Monitoring hypoxia and vasculature during bevacizumab treatment in a murine colorectal cancer model

Antiangiogenic-immune-checkpoint inhibitor combinations: lessons from phase III clinical trials

Antiangiogenic agents, generally antibodies or tyrosine-kinase inhibitors that target the VEGF-VEGFR pathway, are currently among the few combination partners clinically proven to improve the efficacy of immune-checkpoint inhibitors (ICIs). This benefit has been demonstrated in pivotal phase III trials across different cancer types, some with practice-changing results; however, numerous phase III trials have also had negative results. The rationale for using antiangiogenic drugs as partners for ICIs relies primarily on blocking the multiple immunosuppressive effects of VEGF and inducing several different vascular-modulating effects that can stimulate immunity, such as vascular normalization leading to increased intratumoural blood perfusion and flow, and inhibition of pro-apoptotic effects of endothelial cells on T cells, among others. Conversely, VEGF blockade can also cause changes that suppress antitumour immunity, such as increased tumour hypoxia, and reduced intratumoural ingress of co-administered ICIs. As a result, the net clinical benefits from antiangiogenic-ICI combinations will be determined by the balance between the opposing effects of VEGF signalling and its inhibition on the antitumour immune response. In this Perspective, we summarize the results from the currently completed phase III trials evaluating antiangiogenic agent-ICI combinations. We also discuss strategies to improve the efficacy of these combinations, focusing on aspects that include the deleterious functions of VEGF-VEGFR inhibition on antitumour immunity, vessel co-option as a driver of non-angiogenic tumour growth, clinical trial design, or the rationale for drug selection, dosing and scheduling.

Characterization of spatially mapped volumetric molecular ultrasound signals for predicting response to anti-vascular therapy

Quantitative three-dimensional molecular ultrasound is a promising technology for longitudinal imaging applications such as therapy monitoring; the risk profile is favorable compared to positron emission tomography and computed tomography. However, clinical translation of quantitative methods for this technology are limited in that they assume that tumor tissues are homogeneous, and often depend on contrast-destruction events that can produce unintended bioeffects. Here, we develop quantitative features (henceforth image features) that capture tumor spatial information, and that are extracted without contrast destruction. We compare these techniques with the contrast-destruction derived differential targeted enhancement parameter (dTE) in predicting response to therapy. We found thirty-three reproducible image features that predict response to antiangiogenic therapy, without the need for a contrast agent disruption pulse. Multiparametric analysis shows that several of these image features can differentiate treated versus control animals with comparable performance to post-destruction measurements, suggesting that these can potentially replace parameters such as the dTE. The highest performing pre-destruction image features showed strong linear correlations with conventional dTE parameters with less overall variance. Thus, our study suggests that image features obtained during the wash in of the molecular agent, pre-destruction, may replace conventional post-destruction image features or the dTE parameter.

Impact of hypoxia on DNA repair and genome integrity

Hypoxia is a hallmark of the tumour microenvironment with profound effects on tumour biology, influencing cancer progression, the development of metastasis and patient outcome. Hypoxia also contributes to genomic instability and mutation frequency by inhibiting DNA repair pathways. This review summarises the diverse mechanisms by which hypoxia affects DNA repair, including suppression of homology-directed repair, mismatch repair and base excision repair. We also discuss the effects of hypoxia mimetics and agents that induce hypoxia on DNA repair, and we highlight areas of potential clinical relevance as well as future directions.

Hypoxia Induces Transcriptional and Translational Downregulation of the Type I IFN Pathway in Multiple Cancer Cell Types

