Surrogate MR markers of response to chemo- or radiotherapy in association with co-treatments: a retrospective analysis of multi-modal studies

Hypoxia, a Targetable Culprit to Counter Pancreatic Cancer Resistance to Therapy

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and it is a disease of dismal prognosis. While immunotherapy has revolutionized the treatment of various solid tumors, it has achieved little success in PDAC. Hypoxia within the stroma-rich tumor microenvironment is associated with resistance to therapies and promotes angiogenesis, giving rise to a chaotic and leaky vasculature that is inefficient at shuttling oxygen and nutrients. Hypoxia and its downstream effectors have been implicated in immune resistance and could be contributing to the lack of response to immunotherapy experienced by patients with PDAC. Paradoxically, increasing evidence has shown hypoxia to augment genomic instability and mutagenesis in cancer, suggesting that hypoxic tumor cells could have increased production of neoantigens that can potentially enable their clearance by cytotoxic immune cells. Strategies aimed at relieving this condition have been on the rise, and one such approach opts for normalizing the tumor vasculature to reverse hypoxia and its downstream support of tumor pathogenesis. An important consideration for the successful implementation of such strategies in the clinic is that not all PDACs are equally hypoxic, therefore hypoxia-detection approaches should be integrated to enable optimal patient selection for achieving improved patient outcomes.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Natural and Designed Toxins for Precise Therapy: Modern Approaches in Experimental Oncology

Cancer cells frequently overexpress specific surface receptors providing tumor growth and survival which can be used for precise therapy. Targeting cancer cell receptors with protein toxins is an attractive approach widely used in contemporary experimental oncology and preclinical studies. Methods of targeted delivery of toxins to cancer cells, different drug carriers based on nanosized materials (liposomes, nanoparticles, polymers), the most promising designed light-activated toxins, as well as mechanisms of the cytotoxic action of the main natural toxins used in modern experimental oncology, are discussed in this review. The prospects of the combined therapy of tumors based on multimodal nanostructures are also discussed.

MR-CBCT image-guided system for radiotherapy of orthotopic rat prostate tumors

Multi-modality image-guided radiotherapy is the standard of care in contemporary cancer management; however, it is not common in preclinical settings due to both hardware and software limitations. Soft tissue lesions, such as orthotopic prostate tumors, are difficult to identify using cone beam computed tomography (CBCT) imaging alone. In this study, we characterized a research magnetic resonance (MR) scanner for preclinical studies and created a protocol for combined MR-CBCT image-guided small animal radiotherapy. Two in-house dual-modality, MR and CBCT compatible, phantoms were designed and manufactured using 3D printing technology. The phantoms were used for quality assurance tests and to facilitate end-to-end testing for combined preclinical MR and CBCT based treatment planning. MR and CBCT images of the phantoms were acquired utilizing a Varian 4.7 T scanner and XRad-225Cx irradiator, respectively. The geometry distortion was assessed by comparing MR images to phantom blueprints and CBCT. The corrected MR scans were co-registered with CBCT and subsequently used for treatment planning. The fidelity of 3D printed phantoms compared to the blueprint design yielded favorable agreement as verified with the CBCT measurements. The geometric distortion, which varied between -5% and 11% throughout the scanning volume, was substantially reduced to within 0.4% after correction. The distortion free MR images were co-registered with the corresponding CBCT images and imported into a commercial treatment planning software SmART Plan. The planning target volume (PTV) was on average 19% smaller when contoured on the corrected MR-CBCT images relative to raw images without distortion correction. An MR-CBCT based preclinical workflow was successfully designed and implemented for small animal radiotherapy. Combined MR-CBCT image-guided radiotherapy for preclinical research potentially delivers enhanced relevance to human radiotherapy for various disease sites. This novel protocol is wide-ranging and not limited to the orthotopic prostate tumor study presented in the study.

