Preethi Korangath, James Barnett, Anirudh Sharma, Elizabeth Henderson, Jacqueline Stewart, Shu-Han Yu, Sri Kamal Kandala, Chun-Ting Yang, Mohammad Hedayati, Todd Armstrong, Elizabeth Jaffee, Cordula Gruettner, Xian C Zhou, Wei Fu, Chen Hu, Saraswati Sukumar, Brian W Simons and Robert Ivkov¹

¹Johns Hopkins University School of Medicine, Baltimore, USA

The factors that influence selective accumulation of nanoparticles into solid tumors remain an area of intense interest. Five tumorigenic human breast cancer cell lines with varying HER2 status were used to grow orthotopic mammary tumors in nude and NOD/SCID gamma (NSG) mice. A human HER2 overexpressing (huHER2) transgenic mouse (Genentech) was used to develop a syngeneic allograft model that was implanted across FVB/N (immune competent), nude, and NSG mice for comparative studies of tumor retention of nanoparticles. Starch-coated bionized nanoferrite (BNF) nanoparticles labeled with trastuzumab (BNF-HER), unlabeled (BNF-Plain), or PBS (control) were injected into tail veins of mice when tumors had a measured volume of ~150 mm³. 24 hrs following intravenous injection, mice were sacrificed and tissues harvested for analysis. 

We demonstrate using inductively coupled plasma mass spectrometry and extensive histophathology analysis that unlabeled starch-coated magnetic iron oxide nanoparticles showed little accumulation in tumors regardless of tumor model or host strain. Surprisingly, retention of BNF-HER nanoparticles was evident across all tumor models, with little variation among the models. Further analysis showed that retention of the antibody-labeled counterpart in tumors depended more on immune status of the host than on presence of the target antigen. 

In vitro, a T_H1-type activation of murine macrophages and neutrophils led to preferential uptake of antibody-conjugated nanoparticles, suggesting nanoparticle retention in tumors was determined by an inflammatory tumor-microenvironment. In the immune competent huHER2 allograft model, accumulation of plain nanoparticles was minimal as observed in human xenograft models. Conversely, retention of BNF-HER nanoparticles in FVB/N mice bearing huHER2 tumors was dramatically higher than in nude or NSG mice bearing this tumor, with tumor retention occurring primarily in tumor-associated dendritic cells, neutrophils, monocytes, and macrophages as determined by magnetically sorted flow cytometry. An intact immune system with competent T_H1 activation displayed preferential retention of antibody-labeled BNF nanoparticles.

Systemic exposure of immune intact allograft (implanted) huHER2 models to either plain or trastuzumab-labeled BNF nanoparticles delayed tumor growth and caused CD8⁺ T cell infiltration fourteen days after injection.

These findings demonstrate that the immune microenvironment of solid-cancer tumors can be a dominant factor that determines nanoparticle retention in tumors, and that systemic exposure to nanoparticles has potential to initiate systemic immune responses leading to adaptive immune-mediated tumor growth inhibition. Our results show that nanoparticle constructs offer anti-cancer immune-modulating potential that can be exploited for cancer immune therapy.