Breast cancer is the most frequently diagnosed cancer among women worldwide. Here, recombinant human lactoferrin (rhLf) expressed in Pichia pastoris was tested for its potential cytotoxic activity on a panel of six human breast cancer cell lines. The rhLf cytotoxic effect was determined via a live-cell HTS imaging assay. Also, confocal microscopy and flow cytometry protocols were employed to investigate the rhLf mode of action. The rhLf revealed an effective CC50 of 91.4 and 109.46 µg/ml on non-metastatic and metastatic MDA-MB-231 cells, with favorable selective cytotoxicity index values, 11.68 and 13.99, respectively. Moreover, rhLf displayed satisfactory SCI values on four additional cell lines, MDA-MB-468, HCC70, MCF-7 and T-47D (1.55-3.34). Also, rhLf provoked plasma membrane blebbing, chromatin condensation and cell shrinkage in MDA-MB-231 cells, being all three apoptosis-related morphological changes. Also, rhLf was able to shrink the microfilaments, forming a punctuated cytoplasmic pattern in both the MDA-MB-231 and Hs-27 cells, as visualized in confocal photomicrographs. Moreover, performing flow cytometric analysis, rhLf provoked significant phosphatidylserine externalization, cell cycle arrest in the S phase and apoptosis-induced DNA fragmentation in MDA-MB-231 cells. Hence, rhLf possesses selective cytotoxicity on breast cancer cells. Also, rhLf caused apoptosis-associated morphologic changes, disruption of F-actin cytoskeleton organization, phosphatidylserine externalization, DNA fragmentation, and arrest of the cell cycle progression on triple-negative breast cancer MDA-MB-231 cells. Overall results suggest that rhLf is using the apoptosis pathway as its mechanism to inflict cell death. Findings warranty further evaluation of rhLf as a potential anti-breast cancer drug option.
Keywords: Anti-cancer drug discovery; Apoptosis; Cancer; Cell cycle; Cytoskeleton; Lactoferrin.