Toxicity In Healthy Tissues Research Articles

Abstract 3106: Targeted delivery via Elastin Like Polypeptide: Biodistribution of a doxorubicin derivative in MDA-MB231 human breast cancer xenografts in mice

Abstract The anticancer agent doxorubicin has been widely used in the treatment of a variety of hematological malignancies and solid tumors. Despite doxorubicin’s efficiency in eradicating tumor cells, severe damage to healthy tissues, along with cardiotoxicity, limits its use in clinics. To overcome adverse side effects, improve patient safety, and enhance therapeutic efficacy, we have designed a thermally responsive biopolymer doxorubicin carrier that can be specifically targeted to tumor tissue by locally applying mild hyperthermia (41 degrees C). The developed drug vehicle is composed of: a cell penetrating peptide (SynB1) to promote tumor and cellular uptake; thermally responsive Elastin like polypeptide (ELP); and the (6-maleimidocaproyl) hydrazone derivative of doxorubicin (DOXO-EMCH) containing a pH-sensitive hydrazine linker that releases dox in the acidic tumor environment. We used the in vivo imaging system, IVIS, to determine the biodistribution of doxorubicin-delivered ELP in MDA-MB231 triple negative human breast cancer cell line xenografts in nude mice. Tumor bearing mice were treated with a single IV injection of 10 mg/kg doxorubicin equivalent dose with free doxorubicin, thermally responsive SynB1 ELP 1-DOXO, and a thermally nonresponsive control biopolymer, SynB1 ELP 2-DOXO. Following a 2 hour treatment with hyperthermia, tumors showed a 2-fold higher uptake when treated with SynB1 ELP 1-DOXO compared to free doxorubicin. Accumulation of the thermally non-responsive control SynB1 ELP2 -DOXO was comparable to free doxorubicin, indicating that an increase in dox accumulation with ELP is due to aggregation in response to thermal targeting. Higher levels of SynB1 ELP1 -DOXO and SynB1 ELP2 -DOXO with respect to free doxorubicin were observed in kidneys. Fluorescence intensity from hearts of animals treated with SynB1 ELP1 - DOXO show a 5-fold lower accumulation of doxorubicin than the same dose of free doxorubicin. SynB1-ELP1-DOXO biopolymers demonstrated a 6-fold increase in tumor/heart ratio in comparison to free doxorubicin, indicating preferential accumulation of the drug carrier in tumors. Overall, thermally targeted polymers are a promising therapy to enhance tumor targeting and uptake of anticancer drugs and to minimize free drug toxicity in healthy tissues, representing a great potential for clinical application. Citation Format: Sonja Dragojevic, Jung Su Ryu, Felix Kratz, Drazen Raucher. Targeted delivery via Elastin Like Polypeptide: Biodistribution of a doxorubicin derivative in MDA-MB231 human breast cancer xenografts in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3106. doi:10.1158/1538-7445.AM2017-3106

Novel Nano-Therapeutic Approach Actively Targets Human Ovarian Cancer Stem Cells after Xenograft into Nude Mice.

The power of tumorigenesis, chemo-resistance and metastasis in malignant ovarian tumors resides in a tiny population of cancer cells known as ovarian cancer stem cells (OCSCs). Developing nano-therapeutic targeting of OCSCs is considered a great challenge. The potential use of poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) was investigated as a drug delivery system for paclitaxel (PTX) against OCSCs in vitro and in vivo. PTX-loaded PLGA NPs were prepared by an emulsion solvent evaporation method, supported by incorporation of folic acid (FA) as the ligand. NPs were characterized for size, surface morphology, drug loading, and encapsulation efficiency. In vitro cytotoxicity of PTX-loaded FA/PLGA NPs was tested against OCSCs with MTT assay. In vivo anti-tumoral efficiency and active targeting potential of prepared NPs against tumors in nude mice were investigated. In vitro results revealed that IC50 of PTX was significantly reduced after loading on PLGA NPs. On the other hand, in vivo results showed that PLGA NPs enhanced the tumor suppression efficiency of PTX. Investigation with real time quantitative PCR analysis revealed the limiting expression of chemo-resistant genes (ABCG2 and MDR1) after applying PLGA NPs as a drug delivery system for PTX. Histopathological examination of tumors showed the effective biological influence of PTX-loaded FA/PLGA NPs through the appearance of reactive lymphoid follicles. Targeting potential of PTX was activated by FA/PLGA NPs through significant preservation of body weight (p < 0.0001) and minimizing the systemic toxicity in healthy tissues. Immunohistochemical investigation revealed a high expression of apoptotic markers in tumor tissue, supporting the targeting effect of FA/PLGA NPs. A drug delivery system based on FA/PLGA NPs can enhance PTX’s in vitro cytotoxicity and in vivo targeting potential against OCSCs.

