Evaluation of a semi-automated approach for FDG PET image analysis for routine clinical application in patients with multiple myeloma.

BACKGROUND: FDG PET/CT is a tool for assessing response to therapy in various cancers, and may provide an earlier biomarker of clinical response. We developed a novel semi-automated approach for analyzing FDG PET/CT images in patients with multiple myeloma (MM) to standardize FDG PET application. METHODS: Patients (n = 8) with relapsed/refractory MM from the Phase 2 study (NCT02899052) of venetoclax plus carfilzomib and dexamethasone underwent FDG PET/CT at baseline and up to two timepoints during treatment. Images were processed using an established automated segmentation algorithm, with the modification that a red marrow region in an unaffected lumbar vertebra was used to define background standardized uptake value normalized to lean body mass (SUL) threshold above which uptake was considered disease-specific uptake. This approach was compared to lesion segmentation, and to International Myeloma Working Group (IMWG) response criteria, including minimal residual disease (MRD). RESULTS: The two FDG PET analysis techniques agreed on evaluation of patient-level SULpeak for 67% of scans. In the metabolic response assessment per PET Response Criteria in Solid Tumors (PERCIST), the two techniques agreed in 75% of patients. Differences between techniques occurred in low-uptake lesions due to greater reader sensitivity to lesions with uptake marginally above background. PERCIST outcomes were generally in agreement with IMWC and MRD. CONCLUSIONS: This semi-automated analysis was in high agreement with standard approaches for detecting response to MM therapy. This proof-of-concept study suggests that larger studies should be conducted to confirm how FDG PET analysis may aid early response detection in MM.

[18F]BTK-1: A Novel Positron Emission Tomography Tracer for Imaging Bruton's Tyrosine Kinase.

PURPOSE: Bruton's tyrosine kinase (BTK) is a key component of B cell receptor (BCR) signaling, and as such a critical regulator of cell proliferation and survival. Aberrant BCR signaling is important in the pathogenesis of various B cell malignancies and autoimmune disorders. Here, we describe the development of a novel positron emission tomography (PET) tracer for imaging BTK expression and/or occupancy by small molecule therapeutics. METHODS: Radiochemistry was carried out by reacting the precursor with [18F]fluoride on a GE FX-FN TracerLab synthesis module to produce [18F]BTK-1 with a 6% decay-corrected radiochemical yield, 100 ± 6 GBq/µmol molar activity, and a radiochemical purity of 99%. Following intravenous administration of [18F]BTK-1 (3.63 ± 0.59 MBq, 0.084 ± 0.05 µg), 60-min dynamic images were acquired in two xenograft models: REC-1, an efficacious mantle cell lymphoma model, and U87MG, a non-efficacious glioblastoma model. Subsequent studies included vehicle, pretreatment (10 min prior to tracer injection), and displacement (30 min post-tracer injection) studies with different reversible BTK inhibitors to examine BTK binding. Human radiation dosimetry was estimated based on PET imaging in healthy rats. RESULTS: Uptake of [18F]BTK-1 was significantly higher in BTK expressing REC-1 tumors than non-BTK expressing U87MG tumors. Administration of BTK inhibitors prior to tracer administration blocked [18F]BTK-1 binding in the REC-1 tumor model consistent with [18F]BTK-1 binding to BTK. The predicted effective dose in humans was 0.0199 ± 0.0007 mSv/MBq. CONCLUSION: [18F]BTK-1 is a promising PET tracer for imaging of BTK, which could provide valuable information for patient selection, drug dose determination, and improving our understanding of BTK biology in humans.

Utilization of 18F-Fluorodeoxyglucose-Positron Emission Tomography To Understand the Mechanism of Nicotinamide Phosphoribosyltransferase Inhibitors In Vivo.

Cancer cells are highly dependent on NAD+/NADH produced via the nicotinamide salvage pathway. The rate-limiting enzyme in this pathway is the nicotinamide phosphoribosyltransferase (NAMPT), which we have targeted with novel NAMPT inhibitors. NAMPT inhibition elicits depletion of total cellular NAD+ levels and ultimately cytotoxicity via depletion of cellular ATP levels. 18F-fluorodeoxyglucose- positron emission tomography (FDG-PET) is a translational imaging tool to assess glucose utilization in tumors and normal tissue. We used FDG-PET to understand the timing of ATP depletion in vivo and better understand the pharmacology of NAMPT inhibitors. Because of the intimate relationship between cellular ATP levels and cell viability, we developed an in-depth understanding of our NAMPT inhibitor pharmacology and the relationship with changes in tumor FDG uptake. Taken together, we show that FDG-PET could be used as a biomarker in clinical studies to understand dose and provide proof of mechanism for NAMPT inhibitors. SIGNIFICANCE STATEMENT: Our imaging data suggest that tumor 18F-fluorodeoxyglucose uptake can provide insight into the ATP status inside the tumor after nicotinamide phosphoribosyltransferase (NAMPT) therapy, with a novel NAMPT inhibitor. Such an approach could be used clinically as a pharmacodynamic biomarker to help understand the implications of dose, schedule, rescue strategy, or other clinical biomarkers.

