175.

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 right-sided 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.

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.

Abstract 2557: Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, with oxaliplatin on human colorectal or gastric cancers and 5-FU-resistant gastric cancer xenografts

Background: TAS-102 is a novel oral nucleoside antitumor agent composed of trifluridine (FTD) and tipiracil hydrochloride (TPI) at a molar ratio 1:0.5. FTD is the active antitumor component of TAS-102 and its triphosphate form is incorporated into DNA in tumor cells. TPI is a potent inhibitor of thymidine phosphorylase, an enzyme that degrades FTD, allowing adequate plasma concentrations of orally administered FTD to be maintained and potentiating the antitumor activity of FTD. In a recent international multicenter randomized double blind Phase III study (RECOURSE), use of TAS-102 was shown to significantly improve overall survival, progression-free survival and had a favorable safety profile in comparison to the placebo in patients with metastatic colorectal cancer refractory to standard chemotherapies. In this study, we evaluated the antitumor effects of TAS-102 in combination with oxaliplatin on gastrointestinal tumor xenografts, including a 5-FU-resistant subline, in a nude mouse model.

Method: The human colorectal cell lines HCT-116 and SW48 and gastric cancer cell lines SC-2, MKN74 and MKN74/5-FU, a 5-FU-resistant cell line derived from MKN74, were implanted into nude mice subcutaneously. TAS-102 (150 mg/kg/day) was orally administered twice daily from days 1 to 14 and oxaliplatin (7 or 13 mg/kg/day) was administered intravenously on days 1 and 8. Growth inhibitory activity was evaluated by assessing tumor volume and the growth delay period, estimated based on the period required to reach a tumor volume five times greater than the initial volume (RTV5).

Results: TAS-102 and oxaliplatin monotherapy were effective on all the evaluated colorectal and gastric cancers, even for a 5-FU-resistant gastric cancer cell line. The tumor growth inhibitory activity and RTV5 of the group receiving TAS-102 with oxaliplatin were significantly superior to those receiving either monotherapy for all evaluated cancers (P&lt;0.05). Tumor growth inhibition in the combination treatment group was more than 70%. Furthermore, the RTV values on day 29 were less than 5 for SC-2, MKN74 and MKN74/5FU xenografts. These results demonstrate that combination therapy with TAS-102 and oxaliplatin is significantly more effective than either monotherapy in colorectal and gastric cancer xenografts, including a 5-FU-resistant xenograft, when evaluated by tumor growth inhibition and growth delay period. This combination appeared to be well-tolerated, as drug-related death or a reduction in body weight of more than 20% was not observed. Conclusion: The present preclinical findings indicate that combination therapy of TAS-102 and oxaliplatin is a promising treatment option for colorectal or gastric cancer, not only for chemo-naïve tumors, but also for recurrent tumors after 5-FU-based chemotherapy.

Citation Format: Mamoru Nukatsuka, Fumio Nakagawa, Kazuaki Matsuoka, Hiroshi Tsukihara, Teiji Takechi. Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, with oxaliplatin on human colorectal or gastric cancers and 5-FU-resistant gastric cancer xenografts. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2557. doi:10.1158/1538-7445.AM2015-2557

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, 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.

Efficacy of combination chemotherapy using a novel oral chemotherapeutic agent, TAS-102, with irinotecan hydrochloride on human colorectal and gastric cancer xenografts

TAS-102 is a novel oral nucleoside antitumor agent consisting of trifluridine and tipiracil hydrochloride at a molar ratio of 1:0.5. TAS-102 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, enhancement of the therapeutic efficacy using a combination therapy of TAS-102 and irinotecan hydrochloride (CPT-11) was evaluated in a colorectal and gastric cancer xenograft-bearing nude mouse model. TAS-102 was orally administered twice a day from day 1 to 14, and CPT-11 was administered intravenously on days 1 and 8. The growth-inhibitory activity was evaluated based on the tumor volume and the growth-delay period, which was estimated based on the period required to reach a tumor volume that was five-times greater than the initial volume (RTV5). The tumor growth-inhibitory activity and the RTV5 of the group receiving TAS-102 with CPT-11 were significantly superior to those of both agents as monotherapy for mice with KM12C, KM12C/5-FU, DLD-1/5-FU, and SC-2 xenografts (p<0.01). No significant decrease in body weight was observed. The present pre-clinical findings indicated that the combination of TAS-102 and CPT-11 is a promising treatment option for colorectal or gastric cancer, not only for chemo-naïve tumors, but also for recurrent tumors after 5-fluorouracil (5-FU)-based chemotherapy.

