The effect of
beta-cyclodextrin-benzaldehyde (
CDBA) on experimental pulmonary
metastasis in C3H/He mice was examined. In an in vitro assay, the growth of RCT(+) cells was inhibited by 1200 micrograms/ml
CDBA using unrenewed media, and by 600 micrograms/ml
CDBA in that using daily renewed media. When mice were treated daily with
CDBA, 3 weeks later the number of lung nodules developing after i.v. injection of 1 X 10(6) RCT(+) cells was significantly decreased in a dose-dependent manner, i.e., 73.8%, 85.6%, and 95.7% inhibition was observed following 0.5, 5, and 25 mg
CDBA/mouse per day p.o. administration, respectively. The same mice showed almost as much natural killer (NK) activity as normal mice. Therefore, experiments were designed to evaluate the effect of
CDBA on the NK activity of
tumor-free mice whose immunity had been suppressed by
5-fluorouracil (
5FU).
Injections of
5FU only suppressed this activity to about 50% of normal mice, but the combined treatment with
CDBA negated the suppressive effect of
5FU on NK activity. The results suggested that the inhibition of experimental pulmonary
metastasis might be induced by the possible combined effects of
CDBA; that is, the direct inhibition of
tumors and the augmentation of NK cell activity.