¹8F-fluoride PET as a noninvasive imaging biomarker for determining treatment efficacy of bone active agents at the hip: a prospective, randomized, controlled clinical study.

The functional imaging technique of ¹8F-fluoride positron emission tomography (¹8F-PET) allows the noninvasive quantitative assessment of regional bone formation at any skeletal site, including the spine and hip. The aim of this study was to determine if ¹8F-PET can be used as an early biomarker of treatment efficacy at the hip. Twenty-seven treatment-naive postmenopausal women with osteopenia were randomized to receive teriparatide and calcium and vitamin D (TPT group, n = 13) or calcium and vitamin D only (control group, n = 14). Subjects in the TPT group were treated with 20 µg/day teriparatide for 12 weeks. ¹8F-PET scans of the proximal femur, pelvis, and lumbar spine were performed at baseline and 12 weeks. The plasma clearance of ¹8F-fluoride to bone, K(i), a validated measurement of bone formation, was measured at four regions of the hip, lumbar spine, and pelvis. A significant increase in K(i) was observed at all regions of interest (ROIs), including the total hip (+27%, p = 0.002), femoral neck (+25%, p = 0.040), hip trabecular ROI (+21%, p = 0.017), and hip cortical ROI (+51%, p = 0.001) in the TPT group. Significant increases in K(i) in response to TPT were also observed at the lumbar spine (+18%, p = 0.001) and pelvis (+42%, p = 0.001). No significant changes in K(i) were observed for the control group. Changes in BMD and bone turnover markers were consistent with previous trials of teriparatide. In conclusion, this is the first study to our knowledge to demonstrate that ¹8F-PET can be used as an imaging biomarker for determining treatment efficacy at the hip as early as 12 weeks after initiation of therapy.

Downregulation of 18F-FDG uptake in PET as an early pharmacodynamic effect in treatment of non-small cell lung cancer with the mTOR inhibitor everolimus.

UNLABELLED: Everolimus downregulates glucose metabolism-associated genes in preclinical models. Inhibition of glucose metabolism measured by (18)F-FDG PET was postulated to serve as a pharmacodynamic marker in everolimus-treated non-small cell lung cancer (NSCLC) patients. METHODS: In 8 NSCLC patients treated with everolimus, the percentage change in (18)F-FDG PET uptake (days 8 and 28 relative to baseline) was determined using a variety of summed standardized uptake value (SUV) measures. Both maximum and mean SUVs were used, with normalizations to body surface area and body weight and with and without correcting for plasma glucose levels. RESULTS: In 5 patients, a reduction of (18)F-FDG PET uptake on day 8 was observed with all methods, ranging from -12.8% to -72.2%. CONCLUSION: These observations demonstrate that inhibition of glucose metabolism is an early effect of everolimus treatment in NSCLC patients and can be assessed using (18)F-FDG PET.

Discovery of potent, selective, and orally active carboxylic acid based inhibitors of matrix metalloproteinase-13.

The matrix metalloproteinase enzyme MMP-13 plays a key role in the degradation of type II collagen in cartilage and bone in osteoarthritis (OA). An effective MMP-13 inhibitor would therefore be a novel disease modifying therapy for the treatment of arthritis. Our efforts have resulted in the discovery of a series of carboxylic acid inhibitors of MMP-13 that do not significantly inhibit the related MMP-1 (collagenase-1) or tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE). It has previously been suggested (but not proven) that inhibition of the latter two enzymes could lead to side effects. A promising carboxylic acid lead 9 was identified and a convergent synthesis developed. This paper describes the optimization of 9 and the identification of a compound 24f for further development. Compound 24f is a subnanomolar inhibitor of MMP-13 (IC(50) value 0.5 nM and K(i) of 0.19 nM) having no activity against MMP-1 or TACE (IC(50) of >10000 nM). Furthermore, in a rat model of MMP-13-induced cartilage degradation, 24f significantly reduced proteoglycan release following oral dosing at 30 mg/kg (75% inhibition, p < 0.05) and at 10 mg/kg (40% inhibition, p < 0.05).

Colorectal liver metastases: contrast agent diffusion coefficient for quantification of contrast enhancement heterogeneity at MR imaging.

