Radiation and anti-PD-L1 synergize by stimulating a stem-like T cell population in the tumor-draining lymph node

Radiotherapy (RT) and anti-PD-L1 synergize to enhance local and distant (abscopal) tumor control. However, clinical results in humans have been variable. With the goal of improving clinical outcomes, we investigated the underlying synergistic mechanism focusing on a CD8+ PD-1+ Tcf-1+ stem-like T cell subset in the tumor-draining lymph node (TdLN). Using murine melanoma models, we found that RT + anti-PD-L1 induces a novel differentiation program in the TdLN stem-like population which leads to their expansion and differentiation into effector cells within the tumor. Our data indicate that optimal synergy between RT + anti-PD-L1 is dependent on the TdLN stem-like T cell population as either blockade of TdLN egress or specific stem-like T cell depletion reduced tumor control. Together, these data demonstrate a multistep stimulation of stem-like T cells following combination therapy which is initiated in the TdLN and completed in the tumor.

Deformable lung 4DCT image registration via landmark-driven cycle network

BACKGROUND

An automated, accurate, and efficient lung four-dimensional computed tomography (4DCT) image registration method is clinically important to quantify respiratory motion for optimal motion management.

PURPOSE

The purpose of this work is to develop a weakly supervised deep learning method for 4DCT lung deformable image registration (DIR).

METHODS

The landmark-driven cycle network is proposed as a deep learning platform that performs DIR of individual phase datasets in a simulation 4DCT. This proposed network comprises a generator and a discriminator. The generator accepts moving and target CTs as input and outputs the deformation vector fields (DVFs) to match the two CTs. It is optimized during both forward and backward paths to enhance the bi-directionality of DVF generation. Further, the landmarks are used to weakly supervise the generator network. Landmark-driven loss is used to guide the generator's training. The discriminator then judges the realism of the deformed CT to provide extra DVF regularization.

RESULTS

We performed four-fold cross-validation on 10 4DCT datasets from the public DIR-Lab dataset and a hold-out test on our clinic dataset, which included 50 4DCT datasets. The DIR-Lab dataset was used to evaluate the performance of the proposed method against other methods in the literature by calculating the DIR-Lab Target Registration Error (TRE). The proposed method outperformed other deep learning-based methods on the DIR-Lab datasets in terms of TRE. Bi-directional and landmark-driven loss were shown to be effective for obtaining high registration accuracy. The mean and standard deviation of TRE for the DIR-Lab datasets was 1.20 ± 0.72 mm and the mean absolute error (MAE) and structural similarity index (SSIM) for our datasets were 32.1 ± 11.6 HU and 0.979 ± 0.011, respectively.

CONCLUSION

The landmark-driven cycle network has been validated and tested for automatic deformable image registration of patients' lung 4DCTs with results comparable to or better than competing methods.

Safety and efficacy of durvalumab after concurrent chemoradiation in Black patients with locally advanced non-small cell lung cancer

BACKGROUND

The PACIFIC trial established consolidative durvalumab after concurrent chemoradiation as standard-of-care in patients with stage III or unresectable non-small cell lung cancer (NSCLC). Black patients, however, comprised just 2% (n = 14) of randomized patients in this trial, warranting real-world evaluation of the PACIFIC regimen in these patients.

METHODS

This single-institution, multi-site study included 105 patients with unresectable stage II/III NSCLC treated with concurrent chemoradiation followed by durvalumab between 2017 and 2021. Overall survival (OS), progression-free survival (PFS), and grade ≥3 pneumonitis-free survival (PNFS) were compared between Black and non-Black patients using Kaplan-Meier and Cox regression analyses.

RESULTS

A total of 105 patients with a median follow-up of 22.8 months (interquartile range, 11.3-37.3 months) were identified for analysis, including 57 Black (54.3%) and 48 (45.7%) non-Black patients. The mean radiation prescription dose was higher among Black patients (61.5 ± 2.9 Gy vs. 60.5 ± 1.9 Gy; p = .031), but other treatment characteristics were balanced between groups. The median OS (not-reached vs. 39.7 months; p = .379) and PFS (31.6 months vs. 19.3 months; p = .332) were not statistically different between groups. Eight (14.0%) Black patients discontinued durvalumab due to toxicity compared to 13 (27.1%) non-Black patients (p = .096). The grade ≥3 pneumonitis rate was similar between Black and non-Black patients (12.3% vs. 12.5%; p = .973), and there was no significant difference in time to grade ≥3 PNFS (p = .904). Three (5.3%) Black patients and one (2.1%) non-Black patient developed grade 5 pneumonitis.

CONCLUSIONS

The efficacy and tolerability of consolidative durvalumab after chemoradiation appears to be comparable between Black and non-Black patients.

Treatment of Thymoma and Thymic Carcinoma with Proton Beam Therapy: Outcomes from the Proton Collaborative Group Prospective Registry

PURPOSE/OBJECTIVE(S)

Given the generally long natural history of thymic malignancies, proton beam therapy (PBT) is advocated to minimize the risk of long-term toxicities to mediastinal organs. Adverse events (AE) and long-term clinical outcomes for this population have not been well-characterized.

MATERIALS/METHODS

The Proton Collaborative Group registry (NCT01255748), a multi-institutional prospective database of academic and community proton centers in the US, was queried for patients with thymomas and thymic carcinomas treated with PBT. Patients with recurrent/metastatic disease, non-thymic histology, received either prior or palliative radiotherapy (dose < 40 Gy RBE) were excluded. Overall survival (OS) and local control (LC) were estimated using Kaplan-Meier methods.

RESULTS

A total of 97 patients were identified in the PCG registry. After applying relevant exclusion criteria, 70 patients from 12 proton centers treated from 2011-2021 were included for analysis. Median follow-up length was 16 months. Median age was 58.5 years (IQR 46-63), and 60% were female. 81.4% had a diagnosis of thymoma, and 18.6% thymic carcinoma. 59 patients underwent surgical resection. 11 were treated with definitive PBT, of which 5 received concurrent chemotherapy. Median dose was 54 Gy RBE (range 41.4 - 70 Gy RBE), median number of fractions was 30 (range 21 - 38). 73.4% received pencil beam scanning and 23% uniform scanning PBT. Treatment was overall well-tolerated: a single patient developed grade 4 pneumonitis. Grade 3 AEs were seen in 3 patients - dyspnea, anorexia, and heart failure. Highest grade toxicity experienced was grade 2 for 47.1% and grade 1 for 42.9% of patients. 3-year overall survival (OS) was 82.6% for the entire cohort. 3-year OS was 94% for resected/adjuvant cohort and 35.6% in the non-surgical/definitive cohort. 3-year local control (LC) was 91.7% for the entire cohort. By surgery/margin status, 3-year LC was 96.8% in patients with close or negative margins (a single failure in a patient with close margins), whereas 3-year LC was 55.1% for patients with positive margins/unresectable disease.

CONCLUSION

Thymic malignancies treated with PBT appear to have favorable outcomes, especially in the adjuvant setting, in this cohort representing the largest series of such patients.

Deep learning-based fast volumetric imaging using kV and MV projection images for lung cancer radiotherapy: A feasibility study

PURPOSE

The long acquisition time of CBCT discourages repeat verification imaging, therefore increasing treatment uncertainty. In this study, we present a fast volumetric imaging method for lung cancer radiation therapy using an orthogonal 2D kV/MV image pair.

METHODS

The proposed model is a combination of 2D and 3D networks. The proposed model consists of five major parts: (1) kV and MV feature extractors are used to extract deep features from the perpendicular kV and MV projections. (2) The feature-matching step is used to re-align the feature maps to their projection angle in a Cartesian coordinate system. By using a residual module, the feature map can focus more on the difference between the estimated and ground truth images. (3) In addition, the feature map is downsized to include more global semantic information for the 3D estimation, which is useful to reduce inhomogeneity. By using convolution-based reweighting, the model is able to further increase the uniformity of image. (4) To reduce the blurry noise of generated 3D volume, the Laplacian latent space loss calculated via the feature map that is extracted via specifically-learned Gaussian kernel is used to supervise the network. (5) Finally, the 3D volume is derived from the trained model. We conducted a proof-of-concept study using 50 patients with lung cancer. An orthogonal kV/MV pair was generated by ray tracing through CT of each phase in a 4D CT scan. Orthogonal kV/MV pairs from nine respiratory phases were used to train this patient-specific model while the kV/MV pair of the remaining phase was held for model testing.

RESULTS

The results are based on simulation data and phantom results from a real Linac system. The mean absolute error (MAE) values achieved by our method were 57.5 HU and 77.4 HU within body and tumor region-of-interest (ROI), respectively. The mean achieved peak-signal-to-noise ratios (PSNR) were 27.6 dB and 19.2 dB within the body and tumor ROI, respectively. The achieved mean normalized cross correlation (NCC) values were 0.97 and 0.94 within the body and tumor ROI, respectively. A phantom study demonstrated that the proposed method can accurately re-position the phantom after shift. It is also shown that the proposed method using both kV and MV is superior to current method using kV or MV only in image quality.

