Changes in blood perfusion and hypoxia after irradiation of a human squamous cell carcinoma xenograft tumor line

Enhanced perfusion following exposure to radiotherapy: A theoretical investigation

Tumour angiogenesis leads to the formation of blood vessels that are structurally and spatially heterogeneous. Poor blood perfusion, in conjunction with increased hypoxia and oxygen heterogeneity, impairs a tumour's response to radiotherapy. The optimal strategy for enhancing tumour perfusion remains unclear, preventing its regular deployment in combination therapies. In this work, we first identify vascular architectural features that correlate with enhanced perfusion following radiotherapy, using in vivo imaging data from vascular tumours. Then, we present a novel computational model to determine the relationship between these architectural features and blood perfusion in silico. If perfusion is defined to be the proportion of vessels that support blood flow, we find that vascular networks with small mean diameters and large numbers of angiogenic sprouts show the largest increases in perfusion post-irradiation for both biological and synthetic tumours. We also identify cases where perfusion increases due to the pruning of hypoperfused vessels, rather than blood being rerouted. These results indicate the importance of considering network composition when determining the optimal irradiation strategy. In the future, we aim to use our findings to identify tumours that are good candidates for perfusion enhancement and to improve the efficacy of combination therapies.

Repeated Contrast-Enhanced Micro-CT Examinations Decrease Animal Welfare and Influence Tumor Physiology

OBJECTIVES

Computed tomography (CT) imaging is considered relatively safe and is often used in preclinical research to study physiological processes. However, the sum of low-dose radiation, anesthesia, and animal handling might impact animal welfare and physiological parameters. This is particularly relevant for longitudinal studies with repeated CT examinations. Therefore, we investigated the influence of repeated native and contrast-enhanced (CE) CT on animal welfare and tumor physiology in regorafenib-treated and nontreated tumor-bearing mice.

MATERIAL AND METHODS

Mice bearing 4T1 breast cancer were divided into 5 groups: (1) no imaging, (2) isoflurane anesthesia only, (3) 4 mGy CT, (4) 50 mGy CT, and (5) CE-CT (iomeprol). In addition, half of each group was treated with the multikinase inhibitor regorafenib. Mice were imaged 3 times within 1 week under isoflurane anesthesia. Behavioral alterations were investigated by score sheet evaluation, rotarod test, heart rate measurements, and fecal corticosterone metabolite analysis. Tumor growth was measured daily with a caliper. Tumors were excised at the end of the experiment and histologically examined for blood vessel density, perfusion, and cell proliferation.

RESULTS

According to the score sheet, animals showed a higher burden after anesthesia administration and in addition with CT imaging ( P < 0.001). Motor coordination was not affected by native CT, but significantly decreased after CE-CT in combination with the tumor therapy ( P < 0.001). Whereas tumor growth and blood vessel density were not influenced by anesthesia or imaging, CT-scanned animals had a higher tumor perfusion ( P < 0.001) and a lower tumor cell proliferation ( P < 0.001) for both radiation doses. The most significant difference was observed between the control and CE-CT groups.

CONCLUSION

Repeated (CE-) CT imaging of anesthetized animals can lead to an impairment of animal motor coordination and, thus, welfare. Furthermore, these standard CT protocols seem to be capable of inducing alterations in tumor physiology when applied repetitively. These potential effects of native and CE-CT should be carefully considered in preclinical oncological research.

A simple mathematical model of cyclic hypoxia and its impact on hypofractionated radiotherapy

PURPOSE

There is evidence that the population of cells that experience fluctuating oxygen levels ("acute," or, "cyclic" hypoxia) are more radioresistant than chronically hypoxic ones and hence, this population may determine radiotherapy (RT) response, in particular for hypofractionated RT, where reoxygenation may not be as prominent. A considerable effort has been devoted to examining the impact of hypoxia on hypofractionated RT; however, much less attention has been paid to cyclic hypoxia specifically and the role its kinetics may play in determining the efficacy of these treatments. Here, a simple mathematical model of cyclic hypoxia and fractionation effects was worked out to quantify this.

METHODS

Cancer clonogen survival fraction was estimated using the linear quadratic model, modified to account for oxygen enhancement effects. An analytic approximation for oxygen transport away from a random network of capillaries with fluctuating oxygen levels was used to model inter-fraction tissue oxygen kinetics. The resulting survival fraction formula was used to derive an expression for the iso-survival biologically effective dose (BED), BED_iso-SF . These were computed for some common extra-cranial hypofractionated RT regimens.

RESULTS

Using relevant literature parameter values, inter-fraction fluctuations in oxygenation were found to result in an added 1-2 logs of clonogen survival fraction in going from five fractions to one for the same nominal BED (i.e., excluding the effects of oxygen levels on radiosensitivity). BED_iso-SF 's for most ultra-hypofractionated (five or fewer fractions) regimens in a given tumor site are similar in magnitude, suggesting iso-efficacy for common fractionation schedules.

CONCLUSIONS

Although significant, the loss of cell-killing with increasing hypofractionation is not nearly as large as previous estimates based on the assumption of complete reoxygenation between fractions. Most ultra-hypofractionated regimens currently in place offer sufficiently high doses to counter this loss of cell killing, although care should be taken in implementing single-fraction regimens.

Noninvasive optoacoustic microangiography reveals dose and size dependency of radiation-induced deep tumor vasculature remodeling

Tumor microvascular responses may provide a sensitive readout indicative of radiation therapy efficacy, its time course and dose dependencies. However, direct high-resolution observation and longitudinal monitoring of large-scale microvascular remodeling in deep tissues remained challenging with the conventional microscopy approaches.

We report on a non-invasive longitudinal study of morphological and functional neovascular responses by means of scanning optoacoustic (ОА) microangiography. In vivo imaging of CT26 tumor response to a single irradiation at varying dose (6, 12, and 18 Gy) has been performed over ten days following treatment. Tumor oxygenation levels were further estimated using diffuse optical spectroscopy (DOS) with a contact fiber probe.

OA revealed the formation of extended vascular structures on the whole tumor scale during its proliferation, whereas only short fragmented vascular regions were identified following irradiation. On the first day post treatment, a decrease in the density of small (capillary-sized) and medium-sized vessels was revealed, accompanied by an increase in their fragmentation. Larger vessels exhibited an increase in their density accompanied by a decline in the number of vascular segments. Short-lasting response has been observed after 6 and 12 Gy irradiations, whereas 18 Gy treatment resulted in prolonged responses, up to the tenth day after irradiation. DOS measurements further revealed a delayed increase of tumor oxygenation levels for 18 Gy irradiations, commencing on the sixth day post treatment. The ameliorated oxygenation is attributed to diminished oxygen consumption by inhibited tumor cells but not to the elevation of oxygen supply.

This work is the first to demonstrate the differential (size-dependent) nature of vascular responses to radiation treatments at varying doses in vivo. The OA approach thus facilitates the study of radiation-induced vascular changes in an unperturbed in vivo environment while enabling deep tissue high-resolution observations at the whole tumor scale.

The Potential of Photoacoustic Imaging in Radiation Oncology

Radiotherapy is recognized globally as a mainstay of treatment in most solid tumors and is essential in both curative and palliative settings. Ionizing radiation is frequently combined with surgery, either preoperatively or postoperatively, and with systemic chemotherapy. Recent advances in imaging have enabled precise targeting of solid lesions yet substantial intratumoral heterogeneity means that treatment planning and monitoring remains a clinical challenge as therapy response can take weeks to manifest on conventional imaging and early indications of progression can be misleading. Photoacoustic imaging (PAI) is an emerging modality for molecular imaging of cancer, enabling non-invasive assessment of endogenous tissue chromophores with optical contrast at unprecedented spatio-temporal resolution. Preclinical studies in mouse models have shown that PAI could be used to assess response to radiotherapy and chemoradiotherapy based on changes in the tumor vascular architecture and blood oxygen saturation, which are closely linked to tumor hypoxia. Given the strong relationship between hypoxia and radio-resistance, PAI assessment of the tumor microenvironment has the potential to be applied longitudinally during radiotherapy to detect resistance at much earlier time-points than currently achieved by size measurements and tailor treatments based on tumor oxygen availability and vascular heterogeneity. Here, we review the current state-of-the-art in PAI in the context of radiotherapy research. Based on these studies, we identify promising applications of PAI in radiation oncology and discuss the future potential and outstanding challenges in the development of translational PAI biomarkers of early response to radiotherapy.

