The effect of combretastatin A-4 disodium phosphate in a C3H mouse mammary carcinoma and a variety of murine spontaneous tumors.

PURPOSE

To investigate the activity of combretastatin A-4 disodium phosphate in a transplanted C3H mouse mammary carcinoma and several murine spontaneous tumors.

METHODS AND MATERIALS

The C3H mammary carcinoma was grown in the right rear foot of female CDF1 mice and treated when 200 mm3 in size. Spontaneous tumors (341-1437 mm3 in size) arose at different sites in female CDF1 mice that, 19-21 months earlier, had been irradiated. Oxygen partial pressure (pO2) distributions in the C3H tumors were measured with an Eppendorf oxygen electrode at various times after injecting combretastatin (100 mg/kg, i.p.) in restrained, nonanesthetized mice. Immediately after measurement, tumors were excised and necrotic fraction determined from histological sections. In the spontaneous tumors, pO2 was measured before and 3 h after giving combretastatin. The location of these spontaneous tumors required that measurements be made in anesthetised animals, achieved by injecting a mixture of hypnorm and diazepam.

RESULTS

In untreated C3H tumors, the mean (+/- 1 SE) percentage of pO2 values < or = 2.5 mmHg was 32% (+/- 11). This was significantly (Student's t-test; p < 0.05) increased to 74% (+/- 4) within 1 h after injecting combretastatin, and remained at this level for at least 6 h, although some recovery was seen at 12 and 24 h. The necrotic fraction in control tumors was 1.9% (+/- 0.4) and this was significantly increased to 16.1% (+/- 3.7) 24 h after drug administration. In spontaneous tumors, the pO2 measurements indicated that 5 of 6 showed some response to combretastatin, although the degree of change was variable.

CONCLUSIONS

Combretastatin increased tumor hypoxia and necrosis in the C3H mammary carcinoma, consistent with the induction of vascular damage. Drug-induced changes in pO2 were also found in spontaneous tumors, suggesting that the activity of this drug is not restricted to transplanted tumors alone.