Breast cancer redox heterogeneity detectable with chemical exchange saturation transfer (CEST) MRI

Symmetric CEST-active lanthanide complexes for redox monitoring

Two symmetric ligands harbouring two TEMPO radicals and two functionalized acetamide arms (R = OMe (L1), CF₃ (L2)) were prepared and chelated to lanthanide ions (Eu^III, Yb^III for both L1 and L2, Dy^III for L1). Luminescence measurements on the europium complexes support the coordination of a single water molecule. The TEMPO arms are magnetically interacting in L1 (and its complexes) but not in L2. The TEMPO moieties can be reversibly oxidized into an oxoammonium (0.33-0.36 V vs. Fc⁺/Fc) or reduced into a hydroxylamine (ill-defined redox wave, reduction by ascorbate), which are both diamagnetic. The europium complexes [Eu(L1)]3+ and [Eu(L2)]3+ in their hydroxylamine form exhibit a temperature dependent CEST effect, which is maximal at 25 °C (30%) and 37 °C (12%), respectively. The CEST activity is dramatically reduced in the corresponding nitroxide forms due to the paramagnetism of the ligand. The europium complexes show no cytotoxicity against M21 cell lines over long incubation times (72 h) at high concentration (40 μM).

CEST MRI and MALDI imaging reveal metabolic alterations in the cervical lymph nodes of EAE mice

BACKGROUND

Multiple sclerosis (MS) is a neurodegenerative disease, wherein aberrant immune cells target myelin-ensheathed nerves. Conventional magnetic resonance imaging (MRI) can be performed to monitor damage to the central nervous system that results from previous inflammation; however, these imaging biomarkers are not necessarily indicative of active, progressive stages of the disease. The immune cells responsible for MS are first activated and sensitized to myelin in lymph nodes (LNs). Here, we present a new strategy for monitoring active disease activity in MS, chemical exchange saturation transfer (CEST) MRI of LNs.

METHODS AND RESULTS

We studied the potential utility of conventional (T2-weighted) and CEST MRI to monitor changes in these LNs during disease progression in an experimental autoimmune encephalomyelitis (EAE) model. We found CEST signal changes corresponded temporally with disease activity. CEST signals at the 3.2 ppm frequency during the active stage of EAE correlated significantly with the cellular (flow cytometry) and metabolic (mass spectrometry imaging) composition of the LNs, as well as immune cell infiltration into brain and spinal cord tissue. Correlating primary metabolites as identified by matrix-assisted laser desorption/ionization (MALDI) imaging included alanine, lactate, leucine, malate, and phenylalanine.

CONCLUSIONS

Taken together, we demonstrate the utility of CEST MRI signal changes in superficial cervical LNs as a complementary imaging biomarker for monitoring disease activity in MS. CEST MRI biomarkers corresponded to disease activity, correlated with immune activation (surface markers, antigen-stimulated proliferation), and correlated with LN metabolite levels.

Enzyme/GSH dual-responsive biodegradable nanohybrid for spatiotemporally specific photodynamic and hypoxia-augmented therapy against tumors

Photodynamic therapy (PDT) efficacy has been severely limited by the hypoxia in tumor microenvironment. A multitherapy modality was developed, integrating the advantages of each therapy and a nanocarrier: PDT and PDT-induced hypoxia-activated chemotherapy. Following PDT-induced hypoxia augmented in the periphery of the tumors, chemotherapy was locally activated. To this end, new indocyanine green (IR820) and a hypoxia-activated prodrug tirapazamine (TPZ) were loaded in glutathione (GSH) decomposable mesoporous organic silica nanoparticles (GMONs), tethered by hyaluronic acid (HA). This nanohybrid showed a tendency to accumulate and be retained in tumors, due to passive and active targeting. The IR820 produced singlet oxygen (¹O₂) under near-infrared (NIR) laser irradiation and concomitantly tumorous abnormality exacerbated hypoxia. TPZ-mediated hypoxia-activated chemotherapy acted to kill more tumor cells. In vivo results indicated that the tumor inhibition rate of dual-loaded nanohybrids was up to 76% under NIR laser irradiation. The immunofluorescence staining of tumor slices demonstrated that the superficial part of tumors experienced exacerbated hypoxia with laser irradiation, resulting in TPZ exerting powerful chemotherapy effects. This nanohybrid is expected to be valuable as spatiotemporally specific therapy for cancer.

