Human melanoma: drug resistance

Therapeutic potential of marine peptides in malignant melanoma

Malignant melanoma is the most dangerous type of skin cancer. It is becoming more common globally and is increasingly resistant to treatment options. Despite extensive research into its pathophysiology, there are still no proven cures for metastatic melanoma. Unfortunately, current treatments are frequently ineffective and costly, and have several adverse effects. Natural substances have been extensively researched for their anti-MM capabilities. Chemoprevention and adjuvant therapy with natural products is an emerging strategy to prevent, cure or treat melanoma. Numerous prospective drugs are found in aquatic species, providing a plentiful supply of lead cytotoxic chemicals for cancer treatment. Anticancer peptides are less harmful to healthy cells and cure cancer through several different methods, such as altered cell viability, apoptosis, angiogenesis/metastasis suppression, microtubule balance disturbances and targeting lipid composition of the cancer cell membrane. This review addresses marine peptides as effective and safe treatments for MM and details their molecular mechanisms of action.

Silencing of STAT3 via Peptidomimetic LNP-Mediated Systemic Delivery of RNAi Downregulates PD-L1 and Inhibits Melanoma Growth

Cutaneous melanoma is the most aggressive skin cancer with notorious drug resistance. Inhibition of immune checkpoint molecules is one of the most promising approaches for cancer therapy. Herein, we show that RNAi mediated silencing of STAT3 expression in the tumor tissue robustly inhibit tumor growth in B16F10 mouse model of melanoma. We designed a peptidomimetic-based lipid nanoparticles (LNPs) for the delivery of siRNA in mouse model of melanoma. When systemically administered, the novel formulation (denote DoCh) preferentially delivered siRNA to the tumor tissue. Remarkably, sequential intravenous injections of siRNA against STAT3 induced profound silencing of STAT3 expression in tumor tissue, which resulted in significant downregulation of PD-L1, leading to significant inhibition of tumor growth through inhibition of tumor immune checkpoint. Moreover, DoCh-mediated siRNA delivery did not show noticeable damage to the major organs. Collectively, our data demonstrated that DoCh LNP is a promising tumor-targeted siRNA delivery system.

Lunasin is a novel therapeutic agent for targeting melanoma cancer stem cells

Recent studies provide compelling evidence that melanoma is initiated and maintained by a small population of malignant cells called cancer-initiating cells (CICs) that exhibit stem-cell-like properties. Observations that CICs have a distinct biology when compared to that of the bulk tumor cells and, importantly, are resistant to chemotherapies and radiation, suggest that CICs are involved in invasion, metastasis, and ultimately relapse. Lunasin, a bioactive peptide present in soybean, has both chemopreventive activity and chemotherapeutic activity against multiple cancer types. In this study, we tested the potential of Lunasin to specifically target CICs in melanoma tumor cell populations. In vitro studies using human melanoma cell lines showed that Lunasin treatment decreased the size of a subpopulation of melanoma cells expressing the surrogate CIC marker, Aldehyde Dehydrogenase, concomitant with a reduction in the ability to form colonies in soft agar assays, and reduced tumor growth in mouse xenografts. Similarly, Lunasin inhibited colony formation by isolated melanoma CICs in soft agar and reduced oncosphere formation in vitro and substantially inhibited tumor growth in mouse xenografts. Mechanistic studies revealed that Lunasin treatment of isolated melanoma CICs induced expression of the melanocyte-associated differentiation markers Tyrosinase and Microphthalmia-associated Transcription Factor concomitant with reduced expression of the stemness factor NANOG. These findings document for the first time that Lunasin has significant therapeutic activity against melanoma by specifically targeting melanoma CICs, and inducing a more differentiated, non-CIC phenotype. Thus, Lunasin may represent a novel therapeutic option for both chemoresistant and advanced metastatic melanoma management.