Abstract 1981: Drug-tolerant gastric cancer cell subpopulation enriched by 5-fluorouracil acquires malignant phenotype

Background: Post-operative adjuvant chemotherapy for gastric cancer is a treatment for suppressing the growth of invisible cancer cells, but substantial numbers of patients experience recurrence despite of this therapy. We attempted to clarify the mechanism of cancer relapse after chemotherapy using 5-FU tolerant human gastric cancer cell line, MKN45.

Methods: Through a stepwise dose escalation of 5-fluorouracil (5-FU) for one year, a 5-FU-tolerant cell subpopulation, MKN45T, was established from a human gastric cancer cell line, MKN45. Nucleotide variation was screened with a panel of 46 cancer-associated genes, and western blot analyses were performed to examine whether known proteins were involved in the acquisition of the drug-tolerant phenotype. For molecular profiling, cancer cell subpopulations emerging as colonies in the presence of anticancer drugs including 5-FU, cisplatin, and docetaxel, “reverse-phase” protein arrays (RPPAs) were produced with the drug-tolerant 480 colonies. Subcutaneous or orthotopic xenografts of MKN45 and MKN45T to immunodeficient mice were performed to examine tumorigenicity.

Results: Western blot analysis revealed that most of protein expression levels were not visibly different between MKN45 and MKN45T, except that p53 showed slight reduction in MKN45T. Analysis of 46 cancer-associated genes revealed that all gene variations were identical in both MKN45 and MKN45T, suggesting that gene mutations had a limited effect on the acquisition of the drug-tolerant phenotype. RPPA analysis revealed that colonies from MKN45T exhibited a protein level increase in a 5-FU concentration-dependent manner in Atg5, Atg7, and PI3K, suggesting a functional association between drug-tolerance and autophagy/glucose metabolism. An orthotopic xenograft to the stomach demonstrated tumors in the stomach (9 out of 9, 100%), and lymph node and liver metastases only in MKN45T at a high frequency (6 out of 9, 67%). No difference in tumorigenicity was observed when MKN45 and MKN45T were transplanted subcutaneously. The orthotopic xenograft of MKN45T followed by administration of 5-FU (30mg/kg/day) for five post-xenograft days suppressed metastasis in 4 out of 5 mice (80%) at 42 post-xenograft days, indicating that chemotherapy is particularly effective if it is performed before initiating tumor formation.

Conclusion: Chemotherapy does not only reduce tumor size, but may also be selecting for tumors that are resistant to the chemotherapy. Our clinical experiences are well-explained by this observation, as relapse after chemotherapy is often chemotherapy resistant.

Citation Format: Kaoru Ishida, Satoshi S. Nishizuka, Kohei Kume, Mamoru Nukatsuka, Kei Sato, Fumitaka Endo, Hirokatsu Katagiri, Takashi Kobunai, Teiji Takechi, Keisuke Koeda, Go Wakabayashi. Drug-tolerant gastric cancer cell subpopulation enriched by 5-fluorouracil acquires malignant phenotype. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1981. doi:10.1158/1538-7445.AM2014-1981

Abstract 781: Efficacy of trifluridine for 5-fluorouracil-resistant human gastric cancer cell lines and their mechanisms

Background: TAS-102 is a novel oral nucleoside antitumor agent consisting of trifluridine (FTD) and tipiracil hydrochloride (TPI). TAS-102 was found to significantly improve the overall survival of patients with metastatic colorectal cancer who were refractory to treatment with a fluoropyrimidine, irinotecan, and oxaliplatin in a double-blind randomized phase II study. Although significant survival benefits from 5-fluorouracil (5-FU)-based chemotherapy have also been reported in patients with gastric cancer, many patients experience recurrences after several courses of 5-FU-based chemotherapy. The resistance of gastric tumors to 5-FU therapy is thus a major clinical problem. In this study, the efficacy of FTD against 5-FU-resistant human gastric cancer cell lines was investigated. Method: 5-FU-resistant cell lines established by continuously exposing the parent cell lines (MKN-45, MKN-74, and KATOIII) to escalating concentrations (1-5 μM) of 5-FU over a 1-year period were used. The sensitivities of the cell lines to FTD were evaluated using a crystal violet staining assay. To elucidate the mechanism by which resistance is overcome, the mRNA levels of TK1, which converts FTD into an active monophosphate form, and hENT1, which is involved in the cellular uptake of FTD, were determined using RT-PCR. Results: The resistant cell lines KATOIII/5FU, MKN74/5FU, and MKN45/5FU exhibited a 2.0-fold, 4.8-fold, and 14.2-fold resistance to 5-FU, compared with their parent cell lines, respectively. MKN-45/5FU also showed a 3.7-fold resistance to FTD, whereas MKN-74/5FU (1.0-fold) and KATOIII/5FU (1.2-fold) showed no cross-resistance to FTD. The TK1 mRNA level was decreased by 40% in the MKN-45/5FU cells, compared with the parent cell line. Furthermore, this cell line showed a 60% decrease in the mRNA level for hENT1. In contrast, the hENT1 mRNA level increased by 1.6-fold in the KATOIII/5FU cells, with a 50% decrease in the TK1 mRNA level. The TK1 and hENT1 mRNA levels in MKN-74/5FU were increased by 1.9-fold and 1.7-fold, respectively. Conclusion: FTD was able to overcome the resistance to 5-FU in 2 out of 3 resistant cell lines in vitro, with MKN45/5FU exhibiting a partial cross-resistance to FTD. These results suggest that TAS-102 might be a promising chemotherapeutic agent for the treatment of gastric cancer relapses after 5-FU-based treatment. Furthermore, TK1 and hENT1 might be involved in FTD-related cytotoxicity.

