Phototherapeutic Window Research Articles

Investigation of protonation effects on the electronic and structural properties of halogenated sulfonated porphyrins

The present study aimed at evaluating pH effects on the electronic and structural properties of halogenated sulfonated porphyrins. We used UV–Vis absorption, fluorescence emission, and NMR spectroscopies, combined with quantum chemical calculations using Density Functional Theory. We observed that the presence of one or two halogen atoms (chlorine or fluorine) at ortho-position of phenyl ring reduces the flexibility of the porphyrin structures, making their protonation harder. Since the protonation of anionic porphyrins provides a convenient way for their aggregation, the protonation observed only in extremely acid environment is indicative of the low probability for the aggregation of these porphyrins, which is an important characteristic of an efficient photosensitizer. Furthermore, the enhancement in the absorbance (9–13.5 times) in the phototherapeutic window suggests that the protonation of halogenated sulfonated porphyrins could be a possible strategy for a higher photodynamic efficiency.

Photodynamic Therapy Efficacy Enhanced by Dynamics: The Role of Charge Transfer and Photostability in the Selection of Photosensitizers

Progress in the photodynamic therapy (PDT) of cancer should benefit from a rationale to predict the most efficient of a series of photosensitizers that strongly absorb light in the phototherapeutic window (650-800 nm) and efficiently generate reactive oxygen species (ROS = singlet oxygen and oxygen-centered radicals). We show that the ratios between the triplet photosensitizer-O2 interaction rate constant (kD) and the photosensitizer decomposition rate constant (kd), kD/kd, determine the relative photodynamic activities of photosensitizers against various cancer cells. The same efficacy trend is observed in vivo with DBA/2 mice bearing S91 melanoma tumors. The PDT efficacy intimately depends on the dynamics of photosensitizer-oxygen interactions: charge transfer to molecular oxygen with generation of both singlet oxygen and superoxide ion (high kD) must be tempered by photostability (low kd). These properties depend on the oxidation potential of the photosensitizer and are suitably combined in a new fluorinated sulfonamide bacteriochlorin, motivated by the rationale.

Synthesis and bio-evaluation of novel hypocrellin derivatives: Potential photosensitizers for photodynamic therapy of age-related macular degeneration

The phototherapeutic window from 600 to 900 nm is necessary for photodynamic therapy (PDT) of solid tumors, but may not suitable for PDT of some microvascular diseases, like age-related macular degeneration (AMD), because of its deep penetration. Moreover, absorption of some neighboring photoreceptors should be avoided for PDT of AMD. Considering these, yellow-orange light may be a proper phototherapeutic window of AMD. Herein, two novel amino-alkyl-sulfonic acid-substituted hypocrellin B derivatives, 3 and 4 were designed and synthesized. They exhibited the maximal absorption at yellow-orange light, and possessed higher PDT activity than 2, proved by the in vitro or in vivo experiments. Besides, 4 showed much higher PDT activity than 3, ascribed to its higher cellular uptake suggested by its optimized amphiphilicity and liposome–mimic results. And the vascular leakage of 4 was close to 2. Consequently, 4 has great potential for PDT of AMD or other superficial diseases.

The challenging combination of intense fluorescence and high singlet oxygen quantum yield in photostable chlorins — a contribution to theranostics

High fluorescence quantum yields, high singlet oxygen quantum yields and intense absorptions in the phototherapeutic window are fundamental properties for compounds intended for fluorescence diagnosis and photodynamic therapy. We report on photostable chlorins that combine these properties. The fluorinated tetraphenylchlorin FCMet has ΦF = 0.396 and ΦΔ = 0.58 ± 0.07, whereas F2CMet has ΦF = 0.360 and ΦΔ = 0.54 ± 0.05, and both have molar absorption coefficients larger than 30,000 M(-1) cm(-1) above 650 nm. These dual functional agents use nearly all the energy absorbed to perform the desired functions and are appropriate for theranostics applications.

