Topiramate induces acute intracellular acidification in glioblastoma

Intracellular Acidification in a Rat C6 Glioma Model following Cariporide Injection Investigated by CEST-MRI

Acidification of cancerous tissue induced pharmacologically may slow tumor growth and can be detected using magnetic resonance imaging. Numerous studies have shown that pharmacologically inhibiting specific transporters, such as the Na⁺/H⁺ exchanger 1 (NHE1), can alter glycolitic metabolism and affect tumor acidosis. The sodium proton exchanger inhibitor Cariporide can acidify U87MG gliomas in mice. This study aimed to determine whether Cariporide could acidify C6 glioma tumors in rats with an intact immune system. C6 glioma cells were implanted in the right brain hemisphere of ten rats. Chemical exchange saturation transfer (CEST) MRI (9.4T) was acquired on days 7-8 and 14-15 after implantation to measure in vivo tissue intracellular pH (pH_i) within the tumors and on the contralateral side. pH_i was basic relative to contralateral tissue at both time points assessed using the amine and amide concentration-independent detection (AACID) value. On day 14-15, measurements were made before and up to 160 min after Cariporide injection (N = 6). Twenty minutes after drug injection, the average AACID value in the tumor significantly increased by ∼6.4% compared to pre-injection, corresponding to 0.31 ± 0.20 lower pH_i, while in contralateral tissue, AACID value increased significantly by ∼4.3% compared to pre-injection, corresponding to 0.22 ± 0.19 lower pH_i. Control rats without tumors showed no changes following injection of Cariporide dissolved in 10% or 1% DMSO and diluted in PBS. This study demonstrates the sensitivity of CEST-based pH-weighted imaging for monitoring the response of tumors to pharmacologically induced acidification.

Chemical Exchange Saturation Transfer for Pancreatic Ductal Adenocarcinoma Evaluation

OBJECTIVES

The aims of the study are to evaluate the feasibility of using pH-sensitive magnetic resonance imaging, chemical exchange saturation transfer (CEST) in pancreatic imaging and to differentiate pancreatic ductal adenocarcinoma (PDAC) with the nontumor pancreas (upstream and downstream) and normal control pancreas.

METHODS

Sixteen CEST images with PDAC and 12 CEST images with normal volunteers were acquired and magnetization transfer ratio with asymmetric analysis were measured in areas of PDAC, upstream, downstream, and normal control pancreas. One-way analysis of variance and receiver operating characteristic curve were used to differentiate tumor from nontumor pancreas.

RESULTS

Areas with PDAC showed higher signal intensity than upstream and downstream on CEST images. The mean (standard deviation) values of magnetization transfer ratio with asymmetric analysis were 0.015 (0.034), -0.044 (0.030), -0.019 (0.027), and -0.037 (0.031), respectively, in PDAC area, upstream, downstream, and nontumor area in patient group and -0.008 (0.024) in normal pancreas. Significant differences were found between PDAC and upstream ( P < 0.001), between upstream and normal pancreas ( P = 0.04). Area under curve is 0.857 in differentiating PDAC with nontumor pancreas.

CONCLUSIONS

pH-sensitive CEST MRI is feasible in pancreatic imaging and can be used to differentiate PDAC from nontumor pancreas. This provides a novel metabolic imaging method in PDAC.

Ion Channel Drugs Suppress Cancer Phenotype in NG108-15 and U87 Cells: Toward Novel Electroceuticals for Glioblastoma

Glioblastoma is a lethal brain cancer that commonly recurs after tumor resection and chemotherapy treatment. Depolarized resting membrane potentials and an acidic intertumoral extracellular pH have been associated with a proliferative state and drug resistance, suggesting that forced hyperpolarization and disruption of proton pumps in the plasma membrane could be a successful strategy for targeting glioblastoma overgrowth. We screened 47 compounds and compound combinations, most of which were ion-modulating, at different concentrations in the NG108-15 rodent neuroblastoma/glioma cell line. A subset of these were tested in the U87 human glioblastoma cell line. A FUCCI cell cycle reporter was stably integrated into both cell lines to monitor proliferation and cell cycle response. Immunocytochemistry, electrophysiology, and a panel of physiological dyes reporting voltage, calcium, and pH were used to characterize responses. The most effective treatments on proliferation in U87 cells were combinations of NS1643 and pantoprazole; retigabine and pantoprazole; and pantoprazole or NS1643 with temozolomide. Marker analysis and physiological dye signatures suggest that exposure to bioelectric drugs significantly reduces proliferation, makes the cells senescent, and promotes differentiation. These results, along with the observed low toxicity in human neurons, show the high efficacy of electroceuticals utilizing combinations of repurposed FDA approved drugs.

