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

Synthesis of Fluorinated Nucleosides/Nucleotides and Their Antiviral Properties

The FDA has approved several drugs based on the fluorinated nucleoside pharmacophore, and numerous drugs are currently in clinical trials. Fluorine-containing nucleos(t)ides offer significant antiviral and anticancer activity. The insertion of a fluorine atom, either in the base or sugar of nucleos(t)ides, alters its electronic and steric parameters and transforms the lipophilicity, pharmacodynamic, and pharmacokinetic properties of these moieties. The fluorine atom restricts the oxidative metabolism of drugs and provides enzymatic metabolic stability towards the glycosidic bond of the nucleos(t)ide. The incorporation of fluorine also demonstrates additional hydrogen bonding interactions in receptors with enhanced biological profiles. The present article discusses the synthetic methodology and antiviral activities of FDA-approved drugs and ongoing fluoro-containing nucleos(t)ide drug candidates in clinical trials.

Quantitative Analysis of the Concentration of Trifluridine in Tumor Hypoxic Regions Using a Novel Platform Combining Functional Endoscopy and Mass Spectrometry

Hypoxic regions in solid tumors are highly resistant to drugs and thus represents an obstacle in drug discovery. Currently, however, there are technical barriers in sampling human hypoxic tumors and examining drug delivery with high sensitivity and accuracy. Herein, we present a new platform combining functional endoscopy and highly sensitive liquid chromatography-mass spectrometry (LC-MS) to assess drug delivery to hypoxic regions. Because oxygen saturation endoscopic imaging (OXEI), a functional endoscopy, can evaluate lesions and hypoxia in real-time by simultaneously acquiring a pseudocolor map of oxygen saturation and conventional endoscopic images, this platform can be used to evaluate drug delivery with human samples from hypoxic regions. As the first clinical application of this platform, the relationship between hypoxic regions and the concentration of trifluridine (FTD) incorporated into DNA was evaluated in patients with advanced gastric cancer treated with FTD/tipiracil (FTD/TPI; n = 13) by obtaining and analysis of tissue samples by OXEI and LC-MS and vascular maturity index by CD31/α-SMA staining ex vivo. The results showed that the concentration of FTD was significantly higher in the normoxic region than in the hypoxic region (P < 0.05) and there were significantly more immature vessels in hypoxic regions than in normoxic regions (P < 0.05). These results indicate that the platform was sufficiently sensitive to evaluate differences in drug anabolism in different oxygenic regions of human tumor tissue. This new platform allows quantitative drug analysis in hypoxic regions and is expected to initiate a new era of drug discovery and development.

A Retrospective Study of Trifluridine/Tipiracil with Fruquintinib in Patients with Chemorefractory Metastatic Colorectal Cancer

INTRODUCTION

Trifluridine/tipiracil (TAS-102) and fruquintinib are novel antitumor agents for patients with refractory metastatic colorectal cancer (mCRC). We conducted a retrospective study to explore the clinical efficacy and drug toxicities of combination therapy with TAS-102 and fruquintinib in real-life clinical practice.

METHODS

Between March 2021 and February 2023, patients at two different centers with mCRC who failed two or more lines of prior therapy and received TAS-102 in combination with fruquintinib were recruited.

RESULTS

In total, 32 mCRC patients were included in the analysis. The objective response rate (ORR) and the disease control rate (DCR) were 9.4% and 75%. The median progression-free survival (PFS) and overall survival (OS) were 6.3 (95% CI: 5.3-7.3) and 13.5 (95% CI: 9.5-17.5) months, respectively. Patients without liver metastasis or peritoneal metastasis obtained better median PFS (7.1 m vs. 5.6 m, p = 0.03 and 6.3 m vs. 3.4 m, p = 0.04), and OS (15.2 m vs. 10.4 m, p = 0.01 and 13.6 m vs. 7.1 m, p = 0.03), respectively. Other clinicopathological features, including age, tumor site, KRAS status, dosage of fruquintinib, and treatment line, did not affect the clinical efficacy of TAS-102 combined with fruquintinib. The most common grade three-four toxicities were neutropenia (46.9%), anemia (21.9%), diarrhea (15.6%), nausea (12.5%), and hand-foot syndrome rash (12.5%).