BODIPY-modified Ru(ii) arene complex—a new ligand dissociation mechanism and a novel strategy to red shift the photoactivation wavelength of anticancer metallodrugs

A Ru(II) arene complex [(η(6)-p-cymene)Ru(bpy)(py-BODIPY)](PF(6))(2), where bpy is 2,2'-bipyridine and py-BODIPY is a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dye containing a pyridine group at the 8-position, was designed and synthesized. BODIPY modification renders the monodentate pyridine ligand with long wavelength absorbing capability, and an absorption maximum at 504 nm. Upon selective irradiation of the absorption band of the py-BODIPY ligand, the dissociation of the monodentate ligand occurs efficiently, followed by substitution by 9-ethylguanine if it is present in the solution. The photoinduced ligand dissociation quantum yield was measured to be 4.1% at 480 nm. The photoinduced electron transfer from the BODIPY chromophore to the Ru(II) arene moiety plays an important role in the ligand dissociation. Such a photosensitization strategy can be utilized to develop novel anticancer metallodrugs that may respond to light in the phototherapeutic window (650-900 nm).

Red‐Light‐Induced Inhibition of DNA Replication and Amplification by PCR with an Os/Rh Supramolecule

Bimetallic: Upon irradiation with light in the phototherapeutic window, the bimetallic complex [(bpy)2Os(dpp)RhCl2(phen)]3+ binds to and cleaves DNA through an oxygen-independent mechanism. PCR is used as a model for in vitro DNA replication. The results show that the metal complex does not interfere with DNA amplification in the dark without O2, but completely inhibits DNA amplification in samples exposed to red light. Taq=polymerase, PS=photosensitizer.

Oxovanadium(iv) based hypocrellin B complexes with enhanced photodynamic activity

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, three new oxovanadium(IV) complexes were designed and synthesized with HB as a bridging ligand and phen (1,10-phenanthroline, complex 1), tmp (3,4,7,8-tetramethyl-1,10-phenanthroline, complex 2) and dpq (dipyrido[3,2-f:2'3'-h]quinoxaline, complex 3) as terminal ligands. The use of a diimine terminal ligand avoids the formation of polymeric complexes and ensures the three VO(2+)-HB complexes possess a definite molecular formula and molecular weight to meet the single component requirement for an ideal PDT agent. Compared to HB, the VO(2+)-HB complexes exhibit improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity toward dsDNA, and similar singlet oxygen quantum yield, therefore advanced DNA photocleavage activity. Both the DNA binding constants and photo nuclease activities of the complexes follow the order 2 (tmp) > 3 (dpq) > 1 (phen), demonstrating the importance of the binding affinity to biomolecules, which improves the bioavailability of reactive oxygen species. Our work opens a new avenue for the development of HB-based PDT agents.

A new Co(III)–hypocrellin B complex with enhanced photonuclease activity

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, a new Co(III) complex [Co 2(HB)(tmp) 4] 4+ (tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. [Co 2HB(tmp) 4] 4+ exhibits improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity and DNA photocleavage capability toward dsDNA with respect to HB. The photodynamic activity of [Co 2(HB)(tmp) 4] 4+ stems from its 1O 2 photosensitization ability, in sharp contrast to [Cu 2(HB)(tmp) 2] 2+ which relies on superoxide anion radical (O 2 - ) and hydroxyl radical (·OH) to photocleave DNA, though the both complexes possess similar electrochemical properties. The remarkable difference between the photodynamic mechanisms of [Co 2(HB)(tmp) 4] 4+ and [Cu 2(HB)(tmp) 2] 2+ was discussed in detail.

Dinuclear Cu(II) Hypocrellin B Complexes with Enhanced Photonuclease Activity

Five new dinuclear Cu(II) complexes were designed and synthesized, using hypocrellin B, a naturally occurring photosensitizer that has received extensive studies as promising photodynamic therapy (PDT) agent, as bridging ligand, and five kinds of diimine ligands, including 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), and dipyrido[3,2-a:2',3'-c]phenazene (dppz), as terminal ligands, respectively. The Cu(2+)-HB complexes exhibit improved water solubility, enhanced absorptivity in the phototherapeutic window of 600-900 nm, and increased binding affinity toward dsDNA than their parent HB. The biologically accessible redox potential of Cu(II)/Cu(I) couple renders the five Cu(2+)-HB complexes chemical nuclease activities in the presence of reducing agent such as ascorbic acid. Moreover, the readily available redox potential of Cu(II)/Cu(I) couple switches the photodynamic activity from type II mechanism (singlet oxygen mechanism) for HB to type I mechanism (radical mechanism) for the Cu(2+)-HB complexes. Of the five Cu(2+)-HB complexes, complex 3-5 with terminal diimine ligands of tmp, dpq, and dppz, respectively, can photocleave supercoiled pBR322 DNA more efficiently than HB. These findings open a new avenue for the development of the HB derivatives with higher photodynamic activity and better clinical applicability.

