Giovanni Signore

Polarity-Sensitive Coumarins Tailored to Live Cell Imaging

Polarity-dependent fluorescent probes are recently attracting interest for high-resolution cell imaging. Following a stepwise rational approach, we prepared and tested a toolbox of new coumarin derivatives tailored to in vivo imaging applications. Our compounds are characterized by a donor-(coumarin core)-acceptor molecular structure, where the electron donor is represented by alkylether or naphthyl groups, and the electron acceptor is represented by benzothiazene and cyano groups. Prior to synthesis, the substitution patterns were screened by computational methods to provide functional fluorescent derivatives easy to synthesize, and with excitation in the visible region of spectrum. We set up a robust synthetic procedure tunable on the substitution patterns to achieve. These coumarins possess excellent fluorescence quantum yields (up to 0.95), high molar extinction coefficients (up to 46,000 M(-1) cm(-1)), and large Stokes shifts. Furthermore, they display strong solvatochromism, being almost non-emissive in water and very fluorescent in less polar media (up to 780-fold enhancement in brightness). The solvatochromism of these compounds can be accounted for by a photophysical method encompassing two communicating excited states. When tested on cultured cells, the results showed that the developed coumarins were not harmful and their photophysical properties were unchanged compared to free solution. According to the determined solvatochromic properties, the coumarin fluorescence was detected only in the most lipophilic environments of the cell. The prepared compounds represent remarkable tools to investigate subtle biochemical processes in the cell environment after appropriate conjugation to biomolecules, and at the same time constitute the basis for further engineering of a new generation of biosensors.

Recurrent ETNK1 mutations in atypical chronic myeloid leukemia

Despite the recent identification of recurrent SETBP1 mutations in atypical chronic myeloid leukemia (aCML), a complete description of the somatic lesions responsible for the onset of this disorder is still lacking. To find additional somatic abnormalities in aCML, we performed whole-exome sequencing on 15 aCML cases. In 2 cases (13.3%), we identified somatic missense mutations in the ETNK1 gene. Targeted resequencing on 515 hematological clonal disorders revealed the presence of ETNK1 variants in 6 (8.8%) of 68 aCML and 2 (2.6%) of 77 chronic myelomonocytic leukemia samples. These mutations clustered in a small region of the kinase domain, encoding for H243Y and N244S (1/8 H243Y; 7/8 N244S). They were all heterozygous and present in the dominant clone. The intracellular phosphoethanolamine/phosphocholine ratio was, on average, 5.2-fold lower in ETNK1-mutated samples (P < .05). Similar results were obtained using myeloid TF1 cells transduced with ETNK1 wild type, ETNK1-N244S, and ETNK1-H243Y, where the intracellular phosphoethanolamine/phosphocholine ratio was significantly lower in ETNK1-N244S (0.76 ± 0.07) and ETNK1-H243Y (0.37 ± 0.02) than in ETNK1-WT (1.37 ± 0.32; P = .01 and P = .0008, respectively), suggesting that ETNK1 mutations may inhibit the catalytic activity of the enzyme. In summary, our study shows for the first time the evidence of recurrent somatic ETNK1 mutations in the context of myeloproliferative/myelodysplastic disorders.

Dual fluorescence through Kasha's rule breaking: an unconventional photomechanism for intracellular probe design.

Dual fluorescence is an anomalous photophysical phenomenon observed in very few chromophores in which a two-color radiative process occurs that involves two distinct excited electronic states. To date its observation was linked either to electronic rearrangement of an excited fluorophore leading to two conformers with distinct emissive properties, or to a photochemical modification leading to different fluorescent species. In both cases, emission originates from the lowest excited state of the resulting molecular configurations, in line with the so-called Kashas rule. We report here a combined theoretical and spectroscopic study showing, for the first time, an anti-Kasha dual-emission mechanism, in which simultaneous two-color emission takes place from the first and second excited state of a coumarin derivative. We argue that the observed environmental sensitivity of this peculiar optical response makes the present compound ideally suited for biosensing applications in living cells.

Multiphoton molecular photorelease in click-chemistry-functionalized gold nanoparticles.

Yellow-green controlled photorelease: probes click-linked to peptide-coated gold nanospheres by a triazole ring can be released in living cells under a focused 561 nm laser at low power. Photocleaving follows a three-photon event stimulated by the excitation of the localized surface plasmon resonance.

Antimicrobial Peptides Design by Evolutionary Multiobjective Optimization

Antimicrobial peptides (AMPs) are an abundant and wide class of molecules produced by many tissues and cell types in a variety of mammals, plant and animal species. Linear alpha-helical antimicrobial peptides are among the most widespread membrane-disruptive AMPs in nature, representing a particularly successful structural arrangement in innate defense. Recently, AMPs have received increasing attention as potential therapeutic agents, owing to their broad activity spectrum and their reduced tendency to induce resistance. The introduction of non-natural amino acids will be a key requisite in order to contrast host resistance and increase compounds life. In this work, the possibility to design novel AMP sequences with non-natural amino acids was achieved through a flexible computational approach, based on chemophysical profiles of peptide sequences. Quantitative structure-activity relationship (QSAR) descriptors were employed to code each peptide and train two statistical models in order to account for structural and functional properties of alpha-helical amphipathic AMPs. These models were then used as fitness functions for a multi-objective evolutional algorithm, together with a set of constraints for the design of a series of candidate AMPs. Two ab-initio natural peptides were synthesized and experimentally validated for antimicrobial activity, together with a series of control peptides. Furthermore, a well-known Cecropin-Mellitin alpha helical antimicrobial hybrid (CM18) was optimized by shortening its amino acid sequence while maintaining its activity and a peptide with non-natural amino acids was designed and tested, demonstrating the higher activity achievable with artificial residues.

