Table 1.

The main molecular mechanisms of regulations of MSA cytotoxicity on the example of various cancer cell lines.

Cancer Cell Line Name	Molecular Mechanisms of Regulations of MSA Cytotoxicity	Reference
A-172 (human glioblastoma)	Treatment with 1 μM MSA during 24 h reduces proliferation by 70–80% and increases the expression of mRNA of the transcription factors ATF-4 and ATF-6. Silencing of SELENOT under ER-stress induced by 0.1 μM MSA resulted in an increase in the expression of SELENOM and decreases the expression of AMFR (autocrine motility factor receptor) and RNF5 (ring finger protein 5), which are E3-ubiquitin ligases, important enzymes of the ERAD-system.	[3]
A549 (human lung cancer cells)	MSA reduced cell growth by 50% when cells were treated with 2.2 ± 0.3, 1.6 ± 0.2, and 1.3 ± 0.1 μM for 24, 48, and 72 h, respectively.	[32,54]
	Micromolar concentrations of MSA markedly inhibited the growth of A549 cells. MSA induces G1 arrest by down-regulating cyclin E1 and up-regulating p27Kip1. MSA was simultaneously shown to enhance apoptosis induction in the presence of intracellular GSH. Over 67% of cells were consecutively inhibited at the G0/G1 phase.
	5 μM MSA attenuates the activity of glycolysis, TCA cycle, PPP, and/or nucleotide biosynthesis. MSA effects are associated with the inhibition of the Akt pathway, leading to dephosphorylation of FOXO proteins and their nuclear translocation, which in turn activate the expression of FOXO target genes. FOXO dephosphorylation and relocalization to the nucleus are early events that activate the antiproliferative response of A549 cells to MSA
Cal27 (tongue origin, CRL-2095), SCC25 (tongue origin, CRL-1628) (head and neck squamous carcinoma cells)	Treatment with 10 μM MSA during 24 h appears to be more toxic to SCC25 compared to Cal27 cells. MSA inhibits cell proliferation by more than 90%.	[34]
	Lipid peroxidation (LPO) is an essential step in the MSA-induced toxicity of HNSCC cells. MSA sensitizes HNSCC cells to radiation and exhibits toxicity through a GSH-dependent induction of LPO. Cal27 cells treated with 10 µM MSA for 72 h were found to have 1.16 fmol lipid hydroperoxide per cell, nearly 40 times as much as untreated cells
DU145 (human prostate carcinoma epithelial cells)	At 1 μM MSA, the viability of these cell lines decreases by 70–80%. MSA promoted the activation of the PERK signaling pathway, increases expression of apoptosis genes, as well as effector caspase-3 and inflammatory caspase-4. When DU 145 cells were treated with 1 μM MSA for 24 h, a significant increase in the expression of the SELENOF and SELENOM genes was observed.	[3]
Eca109 (human esophageal carcinoma cell line)	Treatment of cells with 20 and 40 μM MSA for 72 h reduced cell viability by only approximately 50%.	[65]
	After treatment of Eca109 cells with 20 μM MSA for 48 h cell cycle was arrested in G0/G1 phase, and the cell population was increased in the S phase. MSA significantly reduces the expression of FAL1 (focally amplified lncRNA on chromosome 1), and thus, the level of PTEN (phosphatase and tensin homolog deleted on chromosome 10) is increased.
