Abstract 2002: Disrupting immunosuppressive tumor microenvironment via stealthy nanobombs to enhance T-cell anticancer efficacy
Authors: Chen Hongwei , Paholak Hayley J. , Luan Xin , Burnett Joseph P. , Stevers Nicholas O. , Sansanaphongpricha Kanokwan , Sun Duxin 
Published: July 2017

Abstract
Despite the fact that the immunosuppressive tumor microenvironment (ISTME) has long been recognized as a major hurdle that significantly limits the anticancer efficacy of various therapeutic strategies, including T-cell-based immunotherapy, there is currently no effective way to address this challenge. In this work, we prove that sequential photothermal therapy (PTT), mediated with stealthy laser-triggerable nanobombs composed of iron oxide nanoparticles (IONPs) following systemic delivery, can remove both pre-resident and also newly triggered immunosuppressor cells in established tumors to enhance the efficacy of T-cell anticancer therapy. Using flow cytometry to study various T-cell populations in tumor tissues 48 h post PTT in a 4T1 mouse model, our data suggest that IONP-mediated PTT could significantly reduce the CD4+FoxP3+ regulatory T-cell population. Our data also suggest that CD8+ cytotoxic T-cell populations in PTT-treated tumor tissues return to those of non-treated tumors, and are believed to be newly activated at the tumor site or recruited from periphery blood following PTT. Our data further suggest that PTT twice spaced by a 24 h interval has the best anticancer efficacy, compared to PTT once or three times at 24 h increments. This enhanced anticancer effect from the sequential IONP-mediated PTT (twice) is believed to be due to an enhanced ability to eliminate triggered immunosuppressor cells that respond faster than cytotoxic CD8+ T-cells. Furthermore, our Luminex analysis of chemokine serum concentrations indicates that IONP-mediated PTT can decrease suppressor-cell-attractive protein secretion, such as G-CSF. In addition, our immunohistochemistry data from tumor tissue staining indicate that IONP-mediated PTT down-regulates tumor cell PD-L1 expression to disrupt tumor-cell-mediated immunosuppression. The capability of IONP-mediated PTT to disrupt ISTME can significantly enhance T-cell anticancer efficacy toward both treated established tumors and distal tumor cells. When combining IONP-mediated PTT with anti-CTLA-4 therapy to block CD8+ T-cell inhibition, our data suggest that combination treatment significantly inhibits tumor growth (p &lt; 0.01), while control treatments, including the antibody alone, IONP-mediated PTT alone, and mock treatment, fail to do so. Our data further show that in a metastasis-mimic model, mice (6/6) that had primary tumors treated with PTT/anti-CTLA-4 reject pre-inoculated cancer cells at a distal site. Our data also show that the majority of the PTT/anti-CTLA-4 treatment-cured mice can reject subcutaneously (8/12) or tail-vein injected 4T1 cancer cells (9/9), indicating memory T-cell immune surveillance. In conclusion, this study provides a nanotechnology-based novel strategy to effectively disrupt not only pre-existing but also treatment-induced ISTME to boost T-cell-based cancer immunotherapy.
Citation Format: Hongwei Chen, Hayley J. Paholak, Xin Luan, Joseph P. Burnett, Nicholas O. Stevers, Kanokwan Sansanaphongpricha, Duxin Sun. Disrupting immunosuppressive tumor microenvironment via stealthy nanobombs to enhance T-cell anticancer efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2002. doi:10.1158/1538-7445.AM2017-2002