Differentiation of human prostate cancer from benign hypertrophy by in vitro 1H NMR

Potential of in vitro nuclear magnetic resonance of biofluids and tissues in clinical research

Body fluids, cells, and tissues contain a wide variety of metabolites that consist of a mixture of various low-molecular-weight compounds, including amino acids, peptides, lipids, nucleic acids, and organic acids, which makes comprehensive analysis more difficult. Quantitative nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique for analyzing the metabolic profiles of body fluids, cells, and tissues. It enables fast and comprehensive detection, characterization, a high level of experimental reproducibility, minimal sample preparation, and quantification of various endogenous metabolites. In recent times, NMR-based metabolomics has been appreciably utilized in diverse branches of medicine, including microbiology, toxicology, pathophysiology, pharmacology, nutritional intervention, and disease diagnosis/prognosis. In this review, the utility of NMR-based metabolomics in clinical studies is discussed. The significance of in vitro NMR-based metabolomics as an effective tool for detecting metabolites and their variations in different diseases are discussed, together with the possibility of identifying specific biomarkers that can contribute to early detection and diagnosis of disease.

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of 1H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of 1H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management.

Metabolism of prostate cancer by magnetic resonance spectroscopy (MRS)

Understanding the metabolism of prostate cancer (PCa) is important for developing better diagnostic approaches and also for exploring new therapeutic targets. Magnetic resonance spectroscopy (MRS) techniques have been shown to be useful in the detection and quantification of metabolites. PCa illustrates metabolic phenotype, showing lower levels of citrate (Cit), a key metabolite of oxidative phosphorylation and alteration in several metabolic pathways to sustain tumor growth. Recently, dynamic nuclear polarization (DNP) studies have documented high rates of glycolysis (Warburg phenomenon) in PCa. High-throughput metabolic profiling strategies using MRS on variety of samples including intact tissues, biofluids like prostatic fluid, seminal fluid, blood plasma/sera, and urine have also played a vital role in understanding the abnormal metabolic activity of PCa patients. The enhanced analytical potential of these techniques in the detection and quantification of a large number of metabolites provides an in-depth understanding of metabolic rewiring associated with the tumorigenesis. Metabolomics analysis offers dual advantages of identification of diagnostic and predictive biomarkers as well as in understanding the altered metabolic pathways which can be targeted for inhibiting the cancer progression. This review briefly describes the potential applications of in vivo ¹H MRS, high-resolution magic angle spinning spectroscopy (HRMAS) and in vitro MRS methods in understanding the metabolic changes of PCa and its usefulness in the management of PCa patients.

Lost in translation: lessons learned from the "demise" of MRSI of the prostate

At times, technologies fail for reasons other than an inability to deliver on their promises. The iconic Blackberry, for example, was once coined "Research in Motion", sold tens of millions of units, and then "disappeared" from the market because it did not accompany the new trends in design. Promising technologies may also "disappear" in the medical field. What follows is the tale of the rise and fall of proton magnetic resonance spectroscopic imaging (¹H MRSI) of the prostate.

Response of Degarelix treatment in human prostate cancer monitored by HR-MAS 1H NMR spectroscopy

INTRODUCTION

The androgen receptor (AR) is the master regulator of prostate cancer cell metabolism. Degarelix is a novel gonadotrophin-releasing hormone blocker, used to decrease serum androgen levels in order to treat advanced human prostate cancer. Little is known of the rapid metabolic response of the human prostate cancer tissue samples to the decreased androgen levels.

OBJECTIVES

To investigate the metabolic responses in benign and cancerous tissue samples from patients after treatment with Degarelix by using HRMAS 1H NMR spectroscopy.

METHODS

Using non-destructive HR-MAS 1H NMR spectroscopy we analysed the metabolic changes induced by decreased AR signalling in human prostate cancer tissue samples. Absolute concentrations of the metabolites alanine, lactate, glutamine, glutamate, citrate, choline compounds [t-choline = choline + phosphocholine (PC) + glycerophosphocholine (GPC)], creatine compounds [t-creatine = creatine (Cr) + phosphocreatine (PCr)], taurine, myo-inositol and polyamines were measured in benign prostate tissue samples (n = 10), in prostate cancer specimens from untreated patients (n = 7) and prostate cancer specimens from patients treated with Degarelix (n = 6).

RESULTS

Lactate, alanine and t-choline concentrations were significantly elevated in high-grade prostate cancer samples when compared to benign samples in untreated patients. Decreased androgen levels resulted in significant decreases of lactate and t-choline concentrations in human prostate cancer biopsies.

CONCLUSIONS

The reduced concentrations of lactate and t-choline metabolites due to Degarelix could in principle be monitored by in vivo 1H MRS, which suggests that it would be possible to monitor the effects of physical or chemical castration in patients by that non-invasive method.

NMR-based metabolomics of prostate cancer: a protagonist in clinical diagnostics

Advances in the application of NMR spectroscopy-based metabolomic profiling of prostate cancer comprises a potential tactic for understanding the impaired biochemical pathways arising due to a disease evolvement and progression. This technique involves qualitative and quantitative estimation of plethora of small molecular weight metabolites of body fluids or tissues using state-of-the-art chemometric methods delivering an important platform for translational research from basic to clinical, to reveal the pathophysiological snapshot in a single step. This review summarizes the present arrays and recent advancements in NMR-based metabolomics and a glimpse of currently used medical imaging tactics, with their role in clinical diagnosis of prostate cancer.

Recent Advances in Metabolic Profiling And Imaging of Prostate Cancer

Cancer is a metabolic disease. Cancer cells, being highly proliferative, show significant alterations in metabolic pathways such as glycolysis, respiration, the tricarboxylic acid (TCA) cycle, oxidative phosphorylation, lipid metabolism, and amino acid metabolism. Metabolites like peptides, nucleotides, products of glycolysis, the TCA cycle, fatty acids, and steroids can be an important read out of disease when characterized in biological samples such as tissues and body fluids like urine, serum, etc. The cancer metabolome has been studied since the 1960s by analytical techniques such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Current research is focused on the identification and validation of biomarkers in the cancer metabolome that can stratify high-risk patients and distinguish between benign and advanced metastatic forms of the disease. In this review, we discuss the current state of prostate cancer metabolomics, the biomarkers that show promise in distinguishing indolent from aggressive forms of the disease, the strengths and limitations of the analytical techniques being employed, and future applications of metabolomics in diagnostic imaging and personalized medicine of prostate cancer.

