Prospective randomized reappraisal of 5-fluorouracil in metastatic colorectal carcinoma. A comparative trial with 6-thioguanine

The continuous rediscovery and the benefit-risk ratio of thioguanine, a comprehensive review

Introduction: In the 1950s, thioguanine (TG), a thiopurine-derivative together with azathioprine (AZA) and mercaptopurine (MP), were developed for the treatment of childhood leukemia. Over the years, the use of TG was also explored for other, mainly immune-mediated and inflammatory, diseases such as in the field of dermatology and rheumatology (e.g. psoriasis, systemic lupus erythematosus (SLE)) and gastroenterology and hepatology (e.g. inflammatory bowel diseases (IBD), autoimmune hepatitis).Areas covered: This review provides a comprehensive overview of all the clinical uses of TG and describes its mechanism of action, pharmacokinetic/pharmacodynamic features, and toxicity.Expert opinion: Thioguanine has shown beneficial clinical effects in hematological (particularly leukemia) and several immune-inflammatory diseases including psoriasis, SLE, polycythemia vera, Churg-Strauss syndrome, IBD, collagenous sprue, refractory celiac disease, and autoimmune hepatitis. Thioguanine is not effective in treating solid-cancers. At relatively low dosages, i.e. 0.2- 0.3mg/kg/day or 20 mg/day, TG has a favorable risk-benefit ratio and is a safe and effective drug in the long-term treatment of amongst other IBD patients. Thioguanine toxicity, especially myelotoxicity, and hepatotoxicity, including nodular regenerative hyperplasia (NRH) of the liver, is limited when dosed adequately. The occurrence of NRH appears dose-dependent and has been especially described during high dose TG above 40 mg/day.

Repurposing Screen Identifies Unconventional Drugs With Activity Against Multidrug Resistant Acinetobacter baumannii

Antibiotic-resistant nosocomial infections are an emerging public health issue; carbapenem-resistant gram-negative bacteria such as Acinetobacter baumannii are among the pathogens against which new therapeutic agents are desperately needed. Drug repurposing has recently emerged as an alternative approach to rapidly identifying effective drugs and drug combinations to combat drug resistant bacteria. We performed a drug repurposing screen against a highly virulent, multidrug resistant, Acinetobacter baumannii strain AB5075. This strain, isolated from a patient, is resistant to 25 first-line antibiotics for gram-negative bacteria. A compound screen using a bacterial growth assay led to identification and confirmation of 43 active compounds. Among these confirmed compounds, seven are approved drugs or pharmacologically active compounds for non-antimicrobial indications. Three of these drugs, 5-fluorouracil, fluspirilene, and Bay 11-7082 resensitized strain AB5075 to azithromycin and colistin in a two-drug combination format. The approach using a drug repurposing screen with a pathogen sample isolated from a patient and a high throughput bacterial growth assay led to the successful identification of new drug combinations to overcome a multidrug resistant bacterial infection.

Increasing Doses of 5-Fluorouracil and High-Dose Folinic ACID in the Treatment of Metastatic Colorectal Cancer

AIMS AND BACKGROUND

Combined 5-fluorouracil (5FU) and folinic acid (FA) is the first-line treatment of metastatic colorectal cancer. The aims of this study were to individualize the dose of 5FU in a weekly schedule in which the maximum tolerated dose of 5FU is administered to each patient, and to evaluate the impact of increasing 5FU doses on response and survival.

METHODS

Thirty-two patients (30 evaluable for response) with metastatic colorectal cancer were treated with weekly intravenous doses of FA 150 mg/m2 and a fast infusion of 5FU, at an initial dose of 600 mg/m2 which was increased by 60 mg/m2 every week until the appearance of a side effect, in order to determine the maximum tolerated dose for the patient.

RESULTS

We obtained 11 objective responses (36.7%, median survival 22 months) and 15 disease stabilizations (50%, median survival 15 months); there were four cases of progressive disease (13.3%, median survival 4 months). The overall survival was 15 months. Twenty-eight patients (87.5%) tolerated 5FU doses of 720 mg/m2 or more.

