Novel oral fluoropyrimidines in the treatment of metastatic colorectal cancer

Irinotecan: a new treatment in metastatic colorectal cancer

Objective. Historically, outcomes of metastatic colorectal cancer therapy have been disappointing, with fluorouracil (5-FU) producing response rates of no more than 15%. The addition of leucovorin increases response rates; however, survival rates are largely unaffected. Recently, the topoisomerase I inhibitor, irinotecan, has proved active in metastatic colorectal cancer and is indicated as second-line therapy following disease recurrence or progression after 5-FU-based therapy. More recently, irinotecan plus 5-FU-LV was compared with 5-FU-LV as first line treatment of colorectal cancer, showing impressive results. This article discusses the role of irinotecan, as a single agent and in combination with 5-FU-LV, in the treatment of advanced colorectal cancer.

Data sources. A MEDLINE search was conducted using 5-fluorouracil, irinotecan, leucovorin, and metastatic colorectal cancer as primary search terms. Reference lists, bibliographies of pertinent articles, and abstracts from the American Society of Clinical Oncology and the European Society for Medical Oncology annual meetings were also identified and reviewed. Clinical literature was reviewed and analyzed.

Data synthesis. Results of studies comparing irinotecan with continuos infusion 5-FU or best supportive care suggest that irinotecan is superior to either treatment as second-line therapy of metastatic colorectal cancer. Based on these study results, along with irinotecan's lack of cross-resistance with other chemotherapy agents and mechanism of action that differs from 5-FU, phase III trials evaluating the use of irinotecan in combination with 5-FU-LV as first-line treatment for advanced colorectal cancer were conducted. The results of a pivotal trial evaluating irinotecan plus 5-FU-LV in this setting show superior response rates (RRs), time to tumor progression (TTP), and median survival times (MSTs) when compared with 5-FU-LV alone. This combination represents a major advance in the treatment of metastatic colorectal cancer and should be considered the first-line treatment standard.

On the Electron Donor and the Electrophilic Substitution Activating Abilities of Substituents in Uracil

QTAIM properties for uracil and 18 derivatives containing the substituents -NH(2), -OH, -OCH(3), -SH, -F, -Cl, -CH(3) -NO(2), and -Li in position 5 or 6 were computed on MP2/6-31++G//MP2/6-31G charge densities. The results indicate that -OH, -OCH(3), and -NH(2) groups are really retrieving charge from the ring. Also, the activating ability of the substituent groups, usually considered as the variation of electron population at the carbon where the electrophilic attack takes place, C, was studied. The study shows that the activating ability is reflected by the variation of pi charge or quadrupole moment at C, and also by the variation of the Laplacian of the charge density in the secondary charge concentration points around C (SCC-C). They indicate a similar, but not exactly equal, graduation of activating ability. The relative behavior of the substituents is basically the same as in benzene, though benzene has more tendency to concentrate charge in the SCC-C regions than uracil, where this tendency is larger for 6- than for 5-derivatives. sigma(+/-)(R) Taft parameters are found to display good correlations with the above indicated activating indexes. Finally, the resonance model predicts most of the main variations displayed by QTAIM atomic pi electron populations of derivatives with regard to uracil, but there are still some significant variations of the pi electron charge that it cannot predict.

Physiologically based pharmacokinetic modelling of the three-step metabolism of pyrimidine using C-uracil as an in vivo probe

AIMS

Approximately 80% of uracil is excreted as beta-alanine, ammonia and CO2 via three sequential reactions. The activity of the first enzyme in this scheme, dihydropyrimidine dehydrogenase (DPD), is reported to be the key determinant of the cytotoxicity and side-effects of 5-fluorouracil. The aim of the present study was to re-evaluate the pharmacokinetics of uracil and its metabolites using a sensitive assay and based on a newly developed, physiologically based pharmacokinetic (PBPK) model.

METHODS

[2-(13)C]Uracil was orally administrated to 12 healthy males at escalating doses of 50, 100 and 200 mg, and the concentrations of [2-(13)C]uracil, [2-(13)C]5,6-dihydrouracil and beta-ureidopropionic acid (ureido-(13)C) in plasma and urine and (13)CO2 in breath were measured by liquid chromatography-tandem mass spectrometry and gas chromatograph-isotope ratio mass spectrometry, respectively.

RESULTS

The pharmacokinetics of [2-(13)C]uracil were nonlinear. The elimination half-life of [2-(13)C]5,6-dihydrouracil was 0.9-1.4 h, whereas that of [2-(13)C]uracil was 0.2-0.3 h. The AUC of [2-(13)C]5,6-dihydrouracil was 1.9-3.1 times greater than that of [2-(13)C]uracil, whereas that of ureido-(13)C was 0.13-0.23 times smaller. The pharmacokinetics of (13)CO2 in expired air were linear and the recovery of (13)CO2 was approximately 80% of the dose. The renal clearance of [2-(13)C]uracil was negligible.

CONCLUSION

A PBPK model to describe (13)CO2 exhalation after orally administered [2-(13)C]uracil was successfully developed. Using [2-(13)C]uracil as a probe, this model could be useful in identifying DPD-deficient patients at risk of 5-fluorouracil toxicity.

