Blood Pharmacokinetics Imaging by Noninvasive Heart Fluorescence Tomography and Application to Kidney Glomerular Filtration Rate Assessment.

In mouse pharmacokinetic (PK) studies, current standard methods often require large numbers of animals to support collection of blood samples serially over a defined time range. We have developed and validated a noninvasive fluorescence molecular tomography (FMT) heart imaging approach for blood PK quantification that uses small numbers of mice and has the advantage of repeated, longitudinal live imaging. This method was validated using a variety of near infrared (NIR) fluorescent-labeled molecules, ranging in size from 1.3 to 150 kDa, that were assessed by microplate blood assays as well as by noninvasive FMT 4000 imaging. Excellent agreement in kinetic profiles and calculated PK metrics was seen for the two methods, establishing the robustness of this noninvasive optical imaging approach. FMT heart imaging was further assessed in the challenging application of inulin-based glomerular filtration rate (GFR) measurement. After a single bolus injection of an NIR fluorescent-labeled inulin probe in small cohorts of mice (n = 5 per group), 2-minute heart scans (at 2, 6, 15, 30, and 45 minutes) were performed by FMT imaging. GFR was calculated using two-compartment PK modeling, determining an average rate of 240 ± 21 µl/min in normal mice, in agreement with published mouse GFR ranges. Validation of GFR assessment in unilaterally nephrectomized mice and cyclosporin A-treated mice both measured ∼50% decreases in GFR. Imaging results correlated well with ex vivo plasma microplate assays for inulin blood kinetics, and the decreases in GFR were accompanied by increases in plasma creatinine and blood urea nitrogen.

Fluorescence imaging of bombesin and transferrin receptor expression is comparable to 18F-FDG PET in early detection of sorafenib-induced changes in tumor metabolism.

Physical measurement of tumor volume reduction is the most commonly used approach to assess tumor progression and treatment efficacy in mouse tumor models. However, it is relatively insensitive, and often requires long treatment courses to achieve gross physical tumor destruction. As alternatives, several non-invasive imaging methods such as bioluminescence imaging (BLI), fluorescence imaging (FLI) and positron emission tomography (PET) have been developed for more accurate measurement. As tumors have elevated glucose metabolism, 18F-fludeoxyglucose (18F-FDG) has become a sensitive PET imaging tracer for cancer detection, diagnosis, and efficacy assessment by measuring alterations in glucose metabolism. In particular, the ability of 18F-FDG imaging to detect drug-induced effects on tumor metabolism at a very early phase has dramatically improved the speed of decision-making regarding treatment efficacy. Here we demonstrated an approach with FLI that offers not only comparable performance to PET imaging, but also provides additional benefits, including ease of use, imaging throughput, probe stability, and the potential for multiplex imaging. In this report, we used sorafenib, a tyrosine kinase inhibitor clinically approved for cancer therapy, for treatment of a mouse tumor xenograft model. The drug is known to block several key signaling pathways involved in tumor metabolism. We first identified an appropriate sorafenib dose, 40 mg/kg (daily on days 0-4 and 7-10), that retained ultimate therapeutic efficacy yet provided a 2-3 day window post-treatment for imaging early, subtle metabolic changes prior to gross tumor regression. We then used 18F-FDG PET as the gold standard for assessing the effects of sorafenib treatment on tumor metabolism and compared this to results obtained by measurement of tumor size, tumor BLI, and tumor FLI changes. PET imaging showed ~55-60% inhibition of tumor uptake of 18F-FDG as early as days 2 and 3 post-treatment, without noticeable changes in tumor size. For comparison, two FLI probes, BombesinRSense™ 680 (BRS-680) and Transferrin-Vivo™ 750 (TfV-750), were assessed for their potential in metabolic imaging. Metabolically active cancer cells are known to have elevated bombesin and transferrin receptor levels on the surface. In excellent agreement with PET imaging, the BRS-680 imaging showed 40% and 79% inhibition on days 2 and 3, respectively, and the TfV-750 imaging showed 65% inhibition on day 3. In both cases, no significant reduction in tumor volume or BLI signal was observed during the first 3 days of treatment. These results suggest that metabolic FLI has potential preclinical application as an additional method for detecting drug-induced metabolic changes in tumors.