Brain pH Measurement Using AACID CEST MRI Incorporating the 2 ppm Amine Resonance

Many pathological conditions lead to altered intracellular pH (pH_i) disrupting normal cellular functions. The chemical exchange saturation transfer (CEST) method, known as Amine and Amide Concentration Independent Detection (AACID), can produce image contrast that is predominantly dependent on tissue intracellular pH_i. The AACID value is linearly related to the ratio of the 3.5 ppm amide CEST effect and the 2.75 ppm amine CEST effect in the physiological range. However, the amine CEST effect at 2 ppm is often more clearly defined in vivo, and may provide greater sensitivity to pH changes. The purpose of the current study was to compare AACID measurement precision utilizing the 2.0 and 2.75 ppm amine CEST effects. We hypothesized that the 2.0 ppm amine CEST resonance would produce measurements with greater sensitivity to pH changes. In the current study, we compare the range of the AACID values obtained in 24 mice with brain tumors and in normal tissue using the 2 ppm and 2.75 ppm amine resonances. All CEST data were acquired on a 9.4T MRI scanner. The AACID measurement range increased by 39% when using the 2 ppm amine resonance compared to the 2.75 ppm resonance, with decreased measurement variability across the brain. These data indicate that in vivo pH measurements made using AACID CEST can be enhanced by incorporating the 2 ppm amine resonance. This approach should be considered for pH measurements made over short intervals when no changes are expected in the concentration of metabolites that contribute to the 2 ppm amine resonance.

Tracing of intracellular pH in cancer cells in response to Taxol treatment

Genetically encoded pH-sensors are the promising instrument for intracellular pH (pHi) registration. In tumor tissue the reversed pH gradient is known to be the important hallmark of cancer and regulator of tumor response on chemotherapy. However the effect of chemotherapeutic drugs on the pHi of tumor cells is largely unknown. Here we using genetically encoded ratiometric pH-sensor SypHer2 were able to monitor pHi in vitro in cell monolayer and tumor spheroids and in vivo in tumor xenografts. In tumor cell monolayer different pHi dynamic was revealed in the dying cell and division-arrested surviving cells. The treatment effect of taxol varied in monolayer and tumor spheroids and pHi changes were able to reflect these difference. The tend to pHi decrease in respect to taxol in vivo matched with results obtained for the cell monolayer. Also in both cases the cell cycle-arrest was the main treatment effect in contrast to tumor spheroid, where the cell death was the primary result. These findings elucidate the significance of pHi in the mechanisms of taxol action on cervical cancer cells and will be valuable for development of new approaches for cancer treatment.

The Ph paradigm in cancer

Malignant tissues show a peculiar feature regarding pH: while normal tissues have a higher extracellular pH than intracellular pH, in cancer is exactly the opposite. This phenomenon is called the inversion of the pH gradient and is now considered a hallmark of malignancy. For some time, this inverted pH gradient was believed to be a secondary effect of cancer. Now, it is becoming clear that pH inversion is not an innocent consequence, but a key player in the etiopathogenesis of cancer. Therefore, addressing this issue as part of an integral treatment of neoplasia should be a necessary step for improving cancer patients' outcomes. However, the knowledge acquired in this regard through basic research has not reached bedside treatments. The most striking fact is that there are repurposed drugs and nutraceuticals with low or no toxicity that can modify the pH gradient inversion. However, these drugs have not even been tested in cancer treatment.

Adding high-dose celecoxib to increase effectiveness of standard glioblastoma chemoirradiation

Over one hundred clinical trials since 2005 have failed to significantly improve the prognosis of glioblastoma. Since 2005, the standard of care has been maximal resection followed by 60Gy irradiation over six weeks with daily temozolomide. With this, a median survival of 2 years can be expected. This short paper reviewed how the pharmacodynamic attributes of an EMA/FDA approved, cheap, generic drug to treat pain, celecoxib, intersect with pathophysiological elements driving glioblastoma growth, such that growth drive inhibition can be expected from celecoxib. The two main attributes of celecoxib are carbonic anhydrase inhibition and cyclooxygenase-2 inhibition. Both attributes individually have been in active study as adjuncts during current cancer treatment, including that of glioblastoma. That research is briefly reviewed here. This paper concludes from the collected data, that starting celecoxib, 600 to 800mg twice daily before surgery and continuing it through the chemoirradiation phase of treatment would be a low-risk intervention with sound rationale.

