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We report a novel nanoassembly formulation for photodynamic therapy, which is composed of covalently iodine-concentrated organically modified silica (ORMOSIL) nanoparticles (diameter < 30 nm) and a hydrophobic photosensitizer embedded therein. Comparative studies with iodinated and noniodinated nanoparticles have demonstrated that the intraparticle external heavy-atom effect on the encapsulated photosensitizer molecules significantly enhances the efficiency of 1O2 generation and, thereby, the in vitro PDT efficacy.

New methods for conversion of unstable bacteriochlorophyll-a present in Rb. sphaeroides into stable bacteriochlorins are presented. Cyclic imide derivatives from related cyclic isoimide or amide analogs are obtained by intramolecular base catalyzed cyclization. Most of the new bacteriochlorins have long wavelength absorptions in the range of 796–822 nm. In preliminary screening, the isoimide analogs have shown promising in vivo photosensitizing activity for the treament of cancer by photodynamic therapy.

A first regioselective synthesis of bacteriochlorin by hydroxylation of metallated chlorin with OsO4 is discussed. This is the first example for the preparation of metallobacteriochlorin. This methodology can also be used for the preparation of unsymmetrical isobacteriochlorins by introducing electron-withdawing substituent(s) at the adjacent position(s) of the reduced ring. The Zn(II) vic-dihydroxybacteriochlorin obtained from 2-formyl-purpurin methyl ester showed long wavelength absorption at 828 nm which seems to be associated with electronic interactions of the substituents with the π-system of the macrocycle.

Efficient approaches to the synthesis of methyl esters and aspartyl amides of so-called ring ‘A’-benzoporphyrin derivatives from rhodoporphyrin XV dimethyl ester 10 and 3-vinylphylloerythrin methyl ester 22 are reported. The benzo-rings in the products are obtained by way of Diels-Alder [4+2] cyclizations which employ a dieneophile and the vinyl and 2,3-double bonds in the starting materials as the diene. In the 3-vinyl-phylloerythrin series, the presence of the 131-keto-group in ring E inhibits the Diels-Alder reaction with dimethyl acetylenedicarboxylate, but with more reactive dienophiles, such as tetracyanoethylene, the Diels-Alder adduct was isolated in modest yield. Protection of the 131-keto- group as a ketal or thioketal afforded the intermediate benzoporphyrin adducts, which were rearranged to trans- and cis- isomers on reacting with triethylamine and 1,8-diazabiclo[5,4,0]undec-7-ene, respectively. Among the sensitizers tested so far, the benzoporphyrin derivative (cis- isomer) obtained from rhodoporphyrin XV di-tert- butyl aspartate showed the best in vivo photosensitizing activity in DBA/2 mice transplanted with SMT/F tumors.

The anti-cancer activity of dimers joined with ether, ester or carbon-carbon bonds by photodynamic therapy (PDT) was compared by using DBA/2 mice transplanted with SMT/F tumors. Dimers with ether and carbon-carbon linkages were found to be more effective than those linked with ester bonds. Variation of the substituents at peripheral positions made a significant difference in in vivo efficacy. Among the ether and carbon-carbon linked dimers, the divinyl analogs were found to be most effective. The preliminary in vivo results also suggest that the position(s) of the hydrophilic substituents in the molecules make a remarkable difference in photosensitizing activity. An unsymmetrical dimer with an amide linkage, obtained from 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH) was found to be less effective than HPPH.

Nuclear Overhauser enhancement experiments show that migratory aptitudes of alkyl groups in various vis-dihydroxybacteriopurpurins are different for individual stereoisomers. Long wavelength absorption maxima of ketobacteriopurpurins obtained from pinacol-pinacolone rearrangements of the corresponding diols are influenced by the position of the keto group in the macrocycle; differences in these maxima are diminished by introduction of electron-withdrawing substituents.

