Tissue levels, histologic changes and plasma pharmacokinetics of meta-Tetra (hydroxyphenyl) chlorin (mTHPC) in the cat

Advanced in silico modeling explains pharmacokinetics and biodistribution of temoporfin nanocrystals in humans

Foscan®, a formulation comprising temoporfin dissolved in a mixture of ethanol and propylene glycol, has been approved in Europe for palliative photodynamic therapy of squamous cell carcinoma of the head and neck. During clinical and preclinical studies it was observed that considering the administration route, the drug presents a rather atypical plasma profile as plasma concentration peaks delayed. Possible explanations, as for example the formation of a drug depot or aggregation after intravenous administration, are discussed in current literature. In the present study an advanced in silico model was developed and evaluated for the detailed description of Foscan® pharmacokinetics. Therefore, in vitro release data obtained from experiments with the dispersion releaser technology investigating dissolution pressures of various release media on the drug as well as in vivo data obtained from a clinical study were included into the in silico models. Furthermore, precipitation experiments were performed in presence of biorelevant media and precipitates were analyzed by nanoparticle tracking analysis. Size analysis and particle fraction were also incorporated in this model and a sensitivity analysis was performed. An optimal description of the in vivo situation based on in vitro release and particle characterization data was achieved, as demonstrated by an absolute average fold error of 1.21. This in vitro-in vivo correlation provides an explanation for the pharmacokinetics of Foscan® in humans.

Optimal treatment opportunity for mTHPC-mediated photodynamic therapy of liver cancer

Photodynamic therapy (PDT) has been clinically used for liver cancer. The pharmacokinetics of a photosensitizer needs to be monitored so that PDT can be performed at the most favorable time and with the proper dose to increase the cure rate. As mTHPC is a fluorescent compound, we investigate its pharmacokinetics, distribution, and elimination in the rat orthotropic liver cancer model in order to confirm an optimal treatment opportunity of liver cancer PDT. After intravenous administration at a single dose of 300 μg/kg, mTHPC was extracted from tissue homogenates or plasma. Then, mTHPC concentrations were assessed by fluorescence spectroscopy and the data were processed with PK-GRAPH pharmacokinetic procedure. The plasma concentration-time profile of mTHPC showed a short distribution half-life (T½α = 0.082 h) and a relatively longer elimination half-life (T½β = 28.23 h), which quite fitted with a two-compartment model. The results of mTHPC tissue distributions showed that the highest drug accumulation was in tumor tissue, and successively decreased in liver, heart, spleen, muscle, and skin tissues. The drug distribution ratio of tumor to normal tissue reached the peak at 24 h after mTHPC administration. mTHPC was eliminated at a suitable rate in rat orthotropic liver cancer model, and there was no long-term accumulation of mTHPC in rat tissues. For PDT of orthotropic liver cancer, 24 h after mTHPC intravenous injection may be the optimal treatment time point, which might provide higher clinical efficacy and reduce side effects.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

The pharmacokinetic behavior of the photosensitizer meso-tetra-hydroxyphenyl-chlorin in mice and men

PURPOSE

Meso-tetra-hydroxyphenyl-chlorin (mTHPC) is a hydrophobic photosensitizer that binds to plasma lipoproteins after intravenous injection. In vitro experiments with human plasma have shown that mTHPC initially binds to an unknown protein and subsequently redistributes to lipoprotein fractions. It has been suggested that this might explain the unusual pharmacokinetic profile of mTHPC humans. In humans, unlike in rodents, reappearance of mTHPC has been reported, resulting in a second plasma peak after intravenous injection. However, previous studies analyzed only limited time points during the first 24 h after injection. Our aim was to determine the pharmacokinetics of mTHPC in detail, and to investigate whether the pharmacokinetic behavior of the drug is affected by binding of mTHPC to lipoproteins in vivo.

METHODS

Plasma of cancer patients and mice, intravenously injected with mTHPC, was analyzed for total drug content and drug distribution over the lipoprotein fractions.

RESULTS

Pharmacokinetic profiles of mTHPC in a group of human subjects showed that apparent steady state drug levels were maintained for at least 10 h. Closer examination of individual profiles showed that the initial (5 min) plasma drug levels were on average 86% of the maximal plasma concentration, which occurred at about 5 h after injection. In mice, however, plasma pharmacokinetics were described by a standard bi-exponential decline of the drug concentration. The majority (>58%) of mTHPC injected into both BALB/c nude mice and patients initially bound to the HDL plasma fraction. We extended our study to ApoE -/- mice, with highly elevated lipoprotein levels, and SR-BI -/- mice, which are lacking the main clearance pathway for HDL associated cholesteryl esters, to take into account the differences between lipoprotein levels and clearance in mice and man. Although mTHPC distribution over the lipoproteins changed in these mice, pharmacokinetic profiles of mTHPC remained the same.

CONCLUSIONS

We conclude that neither lipoprotein levels nor cholesterol metabolism affects the pharmacokinetics of mTHPC in plasma.

