Hariprasad Gali

A “dose on demand” Biomarker Generator for automated production of [18F]F− and [18F]FDG

The University of Oklahoma-College of Pharmacy has installed the first Biomarker Generator (BG75) comprising a self-shielded 7.5-MeV proton beam positive ion cyclotron and an aseptic automated chemistry production and quality control module for production of [(18)F]F(-) and clinical [(18)F]FDG. Performance, reliability, and safety of the system for the production of dose on demand were tested over several months. No-carrier-added [(18)F]F(-) was obtained through the (18)O(p,n)(18)F nuclear reaction by irradiation (20-40 min) of a >95% enriched [(18)O]H2O target (280 μl) with a 7.5-MeV proton beam (3.5-5.0 μA). Automated quality control tests were performed on each dose. The HPLC-based analytical methods were validated against USP methods of quality control. [(18)F]FDG produced by BG75 was tested in a mouse tumor model implanted with H441 human lung adenocarcinoma cells. After initial installment and optimization, the [(18)F]F(-) production has been consistent since March 2011 with a maximum production of 400 to 450 mCi in a day. The average yield is 0.61 mCi/min and 0.92 mCi/min at 3.8 µA and 5 µA, respectively. The current target window has held up for over 25 weeks against >400 bombardment cycles. [(18)F]FDG production has been consistent since June 2012 with an average of six doses/day in an automated synthesis mode (RCY≈50%). The release criteria included USP-specified limits for pH, residual solvents (acetonitrile/ethanol), kryptofix, radiochemical purity/identity, and filter integrity test. The entire automated operation generated minimal radiation exposure hazard to the operator and environment. As expected, [(18)F]FDG produced by BG75 was found to delineate tumor volume in a mouse model of xenograft tumor. In summary, production and quality control of [(18)F]FDG dose on demand have been accomplished in an automated and safe manner by the first Biomarker Generator. The implementation of a cGMP quality system is under way towards the ANDA submission and first clinical use of [(18)F]FDG produced by BG75.

Single-step radiosynthesis and in vivo evaluation of a novel fluorine-18 labeled hippurate for use as a PET renal agent.

OBJECTIVEnThe objective of this study was to investigate a new fluorine-18 labeled hippurate, m-cyano-p-[(18)F]fluorohippurate ([(18)F]CNPFH), as a potential radiopharmaceutical for evaluating renal function by PET.nnnMETHODSn[(18)F]CNPFH was synthesized by a direct one-step nucleophilic aromatic substitution using an (18)F-for-[N(CH(3))(3)](+)-reaction. In vivo stability was determined by HPLC analysis of urine collected from a healthy rat at 30min p.i. of [(18)F]CNPFH. The plasma protein binding (PPB) and erythrocyte uptake of [(18)F]CNPFH were determined using blood collected from healthy rats at 5min p.i. Biodistribution studies were conducted in healthy rats at 10min and 1h p.i. of [(18)F]CNPFH. Dynamic PET/CT imaging data were acquired in normal rats. For comparison, the same rats underwent an identical imaging study using the previously reported p-[(18)F]fluorohippurate ([(18)F]PFH) renal agent.nnnRESULTSn[(18)F]CNPFH demonstrated high in vivo stability with no metabolic degradation. The in vivo PPB and erythrocyte uptake of [(18)F]CNPFH were found to be comparable to those of [(18)F]PFH. Biodistribution and dynamic PET/CT imaging studies revealed a rapid clearance of [(18)F]CNPFH primarily through the renal-urinary pathway. However, unlike [(18)F]PFH, a minor (about 12%) fraction was eliminated via the hepatobiliary route. The PET-derived [(18)F]CNPFH renograms revealed an average time-to-peak (T(max)) of 3.2±0.4min which was similar to [(18)F]PFH, but the average time-to-half-maximal activity (11.4±2.8min) was found to be higher than that of [(18)F]PFH (7.1±1.3min).nnnCONCLUSIONSnOur in vivo results indicate that [(18)F]CNPFH has renogram characteristics similar to those of [(18)F]PFH, however, the unexpected hepatobiliary elimination is adding undesirable background signal in the PET images.

