Incorporation of 5-Iododeoxyuridine131I in Spontaneous C3H Mouse Mammary Tumours

Bromodeoxyuridine alternating with radiation for advanced uterine cervix cancer: a phase I and drug incorporation study

PURPOSE

Preclinical studies show a significant increase in the ratio of the radiosensitizer bromodeoxyuridine (BUdR) in tumors versus the intestinal mucosa during the drug elimination period, compared with the ratio during drug infusion. We constructed a phase I study in patients with locally advanced cervix cancer, using alternating cycles of BUdR and radiation therapy (RT).

PATIENTS AND METHODS

Eighteen patients with stage IIB to IVA cervix cancer participated. A treatment cycle consisted of a 4-day BUdR infusion followed by a week of pelvic RT, 15 Gy twice daily in 1.5-Gy fractions. After three cycles, additional BUdR was infused, followed by brachytherapy. The fraction of thymidine replaced by BUdR and the fraction of cells incorporating BUdR were determined in rectal mucosa and tumor biopsies at the end of the first BUdR infusion (day 5), at the middle of the first RT week (day 10), and at the time of brachytherapy.

RESULTS

Dose-limiting toxicity was observed in one of 16 patients receiving 1,000 mg/m2/d x 4 days and in both patients receiving 1,333 mg/m2/d x 4 days each cycle. After a median follow-up of 39 months, 12 patients (66%) were free of pelvic disease and nine (50%) were alive and disease free. The ratio of tumor to rectum BUdR incorporation averaged 1.5 to 1.8 and did not differ significantly between day 5 and day 10. A trend toward reduced ratio was observed at brachytherapy. Drug-containing cells in rectal biopsies migrated from the crypts to the mucosal surface.

CONCLUSION

In this schedule, 1,000 mg/m2/d is the maximum-tolerated dose of BUdR. BUdR incorporation levels in tumors were consistent with clinically significant radiosensitization. The migration of BUdR-containing rectal mucosa cells from the crypts to the surface at the time of RT suggests that this regimen may offer a relative sparing of the mucosa from radiosensitization.

Effect of irradiation on bromodeoxyuridine incorporation in human colon cancer xenografts

PURPOSE

Although we have characterized the incorporation of the thymidine analog bromodeoxyuridine (BrdUrd) into human colon cancer xenografts under a wide variety of conditions, little is known about the effect of radiation on subsequent incorporation. Because clinical protocols include, as one component, BrdUrd administration after radiation, it was important to confirm that irradiation did not prevent subsequent BrdUrd incorporation. Therefore, we studied the effect of irradiation on BrdUrd incorporation into HT29 human colon cancer xenografts.

METHODS AND MATERIALS

Two types of experiments were performed. In the first, the effect of radiation on subsequent incorporation was measured. Tumors received doses of 0, 2, 8, and 12 Gy, animals were infused with BrdUrd for 4 days, and incorporation was assessed at the end of the infusion. In the second, the effect of radiation on the elimination of BrdUrd from tumors was determined. Animals were infused with BrdUrd, tumors were irradiated with either 0 or 12 Gy, and tumor incorporation of BrdUrd was measured 1 and 3 days later.

RESULTS

Radiation affected neither the incorporation into nor the elimination of BrdUrd from human tumor xenografts.

CONCLUSIONS

These findings support the feasibility of clinical trials interdigitating BrdUrd infusion and radiation.

The effect of radiosensitizers on radio-immunotherapy, using 131I-labelled anti-CEA antibodies in a human colonic xenograft model

Anti-CEA antibodies were used for radio-immunotherapy in an established LS174T colonic xenograft in nude mice. A single IV dose of either 131I-PK4S (polyclonal) or -A5B7 (monoclonal) antibody produced tumour regression, and significantly delayed subsequent tumour growth. Administration of a clearing second antibody, 24 hr post 131I-PK4S and at 5 times the dose, significantly reduced the therapeutic effect of radio-antibody alone. Tumours of mice given non-specific antibody or unlabelled anti-CEA antibody grew like those of untreated controls. In an attempt to enhance therapy without increasing dose, radiosensitizers normally employed with external beam radiation were used in combination therapy. When the hypoxic cell radiosensitizer misonidazole was combined with 131I-A5B7, it significantly prolonged tumour-growth inhibition over radio-antibody alone. Conversely, the therapeutic effect of either radio-antibody was significantly reduced when used in combination with the halogenated pyrimidine radiosensitizer 5-iododeoxyuridine. Neither sensitizer alone affected tumour growth.

Modulation of 5-iodo-2'-deoxyuridine metabolism and cytotoxicity in human bladder cancer cells by fluoropyrimidines

Iododeoxyuridine (IdUrd) potentiated the lethal but not the growth inhibitory properties of fluorouracil (FUra) and fluorodeoxyuridine (FdUrd) in human bladder cancer cells (T24). The rate of incorporation of IdUrd into DNA was enhanced by both fluoropyrimidines, but to a significantly greater extent by FdUrd. Both inhibition of iododeoxyridylate dehalogenation and the depletion of thymidine triphosphate pools contributed to the increased incorporation rate. Inhibition of dehalogenation accounted for 67% of the observed stimulation in the case of FUra, but only 37% of the increase produced by FdUrd. The depletion of dTTP pools, both in the presence and absence of IdUrd, was greater after FdUrd than FUra exposure. The observed increase in the rate of incorporation of IdUrd appears to account for the enhanced toxicity seen with FdUrd, but other factors may be involved in the case of FUra. Since FUra and IdUrd appear to be mutually potentiating and do not share a dependence on thymidine kinase activity, this drug combination warrants further investigation.

USE OF I125-LABELED 5-IODO-2′-DEOXYURIDINE FOR THE MEASUREMENT OF DNA SYNTHESIS IN MAMMALIAN CELLS IN VITRO

The use of isotopically labeled 5-iodo-2′-deoxyuridine (I125UdR) for determination of the rate of deoxyribonucleic acid synthesis in mammalian cells in vitro has been investigated. The results obtained indicate that for this purpose I125UdR is a suitable substitute for the more commonly used DNA precursor, tritium-labeled thymidine (H3TdR). I125UdR appears to be incorporated specifically into the DNA of cells in culture, and has been demonstrated to compete with H3TdR, although the Km for H3TdR was smaller than that of I125UdR by a factor of approximately 4. The amount of label incorporated into DNA of cells increased linearly with time. When the rate of DNA synthesis was reduced by exposure of the cells to various doses of X-rays, the ratio of I125UdR incorporation to H3TdR incorporation into DNA of cells was found to be a constant, which supports the view that uptake of the analogue provides as reliable an indication of effects upon the rate of DNA synthesis as does that of H3TdR. The chief advantage of I125UdR over H3TdR is that I125 is a gamma emitter, so that the difficulties encountered in detection of the low energy beta particles from H3 may be avoided.