Table 1 The summary of the final selected studies

Choi et al., 2014

The human melanoma cell line G361

Although Nrf2 expresses in normal skin cells, it is downregulated in skin cancers, including malignant melanoma. However, the Keap-1 expression varies in normal cells and skin cancers, suggesting that Nrf2 translocation to nucleus may occur through Keap-1 independent pathways in human skin cancers.

The Nrf2/Keap1 pathway dysregulation relates to skin cancers, including melanoma.

[15]

Funes et al., 2014

Human mesenchymal stem cells, and human mammary epithelial cells

The intracellular level of ROS elevates during human cell transformation, which accompanied by Nrf2 repression through stimulation of RAS/RAF/ERK signaling pathway.

Interestingly, regeneration of Nrf2 level in transformed cells elicits antioxidant responses and inhibit tumor growth.

Nrf2 expression is suppressed in some types of cancers. However, there are no significant differences between normal and melanoma cells in the NFE2L2 expression. Down-regulation of NFE2L2 is associated with poor prognosis in melanoma.

[16]

Smith et al., 2014

NOX activity has a crucial role in UVA-induced oxidative stress.

UV radiation leads to Nrf2 protein accumulation as well as Nox1 protein expression and NOX activity. Overexpression of Nrf2 and Nox1 has been observed in all melanoma cell lines and tissue samples.

Redox imbalance following UVR favors the condition for melanoma formation. Co-activation of oxidant and antioxidant responses leads to tumor growth and progression.

[17]

Shinpei et al., 2014

Constitutive activation of Nrf2 has a significant role in emerging melanoma-resistant cells.

Intracellular ROS levels are significantly higher in Nrf2 knockout cells than in wild-type cells, sensitizing the melanoma cells to cisplatin or dacarbazine.

[18]

Hambright et al., 2015

Human melanoma cell lines: MeWo, WM793B, and 1205Lu, human epidermal neonatal melanocytes (HEMn)

Nrf2 protein level was higher in all melanoma cell lines than HEMn. NQO1 was meaningfully increased in WM793B cell lines, and HMOX1 transcript was higher in MeWo and 1205Lu than HEMn.

Basal oxidative stress in melanoma cells is higher than in normal melanocytes, consequently up-regulating the Keap1/Nrf2 signaling pathway to adapt to this oxidative stress. The elevated oxidative stress inhibits the dependency of melanoma cell survival on PI3K/AKT/mTOR pathway.

The oxidative stress level is directly related to an advanced stage of melanoma and metastasis.

Redox therapeutic agents inhibit cell growth and survival by disrupting PI3K/AKT/mTOR pathway.

[19]

Hintsala et al., 2016

Human tissue sample;

Cell lines: COLO-800, SK-MEL-1 with BRAF mutation, SK-MEL-30, and IPC-298 with NRAS mutation

In melanoma cells with BRAF\NRAS mutations, administration of their inhibitors would decrease the expression of Nrf2.

Nuclear expression of Nrf2 in melanoma correlates with higher Clark level, deeper Breslow index, nodular growth, and poor survival.

Nrf2 is an influential factor in determining the prognosis of melanoma patients.

[20]

Chaiprasongsuk et al., 2016

Primary human epidermal melanocytes (HEMn), B16-F10 mouse melanoma cells

Knockdown of the Nrf2 gene in B16-F10 and HEMn cells results in melanogenesis enhancement in response to UVA exposure.

UVA irradiation affects Nrf2 nuclear accumulation, and Nrf2 target antioxidants time-dependently.

Nrf2 has a protective role against melanogenesis under UVA irradiation.

[21]

Kasai et al., 2016

Cell lines; A7, C32, GAK, G-361, HMY-I, HMV-II, MM-AN, MeWo, SK-MEL-2, SK-MEL-28 and SK-MEL-31, nine non-small cell lung cancer cell lines, normal human dermal fibroblasts, and neonatal skin fibroblasts

A high proportion of NQO1-high melanomas present Nrf2 activation independent of KEA1 mutation.

Melanoma cell lines presenting NQO1 overexpression show sensitivity to 17-AAG compared to cell lines with low expression of NQO1.

17-AAG is a potential therapeutic option for NQO1-high melanoma.

