Photooxygenation of Δ8 tetrahydrocannabinol (Δ8-THC), Δ9 tetrahydrocannabinol (Δ9-THC), Δ9 tetrahydrocannabinolic acid (Δ9-THCA) and some derivatives (acetate, tosylate and methyl ether) yielded 24 oxygenated derivatives, 18 of which were new and 6 were previously reported, including allyl alcohols, ethers, quinones, hydroperoxides, and epoxides. Testing these compounds for their modulatory effect on cannabinoid receptors CB1 and CB2 led to the identification of 7 and 21 as CB1 partial agonists with Ki values of 0.043 μM and 0.048 μM, respectively and 23 as a cannabinoid with high binding affinity for CB2 with Ki value of 0.0095 μM, but much less affinity towards CB1 (Ki 0.467 μM). The synthesized compounds showed cytotoxic activity against cancer cell lines (SK-MEL, KB, BT-549, and SK-OV-3) with IC50 values ranging from 4.2 to 8.5 μg/mL. Several of those compounds showed antimicrobial, antimalarial and antileishmanial activities, with compound 14 being the most potent against various pathogens.

To investigate the impact of linker(s) joining the photosensitizer HPPH [3-(1'-hexyloxy) ethyl-3-devinylpyropheophorbide-a] and the cyanine dye (CD) in tumor-imaging and photodynamic therapy (dual-function agents), a series of HPPH-CD conjugates were synthesized. The modifications were done in an attempt to minimize Forster Resonance Energy Transfer (FRET) between the two chromophores and maximize singlet oxygen production. Among the conjugates containing variable length of linkers, the HPPH-CD conjugate, in which the photosensitizer (PS) and the CD was joined by four Carbon [(CH2)4] units showed higher tumor uptake, improved tumor contrast and limited skin uptake in mice bearing Colon-26 (BALB/c) or U87 tumors in Nude mice. The bi-functional agents in which the HPPH was linked at the meta-position of phenyl-substituted CD 5, 6 and 7 showed longer tumor response (cure) than the corresponding para-substituted analogs 2, 3, and 4, which suggests that the orientation of the PS and CD moieties within the conjugate also makes a substantial difference in tumor-specificity. Compared to HPPH, the singlet oxygen yields of all the HPPH-CD conjugates were significantly low, and required a higher therapeutic dose to achieve the same in vivo response obtained by HPPH-PDT alone. However, conjugate 6 produced a higher singlet oxygen yield with reduced FRET and exhibited enhanced long-term PDT efficacy in mice bearing Colon-26 (BALB/c) and U87 tumors (nude) than its counterparts, including our lead compound (HPPH-CD), making it the most efficacious of the series. Thus, these conjugates bearing cyanine dye moiety (CD) provide an opportunity of imaging deeply seated tumors for fluorescence-guided surgery with an option of PDT.

A ferrocenyl boron dipyrromethene (BODIPY) has been developed and utilized as a dark quencher to construct a cathepsin B-responsive fluorescent probe and photosensitizer. The smart fluorescent probe and photosensitizer (Pc-FcQ) contains a zinc(II) phthalocyanine as the fluorescent and photosensitizing unit which is conjugated to the ferrocenyl BODIPY dark quencher via a cathepsin B-cleavable peptide substrate [Gly-Phe-Leu-Gly-Lys]. The photosensitizing properties of Pc-FcQ, including fluorescence and singlet oxygen generation, are significantly quenched through energy transfer to the BODIPY unit and subsequently by the photoinduced electron transfer from the nearby ferrocenyl moiety. Upon exposure of cathepsin B in human hepatocellular carcinoma HepG cells, the fluorescence emission of Pc-FcQ could be restored, indicating the cleavage of the peptide substrate and the separation of the phthalocyanine and ferrocenyl BODIPY unit. However, the intracellular fluorescence intensity of Pc-FcQ was largely diminished after the cells were pre-treated with cathepsin B inhibitor. Its intracellular fluorescence intensity was comparable to that of the control compound in which the peptide substrate was replaced by the non-cleavable one [Gly-Gly-Gly-Gly-Lys]. The singlet oxygen generation of Pc-FcQ was also examined in HepG2 cells as reflected by the cytotoxicity assay. The Pc-FcQ exhibited higher potency when compared with the non-cleavable analogue due to the cleavage of peptide substrate and the detachment of the BODIPY dark quencher from the phthalocyanine. The activation of the Pc-FcQ was also demonstrated in tumor-bearing nude mice. After intratumoral injection of Pc-FcQ, the fluorescence intensity at the tumor region increased gradually over 10 h as a result of the detachment of the dark quencher upon the action of cathepsin B. All the results suggest that this ferrocenyl BODIPY could serve as an efficient dark quencher and the resulting Pc-FcQ could act as the cathepsin B-responsive fluorescent probe and activatable photosensitizer.

