Circulating miRNAs as sensitive and specific biomarkers for the diagnosis and monitoring of human diseases: promises and challenges

The regulation and modulation of gene expression has been a central focus of modern biomedical research ever since the first molecular elucidation of DNA. The cellular mechanisms by which genes are expressed and repressed hold valuable insight for maintaining tissue homeostasis or conversely provide mechanistic understanding of disease progression. Hence, the discovery of the first miRNA in humans roughly a decade ago profoundly shook the previously established dogmas of gene regulation. Since, these small RNAs of around 20 nucleotides have unquestionably influenced almost every area of medical research. This momentum has now spread to the clinical arena. Hundreds of papers have already been published shedding light on the mechanisms of action of miRNAs, their profound stability in almost every bodily fluid and relating their presence to disease state and severity of disease progression. In this review, we explore the diagnostic potential of miRNAs in the clinical laboratory with a focus on studies reporting the detection of miRNAs in blood and urine for investigation of human disease. Sensitivities, specificities, areas under the curve, group descriptions and miRNAs of interest for 69 studies covering a broad range of diseases are provided. We discuss the practicality of miRNAs in the screening, diagnosis and prognosis of a range of pathologies. Characteristics and pitfalls of miRNA detection in blood are also discussed. The topics covered here are pertinent in the design of future miRNA-based detection strategies for use in clinical biochemistry laboratory settings.

Changes in apparent diffusion coefficient and T2 relaxation during radiotherapy for prostate cancer

PURPOSE

To evaluate regional and temporal changes in apparent diffusion coefficient (ADC) and T2 relaxation during radiation therapy (RT) in patients with low and intermediate risk localized prostate cancer.

MATERIALS AND METHODS

Seventeen patients enrolled on a prospective clinical trial where MRI was acquired every 2 weeks throughout eight weeks of image-guided prostate IMRT (78 Gy/39 fractions). ADC and T2 quantification used entire prostate, central gland, benign peripheral zone, and tumor-dense regions-of-interest, and mean values were evaluated for common response trends.

RESULTS

Overall, the RT responses were greater than volunteer measurement repeatability, and week 6 appeared to be an optimum time-point for early detection. RT effects on the entire prostate were best detected using ADC (5-7% by week 2, P < 0.0125), effects on peripheral zone were best detected using T2 (19% reduction at week 6; P = 0.004) and effects on tumors were best detected using ADC (14% elevation at week 6; P = 0.004).

CONCLUSION

ADC and T2 may be candidate biomarkers of early response to RT warranting further investigation against clinical outcomes.

Imaging biomarker dynamics in an intracranial murine glioma study of radiation and antiangiogenic therapy

PURPOSE

There is a growing need for noninvasive biomarkers to guide individualized spatiotemporal delivery of radiation therapy (RT) and antiangiogenic (AA) therapy for brain tumors. This study explored early biomarkers of response to RT and the AA agent sunitinib (SU), in a murine intracranial glioma model, using serial magnetic resonance imaging (MRI).

METHODS AND MATERIALS

Mice with MRI-visible tumors were stratified by tumor size into 4 therapy arms: control, RT, SU, and SU plus RT (SURT). Single-fraction conformal RT was delivered using MRI and on-line cone beam computed tomography (CT) guidance. Serial MR images (T2-weighted, diffusion, dynamic contrast-enhanced and gadolinium-enhanced T1-weighted scans) were acquired biweekly to evaluate tumor volume, apparent diffusion coefficient (ADC), and tumor perfusion and permeability responses (K(trans), K(ep)).

RESULTS

Mice in all treatment arms survived longer than those in control, with a median survival of 35 days for SURT (P<.0001) and 30 days for RT (P=.009) and SU (P=.01) mice vs 26 days for control mice. At Day 3, ADC rise was greater with RT than without (P=.002). Sunitinib treatment reduced tumor perfusion/permeability values with mean K(trans) reduction of 27.6% for SU (P=.04) and 26.3% for SURT (P=.04) mice and mean K(ep) reduction of 38.1% for SU (P=.01) and 27.3% for SURT (P=.02) mice. The magnitude of individual mouse ADC responses at Days 3 and 7 correlated with subsequent tumor growth rate R values of -0.878 (P=.002) and -0.80 (P=.01), respectively.

CONCLUSIONS

Early quantitative changes in diffusion and perfusion MRI measures reflect treatment responses soon after starting therapy and thereby raise the potential for these imaging biomarkers to guide adaptive and potentially individualized therapy approaches in the future.

