Multimodality imaging of tumor and bone response in a mouse model of bony metastasis

Magnetic Resonance Imaging as a Tool for Monitoring Intratibial Growth of Experimental Prostate Cancer Metastases in Mice

Bone metastases cause morbidity and mortality in several human cancer forms. Experimental models are used to unravel the mechanisms and identify possible treatment targets. The location inside the skeleton complicates accurate assessment. This study evaluates the performance of magnetic resonance imaging (MRI) of prostate cancer tumors growing intratibially in mice. MRI detected intratibial tumor lesions with a sensitivity and specificity of 100% and 89%, respectively, compared to histological evaluation. Location and some phenotypical features could also be readily detected with MRI. Regarding volume estimation, the correlation between MRI and histological assessment was high (p < 0.001, r = 0.936). In conclusion, this study finds MRI to be a reliable tool for in vivo, non-invasive, non-ionizing, real-time monitoring of intratibial tumor growth.

Parametric Response Mapping of FLAIR MRI Provides an Early Indication of Progression Risk in Glioblastoma

RATIONALE AND OBJECTIVES

Glioblastoma image evaluation utilizes Magnetic Resonance Imaging contrast-enhanced, T1-weighted, and noncontrast T2-weighted fluid-attenuated inversion recovery (FLAIR) acquisitions. Disease progression assessment relies on changes in tumor diameter, which correlate poorly with survival. To improve treatment monitoring in glioblastoma, we investigated serial voxel-wise comparison of anatomically-aligned FLAIR signal as an early predictor of GBM progression.

MATERIALS AND METHODS

We analyzed longitudinal normalized FLAIR images (rFLAIR) from 52 subjects using voxel-wise Parametric Response Mapping (PRM) to monitor volume fractions of increased (PRM_rFLAIR+), decreased (PRM_rFLAIR-), or unchanged (PRM_rFLAIR0) rFLAIR intensity. We determined response by rFLAIR between pretreatment and 10 weeks posttreatment. Risk of disease progression in a subset of subjects (N = 26) with stable disease or partial response as defined by Response Assessment in Neuro-Oncology (RANO) criteria was assessed by PRM_rFLAIR between weeks 10 and 20 and continuously until the PRM_rFLAIR+ exceeded a defined threshold. RANO defined criteria were compared with PRM-derived outcomes for tumor progression detection.

RESULTS

Patient stratification for progression-free survival (PFS) and overall survival (OS) was achieved at week 10 using RANO criteria (PFS: p <0.0001; OS: p <0.0001), relative change in FLAIR-hyperintense volume (PFS: p = 0.0011; OS: p <0.0001), and PRM_rFLAIR+ (PFS: p <0.01; OS: p <0.001). PRM_rFLAIR+ also stratified responding patients' progression between weeks 10 and 20 (PFS: p <0.05; OS: p = 0.01) while changes in FLAIR-volume measurements were not predictive. As a continuous evaluation, PRM_rFLAIR+ exceeding 10% stratified patients for PFA after 5.6 months (p<0.0001), while RANO criteria did not stratify patients until 15.4 months (p <0.0001).

CONCLUSION

PRM_rFLAIR may provide an early biomarker of disease progression in glioblastoma.

Changing landscape of optical imaging in skeletal metastases

Optical imaging is an emerging strategy for in vitro and in vivo visualization of the molecular mechanisms of cancer over time. An increasing number of optical imaging contrast agents and techniques have been developed in recent years specifically for bone research and skeletal metastases. Visualizing molecular processes in relation to bone remodeling in metastasized cancers provides valuable information for understanding disease mechanisms and monitoring expression of primary molecular targets and therapeutic efficacy. This review is intended to provide an overview of tumor-specific and non-specific contrast agents in the first near-infrared window (NIR-I) window from 650 nm to 950 nm that can be used to study functional and structural aspects of skeletal remodeling of cancer in preclinical animal models. Near-infrared (NIR) optical imaging techniques, specifically NIR spectroscopy and photoacoustic imaging, and their use in skeletal metastases will also be discussed. Perspectives on the promises and challenges facing this exciting field are then given.

