Evaluation of changes in the tumor microenvironment after sorafenib therapy by sequential histology and 18F-fluoromisonidazole hypoxia imaging in renal cell carcinoma

The roles of cancer stem cell-derived secretory factors in shaping the immunosuppressive tumor microenvironment in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies worldwide and has a poor prognosis. Although immune checkpoint inhibitors have entered a new era of HCC treatment, their response rates are modest, which can be attributed to the immunosuppressive tumor microenvironment within HCC tumors. Accumulating evidence has shown that tumor growth is fueled by cancer stem cells (CSCs), which contribute to therapeutic resistance to the above treatments. Given that CSCs can regulate cellular and physical factors within the tumor niche by secreting various soluble factors in a paracrine manner, there have been increasing efforts toward understanding the roles of CSC-derived secretory factors in creating an immunosuppressive tumor microenvironment. In this review, we provide an update on how these secretory factors, including growth factors, cytokines, chemokines, and exosomes, contribute to the immunosuppressive TME, which leads to immune resistance. In addition, we present current therapeutic strategies targeting CSC-derived secretory factors and describe future perspectives. In summary, a better understanding of CSC biology in the TME provides a rational therapeutic basis for combination therapy with ICIs for effective HCC treatment.

The relevance between hypoxia-dependent spatial transcriptomics and the prognosis and efficacy of immunotherapy in claudin-low breast cancer

Introduction

Hypoxia is an important characteristic of solid tumors. However, spatial transcriptomics (ST) of hypoxia-associated heterogeneity is not clear.

Methods

This study integrated Spatial Transcriptomics (ST) with immunofluorescence to demonstrate their spatial distribution in human claudin-low breast cancer MDA-MB-231 engraft. ST spots were clustered with differentially expression genes. The data were combined with hypoxia-specific marker and angiogenesis marker-labeled serial sections to indicate the spatial distribution of hypoxia and hypoxia-inducted transcriptional profile. Moreover, marker genes, cluster-specific hypoxia genes, and their co-essential relationship were identified and mapped in every clusters. The clinicopathological association of marker genes of hypoxia-dependent spatial clusters was explored in 1904 breast cancers from METABRIC database.

Results

The tumor from center to periphery were enriched into five hypoxia-dependent subgroups with differentially expressed genes, which were matched to necrosis, necrosis periphery, hypoxic tumor, adaptive survival tumor, and invasive tumor, respectively. Different subgroups demonstrated distinct hypoxia condition and spatial heterogeneity in biological behavior and signaling pathways. Cox regression analysis showed that the invasive tumor (cluster 0) and hypoxic tumor (cluster 6) score could be served as independent prognostic factors in claudin-low patients. KM analysis indicated that high invasive tumor (cluster 0) and hypoxic tumor (cluster 6) score was associated with poor prognoses of claudin-low patients. Further analysis showed that hypoxia-induced immune checkpoints, such as CD276 and NRP1, upregulation in invasive tumor to block infiltration and activation of B cells and CD8+ T cells to change tumor immune microenvironment.

Discussion

This study reveals hypoxia-dependent spatial heterogeneity in claudin-low breast cancer and highlights its potential value as a predictive biomarker of clinical outcomes and immunotherapy response. The molecules found in this study also provided potential molecular mechanisms and therapeutic targets for subsequent studies.

Choosing The Right Animal Model for Renal Cancer Research

The increase in the life expectancy of patients with renal cell carcinoma (RCC) in the last decade is due to changes that have occurred in the area of preclinical studies. Understanding cancer pathophysiology and the emergence of new therapeutic options, including immunotherapy, would not be possible without proper research. Before new approaches to disease treatment are developed and introduced into clinical practice they must be preceded by preclinical tests, in which animal studies play a significant role. This review describes the progress in animal model development in kidney cancer research starting from the oldest syngeneic or chemically-induced models, through genetically modified mice, finally to xenograft, especially patient-derived, avatar and humanized mouse models. As there are a number of subtypes of RCC, our aim is to help to choose the right animal model for a particular kidney cancer subtype. The data on genetic backgrounds, biochemical parameters, histology, different stages of carcinogenesis and metastasis in various animal models of RCC as well as their translational relevance are summarized. Moreover, we shed some light on imaging methods, which can help define tumor microstructure, assist in the analysis of its metabolic changes and track metastasis development.

Cellular and Extracellular Components in Tumor Microenvironment and Their Application in Early Diagnosis of Cancers

Tumors are surrounded by complex environmental components, including blood and lymph vessels, fibroblasts, endothelial cells, immune cells, cytokines, extracellular vesicles, and extracellular matrix. All the stromal components together with the tumor cells form the tumor microenvironment (TME). In addition, extracellular physical and chemical factors, including extracellular pH, hypoxia, elevated interstitial fluid pressure, and fibrosis, are closely associated with tumor progression, metastasis, immunosuppression, and drug resistance. Cellular and extracellular components in TME contribute to nearly all procedures of carcinogenesis. By summarizing the recent work in this field, we make a comprehensive review on the role of cellular and extracellular components in the process of carcinogenesis and their potential application in early diagnosis of cancer. We hope that a systematic review of the diverse aspects of TME will help both research scientists and clinicians in this field.