New Halogenated Water‐Soluble Chlorin and Bacteriochlorin as Photostable PDT Sensitizers: Synthesis, Spectroscopy, Photophysics, and in vitro Photosensitizing Efficacy

Chlorin and bacteriochlorin derivatives of 5,10,15,20-tetrakis(2-chloro-5-sulfophenyl)porphyrin have intense absorptions in the phototherapeutic window, high water solubility, high photostability, low fluorescence quantum yield, long triplet lifetimes, and high singlet oxygen quantum yields. Biological studies revealed their negligible dark cytotoxicity, yet significant photodynamic effect against A549 (human lung adenocarcinoma), MCF7 (human breast carcinoma) and SK-MEL-188 (human melanoma) cell lines upon red light irradiation (cutoff λ<600 nm) at low light doses. Time-dependent cellular accumulation of the chlorinated sulfonated chlorin reached a plateau at 2 h, as previously observed for the related porphyrin. However, the optimal incubation time for the bacteriochlorin derivative was significantly longer (12 h). The spectroscopic, photophysical, and biological properties of the compounds are discussed in relevance to their PDT activity, leading to the conclusion that the bacteriochlorin derivative is a promising candidate for future in vivo experiments.

The synthesis and characterization of ethylenediamine-modified Elsinochrome A

To overcome the lack of appreciable absorption in the phototherapeutic window (600–900 nm) of the naturally occurring perylenequinonoid pigment, Elsinochrome A, which limits its clinical application, an ethylenediamine-modified elsinochrome A, possessing long wavelength absorption (708 nm) was synthesized. Electron paramagnetic resonance and chemiluminescence assays indicated that ethylenediamine-modified Elsinochrome A possessed photosensitizing activity and its photodamage efficacy is greater than that of unmodified Elsinochrome A.

Boron-Containing Conjugates of Natural Chlorophylls

Boron neutron capture therapy (BNCT) is binary method for the treatment of cancer, which is based on the nuclear reaction of two essentially nontoxic species, nonradioactive 10B and low energy thermal neutrons. The neutron capture reaction by 10B produces high-linear-energy transfer ions 4He2+ and 7Li+ that dissipate their kinetic energy during traveling one cell diameter (5–9 μm) in biological tissues, giving them the potential for precise cell-killing. Efficient BNCT requires selective accumulation of 10B atoms in cancer cells. Since tetrapyrrole compounds have a unique property of being selectively accumulated in tumor tissues, they have attracted attention as agents for both the targeted delivery of boron clusters to tumor cells and the combined PDT—BNCT therapy, which would undoubtedly enhance the efficiency of antitumor therapy. From this point of view, chlorin based photosensitizers with intense near IR absorption are of particular interest. Chlorins are photosensitizers that have high quantum yields of singlet oxygen production and absorb light in the 640–690 nm region, i.e. within the so-called ‘phototherapeutic window’ (630–900 nm), where light absorption and scattering in human tissues are minimized and they are relatively transparent for activating light. In this contribution we describe the synthesis of conjugates of natural chlorins and bacteriochlorins with closo-dodecaborate and cobaltbis(dicarbollide) anions. In the present work, the Sonogashira reaction, the ‘click’ methodology, which are actively employed in modern organic chemistry were used for the synthesis of boron-containing conjugates of natural chlorins and bacteriochlorins.

Photochemical Triggering of the Bergman and Myers - Saito Cyclizations

Two strategies for the photochemical generation of reactive enediyne compounds and their subsequent cycloaromatization to p-benzyne or α,3-didehydrotoluene derivatives are discussed in this account. The first method employs a photo-Wolff reaction of stable 11- or 12-membered ring precursor enediynes containing the 2-diazo-1,3-diketone moiety. Irradiation of these compounds results in ring contraction and the formation of two isomeric enediynes possessing an enolized β-ketoester fragment. One of the isomers undergoes the conventional Bergman cyclization, whereas the other isomerizes into the enyne-allene tautomer, which rapidly cyclizes via a Myers–Saito mechanism. The second strategy consists of replacing the triple bond in a cyclic enediyne or enyne-allene structure with a cyclopropenone group, rendering them thermally stable. Photolysis of cyclopropenones results in efficient decarbonylation and the regeneration of a triple bond, restoring the enediyne π-system. The generation of reactive enediynes by non-resonant two-photon excitation using wavelengths within a ‘phototherapeutic window’ was also demonstrated. Photogenerated enediynes show significant nuclease activity, efficiently inducing single-strand dDNA cleavage.

