Structural Change from Nonparallel to Parallel G-Quadruplex Structures in Live Cancer Cells Detected in the Lysosomes Using Fluorescence Lifetime Imaging Microscopy.

Time-gated fluorescence lifetime imaging microscopy with the o-BMVC fluorescent probe provides a visualizing method for the study of exogenous G-quadruplexes (G4s) in live cancer cells. Previously, imaging results showed that the parallel G4s are accumulated and that nonparallel G4s are not detected in the lysosomes of CL1-0 live cells. In this work, the detection of the G4 signals from exogenous GTERT-d(FN) G4s in the lysosomes may involve a structural change in live cells from intramolecular nonparallel G4s to intermolecular parallel G4s. Moreover, the detection of the G4 signals in the lysosomes after the 48 h incubation of HT23 G4s with CL1-0 live cells indicates the occurrence of structural conversion from the nonparallel G4s to the parallel G4s of HT23 in the live cells. In addition, the detection of much stronger G4 signals from ss-GTERT-d(FN) than ss-HT23 in the lysosomes of CL1-0 live cells may be explained by the quick formation of the intermolecular parallel G4s of ss-GTERT-d(FN) and the degradation of ss-HT23 before its intramolecular parallel G4 formation. This work provides a new approach to studying G4-lysosome interactions in live cells.

Folding and Unfolding of Exogenous G-Rich Oligonucleotides in Live Cells by Fluorescence Lifetime Imaging Microscopy of o-BMVC Fluorescent Probe.

Guanine-rich oligonucleotides (GROs) can self-associate to form G-quadruplex (G4) structures that have been extensively studied in vitro. To translate the G4 study from in vitro to in live cells, here fluorescence lifetime imaging microscopy (FLIM) of an o-BMVC fluorescent probe is applied to detect G4 structures and to study G4 dynamics in CL1-0 live cells. FLIM images of exogenous GROs show that the exogenous parallel G4 structures that are characterized by the o-BMVC decay times (≥2.4 ns) are detected in the lysosomes of live cells in large quantities, but the exogenous nonparallel G4 structures are hardly detected in the cytoplasm of live cells. In addition, similar results are also observed for the incubation of their single-stranded GROs. In the study of G4 formation by ssHT23 and hairpin WT22, the analyzed binary image can be used to detect very small increases in the number of o-BMVC foci (decay time ≥ 2.4 ns) in the cytoplasm of live cells. However, exogenous ssCMA can form parallel G4 structures that are able to be detected in the lysosomes of live CL1-0 cells in large quantities. Moreover, the photon counts of the o-BMVC signals (decay time ≥ 2.4 ns) that are measured in the FLIM images are used to reveal the transition of the G4 formation of ssCMA and to estimate the unfolding rate of CMA G4s with the addition of anti-CMA into live cells for the first time. Hence, FLIM images of o-BMVC fluorescence hold great promise for the study of G4 dynamics in live cells.

Antisense Oligonucleotides Used to Identify Telomeric G-Quadruplexes in Metaphase Chromosomes and Fixed Cells by Fluorescence Lifetime Imaging Microscopy of o-BMVC Foci.

Identification of the existence of G-quadruplex (G4) structure, from a specific G-rich sequence in cells, is critical to the studies of structural biology and drug development. Accumulating evidence supports the existence of G4 structure in vivo. Particularly, time-gated fluorescence lifetime imaging microscopy (FLIM) of a G4 fluorescent probe, 3,6-bis(1-methyl-2-vinylpyridinium) carbazole diiodide (o-BMVC), was used to quantitatively measure the number of G4 foci, not only in different cell lines, but also in tissue biopsy. Here, circular dichroism spectra and polyacrylamide gel electrophoresis assays show that the use of antisense oligonucleotides unfolds their G4 structures in different percentages. Using antisense oligonucleotides, quantitative measurement of the number of o-BMVC foci in time-gated FLIM images provides a method for identifying which G4 motifs form G4 structures in fixed cells. Here, the decrease of the o-BMVC foci number, upon the pretreatment of antisense sequences, (CCCTAA)3CCCTA, in fixed cells and at the end of metaphase chromosomes, allows us to identify the formation of telomeric G4 structures from TTAGGG repeats in fixed cells.

Effects of Length and Loop Composition on Structural Diversity and Similarity of (G3TG3NmG3TG3) G-Quadruplexes.

