Passive targeting is one such strategy which exploits the leaky tumor vasculature present in the vicinity of cancer cells[54]. Quick formation of new blood vessels in rapidly growing cancer cells is a common phenomenon. This vasculature formation is inherently defective in nature, which in turn, allows large molecules and lipids to easily enter the extravascular space in tumors[58]. In addition, due to fast development of cancerous cells, lymphatic drainage is undeveloped, leading to retention of large molecules and lipids in the extravascular space of the tumors[58]. This phenomenon is termed as enhanced permeability and retention (EPR) effect[59]. Another approach that is widely used to deliver drugs is the active targeting approach which is based on the targeting of drugs to the overexpressed receptors on cancer cells [60] [61, 62]. Tumor cells require various nutrients and vitamins for rapid development, and hence they overexpress many tumor-specific receptors, which can be used as targets to deliver cytotoxic agents into tumors[63]. Various ligands or active targeting agents used are antibodies, growth factors (vascular endothelial growth factor), receptors (such as transferrin, epidermal growth factor receptor), ligands (including peptides and small synthetic organic molecules), nutrient
Passive targeting is one such strategy which exploits the leaky tumor vasculature present in the vicinity of cancer cells[54]. Quick formation of new blood vessels in rapidly growing cancer cells is a common phenomenon. This vasculature formation is inherently defective in nature, which in turn, allows large molecules and lipids to easily enter the extravascular space in tumors[58]. In addition, due to fast development of cancerous cells, lymphatic drainage is undeveloped, leading to retention of large molecules and lipids in the extravascular space of the tumors[58]. This phenomenon is termed as enhanced permeability and retention (EPR) effect[59]. Another approach that is widely used to deliver drugs is the active targeting approach which is based on the targeting of drugs to the overexpressed receptors on cancer cells [60] [61, 62]. Tumor cells require various nutrients and vitamins for rapid development, and hence they overexpress many tumor-specific receptors, which can be used as targets to deliver cytotoxic agents into tumors[63]. Various ligands or active targeting agents used are antibodies, growth factors (vascular endothelial growth factor), receptors (such as transferrin, epidermal growth factor receptor), ligands (including peptides and small synthetic organic molecules), nutrient