Autophagy in antitumor activity of aloin for breast cancer cells compared with doxorubicin

Abstract

Breast cancer is the most commonly diagnosed cancer and is one of the leading causes of cancer mortality in women worldwide. Natural product compounds have attracted significant attention for their potent effects against human cancers. Aloin, a natural phytochemical anthraquinone glycoside extracted from Aloe sp., has been previously reported for its antitumor activity. Autophagy is a highly conserved process that mediates the degradation of dysfunctional cellular components, such as senescent proteins and organelles. In the present study, we verified the involvement of autophagy in tolerance to aloin, especially in breast cancer cells with negative estrogen receptors, and as an alternative pathway to promote cell death in cells expressing mutant p53 status, which often limits the efficacy and accounts for resistance to chemotherapy. We studied the effect of aloin on 2 types of breast cancer cell lines, estrogen receptor-positive (T47D) and triple negative (MDA-MB231), and compared to an anthraquinone analog, doxorubicin (Dox) as a reference compound. Aloin inhibited the cell growth of both T47D and MDA-MB231 cancer cells, in a time- and dose-dependent manner with a more pronounced effect in the 72 h exposure regimen, and in the ERα+ breast cell line. The autophagic activity of aloin was emphasized by the formation of autophagosomes and autolysophagosomes, as early and late autophagic compartments, respectively, as well as the accumulation of acidic vesicular organelles in the tumor cells. Also, upregulation in the protein expression of some marker genes of autophagy such as beclin 1 and LC3BII/LC3I, and conversely down-regulation in pmTOR and p62 was recorded. The results suggest that autophagy can be regarded as one of the mechanistic modes of aloin cytotoxicity in breast cancer cells that evade apoptosis through genetic mutations in p53.