Melanoma Expressed-CD70 Is Regulated by RhoA and MAPK Pathways without Affecting Vemurafenib Treatment Activity

Advanced Acral Melanoma Therapies: Current Status and Future Directions

Melanoma is one of the deadliest malignancies. Its incidence has been significantly increasing in most countries in recent decades. Acral melanoma (AM), a peculiar subgroup of melanoma occurring on the palms, soles, and nails, is the main subtype of melanoma in people of color and is extremely rare in Caucasians. Although great progress has been made in melanoma treatment in recent years, patients with AM have shown limited benefit from current therapies and thus consequently have worse overall survival rates. Achieving durable therapeutic responses in this high-risk melanoma subtype represents one of the greatest challenges in the field. The frequency of BRAF mutations in AM is much lower than that in cutaneous melanoma, which prevents most AM patients from receiving treatment with BRAF inhibitors. However, AM has more frequent mutations such as KIT and CDK4/6, so targeted therapy may still improve the survival of some AM patients in the future. AM may be less susceptible to immune checkpoint inhibitors because of the poor immunogenicity. Therefore, how to enhance the immune response to the tumor cells may be the key to the application of immune checkpoint inhibitors in advanced AM. Anti-angiogenic drugs, albumin paclitaxel, or interferons are thought to enhance the effectiveness of immune checkpoint inhibitors. Combination therapies based on the backbone of PD-1 are more likely to provide greater clinical benefits. Understanding the molecular landscapes and immune microenvironment of AM will help optimize our combinatory strategies.

An alternative pathway for cellular protection in BRAF inhibitor resistance in aggressive melanoma type skin cancer

Oncogenic alterations in the BRAF gene are identified in an estimate of 50% of melanomas and cause melanoma development. BRAF kinase inhibitors (BRAFi), including vemurafenib and dabrafenib, were discovered and used in the clinical treatment of BRAF-mutant metastatic melanoma. Though, BRAFi's therapeutic advantages are short term and short-lived associated with drug resistance. Although a few pathways of developed BRAFi resistance have also been established, in approximately 40% of melanomas, the cause for inherited resistance remains unclear. Recognizing a new process of developed BRAFi resistance might provide new possibilities to successfully treat BRAF mutant melanoma. In this study, we are exploring the compensatory alternative pathway followed by BRAFi/MEKi treated resistant cell for maintaining the long-term integrity and survival.

Rho-mediated signaling promotes BRAF inhibitor resistance in de-differentiated melanoma cells

Over half of cutaneous melanoma tumors have BRAFV600E/K mutations. Acquired resistance to BRAF inhibitors (BRAFi) remains a major hurdle in attaining durable therapeutic responses. In this study we demonstrate that ~50-60% of melanoma cell lines with vemurafenib resistance acquired in vitro show activation of RhoA family GTPases. In BRAFi-resistant melanoma cell lines and tumors, activation of RhoA is correlated with decreased expression of melanocyte lineage genes. Using a machine learning approach, we built gene expression-based models to predict drug sensitivity for 265 common anticancer compounds. We then projected these signatures onto the collection of TCGA cutaneous melanoma and found that poorly differentiated tumors were predicted to have increased sensitivity to multiple Rho kinase (ROCK) inhibitors. Two transcriptional effectors downstream of Rho, MRTF and YAP1, are activated in the RhoHigh BRAFi-resistant cell lines, and resistant cells are more sensitive to inhibition of these transcriptional mechanisms. Taken together, these results support the concept of targeting Rho-regulated gene transcription pathways as a promising therapeutic approach to restore sensitivity to BRAFi-resistant tumors or as a combination therapy to prevent the onset of drug resistance.

Low RhoA expression is associated with adverse outcome in melanoma patients: a clinicopathological analysis

RhoA GTPase is physiologically involved in the formation of stress fibers, cellular contractility and polarity, maintenance of cell cycle and transcriptional control. During tumorigenesis, it plays roles in cancer cell proliferation, apoptosis, adhesion, invasion and metastasis. While RhoA seems to act as a tumor promotor in most malignancies, data regarding its function in skin melanoma are fragmentary and conflicting. We aimed to clarify the clinical significance of RhoA expression in melanoma by immunohistochemical evaluation of 134 primary tumors and subsequent statistical analysis with clinicopathological profiles of patients. Increased RhoA expression was associated with thinner tumors, higher grade of tumor-infiltrating lymphocytes and lack of disease recurrence. Moreover, we observed a trend towards higher RhoA expression in cases without concurrent metastases. Recurrence-free survival and melanoma-specific survival of patients with high RhoA-expressing tumors were significantly prolonged. Multivariable regression model adjusting for melanoma thickness and status of regional lymph nodes confirmed independent prognostic value of RhoA immunoreactivity. In summary, we found associations between RhoA expression and histopathological phenotype of primary tumors as well as patient survival which suggest a suppressive role of RhoA in skin melanoma.