Citation Format: Kazuaki Matsuoka, Takashi Kobunai, Teiji Takechi. Efficacy of trifluridine for 5-fluorouracil-resistant human gastric cancer cell lines and their mechanisms. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 781. doi:10.1158/1538-7445.AM2014-781

Enhancement of 5-fluorouracil-induced cytotoxicity by leucovorin in 5-fluorouracil-resistant gastric cancer cells with upregulated expression of thymidylate synthase

BACKGROUND

Elucidation of the mechanisms by which gastric cancer cells acquire resistance to 5-fluorouracil (5FU) may provide important clues to the development of effective chemotherapy for 5FU-resistant gastric cancer

METHODS

Four 5FU-resistant cell lines (MKN45/5FU, MKN74/5FU, NCI-N87/5FU, and KATOIII/5FU) were established by continuous exposure of the cells to progressively increasing concentrations of 5FU for about 1 year. Then, mRNA expression levels of four genes associated with 5FU metabolism, i.e., thymidylate synthase (TS), dihydropyrimidine dehydrogenase, thymidine phosphorylase, and orotate phosphoribosyltransferase, were quantitatively evaluated by real-time reverse transcriptase-polymerase chain reaction. In addition, TS protein expression was measured by Western blot analysis.

RESULTS

As compared with the parent cell lines, the 5FU-resistant cell lines showed 3.8- to 11.6-fold higher resistance to 5FU, as well as 1.9- to 3.5-fold higher TS mRNA expression and 1.6- to 7.1-fold higher TS protein expression. In contrast, the expressions of other genes did not differ significantly among the cell lines. The cytotoxicity of 5FU was enhanced 2.3- to 2.8 fold by leucovorin (LV) against three of the four 5FU-resistant cell lines.

CONCLUSIONS

Collectively, LV enhanced the cytotoxicity of 5FU not only against the parent gastric cancer cell lines, but also against the 5FU-resistant cell lines, even those with elevated TS expression levels. These results suggest that clinical studies of a combination of 5FU and LV are warranted in patients who have recurrent gastric cancer after 5FU-based therapy.

Abstract 990: Efficacy of various chemotherapeutic agents on 5-FU-resistant human gastric cancer cell lines and their mechanisms

Purpose: Four 5-fluorouracil (5-FU)-resistant human gastric cancer cell lines were established by the long-term exposure of parent cell lines (MKN45, MKN-74, KATO-III, and NCI-N87) to 5-FU. The cytotoxicity and mechanisms of several chemotherapeutic agents were then investigated using 5-FU-resistant gastric cancer cell lines.

Method: 5-FU-resistant cell lines were established by continuous exposure to escalating concentrations (1-5 μM) of 5-FU over a 1-year period. The sensitivities of the cell lines to chemotherapeutic agents (paclitaxel, docetaxel, cisplatin, oxaliplatin, epirubicin, and SN-38) were then evaluated using the WST-8 colorimetric assay. To elucidate the mechanisms of resistance, the gene expressions and copy numbers were measured using an Agilent Technologies whole human genome oligo DNA microarray and a CGH microarray. The protein and mRNA expressions of a target enzyme of 5-FU, thymidylate synthase (TS), were also investigated using western blotting and RT-PCR, respectively.

Results: The IC50 ratios of the 5-FU-resistant cell lines were 2.6 to 15.6 times higher than those of the parent cell lines in vitro. MKN-45/5-FU showed cross-resistance to cisplatin and oxaliplatin and KATO-III/5-FU showed cross-resistance to SN-38, while MKN-74/5-FU showed collateral sensitivities to docetaxel, cisplatin, and oxaliplatin, and NCI-N87/5-FU showed collateral sensitivities to cisplatin, oxaliplatin, SN-38, and epirubicin. RT-PCR showed that TS mRNA expression was higher in the parent cell lines than in the 5-FU-resistant cell lines, and the TS protein expression level was also higher in all the resistant cell lines. For MKN-45/5-FU and KATO-III/5-FU, not only the mRNA expression level but also the TS gene copy number was increased. Interestingly, the expression of MAP3K15, which is an apoptosis-facilitating factor, increased in NCI-N87/5-FU, which showed collateral sensitivity to cisplatin, oxaliplatin, SN-38, and epirubicin.