Tumor hypoxia predicts biochemical failure following radiotherapy for clinically localized prostate cancer

PURPOSE

Tumor hypoxia is an important determinant of outcome in many human malignancies and is associated with treatment resistance and metastases. The aim of this study was to determine the effect of hypoxia in patients with prostate cancer treated with radiotherapy.

EXPERIMENTAL DESIGN

Tumor hypoxia was measured in 247 patients with clinically localized prostate cancer before radiotherapy, with or without hormonal therapy. The median pO(2) was 6.8 mm Hg and the median hypoxic percentage less than 10 mm Hg (HP(10)) was 63%. The median follow-up was 6.6 years.

RESULTS

The 5-year biochemical relapse-free rate (bRFR) was 78%. Prostrate-specific antigen and Gleason score were both associated with biochemical relapse and formed a baseline clinical model. The effect of hypoxia was found to vary with the duration of patient follow-up. HP(10), when added to the clinical model, was an independent predictor of early bRFR (P = 0.019). The relationship between hypoxia and early bRFR was more pronounced when the analysis was restricted to 142 patients with bulk tumor at the site of the oxygen measurements (P = 0.004). Hypoxia was the only factor predictive of local recurrence in 70 patients who had biopsies conducted during follow-up (P = 0.043), again with the effect being greatest early after completing treatment.

CONCLUSIONS

This is the largest clinical study of prostate cancer hypoxia with direct measurement of tumor oxygen levels. It shows that hypoxia is associated with early biochemical relapse after radiotherapy and also with local recurrence in the prostate gland.

An MRI-compatible robotic system with hybrid tracking for MRI-guided prostate intervention

This paper reports the development, evaluation, and first clinical trials of the access to the prostate tissue (APT) II system-a scanner independent system for magnetic resonance imaging (MRI)-guided transrectal prostate interventions. The system utilizes novel manipulator mechanics employing a steerable needle channel and a novel six degree-of-freedom hybrid tracking method, comprising passive fiducial tracking for initial registration and subsequent incremental motion measurements. Targeting accuracy of the system in prostate phantom experiments and two clinical human-subject procedures is shown to compare favorably with existing systems using passive and active tracking methods. The portable design of the APT II system, using only standard MRI image sequences and minimal custom scanner interfacing, allows the system to be easily used on different MRI scanners.

Biomechanical model-based deformable registration of MRI and histopathology for clinical prostatectomy

A biomechanical model-based deformable image registration incorporating specimen-specific changes in material properties is optimized and evaluated for correlating histology of clinical prostatectomy specimens with in vivo MRI. In this methodology, a three-step registration based on biomechanics calculates the transformations between histology and fixed, fixed and fresh, and fresh and in vivo states. A heterogeneous linear elastic material model is constructed based on magnetic resonance elastography (MRE) results. The ex vivo tissue MRE data provide specimen-specific information for the fresh and fixed tissue to account for the changes due to fixation. The accuracy of the algorithm was quantified by calculating the target registration error (TRE) by identifying naturally occurring anatomical points within the prostate in each image. TRE were improved with the deformable registration algorithm compared to rigid registration alone. The qualitative assessment also showed a good alignment between histology and MRI after the proposed deformable registration.

Evaluation of early imaging response criteria in glioblastoma multiforme

Background

Early and accurate prediction of response to cancer treatment through imaging criteria is particularly important in rapidly progressive malignancies such as Glioblastoma Multiforme (GBM). We sought to assess the predictive value of structural imaging response criteria one month after concurrent chemotherapy and radiotherapy (RT) in patients with GBM.

Methods

Thirty patients were enrolled from 2005 to 2007 (median follow-up 22 months). Tumor volumes were delineated at the boundary of abnormal contrast enhancement on T1-weighted images prior to and 1 month after RT. Clinical Progression [CP] occurred when clinical and/or radiological events led to a change in chemotherapy management. Early Radiologic Progression [ERP] was defined as the qualitative interpretation of radiological progression one month post-RT. Patients with ERP were determined pseudoprogressors if clinically stable for ≥6 months. Receiver-operator characteristics were calculated for RECIST and MacDonald criteria, along with alternative thresholds against 1 year CP-free survival and 2 year overall survival (OS).

Results

13 patients (52%) were found to have ERP, of whom 5 (38.5%) were pseudoprogressors. Patients with ERP had a lower median OS (11.2 mo) than those without (not reached) (p < 0.001). True progressors fared worse than pseudoprogressors (median survival 7.2 mo vs. 19.0 mo, p < 0.001). Volume thresholds performed slightly better compared to area and diameter thresholds in ROC analysis. Responses of > 25% in volume or > 15% in area were most predictive of OS.

