alpha-fluoro-beta-alanine: effects on the antitumor activity and toxicity of 5-fluorouracil

Downregulating miRNA-199a-5p exacerbates fluorouracil-induced cardiotoxicity by activating the ATF6 signaling pathway

BACKGROUND

Fluorouracil (5-FU) might produce serious cardiac toxic reactions. miRNA-199a-5p is a miRNA primarily expressed in myocardial cells and has a protective effect on vascular endothelium. Under hypoxia stress, the expression level of miRNA-199a-5p was significantly downregulated and is closely related to cardiovascular events such as coronary heart disease, heart failure, and hypertension. We explored whether 5-FU activates the endoplasmic reticulum stress ATF6 pathway by regulating the expression of miRNA-199a-5p in cardiac toxicity.

METHODS

This project established a model of primary cardiomyocytes derived from neonatal rats and treated them with 5-FU in vitro. The expression of miRNA-199a-5p and its regulation were explored in vitro and in vivo.

RESULTS

5-FU decreases the expression of miRNA-199a-5p in cardiomyocytes, activates the endoplasmic reticulum stress ATF6 pathway, and increases the expression of GRP78 and ATF6, affecting the function of cardiomyocytes, and induces cardiac toxicity. The rescue assay further confirmed that miRNA-199a-5p supplementation can reduce the cardiotoxicity caused by 5-FU, and its protective effect on cardiomyocytes depends on the downregulation of the endoplasmic reticulum ATF6 signaling pathway.

CONCLUSIONS

5-FU can down-regulate expression of miRNA-199a-5p, then activate the endoplasmic reticulum stress ATF6 pathway, increase the expression of GRP78 and ATF6, affect the function of cardiomyocytes, and induce cardiac toxicity.

AraC-FdUMP[10] Is a Next-Generation Fluoropyrimidine with Potent Antitumor Activity in PDAC and Synergy with PARG Inhibition

AraC-FdUMP[10] (CF10) is a second-generation polymeric fluoropyrimidine that targets both thymidylate synthase (TS), the target of 5-fluorouracil (5-FU), and DNA topoisomerase 1 (Top1), the target of irinotecan, two drugs that are key components of FOLFIRNOX, a standard-of-care regimen for pancreatic ductal adenocarcinoma (PDAC). We demonstrated that F10 and CF10 are potent inhibitors of PDAC cell survival (in multiple cell lines including patient-derived lines) with IC₅₀s in the nanomolar range and are nearly 1,000-fold more potent than 5-FU. The increased potency of CF10 relative to 5-FU correlated with enhanced TS inhibition and strong Top1 cleavage complex formation. Furthermore, CF10 displayed single-agent activity in PDAC murine xenografts without inducing weight loss. Through a focused drug synergy screen, we identified that combining CF10 with targeting the DNA repair enzyme, poly (ADP-ribose) glycohydrolase, induces substantial DNA damage and apoptosis. This work moves CF10 closer to a clinical trial for the treatment of PDAC. IMPLICATIONS: CF10 is a promising polymeric fluoropyrimidine with dual mechanisms of action (i.e., TS and Top1 inhibition) for the treatment of PDAC and synergizes with targeting of DNA repair. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/4/565/F1.large.jpg.

Fluoropyrimidine Modulation of the Anti-Tumor Immune Response-Prospects for Improved Colorectal Cancer Treatment

Chemotherapy modulates the anti-tumor immune response and outcomes depend on the balance of favorable and unfavorable effects of drugs on anti-tumor immunity. 5-Florouracil (5-FU) is widely used in adjuvant chemotherapy regimens to treat colorectal cancer (CRC) and provides a survival benefit. However, survival remains poor for CRC patients with advanced and metastatic disease and immune checkpoint blockade therapy benefits only a sub-set of CRC patients. Here we discuss the effects of 5-FU-based chemotherapy regimens to the anti-tumor immune response. We consider how different aspects of 5-FU's multi-factorial mechanism differentially affect malignant and immune cell populations. We summarize recent studies with polymeric fluoropyrimidines (e.g., F10, CF10) that enhance DNA-directed effects and discuss how such approaches may be used to enhance the anti-tumor immune response and improve outcomes.

