The impact of aggregation on the biodistribution of hypericin

Abstract

Hypericin is a potent agent in the photodynamic therapy of cancers and accumulates to a large extent in tumor tissue. To better understand the impact of hypericin aggregates present in the delivery vehicle on the biodistribution of the compound, we compared the in vivo tissue accumulation after administering hypericin suspended as coarse aggregates in phosphate-buffered saline, with the biodistribution found after injection of a solution of hypericin in a mixture of DMSO, polyethylene glycol and water. When administered as coarse aggregates, hypericin showed a pronounced uptake in liver, spleen and lung and a slow body clearance with a complete decline in tumor/normal tissue ratios (far less than 1). In contrast, delivery of hypericin as a solution resulted in dramatically improved tumor to normal tissue ratios and a relatively fast elimination from the body. To elucidate the exact localization of hypericin in both conditions, a fluorescence microscopy study was performed on sections of spleen, liver, lung and tumor tissue. At 24 h after injection, fluorescence in spleen, liver and lung was faint and homogeneous for dissolved hypericin, whereas bright fluorescent spots covering the entire tissue sections were found when coarse aggregates were injected. We found that aggregates get trapped within these tissues, followed by a gradual monomerization. A direct involvement of monocytes and macrophages, however, could not be demonstrated. In conclusion, it is of critical importance that the delivery vehicle prevents extensive aggregation of hypericin before injection and assures an efficient transfer to serum lipoproteins upon injection. These results may also be extended to radiolabeled derivatives and other lipophilic photosensitizers, such as porphyrins, phthalocyanines, naphthalocyanines and chlorines, with similar aggregation properties.

Sodium cholate, a solubilizing agent for the necrosis avid radioiodinated hypericin in rabbits with acute myocardial infarction

“…Indeed, the relatively low accumulation in MPS organs such as lungs and spleen indicated the presence of no or minimal aggregate formation of 123 I-Hyp/Hyp. Otherwise, prolonged radioactivity retention in such organs would happen due to aggregates entrapment, as was previously reported (Van De Putte et al, 2006). In accordance with previous investigations, thyroid and stomach radioactivities were negligible, corroborating the in vivo stability of the radioiodinated Hyp over time (Cona et al, 2013a).…”

“…In biological media, it has been found in soluble form owing to the complex formation with biological macromolecules, mainly low-density lipoprotein and human serum albumin (Miskovsky, 2002). However, its poor biocompatible solubility in water-based formulations is a major limiting factor for its successful launch in market despite its pharmacological potentials (Van De Putte et al, 2006). In organic solvents, at the pH interval between 4 and 11, it forms monobasic salts (Weiner & Mazur, 1992;Yamazaki et al, 1993), which undergo homoassociation in the presence of water.…”

“…In organic solvents, at the pH interval between 4 and 11, it forms monobasic salts (Weiner & Mazur, 1992;Yamazaki et al, 1993), which undergo homoassociation in the presence of water. The resulting aggregates lack necrosis targetability and exhibit unwanted retention in organs of the mononuclear phagocyte system (MPS) (Van De Putte et al, 2006).…”

Solubilization of poorly soluble photosensitizer hypericin by polymeric micelles and polyethylene glycol

“…This compound is sparingly soluble in non-polar organic solvents and oil, and in aqueous environment forms insoluble non-fluorescent aggregates (Falk and Meyer 1994;Falk 1999). The formation of aggregates significantly suppresses Hyp photodynamic activity (Falk and Meyer 1994;Kascakova et al 2005;van de Putte et al 2006). Moreover, this aqueous insolubility makes intravenous injection of Hyp problematic and restricts its medical applications.…”

Biodistribution of PVP-hypericin and hexaminolevulinate-induced PpIX in normal and orthotopic tumor-bearing rat urinary bladder

“…In water hypericin forms aggregates, thereby loosing its spectroscopic and tumor-selective properties [13]. In previous studies, this problem was overcome by including plasma proteins like human serum albumin (HSA) into the formulation to which hypericin adsorbs [8,9].…”