ABT-165, a Dual Variable Domain Immunoglobulin (DVD-Ig) Targeting DLL4 and VEGF, Demonstrates Superior Efficacy and Favorable Safety Profiles in Preclinical Models.

Antiangiogenic therapy is a clinically validated modality in cancer treatment. To date, all approved antiangiogenic drugs primarily inhibit the VEGF pathway. Delta-like ligand 4 (DLL4) has been identified as a potential drug target in VEGF-independent angiogenesis and tumor-initiating cell (TIC) survival. A dual-specific biologic targeting both VEGF and DLL4 could be an attractive strategy to improve the effectiveness of anti-VEGF therapy. ABT-165 was uniquely engineered using a proprietary dual-variable domain immunoglobulin (DVD-Ig) technology based on its ability to bind and inhibit both DLL4 and VEGF. In vivo, ABT-165 induced significant tumor growth inhibition compared with either parental antibody treatment alone, due, in part, to the disruption of functional tumor vasculature. In combination with chemotherapy agents, ABT-165 also induced greater antitumor response and outperformed anti-VEGF treatment. ABT-165 displayed nonlinear pharmacokinetic profiles in cynomolgus monkeys, with an apparent terminal half-life > 5 days at a target saturation dose. In a GLP monkey toxicity study, ABT-165 was well-tolerated at doses up to 200 mg/kg with non-adverse treatment-related histopathology findings limited to the liver and thymus. In summary, ABT-165 represents a novel antiangiogenic strategy that potently inhibits both DLL4 and VEGF, demonstrating favorable in vivo efficacy, pharmacokinetic, and safety profiles in preclinical models. Given these preclinical attributes, ABT-165 has progressed to a phase I study. Mol Cancer Ther; 17(5); 1039-50. ©2018 AACR.

Characterization of ABBV-221, a Tumor-Selective EGFR-Targeting Antibody Drug Conjugate.

Depatuxizumab mafodotin (depatux-m, ABT-414) is a tumor-selective antibody drug conjugate (ADC) comprised of the anti-EGFR antibody ABT-806 and the monomethyl auristatin F (MMAF) warhead. Depatux-m has demonstrated promising clinical activity in glioblastoma multiforme (GBM) patients and is currently being evaluated in clinical trials in first-line and recurrent GBM disease settings. Depatux-m responses have been restricted to patients with amplified EGFR, highlighting the need for therapies with activity against tumors with nonamplified EGFR overexpression. In addition, depatux-m dosing has been limited by corneal side effects common to MMAF conjugates. We hypothesized that a monomethyl auristatin E (MMAE) ADC utilizing an EGFR-targeting antibody with increased affinity may have broader utility against tumors with more modest EGFR overexpression while mitigating the risk of corneal side effects. We describe here preclinical characterization of ABBV-221, an EGFR-targeting ADC comprised of an affinity-matured ABT-806 conjugated to MMAE. ABBV-221 binds to a similar EGFR epitope as depatux-m and retains tumor selectivity with increased binding to EGFR-positive tumor cells and greater in vitro potency. ABBV-221 displays increased tumor uptake and antitumor activity against wild-type EGFR-positive xenografts with a greatly reduced incidence of corneal side effects relative to depatux-m. ABBV-221 has similar activity as depatux-m against an EGFR-amplified GBM patient derived xenograft (PDX) model and is highly effective alone and in combination with standard-of-care temozolomide in an EGFRvIII-positive GBM xenograft model. Based on these results, ABBV-221 has advanced to a phase I clinical trial in patients with advanced solid tumors associated with elevated levels of EGFR. Mol Cancer Ther; 17(4); 795-805. ©2018 AACR.

Molecular imaging in oncology drug development.

