Pui-Chi Lo

Phthalocyanine−Polyamine Conjugates as Highly Efficient Photosensitizers for Photodynamic Therapy

A series of silicon(IV) phthalocyanines substituted axially with different polyamine moieties have been prepared. Their fluorescence quantum yields (Φ(F) = 0.03-0.08) in N,N-dimethylformamide are low because of reductive quenching by the amino moieties. The values are significantly increased in aqueous media (Φ(F) = 0.12-0.21) as a result of protonation of the amino substituents. All the compounds are highly photocytotoxic against human colon adenocarcinoma HT29 cells and Chinese hamster ovary cells with IC(50) values as low as 1.1 nM. Flow cytometric studies of two selected compounds (2 and 5) against HT29 cells have shown that they induce apoptosis extensively. As shown by confocal microscopy, these two compounds also show high affinity toward the lysosomes, but not the mitochondria, of the cells. Their in vivo photodynamic activity has also been investigated using HT29 tumor bearing nude mice. Both of them can effectively inhibit the growth of the tumor without causing apparent injury to the liver of the mice.

HDL‐Mimicking Peptide–Lipid Nanoparticles with Improved Tumor Targeting

Targeted delivery of intracellularly active diagnostics and therapeutics in vivo is a major challenge in cancer nanomedicine. A nanocarrier should possess long circulation time yet be small and stable enough to freely navigate through interstitial space to deliver its cargo to targeted cells. Herein, it is shown that by adding targeting ligands to nanoparticles that mimic high-density lipoprotein (HDL), tumor-targeted sub-30-nm peptide-lipid nanocarriers are created with controllable size, cargo loading, and shielding properties. The size of the nanocarrier is tunable between 10 and 30 nm, which correlates with a payload of 15-100 molecules of fluorescent dye. Ligand-directed nanocarriers targeting epidermal growth factor receptor (EGFR) are confirmed both in vitro and in vivo. The nanocarriers show favorable circulation time, tumor accumulation, and biodistribution with or without the targeting ligand. The EGFR targeting ligand is proved to be essential for the EGFR-mediated tumor cell uptake of the nanocarriers, a prerequisite of intracellular delivery. The results demonstrate that targeted HDL-mimetic nanocarriers are useful delivery vehicles that could open new avenues for the development of clinically viable targeted nanomedicine.

Photodynamic Molecular Beacon Triggered by Fibroblast Activation Protein on Cancer-Associated Fibroblasts for Diagnosis and Treatment of Epithelial Cancers

Fibroblast activation protein (FAP) is a cell-surface serine protease highly expressed on cancer-associated fibroblasts of human epithelial carcinomas but not on normal fibroblasts, normal tissues, and cancer cells. We report herein a novel FAP-triggered photodynamic molecular beacon (FAP-PPB) comprising a fluorescent photosensitizer and a black hole quencher 3 linked by a peptide sequence (TSGPNQEQK) specific to FAP. FAP-PPB was effectively cleaved by both human FAP and murine FAP. By use of the HEK293 transfected cells (HEK-mFAP, FAP(+); HEK-vector, FAP(-)), systematic in vitro and in vivo experiments validated the FAP-specific activation of FAP-PPB in cancer cells and mouse xenografts, respectively. FAP-PPB was cleaved by FAP, allowing fluorescence restoration in FAP-expressing cells while leaving non-expressing FAP cells undetectable. Moreover, FAP-PPB showed FAP-specific photocytotoxicity toward HEK-mFAP cells whereas it was non-cytotoxic toward HEK-Vector cells. This study suggests that the FAP-PPB is a potentially useful tool for epithelial cancer detection and treatment.

Preparation of unsymmetrical distyryl BODIPY derivatives and effects of the styryl substituents on their in vitro photodynamic properties

A series of unsymmetrical distyryl BODIPYs have been prepared which function as highly potent photosensitisers with in vitro IC(50) values as low as 15 nM. Their cellular uptake, subcellular localisation and photocytotoxicity depend greatly on the styryl substituents.

Phthalocyanine–Polyamine Conjugates as pH‐Controlled Photosensitizers for Photodynamic Therapy

A series of aryl hydroxyamines prepared by reductive amination were treated with silicon(IV) phthalocyanine dichloride in the presence of pyridine to give the diaxially substituted phthalocyanine-polyamine conjugates 1-5. The electronic absorption, fluorescence emission, and efficiency at generating reactive oxygen species of these compounds were all sensitive to the pH environment. Under acidic conditions, the fluorescence quantum yields and the singlet oxygen quantum yields of these compounds were greatly enhanced in DMF as a result of protonation of the amino moieties, which inhibited the photoinduced electron-transfer deactivation pathway. The Q band was diminished and broadened, and the fluorescence intensity decreased as the pH increased in citrate buffer solutions. The rate of superoxide radical formation was also reduced in a higher pH environment. Compound 3, containing a terminal 4-chlorophenyl group at the axial substituent, showed the most desirable pH-responsive properties, which makes it a promising tumor-selective fluorescence probe and photosensitizer for photodynamic therapy. All of the phthalocyanines 1-5 were highly photocytotoxic against HT29 and HepG2 cells with IC(50) values as low as 0.03 microM. Compound 3 was highly selective toward lysosomes, but not mitochondria of HT29 cells.

