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      Bystander or No Bystander for Gene Directed Enzyme Prodrug Therapy

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          Abstract

          Gene directed enzyme prodrug therapy (GDEPT) of cancer aims to improve the selectivity of chemotherapy by gene transfer, thus enabling target cells to convert non-toxic prodrugs to cytotoxic drugs. A zone of cell kill around gene-modified cells due to transfer of toxic metabolites, known as the bystander effect, leads to tumour regression. Here we discuss the implications of either striving for a strong bystander effect to overcome poor gene transfer, or avoiding the bystander effect to reduce potential systemic effects, with the aid of three successful GDEPT systems. This review concentrates on bystander effects and drug development with regard to these enzyme prodrug combinations, namely herpes simplex virus thymidine kinase (HSV-TK) with ganciclovir (GCV), cytosine deaminase (CD) from bacteria or yeast with 5-fluorocytodine (5-FC), and bacterial nitroreductase (NfsB) with 5-(azaridin-1-yl)-2,4-dinitrobenzamide (CB1954), and their respective derivatives.

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          Bevacizumab in combination with oxaliplatin-based chemotherapy as first-line therapy in metastatic colorectal cancer: a randomized phase III study.

          To evaluate the efficacy and safety of bevacizumab when added to first-line oxaliplatin-based chemotherapy (either capecitabine plus oxaliplatin [XELOX] or fluorouracil/folinic acid plus oxaliplatin [FOLFOX-4]) in patients with metastatic colorectal cancer (MCRC). Patients with MCRC were randomly assigned, in a 2 x 2 factorial design, to XELOX versus FOLFOX-4, and then to bevacizumab versus placebo. The primary end point was progression-free survival (PFS). A total of 1,401 patients were randomly assigned in this 2 x 2 analysis. Median progression-free survival (PFS) was 9.4 months in the bevacizumab group and 8.0 months in the placebo group (hazard ratio [HR], 0.83; 97.5% CI, 0.72 to 0.95; P = .0023). Median overall survival was 21.3 months in the bevacizumab group and 19.9 months in the placebo group (HR, 0.89; 97.5% CI, 0.76 to 1.03; P = .077). Response rates were similar in both arms. Analysis of treatment withdrawals showed that, despite protocol allowance of treatment continuation until disease progression, only 29% and 47% of bevacizumab and placebo recipients, respectively, were treated until progression. The toxicity profile of bevacizumab was consistent with that documented in previous trials. The addition of bevacizumab to oxaliplatin-based chemotherapy significantly improved PFS in this first-line trial in patients with MCRC. Overall survival differences did not reach statistical significance, and response rate was not improved by the addition of bevacizumab. Treatment continuation until disease progression may be necessary in order to optimize the contribution of bevacizumab to therapy.
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            Irinotecan plus fluorouracil and leucovorin for metastatic colorectal cancer. Irinotecan Study Group.