Conclusions

We show that while a subjective interpretation of early radiological progression from baseline is generally associated with poor outcome, true progressors cannot be distinguished from pseudoprogressors. In contrast, the magnitude of early imaging volumetric response may be a predictive and quantitative metric of favorable outcome.

Determination of melamine, ammeline, ammelide and cyanuric acid in infant formula purchased in Canada by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry-based isotope dilution method was developed for the analysis of the triazine compounds melamine (MEL), ammeline (AMN), ammelide (AMD) and cyanuric acid (CYA) in infant formula samples purchased in Canada in 2008 for the purpose of a combined exposure and risk assessment. Infant formula samples were extracted with 1:1 acetonitrile-water, cleaned up on disposable ion-exchange solid-phase extraction cartridges, and analysed by ultra-high-performance liquid chromatography-tandem mass spectrometry. MEL and CYA were detected in almost all infant formula products: the highest concentrations observed were 0.32 mg kg(-1) MEL and 0.45 mg kg(-1) CYA. Samples that were relatively high in MEL in this survey tended to be low in CYA, and vice versa. Concentrations of AMN and AMD were very low in all samples. The total of MEL-related compounds (sum of all four analytes) in all samples was below the interim standard of 0.5 mg kg(-1) for infant formula products established by Health Canada.

Prostate T(1) quantification using a magnetization-prepared spiral technique

PURPOSE

To adapt a magnetization-prepared spiral imaging technique, termed T1prep, for time-efficient radiofrequency (RF)-insensitive prostate T(1) quantification at 1.5 T and evaluate signal-to-noise ratio (SNR) limits to voxel-based versus subregion analysis.

MATERIALS AND METHODS

A magnetization-prepared spiral imaging technique was adapted for robust T(1) contrast development, multislice imaging within 5 minutes, and data regression to a monoexponential decay. In vitro testing evaluated RF insensitivity of the multislice acquisition plus method accuracy. A pilot study was performed in 15 patients with low or intermediate risk localized prostate cancer.

RESULTS

The multislice design displayed excellent RF insensitivity (<1% error for RF mistunings to ± 20%) and accuracy (within 3% of gold standard for T(1) values between 140 and 2100 msec). A clinical pilot study reported significantly reduced T(1) from PZ to CG to tumor subregions (PZ: 1421 ± 168 msec, n = 11; CG: 1314 ± 49 msec, n = 13; 1246 ± 68 msec, n = 8). SNR measurements identified an inappropriateness of voxel-based analysis.

CONCLUSION

T1prep can quantify prostate T(1) as an adjunct measure for quantitative perfusion measurements and longitudinal treatment response monitoring. Intrapatient heterogeneities support T(1) assessment within individual patients. SNR calculations will support a transition to voxel-based analysis in future trials.

Development of a geometrically accurate imaging protocol at 3 Tesla MRI for stereotactic radiosurgery treatment planning

The purpose of this study is to develop a geometrically accurate imaging protocol at 3 T magnetic resonance imaging (MRI) for stereotactic radiosurgery (SRS) treatment planning. In order to achieve this purpose, a methodology is developed to investigate the geometric accuracy and stability of 3 T MRI for SRS in phantom and patient evaluations. Forty patients were enrolled on a prospective clinical trial. After frame placement prior to SRS, each patient underwent 3 T MRI after 1.5 T MRI and CT. MR imaging protocols included a T1-weighted gradient echo sequence and a T2-weighted spin echo sequence. Phantom imaging was performed on 3 T prior to patient imaging using the same set-up and imaging protocols. Geometric accuracy in patients and phantoms yielded comparable results for external fiducial reference deviations and internal landmarks between 3 T and 1.5 T MRI (mean ≤ 0.6 mm; standard deviation ≤ 0.3 mm). Mean stereotactic reference deviations between phantoms and patients correlated well (T1: R = 0.79; T2: R = 0.84). Statistical process control analysis on phantom QA data demonstrated the stability of our SRS imaging protocols, where the geometric accuracy of the 3 T SRS imaging protocol is operating within the appropriate tolerance. Our data provide evidence supporting the spatial validity of 3 T MRI for targeting SRS under imaging conditions investigated. We have developed a systematic approach to achieve confidence on the geometric integrity of a given imaging system/technique for clinical integration in SRS application.