Photoactivated full-API nanodrug (FAND): harnessing transition metal complexes and MTH1 inhibitor for enhanced DNA damage in cancer cells.

The effectiveness of photodynamic therapy (PDT) has been greatly restricted by the hypoxic tumor microenvironment and the susceptible resistance of monotherapy. Although nanodrugs based on transition metal complexes capable of integrating PDT with photoactivated chemotherapy (PACT) have garnered tremendous attention as promising candidates for overcoming the above limitations, the therapeutic efficacy of these nanodrugs is still hampered by inadequate loading of active pharmaceutical ingredients (APIs) and the inherent ability of cancer cells to repair damaged DNA. Herein, we developed a photoactivated full-API nanodrug, Ru-T FAND, by one-step self-assembly of RuDPB and TH287. By virtue of its 100 wt% API content and favorable stability in water, the Ru-T FAND exhibited improved cellular uptake behavior and intracellular 1O2 generation. Attractively, the Ru-T FAND with triple anti-cancer modalities can photogenerate 1O2, photo-release DPB ligand and inhibit the repair of DNA damage, ultimately enhancing its phototherapeutic effect on cancer cells. Importantly, the uncaged DPB ligand from RuDPB emits red fluorescence, enabling real-time monitoring of the drug's absorption, distribution and efficacy. Collectively, the presented photoactivated Ru-T FANDs with multiple anti-cancer mechanisms will expand new horizons for the development of safe, efficient and synergistic tumor phototherapy strategies.

A photo-degradable BODIPY-modified Ru(II) photosensitizer for safe and efficient PDT under both normoxic and hypoxic conditions.

Photodynamic therapy (PDT) is promising for cancer treatment but still suffers from some limitations. For instance, PDT based on 1O2 generation (in a type-II mechanism) is heavily dependent on high oxygen concentrations and will be significantly depressed in hypoxic tumors. In addition, the residual photosensitizers after PDT treatment may cause severe side-effects under light irradiation. To solve these problems, herein a BODIPY (boron dipyrromethene)-modified Ru(II) complex [Ru(dip)2(tpy-BODIPY)]2+ (complex 1, dip = 4,7-diphenyl-1,10-phenanthroline, tpy = 2,2':6',2''-terpyridine) was designed and synthesized. Complex 1 exhibited both high singlet oxygen quantum yield (Φ = 0.7 in CH3CN) and excellent superoxide radical (O2˙-) generation, and thus demonstrated efficient PDT activity under both normoxic and hypoxic conditions. Moreover, complex 1 is photo-degradable in water, and greatly loses its ROS generation ability after PDT treatment. These novel properties of complex 1 make it promising for efficient PDT under both normoxic and hypoxic conditions with reduced side-effects.

Nitroreductase-Responsive Photosensitizers for Selective Imaging and Photo-Inactivation of Intracellular Bacteria.

Intracellular Staphylococcus aureus (S. aureus), especially the methicillin resistant staphylococcus aureus (MRSA), are difficult to detect and eradicate due to the protection by the host cells. Antibacterial photodynamic therapy (aPDT) offers promise in treating intracellular bacteria, provided that selective damage to the bacteria ranther than host cells can be realized. According to the different nitroreductase (NTR) levels in mammalian cells and S. aureus, herein NTR-responsive photosensitizers (PSs) (T)CyI-NO2 were designed and synthesized. The emission and 1O2 generation of (T)CyI-NO2 are quenched by the 4-nitrobenzyl group, but can be specifically switched on by bacterial NTR. Therefore, selective imaging and photo-inactivation of intracellular S. aureus and MRSA were achieved. Our findings may pave the way for the development of more efficient and selective aPDT agents to combat intractable intracellular infections.

A Photoactivated Ru (II) Polypyridine Complex Induced Oncotic Necrosis of A549 Cells by Activating Oxidative Phosphorylation and Inhibiting DNA Synthesis as Revealed by Quantitative Proteomics.