CONCLUSIONS

Our results suggest that TAS-102 combined with fruquintinib has promising clinical efficacy and manageable safety for refractory mCRC patients in a real-world clinical setting. Further prospective trials are warranted to confirm our results.

Long-Term Progression-Free Survival of a Pre-Treated Patient with Metastatic Colorectal Cancer Receiving Trifluridine/Tipiracil

Trifluridine/tipiracil is approved for the use in later or last-line setting in previously treated metastatic colorectal cancer (mCRC) patients who progressed on standard anti-tumor drugs including 5-fluorouracil (5-FU), irinotecan, oxaliplatin, anti-VEGF and anti-EGFR antibodies, or who are not considered candidates for those standard therapies. In this report, we describe a 67-year-old male patient with KRAS-mutated mCRC and metachronous liver and lung metastasis who failed prior 5-FU- and irinotecan-containing regimens, but then showed long-term disease control for 31 months on single-agent trifluridine/tipiracil given as second-line treatment. According to our experience, trifluridine/tipiracil is a feasible and effective treatment option in earlier but not necessarily last-line therapy in mCRC patients who are not considered candidates for doublet or triplet chemotherapy. Besides its efficacy, it is associated with maintained quality of life and a manageable toxicity profile. Considering increasing age of mCRC patients and their wish for maintaining an independent lifestyle, further research on the use of trifluridine/tipiracil in earlier lines of systemic mCRC therapy is warranted.

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.

Targeting thymidine phosphorylase alleviates resistance to dendritic cell immunotherapy in colorectal cancer and promotes antitumor immunity

T-cell exhaustion plays a pivotal role in the resistance of microsatellite-stable colorectal cancer (CRC) to immunotherapy. Identifying and targeting T-cell exhaustion-activating mechanisms is a promising strategy to augment the effects of immunotherapy. Here, we found that thymidine phosphorylase (TYMP) plays a decisive role in inducing systemic T-cell exhaustion and abrogating the efficacy of dendritic cell (DC) therapy in a CRC model. Targeting TYMP with tipiracil hydrochloride (TPI) induces immunological cell death (ICD). The combined effects of TPI and imiquimod-activated DCs turn CT26 tumors into immunologically ‘hot’ tumors by inducing ICD in vivo. High-dimensional cytometry analysis revealed T-cell and IFN-γ dependency on the therapeutic outcome. In addition, chemoimmunotherapy converts intratumoral Treg cells into Th1 effector cells and eliminates tumor-associated macrophages, resulting in higher cytotoxic T lymphocyte infiltration and activation. This effect is also associated with the downregulation of PD-L1 expression in tumors, leading to the prevention of T-cell exhaustion. Thus, cooperative and cognitive interactions between dendritic cells and immunogenic cell death induced by therapy with TPI promote the immune response and tumoricidal activities against microsatellite stable colorectal cancer. Our results support TYMP targeting to improve the effects of DC immunotherapy and outcomes in CRC.

Multicenter phase II study of trifluridine/tipiracil for esophageal squamous carcinoma refractory/intolerant to 5-fluorouracil, platinum compounds, and taxanes: the ECTAS study

BACKGROUND

The standard treatment for unresectable advanced/recurrent esophageal cancer in Japan is 5-fluorouracil plus platinum-containing drugs as first-line chemotherapy and taxanes as second-line chemotherapy. However, the standard regimen after patients become refractory to these treatments remains to be established. Therefore, we investigated the efficacy of trifluridine/tipiracil (FTD/TPI) in patients with esophageal cancer who are refractory or intolerant to 5-fluorouracil, platinum-containing drugs, and taxanes.