Optimization of photon beam energies in gold nanoparticle enhanced arc radiation therapy using Monte Carlo methods

As a recent area of development in radiation therapy, gold nanoparticle (GNP) enhanced radiation therapy has shown potential to increase tumour dose while maintaining acceptable levels of healthy tissue toxicity. In this study, the effect of varying photon beam energy in GNP enhanced arc radiation therapy (GEART) is quantified through the introduction of a dose scoring metric, and GEART is compared to a conventional radiotherapy treatment. The PENELOPE Monte Carlo code was used to model several simple phantoms consisting of a spherical tumour containing GNPs (concentration: 15 mg Au g−1 tumour, 0.8 mg Au g−1 normal tissue) in a cylinder of tissue. Several monoenergetic photon beams, with energies ranging from 20 keV to 6 MeV, as well as 100, 200, and 300 kVp spectral beams, were used to irradiate the tumour in a 360° arc treatment. A dose metric was then used to compare tumour and tissue doses from GEART treatments to a similar treatment from a 6 MV spectrum. This was also performed on a simulated brain tumour using patient computed tomography data. GEART treatments showed potential over the 6 MV treatment for many of the simulated geometries, delivering up to 88% higher mean dose to the tumour for a constant tissue dose, with the effect greatest near a source energy of 50 keV. This effect is also seen with the inclusion of bone in a brain treatment, with a 14% increase in mean tumour dose over 6 MV, while still maintaining acceptable levels of dose to the bone and brain.

Re-assessing gallium-67 as a therapeutic radionuclide

Abstract Introduction Despite its desirable half-life and low energy Auger electrons that travel further than for other radionuclides, 67 Ga has been neglected as a therapeutic radionuclide. Here, 67 Ga is compared with Auger electron emitter 111 In as a potential therapeutic radionuclide. Methods Plasmid pBR322 studies allowed direct comparison between 67 Ga and 111 In (1MBq) in causing DNA damage, including the effect of chelators (EDTA and DTPA) and the effects of a free radical scavenger (DMSO). The cytotoxicity of internalized (by means of delivery in the form of oxine complexes) and non-internalized 67 Ga and 111 In was measured in DU145 prostate cancer cells after a one-hour incubation using cell viability (trypan blue) and clonogenic studies. MDA-MB-231 and HCC1954 cells were also used. Results Plasmid DNA damage was caused by 67 Ga and was comparable to that caused by 111 In; it was reduced in the presence of EDTA, DTPA and DMSO. The A 50 values (internalized activity of oxine complexes per cell required to kill 50% of cells) as determined by trypan blue staining was 1.0Bq/cell for both 67 Ga and 111 In; the A 50 values determined by clonogenic assay were 0.7Bq/cell and 0.3Bq/cell for 111 In and 67 Ga respectively. At the concentrations required to achieve these uptake levels, non-internalized 67 Ga and 111 In caused no cellular toxicity. Qualitatively similar results were found for MDA-MB-231 and HCC1954 cells. Conclusion 67 Ga causes as much damage as 111 In to plasmid DNA in solution and shows similar toxicity as 111 In at equivalent internalized activity per cell. 67 Ga therefore deserves further evaluation for radionuclide therapy. Advances in knowledge and implications for patient care The data presented here is at the basic level of science. If future in vivo and clinical studies are successful, 67 Ga could become a useful radionuclide with little healthy tissue toxicity in the arsenal of weapons for treating cancer.

Next generation predictive biomarkers for immune checkpoint inhibition.

With the advent of targeted therapies, there has been a revolution in the treatment of cancer across multiple histologies. Immune checkpoint blockade has made it possible to take advantage of receptor-ligand interactions between immune and tumor cells in a wide spectrum of malignancies. Toxicity in healthy tissue, however, can limit our use of these agents. Immune checkpoint blockade has been approved in advanced melanoma, renal cell cancer, non-small cell lung cancer, relapsed refractory Hodgkin's lymphoma, and urothelial cancer. Though FDA-approved indications for use of some of these novel agents depend on current protein-based programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) assays, detection methods come with several caveats. Additional predictive tools must be interrogated to discern responders from non-responders. Some of these include measurement of microsatellite instability, PD-L1 amplification, cluster of differentiation 8 (CD8) infiltrate density, and tumor mutational burden. This review serves to synthesize biomarker detection at the DNA, RNA, and protein level to more accurately forecast benefit from these novel agents.