4-Hydroxy-7-oxo-5-heptenoic acid lactone is a potent inducer of brain cancer cell invasiveness that may contribute to the failure of anti-angiogenic therapies

Previously, we discovered that free radical-induced oxidative fragmentation of the docosahexaenoate ester of 2-lysophosphatidylcholine produces 4-hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone that, in turn, promotes the migration and invasion of endothelial cells. This suggested that HOHA lactone might similarly promote migration and invasion of glioblastoma multiformae (GBM) brain cancer stem cells (CSCs). A bioinformatics analysis of clinical cancer genomic data revealed that matrix metalloproteinase (MMP)1 and three markers of oxidative stress - superoxide dismutase 2, NADPH oxidase 4, and carbonic anhydrase 9 - are upregulated in human mesenchymal GBM cancer tissue, and that MMP1 is positively correlated to all three of these oxidative stress markers. In addition, elevated levels of MMP1 are indicative of GBM invasion, while low levels of MMP1 indicate survival. We also explored the hypothesis that the transition from the proneural to the more aggressive mesenchymal phenotype, e.g., after treatment with an anti-angiogenic therapy, is promoted by the effects of lipid oxidation products on GBM CSCs. We found that low micromolar concentrations of HOHA lactone increase the cell migration velocity of cultured GBM CSCs, and induce the expression of MMP1 and two protein biomarkers of the proneural to mesenchymal transition (PMT): p65 NF-κβ and vimentin. Exposure of cultured GBM CSCs to HOHA lactone causes an increase in phosphorylation of mitogen-activated protein kinases and Akt kinases that are dependent on both protease-activated receptor 1 (PAR1) and MMP1 activity. We conclude that HOHA lactone promotes the PMT in GBM through the activation of PAR1 and MMP1. This contributes to a fatal flaw in antiangiogenic, chemo, and radiation therapies: they promote oxidative stress and the generation of HOHA lactone in the tumor that fosters a change from the proliferative proneural to the migratory mesenchymal GBM CSC phenotype that seeds new tumor growth. Inhibition of PAR1 and HOHA lactone are potential new therapeutic targets for impeding GBM tumor recurrence.

Elimination of tumor hypoxia by eribulin demonstrated by 18F-FMISO hypoxia imaging in human tumor xenograft models

BACKGROUND

Eribulin, an inhibitor of microtubule dynamics, shows antitumor potency against a variety of solid cancers through its antivascular activity and remodeling of tumor vasculature. ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) is the most widely used PET probe for imaging tumor hypoxia. In this study, we utilized ¹⁸F-FMISO to clarify the effects of eribulin on the tumor hypoxic condition in comparison with histological findings.

MATERIAL AND METHODS

Mice bearing a human cancer cell xenograft were intraperitoneally administered a single dose of eribulin (0.3 or 1.0 mg/kg) or saline. Three days after the treatment, mice were injected with ¹⁸F-FMISO and pimonidazole (hypoxia marker for immunohistochemistry), and intertumoral ¹⁸F-FMISO accumulation levels and histological characteristics were determined. PET/CT was performed pre- and post-treatment with eribulin (0.3 mg/kg, i.p.).

RESULTS

The ¹⁸F-FMISO accumulation levels and percent pimonidazole-positive hypoxic area were significantly lower, whereas the number of microvessels was higher in the tumors treated with eribulin. The PET/CT confirmed that ¹⁸F-FMISO distribution in the tumor was decreased after the eribulin treatment.

CONCLUSIONS

Using ¹⁸F-FMISO, we demonstrated the elimination of the tumor hypoxic condition by eribulin treatment, concomitantly with the increase in microvessel density. These findings indicate that PET imaging using ¹⁸F-FMISO may provide the possibility to detect the early treatment response in clinical patients undergoing eribulin treatment.

Genetic Variants of VEGFA and FLT4 Are Determinants of Survival in Renal Cell Carcinoma Patients Treated with Sorafenib

Molecular markers of sorafenib efficacy in patients with metastatic renal cell carcinoma (mRCC) are not available. The purpose of this study was to discover genetic markers of survival in patients with mRCC treated with sorafenib. Germline variants from 56 genes were genotyped in 295 patients with mRCC. Variant-overall survival (OS) associations were tested in multivariate regression models. Mechanistic studies were conducted to validate clinical associations. VEGFA rs1885657, ITGAV rs3816375, and WWOX rs8047917 (sorafenib arm), and FLT4 rs307826 and VEGFA rs3024987 (sorafenib and placebo arms combined) were associated with shorter OS. FLT4 rs307826 increased VEGFR-3 phosphorylation, membrane trafficking, and receptor activation. VEGFA rs1885657 and rs58159269 increased transcriptional activity of the constructs containing these variants in endothelial and RCC cell lines, and VEGFA rs58159269 increased endothelial cell proliferation and tube formation. FLT4 rs307826 and VEGFA rs58159269 led to reduced sorafenib cytotoxicity. Genetic variation in VEGFA and FLT4 could affect survival in sorafenib-treated patients with mRCC. These markers should be examined in additional malignancies treated with sorafenib and in other angiogenesis inhibitors used in mRCC. SIGNIFICANCE: Clinical and mechanistic data identify germline genetic variants in VEGFA and FLT4 as markers of survival in patients with metastatic renal cell carcinoma.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

