Advances in myotonic dystrophy type 1 drug discovery through design of novel ligands and mechanism establishment

Myotonic dystrophy type 1 (DM1) is caused by an expanded CUG repeat (CUGexp) that sequesters muscleblind-like 1 protein (MBNL1), a protein that regulates alternative splicing. CUGexp RNA is a validated drug target for this currently untreatable disease. Herein, we describe the development of a bioactive small molecule (Chapter 2) and a small library of dimeric ligands (Chapter 3) leading to an optimized bivalent ligand. These novel ligands target CUGexp RNA and are able to inhibit the CUGexp⋅MBNL1 interaction in cells that model DM1. In a DM1 cell model these ligands were found to disperse CUGexp ribonuclear foci, release MBNL1, and partially reverse the mis-splicing of the insulin receptor pre-mRNA. Direct evidence for ribonuclear foci dispersion by this ligand was obtained in a live DM1 cell model using time-lapse confocal microscopy. In Chapter 4, We report a single-molecule approach to study the binding of MBNL1 to (CUG)n=4,6 and the effect of small molecules on this interaction. MBNL1 is able to bind to the (CUG)n･inhibitor complex indicating that the inhibition is not a straight forward competitive process. A simple bivalent ligand, shows a binding to (CUG)n almost 50-fold more tightly than the corresponding monomeric ligand and is more effective in destabilizing MBNL1･(CUG)4. The single-molecule method and the analysis framework might be extended to the study of other biomolecular interactions. Chapter 5 includes a preliminary effort to solve the mystery of CUGexp unfolding/folding upon interaction with MBNL1. To approach this unanswered yet key structural question about how MBNL1 binds CUGexp, preliminary bulk FRET (Fluorescence Resonance Energy Transfer) studies, as well as single-molecule FRET studies are describe

Ectopic “Ectopic” Gastric Mucosa

Meckel’s diverticulum is a developmental GI anomaly. It is a remnant of the omphalomesenteric duct (vitelline duct) and the most common congenital anomaly found in the small intestine. It contains ectopic/heterotopic gastric mucosa in half of the cases. Imaging investigations for diagnosing Meckel’s diverticulum may include a plain radiography; however, this has a very limited diagnostic value. A blind-ending fluid-filled structure can sometimes be seen with sonography, but again, this technique’s diagnostic value is limited due to multiple factors. A CT scan may be helpful in localizing the bleeding diverticulum, which can be better visualized with CT enterography. Diverticula containing gastric mucosa can be diagnosed with a higher sensitivity with Tc-99 scintigraphy. The typical location of Meckel’s diverticulum is within two feet of the ileocecal valve; thus, ectopic gastric mucosal uptake is typically seen in the lower right quadrant in scintigraphy. We present a rare case of Tc-99 pertechnetate scintigraphy showing ectopic gastric mucosa in the upper mid abdomen, which was surgically proven to be at the mid ileum. To our knowledge, there is no ectopic Meckel’s diverticulum case published in the literature. Familiarity with this atypical imaging presentation of relatively common ectopic gastric mucosa may help the radiologists in the timely diagnosis and management of the patient

Variant allele fraction of genomic alterations in circulating tumor DNA (%ctDNA) correlates with SUV

The relationship between higher variant allele fraction (VAF) of genomic alterations in circulating tumor DNA (%ctDNA), an indicator of poor outcome, and maximum standardized uptake value (SU

Fluorous-Soluble Metal Chelate for Sensitive Fluorine-19 Magnetic Resonance Imaging Nanoemulsion Probes.