Re-assessing gallium-67 as a therapeutic radionuclide

IntroductionDespite its desirable half-life and low energy Auger electrons that travel further than for other radionuclides, 67Ga has been neglected as a therapeutic radionuclide. Here, 67Ga is compared with Auger electron emitter 111In as a potential therapeutic radionuclide. MethodsPlasmid pBR322 studies allowed direct comparison between 67Ga and 111In (1MBq) in causing DNA damage, including the effect of chelators (EDTA and DTPA) and the effects of a free radical scavenger (DMSO). The cytotoxicity of internalized (by means of delivery in the form of oxine complexes) and non-internalized 67Ga and 111In was measured in DU145 prostate cancer cells after a one-hour incubation using cell viability (trypan blue) and clonogenic studies. MDA-MB-231 and HCC1954 cells were also used. ResultsPlasmid DNA damage was caused by 67Ga and was comparable to that caused by 111In; it was reduced in the presence of EDTA, DTPA and DMSO. The A50 values (internalized activity of oxine complexes per cell required to kill 50% of cells) as determined by trypan blue staining was 1.0Bq/cell for both 67Ga and 111In; the A50 values determined by clonogenic assay were 0.7Bq/cell and 0.3Bq/cell for 111In and 67Ga respectively. At the concentrations required to achieve these uptake levels, non-internalized 67Ga and 111In caused no cellular toxicity. Qualitatively similar results were found for MDA-MB-231 and HCC1954 cells. Conclusion67Ga causes as much damage as 111In to plasmid DNA in solution and shows similar toxicity as 111In at equivalent internalized activity per cell. 67Ga therefore deserves further evaluation for radionuclide therapy. Advances in knowledge and implications for patient careThe data presented here is at the basic level of science. If future in vivo and clinical studies are successful, 67Ga could become a useful radionuclide with little healthy tissue toxicity in the arsenal of weapons for treating cancer.

WE-FG-BRA-07: Theranostic Nanoparticles Improve Clinical MR-Guided Radiation Therapy

Purpose: MR-guided radiation therapy is a current and emerging clinical reality. We have designed and tested a silica-based gadolinium chelates nanoparticle (AGuIX) for integration with MR-guided radiation therapy. The AGuIX nanoparticles used in this study are a dual-modality probe with radiosensitization properties and better MRI contrast than current FDA-approved gadolinium chelates. In advance of an approved Phase I clinical trial, we report on the efficacy and safety in multiple animal models and clinically relevant radiation conditions. By modeling our study on current clinic workflows, we show compatibility with modern patient care, thus heightening the translational significance of this research. Methods: The dual imaging and therapy functionality of AGuIX was investigated in mice with clinical radiation beams while safety was evaluated in mice, and nonhuman primates after systemic injection of 0.25 mg/g of nanoparticles. MRI/ICP-MS were used to measure tumor uptake and biodistribution. Due to their small size (2–3 nm), AGuIX have good renal clearance (t1/2=19min). We performed in vitro cell uptake quantification and radiosensitization studies (clonogenic assays and DNA damage quantification). In vivo radiation therapy studies were performed with both 6MV and 6MV-FFF clinical radiation beams. Histology was performed to measure the increase in DNA damage in the tumor and to evaluate the toxicity in healthy tissues. Results: In vitro and in vivo results demonstrate statistically significant increase (P < 0.01) in DNA damage, tumor growth supression and survival (+100 days) compared to radiation alone. Negligible toxicity was observed in all of the animal models. The combination of 6MV-FFF/AGuIX demonstrated a substantial dose enhancement compared to 6MV/AGuIX (DEF = 1.36 vs. 1.22) due to the higher proportion of low energy photons. Conclusion: With demonstrated efficacy and negligible toxicity in mice and non-human primates, AGuIX is a biocompatible nanoplatform with strong translational potential for MR-guided radiation therapy.

Photodynamic therapy platform based on localized delivery of photosensitizer by vaterite submicron particles

The elaboration of biocompatible and biodegradable carriers for photosensitizer targeted delivery is one of the most promising approaches in a modern photodynamic therapy (PDT). This approach is aimed at reducing sides effects connected with incidental toxicity in healthy tissue whilst also enhancing drug accumulation in the tumour area. In the present work, Photosens-loaded calcium carbonate (CaCO3) submicron particles in vaterite modification are proposed as a novel platform for anticancer PDT. Fast penetration of the carriers (0.9±0.2μm in diameter) containing 0.12% (w/w) of the photosensitizer into NIH3T3/EGFP cells is demonstrated. The captured particles provide the dye localization inside the cell increasing its local concentration, compared with ⿿free⿿ Photosens solution which is uniformly distributed throughout the cell. The effect of photosensitizer encapsulation into vaterite submicron particles on cell viability under laser irradiation (670nm, 19mW/cm2, 10min) is discussed in the work. As determined by a viability assay, the encapsulation renders Photosens more phototoxic. By this means, CaCO3 carriers allow improvement of the photosensitizer effectiveness supposing, therefore, the reduction of therapeutic dose. Summation of these effects with the simplicity, upscalability and cheapness of fabrication, biocompatibility and high payload ability of the vaterite particles hold out the prospect of a novel PDT platform.