Assessing Tumor Oxygenation for Predicting Outcome in Radiation Oncology: A Review of Studies Correlating Tumor Hypoxic Status and Outcome in the Preclinical and Clinical Settings

Tumor hypoxia is recognized as a limiting factor for the efficacy of radiotherapy, because it enhances tumor radioresistance. It is strongly suggested that assessing tumor oxygenation could help to predict the outcome of cancer patients undergoing radiation therapy. Strategies have also been developed to alleviate tumor hypoxia in order to radiosensitize tumors. In addition, oxygen mapping is critically needed for intensity modulated radiation therapy (IMRT), in which the most hypoxic regions require higher radiation doses and the most oxygenated regions require lower radiation doses. However, the assessment of tumor oxygenation is not yet included in day-to-day clinical practice. This is due to the lack of a method for the quantitative and non-invasive mapping of tumor oxygenation. To fully integrate tumor hypoxia parameters into effective improvements of the individually tailored radiation therapy protocols in cancer patients, methods allowing non-invasively repeated, safe, and robust mapping of changes in tissue oxygenation are required. In this review, non-invasive methods dedicated to assessing tumor oxygenation with the ultimate goal of predicting outcome in radiation oncology are presented, including positron emission tomography used with nitroimidazole tracers, magnetic resonance methods using endogenous contrasts (R₁ and R2*-based methods), and electron paramagnetic resonance oximetry; the goal is to highlight results of studies establishing correlations between tumor hypoxic status and patients’ outcome in the preclinical and clinical settings.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research

The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

Diffusion MRI and novel texture analysis in osteosarcoma xenotransplants predicts response to anti-checkpoint therapy

Combinations of targeted drugs have been employed to treat sarcomas, however, response rates have not improved notably, therefore emphasizing the need for novel treatments. In addition, imaging approaches to assess therapeutic response is lacking, as currently measurable indices, such as volume and/or diameter, do not accurately correlate with changes in tumor biology. In this study, quantitative and profound analyses of magnetic resonance imaging (MRI) were developed to evaluate these as imaging biomarkers for MK1775 and Gem in an osteosarcoma xenotransplant model at early time-points following treatment. Notably, we showed that Gem and Gem+MK1775 groups had significantly inhibited tumor growth by day 4, which was presaged by elevations in mean ADC by 24 hours post treatment. Significant differences were also observed at later time points for the Gem+MK1775 combination and MK1775 therapy. ADC distribution and entropy (randomness of ADC values) were also elevated by 24 hours following therapy. Immunohistochemistry demonstrated that these treatment-related increases in ADC correlated with apoptosis and observed cell condensations (dense- and exploded bodies). These findings underline the role of ADC as a quantitative imaging biomarker for therapy-induced response and show promising clinical relevance in the sarcoma patient population.

EPR oxygen images predict tumor control by a 50% tumor control radiation dose

Clinical trials to ameliorate hypoxia as a strategy to relieve the radiation resistance it causes have prompted a need to assay the precise extent and location of hypoxia in tumors. Electron paramagnetic resonance oxygen imaging (EPR O2 imaging) provides a noninvasive means to address this need. To obtain a preclinical proof-of-principle that EPR O2 images could predict radiation control, we treated mouse tumors at or near doses required to achieve 50% control (TCD50). Mice with FSa fibrosarcoma or MCa4 carcinoma were subjected to EPR O2 imaging and immediately radiated to a TCD50 or TCD50 ± 10 Gy. Statistical analysis was permitted by collection of approximately 1,300 tumor pO2 image voxels, including the fraction of tumor voxels with pO2 less than 10 mm Hg (HF10). Tumors were followed for 90 days (FSa) or 120 days (MCa4) to determine local control or failure. HF10 obtained from EPR images showed statistically significant differences between tumors that were controlled by the TCD50 and those that were not controlled for both FSa and MCa4. Kaplan-Meier analysis of both types of tumors showed that approximately 90% of mildly hypoxic tumors were controlled (HF10%< 10%), and only 37% (FSA) and 23% (MCa4) tumors controlled if hypoxic. EPR pO2 image voxel distributions in these approximately 0.5 mL tumors provide a prediction of radiation curability independent of radiation dose. These data confirm the significance of EPR pO2 hypoxic fractions. The 90% control of low HF10 tumors argue that 0.5 mL subvolumes of tumors may be more sensitive to radiation and may need less radiation for high tumor control rates. Cancer Res; 73(17); 5328-35. ©2013 AACR.

