Chemotherapy of advanced colorectal cancer

c-Myc overexpression sensitises colon cancer cells to camptothecin-induced apoptosis

The proto-oncogene c-Myc is overexpressed in 70% of colorectal tumours and can modulate proliferation and apoptosis after cytotoxic insult. Using an isogenic cell system, we demonstrate that c-Myc overexpression in colon carcinoma LoVo cells resulted in sensitisation to camptothecin-induced apoptosis, thus identifying c-Myc as a potential marker predicting response of colorectal tumour cells to camptothecin. Both camptothecin exposure and c-Myc overexpression in LoVo cells resulted in elevation of p53 protein levels, suggesting a role of p53 in the c-Myc-imposed sensitisation to the apoptotic effects of camptothecin. This was confirmed by the ability of PFT-α, a specific inhibitor of p53, to attenuate camptothecin-induced apoptosis. p53 can induce the expression of p21^Waf1/Cip1, an antiproliferative protein that can facilitate DNA repair and drug resistance. Importantly, although camptothecin treatment markedly increased p21^Waf1/Cip1 levels in parental LoVo cells, this effect was abrogated in c-Myc-overexpressing derivatives. Targeted inactivation of p21^Waf1/Cip1 in HCT116 colon cancer cells resulted in significantly increased levels of apoptosis following treatment with camptothecin, demonstrating the importance of p21^Waf1/Cip1 in the response to this agent. Finally, cDNA microarray analysis was used to identify genes that are modulated in expression by c-Myc upregulation that could serve as additional markers predicting response to camptothecin. Thirty-four sequences were altered in expression over four-fold in two isogenic c-Myc-overexpressing clones compared to parental LoVo cells. Moreover, the expression of 10 of these genes was confirmed to be significantly correlated with response to camptothecin in a panel of 30 colorectal cancer cell lines.

Fluorouracil modulation in colorectal cancer: lack of improvement with N -phosphonoacetyl- l -aspartic acid or oral leucovorin or interferon, but enhanced therapeutic index with weekly 24-hour infusion schedule--an Eastern Cooperative Oncology Group/Cancer and Leukemia Group B Study

PURPOSE

To investigate mechanism-directed regimens in maximizing the efficacy of fluorouracil (5-FU) in advanced colorected cancer.

PATIENTS AND METHODS

Based on promising phase II data, a randomized comparison of various methods for the biochemical modulation of 5-FU was undertaken in patients with advanced colorectal cancer. The control group received single-agent 5-FU as a 24-hour infusion weekly. Patients (N = 1,120) with no prior chemotherapy for metastatic disease were randomized to one of the following arms: arm A, 5-FU 2,600 mg/m2 by 24-hour infusion, weekly; arm B, N-phosphonoacetyl-l-aspartic acid 250 mg/m2 day l, 5-FU 2,600 mg/m2 by 24-hour infusion day 2, weekly; arm C, 5-FU 600 mg/m2 with oral leucovorin (LV) 125 mg/m2 hourly for the preceding 4 hours, weekly; arm D, 5-FU 600 mg/m2 with intravenous (IV) LV 600 mg/m2, weekly; arm E, 5-FU 750 mg/m2/d IV by continuous infusion for 5 days, then 750 mg/m2 weekly, and recombinant interferon alfa-2a 9 million units subcutaneously three times weekly. Median follow-up was 4.8 years.

RESULTS

Of the 1,098 assessable patients, 57% had measurable disease. The toxicity of all the regimens was tolerable. Grade 4 or worse toxicity occurred in 11%, 11%, 30%, 24%, and 22% on each arm, respectively; diarrhea was the most common adverse effect. These toxicity patterns favored significantly (P <.001) the 24-hour infusion arms. Median survival (months) by arm was A, 14.8; B, 11.9; C, 13.5; D, 13.6; and E, 15.2. These survival durations did not differ significantly.

CONCLUSION

We conclude that a weekly infusion regimen of 5-FU is significantly less toxic than and as effective as 5-FU bolus regimens modulated by either LV or interferon in patients with metastatic colorectal cancer.

19F-MRS studies of fluorinated drugs in humans

The use of 19F-NMR as a noninvasive probe to measure directly the pharmacokinetics of drugs at their target (effector) site(s) is illustrated in this article by human studies with 5-fluorouracil (5-FU). This drug, and several of its metabolites, have been measured in vivo in animals and in patients using standard clinical MRI systems. Using a pharmacokinetic imaging approach the parameter that can be measured most readily is the tumoral t(1/2) of 5-FU. Patients whose tumoral t(1/2) of 5-FU is equal to/greater than 20 min are designated as "trappers", and those whose tumoral t(1/2) of 5-FU is less are nontrappers. Trapping of 5-FU in tumors is a necessary, albeit not a sufficient condition, for response. Problems associated with the technical aspects of these measurements have been discussed, as well as how modulators and other agents will affect the tumoral t(1/2) of 5-FU. The rationale for the biological processes underlying the fate of 5-FU in humans has been illustrated with the use of a 12 compartment model, where several of the steps have been discussed and the consequences of their inhibition/stimulation related to the noninvasive studies that can be performed with modulators of the action of 5-FU. These 19F-NMR studies have now been extended to other fluoropyrimidines, some of which are prodrugs of 5-FU, and others where the fluorine atoms are on the ribose ring. These studies also reveal information that has both scientific and clinical significance. The studies presented here illustrate some of the potential and some of the usefulness of 19F-MRS in patient management and in drug development. It is a technique that has proven itself.