Detection and quantification of enzymatically active prostate-specific antigen in vivo.

Assays for blood levels of prostate-specific antigen (PSA), performed in prostate cancer detection, measure mostly inactive/complexed PSA and do not provide information regarding enzymatically active PSA, which is biologically more relevant. Thus, we designed and synthesized an enzymatically cleavable peptide sequence labeled with near-infrared (NIR) fluorophores (ex/em 740/770 nm) and coupled it to a pharmacokinetic modifier designed to improve its plasma kinetics. In its native state, the agent, PSA750 FAST™ (PSA750), is optically quenched (>95%) and only becomes fluorescent upon cleavage by active PSA, yielding a significant increase in signal. This activation is highly selective for PSA relative to a large panel of disease-relevant enzymes. Active PSA was detected in tumor frozen sections using PSA750 and this activity was abolished in the presence of the inhibitor, alpha-1 anti-chymotrypsin. In vivo imaging of tumor-bearing mice using fluorescence molecular tomography demonstrated a significantly higher fluorescent signal in PSA+ LNCaP tumors as compared to PSA- prostate cancer 3 tumors (13.0±3.7 versus 2.8±0.8 pmol, p=0.023). Ex vivo imaging of tumor sections confirms PSA750-derived NIR signal localization in nonvascular tissue. This is the first report that demonstrates the feasibility and effectiveness of noninvasive, real time, fluorescence molecular imaging of PSA enzymatic activity in prostate cancer.

A fluorogenic near-infrared imaging agent for quantifying plasma and local tissue renin activity in vivo and ex vivo.

The renin-angiotensin system (RAS) is well studied for its regulation of blood pressure and fluid homeostasis, as well as for increased activity associated with a variety of diseases and conditions, including cardiovascular disease, diabetes, and kidney disease. The enzyme renin cleaves angiotensinogen to form angiotensin I (ANG I), which is further cleaved by angiotensin-converting enzyme to produce ANG II. Although ANG II is the main effector molecule of the RAS, renin is the rate-limiting enzyme, thus playing a pivotal role in regulating RAS activity in hypertension and organ injury processes. Our objective was to develop a near-infrared fluorescent (NIRF) renin-imaging agent for noninvasive in vivo detection of renin activity as a measure of tissue RAS and in vitro plasma renin activity. We synthesized a renin-activatable agent, ReninSense 680 FAST (ReninSense), using a NIRF-quenched substrate derived from angiotensinogen that is cleaved specifically by purified mouse and rat renin enzymes to generate a fluorescent signal. This agent was assessed in vitro, in vivo, and ex vivo to detect and quantify increases in plasma and kidney renin activity in sodium-sensitive inbred C57BL/6 mice maintained on a low dietary sodium and diuretic regimen. Noninvasive in vivo fluorescence molecular tomographic imaging of the ReninSense signal in the kidney detected increased renin activity in the kidneys of hyperreninemic C57BL/6 mice. The agent also effectively detected renin activity in ex vivo kidneys, kidney tissue sections, and plasma samples. This approach could provide a new tool for assessing disorders linked to altered tissue and plasma renin activity and to monitor the efficacy of therapeutic treatments.

Noninvasive in vivo quantification of neutrophil elastase activity in acute experimental mouse lung injury.

We developed a neutrophil elastase-specific near-infrared fluorescence imaging agent, which, combined with fluorescence molecular tomographic imaging, allowed us to detect and quantify neutrophil elastase activity in vivo, in real time, and noninvasively in an acute model of lung injury (ALI). Significantly higher fluorescent signal was quantified in mice with LPS/fMLP-induced ALI as compared to healthy controls, correlating with increases in the number of bronchoalveolar lavage cells, neutrophils, and elastase activity. The agent was significantly activated ex vivo in lung sections from ALI but not from control mice, and this activation was ablated by the specific inhibitor sivelestat. Treatment with the specific inhibitor sivelestat significantly reduced lung signal in mice with ALI. These results underscore the unique ability of fluorescence molecular imaging to quantify specific molecular processes in vivo, crucial for understanding the mechanisms underlying disease progression and for assessing and monitoring novel pharmacological interventions.

