Development and validation of a radiofrequency ablation treatment planning system for vertebral metastases

PURPOSE

Bone-targeted radiofrequency ablation (RFA) is widely used in the treatment of vertebral metastases. While radiation therapy utilizes established treatment planning systems (TPS) based on multimodal imaging to optimize treatment volumes, current RFA of vertebral metastases has been limited to qualitative image-based assessment of tumour location to direct probe selection and access. This study aimed to design, develop and evaluate a computational patient-specific RFA TPS for vertebral metastases.

METHODS

A TPS was developed on the open-source 3D slicer platform, including procedural setup, dose calculation (based on finite element modelling), and analysis/visualization modules. Usability testing was carried out by 7 clinicians involved in the treatment of vertebral metastases on retrospective clinical imaging data using a simplified dose calculation engine. In vivo evaluation was performed in a preclinical porcine model (n = 6 vertebrae).

RESULTS

Dose analysis was successfully performed, with generation and display of thermal dose volumes, thermal damage, dose volume histograms and isodose contours. Usability testing showed an overall positive response to the TPS as beneficial to safe and effective RFA. The in vivo porcine study showed good agreement between the manually segmented thermally damaged volumes vs. the damage volumes identified from the TPS (Dice Similarity Coefficient = 0.71 ± 0.03, Hausdorff distance = 1.2 ± 0.1 mm).

CONCLUSION

A TPS specifically dedicated to RFA in the bony spine could help account for tissue heterogeneities in both thermal and electrical properties. A TPS would enable visualization of damage volumes in 2D and 3D, assisting clinicians in decisions about potential safety and effectiveness prior to performing RFA in the metastatic spine.

Polarimetric second harmonic generation microscopy of partially oriented fibers II: Imaging study

Polarimetric second harmonic generation (SHG) microscopy imaging is employed to investigate the ultrastructural organization of biological and biomimetic partially oriented fibrillar structures. The linear polarization-in polarization-out SHG microscopy measurements are conducted with rat tail tendon, rabbit cornea, pig cartilage, and biomimetic meso-tetra(4-sulfonatophenyl)porphine (TPPS4) cylindrical aggregates, which represent different two- and three-dimensional (2D and 3D) configurations of C6 symmetry fibril structures in the focal volume (voxel) of the microscope. The polarization-in polarization-out imaging of rat tail tendon reveals that SHG intensity is affected by parallel/antiparallel arrangements of the fibers, and achiral (R) and chiral (C) susceptibility component ratio values change by tilting the tendon fibers out of image plane. The R ratio changes for the 2D crossing fibers observed in cornea tissue. The 3D crossing of fibers also affects R ratio in cartilage tissue. The distinctly different dependence of R on crossing and tilting of fibers is demonstrated in collagen and TPPS4 aggregates, due to the achiral molecular susceptibility ratio having values below and above 3, respectively. The polarimetric microscopy results correspond well with the analytical expressions of amplitude and R and C ratios dependence on the crossing angle of the fibers. The experimentally measured SHG intensity and R and C ratio maps are consistent with the computational modeling of various fiber configurations presented in the preceding article. The demonstrated SHG intensity and R and C ratio dependencies on fibril configurations provide the basis for interpreting polarimetric SHG microscopy images in terms of 3D ultrastructural organization of fibers in each voxel of the samples.

Wide-field Stokes polarimetric microscopy for second harmonic generation imaging

We employ wide-field second harmonic generation (SHG) microscopy together with nonlinear Stokes polarimetry for quick ultrastructural investigation of large sample areas (700 μm × 700 μm) in thin histology sections. The Stokes vector components for SHG are obtained from the polarimetric measurements with incident and outgoing linear and circular polarization states. The Stokes components are used to construct the images of polarimetric parameters and deduce the maps of ultrastructural parameters of achiral and chiral nonlinear susceptibility tensor components ratios and cylindrical axis orientation in fibrillar materials. The large area imaging was employed for lung tumor margin investigations. The imaging shows reduced SHG intensity, increased achiral susceptibility ratio values, and preferential orientation of collagen strands along the boarder of tumor margin. The wide-field Stokes polarimetric SHG microscopy opens a possibility of quick large area imaging of ultrastructural parameters of tissue collagen, which can be used for nonlinear histopathology investigations.

Irregular porous titanium enhances implant stability and bone ingrowth in an intra-articular ovine model

Two commercially available porous coatings, Gription and Porocoat, were compared for the first time in a challenging intra-articular, weight-bearing, ovine model. Gription has evolved from Porocoat and has higher porosity, coefficient of friction, and microtextured topography, which are expected to enhance bone ingrowth. Cylindrical implants were press-fit into the weight-bearing regions of ovine femoral condyles and bone ingrowth and fixation strength evaluated 4, 8, and 16 weeks postoperatively. Biomechanical push-out tests were performed on lateral femoral condyles (LFCs) to evaluate the strength of the bone-implant interface. Bone ingrowth was assessed in medial femoral condyles (MFCs) as well as implants retrieved from LFCs following biomechanical testing using backscattered electron microscopy and histology. By 16 weeks, Gription-coated implants exhibited higher force (2455 ± 1362 vs. 1002 ± 1466 N; p = 0.046) and stress (12.60 ± 6.99 vs. 5.14 ± 7.53 MPa; p = 0.046) at failure, and trended towards higher stiffness (11,510 ± 7645 vs. 5010 ± 8374 N/mm; p = 0.061) and modulus of elasticity (591 ± 392 vs. 256 ± 431 MPa; p = 0.061). A strong, positive correlation was detected between bone ingrowth in LFC implants and failure force (r = 0.93, p < 10^-13 ). By 16 weeks, bone ingrowth in Gription-coated implants in MFCs was 10.50 ± 6.31% compared to 5.88 ± 2.77% in Porocoat (p = 0.095). Observations of the bone-implant interface, made following push-out testing, showed more bony material consistently adhered to Gription compared to Porocoat at all three time points. Gription provided superior fixation strength and bone ingrowth by 16 weeks.

Establishment and Image based evaluation of a New Preclinical Rat Model of Osteoblastic Bone Metastases

Bone remodeling is disrupted in the presence of metastases and can present as osteolytic, osteoblastic or a mixture of the two. Established rat models of osteolytic and mixed metastases have been identified changes in structural and tissue-level properties of bone. The aim of this work was to establish a preclinical rat model of osteoblastic metastases and characterize bone quality changes through image-based evaluation. Female athymic rats (n = 22) were inoculated with human breast cancer cells ZR-75-1 and tumor development tracked over 3-4 months with bioluminescence and in-vivo µCT imaging. Bone tissue-level stereological features were quantified on ex-vivo µCT imaging. Histopathology verified the presence of osteoblastic bone. Bone mineral density distribution was assessed via backscattered electron microscopy. Newly formed osteoblastic bone was associated with reduced mineral content and increased heterogeneity leading to an overall degraded bone quality. Characterizing changes in osteoblastic bone properties is relevant to pre-clinical therapeutic testing and treatment planning.

Photodynamic therapy outcome modelling for patients with spinal metastases: a simulation-based study

Spinal metastases often occur in the advanced stages of breast, lung or prostate cancer, resulting in a significant impact on the patient's quality of life. Current treatment modalities for spinal metastases include both systemic and localized treatments that aim to decrease pain, improve mobility and structural stability, and control tumour growth. With the development of non-toxic photosensitizer drugs, photodynamic therapy (PDT) has shown promise as a minimally invasive non-thermal alternative in oncology, including for spinal metastases. To apply PDT to spinal metastases, predictive algorithms that optimize tumour treatment and minimize the risk of spinal cord damage are needed to assess the feasibility of the treatment and encourage a broad acceptance of PDT in clinical trials. This work presents a framework for PDT modelling and planning, and simulates the feasibility of using a BPD-MA mediated PDT to treat bone metastases at two different wavelengths (690 nm and 565 nm). An open-source software for PDT planning, PDT-SPACE, is used to evaluate different configurations of light diffusers (cut-end and cylindrical) fibres with optimized power allocation in order to minimize the damage to spinal cord or maximize tumour destruction. The work is simulated on three CT images of metastatically involved vertebrae acquired from three patients with spinal metastases secondary to colorectal or lung cancer. Simulation results show that PDT at a 565 nm wavelength has the ability to treat 90% of the metastatic lesion with less than 17% damage to the spinal cord. However, the energy required, and hence treatment time, to achieve this outcome with the 565 nm is infeasible. The energy required and treatment time for the longer wavelength of 690 nm is feasible ([Formula: see text] min), but treatment aimed at 90% of the metastatic lesion would severely damage the proximal spinal cord. PDT-SPACE provides a simulation platform that can be used to optimize PDT delivery in the metastatic spine. While this work serves as a prospective methodology to analyze the feasibility of PDT for tumour ablation in the spine, preclinical studies in an animal model are ongoing to elucidate the spinal cord damage extent as a function of PDT dose, and the resulting short and long term functional impairments. These will be required before there can be any consideration of clinical trials.

