ECM-Mimetic Multiresponsive Nanobullets Targeted Against Metastasizing Circulating Tumor Clusters in Breast Cancer.

Targeting smaller populations of circulating tumor clusters (CTC) with tumor-initiating and colonization potentials at distant sites in circulation remains a challenge as clusters possess both epithelial and mesenchymal characteristics. Bullet shaped ellipsoidal nanostructures of size 600 ± 11.3 nm (major axis) and 281.9 ± 5.3 nm (minor axis) with 2.2 aspect ratio were self-assembled using inorganic and organic GRAS biomaterials to preferentially target tumor-causing CTCs. Negatively-charged chondroitin sulfate in presence of gelatin guides unidirectional growth of calcium carbonate mesocrystals to form nanobullets, mediates CD44 targeting of CTCs. Switchable multi-responsive drug release profiles (temperature and pH) were recorded for nanobullets promoting spontaneous and efficient cell-killing. CD44 and E-cadherin overexpressing 'seeding' cell clusters of 170 ± 22 µm were developed as in vitro CTC model. pH responsive release of Dox into lysosome stimulates calcium influx resulting in cell death. CD44-blocked CTCs showed significantly reduced internalization when compared to CD44-expressing CTCs thereby confirming CD44 specific internalization of nanobullets. Significantly retarded expansion of clusters when shifted to cell adhesive surfaces depicts the potential of nanobullets against colonization of CTCs. Hence, newer insights on developed anisotropic ECM-mimetic nanohybrids would enhance targeted capture of tumor-initiating clusters in systemic circulation that would potentially reduce the progression of tumor in breast cancer patients.