Optical and magnetic resonance imaging approaches for investigating the tumour microenvironment: state-of-the-art review and future trends

The tumour microenvironment (TME) strongly influences tumorigenesis and metastasis. Two of the most characterized properties of the TME are acidosis and hypoxia, both of which are considered hallmarks of tumours as well as critical factors in response to anticancer treatments. Currently, various imaging approaches exist to measure acidosis and hypoxia in the TME, including magnetic resonance imaging (MRI), positron emission tomography and optical imaging. In this review, we will focus on the latest fluorescent-based methods for optical sensing of cell metabolism and MRI as diagnostic imaging tools applied both in vitro and in vivo. The primary emphasis will be on describing the current and future uses of systems that can measure intra- and extra-cellular pH and oxygen changes at high spatial and temporal resolution. In addition, the suitability of these approaches for mapping tumour heterogeneity, and assessing response or failure to therapeutics will also be covered.

Brain pH Imaging and its Applications

Acid-base homeostasis and pH regulation are critical for normal tissue metabolism and physiology, and brain tissue pH alters in many diseased states. Several noninvasive tissue pH Magnetic Resonance (MR) techniques have been developed over the past few decades to shed light on pH change during tissue function and dysfunction. Nevertheless, there are still challenges for mapping brain pH noninvasively at high spatiotemporal resolution. To address this unmet biomedical need, chemical exchange saturation transfer (CEST) MR techniques have been developed as a sensitive means for non-invasive pH mapping. This article briefly reviews the basic principles of different pH measurement techniques with a focus on CEST imaging of pH. Emerging pH imaging applications in the tumor are provided as examples throughout the narrative, and CEST pH imaging in acute stroke is discussed in the final section.

Targeting the pH Paradigm at the Bedside: A Practical Approach

The inversion of the pH gradient in malignant tumors, known as the pH paradigm, is increasingly becoming accepted by the scientific community as a hallmark of cancer. Accumulated evidence shows that this is not simply a metabolic consequence of a dysregulated behavior, but rather an essential process in the physiopathology of accelerated proliferation and invasion. From the over-simplification of increased lactate production as the cause of the paradigm, as initially proposed, basic science researchers have arrived at highly complex and far-reaching knowledge, that substantially modified that initial belief. These new developments show that the paradigm entails a different regulation of membrane transporters, electrolyte exchangers, cellular and membrane enzymes, water trafficking, specialized membrane structures, transcription factors, and metabolic changes that go far beyond fermentative glycolysis. This complex world of dysregulations is still shuttered behind the walls of experimental laboratories and has not yet reached bedside medicine. However, there are many known pharmaceuticals and nutraceuticals that are capable of targeting the pH paradigm. Most of these products are well known, have low toxicity, and are also inexpensive. They need to be repurposed, and this would entail shorter clinical studies and enormous cost savings if we compare them with the time and expense required for the development of a new molecule. Will targeting the pH paradigm solve the "cancer problem"? Absolutely not. However, reversing the pH inversion would strongly enhance standard treatments, rendering them more efficient, and in some cases permitting lower doses of toxic drugs. This article's goal is to describe how to reverse the pH gradient inversion with existing drugs and nutraceuticals that can easily be used in bedside medicine, without adding toxicity to established treatments. It also aims at increasing awareness among practicing physicians that targeting the pH paradigm would be able to improve the results of standard therapies. Some clinical cases will be presented as well, showing how the pH gradient inversion can be treated at the bedside in a simple manner with repurposed drugs.