EGFR targeted nanobody–photosensitizer conjugates for photodynamic therapy in a pre-clinical model of head and neck cancer

Photodynamic therapy (PDT) induces cell death through local light activation of a photosensitizer (PS) and has been used to treat head and neck cancers. Yet, common PS lack tumor specificity, which leads to collateral damage to normal tissues. Targeted delivery of PS via antibodies has pre-clinically improved tumor selectivity. However, antibodies have long half-lives and relatively poor tissue penetration, which could limit therapeutic efficacy and lead to long photosensitivity. Here, in this feasibility study, we evaluate at the pre-clinical level a recently introduced format of targeted PDT, which employs nanobodies as targeting agents and a water-soluble PS (IRDye700DX) that is traceable through optical imaging. In vitro, the PS solely binds to cells and induces phototoxicity on cells overexpressing the epidermal growth factor receptor (EGFR), when conjugated to the EGFR targeted nanobodies. To investigate whether this new format of targeted PDT is capable of inducing selective tumor cell death in vivo, PDT was applied on an orthotopic mouse tumor model with illumination at 1h post-injection of the nanobody–PS conjugates, as selected from quantitative fluorescence spectroscopy measurements. In parallel, and as a reference, PDT was applied with an antibody–PS conjugate, with illumination performed 24h post-injection. Importantly, EGFR targeted nanobody–PS conjugates led to extensive tumor necrosis (approx. 90%) and almost no toxicity in healthy tissues, as observed through histology 24h after PDT. Overall, results show that these EGFR targeted nanobody–PS conjugates are selective and able to induce tumor cell death in vivo. Additional studies are now needed to assess the full potential of this approach to improving PDT.

TH‐D‐BRD‐00: Real Time Imaging Verification and Tracking for Moving Targets

Radiotherapy of moving targets, such as lung, liver or prostate tumors, is prone to treatment errors due to the uncertainties in the target position. Minimizing such error is critical for radiotherapy treatments, especially hypofractionated SBRT treatments. On‐board real time imaging verification and tracking of moving targets has become one of the most exciting areas in radiotherapy. The tremendous developments in this area enable us to improve targeting accuracy and reduce the healthy tissue toxicity, which paves the road to further margin reduction and dose escalation in conventionally fractionated or SBRT treatments.Over the past few years, several real‐time imaging techniques have been clinically implemented, including techniques using ionizing radiation, such as x‐ray based imaging, and radiation‐free techniques such as MRI, imaging based on implanted electromagnetic transponders and optical imaging. The x‐ray imaging techniques are widely accessible in clinics, although they have limited soft tissue contrast and contribute to patient exposure. Recently, MRI has gained wide interests in radiotherapy due to its better soft tissue contrast and no radiation dose. Imaging based on electromagnetic transponders and optical imaging have also gained popularity in many clinical scenarios due to their unique capabilities.Based on these imaging techniques, various tracking approaches have been developed. The room mounted orthogonal 2D x‐ray system (CyberKnife system) was the first medical device capable to perform real‐time target tracking by combining image guidance with robotically targeted radiation delivery. In the Vero system, tumor tracking is achieved by combining image‐guidance with a two‐dimensional pivot assembly of the linear accelerator. In gantry‐based linear accelerators, target motion can be tracked in real time by repositioning the MLC based on the signal from x‐ray images or electromagnetic transponders implanted.The rapid development of new imaging and tracking technologies raises new challenges in revolutionizing our treatment procedures. It becomes important to understand the functionality, limitations and clinical impact of each technique so that they can be chosen wisely for different clinical settings. The goal of this educational session is to compare and contrast different imaging and tracking techniques implemented in CyberKnife, Vero, MRI based, and gantry‐based radiotherapy machines. The general concepts of real‐time imaging and tracking, from imaging the target to adapting the treatment, will be reviewed for each modality. While discussing the technical aspects of the systems including the overall uncertainties and residual imaging and tracking errors, emphasis will be placed on the clinical implementation and workflow. The increased patient dose due to x‐ray imaging and quality assurance procedures will be described. Additionally, the impact of tracking on treatment volume and margin reduction will be discussed. The session will close with an outlook at future developments.Learning Objectives: Understand the opportunities and challenges of real time imaging and tumor tracking. Understand the advantages and limitations of different imaging and tracking techniques, as well as the clinical implementation of each technique. Understand the clinical impact of real time tumor tracking and future directions in this area. Supported by National Institutes of Health, Varian Medical System, Accuray Inc.