Monitoring of tumor vascular normalization: the key points from basic research to clinical application

Tumor vascular normalization alleviates hypoxia in the tumor microenvironment, reduces the degree of malignancy, and increases the efficacy of traditional therapy. However, the time window for vascular normalization is narrow; therefore, how to determine the initial and final points of the time window accurately is a key factor in combination therapy. At present, the gold standard for detecting the normalization of tumor blood vessels is histological staining, including tumor perfusion, microvessel density (MVD), vascular morphology, and permeability. However, this detection method is almost unrepeatable in the same individual and does not dynamically monitor the trend of the time window; therefore, finding a relatively simple and specific monitoring index has important clinical significance. Imaging has long been used to assess changes in tumor blood vessels and tumor changes caused by the oxygen environment in clinical practice; some preclinical and clinical research studies demonstrate the feasibility to assess vascular changes, and some new methods were in preclinical research. In this review, we update the most recent insights of evaluating tumor vascular normalization.

Tyrosine-Kinase Inhibitors Therapies with Mainly Anti-Angiogenic Activity in Advanced Renal Cell Carcinoma: Value of PET/CT in Response Evaluation

Renal cell carcinoma (RCC) is the most frequent renal tumor and the majority of patients are diagnosed with advanced disease. Tumor angiogenesis plays a crucial role in the development and progression of RCC together with hypoxia and glucose metabolism. These three pathways are strictly connected to the cell growth and proliferation, like a loop that is self-feeding. Over the last few years, the ever-deeper knowledge of its contribution in metastatic RCC led to the discovery of numerous tyrosine kinase inhibitors (TKIs) targeting pro-angiogenic receptors at different levels such as sunitinib, sorafenib, pazopanib, axitinib, tivozanib, and dovitinib. As anti-angiogenic agents, TKIs interfere the loop, being able to inhibit tumor proliferation. TKIs are now available treatments for advanced RCC, which demonstrated to improve overall survival and/or progression free survival. Their effects can be detectable early on Positron Emission Tomography/Computed Tomography (PET/CT) by change in ¹⁸F-fluoro-2-deoxy-2-d-glucose (¹⁸F-FDG) uptake, the main radiotracer used to date, as a strong indicator of biological response. ¹⁸F-FDG PET/CT demonstrated an ability to predict and monitor disease progression, allowing an early and reliable identification of responders, and could be used for image-guided optimization and "personalization" of anti-angiogenic regimens. New radiotracers for biometabolic imaging are currently under investigation, which exploit the other pathways involved in the cancer process, including cellular proliferation, aerobic metabolism, cell membrane synthesis, hypoxia and amino acid transport, as well as the angiogenic process, but they require further studies.

Changes in tumor oxygen state after sorafenib therapy evaluated by 18F-fluoromisonidazole hypoxia imaging of renal cell carcinoma xenografts

A mechanistic dissociation exists between tumor starvation and vascular normalization after antiangiogenic therapy. Thus, improved understanding of tumor responses (tumor starvation or vascular normalization) is important for optimizing treatment strategies. ¹⁸F-fluoromisonidazole (¹⁸F-FMISO) is widely used for imaging tumor hypoxia. To clarify the tumor response to the antiangiogenic drug sorafenib, the present study evaluated the changes in the tumor oxygen state using ¹⁸F-FMISO in mice bearing a renal cell carcinoma xenograft (A498). Mice bearing A498 xenografts were assigned to the control and three sorafenib-treatment groups and administered sorafenib (0, 10, 20 or 40 mg/kg/day, per os) once daily for 3 days. Following one day after the final administration, the mice were injected with ¹⁸F-FMISO and pimonidazole (a hypoxia marker). ¹⁸F-FMISO accumulation in the tumor was determined by autoradiography. Immunohistochemistry of pimonidazole and cluster of differentiation (CD)31 (a vascular marker) was also performed. ¹⁸F-FMISO accumulation levels in the tumor significantly increased by 4.3-, 8.4- and 8.6-fold compared with in the control group following 10, 20 and 40 mg/kg sorafenib treatments, respectively [0.07±0.04, 0.32±0.11, 0.62±0.15 and 0.63±0.23 (%ID/m²) × kg for the control, and 10, 20 and 40 mg treatments, respectively; all P<0.0083 vs. the control]. The number of pimonidazole-positive cells also significantly increased by 6.8-, 12.3- and 20.2-fold compared with in the control group following 10, 20 and 40 mg/kg sorafenib treatments, respectively (0.78±0.79, 5.36±2.29, 9.66±1.58 and 15.85±4.59% pimonidazole-positive cells; all P<0.0083 vs. the control). The number of microvessels in tumors markedly decreased to 33.5, 17.6, and 14.0% of the control following 10, 20 and 40 mg/kg sorafenib treatments, respectively (17.1±2.5, 5.7±1.0, 3.0±1.0 and 2.4±0.3 vessels/mm²; P<0.0083 vs. the control). The ¹⁸F-FMISO expression level in the tumor increased sorafenib-dose-dependently, which is consistent with the increase in the number of pimonidazole-positive cells and decrease in the number of microvessels. These findings indicated that the present sorafenib treatment protocol induces 'tumor hypoxia/starvation' in the renal cell carcinoma xenograft (A498) due to its antiangiogenic properties.

