Tamara Anderson

Influence of morbid obesity on the single-dose pharmacokinetics of daptomycin

ABSTRACT The present study characterized the single-dose pharmacokinetics of daptomycin dosed as 4 mg/kg of total body weight (TBW) in seven morbidly obese and seven age-, sex-, race-, and serum creatinine-matched healthy subjects. The glomerular filtration rate (GFR) was measured for both groups following a single bolus injection of [125I]sodium iothalamate. Noncompartmental analysis was used to determine the pharmacokinetic parameters, and these values were normalized against TBW, ideal body weight (IBW), and fat-free weight (FFW) for comparison of the two groups. All subjects enrolled in this study were female, and the mean (±standard deviation) body mass index was 46.2 ± 5.5 kg/m2 or 21.8 ± 1.9 kg/m2 for the morbidly obese or normal-weight group, respectively. The maximum plasma concentration and area under the concentration-time curve from dosing to 24 h were approximately 60% higher (P < 0.05) in the morbidly obese group than in the normal-weight group, and these were a function of the higher total dose received in the morbidly obese group. No differences in daptomycin volume of distribution (V), total clearance, renal clearance, or protein binding were noted between the two groups. Of TBW, FFW, or IBW, TBW provided the best correlation to V. In contrast, TBW overestimated GFR through creatinine clearance calculations using the Cockcroft-Gault equation. Use of IBW in the Cockcroft-Gault equation or use of the four-variable modification of diet in renal disease equation best estimated GFR in morbidly obese subjects. Further studies of daptomycin pharmacokinetics in morbidly obese patients with acute bacterial infections and impaired renal function are necessary to better predict appropriate dosage intervals.

213Bi-[DOTA0, Tyr3]Octreotide Peptide Receptor Radionuclide Therapy of Pancreatic Tumors in a Preclinical Animal Model

Purpose: The somatostatin analogue [DOTA0, Tyr3]octreotide (DOTATOC) has previously been labeled with low linear energy transfer (LET) β-emitters, such as 177Lu or 90Y, for tumor therapy. In this study, DOTATOC labeled with the high-LET α-emitter, 213Bi, was evaluated. Experimental Design: The radiolabeling, stability, biodistribution, toxicity, safety, and therapeutic efficacy of 213Bi-DOTATOC (specific activity 7.4 MBq/μg) were investigated. Biodistribution studies to determine somatostatin receptor specificity were done in Lewis rats at 1 and 3 hours postinjection. Histopathology of various organs was used to evaluated toxicity and safety. Therapeutic efficacy of 4 to 22 MBq 213Bi-DOTATOC was determined in a rat pancreatic carcinoma model. Results: Radiolabeling of the 213Bi-DOTATOC was achieved with radiochemical purity >95% and an incorporation yield ≥99.9%. Biodistribution data showed specific binding to somatostatin receptor–expressing tissues. Administration of free 213Bi, compared with 213Bi-DOTATOC, resulted in higher radioactivity accumulation at 3 hours postinjection in the kidneys [34.47 ± 1.40% injected dose/g (ID/g) tissue versus 11.15 ± 0.46%, P < 0.0001] and bone marrow (0.31 ± 0.01% ID/g versus 0.06 ± 0.02%, P < 0.0324). A significant decrease in tumor growth rate was observed in rats treated with >11 MBq of 213Bi-DOTATOC 10 days postinjection compared with controls (P < 0.025). Treatment with >20 MBq of 213Bi-DOTATOC showed significantly greater tumor reduction when compared with animals receiving <11 MBq (P < 0.02). Conclusions:213Bi-DOTATOC showed dose-related antitumor effects with minimal treatment-related organ toxicity. No acute or chronic hematologic toxicities were observed. Mild, acute nephrotoxicity was observed without evidence of chronic toxicity. 213Bi-DOTATOC is a promising therapeutic radiopharmaceutical for further evaluation.

Regional particle size dependent deposition of inhaled aerosols in rats and mice

Context: The current data analysis tools in nuclear medicine have not been used to evaluate intra organ regional deposition patterns of pharmaceutical aerosols in preclinical species. Objective: This study evaluates aerosol deposition patterns as a function of particle size in rats and mice using novel image analysis techniques. Materials and Method: Mice and rats were exposed to radiolabeled polydisperse aerosols at 0.5, 1.0, 3.0, and 5.0 µm MMAD followed by SPECT/CT imaging for deposition analysis. Images were quantified for both macro deposition patterns and regional deposition analysis using the LRRI-developed Onion Model. Results: The deposition fraction in both rats and mice was shown to increase as the particle size decreased, with greater lung deposition in rats at all particle sizes. The Onion Model indicated that the smaller particle sizes resulted in increased peripheral deposition. Discussion: These data contrast the commonly used 10% deposition fraction for all aerosols between 1.0 and 5.0 µm and indicate that lung deposition fraction in this range does change with particle size. When compared to historical data, the 1.0, 3.0, and 5.0 µm particles result in similar lung deposition fractions; however, the 0.5 µm lung deposition fraction is markedly different. This is probably caused by the current aerosols that were polydisperse to reflect current pharmaceutical aerosols, while the historical data were generated with monodisperse aerosols. Conclusion: The deposition patterns of aerosols between 0.5 and 5.0 µm showed an increase in both overall and peripheral deposition as the particle size decreased. The Onion Model allows a more complex analysis of regional deposition in preclinical models.

