Radiation Response Of Tumors Research Articles

AMBER: A Modular Model for Tumor Growth, Vasculature and Radiation Response.

Computational models of tumor growth are valuable for simulating the dynamics of cancer progression and treatment responses. In particular, agent-based models (ABMs) tracking individual agents and their interactions are useful for their flexibility and ability to model complex behaviors. However, ABMs have often been confined to small domains or, when scaled up, have neglected crucial aspects like vasculature. Additionally, the integration into tumor ABMs of precise radiation dose calculations using gold-standard Monte Carlo (MC) methods, crucial in contemporary radiotherapy, has been lacking. Here, we introduce AMBER, an Agent-based fraMework for radioBiological Effects in Radiotherapy that computationally models tumor growth and radiation responses. AMBER is based on a voxelized geometry, enabling realistic simulations at relevant pre-clinical scales by tracking temporally discrete states stepwise. Its hybrid approach, combining traditional ABM techniques with continuous spatiotemporal fields of key microenvironmental factors such as oxygen and vascular endothelial growth factor, facilitates the generation of realistic tortuous vascular trees. Moreover, AMBER is integrated with TOPAS, an MC-based particle transport algorithm that simulates heterogeneous radiation doses. The impact of radiation on tumor dynamics considers the microenvironmental factors that alter radiosensitivity, such as oxygen availability, providing a full coupling between the biological and physical aspects. Our results show that simulations with AMBER yield accurate tumor evolution and radiation treatment outcomes, consistent with established volumetric growth laws and radiobiological understanding. Thus, AMBER emerges as a promising tool for replicating essential features of tumor growth and radiation response, offering a modular design for future expansions to incorporate specific biological traits.

Delta radiomics to track radiation response in lung tumors receiving stereotactic magnetic resonance-guided radiotherapy

Background and purposeLung cancer is a leading cause of cancer-related mortality, and stereotactic body radiotherapy (SBRT) has become a standard treatment for early-stage lung cancer. However, the heterogeneous response to radiation at the tumor level poses challenges. Currently, standardized dosage regimens lack adaptation based on individual patient or tumor characteristics. Thus, we explore the potential of delta radiomics from on-treatment magnetic resonance (MR) imaging to track radiation dose response, inform personalized radiotherapy dosing, and predict outcomes. Materials and methodsA retrospective study of 47 MR-guided lung SBRT treatments for 39 patients was conducted. Radiomic features were extracted using Pyradiomics, and stability was evaluated temporally and spatially. Delta radiomics were correlated with radiation dose delivery and assessed for associations with tumor control and survival with Cox regressions. ResultsAmong 107 features, 49 demonstrated temporal stability, and 57 showed spatial stability. Fifteen stable and non-collinear features were analyzed. Median Skewness and surface to volume ratio decreased with radiation dose fraction delivery, while coarseness and 90th percentile values increased. Skewness had the largest relative median absolute changes (22 %–45 %) per fraction from baseline and was associated with locoregional failure (p = 0.012) by analysis of covariance. Skewness, Elongation, and Flatness were significantly associated with local recurrence-free survival, while tumor diameter and volume were not. ConclusionsOur study establishes the feasibility and stability of delta radiomics analysis for MR-guided lung SBRT. Findings suggest that MR delta radiomics can capture short-term radiographic manifestations of the intra-tumoral radiation effect.

MiRNAs in radiotherapy resistance of cancer; a comprehensive review.

While intensity-modulated radiation therapy-based comprehensive therapy increases outcomes, cancer patients still have a low five-year survival rate and a high recurrence rate. The primary factor contributing to cancer patients' poor prognoses is radiation resistance. A class of endogenous non-coding RNAs, known as microRNAs (miRNAs), controls various biological processes in eukaryotes. These miRNAs influence tumor cell growth, death, migration, invasion, and metastasis, which controls how human carcinoma develops and spreads. The correlation between the unbalanced expression of miRNAs and the prognosis and sensitivity to radiation therapy is well-established. MiRNAs have a significant impact on the regulation of DNA repair, the epithelial-to-mesenchymal transition (EMT), and stemness in the tumor radiation response. But because radio resistance is a complicated phenomena, further research is required to fully comprehend these mechanisms. Radiation response rates vary depending on the modality used, which includes the method of delivery, radiation dosage, tumor stage and grade, confounding medical co-morbidities, and intrinsic tumor microenvironment. Here, we summarize the possible mechanisms through which miRNAs contribute to human tumors' resistance to radiation.