Syntheses and comparative in vivo photosensitizing efficacy of a series of chlorophyll-a derivatives with (1-heptyloxyethyl) substituents at various positions are discussed. Compared with Photofrin®, the n-heptyl ether analogues showed better in vivo sensitizing activity (DBA/2 mice transplanted with SMT/F tumors) as well as reduced skin phototoxicity. The Vilsmeier formylation of copper(II) methyl mesopyropheophorbide-a 11 did not produce the expected meso-formyl derivative 12 , but instead gave the α,β-unsaturated chloroformyl analogue 13 as the major product.

Base catalyzed cyclization of a 5,15-di(4-pyridyl)octaalkylporphyrin-5-acrylate 6 yields smoothly the corresponding purpurin 2 . Quaternization with methyl iodide yielded the corresponding cationic N,N′-dimethylpyridiniumpurpurin 3 ; X-ray crystallography of purpurin 2 , the first purpurin to be studied crystallographically, shows the two β-alkyl groups on the saturated ring of the purpurin have a syn configuration, and the macrocycle to have a slight saddle shape with a mean deviation of 0.230 A from the least-squares plane calculated for the core atoms.

A first report on the biological evaluation of a series of isomerically pure benzoporphyrin derivatives (cis- and trans-isomers) as methyl esters is described. In preliminary in vivo studies, the n-hexyl ether analogues of both cis- and trans-isomers of benzoporphyrin derivatives were found to be more active than the industrially prepared benzoporphyrin derivative, a mixture of monocarboxylic acids (BPDMA, Quadralogic Technologies, Vancouver). Further studies with 4-de-vinyl-4- (1-hexyloxyethyl) benzoporphyrin derivative showed that, like BPDMA, it had reduced residual skin phototoxicity compared in mice with Photofrin. The uptake and clearance characteristics of BPDMA were also compared with the 4-(1-hexyloxyethyl)-derivative by in vivo reflection spectroscopy.

Starting from methyl 9-deoxymesopyropheophorbide-a 5 , regioselective synthesis of a series of benzochlorins was achieved. These compounds have long wavelength absorptions in the range of 710–756 nm. The in vivo spectroscopic properties as well as the uptake and clearance characteristics of some of these compounds (e.g. 13 ) were determined by use of in vivo reflection spectroscopy.

Treatment of various vinyl-porphyrins and -chlorins with 2′,3′,5′-tri-O-acetyl-5-chloromercuriuridine under “Heck conditions” affords both trans- and gem-nucleoside adducts in ratios which depend upon the nature of the vinyl-porphyrin or -chlorin.

A series of new bacteriochlorins was synthesized using 13(2)-oxo-bacteriopyropheophorbide a (derived from bacteriochlorophyll a) as a starting material, which on reacting with o-phenylenediamine and 1,10-diaminonaphthalene afforded highly conjugated annulated bacteriochlorins with fused quinoxaline, benzimidazole, and perimidine rings, respectively. The absorption spectra of these novel bacteriochlorins demonstrated remarkably red-shifted intense Q(y) absorption bands observed in the range of 816-850 nm with high molar extinction coefficients (89,900-136,800). Treatment of 13(2)-oxo-bacteriopyropheophorbide a methyl ester with diazomethane resulted in the formation of bacterioverdins containing a fused six-membered methoxy-substituted cyclohexenone (verdin) as an isomeric mixture. The pure isomers which exhibit long-wavelength absorptions in the near-IR region (865-890 nm) are highly stable at room temperature with high reactivity with O(2) at the triplet photoexcited state and favorable redox potential and could be potential candidates for use as photosensitizers in photodynamic therapy (PDT).

