Investigators Discover New Therapeutic Target for High-Grade Serous Ovarian Cancer

James S. Duncan, PhD

James S. Duncan, PhD

Researchers at the Fox Chase Center have identified MRCKA, a serine/threonine-protein kinase, as a target for treating high-grade serous ovarian carcinoma (HGSOC), the most lethal of gynecologic malignancies, for which few targeted therapies exist. The research was recently published inScience Signaling, Fox Chase announced in a press release.¹

In the study, MRCKA was found to be an essential driver for signaling that regulated the cell cycle checkpoint, focal adhesion, and actin remodeling. MRCKA was also integral for cell migration and proliferation, and survival.²

By mapping the kinome landscape of HGSOC using multiplexed inhibitor beads and mass spectrometry (MIB-MS), Kurimchak et al found a shared kinome signature. Several of the HGSOC primary and patient-derived xenograft (PDX) tumors grouped together, showing similar MIB-MS kinome profiles. In a volcano plot comparison, these primary and PDX tumor profiles showed different kinase levels, depending on tumor type, which included elevated levels of myosin light chain kinase, (MYLK), protein kinase D1 (PRKD1), and protein kinase G1 (PKG1) in primary tumors and increased p21-activated kinase 4 (PAK4) and hepatocyte growth factor receptor (MET) levels in the PDX tumors. In primary tumors, the stromal-related functions were consistent with previous studies, which showed gene upregulation. In PDX tumors, the genes were stromal specific.

The main goal of this analysis was to determine if any of the unknown kinases were highly expressed in HGSOC tumors.¹A reproducible difference in expression was indeed found. Some of the kinases were established driver kinases of HGSOC, whereas others had no established function in this cancer type. There were a few kinases that demonstrated 2-fold expression in HGSOC tumors compared with s-SILAC tumors, a fact from which the investigators concluded that the kinases were ample in some HGSOC tumors.²

Among the kinases that were previously unexplored in HGSOC, cell growth was inhibited the most through knockdown of MRCKA. The response was similar to what had been observed with established kinases like checkpoint kinase 1 (CHEK1), a protein kinase 2 (PTK2 or FAK1), PAK4, and aurora kinase A (AURKA). Additionally, knockdown of eukaryotic translation initiation factor 2 alpha kinase 2 (EIF2AK2) inhibited the viability of OVCAR4 cells and established HGSOC targets. These findings signify that MRCKA may be fundamental to cell survival.

An analysis of real-world genomic records was conducted to characterize MRCKA expression in a larger population of patients with HGSOC. The investigators found that MRCKA knockdown increased the amounts of divided PARP in KURAMOCHI, OVSAHO, SNU119, OVCAR4, OVCAR3, JHOS-4, and OVCAR8 cells. MRCKA knockdown did not affect the amount of cleaved PARP in COV362, CAOV3, or JHOS-2 cells, and therefore demonstrated that MRCKA depletion induces apoptosis in 70% of ovarian cancer cells. However, MRCKA was found to have an emergent dependency in some HGSOC cell lines, based on an evaluation of 2 independent immortalized human FTSEC line in which MRCKA did not block cell viability more than 50% or induce apoptosis.

MRCKA knockdown reduced phosphorylation of MLC2 in HGSOC cells, as expected based on prior research. Additionally, the depletion of MRCKA inhibited the migration of COV362 cells, which supports the idea that MRCKA is an important mediating kinase in HGSOC cell migration. The investigators also observed that MRCKA knockdown was not indicated by the levels of phosphorylated MLC2, which suggests that the therapeutic target may have an additional function in HGSOC cells. In a proteomics analysis following the MRCKA knockdown, MRCKA depletion was found to dynamically reprogram kinase signaling in HGSOC cells.

Through other RNAi-based analyses, Kurimchak et al also found that genetic depletion of MRCKA impairs focal adhesion signaling and sensitizes HGSOC cell to carboplatin and PAK inhibitors, and induces apoptosis and block spheroid formation.

An evaluation of treatment with small molecule BDP9066 was the final step in the study. It was discovered that the drug had limited activity in MRCKA inhibition.

Overall, 324 kinases were evaluated with 206 kinases that quantified 70% of the tumors, and most of these therapeutic targets had never been used in HGSOC previously. Several assays were used throughout the study to assess how MRCKA knockdown impacts cell activity in HGSOC.

According to James S. Duncan, PhD, an assistant professor in the Cancer Biology Program at Fox Chase and co-author of the study, the identification of this new target may help address issues with resistance to chemotherapy and recurrent disease and signals what type of new targeted therapies should be developed for the treatment of patients with HGSOC.¹

“This means MRCKA shows strong therapeutic potential because it is involved in this kind of spheroid development, which is one of the key things driving resistance to a lot of drugs,” Duncan said. “Together, this opens the avenue that this kinase could be a very essential kinase for ovarian cancer therapy.”

References

1. Fox Chase Cancer Center. New drug target identified for high-grade serous ovarian cancer [news release]. Philadelphia, PA: Fox Chase Cancer Center; February 18, 2020. https://bit.ly/2Pntx7t. Accessed February 25, 2020.
2. Kurinchak, A, Herrera-Montavez C, Brown J, et al. Functional proteomics interrogation of the kinome identifies MRCKA as a therapeutic target in high-grade serous ovarian carcinoma.Sci. Signal.2020;13 (619), eaax8238. doi: 10.1126/scisignal.aax8238.