Simulating tumor volume dynamics in response to radiotherapy: Implications of model selection

From the beginning of the usage of radiotherapy (RT) for cancer treatment, mathematical modeling has been integral to understanding radiobiology and for designing treatment approaches and schedules. There has been extensive modeling of response to RT with the inclusion of various degrees of biological complexity. In this study, we compare three models of tumor volume dynamics: (1) exponential growth with RT directly reducing tumor volume, (2) logistic growth with direct tumor volume reduction, and (3) logistic growth with RT reducing the tumor carrying capacity with the objective of understanding the implications of model selection and informing the process of model calibration and parameterization. For all three models, we: examined the rates of change in tumor volume during and RT treatment course; performed parameter sensitivity and identifiability analyses; and investigated the impact of the parameter sensitivity on the tumor volume trajectories. In examining the tumor volume dynamics trends, we coined a new metric – the point of maximum reduction of tumor volume (MRV) – to quantify the magnitude and timing of the expected largest impact of RT during a treatment course. We found distinct timing differences in MRV, dependent on model selection. The parameter identifiability and sensitivity analyses revealed the interdependence of the different model parameters and that it is only possible to independently identify tumor growth and radiation response parameters if the underlying tumor growth rate is sufficiently large. Ultimately, the results of these analyses help us to better understand the implications of model selection while simultaneously generating falsifiable hypotheses about MRV timing that can be tested on longitudinal measurements of tumor volume from pre-clinical or clinical data with high acquisition frequency. Although, our study only compares three particular models, the results demonstrate that caution is necessary in selecting models of response to RT, given the artifacts imposed by each model.

Intravoxel Incoherent Motion (IVIM) Magnetic Resonance Imaging (MRI) for Assessment of Treatment Response in Pancreatic Cancer

Intravoxel Incoherent Motion (IVIM) Magnetic Resonance Imaging (MRI) is an emergent technique used to quantify diffusion and perfusion without the use of contrast agent. Our objective was to evaluate changes in IVIM parameters pre- and post-Radiation Therapy (RT) / chemotherapy in Pancreatic Ductal Adenocarcinoma (PDAC) patients to correlate these parameters and their changes with tumor radiation response. Pre- and post-treatment IVIM scans were acquired from 12 patients (median age: 70 [41-83]) with PDAC treated with RT (median: 98 [39-116] Gy BED) and chemotherapy. CA19-9 was used as a surrogate of radiation response and its validity was confirmed using the Kaplan-Meier method and the log-rank test. The Diffusion Weighted Images (DWI) were acquired on a 3T MRI scanner using a free-breathing, spin echo-based echo-planar imaging (SE-EPI) sequence with six b-values (0, 30, 60, 100, 600, 1000 s/mm2). Tumors were segmented using Dynamic Contrast Enhanced (DCE) MRI and registered to the DWI images. A voxel-wise, bi-exponential, IVIM model was fitted to the DWI images to derive the perfusion fraction (f), diffusion coefficient (D), and pseudo-diffusion coefficient (D*) distributions inside the tumor. IVIM parameter distributions were described using histogram analysis by extracting the median, standard deviation, skew, kurtosis, and percentiles (5, 10, 25, 75, 90, 95). Statistical comparisons between pre- and post-RT images were performed using the nonparametric permutation test for small sample sizes. Kaplan-Meier analysis of pre- and post-RT showed significantly reduced survival (p = 0.04) in patients who had a CA19-9 increase (n = 6) compared to those who decreased or stayed the same (n = 6). The median f showed a significant increase (p = 0.03) in patients who experienced a decrease in CA19-9 while D showed a significant decrease (p = 0.03). Among the calculated histogram percentiles, both the 5th and 10th percentile in the f distribution showed a near-significant increase (p = 0.06) when CA19-9 decreased while the 95th of the D distribution showed a near-significant decrease (p = 0.06). In patients who experienced an increase in CA19-9, a near-significant change (p = 0.06) in the skew (decrease) and kurtosis (increase) of the f distribution was observed. D* showed no significant correlations across all testing. Both f and D exhibited significant changes in PDAC patients undergoing RT and chemotherapy, reflecting changes in tumor response to treatment. The findings warrant further investigation to utilize IVIM in characterizing treatment response in PDAC patients.