High-resolution NMR spectroscopy of human body fluids and tissues in relation to prostate cancer

High-resolution NMR spectroscopic studies of prostate tissue extracts, prostatic fluid, seminal fluid, serum and urine can be used for the detection of prostate cancer, based on the differences in their metabolic profiles. Useful diagnostic information is obtained by the detection or quantification of as many metabolites as possible and comparison with normal samples. Only a few studies have shown the potential of high-resolution in vitro NMR of prostate tissues. A survey of the literature has revealed that studies on body fluids, such as urine and serum, in relation to prostate cancer are rare. In addition, the potential of NMR of nuclei other than (1)H, such as (13)C and (31)P, has not been exploited fully. The metabolomic analysis of metabolites, detected by high-resolution NMR, may help to identify metabolites which could serve as useful biomarkers for prostate cancer detection. Such NMR-derived biomarkers would not only help in prostate cancer detection and in understanding the in vivo MRS metabolic profile, but also to investigate the biochemical and metabolic changes associated with cancer. Here, we review the published research work on body fluids in relation to prostate and prostate tissue extracts, and highlight the potential of such studies for future work.

High-resolution magic angle spinning 1H MRS in prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed malignancy in men worldwide, largely as a result of the increased use of the annual serum prostate-specific antigen (PSA) screening test for detection. PSA screening has saved lives, but it has also resulted in the overtreatment of many patients with PCa because of a limited ability to accurately localize and characterize PCa lesions through imaging. High-resolution magic angle spinning (HRMAS) (1)H MRS has proven to be a strong potential clinical tool for PCa diagnosis and prognosis. The HRMAS technique allows valuable metabolic information to be obtained from ex vivo intact tissue samples and also enables the performance of histopathology on the same tissue specimens. Studies have found that the quantification of individual metabolite levels and metabolite ratios, as well as metabolomic profiles, shows strong potential to improve accuracy in PCa detection, diagnosis and monitoring. Ex vivo HRMAS is also a valuable tool for the interpretation of in vivo results, including the localization of tumors, and thus has the potential to improve in vivo diagnostic tests used in the clinic. Here, we primarily review publications of HRMAS (1)H MRS and its use for the study of intact human prostate tissue.

Magic angle spinning NMR-based metabolic profiling of head and neck squamous cell carcinoma tissues

High-resolution magic-angle spinning (HR-MAS) proton NMR spectroscopy is used to explore the metabolic signatures of head and neck squamous cell carcinoma (HNSCC) which included matched normal adjacent tissue (NAT) and tumor originating from tongue, lip, larynx and oral cavity, and associated lymph-node metastatic (LN-Met) tissues. A total of 43 tissues (18 NAT, 18 Tumor and 7 LN-Met) from 22 HNSCC patients were analyzed. Principal Component Analysis of NMR data showed a clear classification between NAT and tumor tissues, however, LN-Met tissues were classified among tumor. A partial least-squares discriminant analysis model generated from NMR metabolic profiles was used to differentiate normal from tumor samples (Q(2) > 0.80, Receiver Operator Characteristic area under the curve >0.86, using 7-fold cross validation). HNSCC and LN-Met tissues showed elevated levels of lactate, amino acids including leucine, isoleucine, valine, alanine, glutamine, glutamate, aspartate, glycine, phenylalanine and tyrosine, choline containing compounds, creatine, taurine, glutathione, and decreased levels of triglycerides. These elevated metabolites were associated with highly active glycolysis, increased amino acids influx (anaplerosis) into the TCA cycle, altered energy metabolism, membrane choline phospholipid metabolism, and oxidative and osmotic defense mechanisms. Moreover, decreased levels of triglycerides may indicate lipolysis followed by β-oxidation of fatty acids that may exist to deliver bioenergy for rapid tumor cell proliferation and growth.

Metabolomic characterization of human prostate cancer bone metastases reveals increased levels of cholesterol

Background

Metastasis to the bone is one clinically important features of prostate cancer (PCa). Current diagnostic methods cannot predict metastatic PCa at a curable stage of the disease. Identification of metabolic pathways involved in the growth of bone metastases therefore has the potential to improve PCa prognostication as well as therapy.

Methodology/Principal Findings

Metabolomics was applied for the study of PCa bone metastases (n = 20) in comparison with corresponding normal bone (n = 14), and furthermore of malignant (n = 13) and benign (n = 17) prostate tissue and corresponding plasma samples obtained from patients with (n = 15) and without (n = 13) diagnosed metastases and from men with benign prostate disease (n = 30). This was done using gas chromatography-mass spectrometry for sample characterization, and chemometric bioinformatics for data analysis. Results were verified in a separate test set including metastatic and normal bone tissue from patients with other cancers (n = 7). Significant differences were found between PCa bone metastases, bone metastases of other cancers, and normal bone. Furthermore, we identified metabolites in primary tumor tissue and in plasma which were significantly associated with metastatic disease. Among the metabolites in PCa bone metastases especially cholesterol was noted. In a test set the mean cholesterol level in PCa bone metastases was 127.30 mg/g as compared to 81.06 and 35.85 mg/g in bone metastases of different origin and normal bone, respectively (P = 0.0002 and 0.001). Immunohistochemical staining of PCa bone metastases showed intense staining of the low density lipoprotein receptor and variable levels of the scavenger receptor class B type 1 and 3-hydroxy-3-methylglutaryl-coenzyme reductase in tumor epithelial cells, indicating possibilities for influx and de novo synthesis of cholesterol.

Conclusions/Significance

We have identified metabolites associated with PCa metastasis and specifically identified high levels of cholesterol in PCa bone metastases. Based on our findings and the previous literature, this makes cholesterol a possible therapeutic target for advanced PCa.

