Thymoquinone-PLGA-PF68 Nanoparticles Induce S Phase Cell Cycle Arrest and Apoptosis, Leading to the Inhibition of Migration and Colony Formation in Tamoxifen-Resistant Breast Cancer Cells.

Abstract

Background: A biocompatible polymeric nanoparticle, TQ-PLGA-PF68, was developed through the interaction of the phytochemical thymoquinone (TQ) encapsulated in poly(L-lactide-co-glycolide)-b-poly(ethylene glycol) (PLGA-PEG) with Pluronics F68. So far, this combination has not been assessed on breast cancer cells resistant to anti-cancer drugs. Therefore, this study aimed to assess the cell death caused by TQ-PLGA-PF68 nanoparticles, particularly in resistant breast cancer cell lines expressing estrogen receptor (ER) positivity, such as TamR MCF-7.

Methods: The antiproliferative activity of TQ-PLGA-PF68 nanoparticles was measured using the MTS assay. The cytotoxic effects were further evaluated through colony formation assay and scratch-wound healing assay. Terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) assay was performed to determine the characteristics of the apoptosis as well as cell cycle arrest induced by TQ-PLGA-PF68 nanoparticles. The localization of these nanoparticles in the cells was examined using Transmission Electron Microscopy (TEM).

Results: With a TQ concentration of 58.5 μM encapsulated within the nanoparticles, cytotoxicity analysis revealed a significant inhibition of cell proliferation (p<0.05). This finding was corroborated by the results of the colony formation assay. Treatment with TQ-PLGA-PF68 nanoparticles significantly decreased the number of surviving TamR MCF-7 cells by 35% (p<0.001) compared to untreated TamR MCF-7 cells. Concurrently, the scratch-wound healing assay indicated a closure rate of 50% versus >80% (p<0.05) in untreated TamR MCF-7 cells at 12 hours post-wounding. The TUNEL assay successfully confirmed the apoptosis characteristics associated with cell cycle arrest. TEM observation confirmed the cellular internalization of these nanoparticles, suggesting the in vitro therapeutic potential of the formulation.

Conclusion: In this study, a significant functional change in TamR MCF-7 cells induced by the TQ nanoparticles was observed. The unique incorporation of TQ into the PLGA-PEG and Pluronics F68 formulation preserved its bioactivity, thereby reducing the migratory and proliferative traits of drug-resistant cells. This discovery may pave the way for exploring the application of biocompatible polymeric TQ nanoparticles as a novel therapeutic approach in future studies pertaining to resistant breast cancer.