Tumour status prediction by means of carbon-ion beam irradiation: comparison of washout rates between in-beam PET and DCE-MRI in rats

Objective. Tumour response to radiation therapy appears as changes in tumour vascular condition. There are several methods for analysing tumour blood circulatory changes one of which is dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), but there is no method that can observe the tumour vascular condition and physiological changes at the site of radiation therapy. Positron emission tomography (PET) has been applied for treatment verification in charged particle therapy, which is based on the detection of positron emitters produced through nuclear fragmentation reactions in a patient’s body. However, the produced positron emitters are washed out biologically depending on the tumour vascular condition. This means that measuring the biological washout rate may allow evaluation of the tumour radiation response, in a similar manner to DCE-MRI. Therefore, this study compared the washout rates in rats between in-beam PET during 12C ion beam irradiation and DCE-MRI. Approach. Different vascular conditions of the tumour model were prepared for six nude rats. The tumour of each nude rat was irradiated by a 12C ion beam with simultaneous in-beam PET measurement. In 10–12 h, the DCE-MRI experiment was performed for the same six nude rats. The biological washout rate of the produced positron emitters (k 2,1st) and the MRI contrast agent (k 2a) were derived using the single tissue compartment model. Main results. A linear correlation was observed between k 2,1st and k 2a, and they were inversely related to fractional necrotic volume. Significance. This is the first animal study which confirmed the biological washout rate of in-beam PET correlates closely with tumour vascular condition measured with the MRI contrast agent administrated intravenously.

Molecular Imaging Investigations of Polymer-Coated Cerium Oxide Nanoparticles as a Radioprotective Therapeutic Candidate.

Cerium oxide nanoparticles (CONPs) have a unique surface redox chemistry that appears to selectively protect normal tissues from radiation induced damage. Our prior research exploring the biocompatibility of polymer-coated CONPs found further study of poly-acrylic acid (PAA)-coated CONPs was warranted due to improved systemic biodistribution and rapid renal clearance. This work further explores PAA-CONPs' radioprotective efficacy and mechanism of action related to tumor microenvironment pH. An ex vivo TUNEL assay was used to measure PAA-CONPs' protection of the irradiated mouse colon in comparison to the established radioprotector amifostine. [18F]FDG PET imaging of spontaneous colon tumors was utilized to determine the effects of PAA-CONPs on tumor radiation response. In vivo MRI and an ex vivo clonogenic assay were used to determine pH effects on PAA-CONPs' radioprotection in irradiated tumor-bearing mice. PAA-CONPs showed excellent radioprotective efficacy in the normal colon that was equivalent to uncoated CONPs and amifostine. [18F]FDG PET imaging showed PAA-CONPs do not affect tumor response to radiation. Normalization of tumor pH allowed some radioprotection of tumors by PAA-CONPs, which may explain their lack of tumor radioprotection in the acidic tumor microenvironment. Overall, PAA-CONPs meet the criteria for clinical application as a radioprotective therapeutic agent and are an excellent candidate for further study.

Preclinical Evaluation of Tumor Treating Fields Combined with Personalized Ultra-Fractionated Stereotactic Adaptive Radiotherapy (PULSAR)