Advanced Approaches to Breast Cancer Classification and Diagnosis

The International Agency for Research on Cancer (IARC) has recently reported a 66% increase in the global number of cancer deaths since 1960. In the US alone, about one in eight women is expected to develop invasive breast cancer(s) (breast cancer) at some point in their lifetime. Traditionally, a BC diagnosis includes mammography, ultrasound, and some high-end molecular bioimaging. Unfortunately, these techniques detect BC at a later stage. So early and advanced molecular diagnostic tools are still in demand. In the past decade, various histological and immuno-molecular studies have demonstrated that BC is highly heterogeneous in nature. Its growth pattern, cytological features, and expression of key biomarkers in BC cells including hormonal receptor markers can be utilized to develop advanced diagnostic and therapeutic tools. A cancer cell's progression to malignancy exhibits various vital biomarkers, many of which are still underrepresented in BC diagnosis and treatment. Advances in genetics have also enabled the development of multigene assays to detect genetic heterogeneity in BC. However, thus far, the FDA has approved only four such biomarkers-cancer antigens (CA); CA 15-3, CA 27-29, Human epidermal growth factor receptor 2 (HER2), and circulating tumor cells (CTC) in assessing BC in body fluids. An adequately structured portable-biosensor with its non-invasive and inexpensive point-of-care analysis can quickly detect such biomarkers without significantly compromising its specificity and selectivity. Such advanced techniques are likely to discriminate between BC and a healthy patient by accurately measuring the cell shape, structure, depth, intracellular and extracellular environment, and lipid membrane compositions. Presently, BC treatments include surgery and systemic chemo- and targeted radiation therapy. A biopsied sample is then subjected to various multigene assays to predict the heterogeneity and recurrence score, thus guiding a specific treatment by providing complete information on the BC subtype involved. Thus far, we have seven prognostic multigene signature tests for BC providing a risk profile that can avoid unnecessary treatments in low-risk patients. Many comparative studies on multigene analysis projected the importance of integrating clinicopathological information with genomic-imprint analysis. Current cohort studies such as MINDACT, TAILORx, Trans-aTTOM, and many more, are likely to provide positive impact on long-term patient outcome. This review offers consolidated information on currently available BC diagnosis and treatment options. It further describes advanced biomarkers for the development of state-of-the-art early screening and diagnostic technologies.

Comparison of amide proton transfer imaging and magnetization transfer imaging in revealing glioma grades and proliferative activities: a histogram analysis

PURPOSE

Comprehensive understanding glioma metabolic characters is of great help for patient management. We aimed to compare amide proton transfer imaging (APTw) and magnetization transfer imaging (MT) in predicting glioma malignancy and reflecting tumor proliferation.

METHODS

Thirty low-grade gliomas (LGGs) and 39 high-grade gliomas (HGGs) were prospectively included, of which 58 samples Ki-67 levels were quantified. Anatomical MRI, APTw, and MT were scanned, and magnetization transfer ratio (MTR) and asymmetric magnetic transfer ratio at 3.5 ppm (MTR_asym(3.5ppm)) were calculated. ROIs were semi-automatically drawn with ImageJ, from which histogram features, including 5th, 25th, 50th, mean, 70th, 90th, and 95th percentiles were extracted. The independent t test was used to test differences in LGGs and HGGs, and correlations between histogram features and tumor grades, Ki-67 were revealed by Spearman's rank or Pearson's correlation analysis.

RESULTS

The maximum correlation coefficient (R) values of APTw were 0.526 (p < 0.001) with tumor grades and 0.397 (p < 0.001) with Ki-67 at 90th percentiles, while only 5th and 25th percentiles of MT significantly correlated with tumor grades. Moreover, APTw features were significantly different in LGGs and HGGs, except 5th percentile. The most significantly different feature was 95th percentile, providing the excellent AUC of 0.808. However, the best feature in MTR was 5th percentiles with AUC of 0.703. Combing 5th and 95th of APTw achieved highest AUC Of 0.837.

