Effects of diflubenzuron on growth of malignant melanoma and skin carcinoma tumors in mice.

The insect growth regulator diflubenzuron (DFB), which may also inhibit growth of imaginal epidermal cells in insects, was studied for antitumor activity in two mouse tumor models of epidermal origin. DFB inhibits chitin deposition, but the mechanisms by which DFB controls chitin deposition or regulates growth of insect epidermal cells are unknown. A single injection of 20 mg (800 mg/kg) of DFB into C57BL/6 mice with B16 malignant melanomas or AKR mice with skin tumors (CA 1025) induced a rapid (24 h) decrease in tumor volume in 78% and 66% of the tumors, respectively. In contrast, 85% of the melanomas and 91% of skin tumors in control mice increased in volume during the same 24-h period. Tumor volume decreased by as much as 55% for about 1% of the tumors, but the median decrease was 20% for both types of tumors. Since control tumors concommitantly increased, DFB-treated tumors decreased, relatively, to 60% of the volume of matched control tumors. After the initial volume decrease, both types of tumors resumed exponential growth resulting in an average growth curve delay, calculated for 12-14 days, of about 2.0 days. Subsequent treatment of melanomas with DFB 24 h after the initial treatment resulted in a further decrease in relative tumor volume to 40-50% of control tumor volume and a growth curve delay of 2.6 days. The most effective regimen used was 5 daily, 20-mg doses of DFB. Melanomas decreased to 40% of control tumor volume after the third injection and the mean growth curve delay was extended to 4.3 days.(ABSTRACT TRUNCATED AT 250 WORDS)