CONCLUSION

These results demonstrate the feasibility and accuracy of our proposed fast volumetric imaging method from an orthogonal kV/MV pair, which provides a potential solution for daily treatment setup and verification of patients receiving radiation therapy for lung cancer.

The mitochondrial pyruvate carrier complex potentiates the efficacy of proteasome inhibitors in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy that emerges from antibody-producing plasma B cells. Proteasome inhibitors, including the US Food and Drug Administration-approved bortezomib (BTZ) and carfilzomib (CFZ), are frequently used for the treatment of patients with MM. Nevertheless, a significant proportion of patients with MM are refractory or develop resistance to this class of inhibitors, which represents a significant challenge in the clinic. Thus, identifying factors that determine the potency of proteasome inhibitors in MM is of paramount importance to bolster their efficacy in the clinic. Using genome-wide CRISPR-based screening, we identified a subunit of the mitochondrial pyruvate carrier (MPC) complex, MPC1, as a common modulator of BTZ response in 2 distinct human MM cell lines in vitro. We noticed that CRISPR-mediated deletion or pharmacological inhibition of the MPC complex enhanced BTZ/CFZ-induced MM cell death with minimal impact on cell cycle progression. In fact, targeting the MPC complex compromised the bioenergetic capacity of MM cells, which is accompanied by reduced proteasomal activity, thereby exacerbating BTZ-induced cytotoxicity in vitro. Importantly, we observed that the RNA expression levels of several regulators of pyruvate metabolism were altered in advanced stages of MM for which they correlated with poor patient prognosis. Collectively, this study highlights the importance of the MPC complex for the survival of MM cells and their responses to proteasome inhibitors. These findings establish mitochondrial pyruvate metabolism as a potential target for the treatment of MM and an unappreciated strategy to increase the efficacy of proteasome inhibitors in the clinic.

Definitive intensity modulated proton re-irradiation for lung cancer in the immunotherapy era

Introduction

As immunotherapy has improved distant metastasis-free survival (DMFS) in Non-Small Cell Lung Cancer (NSCLC), isolated locoregional recurrences have increased. However, management of locoregional recurrences can be challenging. We report our institutional experience with definitive intent re-irradiation using Intensity Modulated Proton Therapy (IMPT).

Method

Retrospective cohort study of recurrent or second primary NSCLC or LS-SCLC treated with IMPT. Kaplan-Meier method and log-rank test were used for time-to-event analyses.

Results

22 patients were treated from 2019 to 2021. After first course of radiation (median 60 Gy, range 45-70 Gy), 45% received adjuvant immunotherapy. IMPT re-irradiation began a median of 28.2 months (8.8-172.9 months) after initial radiotherapy. The median IMPT dose was 60 GyE (44-60 GyE). 36% received concurrent chemotherapy with IMPT and 18% received immunotherapy after IMPT. The median patient's IMPT lung mean dose was 5.3 GyE (0.9-13.9 GyE) and 5 patients had cumulative esophagus max dose >100 GyE with 1-year overall survival (OS) 68%, 1-year local control 80%, 1-year progression free survival 45%, and 1-year DMFS 60%. Higher IMPT (HR 1.4; 95% CI 1.1-1.7, p=0.01) and initial radiotherapy mean lung doses (HR 1.3; 95% CI 1.0-1.6, p=0.04) were associated with worse OS. Two patients developed Grade 3 pneumonitis or dermatitis, one patient developed Grade 2 pneumonitis, and seven patients developed Grade 1 toxicity. There were no Grade 4 or 5 toxicities.

Discussion

Definitive IMPT re-irradiation for lung cancer can prolong disease control with limited toxicity, particularly in the immunotherapy era.

Automated lung tumor delineation on positron emission tomography/computed tomography via a hybrid regional network

BACKGROUND

Multimodality positron emission tomography/computed tomography (PET/CT) imaging combines the anatomical information of CT with the functional information of PET. In the diagnosis and treatment of many cancers, such as non-small cell lung cancer (NSCLC), PET/CT imaging allows more accurate delineation of tumor or involved lymph nodes for radiation planning.

PURPOSE

In this paper, we propose a hybrid regional network method of automatically segmenting lung tumors from PET/CT images.

METHODS

The hybrid regional network architecture synthesizes the functional and anatomical information from the two image modalities, whereas the mask regional convolutional neural network (R-CNN) and scoring fine-tune the regional location and quality of the output segmentation. This model consists of five major subnetworks, that is, a dual feature representation network (DFRN), a regional proposal network (RPN), a specific tumor-wise R-CNN, a mask-Net, and a score head. Given a PET/CT image as inputs, the DFRN extracts feature maps from the PET and CT images. Then, the RPN and R-CNN work together to localize lung tumors and reduce the image size and feature map size by removing irrelevant regions. The mask-Net is used to segment tumor within a volume-of-interest (VOI) with a score head evaluating the segmentation performed by the mask-Net. Finally, the segmented tumor within the VOI was mapped back to the volumetric coordinate system based on the location information derived via the RPN and R-CNN. We trained, validated, and tested the proposed neural network using 100 PET/CT images of patients with NSCLC. A fivefold cross-validation study was performed. The segmentation was evaluated with two indicators: (1) multiple metrics, including the Dice similarity coefficient, Jacard, 95th percentile Hausdorff distance, mean surface distance (MSD), residual mean square distance, and center-of-mass distance; (2) Bland-Altman analysis and volumetric Pearson correlation analysis.

RESULTS

In fivefold cross-validation, this method achieved Dice and MSD of 0.84 ± 0.15 and 1.38 ± 2.2 mm, respectively. A new PET/CT can be segmented in 1 s by this model. External validation on The Cancer Imaging Archive dataset (63 PET/CT images) indicates that the proposed model has superior performance compared to other methods.

CONCLUSION

The proposed method shows great promise to automatically delineate NSCLC tumors on PET/CT images, thereby allowing for a more streamlined clinical workflow that is faster and reduces physician effort.

Compact portable sources of high-LET radiation: Validation and potential application for galactic cosmic radiation countermeasure discovery

Implementation of a systematic program for galactic cosmic radiation (GCR) countermeasure discovery will require convenient access to ground-based space radiation analogs. The current gold standard approach for GCR simulation is to use a particle accelerator for sequential irradiation with ion beams representing different GCR components. This has limitations, particularly for studies of non-acute responses, strategies that require robotic instrumentation, or implementation of complex in vitro models that are emerging as alternatives to animal experimentation. Here we explore theoretical and practical issues relating to a different approach to provide a high-LET radiation field for space radiation countermeasure discovery, based on use of compact portable sources to generate neutron-induced charged particles. We present modeling studies showing that DD and DT neutron generators, as well as an AmBe radionuclide-based source, generate charged particles with a linear energy transfer (LET) distribution that, within a range of biological interest extending from about 10 to 200 keV/μm, resembles the LET distribution of reference GCR radiation fields experienced in a spacecraft or on the lunar surface. We also demonstrate the feasibility of using DD neutrons to induce 53BP1 DNA double-strand break repair foci in the HBEC3-KT line of human bronchial epithelial cells, which are widely used for studies of lung carcinogenesis. The neutron-induced foci are larger and more persistent than X ray-induced foci, consistent with the induction of complex, difficult-to-repair DNA damage characteristic of exposure to high-LET (>10 keV/μm) radiation. We discuss limitations of the neutron approach, including low fluence in the low LET range (<10 keV/μm) and the absence of certain long-range features of high charge and energy particle tracks. We present a concept for integration of a compact portable source with a multiplex microfluidic in vitro culture system, and we discuss a pathway for further validation of the use of compact portable sources for countermeasure discovery.

Impact of Radiation Dose to the Immune Cells in Unresectable or Stage III Non-Small Cell Lung Cancer in the Durvalumab Era

BACKGROUND /PURPOSE

Higher estimated radiation doses to immune cells (EDIC) have correlated with worse overall survival (OS) in patients with locally-advanced non-small cell lung cancer (NSCLC) prior to the PACIFIC trial, which established consolidative durvalumab as standard-of-care. Here, we examine the prognostic impact of EDIC in the durvalumab era.

MATERIALS/METHODS

This single-institution, multi-center study included patients with unresectable stage II/III NSCLC treated with chemoradiation followed by durvalumab. Associations between EDIC [analyzed continuously and categorically (≤6 Gy vs. >6 Gy)] and OS, progression-free survival (PFS), and locoregional control (LRC) were evaluated by Kaplan-Meier and Cox proportional methods.

RESULTS

100 patients were included with median follow-up of 23.7 months. The EDIC >6 Gy group had a significantly greater percentage of stage IIIB/IIIC disease (76.0% vs. 32.6%; p<0.001) and larger tumor volumes (170cc vs. 42cc; p<0.001). There were no differences in early durvalumab discontinuation from toxicity (24.1% vs. 15.2%; p=0.27). Median OS was shorter among the EDIC >6 Gy group (29.6 months vs. not reached; p<0.001). On multivariate analysis, EDIC >6 Gy correlated with worse OS (HR: 4.15, 95%CI: 1.52-11.33; p=0.006), PFS (HR: 3.79; 95%CI: 1.80-8.0; p<0.001), and LRC (HR: 2.66, 95%CI: 1.15-6.18; p=0.023). Analyzed as a continuous variable, higher EDIC was associated with worse OS (HR: 1.34; 95%CI: 1.16-1.57; p<0.001), PFS (HR: 1.52; 95%CI: 1.29-1.79; p<0.001), and LRC (HR: 1.34, 95%CI: 1.13-1.60; p=0.007).