CONCLUSIONS

Both APTw and MT provide quantitative information for tumor metabolite imaging. However, APTw supplys more specific information in reflecting glioma biological behaviors than MT, and well differentiates glioma malignancy.

Efficacy of Combination Neoadjuvant Chemotherapy and Regional Inductive Moderate Hyperthermia in the Treatment of Patients With Locally Advanced Breast Cancer

PURPOSE

To evaluate the efficacy of neoadjuvant chemotherapy in combination with regional inductive moderate hyperthermia for patients with locally advanced breast cancer.

PATIENTS AND METHODS

200 patients with stage IIB-IIIA breast cancer received neoadjuvant chemotherapy (control group, n = 97) or chemotherapy combined with hyperthermia (experimental group, n = 103). Inductive hyperthermia was set at 27.12 ± 0.16 MHz and the 50 W output power.

RESULTS

Thermal and color Doppler ultrasound imaging demonstrated that hyperthermia increased the surface temperature on the breasts to < 4°С while the mean values for systolic blood flow were 3.5 times as high as those prior to treatment. Assessment of tumor size and response found a (31.24 ± 3.85)% reduction in the size of the primary tumor in patients receiving chemotherapy + hyperthermia, while chemotherapy alone showed a (22.95 ± 3.61)% decrease on average (p = 0.034). The rate of objective response increased by 15.9% in the experimental group (р = 0.034) compared with the control group. The patients in the experimental group also had axillary lymph node regression of 14.17% greater than in the control group (p = 0.011). Moreover, the combination treatment allowed to increase the proportion of women eligible for breast-conserving and reconstructive surgery by 13.63% in the experimental group. The viable tumor volume was lower in patients receiving neoadjuvant chemotherapy + hyperthermia (24.4 ± 0.2)% compared with those given chemotherapy alone (30.4 ± 0.25)%. The 10-year overall survival rates were higher (log-rank: p = 0.009) in breast cancer patients who underwent chemotherapy combined with hyperthermia than in patients receiving chemotherapy only.

CONCLUSION

The combination neoadjuvant chemotherapy and the technology of regional inductive moderate hyperthermia improved the efficacy of treatment for patients with locally advanced breast cancer staged IIB-IIIA.

Evaluation of B0-correction of relative CBF maps using tagging distance dependent Z-spectrum (TADDZ)

Arterial spin labeling (ASL) MRI, based on endogenous contrast from blood water, is used in research and diagnosis of cerebral vascular conditions. However, artifacts due to imperfect imaging conditions such as B₀-inhomogeneity (ΔB₀) could lead to variations in the quantification of relative cerebral blood flow (CBF). In this study, we evaluate a new approach using tagging distance dependent Z-spectrum (TADDZ) data, similar to the ΔB₀ corrections in the chemical exchange saturation transfer (CEST) experiments, to remove the imaging plane B₀ inhomogeneity induced CBF artifacts in ASL MRI. Our results indicate that imaging-plane B₀-inhomogeneity can lead to variations and errors in the relative CBF maps especially under small tagging distances. Along with an acquired B₀ map, TADDZ data helps to eliminate B₀-inhomogeneity induced artifacts in the resulting relative CBF maps. We demonstrated the effective use of TADDZ data to reduce variation while subjected to systematic changes in ΔB₀. In addition, TADDZ corrected ASL MRI, with improved consistency, was shown to outperform conventional ASL MRI by differentiating the subtle CBF difference in Alzheimer's disease (AD) mice brains with different APOE genotypes.

Emerging Technologies to Image Tissue Metabolism

Due to the implication of altered metabolism in a large spectrum of tissue function and disease, assessment of metabolic processes becomes essential in managing health. In this regard, imaging can play a critical role in allowing observation of biochemical and physiological processes. Nuclear imaging methods, in particular positron emission tomography, have been widely employed for imaging metabolism but are mainly limited by the use of ionizing radiation and the sensing of only one parameter at each scanning session. Observations in healthy individuals or longitudinal studies of disease could markedly benefit from non-ionizing, multi-parameter imaging methods. We therefore focus this review on progress with the non-ionizing radiation methods of MRI, hyperpolarized magnetic resonance and magnetic resonance spectroscopy, chemical exchange saturation transfer, and emerging optoacoustic (photoacoustic) imaging. We also briefly discuss the role of nuclear and optical imaging methods for research and clinical protocols.