Purpose/Objective(s)The PULSAR paradigm, treats patients using a few large dose “pulses,” delivered at least a week apart. These split treatments represent a radical break from conventional radiation treatments lasting six to nine weeks. The expectation is that therapy will be less toxic and will allow treatments to personalized based upon noted changes in tumor morphology, location and radiation response. Early pre-clinical experiments identified an optimal timing between radiation pulses with the use of immune checkpoint inhibitors (ICI). Other therapeutic combinations are being explored. Tumor Treating Fields (TTFields) is a novel noninvasive physical modality of cancer therapy that disrupts mitosis, causes replication stress, inhibits DNA damage repair, and sets up a conditional vulnerability to DNA damaging agents. This study combined the conditional vulnerabilities caused by TTFields exposure with a preclinical model of PULSAR to determine treatment efficacy for this combination.Materials/MethodsThe Inovivo system was used to generate Tumor Treating Fields across subcutaneously implanted tumors. Three distinct syngeneic mouse tumor models, LLC (Murine Lewis Lung Carcinoma), KPC63 (Pancreatic Cancer) and MC38 (Colon Cancer). Tumor growth delay (TGD) was the endpoint determined.ResultsIn the three mice models tested in vitro, TTFields exposure alone modestly decreased tumor volume. A difference in tumor growth rate between the heat (sham) and TTFields group was not statistically significant. TTFields combined with 8 or 10 Gy radiation pulses, depending on tumor model radiosensitivity, produced a significant TGD effect on the MC38 mouse model after one round. The second round of TTFields and radiation treatment further delayed TGD, in a synergistic manner, confirming that TTFields induces a conditional vulnerability that is particularly suited to the PULSAR concept. The combination of TTFields, PULSAR and an ICI is being tested and will be reported.ConclusionThe addition of TTFields with a pre-clinical model of PULSAR resulted in synergistic delays in tumor growth compared to the PULSAR strategy alone when tested using three different subcutaneous tumor models. This combination is well suited for the addition of an ICI. The PULSAR paradigm, treats patients using a few large dose “pulses,” delivered at least a week apart. These split treatments represent a radical break from conventional radiation treatments lasting six to nine weeks. The expectation is that therapy will be less toxic and will allow treatments to personalized based upon noted changes in tumor morphology, location and radiation response. Early pre-clinical experiments identified an optimal timing between radiation pulses with the use of immune checkpoint inhibitors (ICI). Other therapeutic combinations are being explored. Tumor Treating Fields (TTFields) is a novel noninvasive physical modality of cancer therapy that disrupts mitosis, causes replication stress, inhibits DNA damage repair, and sets up a conditional vulnerability to DNA damaging agents. This study combined the conditional vulnerabilities caused by TTFields exposure with a preclinical model of PULSAR to determine treatment efficacy for this combination. The Inovivo system was used to generate Tumor Treating Fields across subcutaneously implanted tumors. Three distinct syngeneic mouse tumor models, LLC (Murine Lewis Lung Carcinoma), KPC63 (Pancreatic Cancer) and MC38 (Colon Cancer). Tumor growth delay (TGD) was the endpoint determined. In the three mice models tested in vitro, TTFields exposure alone modestly decreased tumor volume. A difference in tumor growth rate between the heat (sham) and TTFields group was not statistically significant. TTFields combined with 8 or 10 Gy radiation pulses, depending on tumor model radiosensitivity, produced a significant TGD effect on the MC38 mouse model after one round. The second round of TTFields and radiation treatment further delayed TGD, in a synergistic manner, confirming that TTFields induces a conditional vulnerability that is particularly suited to the PULSAR concept. The combination of TTFields, PULSAR and an ICI is being tested and will be reported. The addition of TTFields with a pre-clinical model of PULSAR resulted in synergistic delays in tumor growth compared to the PULSAR strategy alone when tested using three different subcutaneous tumor models. This combination is well suited for the addition of an ICI.

HPV16 E6 Induces Chromosomal Instability due to Misaligned Chromosomes Caused by E6AP-Dependent Degradation of the Mitotic Kinesin CENP-E

