Yes Associated Protein 1 (YAP) and Transcriptional coactivator with PDZ-Binding Motif (TAZ) have gained notoriety for their ability to drive tumor initiation and progression in a wide variety of cancers, including melanoma. YAP and TAZ act as drivers of melanoma through its interaction with the TEAD family of transcription factors. Verteporfin is a benzoporphyrin derivative that is used clinically for photodynamic treatment of macular degeneration. Recently it has emerged as a potential inhibitor of YAP/TAZ-TEAD interaction independent of light activation. In this study we determine if verteporfin has clinical potential by testing this compound on human melanoma cell cultures and in a clinically significant mouse model, Braf^CA; Tyr-CreERT2; Pten^f/f, which parallels human melanoma in terms of disease progression, genetics, and histopathology. In culture, Verteporfin treatment induces a rapid drop in YAP and TAZ protein levels and cell numbers. In the transgenic model, utilizing drug levels that correspond to previously determined safe doses in human patients and with a dosing regimen calculated in this study, Verteporfin did not inhibit melanoma initiation or progression in comparison to mock treated controls. Taken together, our study suggests that although Verteporfin induces YAP/TAZ degradation in melanoma cell lines, Verteporfin was not effective as a YAP/TAZ-TEAD specific inhibitor of melanoma in our studies that aimed to mimic conditions found in clinic in terms of treatment regimen and disease model.

The failure of once promising target-specific therapeutic strategies often arises from redundancies in gene expression pathways. Even with new melanoma treatments, many patients are not responsive or develop resistance, leading to disease progression in terms of growth and metastasis. We previously discovered that the transcription factors ETS1 and PAX3 drive melanoma growth and metastasis by promoting the expression of the MET receptor. Here, we find that there are multiple ETS family members expressed in melanoma and that these factors have redundant functions. The small molecule YK-4-279, initially developed to target the ETS gene–containing translocation product EWS-FLI1, significantly inhibited cellular growth, invasion, and ETS factor function in melanoma cell lines and a clinically relevant transgenic mouse model, BrafCA;Tyr-CreERT2;Ptenf/f. One of the antitumor effects of YK-4-279 in melanoma is achieved via interference of multiple ETS family members with PAX3 and the expression of the PAX3-ETS downstream gene MET. Expression of exogenous MET provided partial rescue of the effects of YK-4-279, further supporting that MET loss is a significant contributor to the antitumor effects of the drug. This is the first study identifying multiple overlapping functions of the ETS family promoting melanoma. In addition, targeting all factors, rather than individual members, demonstrated impactful deleterious consequences in melanoma progression. Given that multiple ETS factors are known to have oncogenic functions in other malignancies, these findings have a high therapeutic impact. Significance: These findings identify YK-4-279 as a promising therapeutic agent against melanoma by targeting multiple ETS family members and blocking their ability to act as transcription factors.

More options are needed for the effective treatment of melanoma. In a previous study, we discovered the small molecule drug YK-4-279 almost completely inhibited tumor progression in the Braf^CA;Tyr-CreERT2;Pten^flox/flox transgenic mouse model. YK-4-279 had no effect on tumor initiation but blocked progression of invasive melanoma. Our current study was designed as a treatment model, where YK-4-279 was administered during pigmented lesion formation. The study design included the use of three groups: (1) a control group that received only DMSO without a drug (MOCK), (2) mice following our prior studies with YK-4-279 administered at the time of tumor induction (YK-4-279), and (3) mice treated during tumor initiation (YK-4-279 delay). While the MOCK mice had progression of tumors, both YK-4-279 and YK-4-279 delay groups had a significant block or delay of progression. The majority of mice in the YK-4-279 groups had a block of progression, while the YK-4-279 delay group had either a partial block (60% in male mice or 29% in females) or a delay in disease progression in females (28 days in controls to 50 days in YK-4-279 delay group). Here, we demonstrate that YK-4-279 has a significant impact on blocking or delaying tumor progression in a pre-clinical treatment model of melanoma.

Background/Objectives: PAX3 is a transcription factor that drives melanoma progression by promoting cell growth, migration, and survival, while inhibiting cellular terminal differentiation. However, known PAX3 target genes are limited and cannot fully explain the wide impact of PAX3 function. The PAX3 protein can regulate DNA through two separate binding domains, the Paired Domain (PD) and Homeodomain (HD), which bind different DNA motifs. It is not clear if these two domains bind and work together to regulate genes and if they promote all or only a subset of downstream cellular events. Methods: PAX3 direct downstream targets were identified using Cleavage Under Targets & Release Using Nuclease (CUT&RUN) assays in SK-MEL-5 melanoma cells. PAX3-binding genomic regions were identified through MACS2 peak calling, and peaks were categorized based on the presence of PD and/or HD binding sites (or neither) through HOMER motif analysis. The peaks were further characterized as Active, Primed, Poised, Repressed, or Closed based on ATAC-seq data and CUT&RUN for histone Post-Translational Modifications H3K4me1, H3K4me3, H3K27me3, and H3K27Ac. Results: This analysis revealed that most of the PAX3 binding sites in the SK-MEL-5 cell line were primarily through the PD and connected to Active genes. Surprisingly, PAX3 does not commonly act as a repressor in SK-MEL-5 cells. Pathway analysis identified genes involved with transcription, RNA modification, and cell growth. Peaks located in distal enhancer elements were connected to genes involved in neuronal growth, function, and signaling. Conclusions: Our results reveal novel PAX3 regulatory regions and putative genes in a melanoma cell line, with a predominance of PAX3 PD binding on active sites.