CONCLUSIONS

Weekly 5FU with high-dose FA modulation can be individualized by dose escalation. A 5FU dose of 720 mg/m2 per week seems to be critical, as higher doses are no more effective and lead to severe side effects. This schedule gives good results in terms of response, even though the complete response rate remains low.

6-thioguanine: a drug with unrealized potential for cancer therapy

Sixty years ago, 6-thioguanine (6-TG) was introduced into the clinic. We suggest its full potential in therapy may not have been reached. In this paper, we contrast 6-TG and the more widely used 6-mercaptopurine; discuss 6-TG metabolism, pharmacokinetics, dosage and schedule; and summarize many of the early studies that have shown infrequent but nevertheless positive results with 6-TG treatment of cancers. We also consider studies that suggest that combinations of 6-TG with other agents may enhance antitumor effects. Although not yet tested in man, 6-TG has recently been proposed to treat a wide variety of cancers with a high frequency of homozygous deletion of the gene for methylthioadenosine phosphorylase (MTAP), often codeleted with the adjacent tumor suppressor CDKN2A (p16). Among the cancers with a high frequency of MTAP deficiency are leukemias, lymphomas, mesothelioma, melanoma, biliary tract cancer, glioblastoma, osteosarcoma, soft tissue sarcoma, neuroendocrine tumors, and lung, pancreatic, and squamous cell carcinomas. The method involves pretreatment with the naturally occurring nucleoside methylthioadenosine (MTA), the substrate for the enzyme MTAP. MTA pretreatment protects normal host tissues, but not MTAP-deficient cancers, from 6-TG toxicity and permits administration of doses of 6-TG that are much higher than can now be safely administered. The combination of MTA/6-TG has produced substantial shrinkage or slowing of growth in two different xenograft human tumor models: lymphoblastic leukemia and metastatic prostate carcinoma with neuroendocrine features. Further development and a clinical trial of the proposed MTA/6-TG treatment of MTAP-deficient cancers seem warranted.

5-Fluorouracil (5FU) with or without folinic acid (LV) in human colorectal cancer? Multivariate meta-analysis of the literature

This meta-analysis is based on 106 evaluations of response from 77 clinical studies about 5-fluorouracil (5FU) treatment with or without leucovorin (LV) in metastatic colorectal carcinoma. Overall, in naive patients, LV is associated with a median response rate of 31% as compared with a 12% figure with 5FU alone. Using a forward stepwise multilinear regression analysis, it is shown that as much as 44% of the variance in the reported response rates in naive patients can be accounted for by treatment-related variables (P less than 0.001). The significant parameters are LV adjunction (partial R = 0.636), cumulative total 5FU dose (R = 0.344), and 5FU weekly schedule (R = 0.246). In pretreated patients, the latter parameter is the only significant one (R = 0.443). Unexpectedly, LV administration behaves like an all-or-nothing governor, without any obvious dose-effect relationship. Protracted 5FU infusion over weeks allows a mean cumulative drug delivery, 3 times higher than bolus regimens (21.3 vs 7.02 g m-2, P less than 0.001) and may represent the best clinical approach to influence the 5FU-related variables. Accordingly, it is suggested that 5FU protracted infusion, titrated to the highest tolerable doses and potentiated with low doses of leucovorin, could represent the most efficacious way for using 5FU in colorectal disseminated cancer. This hypothesis and its eventual impact on survival should be tested in randomized trials.

Second-line chemotherapy of advanced colorectal cancer with sequential high-dose methotrexate and 5-fluorouracil

Twenty-five patients with pretreated advanced colorectal carcinoma were subjected to second-line chemotherapy with sequential high-dose methotrexate and 5-fluorouracil. In 20 evaluable patients 2 (10%) partial responses, 12 (60%) stable disease and 6 (30%) progressions were observed. Partial responses were maintained for 3 and 4 months respectively; stable disease had a median duration of 4 months. The overall median survival after progression was 7 months. From our results sequential high-dose methotrexate and 5-fluorouracil cannot be recommended as second-line chemotherapy in advanced colorectal cancer.