Therapeutic targeting of the hypoxic tumour microenvironment

Hypoxia is prevalent in human tumours and contributes to microenvironments that shape cancer evolution and adversely affect therapeutic outcomes. Historically, two different tumour microenvironment (TME) research communities have been discernible. One has focused on physicochemical gradients of oxygen, pH and nutrients in the tumour interstitium, motivated in part by the barrier that hypoxia poses to effective radiotherapy. The other has focused on cellular interactions involving tumour and non-tumour cells within the TME. Over the past decade, strong links have been established between these two themes, providing new insights into fundamental aspects of tumour biology and presenting new strategies for addressing the effects of hypoxia and other microenvironmental features that arise from the inefficient microvascular system in solid tumours. This Review provides a perspective on advances at the interface between these two aspects of the TME, with a focus on translational therapeutic opportunities relating to the elimination and/or exploitation of tumour hypoxia.

Letter to the editor: Hypoxia kinetics and histology in combined radiotherapy and oxidative phosphorylation inhibition effects on antitumor immunity

In response to the recent paper by Chen et al investigating the triple combination of oxidative phosphorylation inhibition, immunotherapy and radiotherapy, we would like to stress that after irradiation, a strong reduction in hypoxia (within 24 hours) can be followed by a strong increase (several days). This is especially the case with larger fraction sizes of radiation therapy, which are often applied in combination with immunotherapy, and is likely to be tumor dependent. All together this may strongly affect the synergistic effect of such a triple combination therapy.

Cherenkov emissions for studying tumor changes during radiation therapy: An exploratory study in domesticated dogs with naturally-occurring cancer

PURPOSE

Real-time monitoring of physiological changes of tumor tissue during radiation therapy (RT) could improve therapeutic efficacy and predict therapeutic outcomes. Cherenkov radiation is a normal byproduct of radiation deposited in tissue. Previous studies in rat tumors have confirmed a correlation between Cherenkov emission spectra and optical measurements of blood-oxygen saturation based on the tissue absorption coefficients. The purpose of this study is to determine if it is feasible to image Cherenkov emissions during radiation therapy in larger human-sized tumors of pet dogs with cancer. We also wished to validate the prior work in rats, to determine if Cherenkov emissions have the potential to act an indicator of blood-oxygen saturation or water-content changes in the tumor tissue-both of which have been correlated with patient prognosis.

METHODS

A DoseOptics camera, built to image the low-intensity emission of Cherenkov radiation, was used to measure Cherenkov intensities in a cohort of cancer-bearing pet dogs during clinical irradiation. Tumor type and location varied, as did the radiation fractionation scheme and beam arrangement, each planned according to institutional standard-of-care. Unmodulated radiation was delivered using multiple 6 MV X-ray beams from a clinical linear accelerator. Each dog was treated with a minimum of 16 Gy total, in ≥3 fractions. Each fraction was split into at least three subfractions per gantry angle. During each subfraction, Cherenkov emissions were imaged.

RESULTS

We documented significant intra-subfraction differences between the Cherenkov intensities for normal tissue, whole-tumor tissue, tissue at the edge of the tumor and tissue at the center of the tumor (p<0.05). Additionally, intra-subfraction changes suggest that Cherenkov emissions may have captured fluctuating absorption properties within the tumor.

CONCLUSION

Here we demonstrate that it is possible to obtain Cherenkov emissions from canine cancers within a fraction of radiotherapy. The entire optical spectrum was obtained which includes the window for imaging changes in water and hemoglobin saturation. This lends credence to the goal of using this method during radiotherapy in human patients and client-owned pets.

Dual-Tracer Assessment of Dynamic Changes in Reoxygenation and Proliferation Decrease During Fractionated Radiotherapy in Murine Tumors

Objective: The present work aimed to assess reoxygenation and tumor inhibition during fractionated radiotherapy (FRT) in murine tumors using ¹⁸F-fluoromisonidazole (¹⁸F-FMISO) and ¹⁸F-fluorothymidine (¹⁸F-FLT) based micro positron emission tomography/computed tomography (PET/CT).

Materials and Methods: A nude mouse xenograft model was established with the head and neck squamous carcinoma cell (FaDu), followed by administration of FRT. Imaging was carried out with both ¹⁸F-FMISO and ¹⁸F-FLT PET/CT, prior to FRT (Pre-FRT, 0 Gy), during FRT (Inter-FRT, 21 Gy), and after FRT (Post-FRT, 40 Gy). The maximum standardized uptake (SUVmax) and tumor-to-normal muscle ratio (TNR) were determined in regions of interest (ROIs) in ¹⁸F-FMISO and ¹⁸F-FLT PET/CT images. Then, hypoxic (HV) and proliferative tumor (PTV) volumes obtained by PET/CT were analyzed. Immunohistochemistry was performed to analyze the changes of hypoxia-inducible factor- (HIF)-1α, carbonic anhydrase 9 (CAIX), Ki67 and proliferating cell nuclear antigen (PCNA). Associations of the levels of these biomarkers with PET/CT parameters were analyzed.

Results:¹⁸F-FMISO PET/CT demonstrated markedly elevated reduction rates of SUVmax (30.3 vs. 14.5%, p = 0.012), TNR (27.9 vs. 18.3%, p = 0.032) and HV (85.0 vs. 71.4%, p = 0.047) from Pre-FRT to Inter-FRT compared with values from Inter-FRT to Post-FRT. Meanwhile, PTV reduction rate in ¹⁸F-FLT PET/CT from Pre-FRT to Inter-FRT was significantly decreased compared with that from Inter-FRT to Post-FRT (21.2 vs. 82.7%, p = 0.012). Tumor HIF-1α, CAIX, Ki67, and PCNA amounts were continuously down-regulated during radiotherapy. TNR (FMISO) showed significant correlations with HIF-1α (r = 0.692, p = 0.015) and CAIX (r = 0.801, p = 0.006) amounts in xenografts, while associations of SUVmax (FMISO) with hypoxia markers were weak (r = 0.418, p = 0.041 and r = 0.389, p = 0.037, respectively). SUVmax (FLT) was significantly correlated with Ki67 (r = 0.792, p = 0.003) and PCNA (r = 0.837, p = 0.004).

Conclusions: Tumor reoxygenation occurs early during radiotherapy, while inhibition of cell proliferation by tumoricidal effects mainly takes place gradually with the course of radiotherapy. ¹⁸F-FMISO and ¹⁸F-FLT PET/CT are sensitive and non-invasive tools for the monitoring of tumor reoxygenation and proliferation during radiotherapy.

Noninvasive imaging of tumor hypoxia after nanoparticle-mediated tumor vascular disruption

We have previously demonstrated that endothelial targeting of gold nanoparticles followed by external beam irradiation can cause specific tumor vascular disruption in mouse models of cancer. The induced vascular damage may lead to changes in tumor physiology, including tumor hypoxia, thereby compromising future therapeutic interventions. In this study, we investigate the dynamic changes in tumor hypoxia mediated by targeted gold nanoparticles and clinical radiation therapy (RT). By using noninvasive whole-body fluorescence imaging, tumor hypoxia was measured at baseline, on day 2 and day 13, post-tumor vascular disruption. A 2.5-fold increase (P<0.05) in tumor hypoxia was measured two days after combined therapy, resolving by day 13. In addition, the combination of vascular-targeted gold nanoparticles and radiation therapy resulted in a significant (P<0.05) suppression of tumor growth. This is the first study to demonstrate the tumor hypoxic physiological response and recovery after delivery of vascular-targeted gold nanoparticles followed by clinical radiation therapy in a human non-small cell lung cancer athymic Foxn1^nu mouse model.

