Characterization of DMXAA‐Loaded Reconstituted High‐Density Lipoprotein Nanoparticles

Abstract

DMXAA is a drug agonist of the stimulator of interferon genes (STING) receptor. As such, it is capable of modulating the functional phenotype of tumor‐associated macrophages (TAMs) that originate from infiltrating monocytes and tissue‐resident macrophages. TAMs can account for up to 50% of the tumor mass and are recognized as major contributors to tumorigenesis. The pro‐tumoral activity of TAMs is linked to the ability of cancer cells and other components of the tumor microenvironment (TME) to educate TAMs, inducing them to take on a tumor‐promoting (M2) phenotype. The classical phenotype of macrophages (M1) is pro‐inflammatory and can facilitate anti‐tumoral effects. The M2 phenotype, on the other hand, sustains tumor growth, immunosuppression, matrix remodeling and metastasis. Amongst the several immunotherapy strategies used to target TAMs, DMXAA has been used to reverse the phenotype of TAMs back to the anti‐tumoral M1 phenotype in murine models of cancer. In order to avoid off‐target effects, there is a need to develop delivery strategies to direct such macrophage phenotype‐modulating drugs specifically to the tumor site since macrophages are present in all vertebrate tissues, contribute to homeostasis and act as central mediators of immune response. Biocompatible nanoparticles offer a way to achieve the selective delivery of DMXAA to TAMs, and reconstituted high‐density lipoprotein type nanoparticles (rHDL Nps) are particularly suitable for such task. Previous studies have shown that rHDL Nps readily penetrate the TME and scavenger receptors mediate the intracellular delivery of the rHDL payload. Protein expression analysis showed that M2 macrophages express these scavenger receptors. For the purpose of delivering DMXAA to TAMs and achieving a phenotype reversal, rHDL Nps transporting DMXAA (rHDL‐DMXAA) were prepared via a microfluidics process and characterized via dynamic light scattering (33.9 ± 14.28 nm particle diameter size). The fast protein liquid chromatography profile of this formulation suggested a homogeneous preparation with an estimated molecular weight of particles of about 132.3 kDa. The DMXAA encapsulation efficiency which was initially about 30.4 ± 12.4 % doubled when polyethylene glycol–phosphatidylethanolamine was included in the formulation. The rHDL‐DMXAA particles displayed increased fluorescence anisotropy over the free drug, indicating that the majority of DMXAA molecules were trapped in the core of the rHDL carrier. The characteristics of the rHDL‐DMXAA such as the small size of the particle and the receptor‐mediated uptake by the target cells suggest that DMXAA will be efficiently delivered to TAMs in the TME via the rHDL Nps. Thus, the rHDL‐DMXAA formulation is likely to impact tumor progression with potential therapeutic implications.Support or Funding Information2019 UNTHSC intramural seed grant