Conclusion: Analyzing the molecular mechanisms of 5-FU-resistant cell lines may be useful for the development of effective chemotherapy regimens for relapsed gastric cancer after 5-FU-based chemotherapy.

Citation Format: Mamoru Nukatsuka, Takashi Kobunai, Ayako Nakamura, Kazuhiko Hayashi, Teiji Takechi. Efficacy of various chemotherapeutic agents on 5-FU-resistant human gastric cancer cell lines and their mechanisms. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 990. doi:10.1158/1538-7445.AM2013-990

Abstract 991: Integrated analysis of gene expression, DNA copy number, and CpG island methylation of 5-fluorouracil-resistant human gastric cancer cell lines

Background: A major problem in chemotherapy is treatment failure due to anticancer drug resistance. A better understanding of mechanisms underlying acquired resistance may facilitate the development of an optimal second-line therapy for recurrent cancer. This study was designed to elucidate mechanisms underlying acquisition of 5-fluoroucacil (5-FU) resistance by human gastric cancer cells. Method: 5-FU resistant cell lines were established by continuously exposing parent cell lines (MKN45, MKN-74, KATO-III, and NCI-N87) to escalating concentrations (1-5 μM) of 5-FU over 1 year. To elucidate mechanisms of resistance, gene expression, DNA copy number, and DNA methylation were measured by Whole Human Genome 44K oligo DNA microarray, 244K CGH microarray, and 244K CpG Island Microarray (Agilent Technologies, Santa Clara, CA), respectively. Data analysis was done with GeneSpring GX™ software, version 11.0 (Agilent Technologies) and Partek genomic suite software, version 6.5 (Partek Inc., St. Louis, MO). Results: Each of the cell lines acquired high resistance to 5-FU, although the degree of resistance varied. IC50 of the 5-FU-resistant cell lines was 3.8- to 11.6-fold higher than that of the parent cell lines. On gene expression analysis, 3.0%, 2.3%, 1.4%, and 1.4% of 41,093 probes were differentially expressed with more than 5-fold changes in MKN45/FU, KATOIII/FU, NCI-N87/FU, and MKN74/FU as compared with their parental cell lines, respectively. Changes occurring in at least 3 cell lines were expressed by only 0.2% of probes. Copy number analysis revealed that DNA copy gains occurred at 16.6%, 6.7%, 5.1%, and 5.6% of all genomic segments elucidated in MKN45/FU, KATOIII/FU, NCI-N87/FU and MKN74/FU, respectively. The frequencies of DNA copy losses were 35.6%, 14.0%, 3.2%, and 8.9%, respectively. Methylation analysis revealed that the number of methylated CpG sites in NCI-N87/FU and MKN74/FU increased by 1.5 times as compared with the parental cell lines. In contrast, the numbers of methylated CpG sites in MKN45/FU and KATOIII/FU rarely changed (around 40% each). Conclusions: Mechanisms leading to acquired resistance against 5-FU differed among the 4 gastric cancer cell lines. Changes in copy number most frequently occurred in MKN45/FU cells. In NCI-N87/FU and MKN74/FU, the numbers of methylated CpG sites increased. Such genome-wide integrated analysis will facilitate an understanding of mechanisms for 5-FU acquired resistance and help to identify therapeutic target genes.

Citation Format: Takashi Kobunai, Ayako Nakamura, Mamoru Nukatsuka, Kazuhiko Hayashi, Teiji Takechi. Integrated analysis of gene expression, DNA copy number, and CpG island methylation of 5-fluorouracil-resistant human gastric cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 991. doi:10.1158/1538-7445.AM2013-991

Enhancing 5-fluorouracil cytotoxicity by inhibiting dihydropyrimidine dehydrogenase activity with uracil in human tumor cells