CEST MRI of sepsis-induced acute kidney injury

Sepsis-induced acute kidney injury (SAKI) is a major complication of kidney disease associated with increased mortality and faster progression. Therefore, the development of imaging biomarkers to detect septic AKI is of great clinical interest. In this study, we aimed to characterize the endogenous chemical exchange saturation transfer (CEST) MRI contrast in the lipopolysaccharide (LPS)-induced SAKI mouse model and to investigate the use of CEST MRI for detecting such injury. We used a SAKI mouse model that was generated by i.p. injection of 10 mg/kg LPS. The resulting kidney injury was confirmed by the elevation of serum creatinine and histology. MRI assessments were performed 24 h after LPS injection, including CEST MRI at different B₁ strengths (1, 1.8 and 3 μT), T₁ mapping, T₂ mapping and conventional magnetization transfer contrast (MTC) MRI. The CEST MRI results were analyzed using Z-spectra, in which the normalized water signal saturation (S_sat /S₀ ) is measured as a function of saturation frequency. Substantial decreases in CEST contrast were observed at both 3.5 and - 3.5 ppm frequency offset from water at all B₁ powers, with the most significant difference obtained at a B₁ of 1.8 μT. The average S_sat /S₀ differences between injured and normal kidneys were 0.07 (0.55 ± 0.04 versus 0.62 ± 0.04, P = 0.0028) and 0.07 (0.50 ± 0.04 versus 0.57 ± 0.03, P = 0.0008) for 3.5 and - 3.5 ppm, respectively. In contrast, the T₁ and T₂ relaxation times and MTC contrast in the injured kidneys did not show a significant change compared with the normal control. Our results showed that CEST MRI is more sensitive to the pathological changes in injured kidneys than the changes in T₁ , T₂ and MTC effect, indicating its potential clinical utility for molecular imaging of renal diseases.

Light-Activated Core-Shell Nanoparticles for Spatiotemporally Specific Treatment of Metastatic Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) tumors are heterogeneous, with mesenchymal-like cells at their core and fast proliferating cells on the periphery. It is desirable and beneficial to treat TNBC cells of different phenotypes with the most appropriate drugs. Here, we report a 78 nm, chlorin e6-, docetaxel-, and anti-Twist siRNA-containing polymeric nanoparticle (CDTN) with spatiotemporally specific activity when irradiated by light. Under conditions mimicking superficial tumor tissue with sufficient light input, TNBC cells are mainly killed by the photodynamic therapy (PDT) function of CDTNs. In contrast, under conditions mimicking deep tumor tissue with weak light input, PDT potentiates chemotherapy (CT) and gene therapy (GT) by facilitating the endolysosomal escape of CDTNs. Compared with free drugs, CDTNs improve the intratumoral exposure of docetaxel and anti-Twist siRNA by 2.5- and 2-fold, respectively. When combined with laser irradiation applied at the time of maximal intratumoral accumulation, the CDTNs significantly inhibit the growth of primary tumors and their lung metastasis (both >80%) by killing the peripheral cells, mainly through PDT and prohibiting the growth and metastasis of deep cells through PDT as enhanced CT and GT. On the contrary, dual-modality nanomedicine lacking CT, GT, or PDT showed fast primary tumor growth, poor metastasis control, or both, respectively. This study reveals the spatiotemporally specific mechanism of CDTNs in treating metastatic TNBC and highlights the importance of combined therapy in treating TNBC.

Quantitative evaluation of redox ratio and collagen characteristics during breast cancer chemotherapy using two-photon intrinsic imaging

Preoperative neoadjuvant treatment in locally advanced breast cancer is recognized as an effective adjuvant therapy, as it improves treatment outcomes. However, the potential complications remain a threat, so there is an urgent clinical need to assess both the tumor response and changes in its microenvironment using non-invasive and precise identification techniques. Here, two-photon microscopy was employed to detect morphological alterations in breast cancer progression and recession throughout chemotherapy. The changes in structure were analyzed based on the autofluorescence and collagen of differing statuses. Parameters, including optical redox ratio, the ratio of second harmonic generation and auto-fluorescence signal, collagen density, and collagen shape orientation, were studied. Results indicate that these parameters are potential indicators for evaluating breast tumors and their microenvironment changes during progression and chemotherapy. Combined analyses of these parameters could provide a quantitative, novel method for monitoring tumor therapy.