Towards an Integral Therapeutic Protocol for Breast Cancer Based upon the New H+-Centered Anticancer Paradigm of the Late Post-Warburg Era

A brand new approach to the understanding of breast cancer (BC) is urgently needed. In this contribution, the etiology, pathogenesis, and treatment of this disease is approached from the new pH-centric anticancer paradigm. Only this unitarian perspective, based upon the hydrogen ion (H+) dynamics of cancer, allows for the understanding and integration of the many dualisms, confusions, and paradoxes of the disease. The new H+-related, wide-ranging model can embrace, from a unique perspective, the many aspects of the disease and, at the same time, therapeutically interfere with most, if not all, of the hallmarks of cancer known to date. The pH-related armamentarium available for the treatment of BC reviewed here may be beneficial for all types and stages of the disease. In this vein, we have attempted a megasynthesis of traditional and new knowledge in the different areas of breast cancer research and treatment based upon the wide-ranging approach afforded by the hydrogen ion dynamics of cancer. The concerted utilization of the pH-related drugs that are available nowadays for the treatment of breast cancer is advanced.

Protein conformational changes affect the sodium triple-quantum MR signal

The aim of this study was to investigate possible sodium triple-quantum (TQ) signal dependence on pH variation and protein unfolding which may happen in vivo. The model system, composed of bovine serum albumin (BSA), was investigated over a wide pH range of 0.70 to 13.05 and during urea-induced unfolding. In both experimental series, the sodium and BSA concentration were kept constant so that TQ signal changes solely arose from an environmental change. The experiments were performed using unique potential to detect weak TQ signals by implementing a TQ time proportional phase increment pulse sequence. At a pH of 0.70, in which case the effect of the negatively charged groups was minimized, the minimum TQ percentage relative to single-quantum of 1.34% ± 0.05% was found. An increase of the pH up to 13.05 resulted in an increase of the sodium TQ signal by 225%. Urea-induced unfolding of BSA, without changes in pH, led to a smaller increase in the sodium TQ signal of up to 40%. The state of BSA unfolding was verified by fluorescence microscopy. Results of both experiments were well fitted by sigmoid functions. Both TQ signal increases were in agreement with an increase of the availability of negatively charged groups. The results point to vital contributions of the biochemical environment to the TQ MR signals. The sodium TQ signal in vivo could be a valuable biomarker of cell viability, and therefore possible effects of pH and protein unfolding need to be considered for a proper interpretation of changes in sodium TQ signals.

The Expression of Carbonic Anhydrases II, IX and XII in Brain Tumors

Carbonic anhydrases (CAs) are zinc-containing metalloenzymes that participate in the regulation of pH homeostasis in addition to many other important physiological functions. Importantly, CAs have been associated with neoplastic processes and cancer. Brain tumors represent a heterogeneous group of diseases with a frequently dismal prognosis, and new treatment options are urgently needed. In this review article, we summarize the previously published literature about CAs in brain tumors, especially on CA II and hypoxia-inducible CA IX and CA XII. We review here their role in tumorigenesis and potential value in predicting prognosis of brain tumors, including astrocytomas, oligodendrogliomas, ependymomas, medulloblastomas, meningiomas, and craniopharyngiomas. We also introduce both already completed and ongoing studies focusing on CA inhibition as a potential anti-cancer strategy.

Non-invasive Investigation of Tumor Metabolism and Acidosis by MRI-CEST Imaging

Altered metabolism is considered a core hallmark of cancer. By monitoring in vivo metabolites changes or characterizing the tumor microenvironment, non-invasive imaging approaches play a fundamental role in elucidating several aspects of tumor biology. Within the magnetic resonance imaging (MRI) modality, the chemical exchange saturation transfer (CEST) approach has emerged as a new technique that provides high spatial resolution and sensitivity for in vivo imaging of tumor metabolism and acidosis. This mini-review describes CEST-based methods to non-invasively investigate tumor metabolism and important metabolites involved, such as glucose and lactate, as well as measurement of tumor acidosis. Approaches that have been exploited to assess response to anticancer therapies will also be reported for each specific technique.

Imaging tumor acidosis: a survey of the available techniques for mapping in vivo tumor pH

Cancer cells are characterized by a metabolic shift in cellular energy production, orchestrated by the transcription factor HIF-1α, from mitochondrial oxidative phosphorylation to increased glycolysis, regardless of oxygen availability (Warburg effect). The constitutive upregulation of glycolysis leads to an overproduction of acidic metabolic products, resulting in enhanced acidification of the extracellular pH (pHe ~ 6.5), which is a salient feature of the tumor microenvironment. Despite the importance of pH and tumor acidosis, there is currently no established clinical tool available to image the spatial distribution of tumor pHe. The purpose of this review is to describe various imaging modalities for measuring intracellular and extracellular tumor pH. For each technique, we will discuss main advantages and limitations, pH accuracy and sensitivity of the applied pH-responsive probes and potential translatability to the clinic. Particular attention is devoted to methods that can provide pH measurements at high spatial resolution useful to address the task of tumor heterogeneity and to studies that explored tumor pH imaging for assessing treatment response to anticancer therapies.