Pharmacokinetics of a tri-glucoconjugated 5,10,15-(meta)-trihydroxyphenyl-20-phenyl porphyrin photosensitizer for PDT. A single dose study in the rat

Photodynamic therapy (PDT) involves a non invasive treatment of small and superficial cancers using a photosensitive drug and light to kill tumoral cells. 5,10,15-meso-tri-(meta-O-beta-D-glucosyloxyphenyl)-20-phenylporphyrin [m-TPP(glu)3] is a new photosensitizer (PS) with more enhanced photocytotoxicity relative to 5,10,15,20-meso-tetra-(meta-hydroxyphenyl) chlorin [m-THPC] (Foscan). It was injected intravenously once to healthy rats at three different doses (0.25, 0.5 and 1 mg kg(-1)) and compared to m-THPC (0.3 mg kg(-1)). Pharmacokinetic parameters for both photosensitizers were derived from plasma concentration-time data using a non-compartmental analysis and a two-compartment pharmacokinetic model. m-TPP(glu)3 is more rapidly eliminated throughout the organism than m-THPC. Its mean plasma clearance is 19 mL h(-1) kg(-1) (6 mL h(-1) kg(-1) for m-THPC), and its mean residence time is 5h (20 h for m-THPC). The area under curve (AUC) and initial mean serum concentration (C0) were found to be proportional to the dose. As for Foscan, no metabolite of m-TPP(glu)3 was detected in plasma. The biodistribution study demonstrates that the most significant amount of m-TPP(glu)3 was concentrated in organs such as lung, liver and spleen which are rich in reticulo-endothelial cells. Maximum concentrations were reached in organs 14 h after IV administration. At 48 h, the photosensitizer was essentially eliminated from all organs. Because of its shorter elimination time, m-TPP(glu)3 is more attractive than m-THPC as a PDT agent since secondary side effects of shorter duration could be expected.

Optimizing Photodynamic Therapy: In vivo Pharmacokinetics of Liposomal meta-(Tetrahydroxyphenyl)Chlorin in Feline Squamous Cell Carcinoma

PURPOSE

The aim of the present study was to optimize and simplify photodynamic therapy using a new liposomal formulation of the photosensitizer meta-(tetrahydroxyphenyl)chlorin [m-THPC (Foscan); liposomal m-THPC (Fospeg)] and to reduce systemic reactions to the photosensitizer.

EXPERIMENTAL DESIGN

To examine the pharmacokinetics of liposomal m-THPC, we determined tissue and plasma variables in feline patients with spontaneous squamous cell carcinoma. In vivo fluorescence intensity measurements of tumor and skin were done with a fiber spectrophotometer after i.v. injection of m-THPC or liposomal m-THPC in 10 cats. Blood samples, drawn at several time points after photosensitizer administration, were analyzed by high-performance liquid chromatography.

RESULTS

None of the liposomal m-THPC-treated cats showed side effects during or after drug injection. Fluorescence intensities, fluorescence ratios (tumor fluorescence divided by skin fluorescence), and bioavailability in the tumor were 2 to 4 times higher with liposomal m-THPC compared with m-THPC. Liposomal m-THPC concentration in the tumor increased constantly to reach a maximum at 4 hours after injection. Plasma concentration and bioavailability were approximately 3 times higher with liposomal m-THPC compared with m-THPC measured at the time points of highest plasma concentration. The distribution half-life was shorter with liposomal m-THPC, resulting in maximal tumor accumulation up to 5.5 times earlier. Maximal tumor accumulation and maximal fluorescence ratio with liposomal m-THPC occurred at the same time point, indicating maximal selectivity. In both groups, all cats responded to therapy.

CONCLUSIONS

Liposomal m-THPC was well tolerated by all cats and seems to have superior pharmacokinetic properties compared with m-THPC. The efficacy of the drug warrants further study.

A study of the stability of tri(glucosyloxyphenyl)chlorin, a sensitizer for photodynamic therapy, in human colon tumoural cells: a liquid chromatography and MALDI-TOF mass spectrometry analysis

Asymmetrical glycoconjugated tetrapyrrolic macrocycles are under study as efficient sensitizers for photodynamic therapy (PDT). In this context, tri(meta-O-beta-glucopyranosyloxyphenyl)chlorin [TPC(m-O-Glu)(3)] 2a/3a was found to be four times more photoactive in vitro than Foscan. In a further study of this interesting glycoconjugate, its metabolism by cellular glycosidases in HT29 cells has to be explored. Cellular extracts of HT29 cells incubated with TPC(m-O-Glu)(3) (24h, 6microM) were analyzed by MALDI-TOF mass spectrometry and high performance liquid chromatography (HPLC). In MALDI-TOF mass spectra, the presence of compounds distinct from TPC(m-O-Glu)(3) (m/z 1151) were observed at m/z 989, 827 and 665 corresponding to the loss of one, two or three glucose units (162u) and were be ascribed to TPC(m-OH)(m-O-Glu)(2) 2/3b,b',b", TPC(m-OH)(2)(m-O-Glu) 2/3c,c',c" and TPC(m-OH)(3) isomers 2d/3d, respectively. The porphyrins resulting from chlorin oxidation TPP(m-O-Glu)(3) 4a, TPP(m-OH)(m-O-Glu)(2) 4b,b", TPP(m-OH)(2)(m-O-Glu) 4c,c" and TPP(m-OH)(3) 4d were also observed. The HPLC profile (lambda(anal)=420 nm) showed eight peaks consistent with mass spectra. The kinetics of deglucosylation was studied from HPLC profiles between 1 and 48h incubation. The concentration of triglucoconjugated and diglucoconjugated molecules was maximum around 3 and 8h incubation, respectively, whereas, totally deglucosylated species appeared only after incubation for more than 10h. The fully deglycosylated porphyrin TPP(m-OH)(3) is the final metabolite, being observed at a concentration 15 times higher than that of the remaining TPC(m-O-Glu)(3) 2a/3a. Compared to the photobiological activity of the parent molecule [TPC(m-O-Glu)(3)], a three times higher TPP(m-OH)(3) concentration was necessary to observe a similar in vitro photoactivity.