Creatine CEST MRI for Differentiating Gliomas with Different Degrees of Aggressiveness

PURPOSE

Creatine (Cr) is a major metabolite in the bioenergetic system. Measurement of Cr using conventional MR spectroscopy (MRS) suffers from low spatial resolution and relatively long acquisition times. Creatine chemical exchange saturation transfer (CrCEST) magnetic resonance imaging (MRI) is an emerging molecular imaging method for tissue Cr measurements. Our previous study showed that the CrCEST contrast, obtained through multicomponent Z-spectral fitting, was lower in tumors compared to normal brain, which further reduced with tumor progression. The current study was aimed to investigate if CrCEST MRI can also be useful for differentiating gliomas with different degrees of aggressiveness.

PROCEDURES

Intracranial 9L gliosarcoma and F98 glioma bearing rats with matched tumor size were scanned with a 9.4 T MRI scanner at two time points. CEST Z-spectra were collected using a customized sequence with a frequency-selective rectangular saturation pulse (B1 = 50 Hz, duration = 3 s) followed by a single-shot readout. Z spectral data were fitted pixel-wise with five Lorentzian functions, and maps of CrCEST peak amplitude, linewidth, and integral were produced. For comparison, single-voxel proton MR spectroscopy (1H-MRS) was performed to quantify and compare the total Cr concentration in the tumor.

RESULTS

CrCEST contrasts decreased with tumor progression from weeks 3 to 4 in both 9L and F98 phenotypes. More importantly, F98 tumors had significantly lower CrCEST integral compared to 9L tumors. On the other hand, integrals of other Z-spectral components were unable to differentiate both tumor progression and phenotype with limited sample size.

CONCLUSIONS

Given that F98 is a more aggressive tumor than 9L, this study suggests that CrCEST MRI may help differentiate gliomas with different aggressiveness.

Optical redox imaging indices discriminate human breast cancer from normal tissues

Our long-term goal was to investigate the potential of incorporating redox imaging technique as a breast cancer (BC) diagnosis component to increase the positive predictive value of suspicious imaging finding and to reduce unnecessary biopsies and overdiagnosis. We previously found that precancer and cancer tissues in animal models displayed abnormal mitochondrial redox state. We also revealed abnormal mitochondrial redox state in cancerous specimens from three BC patients. Here, we extend our study to include biopsies of 16 patients. Tissue aliquots were collected from both apparently normal and cancerous tissues from the affected cancer-bearing breasts shortly after surgical resection. All specimens were snap-frozen and scanned with the Chance redox scanner, i.e., the three-dimensional cryogenic NADH/Fp (reduced nicotinamide adenine dinucleotide/oxidized flavoproteins) fluorescence imager. We found both Fp and NADH in the cancerous tissues roughly tripled that in the normal tissues ( p < 0.05 ). The redox ratio Fp/(NADH + Fp) was ? 27 % higher in the cancerous tissues ( p < 0.05 ). Additionally, Fp, or NADH, or the redox ratio alone could predict cancer with reasonable sensitivity and specificity. Our findings suggest that the optical redox imaging technique can provide parameters independent of clinical factors for discriminating cancer from noncancer breast tissues in human patients.

Progress in the clinical detection of heterogeneity in breast cancer

Breast cancer is currently the most common form of cancer and the second‐leading cause of death from cancer in women. Though considerable progress has been made in the treatment of breast cancer, the heterogeneity of tumors (both inter‐ and intratumor) remains a considerable diagnostic and prognostic challenge. From clinical observation to genetic mutations, the history of understanding the heterogeneity of breast cancer is lengthy and detailed. Effectively detecting heterogeneity in breast cancer is important during treatment. Various methods of depicting this heterogeneity are now available and include genetic, pathologic, and imaging analysis. These methods allow characterization of the heterogeneity of breast cancer on a genetic level, providing greater insight during the process of establishing an effective therapeutic plan. This study reviews how the understanding of tumor heterogeneity in breast cancer evolved, and further summarizes recent advances in the detection and monitoring of this heterogeneity in patients with breast cancer.