31P NMR of phospholipid metabolites in prostate cancer and benign prostatic hyperplasia

(1)H MRSI in vivo is increasingly being used to diagnose prostate cancer noninvasively by measurement of the resonance from choline-containing phospholipid metabolites. Although (31) P NMR in vivo or in vitro is potentially an excellent method for probing the phospholipid metabolites prominent in prostate cancer, it has been little used recently. Here, we report an in vitro (31)P NMR comparison of prostate cancer and benign prostatic hyperplasia, focusing on the levels of the major phospholipid metabolites. Unlike phosphocholine and glycerophosphocholine, phosphoethanolamine and glycerophosphoethanolamine (and their ratio) were significantly different between cancer and benign prostatic hyperplasia. The high level of phosphoethanolamine+glycerophosphoethanolamine relative to phosphocholine+glycerophosphocholine suggests that the former may be significant contributors to the "total choline" resonance observed by (1)H MRSI in vivo.

Quantitative (1) H MR spectroscopic imaging of the prostate gland using LCModel and a dedicated basis-set: correlation with histologic findings

Proton magnetic resonance spectroscopic imaging ((1) H-MRSI) has been advocated as a valuable tool for prostate cancer diagnosis. However, a barrier to widespread clinical use of this technique is the lack of robust quantification methods that yield reproducible results in an institution-independent manner. The main goal of this study was to develop a standardized and fully automated approach (LCModel-based) for quantitative prostate (1) H-MRSI. To this end, a dedicated basis set was constructed by the combination of simulated (citrate, Cit; choline, Cho, and creatine, CR) and experimentally acquired (spermine, Spm) spectra. The overlapping Spm, Cho, and Cr could be resolved and quantified individually, thus allowing for the independent assessment of glandular (Cit and Spm) and proliferative (Cho) components. Several metabolite ratios were calculated and compared to the histologic findings of prostatectomy specimens from 10 prostate cancer patients with Gleason scores (3 + 3) and (3 + 4). The Cho mole fraction and the Cho/(Cit + Spm) ratio were found to best discriminate between prostate cancer and healthy tissue. The comparison between the quantitative MRSI results and the histologic findings suggests that no correlation exists between the detected metabolic alterations and the Gleason score of low-grade tumors.

Quantitative J-resolved prostate spectroscopy using two-dimensional prior-knowledge fitting

Two-dimensional (2D) prior-knowledge fitting (ProFit) was adapted and applied for the quantification of J-resolved (JPRESS) spectra acquired at a field strength of 3T from the human prostate in vivo. In contrast to methods based on simple line fitting and peak integration, commonly applied for metabolite quantification in the prostate, ProFit yields metabolite concentration ratios that are independent of sequence and field strength, since it is based on the linear combination of 2D basis spectra. It is demonstrated that ProFit benefits from the increased information content and reduced baseline distortion in JPRESS prostate spectra, in particular for the quantification of coupled metabolites like citrate (Cit), spermine (Spm), and myo-inositol (mI). The method is validated with 10 repetitive prostate measurements on the same subject. Furthermore, a study carried out on 10 healthy subjects shows that the six prostate metabolites creatine (Cr), total choline (Cho), Cit, Spm, mI, and scyllo-inositol (sI) can be reliably detected in vivo, some of which--especially total Cho and Cit--have proven to be useful markers for the detection of prostate cancer.

Two-dimensional MR spectroscopy of healthy and cancerous prostates in vivo

OBJECTIVES

A major goal of this article is to summarize the current status of evaluating prostate metabolites non-invasively using spatially resolved two-dimensional (2D) MR Spectroscopy (MRS).

MATERIALS AND METHODS

Due to various technical challenges, the spatially resolved versions of 2D MRS techniques are currently going through the developmental stage. During the last decade, four different versions of 2D MRS sequences have been successfully implemented on 3T and 1.5T MRI scanners manufactured by three different vendors. These sequences include half and maximum echo sampled J-resolved spectroscopy (JPRESS), S-PRESS and L-COSY, which are single volume localizing sequences, and the multi-voxel based JPRESS sequence.

RESULTS

Even though greater than 1ml voxels have been used, preliminary evaluations of 2D JPRESS, S-PRESS and L-COSY sequences have demonstrated unambiguous detection of citrate, creatine, choline, spermine and more metabolites in human prostates. ProFIT-based quantitation of JPRESS and L-COSY data clearly shows the superiority of 2D MRS over conventional one-dimensional (1D) MRS and more than six metabolites have been successfully quantified. These sequences have been evaluated in a small group of prostate pathologies and pilot investigations using these sequences show promising results in prostate pathologies.

CONCLUSION

Implementation of the state-of-the-art 2D MRS techniques and preliminary evaluation in prostate pathologies are discussed in this review. Even though these techniques are going through developmental and early testing phases, it is evident that 2D MRS can be easily added on to any clinical Magnetic Resonance Imaging (MRI) protocol to non-invasively record the biochemical contents of the prostate.

[Prostate MRI spectroscopy]

MRI spectroscopy is a non invasive method for detecting active metabolites used as markers. Chorine and citrate are used for analyzing prostate cancer. MRI spectroscopy combines morphologic imaging and metabolic cartography. This combination allows a new approach for the diagnosis of prostate cancer in patients with negative biopsy and high Levels of PSA. With MRI spectroscopy the Local staging of prostate cancer has a better accuracy than with MRI alone. It can also be used for the diagnosis of residual disease and recurrence in patients treated with conservative therapy.

