PIK3CA-mutated melanoma cells rely on cooperative signaling through mTORC1/2 for sustained proliferation

Area of Science:

• Oncology
• Molecular Biology
• Cancer Signaling Pathways

Background:

• PI3'-lipid signaling promotes malignant transformation in BRAF- or NRAS-mutated melanocytes.
• The interplay between PI3'-lipid signaling and activated BRAF/NRAS in melanoma remains incompletely understood.

Purpose of the Study:

• To investigate the role of PI3'-lipid signaling in cell proliferation in melanoma cells with co-occurring PIK3CA mutations alongside BRAF or NRAS mutations.
• To explore the therapeutic potential of combined MEK1/2 and PI3K inhibition in PIK3CA-mutated melanoma.

Main Methods:

• Utilized human melanoma cell lines with NRAS/BRAF mutations and co-expressed PIK3CA mutations.
• Assessed sensitivity to PI3K inhibitors (broad-spectrum vs. α-selective).
• Evaluated combined pharmacological inhibition of MEK1/2 and PI3K signaling.
• Analyzed downstream signaling pathways including mTORC1, S6, 4E-BP1, and AKT phosphorylation.
• Tested efficacy in xenograft models of NRAS/PIK3CA-mutated melanoma.

Main Results:

• Melanoma cells with PIK3CA mutations showed greater sensitivity to broad-spectrum PI3K inhibitors than α-selective ones.
• Combined MEK1/2 and PI3K inhibition demonstrated superior antiproliferative effects and cell cycle arrest compared to single agents.
• Cooperative regulation of cell proliferation by MEK1/2 and PI3K pathways occurs via mTORC1-mediated effects on S6 and 4E-BP1 phosphorylation in an AKT-dependent manner.
• Combined MEK1/2 and PI3K inhibition led to significant melanoma regression in xenografts, unlike PI3K inhibition alone which caused cytostatic effects.

Conclusions:

• Mutationally activated PIK3CA cooperates with MEK1/2 signaling to sustain melanoma proliferation through mTORC1/2 regulation.
• Combined inhibition of MEK1/2 and PI3K signaling represents a potent therapeutic strategy for PIK3CA-mutated melanoma.