Oral fluoropyrimidine treatment of colorectal cancer

Oral drugs in the treatment of metastatic colorectal cancer

Colorectal cancer (CRC) is one of the most common forms of cancer, with an estimated 1.36 million new cases and almost 700,000 deaths annually. Approximately 21% of patients with CRC have metastatic disease at diagnosis. The objective of this article is to review the literature on the efficacy and safety of oral drugs available for the treatment of metastatic colorectal cancer (mCRC). Several such drugs have been developed, and fluoropyrimidines are the backbone of chemotherapy in this indication. They exert their antitumour activity by disrupting the synthesis and function of DNA and RNA. Oral fluoropyrimidines include prodrugs capecitabine, tegafur, eniluracil/5-fluorouracil, tegafur/uracil, tegafur/gimeracil/oteracil and trifluridine/tipiracil (FTD/TPI). Oral drugs offer several advantages over injectable formulations, including convenience, flexibility, avoidance of injection-related adverse events (AEs) and, in some circumstances, lower costs. However, oral drugs may not be suitable for patients with gastrointestinal obstruction or malabsorption, they may result in reduced treatment adherence and should not be co-administered with drugs that interfere with absorption or hepatic metabolism. Oral fluoropyrimidines such as capecitabine, as monotherapy or in combination with oxaliplatin, irinotecan or bevacizumab, are as effective as intravenous 5-fluorouracil (5-FU) in first-line treatment of mCRC. Other oral fluoropyrimidines, such as FTD/TPI, are effective in patients with mCRC who are refractory, intolerant or ineligible for 5-FU. In addition, oral fluoropyrimidines are used in adjuvant treatment of mCRC. Regorafenib is an oral multikinase inhibitor used in patients in whom several previous lines of therapy have failed. Frequent AEs associated with oral drugs used in the treatment of CRC include hand-foot syndrome and gastrointestinal and haematological toxicities.

Changes in expression levels of ERCC1, DPYD, and VEGFA mRNA after first-line chemotherapy of metastatic colorectal cancer: results of a multicenter study

Our previous study showed that administering oxaliplatin as first-line chemotherapy increased ERCC1 and DPD levels in liver colorectal cancers (CRCs) metastases. Second, whether the anti-VEGF monoclonal antibody bevacizumab alters tumoral VEGFA levels is unknown. We conducted this multicenter observational study to validate our previous findings on ERCC1 and DPD, and clarify the response of VEGFA expression to bavacizumab administration. 346 CRC patients with liver metastases were enrolled at 22 Japanese institutes. Resected liver metastases were available for 175 patients previously treated with oxaliplatin-based chemotherapy (chemotherapy group) and 171 receiving no previous chemotherapy (non-chemotherapy group). ERCC1, DPYD, and VEGFA mRNA levels were measured by real-time RT-PCR. ERCC1 mRNA expression was significantly higher in the chemotherapy group than in the non-chemotherapy group (P = 0.033), and were significantly correlated (Spearman's correlation coefficient = 0.42; P < 0.0001). VEGFA expression level was higher in patients receiving bevacizumab (n = 51) than in those who did not (n = 251) (P = 0.007). This study confirmed that first-line oxaliplatin-based chemotherapy increases ERCC1 and DPYD expression levels, potentially enhancing chemosensitivity to subsequent therapy. We also found that bevacizumab induces VEGFA expression in tumor cells, suggesting a biologic rationale for extending bevacizumab treatment beyond first progression.

5-Fluorouracil derivatives: a patent review

INTRODUCTION

The fluorinated analog of uracil 5-FU is an antimetabolite, active against a wide range of solid tumors. The main mechanism of action consists in interfering with DNA synthesis and mRNA translation. However, patients treated with 5-FU display several side effects, a result of its nonspecific cytotoxicity for tumor cells. Numerous modifications of the 5-FU structure have been performed in order to overcome these disadvantages.

AREAS COVERED

In this review, the metabolic pathways, pharmacokinetics and clinical pharmacology of 5-FU are briefly introduced. Moreover, several derivatives developed and patented, including oral 5-FU prodrugs and combinations with other active compounds, are presented. Finally, new innovative methods for administration and vehiculization of 5-FU and its derivatives are described.

EXPERT OPINION

The search for less toxic 5-FU derivatives, which diminish or circumvent some of its disadvantages, has allowed the development of selective antitumor prodrugs and novel methods for tissue-specific drug delivery. Although some of these oral prodrugs are being used clinically, either alone or in combination therapy with other anticancer agents, it seems that the potential of personalized medicine, including pharmacogenomics and targeted therapy with novel 5-FU derivatives, will improve the management and clinical responses of patients treated with 5-FU-based therapy.