Impact of radiofrequency ablation (RFA) on bone quality in a murine model of bone metastases

Thermal therapies such as radiofrequency ablation (RFA) are gaining widespread clinical adoption in the local treatment of skeletal metastases. RFA has been shown to successfully destroy tumor cells, yet the impact of RFA on the quality of the surrounding bone has not been well characterized. RFA treatment was performed on femora of rats with bone metastases (osteolytic and osteoblastic) and healthy age matched rats. Histopathology, second harmonic generation imaging and backscatter electron imaging were used to characterize changes in the structure, organic and mineral components of the bone after RFA. RFA treatment was shown to be effective in targeting tumor cells and promoting subsequent new bone formation without impacting the surrounding bone negatively. Mineralization profiles of metastatic models were significantly improved post-RFA treatment with respect to mineral content and homogeneity, suggesting a positive impact of RFA treatment on the quality of cancer involved bone. Evaluating the impact of RFA on bone quality is important in directing the growth of this minimally invasive therapeutic approach with respect to fracture risk assessment, patient selection, and multimodal treatment planning.

An Orthotopic Endometrial Cancer Model with Retroperitoneal Lymphadenopathy Made From In Vivo Propagated and Cultured VX2 Cells

Endometrial cancer is the most common gynecologic malignancy in North America and the incidence is rising worldwide. Treatment consists of surgery with or without adjuvant therapy depending on lymph node involvement as determined by lymphadenectomy. Lymphadenectomy is a morbid procedure, which has not been shown to have a therapeutic benefit in many patients, and thus a new method to diagnose lymph node metastases is required. To test novel imaging agents, a reliable model of endometrial cancer with retroperitoneal lymph node metastases is needed. The VX2 endometrial cancer model has been described frequently in the literature; however, significant variation exists with respect to the method of model establishment. Furthermore, no studies have reported on the use of cultured VX2 cells to create this model as only cells propagated in vivo have been previously used. Herein, we present a standardized surgical method and post-operative monitoring method for the establishment of the VX2 endometrial cancer model and report on the first use of cultured VX2 cells to create this model.

Complex Susceptibilities and Chiroptical Effects of Collagen Measured with Polarimetric Second-Harmonic Generation Microscopy

Nonlinear optical properties of collagen type-I are investigated in thin tissue sections of pig tendon as a research model using a complete polarimetric second-harmonic generation (P-SHG) microscopy technique called double Stokes-Mueller polarimetry (DSMP). Three complex-valued molecular susceptibility tensor component ratios are extracted. A significant retardance is observed between the chiral susceptibility component and the achiral components, while the achiral components appear to be in phase with each other. The DSMP formalism and microscopy measurements are further used to explain and experimentally validate the conditions required for SHG circular dichroism (SHG-CD) of collagen to occur. The SHG-CD can be observed with the microscope when: (i) the chiral second-order susceptibility tensor component has a non-zero value, (ii) a phase retardance is present between the chiral and achiral components of the second-order susceptibility tensor and (iii) the collagen fibres are tilted out of the image plane. Both positive and negative areas of SHG-CD are observed in microscopy images, which relates to the anti-parallel arrangement of collagen fibres in different fascicles of the tendon. The theoretical formalism and experimental validation of DSMP imaging technique opens new opportunities for ultrastructural characterisation of chiral molecules, in particular collagen, and provides basis for the interpretation of SHG-CD signals. The nonlinear imaging of chiroptical parameters offers new possibilities to further improve the diagnostic sensitivity and/or specificity of nonlinear label-free histopathology.

Collagen chirality and three-dimensional orientation studied with polarimetric second-harmonic generation microscopy

Polarization-dependent second-harmonic generation (P-SHG) microscopy is used to characterize molecular nonlinear optical properties of collagen and determine a three-dimensional (3D) orientation map of collagen fibers within a pig tendon. C₆ symmetry is used to determine the nonlinear susceptibility tensor components ratios in the molecular frame of reference χzzz2/χzxx2 and χxyz2/χzxx2 , where the latter is a newly extracted parameter from the P-SHG images and is related to the chiral structure of collagen. The χxyz2/χzxx2 is observed for collagen fibers tilted out of the image plane, and can have positive or negative values, revealing the relative polarity of collagen fibers within the tissue. The P-SHG imaging was performed using a linear polarization-in polarization-out (PIPO) method on thin sections of pig tendon cut at different angles. The nonlinear chiral properties of collagen can be used to construct the 3D organization of collagen in the tissue and determine the orientation-independent molecular susceptibility ratios of collagen fibers in the molecular frame of reference.

The impact of thermal cycling on Staphylococcus aureus biofilm growth on stainless steel and titanium orthopaedic plates

Background

Orthopaedic implant infections are difficult to eradicate because bacteria adhering to implant surfaces inhibit the ability of the immune system and antibiotics to combat these infections. Thermal cycling is a temperature modulation process that improves performance and longevity of materials through molecular structural reorientation, thereby increasing surface uniformity. Thermal cycling may change material surface properties that reduce the ability for bacteria to adhere to the surface of orthopaedic implants. This study aims to determine whether thermal cycling of orthopaedic implants can reduce bacterial growth.

Methods

In a randomized, blinded in-vitro study, titanium and stainless steel plates treated with thermal cycling were compared to controls. Twenty-seven treated and twenty-seven untreated plates were covered with 10 ml tryptic soy broth containing ~ 10⁵ colony forming units (CFU)/ml of bioluminescent Staphylococcus aureus (S. aureus)Xen29 and incubated at 37 °C for 14d. Quantity and viability of bacteria were characterized using bioluminescence imaging, live/dead staining and determination of CFUs.

Results

Significantly fewer CFUs grow on treated stainless steel plates compared to controls (p = 0.0088). Similar findings were seen in titanium plates (p = 0.0048) following removal of an outlier. No differences were evident in live/dead staining using confocal microscopy, or in metabolic activity determined using bioluminescence imaging (stainless steel plates: p = 0.70; titanium plates: p = 0.26).

Conclusion

This study shows a reduction in CFUs formation on thermal cycled plates in-vitro. Further in-vivo studies are necessary to investigate the influence of thermal cycling on bacterial adhesion during bone healing. Thermal cycling has demonstrated improved wear and strength, with reductions in fatigue and load to failure. The added ability to reduce bacterial adhesions demonstrates another potential benefit of thermal cycling in orthopaedics, representing an opportunity to reduce complications following fracture fixation or arthroplasty.

Post-euthanasia micro-computed tomography-based strain analysis is able to represent quasi-static in vivo behavior of whole vertebrae

Three-dimensional image-based strain measurement in whole bones allows representation of physiological, albeit quasi-static, loading conditions. However, such work to date has been limited to specimens postmortem. The main purpose of this study is to verify the efficacy of deformable image registration of post-euthanasia strain to characterize the in vivo mechanical behavior of rat vertebrae. A micro-computed tomography-compatible custom loading device was used to apply 75 N load to a three-level caudal motion segment of a healthy rat. Loaded and unloaded micro-computed tomography scans were acquired in vivo and post-sacrifice. A micro-computed tomography-based deformable image registration algorithm was used to calculate vertebral strains live and post-euthanasia. No significant difference was found in the in vivo strains (-0.011 ± 0.001) and ex vivo strains (-0.012 ± 0.001) obtained from the comparisons of loaded and unloaded images (p = 0.3). Comparisons between unloaded-unloaded and loaded-loaded scans yielded significantly lower axial strains, representing the error of the method. Qualitatively, high strains were observed adjacent to growth plate regions in evaluating the loaded-unloaded images. Strain patterns in the loaded-loaded and unloaded-unloaded scans were inconsistent as would be expected in representing noise. Overall, live and dead loaded to unloaded comparisons yielded similar strain patterns and magnitudes. Point-wise differences in axial strain fields also supported this observation. This study demonstrated a proof of concept, suggesting that post-euthanasia micro-computed tomography-based strain analysis is able to represent the in vivo quasi-static behavior of rat tail vertebrae.

Closure of the annulus fibrosus of the intervertebral disc using a novel suture application device-in vivo porcine and ex vivo biomechanical evaluation

BACKGROUND CONTEXT

Defects in the annulus fibrosus (AF) remain a challenge in the surgical treatment of lumbar disc herniations with persistent defects, allowing potential re herniation of nucleus pulposus (NP) tissue. A cervical porcine model was chosen to simulate human lumbar intervertebral disc (IVD).