In vivo MRI Follow-up of Murine Tumors Treated by Electrochemotherapy and other Electroporation-based Treatments

In vivo cell electropermeabilization can be used alone or in combination with a hydrophilic, nonpermeant cytotoxic drug such as bleomycin (electrochemotherapy) to efficiently treat tumors. We used magnetic resonance imaging to detect rapid structural modifications in tumors treated by electroporation-based methods. Water diffusion coefficient (ADC), transverse relaxation time (T2) and tumor volume of fibrosarcomas xenografted on syngenic mice were measured upon 3 groups of 6 treated mice within the 48 hrs following ECT done with a normal (BE) or a high dose of bleomycin (HBE), and after irreversible electroporation (IRE), and in three control groups. As expected, the tumor volume increased in the control groups at 48 hrs (p < 0.05) and the values of ADC and T2 did not varied significantly in the control groups except for ADC decrease and T2 increase observed between 3 hrs and 24 hrs (p < 0.03) in the group that received bleomycin only. Tumor volumes decreased significantly at 24 hrs in the IRE and HBE groups. The mean tumor ADC increased significantly at 24 hrs (+17.6%, p < 0.03) in the BE group, probably reflecting apoptosis, while in the HBE group the mean tumor ADC increased earlier, at 10 hrs (+19%, p < 0.03) because of the speed of the pseudoapopototic process. In the IRE group, the mean tumor ADC decreased significantly at 1 hrs (p < 0.05) and 3 hrs (p < 0.03), and T2 decreased (p < 0.03), both probably reflecting cell swelling induced by the vascular lock. Thus ADC and T2 changes in the treated tumors correlated with previous histological observations on the same tumor models. Noteworthy, ADC allowed the visualization of early and rapid changes in the treated tumors, when tumor volume monitoring was not yet able to detect any effect of the treatments.

Comparison of two vascular-disrupting agents at a clinically relevant dose in rodent liver tumors with multiparametric magnetic resonance imaging biomarkers

We sought to compare the therapeutic efficacy between two vascular-disrupting agents, combretastatin A4 phosphate (CA4P) and ZD6126, at a clinically relevant dose on tumor models with magnetic resonance imaging (MRI). Thirty rats with liver rhabdomyosarcoma were randomized into CA4P (10 mg/kg), ZD6126 (10 mg/kg), and control group (n=10 for each group). Multiparametric MRI biomarkers including tumor volume, enhancement ratio, necrosis ratio, apparent diffusion coefficient (ADC), and K (volume transfer constant) derived from T2-weighted, T1-weighted, contrast-enhanced T1-weighted, and diffusion-weighted imaging, and dynamic contrast-enhanced MRI were compared at pretreatment, 1 h, 6 h, 24 h, 48 h, and 120 h posttreatment; they were validated using ex-vivo techniques. Relative to rapidly growing tumors without necrosis in control rats, tumors grew slower in the CA4P group compared with the ZD6126 group with a higher necrosis ratio at 120 h (P<0.05), as proven by histopathology. In the CA4P group, K decreased from 1 h until 6 h, and partially recovered at 120 h. In the ZD6126 group, the reduced K at 1 h began to rebound from 6 h and exceeded the baseline value at 120 h (P<0.05), parallel to evolving enhancement ratios (P<0.05). ADC revealed more necrotic tumors with CA4P versus ZD6126 at 120 h (P<0.05). The different tumor responses were confirmed by ex-vivo microangiography and histopathology. CA4P was more effective than ZD6126 in impairing blood supply, inducing necrosis, and delaying growth in rat liver tumors at a clinically relevant dose. A single dose of vascular-disrupting agent was insufficient to destroy the tumor. The multiparametric MRI biomarkers enabled in-vivo noninvasive comparison of therapeutic efficacy between CA4P and ZD6126.

Tumor reoxygenation following administration of Mitogen-Activated Protein Kinase inhibitors: a rationale for combination with radiation therapy

BACKGROUND AND PURPOSE

The relevance of Mitogen Activated Protein Kinase (MAPK) inhibitors as co-treatments for radiation therapy is investigated, with special focus on a potential link between the MAPK pathway and tumor hypoxia, which is a critical determinant for response to therapy.