Dacarbazine with or without oblimersen (a Bcl-2 antisense oligonucleotide) in chemotherapy-naive patients with advanced melanoma and low-normal serum lactate dehydrogenase: 'The AGENDA trial'

In a previous large randomized, open-label study, retrospective subset analysis revealed that the addition of the Bcl-2 antisense oligonucleotide oblimersen to dacarbazine (Dac) significantly improved overall survival, progression-free survival, and the response rate in chemotherapy-naive patients with advanced melanoma and normal baseline serum lactate dehydrogenase (LDH) levels. To confirm and expand on this observation, we conducted a prospective double-blind, placebo-controlled study to determine whether oblimersen augmented the efficacy of Dac in advanced melanoma patients with low-normal baseline LDH levels. A total of 314 chemotherapy-naive patients were randomly assigned to receive Dac (1000 mg/m(2)) preceded by a 5-day continuous intravenous infusion of either oblimersen sodium (7 mg/kg/day) or placebo every 21 days for less than eight cycles. Co-primary efficacy endpoints were overall survival and progression-free survival. Response and progression of the disease were assessed by independent blinded review of computed tomography scan images. No difference in overall nor progression-free survival was observed between the Dac-oblimersen and Dac-placebo groups. Although the overall (17.2 vs. 12.1%) and durable (10.8 vs. 7.6%) response rates numerically favored Dac-oblimersen over Dac-placebo, they did not differ significantly (P=0.19 and 0.32, respectively). The incidence of hematologic adverse events, particularly thrombocytopenia and neutropenia, was higher in the Dac-oblimersen group than in the Dac-placebo group. Withdrawals from the study because of treatment-related adverse events were low (i.e. <2.5%) in both groups. The addition of oblimersen to Dac did not significantly improve overall survival nor progression-free survival in patients with advanced melanoma and low-normal levels of LDH at baseline.

CSMD1 exhibits antitumor activity in A375 melanoma cells through activation of the Smad pathway

In this work, we studied the effects of CUB and Sushi multiple domains 1 gene (CSMD1) expression in A375 melanoma cells in vivo and in vitro. CSDM1 expression decreased proliferation and migration, and increased apoptosis and G(1) arrest in A375 cells in vitro. Expression of CSDM1 in established xenografted tumors decreased tumor size and weight, and decreased the density of intratumor microvessels. The survival rate of mice with tumors expressing CSMD1 was significantly higher than mice with tumors that did not express CSDM1. These results confirm the role of CSDM1 as a tumor suppressor gene in melanoma cells. Furthermore, we found that CSMD1 can interact with Smad3, activate Smad1, Smad2, and Smad3, and increase the expression of Smad4. These results might prove helpful for the development of novel therapies for melanoma treatment.

Identification and analysis of CD133(+) melanoma stem-like cells conferring resistance to taxol: An insight into the mechanisms of their resistance and response

The presence and the involvement of cancer stem-like cells (CSCs) in tumor initiation and progression, and chemo-resistance are documented. Herein, we functionally analyzed melanoma stem-like cells (MSC)/CD133(+) cells on their resistance and response to taxol-induced apoptosis. Besides being taxol resistant, the CD133(+) cells demonstrated a growth advantage over the CD133(-) subpopulation. Taxol induced apoptosis on CD133(-) cells, but not on CD133(+) cells. In the CD133(-) subpopulation, the exposure to taxol induced the activation of apoptosis signal-regulating kinase1 (ASK1)/c-jun-N-terminal kinase (JNK), p38, extracellular signal regulated kinase (ERK) pathways and Bax expression, while in CD133(+) cells taxol was able only to enhance the activity of the ERK pathway. In CD133(+) cells, the direct gene transfer of Bax overcame the acquired resistance to taxol. Taken together, our data provide an insight into the mechanistic cascade of melanoma resistance to taxol and suggest Bax gene transfer as a complementary approach to chemotherapy.