Modulation of fluoropyrimidines by leucovorin: rationale and status

In recent years the concept of metabolic modulation of fluoropyrimidines by leucovorin has been introduced clinically in patients with advanced colorectal cancer, breast cancer, gastric cancer and head and neck cancer among others. The concept of metabolic modulation was developed in the laboratory and employed clinically. Leucovorin is a noncytotoxic compound used to increase the therapeutic efficacy of 5-fluorouracil. Following 5-fluorouracil activation to 5-fluorodeoxyuridine monophosphates, its binding to thymidylate synthase is stabilized by the active cofactor, 5,10 methylene tetrahydrofolate and its polyglutamate forms. Under these conditions, both the extent and duration of inhibition of thymidylate synthase and consequently, DNA synthesis are more pronounced. The results of clinical trials (phase II and III) indicate that the response rates to 5-fluorouracil/leucovorin modulation are significantly higher than that of fluorouridine alone.

Efficacy and toxicity of 5-fluorouracil and folates in advanced colon cancer

From February 1987 to December 1988, 34 patients with histologically confirmed advanced colorectal carcinoma were entered in a phase II trial with 5-fluorouracil (5-FU) and folinic acid, for evaluation of treatment effectiveness and toxicity. Our data confirmed that the association 5-FU and folates represents an effective and moderately tolerated palliative treatment, with diarrhea being the only dose-limiting toxicity.

A-phase II study of intravenous 6-thioguanine (NSC-752) in multiple myeloma. A Southwest Oncology Group study

Thirty-three patients with relapsing or refractory multiple myeloma were treated with 6-Thioguanine (6TG) at a dose of 1 g/M2, with therapy given over four hours every three weeks. The major toxicity seen was myelotoxicity; thrombocytopenia was more commonly noted than neutropenia. One patient achieved a PR, two were clinically improved. 6TG in this short infusion schedule proved to be myelotoxic, but demonstrated little activity in previously treated myeloma patients.

Leucovorin enhancement of the effects of the fluoropyrimidines on thymidylate synthase

Exposure of tumor cells to reduced folates before or with the fluoropyrimidines, 5-fluorouracil or 5-fluoro-2'deoxyuridine, results in a substantial increase in the activity of these drugs. Available evidence suggests that the mechanism of this synergism is a kinetic stabilization of complex formed between thymidylate synthase and fluorodeoxyuridylate that also involves a mole of the cofactor for the thymidylate synthase reaction, 5,10-methylenetetrahydrofolate. This effect results in an extended time of depletion of thymidine nucleotides with a resultant increased level of cell death. The biochemical aspects of this interaction are discussed and related to the therapeutics of this combination.

Continuous systemic 5-fluorouracil infusion in advanced colorectal cancer: results in 91 patients

Ninety-one patients with metastatic colorectal cancer were treated with continuous ambulatory 5-fluorouracil (5FU) infusion 250-300 mg/m2/day through a chronic indwelling central venous catheter. Twenty-six of the 91 patients (29%) had received previous bolus 5FU. Fifty-eight of the 91 patients (64%) had two or more sites of disease, and 74 of 91 patients (81%) had liver metastases. Results were complete remission in 5 of 91 (6%), partial remission in 25 of 91 (27%), stable disease in 33 of 91 (36%), and progressive disease in 28 of 91 (31%), for an overall response rate of 30 of 91 (33%); median duration of response was 7 months. Twenty-six of 65 previously untreated patients (40%) experienced objective response. Median survival from initiation of treatment for all patients was 11 months. Forty-one percent of patients experienced no significant toxicity and were able to continue therapy without treatment interruption. Toxicities necessitating treatment interruption included stomatitis in 35 patients (39%), hand-foot syndrome in 33 patients (36%), and diarrhea in 10 patients (11%). No significant myelosuppression or serious catheter-related complications were encountered. We conclude that continuous systemic venous infusion of 5FU produces a higher response rate than traditional bolus 5FU schedules, with apparent enhancement of survival and easily managed toxicity.