PURPOSE: To describe and determine the reproducibility of a simplified model to quantitatively measure heterogeneous intralesion contrast agent diffusion in colorectal liver metastases. MATERIALS AND METHODS: This HIPAA-compliant retrospective study received institutional review board approval, and written informed consent was obtained from 14 patients (mean age, 61 years +/- 9 [standard deviation]; range, 41-78 years), including 10 men (mean age, 65 years +/- 8; range, 47-78 years) and four women (mean age, 54 years +/- 9; range, 41-59 years), with colorectal liver metastases. Magnetic resonance (MR) imaging was performed twice (first baseline MR image [B(1)] and second baseline MR image [B(2)]) in a single target lesion prior to therapy. Dynamic contrast material-enhanced MR imaging was performed by using a saturation-recovery fast gradient-echo sequence. A simplified contrast agent diffusion model was proposed, and a contrast agent diffusion coefficient (CDC) was calculated. The reproducibility of the CDC measurement was evaluated by using the Bland-Altman plot and a linear regression model. RESULTS: The mean CDC was 0.22 mm(2)/sec (range, 0.01-0.73 mm(2)/sec) on B(1) and 0.24 mm(2)/sec (range, 0.01-0.71 mm(2)/sec) on B(2), with an intraclass correlation coefficient of 0.91 (P < .0001). Bland-Altman plot showed good agreement, with a mean difference in measurement pairs of 0.017 mm(2)/sec +/- 0.096. The slope from the linear regression model was 0.89 (95% confidence interval: 0.63, 1.15) and the intercept was 0.01 (95% confidence interval: -0.08, 0.09). CONCLUSION: The CDC enables a quantitative description of contrast enhancement heterogeneity in lesions. Given the high reproducibility of the CDC metric, CDC appears promising for further qualification as an imaging biomarker of change measurement in response assessment. SUPPLEMENTAL MATERIAL: http://radiology.rsnajnls.org/cgi/content/full/248/3/901/DC1.

In vivo MRI of cartilage pathogenesis in surgical models of osteoarthritis.

OBJECTIVE: To examine in vivo time-course changes in macromolecular composition of articular cartilage in two surgical models of osteoarthritis (goat: meniscal transection and cartilage incision; rabbit: medial meniscectomy). DESIGN: Collagen integrity and proteoglycan (PG) content were evaluated in both models by magnetization transfer (MT) and contrast-enhanced MRI, respectively. The MT rate k(m) for the exchange process between the bulk water and water bound to collagen was determined as a marker of the collagen network. Local changes in cartilage fixed charge density, i.e., where PGs are depleted, were derived from T(1) relaxation maps as obtained after an infusion of Gd(DTPA)(2-), a paramagnetic agent. RESULTS: In the goat model, the MT rate constant k(m) was significantly higher at 2 weeks post surgery, a possible sign of cartilage swelling, then decreased below baseline values, most likely indicative of disruption in the collagen framework. Meanwhile, post-Gd(DTPA)(2-) MRI acquisition indicated a significant and sustained loss of PGs. The rabbit model produced milder lesions. Although the difference was non-significant, k(m) steadily decreased in response to the surgical insult while kinetics of Gd(DTPA)(2-) uptake, after reaching a peak level at 6 weeks, were back to normal values after 12 weeks. CONCLUSION: In the goat model, joint instability and cartilage damage was a permanent trigger for cartilage degeneration producing MRI changes. However, biomechanical stress due to partial medial meniscectomy in knees of mature rabbits produced only mild, focal lesions and PG depletion that was partially reversible. This proof-of-concept study identified MT and T(1) parameters as useful surrogate markers in animal models of osteoarthritis.

Pain related behaviour in two models of osteoarthritis in the rat knee.

Osteoarthritis (OA) is a major healthcare burden, with increasing incidence. Pain is the predominant clinical feature, yet therapy is ineffective for many patients. While there are considerable insights into the mechanisms underlying tissue remodelling, there is poor understanding of the link between disease pathology and pain. This is in part owing to the lack of animal models that combine both osteoarthritic tissue remodelling and pain. Here, we provide an analysis of pain related behaviours in two models of OA in the rat: partial medial meniscectomy and iodoacetate injection. Histological studies demonstrated that in both models, progressive osteoarthritic joint pathology developed over the course of the next 28 days. In the ipsilateral hind limb in both models, changes in the percentage bodyweight borne were small, whereas marked mechanical hyperalgesia and tactile allodynia were seen. The responses in the iodoacetate treated animals were generally more robust, and these animals were tested for pharmacological reversal of pain related behaviour. Morphine was able to attenuate hyperalgesia 3, 14 and 28 days after OA induction, and reversed allodynia at days 14 and 28, providing evidence that this behaviour was pain related. Diclofenac and paracetamol were effective 3 days after arthritic induction only, coinciding with a measurable swelling of the knee. Gabapentin varied in its ability to reverse both hyperalgesia and allodynia. The iodoacetate model provides a basis for studies on the mechanisms of pain in OA, and for development of novel therapeutic analgesics.