We analyzed dihydropyrimidine dehydrogenase (DPD) activity (radioenzymatic assay) and 5-fluorouracil (5-FU) cytotoxicity (MTT test) in the absence or presence of uracil in two human cancer cell lines, MIAPaCa-2 (pancreas tumor) and HuTu80 (duodenum tumor). Basal DPD activities in both were comparatively high; MIAPaCa-2, 101 and HuTu80, 153 pmol/min/mg protein, respectively. Twenty mu g/ml of uracil, a dose which did not influence cell proliferation, enhanced 5-FU cytotoxicity; MIAPaCa-2, 2.0-fold and HuTu80, 1.5-fold, respectively. Uracil inhibited both DPD activity and cell growth in a concentration-dependent manner, and exhibited maximum effect at molar ratios to 5-FU of more than 10 (DPD activity, almost complete inhibition; growth-inhibitory effect, about a 30% increase). In addition, the cytosolic DPD activity of OCC-1 human head and neck tumors, collected following the oral administration of ss mg/kg of uracil to tumor-bearing nude mice, decreased to about 50% of that of OCC-1 tumors not treated with uracil. These findings suggested that combined fluoropyrimidine and uracil treatment of tumors with high basal DPD, elicits a greater antitumor effect than fluoropyrimidines alone, since uracil could inhibit the degradation of 5-FU in the tumor. UFT, an oral fluoropyrimidine combined with uracil, is expected to be more effective in such tumors.

Efficacy of combination chemotherapy using oral fluoropyrimidine S-1 with oxaliplatin (SOX) against colorectal cancer in vivo

Oxaliplatin is effective when used with 5-fluorouracil (5-FU) and leucovorin, or with capecitabine (COX) for the treatment of colorectal cancer. In this experiment, we investigated the optimal combination schedule and antitumor activity of oral S-1 with oxaliplatin combination therapy (SOX) against human colorectal cancer xenografts in vivo. Using human colon cancer COL-1-bearing nude mice, oxaliplatin was administered at a total dose of 8.3 mg/kg on day 1 alone, on day 8 alone, or in divided doses administered on days 1 and 8 with S-1 (6.9 mg/kg, days 1-14). The antitumor activity of SOX, administered according to the divided schedule was significantly superior to both monotherapies (p<0.01), and the toxicity was tolerable. However, administration on day 8 alone failed to significantly increase the antitumor activity, when compared with that of monotherapy, while administration on day 1 alone was toxic in this model. Next, the efficacy of SOX was compared with that of COX (360 mg/kg, days 1-14). The antitumor effect of SOX was significantly superior to that of COX (p<0.01), with an equivalent toxicity; moreover SOX suppressed COL-1 tumor growth for a longer period of time (2.2 times) than did COX. The antitumor activity of SOX against the 5-FU-resistant colorectal cancer cell line KM12C/5-FU was equivalent to that of COX. The evaluation of intermittent SOX administration in a clinical trial might be of critical value.

Combination therapy using oral S-1 and targeted agents against human tumor xenografts in nude mice

In this study, combination therapies using the oral fluoropyrimidine tegafur-gimeracil-oteracil (S-1) with several targeted agents or antibodies, were evaluated. First, the effects of tyrosine kinase inhibitors (erlotinib hydrochloride, sorafenib tosilate and sunitinib malate) against human non-small cell lung cancer (NSCLC), breast cancer and colorectal cancer were evaluated in vivo. The effects of the combination of S-1 and targeted antibodies (bevacizumab and cetuximab) against human colorectal cancers was also evaluated in vivo. S-1 and the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, erlotinib, showed a significant inhibition of growth in human NSCLC (Lu-99 and PC-9 cell lines). The antitumor activity of the combination of S-1 and erlotinib against Lu-99 and PC-9 cancer cell lines was significantly superior to either monotherapy (P<0.05). Combination therapy using the multi-tyrosine kinase inhibitors, sorafenib or sunitinib, with S-1 against breast cancer (MX-1 cell line) and NSCLC (NCI-H460 cell line) was significantly superior to either monotherapy (P<0.01). The combination of the anti-vascular endothelial growth factor antibody bevacizumab or the anti-EGFR antibody, cetuximab, with S-1 against human colorectal cancer [Col-1, KM20C (bevacizumab) and DLD-1 (cetuximab) cell lines] and a 5-fluorouracil (5-FU)-resistant cell line (KM12C/5-FU) was significantly superior to either monotherapy (p<0.01). In particular, the growth of the Col-1 cells was completely inhibited by the combination of S-1 and bevacizumab. No toxic mortalities and no significant difference in the body weight changes of the animals treated with S-1 combined with the targeted agents or with the mono-therapies were observed; therefore, the treatments appeared to be well-tolerated. Our preclinical findings indicate that the combination therapies of S-1 and targeted agents are promising treatment options.