Role of chemotherapy in the treatment of colorectal carcinoma

Large bowel cancer afflicts more patients in the United States than any other malignancy excluding skin cancer. Fifty percent of patients who undergo resection of colorectal carcinoma have positive lymph nodes, and approximately 18% have liver metastases at initial presentation. To improve survival, more effective treatment than surgical resection of the primary must be developed. The most active single agent in the treatment of colorectal carcinoma is 5-fluorouracil (5-FU). To increase the response rate obtained with this agent, work has been done on the modulation of 5-FU by other agents, using drugs that are synergistic with 5-FU and manipulating the method of 5-FU administration. Combination chemotherapy has improved response rates in some situations, though generally it has not been shown to improve survival. Studies using direct hepatic infusion clearly demonstrate an increase in response rates, but again, it is too early to say whether this type of treatment increases survival. Early adjuvant chemotherapy trials used inadequate doses of chemotherapy for short periods of time and demonstrated no added efficacy to surgery alone. Later studies with more aggressive therapy suggested some benefit to treating patients with rectal carcinoma; however, there is still little evidence that adjuvant chemotherapy improves survival in patients with colon carcinoma. To compare and understand the various chemotherapy trials, more stringent reporting of baseline laboratory values, performance status, and estimation of tumor involvement are needed.

Systemic infusional chemotherapy for liver metastasis: an improved schedule for 5-fluorouracil

The clinical studies of infusion schedules for cancer chemotherapy have established that this schedule substantially alters the pattern of drug toxicity without necessarily compromising therapeutic effectiveness. Although increased tumor cell killing has not been definitively established, in at least two prospective comparative trials of 5-FU the infusion schedule was superior to bolus delivery in terms of response rate. It is possible that the infusion schedule may be the primary determinant of the effectiveness of hepatic arterial chemotherapy, and preliminary reports of prospective trials comparing systemic infusion with hepatic infusion do suggest that response rates for both routes are similar. An important consideration with regard to infusion schedules is establishing whether or not tumor cell resistance is augmented by the continuous exposure. Almost all chronic disease therapy necessitates maintaining adequate drug levels to ensure disease control including infections, seizure disorders, arthritis, and cardiovascular diseases. For cancer, the intermittent schedule of drug delivery has been dictated by the concept of the primacy of dose and the substantial toxicity associated with these agents. With the technological capability of providing an ambulatory setting for infusion chemotherapy and the substantial modification of toxicity, therapeutic regimens may be more cost effective with the constant infusion schedule.

Long-term ambulatory treatment of metastatic colorectal adenocarcinoma by continuous intravenous infusion of 5-fluorouracil

To delineate the efficacy of continuous intravenous 5-fluorouracil (5-FU) infusion therapy for advanced colorectal adenocarcinoma, a study of 36 patients with measurable metastatic disease was conducted. Patients received a daily intravenous infusion of 300 mg/m2 5-FU over a 24-h period utilizing portable infusion devices and central venous catheters. In a population characterized by substantial pretreatment exposure to radiotherapy, chemotherapy, and other indicators of poor prognosis, 13/36 (36%) patients achieved an objective response. An additional 10/36 (28%) patients manifested stable disease (no change) and experienced survival comparable to that of patients with objective response. Toxicity was minimal; patients were able to continue 5-FU infusions 95% of the total time on protocol. There were no adverse hematologic effects or catheter complications. Because previously untreated patients benefited more frequently (positive response, 50%), continuous intravenous infusion should be evaluated further as a primary modality option when 5-fluorouracil antitumor chemotherapy is contemplated.