Radiation Damage to Tumor Vasculature Initiates a Program That Promotes Tumor Recurrences

This review, mostly of preclinical data, summarizes the evidence that radiation at doses relevant to radiation therapy initiates a pathway that promotes the reconstitution of the tumor vasculature leading to tumor recurrence. The pathway is not specific to tumors; it promotes repair of damaged and ischemic normal tissues by attracting proangiogenic cells from the bone marrow. For irradiated tumors the pathway comprises: (1) loss of endothelial cells and reduced tumor blood perfusion leading to increased tumor hypoxia and increased levels of hypoxia inducible factor-1 (HIF-1). Alternatively, increased HIF-1 levels may arise by reactive oxygen species (ROS) production caused by tumor reoxygenation. (2) Increased HIF-1 levels lead to increased levels in the tumor of the chemokine stromal cell-derived factor-1 (SDF-1, CXCL12), which captures monocytes/macrophages expressing the CXCR4 receptor of CXCL12. (3) The increased levels of tumor-associated macrophages (TAMs) become highly proangiogenic (M2 polarized) and restore the tumor vasculature, thereby promoting tumor recurrence. The relevance of this pathway for radiation therapy is that it can be blocked in a number of different ways including by inhibitors of monocytes/macrophages, of HIF-1, of CXCL12, of CXCR4, and of CSF-1R, the latter of which is responsible for the M2 polarization of the TAMs. All of these inhibitors produce a robust enhancement of the radiation response of a wide variety of preclinical tumor models. Further, the same inhibitors actually provide protection against radiation damage of several normal tissues. Some of these pathway inhibitors are available clinically, and a first-in-human trial of the CXCR4 inhibitor, plerixafor, with radiation therapy of glioblastoma has yielded promising results, including an impressive increase in local tumor control. Further clinical trials are warranted.

Double Diffusion Encoding for Probing Radiation-Induced Microstructural Changes in a Tumor Model: A Proof-of-Concept Study With Comparison to the Apparent Diffusion Coefficient and Histology

BACKGROUND

Microstructure analyses are gaining interest in cancer MRI as an alternative to the conventional apparent diffusion coefficient (ADC), of which the determinants remain unclear.

PURPOSE

To assess the sensitivity of parameters calculated from a double diffusion encoding (DDE) sequence to changes in a tumor's microstructure early after radiotherapy and to compare them with ADC and histology.

STUDY TYPE

Cohort study on experimental tumors.

ANIMAL MODEL

Sixteen WAG/Rij rats grafted with one rhabdomyosarcoma fragment in each thigh. Thirty-one were imaged at days 1 and 4, of which 17 tumors received a 20 Gy radiation dose after the first imagery.

FIELD STRENGTH/SEQUENCE

3T. Diffusion-weighted imaging, DDE with flow compensated, and noncompensated measurements.

ASSESSMENTS

1) To compare, after irradiation, DDE-derived parameters (intracellular fraction, cell size, and cell density) to their histological counterparts (fraction of stained area, minimal Feret diameter, and nuclei count, respectively). 2) To compare percentage changes in DDE-derived parameters and ADC. 3) To evaluate the evolution of DDE-derived parameters describing perfusion.

STATISTICAL TESTS

Wilcoxon rank sum test.

RESULTS

1) Intracellular fraction, cell size, and cell density were respectively lower (-24%, P < 0.001), higher (+7.5%, P < 0.001) and lower (-38%, P < 0.001) in treated tumors as compared to controls. Fraction of stained area, minimal Feret diameter, and nuclei count were respectively lower (-20%, P < 0.001), higher (+28%, P < 0.001), and lower (-34%, P < 0.001) in treated tumors. 2) The magnitude of ADC's percentage change due to irradiation (16.4%) was superior to the one of cell size (8.4%, P < 0.01) but inferior to those of intracellular fraction (35.5%, P < 0.001) and cell density (42%, P < 0.001). 3) After treatment, the magnitude of the vascular fraction's decrease was higher than the increase of flow velocity (33.3%, vs. 13.3%, P < 0.001).

DATA CONCLUSION

The DDE sequence allows quantitatively monitoring the effects of radiotherapy on a tumor's microstructure, whereas ADC only reveals global changes.

EVIDENCE LEVEL

2.

TECHNICAL EFFICACY

Stage 4. J. Magn. Reson. Imaging 2020;52:941-951.

Diffuse optical spectroscopy assessment of rodent tumor model oxygen state after single-dose irradiation

Modern radiation therapy of malignant tumors requires careful selection of conditions that can improve the effectiveness of the treatment. The study of the dynamics and mechanisms of tumor reoxygenation after radiation therapy makes it possible to select the regimens for optimizing the ongoing treatment. Diffuse optical spectroscopy (DOS) is among the methods used for non-invasive assessment of tissue oxygenation. In this work DOS was used forin vivoregistration of changes in oxygenation level of an experimental rat tumor after single-dose irradiation at a dose of 10 Gy and investigation of their possible mechanisms. It was demonstrated that in 24 h after treatment, tumor oxygenation increases, which is mainly due to an increase in the oxygen supply to the tissues. DOS is demonstrated to be efficient for study of changes in blood flow parameters when monitoring tumor response to therapy.

Adaptive hypofractionated gamma knife radiosurgery in the acute management of brainstem metastases

Background:

Intrinsic brainstem metastases are life-threatening neoplasms requiring rapid, effective intervention. Microsurgery is considered not feasible in most cases and systemic treatment seldom provides a successful outcome. In this context, radiation therapy remains the best option but adverse radiation effects (ARE) remain a major concern. A dose-adaptive gamma knife procedure coined as Rapid Rescue Radiosurgery (3R) offers the possibility to treat these lesions whilst reducing the risk of ARE evolvement. We report the results of 3R applied to a group of patients with brainstem metastases.

Methods:

Eight patients with nine brainstem metastases, having undergone three separate, dose-adapted gamma knife radiosurgery (GKRS) procedures over 7 days, were retrospectively analyzed in terms of tumor volume reduction, local control rates, and ARE-development under the period of treatment and at least 6 months after treatment completion.

Results:

Mean peripheral doses at GKRS 1, GKRS 2, and GKRS 3 were 7.4, 7.7, and 8.2 Gy (range 6–9 Gy) set at the 35–50% isodose lines. Mean tumor volume reduction between GKRS 1 and GKRS 3 was −15% and −56% at first follow-up. Four patients developed radiologic signs of ARE but remained clinically asymptomatic. One patient developed a local recurrence at 34 months. Mean survival from GKRS 1 was 13 months. Two patients were still alive at the time of paper submission (10 and 23 months from GKRS 1).

Conclusions:

In this study, 3R proved effective in terms of tumor volume reduction, rescue/preservation of neurological function, and limited ARE evolvement.

Transportable system enabling multiple irradiation studies under simultaneous hypoxia in vitro

Background

Cells in solid tumours are variably hypoxic and hence resistant to radiotherapy - the essential role of oxygen in the efficiency of irradiation has been acknowledged for decades. However, the currently available methods for performing hypoxic experiments in vitro have several limitations, such as a limited amount of parallel experiments, incapability of keeping stable growth conditions and dependence on CO₂ incubator or a hypoxia workstation. The purpose of this study was to evaluate the usability of a novel portable system (Minihypoxy) in performing in vitro irradiation studies under hypoxia, and present supporting biological data.

Materials and methods

This study was conducted on cancer cell cultures in vitro. The cells were cultured in normoxic (~ 21% O₂) or in hypoxic (1% O₂) conditions either in conventional hypoxia workstation or in the Minihypoxy system and irradiated at dose rate 1.28 Gy/min ± 2.9%. The control samples were sham irradiated. To study the effects of hypoxia and irradiation on cell viability and DNA damage, western blotting, immunostainings and clonogenic assay were used. The oxygen level, pH, evaporation rate and osmolarity of the culturing media on cell cultures in different conditions were followed.

Results

The oxygen concentration in interest (5, 1 or 0% O₂) was maintained inside the individual culturing chambers of the Minihypoxy system also during the irradiation. The radiosensitivity of the cells cultured in Minihypoxy chambers was declined measured as lower phosphorylation rate of H2A.X and increased clonogenic capacity compared to controls (OER~ 3).

