Bioorthogonal Swarming: In Situ Generation of Dendrimers.

With the aid of bioorthogonal chemistry, we demonstrate the fabrication of synthetic dendrimers in situ around living cells. Using tetrazine dienophile and aminooxyl/hydrazide aldehyde chemistries, the density of functional groups on the dendrimers exponentially amplified intensities of fluorescent markers in antibody-targeted live cell imaging. This novel "swarming" approach highlights the power of bioorthogonal chemistry and provides a route to non-natural chemical structures on cells, paving the way for the generation of various artificial cellular nanostructures and scaffolds.

The Emerging Role of Tetrazines in Drug-Activation Chemistries.

Traditionally, prodrug activation has been limited to enzymatic triggers or gross physiological aberrations, such as pH, that offer low selectivity and control over dosage. In recent years, the field of prodrug activation chemistry has been transformed by the use of bioorthogonal reactions that can be carried out under biological conditions at sub-millimolar concentrations, with the tetrazine-mediated inverse electron demand Diels-Alder reaction amongst the most recognised. Their high reaction rates, chemoselectivity and excellent biocompatibility make tetrazines ideal small molecules for activating prodrugs. Recently the tetrazine moiety has been used as a prodrug for a pyridazine thus broadening the scope of prodrug systems. This article discusses the concept of using tetrazines as small-molecule activators for prodrugs, and provides an overview of tetrazine-based prodrug systems, with a particular focus on the recently reported prodrug-prodrug activation strategy.

A Dual Killing Strategy: Photocatalytic Generation of Singlet Oxygen with Concomitant PtIV Prodrug Activation.

A ruthenium-based mitochondrial-targeting photosensitiser that undergoes efficient cell uptake, enables the rapid catalytic conversion of PtIV prodrugs into their active PtII counterparts, and drives the generation of singlet oxygen was designed. This dual mode of action drives two orthogonal cancer-cell killing mechanisms with temporal and spatial control. The designed photosensitiser was shown to elicit cell death of a panel of cancer cell lines including those showing oxaliplatin-resistance.

Tetrazine-Responsive Self-immolative Linkers.

Molecules that undergo activation or modulation following the addition of benign external small-molecule chemical stimuli have numerous applications. Here, we report the highly efficient "decaging" of a variety of moieties by activation of a "self-immolative" linker, by application of water-soluble and stable tetrazine, including the controlled delivery of doxorubicin in a cellular context.

Solid-Phase Synthesis of s-Tetrazines.

An efficient synthesis of s-tetrazines by solid-phase methods is described. This synthesis route was compatible with different solid-phase resins and linkers and did not require metal catalysts or high temperatures. Monosubstituted tetrazines were routinely synthesized using thiol-promoted chemistry, using dichloromethane as a carbon source, while disubstituted unsymmetrical aryl or alkyl tetrazines were synthesized using readily available nitriles. This efficient approach enabled the synthesis of s-tetrazines in high yields (70-94%), eliminating the classical solution-phase problems of mixtures of symmetrical and unsymmetrical tetrazines, with only a single final purification step required, and paves the way to the rapid synthesis of s-tetrazines with various applications in bioorthogonal chemistry and beyond.

Multifunctional, histidine-tagged polymers: antibody conjugation and signal amplification.

A polymer scaffold, with multiple reactive centres, was synthesised by RAFT polymerisation and conjugated to the antibody herceptin. A hexahistidine RAFT agent enabled the rapid and simple purification of polymer-protein conjugates, while the tetrazine conjugation strategy allows myriad cargos to be attached and amplified.

Comparison of IVF and ICSI when only few oocytes are available for insemination.