Microglial priming through the lung–brain axis: the role of air pollution–induced circulating factors

Air pollution is implicated in neurodegenerative disease risk and progression and in microglial activation, but the mechanisms are unknown. In this study, microglia remained activated 24 h after ozone (O3) exposure in rats, suggesting a persistent signal from lung to brain. Ex vivo analysis of serum from O3‐treated rats revealed an augmented microglial proinflammatory response and β‐amyloid 42 (Aβ42) neurotoxicity independent of traditional circulating cytokines, where macrophage‐1 antigen‐mediated microglia proinflammatory priming. Aged mice exhibited reduced pulmonary immune profiles and the most pronounced neuroinflammation and microglial activation in response to mixed vehicle emissions. Consistent with this premise, cluster of differentiation 36 (CD36)–/– mice exhibited impaired pulmonary immune responses concurrent with augmented neuroinflammation and microglial activation in response to O3. Further, aging glia were more sensitive to the proinflammatory effects of O3 serum. Together, these findings outline the lung‐brain axis, where air pollutant exposures result in circulating, cytokine‐independent signals present in serum that elevate the brain proinflammatory milieu, which is linked to the pulmonary response and is further augmented with age.—Mumaw, C. L., Levesque, S., McGraw, C., Robertson, S., Lucas, S., Stafflinger, J. E., Campen, M. J., Hall, P., Norenberg, J. P., Anderson, T., Lund, A. K., McDonald, J. D., Ottens, A. K., Block, M. L. Microglial priming through the lung‐brain axis: the role of air pollution‐induced circulating factors. FASEB J. 30, 1880–1891 (2016). www.fasebj.org

Longitudinal In Vivo SPECT/CT Imaging Reveals Morphological Changes and Cardiopulmonary Apoptosis in a Rodent Model of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) has a complex pathogenesis involving both heart and lungs. Animal models can reflect aspects of the human pathology and provide insights into the development and underlying mechanisms of disease. Because of the variability of most animal models of PAH, serial in vivo measurements of cardiopulmonary function, morphology, and markers of pathology can enhance the value of such studies. Therefore, quantitative in vivo SPECT/CT imaging was performed to assess cardiac function, morphology and cardiac perfusion utilizing 201Thallium (201Tl) in control and monocrotaline-treated rats. In addition, lung and heart apoptosis was examined with 99mTc-Annexin V (99mTc-Annexin) in these cohorts. Following baseline imaging, rats were injected with saline or monocrotaline (50 mg/kg, i.p.) and imaged weekly for 6 weeks. To assess a therapeutic response in an established pulmonary hypertensive state, a cohort of rats received resveratrol in drinking water (3 mg/kg/day) on days 28–42 post-monocrotaline injection to monitor regression of cardiopulmonary apoptosis. PAH in monocrotaline-treated rats was verified by conventional hemodynamic techniques on day 42 (right ventricular systolic pressure (RSVP) = 66.2 mmHg in monocrotaline vs 28.8 mmHg in controls) and in terms of right ventricular hypertrophy (RV/LVS = 0.70 in monocrotaline vs 0.32 in controls). Resveratrol partially reversed both RVSP (41.4 mmHg) and RV/LVS (0.46), as well as lung edema and RV contractility +dP/dtmax. Serial 99mTc-Annexin V imaging showed clear increases in pulmonary and cardiac apoptosis when compared to baseline, which regressed following resveratrol treatment. Monocrotaline induced modest changes in whole-heart perfusion as assessed by 201TI imaging and cardiac morphological changes consistent with septal deviation and enlarged RV. This study demonstrates the utility of functional in vivo SPECT/CT imaging in rodent models of PAH and further confirms the efficacy of resveratrol in reversing established monocrotaline-induced PAH presumably by attenuation of cardiopulmonary apoptosis.

Muscle RING Finger-1 Promotes a Maladaptive Phenotype in Chronic Hypoxia-Induced Right Ventricular Remodeling

Exposure to chronic hypoxia (CH) induces elevated pulmonary artery pressure/resistance, leading to an eventual maladaptive right ventricular hypertrophy (RVH). Muscle RING finger-1 (MuRF1) is a muscle-specific ubiquitin ligase that mediates myocyte atrophy and has been shown to play a role in left ventricular hypertrophy and altered cardiac bioenergetics in pressure overloaded hearts. However, little is known about the contribution of MuRF1 impacting RVH in the setting of CH. Therefore, we hypothesized that MuRF1 deletion would enhance RVH compared to their wild-type littermates, while cardiac-specific overexpression would reduce hypertrophy following CH-induced pulmonary hypertension. We assessed right ventricular systolic pressure (RVSP), right ventricle to left ventricle plus septal weight ratio (RV/LV+S) and hematocrit (Hct) following a 3-wk isobaric CH exposure. Additionally, we conducted dual-isotope SPECT/CT imaging with cardiac function agent 201Tl-chloride and cell death agent 99mTc-annexin V. Predictably, CH induced pulmonary hypertension, measured by increased RVSP, RV/LV+S and Hct in WT mice compared to normoxic WT mice. Normoxic WT and MuRF1-null mice exhibited no significant differences in RVSP, RV/LV+S or Hct. CH-induced increases in RVSP were also similar between WT and MuRF1-null mice; however, RV/LV+S and Hct were significantly elevated in CH-exposed MuRF1-null mice compared to WT. In cardiac-specific MuRF1 overexpressing mice, RV/LV+S increased significantly due to CH exposure, even greater than in WT mice. This remodeling appeared eccentric, maladaptive and led to reduced systemic perfusion. In conclusion, these results are consistent with an atrophic role for MuRF1 regulating the magnitude of right ventricular hypertrophy following CH-induction of pulmonary hypertension.

