#IDIBELLfellows: Laura Moya Borrego

Exploring the antitumor activity of the pore-forming toxin parasporin as a candidate transgene for oncolytic adenoviruses
Laura Moya Borrego – Cancer Immunotherapy Group

Oncolytic viruses (OVs) have regained clinical interest in oncology for their potential to restore host anti-tumor immunity in addition to directly replicating in and killing cancer cells, making them ideal partners for combination with other immunotherapies. Among OV vector platforms, oncolytic adenoviruses (OAds) are one of the most widely studied for their tumor selectivity, safety, and transgene-arming capacity. However, one of the major challenges remaining is the fact that highly immunogenic viral epitopes often give rise to biased immune responses against them over tumor epitopes, a phenomenon known as viral immunodominance.

Parasporin-2 (PS2) is a pore-forming toxin (PFT) from Bacillus thuringiensis that upon proteolytic activation kills preferentially tumor cells while not harming normal cells, making it a promising anticancer treatment. However, no data exist regarding the antitumor activity of parasporins in animal models. An expression and accumulation of PFTs in the tumor, resulting from the selective tumor replication of the OV, would promote the oligomerization and pore formation of the toxin in the membrane of tumor cells, providing a potential benefit for an antitumor therapy based on PFTs. In this work, we generated a PS2 modified to be produced, secreted, and activated by tumor cells. Supernatants of PS2-transfected cells induced cell swelling and bubbling in multiple cell lines in vitro, as well as ATP release, which constitutes one of the three hallmarks of immunogenic cell death (ICD). Moreover, mice vaccinated with PS2-treated MC38 mouse colon carcinoma cells showed a better tumor growth control when rechallenged, suggesting that tumor cells lysed by PS2 triggered an antitumor immune response. Finally, we armed an OAd with the modified PS2 transgene. Supernatants from tumor cells infected with this virus induced the same phenotypic changes as observed with expression plasmids. One intravenous injection in immunodeficient mice bearing human hepatocellular carcinoma HepG2 tumors induced significant antitumor efficacy.

Overall, these data showed the antitumor potential of our modified PS2 as a candidate to be armed in an OAd. We propose that arming OAds with PS2 may enhance antitumoral immune responses through ICD and, in turn, the toxin secreted by the virus may promote a bystander ICD in the neighboring cells that could diminish the viral immunodominance.