PURPOSE

The aim of this study was to determine the technical feasibility of closure of the AF of the IVD using a novel minimally invasive Kerrison-shaped suture application device.

STUDY DESIGN

Ex vivo biomechanical and in vivo porcine device evaluations were performed.

METHODS

Ex vivo biomechanical evaluation: 15 porcine spinal units were explanted and subjected to mock discectomy. The annular defect was closed using 2-0 non-absorbable (ultra-high molecular-weight polyethylene, UHMWPE) suture and Dines knot. The knot was backed up with two, three, or four throws. The spinal unit was subject to 4000 cycles of flexion/extension with 1500 N of axial load, and assessed for knot slippage. In vivo porcine device evaluation: three pigs (53-57 kg) were anesthetized and underwent a ventral surgical approach to the cervical spine. The AF of two discs was incised, and simulated partial NP discectomy was performed. The defect was closed at one level using the AnchorKnot device to apply the suture with a Dines knot and four throws. The pigs were observed for 4 weeks before euthanasia, allowing 7T magnetic resonance imaging (MRI) and histological evaluation.

RESULTS

A Dines knot with four throws experienced no slippage after 4000 cycles. This configuration was tested in vivo. Clinically, the neurological examination in treated pigs was normal following surgery. Histological and MRI assessment confirmed sustained defect closure at 4 weeks. There was no reaction to the suture material and no NP extrusion at any of the sutured levels.

CONCLUSIONS

This study demonstrates that it is technically feasible to perform AF defect closure in a porcine model. This novel device achieved AF defect closure that was maintained through 4 weeks in vivo.

Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation

High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles.

μFE models can represent microdamaged regions of healthy and metastatically involved whole vertebrae identified through histology and contrast enhanced μCT imaging

Micro-damage formation within the skeleton is an important stimulant for bone remodeling, however abnormal build-up of micro-damage can lead to skeletal fragility. In this study, µCT imaging based micro finite element (μFE) models were used to evaluate tissue level damage criteria in whole healthy and metastatically-involved vertebrae. T13-L2 spinal segments were excised from osteolytic (n=3) and healthy (n=3) female athymic rnu/rnu rats. Osteolytic metastasis was generated by intercardiac injection of HeLa cancer cells. Micro-mechanical axial loading was applied to the spinal motion segments under μCT imaging. Vertebral samples underwent BaSO4 staining and sequential calcein/fuchsin staining to identify load induced micro-damage. μCT imaging was used generate specimen specific μFE models of the healthy and osteolytic whole rat vertebrae. Model boundary conditions were generated through deformable image registration of loaded and unloaded scans. Elevated stresses and strains were detected in regions of micro-damage identified through histological and BaSO4 staining within healthy and osteolytic vertebral models, as compared to undamaged regions. Additionally, damaged regions of metastatic vertebrae experienced significantly higher local stresses and strains than those in the damaged regions of healthy specimens. Areas identified by BaSO4 staining, however, yielded lower levels of stress and strain in damaged and undamaged regions of healthy and metastatic vertebrae as compared to fuschin staining. The multimodal (experimental, image-based and computational) techniques used in this study demonstrated the ability of local stresses and strains computed through µFE analysis to identify trabecular micro-damage, that can be applied to biomechanical analyses of healthy and diseased whole bones.

Matrix metalloproteinase-based photodynamic molecular beacons for targeted destruction of bone metastases in vivo

The metastatic spread of cancer from the primary site or organ is one of its most devastating aspects, being responsible for up to 90% of cancer-associated mortality. Bone is one of the common sites of metastatic spread, including the vertebrae. Regardless of the treatment strategy, the clinical goals for patients with vertebral metastases are to improve the quality of life by preventing neurologic decline, to achieve durable pain relief and enhance local tumor control. However, in part due to the close proximity of the spinal cord, current treatment options are limited. We propose a novel therapeutic strategy with the use of photodynamic molecular beacons (PMBs) for targeted destruction of spinal metastases, particularly to de-bulk lesions as an adjuvant to vertebroplasty or kyphoplasty in order to mechanically stabilize weak or fractured vertebrae. The PDT efficacy of a matrix metalloproteinase-specific PMB is reported in a metstatic model that recapitulates the clinical features of tumor growth within the bone. We demonstrate that not only does tumor cell destruction occur but also the killing of bone stromal cells. The potential of PMB-PDT to destroy metastatic tumors, disrupt the osteolytic cycle and better preserve critical organs with an increased therapeutic window compared with conventional photosensitizers is demonstrated.

Phototheranostic Porphyrin Nanoparticles Enable Visualization and Targeted Treatment of Head and Neck Cancer in Clinically Relevant Models

Head and neck cancer is the fifth most common type of cancer worldwide and remains challenging for effective treatment due to the proximity to critical anatomical structures in the head and neck region, which increases the probability of toxicity from surgery and radiotherapy, and therefore emphasizes the importance of maximizing the targeted ablation. We have assessed the effectiveness of porphysome nanoparticles to enhance fluorescence and photoacoustic imaging of head and neck tumors in rabbit and hamster models. In addition, we evaluated the effectiveness of this agent for localized photothermal ablative therapy of head and neck tumors. We have demonstrated that porphysomes not only enabled fluorescence and photoacoustic imaging of buccal and tongue carcinomas, but also allowed for complete targeted ablation of these tumors. The supremacy of porphysome-enabled photothermal therapy over surgery to completely eradicate primary tumors and metastatic regional lymph node while sparing the adjacent critical structures' function has been demonstrated for the first time. This study represents a novel breakthrough that has the potential to revolutionize our approach to tumor diagnosis and treatment in head and neck cancer and beyond.

Helical coil electrode radiofrequency ablation designed for application in osteolytic vertebral tumors--initial evaluation in a porcine model

BACKGROUND CONTEXT

Radiofrequency ablation (RFA) is emerging as a complementary treatment for vertebral metastases. Traditional RFA induces frictional heating leading to local tissue necrosis but often yields small, incomplete, and inhomogeneous zones of ablation in bone. We have developed a new bone-specific RFA electrode that uses a nontraditional frequency (27.12 MHz) and geometry (helical), exploiting a magnetic field and an electric field to generate larger and more comprehensive treatment zones.

PURPOSE

The purpose of the study was to evaluate the feasibility and safety of the Bone Coil RFA electrode in the spine.

STUDY DESIGN

This is a preclinical in vivo study based on basic science.

METHODS

Under institutional approval, six healthy Yorkshire pigs received a sham and an RF treatment in two adjacent cervical vertebrae. To deploy the Bone Coil RFA device in dense porcine vertebrae, a surgical approach was required; an irrigated coring drill bit created a cylindrical path in the vertebral bodies through which the RFA electrodes were placed. The electronic circuit was completed by four grounding pads. Treatment was delivered for 10 minutes at 20 W (n=1), 25 W (n=1), and 30 W (n=4). To monitor the thermal rise and for safety, fiber-optic probes recorded temperatures in the center of each coil and near the spinal foramen. After the procedure, animals were monitored for 2 weeks. Magnetic resonance imaging (MRI) was completed immediately after treatment and at 14 days. Magnetic resonance image segmentation and histology were used to evaluate the ablation volume.

RESULTS

Comprehensive treatment of the porcine vertebrae was demonstrated by temperature monitoring, MRI, and histology. Large zones of RF ablation were obtained (RF: 3.72±0.73 cm3 vs. sham: 1.98±0.16 cm3, p<.05), confined within the vertebral body. Internal temperatures were elevated with RF (66.1 °C-102.9 °C), without temperature rise outside of the vertebrae (38.2 °C ± 1.5 °C). Mobility, neurological responses, and behavior were normal, consistent with preprocedural examination. Magnetic resonance imaging best visualized ablation at Day 14. Histology revealed comprehensive homogeneous coagulative necrosis with little peripheral sign of repair.

CONCLUSIONS

The Bone Coil RFA device created large intravertebral ablation volumes with no neurologic sequelae. Radiofrequency thermal ablation (clearly distinguished from the much smaller effects arising from core drilling) corresponded to the homogeneous necrosis visible on histology.

