Pharmaceutical Approach to Develop Novel Photosensitizer Nanoformulation: An Example of Design and Characterization Rationale of Chlorophyll α Derivative.

In this study, we described physico-chemical properties of novel nanoformulation of photosensitizer-pyropheophorbide α 17-diethylene glycol ester (XL) (chlorophyll α derivative), revealing insights into antitumor activity and maintaining quality, meeting the pharmaceutical approach of new nanoformulation design. Our formulation, based on poly(lactic-co-glycolic acid) (PLGA) nanoparticles, increased XL solubility and selective tumor-targeted accumulation. In our research, we revealed, for the first time, that XL binding to polyvinyl alcohol (PVA) enhances XL photophysical activity, providing the rationale for PVA application as a stabilizer for nanoformulations. Results of FTIR, DSC, and XRD revealed the physical interactions between XL and excipients, including PVA, indicating that the encapsulation maintained XL binding to PVA. The encapsulated XL exhibited higher photophysical activity compared to non-encapsulated substance, which can be attributed to the influence of residual PVA. Gamma-irradiation led to degradation of XL; however, successful sterilization of the samples was achieved through the filtration. Importantly, the encapsulated and sterilized XL retained cytotoxicity against both 2D and 3D tumor cell models, demonstrating the potential of the formulated NP-XL for photodynamic therapy applications, but lacked the ability to reactivate epigenetically silenced genes. These findings provide valuable insights into the design and characterization of PLGA-based nanoparticles for the encapsulation of photosensitizers.

Solvation, Cancer Cell Photoinactivation and the Interaction of Chlorin Photosensitizers with a Potential Passive Carrier Non-Ionic Surfactant Tween 80.

Cancer and drug-resistant superinfections are common and serious problems afflicting millions worldwide. Photodynamic therapy (PDT) is a successful and clinically approved modality used for the management of many neoplastic and nonmalignant diseases. The combination of the light-activated molecules, so-called photosensitizers (PSs), with an appropriate carrier, is proved to enhance PDT efficacy both in vitro and in vivo. In this paper, we focus on the solvation of several potential chlorin PSs in the 1-octanol/phosphate saline buffer biphasic system, their interaction with non-ionic surfactant Tween 80 and photoinactivation of cancer cells. The chlorin conjugates containing d-galactose and l-arginine fragments are found to have a much stronger affinity towards a lipid-like environment compared to ionic chlorins and form molecular complexes with Tween 80 micelles in water with two modes of binding. The charged macrocyclic PSs are located in the periphery of surfactant micelles near hydrophilic head groups, whereas the d-galactose and l-arginine conjugates are deeper incorporated into the micelle structure occupying positions around the first carbon atoms of the hydrophobic surfactant residue. Our results indicate that both PSs have a pronounced affinity toward the lipid-like environment, leading to their preferential binding to low-density lipoproteins. This and the conjugation of chlorin e6 with the tumor-targeting molecules are found to enhance their accumulation in cancer cells and PDT efficacy.

Characterization of a Novel Amphiphilic Cationic Chlorin Photosensitizer for Photodynamic Applications.

A novel amphiphilic cationic chlorin e6 derivative was investigated as a promising photosensitizer for photodynamic therapy. Two cationic -N(CH3)3+ groups on the periphery of the macrocycle provide additional hydrophilization of the molecule and ensure its electrostatic binding to the mitochondrial membranes and bacterial cell walls. The presence of a hydrophobic phytol residue in the same molecule results in its increased affinity towards the phospholipid membranes while decreasing its stability towards aggregation in aqueous media. In organic media, this chlorin e6 derivative is characterized by a singlet oxygen quantum yield of 55%. Solubilization studies in different polymer- and surfactant-based supramolecular systems revealed the effective stabilization of this compound in a photoactive monomolecular form in micellar nonionic surfactant solutions, including Tween-80 and Cremophor EL. A novel cationic chlorin e6 derivative also demonstrates effective binding towards serum albumin, which enhances its bioavailability and promotes effective accumulation within the target tissues. Laser confocal scanning microscopy demonstrates the rapid intracellular accumulation and distribution of this compound throughout the cells. Together with low dark toxicity and a rather good photostability, this compound demonstrates significant phototoxicity against HeLa cells causing cellular damage most likely through reactive oxygen species generation. These results demonstrate a high potential of this derivative for application in photodynamic therapy.