[22]

Saddawi-Konefka et al., 2016

Mice cell lines: MCA-induced sarcoma, Ramos, B16, and LLC

Tert-butylhydroquinone (tBHQ) induced activation of Nrf2 results in elevated expression of il17d transcript in the B16 cell line.

IL-17D induction leads to NK cell-dependent tumor inhibition.

Activation of the Nrf2-IL17D pathway in primary tumorigenesis leads to NK cell-dependent tumor inhibition. However, the role of the Nrf2-IL17D axis is context-dependent and may not always associate with NK infiltration or better survival.

Nrf2 stimulates both internal and external anti-tumor immune responses, prevents tumor progression, and improves survival.

[23]

Zhu et al., 2016

Nrf2-null C57BL/6 mice, and male Nrf2-null and wild-type mice

Cell line: B16-F10-luc-G5

Nrf2 deficiency results in tumor growth and a higher risk of lung metastasis in B16-F10 melanoma cells.

The exact role of the Nrf2 pathway in carcinogenesis needs to be investigated. However, diverse factors such as type of carcinogens, cancer type, and host immunity appear to contribute to the oncosuppressor/oncogene role of Nrf2.

[24]

Rocha et al., 2016

Human melanoma cell lines: SKMEL 28 and SKMEL 94

Murine melanoma B16

human glioma cell lines: U138MG and U87MG

Temozolomide (TMZ) increases the intracellular ROS level and triggers Nrf2 and its downstream GCLM and GSTπ genes. Consequently, the elevated level of GSH mediates temozolomide resistance. In addition, GSH depletion increases melanoma cells’ sensitivity to temozolomide. Nrf2 silencing results in temozolomide-induced cell death in vitro and in vivo.

Nrf2 is a key factor in developing TMZ drug resistance in melanoma.

[25]

Benlloch et al., 2016

Female nu/nu nude mice, Human epidermal melanocytes: HEMa-LP, pancreatic adenocarcinoma: ASPC-1 and BxPC-3, Human A2058, MeWo, and MelJuso melanoma cells, murine B16 melanoma F1, mouse pituitary corticotroph tumor cells: AtT-20

Pterostilbene indirectly downregulates Nrf2 and the downstream antioxidant defense system by inhibiting ACTH production, and reducing plasma levels of corticosterone, thus restricting melanoma tumor growth. In contrast, genetically induced Nrf2 overexpression or administration of exogenous corticosterone hindered tumor growth suppression of melanoma cells.

Pterostilbene prevents human melanoma growth in vivo. However, it does not affect melanoma growth in vitro at levels tested within the tumors. The anti-tumor effect of pterostilbene is dependent on the Nrf2 signaling pathway.

[26]

Cai et al., 2017

Melanoma patient (case report)

A variation of NFE2L2 (NFE2L2 p.Leu266Phe) is identified in a patient with stage III metastatic melanoma.

NFE2L2 mutation may play a role in melanogenesis and cancer progression.

[27]

Hintsala et al., 2017

Human tissue sample

The nuclear expression of Nrf2 is significantly higher in metastatic melanoma than in primary melanoma, whereas the level of cytoplasmic Keap1 in metastatic melanoma is lower than in primary melanoma.

Nuclear expression of Nrf2 is associated with distant metastasis and poor prognosis.

[28]

Zhao et al., 2017

WT/Sesn2 KO mouse embryonic fibroblast, A375, iMC23 melanocytes, and normal human epidermal melanocytes

UV irradiation induces Sesn2 expression in melanoma cells. Sesn2 silencing stimulates UVA-induced Nrf2 activation, inhibiting UVA-induced ROS generation.

Nrf2 silencing does not affect UVA-induced expression of Sesn2 in A375 cells.

Sesn2 seems to be the upstream suppressor of Nrf2 in response to UVA exposure.

[29]

Gao et al., 2018

B16-F10 melanoma cells

UV radiation induces Nrf2 and caspase-3 expression in B16-F10 melanoma cells, decreasing cell viability. However, Inhibition of Nrf2 by siRNA also leads to a decrease in cell viability, invasion, and migration of irradiated melanoma cells and an increase in caspase 3 expression.

Nrf2 signaling pathway exerts a dual role in melanoma. The effect of UV on the Nrf2 signaling pathway is dose-dependent.