Bone targeted bipolar cooled radiofrequency ablation in a VX-2 rabbit femoral carcinoma model

To determine the effect of bipolar cooled radiofrequency ablation (BCRF) on bone and tumour in a lapine pathologic femoral model. Under institutional approval, twelve New Zealand white rabbits received a single femoral injection of VX2 carcinoma cells (day 0). The rabbit femora, (n = 24), were block-randomized into four experimental groups: tumour-bearing radiofrequency ablation (RFA) treated, healthy bone RFA treated, tumour-bearing shams and healthy bone shams (n = 6 per group). 15 min of thermally regulated (65 °C) BCRF was applied at day 14. Pre- and post-treatment MR imaging was performed and repeated at day 28 prior to euthanasia. Histologic evaluation was used to determine treatment effect on tumour and bone tissue. A thirteenth injected rabbit served as a histologic control (no BCRF electrode placement). Large volumes (12.9 ± 5.5 cm(3)) of thermal ablation were achieved. An eight-fold reduction in tumour growth resulted in RFA treated animals compared to tumour-bearing sham controls (p < 0.001). Osteolysis was controlled in the tumour-treated group. Therapeutic effects were best imaged using MR contrast-enhanced SPoiled Gradient Recalled (SPGR) sequences. Osteoclasts and osteoblasts were observed to be sensitive to BCRF but osteocytes were more resilient. A small number of tumour cells within BCRF treated regions appeared viable post treatment. New bone formation was stimulated in the periphery of the targeted BCRF treatment zone. Structurally large VX2 tumour volumes within bone were successfully ablated with BCRF, stimulating new bone formation in the treatment periphery, although viable appearing osteocytes and tumour cells were observed in some treated regions.

The benefits of photodynamic therapy on vertebral bone are maintained and enhanced by combination treatment with bisphosphonates and radiation therapy

Photodynamic therapy (PDT) has been shown to ablate tumors within vertebral bone and yield short-term improvements in vertebral architecture and biomechanical strength, in particular when combined with bisphosphonate (BP) treatment. Longer-term outcomes of PDT combined with current treatments for skeletal metastases are essential to understand its therapeutic potential. The objective of this study is to evaluate the response of vertebrae to PDT after a longer (6-week) time period, alone and combined with previous BP or radiation treatment (RT). Sixty-three female rnu/rnu rats were randomized to six treatment groups: untreated control, BP-only, RT-only, PDT-only, combined BP + PDT and combined RT + PDT. L2 vertebrae were structurally analyzed through µCT-based analysis, axial compressive load-to-failure testing and histological analysis of morphology, osteoid formation and osteoclast activity. Combined BP + PDT treatment yielded the largest improvements in bone architecture with combined RT + PDT treatment yielding similar findings, but of a lesser magnitude. Mechanically, ultimate force and stress were correlated to stereological parameters that demonstrated a positive structural effect from combinatory treatment. Increased osteoid formation was observed in both combination therapies without any significant differences in osteoclast activity. Overall, multimodality treatment demonstrated a sustained positive effect on vertebral structural integrity, motivating PDT as a minimally-invasive adjuvant treatment for spinal metastases.

Abstract P4-03-04: The potential use of Optical Coherence Tomography for intraoperative breast tumour margin width estimation

Total mastectomy and lumpectomy with radiation have been shown to have equivalent patient outcomes, which has likely contributed to the more widespread adoption of breast conserving surgery (BCS) procedures. Assessment of breast lumpectomy margin widths in both an accurate and timely manner is essential to successful breast conservation procedures. Current BCS methodologies have been reported to result in reoperation rates of up to 20–60%, which represents a significant and unmet need for improved margin assessment. High reoperation rates present both increased treatment risk to patients and increased burden on healthcare systems. In the USA alone, over 150,000 lumpectomies are performed per year at an average cost between $11,000 and $19,000 USD per procedure. Assuming a relatively modest average repeat operation rate of 25%, potentially preventable repeat surgeries represent an approximate cost to the US healthcare system of $500M (USD) annually.

Reducing the prevalence of repeat surgeries may be accomplished by providing faster and more accurate intraoperative tools for assessing margin widths during the time of the first surgery. One such potential technique involves the use of Optical Coherence Tomography (OCT) imaging, which uses light to produce images in much the same way that ultrasound produces images with sound. Compared to ultrasound, OCT provides decreased depth of penetration, but increased resolution capabilities. The increased resolution that OCT provides allows for the visualization of the internal cellular structure within a tissue sample and therefore, provides the potential ability to differentiate cancerous from normal or benign cells. We propose the use of an intraoperative OCT imaging system to provide near real-time imaging information about the internal structure of tissue samples excised during BCS procedures. Our hypothesis is that the overall rate of repeat operations can be reduced by providing a tool to assist surgeons with the task of margin width estimation during the time of surgery.

We have developed an early stage prototype OCT imaging system that has completed laboratory phantom and preclinical studies. This paper will present the capabilities of an OCT imaging system to provide margin assessment information in biological breast tissue mimicking phantoms. The phantoms were designed to encompass imaging characteristics across a wide range of human breast densities. The paper will go on to describe preclinical imaging that was done in tumor specimens excised from human breast cancer rat models. The results obtained in the phantom and preclinical studies suggest the potential for OCT as a near-real time, intraoperative imaging tool to aid surgeons with breast lumpectomy margin width estimation. To help realize this potential, further research is required in to the use of OCT during BCS.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-03-04.

Hierarchical model of fibrillar collagen organization for interpreting the second-order susceptibility tensors in biological tissue

The second-order nonlinear polarization properties of fibrillar collagen in various rat tissues (vertebrae, tibia, tail tendon, dermis, and cornea) are investigated with polarization-dependent second-harmonic generation (P-SHG) microscopy. Three parameters are extracted: the second-order susceptibility ratio, R = [Formula: see text] ; a measure of the fibril distribution asymmetry, |A|; and the weighted-average fibril orientation, <δ>. A hierarchical organizational model of fibrillar collagen is developed to interpret the second-harmonic generation polarization properties. Highlights of the model include: collagen type (e.g., type-I, type-II), fibril internal structure (e.g., straight, constant-tilt), and fibril architecture (e.g., parallel fibers, intertwined, lamellae). Quantifiable differences in internal structure and architecture of the fibrils are observed. Occurrence histograms of R and |A| distinguished parallel from nonparallel fibril distributions. Parallel distributions possessed low parameter values and variability, whereas nonparallel distributions displayed an increase in values and variability. From the P-SHG parameters of vertebrae tissue, a three-dimensional reconstruction of lamellae of intervertebral disk is presented.

Quantification of the effect of osteolytic metastases on bone strain within whole vertebrae using image registration

The vertebral column is the most frequent site of metastatic involvement of the skeleton with up to 1/3 of all cancer patients developing spinal metastases. Longer survival times for patients, particularly secondary to breast cancer, have increased the need for better understanding the impact of skeletal metastases on structural stability. This study aims to apply image registration to calculate strain distributions in metastatically involved rodent vertebrae utilizing µCT imaging. Osteolytic vertebral lesions were developed in five rnu/rnu rats 2-3 weeks post intracardiac injection with MT-1 human breast cancer cells. An image registration algorithm was used to calculate and compare strain fields due to axial compressive loading in metastatically involved and control vertebrae. Tumor-bearing vertebrae had greatly increased compressive strains, double the magnitude of strain compared to control vertebrae (p=0.01). Qualitatively strain concentrated within the growth plates in both tumor bearing and control vertebrae. Most interesting was the presence of strain concentrations at the dorsal wall in metastatically involved vertebrae, suggesting structural instability. Strain distributions, quantified by image registration were consistent with known consequences of lytic involvement. Metastatically involved vertebrae had greater strain magnitude than control vertebrae. Strain concentrations at the dorsal wall in only the metastatic vertebrae, were consistent with higher incidence of burst fracture secondary to this pathology. Future use of image registration of whole vertebrae will allow focused examination of the efficacy of targeted and systemic treatments in reducing strains and the related risk of fracture in pathologic bones under simple and complex loading.

Evaluating the effects of mixed osteolytic/osteoblastic metastasis on vertebral bone quality in a new rat model

Spinal metastases often show mixed areas of enhanced (osteoblastic) bone growth adjacent to areas of thinning (osteolytic) bone. This study aims to quantitatively characterize bone quality and tumor burden within a new rat model of mixed osteolytic/osteoblastic spinal metastases. Mixed vertebral metastases were analyzed in nude rats 21-days post intracardiac injection of Ace-1 canine prostate cancer cells. Vertebral micro-architecture was assessed in µCT images. Histologic processing quantified tumor burden (PTHrP), osteoclast activity (TRAP), and osteoid formation (Goldner's Trichrome) in ½ of all samples. Remaining samples were mechanically tested to failure in compression. Metastatically involved vertebrae exhibited extreme osteolysis, evident through an increase in osteoclasts leading to significantly reduced trabecular bone volume. Metastatically involved vertebrae also exhibited increased osteoid characteristic of osteoblastic lesions. While mechanical properties in tumor-bearing vertebrae were not significantly decreased compared to controls, a strong correlation was found between trabecular volumetric BMD and ultimate force. The highly aggressive Ace-1 skeletal metastases demonstrated predominant osteolysis with some areas of immature, new osteoblastic bone formation. Bone quality resulting from these lesions consisted of decreased structural properties, but without a significant impact on mechanical integrity.