Hypoxia is a common phenomenon in solid tumors and is strongly linked to hallmarks of cancer. Recent evidence has shown that hypoxia promotes local immune suppression. Type I IFN supports cytotoxic T lymphocytes by stimulating the maturation of dendritic cells and enhancing their capacity to process and present antigens. However, little is known about the relationship between hypoxia and the type I IFN pathway, which comprises the sensing of double-stranded RNA and DNA (dsRNA/dsDNA) followed by IFNα/β secretion and transcriptional activation of IFN-stimulated genes (ISG). In this study, we determined the effects of hypoxia on the type I IFN pathway in breast cancer and the mechanisms involved. In cancer cell lines and xenograft models, mRNA and protein expressions of the type I IFN pathway were downregulated under hypoxic conditions. This pathway was suppressed at each level of signaling, from the dsRNA sensors RIG-I and MDA5, the adaptor MAVS, transcription factors IRF3, IRF7, and STAT1, and several ISG including RIG-I, IRF7, STAT1, and ADAR-p150. Importantly, IFN secretion was reduced under hypoxic conditions. HIF1α- and HIF2α-mediated regulation of gene expression did not explain most of the effects. However, ATAC-seq data revealed in hypoxia that peaks with STAT1 and IRF3 motifs had decreased accessibility. Collectively, these results indicate that hypoxia leads to an overall downregulation of the type I IFN pathway due to repressed transcription and lower chromatin accessibility in an HIF1/2α-independent manner, which could contribute to immunosuppression in hypoxic tumors. SIGNIFICANCE: These findings characterize a new mechanism of immunosuppression by hypoxia via downregulation of the type I IFN pathway and its autocrine/paracrine effects on tumor growth.

Resolution of Spatial and Temporal Heterogeneity in Bevacizumab-Treated Breast Tumors by Eigenspectra Multispectral Optoacoustic Tomography

Understanding temporal and spatial hemodynamic heterogeneity as a function of tumor growth or therapy affects the development of novel therapeutic strategies. In this study, we employed eigenspectra multispectral optoacoustic tomography (eMSOT) as a next-generation optoacoustic method to impart high accuracy in resolving tumor hemodynamics during bevacizumab therapy in two types of breast cancer xenografts (KPL-4 and MDA-MB-468). Patterns of tumor total hemoglobin concentration (THb) and oxygen saturation (sO₂) were imaged in control and bevacizumab-treated tumors over the course of 58 days (KPL-4) and 16 days (MDA-MB-468), and the evolution of functional vasculature "normalization" was resolved macroscopically. An initial sharp drop in tumor sO₂ and THb content shortly after the initiation of bevacizumab treatment was followed by a recovery in oxygenation levels. Rim-core subregion analysis revealed steep spatial oxygenation gradients in growing tumors that were reduced after bevacizumab treatment. Critically, eMSOT imaging findings were validated directly by histopathologic assessment of hypoxia (pimonidazole) and vascularity (CD31). These data demonstrate how eMSOT brings new abilities for accurate observation of entire tumor responses to challenges at spatial and temporal dimensions not available by other techniques today. SIGNIFICANCE: Accurate assessment of hypoxia and vascularization over space and time is critical for understanding tumor development and the role of spatial heterogeneity in tumor aggressiveness, metastasis, and response to treatment.

Relieving immunosuppression during long-term anti-angiogenesis therapy using photodynamic therapy and oxygen delivery

Angiogenesis is an irreplaceable therapeutic cancer target, where anti-angiogenesis are drugs that are limited by their hydrophobicity and low therapeutic effects. What is more, the long-term shutdown of tumor blood vessel density also aggravates hypoxia and causes immunosuppression in the tumor microenvironment (TME). In order to solve these shortcomings, we developed a single therapeutic agent based on a bovine serum albumin nanocarrier that can co-deliver the anti-angiogenic drug Sorafenib ("S") and the photosensitizer Ce6 ("C") along with a molecular oxygen supply based on MnO2 ("M") as a convenient one-pot formulated nanoscale agent (SCM@BSA). Compared with anti-angiogenesis monotherapy, SCM@BSA can not only improve upon the solubility and therapeutic effects of anti-angiogenesis agents, but it also reshapes the immunosuppressive TME during anti-angiogenic therapy. Together, these results point out that SCM@BSA synthesized via a very simple method can solve the shortcomings usually experienced during long-term anti-angiogenic therapy.

Cancer Stem Cells as a Potential Target to Overcome Multidrug Resistance

Multidrug resistance (MDR), which is a significant impediment to the success of cancer chemotherapy, is attributable to various defensive mechanisms in cancer. Initially, overexpression of ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) was considered the most important mechanism for drug resistance; hence, many investigators for a long time focused on the development of specific ABC transporter inhibitors. However, to date their efforts have failed to develop a clinically applicable drug, leaving only a number of problems. The concept of cancer stem cells (CSCs) has provided new directions for both cancer and MDR research. MDR is known to be one of the most important features of CSCs and thus plays a crucial role in cancer recurrence and exacerbation. Therefore, in recent years, research targeting CSCs has been increasing rapidly in search of an effective cancer treatment. Here, we review the drugs that have been studied and developed to overcome MDR and CSCs, and discuss the limitations and future perspectives.

