Cellular delivery and photochemical release of a caged inositol-pyrophosphate induces PH-domain translocation in cellulo.

Inositol pyrophosphates, such as diphospho-myo-inositol pentakisphosphates (InsP7), are an important family of signalling molecules, implicated in many cellular processes and therapeutic indications including insulin secretion, glucose homeostasis and weight gain. To understand their cellular functions, chemical tools such as photocaged analogues for their real-time modulation in cells are required. Here we describe a concise, modular synthesis of InsP7 and caged InsP7. The caged molecule is stable and releases InsP7 only on irradiation. While photocaged InsP7 does not enter cells, its cellular uptake is achieved using nanoparticles formed by association with a guanidinium-rich molecular transporter. This novel synthesis and unprecedented polyphosphate delivery strategy enable the first studies required to understand InsP7 signalling in cells with controlled spatiotemporal resolution. It is shown herein that cytoplasmic photouncaging of InsP7 leads to translocation of the PH-domain of Akt, an important signalling-node kinase involved in glucose homeostasis, from the membrane into the cytoplasm.

Induction of Cytotoxicity through Photorelease of Aminoferrocene.

Reactive oxygen species (ROS)-activated aminoferrocene-based anticancer prodrug candidates successfully take advantage of intrinsically high amounts of ROS in tumor tissues. Interestingly, the ROS-initiated activation of these prodrug candidates leads to formation of unstable aminoferrocene (Fc-NH2) derivatives, which decay to iron ions. The latter catalytically increases ROS concentration to a lethal level. In this work, we prepared light-controlled aminoferrocene prodrug candidates by derivatizing Fc-NH2 with an o-nitrophenyl and an o-nitrobiphenyl photolabile protecting group (PLPG), respectively, and by further conjugation to a mitochondria localization signal (MLS) peptide (Cys-D-Arg-Phe-Lys-NH2). The resulting bioconjugates were found to be more stable and less cytotoxic, in the dark, toward human promyelocytic leukemia cells (HL-60) compared to Fc-NH2. Upon light irradiation at 355 nm, both conjugates released Fc-NH2, albeit with very different photolysis quantum yields. The o-nitrobiphenyl photocage was in fact several orders of magnitude more efficient than the o-nitrophenyl photocage in releasing Fc-NH2. This difference was reflected by the light irradiation experiments on the HL-60 cell line, in which aminoferrocene conjugated with the o-nitrobiphenyl cage and the MLS displayed the highest phototoxicity index (2.5 ± 0.4) of all the compounds tested. The iron release assays confirmed the rise in iron ion concentrations upon light irradiation of both caged aminoferrocene derivatives. Together with the absence of phototoxicity on the nonmalignant hTERT-immortalized retinal pigment epithelial (hTERT RPE-1) cell line, these results indicate catalytic generation of ROS as possible mode of action.

Two-photon uncageable enzyme inhibitors bearing targeting vectors.

The activity of two cyclooxygenase-2 enzyme inhibitors, Celecoxib and Lumiracoxib, could be suppressed by coupling to photo-labile protecting groups, so-called photocages. These groups could be further functionalized with a peptide targeting vector for specific cellular delivery. The enzyme inhibition potential of the cyclooxygenase-2 inhibitors could be regained upon two-photon excitation with tissue-transparent near-IR light at 800 nm.

Caged Phosphate and the Slips and Misses in Determination of Quantum Yields for Ultraviolet-A-Induced Photouncaging.

The quantum yields for photouncaging reactions are mostly determined relative to other uncaging reactions, often using 1-(2-nitrophenyl)ethyl-phosphate ("caged phosphate"). Herein, we demonstrate that the quantum yields acquired by using this method can be off by an order of magnitude at the typical irradiation wavelengths around 350 nm and describe an easy-to-use alternative procedure using inexpensive azobenzene.

Synthesis, characterization, and biological evaluation of new Ru(II) polypyridyl photosensitizers for photodynamic therapy.

Two Ru(II) polypyridyl complexes, Ru(DIP)2(bdt) (1) and [Ru(dqpCO2Me)(ptpy)](2+) (2) (DIP = 4,7-diphenyl-1,10-phenanthroline, bdt = 1,2-benzenedithiolate, dqpCO2Me = 4-methylcarboxy-2,6-di(quinolin-8-yl)pyridine), ptpy = 4'-phenyl-2,2':6',2″-terpyridine) have been investigated as photosensitizers (PSs) for photodynamic therapy (PDT). In our experimental settings, the phototoxicity and phototoxic index (PI) of 2 (IC50(light): 25.3 µM, 420 nm, 6.95 J/cm(2); PI >4) and particularly of 1 (IC50(light): 0.62 µM, 420 nm, 6.95 J/cm(2); PI: 80) are considerably superior compared to the two clinically approved PSs porfimer sodium and 5-aminolevulinic acid. Cellular uptake and distribution of these complexes was investigated by confocal microscopy (1) and by inductively coupled plasma mass spectrometry (1 and 2). Their phototoxicity was also determined against the Gram-(+) Staphylococcus aureus and Gram-(-) Escherichia coli for potential antimicrobial PDT (aPDT) applications. Both complexes showed significant aPDT activity (420 nm, 8 J/cm(2)) against Gram-(+) (S. aureus; >6 log10 CFU reduction) and, for 2, also against Gram-(-) E. coli (>4 log10 CFU reduction).

Peptide nucleic acid - an opportunity for bio-nanotechnology.

DNA is a major player in the field of bio-nanotechnology and many interesting applications have been realized using this oligonucleotide. In contrast, the use of peptide nucleic acid (PNA), which is a non-natural, neutral analogue of DNA with superior hybridization strengths compared to DNA, is still in its infancy in bio-nanotechnology. However, as demonstrated in this short review using selected studies, promising examples demonstrating the tremendous opportunities that PNA can offer for bio-nanotechnology were recently described.

Reductive elimination of ArCF3 from bidentate Pd(II) complexes: a computational study.

The reductive eliminations of ArCF(3) from Pd(II) complexes bearing small- and large-bite-angle phosphane ligands have been investigated using computational methods. QM/QM' and QM/MM studies were applied and complemented with CP2K molecular dynamics investigations. The ligand substituents were varied and a decomposition analysis was performed to allow us to gain insights into the steric and electronic properties of the ligands. The greater reactivity of Xantphos-derived (Xantphos=4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) complexes in the reductive elimination of ArCF(3) is primarily due to the lower repulsive effect of the phoshine substituents in the transition state than in the reactant complex, combined with the increased electronic interaction in the transition state. For DPPE (1,2-bis(diphenylphosphino)ethane), the steric effect of the ligand substituents is greater in the transition state, leading to a higher reaction barrier overall for reductive elimination. There is no direct correlation of the reactivity with the bite angle of the reactant complexes. Only for complexes with large ligand substituents may the bite angle of the Pd complexes be used as a guide for reactivity.