Synthesis and evaluation of novel fluorinated hematoporphyrin ether derivatives for photodynamic therapy

A photosensitizer with high phototoxicity, suitable amphipathy and low dark toxicity could play a pivotal role in photodynamic therapy (PDT). In this study, a facile and versatile approach was adopted to synthesize a series of novel fluorinated hematoporphyrin ether derivatives (I1-I5 and II1-II4), and the photodynamic activities of these compounds were studied. Compared to hematoporphyrin monomethyl ether (HMME), all PSs showed preferable photodynamic activity against A549 lung tumor cells. The longest visible absorption wavelength of these compounds was approximately 622 nm. Among them, II3 revealed the highest singlet oxygen yield (0.0957 min-1), the strongest phototoxicity (IC50 = 1.24 μM), the lowest dark toxicity in vitro, and exhibited excellent anti-tumor effects in vivo. So compound II3 could act as new drug candidate for photodynamic therapy.

Synthesis and evaluation of a hematoporphyrin derivative in a folate receptor-targeted solid-lipid nanoparticle formulation

PURPOSE

This study was aimed at the synthesis, formulation and in vitro evaluation of folate receptor (FR)-targeted solid-lipid nanoparticles (SLNs) as a carrier for a lipophilic derivative of the photosensitizer hematoporphyrin (Hp), in FR-overexpressing tumor cells.

MATERIALS AND METHODS

FR-targeted hematoporphyrin-stearylamine (HpSa) SLN composed of Triolein:Egg-phosphatidylcholine (EPC):Tween-80 (T-80) (64:25:10), with 0.5 mole % of folate-polyethyleneglycol-cholesterol (FPC) or polyethyleneglycol-distearoylphosphatidylethanolamine (PEG-DSPE), were prepared by ethanol injection method. Stability of the SLN was monitored by changes in particle size at 4 degrees C and drug retention at various time points. Cellular uptake and IC50 values of the FR-targeted formulations were determined in vitro in the FR (+) KB cells.

RESULTS

Stable targeted SLNs were prepared by ethanol injection encapsulating greater than 95 percent of 5 mole % of HpSa, having a mean diameter < 200 nm. In vitro cytotoxicity assay on the FR-targeted SLN gave IC50 of 1.57 microM in KB cells and non-targeted SLNs gave an IC50 of 5.17 microM. FR selectivity was confirmed by fluorescence microscopy.

CONCLUSION

FR-targeted SLNs incorporating the lipophilic drug HpSa were capable of specific receptor binding in cultured KB cells, which warrants further investigation.

Synthesis, biodistribution and antitumor activity of hematoporphyrin-platinum(II) conjugates

A new series of platinum(II) complexes of pegylated hematoporphyrin derivatives with controlled hydrophobic/hydrophilic balance were synthesized by introducing different kinds of poly(ethylene glycol) and amine ligands to the porphyrin ring. The antitumor activity of the porphyrin-platinum(II) conjugates was assayed in vitro and in vivo against leukemia L1210 cell line and various human tumor cell lines. The present complexes exhibited high antitumor activity and improved water solubility as well as considerable lipophilicity. In particular, complex 16 showed not only higher in vivo activity (T/C%=258) than cisplatin (T/C%=184) and carboplatin (T/C%=168), but also excellent solubility in water and organic solvent. The antitumor activity of complex 20 was superior to that of carboplatin against all human tumor cell lines tested. Moreover, some amphiphilic complexes (7 and 12) exhibited elevated tumor-localizing effect (tumor/muscle ratio>2).

Hematoporphyrin-derived soluble porphyrin-platinum conjugates with combined cytotoxic and phototoxic antitumor activity

To combine the cytotoxic activity of cisplatin and the phototoxicicity of hematoporphyrin derivatives in the same molecule, hematoporphyrin was derivatized at the two secondary alcohol positions by etherification with oligo- and poly(ethylene glycol) units. The two carboxylic acid groups of the propionate side chains were used to bind platinum fragments. The antiproliferative activity of 35 platinum complexes (0.5, 1, and 5 microM) differing in solubility and type of the platinum fragment and the corresponding porphyrin ligands were studied in tests with TCC-SUP and J82 transitional bladder cancer cells in the dark and after irradiation (lambda = 600-730 nm, 24 J/cm(2)). The most active compounds were found among the porphyrin-platinum conjugates bearing the diammine and (RR/SS)-trans-1,2-diaminocyclohexane ligand. These porphyrin-platinum conjugates, especially the water-soluble species, such as diammine(7,12-bis[1-(poly(ethylene glycol)-750-monomethyl ether-1-yl)ethyl]-3,8,13,17-tetramethylporphyrin-2,18-dipropionato)platinum(II), are promising candidates for the development of a novel type of photosensitizers with intrinsic cytotoxicity, which due to the porphyrin constituent may selectively enrich in tumor tissues.