We describe the development of novel and biocompatible core/shell (α-NaYbF(4):Tm(3+))/CaF(2) nanoparticles that exhibit highly efficient NIR(in)-NIR(out) upconversion (UC) for high contrast and deep bioimaging. When excited at ~980 nm, these nanoparticles emit photoluminescence (PL) peaked at ~800 nm. The quantum yield of this UC PL under low power density excitation (~0.3 W/cm(2)) is 0.6 ± 0.1%. This high UC PL efficiency is realized by suppressing surface quenching effects via heteroepitaxial growth of a biocompatible CaF(2) shell, which results in a 35-fold increase in the intensity of UC PL from the core. Small-animal whole-body UC PL imaging with exceptional contrast (signal-to-background ratio of 310) is shown using BALB/c mice intravenously injected with aqueously dispersed nanoparticles (700 pmol/kg). High-contrast UC PL imaging of deep tissues is also demonstrated, using a nanoparticle-loaded synthetic fibrous mesh wrapped around rat femoral bone and a cuvette with nanoparticle aqueous dispersion covered with a 3.2 cm thick animal tissue (pork).

We describe here the development of multifunctional nanocarriers, based on amine-functionalized biodegradable polyacrylamide nanoparticles (NPs), for cancer theranostics, including active tumor targeting, fluorescence imaging, and photodynamic therapy. The structural design involves adding primary amino groups and biodegradable cross-linkers during the NP polymerization, while incorporating photodynamic and fluorescent imaging agents into the NP matrix, and conjugating PEG and tumor-targeting ligands onto the surface of the NPs. The as-synthesized NPs are spherical, with an average diameter of 44 nm. An accelerated biodegradation study, using sodium hydroxide or porcine liver esterase, indicated a hydrogel polymer matrix chain collapse within several days. By using gel permeation chromatography, small molecules were detected, after the degradation. In vitro targeting studies on human breast cancer cells indicate that the targeted NPs can be transported efficiently into tumor cells. Incubating the multifunctional nanocarriers into cancer cells enabled strong fluorescence imaging. Irradiation of the photosensitizing drug, incorporated within the NPs, with light of a suitable wavelength, causes significant but selective damage to the impregnated tumor cells, but only inside the illuminated areas. Overall, the potential of polymeric-based NPs as biodegradable, multifunctional nanocarriers, for cancer theranostics, is demonstrated here.

The synthesis and spectroscopic properties of a novel biliverdin 4 with one inverted pyrrole ring are described; the dipyrromethane 8 and a,c-biladiene 6 were the key intermediates in the synthesis of 4 .

Three new metal-free porphyrins, corallistin B, corallistin C and corallistin E isolated from the demosponge Corallistes sp. were synthesized as methyl esters in excellent yield by using either the MacDonald or a,c-biladiene routes to porphyrins.

Purpurin-18 methyl ester 1a was converted into a series of new bacteriochlorins 2b , 2c , 2f and 4b . These stable bacteriochlorins have strong long wavelength absorptions in the range of 760 to 816 nm, and were tested for in vivo photosensitizing activity using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. In preliminary screening, among the photosensitizers tested so far, bacteriochlorins 2f and 4b have shown promising anti-tumor activity.

A hydrophobic photosensitizer, 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH), was loaded into nontoxic biodegradable amine functionalized polyacrylamide (AFPAA) nanoparticles using three different methods (encapsulation, conjugation, and post-loading), forming a stable aqueous dispersion. Each formulation was characterized for physicochemical properties as well as for photodynamic performance so as to determine the most effective nanocarrier formulation containing HPPH for photodynamic therapy (PDT).HPPH or HPPH-linked acrylamide was added into monomer mixture and polymerized in a microemulsion for encapsulation and conjugation, respectively. For post-loading, HPPH was added to an aqueous suspension of pre-formed nanoparticles. Those nanoparticles were tested for optical characteristics, dye loading, dye leaching, particle size, singlet oxygen production, dark toxicity, in vitro photodynamic cell killing, whole body fluorescence imaging and in vivo PDT.HPPH was successfully encapsulated, conjugated or post-loaded into the AFPAA nanoparticles. The resultant nanoparticles were spherical with a mean diameter of 29 ± 3 nm. The HPPH remained intact after entrapment and the HPPH leaching out of nanoparticles was negligible for all three formulations. The highest singlet oxygen production was achieved by the post-loaded formulation, which caused the highest phototoxicity in in vitro assays. No dark toxicity was observed. Post-loaded HPPH AFPAA nanoparticles were localized to tumors in a mouse colon carcinoma model, enabling fluorescence imaging, and producing a similar photodynamic tumor response to that of free HPPH in equivalent dose.Post-loading is the promising method for loading nanoparticles with hydrophobic photosensitizers to achieve effective in vitro and in vivo PDT.