TH‐D‐BRD‐01: X‐Ray Based Real Time Imaging Verification

Radiotherapy of moving targets, such as lung, liver or prostate tumors, is prone to treatment errors due to the uncertainties in the target position. Minimizing such error is critical for radiotherapy treatments, especially hypofractionated SBRT treatments. On‐board real time imaging verification and tracking of moving targets has become one of the most exciting areas in radiotherapy. The tremendous developments in this area enable us to improve targeting accuracy and reduce the healthy tissue toxicity, which paves the road to further margin reduction and dose escalation in conventionally fractionated or SBRT treatments.Over the past few years, several real‐time imaging techniques have been clinically implemented, including techniques using ionizing radiation, such as x‐ray based imaging, and radiation‐free techniques such as MRI, imaging based on implanted electromagnetic transponders and optical imaging. The x‐ray imaging techniques are widely accessible in clinics, although they have limited soft tissue contrast and contribute to patient exposure. Recently, MRI has gained wide interests in radiotherapy due to its better soft tissue contrast and no radiation dose. Imaging based on electromagnetic transponders and optical imaging have also gained popularity in many clinical scenarios due to their unique capabilities.Based on these imaging techniques, various tracking approaches have been developed. The room mounted orthogonal 2D x‐ray system (CyberKnife system) was the first medical device capable to perform real‐time target tracking by combining image guidance with robotically targeted radiation delivery. In the Vero system, tumor tracking is achieved by combining image‐guidance with a two‐dimensional pivot assembly of the linear accelerator. In gantry‐based linear accelerators, target motion can be tracked in real time by repositioning the MLC based on the signal from x‐ray images or electromagnetic transponders implanted.The rapid development of new imaging and tracking technologies raises new challenges in revolutionizing our treatment procedures. It becomes important to understand the functionality, limitations and clinical impact of each technique so that they can be chosen wisely for different clinical settings. The goal of this educational session is to compare and contrast different imaging and tracking techniques implemented in CyberKnife, Vero, MRI based, and gantry‐based radiotherapy machines. The general concepts of real‐time imaging and tracking, from imaging the target to adapting the treatment, will be reviewed for each modality. While discussing the technical aspects of the systems including the overall uncertainties and residual imaging and tracking errors, emphasis will be placed on the clinical implementation and workflow. The increased patient dose due to x‐ray imaging and quality assurance procedures will be described. Additionally, the impact of tracking on treatment volume and margin reduction will be discussed. The session will close with an outlook at future developments.Learning Objectives: Understand the opportunities and challenges of real time imaging and tumor tracking. Understand the advantages and limitations of different imaging and tracking techniques, as well as the clinical implementation of each technique. Understand the clinical impact of real time tumor tracking and future directions in this area. Supported by National Institutes of Health, Varian Medical System, Accuray Inc.

TH‐D‐BRD‐03: Real Time Tumor Motion Tracking with CyberKnife

Radiotherapy of moving targets, such as lung, liver or prostate tumors, is prone to treatment errors due to the uncertainties in the target position. Minimizing such error is critical for radiotherapy treatments, especially hypofractionated SBRT treatments. On‐board real time imaging verification and tracking of moving targets has become one of the most exciting areas in radiotherapy. The tremendous developments in this area enable us to improve targeting accuracy and reduce the healthy tissue toxicity, which paves the road to further margin reduction and dose escalation in conventionally fractionated or SBRT treatments.Over the past few years, several real‐time imaging techniques have been clinically implemented, including techniques using ionizing radiation, such as x‐ray based imaging, and radiation‐free techniques such as MRI, imaging based on implanted electromagnetic transponders and optical imaging. The x‐ray imaging techniques are widely accessible in clinics, although they have limited soft tissue contrast and contribute to patient exposure. Recently, MRI has gained wide interests in radiotherapy due to its better soft tissue contrast and no radiation dose. Imaging based on electromagnetic transponders and optical imaging have also gained popularity in many clinical scenarios due to their unique capabilities.Based on these imaging techniques, various tracking approaches have been developed. The room mounted orthogonal 2D x‐ray system (CyberKnife system) was the first medical device capable to perform real‐time target tracking by combining image guidance with robotically targeted radiation delivery. In the Vero system, tumor tracking is achieved by combining image‐guidance with a two‐dimensional pivot assembly of the linear accelerator. In gantry‐based linear accelerators, target motion can be tracked in real time by repositioning the MLC based on the signal from x‐ray images or electromagnetic transponders implanted.The rapid development of new imaging and tracking technologies raises new challenges in revolutionizing our treatment procedures. It becomes important to understand the functionality, limitations and clinical impact of each technique so that they can be chosen wisely for different clinical settings. The goal of this educational session is to compare and contrast different imaging and tracking techniques implemented in CyberKnife, Vero, MRI based, and gantry‐based radiotherapy machines. The general concepts of real‐time imaging and tracking, from imaging the target to adapting the treatment, will be reviewed for each modality. While discussing the technical aspects of the systems including the overall uncertainties and residual imaging and tracking errors, emphasis will be placed on the clinical implementation and workflow. The increased patient dose due to x‐ray imaging and quality assurance procedures will be described. Additionally, the impact of tracking on treatment volume and margin reduction will be discussed. The session will close with an outlook at future developments.Learning Objectives: Understand the opportunities and challenges of real time imaging and tumor tracking. Understand the advantages and limitations of different imaging and tracking techniques, as well as the clinical implementation of each technique. Understand the clinical impact of real time tumor tracking and future directions in this area. Supported by National Institutes of Health, Varian Medical System, Accuray Inc.