METHODS

This single-arm phase II trial was conducted in seven hospitals in Japan. Eligible patients were those with unresectable advanced/recurrent esophageal cancer that was refractory or intolerant to 5-fluorouracil, platinum-containing drugs, and taxanes. The primary endpoint was the 3-month progression-free survival rate, and the secondary endpoints were the 6-month progression-free survival rate, progression-free survival, overall survival, response rate, disease control rate, and toxicity.

RESULTS

Forty-two patients were enrolled between October 2015 and June 2016. All tumors were squamous cell carcinomas. The progression-free survival rates at 3 and 6 months were 15.4% (90% confidence interval 7.4-26.0%) and 7.7% (90% confidence interval 2.6-16.6%), respectively. The median progression-free survival and median overall survival were 1.3 (95% confidence interval 1.0-1.8) months and 4.5 (95% confidence interval 3.6-5.7) months, respectively. The response rate was 0%, and the disease control rate was 23.8% (95% confidence interval 13.5-38.5%). The major grade 3/4 toxicities were neutropenia (47.6%), leukocytopenia (35.7%), and anemia (21.4%). No treatment-related deaths occurred. Exploratory subgroup analyses showed better progression-free survival in the subgroup without distant metastasis at diagnosis.

CONCLUSIONS

Trifluridine/tipiracil monotherapy is feasible and shows modest activity in patients with refractory esophageal squamous cell carcinoma.

Targeting nucleotide metabolism as the nexus of viral infections, cancer, and the immune response

Virus-infected cells and cancers share metabolic commonalities that stem from their insatiable need to replicate while evading the host immune system. These similarities include hijacking signaling mechanisms that induce metabolic rewiring in the host to up-regulate nucleotide metabolism and, in parallel, suppress the immune response. In both cancer and viral infections, the host immune cells and, specifically, lymphocytes augment nucleotide synthesis to support their own proliferation and effector functions. Consequently, established treatment modalities targeting nucleotide metabolism against cancers and virally infected cells may result in restricted immune response. Encouragingly, following the introduction of immunotherapy against cancers, multiple studies improved our understanding for improving antigen presentation to the immune system. We propose here that understanding the immune consequences of targeting nucleotide metabolism against cancers may be harnessed to optimize therapy against viral infections.

TAS-102: A resurrected novel Fluoropyrimidine with expanding role in the treatment of gastrointestinal malignancies

TAS-102 is an orally administered fixed-dose formulation consisting of trifluorothymidine (TFT), a fluoropyrimidine antimetabolite, and tipiracil (TPI), an inhibitor of thymidine phosphorylase (TP) that prevents rapid degradation of TFT and ensures its bioavailability. The novelty of TAS-102 lies in its antitumor activity against 5-fluorouracil (5-FU) resistant tumors, demonstrated both in the in vitro models and xenografts. The cytotoxic activity of TFT relies primarily on extensive incorporation of the TFT metabolite into the cellular DNA inducing DNA dysfunction and cell death. In contrast, 5-fluorouracil (5-FU) interferes with DNA biosynthesis by inhibiting thymidylate synthase(TS), which partly explains the absence of cross-resistance between TAS-102 and 5-FU. TAS-102 is currently approved in the third-line setting for patients with metastatic colorectal and gastric cancer based on phase III randomized clinical trial data confirming an overall survival benefit with TAS-102. The preliminary data from recently reported studies suggest a potential expanding role of TAS-102 in a variety of gastrointestinal (GI) cancers. The current article presents an overview of the pharmacology, clinical development of TAS-102, and its emerging role in the treatment of GI cancers. In addition, we discussed the rationale underlying the ongoing clinical trials investigating various combinations of TAS-102 with other anticancer agents, including targeted therapies, in a wide range of GI tumors.