Molecular mechanisms of hypoxia in cancer

PURPOSE

Hypoxia is a condition of insufficient oxygen to support metabolism which occurs when the vascular supply is interrupted, or when a tumour outgrows its vascular supply. It is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. This review provides an overview of hypoxia imaging with Positron emission tomography (PET), with an emphasis on the biological relevance, mechanism of action, highlighting advantages, and limitations of the currently available hypoxia radiotracers.

METHODS

A comprehensive PubMed literature search was performed, identifying articles relating to biological significance and measurement of hypoxia, MRI methods, and PET imaging of hypoxia in preclinical and clinical settings, up to December 2016.

RESULTS

A variety of approaches have been explored over the years for detecting and monitoring changes in tumour hypoxia, including regional measurements with oxygen electrodes placed under CT guidance, MRI methods that measure either oxygenation or lactate production consequent to hypoxia, different nuclear medicine approaches that utilise imaging agents the accumulation of which is inversely related to oxygen tension, and optical methods. The advantages and disadvantages of these approaches are reviewed, along with individual strategies for validating different imaging methods. PET is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels.

CONCLUSION

Even though hypoxia could have significant prognostic and predictive value in the clinic, the best method for hypoxia assessment has in our opinion not been realised.

Imaging the Tumor Microenvironment

The tumor microenvironment consists of tumor, stromal, and immune cells, as well as extracellular milieu. Changes in numbers of these cell types and their environments have an impact on cancer growth and metastasis. Non-invasive imaging of aspects of the tumor microenvironment can provide important information on the aggressiveness of the cancer, whether or not it is metastatic, and can also help to determine early response to treatment. This chapter provides an overview on non-invasive in vivo imaging in humans and mouse models of various cell types and physiological parameters that are unique to the tumor microenvironment. Current clinical imaging and research investigation are in the areas of nuclear imaging (positron emission tomography (PET) and single photon emission computed tomography (SPECT)), magnetic resonance imaging (MRI) and optical (near infrared (NIR) fluorescence) imaging. Aspects of the tumor microenvironment that have been imaged by PET, MRI and/or optical imaging are tumor associated inflammation (primarily macrophages and T cells), hypoxia, pH changes, as well as enzymes and integrins that are highly prevalent in tumors, stroma and immune cells. Many imaging agents and strategies are currently available for cancer patients; however, the investigation of novel avenues for targeting aspects of the tumor microenvironment in pre-clinical models of cancer provides the cancer researcher with a means to monitor changes and evaluate novel treatments that can be translated into the clinic.

2-(&#969;-Carboxyethyl)pyrrole Antibody as a New Inhibitor of Tumor Angiogenesis and Growth

BACKGROUND

Angiogenesis is a fundamental process in the progression, invasion, and metastasis of tumors. Therapeutic drugs such as bevacizumab and ranibuzumab have thus been developed to inhibit vascular endothelial growth factor (VEFG)-promoted angiogenesis. While these anti-angiogenic drugs have been commonly used in the treatment of cancer, patients often develop significant resistance that limits the efficacy of anti-VEGF therapies to a short period of time. This is in part due to the fact that an independent pathway of angiogenesis exists, which is mediated by 2-(ω-carboxyethyl)pyrrole (CEP) in a TLR2 receptor-dependent manner that can compensate for inhibition of the VEGF-mediated pathway.

AIMS

In this work, we evaluated a CEP antibody as a new tumor growth inhibitor that blocks CEP-induced angiogenesis.

METHOD

We first evaluated the effectiveness of a CEP antibody as a monotherapy to impede tumor growth in two human tumor xenograft models. We then determined the synergistic effects of bevacizumab and CEP antibody in a combination therapy, which demonstrated that blocking of the CEP-mediated pathway significantly enhanced the anti-angiogenic efficacy of bevacizumab in tumor growth inhibition indicating that CEP antibody is a promising chemotherapeutic drug. To facilitate potential translational studies of CEP-antibody, we also conducted longitudinal imaging studies and identified that FMISO-PET is a non-invasive imaging tool that can be used to quantitatively monitor the anti-angiogenic effects of CEP-antibody in the clinical setting.

RESULTS

That treatment with CEP antibody induces hypoxia in tumor tissue WHICH was indicated by 43% higher uptake of [18F]FMISO in CEP antibody-treated tumor xenografs than in the control PBS-treated littermates.

Dynamic PET evaluation of elevated FLT level after sorafenib treatment in mice bearing human renal cell carcinoma xenograft

Background

Sorafenib, an oral multikinase inhibitor, has anti-proliferative and anti-angiogenic activities and is therapeutically effective against renal cell carcinoma (RCC). Recently, we have evaluated the tumor responses to sorafenib treatment in a RCC xenograft using [Methyl-³H(N)]-3′-fluoro-3′-deoxythythymidine ([³H]FLT). Contrary to our expectation, the FLT level in the tumor significantly increased after the treatment. In this study, to clarify the reason for the elevated FLT level, dynamic 3′-[¹⁸F]fluoro-3′-deoxythymidine ([¹⁸F]FLT) positron emission tomography (PET) and kinetic studies were performed in mice bearing a RCC xenograft (A498).