Local treatment of mixed osteolytic/osteoblastic spinal metastases: is photodynamic therapy effective?

The widespread use of systemic and local therapies aimed at spinal metastatic lesions secondary to breast cancer has increased the incidence of mixed osteolytic/osteoblastic patterns of bony disease. The complex structure of these lesions requires novel therapeutic approaches to both reduce tumor burden and restore structural stability. In photodynamic therapy (PDT), a minimally invasive approach can be used to employ light to activate a photosensitizing agent that preferentially accumulates in tumor tissue, leading to cell toxicity and death. Previous work in an osteolytic rat model (MT-1) demonstrated that PDT effectively ablates tumor and improves vertebral structural properties. The aim of this study was to assess the efficacy of PDT in a rat model of mixed osteolytic/osteoblastic spinal metastases. Mixed spinal metastases were generated through intracardiac injection of Ace-1 canine prostate cancer cells into female athymic rats (day 0). A single PDT treatment was applied to lumbar vertebra L2 of tumor-bearing and healthy control rats (day 14). PDT-treated and untreated control rats were euthanized and excised spines imaged with μCT to assess bone quality (day 21). Spines were mechanically tested or histologically processed to assess mechanical integrity, tumor burden, and remodelling properties. Untreated tumor-bearing vertebrae showed large areas of osteolysis and areas of immature, new bone formation. The overall bone quality resulting from these lesions consisted of decreased structural properties but without a significant reduction in mechanical integrity. PDT was shown to significantly decrease tumor burden and osteoclastic activity, thereby improving vertebral bone structural properties. While non-tumor-bearing vertebrae exhibited significantly more new bone formation following PDT, the already heightened level of new bone formation in the mixed tumor-bearing vertebrae was not further increased. As such, the effect of PDT on mixed metastases may be more influenced by suppression of osteoclastic resorption as opposed to the triggering of new bone formation.

Imaging of specific activation of photodynamic molecular beacons in breast cancer vertebral metastases

Breast cancer is the second leading cause of cancer-related death in women. Approximately 85% of patients with advanced cases will develop spinal metastases. The vertebral column is the most common site of breast cancer metastases, where overexpression of matrix metalloproteinases (MMPs) promotes the spread of cancer. Current therapies have significant limitations due to the high associated risk of damaging the spinal cord. An attractive alternative is photodynamic therapy providing noninvasive and site-selective treatment. However, current photosensitizers are limited by their nonspecific accumulation. Photodynamic molecular beacons (PP(MMP)B), activated by MMPs, offer another level of PDT selectivity and image-guidance preserving criticial tissues, specifically the spinal cord. Metastatic human breast carcinoma cells, MT-1, were used to model the metastatic behavior of spinal lesions. In vitro and in vivo evidence demonstrates MMP specific activation of PP(MMP)B in MT-1 cells. Using a clinically relevant metastatic model, fluorescent imaging establishes the specific activation of PP(MMP)B by vertebral metastases versus normal tissue (i.e., spinal cord) demonstrating the specificity of these beacons. Here, we validate that the metastasis-selective mechanism of PP(MMP)Bs can specifically image breast cancer vertebral metastases, thereby differentiating tumor and healthy tissue.

Quantitative MRI assessment of VX2 tumour oxygenation changes in response to hyperoxia and hypercapnia

Magnetic resonance imaging (MRI) relaxation times provide indirect estimates of tissue O(2) for monitoring tumour oxygenation. This study provides insight into mechanisms underlying longitudinal (R(1) = 1/T(1)) and transverse effective (R(2)* = 1/T(2)*) relaxation rate changes during inhalation of 100% O(2) and 3%, 6% and 9% CO(2) (balanced O(2)) in a rabbit tumour model. Quantitative R(1), R(2)*, and dynamic contrast-enhanced (DCE) imaging was performed in six rabbits 12-23 days following implantation of VX2 carcinoma cells in the quadricep muscle. Invasive measurements of tissue partial pressure of O(2) (pO(2)) and perfusion were also performed, which revealed elevated pO(2) levels in all tumour regions for all hyperoxic gases compared to baseline (air) and reduced perfusion for carbogen. During 100% O(2) breathing, an R(1) increase and R(2)* decrease consistent with elevated pO(2) were observed within tumours. DCE-derived blood flow was weakly correlated with R(1) changes from air to 100% O(2). Further addition of CO(2) (carbogen) did not introduce considerable changes in MR relaxation rates, but a trend towards higher R(1) relative to breathing 100% O(2) was observed, while R(2)* changes were inconsistent. This observation supports the predominance of dissolved O(2) on R(1) sensitivity and demonstrates the value of R(1) over R(2)* for tissue oxygenation measures.

Assessment of photobleaching during endoscopic autofluorescence imaging of the lower GI tract

BACKGROUND AND OBJECTIVES

In autofluorescence endoscopy, the difference in the fluorescence of intrinsic fluorophores is imaged to help visualize pre-malignant lesions, as in the system evaluated here. In this, blue light is used for excitation and the green autofluorescence is normalized by the red diffuse reflectance and presented using a false color scale. The present study was designed to quantify the degree of fluorescence photobleaching induced by the excitation light during use in the colon, since significant photobleaching could lead to false interpretation of the images, particularly false-positive lesions.

STUDY DESIGN

Measurements were made ex vivo and in vivo, both using the endoscopic imaging system and a separate fiberoptic spectroscopy probe in externalized rat jejunum and in patients undergoing routine colonoscopy, using exposures typical of autofluorescence endoscopic examination.

RESULTS

Photobleaching could be potentially caused at blue light exposure. However, at light intensities and exposure times that are typically used in clinical practice, the average photobleaching (% loss of peak fluorescence intensity) was <1% and <6% in the rat and human tissues, respectively. Nevertheless, the range was large: from -17% to +18% in rats and -33% to +43% in patients, where negative values denote an apparent increase in fluorescence. Both the large positive and negative deviations are believed in part to be due to a measurement artifact caused by uncontrollable tissue motility.

SUMMARY AND CONCLUSIONS

It is concluded that, using exposures typically encountered in clinical practice, there is minimal photobleaching during fluorescence endoscopy at exposure such as are used in the Onco-LIFE and comparable systems. The small changes in fluorescence intensity and spectral shift that do occur are not likely to be detectable by eye, and so should not impact significantly on the diagnostic accuracy of the technique.

Defining the therapeutic window of vertebral photodynamic therapy in a murine pre-clinical model of breast cancer metastasis using the photosensitizer BPD-MA (Verteporfin)

Breast cancer is known to cause metastatic lesions in the bone, which can lead to skeletal-related events. Currently, radiation therapy and surgery are the treatment of choice, but the success rate varies and additional adjuncts are desirable. Photodynamic therapy (PDT) has been applied successfully as a non-radiative treatment for numerous cancers. Earlier work has shown that the athymic rat model is suitable to investigate the effect of PDT on bone metastasis and benzoporphyrin-derivative monoacid ring A (BPD-MA; verteporfin) has been shown to be a selective photosensitizer. The aim of this study was to define the therapeutic window of photosensitizer with regard to drug and light dose. Human breast carcinoma cells (MT-1)-stable transfected with the luciferase gene-were injected intra-cardiacally into athymic rats. At 14 days, the largest vertebral lesion by bioluminescence imaging was targeted for single treatment PDT. A drug escalating-de-escalating scheme was used (starting drug dose and light energy of 0.2 mg/kg and 50 J, respectively). Outcomes included 48 h post-treatment bioluminescence of remaining viable tumour, histomorphometric assessment of tumour burden, and neurologic evaluation. The region of effect by bioluminescence and histology increased with increasing drug dose and light energy. A safe and effective drug-light dose combination in this model appears to be 0.5 mg/kg BPD-MA and applied light energy of less than 50 J for the thoracic spine and 1.0 mg/kg and 75 J for the lumbar spine. For translation to clinical use, it is an advantage that BPD-MA (verteporfin), a second-generation photosensitizer, is already approved to treat age-related macular degeneration. Overall, PDT represents an exciting potential new minimally-invasive local, safe and effective therapy in the management of patients with spinal metastases.

