Therapeutic targets in osteoarthritis: from today to tomorrow with new imaging technology

Internal dosimetry of [99m Tc]NTP15-5 radiotracer for cartilage imaging in preclinical and clinical models using the GATE Monte Carlo platform

PURPOSE

This study aims to perform dosimetry for [^99m Tc]NTP15-5 radiotracer used in imaging of articular cartilage in rabbits and humans. The radiotracer (covered by a world patent WO 01/00621 A1) has been proposed in the previous years for the study of cartilage in osteoarthritis diseases. A sensitive imaging approach is essential to quantify osteoarthritis progression and monitor response to new therapies. [^99m Tc]NTP15-5 binds to cartilage proteoglycans whose decreased content is associated to a loss of biomedical function of cartilage. We have implemented the whole dosimetry study concerning this new radiotracer for rabbits and humans using the GATE Monte Carlo platform.

MATERIALS AND METHODS

Absorbed doses to critical organs are determined using the MIRD formalism. Biodistribution data are obtained by organ sampling, measuring the activity in organs for three rabbits sacrificed at various times postadministration, and by SPECT/CT imaging at different times after injection. Most important sources are cartilages (in knees and intervertebral discs), due to localization together with the liver and kidneys due to excretion of the agent. S-values are calculated from rabbit's CT scan and human CT scan using the GATE v8.0 Monte Carlo platform. Cumulated activity in humans is extrapolated from animals using the %kg-dose/g method. Particular attention is given to dose calculation in bones, bone marrow and organs at risk.

RESULTS

The dosimetry performed in rabbits shows highest absorbed doses for liver and kidneys with respectively 22.5 and 43.8 µGy per MBq of injected activity. In humans, we found absorbed doses for a maximum injected activity of 15 MBq/kg, that is, 1050 MBq for an adult of 70 kgs of 9.03 mGy for kidneys and 4.16 mGy for knee cartilages. Effective dose is 2.69 µSv/MBq.

CONCLUSIONS

The dosimetry profile of [^99m Tc]NTP15-5 in the context of preclinical trials is of major importance in order to make sure that organs at risk are not overexposed. GATE provides all the capability needed to calculate dose profiles for internal dosimetry. The extrapolation of the dose for a human model is a first step towards clinical trials.

Diacerein: Benefits, Risks and Place in the Management of Osteoarthritis. An Opinion-Based Report from the ESCEO

Diacerein is a symptomatic slow-acting drug in osteoarthritis (SYSADOA) with anti-inflammatory, anti-catabolic and pro-anabolic properties on cartilage and synovial membrane. It has also recently been shown to have protective effects against subchondral bone remodelling. Following the end of the revision procedure by the Pharmacovigilance Risk Assessment Committee of the European Medicines Agency, the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO) constituted a panel of 11 experts to better define the real place of diacerein in the armamentarium for treating OA. Based on a literature review of clinical trials and meta-analyses, the ESCEO confirms that the efficacy of diacerein is similar to that of non-steroidal anti-inflammatory drugs (NSAIDs) after the first month of treatment, and superior to that of paracetamol. Additionally, diacerein has shown a prolonged effect on symptoms of several months once treatment was stopped. The use of diacerein is associated with common gastrointestinal disorders such as soft stools and diarrhoea, common mild skin reactions, and, uncommonly, hepatobiliary disorders. However, NSAIDs and paracetamol are known to cause potentially severe hepatic, gastrointestinal, renal, cutaneous and cardiovascular reactions. Therefore, the ESCEO concludes that the benefit-risk balance of diacerein remains positive in the symptomatic treatment of hip and knee osteoarthritis. Furthermore, similarly to other SYSADOAs, the ESCEO positions diacerein as a first-line pharmacological background treatment of osteoarthritis, particularly for patients in whom NSAIDs or paracetamol are contraindicated.

