Core-shell polymeric nanoparticles co-loaded with photosensitizer and organic dye for photodynamic therapy guided by fluorescence imaging in near and short-wave infrared spectral regions

BACKGROUND

Biodistribution of photosensitizer (PS) in photodynamic therapy (PDT) can be assessed by fluorescence imaging that visualizes the accumulation of PS in malignant tissue prior to PDT. At the same time, excitation of the PS during an assessment of its biodistribution results in premature photobleaching and can cause toxicity to healthy tissues. Combination of PS with a separate fluorescent moiety, which can be excited apart from PS activation, provides a possibility for fluorescence imaging (FI) guided delivery of PS to cancer site, followed by PDT.

RESULTS

In this work, we report nanoformulations (NFs) of core-shell polymeric nanoparticles (NPs) co-loaded with PS [2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a, HPPH] and near infrared fluorescent organic dyes (NIRFDs) that can be excited in the first or second near-infrared windows of tissue optical transparency (NIR-I, ~ 700-950 nm and NIR-II, ~ 1000-1350 nm), where HPPH does not absorb and emit. After addition to nanoparticle suspensions, PS and NIRFDs are entrapped by the nanoparticle shell of co-polymer of N-isopropylacrylamide and acrylamide [poly(NIPAM-co-AA)], while do not bind with the polystyrene (polySt) core alone. Loading of the NIRFD and PS to the NPs shell precludes aggregation of these hydrophobic molecules in water, preventing fluorescence quenching and reduction of singlet oxygen generation. Moreover, shift of the absorption of NIRFD to longer wavelengths was found to strongly reduce an efficiency of the electronic excitation energy transfer between PS and NIRFD, increasing the efficacy of PDT with PS-NIRFD combination. As a result, use of the NFs of PS and NIR-II NIRFD enables fluorescence imaging guided PDT, as it was shown by confocal microscopy and PDT of the cancer cells in vitro. In vivo studies with subcutaneously tumored mice demonstrated a possibility to image biodistribution of tumor targeted NFs both using HPPH fluorescence with conventional imaging camera sensitive in visible and NIR-I ranges (~ 400-750 nm) and imaging camera for short-wave infrared (SWIR) region (~ 1000-1700 nm), which was recently shown to be beneficial for in vivo optical imaging.

CONCLUSIONS

A combination of PS with fluorescence in visible and NIR-I spectral ranges and, NIR-II fluorescent dye allowed us to obtain PS nanoformulation promising for see-and-treat PDT guided with visible-NIR-SWIR fluorescence imaging.

Uptake of Chlorin e6 Photosensitizer by Polystyrene-Diphenyloxazole-Poly(N-Isopropylacrylamide) Hybrid Nanosystem Studied by Electronic Excitation Energy Transfer

Polystyrene (PS)-diphenyloxazole (PPO) nanoparticles with attached cross-linked poly-N-isopropylacrylamide (PNIPAM) chains were obtained resulting in PS-PPO-PNIPAM hybrid nanosystems (NS). Fluorescence spectra of chlorin e₆ added to PS-PPO-PNIPAM hybrid NS revealed electronic excitation energy transfer (EEET) from PS matrix and encapsulated PPO to chlorin e₆. EEET efficiency increased strongly during 1 h after chlorin e₆ addition, indicating that uptake of chlorin e₆ by PNIPAM part of hybrid NS still proceeds during this time. Heating of PS-PPO-PNIPAM-chlorin e₆ NS from 21 to 39 °C results in an enhancement of EEET efficiency; this is consistent with PNIPAM conformation transition that reduces the distance between PS-PPO donors and chlorin e₆ acceptors. Meanwhile, a relatively small part of chlorin e₆ present in the solution is bound by PNIPAM; thus, further studies in this direction are necessary.