Photodynamic therapy of vertebral metastases: evaluating tumor-to-neural tissue uptake of BPD-MA and ALA-PpIX in a murine model of metastatic human breast carcinoma

Photodynamic therapy has been successfully applied to numerous cancers. Its potential to treat cancer metastases in the spine has been demonstrated previously in a preclinical animal model. The aim of this study was to test two photosensitizers, benzoporphyrin-derivative monoacid ring A (BPD-MA) and by 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PpIX), for their potential use to treat bony metastases. The difference in photosensitizer concentration in the spinal cord and the surrounding tumor-bearing vertebrae was of particular interest to assess the risk of potential collateral damage to the spinal cord. Vertebral metastases in a rat model were generated by intracardiac injection of human breast cancer cells. When tumor growth was confirmed, photosensitizers were injected systemically and the animals were euthanized at different time points. The following tissues were harvested: liver, kidney, ovaries, appendicular bone, spinal cord and lumbar vertebrae. Photosensitizer tissue concentration of BPD-MA or PpIX was determined by fluorescence spectrophotometry. In contrast to BPD-MA, ALA-PpIX did not demonstrate an appreciable difference in the uptake ratio in tumor-bearing vertebrae compared to spinal cord. The highest ratio for BPD-MA concentration was found 15 min after injection, which can be recommended for therapy in this model.

In vivo study of the inflammatory modulating effects of low-level laser therapy on iNOS expression using bioluminescence imaging

This study was designed to demonstrate that bioluminescence imaging (BLI) can be used as a new tool to evaluate the effects of low-level laser therapy (LLLT) during in vivo inflammatory process. Here, the efficacy of LLLT in modulating inducible nitric oxide synthase (iNOS) expression using different therapeutic wavelengths was determined using transgenic animals with the luciferase gene under control of the iNOS gene expression. Thirty transgenic mice, FVB/N-Tg(iNOS-luc)Xen, were allocated randomly to one of four experimental groups treated with different wavelengths (lambda = 635, 785, 808 and 905 nm) or a control group (nontreated). Inflammation was induced by intra-articular injection of zymosan A in both knee joints. Laser treatment (25 mW cm(-2), 200 s, 5 J cm(-2)) was applied to the knees 15 min after inflammation induction. Measurements of iNOS expression were performed at various times (0, 3, 5, 7, 9 and 24 h) by measuring the bioluminescence signal using a highly sensitive charge-coupled device (CCD) camera. The results showed a significant increase in BLI signal after irradiation with 635 nm laser when compared to the nonirradiated animals and the other LLLT-treated groups, indicating wavelength dependence of LLLT effects on iNOS expression during the inflammatory process, and thus demonstrating an action spectrum of iNOS gene expression following LLLT in vivo that can be detected by BLI. Histological analysis was also performed and demonstrated the presence of fewer inflammatory cells in the synovial joints of mice irradiated with 635 nm compared with nonirradiated knee joints.

Mosaicplasty with photooxidized, mushroom shaped, bovine, osteochondral xenografts in experimental sheep

The goal was to study the performance of mushroom shaped, photooxidized, osteochondral grafts in mosaicplasty focusing on graft stability and survival. Mushroom shaped, photooxidized grafts (6 mm for the cartilaginous head of the mushroom, 3 mm for the stem) were implanted in the medial femoral condyle of 10 sheep. Four transplants were inserted per condyle in an overlapping fashion using the pressfit technique (n=40 grafts in 10 condyles). The grafts were followed for 6 and 12 months. Semi-quantitative evaluation of graft performance was performed using a validated score system. All grafts were mechanically stable at 6 and 12 months with one exception, where the mushroom head broke off. The formation of cystic lesions in the subchondral bone area was minimal. Repopulation of the old photooxidized cartilage was noticed with cells invading the matrix from the subchondral bone area and also from the pannus on the surface. Fusion between host and graft cartilage was observed in some of the grafts at 12 months, while remodeling of the calcified cartilage zone and tidemark was noticed in all grafts. Results scored significantly better for the 6 months compared to the 12 months group if cartilage surface integrity was compared (p<0.05). In all other variables no significant differences were found between groups. Despite moderate graft recession in the 12 months group partial fusion of grafts and functional results were satisfactory. The photooxidized mushroom shaped osteochondral transplants may be a suitable type of graft for functional results in cartilage resurfacing if stable anchorage of the grafts can be achieved.

Influence of species and anatomical location on chondrocyte expansion

BACKGROUND

Bovine articular cartilage is often used to study chondrocytes in vitro. It is difficult to correlate in vitro studies using bovine chondrocytes with in vivo studies using other species such as rabbits and sheep. The aim of this investigation was to study the effect of species, anatomical location and exogenous growth factors on chondrocyte proliferation in vitro.

METHODS

Equine (EQ), bovine (BO) and ovine (OV) articular chondrocytes from metacarpophalangeal (fetlock (F)), shoulder (S) and knee (K) joints were cultured in tissue culture flasks. Growth factors (rh-FGFb: 10 ng/ml; rh-TGFbeta: 5 ng/ml) were added to the cultures at days 2 and 4. On day 6, cells were counted and flow cytometry analysis was performed to determine cell size and granularity. A three factor ANOVA with paired Tukey's correction was used for statistical analysis.

RESULTS

After 6 days in culture, cell numbers had increased in control groups of EQ-F, OV-S, OV-F and BO-F chondrocytes. The addition of rh-FGFb led to the highest increase in cell numbers in the BO-F, followed by EQ-F and OV-S chondrocytes. The addition of rh-TGFbeta increased cell numbers in EQ-S and EQ-F chondrocytes, but showed nearly no effect on EQ-K, OV-K, OV-S, OV-F and BO-F chondrocytes. There was an overall difference with the addition of growth factors between the different species and joints.

CONCLUSION

Different proliferation profiles of chondrocytes from the various joints were found. Therefore, we recommend performing in vitro studies using the species and site where subsequent in vivo studies are planned.

Preliminary study of plasma vascular endothelial growth factor (VEGF) during low- and high-dose radiation therapy of dogs with spontaneous tumors

High plasma vascular endothelial growth factor (VEGF) concentrations are associated with radiation resistance and poor prognosis. After an exposure to ionizing radiation in cell culture an early phase and a late phase of increased VEGF have been documented. The activation was dependent on the radiation dose. Therefore, the purpose of this study was to measure baseline plasma VEGF and changes in VEGF over the course of fractionated radiation therapy in dogs with spontaneous tumors. Dogs with tumors had a significantly higher pretreatment plasma VEGF than did dogs without tumors. Immediately after irradiation no increased plasma VEGF was observed. Over the course of radiation therapy there was an increased plasma VEGF in dogs treated with low doses per fraction/high total dose, whereas plasma VEGF remained stable in dogs irradiated with high doses per fraction/low total dose. The regulatory mechanisms are very complex, and therefore the value of plasma VEGF measurements as an indirect marker of angiogenesis induced by radiotherapy is limited.

An experimental animal model of aseptic loosening of hip prostheses in sheep to study early biochemical changes at the interface membrane

BACKGROUND

Aseptic loosening of hip prosthesis as it occurs in clinical cases in human patients was attributed to wear particles of the implants, the response of the tissue dominated by macrophages and the production of inflammatory mediators and matrix degrading enzymes; however, the cascade of events initiating the process and their interaction regarding the time course is still open and discussed controversially. Therefore, the goal of this study was to establish an experimental animal model in sheep allowing to follow the cascade of early mechanical and biochemical events within the interface membrane and study the sequence of how they contribute to the pathological bone resorption necessary for aseptic loosening of the implant.

METHODS

A cemented modular system (Biomedtrix) was used as a hip replacement in 24 adult Swiss Alpine sheep, with one group receiving a complete cement mantle as controls (n = 12), and the other group a cement mantle with a standardized, lateral, primary defect in the cement mantle (n = 12). Animals were followed over time for 2 and 8.5 months (n = 6 each). After sacrifice, samples from the interface membranes were harvested from five different regions of the femur and joint capsule. Explant cell cultures were performed and supernatant of cultures were tested and assayed for nitric oxide, prostaglandin E2, caseinolytic and collagenolytic activity. RNA extraction and quantification were performed for inducible nitric oxide synthase, cyclooxygenase-2, interleukin 1, and interleukin 6. Overall differences between groups and time periods and interactions thereof were calculated using a factorial analysis of variance (ANOVA).

RESULTS

The development of an interface membrane was noticed in both groups at both time points. However, in the controls the interface membrane regressed in thickness and biological activity, while both variables increased in the experimental group with the primary cement mantle defect over time. Nitric oxide (NO) and PGE2 concentrations were higher in the 8.5 months group (P < 0.0001) compared to the 2 months group with a tendency for the unstable group to have higher concentrations. The same was true for collagenolytic activity (P = 0.05), but not for caseinolytic activity that decreased over time (P < 0.0001).

