Intracellular trafficking of nuclear localization signal conjugated nanoparticles for cancer therapy

Doxorubicin (DOX) is an anticancer drug with an intracellular site of action in the nucleus. For high antitumour activity, it should be effectively internalized into the cancer cells and accumulate in the nucleus. In this study, we have prepared a nuclear localization signal conjugated doxorubicin loaded Poly (d,l-lactide-co-glycolide) nanoparticles (NPs), to deliver doxorubicin to the nucleus efficiently. Physico-chemical characterization of these NPs showed that the drug is molecularly dispersed in spherical and smooth surfaced nanoparticles. NPs (～226 nm in diameter, 46% encapsulation efficiency) under in vitro conditions exhibited sustained release of the encapsulated drug (63% release in 60 days). Cell cytotoxicity results showed that NLS conjugated NPs exhibited comparatively lower IC₅₀ value (2.3 μM/ml) than drug in solution (17.6 μM/ml) and unconjugated NPs (7.9 μM/ml) in breast cancer cell line MCF-7 as studied by MTT assay. Cellular uptake studies by confocal laser scanning microscopy (CLSM) and fluorescence spectrophotometer showed that greater amount of drug is targeted to the nucleus with NLS conjugated NPs as compared to drug in solution or unconjugated NPs. Flow cytometry experiments results showed that NLS conjugated NPs are showing greater cell cycle (G2/M phase) blocking and apoptosis than native DOX and unconjugated NPs. In conclusion, these results suggested that NLS conjugated doxorubicin loaded NPs could be potentially useful as novel drug delivery system for breast cancer therapy.