<h3>Purpose/Objective(s)</h3> Chromosome missegregation over multiple cell cycles, termed chromosomal instability (CIN), is common in tumors and often leads to aneuploidy, a hallmark of cancer. High risk human papillomavirus (HPV) causes anogenital and head and neck cancers (HNC). HPV has been shown to cause certain types of CIN, but the mechanisms are unclear and this has not been studied in HNC. Here we describe a specific, novel mechanism of CIN induced by the HPV16 oncoprotein E6, in a physiologically relevant HNC model and in patient tumors. <h3>Materials/Methods</h3> Normal oral keratinocytes (NOKs) were transduced with retrovirus expressing LXSN control vector, HPV16 E6, E7 or E6+E7 and were kept under selection to achieve stable cell lines. CIN was quantified by assessing mitotic defects using immunofluorescence microscopy or H&E-stained slides in the NOKs, HNC cell lines, patient-derived xenografts (PDX), and in patient HNC tumors. Quantitative immunofluorescence and western blotting were used to quantify CENP-E levels. Tetracycline (tet) inducible GFP-CENP-E was introduced into NOKs expressing the Tet repressor using the PiggyBac transposon system. p53 and E6AP null NOKs were created using CRISPR. Significant differences were determined using a two-tailed student's t-test. <h3>Results</h3> HPV+ HNC cell lines have a significant increase specifically in misaligned chromosomes during mitosis, as compared to HPV- cell lines (20% v. 5% of cells, n=4 cell lines each). Using NOKs expressing individual HPV oncogenes, we found that these defects are specifically induced by the HPV oncogene E6 rather than E7. Further studies revealed that HPV16 E6 causes the specific degradation of CENP-E, a mitotic kinesin that plays a critical role in chromosome congression during mitosis. Tetracycline induced over-expression of GFP-CENP-E in LXSN- and E6-expressing NOKs revealed appropriate localization to kinetochores in LXSN cells. Strikingly, E6 mediated degradation of CENP-E was so efficient that CENP-E levels (total and at kinetochores) did not increase even after tet-inducible expression. Degradation of CENP-E occurred post-translationally in a proteasome dependent manner. Proteasome inhibition in E6-expressing NOKs rescued CENP-E protein levels at the kinetochore and rescued the misaligned chromosome phenotype. Furthermore, E6-mediated CENP-E degradation required the ubiquitin ligase E6AP, as evidenced by CENP-E protein restoration and rescue of chromosome alignment in E6AP null NOKs expressing E6. Finally, a significantly increased incidence of misaligned chromosomes was confirmed in HPV+ tumors from HNC patients and HPV+ PDXs. <h3>Conclusion</h3> This study reveals a novel, specific mechanism by which HPV16 E6 induces CIN in HNC, which may play a role in HPV-induced tumor initiation, progression and radiation response. Additionally, there is exciting potential for synergy with a CENP-E inhibitor, currently in clinical trials, and radiation to increase CIN beyond a viable threshold to increase cell death.

Targeting HER3-dependent activation of nuclear AKT improves radiotherapy of non-small cell lung cancer

BackgroundAKT1 must be present and activated in the nucleus immediately after irradiation to stimulate AKT1-dependent double-strand breaks (DSB) repair through the fast non-homologous end-joining (NHEJ) repair process. We investigated the subcellular distribution of AKT1 and the role of HER family receptor members on the phosphorylation of nuclear AKT and radiation response. Materials and methodsUsing genetic approaches and pharmacological inhibitors, we investigated the subcellular distribution of AKT1 and the role of HER family receptor members on the activation of nuclear AKT in non-small cell lung cancer (NSCLC) cells in vitro. ɤH2AX foci assay was applied to investigate the role of AKT activating signaling pathway on DSB repair. A mouse tumor xenograft model was used to study the impact of discovered signaling pathway activating nuclear AKT on the radiation response of tumors in vivo. ResultsOur data suggests that neither ionizing radiation (IR) nor stimulation with HER family receptor ligands induced rapid nuclear translocation of endogenous AKT1. GFP-tagged exogenous AKT1 translocated to the nucleus under un-irradiated conditions and IR did not stimulate this translocation. Nuclear translocation of GFP-AKT1 was impaired by the AKT inhibitor MK2206 as shown by its accumulation in the cytoplasmic fraction. IR-induced phosphorylation of nuclear AKT was primarily dependent on HER3 expression and tyrosine kinase activation of epidermal growth factor receptor. In line with the role of AKT1 in DSB repair, the HER3 neutralizing antibody patritumab as well as HER3-siRNA diminished DSB repair in vitro. Combination of patritumab with radiotherapy improved the effect of radiotherapy on tumor growth delay in a xenograft model. ConclusionIR-induced activation of nuclear AKT occurs inside the nucleus that is mainly dependent on HER3 expression in NSCLC. These findings suggest that targeting HER3 in combination with radiotherapy may provide a logical treatment option for investigation in selected NSCLC patients.

Role of vitamin D3 in tumor aggressiveness and radiation response for hepatocellular carcinoma.