CONCLUSION

In this study, a primary cement mantle defect of the femoral shaft elicited biomechanical instability and biochemical changes over time in an experimental animal study in sheep, that resembled the changes described at the bone cement-interface in aseptic loosening of total hip prosthesis in humans. The early biochemical changes may well explain the pathologic bone resorption and formation of an interface membrane as is observed in clinical cases. This animal model may aid in future studies aiming at prevention of aseptic loosening of hip prosthesis and reflect some aspects of the pathogenesis involved.

The use of photooxidized, mushroom-structured osteochondral grafts for cartilage resurfacing--a comparison to photooxidized cylindrical grafts in an experimental study in sheep

OBJECTIVE

This article addresses the problem of structural design with osteochondral grafts used for cartilage resurfacing.

METHODS

Photooxidized cylindrical or mushroom-shaped grafts were surgically implanted in the weight bearing area of the medial and lateral femoral condyles of eight sheep (condyles: N=8/group). Both types of photooxidized grafts contained no viable chondrocytes at the time of implantation. Results were evaluated at 2 and 6 months after surgical implantation of the grafts. Qualitative and quantitative evaluation of the subchondral bone area was performed using plastic embedded sections of non-decalcified bone and cartilage specimens and placing emphasis on graft anchorage, cyst-like lesions at the base of the cartilage junction and at the base of the graft in the subchondral bone region. Cartilage morphology was studied qualitatively focusing on viability of the graft and adjacent host cartilage, while a score system was developed for semi-quantitative evaluation of the overall articular cartilage performance. The semiquantitative scores and histomorphometrical measurements were subjected to statistical analysis using a factorial analysis of variance (ANOVA-test).

RESULTS

The photooxidized mushroom-shaped grafts developed less fibrous tissue and cyst-like lesions in the subchondral bone area at 2 and 6 months compared to the cylindrical grafts. Areas of endochondral ossification and bone remodeling were noticeable in the mushroom structured grafts at 2 months, and also bone remodeling was more complete at 6 months than with the cylindrical grafts. Increased numbers of cells were seen in the basal remodeling zones of both graft types increased from the 2 months to the 6 months specimens, but mushroom structured grafts showed better results. In both graft types, however, the midzone of the cartilage matrix was still acellular at 6 months. Cells from the subchondral bone area started to penetrate the calcified cartilage zone and tide mark at 2 months and repopulated the old photooxidized cartilage matrix already at 6 months after implantation. Cartilage repopulation was dependent on a stable subchondral bone area in both types of grafts. Matrix degradation of the adjacent host cartilage was minimal at 2 and 6 months. At 6 months a junction between host and graft cartilage was already noticed in some of the mushroom-shaped grafts.

CONCLUSION

This study confirmed the importance of the subchondral bone area for osteochondral graft survival. In addition it demonstrated that the structure of the graft influences considerably the architecture of the subchondral bone, and with this the possibility for the repopulation of the old cartilage matrix including the junction between the host and graft cartilage matrix.

Pharmacokinetics and sedative effects of intramuscular medetomidine in domestic sheep

Intramuscular (i.m.) administration of medetomidine (MED) may avoid the severe pressor effects caused by peripheral actions of MED associated with intravenous (i.v.) dosing. The purpose of this study was to determine the pharmacokinetics, the time course of sedation and occurence of hypoxaemia after i.m. administration of MED in domestic sheep. The MED was injected i.m. at a dose of 30 micro g/kg in nine domestic sheep. Blood was sampled at 0, 5, 10, 20, 30, 40, 60, 120, 180, 240, 360 and 600 min after MED. Sedation was assessed and arterial blood samples were taken before and 35 min after MED application. Mean (SD) pharmacokinetic parameters of i.m. MED were: absorption half-life: 13.2 (7.5) min; terminal half-life: 32.7 (14.9) min; time to peak concentration: 29.2 (8.9) min; peak concentration: 4.98 (1.89) ng/mL; volume of distribution: 3.9 (2.4) l/kg; total body clearance: 81.0 (21.5) mL/(min kg). Peak sedation occurred between 30 and 40 min after injection of MED. The degree of sedation correlated with individual plasma concentrations (rS: 0.926). One animal became hypoxaemic (PaO2 = 54.1 mmHg).

In vitro studies of a photo-oxidized bovine articular cartilage

Bovine articular cartilage was photo-oxidized and cultured with native articular bovine cartilage and synovial membrane to study the interaction between these tissues mimicking the physiological situation in the joint. The photo-oxidation was applied as a pretreatment of cartilage for future use in cartilage resurfacing procedures in joints. Properties of the transplant were assessed by testing the production of local mediators, such as nitric oxide (NO) and prostaglandin E2 (PGE2), and neutral metalloproteinase activities under normal conditions and after stimulation with various stimulants representative of inflammatory changes in pathophysiological conditions. Unlike normal cartilage photo-oxidized cartilage did not release significant amounts of NO and PGE2 and showed less gelatinolytic and caseinolytic activity compared to native bovine articular cartilage. Enzyme activity of the combined cultures was at a level intermediate between that of photo-oxidized cartilage and native cartilage cultures alone. In contrast to normal cartilage, living chondrocytes were not visible in photo-oxidized cartilage using live/dead staining. These results indicate, that the photo-oxidized cartilage may have a beneficial effect on adjacent native host cartilage and therefore be a suitable transplant for use in in vivo experiments.

Tumor regression induced by intratumoral injection of DNA coding for human interleukin 12 into melanoma metastases in gray horses

Preclinical studies investigating new therapeutic principles against melanoma are presently being carried out in mouse models; however, these are not optimal. Here we describe a novel animal model using gray horses. These animals spontaneously develop metastatic melanoma that resembles human disease and is thus highly relevant for preclinical studies testing new immunotherapy protocols. We found that injection of plasmid DNA coding for the human cytokine interleukin 12 into established metastases induced significant regression in all 12 treated lesions in a total of 7 horses. Complete disappearance was observed in one treated lesion, with no recurrence after 6 months. No adverse events have been observed in any of the animals during and after treatment. These results demonstrate the effectiveness and safety of interleukin 12 encoding plasmid DNA therapy against established metastatic disease in a large animal model and serve as a basis for a clinical trial.

Long term in-vivo studies of a photo-oxidized bovine osteochondral transplant in sheep

BACKGROUND

Articular cartilage has limited capacity to repair. Defects greater than 3 mm heal with formation of inferior fibrous cartilage. Therefore, many attempts have been made to find the ideal graft for larger cartilage lesions. Different grafts, such as untreated or cryopreserved osteochondral transplants, have been used with variable success.

METHODS

Photo-oxidized osteochondral grafts were implanted in both femoral condyles of one ovine knee. Untreated xenogeneic and autogeneic grafts served as controls. Three groups of 8 sheep each were formed and they were sacrificed 6, 12 or 18 months after surgery.

RESULTS

The macroscopic evaluation of the condyle and graft showed a well-maintained cartilage surface in most grafts at all time points. However, the host cartilage matrix deteriorated considerably in all xenogeneic, most autogeneic and fewer of the photo-oxidized grafts at 12 and 18 months, respectively. The blue colour of the photo-oxidized grafts resulting from the process of photo-oxidation was visible in all grafts at 6 months, had diminished at 12 months and had completely disappeared at 18 months after surgery. Histologically a loss of matrix staining was almost never noticed in untreated xenografts, transiently at 6 months in photo-oxidized grafts and increased at 12 and 18 months. Fusion between graft and host cartilage could be seen in photo-oxidized grafts at 12 and 18 months, but was never seen in autografts and xenografts.

CONCLUSIONS

The photo-oxidation of osteochondral grafts and its use as transplant appears to have a beneficial effect on cartilage and bone remodelling. Osteochondral grafts pre-treated with photo-oxidation may be considered for articular cartilage replacement and therefore may delay artificial joint replacements in human patients.