Hydrogen Ion Dynamics of Cancer and a New Molecular, Biochemical and Metabolic Approach to the Etiopathogenesis and Treatment of Brain Malignancies

The treatment of cancer has been slowly but steadily progressing during the last fifty years. Some tumors with a high mortality in the past are curable nowadays. However, there is one striking exception: glioblastoma multiforme. No real breakthrough has been hitherto achieved with this tumor with ominous prognosis and very short survival. Glioblastomas, being highly glycolytic malignancies are strongly pH-dependent and driven by the sodium hydrogen exchanger 1 (NHE1) and other proton (H⁺) transporters. Therefore, this is one of those pathologies where the lessons recently learnt from the new pH-centered anticancer paradigm may soon bring a promising change to treatment. This contribution will discuss how the pH-centric molecular, biochemical and metabolic perspective may introduce some urgently needed and integral novel treatments. Such a prospective therapeutic approach for malignant brain tumors is developed here, either to be used alone or in combination with more standard therapies.

Brain tumor acidification using drugs simultaneously targeting multiple pH regulatory mechanisms

INTRODUCTION

Non-invasively distinguishing aggressive from non-aggressive brain tumors is an important clinical challenge. Intracellular pH (pH_i) regulation is essential for normal cell function and is normally maintained within a narrow range. Cancer cells are characterized by a reversed intracellular to extracellular pH gradient, compared to healthy cells, that is maintained by several distinct mechanisms. Previous studies have demonstrated acute pH modulation in glioblastoma detectable by chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) after blocking individual pH regulatory mechanisms. The purpose of the current study was to simultaneously block five pH regulatory mechanisms while also providing glucose as an energy substrate. We hypothesized that this approach would increase the acute pH modulation effect allowing the identification of aggressive cancer.

METHODS

Using a 9.4 T MRI scanner, CEST spectra were acquired sensitive to pH_i using amine/amide concentration independent detection (AACID). Twelve mice were scanned approximately 11 ± 1 days after implanting 10⁵ U87 human glioblastoma multiforme cells in the brain, before and after intraperitoneal injection of a combination of five drugs (quercetin, cariporide, dichloroacetate, acetazolamide, and pantoprazole) with and without glucose.

RESULTS

Two hours after combination drug injection there was a significant 0.1 ± 0.03 increase in tumor AACID value corresponding to a 0.4 decrease in pH_i. After injecting the drug combination with glucose the AACID value increased by 0.18 ± 0.03 corresponding to a 0.72 decrease in pH_i. AACID values were also slightly increased in contralateral tissue.

CONCLUSIONS

The combined drug treatment with glucose produced a large acute CEST MRI contrast indicating tumor acidification, which could be used to help localize brain cancer and monitor tumor response to chemotherapy.

Tumor pH and Protein Concentration Contribute to the Signal of Amide Proton Transfer Magnetic Resonance Imaging

Abnormal pH is a common feature of malignant tumors and has been associated clinically with suboptimal outcomes. Amide proton transfer magnetic resonance imaging (APT MRI) holds promise as a means to noninvasively measure tumor pH, yet multiple factors collectively make quantification of tumor pH from APT MRI data challenging. The purpose of this study was to improve our understanding of the biophysical sources of altered APT MRI signals in tumors. Combining in vivo APT MRI measurements with ex vivo histological measurements of protein concentration in a rat model of brain metastasis, we determined that the proportion of APT MRI signal originating from changes in protein concentration was approximately 66%, with the remaining 34% originating from changes in tumor pH. In a mouse model of hypopharyngeal squamous cell carcinoma (FaDu), APT MRI showed that a reduction in tumor hypoxia was associated with a shift in tumor pH. The results of this study extend our understanding of APT MRI data and may enable the use of APT MRI to infer the pH of individual patients' tumors as either a biomarker for therapy stratification or as a measure of therapeutic response in clinical settings. SIGNIFICANCE: These findings advance our understanding of amide proton transfer magnetic resonance imaging (APT MRI) of tumors and may improve the interpretation of APT MRI in clinical settings.

