Herbal melanin inhibits colorectal cancer cell proliferation by altering redox balance, inducing apoptosis, and modulating MAPK signaling

Abstract

Background: Colorectal carcinoma is one of the most deadly cancers that requests effective and safe chemotherapy. Evaluation of natural product-based anticancer drugs as adjuvant treatment with fewer side effects is largely unexplored research fields. Herbal melanin (HM) is an extract of the seed coats of Nigella sativa that modulates an inflammatory response through toll-like receptor 4 (TLR4). This TLR4 receptor is also involved in the modulation of apoptosis. We therefore explored the anticancer potential of HM and specifically its effect on the molecular mechanisms underlying adenocarcinoma and metastatic colorectal cancer (mCRC) cell death in vitro. Methods:Cell viability was evaluated using the MTT assay. Cellular reactive oxygen species (ROS), glutathione levels, and apoptotic status were assessed using fluorometric and colorimetric detection methods. HM-induced apoptotic and other signaling pathways were investigated using Western blot technology and mitochondrial transition pore assay kit. TLR4 receptor downregulation and blockade were performed using siRNA technology and neutralizing antibody, respectively. Results:Our results showed that HM inhibited the proliferation of the colorectal adenocarcinoma HT29 and mCRC SW620 cell lines. Furthermore, HM enhanced ROS production and decreased glutathione levels. HM-induced apoptosis was associated with mitochondrial outer membrane permeability and cytochrome c release, inhibition of the Bcl2 family proteins, and activation of caspase-3/-7. In addition, HM modulated MAPK pathways by activating the JNK pathway and by inhibiting ERK phosphorylation. TLR4 receptor downregulation enhanced HM-induced apoptosis while TLR4 receptor blockade partially alleviated HM-inhibited ERK phosphorylation. Conclusion:Altogether, these findings indicate that HM exerts pro-apoptotic effects and inhibits MAPK pathway through TLR4 in mCRC and colorectal adenocarcinoma cells, suggesting HM as a promising natural-based drug for the treatment of colorectal cancer.

Bioactivities of the Green Synthesized Silver Nanoparticles Reduced Using Allium cepa L Aqueous Extracts Induced Apoptosis in Colorectal Cancer Cell Lines

“…AgNO 3 alone was found to have some inhibitory effect at higher concentrations (100 μM) in both cell lines. These findings thus demonstrate that AgNP-CEPA has anticancer potential in human colorectal cancer cell lines [51].…”

Recent Updates on Mechanisms of Resistance to 5-Fluorouracil and Reversal Strategies in Colon Cancer Treatment

“…Apoptosis or programmed cell death is a regulated form of cell death triggered upon exposure to irreversible damage or upon cellular senescence. In tumorigenesis, apoptosis is suppressed in an orchestrated manner through upregulations of anti-apoptotic proteins B-cell lymphoma 2 (Bcl-2), B-cell lymphoma-extra large (Bcl-xL), B-cell lymphoma-w (Bcl-W), and induced myeloid leukaemia cell differentiation protein (Mcl-1), and the downregulation of pro-apoptotic proteins Bcl-2 associated X protein (Bax), Bcl-2 interacting protein (Bim), Bcl-2 homologous antagonist/killer (Bak), BH3-interacting domain death agonist (Bid), and NOXA in the intrinsic mitochondrial apoptotic pathway to promote sustained tumor growth [ 42 , 43 , 44 , 45 , 46 ]. The equilibrium between these pro-apoptotic and anti-apoptotic proteins modulate the gateway of apoptosis and is implicated in drug resistance.…”

Nigella sativa L. Phytochemistry and Pharmacological Activities: A Review (2019–2021)

“…No TLR4 expression was observed at the level of HEK293 cells [ 70 ]. The cytotoxic effect of the NS melanin was confirmed in a study performed by Al-Obeed et al in 2020 [ 71 ], which demonstrated that the plant melanin was endowed with an inhibitory action of the colorectal adenocarcinoma HT29, and on the colorectal cancer metastasis SW620. In addition to this cytotoxic effect there was an elevation of the reactive oxygen species, modulation of the MAPK pathway by activation of the JNK pathway, and an inhibition of the ERK phosphorylation.…”