Cell proliferation in cutaneous malignant melanoma: relationship with neoplastic progression

The establishment of the diagnosis of cutaneous malignant melanoma (CMM) always calls for histopathological confirmation. Further to the recognition of the CMM aspects, immunohistochemistry is helpful, in particular, in determining the size of the replicative compartment and the activity in each of the cell cycle phases (G(1), S, G(2), M). The involvement of cancer stem cells and transient amplifier cells in CMM genesis is beyond doubt. The proliferation activity is indicative of the neoplastic progression and is often related to the clinical growth rate of the neoplasm. It allows to distinguish high-risk CMM commonly showing a high growth rate, from those CMMs of lower malignancy associated with a more limited growth rate. The recruitment and progression of CMM cells in the cell cycle of proliferation depend on mitogen-activated protein kinase (MAPK) pathway and result from a loss of control normally involving a series of key regulatory cyclins. In addition, the apoptotic pathways potentially counteracting any excess in proliferative activity are out of the dependency of specific regulatory molecular mechanisms. Key molecular components involved in the deregulation of the growth fraction, the cell cycle phases of proliferation, and apoptosis are presently described in CMM.

Glucocorticoid receptor expression and antiproliferative effect of dexamethasone on human melanoma cells

Glucocorticoids, such as dexamethasone are widely used in cancer therapy and have cell type-specific pro- or antiapoptotic effects. We examined whether melanoma cells are sensitive to dexamethasone treatment. We have demonstrated for the first time that in human melanoma cell lines as well as in benign and malignant melanocytic tumors glucocorticoid receptor (GCR) is present both at mRNA and protein level. Dexamethasone applied at high doses inhibited the in vitro growth of WM983A human melanoma cells. The inhibitory effect was due to apoptosis induction. In the case of this relatively sensitive cell line dexamethasone enhanced the effect of the chemotherapeutic drug DTIC.

Melanoma-associated Chondroitin Sulfate Proteoglycan (MCSP)-targeted delivery of soluble TRAIL potently inhibits melanoma outgrowth in vitro and in vivo

BACKGROUND

Advanced melanoma is characterized by a pronounced resistance to therapy leading to a limited patient survival of ~6 - 9 months. Here, we report on a novel bifunctional therapeutic fusion protein, designated anti-MCSP:TRAIL, that is comprised of a melanoma-associated chondroitin sulfate proteoglycan (MCSP)-specific antibody fragment (scFv) fused to soluble human TRAIL. MCSP is a well-established target for melanoma immunotherapy and has recently been shown to provide important tumorigenic signals to melanoma cells. TRAIL is a highly promising tumoricidal cytokine with no or minimal toxicity towards normal cells. Anti-MCSP:TRAIL was designed to 1. selectively accrete at the cell surface of MCSP-positive melanoma cells and inhibit MCSP tumorigenic signaling and 2. activate apoptotic TRAIL-signaling.

RESULTS

Treatment of a panel of MCSP-positive melanoma cell lines with anti-MCSP:TRAIL induced TRAIL-mediated apoptotic cell death within 16 h. Of note, treatment with anti-MCSP:sTRAIL was also characterized by a rapid dephosphorylation of key proteins, such as FAK, implicated in MCSP-mediated malignant behavior. Importantly, anti-MCSP:TRAIL treatment already inhibited anchorage-independent growth by 50% at low picomolar concentrations, whereas > 100 fold higher concentrations of non-targeted TRAIL failed to reduce colony formation. Daily i.v. treatment with a low dose of anti-MCSP:TRAIL (0.14 mg/kg) resulted in a significant growth retardation of established A375 M xenografts. Anti-MCSP:TRAIL activity was further synergized by co-treatment with rimcazole, a σ-ligand currently in clinical trials for the treatment of various cancers.

CONCLUSIONS

Anti-MCSP:TRAIL has promising pre-clinical anti-melanoma activity that appears to result from combined inhibition of tumorigenic MCSP-signaling and concordant activation of TRAIL-apoptotic signaling. Anti-MCSP:TRAIL alone, or in combination with rimcazole, may be of potential value for the treatment of malignant melanoma.