Proton HR-MAS spectroscopy and quantitative pathologic analysis of MRI/3D-MRSI-targeted postsurgical prostate tissues

Proton high-resolution magic angle spinning ((1)H HR-MAS) NMR spectroscopy and quantitative histopathology were performed on the same 54 MRI/3D-MRSI-targeted postsurgical prostate tissue samples. Presurgical MRI/3D-MRSI targeted healthy and malignant prostate tissues with an accuracy of 81%. Even in the presence of substantial tissue heterogeneity, distinct (1)H HR-MAS spectral patterns were observed for different benign tissue types and prostate cancer. Specifically, healthy glandular tissue was discriminated from prostate cancer based on significantly higher levels of citrate (P = 0.04) and polyamines (P = 0.01), and lower (P = 0.02) levels of the choline-containing compounds choline, phosphocholine (PC), and glycerophosphocholine (GPC). Predominantly stromal tissue lacked both citrate and polyamines, but demonstrated significantly (P = 0.01) lower levels of choline compounds than cancer. In addition, taurine, myo-inositol, and scyllo-inositol were all higher in prostate cancer vs. healthy glandular and stromal tissues. Among cancer samples, larger increases in choline, and decreases in citrate and polyamines (P = 0.05) were observed with more aggressive cancers, and a MIB-1 labeling index correlated (r = 0.62, P = 0.01) with elevated choline. The elucidation of spectral patterns associated with mixtures of different prostate tissue types and cancer grades, and the inclusion of new metabolic markers for prostate cancer may significantly improve the clinical interpretation of in vivo prostate MRSI data.

High-tech in radiation oncology: should there be a ceiling?

PURPOSE

To analyze some of the limitations to improvement of the outcome of radiotherapy (RT) expected from the introduction of sophisticated treatment planning and delivery technology.

METHODS AND MATERIALS

Several recent examples from the literature were analyzed in some detail. Mathematical modeling techniques were used to assess the likely clinical impact of new technologies or biologic principles. The findings of recent randomized controlled trials of RT for prostate, breast, and rectal cancer were analyzed from the perspective of cost-effectiveness and therapeutic gain.

RESULTS

The main findings of the analyses may be summarized as follows. Dosimetric precision should aim for a <2% patient-to-patient variability in the delivered dose. Imprecision in clinical target volume definition remains an obstacle for high-precision RT. Functional imaging and novel biologic assays may facilitate a move from a clinical target volume to the real target volume. Improved target volume coverage is mainly important if RT has high effectiveness. Radiation oncology is increasingly becoming evidence based. However, there is still a long way to go. Hypofractionation in adjuvant RT for breast cancer may represent a favorable balance between cost and benefit. Treatment complications are potentially associated with both suffering and high cost. The identification of high-risk patients would improve the cost-effectiveness of high-tech RT aimed at avoiding complications. Conformal RT may allow the introduction of hypofractionation, which, again, could potentially save resources. With improvement in surgery and more screening-detected cancer cases, the number needed to treat increases, and this will directly affect the cost-effectiveness of high-tech RT unless efficient patient selection can be developed.

CONCLUSION

Sustained technological refinement is only likely to be cost-effective if the clinical and biologic understanding of patient-to-patient variability in the risk of specific types of failure and the optimal multimodality approach to handle these risks is developed at the same time. Mathematical modeling together with methods from health technology assessment and health economics are useful complements to standard methods from evidence-based medicine. Progress in functional imaging and in basic and clinical cancer biology is likely to provide the tools required for individualized risk-adapted RT.

Transition zone prostate cancer: metabolic characteristics at 1H MR spectroscopic imaging--initial results

PURPOSE

To determine whether cancers of the prostate transition zone (TZ) possess a unique metabolic pattern by which they may be identified at proton magnetic resonance (MR) spectroscopic imaging.

MATERIALS AND METHODS

Findings in 40 patients who underwent combined endorectal MR imaging and hydrogen 1 MR spectroscopic imaging before radical prostatectomy and who had TZ tumor identified subsequently at step-section pathologic analysis were retrospectively reviewed. Within this population, a subset of 16 patients whose TZ tumor had a largest diameter of 1 cm or greater and was included in the MR spectroscopic imaging excitation volume was identified. In these 16 patients, the ratios of choline-containing compounds (Cho) and creatine/phosphocreatine (Cr) to citrate (Cit) (ie, [Cho + Cr]/Cit), Cho/Cr, and Cho/Cit were compared in tumor and control tissues. The presence of only Cho and the absence of all metabolites were also assessed.

RESULTS

The mean values of (Cho + Cr)/Cit, Cho/Cr, and Cho/Cit were different between TZ cancer and control tissues (P =.001, P =.003, and P =.001, respectively; Wilcoxon signed rank test). Nine (56%) of 16 patients had at least one tumor voxel in which Cho comprised the only detectable peak, while no control voxels showed only Cho (P =.008, McNemar test). The percentage of voxels in which no metabolites were detected did not differ between tumor and control tissues (P =.134, McNemar test).

CONCLUSION

TZ cancer has a metabolic profile that is different from that of benign TZ tissue; however, the broad range of metabolite ratios observed in TZ cancer precludes the use of a single ratio to differentiate TZ cancer from benign TZ tissue.

Combined magnetic resonance imaging and spectroscopic imaging approach to molecular imaging of prostate cancer

Magnetic resonance spectroscopic imaging (MRSI) provides a noninvasive method of detecting small molecular markers (historically the metabolites choline and citrate) within the cytosol and extracellular spaces of the prostate, and is performed in conjunction with high-resolution anatomic imaging. Recent studies in pre-prostatectomy patients have indicated that the metabolic information provided by MRSI combined with the anatomical information provided by MRI can significantly improve the assessment of cancer location and extent within the prostate, extracapsular spread, and cancer aggressiveness. Additionally, pre- and post-therapy studies have demonstrated the potential of MRI/MRSI to provide a direct measure of the presence and spatial extent of prostate cancer after therapy, a measure of the time course of response, and information concerning the mechanism of therapeutic response. In addition to detecting metabolic biomarkers of disease behavior and therapeutic response, MRI/MRSI guidance can improve tissue selection for ex vivo analysis. High-resolution magic angle spinning ((1)H HR-MAS) spectroscopy provides a full chemical analysis of MRI/MRSI-targeted tissues prior to pathologic and immunohistochemical analyses of the same tissue. Preliminary (1)H HR-MAS spectroscopy studies have already identified unique spectral patterns for healthy glandular and stromal tissues and prostate cancer, determined the composition of the composite in vivo choline peak, and identified the polyamine spermine as a new metabolic marker of prostate cancer. The addition of imaging sequences that provide other functional information within the same exam (dynamic contrast uptake imaging and diffusion-weighted imaging) have also demonstrated the potential to further increase the accuracy of prostate cancer detection and characterization.