5-Fluorouracil (5-FU) resistance and the new strategy to enhance the sensitivity against cancer: Implication of DNA repair inhibition

5-Fluorouracil (5-FU) has been an important anti-cancer drug to date. With an increase in the knowledge of its mechanism of action, various treatment modalities have been developed over the past few decades to increase its anti-cancer activity. But drug resistance has greatly affected the clinical use of 5-FU. Overcoming this chemoresistance is a challenge due to the presence of cancer stem cells like cells, cancer recurrence, metastasis, and angiogenesis. In this review, we have systematically discussed the mechanism of 5-FU resistance and advent strategies to increase the sensitivity of 5-FU therapy including resistance reversal. Special emphasis has been given to the cancer stem cells (CSCs) mediated 5-FU chemoresistance and its reversal process by different approaches including the DNA repair inhibition process.

The effect of trifluridine/tipiracil for patients with heavily pretreated metastatic gastric cancer: A protocol for systematic review and meta-analysis

BACKGROUND

Gastric cancer is a global health problem with high incidence rate and mortality rate. Due to the limitations of traditional chemotherapy drugs, such as patient intolerance, low efficacies and serious adverse effects, trifluridine/tipiracil has been considered to be a promising treatment for patients with heavily pretreated metastatic gastric cancer. However, the relevant systematic review has not been occurring. The presentation of this protocol is to scientifically evaluate the efficacy and safety of trifluridine/tipiracil in patients with highly pretreated metastatic gastric cancer.

METHODS

The protocol followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols. We will systematically search MEDLINE, PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure Database (CNKI), VIP Chinese Science and Technology Periodical Database (VIP), Wan Fang Database up to November 1, 2020 to identify published articles. Using the Cochrane risk assessment tool to assess the methodological quality of the RCTs, and all included studies will be analyzed according to the criteria in the Cochrane Handbook. Review Manager 5.3 software will be used for literature quality evaluation and data analysis.

RESULTS

Objective to evaluate the efficacy and safety of trifluridine/tipiracil in patients with heavily pretreated metastatic gastric cancer by analyzing the eligible data extracted under limited conditions.

CONCLUSION

This study provides clear evidence to evaluate the effectiveness and safety of trifluridine/tipiracil for patients with highly pretreated metastatic gastric cancer, and the findings will also be published in a peer-reviewed journal.

ETHICS AND DISSEMINATION

No ethical statement will be required for this study because there is no direct involvement of human. This review will be published in a peer-reviewed journal as a conference report or an article.

REGISTRATION

OSF registration number: DOI 10.17605/OSF.IO/6MF5U.

Efficacy of Combination Chemotherapy Using a Novel Oral Chemotherapeutic Agent, FTD/TPI, with Ramucirumab Murine Version DC101 in a Mouse Syngeneic Cancer Transplantation Model

Trifluridine/tipiracil (FTD/TPI) (a.k.a. TAS-102) is a combination drug for metastatic colorectal cancer (CRC) and severely pretreated metastatic gastric/gastroesophageal junction (GEJ) cancers, comprising FTD, a thymidine-based antineoplastic nucleoside analog, and TPI, which enhances FTD bioavailability. Herein, in KRAS mutant murine colorectal cancer CT26 syngeneic models, we investigate whether combination therapy with DC101 (a surrogate ramucirumab antibody, rat antimouse vascular endothelial growth factor receptor (VEGFR)-2 monoclonal antibody (mAb)) improves FTD/TPI efficacy. Tumor growth inhibition (TGI) on day 15 was 38.0% and 30.6% upon DC101 monotherapy and FTD/TPI monotherapy respectively, and 60.3% upon combination therapy. Tumor volume was significantly lower (p < 0.001) upon combination treatment than upon FTD/TPI or DC101 monotherapy, indicating the additive effects of FTD/TPI and DC101. DNA-incorporated FTD levels on Day 8 were significantly higher in combination therapy with FTD/TPI (for 5 consecutive days) and DC101 (on alternate days for 7days) than in FTD/TPI monotherapy. Furthermore, vascular endothelial cell-specific marker CD31 was downregulated in DC101-treated tumors on day 8. These results indicate that combination therapy with FTD/TPI and DC101 is a promising treatment alternative regardless of KRAS mutations.