MATERIALS AND METHODS

The effects of two MAPK inhibitors, Sorafenib and PD0325901, were monitored daily using in vivo EPR (Electron Paramagnetic Resonance) oximetry in FSaII and TLT tumor models in order to identify a window of reoxygenation, during which tumor blood flow, oxygen consumption and radiation sensitivity were assessed.

RESULTS

Reoxygenation was shown after two days of treatments with Sorafenib or PD0325901 in two tumor models, which was further successfully exploited with Sorafenib for improving the radiation response of FSaII tumors by a factor of 1.5. The increase in tumor oxygenation was shown to be the result of two major factors: (i) an increase in blood flow for Sorafenib, that might be linked to its anti-angiogenic effect (vascular normalization), and (ii) a decrease in oxygen consumption for Sorafenib and PD0325901, due to an alteration of the mitochondrial activity.

CONCLUSION

We evidenced tumor reoxygenation in vivo following MAPK inhibition and suggest a rationale for the combination of radiation therapy with Sorafenib.

Targeting tumor perfusion and oxygenation to improve the outcome of anticancer therapy

Radiotherapy and chemotherapy are widespread clinical modalities for cancer treatment. Among other biological influences, hypoxia is a main factor limiting the efficacy of radiotherapy, primarily because oxygen is involved in the stabilization of the DNA damage caused by ionizing radiations. Radiobiological hypoxia is found in regions of rodent and human tumors with a tissue oxygenation level below 10 mmHg at which tumor cells become increasingly resistant to radiation damage. Since hypoxic tumor cells remain clonogenic, their resistance to the treatment strongly influences the therapeutic outcome of radiotherapy. There is therefore an urgent need to identify adjuvant treatment modalities aimed to increase tumor pO(2) at the time of radiotherapy. Since tumor hypoxia fundamentally results from an imbalance between oxygen delivery by poorly efficient blood vessels and oxygen consumption by tumor cells with high metabolic activities, two promising approaches are those targeting vascular reactivity and tumor cell respiration. This review summarizes the current knowledge about the development and use of tumor-selective vasodilators, inhibitors of tumor cell respiration, and drugs and treatments combining both activities in the context of tumor sensitization to X-ray radiotherapy. Tumor-selective vasodilation may also be used to improve the delivery of circulating anticancer agents to tumors. Imaging tumor perfusion and oxygenation is of importance not only for the development and validation of such combination treatments, but also to determine which patients could benefit from the therapy. Numerous techniques have been developed in the preclinical setting. Hence, this review also briefly describes both magnetic resonance and non-magnetic resonance in vivo methods and compares them in terms of sensitivity, quantitative or semi-quantitative properties, temporal, and spatial resolutions, as well as translational aspects.

Arsenic trioxide treatment decreases the oxygen consumption rate of tumor cells and radiosensitizes solid tumors

Arsenic trioxide (As(2)O(3)) is an effective therapeutic against acute promyelocytic leukemia and certain solid tumors. Because As(2)O(3) inhibits mitochondrial respiration in leukemia cells, we hypothesized that As(2)O(3) might enhance the radiosensitivity of solid tumors by increasing tumor oxygenation [partial pressure of oxygen (pO(2))] via a decrease in oxygen consumption. Two murine models of radioresistant hypoxic cancer were used to study the effects of As(2)O(3). We measured pO(2) and the oxygen consumption rate in vivo by electron paramagnetic resonance oximetry and (19)fluorine-MRI relaxometry. Tumor perfusion was assessed by Patent blue staining. In both models, As(2)O(3) inhibited mitochondrial respiration, leading to a rapid increase in pO(2). The decrease in oxygen consumption could be explained by an observed decrease in glutathione in As(2)O(3)-treated cells, as this could increase intracellular reactive oxygen species that can disrupt mitochondrial membrane potential. When tumors were irradiated during periods of As(2)O(3)-induced augmented oxygenation, radiosensitivity increased by 2.2-fold compared with control mice. Notably, this effect was abolished when temporarily clamped tumors were irradiated. Together, our findings show that As(2)O(3) acutely increases oxygen consumption and radiosensitizes tumors, providing a new rationale for clinical investigations of As(2)O(3) in irradiation protocols to treat solid tumors.