Efficient use of the iron ortho-nitrophenylporphyrin chloride to mimic biological oxidations of dimethylaminoantipyrine.

Major metabolites of dimethylaminoantipyrine have been synthesized using iron ortho-nitrophenylporphyrin chloride as biomimetic catalyst. Reactivity of iron tetrakis-ortho-nitrophenylporphyrin chloride [Fe(TNO2PP)Cl] has been compared with iron tetrakis-pentafluorophenylporphyrin chloride and iron tetrakis-2,6-dichlorophenylporphyrin chloride using various oxidants such as hydrogen peroxide, iodosobenzene, and cumene hydroperoxide in either protic or aprotic solvent. Effect of imidazole has been showed on the reactivity of Fe(TNO2PP)Cl/cumene hydroperoxide system.

Expression, purification, and characterization of rat interferon-beta, and preparation of an N-terminally PEGylated form with improved pharmacokinetic parameters.

To identify potential new clinical uses and routes of administration for human interferon-beta-1a (IFN-beta-1a), we have developed an expression and purification procedure for the preparation of highly purified rat interferon-beta (IFN-beta) suitable for testing in rat models of human disease. An expression vector containing the rat IFN-beta signal sequence and structural gene was constructed and transfected into Chinese hamster ovary (CHO) cells. The protein was purified from CHO cell conditioned medium and purified to > 99.5% purity using standard chromatographic techniques. Analytical characterization indicated that the protein was a heavily glycosylated monomeric protein, with two of the four predicted N-glycosylation sites occupied. Analysis of the attached oligosaccharides showed them to be a complex mixture of bi-antennary, tri-antennary, and tetra-antennary structures with a predominance of sialylated tri-antennary and tetra-antennary structures. Peptide mapping, N-terminal sequencing, and mass spectrometry confirmed the identity and integrity of the purified protein. The purified protein had a specific activity of 2.1x10(8)U/mg when assayed on rat RATEC cells, which is similar in magnitude to the potencies observed for murine IFN-beta and human IFN-beta-1a assayed on murine and human cells, respectively. We also prepared an N-terminally PEGylated form of rat IFN-beta in which a 20 kDa methoxy polyethylene glycol (PEG)-propionaldehyde was attached to the N-terminal alpha-amino group of Ile-1. The PEGylated protein, which retained essentially full in vitro antiviral activity, had improved pharmacokinetic parameters in rats as compared to the unmodified protein. Both the unmodified and PEGylated forms of rat IFN-beta will be useful for testing in rat models of human disease.

Capillary electrophoresis/electrospray ion trap mass spectrometry for the analysis of negatively charged derivatized and underivatized glycans.

The increasing interest in the development of glycoproteins for therapeutic purposes has created a greater demand for methods to characterize the sugar moieties bound to them. Traditionally, released carbohydrates are derivatized using such methods as permethylation or fluorescent tagging prior to analysis by high performance liquid chromatography (HPLC), capillary electrophoresis (CE), or direct infusion mass spectrometry. However, little research has been performed using CE with on-line mass spectrometry (MS) detection. The CE separation of neutral oligosaccharides requires the covalent attachment of a charged species for electrophoretic migration. Among charged labels which have shown promise in assisting CE and HPLC separation is the fluorophore 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS). This report describes the qualitative profiling of charged ANTS-derivatized and underivatized complex glycans by CE with on-line electrospray ion trap mass spectrometry. Several neutral standard glycans including a maltooligosaccharide ladder were derivatized with ANTS and subjected to CE/UV and CE/MS using low pH buffers consisting of citric and 6-aminocaproic acid salts. The ANTS-derivatized species were detected as negative ions, and multiple stage MS analysis provided valuable structural information. Fragment ions were easily identified, showing promise for the identification of unknowns. N-Linked glycans released from bovine fetuin were used to demonstrate the applicability of ANTS derivatization followed by CE/MS for the analysis of negatively charged glycans. Analyses were performed on both underivatized and ANTS-derivatized species, and sialylated glycans were separated and detected in both forms. The ability of the ion trap mass spectrometer to perform multiple stage analysis was exploited, with MS5 information obtained on selected glycans. This technique presents a complementary method to existing methodologies for the profiling of glycan mixtures.