Interaction of Liposomal Formulations of Meta‐tetra(hydroxyphenyl)chlorin (Temoporfin) with Serum Proteins: Protein Binding and Liposome Destruction

Abstract

mTHPC is a non polar photosensitizer used in photodynamic therapy. To improve its solubility and pharmacokinetic properties, liposomes were proposed as drug carriers. Binding of liposomal mTHPC to serum proteins and stability of drug carriers in serum are of major importance for PDT efficacy; however, neither was reported before. We studied drug binding to human serum proteins using size-exclusion chromatography. Liposomes destruction in human serum was measured by nanoparticle tracking analysis (NTA). Inclusion of mTHPC into conventional (Foslip(®)) and PEGylated (Fospeg(®)) liposomes does not affect equilibrium serum protein binding compared with solvent-based mTHPC. At short incubation times the redistribution of mTHPC from Foslip(®) and Fospeg(®) proceeds by both drug release and liposomes destruction. At longer incubation times, the drug redistributes only by release. The release of mTHPC from PEGylated vesicles is delayed compared with conventional liposomes, alongside with greatly decreased liposomes destruction. Thus, for long-circulation times the pharmacokinetic behavior of Fospeg(®) could be influenced by a combination of protein- and liposome-bound drug. The study highlights the modes of interaction of photosensitizer-loaded nanovesicles in serum to predict optimal drug delivery and behavior in vivo in preclinical models, as well as the novel application of NTA to assess the destruction of liposomes.

Recent Trends in Multifunctional Liposomal Nanocarriers for Enhanced Tumor Targeting

“…The second approach is the incorporation of flexible hydrophilic moieties, mainly polyethylene glycol(PEG), since this component is approved for use by the United States Food and Drug Administration and is currently used in several approved formulations (Doxil, SPI-077, S-CDK602) [7, 10, 44, 46], but also polyvinyl pyrrolidones [8] or Poly[N-(2-hydroxypropyl)methacrylamide] [47]. The inclusion of flexible hydrophobic inert and biocompatible polyethylene glycol, (PEG) with a lipid anchor in liposome allows the formation of an hydrated steric barrier decreasing liposome interaction with blood-borne component, increasing their blood circulation time, decreasing their spleen and liver capture [48, 49], and their resistance to serum degradation [50]. This lack of recognition by the MPS and decreased elimination of PEGylated liposomes led to the term “stealth” liposomes to qualify them [44].…”

Photodynamic therapy with conventional and PEGylated liposomal formulations of mTHPC (temoporfin): comparison of treatment efficacy and distribution characteristics in vivo

“…23 Fospeg ® evidently provides monomerization of the released mTHPC plus the prolonged circulation of its liposomal form.…”

“…23 Blood was drawn from the mice and precipitated in Vacutainer ® SST TM II Advance tubes (BD Diagnostics) to obtain serum (pooled from five mice). Foslip ® and Fospeg ® (mTHPC concentration of 2.0 × 10 −5 M), and 20% filtered serum were incubated in phosphate buffered saline at 37°C for up to 24 hours.…”

Self-assembled liposomal nanoparticles in photodynamic therapy

“…Fospeg ® is another liposomal formulation of mTHPC which has been designed to improve the stability and prolong the half-life of mTHPC by coating with PEG – a synthetic hydrophilic polymer (64, 65), PEG incorporated forms a hydrated shell, which restricts the liposomes-proteins interaction in the plasma thereby reducing the uptake of liposomes by the reticuloendothelial system RES (31). The effects of density and thickness of PEG coating on in vitro cellular uptake, and dark- and phototoxicity of liposomal formulations (Fospeg) of the photodynamic agent m-THPC) was investigated (66).…”

“…With Fospeg ® the lowest concentration (0.22 µm) and fluence [180 mJ/cm 2 ] death of 50% of the cells 24 h post PDT was noted while with Foscan ® , an approximately 10 times higher concentration (1.8 µm) was required in order to achieve same level of cytotoxicity. In order to gain insight into the in vivo behavior of these formulations, a similar study by Reshetov et al compared Foslip ® and Fospeg ® in terms of liposomal stability and redistribution of mTHPC in human serum (65). Inclusion of mTHPC into conventional (Foslip ® ) and PEGylated (Fospeg ® ) liposomes showed no effect on equilibrium serum protein binding compared with solvent-based mTHPC.…”