CONCLUSIONS

In the immunotherapy era, EDIC is an independent predictor of OS and disease control in locally advanced NSCLC, warranting investigation into techniques to reduce dose to the immune compartment.

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

Race, Ethnicity, and Sex Among Senior Faculty in Radiation Oncology From 2000 to 2019

This cross-sectional study investigates intersections among race, ethnicity, and sex from 2000 to 2019 among senior faculty in radiation oncology.

Simple Esterification of [1-13C]-Alpha-Ketoglutarate Enhances Membrane Permeability and Allows for Noninvasive Tracing of Glutamate and Glutamine Production

Alpha-ketoglutarate (α-KG) is a key metabolite and signaling molecule in cancer cells, but the low permeability of α-KG limits the study of α-KG mediated effects in vivo. Recently, cell-permeable monoester and diester α-KG derivatives have been synthesized for use in vivo, but many of these derivatives are not compatible for use in hyperpolarized carbon-13 nuclear magnetic resonance spectroscopy (HP-¹³C-MRS). HP-¹³C-MRS is a powerful technique that has been used to noninvasively trace labeled metabolites in real time. Here, we show that using diethyl-[1-¹³C]-α-KG as a probe in HP-¹³C-MRS allows for noninvasive tracing of α-KG metabolism in vivo.

Lung tumor segmentation in 4D CT images using motion convolutional neural networks

PURPOSE

Manual delineation on all breathing phases of lung cancer 4D CT image datasets can be challenging, exhaustive, and prone to subjective errors because of both the large number of images in the datasets and variations in the spatial location of tumors secondary to respiratory motion. The purpose of this work is to present a new deep learning-based framework for fast and accurate segmentation of lung tumors on 4D CT image sets.

METHODS

The proposed DL framework leverages motion region convolutional neural network (R-CNN). Through integration of global and local motion estimation network architectures, the network can learn both major and minor changes caused by tumor motion. Our network design first extracts tumor motion information by feeding 4D CT images with consecutive phases into an integrated backbone network architecture, locating volume-of-interest (VOIs) via a regional proposal network and removing irrelevant information via a regional convolutional neural network. Extracted motion information is then advanced into the subsequent global and local motion head network architecture to predict corresponding deformation vector fields (DVFs) and further adjust tumor VOIs. Binary masks of tumors are then segmented within adjusted VOIs via a mask head. A self-attention strategy is incorporated in the mask head network to remove any noisy features that might impact segmentation performance. We performed two sets of experiments. In the first experiment, a five-fold cross-validation on 20 4D CT datasets, each consisting of 10 breathing phases (i.e., 200 3D image volumes in total). The network performance was also evaluated on an additional unseen 200 3D images volumes from 20 hold-out 4D CT datasets. In the second experiment, we trained another model with 40 patients' 4D CT datasets from experiment 1 and evaluated on additional unseen nine patients' 4D CT datasets. The Dice similarity coefficient (DSC), center of mass distance (CMD), 95th percentile Hausdorff distance (HD95 ), mean surface distance (MSD), and volume difference (VD) between the manual and segmented tumor contour were computed to evaluate tumor detection and segmentation accuracy. The performance of our method was quantitatively evaluated against four different methods (VoxelMorph, U-Net, network without global and local networks, and network without attention gate strategy) across all evaluation metrics through a paired t-test.

RESULTS

The proposed fully automated DL method yielded good overall agreement with the ground truth for contoured tumor volume and segmentation accuracy. Our model yielded significantly better values of evaluation metrics (p < 0.05) than all four competing methods in both experiments. On hold-out datasets of experiment 1 and 2, our method yielded DSC of 0.86 and 0.90 compared to 0.82 and 0.87, 0.75 and 0.83, 081 and 0.89, and 0.81 and 0.89 yielded by VoxelMorph, U-Net, network without global and local networks, and networks without attention gate strategy. Tumor VD between ground truth and our method was the smallest with the value of 0.50 compared to 0.99, 1.01, 0.92, and 0.93 for between ground truth and VoxelMorph, U-Net, network without global and local networks, and networks without attention gate strategy, respectively.

CONCLUSIONS

Our proposed DL framework of tumor segmentation on lung cancer 4D CT datasets demonstrates a significant promise for fully automated delineation. The promising results of this work provide impetus for its integration into the 4D CT treatment planning workflow to improve the accuracy and efficiency of lung radiotherapy.

Synthesis of [1-13 C-5-12 C]-alpha-ketoglutarate enables noninvasive detection of 2-hydroxyglutarate

Isocitrate dehydrogenase 1 (IDH1) mutations that generate the oncometabolite 2-hydroxyglutarate (2-HG) from α-ketoglutarate (α-KG) have been identified in many types of tumors and are an important prognostic factor in gliomas. 2-HG production can be determined by hyperpolarized carbon-13 magnetic resonance spectroscopy (HP-¹³ C-MRS) using [1-¹³ C]-α-KG as a probe, but peak contamination from naturally occurring [5-¹³ C]-α-KG overlaps with the [1-¹³ C]-2-HG peak. Via a newly developed oxidative-Stetter reaction, [1-¹³ C-5-¹² C]-α-KG was synthesized. α-KG metabolism was measured via HP-¹³ C-MRS using [1-¹³ C-5-¹² C]-α-KG as a probe. [1-¹³ C-5-¹² C]-α-KG was synthesized in high yields, and successfully eliminated the signal from C5 of α-KG in the HP-¹³ C-MRS spectra. In HCT116 IDH1 R132H cells, [1-¹³ C-5-¹² C]-α-KG allowed for unimpeded detection of [1-¹³ C]-2-HG. ¹² C-enrichment represents a novel method to circumvent spectral overlap, and [1-¹³ C-5-¹² C]-α-KG shows promise as a probe to study IDH1 mutant tumors and α-KG metabolism.

Deep learning-based thoracic CBCT correction with histogram matching

Kilovoltage cone-beam computed tomography (CBCT)-based image-guided radiation therapy (IGRT) is used for daily delivery of radiation therapy, especially for stereotactic body radiation therapy (SBRT), which imposes particularly high demands for setup accuracy. The clinical applications of CBCTs are constrained, however, by poor soft tissue contrast, image artifacts, and instability of Hounsfield unit (HU) values. Here, we propose a new deep learning-based method to generate synthetic CTs (sCT) from thoracic CBCTs. A deep-learning model which integrates histogram matching (HM) into a cycle-consistent adversarial network (Cycle-GAN) framework, called HM-Cycle-GAN, was trained to learn mapping between thoracic CBCTs and paired planning CTs. Perceptual supervision was adopted to minimize blurring of tissue interfaces. An informative maximizing loss was calculated by feeding CBCT into the HM-Cycle-GAN to evaluate the image histogram matching between the planning CTs and the sCTs. The proposed algorithm was evaluated using data from 20 SBRT patients who each received 5 fractions and therefore 5 thoracic CBCTs. To reduce the effect of anatomy mismatch, original CBCT images were pre-processed via deformable image registrations with the planning CT before being used in model training and result assessment. We used planning CTs as ground truth for the derived sCTs from the correspondent co-registered CBCTs. The mean absolute error (MAE), peak signal-to-noise ratio (PSNR), and normalized cross-correlation (NCC) indices were adapted as evaluation metrics of the proposed algorithm. Assessments were done using Cycle-GAN as the benchmark. The average MAE, PSNR, and NCC of the sCTs generated by our method were 66.2 HU, 30.3 dB, and 0.95, respectively, over all CBCT fractions. Superior image quality and reduced noise and artifact severity were seen using the proposed method compared to the results from the standard Cycle-GAN method. Our method could therefore improve the accuracy of IGRT and corrected CBCTs could help improve online adaptive RT by offering better contouring accuracy and dose calculation.

Pathways for Recruiting and Retaining Women and Underrepresented Minority Clinicians and Physician Scientists Into the Radiation Oncology Workforce: A Summary of the 2019 ASTRO/NCI Diversity Symposium Session at the ASTRO Annual Meeting

Diversifying the radiation oncology workforce is an urgent and unmet need. During the American Society of Radiation Oncology (ASTRO) 2019 Annual Meeting, ASTRO's Committee on Health Equity, Diversity, and Inclusion (CHEDI) and the National Cancer Institute (NCI) collaborated on the ASTRO-NCI Diversity Symposium, entitled "Pathways for Recruiting and Retaining Women and Underrepresented Minority Clinicians and Physician Scientists Into the Radiation Oncology Workforce." Herein, we summarize the presented data and personal anecdotes with the goal of raising awareness of ongoing and future initiatives to improve recruitment and retention of underrepesented groups to radiation oncology. Common themes include the pivotal role of mentorship and standardized institutional practices – such as protected time and pay parity – as critical to achieving a more diverse and inclusive workplace.

