Photofrin dark effects and heme oxygenase inducers as therapeutic in mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignant neoplasm with a devastating prognosis.
Median survival from the time of diagnosis is approximately 18 months and limited improvement has been gained
in this expectation over the past 25 years. Disease progression is driven through a local inflammatory response,
thus there is therapeutic potential in methods that combat this inflammation or its related effects on innate
immunity. We have revealed a strong, immune-mediated response of murine mesothelioma tumors to the FDA-
approved drug Photofrin. Generally employed as a photosensitizer for photodynamic therapy (PDT), we noted
the antitumor activity of Photofrin to mesothelioma tumor was independent of its light activation for photodynamic
therapy (i.e., “dark effects”). Other of our preliminary data show that Photofrin, again independent of activation
by light, is associated with increased expression of the antioxidant enzyme, heme oxygenase (HO) -1 in both
murine and human mesothelioma. Moreover, another drug used in PDT, the photosensitizing pro-drug 5-
aminolevulinic acid (ALA), is clinically employed as a HO-1 inducer and found in our data to increase the survival
of mice with orthotopic mesothelioma tumors (again, independent of light activation). Due to their antioxidant
properties, HO-1 inducers are applied in inflammatory disease. Although not traditionally employed in cancer
because they could impede oxidative-dependent therapeutics, it is noted that HO-1 expression correlates with
better prognosis in some malignancies. This may be related to the prevalence of inflammation in a particular
histology. Overall, HO-1 inducers may stimulate antitumor immunity via effects on immune cell populations.
Photofrin data show it to establish CD8+ T cell dependent immunity, which could be transferred to new hosts.
Accompanying actions could include anti-inflammatory activity that combats mesothelioma tumor growth, and
antioxidative action in T cells, potentially re-invigorating these cells and associated antitumor immunity.
Moreover, these effects could cooperate with immune checkpoint blockade. Based on the above described
preliminary and published data, studies of this proposal are directed toward the hypothesis that FDA approved
porphyrin derivative, Photofrin, is immunomodulatory in mesothelioma and can augment immune
checkpoint blockade. Research will be conducted with HO-1 inducers, Photofrin, ALA, hemin and
docosahexaenoic acid (DHA) in primarily orthotopic models of murine mesothelioma. The research aims to: 1)
characterize the tumor control and antitumor immunity generated by Photofrin and other HO-1 inducing drugs
and 2) utilize transcriptomics to inform mechanisms of therapeutic effect by HO-1 inducers and guide their
combination with immune checkpoint blockade. Data produced by this proposal will provide insight on application
of Photofrin, ALA and/or other HO-1 inducers for treatment of MPM; fill knowledge gaps in antitumor activity by
HO-1 inducers; and provide the mechanistic foundation for clinical translation of Photofrin, ALA and/or other HO-
1 inducers in combination with immune checkpoint blockade for the treatment of MPM.

Grant Number: 5R21CA286282-02
NIH Institute/Center: NIH
Principal Investigator: Theresa Busch