1981 Volume 21 Issue 1 Pages 19-25
After in vivo treatment with BCNU at 13.3 mg⁄kg, the dose lethal to 10 % (LD10), rats implanted with 9L brain tumors exhibited an increased life span (ILS) of 56%. The growth fraction (GF) of treated tumors, as measured by fractionated doses of 3H-thymidine administered over 40 h, decreased for the first 2 to 10 days post-treatment, then increased and overshot the baseline (though by no more than 10 %) by Day 21. A second treatment with a LD10 of BCNU either 5, 10, or 14 days after the initial treatment increased the ILS to 126-128 % and resulted in long-term survival (ILS>300 %) in 20 % to 30 % of animals, but did not produce a remarkable change in GF beyond that resulting from the initial treatment. Histological examinations revealed increased numbers of giant cells 2 to 6 days after the initial treatment; however, mitosis decreased immediately following treatment and remained low for the next 8 days. These results imply that (in this animal model, at least) a cell cycle non-specific (CCNS) drug is more effective as a second treatment after initial treatment with a CCNS drug than is a cell cycle specific one.