Different histological types of non-small cell lung cancer have distinct folate and DNA methylation levels

Aberrant DNA methylation is a commonly observed epigenetic change in lung cancer. Folate has been suggested to play a role in the homeostasis of DNA methylation and has also been implicated in cancer chemotherapy. We investigated a possible role for folate in DNA methylation by measuring folate concentrations in tumors and adjacent normal tissues from 72 non-small cell lung cancer (NSCLC) patients. These were compared to DNA methylation levels and to clinicopathological features. Folate concentrations were determined as the sum of 5,10-methylenetetrahydrofolate and tetrahydrofolate. The MethyLight assay was used to quantitate methylation in promoter regions of P16(CDKN2A), APC, CDH13, RARB, RASSF1, RUNX3, and MYOD1. Methylation of LINE-1 repeats was used as a surrogate for global methylation. Folate levels in tumors correlated positively with LINE-1, CDH13, and RUNX3 methylation. Folate concentrations and methylation of LINE-1, RASSF1, and RUNX3 were significantly higher in adenocarcinoma compared to squamous cell carcinoma (SCC). Two sets of array-based data retrieved from the Gene Expression Omnibus consistently showed that expression of FOLR1, a folate transport enzyme, and GGH, an enzyme that prevents folate retention, were higher and lower, respectively, in adenocarcinomas compared to SCC. This was independently validated by quantitative RT-PCR in 26 adenocarcinomas and 13 SCC. Our results suggest that folate metabolism plays a role in aberrant DNA methylation in NSCLC. The histological subtype differences in folate concentration and DNA methylation observed here were associated with distinct expression patterns for folate metabolizing enzymes. These findings may have clinical applications for histology-directed chemotherapy with fluoropyrimidine and anti-folates in NSCLC.

Genome-wide screening of loci associated with drug resistance to 5-fluorouracil-based drugs

Resistance to chemotherapeutic agents represents the chief cause of mortality in cancer patients with advanced disease. Chromosomal aberration and altered gene expression are the main genetic mechanisms of tumor chemoresistance. In this study, we have established an algorithm to calculate DNA copy number using the Affymetrix 10K array, and performed a genome-wide correlation analysis between DNA copy number and antitumor activity against 5-fluorouracil (5-FU)-based drugs (S-1, tegafur + uracil [UFT], 5'-DFUR and capecitabine) to screen for loci influencing drug resistance using 27 human cancer xenografts. A correlation analysis confirmed that the single nucleotide polymorphism (SNP) showing significant associations with drug sensitivity were concentrated in some cytogenetic regions (18p, 17p13.2, 17p12, 11q14.1, 11q11 and 11p11.12), and we identified some genes that have been indicated their relations to drug sensitivity. Among these regions, 18p11.32 at the location of the thymidylate synthase gene (TYMS) was strongly associated with resistance to 5-FU-based drugs. A change in copy number of the TYMS gene was reflected in the TYMS expression level, and showed a significant negative correlation with sensitivity against 5-FU-based drugs. These results suggest that amplification of the TYMS gene is associated with innate resistance, supporting the possibility that TYMS copy number might be a predictive marker of drug sensitivity to fluoropyrimidines. Further study is necessary to clarify the functional roles of other genes coded in significant cytogenetic regions. These promising data suggest that a comprehensive DNA copy number analysis might aid in the quest for optimal markers of drug response.

Changes to the dihydropyrimidine dehydrogenase gene copy number influence the susceptibility of cancers to 5-FU-based drugs: Data mining of the NCI-DTP data sets and validation with human tumour xenografts

Patient response to the anti-tumour drug 5-fluorouracil (5-FU) is variable, but predicting the response rate is important for the selection of effective chemotherapy. Our aim was to identify alterations in DNA copy number that influence susceptibility of cancer cells to 5-FU-based drugs. The NCI public database was used to identify chromosome loci associated with drug sensitivity and DNA copy number. One of the 11 candidates, the cytogenetic band 1p21.3, harbours the dihydropyrimidine dehydrogenase (DPD) gene. To validate this finding, the DPD copy number and in vivo sensitivity to 5-FU-based drugs were determined in 31 human tumour xenografts. Those xenografts demonstrating low sensitivity had significantly higher DPD copy numbers than highly sensitive tumours (P<0.002). Moreover, DPD mRNA expression levels were significantly correlated with DPD copy numbers (P<0.046). An assessment of copy number may be a more precise method of predicting the sensitivity of cancer patients to 5-FU related drugs.

Gene expression analysis using human cancer xenografts to identify novel predictive marker genes for the efficacy of 5-fluorouracil-based drugs