High-fidelity detection and sorting of nanoscale vesicles in viral disease and cancer

Biological nanoparticles, including viruses and extracellular vesicles (EVs), are of interest to many fields of medicine as biomarkers and mediators of or treatments for disease. However, exosomes and small viruses fall below the detection limits of conventional flow cytometers due to the overlap of particle-associated scattered light signals with the detection of background instrument noise from diffusely scattered light. To identify, sort, and study distinct subsets of EVs and other nanoparticles, as individual particles, we developed nanoscale Fluorescence Analysis and Cytometric Sorting (nanoFACS) methods to maximise information and material that can be obtained with high speed, high resolution flow cytometers. This nanoFACS method requires analysis of the instrument background noise (herein defined as the “reference noise”). With these methods, we demonstrate detection of tumour cell-derived EVs with specific tumour antigens using both fluorescence and scattered light parameters. We further validated the performance of nanoFACS by sorting two distinct HIV strains to >95% purity and confirmed the viability (infectivity) and molecular specificity (specific cell tropism) of biological nanomaterials sorted with nanoFACS. This nanoFACS method provides a unique way to analyse and sort functional EV- and viral-subsets with preservation of vesicular structure, surface protein specificity and RNA cargo activity.

Three-dimensional alginate hydrogels for radiobiological and metabolic studies of cancer cells

The purpose of this study is to demonstrate calcium alginate hydrogels as a system for in vitro radiobiological and metabolic studies of cancer cells. Previous studies have established calcium alginate as a versatile three-dimensional (3D) culturing system capable of generating areas of oxygen heterogeneity and modeling metabolic changes in vitro. Here, through dosimetry, clonogenic and viability assays, and pimonidazole staining, we demonstrate that alginate can model radiobiological responses that monolayer cultures do not simulate. Notably, alginate hydrogels with radii greater than 500 μm demonstrate hypoxic cores, while smaller hydrogels do not. The size of this hypoxic region correlates with hydrogel size and improved cell survival following radiation therapy. Hydrogels can also be utilized in hyperpolarized magnetic resonance spectroscopy and extracellular flux analysis. Alginate therefore offers a reproducible, consistent, and low-cost means for 3D culture of cancer cells for radiobiological studies that simulates important in vivo parameters such as regional hypoxia and enables long-term culturing and in vitro metabolic studies.

The Future of Radiobiology

Innovation and progress in radiation oncology depend on discovery and insights realized through research in radiation biology. Radiobiology research has led to fundamental scientific insights, from the discovery of stem/progenitor cells to the definition of signal transduction pathways activated by ionizing radiation that are now recognized as integral to the DNA damage response (DDR). Radiobiological discoveries are guiding clinical trials that test radiation therapy combined with inhibitors of the DDR kinases DNA-dependent protein kinase (DNA-PK), ataxia telangiectasia mutated (ATM), ataxia telangiectasia related (ATR), and immune or cell cycle checkpoint inhibitors. To maintain scientific and clinical relevance, the field of radiation biology must overcome challenges in research workforce, training, and funding. The National Cancer Institute convened a workshop to discuss the role of radiobiology research and radiation biologists in the future scientific enterprise. Here, we review the discussions of current radiation oncology research approaches and areas of scientific focus considered important for rapid progress in radiation sciences and the continued contribution of radiobiology to radiation oncology and the broader biomedical research community.

Abstract B097: Dysregulated mevalonate and cholesterol synthesis is a therapeutic vulnerability in glioblastoma

A hallmark of cellular transformation is the evasion of contact-dependent inhibition of growth. To find new therapeutic targets for glioblastoma, we looked for pathways that are inhibited by high cell density in normal astrocytes but have lost this regulation in glioblastoma stem-like cells. Here we report that at high cell density, normal astrocytes turn off mevalonate and cholesterol synthesis but glioma cells keep these pathways active. Correspondingly, mevalonate and cholesterol pathway upregulation is associated with poor prognosis in glioblastoma patients. Densely plated glioma cells increase oxygen consumption to synthesize cholesterol, resulting in a decrease in reactive oxygen species, TCA cycle intermediates, and ATP, but without a compensating increase in aerobic glycolysis. This constitutive cholesterol synthesis is controlled by the cell cycle, as it can be turned off by cyclin-dependent kinase inhibitors and it correlates with disabled cell cycle control though loss of p53 and RB. Mevalonate and cholesterol pathway activation promoted aberrant growth through the LXR and Hippo pathways. Finally, glioma cells, but not astrocytes, are sensitive to cholesterol synthesis inhibition downstream of the mevalonate pathway, suggesting that specifically targeting cholesterol synthesis might be an effective treatment for glioblastoma.

Citation Format: Diane M. Kambach, Alan S. Halim, A. Gesine Cauer, Qian Sun, Carlos A. Tristan, Aparna H. Kesarwala, Uma Shankavaram, Eric Batchelor, Jayne M. Stommel. Dysregulated mevalonate and cholesterol synthesis is a therapeutic vulnerability in glioblastoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B097.

The Role of Advanced Imaging in Assessing Response to Definitive Chemoradiation Before Prophylactic Cranial Irradiation in Limited-Stage Small-Cell Lung Cancer

INTRODUCTION

Prophylactic cranial irradiation (PCI) improves survival for small-cell lung cancer (SCLC). Evidence for PCI in limited-stage SCLC largely derives from studies requiring only chest x-ray (CXR) to determine remission status. We analyzed thoracic chemoradiation therapy (TCRT) outcomes according to imaging modality to determine which patients benefitted most from PCI.

PATIENTS AND METHODS

All limited-stage SCLC patients who received TCRT as well as PCI at our institution were reviewed. Imaging between TCRT end and PCI start was characterized as complete (CR), partial (PR), or other response.

RESULTS

Thirty-eight consecutive patients were assessed for TCRT response before PCI with CXR (n = 21), chest computed tomography (CT; n = 27), and/or positron emission tomography (PET)/CT (n = 11). CR was identified on 71% of CXRs, 41% of CT scans, and 18% of PET/CT scans. Median survival was 28.3 months for the entire cohort and did not differ for patients who had CXR alone versus CT and/or PET/CT for restaging (P = .78) or those with PR using any modality versus CR using all modalities (22.6 months vs. 45.5 months; P = .22). CT CR patients had numerical but not statistically significant improved 2-year (P = .18) and 3-year (P = .13) survival compared with CT PR.

CONCLUSION

CXR remains an appropriate modality to assess TCRT response before PCI in limited-stage SCLC. Advanced imaging did not inform the decision to offer PCI in this study. Because of similar excellent survival profiles independent of imaging modality and TCRT response, this analysis suggests limited-stage SCLC patients with PR using any modality should not be denied PCI, akin to standards for extensive-stage SCLC.

Abstract 833: Alginate hydrogels for three-dimensional culture and real-time monitoring of cancer cell metabolism and radiation response

The purpose of this study was to characterize a three-dimensional calcium alginate culture system for real-time monitoring of cancer cell metabolism and radiation response. HCT116 colorectal cancer cells were encapsulated in 2.5% calcium alginate using a custom electrostatic rig adapted from a previously published system. Bead diameter was a function of voltage and alginate concentration: 4 x 107 cells/mL encapsulated at 4 and 8 kV resulted in mean diameters of 880 and 584 µm, respectively. The distribution of bead radii for all voltages showed positive excess kurtosis (4 kV = 1.6, 8 kV = 3.0) and 72.9% of 4 kV and 77.2% of 8 kV bead diameters fell within one standard deviation of the mean. Encapsulated cell viability was assessed by staining with Trypan Blue and clonogenic survival assays (CSAs). The baseline viability of cells immediately after encapsulation was 93.2%, which decreased 2 days after a single 10 Gy dose (90.7%, p&lt;0.05). After two weeks of continuous culturing, 84.1% of non-irradiated and 73.8% of irradiated encapsulated cells remained viable (p&lt;0.003). Pimonidazole staining demonstrated the presence of hypoxic cores proportional to bead size. CSAs of 8 kV beads showed a dose modifying factor (DMF) of 1.06 relative to cells grown in a monolayer, while larger 4 kV beads showed a DMF of 1.58. Mean oxygen consumption rate rose with increasing number of 8 kV beads/well: 1 bead, 35.5; 2 beads, 97.4; 3 beads, 175.5; 4 beads, 209.9; 2.0 x 104 monolayer cells, 92.6 (all pmol/min, ~8.2 x103 cells/bead, p&lt;0.005). Hyperpolarized 13C-NMR spectroscopy of 400 uL of 8 kV beads containing 1.2 x 108 cells/mL showed a detectable conversion of [1-13C]-pyruvate to [1-13C]-lactate; 1 hour after a single 10 Gy dose, the lactate:pyruvate ratio decreased by 25%. Unpaired 2-tailed Student’s t-tests were used to determine significance between and one-way ANOVA was used to determine significance among groups with α set at p≤0.05. These data demonstrate the versatility of alginate hydrogels for real-time metabolic and radiation response studies which are non-invasive, higher throughput, and lower cost compared to in vivo systems. Future directions include additional metabolic flux analysis and hyperpolarized 13C-NMR spectroscopy to further investigate the cancer cell metabolic response to drug and/or radiation therapy.