Purpurinimide methyl esters, bearing variable lengths of N-substitutions, were conjugated individually to a cyanine dye with a carboxylic acid functionality. The results obtained from in vitro and in vivo studies showed a significant impact of the linkers joining the phototherapeutic and fluorescence imaging moieties. The photosensitizer-fluorophore conjugate with a PEG linker showed the highest uptake in the liver, whereas the conjugate linked with two carbon units showed excellent tumor-imaging and PDT efficacy at 24 h postinjection. Whole body imaging and biodistribution studies at variable time points portrayed enhanced fluorescent uptake of the conjugates in the tumor compared to that in the skin. Interestingly, the conjugate with the shortest linker and the one joining with two carbon units showed faster clearance from normal organs, e.g., the liver, kidney, spleen, and lung, compared to that in tumors. Both imaging and PDT efficacy of the conjugates were performed in BALB/c mice bearing Colon26 tumors. Compared to the others, the short linker conjugate showed poor tumor fluorescent properties and as a corollary does not exhibit the dual functionality of the photosensitizer-fluorophore conjugate. For this reason, it was not evaluated for in vivo PDT efficacy. However, in Colon26 tumor cells (in vitro), the short linker was highly effective. Among the conjugates with variable linkers, the rate of energy transfer from the purpurinimide moiety to the cyanine moiety increased with deceasing linker length, as examined by femtosecond laser flash photolysis measurements. No electron transfer from the purpurinimide moiety to the singlet excited state of the cyanine moiety or from the singlet excited state of the cyanine moiety to the purpurinimide moiety occurred as indicated by a comparison of transient absorption spectra with spectra of the one-electron oxidized and one-electron reduced species of the conjugate obtained by spectroelectrochemical measurements.

In this report, we present a regioselective oxidation of a series bacteriochlorins, which on reacting with either ferric chloride (FeCl(3)) or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) yielded the corresponding ring-B or ring-D reduced chlorins. The effect of the number of electron-withdrawing groups present at the peripheral position, with or without a fused isocyclic ring (ring-E), did not make any significant difference in regioselective oxidation of the pyrrole rings. However, depending on the nature of substituents, the intermediate bis-dihydroxy bacteriochlorins on subjecting to pinacol-pinacolone reaction conditions gave various ketochlorins. The introduction of the keto-group at a particular position in the molecule possibly depends on the stability of the intermediate carbocation species. The newly synthesized bacteriochlorins show strong long-wavelength absorption and produced significant in vitro (Colon26 cells) photosensitizing ability. Among the compounds tested, the bacteriochlorins containing a keto-group at position 7 of ring-B with cleaved five-member isocyclic ring showed the best efficacy.