Conclusions

The Minihypoxy system allows continuous control of hypoxic environment in multiple wells and is transportable. Furthermore, the system maintains the low oxygen environment inside the individual culturing chambers during the transportation and irradiation in experiments which are typically conducted in separate facilities.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1169-9) contains supplementary material, which is available to authorized users.

The concept of rapid rescue radiosurgery in the acute management of critically located brain metastases: A retrospective short-term outcome analysis

Background:

Adaptive hypofractionated gamma knife radiosurgery has been used to treat brain metastases in the eloquent regions while limiting the risk of adverse radiation effect (ARE). Ablative responses might be achieved within days to weeks with the goal to preserve the neurological function. The application of this treatment modality in selected acute/subacute settings has been termed Rapid Rescue Radiosurgery (RRR) in our department. We report the expeditious effects of RRR during treatment and 4 weeks after treatment completion.

Methods:

In all, 34 patients with 40 brain metastases, each treated over a period of 7 days in three separate gamma knife radiosurgery sessions (GKRS 1-3) between November 2013 and August 2017, were retrospectively analyzed in terms of tumor volume reduction, salvage of organs at risk (OAR), and radiation induced toxicity under the period of treatment (GKRS 1-3 = one week) and at first follow-up magnetic resonance imaging (MRI) (4 weeks after GKRS 3).

Results:

Mean tumor volume at GKRS 1 was 12.8 cm3. Mean peripheral doses at GKRS 1, GKRS 2, and GKRS 3 were 7.7 Gy, 8.1 Gy, and 8.4 Gy (range: 6.0-9.5 Gy) at the 35% to 50% isodose lines. In the surviving group at first follow-up (n = 28), mean tumor volume reduction was − 10% at GKRS 3 (1 week) and − 48% four weeks after GKRS 3. There was no further clinical deterioration between GKRS 3 and first follow-up in 21 patients. Six patients died prior to first follow-up due to extracranial disease. No ARE was noticed/reported.

Conclusions:

In this study, RRR proved effective in terms of rapid tumor volume reduction, debulking, and preservation/rescue of neurological function.

Evaluation of a combination tumor treatment using thermo-triggered liposomal drug delivery and carbon ion irradiation

The combination of radiotherapy with chemotherapy is one of the most promising strategies for cancer treatment. Here, a novel combination strategy utilizing carbon ion irradiation as a high-linear energy transfer (LET) radiotherapy and a thermo-triggered nanodevice is proposed, and drug accumulation in the tumor and treatment effects are evaluated using magnetic resonance imaging relaxometry and immunohistology (Ki-67, n = 15). The thermo-triggered liposomal anticancer nanodevice was administered into colon-26 tumor-grafted mice, and drug accumulation and efficacy was compared for 6 groups (n = 32) that received or did not receive the radiotherapy and thermo trigger. In vivo quantitative R₁ maps visually demonstrated that the multimodal thermosensitive polymer-modified liposomes (MTPLs) can accumulate in the tumor tissue regardless of whether the region was irradiated by carbon ions or not. The tumor volume after combination treatment with carbon ion irradiation and MTPLs with thermo-triggering was significantly smaller than all the control groups at 8 days after treatment. The proposed strategy of combining high-LET irradiation and the nanodevice provides an effective approach for minimally invasive cancer treatment.

Theranostic Probes for Targeting Tumor Microenvironment: An Overview

Long gone is the time when tumors were thought to be insular masses of cells, residing independently at specific sites in an organ. Now, researchers gradually realize that tumors interact with the extracellular matrix (ECM), blood vessels, connective tissues, and immune cells in their environment, which is now known as the tumor microenvironment (TME). It has been found that the interactions between tumors and their surrounds promote tumor growth, invasion, and metastasis. The dynamics and diversity of TME cause the tumors to be heterogeneous and thus pose a challenge for cancer diagnosis, drug design, and therapy. As TME is significant in enhancing tumor progression, it is vital to identify the different components in the TME such as tumor vasculature, ECM, stromal cells, and the lymphatic system. This review explores how these significant factors in the TME, supply tumors with the required growth factors and signaling molecules to proliferate, invade, and metastasize. We also examine the development of TME-targeted nanotheranostics over the recent years for cancer therapy, diagnosis, and anticancer drug delivery systems. This review further discusses the limitations and future perspective of nanoparticle based theranostics when used in combination with current imaging modalities like Optical Imaging, Magnetic Resonance Imaging (MRI) and Nuclear Imaging (Positron Emission Tomography (PET) and Single Photon Emission Computer Tomography (SPECT)).

Radiation effects on the tumor microenvironment: Implications for nanomedicine delivery

The tumor microenvironment has an important influence on cancer biological and clinical behavior and radiation treatment (RT) response. However, RT also influences the tumor microenvironment in a complex and dynamic manner that can either reinforce or inhibit this response and the likelihood of long-term disease control in patients. It is increasingly evident that the interplay between RT and the tumor microenvironment can be exploited to enhance the accumulation and intra-tumoral distribution of nanoparticles, mediated by changes to the vasculature and stroma with secondary effects on hypoxia, interstitial fluid pressure (IFP), solid tissue pressure (STP), and the recruitment and activation of bone marrow-derived myeloid cells (BMDCs). The use of RT to modulate nanoparticle drug delivery offers an exciting opportunity to improve antitumor efficacy. This review explores the interplay between RT and the tumor microenvironment, and the integrated effects on nanoparticle drug delivery and efficacy.

Water Exchange Rate Constant as a Biomarker of Treatment Efficacy in Patients With Brain Metastases Undergoing Stereotactic Radiosurgery

PURPOSE

This study was designed to evaluate whether changes in metastatic brain tumors after stereotactic radiosurgery (SRS) can be seen with quantitative MRI early after treatment.

METHODS AND MATERIALS

Using contrast-enhanced MRI, a 3-water-compartment tissue model consisting of intracellular (I), extracellular-extravascular (E), and vascular (V) compartments was used to assess the intra-extracellular water exchange rate constant (k_IE), efflux rate constant (k_ep), and water compartment volume fractions (M_0,I, M_0,E, M_0,V). In this prospective study, 19 patients were MRI-scanned before treatment and 1 week and 1 month after SRS. The change in model parameters between the pretreatment and 1-week posttreatment scans was correlated to the change in tumor volume between pretreatment and 1-month posttreatment scans.

RESULTS

At 1 week k_IE differentiated (P<.001) tumors that had partial response from tumors with stable and progressive disease, and a high correlation (R=-0.76, P<.001) was observed between early changes in the k_IE and tumor volume change 1 month after treatment. Other model parameters had lower correlation (M_0,E) or no correlation (k_ep, M_0,V).

CONCLUSIONS

This is the first study that measured k_IE early after SRS, and it found that early changes in k_IE (1 week after treatment) highly correlated with long-term tumor response and could predict the extent of tumor shrinkage at 1 month after SRS.

Radiation Promptly Alters Cancer Live Cell Metabolic Fluxes: An In Vitro Demonstration

Quantitative data is presented that shows significant changes in cellular metabolism in a head and neck cancer cell line 30 min after irradiation. A head and neck cancer cell line (UM-SCC-22B) and a comparable normal cell line, normal oral keratinocyte (NOK) were each separately exposed to 10 Gy and treated with a control drug for disrupting metabolism (potassium cyanide; KCN). The metabolic changes were measured live by fluorescence lifetime imaging of the intrinsically fluorescent intermediate metabolite nicotinamide adenosine dinucleotide (NADH) fluorescence; this method is sensitive to the ratio of bound to free NADH. The results indicated a prompt shift in metabolic signature in the cancer cell line, but not in the normal cell line. Control KCN treatment demonstrated expected metabolic fluxes due to mitochondrial disruption. The detected radiation shift in the cancer cells was blunted in the presence of both a radical scavenger and a HIF-1α inhibitor. The HIF-1α abundance as detected by immunohistochemical staining also increased substantially for these cancer cells, but not for the normal cells. This type of live-cell metabolic monitoring could be helpful for future real-time studies and in designing adaptive radiotherapy approaches.

