Applications of Porphyrin Nanoparticles in Enhancing Cancer Immunotherapies
Keywords: abscopal effect
adoptive cellular therapy
nanoparticle
photodynamic therapy
porphyrin

Harnessing the immune system can be an effective means of combating cancer. Activation of the immune system can result in the specific targeting of tumor cells, elimination of residual disease and metastases, and generation of immune memory to prevent recurrence. In this thesis, applications of porphyrin nanoparticles to stimulate antitumor immunity are explored. Treatments such as photodynamic therapy (PDT), which are specific and targeted to tumors, are intriguing for their potential to induce the abscopal effect. This rare phenomenon occurs after initial treatment promotes a systemic immune response that results in the delay in growth, or even shrinkage, of untreated tumors or metastases. As such, finding methods to enhance the abscopal effect can improve patient outcomes. This thesis first sought to determine the ability of porphyrin lipoprotein (PLP) nanoparticles to serve as a photosensitizer for PDT and whether PLP-mediated PDT can induce the abscopal effect. In mice bearing subcutaneous AE17-OVA+ mesothelioma on both hindlimbs, four repeated cycles of PLP mediated PDT (R-PDT) delayed the growth of distal, non-irradiated tumors four-fold, relative to control mice. Moreover, combining R-PDT with anti-PD-1 therapy to strengthen the abscopal effect, resulted in prolonged survival, compared to mice who were treated with PBS, R-PDT or anti-PD-1 therapy alone. Next, the immune mechanisms underlying the abscopal effect and the safety of R-PDT were evaluated. Antigen presentation in the spleen and distal, non-irradiated tumor draining lymph nodes were observed, and corresponded to alterations in T-cell subsets in the spleen and non-irradiated tumor draining lymph nodes. Upon examination of histology and blood chemistry, R-PDT had an acceptable safety profile, whereas combination R-PDT + αPD-1 induced 1.3-fold higher serum potassium and 1.3-fold phosphorus in mice, which is consistent with mild laboratory tumor lysis syndrome. Therefore, this work shows the abilityof PLP-mediated PDT to induce the abscopal effect to improve antitumor efficacy, while maintaining a reasonable safety profile. Conventional means of activating the immune system include the use of cytokines, immune checkpoint blockades, cancer vaccines, and adoptive cellular therapies. However, the immunosuppressive tumor microenvironment has impeded the efficacy of these treatments, particularly for adoptive cellular therapies. To address the immunosuppressive tumor microenvironment, we proposed the delivery of immunostimulants in a localized manner: we conjugated OKT3 antibody loaded porphyrin liposomes (ie. porphysomes) to the plasma membranes of double negative T cells (DNTs). Conjugation of OKT3-loaded porphysomes to DNTs improved cytotoxicity of DNTs relative to DNTs conjugated to empty porphysomes for up to five days post-incubation. Accordingly, the proof-of-concept for this conjugate system was demonstrated. Taken together, this thesis demonstrates two methods in which porphyrin nanoparticles can boost immunity to combat cancer.