The aim of this work was to evaluate the efficiency of IVF and intracytoplasmic sperm injection (ICSI) when few eggs available for insemination. A total of 601 women (group A, mean age 31.2 +/- 2.8 years) who were undergoing a total of 671 assisted reproduction cycles donated their excess oocytes to 694 patients (group B, mean age 41.0 +/- 0.2) for 1606 replacement cycles. Each recipient received three to five eggs. The recipients were divided into two groups depending on the insemination method used (IVF, group B1; or ICSI, group B2); ICSI patients were then subdivided into two further groups based on the semen parameters: B2A adequate for IVF and B2B only suitable for ICSI. The results showed that, when comparing A versus B and B1 versus B2, no significant differences were found in terms of pregnancy (28.0 versus 24.1% and 25.5 versus 21.4%), implantation (15.6 versus 14.9% and 15.9 versus 13.1%) and miscarriage (15.4 versus 20.5% and 17.9 versus 26.3) rates respectively. Comparing subgroups B2A and B2B, no significant differences were found in terms of pregnancy (20.0 versus 21.9%), implantation (14.4 versus 12.7%) and miscarriage rates (18.2 versus 28.6%) respectively. In conclusion, ICSI does not seem to yield better outcomes.

Characterization, expression, and functional activity of pituitary adenylate cyclase-activating polypeptide and its receptors in human granulosa-luteal cells.

CONTEXT: Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are found in the ovary of mammalian species, although nothing is known about the possible role of PACAP and VIP in the human ovary. OBJECTIVE: We investigated the expression of PACAP and PACAP/VIP receptors in human granulosa-luteal (GL) cells obtained from consenting in vitro fertilization patients attending a private fertility clinic and assessed a possible antiapoptotic effect of these molecules. MAIN OUTCOME MEASURES: We measured the expression of PACAP and PACAP/VIP receptor mRNAs in GL cells in response to FSH or LH, as well as the effects of PACAP and VIP on apoptosis. We also evaluated the levels of procaspase-3 in GL cells cultured in the absence of serum. RESULTS: After 7 d in culture, GL cells displayed increased responsiveness to FSH and LH (100 ng/ml). FSH and LH promoted PACAP expression, LH doing so in a time-dependent fashion. VIP receptor (VPAC1-R and VPAC2-R) mRNAs were also induced by gonadotropin stimulation. Although PACAP receptor (PAC1-R) mRNA was barely detectable, Western blot analysis revealed its presence. The apoptotic effect of serum withdrawal from the culture environment was reverted by both PACAP and VIP. Both peptides showed the ability to reverse a decrease in procaspase-3 levels induced by culture in the absence of serum. CONCLUSIONS: PACAP and VIP appear to play a role in maintenance of follicle viability as a consequence of the antiapoptotic effect. Further studies are warranted to evaluate the respective roles of PACAP and VIP in ovarian physiology and to identify their mechanism of action.

Tetrazine-mediated bioorthogonal prodrug-prodrug activation.

The selective and biocompatible activation of prodrugs within complex biological systems remains a key challenge in medical chemistry and chemical biology. Herein we report, for the first time, a dual prodrug activation strategy that fully satisfies the principle of bioorthogonality by the symbiotic formation of two active drugs. This dual and traceless prodrug activation strategy takes advantage of the INVDA chemistry of tetrazines (here a prodrug), generating a pyridazine-based miR21 inhibitor and the anti-cancer drug camptothecin and offers a new concept in prodrug activation.

A Tetrazine-Labile Vinyl Ether Benzyloxycarbonyl Protecting Group (VeZ): An Orthogonal Tool for Solid-Phase Peptide Chemistry.

The vinyl ether benzyloxycarbonyl (VeZ) protecting group is selectively cleaved by treatment with tetrazines via an inverse electron-demand Diels-Alder reaction. This represents a new orthogonal protecting group for solid-phase peptide synthesis, with Fmoc-Lys(VeZ)-OH as a versatile alternative to Fmoc-Lys(Alloc)-OH and Fmoc-Lys(Dde)-OH, as demonstrated by the synthesis of two biologically relevant cyclic peptides.