Mechanisms of Resistance to BRAF-Targeted Melanoma Therapies

Skin-Resident γδ T Cells Mediate Potent and Selective Antitumor Cytotoxicity through Directed Chemotactic Migration and Mobilization of Cytotoxic Granules

Dendritic epidermal T cells (DETCs) are a unique subset of γδ T cells that reside predominantly in mouse epidermis; yet, their antitumor functions remain enigmatic. In this study, we report that DETCs mediate potent and exquisitely selective cytotoxicity against diverse tumor types while sparing healthy cells. In vitro, DETCs induced apoptosis in melanoma, hepatoma, colon carcinoma, and lymphoma lines in a dose- and time-dependent manner that required direct cell-cell contact. In vivo, adoptive DETC transfer significantly suppressed melanoma growth and metastasis while prolonging survival. Mechanistically, DETCs upregulated perforin/granzyme B expression upon tumor recognition, and inhibition of this pathway ablated cytotoxicity. DETCs selectively homed to and formed intimate contacts with tumor cells in vivo through directed chemotaxis and aggregation. Tumor engagement triggered proinflammatory DETC activation while dampening immunosuppressive factors in the microenvironment. Notably, mTOR signaling coupled tumor recognition to DETC trafficking, cytotoxicity, and inflammatory programs because rapamycin treatment impaired effector functions and therapeutic efficacy. Collectively, these findings establish DETCs as multidimensional antitumor effectors and provide insights for harnessing their unique biology for cancer immunotherapy.

BRAF-Mutated Melanoma Cell Lines Develop Distinct Molecular Signatures After Prolonged Exposure to AZ628 or Dabrafenib: Potential Benefits of the Antiretroviral Treatments Cabotegravir or Doravirine on BRAF-Inhibitor-Resistant Cells

Melanoma is an aggressive cancer characterized by rapid growth, early metastasis, and poor prognosis, with resistance to current therapies being a significant issue. BRAF mutations drive uncontrolled cell division by activating the MAPK pathway. In this study, A375 and FO-1, BRAF-mutated melanoma cell lines, were treated for 4-5 months with RAF inhibitor dabrafenib or AZ628, leading to drug resistance over time. The resistant cells showed altered molecular signatures, with differences in cell cycle regulation and the propensity of cell death. Dabrafenib-resistant cells maintained high proliferative activity, while AZ628-resistant cells, especially A375 cells, exhibited slow-cycling, and a senescent-like phenotype with high susceptibility to ferroptosis, a form of cell death driven by iron. Antiretroviral drugs doravirine and cabotegravir, known for their effects on human endogenous retroviruses, were tested for their impact on these resistant melanoma cells. Both drugs reduced cell viability and colony formation in resistant cell lines. Doravirine was particularly effective in reactivating apoptosis and reducing cell growth in highly proliferative resistant cells by increasing tumor-suppressor proteins p16Ink4a and p27Kip1. These findings suggest that antiretroviral drugs can influence apoptosis and cell proliferation in RAF-inhibitor-resistant melanoma cells, offering potential therapeutic strategies for overcoming drug resistance.

Tumor Microenvironment as a Therapeutic Target in Melanoma Treatment

The role of the tumor microenvironment in tumor growth and therapy has recently attracted more attention in research and drug development. The ability of the microenvironment to trigger tumor maintenance, progression, and resistance is the main cause for treatment failure and tumor relapse. Accumulated evidence indicates that the maintenance and progression of tumor cells is determined by components of the microenvironment, which include stromal cells (endothelial cells, fibroblasts, mesenchymal stem cells, and immune cells), extracellular matrix (ECM), and soluble molecules (chemokines, cytokines, growth factors, and extracellular vesicles). As a solid tumor, melanoma is not only a tumor mass of monolithic tumor cells, but it also contains supporting stroma, ECM, and soluble molecules. Melanoma cells are continuously in interaction with the components of the microenvironment. In the present review, we focus on the role of the tumor microenvironment components in the modulation of tumor progression and treatment resistance as well as the impact of the tumor microenvironment as a therapeutic target in melanoma.

