Nonionic pluronic triblock copolymers received considerable attention as modern drug delivery carriers. They have the general formula PEOx-PPOy-PEOx (for F127 x=100, y=65), and are composed of a hydrophobic poly(propylene oxide) (PPO) block and two units of a hydrophilic poly(ethylene oxide) (PEO) block. Their amphiphilic character results into surfactant properties, which include the ability to interact with hydrophobic surfaces and biological membranes. Above their critical micelle concentration (cmc), these copolymers self-assemble into micelles. Due to their unique core - shell structure, polymeric micelles such as F127 have the ability to solubilize hydrophobic drugs in the PPO core, thereby enhancing their solubility in water media. In addition they are suitable for drug delivery in medicine as they are non-toxic and stabilized to aggregation, protein adsorption and deactivation because of the presence of the PEO corona. The stability of the loaded pluronic micelles is however low due to their high cmc (~1 mM for F127) resulting in their disaggregation by dilution or interaction with the blood components. The mixture of pluronic micelles with other polymers/surfactants enhances the stability of the resulting micelles thus increasing the bioavailability of the encapsulated drugs. To this end, the loading efficiency of bile salt/pluronic coformulation toward the fluorescent anticancer antibiotic doxorubicin (DX) has been studied. DX is administered as chlorohydrate to enhance its solubility in water. This limits its solubilization to the corona region of the F127 micelles . To promote its solubility in the hydrophobic core of F127 micelles the coformulation with the cationic bile salt sodium cholate (NaC) will be used. By studying the fluorescence properties of DX, informations on the micropolarity of the environment surrounding the drug can be obtained.
The use of pluronic micellar carriers as drug delivery systems is very promising since some of them have already reached phase II/III clinical trials (SP1049C). However, the clinical use is at present limited to gastrointestinal cancer. Thus, the development of new pluronic carriers might open the way to further applications. Our system is a formulation different from those in use in the clinical trials. It is a catanionic mixture of the positively charged doxorubicin (DX) and a negatively charged bile salt, sodium cholate (NaC), that should drive the drug solubilization in the apolar inner compartment of pluronic F127 micelles. The screen provided by the pluronic/NaC mixed micelles should possibly slow down the degradation of the drug, thus enhancing its anticancer efficacy. These new systems could hopefully be used for different targets expanding the clinical applications. Moreover the use of pluronics has been suggested as a help to overcome multiple drug resistance (MDR) phenomena in antineoplastic therapy due to the ability to promote active membrane transport.