The ATP-dependent transporter ABCG2 exports certain photosensitizers (PS) from cells, implying that the enhanced expression of ABCG2 by cancer cells may confer resistance to photodynamic therapy (PDT) mediated by those PS. In 35 patient-derived primary cultures of lung epithelial and stromal cells, PS with different subcellular localization and affinity for ABCG2 displayed cell-type specific retention both independent and dependent on ABCG2. In the majority of cases, the ABCG2 substrate 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH) was lost from fibroblastic cells more rapidly than from their epithelial counterparts, even in the absence of detectable ABCG2 expression, facilitating selective eradication by PDT of epithelial over fibroblastic cells in tumor/stroma co-cultures. Pairwise comparison of normal and transformed epithelial cells also identified tumor cells with elevated or reduced retention of HPPH, depending on ABCG2. Enhanced ABCG2 expression led to the selective PDT survival of tumor cells in tumor/stroma co-cultures. This survival pattern was reversible through HPPH derivatives that are not ABCG2 substrates or the ABCG2 inhibitor imatinib mesylate. PS retention, not differences in subcellular distribution or cell signaling responses, was determining cell type selective death by PDT. These data suggest that up-front knowledge of tumor characteristics, specifically ABCG2 status, could be helpful in individualized PDT treatment design.

In recent years several review articles and books have been published on the use of porphyrin-based compounds in photodynamic therapy (PDT). This critical review is focused on (i) the basic concept of PDT, (ii) advantages of long-wavelength absorbing photosensitizers (PS), (iii) a brief discussion on recent advances in developing PDT agents, and (iv) the various synthetic strategies designed at the Roswell Park Cancer Institute, Buffalo, for developing highly effective long-wavelength PDT agents and their utility in constructing the conjugates with tumor-imaging and therapeutic potential (Theranostics). The clinical status of certain selected PDT agents is also summarized (205 references).

Both bacteriopyropheophorbide-a and ring-B reduced pyropheophorbide-a on reacting with NBS (N-bromosuccinamide) undergo electrophilic bromination to provide 10-bromo analogs. The electronic nature of the substituents present at position-3 did not make any difference in the regioselective outcome of the brominated products. These relatively stable brominated chlorins and bacteriochlorins provide an easy way of introducing a wide variety of functionalities, which could be extremely useful in developing improved agents for biomedical applications and supramolecular chemistry.

Starting from rhodoporphyrin-SV dimethylo ester 4 and phylloerythrin methyl ester 5 new classes of isomerically pure benzoporphyrin analogues 7, 8, 11–17 were synthesized in high yields. These compounds have strong long wavelength absorptions in the red region and demonstrate activity against a transplanted mouse tumor.

Biophysical and photobiological properties of a group of bacteriochlorins were compared with efficacy of these products for photodynamic therapy of murine tumors. Predictive factors for selective photosensitization in vivo include affinity binding to lipoproteins greater than albumin, extinction coefficient at the wavelength of irradiation and tumor/skin distribution. Efficacy was correlated with circulating plasma levels of the different sensitizers but not with the photodynamic therapy response in cell culture.

The reconstitution kinetics of horse heart myoglobin, as met-cyano derivative, with two synthetic hemins in which the 6- or the 7-propionate is replaced by a methyl group, has been investigated by circular dichroism, in order to gain information on the heme re-orientation process following the heme insertion into the globin pocket. The results obtained confirm that the preferred heme orientation places the sole propionate into the position occupied by the 6-propionate in the crystal structure, supporting the importance of the salt bridge occurring between this propionate and the basic CD3 residue of the apoprotein. Moreover, they provide new information on the correlations existing between the shape and the intensity of the dichroic bands and the heme orientation inside the reconstituted protein. Our data suggest that positive Soret CD bands are associated with hemoglobins possessing, at equilibrium, the heme in the so-called ‘correct’ orientation (as in horse heart myoglobin), and negative dichroic bands are associated with hemoglobins possessing, at equilibrium, the heme in the so-called ‘reversed’ orientation (as for example, in Glycera dibranchiata hemoglobins). Thus, negligible contribution to the CD signal in reconstituted proteins can be associated to a ‘wrong’ orientation of the heme group, no matter whether the orientation at the equilibrium is the ‘correct’ or the ‘reversed’ one. Finally, the results obtained indicate that the perturbations due to the heme re-orientation appear as a local phenomenon, not affecting the distant domains of the macromolecule.