TH‐D‐BRD‐04: A Review of Present and Near‐Future Methods for Real‐Time Target Tracking and Adaptation

Radiotherapy of moving targets, such as lung, liver or prostate tumors, is prone to treatment errors due to the uncertainties in the target position. Minimizing such error is critical for radiotherapy treatments, especially hypofractionated SBRT treatments. On‐board real time imaging verification and tracking of moving targets has become one of the most exciting areas in radiotherapy. The tremendous developments in this area enable us to improve targeting accuracy and reduce the healthy tissue toxicity, which paves the road to further margin reduction and dose escalation in conventionally fractionated or SBRT treatments.Over the past few years, several real‐time imaging techniques have been clinically implemented, including techniques using ionizing radiation, such as x‐ray based imaging, and radiation‐free techniques such as MRI, imaging based on implanted electromagnetic transponders and optical imaging. The x‐ray imaging techniques are widely accessible in clinics, although they have limited soft tissue contrast and contribute to patient exposure. Recently, MRI has gained wide interests in radiotherapy due to its better soft tissue contrast and no radiation dose. Imaging based on electromagnetic transponders and optical imaging have also gained popularity in many clinical scenarios due to their unique capabilities.Based on these imaging techniques, various tracking approaches have been developed. The room mounted orthogonal 2D x‐ray system (CyberKnife system) was the first medical device capable to perform real‐time target tracking by combining image guidance with robotically targeted radiation delivery. In the Vero system, tumor tracking is achieved by combining image‐guidance with a two‐dimensional pivot assembly of the linear accelerator. In gantry‐based linear accelerators, target motion can be tracked in real time by repositioning the MLC based on the signal from x‐ray images or electromagnetic transponders implanted.The rapid development of new imaging and tracking technologies raises new challenges in revolutionizing our treatment procedures. It becomes important to understand the functionality, limitations and clinical impact of each technique so that they can be chosen wisely for different clinical settings. The goal of this educational session is to compare and contrast different imaging and tracking techniques implemented in CyberKnife, Vero, MRI based, and gantry‐based radiotherapy machines. The general concepts of real‐time imaging and tracking, from imaging the target to adapting the treatment, will be reviewed for each modality. While discussing the technical aspects of the systems including the overall uncertainties and residual imaging and tracking errors, emphasis will be placed on the clinical implementation and workflow. The increased patient dose due to x‐ray imaging and quality assurance procedures will be described. Additionally, the impact of tracking on treatment volume and margin reduction will be discussed. The session will close with an outlook at future developments.Learning Objectives: Understand the opportunities and challenges of real time imaging and tumor tracking. Understand the advantages and limitations of different imaging and tracking techniques, as well as the clinical implementation of each technique. Understand the clinical impact of real time tumor tracking and future directions in this area. Supported by National Institutes of Health, Varian Medical System, Accuray Inc.

