Abstract B29: Innate immune modulation: The novel immunotherapeutic Imprime PGG triggers the anti-cancer immunity cycle in concert with tumor-targeting, anti-angiogenic and checkpoint inhibitor antibodies

Abstract

Abstract Cancer immunotherapeutics largely focus on awakening T cell mediated recognition and eradication of tumor cells. Indeed, checkpoint inhibitor antibodies (e.g. pembrolizumab) unleash T cells already involved in anti-cancer responses and have shown remarkable clinical activity, though only in ~20-30% of solid tumor patients. Numerous approaches are being explored to enhance the percent of patients who benefit from checkpoint inhibitor therapies. Chief amongst these are the innate immune modulating therapies collectively designated as PAMPs- pathogen- associated molecular patterns. PAMPs operate as the critical non-self signals that, in response to pathogen infection, ignite the function of the innate immune system to trigger the immunity cycle. TLR and STING agonists acts as PAMPs and reflect bacterial and viral danger signals that can drive dendritic cell maturation, enhancing T cell function. These agents are in development in combination with other immunotherapies, including checkpoint inhibitors, but inspire intolerable cytokine storms and are thereby limited to direct intra-tumoral delivery approaches. We therefore sought to discover and develop a novel, systemically administered PAMP- Imprime PGG (Imprime). Ex vivo studies with whole blood from healthy human donors show that Imprime consistently elicits the activation of innate immune cells. M2 state macrophages repolarize, showing increased expression of M1 markers (CD86, PD-L1) with coincident reduction in M2 markers (CD163, CD206). Dendritic cells (DCs) mature, showing enhanced surface expression of CD80, CD86 and MHC class II. Functionally, the antigen presentation capability of these re-polarized macrophages and activated DCs is substantially enhanced and drives the robust expansion of co-cultured CD8 T cells as well as the marked upregulation of the potent anti-tumor cytokine interferon gamma. In preclinical tumor studies, Imprime is administered IV and profoundly enhances the efficacy of numerous antibody therapies. Using the B16 experimental metastasis model, we show that Imprime (administered IV) synergizes with the anti-TRP1 tumor-targeting antibody TA-99, nearly eradicating B16 metastases as measured by visual counts, TRP-1 RT-PCR and in situ immunofluorescence for TRP1. In the H441 and H1299 non-small cell lung cancer xenografts, Imprime synergizes with the anti-VEGFR2 antibody DC101 to flat-line tumor growth. In the MC-38, CT-26 and 4T-1 syngeneic tumor models, Imprime synergizes with both anti-PD-1 and PD-L1 checkpoint inhibitor antibodies to repress tumor growth and/or to eradicate cancer lesions. In situ imaging of these preclinical tumor tissues repeatedly shows that Imprime instigates a re-orientation of the immune microenvironment, promoting an M1 state (e.g. increased iNOS2, decreased Arginase 1), as well as the influx of myeloid cells and, in the syngenic models, CD8 T cells. In clinical trials in > 400 total patients to date, Imprime has been safely administered by IV infusion (4mg/kg over 2 hours) and has repeatedly shown evidence for efficacy in combination with tumor targeting or anti-angiogenic antibodies. Studies with checkpoint inhibitor antibodies are slated to begin summer of 2016. We now provide the first evidence in healthy human volunteers that Imprime (IV- 4mg/kg, 2 hours) drives the same innate immune activation events evident in the preclinical studies (e.g. chemokine and cytokine release, PD-L1 and CD86 upregulation) verifying that the clinical dose activates the innate immune system. Together, these preclinical and clinical studies provide evidence that the novel PAMP, Imprime PGG, can be safely administered systemically and can drive the critical innate immune activation necessary to spark the anti-cancer immunity cycle. Citation Format: N Bose, K Gorden, A Chan, A Jonas Bykowski, N Ottoson, D Walsh, X Qiu, B Harrison, T Kangas, K Fraser, R Fulton, S Leonardo, M Uhlik, J Graff. Innate immune modulation: The novel immunotherapeutic Imprime PGG triggers the anti-cancer immunity cycle in concert with tumor-targeting, anti-angiogenic and checkpoint inhibitor antibodies. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B29.