Translocator protein (TSPO) 18 kDa overexpression has been observed in a large variety of human cancers, especially breast cancers. PK 11195, an isoquinoline analogue, is one of the ligands of highest TSPO binding affinity. Due to the long biological half life of our photosensitizers, there is a need to label them with a long lived radioisotope, for example I-124. Our objectives are to find translocator protein targeted photosensitizers for both tumor imaging (PET) and photodynamic therapy (PDT). I-PK 11195 is conjugated with the tumor avid photosensitizer HPPH. We find that those two tumor avid components complement each other and make the conjugate molecule even more tumor avid; compared to the photosensitizer itself, the conjugate is found to show improved PDT efficacy. It is concluded that I-PK 11195 can be a good vehicle to deliver radionuclide and photosensitizer to TSPO overexpressed tumor regions. Such conjugates could be useful for both tumor imaging (PET) and PDT.

Photosensitizers (PS) synthesized with the aim of optimizing photodynamic therapy (PDT) of tumors do not always fulfill their potential when tested in vitro and in vivo in different tumor models. The ATP-dependent transporter ABCG2 a multi-drug resistant pump expressed at variable levels in cancerous cells, can bind and efflux a wide range of structurally different classes of compounds including several PS used pre-clinically and clinically such as porphyrins and chlorins. ABCG2 may lower intracellular levels of substrate PS below the threshold for cell death in tumors treated by PDT, leaving resistant cells to re-populate the tumor. To determine some of the structural factors that affect substrate affinity of PS for ABCG2, we used an ABCG2 expressing cell line (HEK 293 482R) and its non-expressing counterpart, and tyrosine kinase ABCG2 inhibitors in a simple flow cytometric assay to identify PS effluxed by the ABCG2 pump. We tested a series of conjugates of substrate PS with different groups attached at different positions on the tetrapyrrole macrocycle to examine whether a change in affinity for the pump occurred and whether such changes depended on the position or the structure/type of the attached group. PS without substitutions including pyropheophorbides and purpurinimides were generally substrates for ABCG2, but carbohydrate groups conjugated at positions 8, 12, 13 and 17 but not at position 3 abrogated ABCG2 affinity regardless of structure or linking moiety. At position 3, affinity was retained with the addition of iodobenzene, alkyl chains and monosaccharides, but not with disaccharides. This suggests that structural characteristics at position 3 may offer important contributions to requirements for binding to ABCG2. We examined several tumor cell lines for ABCG2 activity, and found that although some cell lines had negligible ABCG2 activity in bulk, they contained a small ABCG2-expressing side population (SP) thought to contain cells which are responsible for initiating tumor regrowth. We examined the relevance of the SP to PDT resistance with ABCG2 substrates in vitro and in vivo in the murine mammary tumor 4T1. We show for the first time in vivo that the substrate PS HPPH (2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a) but not the non-substrate PS HPPH-Gal (a galactose conjugate of HPPH) selectively preserved the SP which was primarily responsible for regrowth in vitro. The SP could be targeted by addition of imatinib mesylate, a tyrosine kinase inhibitor which inhibits the ATPase activity of ABCG2, and prevents efflux of substrates. A PDT resistant SP may be responsible for recurrences observed both pre-clinically and clinically. To prevent ABCG2 mediated resistance, choosing non-substrate PS or administering an ABCG2 inhibitor alongside a substrate PS might be advantageous when treating ABCG2 expressing tumors with PDT.

Reactions of vinylchlorins and vinylporphyrins with N,N-dimethylmethyleneammonium iodide (“Eschenmoser's Reagent”) gives Mannich adducts in which substitution (with CH2NMe2) has taken place on the terminal carbon of the vinyl group to yield a trans-3-(N,N-dimethylaminomethyl)prop-1-enyl derivative. Under no circumstances was meso substitution observed. Use of zinc(II) vinylchlorins or zinc(II) vinylporphyrins afforded the corresponding zinc(II) trans-vinyl adducts at a significantly faster rate than the metal-free substrates. Reaction of Eschenmoser's reagent with deuteroporphyrin-IX dimethyl ester (29) (which possesses two peripherally unsubstituted positions) produces the bis-(N,N-dimethylaminomethyl) product (30). Treatment of the dimethylamino chlorins and porphyrins with methyl iodide, in all cases, gives an excellent yield of the corresponding quaternary ammonium iodides, and these compounds are highly water-soluble.