TH‐D‐BRD‐02: Non‐Ionizing Methods for On‐Table Positioning and Tracking

Radiotherapy of moving targets, such as lung, liver or prostate tumors, is prone to treatment errors due to the uncertainties in the target position. Minimizing such error is critical for radiotherapy treatments, especially hypofractionated SBRT treatments. On‐board real time imaging verification and tracking of moving targets has become one of the most exciting areas in radiotherapy. The tremendous developments in this area enable us to improve targeting accuracy and reduce the healthy tissue toxicity, which paves the road to further margin reduction and dose escalation in conventionally fractionated or SBRT treatments.Over the past few years, several real‐time imaging techniques have been clinically implemented, including techniques using ionizing radiation, such as x‐ray based imaging, and radiation‐free techniques such as MRI, imaging based on implanted electromagnetic transponders and optical imaging. The x‐ray imaging techniques are widely accessible in clinics, although they have limited soft tissue contrast and contribute to patient exposure. Recently, MRI has gained wide interests in radiotherapy due to its better soft tissue contrast and no radiation dose. Imaging based on electromagnetic transponders and optical imaging have also gained popularity in many clinical scenarios due to their unique capabilities.Based on these imaging techniques, various tracking approaches have been developed. The room mounted orthogonal 2D x‐ray system (CyberKnife system) was the first medical device capable to perform real‐time target tracking by combining image guidance with robotically targeted radiation delivery. In the Vero system, tumor tracking is achieved by combining image‐guidance with a two‐dimensional pivot assembly of the linear accelerator. In gantry‐based linear accelerators, target motion can be tracked in real time by repositioning the MLC based on the signal from x‐ray images or electromagnetic transponders implanted.The rapid development of new imaging and tracking technologies raises new challenges in revolutionizing our treatment procedures. It becomes important to understand the functionality, limitations and clinical impact of each technique so that they can be chosen wisely for different clinical settings. The goal of this educational session is to compare and contrast different imaging and tracking techniques implemented in CyberKnife, Vero, MRI based, and gantry‐based radiotherapy machines. The general concepts of real‐time imaging and tracking, from imaging the target to adapting the treatment, will be reviewed for each modality. While discussing the technical aspects of the systems including the overall uncertainties and residual imaging and tracking errors, emphasis will be placed on the clinical implementation and workflow. The increased patient dose due to x‐ray imaging and quality assurance procedures will be described. Additionally, the impact of tracking on treatment volume and margin reduction will be discussed. The session will close with an outlook at future developments.Learning Objectives: Understand the opportunities and challenges of real time imaging and tumor tracking. Understand the advantages and limitations of different imaging and tracking techniques, as well as the clinical implementation of each technique. Understand the clinical impact of real time tumor tracking and future directions in this area. Supported by National Institutes of Health, Varian Medical System, Accuray Inc.

Genome-wide association analysis of radiation resistance in Drosophila melanogaster.

BackgroundIonizing radiation is genotoxic to cells. Healthy tissue toxicity in patients and radiation resistance in tumors present common clinical challenges in delivering effective radiation therapies. Radiation response is a complex, polygenic trait with unknown genetic determinants. The Drosophila Genetic Reference Panel (DGRP) provides a model to investigate the genetics of natural variation for sensitivity to radiation.Methods and FindingsRadiation response was quantified in 154 inbred DGRP lines, among which 92 radiosensitive lines and 62 radioresistant lines were classified as controls and cases, respectively. A case-control genome-wide association screen for radioresistance was performed. There are 32 single nucleotide polymorphisms (SNPs) associated with radio resistance at a nominal p<10−5; all had modest effect sizes and were common variants with the minor allele frequency >5%. All the genes implicated by those SNP hits were novel, many without a known role in radiation resistance and some with unknown function. Variants in known DNA damage and repair genes associated with radiation response were below the significance threshold of p<10−5 and were not present among the significant hits. No SNP met the genome-wide significance threshold (p = 1.49×10−7), indicating a necessity for a larger sample size.ConclusionsSeveral genes not previously associated with variation in radiation resistance were identified. These genes, especially the ones with human homologs, form the basis for exploring new pathways involved in radiation resistance in novel functional studies. An improved DGRP model with a sample size of at least 265 lines and ideally up to 793 lines is recommended for future studies of complex traits.

Caffeine-Based Gold(I) N-Heterocyclic Carbenes as Possible Anticancer Agents: Synthesis and Biological Properties

A new series of gold(I) N-heterocyclic carbene (NHC) complexes based on xanthine ligands have been synthesized and characterized by mass spectrometry, NMR, and X-ray diffraction. The compounds have been tested for their antiproliferative properties in human cancer cells and nontumorigenic cells in vitro, as well as for their toxicity in healthy tissues ex vivo. The bis-carbene complex [Au(caffein-2-ylidene)2][BF4] (complex 4) appeared to be selective for human ovarian cancer cell lines and poorly toxic in healthy organs. To gain preliminary insights into their actual mechanism of action, two biologically relevant in cellulo targets were studied, namely, DNA (more precisely a higher-order DNA structure termed G-quadruplex DNA that plays key roles in oncogenetic regulation) and a pivotal enzyme of the DNA damage response (DDR) machinery (poly-(adenosine diphosphate (ADP)-ribose) polymerase 1 (PARP-1), strongly involved in the cancer resistance mechanism). Our results indicate that complex 4 acts as an efficient and selective G-quadruplex ligand while being a modest PARP-1 inhibitor (i.e., poor DDR impairing agent) and thus provide preliminary insights into the molecular mechanism that underlies its antiproliferative behavior.