The ruthenium polypyridine complex [Ru(dppa)2(pytp)] (PF6)2 (termed as ZQX-1), where dppa = 4,7-diphenyl-1,10-phenanthroline and pytp = 4'-pyrene-2,2':6',2''-terpyridine, has been shown a high and selective cytotoxicity to hypoxic and cisplatin-resistant cancer cells either under irradiation with blue light or upon two-photon excitation. The IC50 values of ZQX-1 towards A549 cancer cells and HEK293 health cells are 0.16 ± 0.09 µM and >100 µM under irradiation at 420 nm, respectively. However, the mechanism of action of ZQX-1 remains unclear. In this work, using the quantitative proteomics method we identified 84 differentially expressed proteins (DEPs) with |fold-change| ≥ 1.2 in A549 cancer cells exposed to ZQX-1 under irradiation at 420 nm. Bioinformatics analysis of the DEPs revealed that photoactivated ZQX-1 generated reactive oxygen species (ROS) to activate oxidative phosphorylation signaling to overproduce ATP; it also released ROS and pyrene derivative to damage DNA and arrest A549 cells at S-phase, which synergistically led to oncotic necrosis and apoptosis of A549 cells to deplete excess ATP, evidenced by the elevated level of PRAP1 and cleaved capase-3. Moreover, the DNA damage inhibited the expression of DNA repair-related proteins, such as RBX1 and GPS1, enhancing photocytotoxicity of ZQX-1, which was reflected in the inhibition of integrin signaling and disruption of ribosome assembly. Importantly, the photoactivated ZQX-1 was shown to activate hypoxia-inducible factor 1A (HIF1A) survival signaling, implying that combining use of ZQX-1 with HIF1A signaling inhibitors may further promote the photocytotoxicity of the prodrug.

Ru(II) Complexes with Enaminone Structures for Rapid Sterilization of Staphylococcus aureus and MRSA with Little Accumulation of Drug Resistance.

Drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose a serious threat to human life. Therefore, there is urgent need to develop antibiotics with new chemical structures and antibacterial mechanisms, especially those that elicit little drug resistance after long-term use. Herein we synthesized three novel ruthenium complexes (Ru1-Ru3) containing the enaminone structures for the first time. At a concentration of 5 µM, Ru1-Ru3 can lead to a CFU reduction of about 5 log units towards S. aureus and MRSA. Interestingly, Ru3 displayed rapid bactericidal effects and could decrease the CFU numbers of both pathogens by 5 log units within 40 min. The control compounds (Ru4 and Ru5) without the enaminone structures displayed very poor antibacterial activity under the same conditions. Moreover, S. aureus did not show apparent drug resistance towards Ru3 after 20 passages incubation with a sublethal concentration. These results highlight the critical role of enaminone structures for antibacterial applications.

Biocompatible hypocrellin A-Fe(III) nanoparticles exhibiting efficient photo-activated CDT in vitro and in vivo.

Chemodynamic therapy (CDT) is novel and promising for cancer treatment, however, the potential systematic toxicity of the used nanoparticles is still a big concern. In this work the biocompatible hypocrellin A-Fe(III) nanoparticles (HA-Fe(III) NPs) were synthesized and studied. The CDT effect of HA-Fe(III) NPs in the dark is negligible but can be photo-activated upon red light irradiation, which is meaningful to realize precise CDT treatment by selective light irradiation. Moreover, HA-Fe(III) NPs can also generate O2˙-, which may be converted into H2O2 to further enhance the CDT effect. As a result, HA-Fe(III) NPs had little cytotoxicity in the dark at the concentration up to 200 µg ml-1, but exhibited efficient CDT activity upon red light irradiation under both normoxic and hypoxic conditions. The in vivo results also showed that HA-Fe(III) NPs can efficiently inhibit tumor growth upon 628 nm light irradiation.

An Alkynyl-Dangling Ru(II) Polypyridine Complex for Targeted Antimicrobial Photodynamic Therapy.

To realize clinical application of antibacterial photodynamic therapy (aPDT), one of the most arduous challenges is how to render aPDT agents high selectivity against bacterial pathogens. In light of the fact that amino group-containing lipids are rich on the outer surfaces of Gram-positive bacteria, we herein constructed an alkynyl-dangling ruthenium(II) polypyridine complex (Ru2) to preferentially label Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) over mammalian cells via the amino-yne bio-orthogonal click reaction. Thanks to the strong singlet oxygen generation ability, Ru2 could photo-inactivate S. aureus and MRSA effectively and specifically. Phosphatidylethanolamine (PE) molecules also exist in mammalian cells but are not accessible for Ru2, leading to its poor binding/uptake and negligible cytotoxicity in the dark and upon irradiation towards mammalian cells as well as low hemolysis, all favorable for aPDT application.

The Development of Ru(II)-Based Photoactivated Chemotherapy Agents.