The A498 xenograft was established in nude mice, and the mice were assigned to the control (n = 5) and treatment (n = 5) groups. The mice in the treatment group were orally given sorafenib (20 mg/kg/day p.o.) once daily for 3 days. Twenty-four hours after the treatment, dynamic [¹⁸F]FLT PET was performed by small-animal PET. Three-dimensional regions of interest (ROIs) were manually defined for the tumors. A three-compartment model fitting was carried out to estimate four rate constants using the time activity curve (TAC) in the tumor and the blood clearance rate of [¹⁸F]FLT.

Results

The dynamic pattern of [¹⁸F]FLT levels in the tumor significantly changed after the treatment. The rate constant of [¹⁸F]FLT phosphorylation (k₃) was significantly higher in the treatment group (0.111 ± 0.027 [1/min]) than in the control group (0.082 ± 0.009 [1/min]). No significant changes were observed in the distribution volume, the ratio of [¹⁸F]FLT forward transport (K₁) to reverse transport (k₂), between the two groups (0.556 ± 0.073 and 0.641 ± 0.052 [mL/g] in the control group).

Conclusions

Our dynamic PET studies indicated that the increase in FLT level may be caused by the phosphorylation of FLT in the tumor after the sorafenib treatment in the mice bearing a RCC xenograft. Dynamic PET studies with kinetic modeling could provide improved understanding of the biochemical processes involved in tumor responses to therapy.

Diagnostic Challenges of Kidney Cancer: A Systematic Review of the Role of Positron Emission Tomography-Computerized Tomography

PURPOSE

Positron emission tomography-computerized tomography is a leading imaging modality for many types of solid tumors. The ability to characterize molecular processes noninvasively during a relatively fast whole-body scan is the major advantage of this technology. We reviewed the literature in an attempt to clarify the usefulness of positron emission tomography-computerized tomography in patients with a renal mass.

MATERIALS AND METHODS

We searched PubMed® for articles published from 2004 through September 2015 using the keywords "renal," "kidney," "mass," "tumor," "cancer," and "PET/CT."

RESULTS

A total of 158 relevant articles were included in the review. Most diagnostic studies used (18)F-fluorodeoxyglucose, a marker of glucose metabolism, as the radiotracer. The results were substandard, with sensitivity rates in the range of 31.5% to 77% for diagnosis of renal cell carcinomas. There were higher success rates for diagnosis of clear cell carcinomas. Carbonic anhydrase IX is an enzyme expressed in 95% of clear cell carcinomas but not in normal renal tissue or in benign or nonclear cell malignancies. A chimeric mouse-human antibody to carbonic anhydrase IX labeled with (124)I-girentuximab was demonstrated to diagnose clear cell tumors with sensitivity of 86.2% and specificity of 85.9%. For diagnosis of metastases positron emission tomography-computerized tomography with (18)F-fluorodeoxyglucose was observed to be more accurate than computerized tomography alone (94% vs 89%). Studies with other tracers also reveal encouraging results. Positron emission tomography-computerized tomography holds great promise in predicting prognosis and response to tyrosine kinase inhibitors. Current tyrosine kinase inhibitor treatments usually induce only mild lesion shrinkage. Thus, assessment of response based on changes in size of metastases is insufficient. Low (18)F-fluorodeoxyglucose uptake before treatment and decreased uptake after 2 cycles of treatment are associated with better survival. Using labeled medications as radiotracers before actual treatment may assist in selection of the most effective medication for a specific patient.

CONCLUSIONS

Positron emission tomography-computerized tomography with (18)F-fluorodeoxyglucose currently has lower sensitivity compared to enhanced computerized tomography for diagnosis of primary renal masses but better sensitivity for diagnosis of metastases. Predicting and monitoring response to targeted therapy could direct the clinician toward drug selection or modification during therapy. The possibility of treating patients with advanced renal cell carcinoma with (124)I-girentuximab attached to (177)Lu, a strong β-emitter, is investigated.

Combining radiotherapy with sunitinib: lessons (to be) learned

To improve the efficacy of radiotherapy (RTx), there is a growing interest in combining RTx with drugs that inhibit angiogenesis, i.e., the process of neo-vessel formation out of preexisting capillaries. A frequently used drug to inhibit angiogenesis is sunitinib (Sutent, SU11248), a receptor tyrosine kinase inhibitor that is currently FDA approved for the treatment of several cancer types. The current review presents an overview of the preclinical studies and clinical trials that combined sunitinib with RTx. We discuss the findings from preclinical and clinical observations with a focus on dose scheduling and commonly reported toxicities. In addition, the effects of combination therapy on tumor response and patient survival are described. Finally, the lessons learned from preclinical and clinical studies are summarized and opportunities and pitfalls for future clinical trials are presented.