Clinical outcome of stereotactic body radiotherapy for primary and oligometastatic lung tumors: a single institutional study with almost uniform dose with different five treatment schedules

Background

To evaluate clinical outcomes of stereotactic body radiotherapy (SBRT) for localized primary and oligometastatic lung tumors by assessing efficacy and safety of 5 regimens of varying fraction size and number.

Methods

One-hundred patients with primary lung cancer (n = 69) or oligometastatic lung tumors (n = 31), who underwent SBRT between May 2003 and August 2010, were included. The median age was 75 years (range, 45–88). Of them, 98 were judged to have medically inoperable disease, predominantly due to chronic illness or advanced age. SBRT was performed using 3 coplanar and 3 non-coplanar fixed beams with a standard linear accelerator. Fraction sizes were escalated by 1 Gy, and number of fractions given was decreased by 1 for every 20 included patients. Total target doses were between 50 and 56 Gy, administered as 5–9 fractions. The prescribed dose was defined at the isocenter, and median overall treatment duration was 10 days (range, 5–22).

Results

The median follow-up was 51.1 months for survivors. The 3-year local recurrence rates for primary lung cancer and oligometastasis was 6 % and 3 %, respectively. The 3-year local recurrence rates for tumor sizes ≤3 cm and >3 cm were 3 % and 14 %, respectively (p = 0.124). Additionally, other factors (fraction size, total target dose, and BED₁₀) were not significant predictors of local control. Radiation pneumonia (≥ grade 2) was observed in 2 patients. Radiation-induced rib fractures were observed in 22 patients. Other late adverse events of greater than grade 2 were not observed.

Conclusion

Within this dataset, we did not observe a dose response in BED₁₀ values between 86.4 and 102.6 Gy. SBRT with doses between 50 and 56 Gy, administered over 5–9 fractions achieved acceptable tumor control without severe complications.

Hypoxia-induced alterations of G2 checkpoint regulators

Hypoxia promotes an aggressive tumor phenotype with increased genomic instability, partially due to downregulation of DNA repair pathways. However, genome stability is also surveilled by cell cycle checkpoints. An important issue is therefore whether hypoxia also can influence the DNA damage-induced cell cycle checkpoints. Here, we show that hypoxia (24 h 0.2% O2) alters the expression of several G2 checkpoint regulators, as examined by microarray gene expression analysis and immunoblotting of U2OS cells. While some of the changes reflected hypoxia-induced inhibition of cell cycle progression, the levels of several G2 checkpoint regulators, in particular Cyclin B, were reduced in G2 phase cells after hypoxic exposure, as shown by flow cytometric barcoding analysis of individual cells. These effects were accompanied by decreased phosphorylation of a Cyclin dependent kinase (CDK) target in G2 phase cells after hypoxia, suggesting decreased CDK activity. Furthermore, cells pre-exposed to hypoxia showed increased G2 checkpoint arrest upon treatment with ionizing radiation. Similar results were found following other hypoxic conditions (∼0.03% O2 20 h and 0.2% O2 72 h). These results demonstrate that the DNA damage-induced G2 checkpoint can be altered as a consequence of hypoxia, and we propose that such alterations may influence the genome stability of hypoxic tumors.

Biology of hypoxia

There is an important and strong, but complex influence of the tumor microenvironment on tumor cells' phenotype, aggressiveness, and treatment sensitivity. One of the most frequent and best-studied aspects of the tumor microenvironment is hypoxia. Low oxygen tension often occurs in tumor cells by several mechanisms, for example, poor angiogenesis and increased oxygen consumption. Hypoxia is a heterogeneous concept with oxygen tensions ranging from <0.01% (anoxia) to 5%, and can be chronic, acute, or cycling, all with differential effects on tumor cells. Quantification of tumor hypoxia can be performed directly or indirectly, and with exogenous or endogenous markers. Tumor cells launch different intracellular signaling pathways to survive hypoxia, such as hypoxia-inducible factor 1-mediated gene expression, the unfolded protein response, and AKT-mammalian target of rapamycin signaling. These pathways induce aggressive, metastatic, and treatment-insensitive tumors and are considered potential targets for (additive) therapy. Hypoxia leads to important, yet currently not well-understood changes in microRNA expression, epigenetics, and metabolism. Further, treatment-insensitive tumors arise through hypoxia-induced Darwinian selection of apoptosis-deficient, p53-mutated tumor cells. In conclusion, hypoxia has profound and largely still poorly understood effects on tumor cells with a major effect on the tumor's biology.

Spatial oxygenation profiles in tumors during normo- and hyperbaric hyperoxia

BACKGROUND

Inspiratory hyperoxia reduces tumor hypoxia, which is responsible for limited radiosensitivity of tumors. However, very little is known about the heterogeneity of intratumoral oxygenation during this supportive treatment. The study analyzes whether local hypoxia is still present during normobaric and hyperbaric inspiratory hyperoxia and whether the addition of CO2 to the inspiratory gas affects the spatial pO2 distribution.

MATERIAL AND METHODS

Tumor oxygenation of experimental DS-sarcomas in rats was assessed by polarographic needle electrodes at 1 and 2 atm (bar) environmental pressure during pure O2 or carbogen (95 % O2 + 5 % CO2) breathing. Up to 320 individual pO2 measurements were performed in a strictly oriented grid resulting in an oxygenation profile in a horizontal tumor layer.

RESULTS

In the experimental tumors used the oxygenation showed pronounced heterogeneities with closely adjacent hypoxic and oxygenated regions. This heterogeneity was still visible under normobaric hyperoxia where large confluent hypoxic regions were detectable. At 1 atm, the addition of CO2 improved tumor oxygenation significantly (at least in large tumors). At 2 atm, only very small local regions of hypoxia were detected. However, under this condition hypercapnia had no impact on tumor oxygenation.

CONCLUSIONS

The data show that even under hyperbaric hyperoxia, hypoxic regions are detectable despite the average pO2 increased by a factor of 100. The results also clearly indicate that the oxygenation pattern improves disproportionally with increasing environmental pressure.

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.

Imaging tumor hypoxia to advance radiation oncology

SIGNIFICANCE

Most solid tumors contain regions of low oxygenation or hypoxia. Tumor hypoxia has been associated with a poor clinical outcome and plays a critical role in tumor radioresistance.

RECENT ADVANCES

Two main types of hypoxia exist in the tumor microenvironment: chronic and cycling hypoxia. Chronic hypoxia results from the limited diffusion distance of oxygen, and cycling hypoxia primarily results from the variation in microvessel red blood cell flux and temporary disturbances in perfusion. Chronic hypoxia may cause either tumor progression or regressive effects depending on the tumor model. However, there is a general trend toward the development of a more aggressive phenotype after cycling hypoxia. With advanced hypoxia imaging techniques, spatiotemporal characteristics of tumor hypoxia and the changes to the tumor microenvironment can be analyzed.

CRITICAL ISSUES

In this review, we focus on the biological and clinical consequences of chronic and cycling hypoxia on radiation treatment. We also discuss the advanced non-invasive imaging techniques that have been developed to detect and monitor tumor hypoxia in preclinical and clinical studies.

FUTURE DIRECTIONS

A better understanding of the mechanisms of tumor hypoxia with non-invasive imaging will provide a basis for improved radiation therapeutic practices.

An Experimental Study of Radiation Effect on Normal Tissue: Analysis of HIF-1α, VEGF, eIF2, TIA-1, and TSP-1 Expression

Objective:

This study investigated whether or not the stress and hypoxia, which are the effects of radiation on normal vascular endothelium, leading to the release of HIF-1α, VEGF, eIF2, TIA-1, and TSP-1 were related and the possibility of them stimulating angiogenesis.