Impairment of energy metabolism in cardiomyocytes caused by 5-FU catabolites can be compensated by administration of amino acids

Identification of patients with increased risk of 5-fluorouracil (5-FU)-related toxicity is an important challenge for cancer treatment. Research often focus on dihydropyrimidine dehydrogenase (DPYD) deficiency in this context. However, patients with normal DPYD activity may also develop life-threatening 5-FU adverse effects. DPYD initiates the catabolic route of 5-FU generating metabolites such as fluoroacetate (FAC). The catabolite FAC is known to inhibit the TCA cycle enzyme aconitase, which is supposed to impair mitochondrial energy metabolism. Therefore, we aim for a systems understanding of the association of 5-FU-related cardiac side effects with aconitase inhibition caused by FAC. Using a mitochondrial model of cardiomyocytes we found strong depletion of ATP production and citrate accumulation as main effects of aconitase inhibition. Shadow price analysis revealed that the uptakes of valine, arginine, proline and glutamate are most effective in compensating the impairment of energy metabolism. Our findings suggest that 5-FU catabolism contributes to the occurrence of cardiac adverse effects and are the basis for further biomarker identifications and development of side effect treatment.

Altered dihydropyrimidine dehydrogenase activity associated with mild toxicity in patients treated with 5-fluorouracil containing chemotherapy

Dihydropyrimidine dehydrogenase (DPD) plays a pivotal role in the metabolism of 5-fluorouracil (5FU). In patients treated with capecitabine or 5FU combined with other chemotherapeutic drugs, DPD activity in peripheral blood mononuclear cells was increased in patients experiencing grade I/II neutropenia. In contrast, decreased DPD activity proved to be associated with grade I/II dermatological toxicity, including hand-foot syndrome. Thus, patients with a low-normal or high-normal DPD activity proved to be at risk of developing mild toxicity upon treatment with 5FU-based chemotherapy, demonstrating the important role of DPD in the etiology of toxicity associated with 5FU and the catabolites of 5FU.

Increased dihydropyrimidine dehydrogenase activity associated with mild toxicity in patients treated with 5-fluorouracil and leucovorin

Dihydropyrimidine dehydrogenase (DPD) plays a pivotal role in the metabolism of 5FU. The prognostic significance of DPD activity in peripheral blood mononuclear (PBM) cells and buccal mucosa cells with respect to toxicity was investigated in 44 patients treated with 5FU-leucovorin. Grade III/IV haematological and grade III/IV gastrointestinal toxicity were observed in 25% and 21% of the patients, respectively. No association was observed between the DPD activity in buccal mucosa cells and toxicity. In contrast, the mean DPD activity in PBM cells proved to be increased in patients experiencing grade I/II neutropenia when compared to patients without neutropenia and those suffering from grade III/IV neutropenia (P=0.002). Patients with a high-normal DPD activity proved to be at risk of developing mild toxicity upon treatment with 5FU-leucovorin, suggesting an important role of DPD in the aetiology of toxicity associated with catabolites of 5FU.

A phase II trial of S-1 monotherapy in metastatic colorectal cancer after failure of irinotecan- and oxaliplatin-containing regimens

This is the first phase II study of S-1 monotherapy for patients with metastatic colorectal cancer after failure of both irinotecan- and oxaliplatin-containing regimens. The initial dose of S-1 was 35 mg m⁻², administered twice daily for 14 days every 3 weeks. Treatment was repeated until the occurrence of disease progression. Twenty-eight patients were enrolled. S-1 was administered to 21 patients as third-line therapy and to the remaining seven patients as fourth-line therapy. Of 26 evaluable patients, the overall response rate was 14.3% (95% CI, 0.4–28.1), and the disease control rate was 42.9% (95% CI, 23.3–62.4). With a median follow-up period of 227 days, median time to progression and overall survival duration were 91 and 414 days, respectively. The 1-year survival rate of all patients was 60.7%. There was no grade 4 toxicity. Grade 3 haematological toxicities were documented only in two patients. In conclusion, S-1 shows potential as a salvage regimen in heavily pretreated colorectal cancer patients. The twice-daily dose of 35 mg m⁻² was well tolerated and can be used in designing further combination chemotherapy.

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.

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.

Enhancement of the antitumour activity of 5-fluorouracil (5-FU) by inhibiting dihydropyrimidine dehydrogenase activity (DPD) using 5-chloro-2,4-dihydroxypyridine (CDHP) in human tumour cells