The Crucial Roles and Research Advances of cGAS-STING Pathway in Cutaneous Disorders

The cGAS-STING signaling pathway senses the presence of cytosolic DNA, induces strong type I interferon responses, and enhances inflammatory cytokine production, placing it as an important axis in infection, autoimmunity, and tumor immunity. Recent studies have shown that the abnormalities and/or dysfunctions of cGAS-STING signaling are closely related to the pathogenesis of skin diseases and/or cancers. Additionally, a variety of new therapeutics targeting the cGAS-STING signaling are in development for the treatment of skin disorders. However, the precise molecular mechanisms of cGAS-STING-mediated cutaneous disorders have not been fully elucidated. In this review, we will summarize the regulatory roles and mechanisms of cGAS-STING signaling in skin disorders and recent progresses of cGAS-STING-related drugs as well as their potential clinical applications.

Focal adhesion alterations in G0 ‐positive melanoma cells

BACKGROUND

Melanoma is a highly heterogeneous malignant tumor that exhibits various forms of drug resistance. Recently, reversal transition of cancer cells to the G₀ phase of the cell cycle under the influence of therapeutic drugs has been identified as an event associated with tumor dissemination. In the present study, we investigated the ability of chemotherapeutic agent dacarbazine to induce a transition of melanoma cells to the G₀ phase as a mechanism of chemoresistance.

METHODS

We used the flow cytometry to analyze cell distribution within cell cycle phases after dacarbazine treatment as well as to identifyG₀ -positive cells population. Transcriptome profiling was provided to determine genes associated with dacarbazine resistance. We evaluated the activity of β-galactosidase in cells treated with dacarbazine by substrate hydrolysis. Cell adhesion strength was measured by centrifugal assay application with subsequent staining of adhesive cells with Ki-67 monoclonal antibodies. Ability of melanoma cells to metabolize dacarbazine was determined by expressional analysis of CYP1A1, CYP1A2, CYP2E1 followed by CYP1A1 protein level evaluation by the ELISA method.

RESULTS

The present study determined that dacarbazine treatment of melanoma cells could induce an increase in the percentage of cells in G₀ phase without alterations of β-galactosidase positive cells which corresponded to the fraction of the senescent cells. Transcriptomic profiling of cells under dacarbazine induction of G₀ -positive cells percentage revealed that 'VEGFA-VEGFR2 signaling pathway' and 'Cell cycle' signaling were mostly enriched by dysregulated genes. 'Focal adhesion' signaling was also found to be triggered by dacarbazine. In melanoma cells treated with dacarbazine, an increase in G₀ -positive cells among adherent cells was found.

CONCLUSIONS

Dacarbazine induces the alteration in a percentage of melanoma cells residing in G₀ phase of a cell cycle. The altered adhesive phenotype of cancer cells under transition in the G₀ phase may refer to a specific intercellular communication pattern of quiescent/senescent cancer cells.

BRAF V600E Immunohistochemistry Predicts Prognosis of Patients with Cutaneous Melanoma in Thai population

The BRAF V600E mutation in the Thai population has been identified in a considerable percentage of people with cutaneous melanoma. The objectives of this study were to determine the prevalence of this mutation in cutaneous melanomas, conduct a clinicopathological association analysis with the BRAF V600E mutation, and develop a treatment strategy for patients with this mutation that would take advantage of the medications currently available to treat them.

METHODS

Anti-BRAF V600E (clone VE1) immunohistochemistry was performed on 50 pathological samples of cutaneous melanoma after excluding the samples with a low amount of pathologic tissue, a lack of clinical data' and poor follow-up. BRAF V600E expression DNA sequencing was performed to confirm the results of several cases.

RESULTS

Anti-BRAF V600E antibody positivity was noted in 56% (28/50) of cutaneous melanoma cases. DNA sequencing results were consistent with immunohistochemistry results. In cutaneous melanoma, the BRAF V600E mutation was significantly associated with adverse prognosis of patients, including reduced overall survival and disease-free survival.

CONCLUSIONS

An increased prevalence of the BRAF V600E mutation was determined in a collection of cutaneous melanomas in the Thai population, implying that BRAF-targeted therapy may be a promising strategy for patients with BRAF-mutated cutaneous melanoma. This study revealed an association between the clinicopathological aspects of cutaneous melanoma and overall survival, disease-free survival, and overall mortality. A treatment with anti-BRAF-targeted therapy, which incorporates the already available medications' is being researched and developed.

