Tumor Growth Inhibition and Potentiation of Immunotherapy by Indomethacin in Mice2

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Abstract
Indomethacin was continuously administered in the drinking water of inbred C3H mice given grafts of syngeneic 3-methylcholanthrene-induced fibrosarcomas. A minor proportion of these animals died at the same time as the untreated controls, and others completely rejected their tumors; however, in most cases, the tumor growth rate was significantly slowed, and growth recommenced rapidly after drug withdrawal. This was the pattern for tumors either in their 10th to 14th transplant generation or only their third in vivo passage. Indomethacin exerted little prophylactic effect, in that it neither increased the minimal cell number required to initiate tumor growth nor significantly decreased the proportion of tumors established in drug-treated animals receiving tumor grafts. The injection of killed Corynebacterium parvum organisms into small, growing McC3-1 tumors [intratumor (IT) route] caused the regression of most of these. In contrast, IT injection of BCG, ip injection of C. parvum, or IT injection of C. parvum into larger tumors had no effect. Oral administration of indomethacin enhanced BCG treatment and augmented the activity of C. parvum injected either systemically into animals with small tumors or IT into those with substantial tumor burdens. The duration of these effects was, however, often dependent on the continued administration of the drug.