An atomic basis of cancer (V): A new marker in animal tumors

Particle-induced X-ray emission (PIXE) analysis can be applied to mark (or to localize) a cancer lesion in a benign environment in test animals. We synthesized hematoporphyrin derivative (HPD) with rare earth metals to form lanthanide-HPD to enhance the localizing efficiency. The sensitive PIXE detection of trace elements in amounts on the order of nanograms or less could possibly be used to probe carcinogenesis at the level of the cell. To explain the present approach, we present the results of an experiment in which we used paraseodynium-HPD localizer.

Photosensitizer targeting in photodynamic therapy. I. Conjugates of haematoporphyrin with albumin and transferrin

Conjugates of haematoporphyrin (HP) with serum albumin and transferrin were prepared, purified by gel filtration and characterized by high performance liquid chromatography (HPLC), polyacrylamide gel electrophoresis (PAGE) and spectroscopy. Although the fluorescence was somewhat quenched, the conjugates had similar singlet oxygen quantum yields to free porphyrin. The albumin conjugate (HP-BSA) could be divided into monomeric and cross-linked fractions. In NIH 3T3 and HT29 cells, native albumin could not compete with the uptake of HP-BSA and the uptake was greatly enhanced in the absence of serum and in the presence of poly-L-lysine. We infer that the conjugate was mostly associated with the plasma membrane in these cells. The uptake of HP-transferrin showed evidence of a receptor-mediated component in that it was partially inhibited by native protein and increased when transferrin receptors were upregulated by an iron chelator. J774 macrophage-like cells accumulated fluorescence from HP-BSA to a much higher degree than HT29 cells, even though the protein was extensively degraded (HT29 cells did not appear to degrade the protein). The time course of the photocytotoxicity of HP-BSA was prolonged in J774 cells, although their response to free porphyrins was similar to that seen in HT29 cells. Chloroquine inhibited protein degradation without having an effect on the fluorescence uptake. J774 cells acquired more fluorescence and degraded more protein when supplied with cross-linked HP-BSA compared with monomeric fraction. For a given fluorescence uptake, the cross-linked fraction was also more photocytotoxic. We conclude that macrophages can acquire photosensitizer-protein conjugates avidly and that these are delivered to the lysosomes. These types of conjugate may have applications in targeting fluorescent molecules for diagnostic imaging and for the photodynamic treatment of macrophage malignancies.

Haematoporphyrin derivatives: distribution in a living organism

Pharmacokinetics of accumulation in organs and tissues was studied for two haematoporphyrin-based photosensitizers. These sensitizers, haematoporphyrin derivative (HpD) and an oligomeric haematoporphyrin (OHp), contained different amounts of monomeric fraction (25% and 5% respectively) and in OHp the macrocycles were bonded together with ether bonds. OHp was shown to accumulate in tumours in higher amounts than HpD. The maximal tumour to tissue concentration ratio for OHp was 6.7 observed 54 h after injection; the same ratio for HpD was 2.8 after 48 h.

Mn (III) hematoporphyrin. A potential MR contrast agent

Manganese (III) hematoporphyrin (MnHP), a new and stable complex, was prepared, and its toxicity and magnetic resonance (MR) imaging properties were evaluated. In tests of acute and subacute toxicity, no deaths resulted from bolus intravenous injections of 13 or 19 mumols/kg of MnHP, but there was a 33% mortality when the dose was 38 mumols/kg. Laboratory results were normal in the surviving rats. Ultraviolet- visible spectroscopy of the urine and serum of two rats injected 24 hours previously with 38 mumols/kg MnHP revealed no free HP, suggesting in vivo stability of MnHP. Finally, using a standardized imaging protocol, there was a mean increase of 37% in the liver-to-muscle intensity ratios in four rats injected 24 hours previously with 25 mumols/kg MnHP when compared to paired controls (P less than .005). In addition, obvious visual increase in the signal intensity of the liver on T1-weighted images was seen in animals tested with 13 and 19 mumols/kg of MnHP. The results suggest that further evaluation of MnHP as an MR contrast agent for the liver is warranted.