Overexpression of CDCA8 promotes the malignant progression of cutaneous melanoma and leads to poor prognosis

Cutaneous melanoma is very aggressive and results in high mortality rates for cancer patients. Determining molecular targets is important for developing novel therapies for cutaneous melanoma. Cell division cycle associated 8 (CDCA8) is a putative oncogene that is upregulated in multiple types of cancer. The present study aimed to examine the role of CDCA8 in cutaneous melanoma, with a focus on the association of its expression to prognosis and metastasis. First, the mRNA expression of CDCA8 in cutaneous melanoma tissues was investigated using the ONCOMINE and Gene Expression Omnibus (GEO) databases. Furthermore, the relationship between the expression of CDCA8 and cutaneous melanoma patient survival was analyzed using a Kaplan‑Meier plot and Log Rank test. In addition, the effects of CDCA8 on proliferation, migration and invasion of cutaneous melanoma cell lines were investigated using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), Cell Counting kit‑8, colony formation assay, wound healing and Matrigel assay. Finally, the expression levels of key proteins related to the Rho‑associated coiled‑coil‑containing protein kinase (ROCK) signaling pathway were measured by western blot assay. The results demonstrated that CDCA8 was overexpressed in cutaneous melanoma tissues and cells lines compared with normal tissues, and high expression of CDCA8 was significantly associated with poorer prognosis in patients with cutaneous melanoma. In in vitro experiments, CDCA8 knockdown inhibited A375 and MV3 cell proliferation, migration and invasion. In addition, CDCA8 knockdown reduced the phosphorylation levels of ROCK1 and myosin light chain, two downstream effector proteins of the ROCK pathway. In summary, the present findings suggested that CDCA8 may be a promising therapeutic target for the treatment of cutaneous melanoma.

Expression of Rho GTPases family in melanoma cells and its influence on cytoskeleton and migration

Rho GTPases family members influenced the filopodia, lamellipodia, stress fiber and adhesion plaque of melanoma cells through regulating cytoskeleton recombination. The role of Rho GTPases family in the migration and invasion of melanoma and its molecular mechanism were explored. The morphological difference between three types of melanoma cells (M14, A375 and MV3) and human melanocyte (MC) was observed by the Hoffman microscope. Cells were stained by phalloidin labeled by rhodamine. The differences between 4 types of cells in filopodia, lamellipodia, stress fiber and adhesion plaque (microfilament is the main constituent) were observed under the super-high resolution microscope. The migration ability of 4 types of cells was detected by Transwell migration assay. QPCR was used to detect the mRNA transcription level of Rho GTPases family. WB was adopted to detect the expression of RhoD and DIAPH2 proteins. There were significant differences in filopodia, lamellipodia, stress fiber and adhesion plaque between MC and 3 types of melanoma cells (M14, A375 and MV3). MC did not have stress fiber or adhesion plaque, while M14, A375 and MV3 had stress fiber and adhesion plaque. All 4 types of cells had thin and short filopodia. MV3 had fewer but thicker stress fibers than the latter two. Transwell migration test indicated the followings: M14 and A375 had a similar high migration rate; the migration rate of MV3 was slightly low; MC did not have the ability of transmembrane migration. QPCR results of Rho GTPases family in 4 types of cells showed the change corresponding to immunofluorescence. WB results showed that RhoD was barely expressed in M14, A375 or MV3. DIAPH2, the downstream effector molecule of RhoD, had the corresponding change. Rho GTPases influences the migration and invasion of melanoma cells through regulating filopodia, lamellipodia, stress fiber and adhesion plaque (microfilament is the main constituent).

Regulatory properties of statins and rho gtpases prenylation inhibitiors to stimulate melanoma immunogenicity and promote anti-melanoma immune response

Melanoma is a highly lethal cutaneous tumor, killing affected patients through development of multiple poorly immunogenic metastases. Suboptimal activation of immune system by melanoma cells is often due to molecular modifications occurring during tumor progression that prevent efficient recognition of melanoma cells by immune effectors. Statins are HMG-CoA reductase inhibitors, which block the mevalonate synthesis pathway, used by millions of people as hypocholesterolemic agents in cardiovascular and cerebrovascular diseases. They are also known to inhibit Rho GTPase activation and Rho dependent signaling pathways. Rho GTPases are regarded as molecular switches that regulate a wide spectrum of cellular functions and their dysfunction has been characterized in various oncogenic process notably in melanoma progression. Moreover, these molecules can modulate the immune response. Since 10 years we have demonstrated that Statins and other Rho GTPases inhibitors are critical regulators of molecules involved in adaptive and innate anti-melanoma immune response. In this review we summarize our major observations demonstrating that these pharmacological agents stimulate melanoma immunogenicity and suggest a potential use of these molecules to promote anti-melanoma immune response.