In vivo assessment of macromolecular content in articular cartilage of the goat knee.

Loss of proteoglycans (PGs) from the extracellular matrix of cartilage is an early event of osteoarthritis. The capability of Gd(DTPA)(2-)-enhanced MRI to quantitatively assess PG content was explored in a goat model of cartilage degeneration. Partial to total PG depletion was induced by an intraarticular injection of papain 1 day prior to the MRI session. A close correlation was found between the extent of the PG loss and the Gd(DTPA)(2-)-induced T(1) decrease. Papain-induced PG depletion was confirmed by post-mortem histological and biochemical assessments. A 2-hr delay after Gd(DTPA)(2-) injection was found to be optimal for an accurate quantitation of the cartilage defect. A series of knee flexions were performed post-Gd(DTPA)(2-) injection to facilitate penetration of the contrast agent into cartilage. However, DeltaT(1)'s observed in cartilage of exercised goat knees were not affected by papain or IL1beta pretreatment. Therefore, as long as a preinjection T(1) map was obtained, the Gd(DTPA)(2-)-enhanced MRI technique provided good sensitivity in detecting partial loss of PG in articular cartilage. This was true only when the animal was maintained in a resting state during diffusion of the Gd(DTPA)(2-). This approach is of particular interest for long-term evaluations of cartilage degeneration and regeneration.

Qualitative and quantitative in vivo assessment of articular cartilage using magnetic resonance imaging.

The molecular organization and biochemical composition that give cartilage the viscoelasticity necessary for load distribution also convey unique magnetic resonance (MR) properties. In that context, MR imaging has the potential to detect cartilage degeneration and regeneration. Magnetization transfer (MT) imaging probes the exchange of magnetization between the bulk water pool and the water pool bound to macromolecules such as collagen and hence MT may be applied for evaluation of collagen integrity. In addition, Gd(DTPA)(2-)-induced T1 changes have been proposed as a surrogate marker of proteoglycan (PG) loss based on the principle that the paramagnetic agent Gd(DTPA)2- penetrates cartilage to an equilibrium concentration inversely proportional to the negative charge density (i.e. the PG concentration). Results obtained in vivo from MT and Gd(DTPA)(2-)-enhanced MRI acquisitions on the goat knee showed early signs of biochemical changes in response to a papain injection. A dose-dependent effect of papain was observed with both approaches over a wide range of PG depletion (i.e. T1 measurement) and collagen damage (i.e. MT measurement) as confirmed with post-mortem biochemistry and histology. Development of MRI protocols for non-invasive assessment of cartilage will facilitate diagnosis and monitoring of treatment efficacy in the clinic.

Fluorescently labeled mesenchymal stem cells (MSCs) maintain multilineage potential and can be detected following implantation into articular cartilage defects.

Several studies have reported enhanced repair of damaged cartilage following implantation of mesenchymal stem cells (MSCs) into full-thickness cartilage defects suggesting that the cells in the repair tissue were derived from the implant. However, it cannot be excluded that the enhanced tissue repair is derived from host cells recruited to the defect in response to the implant, rather than the re-population of the tissue by the implanted MSCs. Our objective was to study the short-term fate of fluorescently labeled MSCs after implantation into full-thickness cartilage defects in vivo. The fluorescent dye used in our studies did not affect MSC viability or their ability to undergo osteogenic and chondrogenic differentiation in vitro. MSC gelatin constructs were implanted into full-thickness cartilage defects in goats. These cells retained the dye and were detectable by histology and flow cytometry. At intervals spanning 2 weeks post-implantation we observed gradual loss of implanted cells in the defect as well as fragments of gelatin sponge containing labeled MSCs in deep marrow spaces indicating fragmentation, dislodgement and passive migration. Fluorescent labeling enabled us to determine whether the implanted cells were lost during early time points after implantation as well as their spatial orientation throughout the defect. By determining the fate of implanted cells, new biomaterials could be engineered to correct undesirable characteristics. Testing of new biomaterials in short-term in vivo models would provide faster optimization for cell retention needed for successful, long-term cartilage regeneration.