Photoactivated chemotherapy (PACT) is a novel cancer treatment method that has drawn increasing attention due to its high selectivity and low side effects by spatio-temporal control of irradiation. Compared with photodynamic therapy (PDT), oxygen-independent PACT is more suitable for treating hypoxic tumors. By finely tuning ligand structures and coordination configurations, many Ru(II) complexes can undergo photoinduced ligand dissociation, and the resulting Ru(II) aqua species and/or free ligands may have anticancer activity, showing their potential as PACT agents. In this mini-review, we summarized the progress in Ru(II)-based PACT agents, as well as challenges that researchers in this field still face.

A Ru-anthraquinone dyad with triple functions of PACT, photoredox catalysis and PDT upon red light irradiation.

Phototherapy for cancer treatment has received much attention in recent years, and compounds with multiple anticancer mechanisms upon irradiation are particularly appealing. In this work, a nitro-anthraquinone group was attached to a biq (2,2'-biquinoline) ligand based Ru(ii) complex, endowing the resultant Ru1 compound with multiple anticancer mechanisms upon 600 nm light irradiation. Ru1 can undergo biq ligand photodissociation, showing its potential as a photoactivated chemotherapy (PACT) agent. Moreover, a Ru(iii) centre and an anthraquinone anion centre may be generated upon irradiation, which can further oxidize NADH/NADPH and generate O2˙-, successfully eliciting photoredox catalysis and photodynamic therapy (PDT). Compared to the control complex Ru2 without the nitroanthraquinone group, Ru1 exhibited much enhanced photocytotoxicity towards a series of cancer cell lines and 3D multicellular spheroids upon red light irradiation.

Selective and Efficient Photoinactivation of Intracellular Staphylococcus aureus and MRSA with Little Accumulation of Drug Resistance: Application of a Ru(II) Complex with Photolabile Ligands.

Novel antibacterial agents capable of efficiently sterilizing intracellular Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) but with low cytotoxicity and low resistance development are quite appealing. In this work, three Ru(II) complexes with photolabile ligands were explored to realize such a goal. Complex 3 (5 µM) can inhibit more than 90% growth of S. aureus/MRSA that has invaded in J774A.1 cells upon visible light irradiation, being much more efficient than vancomycin. In similar conditions, negligible dark- and phototoxicity were found toward the host cells. The bactericidal activity is highly correlated with DNA covalent binding by the Ru(II) fractions generated after ligand photodissociation. Moreover, S. aureus quickly developed resistance toward vancomycin, while negligible resistance toward complex 3 even after 700 generations was obtained. These appealing results may pave a new way for fighting against intracellular antibiotic-resistant pathogens.

UCNP@BSA@Ru nanoparticles with tumor-specific and NIR-triggered efficient PACT activity in vivo.

Ru(ii)-based photoactivated chemotherapy (PACT) agents are promising; however, their short wavelength absorption (generally <550 nm) and poor tumor accumulation ability limit their in vivo applications. Herein, bovine serum albumin (BSA) coated lanthanide-doped upconversion nanoparticles (NaYF4:Yb:Tm@NaYF4 (UCNPs)) were loaded with a Ru(ii) PACT agent, i.e. [Ru(dip)2(spc)]+ (dip = 4,7-diphenyl-1,10-phenanthroline; spc = 2-sulfonic acid pyridine-3-carboxylic acid). The resultant UCNP@BSA@Ru can transfer [Ru(dip)2(spc)]+ to tumor cells in vitro as well as tumor tissues in vivo highly efficiently and selectively owing to the targeting ability of BSA and the enhanced permeability and retention effect of the nanoparticles. The subsequent near infrared (NIR) light irradiation at 980 nm or visible light irradiation at 470 nm can initiate dissociation of the spc ligand, and the released Ru(ii) aqua compounds ([Ru(dip)2(H2O)2]2+) may exert a potent cytotoxicity towards a series of cancer cells but a much weaker effect on the normal IOSE80 cells. The in vivo (mouse) results showed that UCNP@BSA@Ru could inhibit tumor growth upon 980 nm irradiation more efficiently than in the dark and more efficiently than cisplatin (in the dark).

Photo-induced mitochondrial DNA damage and NADH depletion by -NO2 modified Ru(II) complexes.

Two mitochondria-localized Ru(ii) complexes with photo-labile ligands were reported to exert one- and two-photon activatable anticancer activity through a dual-function mechanism, i.e. mitochondrial DNA covalent binding after photo-induced ligand dissociation and photo-catalyzed NADH depletion, thus displaying good activity towards cisplatin-resistant cancer cells under both normoxic and hypoxic conditions.

The modification of a pyrene group makes a Ru(ii) complex versatile.

In this work, the simple modification of a pyrene group on the labile ligand gives the resultant complex 1 versatility, for example, "turn-on" fluorescence after photo-dissociation, dual PDT and PACT activity, and a large two-photon absorption cross section.

