Abstract
We have recently demonstrated that bolus FUra treatments of human colon carcinoma cells, HCT-8, produce resistance via an RNA-related mechanism, while prolonged exposures to the fluoropyrimidine is responsible for a DNA-related mechanism of resistance. In addition, cells resistant to short term FUra exposure retain full sensitivity to the continuous exposure to the same agent. These data suggest that biochemical modulation of FUra should take into account the schedule of fluoropyrimidine administration. Based on this rationale, we completed a phase 2 trial of schedule-oriented biochemical modulation of FUra in advanced colorectal cancer patients, based upon a hybrid regimen of 2 biweekly-cycles of FUra bolus (600 mg/sqm), preceeded by (24 h interval) MTX, 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). Among the 33 consecutive patients accrued there were 3 CR and 13 PR (RR = 48%, 95% CL, 31–66%). Eleven patients had a minor response and 4 of them showed tumor shrinkage ranging between 46% and 49%. After a median follow-up time of 26 months, 10 patients are still alive. The median PFS and overall S were 9.6 and 20.2 months, respectively. The low toxicity of the bolus part of our regimen prompted us to pursue its intensification by adding a further modulator to MTX. Our recent finding of a strong synergism between bolus FUra and IFN, obtained in vitro on the same tumor model, generated a phase 2 trial employing the same regimen plus IFN (3,000,000 U im q12 h × 4, starting at the time of FUra bolus administration). Among 42 patients 4 CR, 15 PR (RR = 45%), 6 MR and 10 SD were obtained. Since the results of the two trials are similar showing twice as much activity and less toxicity than bolus FUra + LV or MTX → FUra, a randomized comparison is now ongoing between our original hybrid regimen without IFN and MTX → FUra.
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