Effect of photodynamic pretreatment on the susceptibility of murine tumor cells to macrophage antitumor mechanisms.

In vitro photodynamic treatment of YAC-1 murine T-lymphoma cells with the hematoporphyrin derivative Photosan 3 and red light resulted in dose-dependent phototoxicity. Photodynamic pretreatment, however, did not render these cells more susceptible to macrophage-mediated tumor cytotoxicity or the cytotoxic effects of macrophage-derived antitumor mediators like tumor necrosis factor alpha (TNF-alpha) or interferon beta (IFN-beta). Independent of the degree of photosensitization used, the cytotoxicity values obtained with macrophages or the different mediators were shifted by the respective values for phototoxicity, suggesting these effects to be additive and thus not interdependent. These data show that while higher overall tumor cytotoxicity can be achieved by a combination of photodynamic treatment and macrophage-mediated tumor destruction, this apparently is not a result of enhanced sensitivity of photodynamically treated tumor cells to macrophage antitumor mechanisms in general.