Boronated derivatives of chlorin e(6) and fluoride-containing porphyrins as penetrating anions: a study using bilayer lipid membranes

Photodynamic therapy of the experimental tumors of different morphological types with liposomal boronated chlorin е6

The article summarizes the results of studies of the effectiveness of photodynamic therapy using a new domestic photosensitizer liposomal borated chlorin e6 (LBC) after its parenteral administration (intraperitoneal and intravenous). Antitumor efficacy was evaluated in rats with M-1 sarcoma and PC-1 alveolar liver cancer and mice with B16 melanoma and Ehrlich’s carcinoma, which were transplanted subcutaneously into the thigh area of the animals. The aim of the study was to determine the optimal regimes of photodynamic therapy that would allow achieving the maximum antitumor effect up to 21 days after the photodynamic therapy. The therapy was carried out under the control of the accumulation of the photosensitizer in the tumor and surrounding tissues of the thigh by selecting the doses of the drug and the parameters of laser radiation (energy density and power density). The effectiveness of therapy was assessed by the inhibition of tumor growth, by the percentage of animals with complete tumor regression, by the absolute growth rate in animals with continued tumor growth compared to controls. The results of our studies have shown that the domestic photosensitizer liposomal borated chlorin e6 has high antitumor activity in vivo. In an experimental study of the photosensitizer under certain PDT modes, the maximum antitumor effect (complete tumor regression in 100% of animals) was obtained up to 21 days after PDT in all tumor models used.

Tetra-arylborate lipophilic anions as targeting groups

Tetraphenylborate (TPB) anions traverse membranes but are excluded from mitochondria by the membrane potential (Δψ). TPB-conjugates also distributed across membranes in response to Δψ, but surprisingly, they rapidly entered cells. They accumulated within lysosomes following endocystosis. This pH-independent targeting of lysosomes makes possible new classes of probe and bioactive molecules.

Effect of Alkyl Chain Length on Translocation of Rhodamine B n-Alkyl Esters across Lipid Membranes

Voltage-dependent translocation of a series of cationic rhodamine B derivatives differing in n-alkyl chain length (ethyl, butyl, octyl, dodecyl, octadecyl) from one lipid monolayer to another was studied by measuring electrical current relaxation after a voltage jump on a planar bilayer phosphatidylcholine (PC) membrane. The rate of the translocation decreased in the following series of lipids: diphytanyl-PC > dioleyl-PC > diphytanoyl-PC > dierucoyl-PC. For all the lipids studied, the rate increased with lengthening of the hydrocarbon chain of the rhodamine derivatives, with the increase being most pronounced for the compounds having a short alkyl chain. The results could be well explained by involvement of molecule reorientations in the process of transmembrane flip-flop of the hydrophobic membrane-bound compounds. However, an impact of membrane dipole potential on the translocation rate could not be excluded, because the dipole potential could contribute to the energy barrier for translocation of the compounds located at different depths in the water-membrane interface. Based on the data obtained, a difference in the dipole potential of ester diphytanoyl-PC membranes with respect to ether diphytanyl-PC was estimated to be 108 mV, highlighting the contribution of a layer of oriented carbonyl groups of the lipids to the membrane dipole potential.

Carboranyl-Chlorin e6 as a Potent Antimicrobial Photosensitizer

Antimicrobial photodynamic inactivation is currently being widely considered as alternative to antibiotic chemotherapy of infective diseases, attracting much attention to design of novel effective photosensitizers. Carboranyl-chlorin-e₆ (the conjugate of chlorin e₆ with carborane), applied here for the first time for antimicrobial photodynamic inactivation, appeared to be much stronger than chlorin e₆ against Gram-positive bacteria, such as Bacillus subtilis, Staphyllococcus aureus and Mycobacterium sp. Confocal fluorescence spectroscopy and membrane leakage experiments indicated that bacteria cell death upon photodynamic treatment with carboranyl-chlorin-e₆ is caused by loss of cell membrane integrity. The enhanced photobactericidal activity was attributed to the increased accumulation of the conjugate by bacterial cells, as evaluated both by centrifugation and fluorescence correlation spectroscopy. Gram-negative bacteria were rather resistant to antimicrobial photodynamic inactivation mediated by carboranyl-chlorin-e₆. Unlike chlorin e₆, the conjugate showed higher (compared to the wild-type strain) dark toxicity with Escherichia coli ΔtolC mutant, deficient in TolC-requiring multidrug efflux transporters.

Boron clusters in medicinal chemistry: perspectives and problems

Boron clusters have been employed successfully as constituents in bioactive substances. In this review, the perspectives of boron clusters for drug design and problems to be solved for a broader application are discussed, and a list of actions is given for overcoming the problems.

Unsaturated lipids protect the integral membrane peptide gramicidin A from singlet oxygen

In contrast to expectations that unsaturated fatty acids contribute to oxidative stress by providing a source of lipid peroxides, we demonstrated the protective effect of double bonds in lipids on oxidative damage to membrane proteins. Photodynamic inactivation of gramicidin channels was decreased in unsaturated lipid compared to saturated lipid bilayers. By estimating photosensitizer (boronated chlorine e6 amide) binding to the membrane with the current relaxation technique, the decrease in gramicidin photoinactivation was attributed to singlet oxygen scavenging by double bonds in lipids rather than to the reduction in photosensitizer binding. Gramicidin protection by unsaturated lipids was also observed upon induction of oxidative stress with tert-butyl hydroperoxide.