Nitric oxide and singlet oxygen photo-generation by light irradiation in the phototherapeutic window of a nitrosyl ruthenium conjugated with a phthalocyanine rare earth complex

The photochemical, photophysical and photobiological studies of a mixture containing cis-[Ru(H-dcbpy −) 2(Cl)(NO)] (H 2-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and Na 4[Tb(TsPc)(acac)] (TsPc = tetrasulfonated phthalocyanines; acac = acetylacetone), a system capable of improving photodynamic therapy (PDT), were accomplished. cis-[Ru(H-dcbpy −) 2(Cl)(NO)] was obtained from cis-[Ru(H 2-dcbpy) 2Cl 2]·2H 2O, whereas Na 4[Tb(TsPc)(acac)] was obtained by reacting phthalocyanine with terbium acetylacetonate. The UV–Vis spectrum of cis-[Ru(H-dcbpy −) 2(Cl)(NO)] displays a band in the region of 305 nm ( λ max in 0.1 mol L −1 HCl)(π–π∗) and a shoulder at 323 nm (MLCT), while the UV–Vis spectrum of Na 4[Tb(TsPc)(acac)] presents the typical phthalocyanine bands at 342 nm (Soret λ max in H 2O) and 642, 682 ( Q bands). The cis-[Ru(H-dcbpy −) 2(Cl)(NO)] FTIR spectrum displays a band at 1932 cm −1 (Ru–NO +). The cyclic voltammogram of the cis-[Ru(H-dcbpy −) 2(Cl)(NO)] complex in aqueous solution presented peaks at E = 0.10 V (NO +/0) and E = −0.50 V (NO 0/−) versus Ag/AgCl. The NO concentration and 1O 2 quantum yield for light irradiation in the λ > 550 nm region were measured as [NO] = 1.21 ± 0.14 μmol L −1 and ø OS = 0.41, respectively. The amount of released NO seems to be dependent on oxygen concentration, once the NO concentration measured in aerated condition was 1.51 ± 0.11 μmol L −1 The photochemical pathway of the cis-[Ru(H-dcbpy −) 2(Cl)(NO)] /Na 4[Tb(TsPc)(acac)] mixture could be attributed to a photoinduced electron transfer process. The cytotoxic assays of cis-[Ru(H-dcbpy -) 2(Cl)(NO)] and of the mixture carried out with B16F10 cells show a decrease in cell viability to 80% in the dark and to 20% under light irradiation. Our results document that the simultaneous production of NO and 1O 2 could improve PDT and be useful in cancer treatment.

Biophysical evaluation of two red-shifted hypocrellin B derivatives as novel PDT agents

Two novel cyclohexane-1,2-diamino and N,N dimethyl amino-propyl substituted hypocrellin B derivatives, abbreviated as CHA 2HB and DMAHB, respectively were synthesized. These derivatives exhibited enhanced absorption in phototherapeutic window. Photodynamic action of these derivatives, investigated using optical and electron spin resonance methods, depended on both Type I and Type II mechanisms. Gel electrophoresis indicated 1O 2/ O 2 - mediated DNA damage. CHA 2HB displayed 20 fold increase in light dependent cytotoxicity on colon cancer cell line (HCT 116) than the well-known hypocrellin B (HB). The light induced, LD 50 values for CHA 2HB and DMAHB were found to be 0.1 μM and 1.5 μM, respectively. The singlet oxygen generating efficiency followed the order HB > CHA 2HB > DMAHB. But, the enhanced red absorption as well as the hydrophilicity renders the CHA 2HB a better photodynamic therapeutic agent.