Molecular mechanisms underlying the resistance of BRAF V600E-mutant metastatic colorectal cancer to EGFR/BRAF inhibitors

Background

Combinatorial inhibition of epidermal growth factor receptor (EGFR) and BRAF shows remarkable clinical benefits in patients with BRAF V600E-mutant metastatic colorectal cancer (mCRC). However, the tumor may inevitably develop resistance to the targeted therapy, thereby limiting the response rate and durability. This study aimed to determine the genetic alterations associated with intrinsic and acquired resistance to EGFR/BRAF inhibitors in BRAF V600E-mutant mCRC.

Methods

Targeted sequencing of 520 cancer-related genes was performed in tumor tissues and in plasma samples collected from patients with BRAF V600E-mutant mCRC, who were treated with EGFR/BRAF ± MEK inhibitors, before and after the targeted treatment. Clinical benefit was defined as an objective response or a stable disease lasting longer than the median progression-free survival (PFS).

Results

In all, 25 patients with BRAF V600E-mutant mCRC were included in this study. Those with RNF43 mutations (n = 8) were more likely to achieve clinical benefit from EGFR/BRAF inhibitors than those with wild-type RNF43 (87.5% versus 37.5%, p = 0.034). Genetic alterations in receptor tyrosine kinase genes (n = 6) were associated with worse PFS (p = 0.005). Among the 23 patients whose disease progressed after the EGFR/BRAF-targeted therapy, at least one acquired resistance-related mutation was detected in 12 patients. Acquired mutations were most frequently observed in the mitogen-activated protein kinase pathway-related genes (n = 9), including KRAS (G12D and Q61H/R), NRAS (Q61L/R/K and amplification), BRAF (amplification), and MEK1 (K57T). MET amplification and PIK3R1 Q579fs mutation emerged in three patients and one patient, respectively, after disease progression.

Conclusion

Multiple genetic alterations are associated with clinical benefits and resistance to EGFR/BRAF inhibitors in BRAF V600E-mutant mCRC. Our findings provide novel insights into strategies for overcoming resistance to EGFR/BRAF inhibitors in patients with BRAF V600E-mutant mCRC.

Novel natural inhibitors targeting B-RAF(V600E) by computational study

The aim of this research was to screen the ZINC15 database to select lead compounds and drug candidates which can inhibit B-RAF (V600E). In order to identify drugs potentially inhibited B-RAF (V600E), numerous modules of Discovery Studio 4.5 were employed. Structure-based screening using LibDock was carried out followed by ADME (absorption, distribution, metabolism, excretion) and toxicity prediction. CDOCKER was performed to demonstrate the binding affinity and mechanism between ligands and B-RAF(V600E). To evaluate whether ligand-receptor complexes were stable, molecular dynamics were employed. Two novel natural compounds (ZINC000100168592 and ZINC000049784088) from ZINC15 database were found binding to B-RAF(V600E) with more favorable interaction energy in comparison with the reference drug Vemurafenib. Also, they were predicted with less ames mutagenicity, rodent carcinogenicity, non-developmental toxic potential and tolerance to cytochrome P450 2D6 (CYP2D6). The molecular dynamics simulation analysis indicated that the compound-B-RAF(V600E) complexes had more favorable potential energy compared with Vemurafenib and they can exist in natural environments stably. The result of this study shows that ZINC000100168592 and ZINC000049784088 are ideal leading potential compounds to inhibit B-RAF(V600E). The findings of this study and these selected drug candidates greatly contributed to the medication design and improvement of B-RAF(V600E) and other proteins.

Resistance to Targeted Therapy and RASSF1A Loss in Melanoma: What Are We Missing?

Melanoma is one of the most aggressive forms of skin cancer and is therapeutically challenging, considering its high mutation rate. Following the development of therapies to target BRAF, the most frequently found mutation in melanoma, promising therapeutic responses were observed. While mono- and combination therapies to target the MAPK cascade did induce a therapeutic response in BRAF-mutated melanomas, the development of resistance to MAPK-targeted therapies remains a challenge for a high proportion of patients. Resistance mechanisms are varied and can be categorised as intrinsic, acquired, and adaptive. RASSF1A is a tumour suppressor that plays an integral role in the maintenance of cellular homeostasis as a central signalling hub. RASSF1A tumour suppressor activity is commonly lost in melanoma, mainly by aberrant promoter hypermethylation. RASSF1A loss could be associated with several mechanisms of resistance to MAPK inhibition considering that most of the signalling pathways that RASSF1A controls are found to be altered targeted therapy resistant melanomas. Herein, we discuss resistance mechanisms in detail and the potential role for RASSF1A reactivation to re-sensitise BRAF mutant melanomas to therapy.