Radiosensitisation and enhanced tumour growth delay of colorectal cancer cells by sustained treatment with trifluridine/tipiracil and X-rays

Trifluridine/tipiracil (FTD/TPI; marketed as Lonsurf®) has shown clinically relevant activity after fluoropyrimidine failure in colorectal cancer and may thus be of increased efficacy compared with current standard capecitabine chemoradiation. Here we investigated the colorectal cancer cell lines HT29, HCT116, SW48 and Caco-2 to provide a preclinical rationale for FTD/TPI-based chemoradiation treatment. All lines incorporated similar amounts of FTD, irrespective of treatment concentration and duration, then arrested in S phase, showed persistent γH2AX induction and eventually underwent endoreplication, resulting in polyploidy. Clonogenic assays performed for four combined treatment schedules demonstrated additivity for treatments given within 6 h of each other. However, 24 h FTD/TPI treatment prior to irradiation caused 1.6-2.4 fold radiosensitisation. Combined in vivo treatment was well tolerated and caused a marked tumour growth delay, similar to capecitabine radiochemotherapy regimes. Prolonged S phase arrest, persistent γH2AX signalling, endoreplication and polyploidy may contribute to the cytotoxicity of FTD/TPI. The strong radiosensitising effect observed in vitro after prolonged treatment with FTD/TPI and equivalence with capecitabine-based chemoradiation in vivo support a daily fractionated combined regime of FTD/TPI and radiation in rectal cancer treatment. This is now being tested in a phase I/II clinical trial (NCT04177602).

Loganetin and 5-fluorouracil synergistically inhibit the carcinogenesis of gastric cancer cells via down-regulation of the Wnt/β-catenin pathway

Although most gastrointestinal tumours are sensitive to 5-fluorouracil (5FU), drug resistance is commonly occurred after 5FU therapy in gastric cancer (GC). Loganetin is the primary active compound in Cornus officinali. However, the synergetic effects of loganetin and 5FU on GC remain unknown. Here, we investigated the synergetic effects and the underlying mechanism of loganetin and 5FU on proliferation, stem-like properties, migration, and invasion of GC both in vitro and in vivo. We found that loganetin alone inhibited the proliferation, stem-like properties, migration and invasion of GC cells in vitro. Importantly, the loganetin remarkably enhanced the anti-cancer effect of 5FU on GC cells and the Wnt/β-catenin pathway might be involved in this process. Animal experiments further confirmed the synergistic effects of 5FU and loganetin on inhibiting cell growth and metastasis of GC. These results suggested that loganetin could synergistically increase the effect of 5FU against GC, which sheds light on effective combinational drug strategies for GC treatment.

Clinical Evaluation of the Safety and Efficacy of Trifluridine/Tipiracil in the Treatment of Advanced Gastric/Gastroesophageal Junction Adenocarcinoma: Evidence to Date