Pharmacological methods to transcriptionally modulate double-strand break DNA repair

There is much interest in targeting DNA repair pathways for use in cancer therapy, as the effectiveness of many therapeutic agents relies on their ability to cause damage to DNA, and deficiencies in DSB repair pathways can make cells more sensitive to specific cancer therapies. For example, defects in the double-strand break (DSB) pathways, non-homologous end joining (NHEJ) and homology-directed repair (HDR), induce sensitivity to radiation therapy and poly(ADP)-ribose polymerase (PARP) inhibitors, respectively. However, traditional approaches to inhibit DNA repair through small molecule inhibitors have often been limited by toxicity and poor bioavailability. This review identifies several pharmacologic manipulations that modulate DSB repair by reducing expression of DNA repair factors. A number of pathways have been identified that modulate activity of NHEJ and HDR through this mechanism, including growth and hormonal receptor signaling pathways as well as epigenetic modifiers. We also discuss the effects of anti-angiogenic therapy on DSB repair. Preclinically, these pharmacological manipulations of DNA repair factor expression have been shown to increase sensitivity to specific cancer therapies, including ionizing radiation and PARP inhibitors. When applicable, relevant clinical trials are discussed and areas for future study are identified.

Low dose-rate irradiation with [3H]-labelled valine to selectively target hypoxic cells in a human colorectal cancer xenograft model

BACKGROUND

Earlier in vitro studies show that irradiation with an ultra-low dose-rate of 15 mGy/h delivered with [³H]-valine leads to loss of clonogenicity in hypoxic T-47D cells. Here, the aim was to determine if [³H]-valine could be used to deliver low dose-rate irradiation in a colorectal cancer model.

METHODS

Clonogenicity was measured in cultured cancer cell line HT29 irradiated with 15 mGy/h combined with intermittent hypoxia. Mice with HT29 xenografts were irradiated by repeated injections of [³H]-valine intravenously. The activity in the tumor tissue was measured by scintillation counting and tumor growth, hypoxic fraction and tritium distribution within tumors were assessed by pimonidazole staining and autoradiography.

RESULTS

Ultra-low dose-rate irradiation decreased clonogenicity in hypoxic colorectal cancer cells. In vivo, the tumor growth, hypoxic fraction and weight of the mice were similar between the treated and untreated group. Autoradiography showed no [³H]-valine uptake in hypoxic tumor regions in contrast to aerobic tissue.

CONCLUSION

Continuous low-dose-rate irradiation was well tolerated by aerobic tissue. This indicates a potential use of low dose-rate irradiation to target hypoxic tumor cells in combination with high dose-rate irradiation to eradicate the well oxygenated tumor regions. However, [³H]-valine is not the appropriate method to deliver ultra-low dose-rate irradiation in vivo.

Antiangiogenic therapy: Markers of response, "normalization" and resistance

Currently in cancer treatment, one premise is to use antiangiogenic therapies in association with chemotherapy or radiotherapy to augment their efficacy by benefiting from the vascular "normalization" induced by antiangiogenic therapy. This concept defines the time during which the tumor blood vessels adopt normal-like morphology and functionality, i.e. the blood vessels become more mature, the perfusion augments and hypoxia decreases. To date, there is such a diversity of treatment protocols where the type of antiangiogenic to adopt, its dose and duration of administration are different, that knowing when and how to treat is problematic. In this review, we analyzed thoroughly preclinical and clinical studies that use antiangiogenic treatments to benefit from the "normalization" and showed that the effects depend on the type of antiangiogenic administrated (anti-VEGF, anti-VEGFR, Multi-Kinase Inhibitor) and on the duration of treatment. Finally, biomarkers of "normalization" and resistance that could be used in the clinic are presented.