While photodynamic therapy is known for significant advantages over conventional cancer therapies, its dependence on light has limited it to treating tumors on or just under the skin or on the outer lining of organs/cavities. Herein, we have developed a single-molecule photosensitizer capable of intracellular self-activation and with potential tumor-selectivity due to a chemiluminescent reaction involving only a cancer marker. Thus, the photosensitizer is directly chemiexcited to a triplet excited state capable of generating singlet oxygen, without requiring either a light source or any catalyst/co-factor. Cytotoxicity assays involving the photosensitizer show significant toxicity toward tumor cells, even better than reference drugs, while not inducing toxicity toward normal cells. This work provides a proof-of-concept for a novel type of photosensitizer that eliminates the current restrictions that photodynamic therapy presents regarding tumor size and localization.

Chemo-photodynamic therapy is a promising strategy for cancer treatments. However, it remains a challenge to develop a chemo-photodynamic therapeutic agent with little side effect, high tumor-targeting, and efficient synergistic effect simultaneously. Herein, we report a zinc(II) phthalocyanine (ZnPc)-doxorubicin (DOX) prodrug linked with a fibroblast activation protein (FAP)-responsive short peptide with the sequence of Thr-Ser-Gly-Pro for chemo-photodynamic therapy. In the conjugate, both photosensitizing activity of ZnPc and cytotoxicity of DOX are inhibited obviously. However, FAP-triggered separation of the photosensitizer and DOX can enhance fluorescence emission, singlet oxygen generation, dark- and photo-cytotoxicity significantly, and lead to a synergistic anticancer efficacy against HepG2 cells. The prodrug can also be specifically and efficiently activated in tumor tissue of mice. Thus, this prodrug shows great potential for clinical application in chemo-photodynamic therapy.

Photodynamic therapy (PDT) has been developed as a promising therapeutic method in cancer treatment. The discovery of effective photosensitizer, which is the key factor of PDT, is highly desired. This paper reports the synthesis of novel chlorin derivatives, 5,10,15,20-tetraphenyl-[2:3]-[(methoxycarbonyl, carboxy)methano] chlorin I and 5,10,15,20-tetraphenyl-[2:3]- {[methoxycarbonyl, (2-hydroxyethyl)amide]methano}chlorin II. Their structures were characterized with UV-vis, 1HNMR, 13CNMR and HRMS spectroscopies. Photophysical and photochemical experiments results showed that compound I and II had an absorption maximum around 650 nm, with molar extinction coefficients of 1 × 104 M-1 cm-1. They had strong fluorescence emission in 650-660 nm upon excitation with 419-422 nm light. ESR showed that singlet oxygen was produced upon irradiation of compounds with 650 nm light in the presence of molecular oxygen. The photo-bleaching test indicated that the structure of compounds was stable. These new compounds exhibit excellent anti-tumor effects and lower toxicity compared to m-THPC in vitro and in vivo. Compound I and II had high tumor selectivity, which could induced tumor cells shrinkage and necrosis under 650 nm laser irradiation. Flow cytometry revealed that the compounds might mediate PDT effect at late apoptotic phase. These results make these compound I and II promising candidates for future study in photo-diagnosis and photodynamic therapy of cholangiocarcinoma.

The synthesis, photophysical behaviour and photosensitization ability of novel 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused 5,15-diphenylchlorins against melanoma cells are described. All studied chlorins were found to be extremely active against melanoma cell lines A375 showing IC50 values below 20 nM. Furthermore, a dihydroxymethyl diphenylchlorin was identified as an excellent candidate to allow modulating of different types of cell death, apoptosis vs. necrosis, by varying its concentration. This can be explored as a tool to improve the effectiveness of PDT since inflammatory response resulting from necrotic cell death after PDT can activate the antitumor immune response with implications also regarding the vascular damage. This feature combined with very low cytotoxicity against human melanoma cells in the absence of light activation and against human fibroblast HFF-1 cells makes this chlorin a candidate of choice as a photosensitizer for PDT. A comprehensive photophysical investigation including the determination of quantum yields for fluorescence, singlet oxygen sensitization and internal conversion, lifetimes and rate constants of all the excited state deactivation processes has been undertaken.