The purpose of this study was to evaluate the use of 5-chloro-2,4-dihydroxypyridine (CDHP), a potent inhibitor of dihydropyrimidine dehydrogenase (DPD), to enhance the antitumour activity of the fluoropyrimidines. In an in vitro study, CDHP did not influence cell proliferation by itself. However, CDHP did inhibit 5-fluorouracil (5-FU) degradation and enhanced 5-FU cytotoxicity in a concentration-dependent manner in two human tumour cell lines (MIAPaCa-2 and HuTu80) with relatively high basal DPD activity. CDHP exhibited a maximum effect at a molar ratio (CDHP:5-FU) of more than 0.2. However, CDHP did not have any effect on 5-FU cytotoxicity in the CAL27 tumour cell line, which has a relatively low basal DPD activity, even at concentrations where the DPD activity is almost completely inhibited. In an in vivo study, the maximal tolerable doses (MTD) of tegafur (FT) and a combination of FT and CDHP at a molar ratio of 1:0.4 (FT/CDHP) for nude mice were determined by oral administration for 14 consecutive days. After a single oral administration of either FT or FT/CDHP at the MTD, the 5-FU serum concentration-time profiles were almost the same for both treatment strategies. When nude mice bearing subcutaneous (s.c.) MIAPaCa-2 cells were treated with either FT or FT/CDHP at the MTD, the FT/CDHP treatment showed a significantly higher antitumour effect than the FT treatment (tumour growth inhibition: FT/CDHP, 51+/-12%; FT, 21+/-25%; P<0.05). However, the host-body weight suppression induced by FT/CDHP and FT was equivalent. These findings suggest that the combination of fluoropyrimidine and CDHP for the treatment of tumours with a high basal DPD elicits a greater antitumour effect than treatment with fluoropyrimidines alone and we suggest that CDHP inhibits the degradation of 5-FU in the tumour.

Pharmacokinetics of 5-fluorouracil and its catabolites determined by 19F nuclear magnetic resonance spectroscopy for a patient on chronic hemodialysis

5-fluorouracil (5-FU), widely used for chemotherapy of colorectal carcinoma, requires intracellular anabolic conversion to cytotoxic nucleotides and exhibits a narrow therapeutic range with dose-dependent and concentration-dependent effects. 5-FU undergoes extensive metabolic degradation to several catabolites, which are excreted mainly by the kidneys. Alteration of the pharmacokinetics of 5-FU and its catabolites as a result of renal dysfunction might augment systemic toxicity. Because no data are available for patients with severe renal failure, the pharmacokinetic parameters of 5-FU and its catabolites were determined for a patient with colorectal carcinoma and end-stage renal disease on maintenance hemodialysis therapy. Plasma was analyzed by 19F nuclear magnetic resonance spectroscopy for the first 5-day treatment cycle (daily bolus injections of 5-FU for 5 days in combination with low-dose folinic acid). On days 1 and 5, the pharmacokinetic parameters for 5-FU (total area under the plasma concentration-time curve, terminal half-life, total plasma clearance, volume of distribution based on the terminal phase) and its initial catabolite dihydrofluorouracil (total area under the plasma concentration-time curve, terminal half-life) were in the ranges reported in the literature for patients with normal renal function, implying no need for primary dose adjustment. In contrast, the final 5-FU catabolite alpha-fluoro-beta-alanine (FBAL) accumulated to a concentration of 276 micromol/L on day 5 (approximately twofold higher than expected from the literature) despite good removal by hemodialysis with extraction ratios of 0.6 to 0.85 over the filter membrane. Negative effects of FBAL or enhancement of 5-FU-related toxicity could not be judged in this individual case, but further study is warranted to determine the possible benefits of more intensive dialysis treatment.

Eniluracil: an irreversible inhibitor of dihydropyrimidine dehydrogenase

One of the most widely used drugs in cancer chemotherapy is 5-fluorouracil (5-FU). 5-FU is optimally delivered via continuous iv. infusion, which is both cumbersome and expensive. Prolonged oral dosing of 5-FU could mimic continuous infusion with less inconvenience and cost. However, oral administration of 5-FU has been hampered by incomplete and erratic bioavailability due to substantial variability in the activity of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-FU catabolism. Eniluracil (ethynyluracil, GlaxoWellcome, USA), a uracil analogue, which irreversibly inhibits DPD, increases the oral bioavailability of 5-FU to 100%, facilitating uniform absorption and predictable toxicity. Cytotoxicity is enhanced one- to five-fold in cell lines treated with eniluracil plus 5-FU compared with 5-FU alone. Though eniluracil is neither toxic nor active as a single agent in animals, it improves the antitumour efficacy and therapeutic index of 5-FU. In Phase I trials, eniluracil markedly reduced the maximum tolerated dose of oral 5-FU, increased the half-life 20-fold and decreased the clearance 22-fold. DPD is completely inactivated within 1 h of eniluracil administration. Two dosing schedules have been evaluated in combination with oral 5-FU: a 5-day schedule every 28 days and a 28-day schedule every 35 days. The dose-limiting toxicity on the first schedule is myelosuppression with diarrhoea being dose-limiting on the 28-day schedule. Phase II trials employing the 28-day schedule have been completed in cancers of the colon, breast, liver and pancreas. Phase III trials in colorectal and pancreatic carcinoma have been completed and await analysis. Eniluracil is a promising drug, which permits reliable and safe administration of oral 5-FU and has the potential to overcome 5-FU resistance mediated by overexpression of DPD.