Intratibial injection of patient-derived tumor cells from giant cell tumor of bone elicits osteolytic reaction in nude mouse

There have been various reports in the literature of an in vivo model for giant cell tumor of bone (GCTB). However, few suitable animal models of GCTB have been established, due to the fact that GCTB contains three histologically different cell types. To the best of our knowledge, injection of patient-derived GCTB cells into bone environment has not been reported until now. In the present study, the biological behavior of GCTB cells in nude mice was investigated through intratibial injection of patient-derived GCTB cells. Patient-derived GCTB cells were obtained from 5 patients who had not undergone chemo- and radiotherapy. Once isolated, the cell suspension was injected into the tibias of nude mice. The growth process was monitored by weekly observation and photographic documentation using X-ray. Four months after injection, nude mice were sacrificed and the injected tibial samples were fixed, and further analyzed using micro-computed tomography (micro-CT), standard histology, tartrate-resistant acid phosphatase (TRAP) staining and mitochondrial immunofluorescence staining. X-ray, micro-CT and standard histology revealed osteolytic destruction in the proximal end of the tibia. TRAP staining identified TRAP-positive, osteoclast-like cells distributed in the bone marrow interface of the lesion area. Anti-human mitochondrial immunofluorescence staining confirmed that the surviving cells in the osteolytic destruction were of human GCTB cell origin. These findings indicate that intratibial injection of patient-derived GCTB cells may elicit osteolytic destruction in nude mice. The results of the current study present a novel animal model for GCTB, opening new perspectives to investigate this disease and develop therapeutic agents.

Multimodal imaging provides insight into targeted therapy response in metastatic prostate cancer to the bone

Metastatic prostate cancer to bone remains incurable, driving efforts to develop individualized, targeted therapies to improve clinical outcomes while limiting adverse side-effects. Due to the complexity in cellular signaling pathways and the interaction between cancer and its microenvironment, multiparametric imaging approaches for treatment response may improve understanding of the biological effects of therapy. An orthotopic model of castration resistant prostate cancer (CRPC) bone metastasis was treated with the tyrosine kinase inhibitor Cabozantinib (CABO). Response was assessed using CT to monitor bone volumes, ^99mTc-MDP SPECT for bone metabolism, and anatomical and diffusion MRI for tumor volume and cell death. A concurrent clinical trial of CABO for CRPC patients also evaluated multimodality imaging in correlation with standard response criteria. Response in the preclinical study found significant slowing in tumor growth rate (P<0.01), rise in tumor apparent diffusion coefficient (ADC, P<0.001), and drop in ^99mTc-MDP adsorption (P<0.05). Loss of bone volume did not slow with treatment, attributed to the highly aggressive and osteolytic nature of the PC3 cell line. Clinical trial analysis found only a single subject who progressed after 12 weeks of therapy. Imaging at 6 weeks corroborated the 12-week radiological assessment with positive response visible as increased ADC and decreased vascular metrics. Conversely, the subject who progressed at 12 weeks had no change in ADC, and substantial drops in vascular metrics. These results showcase a multifaceted translational imaging approach for detecting targeted treatment response with effective blockade of tumor vascularization, tumor cell kill, and reduced proliferation.

Rationale for Modernising Imaging in Advanced Prostate Cancer

CONTEXT

To effectively manage patients with advanced prostate cancer (APC), it is essential to have accurate, reproducible, and validated methods for detecting and quantifying the burden of bone and soft tissue metastases and for assessing their response to therapy. Current standard of care imaging with bone and computed tomography (CT) scans have significant limitations for the assessment of bone metastases in particular.

OBJECTIVE

We aimed to undertake a critical comparative review of imaging methods used for diagnosis and disease monitoring of metastatic APC from the perspective of their availability and ability to assess disease presence, extent, and response of bone and soft tissue disease.

EVIDENCE ACQUISITION

An expert panel of radiologists, nuclear medicine physicians, and medical physicists with the greatest experience of imaging in advanced prostate cancer prepared a review of the practicalities, performance, merits, and limitations of currently available imaging methods.