            The combination of fluorouracil and leucovorin has until recently been standard therapy for metastatic colorectal cancer. Irinotecan prolongs survival in patients with colorectal cancer that is refractory to treatment with fluorouracil and leucovorin. In a multicenter trial, we compared a combination of irinotecan, fluorouracil and leucovorin with bolus doses of fluorouracil and leucovorin as first-line therapy for metastatic colorectal cancer. A third group of patients received irinotecan alone. Patients were randomly assigned to receive irinotecan (125 mg per square meter of body-surface area intravenously), fluorouracil (500 mg per square meter as an intravenous bolus), and leucovorin (20 mg per square meter as an intravenous bolus) weekly for four weeks every six weeks; fluorouracil (425 mg per square meter as an intravenous bolus) and leucovorin (20 mg per square meter as an intravenous bolus) daily for five consecutive days every four weeks; or irinotecan alone (125 mg per square meter intravenously) weekly for four weeks every six weeks. End points included progression-free survival and overall survival. Of 683 patients, 231 were assigned to receive irinotecan, fluorouracil, and leucovorin; 226 to receive fluorouracil and leucovorin; and 226 to receive irinotecan alone. In an intention-to-treat analysis, as compared with treatment with fluorouracil and leucovorin, treatment with irinotecan, fluorouracil, and leucovorin resulted in significantly longer progression-free survival (median, 7.0 vs. 4.3 months; P=0.004), a higher rate of confirmed response (39 percent vs. 21 percent, P<0.001), and longer overall survival (median, 14.8 vs. 12.6 months; P=0.04). Results for irinotecan alone were similar to those for fluorouracil and leucovorin. Grade 3 (severe) diarrhea was more common during treatment with irinotecan, fluorouracil, and leucovorin than during treatment with fluorouracil and leucovorin, but the incidence of grade 4 (life-threatening) diarrhea was similar in the two groups (<8 percent). Grade 3 or 4 mucositis, grade 4 neutropenia, and neutropenic fever were less frequent during treatment with irinotecan, fluorouracil, and leucovorin. Adding irinotecan to the regimen of fluorouracil and leucovorin did not compromise the quality of life. Weekly treatment with irinotecan plus fluorouracil and leucovorin is superior to a widely used regimen of fluorouracil and leucovorin for metastatic colorectal cancer in terms of progression-free survival and overall survival.
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              Irinotecan combined with fluorouracil compared with fluorouracil alone as first-line treatment for metastatic colorectal cancer: a multicentre randomised trial.

              Irinotecan is active against colorectal cancer in patients whose disease is refractory to fluorouracil. We investigated the efficacy of these two agents combined for first-line treatment of metastatic colorectal cancer. 387 patients previously untreated with chemotherapy (other than adjuvant) for advanced colorectal cancer were randomly assigned open-label irinotecan plus fluorouracil and calcium folinate (irinotecan group, n=199) or fluorouracil and calcium folinate alone (no-irinotecan group, n=188). Infusion schedules were once weekly or every 2 weeks, and were chosen by each centre. We assessed response rates and time to progression, and also response duration, survival, and quality of life. Analyses were done on the intention-to-treat population and on evaluable patients. The response rate was significantly higher in patients in the irinotecan group than in those in the no-irinotecan group (49 vs 31%, p<0.001 for evaluable patients, 35 vs 22%, p<0.005 by intention to treat). Time to progression was significantly longer in the irinotecan group than in the no-irinotecan group (median 6.7 vs 4.4 months, p<0.001), and overall survival was higher (median 17.4 vs 14.1 months, p=0.031). Some grade 3 and 4 toxic effects were significantly more frequent in the irinotecan group than in the no-irinotecan group, but effects were predictible, reversible, non-cumulative, and manageable. Irinotecan combined with fluorouracil and calcium folinate was well-tolerated and increased response rate, time to progression, and survival, with a later deterioration in quality of life. This combination should be considered as a reference first-line treatment for metastatic colorectal cancer.
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                Author and article information

                Journal
                Molecules
                Molecules
                molecules
                Molecules
                Molecular Diversity Preservation International
                1420-3049
                10 November 2009
                November 2009
                : 14
                : 11
                : 4517-4545
                Affiliations
                [1 ] Angiogenesis and Cancer Research Group, University of Otago, Christchurch, PO Box 4345, Christchurch 8140, New Zealand; E-Mail: michelle.hunt@ 123456otago.ac.nz (M.A.H.)
                [2 ] Auckland Cancer Society Research Centre, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; E-Mails: s.syddall@ 123456auckland.ac.nz (S.S.); deancraigsingleton@ 123456hotmail.com (D-C.S.); a.patterson@ 123456auckland.ac.nz (A-V.P.)
                Author notes
                [* ] Author to whom correspondence should be addressed; E-Mail: gabi.dachs@ 123456otago.ac.nz
                Article
                molecules-14-04517
                10.3390/molecules14114517
                6255103
                19924084
                5dfa8311-eeda-432c-b700-3623d81e2265
                © 2009 by the authors;

                licensee Molecular Diversity Preservation International, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 10 October 2009
                : 03 November 2009
                : 05 November 2009
                Categories
                Review

                nitroreductase,thymidine kinase,cytosine deaminase,alkylating agents,chemotherapy

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