Trifluridine/tipiracil or TAS-102 (Taiho Oncology, Lonsurf^®, Princeton, NJ, USA) is a combination tablet of trifluridine, a thymidine-based nucleoside analog, and tipiracil, a thymidine phosphorylase inhibitor, in a 1:0.5 molar ratio. This drug was first approved for use in metastatic colorectal cancer patients. Recently, the U S Food and Drug Administration (FDA) and the European Medicines Agency (EMA) have granted approval of trifluridine/tipiracil for treatment of metastatic gastric and gastroesophageal junction adenocarcinoma in patients following at least two lines of chemotherapy including fluoropyrimidine and platinum chemotherapy agents, as well as taxanes or irinotecan. This approval was granted after the findings from first a Phase II trial (EPOC1201) investigating trifluridine/tipiracil, and later a global Phase III trial (TAGS trial) that compared trifluridine/tipiracil vs placebo with best supportive care. Both trials primarily utilized trifluridine/tipiracil at a dose of 35 mg/m² twice daily. In the EPOC1201 trial, the primary end point of disease control rate was greater than 50% after eight weeks of therapy. The most common grade three or four adverse event was neutropenia; additional toxicities included leukopenia, anemia, and anorexia. In the TAGS trial, overall survival in patients treated with trifluridine/tipiracil (5.7 months) was significantly improved as compared to the placebo-controlled group (3.6 months). Treatment with trifluridine/tipiracil not only did not impair quality of life but also tended to reduce the risk of deterioration of quality of life. The results of these studies along with the subsequent FDA and EMA approval have generated an important breakthrough in regard to treatment options for patients with refractory metastatic gastric or gastroesophageal junction adenocarcinoma.

DNA Replication Stress Induced by Trifluridine Determines Tumor Cell Fate According to p53 Status

DNA replication stress (DRS) is a predominant cause of genome instability, a driver of tumorigenesis and malignant progression. Nucleoside analogue-type chemotherapeutic drugs introduce DNA damage and exacerbate DRS in tumor cells. However, the mechanisms underlying the antitumor effect of these drugs are not fully understood. Here, we show that the fluorinated thymidine analogue trifluridine (FTD), an active component of the chemotherapeutic drug trifluridine/tipiracil, delayed DNA synthesis by human replicative DNA polymerases by acting both as an inefficient deoxyribonucleotide triphosphate source (FTD triphosphate) and as an obstacle base (trifluorothymine) in the template DNA strand, which caused DRS. In cells, FTD decreased the thymidine triphosphate level in the dNTP pool and increased the FTD triphosphate level, resulting in the activation of DRS-induced cellular responses during S-phase. In addition, replication protein A-coated single-stranded DNA associated with FancD2 and accumulated after tumor cells completed S-phase. Finally, FTD activated the p53-p21 pathway and suppressed tumor cell growth by inducing cellular senescence via mitosis skipping. In contrast, tumor cells that lost wild-type p53 underwent apoptotic cell death via aberrant late mitosis with severely impaired separation of sister chromatids. These results demonstrate that DRS induced by a nucleoside analogue-type chemotherapeutic drug suppresses tumor growth irrespective of p53 status by directing tumor cell fate toward cellular senescence or apoptotic cell death according to p53 status. IMPLICATIONS: Chemotherapeutic drugs that increase DRS during S-phase but allow tumor cells to complete S-phase may have significant antitumor activity even when functional p53 is lost.

TAS-102 in gastric cancer: Development and perspectives of a new biochemically modulated fluroropyrimidine drug combination

TAS-102 is a preconstituted drug combination comprising an oral fluoropyrimidine (trifluridine, TFT) and a potent inhibitor of thymidine phosphorylase (tipiracil hydrochloride, TPI). TFT/TPI has recently received Food and Drug Administration (FDA) approval also for the treatment of gastric cancer after at least two lines of chemotherapy. The approval was based on a large phase 3 trial (TAGS), in which TAS-102 showed a 31 % decrease in the risk of death compared with placebo. Here, we review the pharmacological properties, clinical development and potential future directions of TAS-102 in gastric cancer.

