Targeting Drug Resistant Cancer Stem-like Cells Using Nanoparticles: A Novel Strategy for Anti-cancer Treatment

Abstract

Cancer has remained an enigma till date whose solution has evaded the inquisitive scientific minds for long. In 2012 alone, cancer caused 8.2 million deaths globally and 14 million new cases were reported. Current cancer therapies face several problems such as multi drug resistance, distant metastasis and the recurrence of the tumor post treatment. These impediments have been largely attributed to the presence of cancer stem cells (CSCs). Hence, targeting them could be a solution to the problems faced by current treatments. Biodegradable polymeric nanoparticles have greatly enhanced the targeted therapy scenario. Active and passive targeting, which they offer, has increased the therapies to reach the tumor site more efficiently. Several reports indicate GLUT1 receptor to be overexpressed in cancer stem cells. Glucosamine (GLN) is a strong ligand for the same. In our study we have developed two formulations viz., Glucosamine coated doxorubicin loaded PLGA nanoparticles (GLN-DOXPLGA- NPs) and Glucosamine coated paclitaxel loaded PLGA nanoparticles (GLN-PTXPLGA- NPs) targeting the overexpressed GLUT1 receptors on drug resistant cancer stem-like cells (DCSLCs). GLN-DOX-PLGA-NPs and GLN-PTX-PLGA-NPs were prepared using single emulsion method and nanoprecipitation respectively. The formulation optimization was done using Box-Benken Design. The NPs were coated with GLN using carbodiimide chemistry. The NPs were characterized for size, PDI and zeta potential using DLS. They were also characterized using techniques like FTIR, DSC and TEM. Lastly, the NPs were checked for colloidal stability in ex-vivo conditions. Drug resistant cancer stem-like cells (DCSLCs) were enriched from A549 and HepG2 cells by gradually increasing the dose of DOX. DCSLCs were characterized using assays such as sphere formation assay, soft agar colony formation assay, PCR, FACS analysis and tumor xenograft formation. The DCSLCs were used to analyze the activity of the formulations. Cell viability was performed using MTT and cellular uptake study was undertaken using FITC loaded NPs. Mechanism of cellular uptake was also studied. The formulations were tested for their in-vivo activity using tumor xenograft model developed using DCSLCs from both the cell lines. Additionally biodistribution study was also carried out using FITC loaded NPs and the tissue sections were observed under fluorescence microscope. The results showed that the formulation were optimized and showed enhanced activity for GLN coated NPs both in-vitro and in-vivo via GLUT1 transport receptor. The GLN coated NPs were transported into the cells in energy dependent manner as observed during the cellular uptake mechanism study. The NPs were rapidly and efficiently deposited in the tumor as compared to other vital organs as revealed by biodistribution study.