The Mechanism of Benzothiazole Styrylcyanine Dyes Binding with dsDNA: Studies by Spectral-Luminescent Methods

In the presented work studies of the interaction mode of monomer and two homodimer benzothiazole styryl dyes containing spermine-like linkage/tail group with the double stranded (ds) DNA are reported. For these dyes, equilibrium constant of dye binding to DNA (K(b)), as well as the number of dsDNA base pairs occupied by one bound dye molecule (n) were determined. The data obtained show that the presence of spermine-like group containing quaternary nitrogen (Bos-5) results in increase of K(b) value as compared to this of unsubstituted analogue (Sbt). Besides, for the dimer dyes containing benzothiazole styryl chromophores, the K(b) value is either five times higher (DBos-13) or almost the same (DBsu-10) as compared to this of corresponding monomer Sbt, depending on the position in the benzothiazole ring where the linker is attached. Moreover, the n values for both dimers are significantly different as well, pointing to the bis-intercalative binding mechanism for DBos-13 and for the groove-binding one for DBsu-10. The conclusion about the dimer dyes-dsDNA binding mechanisms is also supported by the study of the fluorescent response of these dyes on the presence of AT- and GC-containing polynucleotides.

Studies of monomeric and homodimeric oxazolo[4,5-b]pyridinium cyanine dyes as fluorescent probes for nucleic acids visualization

The series of recently synthesized monomeric and homodimeric cyanine dyes based on monomethine cyanine chromophore with oxazolo[4,5-b]pyridinium and quinoline end groups [Vassilev A, Deligeorgiev T, Gadjev N, Drexhage K-H. Synthesis of novel monomeric and homodimeric cyanine dyes based on oxazolo[4,5-b]pyridinium and quinolinium end groups for nucleic acid detection, Dyes Pigm 2005;66:135-142] were studied as possible fluorescent probes for nucleic acids detection. Significant fluorescence enhancement and intensity level (quantum yield up to 0.75) was observed for all the dyes in the presence of DNA. The oxazolo[4,5-b]pyridinium cyanines demonstrated high sensitivity as fluorescent stains for post-electrophoretic visualization of nucleic acids in agarose gels upon both VIS and UV transillumination, and the visualized band contained 0.8 ng of dsDNA.

Fluorescence of Styryl Dyes-DNA Complexes Induced by Single- and Two-Photon Excitation

The series of novel monomer and homodimer styryl dyes based on (p-dimethylaminostyryl) benzothiazolium residues were synthesized and studied as possible fluorescent probes for nucleic acids detection. Spectral-luminescent and spectral-photometric properties of obtained dyes in the unbound state and in DNA presence were studied. Fluorescence emission induced by two-photon excitation of dye-DNA complexes in aqueous buffer solution was registered. Two-photon absorption cross section values of the studied dyes in DNA presence were evaluated.

Fluorescent properties of pentamethine cyanine dyes with cyclopentene and cyclohexene group in presence of biological molecules

A series of pentamethine cyanine dyes with cyclohexene or cyclopentene group in polymethyne chain, assumed as DNA groove-binders, were studied as fluorescent probes for nucleic acids as well as for native and denatured proteins. It was revealed that the presence of methyl or dimethyl substituent in 5 position of the cyclohexene group hinders the formation of dye-DNA fluorescent complex, while the methyl substituent in 2 position leads to the increasing of the dye-DNA complex fluorescence intensity. The dyes SL-251, SL-1041, and SL-1046 containing methyl group in the 2 position of the cyclic group, are reported as bright DNA-sensitive dyes. The study of the dyes DNA-binding specificity demonstrated significant AT-preference that points to the groove-binding interaction mode. At the same time, the dyes SL-251, SL-377, and SL-957 with the 2-methyl substituted cyclohexene group were shown to be sensitive fluorescent dyes both for nonspecific (in SDS presence) proteins detection and for native BSA.

Luminescence spectroscopic studies of trimethinecyanines substituted in polymethine chain with nucleic acids and proteins

The series of symmetrical beta-substituted and alpha,gamma-substituted trimethinecyanine dyes were studied for their absorption and fluorescent characteristics in unbound state and in the presence of nucleic acids and proteins. It was shown that beta-substituted and alpha,gamma-bridged trimethinecyanines containing extended heterocyclic systems or N-phenyl as well as N-cyclohexyl substituents demonstrate increased affinity to proteins. At the same time the presence of both N-phenyl and N-cyclohexyl substituents leads to the decrease of the dye fluorescence intensity in complexes with nucleic acids. For trimethinecyanines similarly to unsymmetrical monomethines the presence of N-omega-hydroxy alkyl substituents results in the increase of fluorescence intensity of dye-DNA complex and the emission decrease of dye-RNA complex.