Citation Format: Aparna H. Kesarwala, Jenna L. Carter, Graham H. Read, Natsuko Miura, Kazutoshi Yamamoto, James B. Mitchell, Murali C. Krishna. Alginate hydrogels for three-dimensional culture and real-time monitoring of cancer cell metabolism and radiation response [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 833. doi:10.1158/1538-7445.AM2017-833

Abstract 3116: Dysregulated cholesterol synthesis is a therapeutic vulnerability in glioblastoma

A hallmark of cellular transformation is the evasion of contact-dependent inhibition of growth. To find new therapeutic targets for glioblastoma, we looked for pathways that are inhibited by high cell density in normal astrocytes but have lost this regulation in glioma cells. Here we report that at high cell density, normal astrocytes turn off cholesterol synthesis but glioma cells keep this pathway on. Correspondingly, cholesterol pathway upregulation is associated with poor prognosis in glioblastoma patients. Densely-plated glioma cells increase oxygen consumption to synthesize cholesterol, resulting in a decrease in reactive oxygen species, TCA cycle intermediates, and ATP, but without a compensating increase in aerobic glycolysis. This constitutive cholesterol synthesis is controlled by the cell cycle, as it can be turned off by cyclin dependent kinase inhibitors and it correlates with disabled cell cycle control though loss of p53 and RB. Finally, glioma cells, but not astrocytes, are sensitive to cholesterol synthesis inhibition downstream of the mevalonate pathway, suggesting that specifically targeting cholesterol synthesis might be an effective treatment for glioblastoma.

Citation Format: Diane M. Kambach, Alan S. Halim, A. Gesine Cauer, Qian Sun, Carlos A. Tristan, Orieta Celiku, Aparna H. Kesarwala, Uma Shankavaram, Eric Batchelor, Jayne M. Stommel. Dysregulated cholesterol synthesis is a therapeutic vulnerability in glioblastoma [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 3116. doi:10.1158/1538-7445.AM2017-3116

Disabled cell density sensing leads to dysregulated cholesterol synthesis in glioblastoma

A hallmark of cellular transformation is the evasion of contact-dependent inhibition of growth. To find new therapeutic targets for glioblastoma, we looked for pathways that are inhibited by high cell density in astrocytes but not in glioma cells. Here we report that glioma cells have disabled the normal controls on cholesterol synthesis. At high cell density, astrocytes turn off cholesterol synthesis genes and have low cholesterol levels, but glioma cells keep this pathway on and maintain high cholesterol. Correspondingly, cholesterol pathway upregulation is associated with poor prognosis in glioblastoma patients. Densely-plated glioma cells increase oxygen consumption, aerobic glycolysis, and the pentose phosphate pathway to synthesize cholesterol, resulting in a decrease in reactive oxygen species, TCA cycle intermediates, and ATP. This constitutive cholesterol synthesis is controlled by the cell cycle, as it can be turned off by cyclin-dependent kinase inhibitors and it correlates with disabled cell cycle control though loss of p53 and RB. Finally, glioma cells, but not astrocytes, are sensitive to cholesterol synthesis inhibition downstream of the mevalonate pathway, suggesting that specifically targeting cholesterol synthesis might be an effective treatment for glioblastoma.

NAFLD causes selective CD4(+) T lymphocyte loss and promotes hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the second most common cause of cancer related death. Non-alcoholic fatty liver disease (NAFLD) affects a large proportion of the US population and is considered a metabolic predisposition to liver cancer ^1-5. However, the role of adaptive immune responses in NAFLD-promoted HCC is largely unknown. Here, we show that dysregulation of lipid metabolism in NAFLD causes a selective loss of intrahepatic CD4⁺ but not CD8⁺ T lymphocytes leading to accelerated hepatocarcinogenesis. We also found that CD4⁺ T lymphocytes have greater mitochondrial mass than CD8⁺ T lymphocytes and generate higher levels of mitochondrially-derived reactive oxygen species (ROS). Disruption of mitochondrial function by linoleic acid, a fatty acid accumulated in NAFLD, causes more oxidative damage than other free fatty acids such as palmitic acid, and mediates selective loss of intrahepatic CD4⁺ T lymphocytes. In vivo blockade of ROS reversed NAFLD-induced hepatic CD4⁺ T lymphocyte decrease and delayed NAFLD-promoted HCC. Our results provide an unexpected link between lipid dysregulation and impaired anti-tumor surveillance.

Biological signaling by small inorganic molecules

Small redox active molecules such as reactive nitrogen and oxygen species and hydrogen sulfide have emerged as important biological mediators that are involved in various physiological and pathophysiological processes. Advancement in understanding of cellular mechanisms that tightly regulate both generation and reactivity of these molecules is central to improved management of various disease states including cancer and cardiovascular dysfunction. Imbalance in the production of redox active molecules can lead to damage of critical cellular components such as cell membranes, proteins and DNA and thus may trigger the onset of disease. These small inorganic molecules react independently as well as in a concerted manner to mediate physiological responses. This review provides a general overview of the redox biology of these key molecules, their diverse chemistry relevant to physiological processes and their interrelated nature in cellular signaling.

Signaling and stress: The redox landscape in NOS2 biology

Nitric oxide (NO) has a highly diverse range of biological functions from physiological signaling and maintenance of homeostasis to serving as an effector molecule in the immune system. However, deleterious as well as beneficial roles of NO have been reported. Many of the dichotomous effects of NO and derivative reactive nitrogen species (RNS) can be explained by invoking precise interactions with different targets as a result of concentration and temporal constraints. Endogenous concentrations of NO span five orders of magnitude, with levels near the high picomolar range typically occurring in short bursts as compared to sustained production of low micromolar levels of NO during immune response. This article provides an overview of the redox landscape as it relates to increasing NO concentrations, which incrementally govern physiological signaling, nitrosative signaling and nitrosative stress-related signaling. Physiological signaling by NO primarily occurs upon interaction with the heme protein soluble guanylyl cyclase. As NO concentrations rise, interactions with nonheme iron complexes as well as indirect modification of thiols can stimulate additional signaling processes. At the highest levels of NO, production of a broader range of RNS, which subsequently interact with more diverse targets, can lead to chemical stress. However, even under such conditions, there is evidence that stress-related signaling mechanisms are triggered to protect cells or even resolve the stress. This review therefore also addresses the fundamental reactions and kinetics that initiate signaling through NO-dependent pathways, including processes that lead to interconversion of RNS and interactions with molecular targets.

Abstract 4140: Role of nitric oxide in invasiveness of tumor cells irradiated with carbon-ion beams

We previously reported that carbon-ion (C-ion) irradiation suppresses the invasiveness of several pancreatic cancer cell lines such as MIAPaCa-2, BxPC-3, and AsPC-1; however, we also observed that C-ion irradiation enhanced PANC-1 invasion. Most invading PANC-1 cells were nitric oxide (NO)-producing cells; the NOS-NO-PI3K-AKT pathway was activated in these cells. In addition, the actin-binding AKT substrate, Girdin, which modulates the actin organization and has important role in AKT-dependent cell motility, was activated and co-localized with p-AKT at the lamellipodia. C-ion irradiation increased the NO-producing cell population, thereby enhancing C-ion irradiation-enhanced PANC-1 invasion. In contrast to PANC-1 cells, NO levels as well as the number of NO-producing cells were decreased in C-ion irradiated MIAPaCa-2, indicated that the NO reduction might cause the suppression of MIAPaCa-2 invasion. The aim of this study is to clarify the role of NO in altered invasiveness of C-ion irradiated tumor cells. Treatment of PANC-1 with NO donor, DETA/NO, enhanced PANC-1 invasion. Interestingly, DETA/NO also increased MIAPaCa-2 invasion, indicated that NO contributes to the enhancement of MIAPaCa-2 invasiveness. The reduced invasiveness of C-ion irradiated MIAPaCa-2 was slightly but significantly recovered by the treatment with DETA/NO, but the recovered levels were still much less than the invasiveness of non-irradiated MIAPaCa-2. Thus, the reduction of NO levels involves in the decreased invasiveness of C-ion irradiated MIAPaCa-2, but there are additional factor regulating the invasiveness of cells irradiated with C-ion beams. Indeed, C-ion irradiation reduced GTP-Rac1 and GTP-RhoA expression, the active form of Rac1 and RhoA, which are known as two master regulators of cell motility. The reduction of GTP-Rac1 or GTP-RhoA was recovered by the treatment of proteasome inhibitor, indicated that those proteins were undergo degradation via the ubiquitin-proteasome pathway. So far, IAPs, Inhibitors of Apoptosis Proteins, and HACE1, HECT-domain containing E3 ubiquitin-ligase, were reported as direct E3 ubiquitin ligase of Rac1. Of those, XIAP was selectively induced and was co-precipitated with GTP-Rac1 in C-ion irradiated MIAPaCa-2. In conclusion, NO has a significant role in enhancing invasive potential of both PANC-1 and MIAPaCa-2 cells. The alteration of NO levels upon C-ion irradiation modulates the invasiveness of irradiated cells. Also, reductions of GTP-Rac1 and GTP-RhoA have the additional effects on the C-ion reduced MIAPaCa-2 invasion. Several studies have reported that NO modulates ubiquitin-proteasomal degradation of proteins. The effect of NO on the GTP-Rac1 and GTP-RhoA degradation remain unknown, and further researches are needed to clarify whether the NO reduction affects to the GTP-Rac1 or GTP-RhoA degradation observed in C-ion irradiated MIAPaCa-2.