Dynamic contrast-enhanced magnetic resonance imaging assessment of kidney function and renal masses: single slice versus whole organ/tumor

OBJECTIVES

The aim of this study was to compare single-slice and 3-dimensional (3D) analysis for magnetic resonance renography (plasma flow [FP], plasma volume [VP], and glomerular filtration rate [GFR]) and for dynamic contrast-enhanced magnetic resonance imaging (MRI) of renal tumors (FP, VP, permeability-surface area product), respectively.

MATERIAL AND METHODS

We prospectively included 22 patients (43 kidneys with 22 suspicious renal lesions) and performed preoperative and postoperative imaging before and after partial nephrectomy, respectively. Of the 22 renal lesions, 15 turned out to be renal cell carcinoma and were included in the tumor analysis, altogether leading to 86 renal and 15 tumor MRI scans, respectively. Dynamic contrast-enhanced MRI was performed with a time-resolved angiography with stochastic trajectories sequence (spatial resolution, 2.6 × 2.6 × 2.6 mm3; temporal resolution, 2.5 seconds) at 3 T (Magnetom Verio; Siemens Healthcare Sector) after injection of 0.05 mmol/kg body weight Gadobutrol (Bayer Healthcare Pharmaceuticals). Analysis was performed using regions of interest encompassing a single central slice and the whole kidney/tumor, respectively. A 2-compartment model yielding FP, VP, GFR, or tumor permeability-surface area product was used for kinetic modelling. Modelling was performed based on relative contrast enhancement to account for coil-related inhomogeneity. Significance in difference, agreement, and goodness of fit of the data to the curve was assessed with paired t tests, Bland-Altman plots, and χ2 test, respectively.

RESULTS

Bland-Altman analysis revealed a good agreement between both types of measurement for kidneys and tumors, respectively. Results between single-slice and whole-kidney regions of interest showed significant differences for Fp (single slice, 256.1 ± 104.1 mL/100 mL/min; whole kidney, 217.2 ± 92.5 mL/100 mL/min; P < 0.01). Regarding VP and GFR, no significant differences were observed. The χ2 test showed a significantly better goodness of fit of the data to the curve for whole kidneys (0.30% ± 0.18%) than for single slices (0.43% ± 0.26%) (P < 0.01). In contrast to renal assessment, tumor analysis showed no significant differences regarding functional parameters and χ test, respectively.

CONCLUSION

In dynamic contrast-enhanced MRI of the kidney, both 3D whole-organ/tumor and single-slice analyses provide roughly comparable values in functional analysis. However, 3D assessment is considerably more precise and should be preferred if available.

Pre-clinical activity of PR-104 as monotherapy and in combination with sorafenib in hepatocellular carcinoma

PR-104 is a clinical stage bioreductive prodrug that is converted in vivo to its cognate alcohol, PR-104A. This dinitrobenzamide mustard is reduced to activated DNA cross-linking metabolites (hydroxylamine PR-104H and amine PR-104M) under hypoxia by one-electron reductases and independently of hypoxia by the 2-electron reductase aldo-keto reductase 1C3 (AKR1C3). High expression of AKR1C3, along with extensive hypoxia, suggested the potential of PR-104 for treatment of hepatocellular carcinoma (HCC). However, a phase IB trial with sorafenib demonstrated significant toxicity that was ascribed in part to reduced PR-104A clearance, likely reflecting compromised glucuronidation in patients with advanced HCC. Here, we evaluate the activity of PR-104 in HCC xenografts (HepG2, PLC/PRF/5, SNU-398, Hep3B) in mice, which do not significantly glucuronidate PR-104A. Cell line differences in sensitivity to PR-104A in vitro under aerobic conditions could be accounted for by differences in both expression of AKR1C3 (high in HepG2 and PLC/PRF/5) and sensitivity to the major active metabolite PR-104H, to which PLC/PRF/5 was relatively resistant, while hypoxic selectivity of PR-104A cytotoxicity and reductive metabolism was greatest in the low-AKR1C3 SNU-398 and Hep3B lines. Expression of AKR1C3 in HepG2 and PLC/PRF/5 xenografts was in the range seen in 21 human HCC specimens. PR-104 monotherapy elicited significant reductions in growth of Hep3B and HepG2 xenografts, and the combination with sorafenib was significantly active in all 4 xenograft models. The results suggest that better-tolerated analogs of PR-104, without a glucuronidation liability, may have the potential to exploit AKR1C3 and/or hypoxia in HCC in humans.

Detecting functional changes with [(18)F]FAZA in a renal cell carcinoma mouse model following sunitinib therapy

BACKGROUND

The multitargeting tyrosine kinase inhibitor (TKI) sunitinib is currently the first-line drug therapy for metastasizing renal cell carcinoma (RCC). TKIs have profound effects on tumor angiogenesis, leading to modifications of the tumor microenvironment. The goal of this study was to determine whether these treatment-induced changes can be detected with [(18)F]FAZA.

METHODS

The present study utilized positron emission tomography (PET) to analyze tumor oxygenation status during and after sunitinib therapy in the murine Caki-1 RCC tumor model. Dynamic and static scans were performed, as well as ex vivo biodistributions at 3 h post injection (p.i.). Immunohistochemical analysis of tumor tissue was carried out for the quantification of pimonidazole binding and the hypoxia-associated factors CD-31, Ki-67, and Von Willebrand factor (VWF). In addition, in vitro cellular uptake studies were done to analyze the direct effects of sunitinib on the Caki-1 cells.