Tremendous breakthroughs are being made in cancer drug discovery and development. However, such breakthroughs come at a high financial cost. At a time when there is increasing pressure on drug pricing, in part because of increased life expectancy, it is more important than ever to drive new therapeutics towards patients as efficiently as possible. In this review we discuss the applications of molecular imaging in oncology drug development, with a focus on its ability to enable better early decision making, to increase efficiency and thereby to lower costs.

Image quality of Zr-89 PET imaging in the Siemens microPET Focus 220 preclinical scanner.

PURPOSE: Zr-89 positron emission tomography (PET) is a valuable tool for understanding the biodistribution and pharmacokinetics of antibody-based therapeutics. We compared the image quality of Zr-89 PET and F-18 PET in the Siemens microPET Focus 220 preclinical scanner using different reconstruction methods. PROCEDURES: Image quality metrics were measured in various Zr-89 and F-18 PET phantoms, including the NEMA NU 4-2008 image quality phantom. Images were reconstructed using various algorithms. RESULTS: Zr-89 PET had greater image noise, inferior spatial resolution, and greater spillover than F-18 PET, but comparable recovery coefficients for cylinders of various diameters. Of the reconstruction methods, OSEM3D resulted in the lowest noise, highest recovery coefficients, best spatial resolution, but also the greatest spillover. Scatter correction results were found to be sensitive to varying object sizes. CONCLUSIONS: Zr-89 PET image quality was inferior to that of F-18, and no single reconstruction method was superior in all aspects of image quality.

Monitoring tumor response to linifanib therapy with SPECT/CT using the integrin αvß3-targeted radiotracer 99mTc-3P-RGD2.

The objective of this study was to determine the utility of (99m)Tc-3P-Arg-Gly-Asp (RGD2) single photon emission computed tomography (SPECT)/computed tomography (CT) for noninvasive monitoring of integrin αvß3-expression response to antiangiogenic treatment with linifanib. Linifanib or vehicle therapy was carried out in female athymic nu/nu mice bearing U87MG glioma (high αvß3 expression) or PC-3 prostate (low αvß3 expression) tumors at 12.5 mg/kg twice daily. The average tumor volume was 180 ± 90 mm(3) the day prior to baseline SPECT/CT. Longitudinal (99m)Tc-3P-RGD2 SPECT/CT imaging was performed at baseline (-1 day) and days 1, 4, 11, and 18. Tumors were harvested at all imaging time points for histopathological analysis with H&E and immunohistochemistry. A significant difference in tumor volumes between vehicle- and linifanib-treated groups was observed after 4 days of linifanib therapy in the U87MG model. The percent injected dose (%ID) tumor uptake of (99m)Tc-3P-RGD2 peaked in the vehicle-treated group at day 11, while the %ID/cm(3) tumor uptake decreased slowly over the whole study period. During the first 2 days of linifanib treatment, a rapid decrease in both %ID/cm(3) tumor uptake and tumor/muscle ratios of (99m)Tc-3P-RGD2 was observed, followed by a slow decrease until day 18. No decrease in tumor uptake of (99m)Tc-3P-RGD2 or tumor volume was observed for either treatment group in the PC-3 model. Changes in tumor vasculature were confirmed by histopathological H&E analysis and immunohistochemistry. Longitudinal imaging using (99m)Tc-3P-RGD2 SPECT/CT may be a useful tool for monitoring the downstream biologic effects of linifanib therapy.

Application of a whole-body pharmacokinetic model for targeted radionuclide therapy to NM404 and FLT.