Clinical comparison of preanaesthetic intramuscular medetomidine and dexmedetomidine in domestic sheep

Medetomidine and its active d-enantiomer, dexmedetomidine, are highly selective alpha-2 agonists with potent sedative, anaesthetic-sparing and analgesic effects. These properties make them an ideal pre-anaesthetic medication for noxious surgical procedures. However, sheep can develop adverse hypoxaemic effects after intravenous alpha-2 agonists. Objective of the present study was to compare intramuscular injection of medetomidine or dexmedetomidine at equipotent doses as preanaesthetic medication prior to isoflurane anaesthesia in sheep. Nineteen healthy, adult, non-pregnant, female sheep of various breeds were used. The study was carried out as a randomised, blind trial. Group A received 15 micrograms/kg bwt dexmedetomidine and group B received 30 micrograms/kg bwt medetomidine intramuscularly (i.m.) 30 minutes prior to induction of anaesthesia. Anaesthesia was induced with ketamine (2.0 mg/kg bwt i.v.) and maintained with isoflurane in 100% oxygen. End expired anaesthetic concentration (FEiso), respiratory frequency (fR), direct arterial blood pressures and heart rates (HR) were measured. Arterial blood samples were taken at intervals. Data were averaged over time (sum of measurements/number of measurements) and tested for differences between groups by independent t-tests, and ANOVA for repeated measures followed by Bonferroni corrected t-tests. There were no differences in demographic data between the groups. Duration of anaesthesia [A: 170 (42) minutes, B: 144 (33) minutes] and duration of surgery [A: 92 (32) minutes, B: 85 (31) minutes] were similar in both groups. Average FEiso concentrations required to maintain a surgical plane of anaesthesia were not significantly different between groups [A: 0.82 (0.14)%; B: 1.00 (0.25)%]. Mean average fR, did not differ between groups [A: 31 (14), B: 37 (15)]. Heart rates were significantly lower in group B over the course of the anaesthesia. Mean arterial blood pressures (MAP) were not significantly different between the groups. The PaO2 was less variable in group A than in group B. Individual minimum values were 19.1 kPa and 7.9 kPa in group A and B, respectively. There were no significant differences in PaCO2 and paH between the groups and over time. In conclusion, intramuscular application of dexmedetomidine at 15 micrograms/kg bwt and medetomidine at 30 micrograms/kg bwt prior to isoflurane anaesthesia induced similar changes in clinically monitored cardiorespiratory parameters. The observed differences (heart rates, PaO2) between dexmedetomidine and medetomidine at the chosen dose relationship can be considered clinically not significant. At the chosen dose rates individual animals responded with a transient drop in blood oxygenation, therefore careful monitoring is required. In addition, in compromised sheep medetomidine and dexmedetomidine should be used carefully.

Upregulation of mRNA of interleukin-1 and -6 in subchondral cystic lesions of four horses

This study investigated the potential association of interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) in subchondral cystic lesions (SCL) in horses. With the technique of in situ hybridisation in paraffin sections of fibrous tissue of SCL and quantitative real-time PCR in fresh frozen fibrous tissue and undecalcified bone sections of SCL embedded in acrylic resin, upregulation of mRNA of both cytokines could be demonstrated. mRNA of IL-1beta was upregulated at the periphery of the cystic lesion adjacent to normal bone, whereas IL-6 mRNA was upregulated within the fibrous tissue found within the centre of the SCL. It was concluded that both cytokines are associated in pathological bone resorption observed in SCL and, in combination with increased production of prostaglandin E2, may be responsible for the slow healing, maintenance or further expansion of the cystic lesions.

Cytokine mRNA levels in isolated feline monocytes

Real-time PCR systems were developed to quantitate cytokine expression in short-time cultivated feline monocytes. Feline-specific interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) primers as well as TaqMan probes were designed and were adapted to a quantitative PCR system which had been previously established for feline IL-10 and IL-12 p40. Quantitative analysis of cytokine messenger RNA (mRNA) transcription based on the comparison of the cytokine with the housekeeping gene feline glyceraldehyde-3-phosphate dehydrogenase (GAPDH), providing universally expressed mRNA. GAPDH mRNA was readily detectable in cDNA prepared from short-time cultivated peripheral blood monocytes. Cytokine mRNA was demonstrated in all samples at variable amounts. IL-1beta and TNF-alpha mRNA was constitutively expressed whereas IL-6, IL-10 and IL-12 p40 mRNA was generally expressed at a lower level and was occasionally not detected. There was a great variability of cytokine production between individual cats and at different time points in the same cat.

Fibrous tissue of subchondral cystic lesions in horses produce local mediators and neutral metalloproteinases and cause bone resorption in vitro

OBJECTIVES

To define the release of nitric oxide (NO), prostaglandin E2 (PGE2), and the neutral metalloproteinases (NMPs) in horses with subchondral cystic lesions (SCL) and to study bone resorption triggered by conditioned media of fibrous tissue of SCL in vitro.

STUDY DESIGN

Equine explant cultures of fibrous tissue of SCL, and synovial membrane and articular cartilage of normal horses and horses affected with moderate and severe osteoarthritis were performed. NO, PGE2, and NMP concentrations of media samples were measured, and osteoclast formation and activation was studied in vitro.

ANIMALS

Experiment 1: 32 horses with SCL (n = 8), normal joints (7), and joints with moderate (7) and severe (10) osteoarthritis (OA). Experiment 2: 22 horses with SCL (n = 3), normal joints (7), and chip fractures (12). Experiment 3: Conditioned media of fibrous tissue from 3 horses with SCL of the medial femoral condyle (n = 1), distal metacarpal bone (1), and tarsal bone (1).

METHODS

Determinations of local mediator concentrations were made with the Griess assay for NO and an enzyme immunoassay kit for PGE2 concentrations in biological fluids. Enzyme activities were assessed with radiolabeled substrates indicating collagenolytic, gelatinolytic, and caseinolytic activities. The resorption pit assay was used to assess osteoclast recruitment and activity.

RESULTS

Fibrous tissue of SCL produced NO, PGE2, and NMPs. Of all the variables measured, PGE2 concentrations were the highest in cystic tissue of SCL compared with synovial membrane and articular cartilage from normal joints and joints with chip fractures, indicating that this mediator may play an important role in pathological bone resorption associated with SCL. These findings were supported by the observation that conditioned media of SCL tissue were capable of recruiting osteoclasts and increasing their activity.

CONCLUSION

Fibrous tissue of SCL released NO, PGE2, and NMPs into the culture media. It is suspected that intralesional fibrous tissue may play an active role in the pathological process of bone resorption occurring in SCL in horses and may be partly responsible for the maintenance, slow healing rate, and expansion of these lesions.

CLINICAL RELEVANCE

Understanding the pathogenesis of SCL will help to establish successful therapy in horses affected with SCL.

Spontaneous production of nitric oxide (NO), prostaglandin (PGE2) and neutral metalloproteinases (NMPs) in media of explant cultures of equine synovial membrane and articular cartilage from normal and osteoarthritic joints

Nitric oxide (NO), prostaglandin E2 (PGE2), and the activity of neutral metalloproteinases (NMPs) were measured in conditioned media of equine synovial membrane and articular cartilage explant cultures from horses with normal joints (n = 7) and from horses affected with moderate (n = 7) or severe osteoarthritis (n = 14) as judged by macroscopic appearance. Normal articular cartilage appeared glossy and bluish-white, was of normal thickness and showed no evidence of discolouration, fibrillation or other cartilage discontinuity. Slight discolouration and fibrillation or minor clefts of the cartilage were considered as moderate OA, whereas erosions of articular cartilage down to the subchondral bone were considered as cases of severe OA. Explant cultures of equine synovial membrane and articular cartilage released the local mediators, NO and PGE2, as well as detectable levels of NMP activity into culture media. Concentrations of NO were higher in articular cartilage explants compared to synovial membrane explants, whereas concentrations of PGE2 were higher in synovial membrane explants. The NMPs with collagenolytic activities were similar in both explant cultures, whereas gelatinolytic activities were higher in synovial membrane explant cultures and caseinolytic activities were generally higher in articular cartilage explant cultures. Furthermore it was shown that concentrations or enzyme activities increased according to the severity of disease of the joints. Concentrations for NO, collagenolytic and gelatinolytic NMPs were relatively stable, whereas PGE2 and caseinolytic NMP concentrations increased over time in culture.

Quantitative real-time PCR for equine cytokine mRNA in nondecalcified bone tissue embedded in methyl methacrylate

Specific amplification and quantitation of nucleic acid sequences by the polymerase chain reaction (PCR) has been extensively used for the detection of viral infection and gene expression. Although successful amplification of DNA and RNA sequences extracted from paraffin embedded tissue have been described, there are presently no reports available regarding RNA analysis from bone and calcified tissues embedded in hydrophobic acrylic resin. Here we describe a general method for quantitation of specific mRNA sequences extracted from undecalcified bone sections, fixed in paraformaldehyde, and embedded in a hydrophobic acrylic resin. Total RNA was extracted from defined regions of single 50 microm sawed sections. These RNA preparations are suitable for quantitative PCR analysis of mRNA of different cytokines. In addition, the universally expressed housekeeping GAPDH mRNA proved to be useful as an amplification control and to correct for the degree of RNA degradation, which may vary considerably among samples. Reverse transcribed mRNA was amplified and quantitated in Real-Time PCR using a fluorescein labeled internal TaqMan probe.