Effect of different components of laser immunotherapy in treatment of metastatic tumors in rats.

Induction of a long-term tumor-specific immunity is the ultimate cure of metastatic cancers. Laser immunotherapy is a novel approach that aims at the tumor-directed stimulation of the immune system of the host. It involves an intratumor administration of a laser-absorbing dye and an immunoadjuvant, followed by noninvasive laser irradiation. Previous studies using glycated chitosan (GC) as immunoadjuvant and indocyanine green (ICG) as laser-absorbing dye have shown positive effects of the treatment on metastatic breast tumors in rats. In vivo experiments showed promising results such as: (a) eradication of treated primary tumors; (b) regression of untreated metastases; (c) induced antitumor immune response; and (d) long-term resistance to tumor rechallenge. In this study, rats bearing metastatic breast tumors and metastatic prostate tumors were treated with various combinations of the three components of laser immunotherapy. The rat survival rates and profiles of primary and metastatic tumors, after treatment by individual components and various combinations of the components, were analyzed. In the treatment of breast tumors, all of the experimental groups without immunoadjuvant showed little or no positive effect. The use of GC, either by itself or in combination with other components, had a noticeable impact on the survival rate of tumor-bearing rats. However, it was the combination of all of the three components that resulted in the highest cure rate. Three different concentrations of GC, 0.5, 1, and 2%, were also used to treat the metastatic breast tumors. The results showed that 1% GC was most effective in laser immunotherapy. In the treatment of metastatic prostate tumors, both the laser-ICG and laser-ICG-GC treatments significantly reduced the growth of primary tumors and lung metastases. Long-term survival of the rats bearing the prostate tumors was also observed after the laser immunotherapy treatment in our preliminary studies. These results revealed the important function of the immunoadjuvant in laser immunotherapy.