Stroma-derived HGF drives metabolic adaptation of colorectal cancer to angiogenesis inhibitors

The role of paracrine Hepatocyte Growth Factor (HGF) in the resistance to angiogenesis inhibitors (AIs) is hidden in xenograft models because mouse HGF fails to fully activate human MET. To uncover it, we compared the efficacy of AIs in wild-type and human HGF knock-in SCID mice bearing orthotopic human colorectal tumors. Species-specific HGF/MET signaling dramatically impaired the response to anti-angiogenic agents and boosted metastatic dissemination. In cell-based assays mimicking the consequences of anti-angiogenic therapy, colorectal cancer cells were completely resistant to hypoxia but extremely sensitive to nutrient deprivation. Starvation-induced apoptosis could be prevented by HGF, which promoted GLUT1-mediated glucose uptake, sustained glycolysis and activated autophagy. Pharmacological inhibition of GLUT1 in the presence of glucose killed tumor cells as effectively as glucose deprivation, and this effect was antagonized by HGF. Concomitant targeting of GLUT1 and HGF potently suppressed growth and dissemination of AI-resistant human tumors in human HGF knock-in SCID mice without exacerbating tumor hypoxia. These data suggest that stroma-derived HGF protects CRC cells against glucose starvation-induced apoptosis, promoting resistance to both AIs and anti-glycolytic agents. Combined inhibition of glucose metabolism and HGF/MET signaling (‘anti-METabolic therapy’) may represent a more effective CRC treatment compared to utterly blocking tumor blood supply.

The quaternary state of polymerized human hemoglobin regulates oxygenation of breast cancer solid tumors: A theoretical and experimental study

A major constraint in the treatment of cancer is inadequate oxygenation of the tumor mass, which can reduce chemotherapeutic efficacy. We hypothesize that polymerized human hemoglobin (PolyhHb) can be transfused into the systemic circulation to increase solid tumor oxygenation, and improve chemotherapeutic outcomes. By locking PolyhHb in the relaxed (R) quaternary state, oxygen (O2) offloading at low O2 tensions (<20 mm Hg) may be increased, while O2 offloading at high O2 tensions (>20 mm Hg) is facilitated with tense (T) state PolyhHb. Therefore, R-state PolyhHb may deliver significantly more O2 to hypoxic tissues. Biophysical parameters of T and R-state PolyhHb were used to populate a modified Krogh tissue cylinder model to assess O2 transport in a tumor. In general, we found that increasing the volume of transfused PolyhHb decreased the apparent viscosity of blood in the arteriole. In addition, we found that PolyhHb transfusion decreased the wall shear stress at large arteriole diameters (>20 μm), but increased wall shear stress for small arteriole diameters (<10 μm). Therefore, transfusion of PolyhHb may lead to elevated O2 delivery at low pO2. In addition, transfusion of R-state PolyhHb may be more effective than T-state PolyhHb for O2 delivery at similar transfusion volumes. Reduction in the apparent viscosity resulting from PolyhHb transfusion may result in significant changes in flow distributions throughout the tumor microcirculatory network. The difference in wall shear stress implies that PolyhHb may have a more significant effect in capillary beds through mechano-transduction. Periodic top-load transfusions of PolyhHb into mice bearing breast tumors confirmed the oxygenation potential of both PolyhHbs via reduced hypoxic volume, vascular density, tumor growth, and increased expression of hypoxia inducible genes. Tissue section analysis demonstrated primary PolyhHb clearance occurred in the liver and spleen indicating a minimal risk for renal damage.

Early prediction of tumor response to bevacizumab treatment in murine colon cancer models using three-dimensional dynamic contrast-enhanced ultrasound imaging

Due to spatial tumor heterogeneity and consecutive sampling errors, it is critically important to assess treatment response following antiangiogenic therapy in three dimensions as two-dimensional assessment has been shown to substantially over- and underestimate treatment response. In this study, we evaluated whether three-dimensional (3D) dynamic contrast-enhanced ultrasound (DCE-US) imaging allows assessing early changes in tumor perfusion following antiangiogenic treatment (bevacizumab administered at a dose of 10 mg/kg b.w.), and whether these changes could predict treatment response in colon cancer tumors that either are responsive (LS174T tumors) or none responsive (CT26) to the proposed treatment. Our results showed that the perfusion parameters of 3D DCE-US including peak enhancement (PE) and area under curve (AUC) significantly decreased by up to 69 and 77%, respectively, in LS174T tumors within 1 day after antiangiogenic treatment (P = 0.005), but not in CT26 tumors (P > 0.05). Similarly, the percentage area of neovasculature significantly decreased in treated versus control LS174T tumors (P < 0.001), but not in treated versus control CT26 tumors (P = 0.796). Early decrease in both PE and AUC by 45-50% was predictive of treatment response in 100% (95% CI 69.2, 100%) of responding tumors, and in 100% (95% CI 88.4, 100%) and 86.7% (95% CI 69.3, 96.2%), respectively, of nonresponding tumors. In conclusion, 3D DCE-US provides clinically relevant information on the variability of tumor response to antiangiogenic therapy and may be further developed as biomarker for predicting treatment outcomes.

