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Notes: Abstract Background:We have recently suggested that bolus 5-fluorouracil(5-FU) may work via a RNA directed mechanism while continuous infusion 5-FUmay kill cells via a thymidylate synthase related pathway. It may thus bepossible to selectively modulate each schedule biochemically. We have comparedan alternating regimen of bolus and continuous infusion 5-FU, selectivelymodulated for the schedule of administration, with modulated bolus 5-FU inadvanced colorectal cancer patients. Patients and methods:Two hundred fourteen patients from nineteenItalian centers were randomized to the control arm consisting of biweeklycycles of MTX, 200 mg/m2 on day 1, followed by bolus 5-FU 600mg/m2 on day 2 and 6-S-leucovorin rescue, or to the experimentalarm consisting of two biweekly cycles of the same regimen as in the controlarm alternated to three weeks of continuous infusion 5-FU (200mg/m2 day) + weekly bolus 6-S-leucovorin, 20 mg/m2. Results:Nine CR and twenty-seven PR were obtained on one hundredeleven evaluable patients treated in experimental arm (RR = 32%,95% confidence interval (95% CI): 24%–42%),while two CR and eleven PR were observed among one hunderd three evaluablepatients in control arm (RR = 13%, 95% CI:7%–21%). WHO grade 3–4 toxicity occurred in13% of cycles of experimental arm and in 8% of cycles in controlarm. The PFS was significantly longer in experimental arm (6.2 vs. 4.3 months,odds ratio 0.66, P = 0.003), while the overall survival was similarin both arms (14.8 months in experimental arm vs. 14.1 months in control arm);quality of life was similar as well. Eighty percent of patients receivingsecond-line chemotherapy in control arm were treated with continuous infusion5-FU. Conclusions:Alternating, schedule-specific biochemical modulationof FU is more active than MTX → 5-FU as first-line treatment of advancedcolorectal cancer. However, the overall survival was similar suggesting thatalternating bolus and infusional 5-FU upfront may be as effective as givingthem in sequence as first- and second-line treatment.

Notes: Abstract Focusing our effort on the importance of FUra scheduling we have tested the hypothesis that pulse and continuous infusion (CI) of the fluoropyrimidine have different mechanisms of cytotoxicity. Our initial approach was to compare the mechanism of resistance of a cell line resistant to a short term exposure to FUra (HCT-8/FU4hR) to that of a cell line resistant to a prolonged exposure to the fluoropyrimidine (HCT-8/FU7dR). Cytotoxicity studies showed that HCT-8/FU4hR cells were still sensitive to FUra given as a 7-d exposure, suggesting different mechanisms of resistance. Indeed, rapid recovery of TS activity after drug removal was evident in the HTC-8/FU7dR cell line while HCT-8/FU4hR cells were similar to the parental cell line with regard to both the degree of in situ TS inhibition by FUra and duration of inhibition after FUra removal. In contrast, labelling studies with [3H-6] FUra (4 h exposure, 100 μM) showed that the incorporation of the fluoropyrimidine into RNA is significantly decreased in HCT-8/FU4hR cells as compared to parental HCT-8 cells. Given the lack of cross resistance between the two schedulesin vitro, a pilot trial was done on patients with colorectal cancer refractory to bolus FUra. On 15 patients failing after FUra+LV or FUra alone 1 PR, 3 MR, 3 SD and 8 P were observed, confirmng a certain degree of activity of CI FUra in patients clinically resistant to bolus FUra. Based on this rationale, a phase II trial of schedule-oriented biochemical modulation of FUra in advanced colorectal cancer patients was conducted, employing a hybrid regimen of 2 biweekly cycles of FUra bolus (600 mg/sqm), preceeded by (24 h interval) methotrexate, 200 mg/sqm (in order to maximize the RNA effect of the drug) alternating with FUra continuous infusion, 200 mg/sqm daily for 3 weeks, modulated by leucovorin, 20 mg/sqm weekly bolus (in order to maximize the DNA effect). Thirty-three consecutive patients (median ECOG PS 1) with advanced measurable colorectal cancer and no prior therapy for metastatic disease entered the study, from February 1992 to August 1993. Three complete and 13 partial responses were obtained among these 33 patients (RR=48%, 95% confidence limis, 31–66%). After a median follow-up time of 23 months, 16 patients are still alive. The median progression free survival and overall survival were 9.6 and 20.8 months, respectively. No toxic deaths or grade 4 toxicity occurred. The incidence of grade 3 toxicity per patient in any cycle was: mucositis 6%, diarrhea 3% and vomiting 3% for the bolus part and 21%, 3% and 6% respectively, for the continuous infusion part of the regimen. Hand-foot syndrome occurred in 27% of the patients treated with the continuous infusion regimen. In conclusion, this experimental and clinical project has generated a novel regimen of schedule oriented biochemical modulation that is twice as active and half as toxic compared to bolus FU+LV given with either the daily x 5 or the weekly schedule. This high clinical activity is very encouraging, especially considering that 1) consecutive patients were entered, 2) the responses were independently reviewed, 3) the progression free survival and survival were much longer than those actually reported for this disease, 4) the toxicity of the program, in particular the bolus regimen, was relatively low allowing further intensification.