QUESPOWR MRI: QUantification of Exchange as a function of Saturation Power On the Water Resonance

QUantification of Exchange as a function of Saturation Power On the Water Resonance (QUESPOWR) MRI is a new method that can estimate chemical exchange rates. This method acquires a series of OPARACHEE MRI acquisitions with a range of RF powers for the WALTZ16(∗) pulse train, which are applied on the water resonance. A QUESPOWR plot can be generated from the power dependence of the % water signal, which is similar to a QUESP plot that is generated from CEST MRI acquisition methods with RF saturation applied off-resonance from water. A QUESPOWR plot can be quantitatively analyzed using linear fitting methods to provide estimates of average chemical exchange rates. Analyses of the shapes of QUESPOWR plots can also be used to estimate relative differences in average chemical exchange rates and concentrations of biomolecules. The performance of QUESPOWR MRI was assessed via simulations, an in vitro study with iopamidol, and an in vivo study with a mouse model of mammary carcinoma. The results showed that QUESPOWR MRI is especially sensitive to chemical exchange between water and biomolecules that have intermediate to fast chemical exchange rates and chemical shifts that are close to water, which are notoriously difficult to assess with other CEST MRI methods. In addition, in vivo QUESPOWR MRI detected acidic tumor tissues relative to normal tissues that are pH-neutral, and therefore may be a new paradigm for tumor detection with MRI.

CEST-MRI detects metabolite levels altered by breast cancer cell aggressiveness and chemotherapy response

Chemical exchange saturation transfer (CEST) is an MRI contrast mechanism that detects the exchange of protons from distinct hydroxyl, amine, and amide groups to tissue water through the transfer of signal loss, with repeated exchange enhancing their effective signal. We applied CEST to detect systematically 15 common cellular metabolites in a panel of differentially aggressive human breast cancer cell lines. The highest CEST contrast was generated by creatine, myo-inositol, glutamate, and glycerophosphocholine, whose cellular concentrations decreased with increasing breast cancer aggressiveness. These decreased metabolite concentrations resulted in turn in a decreased CEST profile with increasing breast cancer aggressiveness in water-soluble extracts of breast cell lines. Treatment of both breast cancer cell lines with the chemotherapy drug doxorubicin resulted in increased metabolic CEST profiles, which correlated with significant increases in creatine, phosphocreatine, and glycerophosphocholine. CEST can detect breast cancer aggressiveness and response to chemotherapy in water-soluble extracts of breast cell lines. The presented results help shed light on possible contributions from CEST-active metabolites to the CEST contrast produced by breast cancers. The metabolic CEST profile may improve detection sensitivity over conventional MRS, and may have the potential to assess breast cancer aggressiveness and response to chemotherapy non-invasively using MRI if specialized metabolic CEST profile detection can be realized in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Assessment of the Tumor Redox Status in Head and Neck Cancer by 62Cu-ATSM PET

Purpose

Tumor redox is an important factor for cancer progression, resistance to treatments, and a poor prognosis. The aim of the present study was to define tumor redox (over-reduction) using ⁶²Cu-diacetyl-bis(N⁴-methylthiosemicarbazone) (⁶²Cu-ATSM) PET and compare its prognostic potential in head and neck cancer (HNC) with that of 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG).

Methods

Thirty HNC patients (stage II–IV) underwent pretreatment ⁶²Cu-ATSM and ¹⁸F-FDG PET scans. Maximum standardized uptake values (SUV_ATSM and SUV_FDG) and tumor-to-muscle activity concentration ratios (TMR_ATSM and TMR_FDG) were measured. Reductive-tumor-volume (RTV) was then determined at four thresholds (40%, 50%, 60%, and 70% SUV_ATSM), and total-lesion-reduction (TLR) was calculated as the product of the mean SUV and RTV for ⁶²Cu-ATSM. In ¹⁸F-FDG, metabolic-tumor-volume (MTV) and total-lesion-glycolysis (TLG) were obtained at a threshold of 40%. A ROC analysis was performed to determine % thresholds for RTV and TLR showing the best predictive performance, and these were then used to determine the optimal cut-off values to stratify patients for each parameter. Progression-free-survival (PFS) and cause-specific-survival (CSS) were evaluated by the Kaplan-Meier method.