EVIDENCE SYNTHESIS

Meta-analyses showed that positron emission tomography (PET)/CT with different radiotracers and whole-body magnetic resonance imaging (WB-MRI) are more accurate for bone lesion detection than CT and bone scans (BSs). At a patient level, the pooled sensitivities for bone disease by using choline (CH)-PET/CT, WB-MRI, and BS were 91% (95% confidence interval [CI], 83-96%), 97% (95% CI, 91-99%), and 79% (95% CI, 73-83%), respectively. The pooled specificities for bone metastases detection using CH-PET/CT, WB-MRI, and BS were 99% (95% CI, 93-100%), 95% (95% CI, 90-97%), and 82% (95% CI, 78-85%), respectively. The ability of PET/CT and WB-MRI to assess therapeutic benefits is promising but has not been comprehensively evaluated. There is variability in the cost, availability, and quality of PET/CT and WB-MRI.

CONCLUSIONS

Standardisation of acquisition, interpretation, and reporting of WB-MRI and PET/CT scans is required to assess the performance of these techniques in clinical trials of treatment approaches in APC.

PATIENT SUMMARY

PET/CT and whole-body MRI scans have the potential to improve detection and to assess response to treatment of all states of advanced prostate cancer. Consensus recommendations on quality standards, interpretation, and reporting are needed but will require validation in clinical trials of established and new treatment approaches.

Imaging of Orthotopic Glioblastoma Xenografts in Mice Using a Clinical CT Scanner: Comparison with Micro-CT and Histology

Purpose

There is an increasing need for small animal in vivo imaging in murine orthotopic glioma models. Because dedicated small animal scanners are not available ubiquitously, the applicability of a clinical CT scanner for visualization and measurement of intracerebrally growing glioma xenografts in living mice was validated.

Materials and Methods

2.5x10⁶ U87MG cells were orthotopically implanted in NOD/SCID/ᵞc^-/- mice (n = 9). Mice underwent contrast-enhanced (300 μl Iomeprol i.v.) imaging using a micro-CT (80 kV, 75 μAs, 360° rotation, 1,000 projections, scan time 33 s, resolution 40 x 40 x 53 μm) and a clinical CT scanner (4-row multislice detector; 120 kV, 150 mAs, slice thickness 0.5 mm, feed rotation 0.5 mm, resolution 98 x 98 x 500 μm). Mice were sacrificed and the brain was worked up histologically. In all modalities tumor volume was measured by two independent readers. Contrast-to-noise ratio (CNR) and Signal-to-noise ratio (SNR) were measured from reconstructed CT-scans (0.5 mm slice thickness; n = 18).

Results

Tumor volumes (mean±SD mm³) were similar between both CT-modalities (micro-CT: 19.8±19.0, clinical CT: 19.8±18.8; Wilcoxon signed-rank test p = 0.813). Moreover, between reader analyses for each modality showed excellent agreement as demonstrated by correlation analysis (Spearman-Rho >0.9; p<0.01 for all correlations). Histologically measured tumor volumes (11.0±11.2) were significantly smaller due to shrinkage artifacts (p<0.05). CNR and SNR were 2.1±1.0 and 1.1±0.04 for micro-CT and 23.1±24.0 and 1.9±0.7 for the clinical CTscanner, respectively.

Conclusion

Clinical CT scanners may reliably be used for in vivo imaging and volumetric analysis of brain tumor growth in mice.

Bone imaging in prostate cancer: the evolving roles of nuclear medicine and radiology

The bone scan continues to be recommended for both the staging and therapy response assessment of skeletal metastases from prostate cancer. However, it is widely recognised that bone scans have limited sensitivity for disease detection and is both insensitive and non-specific for determining treatment response, at an early enough time point to be clinically useful. We, therefore, review the evolving roles of nuclear medicine and radiology for this application. We have reviewed the published literature reporting recent developments in imaging bone metastases in prostate cancer, and provide a balanced synopsis of the state of the art. The development of single-photon emission computed tomography combined with computed tomography has improved detection sensitivity and specificity but has not yet been shown to lead to improvements in monitoring therapy. A number of bone-specific and tumour-specific tracers for positron emission tomography/computed tomography (PET/CT) are now available for advanced prostate cancer that show promise in both clinical settings. At the same time, the development of whole-body magnetic resonance imaging (WB-MRI) that incorporates diffusion-weighted imaging also offers significant improvements for detection and therapy response assessment. There are emerging data showing comparative SPECT/CT, PET/CT, and WB-MRI test performance for disease detection, but no compelling data on the usefulness of these technologies in response assessment have yet emerged.