Starting from rhodoporphyrin-SV dimethylo ester 4 and phylloerythrin methyl ester 5 new classes of isomerically pure benzoporphyrin analogues 7, 8, 11–17 were synthesized in high yields. These compounds have strong long wavelength absorptions in the red region and demonstrate activity against a transplanted mouse tumor.

Base catalyzed cyclization of a 5,15-di(4-pyridyl)octaalkylporphyrin-5-acrylate 6 yields smoothly the corresponding purpurin 2 . Quaternization with methyl iodide yielded the corresponding cationic N,N′-dimethylpyridiniumpurpurin 3 ; X-ray crystallography of purpurin 2 , the first purpurin to be studied crystallographically, shows the two β-alkyl groups on the saturated ring of the purpurin have a syn configuration, and the macrocycle to have a slight saddle shape with a mean deviation of 0.230 A from the least-squares plane calculated for the core atoms.

In recent years several review articles and books have been published on the use of porphyrin-based compounds in photodynamic therapy (PDT). This critical review is focused on (i) the basic concept of PDT, (ii) advantages of long-wavelength absorbing photosensitizers (PS), (iii) a brief discussion on recent advances in developing PDT agents, and (iv) the various synthetic strategies designed at the Roswell Park Cancer Institute, Buffalo, for developing highly effective long-wavelength PDT agents and their utility in constructing the conjugates with tumor-imaging and therapeutic potential (Theranostics). The clinical status of certain selected PDT agents is also summarized (205 references).

A new class of stable bacteriochlorins, namely benzobacteriopurpurin bearing two exo-cyclic rings was synthesized by way of Diels-Alder cycloaddition of 8-vinyl-mesopurpurin-18 methyl ester with tetracyanoethylene (TCNE) and dimethyl acetylenedicarboxylate (DMAD). These novel bacteriochlorins have long wavelength absorptions in the range of 760 to 795 nm.

Multiple, complementary techniques for tumor detection, including magnetic resonance, nuclear and optical imaging, are under active development; each approach has particular strengths and advantages. Efforts are also currently underway to develop bifunctional agents, so that a single molecule can be used for imaging, therapy, and monitoring the long-term tumor response. This chapter is mainly focused on illustrating the utility of certain tumor-avid photosensitizers in developing agents for tumor imaging [fluorescence, magnetic resonance imaging (MRI), positron emission tomography (PET)] and photodynamic therapy. Recent approaches for developing target-specific agents for photodynamic therapy (PDT) and in vivo tumor imaging are also briefly discussed.

Reaction of 3-vinylemeraldin with dimethyl acetylenedicarboxylate (DMAD) produced a benzoporphyrin derivative via [4+2] Diels-Alder adduct and an unexpected porphyrin containing a seven-membered ring system (yield 15%) fused at the 3- and 5-positions of the macrocycle. The benzoporphyrin derivatives containing N-alkylated fused imide ring system exhibit long wavelength absorptions near λmax 725 nm. In preliminary in vivo screening some of these analogs were found to be more effective than the related protoporphyrin IX (PP-IX) based benzoporphyrin derivative (BPDMA).

A first report to demonstrate the utility of (trifluoromethyl)trimethylsilane as an efficient reagent for the synthesis of perfluorinated porphyrins, chlorins and bacteriochlorins is presented.