Results

The means ± standard deviations of PFS and CSS periods were 16.4±13.4 and 19.2±12.4 months, respectively. A ROC analysis determined that the 70% SUV_ATSM threshold for RTV and TLR was the best for predicting disease progression and cancer death. Optimal cut-offs for each index were SUV_ATSM = 3.6, SUV_FDG = 7.9, TMR_ATSM = 3.2, TMR_FDG = 5.6, RTV = 2.9, MTV = 8.1, TLR = 14.0, and TLG = 36.5. When the cut-offs for TMR_ATSM and TLR were set as described above in ⁶²Cu-ATSM PET, patients with higher TMR_ATSM (p = 0.03) and greater TLR (p = 0.02) showed significantly worse PFS, while patients with greater TLR had significantly worse CSS (p = 0.02). Only MTV in ¹⁸F-FDG PET predicted differences in PSF and CSS (p = 0.03 and p = 0.03, respectively).

Conclusion

Tumor redox parameters measured by ⁶²Cu-ATSM PET may be determinants of HNC patient outcomes and help define optimal patient-specific treatments.

Imaging metabolic heterogeneity in cancer

As our knowledge of cancer metabolism has increased, it has become apparent that cancer metabolic processes are extremely heterogeneous. The reasons behind this heterogeneity include genetic diversity, the existence of multiple and redundant metabolic pathways, altered microenvironmental conditions, and so on. As a result, methods in the clinic and beyond have been developed in order to image and study tumor metabolism in the in vivo and in vitro regimes. Both regimes provide unique advantages and challenges, and may be used to provide a picture of tumor metabolic heterogeneity that is spatially and temporally comprehensive. Taken together, these methods may hold the key to appropriate cancer diagnoses and treatments in the future.

Magnetization Transfer MRI Contrast May Correlate with Tissue Redox State in Prostate Cancer

Developing imaging biomarkers for non-invasive measurement of the tissue redox state is a key research area. Recently, we presented the first non-invasive MR imaging method that demonstrated the correlation between the endogenous chemical exchange saturation transfer (CEST) contrast and the tissue redox state. It is well known that the broadband magnetization transfer (MT) can occur via chemical exchange (CEST) and/or dipole-dipole interactions. The present study investigated if the broadband MT also correlated with the tissue redox state. The preliminary result for the prostate tumor xenografts indeed showed a significant correlation between the broadband MT contrast and the NADH redox ratio quantified with the optical redox scanning. In vivo MT contrast, once calibrated, may potentially serve as an imaging biomarker for tissue redox state.

Molecular magnetic resonance imaging in cancer

The ability to identify key biomolecules and molecular changes associated with cancer malignancy and the capacity to monitor the therapeutic outcome against these targets is critically important for cancer treatment. Recent developments in molecular imaging based on magnetic resonance (MR) techniques have provided researchers and clinicians with new tools to improve most facets of cancer care. Molecular imaging is broadly described as imaging techniques used to detect molecular signature at the cellular and gene expression levels. This article reviews both established and emerging molecular MR techniques in oncology and discusses the potential of these techniques in improving the clinical cancer care. It also discusses how molecular MR, in conjunction with other structural and functional MR imaging techniques, paves the way for developing tailored treatment strategies to enhance cancer care.

Highly accelerated chemical exchange saturation transfer (CEST) measurements with linear algebraic modeling

PURPOSE

In clinical studies, compartmental average chemical exchange saturation transfer (CEST) measurements rather than voxel-by-voxel CEST images may suffice for evaluating its diagnostic value. A recently developed method-spectroscopy with linear algebraic modeling, or SLAM-could directly provide compartmental measures with dramatically reduced scan time and optimal signal-to-noise ratios. Here, we test whether SLAM can be adapted to significantly accelerate CEST acquisitions.