RESULTS

During therapy with sunitinib (40 mg/kg/day), uptake of [(18)F]FAZA into Caki-1 mice decreased by 46 ± 5% (n = 4; 5 days) at 3 h post injection (p.i.) during the first study and 22 ± 5% (n = 8; 9 days) during the long-term study, indicating a decrease in the tumor's hypoxia level. However, when drug therapy was stopped, this effect was reversed completely, and the tumor [(18)F]FAZA uptake increased to 126 ± 6% (n = 6) of the control tumor uptake, indicative of an even higher level of tumor hypoxia compared to the therapy starting point. Sunitinib had no direct effect on [(18)F]FAZA uptake into Caki-1 cells in vitro.

CONCLUSION

[(18)F]FAZA PET could be used to monitor drug response during sunitinib therapy in RCC and may guide combination therapies based on the tumor's hypoxia status.

Dual tracer evaluation of dynamic changes in intratumoral hypoxic and proliferative states after radiotherapy of human head and neck cancer xenografts using radiolabeled FMISO and FLT

BACKGROUND

Radiotherapy is an important treatment strategy for head and neck cancers. Tumor hypoxia and repopulation adversely affect the radiotherapy outcome. Accordingly, fractionated radiotherapy with dose escalation or altered fractionation schedule is used to prevent hypoxia and repopulation. 18F-fluoromisonidazole (FMISO) and 18F-fluorothymidine (FLT) are noninvasive markers for assessing tumor hypoxia and proliferation, respectively. Thus, we evaluated the dynamic changes in intratumoral hypoxic and proliferative states following radiotherapy using the dual tracers of 18F-FMISO and 3H-FLT, and further verified the results by immunohistochemical staining of pimonidazole (a hypoxia marker) and Ki-67 (a proliferation marker) in human head and neck cancer xenografts (FaDu).

METHODS

FaDu xenografts were established in nude mice and assigned to the non-radiation-treated control and two radiation-treated groups (10- and 20-Gy). Tumor volume was measured daily. Mice were sacrificed 6, 24, and 48 hrs and 7 days after radiotherapy. 18F-FMISO, and 3H-FLT and pimonidazole were injected intravenously 4 and 2 hrs before sacrifice, respectively. Intratumoral 18F-FMISO and 3H-FLT levels were assessed by autoradiography. Pimonidazole and Ki-67 immunohistochemistries were performed.

RESULTS

In radiation-treated mice, tumor growth was significantly suppressed compared with the control group, but the tumor volume in these mice gradually increased with time. Visual inspection showed that intratumoral 18F-FMISO and 3H-FLT distribution patterns were markedly different. Intratumoral 18F-FMISO level did not show significant changes after radiotherapy among the non-radiation-treated control and radiation-treated groups, whereas 3H-FLT level markedly decreased to 59 and 45% of the non-radiation-treated control at 6 hrs (p<0.0001) and then gradually increased with time in the 10- and 20-Gy-radiation-treated groups. The pimonidazole-positive hypoxic areas were visually similar in both the non-radiation-treated control and radiation-treated groups. No significant differences were observed in the percentage of pimonidazole-positive cells and Ki-67 index.

CONCLUSION

Intratumoral 18F-FMISO level did not change until 7 days, whereas 3H-FLT level markedly decreased at 6 hrs and then gradually increased with time after a single dose of radiotherapy. The concomitant monitoring of dynamic changes in tumor hypoxia and proliferation may provide important information for a better understanding of tumor biology after radiotherapy and for radiotherapy planning, including dose escalation and altered fractionation schedules.

2-Methoxyestradiol synergizes with sorafenib to suppress hepatocellular carcinoma by simultaneously dysregulating hypoxia-inducible factor-1 and -2

Sorafenib is the approved systemic drug of choice for advanced hepatocellular carcinoma (HCC), but has demonstrated limited benefits because of drug resistance. 2-Methoxyestradiol (2ME2) has been shown to be a promising anticancer drug against various types of cancers and acts by dysregulating hypoxia-inducible factor (HIF)-1. Hypoxic cancer cells are extremely resistant to therapies since they elicit strong survival ability due to the cellular adaptive response to hypoxia, which is controlled by HIF-1 and HIF-2. The present study has demonstrated that sorafenib downregulated the expression of HIF-1α, making the hypoxic response switch from HIF-1α- to HIF-2α-dependent pathways, resulting in upregulation of HIF-2α, which contributes to the insensitivity of hypoxic HCC cells to sorafenib. HIF-2α played a dominant role in regulating VEGF, thus sorafenib in turn increased the expression of VEGF (a downstream molecule of both HIF-1 and HIF-2) and cyclin D1 (a downstream molecule of HIF-2), but reduced the expression of LDHA (a downstream molecule of HIF-1), in hypoxic HCC cells. 2ME2 significantly reduced the expression of both HIF-1α and HIF-2α, and their downstream molecules, VEGF, LDHA and cyclin D1, rendering hypoxic HCC cells to increased sensitivity to 2ME2. 2ME2 also inhibited the nuclear translocation of HIF-1α and HIF-2α proteins, but had no effect on their mRNA expression. 2M2 synergized with sorafenib to suppress the proliferation and induction of apoptosis of HCC cells in vitro and in vivo, and inhibited tumoral angiogenesis. These results indicate that 2ME2 given in combination with sorafenib acts synergistically for treating HCC.