Effective drug delivery by PEGylated drug conjugates

The current review presents an update of drug delivery using poly(ethylene glycol) (PEG), that focuses on recent developments in both protein and organic drugs. Certainly the past 10 years has resulted in a renaissance of the field of PEG drug conjugates, initiated by the use of higher molecular weight PEGs (M(w)>20,000), especially 40,000 which is estimated to have a plasma circulating t(1/2) of approximately 10 h in mice. This recent resuscitation of small organic molecule delivery by high molecular weight PEG conjugates was founded on meaningful in vivo testing using established tumor models, and has led to a clinical candidate, PEG-camptothecin (PROTHECAN), an ester based prodrug currently in phase II trials. Additional applications of high molecular weight PEG prodrug strategies to amino containing drugs are presented: similar tripartate systems based on lower M(w) PEG and their use with proteins is expounded on. The modification of a benzyl elimination tripartate prodrug specific for mercaptans is presented, and its successful application to 6-mercaptopurine giving a water soluble formulation is discussed. Recent novel PEG oligonucleotides and immunoconjugates are also covered. Clinical results of FDA approved PEGylated proteins are also presented.

5-Fluorouracil derivatives from the sponge Phakellia fusca

5-Fluorouracil derivatives were isolated from the marine sponge Phakellia fusca collected around the Yongxing Island of the Xisha Islands in the South Sea of China. Their structures were determined on the basis of spectral analysis and X-ray diffraction.

Capecitabine: a review of its use in the treatment of advanced or metastatic colorectal cancer

Capecitabine is an orally administered fluoropyrimidine which is selectively activated in tumour tissue to the active moiety fluorouracil and is cytotoxic through inhibition of DNA synthesis. In patients with advanced or metastatic colorectal cancer, first-line therapy with intermittent capecitabine achieved significantly higher objective tumour response rates than therapy with fluorouracil plus leucovorin in pooled analysis. Response rates were also higher in patients pretreated in the adjuvant setting and whose primary site of metastasis was the lung. However, no significant differences between the two treatment groups were seen in the time to disease progression, time to treatment failure or overall survival. Preliminary data suggest response may be improved by combining capecitabine with other anticancer therapies such as oxaliplatin, irinotecan and radiotherapy. Capecitabine in therapeutic dosage regimens generally has acceptable tolerability. Diarrhoea and hand-and-foot syndrome are the major dose-limiting toxicities associated with capecitabine therapy, with adverse effects generally of a gastrointestinal nature. Overall, diarrhoea, stomatitis, nausea and alopecia were significantly less common with capecitabine than with bolus fluorouracil and leucovorin. In addition, capecitabine recipients experienced significantly less myelosuppression, although more capecitabine recipients discontinued therapy because of adverse events. Importantly, patients spent less time in hospital after capecitabine than after bolus fluorouracil and leucovorin therapy, and the oral route of administration of capecitabine is likely to be preferred. In conclusion, capecitabine has shown superior tumour response and less myelosuppression, although more grade 3 hand-and-foot syndrome, in comparison with the 'Mayo Clinic' regimen of fluorouracil therapy, but is unlikely to improve survival. Significantly, its oral route of administration is likely to be preferred by patients. Future strategies to improve patient response may involve selection of those patients likely to respond best to capecitabine, through determination of relevant enzyme levels and combination of capecitabine with various antineoplastic agents. Data on the effect of the drug on quality of life would help establish its role. In the meantime, capecitabine appears to offer an effective and more convenient alternative to fluorouracil as first-line monotherapy for the treatment of metastatic colorectal cancer.

Survival benefits of adjuvant chemotherapy with oral doxifluridine (5'-DFUR) following radiotherapy in patients with unresectable pancreatic cancer

BACKGROUND AND OBJECTIVES

The combination of 5-fluorouracil and radiotherapy is thought to be the most effective treatment for locally unresectable pancreatic carcinoma. The outcomes, however, are far from acceptable from the viewpoint of long-term survival. We assessed the survival benefits of oral adjuvant chemotherapy with doxifluridine (5'-DFUR) following radiotherapy for patients with the disease.

METHODS

Thirty-five consecutive patients who underwent bypass surgery and radiotherapy for localized advanced unresectable adenocarcinoma of the pancreas head were retrospectively reviewed in regard to disease progression and survival. Ten of the 35 patients underwent adjuvant chemotherapy with 5'-DFUR after radiotherapy in an outpatient setting.

RESULTS

The 1-year survival for patients treated with radiotherapy alone was 29%. The 1-, 2-, and 3-year survivals for patients treated with the adjuvant chemotherapy after radiotherapy were 50, 40, and 30%, respectively (P = 0.0069, log-rank test). The elevation of tumor markers was delayed (P = 0.0346) and local control rate was improved (P = 0.0475) in patients with chemotherapy. Multivariate analysis demonstrated that the adjuvant chemotherapy with 5'-DFUR was a significant independent prognostic factor as well as tumor size.

CONCLUSIONS

The adjuvant chemotherapy with 5'-DFUR following radiotherapy led to a significant prolongation of the survival for patients with unresectable localized pancreatic cancer.