High-resolution magic angle spinning MRS of breast cancer tissue

High-resolution magic angle spinning (HR MAS) may develop into a new diagnostic tool for studying intact tissue samples, and several types of cancer have been investigated with promising results. In this study HR MAS spectra of breast cancer tissue from 10 patients have been compared to conventional high-resolution spectra of perchloric acid extracts of the same tissue type. The HR MAS spectra show resolution comparable to spectra of extracts, and two-dimensional techniques lead to identification of a majority of the constituents. More than 30 different metabolites have been detected and assigned. To our knowledge this is the most detailed assignment of biochemical components in intact human breast tissue. The spectra of intact breast cancer tissue differ from perchloric acid extracts by the presence of lipids and fewer signals in the low field region. HR MAS analysis of intact breast tissue specimens is a rapid method, providing spectra with resolution where relative quantification of the majority of the detected metabolites is possible.

In vivo proton (H1) magnetic resonance spectroscopy for cervical carcinoma

Proton magnetic resonance spectroscopy (MRS) may be a useful tool in both the initial diagnosis of cervical carcinoma and the subsequent surveillance after radiation therapy, particularly when other standard diagnostic methods are inconclusive. Single voxel magnetic resonance (MR) spectral data were acquired from 8 normal volunteers, 16 patients with cervical cancer before radiation therapy, and 18 patients with cervical cancer after radiation therapy using an external pelvic coil at a 1.5-T on a Signa system. The presence or absence of various resonances within each spectrum was evaluated for similarities within each patient group and for spectral differences between groups. Resonances corresponding to lipid and creatine dominated the spectrum for the eight normal volunteers without detection of a choline resonance. Spectra from 16 pretreatment patients with biopsy-proven cervical cancer revealed strong resonances at a chemical shift of 3.25 ppm corresponding to choline. Data acquired from the 18 posttreatment setting studies was variable, but often correlated well with the clinical findings. Biopsy confirmation was obtained in seven patients. H1 MRS of the cervix using a noninvasive pelvic coil consistently demonstrates reproducible spectral differences between normal and neoplastic cervical tissue in vivo. However, signal is still poor for minimal disease recurrence. Further study is needed at intervals before, during, and after definitive irradiation with biopsy confirmation to validate the accuracy of MRS in distinguishing persistence or recurrence of disease from necrosis and fibrosis.

Magnetic resonance imaging and spectroscopic imaging: Improved patient selection and potential for metabolic intermediate endpoints in prostate cancer chemoprevention trials

In the design of prostate cancer chemoprevention trials there is a clear need for improved patient selection and risk stratification, as well as the use of biomarkers that could provide earlier assessment of therapeutic efficacy. Studies in preprostatectomy patients have indicated that the metabolic information provided by 3-dimensional magnetic resonance spectroscopic imaging (3D-MRSI) combined with the morphologic information provided by magnetic resonance imaging (MRI) can improve the assessment of cancer location and extent within the prostate, extracapsular spread, and cancer aggressiveness. Additionally, pre- and posttherapy studies have demonstrated the potential of MRI/3D-MRSI to provide a direct measure of the presence and spatial extent of prostate cancer after therapy, a measure of the time course of response, and information concerning the mechanism of therapeutic response. These studies suggest that the addition of MRI/3D-MRSI data to prostate-specific antigen and biopsy data may improve patient selection and risk stratification for chemoprevention trials, improve tissue sampling for ex vivo molecular marker analysis, and provide shorter-term endpoints in chemoprevention trials. However, future studies are necessary to establish the ability of MRI/3D-MRSI to accurately assess patients with premalignant or very early malignant changes, to validate metabolic markers as intermediate endpoints in chemoprevention trials, and to correlate metabolic endpoints with other promising intermediate biomarkers.

The prostate: MR imaging and spectroscopy. Present and future

The applications of combined MR imaging and MR spectroscopic imaging of prostate cancer have expanded significantly over the past 10 years and have reached the point of clinical trial results to test robustness and clinical significance. MR spectroscopic imaging extends the diagnostic evaluation of prostate cancer beyond the morphologic information provided by MR imaging throughout the detection of cellular metabolites. The combined metabolic and anatomic information provided by MR imaging and MR spectroscopic imaging has allowed a more accurate assessment of the presence, location, extent, and aggressiveness of prostate cancer both before and after treatment. This information has already demonstrated the ability to improve therapeutic planning for individual prostate cancer patients and shows great promise in the assessment of therapeutic response and the evaluation of new treatment regimes.

Three-dimensional magnetic resonance spectroscopic imaging of brain and prostate cancer

Clinical applications of magnetic resonance spectroscopic imaging (MRSI) for the study of brain and prostate cancer have expanded significantly over the past 10 years. Proton MRSI studies of the brain and prostate have demonstrated the feasibility of noninvasively assessing human cancers based on metabolite levels before and after therapy in a clinically reasonable amount of time. MRSI provides a unique biochemical "window" to study cellular metabolism noninvasively. MRSI studies have demonstrated dramatic spectral differences between normal brain tissue (low choline and high N-acetyl aspartate, NAA) and prostate (low choline and high citrate) compared to brain (low NAA, high choline) and prostate (low citrate, high choline) tumors. The presence of edema and necrosis in both the prostate and brain was reflected by a reduction of the intensity of all resonances due to reduced cell density. MRSI was able to discriminate necrosis (absence of all metabolites, except lipids and lactate) from viable normal tissue and cancer following therapy. The results of current MRSI studies also provide evidence that the magnitude of metabolic changes in regions of cancer before therapy as well as the magnitude and time course of metabolic changes after therapy can improve our understanding of cancer aggressiveness and mechanisms of therapeutic response. Clinically, combined MRI/MRSI has already demonstrated the potential for improved diagnosis, staging and treatment planning of brain and prostate cancer. Additionally, studies are under way to determine the accuracy of anatomic and metabolic parameters in providing an objective quantitative basis for assessing disease progression and response to therapy.