Citation Format: Mayumi Fujita, Kaori Imadome, Yoshimi Shoji, Robert Cheng, Aparna H. Kesarwala, David A. Wink, Takashi Imai. Role of nitric oxide in invasiveness of tumor cells irradiated with carbon-ion beams. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4140. doi:10.1158/1538-7445.AM2015-4140

NOS Inhibition Modulates Immune Polarization and Improves Radiation-Induced Tumor Growth Delay

Nitric oxide synthases (NOS) are important mediators of progrowth signaling in tumor cells, as they regulate angiogenesis, immune response, and immune-mediated wound healing. Ionizing radiation (IR) is also an immune modulator and inducer of wound response. We hypothesized that radiation therapeutic efficacy could be improved by targeting NOS following tumor irradiation. Herein, we show enhanced radiation-induced (10 Gy) tumor growth delay in a syngeneic model (C3H) but not immunosuppressed (Nu/Nu) squamous cell carcinoma tumor-bearing mice treated post-IR with the constitutive NOS inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME). These results suggest a requirement of T cells for improved radiation tumor response. In support of this observation, tumor irradiation induced a rapid increase in the immunosuppressive Th2 cytokine IL10, which was abated by post-IR administration of L-NAME. In vivo suppression of IL10 using an antisense IL10 morpholino also extended the tumor growth delay induced by radiation in a manner similar to L-NAME. Further examination of this mechanism in cultured Jurkat T cells revealed L-NAME suppression of IR-induced IL10 expression, which reaccumulated in the presence of exogenous NO donor. In addition to L-NAME, the guanylyl cyclase inhibitors ODQ and thrombospondin-1 also abated IR-induced IL10 expression in Jurkat T cells and ANA-1 macrophages, which further suggests that the immunosuppressive effects involve eNOS. Moreover, cytotoxic Th1 cytokines, including IL2, IL12p40, and IFNγ, as well as activated CD8(+) T cells were elevated in tumors receiving post-IR L-NAME. Together, these results suggest that post-IR NOS inhibition improves radiation tumor response via Th1 immune polarization within the tumor microenvironment.

Intensity-modulated proton therapy for elective nodal irradiation and involved-field radiation in the definitive treatment of locally advanced non-small-cell lung cancer: a dosimetric study

BACKGROUND

Photon involved-field (IF) radiation therapy (IFRT), the standard for locally advanced (LA) non-small cell lung cancer (NSCLC), results in favorable outcomes without increased isolated nodal failures, perhaps from scattered dose to elective nodal stations. Because of the high conformality of intensity-modulated proton therapy (IMPT), proton IFRT could increase nodal failures. We investigated the feasibility of IMPT for elective nodal irradiation (ENI) in LA-NSCLC.

PATIENTS AND METHODS

IMPT IFRT plans were generated to the same total dose of 66.6-72 Gy received by 20 LA-NSCLC patients treated with photon IFRT. IMPT ENI plans were generated to 46 cobalt Gray equivalent (CGE) to elective nodal planning treatment volumes (PTV) plus 24 CGE to IF-PTVs.

RESULTS

Proton IFRT and ENI improved the IF-PTV percentage of volume receiving 95% of the prescribed dose (D95) by 4% (P < .01) compared with photon IFRT. All evaluated dosimetric parameters improved significantly with both proton plans. The lung percentage of volume receiving 20 Gy/CGE (V20) and mean lung dose decreased 18% (P < .01) and 36% (P < .01), respectively, with proton IFRT, and 11% (P = .03) and 26% (P < .01) with ENI. The mean esophagus dose decreased 16% with IFRT and 12% with ENI; heart V25 decreased 63% with both (all P < .01).

CONCLUSION

This study demonstrates the feasibility of IMPT for LA-NSCLC ENI. Potential decreased toxicity indicates that IMPT could allow ENI while maintaining a favorable therapeutic ratio compared with photon IFRT.

Oxidative stress in oral diseases

Oxidative species, including reactive oxygen species (ROS), are components of normal cellular metabolism and are required for intracellular processes as varied as proliferation, signal transduction, and apoptosis. In the situation of chronic oxidative stress, however, ROS contribute to various pathophysiologies and are involved in multiple stages of carcinogenesis. In head and neck cancers specifically, many common risk factors contribute to carcinogenesis via ROS-based mechanisms, including tobacco, areca quid, alcohol, and viruses. Given their widespread influence on the process of carcinogenesis, ROS and their related pathways are attractive targets for intervention. The effects of radiation therapy, a central component of treatment for nearly all head and neck cancers, can also be altered via interfering with oxidative pathways. These pathways are also relevant to the development of many benign oral diseases. In this review, we outline how ROS contribute to pathophysiology with a focus toward head and neck cancers and benign oral diseases, describing potential targets and pathways for intervention that exploit the role of oxidative species in these pathologic processes.

Pyruvate induces transient tumor hypoxia by enhancing mitochondrial oxygen consumption and potentiates the anti-tumor effect of a hypoxia-activated prodrug TH-302

Background

TH-302 is a hypoxia-activated prodrug (HAP) of bromo isophosphoramide mustard that is selectively activated within hypoxic regions in solid tumors. Our recent study showed that intravenously administered bolus pyruvate can transiently induce hypoxia in tumors. We investigated the mechanism underlying the induction of transient hypoxia and the combination use of pyruvate to potentiate the anti-tumor effect of TH-302.

Methodology/Results

The hypoxia-dependent cytotoxicity of TH-302 was evaluated by a viability assay in murine SCCVII and human HT29 cells. Modulation in cellular oxygen consumption and invivo tumor oxygenation by the pyruvate treatment was monitored by extracellular flux analysis and electron paramagnetic resonance (EPR) oxygen imaging, respectively. The enhancement of the anti-tumor effect of TH-302 by pyruvate treatment was evaluated by monitoring the growth suppression of the tumor xenografts inoculated subcutaneously in mice. TH-302 preferentially inhibited the growth of both SCCVII and HT29 cells under hypoxic conditions (0.1% O₂), with minimal effect under aerobic conditions (21% O₂). Basal oxygen consumption rates increased after the pyruvate treatment in SCCVII cells in a concentration-dependent manner, suggesting that pyruvate enhances the mitochondrial respiration to consume excess cellular oxygen. In vivo EPR oxygen imaging showed that the intravenous administration of pyruvate globally induced the transient hypoxia 30 min after the injection in SCCVII and HT29 tumors at the size of 500–1500 mm³. Pretreatment of SCCVII tumor bearing mice with pyruvate 30 min prior to TH-302 administration, initiated with small tumors (∼550 mm³), significantly delayed tumor growth.

Conclusions/Significance

Our invitro and invivo studies showed that pyruvate induces transient hypoxia by enhancing mitochondrial oxygen consumption in tumor cells. TH-302 therapy can be potentiated by pyruvate pretreatment if started at the appropriate tumor size and oxygen concentration.

Gene expression profiles of NO- and HNO-donor treated breast cancer cells: insights into tumor response and resistance pathways

Nitric oxide (NO) synthase 2 (NOS2), a major inflammatory protein, modulates disease progression via NO in a number of pathologies, including cancer. The role of NOS2-derived NO is not only flux-dependent, which is higher in mouse vs human cells, but also varies based on spatial and temporal distribution both within tumor cells and in the tumor microenvironment. NO donors have been utilized to mimic NO flux conditions and to investigate the effects of varied NO concentrations. As a wide range of effects mediated by NO and other nitrogen oxides such as nitroxyl (HNO) have been elucidated, multiple NO- and HNO-releasing compounds have been developed as potential therapeutics, including as tumor modulators. One of the challenges is to determine differences in biomarker expression from extracellular vs intracellular generation of NO or HNO. Taking advantage of new NO and HNO releasing agents, we have characterized the gene expression profile of estrogen receptor-negative human breast cancer (MDA-MB-231) cells following exposure to aspirin, the NO donor DEA/NO, the HNO donor IPA/NO andtheir intracellularly-activated prodrug conjugates DEA/NO-aspirin and IPA/NO-aspirin. Comparison of the gene expression profiles demonstrated that several genes were uniquely expressed with respect to NO or HNO, such as miR-21, HSP70, cystathionine γ-lyase and IL24. These findings provide insight into targets and pathways that could be therapeutically exploited by the redox related species NO and HNO.

Role of particle beam therapy in a trimodality approach to locally advanced non-small cell lung cancer

Lung cancer accounts for nearly one-fifth of all cancer deaths worldwide and is the most common cause of cancer-related death in the United States. Outcomes for locally advanced non-small cell lung cancer remain extremely poor with regards to both local control and overall survival. Modest gains in local control were obtained with the incorporation of multimodality treatment, including preoperative chemotherapy followed by surgical resection; combination chemoradiotherapy also improved survival, secondary to improved local control. While the natural progression to trimodality therapy resulted in superior local control, it did not translate to improved overall survival, secondary to increased toxicity. The additional morbidity is likely from radiation toxicity, the minimization of which will be crucial to the future success of trimodality therapy. One strategy to decrease toxicity is to utilize charged particles, such as protons, which deposit a high dose at the Bragg peak with a minimal dose beyond the peak, thereby reducing the dose to distal normal tissues. Trimodality therapy incorporating preoperative proton radiation therapy and chemotherapy, followed by surgery, is currently being evaluated as a potential strategy to achieve improved local control and overall survival in locally advanced non-small cell lung cancer.