Paths for Improving Bevacizumab Available in 2018: The ADZT Regimen for Better Glioblastoma Treatment

During glioblastoma treatment, the pharmaceutical monoclonal antibody to vascular endothelial growth factor A, bevacizumab, has improved the quality of life and delayed progression for several months, but has not (or only marginally) prolonged overall survival. In 2017, several dramatic research papers appeared that are crucial to our understanding of glioblastoma vis-a-vis the mode of action of bevacizumab. As a consequence of these papers, a new, potentially more effective treatment protocol can be built around bevacizumab. This is the ADZT regimen, where four old drugs are added to bevacizumab. These four drugs are apremilast, marketed to treat psoriasis, dapsone, marketed to treat Hansen’s disease, zonisamide, marketed to treat seizures, and telmisartan, marketed to treat hypertension. The ancillary attributes of each of these drugs have been shown to augment bevacizumab. This paper details the research data supporting this contention. Phase three testing of AZDT addition to bevacizumab is required to establish safety and effectiveness before general use.

The Monocarboxylate transporter inhibitor Quercetin induces intracellular acidification in a mouse model of Glioblastoma Multiforme: in-vivo detection using magnetic resonance imaging

The response of tumor intracellular pH to a pharmacological challenge could help identify aggressive cancer. Chemical exchange saturation transfer (CEST) is an MRI contrast mechanism that is dependent on intracellular pH (pH_i). pH_i is important in the maintenance of normal cell function and is normally maintained within a narrow range by the activity of transporters located at the plasma membrane. In cancer, changes in pH_i have been correlated with both cell proliferation and cell death. Quercetin is a bioflavonoid and monocarboxylate transporter (MCT) inhibitor. Since MCTs plays a significant role in maintaining pH balance in the tumor microenvironment, we hypothesized that systemically administered quercetin could selectively acidify brain tumors. The goals of the current study were to determine whether CEST MRI measurements sensitive to tumor pH could detect acidification after quercetin injection and to measure the magnitude of the pH change (ΔpH). Using a 9.4 T MRI, amine and amide concentration independent detection (AACID) CEST spectra were acquired in six mice approximately 15 ± 1 days after implanting 10⁵ U87 human glioblastoma multiforme cells in the brain, before and after administration of quercetin (dose: 200 mg/kg) by intraperitoneal injection. Three additional mice were studied as controls and received only vehicle dimethyl sulfoxide (DMSO) injection. Repeated measures t-test was used to compare AACID changes in tumor and contralateral tissue regions of interest. Two hours after quercetin injection there was a significant increase in tumor AACID by 0.07 ± 0.03 corresponding to a 0.27 decrease in pH_i, and no change in AACID in contralateral tissue. There was also a small average increase in AACID in tumors within the three mice injected with DMSO only. The use of the natural compound quercetin in combination with pH weighted MRI represents a unique approach to cancer detection that does not require injection of an imaging contrast agent.

In vivo detection of acute intracellular acidification in glioblastoma multiforme following a single dose of cariporide

Glioblastoma is an aggressive brain cancer that is very difficult to treat. Clinically, it is important to be able to distinguish aggressive from non-aggressive brain tumors. Previous studies have shown that some drugs can induce a rapid change in intracellular pH that could help to identify aggressive cancer. The sodium proton exchanger (NHE1) plays a significant role in maintaining pH balance in the tumor microenvironment. Cariporide is a sodium proton exchange inhibitor that is well tolerated by humans in cardiac applications. We hypothesized that cariporide could selectively acidify brain tumors. The purpose of this study was to determine whether amine/amide concentration-independent detection (AACID) chemical exchange saturation transfer (CEST) MRI measurement of tumor pH_i could detect acidification after cariporide injection. Using a 9.4T MRI scanner, CEST spectra were acquired in six mice approximately 14 days after implanting 10⁵ U87 human glioblastoma multiforme cells in the brain, before and after administration of cariporide (dose: 6 mg/kg) by intraperitoneal injection. Three additional mice were studied as controls and received only vehicle injection (DMSO + PBS). Repeated measures t test was used to examine changes in tumor and contralateral tissue regions of interest. Two hours after cariporide injection, there was a significant 0.12 ± 0.03 increase in tumor AACID value corresponding to a 0.48 decrease in pH_i and no change in AACID value in contralateral tissue. A small but significant increase of 0.04 ± 0.017 in tumor AACID value was also observed following vehicle injection. This study demonstrates that acute CEST MRI contrast changes, indicative of intracellular acidification, after administration of cariporide could help localize glioblastoma.