Cancer stem cells and human malignant melanoma

Cancer stem cells (CSC) have been identified in hematological malignancies and several solid cancers. Similar to physiological stem cells, CSC are capable of self-renewal and differentiation and have the potential for indefinite proliferation, a function through which they may cause tumor growth. Although conventional anti-cancer treatments might eradicate most malignant cells in a tumor, they are potentially ineffective against chemoresistant CSC, which may ultimately be responsible for recurrence and progression. Human malignant melanoma is a highly aggressive and drug-resistant cancer. Detection of tumor heterogeneity, undifferentiated molecular signatures, and increased tumorigenicity of melanoma subsets with embryonic-like differentiation plasticity strongly suggest the presence and involvement of malignant melanoma stem cells (MMSC) in the initiation and propagation of this malignancy. Here, we review these findings in the context of functional properties ascribed to melanocyte stem cells and CSC in other cancers. We discuss the association of deregulated signaling pathways, genomic instability, and vasculogenic mimicry phenomena observed in melanoma subpopulations in light of the CSC concept. We propose that a subset of MMSC may be responsible for melanoma therapy-resistance, tumor invasiveness, and neoplastic progression and that targeted abrogation of a MMSC compartment could therefore ultimately lead to stable remissions and perhaps cures of metastatic melanoma.

A single chain immunotoxin, targeting the melanoma-associated chondroitin sulfate proteoglycan, is a potent inducer of apoptosis in cultured human melanoma cells

A recombinant immunotoxin was constructed by fusing a single chain fragment variable antibody fragment, specific for the melanoma-associated chondroitin sulfate proteoglycan (MCSP), to a truncated variant of Pseudomonas exotoxin A (ETA'), carrying a C-terminal KDEL-peptide for improved retrograde intracellular transport. The resulting immunotoxin MCSP-ETA' was periplasmatically expressed in Escherichia coli and purified under native conditions by affinity chromatography resulting in a yield of approximately 30 mug/l bacterial culture. This immunotoxin induced antigen-specific apoptosis in the cultured human melanoma-derived cell lines A2058 and A375M, and treatment with a single dose of the agent eliminated up to 80% of these cells within 72 h. The dose needed for half-maximum killing (EC50) was approximately 1 nmol/l for both cell lines. MCSP-ETA' also displayed cytotoxic activity against cultured primary melanoma cells from patients with advanced disease (pathologic stages IIIC and IV), with net cell death reaching up to 70% within 96 h after treatment with a single dose of 14 nmol/l. MCSP-ETA' induced cell death synergistically with cyclosporin A, both in established human melanoma cell lines and cultured primary melanoma cells. The distinctive antigen-restricted induction of apoptosis and the synergy with cyclosporin A justify further evaluation of this novel agent with regard to its potential application for the treatment of malignant melanoma.

Melanosomal sequestration of cytotoxic drugs contributes to the intractability of malignant melanomas

Multidrug resistance mechanisms underlying the intractability of malignant melanomas remain largely unknown. In this study, we demonstrate that the development of multidrug resistance in melanomas involves subcellular sequestration of intracellular cytotoxic drugs such as cis-diaminedichloroplatinum II (cisplatin; CDDP). CDDP is initially sequestered in subcellular organelles such as melanosomes, which significantly reduces its nuclear localization when compared with nonmelanoma/KB-3-1 epidermoid carcinoma cells. The melanosomal accumulation of CDDP remarkably modulates melanogenesis through a pronounced increase in tyrosinase activity. The altered melanogenesis manifested an approximately 8-fold increase in both intracellular pigmentation and extracellular transport of melanosomes containing CDDP. Thus, our experiments provide evidence that melanosomes contribute to the refractory properties of melanoma cells by sequestering cytotoxic drugs and increasing melanosome-mediated drug export. Preventing melanosomal sequestration of cytotoxic drugs by inhibiting the functions of melanosomes may have great potential as an approach to improving the chemosensitivity of melanoma cells.

The small-molecule immune response modifier imiquimod – its mode of action and clinical use in the treatment of skin cancer

Due to its good clinical efficacy against malignant skin tumours, the topical immune response modifier, imiquimod, has attracted much interest among researchers and clinicians alike. Imiquimod exerts its antitumoural effect, at least in part, through agonistic stimulation of TLR-7 and TLR-8 on dendritic cells, followed by NF-kappaB-dependent secretion of a multitude of pro-inflammatory cytokines. The net result of this pro-inflammatory activity is a profound tumour-directed cellular immune response. Recent research has revealed an additional mode of action inasmuch as imiquimod interferes with adenosine receptor signalling, even in TLR-7- and TLR-8-negative cells, thereby presumably augmenting inflammatory signalling cascades. Moreover, at higher concentrations imiquimod also exerts direct proapoptotic activity against tumour cells. This mode of action appears to be independent of membrane-bound death receptors but is mediated, at least in part, through Bcl-2-dependent release of mitochondrial cytochrome c and subsequent caspase activation. Overall, a combination of several complementary antitumoural modes of action appears to underlie the great utility of imiquimod for treating cutaneous tumours.