Assessment of murine collagen-induced arthritis by longitudinal non-invasive duplexed molecular optical imaging

OBJECTIVE

In the present study we evaluated the use of four commercially available fluorescent probes to monitor disease activity in murine CIA and its suppression during glucocorticoid therapy.

METHODS

Arthritis was induced in male DBA/1 mice by immunization with type II collagen in Complete Freund's Adjuvant, followed by a boost of collagen in PBS. Four fluorescent probes from PerkinElmer in combination [ProSense 750 fluorescent activatable sensor technology (FAST) with Neutrophil Elastase 680 FAST and MMPSense 750 FAST with CatK 680 FAST] were used to monitor disease development from day 5 through to day 40 post-immunization. Fluorescence generated in vivo by the probes was correlated with clinical and histological score and paw measurements.

RESULTS

The fluorescence intensity emitted by each probe was shown to correlate with the conventional measurements of disease. The highest degree of correlation was observed with ProSense 750 FAST in combination with Neutrophil Elastase 680 FAST; these probes were then used to successfully assess CIA suppression during dexamethasone treatment.

CONCLUSION

We have demonstrated that longitudinal non-invasive duplexed optical fluorescence imaging provides a simple assessment of arthritic disease activity within the joints of mice following the induction of CIA and may represent a powerful tool to monitor the efficacy of drug treatments in preclinical studies.

Preclinical imaging and translational animal models of cancer for accelerated clinical implementation of nanotechnologies and macromolecular agents

The majority of animal models of cancer have performed poorly in terms of predicting clinical performance of new therapeutics, which are most often first evaluated in patients with advanced, metastatic disease. The development and use of metastatic models of cancer may enhance clinical translatability of preclinical studies focused on the development of nanotechnology-based drug delivery systems and macromolecular therapeutics, potentially accelerating their clinical implementation. It is recognized that the development and use of such models are not without challenge. Preclinical imaging tools offer a solution by allowing temporal and spatial characterization of metastatic lesions. This paper provides a review of imaging methods applicable for evaluation of novel therapeutics in clinically relevant models of advanced cancer. An overview of currently utilized models of oncology in small animals is followed by image-based development and characterization of visceral metastatic cancer models. Examples of imaging tools employed for metastatic lesion detection, evaluation of anti-tumor and anti-metastatic potential and biodistribution of novel therapies, as well as the co-development and/or use of imageable surrogates of response, are also discussed. While the focus is on development of macromolecular and nanotechnology-based therapeutics, examples with small molecules are included in some cases to illustrate concepts and approaches that can be applied in the assessment of nanotechnologies or macromolecules.

Live cell evaluation of granzyme delivery and death receptor signaling in tumor cells targeted by human natural killer cells

Growing interest in natural killer (NK) cell-based therapy for treating human cancer has made it imperative to develop new tools to measure early events in cell death. We recently demonstrated that protease-cleavable luciferase biosensors detect granzyme B and pro-apoptotic caspase activation within minutes of target cell recognition by murine cytotoxic lymphocytes. Here we report successful adaptation of the biosensor technology to assess perforin-dependent and -independent induction of death pathways in tumor cells recognized by human NK cell lines and primary cells. Cell-cell signaling via both Fc receptors and NK-activating receptors led to measurable luciferase signal within 15 minutes. In addition to the previously described aspartase-cleavable biosensors, we report development of granzyme A and granzyme K biosensors, for which no other functional reporters are available. The strength of signaling for granzyme biosensors was dependent on perforin expression in IL-2-activated NK effectors. Perforin-independent induction of apoptotic caspases was mediated by death receptor ligation and was detectable after 45 minutes of conjugation. Evidence of both FasL and TRAIL-mediated signaling was seen after engagement of Jurkat cells by perforin-deficient human cytotoxic lymphocytes. Although K562 cells have been reported to be insensitive to TRAIL, robust activation of pro-apoptotic caspases by NK cell-derived TRAIL was detectable in K562 cells. These studies highlight the sensitivity of protease-cleaved luciferase biosensors to measure previously undetectable events in live cells in real time. Further development of caspase and granzyme biosensors will allow interrogation of additional features of granzyme activity in live cells including localization, timing, and specificity.