Implementation of a 3D topographic thinning model for assessing aerosol deposition of radioactive assays in small-animal CT/SPECT imaging

Nuclear imaging serves as an important tool for the visualization and analysis of nebulized radiolabeled particle deposition in the lung, enabling assessment of both nebulizer properties and lung function. To date, most research in this field has been focused on mathematical modeling from empirical data. This work examines the use of high-resolution 3D CT/SPECT imaging technology accompanied by automated lung segmentation to build a novel analysis model based on topographic thinning of the dual-modality tomograms.

Abstract 4949: In vitro and in vivo investigation of the novel, first-in-class, Guanylyl Cyclase C (GCC) targeted 68Ga labeled heat stable peptide MLN6907 ([68Ga]MLN6907) for tumor imaging

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA A novel, first-in-class, 68Ga labeled DOTA-para-bn-SCN-Ahx-STp(5-18) 2.2kDa peptide \[MLN6907\] ([68Ga]MLN6907) with high affinity to the guanalyl cyclase C (GCC) receptor has been developed to select cancer patients for treatment with GCC targeted therapies using PET/CT. GCC is sequestered exclusively in the gastrointestinal luminal compartment except under malignant transformation where it is then made accessible to intravenous agents. Conventional patient selection strategies often rely on an analytical IHC or total protein based assessment of a tumor biopsy which can be limited to an archival tissue sample from a single region of a single lesion. Imaging may offer whole body, real time, multi-region and multi lesion assessment of target levels. In addition, functional parameters associated with receptor kinetics may also be explored in vivo. 68Ga has a high avidity for the common chelating moiety DOTA. Furthermore, its short radioactive half life (half-life, 68.3 minutes) matches well to a biological targeting moiety like a peptide with its rapid biological clearance and fast diffusion to target thus providing optimal tumour-to-normal tissue contrast. In vitro: Cellular competitive binding studies confirmed high affinity of non-radiolabeled MLN6907 for its cognate receptor, GCC, with a KD of 3.2 nM. Upon ligand-recpetor binding, MLN6907 is internalized rapidly with a half-life of 56 min. In vivo: Similar to other radiolabeled peptides, [68Ga]MLN6907 clears rapidly from blood (t1/2 = 26 min) through renal excretion as investigated in Long Evans rats and non-human primate studies. The radiation exposure from [68Ga]MLN6907 was highest in the kidney and bladder indicating that renal excretion was a primary route of elimination. Using OLINDA/EXM software, the effective dose was estimated to be 0.013 mSv/MBq in man. In tumor bearing C.B-17 SCID mice, both ex vivo and in vivo signal was measured in both human tumor cell lines and primary human tumor xenografts with varied GCC levels and compared to non tumor bearing tissues. [68Ga]MLN6907 total uptake (%I.D./g) varied across the different tumors investigated. Using the unlabeled precursor, no toxicity was observed in repeat dose rat and monkey studies. Using the rat as the more conservative species for dose estimation, it was calculated that a human equivalent dose of 282 μg would be safe. However, using a saturable effect PK/PD compartment model for mice and humans, we estimated a single human dose of less than 100μg would provide resolution of tumors with different GCC levels. Collectively, biological, pharmacokinetic and safety data obtained with [68Ga]MLN6907 are consistent with an effective GCC PET imaging agent. [68Ga]MLN6907 is being developed clinically as a single, i.v., microdose GCC PET imaging agent in a Phase 1 investigation in patients with surgically resectable metastatic colorectal carcinoma Citation Format: Donna Cvet, Robert Robertson, Melissa Saylor, Jennifer Terkelsen, Ozlem Yardibi, Maria Borland, Nicolas Salem, Petter Veiby, Todd Sells, Mary Carsillo, Johnny Yang, Shu-Wen Teng, John Hoppin, Kelly Orcutt, Jacob Hesterman, Jeffery Norenberg, Tamara Anderson, Mike Schulz, Mary Ruscowski, Marc Berridge, Steven Mather, Daniel P. Bradley. In vitro and in vivo investigation of the novel, first-in-class, Guanylyl Cyclase C (GCC) targeted 68Ga labeled heat stable peptide MLN6907 ([68Ga]MLN6907) for tumor imaging. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4949. doi:10.1158/1538-7445.AM2014-4949