Biological agents versus chemotherapy in the treatment of colorectal cancer

Biological agents are commonly incorporated as an adjunct to cytotoxic chemotherapy in the treatment of patients with advanced colorectal cancer. In contrast to cytotoxic chemotherapy, biological agents have minimal single agent activity and are largely considered to be cytostatic. Recent data supports the use of either combination regimens with chemotherapy and/or biological therapy. Interest in combining biological agents of co-existing molecular pathways is the most recent strategic approach. However, with the advent of these novel therapies, questions have arisen regarding appropriate clinical indication and potential treatment-related toxicities. The role of biological agents in the treatment of colorectal cancer and their role in contrast to cytotoxic chemotherapy will be explored.

Lack of contribution of dihydrofluorouracil and alpha-fluoro-beta-alanine to the cytotoxicity of 5'-deoxy-5-fluorouridine on human keratinocytes

Capecitabine (Xeloda) is a very active oral fluoropyrimidine (colon and breast cancers) whose clinical use is complicated by the presence of hand-foot syndrome (HFS). This cutaneous toxicity is less frequently encountered with other oral fluoropyrimidines containing a dihydropyrimidine dehydrogenase (DPD) inhibitor. The HFS is thus attributed to the presence of the main 5-fluorouracil (5-FU) metabolites, dihydrofluorouracil (5-FUH2) and alpha-fluoro-beta-alanine (FBAL), but without strong pharmacological arguments. The aim of the present study was to closely examine this latter hypothesis. Capecitabine generates 5'-deoxyflourouridine (5'-DFUR) which is transformed into 5-FU at the cellular target site through the intermediary of thymidine phosphorylase (TP). The cytotoxic effects (MTT test, 4-day exposure) of 5'-DFUR, 5-FU, 5-FUH2 and FBAL were tested against the spontaneously immortalized human keratinocyte cell line (HaCaT) and the human cancer colon cell line WiDr as a control. Mean IC50s on HaCaT and WiDr were, respectively, 1.3 and 10 microM for 5'-DFUR, 0.2 and 3.3 microM for 5-FU, 13.4 and 560 microM for 5-FUH2, and greater than 650 and 6500 microM for FBAL. The respective 5'-DFUR IC50s values were not different when cells were exposed to 5'-DFUR alone or in combination with 5-FU, 5-FUH2 and FBAL in both cell lines, the relative proportion of each drug reflecting known pharmacokinetic data for capecitabine (5'-DFUR 12.4%, 5-FUH2 6.4%, 5-FU 1.2% and FBAL 80%). This latter finding demonstrates the relative lack of significant cytotoxic activity of 5-FUH2 and FBAL on human keratinocytes. TP activity was particularly high in HaCaT cells and DPD activity was very low in both cell lines. These data strongly suggest that the presence of 5-FU metabolites does not play a major role in the HFS generated by capecitabine and that it can probably be attributed to particularly high TP activity in keratinocytes. This observation may have important clinical consequences such as a possible local pharmacological inhibition of TP for controlling HFS.

Phase II study of UFT and oxaliplatin in first-line treatment of advanced colorectal cancer

The purpose of this study was to evaluate the efficacy, assesed as response rate, and toxicity of UFT (Tegafur-Uracil) in combination with oxaliplatin as first-line treatment of advanced colorectal cancer (CRC). In all, 84 patients with recurrent or metastatic CRC with measurable disease were included. Treatment consisted of oxaliplatin 85 mg m⁻² in 120-min intravenous (i.v.) infusion on days 1 and 15; i.v. l,leucovorin (l,LV) 250 mg m⁻² given in 2 h on day 1, followed by oral UFT 390 mg m⁻² on days 1–14, and oral l,LV 7.5 mg/12 h on days 2–14. Cycles were repeated every 28 days. A total of 492 cycles of chemotherapy were delivered with a median of six per patient (range 1–12). There was one complete response (1%) and 28 partial responses (34%) for an overall response rate of 35% (95% confidence interval (CI): 24–46%). A total of 36 patients (44%) had stable disease, whereas 17 (21%) had a progression. The median time to progression was 7.3 months and the median overall survival was 16.8 months. A prescheduled preliminary analysis was performed after inclusion of 16 patients who detected a high gastrointestinal toxicity, which led to a reduction of the UFT dose to 300 mg m⁻². With this new dosage, grade 3–4 diarrhoea and grade 3–4 nausea/vomiting dropped to 21 and 14% of patients, respectively. Other grade 3–4 toxicities were stomatitis in one (1%), anaemia in three (5%), neutropenia in two (3%), thrombocytopenia in one(1%), fatigue in six (9%), peripheral sensory neuropathy in nine (14%) and laryngopharyngeal dysesthesia in two patients (2%). The combination of oxaliplatin and UFT–l,LV is an active, easy-to-administer regimen with moderate toxicity. Hence, this regimen is worthy of further investigation.