ABCB5-mediated doxorubicin transport and chemoresistance in human malignant melanoma

Enhanced drug efflux mediated by ABCB1 P-glycoprotein and related ATP-binding cassette transporters is one of several mechanisms of multidrug resistance thought to impair chemotherapeutic success in human cancers. In malignant melanoma, its potential contribution to chemoresistance is uncertain. Here, we show that ABCB5, which functions as a determinant of membrane potential and regulator of cell fusion in physiologic skin progenitor cells, is expressed in clinical malignant melanoma tumors and preferentially marks a subset of hyperpolarized, CD133+ stem cell phenotype-expressing tumor cells in malignant melanoma cultures and clinical melanomas. We found that ABCB5 blockade significantly reversed resistance of G3361 melanoma cells to doxorubicin, an agent to which clinical melanomas have been found refractory, resulting in a 43% reduction in the LD50 from 4 to 2.3 micromol/L doxorubicin (P < 0.05). Our results identified ABCB5-mediated doxorubicin efflux transport as the underlying mechanism of resistance, because ABCB5 blockade significantly enhanced intracellular drug accumulation. Consistent with this novel ABCB5 function and mechanism in doxorubicin resistance, gene expression levels of the transporter across a panel of human cancer cell lines used by the National Cancer Institute for drug screening correlated significantly with tumor resistance to doxorubicin (r = 0.44; P = 0.016). Our results identify ABCB5 as a novel drug transporter and chemoresistance mediator in human malignant melanoma. Moreover, our findings show that ABCB5 is a novel molecular marker for a distinct subset of chemoresistant, stem cell phenotype-expressing tumor cells among melanoma bulk populations and indicate that these chemoresistant cells can be specifically targeted via ABCB5 to enhance cytotoxic efficacy.

In vitroandin vivoantitumor effect of 2-methoxyestradiol on human melanoma

2-methoxyestradiol (2ME(2)) is an endogenous metabolite of estradiol with estrogen-receptor-independent antitumor and antiangiogenic activity. We examined the effects of 2ME(2) on the cellular proliferation of 8 human melanoma cell lines. We show that 2ME(2) inhibited cell proliferation by inducing apoptosis and an arrest in the G(2)/M phase, and the mechanism of action involved microtubules, mitochondrial damage and caspase activation. In male SCID mice, 2ME(2) was effective in reducing primary tumor weight and the number of liver metastases after intrasplenic injection of human melanoma cells. In the metastases, we found a significantly higher rate of apoptotic cells after 2ME(2) treatment. These findings on the antitumor effect of 2ME(2) in cell culture as well as in an animal model may have implications for designing alternative treatment options for patients with advanced malignant melanoma.

Death receptor-independent apoptosis in malignant melanoma induced by the small-molecule immune response modifier imiquimod

Bypassing molecular mechanisms of apoptosis deficiency may be of great utility for the successful treatment of malignant tumors. We have discovered that imiquimod, a small-molecule immunomodulator, exerts rather tumor-selective direct pro-apoptotic activity in vivo and in vitro towards cutaneous metastases of malignant melanoma, an aggressive skin tumor. This pro-apoptotic activity was not detectable with resiquimod, a closely related structural analogue whose pro-inflammatory activity is even greater than that of imiquimod. Unresponsiveness of some melanoma metastases to imiquimod in vivo corresponded to resistance towards imiquimod-induced apoptosis in vivo and in vitro. At the molecular level, the pro-apoptotic activity of imiquimod was independent of membrane-bound death receptors, but depended on Bcl-2 expression as demonstrated by overexpression of Bcl-2 in melanoma cells. Imiquimod is the first topical compound with the potential to bypass molecular mechanisms of apoptosis deficiency, a concept that may be relevant for other tumors as well.