Targeting chemosensitizing doses of toremifene based on protein binding

Area of Science:

• Pharmacology
• Oncology
• Biochemistry

Background:

• Toremifene is investigated as a chemosensitizer for doxorubicin-resistant cancers.
• In vitro studies show toremifene reverses multidrug resistance (MDR) at concentrations above 2 microM.
• Serum protein binding may significantly impact in vivo efficacy by reducing effective drug concentrations.

Purpose of the Study:

• To investigate the impact of high serum concentrations on toremifene cellular accumulation.
• To determine the effect of toremifene on doxorubicin accumulation in varying serum concentrations.
• To measure plasma concentrations of toremifene and its metabolites in patients.

Main Methods:

• Assessed toremifene accumulation in an MDR MDA-MB-A-1 breast cancer cell line under high serum conditions.
• Measured doxorubicin cellular accumulation at different toremifene concentrations and serum levels (5%-100%).
• Quantified toremifene and metabolite plasma levels in two patients receiving 360 mg/day for 5 days.

Main Results:

• High serum concentrations significantly decreased toremifene cellular accumulation.
• Toremifene concentrations up to 2.5 microM enhanced doxorubicin accumulation.
• Achieved plasma toremifene concentrations of 10-15 microM in patients after a 5-day treatment course.

Conclusions:

• In vitro effective concentrations of toremifene may be insufficient in vivo due to serum protein binding.
• Higher plasma toremifene concentrations are necessary to overcome serum binding effects and reverse MDR in patients.
• Clinical dosing strategies should account for serum protein binding to ensure adequate therapeutic levels.