Enhanced DNA-directed effects of FdUMP[10] compared to 5FU

FdUMP[N] molecules and conjugates are much more effective at inhibiting the proliferation of human tumor cells than is the widely used anticancer drug 5-fluorouracil (5FU). We have evaluated the inhibition of thymidylate synthase (TS), the extent of DNA damage, cell cycle arrest, and the induction of apoptosis by FdUMP[10] and 5FU in the human colorectal cancer cell line HT29. The magnitude and duration of TS inhibition following exposure of HT29 cells to FdUMP[10] at 1 x 10(-8) M was greater than that which occurred following exposure of these cells to 5FU at 1 x 10(-6) M. FdUMP[10] exposure also resulted in much more extensive DNA damage to HT29 cells than occurred following exposure to 100-fold higher concentrations of 5FU. Although exposure of HT29 cells to both drugs resulted in S-phase arrest, more complete accumulation of cells in S-phase was achieved following FdUMP[10] exposure at much lower drug concentrations. FdUMP[10] was also much more effective at inducing apoptosis in HT29 cells than was 5FU. The results are consistent with FdUMP[10] being much more efficient that 5FU at inducing DNA damage that results in apoptotic cell death in colon cancer cells.

Adjuvant therapy for rectal cancer--the transatlantic view

In North America there are two conventional treatments for clinically resectable rectal cancer. First is surgery and, if the tumour is T3 and/or N1-2, this is followed by postoperative combined modality therapy. The second, for patients with ultrasound T3 or clinical T4 disease, is pre-operative combined modality therapy followed by surgery and postoperative chemotherapy. Pre-operative therapy (most commonly combined modality therapy) has gained acceptance as a standard adjuvant therapy. The potential advantages of this approach compared with postoperative therapy include less acute toxicity and enhanced sphincter preservation. Recently completed randomized trials in the US and Germany will provide a definitive answer to this theory. In contrast to the combined modality approach to pre-operative therapy a number of European centres advocate an intensive short course of radiation (5 Gy x 5 followed one week later by surgery). The only randomized trial which has revealed a significant advantage in survival is the Swedish Rectal Cancer Trial. The Dutch CKVO 95-04 TME trial did not confirm a survival advantage and two metanalyses report conflicting results. Due to selection bias, it is not possible accurately to compare the local recurrence and survival results of intensive short course radiation with conventional pre-operative combined modality therapy. The intensive short course radiation approach is not used in North America due to its higher toxicity and lack of sphincter preservation. In the Dutch trial the 5-year local recurrence was 12% with TME and was significantly decreased to 6% with pre-operative radiation. The 5-year local recurrence rate in the 324 patients with stage III disease who underwent a TME alone with negative margins was 20%. Therefore, despite TME surgery, radiation therapy is still a necessary component in the adjuvant management of rectal cancer.

Thymidylate synthase: a critical target for cancer chemotherapy

Thymidylate synthase (TS) is a key enzyme in the synthesis of 2'-deoxythymidine-5'-monophosphate, an essential precursor for DNA biosynthesis. For this reason, this enzyme is a critical target in cancer chemotherapy. As the first TS inhibitor in clinical use, 5-fluorouracil (5-FU) remains widely used for the treatment of colorectal, pancreatic, breast, head and neck, gastric, and ovarian cancers. The reduced folate, leucovorin, has been shown to enhance the activity of 5-FU in colorectal cancer. However, response rates of the combination remain in the 25%-30% range, and much effort has been focused on designing new, more potent TS inhibitors. Raltitrexed is a folate analogue that is approved as first-line therapy for advanced colorectal cancer in Europe, Australia, Canada, and Japan, although it remains an investigational agent in the United States. Pemetrexed is an antifolate analogue that has shown promising activity in several solid tumor types, including mesothelioma. ZD9331, a highly specific TS inhibitor that dose not require polyglutamation for its activation, has shown activity in patients with refractory ovarian and colorectal cancer. Capecitabine is an oral fluoropyrimidine carbamate that was designed to generate 5-FU preferentially in tumor cells; this agent was recently approved by the US Food and Drug Administration as first-line therapy for patients with advanced colorectal cancer. As the number of TS inhibitors available for general clinical use increases, further research is needed to elucidate the critical molecular and biochemical elements that determine the efficacy and tumor specificity of each compound.