Fluorine-19 MRI is an emerging cellular imaging approach, enabling lucid, quantitative "hot-spot" imaging with no background signal. The utility of 19F-MRI to detect inflammation and cell therapy products in vivo could be expanded by improving the intrinsic sensitivity of the probe by molecular design. We describe a metal chelate based on a salicylidene-tris(aminomethyl)ethane core, with solubility in perfluorocarbon (PFC) oils, and a potent accelerator of the 19F longitudinal relaxation time ( T1). Shortening T1 can increase the 19F image sensitivity per time and decrease the minimum number of detectable cells. We used the condensation between the tripodal ligand tris-1,1,1-(aminomethyl)ethane and salicylaldehyde to form the salicylidene-tris(aminomethyl)ethane chelating agent (SALTAME). We purified four isomers of SALTAME, elucidated structures using X-ray scattering and NMR, and identified a single isomer with high PFC solubility. Mn4+, Fe3+, Co3+, and Ga3+ cations formed stable and separable chelates with SALTAME, but only Fe3+ yielded superior T1 shortening with modest line broadening at 3 and 9.4 T. We mixed Fe3+ chelate with perfluorooctyl bromide (PFOB) to formulate a stable paramagnetic nanoemulsion imaging probe and assessed its biocompatibility in macrophages in vitro using proliferation, cytotoxicity, and phenotypic cell assays. Signal-to-noise modeling of paramagnetic PFOB shows that sensitivity enhancement of nearly 4-fold is feasible at clinical magnetic field strengths using a 19F spin-density-weighted gradient-echo pulse sequence. We demonstrate the utility of this paramagnetic nanoemulsion as an in vivo MRI probe for detecting inflammation macrophages in mice. Overall, these paramagnetic PFC compounds represent a platform for the development of sensitive 19F probes

Fluorous-Soluble Metal Chelate for Sensitive Fluorine-19 Magnetic Resonance Imaging Nanoemulsion Probes.

Fluorine-19 MRI is an emerging cellular imaging approach, enabling lucid, quantitative "hot-spot" imaging with no background signal. The utility of 19F-MRI to detect inflammation and cell therapy products in vivo could be expanded by improving the intrinsic sensitivity of the probe by molecular design. We describe a metal chelate based on a salicylidene-tris(aminomethyl)ethane core, with solubility in perfluorocarbon (PFC) oils, and a potent accelerator of the 19F longitudinal relaxation time ( T1). Shortening T1 can increase the 19F image sensitivity per time and decrease the minimum number of detectable cells. We used the condensation between the tripodal ligand tris-1,1,1-(aminomethyl)ethane and salicylaldehyde to form the salicylidene-tris(aminomethyl)ethane chelating agent (SALTAME). We purified four isomers of SALTAME, elucidated structures using X-ray scattering and NMR, and identified a single isomer with high PFC solubility. Mn4+, Fe3+, Co3+, and Ga3+ cations formed stable and separable chelates with SALTAME, but only Fe3+ yielded superior T1 shortening with modest line broadening at 3 and 9.4 T. We mixed Fe3+ chelate with perfluorooctyl bromide (PFOB) to formulate a stable paramagnetic nanoemulsion imaging probe and assessed its biocompatibility in macrophages in vitro using proliferation, cytotoxicity, and phenotypic cell assays. Signal-to-noise modeling of paramagnetic PFOB shows that sensitivity enhancement of nearly 4-fold is feasible at clinical magnetic field strengths using a 19F spin-density-weighted gradient-echo pulse sequence. We demonstrate the utility of this paramagnetic nanoemulsion as an in vivo MRI probe for detecting inflammation macrophages in mice. Overall, these paramagnetic PFC compounds represent a platform for the development of sensitive 19F probes

Molecular Imaging of the Glomerulus via Mesangial Cell Uptake of Radiolabeled Tilmanocept

An unmet need for the clinical management of chronic kidney disease is a predictive tool of kidney function during the first decade of the disease, when there is silent loss of glomerular function. The objective of this study was to demonstrate receptor-mediated binding of tilmanocept to CD206 within the kidney and provide evidence of kinetic sensitivity of this binding to renal function. Methods: Rats were positioned in a PET scanner with the liver and kidneys within the field of view. After an intravenous injection of 68Ga-IRDye800-tilmanocept, using 1 of 2 scaled molar doses (0.02 nmol/g, n = 5; or 0.10 nmol/g, n = 5), or coinjection (n = 3) of 68Ga-IRDye800-tilmanocept (0.10 nmol/g) and unlabeled tilmanocept (5.0 nmol/g), or a negative control, 68Ga-IRDye800-DTPA-galactosyl-dextran (0.02 nmol/g, n = 5), each animal was imaged for 20 min followed by a whole-body scan. Frozen kidney sections were stained for podocytes and CD206 using immunofluorescence. Molecular imaging of diabetic db/db mice (4.9 wk, n = 6; 7.3 wk, n = 4; 13.3 wk, n = 6) and nondiabetic db/m mice (n = 6) was performed with fluorescence-labeled 99mTc-tilmanocept (18.5 MBq, 2.6 nmol). Thirty minutes after injection, blood, liver, kidneys, and urine were assayed for radioactivity. Renal time-activity curves were generated. Results: Rat PET whole-body images and time-activity curves of 68Ga-IRDye800-tilmanocept demonstrated receptor-mediated renal accumulation with evidence of glomerular uptake. Activity within the renal cortex persisted during the 40-min study. Histologic examination demonstrated colocalization of CD206 and IRDye800-tilmanocept within the glomerulus. The glomerular accumulation of the coinjection and the negative control studies were significantly less than the CD206-targeted agent. The db/db mice displayed a multiphasic renal time-activity curve with high urinary bladder accumulation; the nondiabetic mice exhibited renal uptake curves dominated by a single phase with low bladder accumulation. Conclusion: This study demonstrated receptor-mediated binding to the glomerular mesangial cells and kinetic sensitivity of tilmanocept to chronic renal disease. Given the role of mesangial cells during the progression of diabetic nephropathy, PET or SPECT renal imaging with radiolabeled tilmanocept may provide a noninvasive quantitative assessment of glomerular function