Materials and Methods:

Twenty-four male Swiss Albino mice were separated into 4 groups. The first group was the control group (Group 1), and the second, third, and fourth groups were euthanized after 24 h (Group 2), 48 h (Group 3), and 7 days (Group 4), respectively. A single-fractioned 10 Gy of ionizing radiation was applied to all mice’s pelvic zone with Co-60. Bladders were removed completely from the pelvic region. Immunohistochemistry and light microscopy were used to investigate whether there would be an increase or not in the angiogenesis pathway by using the HIF-1α, VEGF, eIF2, TIA-1, and TSP-1 antibodies.

Results:

The HIF-1α antibody showed strong staining in Group 3, while the staining intensity was less in other groups. VEGF showed weak staining in Groups 1 and 4, while moderate staining in Group 2 and strong staining in Group 3 was observed. eIF2 showed strong staining in Groups 1 and 4. Groups 2 and 3 were stained weakly. In the present study, staining with TSP-1 was very strong in the samples belonging to Group 1, while other groups showed very weak staining.

Conclusion:

When normal tissue was exposed to radiation, the positively effective factors (HIF-1, VEGF, eIF2, and TIA-1) on the angiogenesis pathway were increased while the negative factor (TSP-1) was decreased. Radiation may initiate physiological angiogenesis in the normal tissue and accelerate healing in the damaged normal tissue.

Correlation between tumor oxygenation and 18F-fluoromisonidazole PET data simulated based on microvessel images

BACKGROUND

Assessing hypoxia with oxygen probes provides a sparse sampling of tumor volumes only, bearing a risk of missing hypoxic regions. Full coverage is achieved with positron emission tomography (PET) using the tracer (18)F-fluoromisonidazole (FMISO). In this study, the correlation between different FMISO PET imaging parameters and the median voxel PO2 (medianPO2) was analyzed. A measure of the median PO2 characterizes the microenvironment in consistency with probe measurements.

MATERIAL AND METHODS

Tissue oxygenations and FMISO diffusion-retention dynamics were simulated. Transport of FMISO and O2 molecules into and out of tissue was modeled by vessel maps derived from histology of head-and-neck squamous cell cancer xenograft tumor lines. Parameter sets were evaluated for 300 distinct 2 × 2 mm(2) vessel configurations, including medianPO2 and two FMISO PET parameters: FH denotes the sub-regional signal four hours post injection (pi) and FH/P denotes the ratio between FH and the time-averaged signal 0-15 min pi. Correlations between O2 and FMISO parameters were evaluated. A receiver operating characteristics (ROC) analysis was performed, regarding the accuracy of FH and FH/P in identifying voxels with medianPO2 < 2.5 mmHg.

RESULTS

In hypoxic sub-regions, the correlation between FH and medianPO2 is low (R(2) = 0.37), while the correlation between FH/P and median PO2 is high (R(2) = 0.99). The ROC analysis showed that hypoxic regions can be identified using FH/P with a higher diagnostic accuracy (YI = sensitivity+ specificity-1 = 1.0), than using FH alone (YI = 0.83). Both FMISO parameters are moderately effective in identifying hypoxia on the microscopic length scale (YI = 0.63 and 0.60).

CONCLUSIONS

A combination of two FMISO PET scans acquired 0-15 min and four hours pi may yield an accurate measure of the medianPO2 in a voxel (FH/P). This measure is comparable to averaged oxygen probe measurements and has the advantage of covering the entire tumor volume. Therefore, it may improve the prediction of radiotherapy outcome and facilitate individualized dose prescriptions.

On the importance of prompt oxygen changes for hypofractionated radiation treatments

This discussion is motivated by observations of prompt oxygen changes occurring prior to a significant number of cancer cells dying (permanently stopping their metabolic activity) from therapeutic agents like large doses of ionizing radiation. Such changes must be from changes in the vasculature that supplies the tissue or from the metabolic changes in the tissue itself. An adapted linear-quadratic treatment is used to estimate the cell survival variation magnitudes from repair and reoxygenation from a two-fraction treatment in which the second fraction would happen prior to significant cell death from the first fraction, in the large fraction limit. It is clear the effects of oxygen changes are likely to be the most significant factor for hypofractionation because of large radiation doses. It is a larger effect than repair. Optimal dose timing should be determined by the peak oxygen timing. A call is made to prioritize near real time measurements of oxygen dynamics in tumors undergoing hypofractionated treatments in order to make these treatments adaptable and patient-specific.

Assessment of predictive molecular variables in feline oral squamous cell carcinoma treated with stereotactic radiation therapy

This study evaluated molecular characteristics that are potentially prognostic in cats with oral squamous cell carcinoma (SCC) that underwent stereotactic radiation therapy (SRT). Survival time (ST) and progression-free interval (PFI) were correlated with mitotic index, histopathological grades, Ki67 and epidermal growth factor receptor expressions, tumour microvascular density (MVD), and tumour oxygen tension (pO(2)). Median ST and PFI were 106 and 87 days, respectively (n = 20). Overall response rate was 38.5% with rapid improvement of clinical symptoms in many cases. Patients with higher MVD or more keratinized SCC had significantly shorter ST or PFI than patients with lower MVD or less keratinized SCC (P = 0.041 and 0.049, respectively). Females had significantly longer PFI and ST than males (P ≤ 0.016). Acute toxicities were minimal. However, treatment-related complications such as fractured mandible impacted quality of life. In conclusion, SRT alone should be considered as a palliative treatment. MVD and degree of keratinization may be useful prognostic markers.

Targeting hypoxia, HIF-1, and tumor glucose metabolism to improve radiotherapy efficacy

Radiotherapy, an important treatment modality in oncology, kills cells through induction of oxidative stress. However, malignant tumors vary in their response to irradiation as a consequence of resistance mechanisms taking place at the molecular level. It is important to understand these mechanisms of radioresistance, as counteracting them may improve the efficacy of radiotherapy. In this review, we describe how the hypoxia-inducible factor 1 (HIF-1) pathway has a profound effect on the response to radiotherapy. The main focus will be on HIF-1-controlled protection of the vasculature postirradiation and on HIF-1 regulation of glycolysis and the pentose phosphate pathway. This aberrant cellular metabolism increases the antioxidant capacity of tumors, thereby countering the oxidative stress caused by irradiation. From the results of translational studies and the first clinical phase I/II trials, it can be concluded that targeting HIF-1 and tumor glucose metabolism at several levels reduces the antioxidant capacity of tumors, affects the tumor microenvironment, and sensitizes various solid tumors to irradiation.

In vivo optical imaging of tumor and microvascular response to ionizing radiation

Radiotherapy is a widely used cancer treatment. However, understanding how ionizing radiation affects tumor cells and their vasculature, particularly at cellular, subcellular, genetic, and protein levels, has been limited by an inability to visualize the response of these interdependent components within solid tumors over time and in vivo. Here we describe a new preclinical experimental platform combining intravital multimodal optical microscopy for cellular-level longitudinal imaging, a small animal x-ray microirradiator for reproducible spatially-localized millimeter-scale irradiations, and laser-capture microdissection of ex vivo tissues for transcriptomic profiling. Using this platform, we have developed new methods that exploit the power of optically-enabled microscopic imaging techniques to reveal the important role of the tumor microvasculature in radiation response of tumors. Furthermore, we demonstrate the potential of this preclinical platform to study quantitatively--with cellular and sub-cellular details--the spatio-temporal dynamics of the biological response of solid tumors to ionizing radiation in vivo.

Vascular responses to radiotherapy and androgen-deprivation therapy in experimental prostate cancer

BACKGROUND

Radiotherapy (RT) and androgen-deprivation therapy (ADT) are standard treatments for advanced prostate cancer (PC). Tumor vascularization is recognized as an important physiological feature likely to impact on both RT and ADT response, and this study therefore aimed to characterize the vascular responses to RT and ADT in experimental PC.

METHODS

Using mice implanted with CWR22 PC xenografts, vascular responses to RT and ADT by castration were visualized in vivo by DCE MRI, before contrast-enhancement curves were analyzed both semi-quantitatively and by pharmacokinetic modeling. Extracted image parameters were correlated to the results from ex vivo quantitative fluorescent immunohistochemical analysis (qIHC) of tumor vascularization (9 F1), perfusion (Hoechst 33342), and hypoxia (pimonidazole), performed on tissue sections made from tumors excised directly after DCE MRI.