Polypyridyl Co complex-based water reduction catalysts: why replace a pyridine group with isoquinoline rather than quinoline?

The electronic effect of the substituent has been fully leveraged to improve the activity of molecular water reduction catalysts (WRCs). However, the steric effect of the substituents has received less attention. In this work, a steric hindrance effect was observed in a quinoline-involved polypyridyl Co complex-based water reduction catalyst (WRC), which impedes the formation of Co(iii)-H from Co(i), two pivotal intermediates for H2 evolution, leading to significantly impaired electrocatalytic and photocatalytic activity with respect to its parent complex, [Co(TPA)Cl]Cl (TPA = tris(2-pyridinylmethyl)-amine). In sharp contrast, two isoquinoline-involved polypyridyl Co complexes exhibited significantly improved H2 evolution efficiencies compared to [Co(TPA)Cl]Cl, benefitting mainly from the more basic and conjugated features of isoquinoline over pyridine. The dramatically different influences caused by the replacement of a pyridine group in the TPA ligand by quinoline and isoquinoline fully demonstrates the important roles of both the electronic and steric effects of a substituent. Our results may provide novel insights for designing more efficient WRCs.

Electronic effects on polypyridyl Co complex-based water reduction catalysts.

Three new isomeric cobalt complexes of TPA (tris(2-pyridylmethyl)amine) based on methoxy substitution at the ortho, meta and para positions, respectively, were constructed and their photocatalytic proton reduction efficiencies were compared. It was found that there are good linear correlations with the Hammett constants of the substituents for the computed Co-N bond lengths, redox potentials of CoII/I and CoI/0 events, and the photocatalytic activities of the complexes. The ortho-substituted Co complex distinguished itself from the others remarkably in all these comparisons, demonstrating the presence of a steric effect besides the electronic effect. For other examined complexes, a stronger electron-donating substituent may lead to a higher hydrogen evolution efficiency, suggesting that the formation of a Co(iii) hydride intermediate is the rate-limiting step.

Smart use of "ping-pong" energy transfer to improve the two-photon photodynamic activity of an Ir(iii) complex.

A two-photon excited "Ping-Pong" type energy transfer process is for the first time disclosed in a pyrene-modified Ir(iii) cyclometalated complex. The energy transfer, from the singlet excited state of the 4-(pyren-1-yl)-tpy (tpy-py) unit to the Ir(iii) moiety and then back again to the triplet excited state of the tpy-py unit, enhances both the two-photon absorption cross sections and singlet oxygen quantum yield of the complex, and dramatically boosts its two-photon photodynamic activity both in vitro and in 3D multicellular spheroids.

Fluorination in enhancing photoactivated antibacterial activity of Ru(ii) complexes with photo-labile ligands.

Fluorination in enhancing photoactivated antibacterial activity of Ru(ii) complexes with photo-labile ligands was studied. Ru(ii) polypyridine complexes containing a di-fluorinated dppz (dipyrido[3,2-a:2',3'-c]phenazine) or mono-trifluoromethylated dppz bidentate ligand and four pyridine monodentate ligands (complexes 3 and 4) were found to show potent photoactivated antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and Escherichia coli (E. coli) in both normoxic and hypoxic conditions. The bactericidal effect of complexes 3 and 4 under hypoxic conditions may stem from the fluorine-containing Ru(ii) aqua species after photo-induced pyridine dissociation, and DNA may be the potential antibacterial target. Photosensitized singlet oxygen may also account for their antibacterial activity under normoxic conditions. Moreover, negligible hemolysis rates as well as low dark- and photo-cytotoxicity toward human normal liver cells (L-O2) were also observed for both complexes. Our work may provide new insights into the development of novel and efficient Ru(ii) complex based photoactivatable antibacterial agents against antibiotic-resistant bacteria.

Incorporation of 7-dehydrocholesterol into liposomes as a simple, universal and efficient way to enhance anticancer activity by combining PDT and photoactivated chemotherapy.

Cholesterol (CHOL) is an indispensable component of liposomes. Incorporation of 7-dehydrocholesterol (7-DHC) instead of CHOL can efficiently enhance the anticancer activity of photosensitizer-encapsulated liposomes upon irradiation, yielding an IC50 value about half of that of CHOL-based controls. The photo-oxidation of 7-DHC into its endoperoxide form by singlet oxygen may account for the enhanced therapeutic effect, realizing an efficient combination of photodynamic therapy (PDT) and photoactivated chemotherapy.