Trifluridine/Tipiracil: A Review in Metastatic Gastric Cancer

Trifluridine/tipiracil (Lonsurf^®) is a fixed-dose combination tablet comprising trifluridine, an antineoplastic nucleoside analogue, and tipiracil, a thymidine phosphorylase inhibitor. Trifluridine/tipiracil has recently been granted an additional indication in the USA for the treatment of metastatic gastric cancer, including gastroesophageal junction adenocarcinoma, in patients who have been previously treated with at least two systemic treatment regimens, and has received a positive opinion for this indication in the EU. In the large pivotal phase III TAGS trial, trifluridine/tipiracil plus best supportive care (BSC) significantly prolonged overall survival (OS; primary endpoint) compared with placebo plus BSC in this patient group. Progression-free survival (PFS) and the disease control rate were also improved with trifluridine/tipiracil relative to placebo. Health-related quality of life was not adversely affected by the addition of trifluridine/tipiracil to BSC and time to deterioration of Eastern Cooperative Oncology Group (ECOG) performance status was significantly delayed. The most common adverse events were mainly haematological (neutropenia, leucopenia and anaemia) and gastrointestinal (nausea, vomiting and diarrhoea), and were generally manageable with dosage modifications and/or supportive care. Adverse events ≥ Grade 3 were most frequently haematological in nature. Thus, trifluridine/tipiracil provides a valuable and much needed treatment option for patients with metastatic gastric or gastroesophageal junction adenocarcinoma that has progressed on at least two prior therapies.

Trifluridine/tipiracil for the treatment of metastatic gastric cancer

Introduction: Trifluridine/tipiracil is a novel oral cytotoxic chemotherapy consisting of a thymidine-based nucleoside analog, trifluridine, and a thymidine phosphorylase inhibitor, tipiracil. Trifluridine/tipiracil was approved for the treatment of metastatic colorectal cancer refractory to standard therapies. A phase II trial in Japan demonstrated that this therapy has antitumor activity and is tolerated by patients with advanced gastric cancer (AGC); as a result, the phase III TAGS trial (Trifluridine/tipiracil versus placebo in patients with heavily pretreated metastatic gastric cancer) was initiated.Area covered: Trifluridine/tipiracil has proved effective for heavily pretreated AGC and has thus been approved for use in the United States in February 2019, Japan in August 2019 and the European Union in September 2019. Detail of the phase III TAGS trial is discussed in this review.Expert opinion: Trifluridine/tipiracil after at least two previous courses of systemic chemotherapy improved rates of survival of gastric cancer; thus it has become one of the treatment options in affected patients. Currently, several clinical trials of trifluridine/tipiracil in combination with other anticancer agents such as ramucirumab (an anti-vascular endothelial growth factor receptor 2 monoclonal antibody) for patients with AGC are ongoing.

Selected nucleos(t)ide-based prescribed drugs and their multi-target activity

Nucleos(t)ide analogues play pivotal roles as antiviral, cytotoxic or immunosuppressive agents. Here, we review recent reports of nucleoside analogues that exhibit broad-spectrum activity towards multiple life-threatening RNA and DNA viruses. We also present a discussion about nucleoside antimetabolites-approved antineoplastic agents-that have recently been shown to have antiviral and/or antibacterial activity. The approved drugs and drug combinations, as well as recently identified candidates for investigation and/or experimentation, are discussed. Several examples of repurposed drugs that have already been approved for use are presented. This strategy can be crucial for the first-line treatment of acute infections or coinfections and for the management of drug-resistant strains.

5-fluorouracil and other fluoropyrimidines in colorectal cancer: Past, present and future

5-Fluorouracil (5-FU) is an essential component of systemic chemotherapy for colorectal cancer (CRC) in the palliative and adjuvant settings. Over the past four decades, several modulation strategies including the implementation of 5-FU-based combination regimens and 5-FU pro-drugs have been developed and tested to increase the anti-tumor activity of 5-FU and to overcome the clinical resistance. Despite the encouraging progress in CRC therapy to date, the patients' response rates to therapy continue to remain low and the patients' benefit from 5-FU-based therapy is frequently compromised by the development of chemoresistance. Inter-individual differences in the treatment response in CRC patients may originate in the unique genetic and epigenetic make-up of each individual. The critical element in the current trend of personalized medicine is the proper comprehension of causes and mechanisms contributing to the low or lack of sensitivity of tumor tissue to 5-FU-based therapy. The identification and validation of predictive biomarkers for existing 5-FU-based and new targeted therapies for CRC treatment will likely improve patients' outcomes in the future. Herein we present a comprehensive review summarizing options of CRC treatment and the mechanisms of 5-FU action at the molecular level, including both anabolic and catabolic ways. The main part of this review comprises the currently known molecular mechanisms underlying the chemoresistance in CRC patients. We also focus on various 5-FU pro-drugs developed to increase the amount of circulating 5-FU and to limit toxicity. Finally, we propose future directions of personalized CRC therapy according to the latest published evidence.