A comparison of exogenous and endogenous CEST MRI methods for evaluating in vivo pH

PURPOSE

Extracellular pH (pHe) is an important biomarker for cancer cell metabolism. Acido-chemical exchange saturation transfer (CEST) MRI uses the contrast agent iopamidol to create spatial maps of pHe. Measurements of amide proton transfer exchange rates (kex ) from endogenous CEST MRI were compared to pHe measurements by exogenous acido-CEST MRI to determine whether endogenous kex could be used as a proxy for pHe measurements.

METHODS

Spatial maps of pHe and kex were obtained using exogenous acidoCEST MRI and an endogenous CEST MRI analyzed with the omega plot method, respectively, to evaluate mouse kidney, a flank tumor model, and a spontaneous lung tumor model. The pHe and kex results were evaluated using pixelwise comparisons.

RESULTS

The kex values obtained from endogenous CEST measurements did not correlate with the pHe results from exogenous CEST measurements. The kex measurements were limited to fewer pixels and had a limited dynamic range relative to pHe measurements.

CONCLUSION

Measurements of kex with endogenous CEST MRI cannot substitute for pHe measurements with acidoCEST MRI. Whereas endogenous CEST MRI may still have good utility for evaluating some specific pathologies, exogenous acido-CEST MRI is more appropriate when evaluating pathologies based on pHe values. Magn Reson Med 79:2766-2772, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Addition of carbonic anhydrase 9 inhibitor SLC-0111 to temozolomide treatment delays glioblastoma growth in vivo

Tumor microenvironments can promote stem cell maintenance, tumor growth, and therapeutic resistance, findings linked by the tumor-initiating cell hypothesis. Standard of care for glioblastoma (GBM) includes temozolomide chemotherapy, which is not curative, due, in part, to residual therapy-resistant brain tumor-initiating cells (BTICs). Temozolomide efficacy may be increased by targeting carbonic anhydrase 9 (CA9), a hypoxia-responsive gene important for maintaining the altered pH gradient of tumor cells. Using patient-derived GBM xenograft cells, we explored whether CA9 and CA12 inhibitor SLC-0111 could decrease GBM growth in combination with temozolomide or influence percentages of BTICs after chemotherapy. In multiple GBMs, SLC-0111 used concurrently with temozolomide reduced cell growth and induced cell cycle arrest via DNA damage in vitro. In addition, this treatment shifted tumor metabolism to a suppressed bioenergetic state in vivo. SLC-0111 also inhibited the enrichment of BTICs after temozolomide treatment determined via CD133 expression and neurosphere formation capacity. GBM xenografts treated with SLC-0111 in combination with temozolomide regressed significantly, and this effect was greater than that of temozolomide or SLC-0111 alone. We determined that SLC-0111 improves the efficacy of temozolomide to extend survival of GBM-bearing mice and should be explored as a treatment strategy in combination with current standard of care.

Clinical applications of chemical exchange saturation transfer (CEST) MRI

Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) has been developed and employed in multiple clinical imaging research centers worldwide. Selective radiofrequency (RF) saturation pulses with standard 2D and 3D MRI acquisition schemes are now routinely performed, and CEST MRI can produce semiquantitative results using magnetization transfer ratio asymmetry (MTR_asym ) analysis while accounting for B₀ inhomogeneity. Faster clinical CEST MRI acquisition methods and more quantitative acquisition and analysis routines are under development. Endogenous biomolecules with amide, amine, and hydroxyl groups have been detected during clinical CEST MRI studies, and exogenous CEST agents have also been administered to patients. These CEST MRI tools show promise for contributing to assessments of cerebral ischemia, neurological disorders, lymphedema, osteoarthritis, muscle physiology, and solid tumors. This review summarizes the salient features of clinical CEST MRI protocols and critically evaluates the utility of CEST MRI for these clinical imaging applications.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:11-27.