Cellular delivery of dinucleotides by conjugation with small molecules: targeting translation initiation for anticancer applications

Analytical Form of the Fluorescence Correlation Spectroscopy Autocorrelation Function in Chemically Reactive Systems

Fluorescence correlation spectroscopy (FCS) applied to chemically reactive systems provides information about chemical reaction equilibrium constants and diffusion coefficients of reactants. These physical quantities are determined from the FCS-measured autocorrelation function, G(t), as a function of time, t. In most of the studied cases, the analytical form of G(t) is well-known for reactions that are much faster than the diffusion time of reactants across the focal volume probed by FCS or when they are much slower than the diffusion time. Here, we develop an analytical form of G(t) for reactions occurring at an intermediate time scale comparable to the diffusion time. G(t) depends on the reaction rates in such reactions. We focus on reversibly binding a fluorescently labeled small molecule to a macromolecule in a diluted solution in thermodynamic equilibrium. Our approach allows the analysis of FCS data over a wide range of diffusion coefficients, reaction rate constants, and brightness levels of fluorescent labels. Our G(t) is valid even when the fluorescent label changes its brightness upon binding. The easy-to-implement analytical form of the autocorrelation function greatly helps experimentalists study chemical reactions, determining the equilibrium constants of reactions and the reaction rates.

Cellular Uptake of Bevacizumab in Cervical and Breast Cancer Cells Revealed by Single-Molecule Spectroscopy

Bevacizumab is a biological drug that is now extensively studied in clinics against various types of cancer. Although bevacizumab's action is preferably extracellular, there are reports suggesting its internalization into cancer cells, consequently decreasing its therapeutic potential. Here we are solving this issue by applying fluorescence correlation spectroscopy in living cells. We tracked single molecules of fluorescent bevacizumab in MDA-MB-231 and HeLa cells and proved that mobility measurements bring significant added value to standard imaging techniques. We confirmed the presence of the drug in intracellular vesicles. Additionally, we explicitly excluded the presence of a free cytosolic fraction of bevacizumab in both studied cell types. Extracellular and intracellular concentrations of the drug were measured, giving a partition coefficient on the order of 10^-5, comparable with the spontaneous uptake of biologically inert nanoparticles. Our work presents how techniques and models developed for physics can answer biological questions.

Fluorescent sterol probes for intracellular transport, imaging, and therapeutics

Sterols play a significant role in many physiological processes affecting membrane organization, transport, permeability, and signal transduction. The development of fluorescent sterol analogs that have immediate functional relevance to the natural biomolecules is one approach to understanding the sterol-driven physiological processes. Visualizing cellular compartments with tailor-made fluorescent molecules through specific labeling methods enables organelle targeting and reveals dynamic information. In this review, we focus on the recent literature published between 2020 and 2022, with particular emphasis on extrinsic fluorophores and their investigations of sterol-driven biological processes involving sterol transport, biomolecular interactions, and biological imaging.

Development of Nucleoside Diphosphate-Bearing Fragile Histidine Triad-Imaging Fluorescence Probes with Well-Tuned Hydrophobicity for Intracellular Delivery

Fluorescence-guided cancer surgery can dramatically improve recurrence rates and postoperative quality of life of patients by accurately distinguishing the boundary between normal and cancer tissues during surgery, thereby minimizing excision of normal tissue. One promising target in early stage cancer is fragile histidine triad (FHIT), a cancer suppressor protein with dinucleoside triphosphate hydrolase activity. In this study, we have developed fluorescence probes containing a nucleoside diphosphate moiety, which dramatically improves the reactivity and specificity for FHIT, and a moderately lipophilic ester moiety to increase the membrane permeability. The ester moiety is cleaved by ubiquitous intracellular esterases, and then, FHIT in the cells specifically cleaves nucleoside monophosphate. The remaining phosphate moiety is rapidly cleaved by ubiquitous intracellular phosphatases to release the fluorescent dye. We confirmed that this probe can detect FHIT activity in living cells. A comprehensive evaluation of the effects of various ester moieties revealed that probes with CLogP = 5-7 showed good membrane permeability and were good substrates of the target enzyme; these findings may be helpful in the rational design of other multiple phosphate-containing probes targeting intracellular enzymes.

eIF4A1 Inhibitor Suppresses Hyperactive mTOR-Associated Tumors by Inducing Necroptosis and G2/M Arrest

Aberrantly activated mechanistic target of rapamycin (mTOR) signaling pathway stimulates translation initiation/protein synthesis and eventually causes tumors. Targeting these processes thus holds potential for treating mTOR-associated diseases. We tested the potential of eFT226, a sequence-selective inhibitor of eIF4A-mediated translation, in the treatment of mTOR hyperactive cells caused by the deletion of tuberous sclerosis complex 1/2 (TSC1/2) or phosphatase and TENsin homology (PTEN). eFT226 preferentially inhibited the proliferation of Tsc2- and Pten-deficient cells by inducing necroptosis and G2/M phase arrest. In addition, eFT226 blocked the development of TSC2-deficient tumors. The translation initiation inhibitor is thus a promising regimen for the treatment of hyperactive mTOR-mediated tumors.

Novel N7-Arylmethyl Substituted Dinucleotide mRNA 5' cap Analogs: Synthesis and Evaluation as Modulators of Translation

Dinucleotide analogs of the messenger RNA cap (m⁷GpppN) are useful research tools and have potential applications as translational inhibitors or reagents for modification of in vitro transcribed mRNAs. It has been previously reported that replacing the methyl group at the N7-position with benzyl (Bn) produces a dinucleotide cap with superior properties. Here, we followed up on this finding by synthesizing 17 novel Bn⁷GpppG analogs and determining their structure-activity relationship regarding translation and translational inhibition. The compounds were prepared in two steps, including selective N7-alkylation of guanosine 5'-monophosphate by arylmethyl bromide followed by coupling with imidazole-activated GDP, with total yields varying from 22% to 62%. The compounds were then evaluated by determining their affinity for eukaryotic translation initiation factor 4E (eIF4E), testing their susceptibility to decapping pyrophosphatase, DcpS-which is most likely the major cellular enzyme targeting this type of compound-and determining their translation inhibitory properties in vitro. We also synthesized mRNAs capped with the evaluated compounds and tested their translational properties in A549 cells. Our studies identified N7-(4-halogenbenzyl) substituents as promising modifications in the contexts of either mRNA translation or translational inhibition. Finally, to gain more insight into the consequences at the molecular level of N7-benzylation of the mRNA cap, we determined the crystal structures of three compounds with eIF4E.