The development of a diagnostic method for predicting the therapeutic efficacy or toxicity of anticancer drugs is a critical issue. We carried out a gene expression analysis to identify genes whose expression profiles were correlated with the sensitivity of 30 human tumor xenografts to 5-fluorouracil (5-FU)-based drugs (tegafur + uracil [UFT], tegafur + gimeracil + oteracil [S-1], 5'-deoxy-5-fluorouridine [5'-DFUR], and N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine [capecitabine]), as well as three other drugs (cisplatin [CDDP], irinotecan hydrochloride [CPT-11], and paclitaxel) that have different modes of action. In the present study, we focused especially on the fluoropyrimidines. The efficacy of all anticancer drugs was assayed using human tumor xenografts in nude mice. The mRNA expression profile of each of these xenografts was analyzed using a Human Focus array. Correlation analysis between the gene expression profiles and the chemosensitivities of seven drugs identified 39 genes whose expression levels were correlated significantly with multidrug sensitivity, and we suggest that the angiogenic pathway plays a pivotal role in resistance to fluoropyrimidines. Furthermore, many genes showing specific correlations with each drug were also identified. Among the candidate genes associated with 5-FU resistance, the dihydropyrimidine dehydrogenase mRNA expression profiles of the tumors showed a significant negative correlation with chemosensitivity to all of the 5-FU based drugs except for S-1. Therefore, the administration of S-1 might be an effective strategy for the treatment of high dihydropyrimidine dehydrogenase-expressing tumors. The results of the present study may enhance the prediction of tumor response to anticancer drugs and contribute to the development of tailor-made chemotherapy.

Correlations between antitumor activities of fluoropyrimidines and DPD activity in lung tumor xenografts

The purposes of this study were to evaluate the antitumor activity of S-1 (1 M tegafur, 0.4 M 5-chloro-2,4-dihydroxypyridine and 1 M potassium oxonate) on human lung tumor xenografts, as compared with other fluoro-pyrimidines, and to investigate the relationships between fluoropyrimidine antitumor activities and four distinct enzymatic activities involved in the phosphorylation and degradation pathways of 5-fluorouracil (5-FU) metabolism. S-1, UFT (1 M tegafur-4 M uracil), 5'-deoxy-5-fluorouridine (5'-DFUR), capecitabine and 5-FU were administered for 14 consecutive days to nude mice bearing lung tumor xenografts. S-1 showed stronger tumor growth inhibition in four of the seven tumors than the other drugs. Cluster analysis, on the basis of antitumor activity, indicated that S-1/UFT and 5'-DFUR/capecitabine/5-FU could be classified into another group. We investigated tumor thymidylate synthase content, dihydropyrimidine dehydrogenase (DPD) activity, thymidine phosphorylase (TP) activity and orotate phosphoribosyl transferase activity in seven human lung tumor xenografts and performed regression analyses for the antitumor activities of fluoropyrimidines. There were inverse correlations between antitumor and DPD activities for 5'-DFUR (r=-0.79, P=0.034), capecitabine (r=-0.56, P=0.19) and 5-FU (r=-0.86, P=0.013). However, no such correlations were observed for S-1 and UFT. These findings suggest that S-1 containing a potent DPD inhibitor may have an antitumor effect on lung tumors, with high basal DPD activity, superior to those of other fluoropyrimidines.

Gene expression in colorectal cancer and in vitro chemosensitivity to 5-fluorouracil: a study of 88 surgical specimens

To predict the sensitivity of colorectal cancer to 5-fluorouracil (5-FU), we compared the gene expression of surgically obtained colorectal cancer specimens with chemosensitivity to 5-FU as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay. Eighty-eight patients with advanced and/or metastatic colorectal cancer provided written informed consent and entered the trial from September 2000 to October 2001. Fresh surgical specimens were used for the MTT assay, and sensitivity to 5-FU was evaluated at a cutoff concentration of 50 microg/ml and 48-h incubation time. Frozen samples were stored at - 80 degrees C until mRNA analysis of thymidylate synthetase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), es-nucleoside transporter (NT), and E2F1 by real-time RT-PCR. The correlations between the variables were analyzed, and the predictive value of these mRNAs was assessed statistically using a receiver operating characteristic (ROC) curve. NT and DPD, TP and DPD, and TP and NT mRNA expression levels correlated significantly, while TS and E2F1 showed no correlations. High NT expression was associated with low sensitivity to 5-FU (P < 0.013), as were high DPD and E2F1 expression (P < 0.022 for both). High TP mRNA expression correlated with low sensitivity to 5-FU (P < 0.034), although high TS mRNA expression did not. ROC curves indicated that DPD and NT mRNAs were possible predictors of sensitivity to 5-FU, with cutoff values of 0.6 and 0.4, respectively. The sensitivity of colorectal cancer to 5-FU may be regulated by DPD, the rate-limiting enzyme of catabolism, and NT, an important transmembrane transporter of nucleosides.