A G-rich sequence containing three loops to connect four G-tracts with each ≥2 guanines can possibly form G-quadruplex structures. Given that all G-quadruplex structures comprise the stacking of G-quartets, the loop sequence plays a major role on their folding topology and thermal stability. Here circular dichroism, NMR, and PAGE are used to study the effect of loop length and base composition in the middle loop, and a single base difference in loop 1 and 3 on G-quadruplex formation of (G3HG3NmG3HG3) sequences with and without flanking nucleotides, where H is T, A, or C and N is T, A, C, or G. In addition, melting curve for G-quadruplex unfolding was used to provide relatively thermal stability of G-quadruplex structure after the addition of K+ overnight. We further studied the effects of K+ concentration on their stability and found structural changes in several sequences. Such (G3HG3NmG3HG3) configuration can be found in a number of native DNA sequences. The study of structural diversity and similarity from these sequences may allow us to establish the correlation between model sequences and native sequences. Moreover, several sequences upon interaction with a G-quadruplex ligand, BMVC, show similar spectral change, implying that structural similarity is crucial for drug development.

Direct evidence of mitochondrial G-quadruplex DNA by using fluorescent anti-cancer agents.

G-quadruplex (G4) is a promising target for anti-cancer treatment. In this paper, we provide the first evidence supporting the presence of G4 in the mitochondrial DNA (mtDNA) of live cells. The molecular engineering of a fluorescent G4 ligand, 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC), can change its major cellular localization from the nucleus to the mitochondria in cancer cells, while remaining primarily in the cytoplasm of normal cells. A number of BMVC derivatives with sufficient mitochondrial uptake can induce cancer cell death without damaging normal cells. Fluorescence studies of these anti-cancer agents in live cells and in isolated mitochondria from HeLa cells have demonstrated that their major target is mtDNA. In this study, we use fluorescence lifetime imaging microscopy to verify the existence of mtDNA G4s in live cells. Bioactivity studies indicate that interactions between these anti-cancer agents and mtDNA G4 can suppress mitochondrial gene expression. This work underlines the importance of fluorescence in the monitoring of drug-target interactions in cells and illustrates the emerging development of drugs in which mtDNA G4 is the primary target.

Automated quantitative analysis of lipid accumulation and hydrolysis in living macrophages with label-free imaging.

The accumulation of lipids in macrophages is a key factor that promotes the formation of atherosclerotic lesions. Several methods such as biochemical assays and neutral lipid staining have been used for the detection of lipids in cells. However, a method for real-time quantitative assessment of the lipid content in living macrophages has yet to be shown, particularly for its kinetic process with drugs, due to the lack of suitable tools for non-invasive chemical detection. Here we demonstrate label-free real-time monitoring of lipid droplets (LDs) in living macrophages by using coherent anti-Stokes Raman scattering (CARS) microscopy. In addition, we have established an automated image analysis method based on maximum entropy thresholding (MET) to quantify the cellular lipid content. The result of CARS image analysis shows a good correlation (R(2) > 0.9) with the measurement of biochemical assay. Using this method, we monitored the processes of lipid accumulation and hydrolysis in macrophages. We further characterized the effect of a lipid hydrolysis inhibitor (diethylumbelliferyl phosphate, DEUP) and determined the kinetic parameters such as the inhibition constant, K(i). Our work demonstrates that the automated quantitative analysis method is useful for the studies of cellular lipid metabolism and has potential for preclinical high-throughput screening of therapeutic agents related to atherosclerosis and lipid-associated disorders.

Pilot imaging study of o-BMVC foci for discrimination of indeterminate cytology in diagnosing fine-needle aspiration of thyroid nodules.

Fluorescence lifetime imaging microscopy of a fluorescence probe, 3,6-bis(1-methyl-2-vinylpyridinium) carbazole diiodide (o-BMVC), provides an objective method for preoperative diagnosis of fine-needle aspiration (FNA) of thyroid nodules. The key of this o-BMVC test of FNA smears is the measurement of the digital number of o-BMVC foci in the nucleus. Thus, there are three categories classified in the o-BMVC test, which are nondiagnostic for unsatisfactory samples, benign for less numbers of o-BMVC foci, and malignant for more numbers of o-BMVC foci. The discrimination of indeterminate (including atypia, follicular neoplasm, suspicious) cytology into benign or malignant cases can reduce diagnostic uncertainty and benefit clinical decision making. This pilot study strongly suggests that the o-BMVC test is an invaluable method for diagnosing FNA samples. Particularly, the combination of FNA cytology and the o-BMVC test holds great promise to improve the efficacy of diagnosis and reduce the healthcare costs.