Human prostate: multisection proton MR spectroscopic imaging with a single spin-echo sequence--preliminary experience

The authors investigated the feasibility of a multisection proton magnetic resonance (MR) spectroscopic imaging technique for the acquisition of metabolic information in the human prostate. Multisection MR spectroscopic imaging was performed of a citrate phantom and of the prostates of eight adult volunteers. High-quality proton MR spectra and citrate metabolite maps of the prostate were obtained with this method.

In vivo proton magnetic resonance spectroscopy of diseased prostate: spectroscopic features of malignant versus benign pathology

In vivo Proton Magnetic Resonance Spectroscopy appears potentially useful for non-invasive discrimination between benign prostatic hyperplasia (BPH) and prostate carcinoma (PC). Aiming to delimit the range within which spectra from one or the other pathology should occur, and establish extreme spectroscopic features of malignant versus benign prostate disease, we performed endorectal proton MR spectroscopy on 20 patients severely affected of either benign prostatic hyperplasia (BPH) (n = 10) or prostate cancer (PC) (n = 10). They were selected on the basis of the large volume and homogeneity of their lesions, which were histologically confirmed after spectroscopy. Consequently, high-quality short-TE proton spectra with well-resolved metabolite signals, and practically free of volume averaging issues were obtained in all cases. Apart from the typical citrate, creatine, and choline signals of prostate spectra, both BPH and PC spectra showed a peak centered at 3.6 ppm which was assigned to myo-inositol. The intensity of this contribution was found significantly increased in PC cases compared to BPH. Possible relationships between neoplastic transformation and the metabolic pathways in which myo-inositol participates are discussed. Average spectroscopic profiles were calculated for both advanced pathologies, and showed obvious differentiated features. In quantitative terms, the ratio of citrate to choline peak areas as well as that of creatine to myo-inositol appeared as the most convenient to discriminate between advanced PC cases (both ratios below 1.0) and advanced BPH cases (both ratios above 1.0).

Citrate in the diagnosis of prostate cancer

BACKGROUND

One of the major current problems involved in prostate cancer (PCa) is the unavailability of sensitive, accurate, and preferably noninvasive procedures for the diagnosis of PCa. Moreover, procedures are needed which will permit the early detection, staging, location, and estimation of the volume of malignancy, and preferably a mapping of the prostate for follow-up of progression and regression of the malignancy.

METHODS

The unique citrate relationships of the prostate, coupled with recent developments and technological advancements in magnetic resonance spectroscopy (MRS) for the in situ determination of citrate levels, now provides an excellent diagnostic procedure which can achieve all these goals. There exist strong, compelling basic and clinical studies in support of the employment of 1H MRS measurements of citrate and other associated metabolites in the diagnosis of PCa.

RESULTS

This review provides the background leading to the current status of MRS citrate analysis, summarizes the data from clinical trials, and describes the applications of the procedure for the diagnosis of PCa and follow-up of patients. The use of MRS studies in defining the functional, as well as pathological relationships of the prostate, is also discussed.

CONCLUSIONS

This review is intended to be informative to the prostate- and oncology-interested community, and, hopefully, to engender much-needed interest and support in future research regarding the prostate relationships described in this report.

Influence of pulse angle variations on stimulated echo acquisition mode proton nuclear magnetic resonance spectra of AB spin systems: theory and experiments with citrate

The influence of pulse angle variations in the localization sequence stimulated echo acquisition mode (STEAM) on the signal of strongly coupled AB spin systems has been examined. Experimental 1H nuclear magnetic resonance (NMR) spectra of citrate were recorded on a 1.5 T whole-body imager. Theoretically calculated spectra were generated, with good correlation to experimental results. The dependence of the signal intensity on sequence timing and pulse angles was calculated analytically. For longer sequence timings, the ratio of the signal intensity from citrate to the signal intensity from uncoupled nuclei depends strongly on the applied flip angles. The shape of spectra also changes with varying flip angles. These effects are clearly less pronounced for STEAM than for point resolved spectroscopy (PRESS). The results have to be considered for quantitative measurements of citrate in spectroscopic investigations as, e.g. of prostate neoplasms.

In vivo differential diagnosis of prostate cancer and benign prostatic hyperplasia: localized proton magnetic resonance spectroscopy using external-body surface coil

Localized proton-stimulated echo acquisition mode (STEAM) spectroscopy was performed in seven patients with benign prostatic hyperplasia (BPH), six patients with prostate cancer, and seven healthy volunteers to determine whether citrate levels detected using a saddle-type external-body surface coil (two loops of 13 cm x 17 cm) could reliably discriminate BPH from prostatic cancer. Relative area ratios of citrate level to choline plus creatine or citrate to lipid signal were compared with postoperative pathologic histology findings. The metabolic signals were well detectable as much as the line width of water resonance was ranging from 5 to 9 hz. Average SNRs of citrate in BPH and prostate cancer were 11.4 and 1.9, respectively. The major finding was consistently lower citrate levels in prostate cancer compared with BPH and normal prostate central gland. This was significantly (p < 0.01) reflected by lower mean citrate/[creatine+choline] peak area ratio and citrate/lipid peak area ratio observed for region of cancer (0.446 +/- 0.063, 0.097 +/- 0.030) compared with BPH (1.458 +/- 0.107, 0.786 +/- 0.162) and normal central gland (1.418 +/- 0.129, 0.175 +/- 0.011), respectively. These studies demonstrate the potential of citrate spectrum detected by an external-body surface coil as an in vivo marker for discriminating prostate cancer from BPH.