HUVEC (human umbilical vein endothelial cells)	A total of 10 μM MSA inhibits cell proliferation by 20% during 24 h.	[41]
	Effectively increases the adherence to collagen I and inhibits cell migration of HUVECs; down-regulates Integrin β3 and inhibits phosphorylation of AKT; disrupts the clustering of integrin β3 surface localization; inhibits VEGF-induced angiogenesis and the phosphorylation of IκBα and NF-κB, and the nuclear translocation of NF-κB
KYSE150, KYSE180, KYSE410, and KYSE510 (ESCC-human esophageal squamous cell carcinoma cells):	MSA treatment significantly down-regulated Keap1 (Kelch-like ECH-associated protein 1), induced nuclear accumulation of Nrf2 (nuclear factor E2-related factor 2), and enhance the ARE (antioxidant response element) promoter activity and significantly induce miR-200a expression.	[31]
MDA-MB-231(human breast adenocarcinoma cells)	The viability of cells treated with 4 μM MSA for 72 h decreased by more than 40%, while simultaneously treating cells with 4 μM MSA and 10 nM paclitaxel for 72 h-by more than 80%.	[83]
	MSA synergistically enhances the growth-inhibitory efficacy of paclitaxel in MDA-MB-231 cells. MSA enhances paclitaxel-induced apoptosis. MSA could enhance paclitaxel-mediated G2/M arrest suggests the potential of using MSA to overcome paclitaxel resistance
PANC-1, PANC-28, Colo357, Bxpc-3, HPAC (human pancreatic cancer cell) lines	PANC-1 treatment with 2.6 μM MSA for 5 d, PANC-28 treatment with 1.2 μM MSA for 3 d, Colo357 treatment with 0.6 μM MSA for 48 h, Bxpc-3 treatment with 1.15 μM MSA for 48 h, HPAC treatment with 3.7 μM MSA for 48 h resulted in a 50% decrease in cells growth.	[64,82]
	MSA induced G1 arrest and caspase-mediated apoptosis in most pancreatic cancer cell lines and manifested a rapid G2 arrest in the PANC-1 and PANC-28 cell lines. MSA induced G1 arrest in Colo357, Bxpc-3, HPAC cells at 12, 24, and 48 h. A total of 7.5 μM MSA induced a modest 2.2-fold of apoptotic fragmentation in PANC-1 cells compared to control.
	When PANC-1 cells were treated with 1 μM MSA for 72 h, a decrease in cell viability was observed only by 20%, while when treated with 50 μM MSA, by more than 90%.
	MSA induced entosis by cell detachment through downregulation of cell division control protein 42 homologs (CDC42) and its downstream effector β1-integrin (CD29). Treatment with MSA led to a unique phenotype, characterized by changes in morphology and cell detachment from the culture plate prior to cell death.
PEL (primary effusion lymphoma)	Treatment with 30 μM MSA during 24 h reduces proliferation by 70–80%.	[8]
	MSA induces pro-apoptotic UPR through transcriptional activation of pro-apoptotic genes, CHOP, Bim, and Puma, via the activation of caspases, induces oxidative stress but not lytic replication
4T1 (mouse malignant breast cancer cells)	MSA significantly induces apoptosis of these cancer cells by activating Bax, caspase-3, PARP. In addition, MSA is able to inhibit tumor angiogenesis by reducing the expression of vascular endothelial growth factors VEGF and Ang-2 in mammary cells of dogs and mouse models. In addition, this series of experiments showed that MSA inhibited the JAK2/STAT3 signaling pathway.	[59,60]
WM1552c, UKRV, Colo875 (human melanoma cell lines), SK-BR-3, BT-474 (human mammary carcinoma cell lines), B16F10 (mouse skin melanoma cells)	Treatment with MSA increased the MHC class I (major histocompatibility complex surface) expression levels in all the tested tumor cell lines. MSA partially mimics IFNγ signaling, such as the upregulation of STAT1(Stat1 signal transducer and activator of transcription 1), JAK1 (janus kinase 1), IRF1, IRF5, IRF7, and IRF9 (interferon-regulated factor1, 5, 7 and 9) on the mRNA and/or protein expression levels. In addition, MSA treatment leads to activation of the transcription factor Nrf2.	[62]
HNSCC (human head and neck squamous cell carcinoma),	MSA effectively inhibits the HIF-1α in hypoxic cells, while PHD 2 and PHD 3, on the contrary, were activated, which was demonstrated in HNSCC cells.	[73]
RC2 and 786-0 (clear cell renal cell carcinoma)	The resistance of these cancer cells, overexpressing the HIF-1α under hypoxia, to SN38-the active metabolite of irinotecan, was reduced after MSA treatment. Similar synergistic activity of MSA in combination with docetaxel was shown in a model of prostate cancer cells, which can also be explained by the inhibition of HIF-1α by the activation of PHDs.	[74,75,76,77]
(PC-3 and PC-3M, PAIII and DU145 (human prostate cancer cells)	Treatment of clear cell renal cell carcinoma (RC2 and 786-0) with a pharmacological dose of MSA (10 μM) promoted inhibition of constitutively expressed transcription factors HIF-1α and HIF-2α in RC2 and 786-0 cells, respectively.	[78]
	MSA inhibits the expression and activity of HIF-1α in invasive rat and human prostate cancer cells [79]. Thus, the treatment of highly aggressive human prostate cancer cell lines (PC-3 and PC-3M) with MSA led to significant inhibition of growth and induction of apoptosis, and MSA has a stronger effect on cells under hypoxia than under normoxia, especially at a physiological dose of MSA (5 μM).	[79]