Abstract 1593: Cellular effects of the mitochondrially-directed antioxidant Tempol

The mitochondrial respiratory chain is a major source of reactive oxygen species, making it a high-yield target for antioxidants and potential radioprotection. The lipophilic cation triphenylphosphonium (TPP) has been used to target antioxidants to the mitochondrial membrane. Its lipophilicity permits it free passage through biological membranes while its positive charge traps it in the mitochondrial membrane, which is characterized by a large membrane potential. Among the agents localized to mitochondria via TPP have been stable nitroxide radicals, superoxide dismutase mimetics which also demonstrate the ability to scavenge free radicals. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, or Tempol (TP), is a nitroxide which is radioprotective both in vitro and in vivo when present during ionizing radiation. As with most chemical radioprotectors, relatively high concentrations of Tempol are required for protection. We questioned whether mito-Tempol (MTP), Tempol directed to mitochondria via TPP, would provide protection against radiation or hydrogen peroxide (HP) cytotoxicity as measured by the clonogenic assay in Chinese hamster V79 cells. MTP (10-500 μM) present 10 min prior to, during, and 4 hr after 12 Gy provided no radioprotection. MTP exhibited no cytotoxicity alone. In contrast, both TP and MTP (500 μM), when present immediately before and during a 1 hr exposure to HP, provided significant protection against HP cytotoxicity. We next evaluated the effects of continuous exposure to TP or MTP (100 μM) on the growth rate of several human tumor cell lines (MCF7, HT29, 786-0). TP had little effect on growth of these cell lines while MTP completely inhibited cell growth. The effects of the TPP-carbon linker alone will be presented; in short-term studies it did not exhibit cytotoxicity to V79 cells. These preliminary data with mitochondrial targeting of Tempol demonstrate that MTP exhibited antioxidant properties similar to TP with regard to protection against HP; at concentrations up to 500 μM, however, MTP did not protect against radiation. The latter finding is consistent with the requirement that chemical radioprotectors be present in sufficient concentration in the nucleus to afford radioprotection. Additional studies will be presented addressing the mechanism of MTP-mediated growth inhibition in human tumor cell lines.

Citation Format: Aparna H. Kesarwala, William DeGraff, Janet Gamson, Rajani Choudhuri, John A. Cook, Murali C. Krishna, James B. Mitchell. Cellular effects of the mitochondrially-directed antioxidant Tempol. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1593. doi:10.1158/1538-7445.AM2013-1593

Abstract P2-11-13: The Effect of Positive Axillary Lymph Nodes on Symptoms, Physical Impairments, and Function

Purpose/Objective(s): The role of axillary lymph node (ALN) sampling in breast cancer (BC) treatment continues to evolve, and BC patients are recommended for post-operative regional nodal radiation therapy (RNRT) based on the number of positive ALN. RNRT is recommended for patients with 4 or more positive ALN, but it remains controversial in patients with 1–3 positive ALN and is rarely recommended for patients without positive ALN. Consideration of anticipated functional impairments often guides decision making. The purpose of this analysis is to investigate functional impairments in BC patients with varying numbers of positive ALN.

Materials/Methods: 166 women were diagnosed with BC between 2001–05 and enrolled and treated in a prospective surveillance physical therapy program. 110 had zero positive ALN, 37 had 1–3 positive ALN, and 19 had 4 or more positive ALN on either sentinel LN biopsy or ALN dissection. Participants' upper extremity (UE) range of motion, strength, and limb volume were assessed pre-operatively and at 1, 3, 6, 9, and 12+ months post-operatively by a physical therapist. Limb volume was assessed using infrared optoelectronic perometry. At 12+ months, overall health status, UE symptoms and function, and physical activity levels were reported using standardized questionnaires. Chi-square tests and one-way ANOVA analyses were used to determine significance between groups (p ≤ 0.05).

Results: Of these 166 patients, 94 received mastectomy and 72 received lumpectomy, while 41 received RNRT and 58 received whole breast tangent RT. No significant differences were found between groups with regard to age or race. The number of dissected LN was not significantly different between those patients with 1–3 positive ALN and 4 or more positive ALN. Rates of lymphedema and seroma were not significantly different between those patients with zero positive ALN and 1–3 positive ALN, and rates of cording were not significantly different between any of the groups. Increased lymphedema (p = 0.03) and seroma (p = 0.005) were seen in those patients with 4 or more positive ALN compared to those patients with zero positive ALN, but this may also be related to a significantly greater number of dissected LN in the former group. By 12+ months post-operatively, there were no differences in shoulder abduction, shoulder flexion, internal rotation, or external rotation between groups. No differences were seen between groups in self-reported fatigue, UE swelling or weakness, arm stiffness, or ability to climb stairs.

Conclusions: Functional impairments represent an important category of morbidity for BC survivors and should be considered in pre-treatment decision making. The number of positive ALN may not correlate with increased impairment over the first year of treatment when a prospective surveillance physical therapy program is part of the plan of care. Additional research is needed to assess longer-term changes and the impact of axillary surgery and/or radiation in the context of aggregate effects of other BC treatment modalities.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-11-13.

Abstract P2-11-14: Symptoms, Physical Impairments, and Function in Breast Cancer Patients with Negative Axillary Lymph Nodes

Purpose/Objective(s): Breast cancer (BC) patients are recommended for post-operative regional nodal radiation therapy (RNRT) based on the number of positive axillary lymph nodes (LN). While RNRT is recommended for patients with 4 or more positive LN, it remains controversial in patients with 1–3 positive LN. For these patients, consideration of anticipated functional impairments often guides decision making, but these considerations are confounded by the inseparable effects of disease in and treatment of the axilla. The purpose of this analysis is to investigate the effect of various therapies on functional impairments in BC patients without axillary disease.

Materials/Methods: 166 women were diagnosed with BC between 2001–05 and enrolled and treated in a prospective surveillance physical therapy program. 110 had zero positive axillary LN on either sentinel LN biopsy or axillary LN dissection and were analyzed for this report. Participants' upper extremity (UE) range of motion, strength, and limb volume were assessed pre-operatively and at 1, 3, 6, 9, and 12+ months post-operatively by a physical therapist. Limb volume was assessed using infrared optoelectronic perometry. At 12+ months, overall health status, UE symptoms and function, and physical activity levels were reported using standardized questionnaires. Chi-square tests and one-way ANOVA analyses were used to determine significance between groups (p ≤ 0.05).

Results: Of these 110 patients, 34 received mastectomy without RT, 21 received mastectomy with RNRT, 10 received lumpectomy alone, and 45 received lumpectomy with whole breast tangent RT. No significant differences were found between groups with regard to stage, ER/PR status, and number of dissected LN. Rates of lymphedema, cording, and seroma were not significantly different between groups. By 12+ months post-operatively, there were no differences in shoulder abduction, shoulder flexion, internal rotation, or external rotation between groups. No differences were seen between groups in self-reported fatigue, UE swelling or weakness, arm stiffness, or ability to climb stairs.

Conclusions: Functional impairments represent an important category of morbidity for BC survivors and should be considered in pre-treatment decision making. In patients without axillary disease, post-operative RNRT or whole breast tangent RT may not contribute significantly to impairment over the first year of treatment when a prospective surveillance physical therapy program is part of the plan of care. Additional research is needed to assess longer-term changes and the impact of radiation in the context of the aggregate effect of disease burden combined with other BC treatment modalities.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-11-14.

Long-term follow-up of prostate cancer patients treated with vaccine and definitive radiation therapy

BACKGROUND

Vaccine therapy in combination with radiation therapy may improve distant and/or local control in prostate cancer. We present long-term follow-up data on the secondary and exploratory endpoints of safety and biochemical failure, respectively, from patients with clinically localized prostate cancer treated definitively with a poxviral vector-based therapeutic vaccine combined with external beam radiation therapy (EBRT).

METHODS

Thirty-six prostate cancer patients received definitive EBRT plus vaccine. A total of 18 patients were treated with adjuvant standard-dose interleukin-2 (S-IL-2) (4 MIU m(-2)) and 18 were treated with very low-dose IL-2 (M-IL-2) (0.6 MIU m(-2)). Seven patients were treated with EBRT alone. Twenty-six patients treated with EBRT plus vaccine returned for follow-up, and we reviewed the most recent labs and clinical notes of the remaining patients.