Halogenated silicon(IV) phthalocyanines with axial poly(ethylene glycol) chains. Synthesis, spectroscopic properties, complexation with bovine serum albumin and in vitro photodynamic activities

A new series of unsubstituted and halogenated silicon(IV) phthalocyanines with two axial poly(ethylene glycol) (PEG) chains having an average molecular weight of 550 or 750 (PEG550 or PEG750) have been synthesised by treating the corresponding silicon phthalocyanine dichloride with PEG methyl ether in the presence of NaH. The compounds have been unambiguously characterised with 1H NMR and MALDI-TOF mass spectrometry. With two bulky polymeric substituents, the compounds are essentially non-aggregated in common organic solvents. The longer PEG750 chain enhances the hydrophilicity of the phthalocyanine ring and is more effective to prevent aggregation and fluorescence quenching by Cu(OAc)2. Substitution with heavier halogen atoms on the periphery of the ring leads to a reduction in fluorescence emission and an increase in singlet oxygen quantum yield, as a result of heavy atom effect. The compounds Si(PcX8)(PEG750)2 [X = H (4b), Cl (4c), Br (4d)] are photocytotoxic towards HepG2 human hepatocarcinoma cells and J774 mouse mammary tumour cells. Although halogenation results in an increase in singlet oxygen quantum yield, the general photocytotoxicity follows the order 4b > 4d > 4c. This can be attributed to the opposite effect of aggregation, which follows the order 4a < 4b < 4c in the growth medium. The interactions of 4b–d with bovine serum albumin (BSA) have also been investigated by a fluorescence quenching method and a non-covalent conjugate of 4b and BSA has been prepared. Conjugation with BSA leads to a higher photocytotoxicity against J774 cells, which have a BSA-loving macrophage origin.

Preparation and photophysical properties of halogenated silicon(IV) phthalocyanines substituted axially with poly(ethylene glycol) chains

Abstract A series of silicon(IV) phthalocyanines with two axial poly(ethylene glycol) chains SiPcX 8 [(OCH 2 CH 2 ) n OCH 3 ] 2 (X=H, Cl, Br; n ≈16) have been prepared of which the photosensitizing properties are enhanced as the periphery of the macrocycle is substituted with heavier halogens.

A tumor mRNA-triggered photodynamic molecular beacon based on oligonucleotide hairpin control of singlet oxygen production

We report a new class of photodynamic molecular beacon (PMB) with tumor specific mRNA-triggered control of singlet oxygen ((1)O(2)) production. The beacon contains a single-stranded oligonucleotide linker that forms a stem-loop structure (hairpin) in which the sequence is an antisense oligonucleotide (AS-ON) complementary to a target mRNA. The stem is formed by the annealing of two complementary arm sequences that are on either side of the loop sequence. A photosensitizer molecule (PS) is attached to the end of one arm and a quencher (Q) is similarly attached to the other end. The conformationally-restricted hairpin forces Q to efficiently silence the photoreactivity of PS. In the presence of target mRNA, the hairpin opens and the PS is no longer silenced. Upon irradiating with light, the PS then emits fluorescence and generates cytotoxic (1)O(2). To show proof of concept, we have synthesized a c-raf-1 mRNA-triggered PMB using pyropheophorbide (Pyro) as PS, carotenoid as Q and c-raf-1 mRNA-targeted AS-ON as the loop sequence. We show that the (1)O(2) production of Pyro is quenched in its native state by 15-fold and is restored 9-fold by the addition of the target RNA. Comparing this to our recently reported self-folding peptide linker-based PMB, the hairpin effect results in an enhanced (1)O(2) quenching efficiency that decreases the residual (1)O(2) production by over 3-fold, thus providing enhanced control of (1)O(2) production upon target-linker interactions. When incubated with c-raf-1 expressing MDA-MB-231 cancer cells, the PMB displayed efficient cellular uptake and subsequently effective PDT activation in targeted cells.

Effects of the number and position of the substituents on the in vitro photodynamic activities of glucosylated zinc(II) phthalocyanines.

A series of mono-beta-, di-alpha- and di-beta-substituted phthalonitriles which contain one or two tetraethylene-glycol-linked 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose unit(s) were prepared by typical substitution reactions. These precursors underwent self-cyclisation or mixed-cyclisation with an excess of unsubstituted phthalonitrile in the presence of Zn(OAc)(2) x 2 H(2)O and DBU to give the corresponding zinc(II) phthalocyanines with 1, 2 or 4 glucosylated substituent(s). For the di-alpha- and tetra-beta-glucosylated analogues, removal of the isopropylidene groups was also performed by the treatment with trifluoroacetic acid and water to give the corresponding water-soluble deprotected glucosylated derivatives. All of these glucoconjugated phthalocyanines were fully characterised with various spectroscopic methods and studied for their photophysical properties and in vitro photodynamic activities against HT29 human colon adenocarcinoma and HepG2 human hepatocarcinoma cells. The tetra-beta-glucosylated phthalocyanines ZnPc(beta-PGlu)(4) (4) and ZnPc(beta-Glu)(4) (5) were found to be essentially non-cytotoxic. By contrast, the mono- and di-glucosylated analogues ZnPc(beta-PGlu) (7), ZnPc(alpha-PGlu)(2) (11), ZnPc(alpha-Glu)(2) (12) and ZnPc(beta-PGlu)(2) (20) exhibited substantial photocytotoxicity. The isopropylidene-protected di-alpha-substituted derivative 11 was particularly potent, having IC(50) values as low as 0.03 microM. The different photodynamic activities of these compounds can be attributed to their different extent of cellular uptake and aggregation tendency in the biological media, which greatly affect their singlet oxygen generation efficiency.

Synthesis and in Vitro Photodynamic Activities of Pegylated Distyryl Boron Dipyrromethene Derivatives

A series of pegylated distyryl boron dipyrromethenes have been prepared and characterized. Their in vitro photodynamic activities in Tween 80 emulsions have also been investigated against HT29 human colorectal carcinoma cells. The derivative having five triethylene glycol chains (compound 8) exhibits the highest photocytotoxicity with an IC(50) as low as 7 nM. It is also localized preferentially in the endoplasmic reticulum of the cells and can induce predominately apoptosis upon illumination.