(701c) Triggered Ligand Clustering on Lipid Nanoparticles Enables Selective Targeting and Killing of Untargetable Cancer Cells: The Case for 'sticky Patches'

Objective: HER2-targeted nanoparticles encapsulating chemotherapeutics have shown promise for reducing the severity of side effects associated with traditional chemotherapeutics. However, the ability of HER2-targeted nanoparticles for effective targeting stops to hold on cancer cells expressing less than 200,000 HER2 receptors per cell (<1+ HER2 by immunohistochemistry). For cases of cancer with HER2 expression below this threshold, there is a lack of targeted treatment options because tumors are still considered untargetable. To address this issue, we have developed pH-responsive lipid nanocarriers (liposomes) that present a high local multivalency (â??very sticky patchesâ??) on the surface of the liposome containing HER2-targeting lipopeptides. Sticky patches are formed by inducing preferential partitioning of lipopeptides into lipid raft-like domains that are triggered to form on the liposome membrane at acidic pH values (6.5<pH<6.7) matching the tumor interstitial pH.

Methods: Using HER2-targeting sticky liposomes loaded with doxorubicin, on a variety of cells expressing a wide range of HER2 (>1M copies per cell to 54,000 copies per cell), we evaluate the: 1) targeting selectivity, 2) killing efficacy, 3) endocytic pathway, 4) intracellular localization, 5) mechanism of action, and 6) potential toxicity to human cardiomyocytes and normal human mammary epithelial cells. In all studies, we compare to liposomes uniformly functionalized with HER2-targeting ligands via (or not) a PEG tether, and to non-targeted liposomes.

Results: Our studies show that sticky liposomes selectively and effectively kill otherwise untargetable breast cancer cells with as few as 54,000 HER2 receptors per cell utilizing both clathrin- and caveolar-mediated endocytosis, and are nontoxic to normal breast cells and cardiomyocytes which minimally express HER2. Sticky liposomes also demonstrate K_D values which are independent of HER2 expression, and long enough residence times on the cell surface (t_1/2 of dissociation ranged from 82 to 140 minutes) to allow for internalization of vesicles (t_1/2 of internalization ranged from 27 to 29 minutes).

Conclusions: These studies demonstrate the potential of sticky liposomes to selectively target and effectively kill cancer cells considered otherwise untargetable.

Acknowledgements: NJCCR, American Cancer Society RSG-12-044-01, NSF DMR-1207022, NSF CBET-1510015, GAANN.