Aptamer-Mediated Codelivery of Doxorubicin and NF-κB Decoy Enhances Chemosensitivity of Pancreatic Tumor Cells

Aptamers able to bind efficiently cell-surface receptors differentially expressed in tumor and in healthy cells are emerging as powerful tools to perform targeted anticancer therapy. Here, we present a novel oligonucleotide chimera, composed by an RNA aptamer and a DNA decoy. Our assembly is able to (i) target tumor cells via an antitransferrin receptor RNA aptamer and (ii) perform selective codelivery of a chemotherapeutic drug (Doxorubicin) and of an inhibitor of a cell-survival factor, the nuclear factor κB decoy oligonucleotide. Both payloads are released under conditions found in endolysosomal compartments (low pH and reductive environment). Targeting and cytotoxicity of the oligonucleotidic chimera were assessed by confocal microscopy, cell viability, and Western blot analysis. These data indicated that the nuclear factor κB decoy does inhibit nuclear factor κB activity and ultimately leads to an increased therapeutic efficacy of Doxorubicin selectively in tumor cells.

Cancer phototherapy in living cells by multiphoton release of doxorubicin from gold nanospheres

Doxorubicin is a widely used but toxic cancer chemotherapeutic agent. In order to localize its therapeutic action and minimize side effects, it was covalently conjugated to peptide-encapsulated gold nanospheres by click-chemistry and then photo-released in a controlled fashion by a multiphoton process. Selective treatment of a chosen region in a 2D layer of U2Os cancer cells is shown by driving photorelease with 561 nm irradiation at μW power. These results show promising directions for the development of practical applications based on nanocarriers that can ensure drug delivery with high spatial and temporal control.

Imaging intracellular viscosity by a new molecular rotor suitable for phasor analysis of fluorescence lifetime

The arsenal of fluorescent probes tailored to functional imaging of cells is rapidly growing and benefits from recent developments in imaging strategies. Here, we present a new molecular rotor, which displays strong absorption in the green region of the spectrum, very little solvatochromism, and strong emission sensitivity to local viscosity. The emission increase is paralleled by an increase in emission lifetime. Owing to its concentration-independent nature, fluorescence lifetime is particularly suitable to image environmental properties, such as viscosity, at the intracellular level. Accordingly, we demonstrate that intracellular viscosity measurements can be efficiently carried out by lifetime imaging with our probe and phasor analysis, an efficient method for measuring lifetime-related properties (e.g., bionalyte concentration or local physicochemical features) in living cells. Notably, we show that it is possible to monitor the partition of our probe into different intracellular regions/organelles and to follow mitochondrial de-energization upon oxidative stress.

Cis – trans photoisomerization properties of GFP chromophore analogs

The photoswitching behaviour of the green fluorescent protein (GFP) chromophore and its analogs opens up exciting horizons for the engineering and development of molecular devices for high sensitivity in vivo studies. In this work we present the synthesis and photophysical study of four GFP chromophore analogs belonging to butenolide and pyrrolinone classes. These chromophores possess an intriguing photoinduced cis–trans isomerization mechanism. Stereochemical structural assignment was unambiguously performed by 1D Nuclear Overhauser Effect NMR measurements. The spectroscopic properties of both cis and trans isomers were studied, and photoconversion quantum yield for cis–trans isomerization was assessed to be in the 0.1–0.4 range. Finally, the 3JC,H coupling constant in the 13C–C=C–H motif was in excellent agreement with theoretical DFT calculations, thus providing a further confirmation of cis–trans photoisomerization of the structurally analog GFP chromophore.

Two Interconvertible Folds Modulate the Activity of a DNA Aptamer Against Transferrin Receptor

Thanks to their ability to recognize biomolecular targets with high affinity and specificity, nucleic acid aptamers are increasingly investigated as diagnostic and therapeutic tools, particularly when their targets are cell-surface receptors. Here, we investigate the relationship between the folding of an anti-mouse transferrin receptor DNA aptamer and its interaction with the transferrin receptor both in vitro and in living cells. We identified and purified two aptamer conformers by means of chromatographic techniques. Fluorescence-anisotropy measurements showed that only one fold is able to bind mouse transferrin receptor. Besides displaying enhanced endocytosis in living mouse fibroblasts, the purified active fold is internalized also in human pancreatic cancer cells. Starting from these observations, we rationally designed variations of the parent sequence aimed at stabilizing the active fold, and consequently increase aptamer activity. A truncated version and full-length mutants with higher affinity than the parent sequence are shown.