We have previously developed a model that provides relative dosimetry estimates for targeted radionuclide therapy (TRT) agents. The whole-body and tumor pharmacokinetic (PK) parameters of this model can be noninvasively measured with molecular imaging, providing a means of comparing potential TRT agents. Parameter sensitivities and noise will affect the accuracy and precision of the estimated PK values and hence dosimetry estimates. The aim of this work is to apply a PK model for TRT to two agents with different magnitudes of clearance rates, NM404 and FLT, explore parameter sensitivity with respect to time and investigate the effect of noise on parameter precision and accuracy. Twenty-three tumor bearing mice were injected with a 'slow-clearing' agent, (124)I-NM404 (n = 10), or a 'fast-clearing' agent, (18)F-FLT (3'-deoxy-3'-fluorothymidine) (n = 13) and imaged via micro-PET/CT pseudo-dynamically or dynamically, respectively. Regions of interest were drawn within the heart and tumor to create time-concentration curves for blood pool and tumor. PK analysis was performed to estimate the mean and standard error of the central compartment efflux-to-influx ratio (k(12)/k(21)), central elimination rate constant (k(el)), and tumor influx-to-efflux ratio (k(34)/k(43)), as well as the mean and standard deviation of the dosimetry estimates. NM404 and FLT parameter estimation results were used to analyze model accuracy and parameter sensitivity. The accuracy of the experimental sampling schedule was compared to that of an optimal sampling schedule found using Cramer-Rao lower bounds theory. Accuracy was assessed using correlation coefficient, bias and standard error of the estimate normalized to the mean (SEE/mean). The PK parameter estimation of NM404 yielded a central clearance, k(el) (0.009 ± 0.003 h(-1)), normal body retention, k(12)/k(21) (0.69 ± 0.16), tumor retention, k(34)/k(43) (1.44 ± 0.46) and predicted dosimetry, D(tumor) (3.47 ± 1.24 Gy). The PK parameter estimation of FLT yielded a central elimination rate constant, k(el) (0.050 ± 0.025 min(-1)), normal body retention, k(12)/k(21) (2.21 ± 0.62) and tumor retention, k(34)/k(43) (0.65 ± 0.17), and predicted dosimetry, D(tumor) (0.61 ± 0.20 Gy). Compared to experimental sampling, optimal sampling decreases the dosimetry bias and SEE/mean for NM404; however, it increases bias and decreases SEE/mean for FLT. For both NM404 and FLT, central compartment efflux rate constant, k(12), and central compartment influx rate constant, k(21), possess mirroring sensitivities at relatively early time points. The instantaneous concentration in the blood, C(0), was most sensitive at early time points; central elimination, k(el), and tumor efflux, k(43), are most sensitive at later time points. A PK model for TRT was applied to both a slow-clearing, NM404, and a fast-clearing, FLT, agents in a xenograft murine model. NM404 possesses more favorable PK values according to the PK TRT model. The precise and accurate measurement of k(12), k(21), k(el), k(34) and k(43) will translate into improved and precise dosimetry estimations. This work will guide the future use of this PK model for assessing the relative effectiveness of potential TRT agents.

FDG-PET as a pharmacodynamic biomarker for early assessment of treatment response to linifanib (ABT-869) in a non-small cell lung cancer xenograft model.

Linifanib (ABT-869) is a multitargeted receptor tyrosine kinase inhibitor. This work aims to evaluate F-fluorodeoxyglucose-positron emission tomography (FDG-PET) as a pharmacodynamic (PD) biomarker for linifanib treatment utilizing the Calu-6 model of human non-small cell lung (NSCLC) cancer in SCID-beige mice. Animals received either vehicle or 12.5 mg/kg linifanib orally twice a day for the duration of the study. Imaging was performed at -1, 1, 3, and 7 days after beginning treatment (n = 12-14 per group). Linifanib inhibited tumor growth and suppressed tumor metabolic activity. Changes in tumor FDG uptake were observed as early as 1 day after beginning linifanib treatment and were sustained for the duration of the study. This study confirms that linifanib is efficacious in this xenograft model of human NSCLC and confirms FDG-PET is a potential PD biomarker strategy for linifanib therapy.

Characterization of 7- and 19-month-old Tg2576 mice using multimodal in vivo imaging: limitations as a translatable model of Alzheimer's disease.

With 90% of neuroscience clinical trials failing to see efficacy, there is a clear need for the development of disease biomarkers that can improve the ability to predict human Alzheimer's disease (AD) trial outcomes from animal studies. Several lines of evidence, including genetic susceptibility and disease studies, suggest the utility of fluorodeoxyglucose positron emission tomography (FDG-PET) as a potential biomarker with congruency between humans and animal models. For example, early in AD, patients present with decreased glucose metabolism in the entorhinal cortex and several regions of the brain associated with disease pathology and cognitive decline. While several of the commonly used AD mouse models fail to show all the hallmarks of the disease or the limbic to cortical trajectory, there has not been a systematic evaluation of imaging-derived biomarkers across animal models of AD, contrary to what has been achieved in recent years in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (Miller, 2009). If animal AD models were found to mimic endpoints that correlate with the disease onset, progression, and relapse, then the identification of such markers in animal models could afford the field a translational tool to help bridge the preclinical-clinical gap. Using a combination of FDG-PET and functional magnetic resonance imaging (fMRI), we examined the Tg2576 mouse for global and regional measures of brain glucose metabolism at 7 and 19 months of age. In experiment 1 we observed that at younger ages, when some plaque burden and cognitive deficits have been reported, Tg2576 mice showed hypermetabolism as assessed with FDG-PET. This hypermetabolism decreased with age to levels similar to wild type (WT) counterparts such that the 19-month-old transgenic (Tg) mice did not differ from age matched WTs. In experiment 2, using cerebral blood volume (CBV) fMRI, we demonstrated that the hypermetabolism observed in Tg mice at 7 months could not be explained by changes in hemodynamic parameters as no differences were observed when compared with WTs. Taken together, these data identify brain hypermetabolism in Tg2576 mice which cannot be accounted for by changes in vascular compliance. Instead, the hypermetabolism may reflect a neuronal compensatory mechanism. Our data are discussed in the context of disease biomarker identification and target validation, suggesting little or no utility for translational based studies using Tg2576 mice.