THEORY AND METHODS

Conventional anatomical images and raw CEST image k-space data were acquired from seven brain tumor patients. SLAM was applied to the CEST data using acceleration factors of R = 1-45, after segmenting compartments from co-registered images. SLAM-CEST measures were compared with average values from the identical compartments obtained by conventional Fourier transform (FT) CEST.

RESULTS

SLAM generated compartmental average CEST z-spectra that were indistinguishable from conventional FT-CEST for R ≤ 45. SLAM-CEST z-spectra at ±3.5 ppm were highly correlated with FT-CEST measures (r(2)  ≥ 0.98 for R ≤ 9; r ≥ 0.995 for R ≤ 45). The average error of SLAM-CEST versus FT-CEST measures was ≤10% for R ≤ 45, in acquisitions requiring as few as a single k-space phase-encoding step.

CONCLUSION

Applied to patients with brain tumors, SLAM-CEST can yield results that are quantitatively equivalent to conventional CEST up to 45 times faster, which could prove enabling in clinical settings where scan time is limiting. Magn Reson Med 76:136-144, 2016. © 2015 Wiley Periodicals, Inc.

Assessment of lymphatic impairment and interstitial protein accumulation in patients with breast cancer treatment-related lymphedema using CEST MRI

PURPOSE

Lymphatic impairment is known to reduce quality of life in some of the most crippling diseases of the 21st century, including obesity, lymphedema, and cancer. However, the lymphatics are not nearly as well-understood as other bodily systems, largely owing to a lack of sensitive imaging technologies that can be applied using standard clinical equipment. Here, proton exchange-weighted MRI is translated to the lymphatics in patients with breast cancer treatment-related lymphedema (BCRL).

METHODS

Healthy volunteers (N = 8) and BCRL patients (N = 7) were scanned at 3 Tesla using customized structural MRI and amide proton transfer (APT) chemical exchange saturation transfer (CEST) MRI in sequence with the hypothesis that APT effects would be elevated in lymphedematous tissue. APT contrast, lymphedema stage, symptomatology, and histology information were evaluated.

RESULTS

No significant difference between proton-weighted APT contrast in the right and left arms of healthy controls was observed. An increase in APT contrast in the affected arms of patients was found (P = 0.025; Cohen's d = 2.4), and variability among patients was consistent with documented damage to lymphatics as quantified by lymphedema stage.

CONCLUSION

APT CEST MRI may have relevance for evaluating lymphatic impairment in patients with BCRL, and may extend to other pathologies where lymphatic compromise is evident.

CEST signal at 2ppm (CEST@2ppm) from Z-spectral fitting correlates with creatine distribution in brain tumor

In general, multiple components such as water direct saturation, magnetization transfer (MT), chemical exchange saturation transfer (CEST) and aliphatic nuclear Overhauser effect (NOE) contribute to the Z-spectrum. The conventional CEST quantification method based on asymmetrical analysis may lead to quantification errors due to the semi-solid MT asymmetry and the aliphatic NOE located on a single side of the Z-spectrum. Fitting individual contributors to the Z-spectrum may improve the quantification of each component. In this study, we aim to characterize the multiple exchangeable components from an intracranial tumor model using a simplified Z-spectral fitting method. In this method, the Z-spectrum acquired at low saturation RF amplitude (50 Hz) was modeled as the summation of five Lorentzian functions that correspond to NOE, MT effect, bulk water, amide proton transfer (APT) effect and a CEST peak located at +2 ppm, called CEST@2ppm. With the pixel-wise fitting, the regional variations of these five components in the brain tumor and the normal brain tissue were quantified and summarized. Increased APT effect, decreased NOE and reduced CEST@2ppm were observed in the brain tumor compared with the normal brain tissue. Additionally, CEST@2ppm decreased with tumor progression. CEST@2ppm was found to correlate with the creatine concentration quantified with proton MRS. Based on the correlation curve, the creatine contribution to CEST@2ppm was quantified. The CEST@2ppm signal could be a novel imaging surrogate for in vivo creatine, the important bioenergetics marker. Given its noninvasive nature, this CEST MRI method may have broad applications in cancer bioenergetics.