Breaking the crosstalk of the cellular tumorigenic network: Hypothesis for addressing resistances to targeted therapies in advanced NSCLC

In the light of current treatment developments for non-small cell lung cancer (NSCLC), the idea of a plastic cellular tumorigenic network bound by key paracrine signaling pathways mediating resistances to targeted therapies is brought forward. Based on a review of available preclinical and clinical data in NSCLC combinational approaches to address drivers of this network with marketed drugs are discussed. Five criteria for selecting drug combination regimens aiming at its disruption and thereby overcoming resistances are postulated.

Targeting Hypoxia-Inducible Factors for Antiangiogenic Cancer Therapy

Hypoxia (low O₂) is a pathobiological hallmark of solid cancers, resulting from the imbalance between cellular O₂ consumption and availability. Hypoxic cancer cells (CCs) stimulate blood vessel sprouting (angiogenesis), aimed at restoring O₂ delivery to the expanding tumor masses through the activation of a transcriptional program mediated by hypoxia-inducible factors (HIFs). Here, we review recent data suggesting that the efficacy of antiangiogenic (AA) therapies is limited in some circumstances by HIF-dependent compensatory responses to increased intratumoral hypoxia. In lieu of this evidence, we discuss the potential of targeting HIFs as a strategy to overcome these instances of AA therapy resistance.

68Ga-TRAP-(RGD)3 Hybrid Imaging for the In Vivo Monitoring of αvß3-Integrin Expression as Biomarker of Anti-Angiogenic Therapy Effects in Experimental Breast Cancer

Objectives

To investigate ⁶⁸Ga-TRAP-(RGD)₃ hybrid imaging for the in vivo monitoring of α_vß₃-integrin expression as biomarker of anti-angiogenic therapy effects in experimental breast cancer.

Materials and Methods

Human breast cancer (MDA-MB-231) xenografts were implanted orthotopically into the mammary fat pads of n = 25 SCID mice. Transmission/emission scans (53 min to 90 min after i.v. injection of 20 MBq ⁶⁸Ga-TRAP-(RGD)₃) were performed on a dedicated small animal PET before (day 0, baseline) and after (day 7, follow-up) a 1-week therapy with the VEGF antibody bevacizumab or placebo (imaging cohort n = 13; therapy n = 7, control n = 6). The target-to-background ratio (TBR, VOImax_tumor/VOImean_muscle) served as semiquantitative measure of tumor radiotracer uptake. Unenhanced CT data sets were subsequently acquired for anatomic coregistration and morphology-based tumor response assessments (CT volumetry). The imaging results were validated by multiparametric ex vivo immunohistochemistry (α_vß₃-integrin, microvascular density–CD31, proliferation–Ki-67, apoptosis–TUNEL) conducted in a dedicated immunohistochemistry cohort (n = 12).

Results

⁶⁸Ga-TRAP-(RGD)₃ binding was significantly reduced under VEGF inhibition and decreased in all bevacizumab-treated animals (ΔTBR_{follow-up/baseline}: therapy -1.07±0.83, control +0.32±1.01, p = 0.022). No intergroup difference in tumor volume development between day 0 and day 7 was observed (Δvolume_therapy 134±77 μL, Δvolume_control 132±56 μL, p = 1.000). Immunohistochemistry revealed a significant reduction of α_vß₃-integrin expression (308±135 vs. 635±325, p = 0.03), microvascular density (CD31, 168±108 vs. 432±70, p = 0.002), proliferation (Ki-67, 5,195±1,002 vs. 7,574±418, p = 0.004) and significantly higher apoptosis (TUNEL, 14,432±1,974 vs. 3,776±1,378, p = 0.002) in the therapy compared to the control group.

Conclusions

⁶⁸Ga-TRAP-(RGD)₃ hybrid imaging allows for the in vivo assessment of α_vß₃-integrin expression as biomarker of anti-angiogenic therapy effects in experimental breast cancer.