Superior antitumour activity of S-1 in tumours with a high dihydropyrimidine dehydrogenase activity

To elucidate the mechanism of the enhanced antitumour activity of S-1 (1 M tegafur, 0.4 M 5-chloro-2, 4-dihydroxypyridine, and 1 M potassium oxonate) in terms of the phosphorylation and degradation pathways of 5-fluorouracil (5-FU) metabolism, we investigated tumoral thymidylate synthase (TS) content, dihydropyrimidine dehydrogenase (DPD) activity, the TS inhibition rate (TS-IR), and 5-FU incorporated into RNA (F-RNA) in four human gastric cancer xenografts (MKN-28, MKN-74, GCIY and GT3TKB) and compared the results obtained with S-1 with those obtained with 5-FU and UFT (1 M tegafur, 4 M uracil). 5-FU was administered intraperitoneally (i.p.) to mice at a dose of 50 mg/kg, three times, on days 0, 4 and 8. S-1 and UFT were administered orally at doses of 10 and 24 mg/kg, respectively, once a day, for 9 consecutive days. Antitumour activity was evaluated as the maximum inhibition of tumour growth in each animal. S-1 showed a better antitumour activity than 5-FU and UFT in tumours with a high DPD activity (GCIY and GT3TKB). There were inverse correlations between the antitumour activity and both TS content and DPD activity in the 5-FU and UFT groups. However, no such correlations were observed in the S-1 group. In GCIY and GT3TKB xenografts, TS-IR was significantly higher in the S-1 group than in the 5-FU or UFT groups. In GT3TKB xenografts, the F-RNA level was significantly higher in the S-1 group than in the 5-FU or UFT groups. The superior cytotoxicity of S-1 appears to be attributable to both an increased inhibition of DNA synthesis and an enhanced blockade of RNA function against tumours with a high DPD activity.

Gene expression in colorectal cancer and in vitro chemosensitivity to 5-fluorouracil: a study of 88 surgical specimens

To predict the sensitivity of colorectal cancer to 5-fluorouracil (5-FU), we compared the gene expression of surgically obtained colorectal cancer specimens with chemosensitivity to 5-FU as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay. Eighty-eight patients with advanced and/or metastatic colorectal cancer provided written informed consent and entered the trial from September 2000 to October 2001. Fresh surgical specimens were used for the MTT assay, and sensitivity to 5-FU was evaluated at a cutoff concentration of 50 microg/ml and 48-h incubation time. Frozen samples were stored at - 80 degrees C until mRNA analysis of thymidylate synthetase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), es-nucleoside transporter (NT), and E2F1 by real-time RT-PCR. The correlations between the variables were analyzed, and the predictive value of these mRNAs was assessed statistically using a receiver operating characteristic (ROC) curve. NT and DPD, TP and DPD, and TP and NT mRNA expression levels correlated significantly, while TS and E2F1 showed no correlations. High NT expression was associated with low sensitivity to 5-FU (P < 0.013), as were high DPD and E2F1 expression (P < 0.022 for both). High TP mRNA expression correlated with low sensitivity to 5-FU (P < 0.034), although high TS mRNA expression did not. ROC curves indicated that DPD and NT mRNAs were possible predictors of sensitivity to 5-FU, with cutoff values of 0.6 and 0.4, respectively. The sensitivity of colorectal cancer to 5-FU may be regulated by DPD, the rate-limiting enzyme of catabolism, and NT, an important transmembrane transporter of nucleosides.

Gene expression in colorectal cancer and in vitro chemosensitivity to 5-fluorouracil: a study of 88 surgical specimens

To predict the sensitivity of colorectal cancer to 5-fluorouracil (5-FU), we compared the gene expression of surgically obtained colorectal cancer specimens with chemosensitivity to 5-FU as detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H tetrazolium bromide (MTT) assay. Eighty-eight patients with advanced and/or metastatic colorectal cancer provided written informed consent and entered the trial from September 2000 to October 2001. Fresh surgical specimens were used for the MTT assay, and sensitivity to 5-FU was evaluated at a cutoff concentration of 50 microg/ml and 48-h incubation time. Frozen samples were stored at - 80 degrees C until mRNA analysis of thymidylate synthetase (TS), dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), es-nucleoside transporter (NT), and E2F1 by real-time RT-PCR. The correlations between the variables were analyzed, and the predictive value of these mRNAs was assessed statistically using a receiver operating characteristic (ROC) curve. NT and DPD, TP and DPD, and TP and NT mRNA expression levels correlated significantly, while TS and E2F1 showed no correlations. High NT expression was associated with low sensitivity to 5-FU (P < 0.013), as were high DPD and E2F1 expression (P < 0.022 for both). High TP mRNA expression correlated with low sensitivity to 5-FU (P < 0.034), although high TS mRNA expression did not. ROC curves indicated that DPD and NT mRNAs were possible predictors of sensitivity to 5-FU, with cutoff values of 0.6 and 0.4, respectively. The sensitivity of colorectal cancer to 5-FU may be regulated by DPD, the rate-limiting enzyme of catabolism, and NT, an important transmembrane transporter of nucleosides.