Assessing response to treatment of bone metastases from breast cancer: what should be the standard of care?

Bone is the most common site for breast cancer metastases, occurring in up to 70% of those with metastatic disease. In order to effectively manage these patients, it is essential to have consistent, reproducible and validated methods of assessing response to therapy. We present current clinical practice of imaging response assessment of bone metastases. We also review the biology of bone metastases and measures of response assessment including clinical assessment, tumour markers and imaging techniques; bone scans (BSs), computed tomography (CT), positron emission tomography, magnetic resonance imaging (MRI) and whole-body diffusion-weighted MRI (WB DW-MRI). The current standard of care of BSs and CT has significant limitations and are not routinely recommended for the purpose of response assessment in the bones. WB DW-MRI has the potential to address this unmet need and should be evaluated in clinical trials.

In vivo fluorescence reflectance imaging of protease activity in a mouse model of post-traumatic osteoarthritis

OBJECTIVE

Joint injuries initiate a surge of inflammatory cytokines and proteases that contribute to cartilage and subchondral bone degeneration. Detecting these early processes in animal models of post-traumatic osteoarthritis (PTOA) typically involves ex vivo analysis of blood serum or synovial fluid biomarkers, or histological analysis of the joint. In this study, we used in vivo fluorescence reflectance imaging (FRI) to quantify protease, matrix metalloproteinase (MMP), and Cathepsin K activity in mice following anterior cruciate ligament (ACL) rupture. We hypothesized that these processes would be elevated at early time points following joint injury, but would return to control levels at later time points.

DESIGN

Mice were injured via tibial compression overload, and FRI was performed at time points from 1 to 56 days after injury using commercially available activatable fluorescent tracers to quantify protease, MMP, and cathepsin K activity in injured vs uninjured knees. PTOA was assessed at 56 days post-injury using micro-computed tomography and whole-joint histology.

RESULTS

Protease activity, MMP activity, and cathepsin K activity were all significantly increased in injured knees relative to uninjured knees at all time points, peaking at 1-7 days post-injury, then decreasing at later time points while still remaining elevated relative to controls.

CONCLUSIONS

This study establishes FRI as a reliable method for in vivo quantification of early biological processes in a translatable mouse model of PTOA, and provides crucial information about the time course of inflammation and biological activity following joint injury. These data may inform future studies aimed at targeting these early processes to inhibit PTOA development.

Real-time detection of CTL function reveals distinct patterns of caspase activation mediated by Fas versus granzyme B

Activation of caspase-mediated apoptosis is reported to be a hallmark of both granzyme B- and Fas-mediated pathways of killing by CTLs; however, the kinetics of caspase activation remain undefined owing to an inability to monitor target cell-specific apoptosis in real time. We have overcome this limitation by developing a novel biosensor assay that detects continuous, protease-specific activity in target cells. Biosensors were engineered from a circularly permuted luciferase, linked internally by either caspase 3/7 or granzyme B/caspase 8 cleavage sites, thus allowing activation upon proteolytic cleavage by the respective proteases. Coincubation of murine CTLs with target cells expressing either type of biosensor led to a robust luminescent signal within minutes of cell contact. The signal was modulated by the strength of TCR signaling, the ratio of CTL/target cells, and the type of biosensor used. Additionally, the luciferase signal at 30 min correlated with target cell death, as measured by a (51)Cr-release assay. The rate of caspase 3/7 biosensor activation was unexpectedly rapid following granzyme B- compared with Fas-mediated signal induction in murine CTLs; the latter appeared gradually after a 90-min delay in perforin- or granzyme B-deficient CTLs. Remarkably, the Fas-dependent, caspase 3/7 biosensor signal induced by perforin-deficient human CTLs was also detectable after a 90-min delay when measured by redirected killing. Thus, we have used a novel, real-time assay to demonstrate the distinct pattern of caspase activation induced by granzyme B versus Fas in human and murine CTLs.