RESULTS

Compared to untreated (Ctrl) tumors, an improved and highly functional vascularization was detected in androgen-deprived (AD) tumors, reflected by increases in DCE MRI parameters and by increased number of vessels (VN), vessel density (VD), and vessel area fraction (VF) from qIHC. Although total hypoxic fractions ( HF) did not change, estimated acute hypoxia scores (AHS)--the proportion of hypoxia staining within 50 μm from perfusion staining--were increased in AD tumors compared to in Ctrl tumors. Five to six months after ADT renewed castration-resistant (CR) tumor growth appeared with an even further enhanced tumor vascularization. Compared to the large vascular changes induced by ADT, RT induced minor vascular changes. Correlating DCE MRI and qIHC parameters unveiled the semi-quantitative parameters area under curve (AUC) from initial time-points to strongly correlate with VD and VF, whereas estimation of vessel size (VS) by DCE MRI required pharmacokinetic modeling. HF was not correlated to any DCE MRI parameter, however, AHS may be estimated after pharmacokinetic modeling. Interestingly, such modeling also detected tumor necrosis very strongly.

CONCLUSIONS

DCE MRI reliably allows non-invasive assessment of tumors' vascular function. The findings of increased tumor vascularization after ADT encourage further studies into whether these changes are beneficial for combined RT, or if treatment with anti-angiogenic therapy may be a strategy to improve the therapeutic efficacy of ADT in advanced PC.

Changes in the fraction of total hypoxia and hypoxia subtypes in human squamous cell carcinomas upon fractionated irradiation: evaluation using pattern recognition in microcirculatory supply units

BACKGROUND AND PURPOSE

Evaluate changes in total hypoxia and hypoxia subtypes in vital tumor tissue of human head and neck squamous cell carcinomas (hHNSCC) upon fractionated irradiation.

MATERIALS AND METHODS

Xenograft tumors were generated from 5 hHNSCC cell lines (UT-SCC-15, FaDu, SAS, UT-SCC-5 and UT-SCC-14). Hypoxia subtypes were quantified in cryosections based on (immuno-)fluorescent marker distribution patterns of Hoechst 33342 (perfusion), pimonidazole (hypoxia) and CD31 (endothelium) in microcirculatory supply units (MCSUs). Tumors were irradiated with 5 or 10 fractions of 2 Gy, 5×/week.

RESULTS

Upon irradiation with 10 fractions, the overall fraction of hypoxic MCSUs decreased in UT-SCC-15, FaDu and SAS, remained the same in UT-SCC-5 and increased in UT-SCC-14. Decreases were observed in the proportion of chronically hypoxic MCSUs in UT-SCC-15, in the fraction of acutely hypoxic MCSUs in UT-SCC-15 and SAS, and in the percentage of hypoxemically hypoxic MCSUs in SAS tumors. After irradiation with 5 fractions, there were no significant changes in hypoxia subtypes. Changes in the overall fraction of hypoxic MCSUs were comparable to corresponding alterations in the proportions of acutely hypoxic MCSUs. There was no correlation between radiation resistance (TCD(50)) and any of the investigated hypoxic fractions upon fractionated irradiation.

CONCLUSIONS

This study shows that there are large alterations in the fractions of hypoxia subtypes upon irradiation that can differ from changes in the overall fraction of hypoxic MCSUs.

Monitoring the longitudinal intra-tumor physiological impulse response to VEGFR2 blockade in breast tumors using DCE-CT

PURPOSE

The purpose of this study was to quantify and model the longitudinal intra-tumor physiological response to a single dose of a monoclonal antibody specific to the VEGFR2 using dynamic contrast-enhanced CT.

MATERIAL AND METHODS

Dynamic contrast-enhanced CT imaging was performed on athymic nude mice bearing xenograft VEGF-transfected MCF-7 tumors (MCF7(VEGF)) to quantify intra-tumor physiology pre- and post-injection (days 2, 7, and 14) of a nonspecific (IgG1, controls) and specific (DC101, treated) monoclonal antibody targeting VEGFR2. Parametrical maps of tumor physiology-perfusion (F), permeability surface area (PS), fractional plasma (f(p)), and interstitial space (f (is))-were obtained at four time points over a 2-week period.

RESULTS

A temporal multistage recovery process whereby a decoupling of the fractional change in physiological parameters (f (p), F) was observed when comparing treated to control tumors: f (p) and perfusion decreased by a combined 27% (P < 0.01) and 65% (P < 0.01) on day 2, while only perfusion remained reduced by 46% (P < 0.01) on day 7. Intra-tumor heterogeneity defined by the change in variance of perfusion decreased on days 2 and 7; no change in the variance of f(p) was observed. Analysis based on a mathematical model linking perfusion and vascular morphology indicates that a decrease in f(p) and perfusion was consistent with a reduction in blood vessel radius, followed by an increase in the vascular radius and tortuosity resulting in the decoupling of f(p) and perfusion before returning to control levels.

CONCLUSION

Inhibiting VEGFR2 activity results in a temporal decoupling of physiological parameters, which can be explained by a combination of morphological changes influencing perfusion. Such a decoupling has the potential to significantly impact the delivery of pharmaceuticals and oxygen within solid tumors, critical factors in combined anti-angiogenic and radio- and chemotherapies.

Modelling and simulation of the influence of acute and chronic hypoxia on [18F]fluoromisonidazole PET imaging

Tumour hypoxia can be assessed by positron emission tomography (PET) using radiotracers like [(18)F]fluoromisonidazole (Fmiso). The purpose of this work was to independently investigate the influence of chronic and acute hypoxia on the retention of Fmiso on the microscale. This was approached by modelling and simulating tissue oxygenation and Fmiso dynamics on the microscale based on tumour histology. Diffusion of oxygen and Fmiso molecules in tissue- and oxygen-dependent Fmiso binding were included in the model. Moreover, a model of fluctuating vascular oxygen tension was incorporated to theoretically predict the effects of acute hypoxia. Simulated tissue oxygen tensions (PO(2)) are strongly influenced by the modelled periodical fluctuations (period 40 min, total amplitude 10 mmHg and mean 35 mmHg). Fluctuations led to variations in mean PO(2) of up to 41% and in the hypoxic fraction (PO(2)  < 5 mmHg) from 56% up to 65%. Significant Fmiso retention is caused by chronic (87%) as well as acute hypoxia (13%). By simulating Fmiso injection during different phases of the vascular PO(2) fluctuation cycle, it was found that acute hypoxia of an empirically valid magnitude does not influence the reproducibility of PET imaging. Thus, it may be impossible to separate acute and chronic hypoxia from serial PET images.

Radiation-induced vascular damage in tumors: implications of vascular damage in ablative hypofractionated radiotherapy (SBRT and SRS)

We have reviewed the studies on radiation-induced vascular changes in human and experimental tumors reported in the last several decades. Although the reported results are inconsistent, they can be generalized as follows. In the human tumors treated with conventional fractionated radiotherapy, the morphological and functional status of the vasculature is preserved, if not improved, during the early part of a treatment course and then decreases toward the end of treatment. Irradiation of human tumor xenografts or rodent tumors with 5-10 Gy in a single dose causes relatively mild vascular damages, but increasing the radiation dose to higher than 10 Gy/fraction induces severe vascular damage resulting in reduced blood perfusion. Little is known about the vascular changes in human tumors treated with high-dose hypofractionated radiation such as stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS). However, the results for experimental tumors strongly indicate that SBRT or SRS of human tumors with doses higher than about 10 Gy/fraction is likely to induce considerable vascular damages and thereby damages the intratumor microenvironment, leading to indirect tumor cell death. Vascular damage may play an important role in the response of human tumors to high-dose hypofractionated SBRT or SRS.