Studies on the photodynamic effect of haematoporphyrin derivative

A case-control photodynamic therapy (PDT) was studied on adenocarcinoma (AC755) in BDF1 mice. Haematoporphyrin derivative (HPD; Porphyrin Products, U.S.A.) and a Bulgarian HPD were used as photosensitizers at doses of 10 mg kg-1. An argon dye laser system with lambda em=630 nm (400 mW cm-2) was used for PDT with a total light dose of 400 J cm-2. The therapeutic effect was assessed by the changes in tumour dimensions, the size of photonecrosis and the mean survival time of the animals. Histologic and ultrastructural studies were carried out. No significant difference was recorded between the antitumour effects of the two photosensitizers. Best results were obtained in small tumours (less than 10 mm) with incision of covering skin. Results are discussed in an attempt to advocate an optimal regimen for PDT in experimental tumours.

Syntheses and photosensitizing activity of porphyrins joined with ester linkages

In order to investigate the structure of hematoporphyrin derivative and its purified version, Photofrin-II, porphyrin dimers with ester linkage were synthesized. 2,4-Diacetyldeuteroporphyrin dimethyl ester and protoporphyrin IX dimethyl ester were used as starting materials. The methyl esters were replaced by trimethylsilylethyl esters to protect the carboxylic groups. Deprotection using tetra-n-butylammonium fluoride in tetrahydrofuran regenerated the carboxylic functions. Reversed phase high performance liquid chromatography was used to compare the synthetic dimers with components of Photofrin-II. Our data indicate that these dimers are not components of Photofrin-II. During the synthesis of a 13C-labeled dimer with an ester linkage, a small amount of trimer was also isolated. The structures of these compounds were confirmed by nuclear magnetic resonance and mass spectroscopy. Using a standard screening system with DBA/2 mice bearing transplanted SMT-F tumors, these dimers were found not to be as active as Photofrin-II.

Nature of the tumor-localizing components of hematoporphyrin derivative

Hematoporphyrin derivative linked by ether bonds (HE) was synthesized by unambiguous procedures in order to compare its properties to hematoporphyrin derivative (HpD). Reverse phase high performance liquid and gel filtration chromatography were used to compare the HE derivatives to HpD. The cellular uptake of HE derivatives was compared to HpD using the WEHI 3B (D+) cell line and was shown to be taken up to a degree and in a manner similar to HpD. The efficiency of HE porphyrins as photosensitizers was compared to HpD using the V79 cell line. HE porphyrins were more efficient in sensitizing the V79 cells than was HpD. The in vivo tumor localizing properties of HE porphyrins were compared to HpD in CBA mice bearing the C6 cerebral glioma, and BALB/c mice bearing the EMT6 mammary tumor. HE derivatives localized in both tumor models as effectively as HpD. We conclude that the properties of ether linked hematoporphyrin derivatives are very similar to properties of HpD.

Hematoporphyrin ethers--I. Generalized synthesis and chemical properties

A series of hematoporphyrin di-ethers, from methyl to hexyl, has been prepared by a generalized procedure based on reaction of the selected carbinol with the HBr adduct of protoporphyrin, followed by hydrolysis of ester functions and chromatographic purification. Spectroscopic and other properties are reported. They crystallize well. HPLC retention time increases linearly with the number of carbon atoms in the alcohol employed. In previous work we have shown that the more hydrophobic ethers are very efficient photosensitizers of malignant cells.

Localization and photosensitization of murine tumors in vivo and in vitro by a chlorin-porphyrin ester

Preparation of the tumor-localizing preparation called hematoporphyrin derivative involves a two-step reaction wherein hematoporphyrin is acetylated and the reaction product subjected to alkaline hydrolysis. We have proposed that the tumor-localizing fraction of this product is composed of hematoporphyrin units joined by ester linkages. Using an analogous synthetic procedure, we prepared some new sensitizers in which hematoporphyrin is esterified to chlorins (reduced porphyrins). Because of the differences in absorption spectra, the porphyrin-chlorin esters are 5-fold more potent photosensitizers than are the porphyrin-porphyrin esters, with light of wavelength greater than 600 nm.