RESULTS

Median follow-up for the S-IL-2, M-IL-2 and EBRT-alone groups was 98, 76 and 79 months, respectively. Actuarial 5-year PSA failure-free probability was 78%, 82% and 86% (P=0.58 overall), respectively. There were no significant differences between the actuarial overall survival and the prostate cancer-specific survival between the two vaccine arms. Of the 26 patients who returned for follow-up, Radiation Therapy Oncology Group grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxicity was seen in 19% and 8%, respectively, with no difference between the arms (P=1.00 and P=0.48 for grade ≥2 GU and GI toxicity, respectively). In all, 12 patients were evaluated for PSA-specific immune responses, and 1 demonstrated a response 66 months post-enrollment.

CONCLUSIONS

We demonstrate that vaccine combined with EBRT does not appear to have significant differences with regard to PSA control or late-term toxicity compared with standard treatment. We also found limited evidence of long-term immune response following vaccine therapy.

PD02-03: The Effect of Breast Conservation Therapy vs Mastectomy on Symptoms, Physical Impairments, and Function

Background: Early-stage breast cancer (BC) patients choose between breast conservation therapy (BCT) and mastectomy based on comparable recurrence rates and overall survival. In the absence of mortality benefit, consideration of anticipated functional impairments could guide decision making. Although BCT offers less extensive surgery, the administration of radiation therapy (RT) may adversely impact upper extremity (UE) function. The purpose of this analysis is to investigate the effect of BCT vs modified radical mastectomy (MRM) without RT on functional impairments among BC survivors.

Materials and Methods: 196 women diagnosed with BC between 200105 were enrolled and treated in a prospective surveillance physical therapy program. 115 received either BCT, including lumpectomy and whole breast RT, or MRM without RT and were analyzed for this report. Participants’ UE range of motion (ROM), strength, and limb volume were assessed pre-operatively and at 1, 3, 6, 9, and 12+ months post-operatively by a physical therapist. Limb volume was assessed using infrared optoelectronic perometry. At 12+ months, overall health status, UE symptoms and function, and physical activity levels were reported using standardized questionnaires. Analysis of variance estimated differences in impairments and self-reported symptoms and function. One-way ANOVA analysis was used to determine significance between groups (p ≤ 0.05).

Results: 65 women (57.5%) received BCT and 50 women (42.5%) received MRM. No significant differences in age, BMI, stage, ER/PR status, and number of dissected lymph nodes were found between groups. At 1 month post-operatively, shoulder internal rotation (p=0.03), abduction (p=0.01), and flexion (p=0.004) were worse in post-MRM patients, with a trend towards worse external rotation (p=0.06). A higher rate of axillary cording was seen in patients post-MRM (p=0.02). By 12+ months post-operatively, there were no differences in any of the shoulder ROM variables. BCT patients reported, however, greater weakness (p=0.03) and diminished ability to perform heavy household tasks (p=0.03). There was no significant difference between BCT vs. MRM in rates of early lymphedema (40% vs 38%) or seroma (14% vs 22%).

Conclusion: Functional impairments represent an important category of morbidity for BC survivors and should be considered in pre-treatment decision making. Post-operative RT as part of BCT may not contribute significantly to impairment over the first year of treatment. The presence of self-reported weakness and difficulty performing heavy household tasks at 12+ months suggest possible future functional deficits, especially considering the potentially progressive nature of RT-associated tissue changes. Additional research is needed to assess longer-term changes and the impact of RT in the context of aggregate effects of other BC treatment modalities.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD02-03.

Proteasome inhibition blocks ligand-induced dynamic processing and internalization of epidermal growth factor receptor via altered receptor ubiquitination and phosphorylation

Epidermal growth factor (EGF) receptor (EGFR), a member of the EGF superfamily of receptor tyrosine kinases, is a critical regulator of cell growth and an important target for single agent and combination anticancer therapeutics. To further investigate the dynamics of ligand-induced EGFR processing and regulation noninvasively, we developed a chimeric EGFR-firefly luciferase (FLuc) fusion reporter to directly monitor processing of EGFR in real-time. In a stable HeLa cell line expressing the reporter at physiologically relevant levels, bioluminescence imaging continuously monitored reporter dynamics, correlating with the ligand-induced response of endogenous EGFR as determined by Western blot, subcellular localization of an EGFR-green fluorescent protein (GFP) fusion protein, and validated pharmacologic responses. The signaling competency of the reporter was confirmed by gene rescue experiments in EGFR-null cells. Bioluminescence analysis further showed that proteasome inhibition with bortezomib or MG132 attenuated overall ligand-induced degradation of EGFR. In cells expressing EGFR-GFP, pretreatment with proteasome inhibitors trapped essentially all of the receptor at the cell membrane both before and after ligand-induced activation with EGF. Furthermore, proteasome inhibition enhanced receptor ubiquitination in both the basal and ligand-activated states as well as delayed the processing of ligand-activated phosphorylation of the receptor, kinetically correlating with attenuated receptor degradation. These observations point to a potential mechanism for the synergistic therapeutic effects of combination EGFR- and proteasome-targeted therapies.

Biochemical and in vivo characterization of a small, membrane-permeant, caspase-activatable far-red fluorescent peptide for imaging apoptosis

Apoptosis is an important process involved in diverse developmental pathways, homeostasis, and response to therapy for a variety of diseases. Thus, noninvasive methods to study regulation and to monitor cell death in cells and whole animals are desired. To specifically detect apoptosis in vivo, a novel cell-permeable activatable caspase substrate, TcapQ647, was synthesized and Km, kcat, and Ki values were biochemically characterized. Specific cleavage of TcapQ647 by effector caspases was demonstrated using a panel of purified recombinant enzyme assays. Of note, caspase 3 was shown to cleave TcapQ647 with a kcat 7-fold greater than caspase 7 and 16-fold greater than caspase 6. No evidence of TcapQ647 cleavage by initiator caspases was observed. In KB 3-1 or Jurkat cells treated with cytotoxic agents or C6-ceramide, TcapQ647 detected apoptosis in individual- and population-based fluorescent cell assays in an effector caspase inhibitor-specific manner. Further, only background fluorescence was observed in cells incubated with dTcapQ647, a noncleavable all d-amino acid control peptide. Finally, in vivo experiments demonstrated the utility of TcapQ647 to detect parasite-induced apoptosis in human colon xenograft and liver abscess mouse models. Thus, TcapQ647 represents a sensitive, effector caspase-specific far-red "smart" probe to noninvasively monitor apoptosis in vivo.

Single photon emission computed tomography and positron emission tomography imaging of multi-drug resistant P-glycoprotein--monitoring a transport activity important in cancer, blood-brain barrier function and Alzheimer's disease

Overexpression of multi-drug resistant P-glycoprotein (Pgp) remains an important barrier to successful chemotherapy in cancer patients and impacts the pharmacokinetics of many important drugs. Pgp is also expressed on the luminal surface of brain capillary endothelial cells wherein Pgp functionally comprises a major component of the blood-brain barrier by limiting central nervous system penetration of various therapeutic agents. In addition, Pgp in brain capillary endothelial cells removes amyloid-beta from the brain. Several single photon emission computed tomography and positron emission tomography radiopharmaceutical have been shown to be transported by Pgp, thereby enabling the noninvasive interrogation of Pgp-mediated transport activity in vivo. Therefore, molecular imaging of Pgp activity may enable noninvasive dynamic monitoring of multi-drug resistance in cancer, guide therapeutic choices in cancer chemotherapy, and identify transporter deficiencies of the blood-brain barrier in Alzheimer's disease.

Second-generation triple reporter for bioluminescence, micro-positron emission tomography, and fluorescence imaging

Bioluminescence, positron emission tomography (PET), and fluorescence modalities are currently available for noninvasive imaging in vivo, each with its own merits. To exploit the combined strengths of each and facilitate multimodality imaging, we engineered a dual-reporter construct in which firefly luciferase (FLuc) and a 12-amino acid nonstructural linker were fused in frame to the N-terminus of a mutant herpes simplex virus thymidine kinase (mNLS-SR39TK) kinetically enhanced for positron emission tomography (PET). Furthermore, a triple-reporter construct was developed in which monster green fluorescent protein (MGFP), a recently available enhanced fluorescent protein, was introduced into the fusion vector downstream of an internal ribosome entry site (IRES) to allow analysis by fluorescence microscopy or flow cytometry without compromising the specific activities of the upstream fusion components. FLuc bioluminescence was measured with a cooled charge-coupled device camera and mNLS-SR39TK activity by 9-[4-[(18)F]fluoro-3-(hydroxymethyl) butyl guanine ((18)F-FHBG) microPET or (3)H-penciclovir net accumulation. Importantly, HeLa cells transiently transfected with the FLuc-mNLS-SR39TK-IRES-MGFP triple reporter retained the same specific activities of the FLuc-mNLS-SR39TK heteroenzyme and the individual unfused enzymes with no change in protein half-lives. The presence of the IRES-MGFP modestly decreased upstream heteroprotein expression. In living mice, somatic gene transfer of a ubiquitin promoter-driven FLuc-mNLS-SR39TK-IRES-MGFP plasmid showed a > 1,000-fold increase in liver photon flux and a > 2-fold increase in liver retention of (18)F-FHBG by microPET compared with mice treated with control plasmid. Multifocal hepatocellular fluorescence was readily observed by standard confocal microscopy. This second-generation triple reporter incorporating enhanced components enables bioluminescence, PET, and fluorescence imaging of cells and living animals.