Evaluating human breast ductal carcinomas with high-resolution magic-angle spinning proton magnetic resonance spectroscopy

We report the results of a study of human breast ductal carcinomas, conducted by using high resolution magic angle spinning proton magnetic resonance spectroscopy (HRMAS 1HMRS). This recently developed spectroscopic technique can measure tissue metabolism from intact pathological specimens and identify tissue biochemical changes, which closely correspond to tumor in vivo state. This procedure objectively indicates diagnostic parameters, independent of the skill and experience of the investigator, and has the potential to reduce the sampling errors inherently associated with procedures of conventional histopathology. In this study, we measured 19 cases of female ductal carcinomas. Our results demonstrate that: (1) highly resolved spectra of intact specimens of human breast ductal carcinomas can be obtained; (2) carcinoma-free tissues and carcinomas are distinguishable by alterations in the intensities and the spin-spin relaxation time T2 of cellular metabolites; and (3) tumor metabolic markers, such as phosphocholine, lactate, and lipids, may correlate with the histopathological grade determined from evaluation of the adjacent specimen. Our results suggest that biochemical markers thus measured may function as a valuable adjunct to histopathology to improve the accuracy of and reduce the time frame required for the diagnosis of human breast cancer.

Proton MRS of human prostatic fluid: correlations between citrate, spermine, and myo-inositol levels and changes with disease

BACKGROUND

This is a study of the unusual small molecular components of human prostatic fluid using a non-destructive technique.

METHODS

Single pulse high resolution proton MRS of 38 human prostatic fluid samples (12 control, 10 with benign prostatic enlargement, 4 with prostatic cancer, 11 with vasal aplasia, and one with prostatodynia). Regression models for the metabolites measured were made and compared, and correlations were analyzed.

RESULTS

A very strong correlation between the secretion of citrate and spermine (r = 0.94), two of the major components of prostatic fluid, was found. The molar ratio was 5:1 citrate: spermine. There was no difference seen between samples obtained by expression or ejaculation. The regression models suggest there is a significant difference (P < 0.02) in the citrate to spermine ratio in prostatic fluid from men with prostate cancer, with a relatively higher level of spermine.

CONCLUSIONS

The authors speculate that citrate and spermine secretion is linked and may be forming a novel complex.

Proton MR spectroscopy of the normal human prostate with an endorectal coil and a double spin-echo pulse sequence

This report describes the use of an endorectal coil and a double spin-echo pulse sequence for localized 1H MR spectroscopy of the normal prostate in volunteers. The spectra showed well-resolved signals for citrate, (phospho)choline, and creatine protons. Additional signals were assigned to taurine and myoinositol protons. J modulation of the main and outer peaks of citrate could be monitored in vivo. Apparent relaxation times T1 and T2 have been estimated for the methyl protons of cholines and creatine. An effective T1 relaxation time was estimated for the main peaks of the citrate multiplet. Ratios of the integrals of these resonances have been evaluated, and tissue contents of choline and creatine were estimated using the H2O signal as an internal reference. Spectroscopic imaging experiments revealed a lower relative citrate signal in central parts of the prostate than in peripheral parts.

Enhanced resolution of proton NMR spectra of malignant lymph nodes using magic-angle spinning

Proton NMR spectroscopy has proven useful in the detection of cancer in lymph node tissue. However, due to the high fat content of this type of tissue, 2D 1H COSY measurements (requiring acquisition times of 4-5 h or longer) are necessary to obtain the spectral information necessary for diagnosis. T2-filtered proton magic-angle spinning (MAS) NMR spectroscopy provides 1D spectra of lymph nodes in approximately 20 min with sufficient spectral resolution allowing for identification of changes in cellular chemistry due to the presence of malignant cells. MAS data from lymph nodes of five control and six rats with mammary adenocarcinoma (R13762) demonstrated increases in the signal intensity of resonances associated primarily with lactate (delta = 4.12 ppm) P < 0.0004, creatines/lysine (delta = 3.04 ppm) P < 0.0032, and glutamate/ glutamine (delta = 2.36 ppm) P < 0.0002 in metastatic compared with normal lymph nodes. The infiltration of lymph nodes by malignant cells is an important prognostic factor for many cancers. The rapid assessment of node tissue without the introduction of sampling errors (inherent in currently employed histological procedures) would allow postoperative therapy decisions to be made more efficiently.

Computer-algebra calculations and measurements on AB spin systems for double-spin-echo sequences

The time evolution of the density operator of an AB spin system during a double-spin-echo pulse sequence is evaluated analytically by a computer-algebra system. The computer-algebra system allows one to generate the extensive formulas describing the density operator and yields an expression for the integral of the spectral signals. The simulation of spectra for arbitrary sequence timings can be easily performed by this new tool without risking errors that might occur in conventional calculations. The computer-algebra method can be extended straightforward to other pulse angles and types of sequences. The double-spin-echo pulse sequence is used in the point-resolved spectroscopy (PRESS) method which is often applied for volume selective examinations in vivo. For verification of the results generated by the computer-algebra system, 1H spectra from a half-liter spherical sample with an aqueous solution that was 0.1 M in sodium citrate and 0.1 M in sodium acetate were recorded after 90 degrees-180 degrees-180 degrees double-spin-echo pulse sequences on a 1.5-T whole-body unit. The measured behavior of the citrate AB spin system corresponds very well with the theoretical predictions. Thus, the theory provides the basis for optimization of sequence timings for double-spin-echo measurements with high signal gain from AB systems as, for example, citrate. In addition, the theoretically predicted signal modulations could be fitted to the experimental data, providing the transverse relaxation time of the AB-coupled protons.

In vitro proton magnetic resonance spectroscopy of four human prostate cancer cell lines

There is accumulating evidence that some biochemical pathways observable by magnetic resonance spectroscopy, e.g., citrate acid and phospholipid metabolism, are altered in human prostate cancer. Four well-established human prostate cancer cell lines were therefore studied with magnetic resonance spectroscopy to compare differences in metabolic content with tumor biological behavior. Herein we demonstrate that, although each cell line has its own metabolic profile, relative creatine and citrate levels can be used to discriminate the androgen-dependent LNCaP cell line from the androgen-independent DU-145, TSU, and PC-3 cell lines.

