Failure to boost the increased clearance of embolic tumor cells from the lung with dose scheduling: Corynebacterium...

Initial suboptimal, optimal and supraoptimal doses of intraperitoneal corynebacterium parvum were followed by 'booster' doses injected intraperitoneally 5, 10 and 25 days later. Mice were challenged intravenously 4-6 days after the booster doses with [125I]IUrd-labeled B16 tumor cells and the extent of clearance of these cells from the lungs analyzed 4 h later. In a second experiment, mice were given booster doses of C. parvum on days 4, 7 and 10 and then challenged on day 14 with labeled B16 tumor cells. In each experiment, the peak response, in the form of tumor cell clearance, to C. parvum occurred between day 5 and day 10. In no instance was a peak response to any of the initial injections of C. parvum increased by a booster dose. Instead, in some instances, the peak response was abrogated. By day 25 but not day 10, it was possible to restore the response to its peak level with a second optimal dose of C. parvum, but not to increase it.