Improved diagnostic accuracy of malignant neck lumps by a simple BMVC staining assay.

A handheld device based on fluorescence of 3,6-bis(1-methyl-4-vinylpyridinium)carbazole diiodide (BMVC) staining was established for the rapid, point-of-care screening of cancer cells (see Chang and co-workers, Analyst, 2007, 132, 745). Offering instant screening of cancer at low cost, here we apply this simple assay in clinical tests on fine needle aspirates of neck masses from 114 outpatients (115 specimens). The diagnostic accuracy of this simple method alone is ca. 80% (80/99). The combination of the BMVC test and the fine needle aspiration (FNA) cytology reduced the non-diagnosis from 17 cases in FNA cytology to 6 cases in the combined method. Moreover, an algorithm is proposed to improve the diagnostic accuracy of malignant neck lumps up to nearly 100%.

The G-quadruplex fluorescent probe 3,6-bis(1-methyl-2-vinyl-pyridinium) carbazole diiodide as a biosensor for human cancers.

Using time-gated fluorescence lifetime imaging microscopy, significantly more signals from 3,6-bis(1-methyl-2-vinyl-pyridinium) carbazole diiodide (o-BMVC) foci, characterized by the longer fluorescent decay time of o-BMVC, were detected in six types of cancer cells than in three types of normal cells. Accumulating evidence suggested that the o-BMVC foci are mainly the G-quadruplex foci. The large contrast in the number of o-BMVC foci can be considered as a common signature to distinguish cancer cells from normal cells. Further study of tissue biopsy showed that the o-BMVC test provides a high accuracy for clinical detection of head and neck cancers.

BMVC test, an improved fluorescence assay for detection of malignant pleural effusions.

The diagnosis of malignant pleural effusions is an important issue in the management of malignancy patients. Generally, cytologic examination is a routine diagnostic technique. However, morphological interpretation of cytology is sometimes inconclusive. Here an ancillary method named BMVC test is developed for rapid detection of malignant pleural effusion to improve the diagnostic accuracy at low cost. A simple assay kit is designed to collect living cells from clinical pleural effusion and a fluorescence probe, 3,6-Bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC), is used to illuminate malignant cells. The fluorescence intensity is quantitatively analyzed by ImageJ program. This method yields digital numbers for the test results without any grey zone or ambiguities in the current cytology tests due to intra-observer and inter-observer variability. Comparing with results from double-blind cytologic examination, this simple test gives a good discrimination between malignant and benign specimens with sensitivity of 89.4% (42/47) and specificity of 93.3% (56/60) for diagnosis of malignant pleural effusion. BMVC test provides accurate results in a short time period, and the digital output could assist cytologic examination to become more objective and clear-cut. This is a convenient ancillary tool for detection of malignant pleural effusions.

Chemical principles for the design of a novel fluorescent probe with high cancer-targeting selectivity and sensitivity.

Understanding of principles governing selective and sensitive cancer targeting is critical for development of chemicals for cancer diagnostics and treatment. We determined the underlying mechanisms of how a novel fluorescent small organic molecule, 3,6-bis(1-methyl-4-vinylpyridinium)carbazole diiodide (BMVC), selectively labels cancer cells but not normal cells. We show that BMVC is retained in the lysosomes of normal cells. In cancer cells, BMVC escapes lysosomal retention and localizes to the mitochondria or to the nucleus, where DNA-binding dramatically increases BMVC fluorescence intensity, allowing it to light up only cancer cells. Structure-function analyses of BMVC derivatives show that hydrogen-bonding capacity is a key determinant of lysosomal retention in normal cells, whereas lipophilicity directs these derivatives to the mitochondria or the nucleus in cancer cells. In addition, drug-resistant cancer cells preferentially retain BMVC in their lysosomes compared to drug-sensitive cancer cells, and BMVC can be released from drug-resistant lysosomes using lysosomotropic agents. Our results further our understanding of how properties of cellular organelles differ between normal and cancer cells, which can be exploited for diagnostic and/or therapeutic use. We also provide physiochemical design principles for selective targeting of small molecules to different organelles. Moreover, our results suggest that agents which can increase lysosomal membrane permeability may re-sensitize drug-resistant cancer cells to chemotherapeutic agents.