Developing Bivalent Ligands to Target CUG Triplet Repeats, the Causative Agent of Myotonic Dystrophy Type 1

An expanded CUG repeat transcript (CUG^exp) is the causative agent of myotonic dystrophy type 1 (DM1) by sequestering muscleblind-like 1 protein (MBNL1), a regulator of alternative splicing. On the basis of a ligand (<b>1</b>) that was previously reported to be active in an in vitro assay, we present the synthesis of a small library containing 10 dimeric ligands (<b>4</b>–<b>13</b>) that differ in length, composition, and attachment point of the linking chain. The oligoamino linkers gave a greater gain in affinity for CUG RNA and were more effective when compared to oligoether linkers. The most potent in vitro ligand (<b>9</b>) was shown to be aqueous-soluble and both cell- and nucleus-permeable, displaying almost complete dispersion of MBNL1 ribonuclear foci in a DM1 cell model. Direct evidence for the bioactivity of <b>9</b> was observed in its ability to disperse ribonuclear foci in individual live DM1 model cells using time-lapse confocal fluorescence microscopy

Developing Bivalent Ligands to Target CUG Triplet Repeats, the Causative Agent of Myotonic Dystrophy Type 1

An expanded CUG repeat transcript (CUG^exp) is the causative agent of myotonic dystrophy type 1 (DM1) by sequestering muscleblind-like 1 protein (MBNL1), a regulator of alternative splicing. On the basis of a ligand (<b>1</b>) that was previously reported to be active in an in vitro assay, we present the synthesis of a small library containing 10 dimeric ligands (<b>4</b>–<b>13</b>) that differ in length, composition, and attachment point of the linking chain. The oligoamino linkers gave a greater gain in affinity for CUG RNA and were more effective when compared to oligoether linkers. The most potent in vitro ligand (<b>9</b>) was shown to be aqueous-soluble and both cell- and nucleus-permeable, displaying almost complete dispersion of MBNL1 ribonuclear foci in a DM1 cell model. Direct evidence for the bioactivity of <b>9</b> was observed in its ability to disperse ribonuclear foci in individual live DM1 model cells using time-lapse confocal fluorescence microscopy

Developing Bivalent Ligands to Target CUG Triplet Repeats, the Causative Agent of Myotonic Dystrophy Type 1

An expanded CUG repeat transcript (CUG^exp) is the causative agent of myotonic dystrophy type 1 (DM1) by sequestering muscleblind-like 1 protein (MBNL1), a regulator of alternative splicing. On the basis of a ligand (<b>1</b>) that was previously reported to be active in an in vitro assay, we present the synthesis of a small library containing 10 dimeric ligands (<b>4</b>–<b>13</b>) that differ in length, composition, and attachment point of the linking chain. The oligoamino linkers gave a greater gain in affinity for CUG RNA and were more effective when compared to oligoether linkers. The most potent in vitro ligand (<b>9</b>) was shown to be aqueous-soluble and both cell- and nucleus-permeable, displaying almost complete dispersion of MBNL1 ribonuclear foci in a DM1 cell model. Direct evidence for the bioactivity of <b>9</b> was observed in its ability to disperse ribonuclear foci in individual live DM1 model cells using time-lapse confocal fluorescence microscopy