Evaluation of monophosphoryl lipid A as an immune adjuvant for photodynamic therapy in a rat sarcoma model: preliminary results

Photodynamic therapy (PDT) is a treatment option for several forms of human cancer, and like traditional chemotherapy and ionizing radiation therapy, PDT alone is not curative for some cases. Recent efforts have aimed at developing strategies for adjuvant therapy for PDT. Given the nature of PDT-mediated cell damage, immunotherapy is a promising adjuvant for long-term control of solid tumors. A candidate immune stimulant for use with PDT is monophosphoryl lipid A (MLA), a non-toxic fraction of the endotoxin molecule. The hypothesis is that adjuvant MLA immunotherapy with PDT will improve local tumor control and prevent growth of subsequently implanted tumor cells when compared to PDT alone. To date, no significant differences in circulating leukocyte populations or tumor infiltrating lymphocyte populations have been identified in 9L tumor-bearing F344 rats after systemic administration of MLA. Likewise, no significant difference has been identified in local tumor control following PDT of 9L tumors with or without adjuvant MLA. Further results are pending.