Reoxygenation of glioblastoma multiforme treated with fractionated radiotherapy concomitant with temozolomide: changes defined by 18F-fluoromisonidazole positron emission tomography: two case reports

Two glioblastoma multiforme patients underwent (18)F-FMISO (fluoromisonidazole) positron emission tomography study to access the tumor oxygenation status before and immediately after fractionated radiotherapy concomitant with temozolomide chemotherapy. In both cases, a prominent (18)F-FMISO tumor accumulation observed in the first study was notably decreased in the second study, which was supposed to be a reoxygenation of the tumor. As far as we investigated, this is the first report of the changes of oxygenation status in glioblastoma multiforme treated through radiation therapy with temozolomide.

Various doses of fractioned irradiation modulates multidrug resistance 1 expression differently through hypoxia-inducible factor 1α in esophageal cancer cells

To evaluate the effect of different regimen of radiotherapy on multidrug resistance 1 (MDR1) expression and analyze the role hypoxia-inducible factor 1α (HIF1α) played in the whole process. Fifty-four cell lines established from 96 esophageal cancer biopsy samples were given various doses of fractioned irradiation. The mRNA and protein levels of HIF1α and MDR1 post-irradiation were measured by quantitative reverse transcription-polymerase chain reaction and Western blot analysis, respectively. HIF1α-siRNA was used to verify the effect of HIF1α on radiation-mediated MDR1 modulation. In esophageal cancer cells surviving 28 Gy irradiation (2 Gy/f, 14 fractions), MDR1 mRNA expression increased 65.27 ± 5.58%, and HIF1α was elevated by 27.21 ± 2.25%. Interestingly, their expression decreased by 54.38 ± 11.53% and 32.08 ± 4.75% after 7 Gy irradiation (0.5 Gy/f, 14 fractions). HIF1α expression showed a positive correlation with MDR1 expression in the whole process (P < 0.05). Silencing of HIF1α decreased MDR1 expression and blocked changes in MDR1 and HIF1α expression induced by fractioned irradiation. These results indicate that MDR1 is differentially modulated by different doses of fractionated radiation, which should be taken into account when combining radiotherapy and chemotherapy for patients with esophageal cancer.

Exploiting the tumor microenvironment for theranostic imaging

The integration of chemistry and molecular biology with imaging is providing some of the most exciting opportunities in the treatment of cancer. The field of theranostic imaging, where diagnosis is combined with therapy, is particularly suitable for a disease as complex as cancer, especially now that genomic and proteomic profiling can provide an extensive 'fingerprint' of each tumor. Using this information, theranostic agents can be shaped for personalized treatment to target specific compartments, such as the tumor microenvironment (TME), whilst minimizing damage to normal tissue. These theranostic agents can also be used to target multiple pathways or networks by incorporating multiple small interfering RNAs (siRNAs) within a single agent. A decade ago genetic alterations were the primary focus in cancer research. Now it is apparent that the tumor physiological microenvironment, interactions between cancer cells and stromal cells, such as endothelial cells, fibroblasts and macrophages, the extracellular matrix (ECM), and a host of secreted factors and cytokines, influence progression to metastatic disease, aggressiveness and the response of the disease to treatment. In this review, we outline some of the characteristics of the TME, describe the theranostic agents currently available to target the TME and discuss the unique opportunities the TME provides for the design of novel theranostic agents for cancer therapy.

Targeting hypoxic cells through the DNA damage response

Exposure to hypoxia-induced replication arrest initiates a DNA damage response that includes both ATR- and ATM-mediated signaling. DNA fiber analysis was used to show that these conditions lead to a replication arrest during both the initiation and elongation phases, and that this correlated with decreased levels of nucleotides. The DNA damage response induced by hypoxia is distinct from the classical pathways induced by damaging agents, primarily due to the lack of detectable DNA damage, but also due to the coincident repression of DNA repair in hypoxic conditions. The principle aims of the hypoxia-induced DNA damage response seem to be the induction of p53-dependent apoptosis or the preservation of replication fork integrity. The latter is of particular importance should reoxygenation occur. Tumor reoxygenation occurs as a result of spontaneous changes in blood flow and also therapy. Cells experiencing hypoxia and/or reoxygenation are, therefore, sensitive to loss or inhibition of components of the DNA damage response, including Chk1, ATM, ATR, and poly(ADP-ribose) polymerase (PARP). In addition, restoration of hypoxia-induced p53-mediated signaling may well be effective in the targeting of hypoxic cells. The DNA damage response is also induced in endothelial cells at moderate levels of hypoxia, which do not induce replication arrest. In this situation, phosphorylation of H2AX has been shown to be required for proliferation and angiogenesis and is, therefore, an attractive potential therapeutic target.

Irradiation-dependent effects on tumor perfusion and endogenous and exogenous hypoxia markers in an A549 xenograft model

PURPOSE

Hypoxia is a major determinant of tumor radiosensitivity, and microenvironmental changes in response to ionizing radiation (IR) are often heterogenous. We analyzed IR-dependent changes in hypoxia and perfusion in A549 human lung adenocarcinoma xenografts.

MATERIALS AND METHODS

Immunohistological analysis of two exogenously added chemical hypoxic markers, pimonidazole and CCI-103F, and of the endogenous marker Glut-1 was performed time dependently after IR. Tumor vessels and apoptosis were analyzed using CD31 and caspase-3 antibodies. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and fluorescent beads (Hoechst 33342) were used to monitor vascular perfusion.

RESULTS

CCI-103F signals measuring the fraction of hypoxic areas after IR were significantly decreased by approximately 50% when compared with pimonidazole signals, representing the fraction of hypoxic areas from the same tumors before IR. Interestingly, Glut-1 signals were significantly decreased at early time point (6.5 h) after IR returning to the initial levels at 30.5 h. Vascular density showed no difference between irradiated and control groups, whereas apoptosis was significantly induced at 10.5 h post-IR. DCE-MRI indicated increased perfusion 1 h post-IR.

CONCLUSIONS

The discrepancy between the hypoxic fractions of CCI-103F and Glut-1 forces us to consider the possibility that both markers reflect different metabolic alterations of tumor microenvironment. The reliability of endogenous markers such as Glut-1 to measure reoxygenation in irradiated tumors needs further consideration. Monitoring tumor microvascular response to IR by DCE-MRI and measuring tumor volume alterations should be encouraged.

Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice

Despite the high doses of radiation delivered in the treatment of patients with glioblastoma multiforme (GBM), the tumors invariably recur within the irradiation field, resulting in a low cure rate. Understanding the mechanism of such recurrence is therefore important. Here we have shown in an intracranial GBM xenograft model that irradiation induces recruitment of bone marrow-derived cells (BMDCs) into the tumors, restoring the radiation-damaged vasculature by vasculogenesis and thereby allowing the growth of surviving tumor cells. BMDC influx was initiated by induction of HIF-1 in the irradiated tumors, and blocking this influx prevented tumor recurrence. Previous studies have indicated that BMDCs are recruited to tumors in part through the interaction between the HIF-1-dependent stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4. Pharmacologic inhibition of HIF-1 or of the SDF-1/CXCR4 interaction prevented the influx of BMDCs, primarily CD11b+ myelomonocytes, and the postirradiation development of functional tumor vasculature, resulting in abrogation of tumor regrowth. Similar results were found using neutralizing antibodies against CXCR4. Our data therefore suggest a novel approach for the treatment of GBM: in addition to radiotherapy, the vasculogenesis pathway needs to be blocked, and this can be accomplished using the clinically approved drug AMD3100, a small molecule inhibitor of SDF-1/CXCR4 interactions.

Cycling hypoxia and free radicals regulate angiogenesis and radiotherapy response

Hypoxia and free radicals, such as reactive oxygen and nitrogen species, can alter the function and/or activity of the transcription factor hypoxia-inducible factor 1 (HIF1). Interplay between free radicals, hypoxia and HIF1 activity is complex and can influence the earliest stages of tumour development. The hypoxic environment of tumours is heterogeneous, both spatially and temporally, and can change in response to cytotoxic therapy. Free radicals created by hypoxia, hypoxia-reoxygenation cycling and immune cell infiltration after cytotoxic therapy strongly influence HIF1 activity. HIF1 can then promote endothelial and tumour cell survival. As discussed here, a constant theme emerges: inhibition of HIF1 activity will have therapeutic benefit.