Interaction of cyanine dyes with nucleic acids: XXVI. Intercalation of the trimethine cyanine dye cyan 2 into double-stranded DNA: study by spectral luminescence methods

The interaction between double-stranded (ds) DNA and the cyanine dye Cyan 2 has been studied with spectral luminescence methods. Binding constant values have been determined by fluorescence titration and dye distribution in the two-phase system ethyl acetate-water (3.6 x 10(4) and 1.5 x 10(4) M(-1), respectively). Cyan 2 exhibits a small specificity for guanine-cytosine (GC) sequences in total DNA and synthetic polydeoxynucleotides poly(dA/dT) and poly(dGdC/dGdC). The DNA complexes with Cyan 2 are stable at high-ionic strength solution when NaCl is added. The dye molecule complexed with DNA is apparently shielded from the anionic quencher--iodide ion. The negative linear dichroism of the visible absorption band of aligned Cyan 2-DNA complexes indicates that the bound dye lies almost perpendicularly to the DNA helix axis. The linear dichroism of the absorption band at 260 nm suggests a considerable change in the DNA B-form. The results are consistent with an intercalative binding interaction between Cyan 2 and ds DNA.

Nonradiative deactivation of the electronic excitation energy in cyanine dyes: influence of binding to DNA

The processes of nonradiative deactivation of electronic excitation energy in cyanine dyes determine their quantum yield. Because of that, the study of the influence of cyanines binding to DNA on these processes can provide information on the causes leading to the cyanines fluorescence intensity enhancement in the presence of DNA. In the presented paper, the activation energies of nonradiative degradation of electronic excitation, quantum yields and rate constants of nonradiative transitions of several cyanines in free state and in the presence of DNA were established and compared. The mechanisms of nonradiative deactivation of dye excitation energy were discussed.

Interaction of cyanine dyes with nucleic acids. XVIII. Formation of the carbocyanine dye J-aggregates in nucleic acid grooves

Spectral properties of carbocyanine dye 3-methyl-2-[3-methyl-2-(3-methyl-2,3-dihydro-1,3-benzothiazole-2-iliden)-1- butenyl]-1,3-benzothiazole-3-il iodide (Cyan betaiPr) in water solution, as well as in the presence of different types of double stranded DNA have been studied. While in water solution of 'free' dye Cyan betaiPr stays mainly in monomeric form, in the presence of DNA the dye molecules form J-aggregates. The molecular structure of these J-aggregates causes the Davydov splitting of their absorption band, corresponding to the first electronic transition. A study of site-specificity showed that in the presence of poly (dA/dT) the majority of Cyan betaiPr molecules form J-aggregates, while in the presence of poly (dGC/dGC) dye molecules stay mainly in monomeric form and in presence of chicken erythrocytes DNA both J-aggregate and monomeric forms of dye are present. We suppose that Cyan betaiPr molecules aggregate in DNA groove, which serves as a template for J-aggregate forming. An increase of ionic strength of solution leads to the release of dye molecules from DNA grooves and prevents J-aggregates formation.

Interaction of cyanine dyes with nucleic acids. XXI. Arguments for half-intercalation model of interaction

The spectral luminescent properties of two groups of monomethine cyanine dyes were studied in the presence of DNA. The first group included five dyes with 5,6-methylenedioxy-[d]-benzo-1,3-thiazole heterocycle and their unsubstituted analogs. Five monomethine pyrylium cyanines and their N-methyl-pyridine analogs were included in the second group. In each pair the pyrylium and pyridine dyes had similar geometry but differed in charge density distribution. The results presented some evidence in favor of the half-intercalation interaction mode between the studied dyes and DNA. When the benzothiazole residue had the lowest electron donor ability between the two heterocycles in the dye molecule, its substitution with the bulky methylenedioxy group led to a significant decrease in fluorescence enhancement of the dye-DNA complex. On the contrary, when the substituents that create steric hindrance (e.g., methylenedioxy and methyl groups) were introduced into the heterocycle with the higher electron donor ability, the fluorescence enhancement value of the dye-DNA complex was virtually unchanged. The changes in the Stock's shift values upon the formation of the dye-DNA complexes were in agreement with the proposed half-intercalation model. Interestingly, in the dye-DNA complexes the pyrylium dyes probably resided in a place similar to the pyridine ones. It is possible that the benzothiazole (or benzooxazole) ring intercalated between the DNA bases and the pyrylium (or pyridine) residue was located in the DNA groove closer to the phosphate backbone.