Pharmacodynamic evaluation of irinotecan therapy by FDG and FLT PET/CT imaging in a colorectal cancer xenograft model.

PURPOSE: Longitudinal changes of 3'-[(18) F]fluoro-3'-deoxythymidine (FLT) and 2-deoxy-2-[(18) F]fluoro-D-glucose (FDG) in response to irinotecan therapy in an animal model of colorectal cancer were compared. PROCEDURES: SCID/CB-17 mice with HCT116 tumors were treated with 50 mg/kg irinotecan by intraperitoneal injection weekly for 3 weeks. FLT and FDG-positron emission tomography (PET) were performed at baseline, the day after each treatment, and 5 days after the first treatment. Proliferation and apoptosis were evaluated by immunohistochemistry (IHC) after day 15 of imaging. RESULTS: Irinotecan treatment resulted in a suppression of tumor growth. Tumor FLT uptake was decreased the day after each treatment but to a lesser extent 5 days after the first treatment. FDG uptake increased the day after each treatment with a continuous increase throughout the experiment. IHC analysis of phospho-H3 and Ki67 confirmed FLT-PET results, indicating a decrease in proliferation the day after the final irinotecan treatment. Increased apoptosis monitored by caspase-3 was observed after day 15 with irinotecan treatment. CONCLUSIONS: FLT-PET may be a better method than FDG-PET for assessing treatment response to irinotecan. Changes in imaging occur before changes in tumor volume.

Hybrid PET/CT for noninvasive pharmacokinetic evaluation of dynamic PolyConjugates, a synthetic siRNA delivery system.

Positron emission tomography/computed tomography (PET/CT) hybrid imaging can be used to gain insights into a synthetic siRNA delivery system targeted to the liver. Either siRNA or the delivery vehicle was labeled with (64)Cu via 1, 4, 7, 10- tetraazacyclododecane- 1, 4, 7, 10- tetraacetic acid (DOTA) chelation. This study confirmed that the siRNA delivery system was successfully targeted to the liver. Incorporation of the siRNA into the delivery system protected the siRNA from renal filtration long enough so that the siRNA could be delivered to the liver. PET/CT imaging was important for confirming biodistribution and for determining differences in the distribution of labeled siRNA, siRNA incorporated into the delivery system, and the delivery system without siRNA.

Reproducibility of tumor volume measurement at microCT colonography in living mice.

RATIONALE AND OBJECTIVES: We sought to demonstrate the viability of microcomputed tomographic colonography (muCTC) as a tool for monitoring tumorigenesis in mouse models of human colorectal cancer during prospective longitudinal studies. The precision and accuracy of volumetric measurements were determined to assess whether changes in tumor volume over time were readily detectable. MATERIALS AND METHODS: All animal studies were conducted under the guidelines set forth by the Institutional Animal Care and Use Committee of the American Association for Assessment and Accreditation of Laboratory Animal Care. muCTC was performed on C57BL/6J (B6) mice carrying the Min allele of Apc, ultimately yielding 18 scans. Assessments of scan quality and tumor volume were both performed once per week over 8 weeks. RESULTS: Scans with a good quality rating had a mean standard deviation in tumor volume measurement of 8%. By contrast, scans with a poor quality rating had a mean standard deviation in tumor volume measurement of 35%. Variables affecting muCTC scan quality in living mice included bowel preparation, motion artifact, and tumor morphology. Tumor volume measurements were highly correlated with tumor weight (r2 = 0.87). CONCLUSIONS: The reproducibility of tumor volume measurement at muCTC in living mice makes prospective longitudinal evaluation of colonic tumor response feasible. For muCTC scans of good quality, a 16% change in tumor volume can be detected at the 95% confidence level.