Monitoring Tumor Hypoxia Using (18)F-FMISO PET and Pharmacokinetics Modeling after Photodynamic Therapy

Photodynamic therapy (PDT) is an efficacious treatment for some types of cancers. However, PDT-induced tumor hypoxia as a result of oxygen consumption and vascular damage can reduce the efficacy of this therapy. Measuring and monitoring intrinsic and PDT-induced tumor hypoxia in vivo during PDT is of high interest for prognostic and treatment evaluation. In the present study, static and dynamic (18)F-FMISO PET were performed with mice bearing either U87MG or MDA-MB-435 tumor xenografts immediately before and after PDT at different time points. Significant difference in tumor hypoxia in response to PDT over time was found between the U87MG and MDA-MB-435 tumors in both static and dynamic PET. Dynamic PET with pharmacokinetics modeling further monitored the kinetics of (18)F-FMISO retention to hypoxic sites after treatment. The Ki and k3 parametric analysis provided information on tumor hypoxia by distinction of the specific tracer retention in hypoxic sites from its non-specific distribution in tumor. Dynamic (18)F-FMISO PET with pharmacokinetics modeling, complementary to static PET analysis, provides a potential imaging tool for more detailed and more accurate quantification of tumor hypoxia during PDT.

VEGFR2-Targeted Three-Dimensional Ultrasound Imaging Can Predict Responses to Antiangiogenic Therapy in Preclinical Models of Colon Cancer

Three-dimensional (3D) imaging capabilities to assess responses to anticancer therapies are needed to minimize sampling errors common to two-dimensional approaches as a result of spatial heterogeneity in tumors. Recently, the feasibility and reproducibility of 3D ultrasound molecular imaging (3D USMI) using contrast agents, which target molecular markers, have greatly improved, due to the development of clinical 3D matrix array transducers. Here we report preclinical proof-of-concept studies showing that 3D USMI of VEGFR2/KDR expression accurately gauges longitudinal treatment responses to antiangiogenesis therapy in responding versus nonresponding mouse models of colon cancer. Tumors in these models exhibited differential patterns of VEGFR2-targeted 3D USMI signals during the course of antiangiogenic treatment with bevacizumab. In responding tumors, the VEGFR2 signal decreased as soon as 24 hours after therapy was started, whereas in nonresponding tumors there was no change in signal at any time point. The early decrease in VEGFR2 signal was highly predictive of treatment outcome at the end of therapy. Our results offer preclinical proof that 3D USMI can predict responses to antiangiogenic therapy, warranting further investigation of its clinical translatability to predicting treatment outcomes in patients. Cancer Res; 76(14); 4081-9. ©2016 AACR.

Radiation treatment monitoring using multimodal functional imaging: PET/CT ((18)F-Fluoromisonidazole & (18)F-Fluorocholine) and DCE-US

Background

This study aims to assess the effect of radiation treatment on the tumour vasculature and its downstream effects on hypoxia and choline metabolism using a multimodal approach in the murine prostate tumour model CWR22. Functional parameters derived from Positron Emission Tomography (PET)/Computer Tomography (CT) with ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) and ¹⁸F-Fluorocholine (¹⁸F-FCH) as well as Dynamic Contrast-Enhanced Ultrasound (DCE-US) were employed to determine the relationship between metabolic parameters and microvascular parameters that reflect the tumour microenvironment. Immunohistochemical analysis was employed for validation.

Methods

PET/CT and DCE-US were acquired pre- and post-treatment, at day 0 and day 3, respectively. At day 1, radiation treatment was delivered as a single fraction of 10 Gy. Two experimental groups were tested for treatment response with ¹⁸F-FMISO and ¹⁸F-FCH.

Results

The maximum Standardized Uptake Values (SUVmax) and the mean SUV (SUVmean) for the ¹⁸F-FMISO group were decreased after treatment, and the SUVmean of the tumour-to-muscle ratio was correlated to microvessel density (MVD) at day 3. The kurtosis of the amplitude of the contrast uptake A was significantly decreased for the control tumours in the ¹⁸F-FCH group. Furthermore, the eliminating rate constant of the contrast agent from the plasma k_el derived from DCE-US was negatively correlated to the SUVmean of tumour-to-muscle ratio, necrosis and MVD.

Conclusions

The present study suggests that the multimodal approach using ¹⁸F-FMISO PET/CT and DCE-US seems reliable in the assessment of both microvasculature and necrosis as validated by histology. Thus, it has valuable diagnostic and prognostic potential for early non-invasive evaluation of radiotherapy.

