Abstract 4008: Pegylated liposomal alendronate: The impact of the drug cargo on carrier-induced immune modulation
Authors: Rajan Robin , Sabnani Manoj K. , Wood Laurence M. , Mavinkurve Vikram , Gabizon Alberto A. , La-Beck Ninh M. 
Published: July 2016

Introduction: Liposomes are commonly used as drug carriers and the majority of approved anticancer nanoparticles utilize this platform. We have reported that liposomes similar to those used in patients can enhance tumor growth through inhibition of the antitumor immune response. However, it is not clear how the drug cargo impacts the immune modulatory effects of the carrier. The primary purpose of this study was to determine how loading of alendronate, an immune modulatory drug, into liposomes affects tumor progression and functionality of immune cells in tumor and spleen.

Methods: Tumor free C57BL/6 mice (n = 12) and mice bearing s.c. TC-1 tumors (n = 24) were treated with up to 2 weekly i.v. injections of empty liposomes similar to the pegylated liposomal carrier used in Doxil, liposomes containing alendronate (PLA), or vehicle control. Tumor size was monitored biweekly and mice were sacrificed at endpoint to obtain tumors and spleens for single cell suspensions. To enumerate myeloid and lymphoid cell populations, cells were stained for CD11b, CD11c, Gr1, and F4/80, or TCR-β, CD8b and CD4 respectively. Separate aliquots of cells were also stimulated ex vivo with CpG (myeloid cells) or PMA/ionomycin (T cells), with monensin followed by intracellular staining for IL-2, IFN gamma, perforin and TNF alpha. All assays included Fc-blocking, CD45 stain, viability dye, and were analyzed by flow cytometry (BD LSR Fortessa).

Results: In tumor free mice, liposomes increased the infiltration of macrophages and MDSC's in the spleen with lowered iNOS production, and increased IL-2, IFN gamma, and perforin production in CD8+ and CD4+ T cells. Loading alendronate into the liposomes mitigated the splenic infiltration of both macrophages and MDSC's and potentiated the T cell cytokine responses (IL-2, IFNg, perforin and TNF alpha). In tumor bearing mice, liposomes increased the infiltration of TAMs and inhibited tumor CTLs. Loading Alendronate (PLA) decreased the iNOS and arginase producing TAMs and mitigated the liposome-associated inhibition of CTL infiltration. Importantly, we found that mean tumor volumes were significantly smaller in PLA treated mice (288.9 mm3) as compared with liposomes (885.7 mm3).

Conclusions: We found that loading alendronate into liposomes mitigates the tumor-promoting potential of the carrier through modulation of macrophage, MDSC, and T cell infiltration and functionality in spleen and tumor. Ongoing studies will identify the mechanisms underlying the interactions between the carrier, drug cargo, and tumor immunologic milieu. This will be especially critical to the successful translation of carrier-mediated immunotherapies into the clinic.

Citation Format: Robin Rajan, Manoj K. Sabnani, Laurence M. Wood, Vikram Mavinkurve, Alberto A. Gabizon, Ninh M. La-Beck. Pegylated liposomal alendronate: The impact of the drug cargo on carrier-induced immune modulation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4008.