Inhibition of p90 ribosomal S6 kinases disrupts melanoma cell growth and immune evasion

Abstract

Background The mitogen-activated protein kinase (MAPK) signaling pathway is frequently hyperactivated in malignant melanoma and its inhibition has proved to be an efficient treatment option for cases harboring BRAFV600 mutations (BRAFMut). However, there is still a significant need for effective targeted therapies for patients with other melanoma subgroups characterized by constitutive MAPK activation, such as tumors with NRAS or NF-1 alterations (NRASMut, NF-1LOF), as well as for patients with MAPK pathway inhibitor-resistant BRAFMut melanomas, which commonly exhibit a reactivation of this pathway. p90 ribosomal S6 kinases (RSKs) represent central effectors of MAPK signaling, regulating cell cycle progression and survival. Methods RSK activity and the functional effects of its inhibition by specific small molecule inhibitors were investigated in established melanoma cell lines and patient-derived short-term cultures from different MAPK pathway-hyperactivated genomic subgroups (NRASMut, BRAFMut, NF-1LOF). Real-time qPCR, immunoblots and flow cytometric cell surface staining were used to explore the molecular changes following RSK inhibition. The effect on melanoma cell growth was evaluated by various two- and three-dimensional in vitro assays as well as with melanoma xenograft mouse models. Co-cultures with gp100- or Melan-A-specific cytotoxic T cells were used to assess immunogenicity of melanoma cells and associated T-cell responses. Results In line with elevated activity of the MAPK/RSK signaling axis, growth and survival of not only BRAFMut but also NRASMut and NF-1LOF melanoma cells were significantly impaired by RSK inhibitors. Intriguingly, RSK inhibition was particularly effective in three-dimensional growth settings with long-term chronic drug exposure and suppressed tumor cell growth of in vivo melanoma models. Additionally, our study revealed that RSK inhibition simultaneously promoted differentiation and immunogenicity of the tumor cells leading to enhanced T-cell activation and melanoma cell killing. Conclusions Collectively, RSK inhibitors exhibited both multi-layered anti-tumor efficacy and broad applicability across different genomic melanoma subgroups. RSK inhibition may therefore represent a promising novel therapeutic strategy for malignant melanoma with hyperactivated MAPK signaling.

Phytochemical composition, antioxidant and cytotoxicity of the aqueous extracts of Dracaena arborea andBridelia ferruginea: in vitro and in silico studies.

“…Molecular docking results of selected compounds docked against PARP10 and p90 RSK PARP10 is involved in various aspects of cell function and its activity is associated to cell survival [71] and DNA repairing [72]. p90 RSK is a member of RSK family involved in the regulation of various cellular and metabolic processes, including cell growth [73,74], cell signaling [75], cellular homeostasis [76] and DNA repair [77]. To predict the cytotoxicity of selected compounds from D. arborea and B. ferruginea, molecular docking on PARP10 and p90 RSK proteins was performed.…”

Therapeutic targeting of p90 ribosomal S6 kinase

“…The on target action of PMD-026 was not reported in these xenograft studies. PMD-026 has also been shown to inhibit the proliferation in vitro and in vivo of melanoma lines with MAPK hyperactivation ( Kosnopfel et al, 2023 ). The phosphorylation of YB-1 was used as a biomarker to show on target inhibition of RSK by PMD-026 ( Figure 2 and Supplementary Table S1 ).…”

“…Importantly, RSK is being recognized as an important drug target in oncology and in support of this statement a RSK inhibitor, PMD-026, is in a phase 1/1b clinical trial. PMD-026 is reported to have a good safety profile in patients in contrast to MEK1/2 and ERK1/2 inhibitors ( Kosnopfel et al, 2023 ). Results from the dose escalation portion of the trial found that PMD-026 extended progression free survival in heavily pre-treated patients with metastatic breast cancer ( Beeram et al, 2021 ).…”

“…Although the ability to generate RSK4 knockout mice seems counterintuitive to the data suggesting that RSK4 inhibits receptor tyrosine kinase signaling in extraembryonic tissue ( Myers et al, 2004 ). RSK also regulates differentiation in the mammary gland ( Pasic et al, 2011 ), melanocytes ( Kosnopfel et al, 2023 ) and osteoblasts ( Yang et al, 2004 ). In summary, these results show that, although the RSK family regulates aspects of homeostasis based on the defects observed by knockout or mutation, targeting RSK in disease states is a reasonable strategy as RSK1/2/3 knockout mice are viable ( Laugel-Haushalter et al, 2014 ).…”

Mitochondrial Signatures Shape Phenotype Switching and Apoptosis in Response to PLK1 and RSK Inhibitors in Melanoma

“…RSK1/2 were also shown to mediate resistance to chemotherapy and BRAF inhibition 7,10 . Recent reports have proposed that RSK1/2 are potential therapeutic target in melanoma with constitutive MAPK activation to overcome the resistance to BRAF and MEK inhibitors 11,12 . Despite the importance of these findings and the identification of new drug candidates, it is crucial to consider the selectivity of RSK inhibitors since some off-target effects may contribute to the observed anti-tumoral activity.…”