Renogram comparison of p-[18F]fluorohippurate with o-[125I]iodohippurate and [99mTc]MAG3 in normal rats

ObjectiveWe recently identified p-[18F]fluorohippurate ([18F]PFH) as a potential positron emission tomography (PET) renal agent. The objective of this study was to compare renogram parameters of [18F]PFH with o-[125I]iodohippurate ([125I]OIH) as a surrogate for the renal imaging gold standard 131I-OIH and with a clinically used agent [99mTc]MAG3. MethodsNormal Sprague−Dawley rats (n=4) were sequentially imaged on days 1, 2, and 3 using [99mTc]MAG3 (18.1–19.1 MBq, dynamic planar), [18F]PFH (2.6–4.1 MBq, dynamic PET), and [125I]OIH (7.7–13.5 MBq, dynamic planar), respectively. The PET data were binned into frames of 30 s each, whereas the planar images were acquired as 30 s per frame. Regions of interest were drawn on both kidneys, and decay-corrected renograms were generated for each imaging modality. ResultsThe PET-derived [18F]PFH renograms revealed an average time-to-peak (Tmax) of 4.8±2.4 min, which was comparable to the Tmax of 3.6±1.7 min and 4.3±1.7 min for [125I]OIH and [99mTc]MAG3 renograms, respectively. The average time-to-half-maximal activity was found to be 16.6±6.6 min, 8.3±2.4 min, and more than 20 min with [18F]PFH, [125I]OIH, and [99mTc]MAG3, respectively. ConclusionsCompared with [99mTc]MAG3, the renogram parameters of [18F]PFH seem to be closer to those obtained from [125I]OIH. The quality of the renogram and the images obtained with the dynamic [18F]PFH PET study were remarkably better than those obtained with the [99mTc]MAG3 dynamic planar imaging study.

Novel Retro-Inverso Peptide Inhibitor Reverses Angiotensin Receptor Autoantibody–Induced Hypertension in the Rabbit

Activating autoantibodies to the angiotensin II type 1 receptor (AT1R) have been implicated in hypertensive disorders. We investigated whether AT1R antibodies produced in immunized rabbits will activate AT1R and contribute to hypertension by a direct contractile effect on the vasculature and whether they can be blocked by a novel decoy peptide. A multiple antigenic peptide containing the AT1R epitope AFHYESQ, which is the receptor-binding epitope of AT1R-activating autoantibodies, was used to immunize 6 rabbits. AT1R antibody activity was analyzed in AT1R-transfected cells, and their contractile effects were assayed using isolated perfused rat cremaster resistance arterioles. A retro-inverso D-amino acid epitope-mimetic peptide was tested for AT1R antibody inhibition in vitro and in vivo. All immunized animals produced high AT1R antibody titers and developed elevated blood pressure. No changes in measured blood chemistry values were observed after immunization. Rabbit anti-AT1R sera induced significant AT1R activation in transfected cells and vasoconstriction in the arteriole assay, both of which were blocked by losartan and the retro-inverso D-amino acid peptide. A single intravenous bolus injection of the retro-inverso D-amino acid peptide (1 mg/kg) into immunized rabbits dropped the mean arterial pressure from 122±11 to 82±6 mmu2009Hg. Rabbit anti-AT1R sera partially suppressed angiotensin II–induced contraction of isolated rat cremaster arterioles, and the pressor response to angiotensin II infusion was attenuated in immunized animals. In conclusion, AT1R-activating autoantibodies and the retro-inverso D-amino acid peptide, respectively, have important etiologic and therapeutic implications in hypertensive subjects who harbor these autoantibodies.

Role of (Drug) Transporters in Imaging in Health and Disease

This report is the summary of presentations at the symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics, April 26–30, at Experimental Biology 2014 in San Diego, CA. The presentations focused on the role of transporters in imaging in health and disease and on assessing transporter function in vivo. Imaging is an important diagnostic tool in clinics and is a novel tool for in vivo visualization of transporter function. Many imaging substrates and endogenous markers for organ function are organic anions. In this symposium, the bile salt transporter sodium taurocholate cotransporting polypeptide and the liver organic anion transporting polypeptides (OATPs) as well as the renal organic anion transporters (OATs) were addressed in detail; e.g., OATPs mediate transport of contrast agents used for magnetic resonance imaging of the liver or transport agents used for hepatobiliary scintigraphy, and OATs transport substances used in renography. In addition, the symposium also focused on the multidrug-resistance transporter 1 (MDR1 or P-gp), which is the most important gatekeeper in epithelial or endothelial barriers for preventing entry of potentially harmful substances into organs. Novel substrates suitable for positron emission tomography (PET) allow the study of such transporters at the blood-brain barrier or while they are mediating uptake of drugs into hepatocytes, and, importantly, PET tracers also now allow renography. Finally, quantitative data on transporter expression in human organs allow the development of improved physiologically based pharmacokinetic (PBPK) models for drug disposition. Hence, the combined efforts using novel substrates for in vivo visualization of transporters and quantification of transporters will lead to a deeper understanding of transporter function in disease and allow development of novel PBPK models for disease states.