Photochemical production of nitric oxide from a nitrosyl phthalocyanine ruthenium complex by irradiation with light in the phototherapeutic window

The photochemical behavior of [Ru(NO)(NO)2pc] (pc=phthalocyanine) is reported in this paper. In addition to ligand localized absorption bands (λ<300nm), the electronic spectrum of this complex in dichloromethane solution was dominated by an intense absorption at 640nm characterized as Q-bands. Irradiation of [Ru(NO)(NO)2pc] at 366 and 660nm led to the production of nitric oxide (NO) as detected by a NO-sensor. NO production by light irradiation at high energy involved excitation of dπ–π∗ transition, while a photoinduced electron transfer occurred at long wavelength irradiation. The NO quantum yields varied from 1.4×10−3 to 2.3×10−2moleinstein−1, depending on oxygen concentration.

Synthesis of a hypocrellin B-polyamide conjugate as DNA-targeting photosensitizer

A new hypocrellin B (HB) derivative bearing a bispyrrolecarboxamide-containing side chain was synthesized, which presents improved absorptivity in phototherapeutic window than HB and affinity feature towards dsDNA.

P104. Photobiological effect of nitric oxide and singlet oxygen in cancer cells occasioned by light irradiation in the phototherapeutic window of a nitrosyl ruthenium conjugated to a phthalocyanine rare earth complex

P104. Photobiological effect of nitric oxide and singlet oxygen in cancer cells occasioned by light irradiation in the phototherapeutic window of a nitrosyl ruthenium conjugated to a phthalocyanine rare earth complex

Synthesis and Characterization of Three Novel Amphiphilic Aminated Hypocrellins as Photodynamic Therapeutic Agents¶

To improve the amphiphilicities and red absorption of the hypocrellins, three novel 2-amino-2-demethoxy-hypocrellins were synthesized by the mild reactions of hypocrellin B with 4-(2-amino-ethyl)morpholine, N,N-dimethylethylenediamine and 1-(2-amino-ethyl)piperazine, respectively. The structures of these derivatives were characterized with proton nuclear magnetic resonance, infrared and mass spectra (MS). The ultraviolet–visible absorption and fluorescence spectra of the derivatives were measured and the new amino-substituted hypocrellins showed strong absorption in the domain of the phototherapeutic window (600–900 nm). Their amphiphilicities evaluated via the partition coefficients between n-octanol and phosphate-buffered saline buffer improved remarkably. Electron paramagnetic resonance spin-trapping measurements were used to investigate the photodynamic action of the three compounds in the presence of oxygen. Singlet oxygen (1O2) and superoxide anion radical (O2•−) generated by illuminating the hypocrellin derivatives in aerobic solution were observed.

New long-wavelength ethanolamino-substituted hypocrellin: photodynamic activity and toxicity to MGC803 cancer cell

To improve hydrophilicity and photoactivity of the new type of therapeutic agent, hypocrellin, a novel long-wavelength ethanolamino-substituted hypocrellin B (EAHB) was synthesized and its molecular structure was characterized by IR, NMR, MS, and UV–vis spectrometers, and EAHB had strong absorption at the phototherapeutic window (600–900 nm). Illumination of deoxygenated DMSO solution containing EAHB generated a strong electron paramagnetic resonance (EPR) signal, which was assigned to the semiquinone anion radical of EAHB (EAHB − ). Absorption measurements displayed that the absorptive bands at 632 and 565 nm (shoulder) arose from the semiquinone anion radical (EAHB − ) and the absorptive bands at 519 and 450 nm (shoulder) belonged to hydroquinone (EAHBH 2), which were formed via the decay of EAHB − in water-contained solution. Superoxide anion radical (O 2 − ) was produced via electron transfer from EAHB − (the precursor) to ground state oxygen. The presence of NADH, a bio-electron donor, significantly enhanced production of EAHB − and O 2 − . Singlet oxygen O 2 ( 1Δ g) could be produced via energy transfer from triplet EAHB to ground state oxygen molecules. The quantum yield of O 2 ( 1Δ g) and the relative quantum yield of O 2 − of EAHB were 0.15 and 0.76, respectively, with the parent compound hypocrellin B (HB) as the standard. It was inferred that Type I pathway was possibly a major photodynamic mechanism of EAHB. The study on photobiological action of EAHB on MGC803 cancer cells revealed that EAHB kept the same good phototoxic ability as HB but reduced 4 times cytotoxicity than HB, and also its photopotentiation factor increased 4-folds.