[30]

Khamari et al., 2018

Tumor specimens, A375 melanoma cell line

A375 melanoma cells present Nrf2 nuclear accumulation, notably higher in BRAFi-resistant cells.

Knockout of Nrf2 in BRAF-resistant melanoma cells reversed vemurafenib resistance partially.

Nrf2-dependent glutathione metabolism plays a crucial role in the emergence of resistant cells.

MAPK-resistant melanomas are OXPHOS dependent, expressing Nrf2 downstream antioxidant response.

[31]

Li et al., 2018

C57BL/6 J male mice and melanoma B16-F10 cells

Mouse lung tissue with melanoma metastasis revealed a high expression of Nrf2 and its downstream antioxidant enzymes and inflammatory factors, including NF-κB P65, IL-6, and TNF-α.

The antioxidant response following oxidative stress plays a significant role in melanoma lung metastasis.

[32]

Sample et al., 2018

Human Skin Samples, A375 melanoma cell line, and WT/KO mouse embryonic fibroblasts

UVA induces P62 up-regulation in an Nrf2-dependent manner.

Knockdown of Nrf2 prevents p62 up-regulation. Conversely, knockdown of P62 inhibits UVA-induced Nrf2 up-regulation.

P62 overexpresses in melanoma and malignant melanoma independent of BRAF/NRAS mutation.

Nrf2 and P62 interact with each other in a positive feedback loop. The P62 overexpression contributes to tumor growth and metastasis.

[33]

Zhu et al., 2018

Female C57BL/6 J mice,

Cell lines: B16-BL6, HPK, and HPM

Nrf2 and PD-L1 are overexpressed in melanomas and metastatic melanomas.

UVA-induced PD-L1 upregulation is positively associated with Nrf2 activation.

UVR induces PD-L1 in an Nrf2-dependent manner, facilitating melanoma progression.

[34]

Arakawa et al., 2018

Human melanoma cell lines: CRL-1585 (C32), GAK, G-361, HMV-II, HMY-1, MeWo, MM-AN, SK-MEL-2, SK-MEL-31, and SK-MEL-28 murine melanoma B16BL6 cell line, and human non-small cell lung cancer H460 cell line

β-lapachone cytotoxicity in melanoma cell lines is dependent on the Nrf2/NQO1 axis activity. Carnosic acid induces NQO1 through further stabilization of Nrf2. Co-treatment of β-lapachone and carnosic acid increases the melanoma cell sensitivity to β-lapachone by elevating the expression of NQO1.

The NRF2/NQO1 axis can play a decisive role in improving the clinical response rate of NQO1-dependent anticancer therapies in malignant melanomas.

[35]

Aksenenko et al., 2019

Melanoma B16-bearing mice

The pro-oncogenic miR-155 is significantly elevated in the target organ of melanoma metastasis, downregulating NFE2L2 gene expression.

A reduction in NFE2L2 gene expression in the premetastatic organs may be associated with metastatic niche formation and stromal progression, results in premetastatic tissue reconstruction.

[36]

Chhabra et al., 2019

Neonatal human skin melanocyte

UVA and/or UVB exposure increase ROS and downregulate Nrf2 expression in melanocytes.

Nrf2-Keap1 pathway plays a key role in protecting skin cells against UVA and UVB induced oxidative damage.

[37]

Gagliardi et al., 2019

Human melanoma cell lines: A2058, A375, C8161, CHL-1, SK-Mel 5, SK-Mel 24, and MeWo

Activation of Nrf2 leads to a constant decrease in erastin-mediated AKR1C1÷3 expression. Moreover, inhibition of Nrf2 causes complete abolishment of ERA-stimulated CHAC1 expression.

Nrf2 expression in tumor cells is lower than in normal tissue samples, without any important fluctuation during the stages of tumor progression. However, there is no association between Nrf2 expression and patient overall survival.

Melanoma cancer cells resistant to ferroptosis cell death efficiently activate Nrf2 and its downstream enzymes HO1.

[38]

Hämälaïnen et al., 2019

Human tissue samples,

Cell lines: human primary melanoma

IPC-298 (ACC 251), adult primary epidermal melanocytes (PSC-200-013), and metastatic melanoma SK-MEL-30

The Nrf2 mRNA decreases from benign lesions to primary melanomas. Moreover, the Nrf2 mRNA level varies in different stages of melanoma. High nuclear expression of Nrf2 protein can play a prognostic role in melanoma patients prior to nodal or distant metastasis. MiR-144-3p, miR-212-3p, miR-23b-3p, miR-340, and miR-93-5p appear to be related with Nrf2.