A pilot study of the effects of mild systemic heating on human head and neck tumour xenografts: Analysis of tumour perfusion, interstitial fluid pressure, hypoxia and efficacy of radiation therapy

PURPOSE

The tumour microenvironment is frequently hypoxic, poorly perfused, and exhibits abnormally high interstitial fluid pressure. These factors can significantly reduce efficacy of chemo and radiation therapies. The present study aims to determine whether mild systemic heating alters these parameters and improves response to radiation in human head and neck tumour xenografts in SCID mice.

MATERIALS AND METHODS

SCID mice were injected with FaDu cells (a human head and neck carcinoma cell line), or implanted with a resected patient head and neck squamous cell carcinoma grown as a xenograft, followed by mild systemic heating. Body temperature during heating was maintained at 39.5 ± 0.5 °C for 4 h. Interstitial fluid pressure (IFP), hypoxia and relative tumour perfusion in the tumours were measured at 2 and 24 h post-heating. Tumour vessel perfusion was measured 24 h post-heating, coinciding with the first dose of fractionated radiotherapy.

RESULTS

Heating tumour-bearing mice resulted in significant decrease in intratumoural IFP, increased the number of perfused tumour blood vessels as well as relative tumour perfusion in both tumour models. Intratumoural hypoxia was also reduced in tumours of mice that received heat treatment. Mice bearing FaDu tumours heated 24 h prior to five daily radiation treatments exhibited significantly enhanced tumour response compared to tumours in control mice.

CONCLUSIONS

Mild systemic heating can significantly alter the tumour microenvironment of human head and neck tumour xenograft models, decreasing IFP and hypoxia while increasing microvascular perfusion. Collectively, these effects could be responsible for the improved response to radiotherapy.

Multimodality imaging to predict response to systemic treatment in patients with advanced colorectal cancer

Aim

Aim of this study was to investigate the potential of ¹⁸F-FDG PET, diffusion weighted imaging (DWI) and susceptibility-weighted (T2*) MRI to predict response to systemic treatment in patients with colorectal liver metastases. The predictive values of pretreatment measurements and of early changes one week after start of therapy, were evaluated.

Methods

Imaging was performed prior to and one week after start of first line chemotherapy in 39 patients with colorectal liver metastases. ¹⁸F-FDG PET scans were performed on a PET/CT scanner and DWI and T2* were performed on a 1.5T MR scanner. The maximum standardized uptake values (SUV), total lesion glycolysis (TLG), apparent diffusion coefficient (ADC) and T2* value were assessed in the same lesions. Up to 5 liver metastases per patient were analyzed. Outcome measures were progression free survival (PFS), overall survival (OS) and size response.

Results

Pretreatment, high SUV_max, high TLG, low ADC and high T2* were associated with a shorter OS. Low pretreatment ADC value was associated with shorter PFS. After 1 week a significant drop in SUV_max and rise in ADC were observed. The drop in SUV was correlated with the rise in ADC (r=-0.58, p=0.002). Neither change in ADC nor in SUV was predictive of PFS or OS. T2* did not significantly change after start of treatment.

Conclusion

Pretreatment SUV_max, TLG, ADC, and T2* values in colorectal liver metastases are predictive of patient outcome. Despite sensitivity of DWI and ¹⁸F-FDG PET for early treatment effects, change in these parameters was not predictive of long term outcome.

High-uptake areas on positron emission tomography with the hypoxic radiotracer (18)F-FRP170 in glioblastomas include regions retaining proliferative activity under hypoxia

Objective

The aim was to evaluate the proliferative activity of high-uptake areas on positron emission tomography (PET) with the hypoxic cell radiotracer, 1-(2-[¹⁸F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP170).

Methods

Thirteen patients with glioblastoma underwent FRP170 PET before tumor resection. During surgery, tumor specimens were stereotaxically obtained from regions corresponding to high (high-uptake areas, HUAs) and relatively low (low-uptake areas, LUAs) accumulation of FRP170. We compared immunohistochemical staining for Ki-67 and hypoxia-inducible factor (HIF)-1α between HUA and LUA.

Results

HIF-1α index was significantly higher in HUAs than in LUAs. In contrast, mean Ki-67 indices did not differ significantly between HUAs and LUAs.

Conclusions

Findings for HIF-1α index clearly indicated that HUAs on FRP170 PET represented hypoxic regions in glioblastoma. However, findings of Ki-67 index suggest that HUAs on FRP170 PET include regions retaining proliferative activity regardless of tissue hypoxia.