In this paper, two new Cu(II) complexes, [Cu(Gluc)(HPB)(H2O)]Gluc (CuG1) and [Cu(Gluc)(HPBC)(H2O)]Gluc (CuG2) (where HPB = 2-(2'-pyridyl)benzimidazole, HPBC = 5-chloro-2-(2'-pyridyl)benzimidazole, Gluc = d-Gluconic acid), with good water solubility were synthesized and characterized. These complexes exhibited a five-coordinated tetragonal pyramidal geometry. The DNA binding and cleavage properties of the complexes were investigated using multi-spectroscopy, viscosity measurement, molecular docking and gel electrophoresis analysis methods. The results showed that the complexes could interact with DNA by insertion and groove binding, and cleave CT-DNA through a singlet oxygen-dependent pathway in the presence of ascorbic acid. The studies on antibacterial and anticancer activities in vitro demonstrated that both complexes had good inhibitory activity against three Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, Listeria monocytogenes) and one Gram-negative bacterium (Escherichia coli) and good cytotoxic activity toward the tested cancer cells (A549, HeLa and SGC-7901). CuG2 showed higher antimicrobial and cytotoxic activities than CuG1, which was consistent with their binding strength and cleavage ability to DNA, indicating that their antimicrobial and cytotoxic activities may be related to the DNA interaction. Moreover, the cell-based mechanism studies have indicated that CuG1 and CuG2 could arrest the cell cycle at G2/M phase, elevate the levels of intracellular reactive oxygen species (ROS) and decrease the mitochondrial membrane potential (MMP). The results showed that the complexes could induce apoptosis through DNA-damaged and ROS-mediated mitochondrial dysfunction pathways. Finally, the in vivo antitumor study revealed that CuG2 inhibited tumor growth by 50.44%, which is better than that of cisplatin (40.94%).

5,7-Diaryl-substituted symmetrical diazepinoporphyrazine and tribenzodiazepinoporphyrazine were synthesized and characterized using UV-Vis, MS MALDI, and various NMR techniques. The expected photosensitizing potentials of these porphyrazines were evaluated by measuring their abilities to generate singlet oxygen in organic solvents and by comparing them with that of the recently obtained dendrimeric G1-type diazepinoporhyrazine. Absorbance and fluorescence measurements were performed to study the aggregation properties of the novel macrocycles. The photocytotoxicity of tribenzodiazepinoporphyrazine towards LNCaP cells in its free form and after its incorporation into liposomes was examined using MTT assay under normoxic and hypoxic conditions. It is interesting that all tested liposome formulations maintained their phototoxic activity in hypoxia. Also, tribenzodiazepinoporphyrazine incorporated into liposomes revealed better photocytotoxic effect (IC50 values of 0.600 ± 0.357 μM and 0.378 ± 0.002 μM) than its free form (IC50 values of 3.135 ± 0.156 μM). Following the in vitro experiments, the most promising liposomal formulation containing l-α-phosphatidyl-DL-glycerol for tribenzodiazepinoporphyrazine was found. Moreover, tribenzodiazepinoporphyrazine incorporated into liposomes containing 1,2-dioleoyl-3-trimethylammonium-propane (chloride salt) revealed moderate phototoxicity at 5 × 10-5 μM for antibacterial photodynamic therapy. It was established that an irradiation of planktonic bacterial strains significantly reduced CFUs of Staphylococcus aureus ATCC 25923 in comparison to tribenzodiazepinoporphyrazine containing l-α-phosphatidyl-DL-glycerol liposomes.

Clinical imaging utilising near-infrared fluorescence is growing as an intraoperative aid for the decision-making processes during complex surgical procedures. Existing uses include perfusion assessment and lymph node identification with many new applications currently being proposed and developed. While imaging hardware and software have significantly progressed in recent times, suitable NIR-fluorophores remain a limiting factor. In this report, we describe the design, synthesis, photophysical characterization and in vivo imaging assessment of new PEGylated NIR-fluorophores based on the BF2-azadipyrromethene fluorophore class. The synthetic route includes PEGylation as the final step, thereby allowing routine access to derivatives substituted with different molecular weights of PEG. Absorption and emission wavelength maxima in PBS lie at 690 and 720 nm respectively with quantum yields over 12%. They show excellent photostability and no light induced singlet oxygen production. A time-course of NIR-fluorescence imaging, post i.v. administration, in BALB/c mice showed a rapid and preferential accumulation in the renal excretion pathway within 20 min, indicative of potential clinical usage for intraoperative identification of vial structures along this pathway. Assessment with clinical imaging equipment showed the NIR-AZA fluorophores to be wavelength compatible and brighter than currently used methylene blue (MB), and that they have the ability to be imaged simultaneously with indocyanine green (ICG) offering a potential for dual colour clinical imaging.