Novel hydrophilic galactose-conjugated chlorin e6 derivatives for photodynamic therapy and fluorescence imaging.

We synthesized new hydrophilic chlorin e6 derivatives with two and four galactose fragments conjugated to the macrocycle via carbon atom in position 6 of the galactose fragment. Galactose fragments were inserted by alkylation of the amino groups of chlorin e6 amides with one and two ethylene diamine fragments on the macrocycle periphery with triflate of diacetone galactose, followed by removal of diisopropylidene protection by 70% aqueous trifluoroacetic acid. The synthesized compounds were shown to be capable of penetrating the membrane of HeLa cells; they have intense red fluorescence inside the cell and have phototoxic properties towards HeLa cells (upon LED irradiation at 660 nm and light exposure value of 12 J/cm2). These properties, along with water solubility, allow us to consider the synthesized compounds to be promising as potential antitumor PSs and diagnostic compounds for visualizing malignant tumors and creating on their basis preparations for simultaneous diagnostics and therapy of oncological diseases.

Dark and Photoinduced Cytotoxic Activity of the New Chlorophyll-a Derivatives with Oligoethylene Glycol Substituents on the Periphery of Their Macrocycles.

In the present work, we investigated the dark and photoinduced cytotoxic activity of the new chlorophyll-a derivatives which contain the substituents of oligoethylene glycol on the periphery of their macrocycles. These compounds were tested using human cell lines to estimate their potential as photosensitizers for photodynamic therapy of cancer. It was shown that all the tested compounds have expressed photoinduced cytotoxic activity in vitro. Detailed study of the biological activity of one of the most perspective compound in this series-pyropheophorbide-a 17-diethylene glycol ester (Compound 21) was performed. This new compound is characterized by lower dark cytotoxicity and higher photoinduced cytotoxicity than previously described in a similar compound (DH-I-180-3) and clinically used PhotolonTM. Using fluorescent microscopy, it was shown that Compound 21 quickly penetrates the cells. Analysis of caspase-3 activity indicated an apoptosis induction 40 min after exposure to red light (λ = 660 nm). The induction of DNA damages and apoptosis was shown using Comet assay. The results of expression analysis of the stress-response genes indicate an activation of the genes which control the cell cycle and detoxification of the free radicals after an exposure of HeLa cells to Compound 21 and to red light. High photodynamic activity of this compound and the ability to oxidize biomolecules was demonstrated on nuclear-free mice erythrocytes. In addition, it was shown that Compound 21 is effectively activated with low energy 700 nm light, which can penetrate deep into the tissue. Thus, Compound 21 is a prospective substance for development of the new drugs for photodynamic therapy of cancer.

Novel boronated chlorin e6-based photosensitizers: synthesis, binding to albumin and antitumour efficacy.

Chlorins, a class of plant porphyrins, are perspective as photosensitizing agents due to light absorption in the long wavelength spectral region and deeper photodamage of tissues. Aiming at optimization of antitumour properties of chlorins, we synthesized a series of boronated derivatives of chlorin e(6) and their complexes containing Zn(II), Pd(II) or Sn(IV). The compounds were synthesized by alkylation of amino or hydroxy derivatives of chlorin e(6) with 1-trifluoromethanesulfonylmethyl-o-carborane. Chlorin e(6) 13(1)-N-{2-[N-(o-carboran-1-yl)methyl]aminoethyl}amide-15(2), 17(3)-dimethyl ester (compound 5) formed complexes with serum albumin, a major porphyrin carrier. The binding constant of these complexes was approximately 4 times bigger than the respective value for the complexes of albumin with boron-free aminochlorin e(6). Compound 5 potently sensitized rat fibroblasts to illumination with monochromatic red light: >98% of cells were necrotic by 24h post-illumination with 1 microM of 5. This compound demonstrated high efficacy in photodynamic therapy of rat M-1 sarcoma. After PDT with 25mg/kg of 5 the residual tumours were significantly smaller than in animals subjected to PDT with equal concentration of boron-free aminochlorin e(6). No signs of general toxicity were detectable after PDT with 5. Thus, boronation can enhance the potency of chlorins in PDT, in particular, due to an increased binding to albumin. Our data expand the therapeutic applicability of boronated chlorins beyond boron neutron capture therapy; these agents emerge as dual efficacy photoradiosensitizers.