Plitidepsin cellular binding and Rac1/JNK pathway activation depend on membrane cholesterol content

Area of Science:

• Pharmacology
• Molecular Biology
• Cancer Research

Background:

• Plitidepsin is a marine cyclic depsipeptide in clinical development for cancer treatment.
• It potently induces apoptosis through sustained activation of Jun N-terminal kinase (JNK).
• This activation is linked to oxidative stress, Rac1 small GTPase activation, and MKP-1 phosphatase down-regulation.

Purpose of the Study:

• To investigate the mechanism of plitidepsin-induced apoptosis.
• To identify the role of membrane cholesterol and Rac1 in plitidepsin's action.
• To characterize plitidepsin binding to cancer cells.

Main Methods:

• Scatchard and saturation binding analyses to determine plitidepsin receptor affinity.
• Cellular binding assays at different temperatures.
• Methyl-beta-cyclodextrin treatment to deplete plasma membrane cholesterol.
• Subcellular fractionation and immunofluorescence microscopy to track Rac1 localization.
• Analysis of plitidepsin-resistant HeLa cells (HeLa-R).

Main Results:

• Plitidepsin binds to a high-affinity receptor in MDA-MB-231 breast cancer cells (Kd of ~40 nM).
• Drug uptake and apoptosis induction are temperature-dependent, suggesting membrane initiation.
• Depletion of membrane cholesterol with methyl-beta-cyclodextrin inhibits plitidepsin binding and Rac1-JNK activation.
• Plitidepsin targets Rac1 to the plasma membrane, an effect blocked by cholesterol depletion.
• HeLa-R cells exhibit reduced cholesterol, lower membrane-bound Rac1, and lack Rac1 activation, confirming cholesterol dependence.

Conclusions:

• Plitidepsin's cellular uptake and apoptosis induction are critically dependent on plasma membrane cholesterol.
• The Rac1-JNK pathway activation by plitidepsin is initiated at the cell membrane and requires cholesterol.
• These findings highlight a novel cholesterol-dependent mechanism for a marine anticancer drug.