Citrate as an in vivo marker to discriminate prostate cancer from benign prostatic hyperplasia and normal prostate peripheral zone: detection via localized proton spectroscopy

OBJECTIVES

This study was designed to determine whether citrate levels detected by localized 1H spectroscopy could reliably discriminate regions of prostate adenocarcinoma from surrounding regions of normal peripheral zone and benign prostatic hyperplasia (BPH).

METHODS

In 28 patients and 5 volunteers stimulated echo proton spectroscopy was used in conjunction with endorectal surface coils to obtain water-suppressed 1H spectra from regions of normal prostate peripheral zone, BPH, and prostate cancer. 1H spectra from prostate cancer patients were correlated with pathologic areas identified on T2-weighted endorectal coil magnetic resonance (MR) images and histologic study of the step-sectioned gland after surgery.

RESULTS

The major finding of in vivo studies was consistently lower citrate levels in prostate cancer compared with BPH and normal prostate peripheral zone. This was reflected by significantly (P < 0.05) lower mean citrate/(creatine plus choline) peak area ratio observed for regions of cancer (0.67 +/- 0.17) compared with BPH (1.21 +/- 0.29) and normal peripheral zone (1.46 +/- 0.28). Moreover, there was no overlap of individual cancer and normal peripheral zone citrate ratios and no significant difference between citrate ratios in regions of normal peripheral zone in young volunteers (1.28 +/- 0.14) and age-matched patients (1.46 +/- 0.28). The observed alterations in vivo citrate levels were supported by citrate concentration data obtained from extracts of histologically proven samples of normal, benign, and malignant prostatic tissues removed at surgery. In vitro citrate levels in the normal peripheral zone (30.9 +/- 8.5 mumol/g wet weight) and BPH (46.3 +/- 5.4 mumol/g wet weight) were significantly higher than those for prostate cancer (3.74 +/- 0.54 mumol/g wet weight).

CONCLUSIONS

These studies further demonstrate the potential of citrate as an in vivo marker for discriminating prostate cancer from surrounding regions of normal peripheral zone and BPH.

Bioenergetic theory of prostate malignancy

Normal and benign prostate hyperplasia (BPH) prostate is characterized by the presence of extraordinarily high levels of citrate. Presumably, this results from the inability of the prostate epithelial cells to oxidize citrate due to a limiting mitochondrial (m-) aconitase. In contrast, prostate carcinoma (CA) is not characterized by high citrate levels. Malignant prostate epithelial cells apparently undergo a metabolic transformation from citrate-producing to citrate-oxidizing cells. A consequence of citrate production in normal and BPH cells is an inefficient and low level of ATP production. It is proposed that the process of malignancy necessitates an energy production that cannot be provided by citrate-producing cells. Consequently, the transformation of prostate epithelial cells to citrate-oxidizing cells which increases the energy production capability is essential to the process of malignancy and metastasis. The metabolic transformation likely occurs as a premalignant or early malignant stage. This bioenergetic theory of prostate malignancy, if correct, will provide new approaches to the diagnosis and treatment of CA.

Magnetic resonance spectroscopy detects metabolic differences between seven Dunning rat prostate tumor sublines with different biological behavior

In this study, it was investigated whether prostate tumor biological parameters correlate with metabolic profiles. 1H and 31P magnetic resonance spectra were acquired from perchloric acid extracts of seven Dunning R-3327 prostate tumor sublines. Several metabolic ratios, for example, phosphocholine/total phosphate, choline/total creatine, and inositol/total creatine, did not correlate specifically with one biological characteristics but, based on each of these ratios, the well-differentiated, nonmetastatic, and hormone-dependent sublines could be discriminated from the poorly differentiated or anaplastic, metastatic, and hormone-independent sublines. The glycerophosphoethanolamine/total phosphate, glycerophosphocholine/total phosphate, and phosphocreatine/total phosphate ratios correlated with differentiation grade, and the differences in glycerophosphorylglycerol/total phosphate ratio between metastatic and nonmetastatic sublines was highly significant. No correlation for hormonal sensitivity with any of the metabolites measured could be found, neither by 31P nor by 1H MRS.

Characterization of human prostate cancer, benign prostatic hyperplasia and normal prostate by in vitro 1H and 31P magnetic resonance spectroscopy

In vitro 1H and 31P magnetic resonance spectra were acquired from perchloric acid extracts of human prostate tissue obtained by transurethral resection. This included tissue of patients with benign prostatic hyperplasia and prostatic adenocarcinoma; one tissue sample was obtained from a patient without any sign of BPH or malignancy. Major resonances in the magnetic resonance spectra were assigned to prostate compounds and were quantified. The citrate/lactate, citrate/total choline, phosphocholine/total creatinine, choline/total creatine, alanine/total creatine, phosphoethanolamine/total phosphate, phosphocholine/total phosphate and glycerophosphoethanolamine/total phosphate ratios were statistically different for the prostate cancer samples as compared with the BPH specimens. These observations may contribute to the understanding of in vivo magnetic resonance spectra of the prostate and indicate that magnetic resonance spectroscopy can aid in the diagnosis of prostate malignancy.

Studies of human tumors by MRS: a review

The literature describing 31P, 1H, 13C, 23Na and 19F MRS in vivo in human cancers is reviewed. Cancers have typical metabolic characteristics in 31P and 1H MRS including high levels of phospholipid metabolites and a cellular pH more alkaline than normal. These alone are not specific for cancer but are diagnostic in appropriate clinical settings. Some metabolic characteristics appear to be prognostic indices and correlation with treatment response is emerging as an important potentially cost-effective use of MRS in oncology. 19F MRS examines pharmacokinetics of 5-fluorouracil and by demonstrating its retention predicts response of a cancer to treatment. Current needs include improvement of diagnostic specificity by use of techniques like multivoxel MRS, proton decoupling of 31P, short echo time and fat-suppressed 1H MRS, 13C MRS direct or via 1H-observe, and statistical analysis of multiple spectral features. Trials in large populations in well defined clinical settings are needed to determine if MRS can provide independent prognostic indices useful in cancer management.