by ecancer reporter Janet Fricker

Combining intralesional (IL) PV-10 with immune check point inhibitors improved regression of melanoma in mouse models and increased markers of T cell activity compared to either agent used alone, reports an abstract¹ at the at the Society for Immunotherapy of Cancer (SITC) Annual Meeting, 6-9 November, National Harbor, Maryland, USA.

In an earlier phase 2 clinical trial, injecting IL PV-10 into the lesions of 80 stage III and IV melanoma patients, with disease refractory to a median of six prior interventions, produced a best overall response rate of 51% and complete response rate of 26% in target lesions².

Responses were found to be dependent on untreated disease burden, with complete response achieved in 50% of patients receiving PV-10 injections to all their disease.

PV-10, a 10% solution of Rose Bengal originally used as an agent to stain necrotic tissue in the cornea and to diagnose liver impairment, has been developed by Provectus Biopharmaceuticals, Inc (Knoxville, Tennessee, USA) to selectively target and destroy cancer cells.

Checkpoint inhibitors (such as ipilimumab) are a class of drugs designed to release the ‘molecular brakes’ cancer cells apply to the body’s immune system.

In the current study investigators from Moffitt Cancer Center, Tampa, Florida, set out to explore whether combining PV-10 with checkpoint inhibitors would enhance immune response.

The team investigated anti-CTLA, and the second generation immune check point inhibitors anti-PD-1 and anti-PD-L1.

For the ‘single’ tumour model, mice had melanoma cell lines implanted into one flank, and then seven to 14 days later underwent injection of IL PV-10 into these tumours, and three days later received intraperitoneal injections of anti-CTLA-4, anti-PD-1 or anti-PD-L1 antibodies, repeated every three days.

Additionally, phosphate buffered saline (PBS) was used as a control for PV-10, and NrlgG (a non-reactive antibody) as a control for checkpoint inhibitors.

Following treatment mice had the area of original tumour measured at different time points and levels of interferon gamma (a surrogate for T cell reactivity) measured.

Secondly, a ‘bilateral’ tumour model was created for mice treated with anti-PD-L1 where melanoma cell lines were injected into both flanks, but only the right side received PV-10.

For the ‘single’ tumour models mice injected with PV-10 and anti-PD-L1 had significant delays in tumour growth compared with mice injected with PBS NrlgG; PBS anti-PD-L1; or PV-10 NrlgG (p<0.05 for all).

Furthermore T cells isolated from spleens of mice injected with both PV-10 and anti-PD-L1 produced significantly more interferon gamma in comparison to the other three groups (p<0.05).

For mice injected with PV-10 and anti-PD-1 antibodies, there was a significant decrease in tumour growth compared with mice receiving anti-PD-1 alone (p<0.05).

For mice in the anti-CTLA-4 group there was a trend for enhanced response, but not enough mice were treated to demonstrate statistically significant differences.

Notably, the ‘bilateral’ model showed mice who received PV-10 and anti-PD-L1 had significant delays in tumour growth in untreated ‘bystander lesions’ compared to mice injected with PBS NrlgG; PBS anti-PD-L1; or PV10 NrlgG (p<0.01 for all).

“This feasibility study supports combination therapy with IL injection of PV-10 and immune check point inhibitors to improve systematic immune responses,” says Shari Pilon-Thomas, the first author, from Moffitt Cancer Center.

Next, she adds, the team plan to investigate types of immune cells released at tumour sites.

Eric Wachter, Chief Technology Officer at Provectus, commented, “These findings support commencement of clinical testing of PV-10 in combination with anti-CLTA-4, anti-PD-1 or anti-PD-L1 agents. We hope to start phase 1 combination studies in early 2015.”

Reference

1. S Pilon-Thomas, H Liu, K Kodumudi, et al. Efficacy of intralesional injection with PV-10in combination with co-inhibitory blockade in a murine model of melanoma. SITC 29th Annual Meeting. Poster 134.

2. J Thompson, S Agarwala, M Smithers, et al. Phase 2 Study of Intralesional PV-10 in Refractory Metastatic Melanoma. Ann Sur Oncol.