Targeting mammalian target of rapamycin to both downregulate and disable the P-glycoprotein pump in...

Area of Science:

• Oncology
• Pharmacology
• Molecular Biology

Background:

• Rapamycin inhibits human tumor cell growth in vitro.
• Rapamycin can reverse multidrug resistance (MDR) in certain cancer cells.
• The effect of rapamycin on P-glycoprotein (P-gp), a key mediator of MDR, is not well understood.

Purpose of the Study:

• To investigate the effect of rapamycin on P-gp function and the MDR phenotype in human tumor cell lines.
• To determine if rapamycin can chemosensitize MDR cells in vivo.
• To confirm rapamycin's modulation of the mammalian target of rapamycin (mTOR) pathway.

Main Methods:

• Treatment of four human tumor cell lines with rapamycin.
• Assessment of P-gp expression and function.
• In vivo xenograft studies in SCID mice.
• Analysis of mTOR pathway components (mTOR, S6K1, 4E-BP1) via Western blotting.

Main Results:

• Rapamycin inhibited the growth of three cell lines in vitro and one xenografted tumor in vivo.
• Rapamycin modulated both the expression and function of P-gp.
• Rapamycin effectively suppressed the phosphorylation of S6K1 and 4E-BP1, confirming mTOR pathway inhibition.
• Rapamycin chemosensitized three cell lines as effectively as verapamil.

Conclusions:

• Rapamycin demonstrates significant anti-tumor activity both in vitro and in vivo.
• Rapamycin effectively overcomes chemoresistance by modulating P-gp expression and function.
• Rapamycin's mechanism involves the inhibition of the mTOR pathway, leading to chemosensitization.