Longitudinal profiling of articular cartilage degradation in osteoarthritis by high-resolution magic angle spinning 1H NMR spectroscopy: experimental study in the meniscectomized guinea pig model

This study assessed the 1H HRMAS NMR spectroscopic profile of articular cartilage in both physiological and osteoarthitic situations. One-dimensional and two-dimensional 1H HRMAS NMR spectra were obtained from the tibial plateau cartilage of healthy and operated (unilateral medial meniscectomy and sham surgery) guinea pigs at different stages of disease, over a 6-month period. The major osteoarthritis-induced 1H HRMAS NMR changes were an increase of the N-acetyl peak of proteoglycans (at day 20 after meniscectomy) and a decrease after day 60 as the pathology evolved. These proteoglycan changes revealed by 1H HRMAS NMR analysis were validated by proteoglycan biochemistry assays. 1H HRMAS NMR analysis also evidenced a sharp increase in methylene resonances of chondrocyte membrane lipids from day 90 as a marker of apoptosis. There was an increase of the mobile methyl group of collagen at day 120, which was associated with collagen breakdown. 1H HRMAS NMR analysis provided a multifactorial and sequential picture of cartilage degradation at the extracellular matrix and chondrocyte levels.

Web-based multilayer viewing interface for knee cartilage

Many adults suffer from osteoarthritis (OA) with the majority of people over 65 showing radiographic evidence of the disease. To carry out effective diagnosis and treatment, it is necessary to understand the progression of cartilage loss and study the effectiveness of therapeutic interventions. Hence, it is important to have accurate, fast diagnosis of the disease. In this paper, we describe a Web-based user interface that enables the direct viewing of 2-D and 3-D image data from the visceral and tissue levels of the biological continuum (i.e., the continuum comprising systems, viscera, tissue, cells, proteins, and genes)--while preserving geometric integrity. This is achieved despite the fact that the data are from different modalities (i.e., magnetic resonance (MR) and light microscopy). The user interface was tested using image data acquired from a study of articular cartilage thickness in the porcine knee. The interface allows the clinician to view both MR and light microscopy images in an integrated manner-with the information linked geometrically.

Early detection and monitoring of cartilage alteration in the experimental meniscectomised guinea pig model of osteoarthritis by 99mTc-NTP 15-5 scintigraphy

PURPOSE

This study in the meniscectomised guinea pig aimed to demonstrate that the radiotracer (99m)Tc-NTP 15-5 would have pathophysiological validity for in vivo osteoarthritis imaging.

METHODS

The specificity of (99m)Tc-NTP 15-5 for cartilage was determined in healthy animals (n = 13), by tissue radioactivity counting, joint autoradiography and scintigraphy. (99m)Tc-NTP 15-5 scintigraphy was performed at 20, 50, 80, 115, 130, 150 and 180 days after medial meniscectomy (n = 10 MNX) or sham operation (n = 5), and scintigraphic ratios (operated/contralateral) were calculated for femoral (F) and tibial (T) areas. F and T ratios were compared with those of (99m)Tc-MDP bone scintigraphy. At the study end-point, autoradiographic analysis of joint (99m)Tc-NTP 15-5 distribution and macroscopic scoring of cartilage integrity were performed.

RESULTS

The high and specific accumulation of (99m)Tc-NTP 15-5 in normal cartilage (about 5.5 +/- 1.7 % of injected dose/g of tissue), which permitted joint imaging with high contrast, was affected by osteoarthritis. In the MNX group, (99m)Tc-NTP 15-5 accumulation in cartilage within the operated joint, relative to the contralateral joint, was observed to change in the same animals as pathology progressed. Although F and T ratios were significantly higher in MNX (F = 1.7 +/- 0.2; T = 1.6 +/- 0.1) than in shams (F = 1.0 +/- 0.1; T = 1.0 +/- 0.1) at day 50, they were significantly lower in MNX (F = 0.6 +/- 0.1; T = 0.7 +/- 0.1) than in shams (F = 1.0 +/- 0.1; T = 0.9 +/- 0.1) at day 180. No change in (99m)Tc-MDP uptake was observed over 6 months. Macroscopic analysis confirmed features of osteoarthritis only in MNX knees.

CONCLUSION

These results in MNX guinea pigs provide additional support for the use of (99m)Tc-NTP 15-5 for in vivo imaging of osteoarthritis.