NANOTECHNOLOGY - NEW TRENDS IN THE TREATMENT OF BRAIN TUMOURS.

High grade gliomas are some of the deadliest human tumours. Conventional treatments such as surgery, radiotherapy and chemotherapy have only a limited effect. Nowadays, resection is the common treatment of choice and although new approaches, such as perioperative magnetic resonance imaging or fluorescent microscopy have been developed, the survival rate of diagnosed patients is still very low. The inefficacy of conventional methods has led to the development of new strategies and the significant progress of nanotechnology in recent years. These platforms can be used either as novel imaging tools or to improve anticancer drug delivery into tumours while minimizing its distribution and toxicity in healthy tissues. Amongst the new nanotechnology platforms used for delivery into the brain tissue are: polymeric nanoparticles, liposomes, dendrimers, nanoshells, carbon nanotubes, superparamagnetic nanoparticles and nucleic acid based nanoparticles (DNA, RNA interference [RNAi] and antisense oligonucleotides [ASO]). These nanoparticles have been applied in the delivery of small molecular weight drugs as well as macromolecules - proteins, peptides and genes. The unique properties of these nanoparticles, such as surface charge, particle size, composition and ability to modify their surface with tissue recognition ligands and antibodies, improve their biodistribution and pharmacokinetics. All of the above mentioned characteristics make of nanoplatforms a very suitable tool for its use in targeted, personalized medicine, where they could possibly carry large doses of therapeutic agents specifically into malignant cells while avoiding healthy cells. This review poses new possibilities in the large field of nanotechnology with special interest in the treatment of high grade brain tumours.

The Molecular Crosstalk between the MET Receptor Tyrosine Kinase and the DNA Damage Response—Biological and Clinical Aspects

Radiation therapy remains an imperative treatment modality for numerous malignancies. Enduring significant technical achievements both on the levels of treatment planning and radiation delivery have led to improvements in local control of tumor growth and reduction in healthy tissue toxicity. Nevertheless, resistance mechanisms, which presumably also involve activation of DNA damage response signaling pathways that eventually may account for loco-regional relapse and consequent tumor progression, still remain a critical problem. Accumulating data suggest that signaling via growth factor receptor tyrosine kinases, which are aberrantly expressed in many tumors, may interfere with the cytotoxic impact of ionizing radiation via the direct activation of the DNA damage response, leading eventually to so-called tumor radioresistance. The aim of this review is to overview the current known data that support a molecular crosstalk between the hepatocyte growth factor receptor tyrosine kinase MET and the DNA damage response. Apart of extending well established concepts over MET biology beyond its function as a growth factor receptor, these observations directly relate to the role of its aberrant activity in resistance to DNA damaging agents, such as ionizing radiation, which are routinely used in cancer therapy and advocate tumor sensitization towards DNA damaging agents in combination with MET targeting.

Membrane Signaling Induced by High Doses of Ionizing Radiation in the Endothelial Compartment. Relevance in Radiation Toxicity

Tumor areas can now be very precisely delimited thanks to technical progress in imaging and ballistics. This has also led to the development of novel radiotherapy protocols, delivering higher doses of ionizing radiation directly to cancer cells. Despite this, radiation toxicity in healthy tissue remains a major issue, particularly with dose-escalation in these new protocols. Acute and late tissue damage following irradiation have both been linked to the endothelium irrigating normal tissues. The molecular mechanisms involved in the endothelial response to high doses of radiation are associated with signaling from the plasma membrane, mainly via the acid sphingomyelinase/ceramide pathway. This review describes this signaling pathway and discusses the relevance of targeting endothelial signaling to protect healthy tissues from the deleterious effects of high doses of radiation.

Anticancer drug delivery system based on calcium carbonate particles loaded with a photosensitizer

In photodynamic therapy (PDT), photosensitizers are required to arrive in high concentrations at selective targets like cancer cells avoiding toxicity in healthy tissue. In this work, we propose the application of porous calcium carbonate carriers in the form of polycrystalline vaterite for this task. We investigated the loading efficiency for the photosensitizer Photosens in vaterite micro- and nanocarriers. A possible release mechanism depending on the surrounding pH was studied, showing a fast degradation of the carriers in buffers below pH7. These results hold out the prospect of a novel PDT drug delivery system. Variation of particle size or additional coatings allow custom-design of workload release curves. An intrinsic cancer-sensitivity can be expected from the pH-dependent release in the acidic microenvironment of cancer tissue.