Prooxidative Activity of Celastrol Induces Apoptosis, DNA Damage, and Cell Cycle Arrest in Drug-Resistant Human Colon Cancer Cells

Abstract

Cancer resistance to chemotherapy is closely related to tumor heterogeneity, i.e., the existence of distinct subpopulations of cancer cells in a tumor mass. An important role is assigned to cancer stem cells (CSCs), a small subset of cancer cells with high tumorigenic potential and capacity of self-renewal and differentiation. These properties of CSCs are sustained by the ability of those cells to maintain a low intracellular reactive oxygen species (ROS) levels, via upregulation of ROS scavenging systems. However, the accumulation of ROS over a critical threshold disturbs CSCs—redox homeostasis causing severe cytotoxic consequences. In the present study, we investigated the capacity of celastrol, a natural pentacyclic triterpenoid, to induce the formation of ROS and, consequently, cell death of the colon cancer cells with acquired resistant to cytotoxic drugs (LOVO/DX cell line). LOVO/DX cells express several important stem-like cell features, including a higher frequency of side population (SP) cells, higher expression of multidrug resistant proteins, overexpression of CSC-specific cell surface marker (CD44), increased expression of DNA repair gene (PARP1), and low intracellular ROS level. We found that celastrol, at higher concentrations (above 1 μM), significantly increased ROS amount in LOVO/DX cells at both cytoplasmic and mitochondrial levels. This prooxidant activity was associated with the induction of DNA double-strand breaks (DSBs) and apoptotic/necrotic cell death, as well as with inhibition of cell proliferation by S phase cell cycle arrest. Coincubation with NAC, a ROS scavenger, completely reversed the above effects. In summary, our results provide evidence that celastrol exhibits effective cytotoxic effects via ROS-dependent mechanisms on drug-resistant colon cancer cells. These findings strongly suggest the potential of celastrol to effectively kill cancer stem-like cells, and thus, it is a promising agent to treat severe, resistant to conventional therapy, colon cancers.

Terminalia bentzoë, a Mascarene Endemic Plant, Inhibits Human Hepatocellular Carcinoma Cells Growth In Vitro via G0/G1 Phase Cell Cycle Arrest

“…Plant extracts and/or the thereby-derived phytochemicals are known to provoke cancer cell death by causing oxidative damage to genetic material-mediated cell cycle arrest and subsequent cell death [ 59 , 60 ]. With this in mind, the DNA damage to HepG2 cellular DNA following T. bentzoë crude extract treatment was investigated using the alkaline comet assay, and scored in terms of tail length, tail intensity and olive tail moment.…”

<strong>Focus on Mascarenes Endemic Plants with Specific Phytochemical Composition, Potent Antioxidant and Antiproliferative Properties</strong>

“…Plant extracts and/or thereby derived phytochemicals are known to provoke cancer cell death by causing oxidative damage to genetic material mediated cell cycle arrest and subsequent cell death [50,51]. With this in mind, the DNA damage to HepG2 cellular DNA following T. bentzoë crude extracts treatment was investigated using the alkaline comet assay and scored in terms of tail length, tail intensity, and olive tail moment.…”

Antitumor Activity of New Olivacine Derivatives

“…According to previous papers, the level of intracellular ROS between drug-resistant cells and their sensitive counterparts differs significantly. Moreira et al [21] demonstrated that the LoVo/DX cell line displayed a significantly lower level of intracellular ROS than the drug-sensitive line LoVo. Maiti had similar results comparing ovarian cancer cell lines [22].…”

“…ROS-induced DNA damage is a well-known mechanism of action of many cytostatics [23]. Elevating the ROS level over a certain level may be an important factor in tumor chemotherapy since the initial level of intracellular ROS level for LoVo/DX is lower than for LoVo [21,22]. Rh-123 accumulation was observed in all examined compounds regardless of the used concentration, except compound 3, where accumulation was observed only for concentrations in the range of 10-20 µ M (Figure 3).…”

“…ROS-induced DNA damage is a well-known mechanism of action of many cytostatics [23]. Elevating the ROS level over a certain level may be an important factor in tumor chemotherapy since the initial level of intracellular ROS level for LoVo/DX is lower than for LoVo [21,22]. Examination of DU-145 cancer cell lines (prostate cancer) demonstrated a correlation between HIF-1 alpha, ROS level, and P-gp expression.…”