The first example demonstrating the utility of enyne metathesis in preparing a chlorin–diene system as a novel and versatile building block is discussed; Diels–Alder reaction [4 + 2] of the diene with fullerene (C60) produced the chlorin–fullerene dyad, a new artificial photosynthetic model; compared to the non-fullerene analogs, the corresponding free base and ZnII chlorin–C60 dyads showed a remarkable decrease in their fluorescence intensity, indicating a rapid quenching of the chlorin excited singlet state by the fullerene moiety.

For a comparative study, 3-(alkyloxyethyl)-3-devinylpurpurin-18-N-hexylimides with ester and amide functionalities were investigated for tumor selectivity and in vivo photosensitizing efficacy. Compared to amide analogues, the related photosensitizers with ester functionalities were found to be more effective. Among these compounds the 3-devinyl-(3-hexyloxyethyl)-purpurin-18-N-hexylimide as methyl ester 12 Download : Download high-res image (209KB) Download : Download full-size image Scheme 1 . (a) Zn(Br)2/HMDS, hexylamine, toluene, reflux; (b) HBr/AcOH; (c) alkyl alcohol; (d) alkyl amine; (e) CH2N2; (g) MeOH/KOH; (f) aq LiOH/MeOH/THF; (g) DCC/H2N–(CH2)5CH3. showed excellent tumor uptake (tumor versus muscle ratio: 8:1), and produced 100% tumor cure on day 30 at a dose of 1.0 μmol/kg. The mice were treated with light (135 J/cm2, 705 nm) at 24 h post injection of the drug.

To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with osmium tetraoxide, and the pinacol−pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol−pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In cont...

Conjugates of 3-(1′-hexyloxyethyl)-3-devinyl pyropheophorbide-a (HPPH) with multiple Gd(III)aminobenzyl diethylenetriamine pentacetic acid (ADTPA) moieties were evaluated for tumor imaging and photodynamic therapy (PDT). In vivo studies performed in both mice and rat tumor models resulted in a significant MR signal enhancement of tumors relative to surrounding tissues at 24h post-injection. The water soluble (pH: 7.4) HPPH-3Gd(III) ADTPA conjugate demonstrated high potential for tumor imaging by MR and fluorescence. This agent also produced long-term tumor cures via PDT. An in vivo biodistribution study with the corresponding 14C-analog also showed significant tumor-uptake 24 hours post-injection. Toxicological evaluations of HPHH-3Gd(III)ADTPA administered at and above imaging/therapeutic doses did not show any evidence of organ toxicity. Our present study illustrates a novel approach for the development of water soluble “multifunctional agents”, demonstrating efficacy for tumor imaging (MR and fluorescence) and phototherapy.

We quantified fluorescence photobleaching of bifunctional agent (HPPH-CD) during PDT with fluorescence imaging. HPPH-CD exhibit preferential uptake in tumors compared to surrounding normal tissue and longer wavelength emitting CD allowed monitoring photobleaching in deep tumors.

Multiple, complementary techniques for tumor detection, including magnetic resonance, nuclear and optical imaging, are under active development; each approach has particular strengths and advantages. Efforts are also currently underway to develop bifunctional agents, so that a single molecule can be used for imaging, therapy, and monitoring the long-term tumor response. This chapter is mainly focused on illustrating the utility of certain tumor-avid photosensitizers in developing agents for tumor imaging [fluorescence, magnetic resonance imaging (MRI), positron emission tomography (PET)] and photodynamic therapy. Recent approaches for developing target-specific agents for photodynamic therapy (PDT) and in vivo tumor imaging are also briefly discussed.

Regiospecificity of pyrrole subunit OsO4 oxidation in porphyrins is affected significantly by the presence of electron-withdrawing groups on the macrocycle, the oxidation taking place at the subunit in the quadrant opposite to the electronegative group. Migratory aptitudes in subsequent pinacol-pinacolone rearrangements of porphyrin and pheophorbide vic-dihydroxy systems are likewise dependent upon the presence of electron-withdrawing functionalities.