Chemodrug delivery using integrin-targeted PLGA-Chitosan nanoparticle for lung cancer therapy

In this study, we report the efficacy of RGD (arginine-glycine-aspartic acid) peptide-modified polylactic acid-co-glycolic acid (PLGA)-Chitosan nanoparticle (CSNP) for integrin αvβ3 receptor targeted paclitaxel (PTX) delivery in lung cancer cells and its impact on normal cells. RGD peptide-modified chitosan was synthesized and then coated onto PTX-PLGA nanoparticles prepared by emulsion-solvent evaporation. PTX-PLGA-CSNP-RGD displayed favorable physicochemical properties for a targeted drug delivery system. The PTX-PLGA-CSNP-RGD system showed increased uptake via integrin receptor mediated endocytosis, triggered enhanced apoptosis, and induced G2/M cell cycle arrest and more overall cytotoxicity than its non-targeted counterpart in cancer cells. PTX-PLGA-CSNP-RGD showed less toxicity in lung fibroblasts than in cancer cells, may be attributed to low drug sensitivity, nevertheless the study invited close attention to their transient overexpression of integrin αvβ3 and cautioned against corresponding uptake of toxic drugs, if any at all. Whereas, normal human bronchial epithelial (NHBE) cells with poor integrin αvβ3 expression showed negligible toxicity to PTX-PLGA-CSNP-RGD, at equivalent drug concentrations used in cancer cells. Further, the nanoparticle demonstrated its capacity in targeted delivery of Cisplatin (CDDP), a drug having physicochemical properties different to PTX. Taken together, our study demonstrates that PLGA-CSNP-RGD is a promising nanoplatform for integrin targeted chemotherapeutic delivery to lung cancer.

Small-Molecule Inhibition of GCNT3 Disrupts Mucin Biosynthesis and Malignant Cellular Behaviors in Pancreatic Cancer.

Pancreatic cancer is an aggressive neoplasm with almost uniform lethality and a 5-year survival rate of 7%. Several overexpressed mucins that impede drug delivery to pancreatic tumors have been therapeutically targeted, but enzymes involved in mucin biosynthesis have yet to be preclinically evaluated as potential targets. We used survival data from human patients with pancreatic cancer, next-generation sequencing of genetically engineered Kras-driven mouse pancreatic tumors and human pancreatic cancer cells to identify the novel core mucin-synthesizing enzyme GCNT3 (core 2 β-1,6 N-acetylglucosaminyltransferase). In mouse pancreatic cancer tumors, GCNT3 upregulation (103-fold; P < 0.0001) was correlated with increased expression of mucins (5 to 87-fold; P < 0.04-0.0003). Aberrant GCNT3 expression was also associated with increased mucin production, aggressive tumorigenesis, and reduced patient survival, and CRISPR-mediated knockout of GCNT3 in pancreatic cancer cells reduced proliferation and spheroid formation. Using in silico small molecular docking simulation approaches, we identified talniflumate as a novel inhibitor that selectively binds to GCNT3. In particular, docking predictions suggested that three notable hydrogen bonds between talniflumate and GCNT3 contribute to a docking affinity of -8.3 kcal/mol. Furthermore, talniflumate alone and in combination with low-dose gefitinib reduced GCNT3 expression, leading to the disrupted production of mucins in vivo and in vitro Collectively, our findings suggest that targeting mucin biosynthesis through GCNT3 may improve drug responsiveness, warranting further development and investigation in preclinical models of pancreatic tumorigenesis. Cancer Res; 76(7); 1965-74. ©2016 AACR.

