Multifunctional conjugated polymer nanoparticles as an anticancer drug carrier and a fluorescent probe for cell imaging

Abstract

The main motivation of this study is to develop multifunctional nanoparticles which can perform simultaneously the drug delivery and cell imaging tasks. To this end, firstly nanoparticles (Nps) with an average diameter of about 25 nm and based on a green emitting, hydrophobic conjugated polymer, poly[(9,9-bis{propenyl}fluorenyl-2,7- diyl))-co-(1,4-benzo-{2,1,3}-thiodiazole)] (PPFBT) and Nps with an average diameter of about 150 nm and based on a red emitting, hydrophobic conjugated polymer, poly[(9,9-bis{3-azido-propyl}fluorenyl-2,7-divinylene)-co-(1,4-benzo- {2,1,3}-thiodiazole)] (PAPFVBT) were prepared, characterized and their convenience as a fluorescent probe for cell imaging was evaluated via in vitro cell assays. Then, drug loaded nanocapsules in which PPFBT or PAPFVBT acts both as a fluorescent reporter and the main matrix of the nanocapsules accommodating an anticancer drug, camptothecin (CPT), were synthesized through a facile, single step reprecipitation method. CPT is a hydrophobic, water-insoluble drug but the encapsulation improved its water-solubility. The CPT loading efficiency in the nanoparticles has been determined to be 100% when a drug to polymer ratio of 1:25 (w/w) was used. Cell viability of Human hepatocellular carcinoma cell line (Huh7) was investigated in the absence and presence of CPT using Sulforhodamine B (SRB) assay. SRB assay results supported further by the fluorescence microscope cell images clearly confirmed that blank and CPT-loaded PPFBT Nps have been taken up by the cells very efficiently and these nanoparticles were accumulated in the cytoplasm. Time and dose dependent SRB assay results indicate that the blank PPFBT Nps are not toxic to the Huh7 cells up to 25 µM. However, even a very low dose of CPT was found to be sufficient to induce the apoptosis of the cells when it was delivered through nanoparticles. Thus, at the end of 48 h, the half maximal inhibitory concentration (IC50) of free CPT and CPT-loaded PPFBT Nps were calculated to be 0.9 µM and 0.1 µM respectively, corresponding to that CPT-loaded PPFBT Nps are 9 times more effective than free CPT. However, at the end of 72 h, the IC50 of free CPT and CPT-loaded PPFBT Nps decreased to 0.1 µM and 0.008 µM, respectively. In this case, CPT-loaded PPFBT Nps are 12.5 times more effective than free CPT in inducing the apoptosis of Huh7 cells. Although the free drug (CPT) reaches IC50 of 0.1 µM after 72 h, it is possible to achieve this value with CPT-loaded Nps at the end of 48 h. On the other hand, dose dependent SRB assay results indicate that the blank PAPFVBT Nps are not toxic to the Huh7 cells up to 16 µM. At the end of 72 h, IC50 of free CPT and CPTloaded PAPFVBT Nps were calculated to be 0.03 µM and 0.1 µM respectively, corresponding to that CPT-loaded PAPFVBT Nps are 3.3 times less effective than free CPT. Having bigger size (~150 nm) of PAPFVBT Nps is the main reason of not being effective as PPFBT Nps (~25 nm).