A novel intraperitoneal therapy for gastric cancer with DFP-10825, a unique RNAi therapeutic targeting thymidylate synthase, in a peritoneally disseminated xenograft model

Purpose

In advanced gastric cancer, peritoneal dissemination is a life‐threatening mode of metastasis. Since the treatment options with conventional chemotherapy remain limited, any novel therapeutic strategy that could control such metastasis would improve the outcome of treatment. We recently developed a unique RNA interference therapeutic regimen (DFP‐10825) consisting of short hairpin RNA against thymidylate synthase (TS shRNA) and cationic liposomes. The treatment with DFP‐10825 has shown remarkable antitumor activity in peritoneally disseminated human ovarian cancer–bearing mice via intraperitoneal administration. In this study, we expanded DFP‐10825 to the treatment of peritoneally disseminated gastric cancer.

Methods

DFP‐10825 was administered intraperitoneally into mice with intraperitoneally implanted human gastric cancer cells (MKN45 or NCI‐N87). Antitumor activity and host survival benefits were monitored. Intraperitoneal distribution of fluorescence‐labeled DFP‐10825 was monitored in this MKN45 peritoneally disseminated mouse model.

Results

Intraperitoneal injection of DFP‐10825 suppressed tumor growth in two peritoneally disseminated cancer models (MKN45 and NCI‐N87) and increased the survival time of the MKN45 model without severe side effects. Throughout the treatment regimen, no significant body weight loss was associated with the administration of DFP‐10825. Interestingly, after intraperitoneal injection, fluorescence‐labeled DFP‐10825 retained for more than 72 hours in the peritoneal cavity and selectively accumulated in disseminated tumors.

Conclusions

Intraperitoneal injection of DFP‐10825 demonstrated effective antitumor activity without systemic severe adverse effects via the selective delivery of RNAi molecules into disseminated tumors in the peritoneal cavity. Our current study indicates that DFP‐10825 could become an alternative option to improve the outcomes of patients with peritoneally disseminated gastric cancer.

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.

Nucleobase and Nucleoside Analogues: Resistance and Re-Sensitisation at the Level of Pharmacokinetics, Pharmacodynamics and Metabolism

Antimetabolites, in particular nucleobase and nucleoside analogues, are cytotoxic drugs that, starting from the small field of paediatric oncology, in combination with other chemotherapeutics, have revolutionised clinical oncology and transformed cancer into a curable disease. However, even though combination chemotherapy, together with radiation, surgery and immunotherapy, can nowadays cure almost all types of cancer, we still fail to achieve this for a substantial proportion of patients. The understanding of differences in metabolism, pharmacokinetics, pharmacodynamics, and tumour biology between patients that can be cured and patients that cannot, builds the scientific basis for rational therapy improvements. Here, we summarise current knowledge of how tumour-specific and patient-specific factors can dictate resistance to nucleobase/nucleoside analogues, and which strategies of re-sensitisation exist. We revisit well-established hurdles to treatment efficacy, like the blood-brain barrier and reduced deoxycytidine kinase activity, but will also discuss the role of novel resistance factors, such as SAMHD1. A comprehensive appreciation of the complex mechanisms that underpin the failure of chemotherapy will hopefully inform future strategies of personalised medicine.