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Tumor-promoting diterpene esters prevent macrophage activation and suppress macrophage tumoricidal capacity
Abstract:
The efficacy of varied diterpene ester type tumor promoters in suppressing the acquisition as well as the manifestation of cytolytic activity by macrophages was investigated. These mechanisms, believed to be basic to natural antitumor resistance, were markedly suppressed not only by the phorbol ester, TPA, but also by several other tumor promoters of the polyfunctional diterpene ester type covering tigliane, ingenane, and daphnane derivatives. The promoters were particularly effective in preventing the lymphokine-induced enhancement of natural cytolytic activity in resting macrophages. Moreover, the same promoters suppressed the manifestation of cytotoxicity by previously activated macrophages. Their influence on the effector phase was less pronounced than on the activation phase. In sharp contrast, typical solitary carcinogens of the polycyclic aromatic hydrocarbon type exerted little or no activity in the macrophage test systems. Since TPA had already been shown to suppress the natural killer activity in vitro and to abrogate host tumor resistance in vivo, the present findings lend further support to the interpretation that tumor promoters, apart from directly stimulating the outgrowth of transformed cells, may function via interference with natural antitumor effector systems.
Insights
Tumor promoters, including TPA, significantly suppress macrophage-mediated natural antitumor resistance. These compounds interfere with both the development and expression of cancer-fighting cell activity.
Area of Science:
- Immunology
- Cancer Biology
- Toxicology
Background:
- Macrophages play a crucial role in natural antitumor resistance.
- Tumor promoters are known to influence cellular processes, but their impact on innate immune responses requires further elucidation.
Purpose of the Study:
- To investigate the effect of various diterpene ester tumor promoters on macrophage cytolytic activity.
- To determine if these promoters interfere with the acquisition and manifestation of macrophage-mediated antitumor functions.
Main Methods:
- Assessing the suppression of cytolytic activity in macrophages exposed to different diterpene ester tumor promoters, including TPA.
- Evaluating the impact of promoters on both resting and activated macrophages.
- Comparing the effects of diterpene ester promoters with polycyclic aromatic hydrocarbon carcinogens.
Main Results:
- Diterpene ester tumor promoters, such as TPA, significantly suppressed the acquisition and manifestation of macrophage cytolytic activity.
- Promoters were particularly effective in inhibiting lymphokine-induced enhancement of activity in resting macrophages.
- While affecting the activation phase more strongly, promoters also suppressed cytotoxicity in previously activated macrophages.
- Polycyclic aromatic hydrocarbon carcinogens showed minimal impact on these macrophage-based antitumor systems.
Conclusions:
- Tumor promoters can interfere with natural antitumor effector systems, potentially contributing to tumor progression.
- This interference with macrophage-mediated immunity represents a mechanism by which tumor promoters may promote cancer, independent of direct cell transformation.
- Findings support the hypothesis that tumor promoters can compromise host defense mechanisms against cancer.