Photodynamic therapy is potentiated by Co60 and intratumoral injection of hematoporphyrin derivative.

Hematoporphyrin derivative injected directly into a subcutaneous rat glioma resulted in a significant greater tumor growth inhibition than hematoporphyrin derivative injected parenterally upon stimulation by light, Co60 or by combination of the above. The photodynamic effect was analyzed in an in vivo and in an in vitro clonogenic assay. The directly injected hematoporphyrin derivative without external activation inhibited tumor growth to 34%. Light and directly injected HPD inhibited tumor growth to 3%, whereas 4, 8 and 16 Gy of Co60 produced a growth inhibition to 11%, 0.05% and 0.00% respectively. This cytotoxic effect of the ionizing radiation is further potentiated by the addition of light, resulting in a growth inhibition to 0.1%, 0.00% and 0.00% respectively for the three corresponding radiation doses. The direct intratumoral injection of HPD minimizes the side effects and increases the effect of the photodynamic therapy as compared to the parenterally administered HPD. This direct injection modality could be of potential value in the treatment of human gliomas or other tumors.