The miRNAs are associated positively with Nrf2 mRNA but negatively with its protein.

[39]

Kuo et al., 2019

Mouse epidermal JB6 P+ cell line, and human hepatocellular HepG2-C8

Nrf2 knockout mice developed multiple skin tumors following exposure to the carcinogens.

Delphinidin prevents JB6 P+ cell transformation by epigenetic activation of the Nrf2-ARE pathway.

Redox imbalance predisposes cells to melanoma formation.

Phytochemicals can play a chemopreventive role by inhibiting the neoplastic transformation of skin cells.

[40]

Estrela et al., 2019

Nude (nu/nu) male mice,

Human A2058, COLO-679 and SK-Mel-28 melanoma cell lines

Pharmacologic silencing of glucocorticoid receptor (GR) reduces the expression of Nrf2 and antioxidant responses in metastatic B16-F10 melanoma cells, causing a drastic reduction of cell survival and tumor growth. The induction of Nrf2 overexpression reversed the anticancer effect of GR inhibition.

The cross-talk among GR, p53, and Nrf2 may be critical in BRAFV600E-mutated melanoma cells survival and metastasis. Combination of GR antagonists (mifepristone, RU486) with BRAF-related therapy could be a novel approach for improving the outcome, and preventing resistance to treatment in BRAFV600E-mutated metastatic melanoma.

[41]

Chipurupalli et al., 2020

C32, and SK-MEL-28 melanoma cell lines

STING activation downregulates the Nrf2 downstream antioxidant enzymes.

diABZI induced STING-activation reduces proliferation, accelerates cell death, and prevents migration of melanoma cells by restricting the Nrf2 signaling pathway.

Increased activity of the Nrf2 in melanoma cancer cells may be due to a defect in STING activation.

[42]

Jasmer et al., 2020

Normal human embryonic melanocytes (NHEM), SK-Mel-2, SK-Mel-5, SK-Mel-28, and HEK293FT melanoma cell lines

Inhibiting Nrf2 or its downstream enzyme, HMOX1 reduces melanosphere formation in BRAF-driven melanoma cell lines.

Melanosphere formation has an HMOX-dependent mechanism correlating with tumorigenic capacity.

HMOX1 contributes to drug resistance, melanoma invasion, and migration.

[43]

Jessen et al., 2020

A375, A-549, SK-MEL-2, SK-MEL-3, SK-MEL-28, UACC-62, UACC-257, M14, and LOXIMVI cell lines

Various internal and external signals activate Nrf2 in melanoma cells. siRNAs-dependent down-regulation of Nrf2 decreases the proliferation rate, promoting cell differentiation. Moreover, Nrf2 knockout prevents melanoma occurrence in vivo.

Activation of Nrf2 by intrinsic and extrinsic triggers present in the melanoma tumor niche results in developing a dedifferentiated phenotype and overproduction of COX2 and PGE2. This phenomenon creates an immune-cold tumor environment. Melanoma benefits from activating of the Nrf2 pathway.

[44]

De Cicco et al., 2021

The A375 human melanoma cell line

Cynaropicrin has an antioxidant effect; treated melanoma cells are less aggressive with lower clonogenic ability.

Cynaropicrin plays a chemopreventive role by inducing Nrf2 activation in melanoma cells.

[45]

Kreß et al., 2021

A375, LOXIMVI, M14, UACC-257, UACC-62, SK-MEL-2, and SK-MEL-28 cell lines

AKT activity was strongly reduced in NRF2-knockout cells in response to EGF induction compared to the control group, indicating the essential role of Nrf2 for full activation of EGFR. Nrf2 facilitates the expression of EGFR and its ligands, attributed to features such as invasion, tumor metastasis, and BRAFi resistance.

There is a positive feedback loop between Nrf2 and EGFR signaling pathway. The activation of that results in the survival and invasiveness of melanoma cancer cells.

[46]

Li et al., 2021

Skin melanoma tissue sample, the A375 human melanoma cell line

The amount of mGPDH protein in melanoma cells is significantly lower compared to normal skin cells, and metastatic melanoma compared to primary melanoma.