Preclinical evaluation of imaging biomarkers for prostate cancer bone metastasis and response to cabozantinib

BACKGROUND

Prostate cancer is incurable once it has metastasized to the bone. Appropriate preclinical models are lacking. The therapeutic efficacy of the multikinase inhibitor cabozantinib was assessed in an orthotopic xenograft model of castration-resistant prostate cancer (CRPC) bone metastasis using noninvasive, multimodality functional imaging.

METHODS

NOD/SCID mice were injected intratibially with luciferase-expressing ERG (v-ets avian erythroblastosis virus E26 oncogene homolog) rearranged VCaP human prostate carcinoma cells. The response of VCaP xenografts (n = 7 per group) to cabozantinib was investigated using bioluminescence imaging and anatomical and diffusion weighted magnetic resonance imaging. This enabled quantitation of tumor volume and apparent diffusion coefficient (ADC). Bone uptake of technetium-methylene diphosphonate ((99m)Tc-MDP) was assessed by single-photon emission computed tomography. Ex vivo micro computed tomography was used to quantify bone volume and correlated with appropriate histopathology. Statistical significance was determined using the two-sided Mann-Whitney test or Wilcoxon signed rank test.

RESULTS

VCaP xenografts were predominantly osteosclerotic with some osteolytic activity. Fluorescent in situ hybridization analysis confirmed retention of ERG oncogene rearrangements. Cabozantinib induced a statistically significant 52% reduction in tumor luminance (P = .02) and stasis in tumor volume after 15 days of treatment. Tumor ADC statistically significantly increased with cabozantinib and was associated with extensive necrosis (after 10 days, mean tumor ADC ± SD = 556±43×10(-6) mm(2)/s vs pretreatment ADC = 485±43×10(-6) mm(2)/s; P = .02 ). Tumor-associated uptake of (99m)Tc-MDP was statistically significantly reduced after 3 days of treatment (P = .02), sustained over 15 days treatment, and associated with a statistically significant (P = .048) reduction in bone growth on the tibial cortex, yet a highly statistically significant (P = .001) increase in trabecular bone volume.

CONCLUSIONS

The intratibial VCaP model faithfully emulates clinical disease. Cabozantinib exerts potent effects on both tumor and tumor-induced bone matrix remodeling, and quantitation of ADC provides a clinically translatable imaging biomarker for early, sensitive assessment of treatment response in CRPC bone metastasis.

Longitudinal imaging of cancer cell metastases in two preclinical models: a correlation of noninvasive imaging to histopathology

Metastatic spread is the leading cause of death from cancer. Early detection of cancer at primary and metastatic sites by noninvasive imaging modalities would be beneficial for both therapeutic intervention and disease management. Noninvasive imaging modalities such as bioluminescence (optical), positron emission tomography (PET)/X-ray computed tomography (CT), and magnetic resonance imaging (MRI) can provide complementary information and accurately measure tumor growth as confirmed by histopathology. Methods. We validated two metastatic tumor models, MDA-MD-231-Luc and B16-F10-Luc intravenously injected, and 4T1-Luc cells orthotopically implanted into the mammary fat pad. Longitudinal whole body bioluminescence imaging (BLI) evaluated metastasis, and tumor burden of the melanoma cell line (B16-F10-Luc) was correlated with (PET)/CT and MRI. In addition, ex vivo imaging evaluated metastasis in relevant organs and histopathological analysis was used to confirm imaging. Results. BLI revealed successful colonization of cancer cells in both metastatic tumor models over a 4-week period. Furthermore, lung metastasis of B16-F10-Luc cells imaged by PET/CT at week four showed a strong correlation (R (2) = 0.9) with histopathology. The presence and degree of metastasis as determined by imaging correlated (R (2) = 0.7) well with histopathology findings. Conclusions. We validated two metastatic tumor models by longitudinal noninvasive imaging with good histopathology correlation.