Hypoxia modulates the activity of a series of clinically approved tyrosine kinase inhibitors

BACKGROUND AND PURPOSE

Hypoxia in tumours is known to cause resistance to conventional chemotherapeutic drugs. In contrast, little is known about the effects of hypoxia on targeted anti-cancer drugs. This study evaluated the effect of hypoxia on a series of clinically approved tyrosine kinase inhibitors (TKIs).

EXPERIMENTAL APPROACH

The effect of hypoxia (0.1% oxygen) on the activity of conventional cytotoxic drugs (5-fluorouracil, doxorubicin and vinblastine), the hypoxia-activated prodrug tirapazamine and 9 TKIs was determined in a panel of cell lines. Where hypoxia had a marked effect on chemosensitivity, Western blot analysis was conducted to determine the effect of hypoxia on target expression and the effect of TKIs on cell signalling response under aerobic and hypoxic conditions.

KEY RESULTS

Three patterns of chemosensitivity were observed: resistance under hypoxia, equitoxic activity against hypoxic and aerobic cells, and preferential cytotoxicity to hypoxic cells. Significant hypoxia selectivity (independent of HIF1) was observed in the case of dasatinib and this correlated with the ability of dasatinib to inhibit phosphorylation of Src at tyrosine 530. Sorafenib was significantly less effective under hypoxic conditions but resistance did not correlate with hypoxia-induced changes in Raf/MEK/ERK signalling.

CONCLUSIONS AND IMPLICATIONS

Hypoxia influences the activity of TKIs but in contrast to conventional cytotoxic drugs, preferential activity against hypoxic cells can occur. The search for hypoxia-targeted therapies has been long and fruitless and this study suggests that some clinically approved TKIs could preferentially target the hypoxic fraction of some tumour types.

Involvement of the NF-кB/p50/Bcl-3 complex in response to antiangiogenic therapy in a mouse model of metastatic renal cell carcinoma

Renal cell carcinoma (RCC) represents approximately 2-3% of human malignancies. Nuclear transcription factor кB (NF-кB) is composed of a family of transcription factors that have been associated with the development and progression of RCC. Endostatin (ES) is a fragment of collagen XVIII that possesses antiangiogenic activity. In this study, we evaluated the expression of NF-кB in metastatic tumor cells from animals treated with ES. Balb/c-bearing Renca-EGFP cells were treated with NIH/3T3-LendSN or NIH/3T3-LXSN cells as a control. At the end of the in vivo experiment, plasma Renca-EGFP-sorted cells and tissue lung samples were collected. A real-time PCR array for NF-κB target genes revealed that ES therapy led to down regulation of Bcl-3 (P<0.031), NF-кB1 (P<0.001) and c-Rel (P<0.004) in the ES-treated group. Using an electrophoretic mobility shift assay (EMSA), we observed a reduction in NF-kB binding activity in ES-treated Renca-EGP cells. Furthermore, a supershift assay showed a clear shift of the NF-кB DNA band in samples incubated with a p50 antibody. By immunohistochemistry analysis, ES treatment resulted in a significant reduction in expression of p50. (ES vs. control P<0.05). The immunoprecipitation experiments confirmed the presence of a p50/Bcl-3 complex in nuclear extracts from cells of metastatic lung tissues. Our findings indicate that p50 and Bcl-3 plays a regulatory role in gene transcription in RCC.

Mechanisms of resistance to sorafenib and the corresponding strategies in hepatocellular carcinoma

Sorafenib, the unique drug as first-line treatment for advanced hepatocellular carcinoma (HCC), has opened a window of hope after searching for effective agents to combat HCC for decades. However, the overall outcomes are far from satisfactory. One of the explanations is the genetic heterogeneity of HCC, which has led to identifying predictive biomarkers for primary resistance to sorafenib, and then applying the concept of personalized medicine, or seeking therapeutic strategies such as combining sorafenib with other anticancer agents. Some of the combinations have demonstrated a better effectiveness than sorafenib alone, with good tolerance. The acquired resistance to sorafenib has also drawn attention. As a multikinase inhibitor, sorafenib targets several cellular signaling pathways but simultaneously or sequentially the addiction switches and compensatory pathways are activated. Several mechanisms are involved in the acquired resistance to sorafenib, such as crosstalks involving PI3K/Akt and JAK-STAT pathways, hypoxia-inducible pathways, epithelial-mesenchymal transition, etc. Based on the investigated mechanisms, some other molecular targeted drugs have been applied as second-line treatment for treat HCC after the failure of sorafenib therapy and more are under evaluation in clinical trials. However, the exact mechanisms accounting for sorafenib resistance remains unclear. Further investigation on the crosstalk and relationship of associated pathways will better our understanding of the mechanisms and help to find effective strategies for overcoming sorafenib resistance in HCC.