Furthermore, the loss of mGPDH triggers Nrf2 expression without changing the NRF2 protein degradation, promoting melanoma migration and invasion.

mGPDH deficient cells are able to activate the Nrf2 signaling pathway, leading to melanoma progression and metastasis.

[47]

Liao et al., 2021

Normal skin cell line PIG1, melanoma cell lines: A375, G-361, HS1-CLS, MEL-CLS1-4, IGR-1, MEWO, NIS-G, WS1-CLS, and MML1

miR-130b-3p activates the Nrf2/HO-1 signaling pathway by inhibiting DKK1 expression in melanoma, leading to reduced melanoma cell ferroptosis.

The expression of miR-130b-3p reinforces activation of the Nrf2/HO-1 pathway followed by DKK1 suppression. The overexpression of Nrf2 correlates with the resistance of melanoma cells to ferroptosis.

[48]

Schmidlin et al., 2021

The HEK293, and A375 cell lines

FAM129B up-regulates Nrf2 by binding to Keap1 protein in A375 melanoma cells. Knockdown of FAM129B plays a protective role against melanoma metastasis.

Constitutive activation of Nrf2 induced by FAM129B potentiates BRAF mutant melanomas for metastasis.

[49]

Weitzenböck et al., 2022

Metastatic MCM1DLN, and Non-metastatic MCM1G lines from a patient with melanoma, metastatic WM1205Lu and Non-metastatic WM793b cell lines from ATCC.

Suppression of Nrf2 leads to a loss of ROS protection and promotes the epithelial-mesenchymal transition (EMT) phenotype, which is hallmarked by the expression of CD44. Cells devoid of NRF2 exhibit higher survival rates after a BRAF or an MYC inhibitor treatment.

Nrf2 silencing increases melanoma cell viability, invasiveness, and the risk of metastasis.

[50]

Wang et al., 2022

The A375, and A2058 cell lines

Following treatment with erastin and RSL3, the level of CAMKK2 mRNA was significantly elevated. Phosphorylation of CAMKK2 reduces during ferroptosis. Moreover, the phosphorylation of AMPK (known as a canonical substrate of CAMKK2) increases during ferroptosis. CAMKK2 prevents ferroptosis by repressing the production of lipid peroxidation in an Nrf2-dependent manner.

CAMKK2 regulates the AMPK–Nrf2 signaling pathway, leading to lower ferroptosis sensitivity of melanoma cancer cells.

[51]

Sanches et al., 2022

B16-F10 murine melanoma cell line

DTIC resistant cells showed a decreased level of Nrf2. However, the addition of metformin in DTIC resistance leads to increased Nrf2 and less resistance to DTIC. Moreover, the exclusive administration of metformin also reduces Nrf2 compared to control group, inducing cellular resistance to DTIC.

Metformin plays a dual role, inhibiting or promoting a DTIC-resistant phenotype in B16-F10 melanoma cells.

[52]

Feng et al., 2022

SK-MEL-28 human melanoma cell line

GSK3 expression in melanoma cells is enhanced by nobiletin, which is usually low in cutaneous melanoma. GSK3β inhibits the Keap1/Nrf2/HO-1 Signaling Pathway. The buildup of iron and ROS and the GSH depletion causes lipid peroxidation, thereby inducing ferroptosis.

Nobiletin stimulates ferroptosis in melanoma cells by GSK3β-mediated suppression of the Nrf2/HO-1 axis.

[53]

Li et al., 2022

A375 human melanoma cell line

Dimethyl fumarate (DMF) suppresses the Nrf2 antioxidant pathway as well as AKT/mTOR/ERK signaling pathways, causing ROS accumulation. The combination of DMF with vemurafenib significantly reduced melanoma cell growth and increased tumor cell death in vitro and in vivo.

A combination of DMF and vemurafenib could be a novel therapeutic method against melanoma

[54]

Argenziano et al., 2022

M14 melanoma cell line

The Nrf2 protein level was downregulated after the treatment of M14 cells with siNrf2-NB. Subsequently, the treated cells showed significant downregulation of the viability cells.

Nrf2 contributes to maintaining the chemoresistance in melanomas. siRNA-mediated inhibition of Nrf2 could be a promising strategy to overcome chemoresistance.

[55]