Synthesis and biodistribution studies of technetium-99m-labeled aminopeptidase N inhibitor conjugates

Probestin is a potent aminopeptidase N (APN) inhibitor. Four probestin conjugates containing a tripeptide chelator (N(3)S) and a PEG(2) linker were synthesized and radiolabeled with Tc-99m. The number of -COOH groups on the chelator was altered to increase the excretion of the radiotracer from blood stream via the renal-urinary pathway and to decrease its hepatobiliary uptake. Biodistribution of the radiolabeled conjugates was evaluated in healthy CF-1™ mice at 1h post-injection. The results revealed that the Tc-99m labeled probestin conjugate preferentially (>85% injected dose) excreted via the renal route when an aspartic acid residue was added to the linker (conjugate 4). These results suggest that the pharmacokinetic properties of probestin-based APN-targeted agents could be optimized by adding an appropriate amino acid residue in between the linker and the payload.

Evaluation of [18F]PFH PET renography to predict future disease progression in a rat model of autosomal dominant polycystic kidney disease

INTRODUCTIONnPrognostic markers for progression of polycystic kidney disease (PKD) are limited. We evaluated the potential of early para-[(18)F]fluorohippurate ([(18)F]PFH) positron emission tomography (PET) renography to predict future progression of PKD in Han:SPRD rats with slowly progressive autosomal dominant PKD.nnnMATERIALS AND METHODSnMale and female heterozygous (Cy/+) and normal littermate (+/+) Han:SPRD rats underwent [(18)F]PFH PET renography and blood sampling to measure serum creatinine (S-Cr) and serum urea nitrogen (SUN) concentrations at 6 and 26 wk of age. T2 and T20 values, which represent the percent of the injected dose of [(18)F]PFH in kidneys at 2 and 20 min after injection, were determined from imaging data. T20/T2 ratio was assessed as a prognostic marker. Rats were euthanized after renography at 26 wk of age, and kidney weight/body weight ratios (KW/BW%) were determined as a measure of PKD progression.nnnRESULTSnMale and female Cy/+ rats are known to manifest PKD of different severity, male Cy/+ rats display much more severe PKD than female rats. S-Cr and SUN concentrations did not differ between +/+ and Cy/+ rats and between female and male Cy/+ rats at 6 wk of age, but they were higher at 26 wk of age and male rats displayed higher values than female rats, which indicates inability of S-Cr and SUN to measure disease severity at an early stage. T20/T2 ratios were higher for Cy/+ than +/+ rats at 6 wk of age. Importantly, male Cy/+ rats displayed higher T20/T2 ratios than female Cy/+ rats. T20/T2 ratios obtained at 6 wk of age correlated well with S-Cr, SUN, and KW/BW% values obtained at 26 wk of age.nnnCONCLUSIONSnThis study indicates that T20/T2 ratio derived from [(18)F]PFH PET renography at an early age could be useful as a novel prognostic marker to predict future disease severity in a rat model of ADPKD.

Synthesis and in vivo evaluation of gallium-68-labeled glycine and hippurate conjugates for positron emission tomography renography

The objective of this study was to evaluate four new (68) Ga-labeled 1,4,7,10-cyclododeca-1,4,7,10-tetraacetic acid (DOTA)/1,4,7-triazacyclononane-1,4,7-triacetic acid derived (NODAGA)-glycine/hippurate conjugates and select a lead candidate for potential application in positron emission tomography (PET) renography. The non-metallated conjugates were synthesized by a solid phase peptide synthesis method. The (68) Ga labeling was achieved by reacting an excess of the non-metallated conjugate with (68) GaCl4 (-) at pH -4.5 and 10-min incubation either at room temperature for NODAGA or 90u2009°C for DOTA. Radiochemical purity of all (68) Ga conjugates was found to be >98%. (68) Ga-NODAGA-glycine displayed the lowest serum protein binding (0.4%) in vitro among the four (68) Ga conjugates. Biodistribution of (68) Ga conjugates in healthy Sprague Dawley rats at 1-h post-injection revealed an efficient clearance from circulation primarily through the renal-urinary pathway with <0.2% of injected dose per gram remaining in the blood. The kidney/blood and kidney/muscle ratios of (68) Ga-NODAGA-glycine were significantly higher than other (68) Ga conjugates. On the basis of these results, (68) Ga-NODAGA-glycine was selected as the lead candidate. (68) Ga-NODAGA-glycine PET renograms obtained in healthy rats suggest (68) Ga-NODAGA-glycine as a PET alternate of (99m) Tc-Diethylenetriaminepentaacetic acid (DTPA).