Locoregional control is a significant prognostic factor for hepatocellular carcinoma (HCC). Historically, the use of radiotherapy (RT) for HCC was limited owing to the low radiotolerance of the liver and the need for high RT doses for disease control. We aimed to examine if 1α,25-dihydroxyvitamin D3 (calcitriol) has a role in the tumor inhibition and the radiation response of HCC in vitro and in vivo, and explore the underlying mechanisms. The human and murine liver cancer cell lines were selected for cellular and animal experiments to investigate the changes in tumor characteristics and the radiation response after calcitriol supplementation. The effects induced by calcitriol supplementation on interleukin-6 (IL-6) signaling and the tumor immune microenvironment following RT were also examined. Our data revealed that calcitriol supplementation attenuated tumor aggressive behavior, decrease IL-6 expression, and augmented radiation-induced tumor inhibition. The biological changes following calcitriol treatment included suppressed epithelial-mesenchymal transition, attenuated cancer stem cell-like properties and increased radiation-induced reactive oxygen species and cell death in vitro. Regarding immune microenvironment, calcitriol attenuated the recruitment of myeloid-derived suppressor cell (MDSC) recruitment and increased the infiltration of cytotoxic T cells in tumor following RT. Furthermore, When the primary liver tumor was irradiated with larger dose per fraction, calcitriol induced a smaller size of synchronous unirradiated tumor in mice, which linked with attenuated IL-6 signaling and MDSC recruitment. In conclusion, calcitriol treatment reduced tumor aggressiveness and enhanced the radiation response. The inhibited IL-6 signaling and subsequently enhanced antitumor immunity might be responsible to augment radiation-induced tumoricidal effect induced by calcitriol. Based on our results, we suggest that calcitriol could exert the antitumor and radiosensitization effects for HCC, especially for multifocal tumors.

MicroRNAs as Biomarkers for Ionizing Radiation Injury.

Accidental radiation exposures such as industrial accidents and nuclear catastrophes pose a threat to human health, and the potential or substantial injury caused by ionizing radiation (IR) from medical treatment that cannot be ignored. Although the mechanisms of IR-induced damage to various organs have been gradually investigated, medical treatment of irradiated individuals is still based on clinical symptoms. Hence, minimally invasive biomarkers that can predict radiation damage are urgently needed for appropriate medical management after radiation exposure. In the field of radiation biomarker, finding molecular biomarkers to assess different levels of radiation damage is an important direction. In recent years, microRNAs have been widely reported as several diseases’ biomarkers, such as cancer and cardiovascular diseases, and microRNAs are also of interest to the ionizing radiation field as radiation response molecules, thus researchers are turning attention to the potential of microRNAs as biomarkers in tumor radiation response and the radiation toxicity prediction of normal tissues. In this review, we summarize the distribution of microRNAs, the progress on research of microRNAs as markers of IR, and make a hypothesis about the origin and destination of microRNAs in vivo after IR.

Immune Stimulating Outcome of Chrysin and γ-Irradiation via Apoptotic Activation Against Solid Ehrlich Carcinoma Bearing Mice.

The rising interest in innovative methods of cancer immunotherapy has prompted research into the immunomodulatory mechanisms of natural and synthetic substances. The goal of this study was to assess chrysin immune-stimulating and pro-apoptotic effects on tumor growth and cell susceptibility to ionizing radiation in order to improve cancer therapy. Chrysin (20 mg/kg/day) was intraperitoneally injected to mice bearing 1 cm3 solid tumor of Ehrlich ascites carcinoma (EAC) for 21 consecutive days. Mice were whole body exposed to 1 Gy of gamma radiation (2 fractionated dose 0.5 Gy each). Treatment with chrysin dramatically reduces tumor proliferation in EAC mice; furthermore, IFN-γ activity is significantly reduced when compared to EAC mice. When compared to EAC mice, the expression of TNF-α, free radicals, and nitric oxide (NO) levels were considerably reduced, along with improvements in apoptotic regulators (caspase-3 activity). Moreover, the histopathological investigation confirms the improvement exerted by chrysin even in the EAC mice group or the EAC + R group. What is more, exposure to gamma radiation sustained the modulatory effect of chrysin on tumor when compared with EAC + Ch mice. Hence, chrysin might represent a potential therapeutic strategy for increasing the radiation response of solid tumor.

Evaluation of Initial Metastatic Tumor Location and Radiation Response to Determine Outcomes in Patients Who Received Combination Stereotactic Body Radiotherapy and Immunotherapy for NSCLC

Combination SBRT and immune checkpoint inhibition is safe and efficacious for metastatic NSCLC. It is unknown whether the site of metastatic disease at diagnosis or SBRT response can be used as predictors of PFS or OS. We report follow-up from a prospective phase I clinical trial examining predictors of OS and PFS based on initial metastatic tumor disease location, as well as SBRT response.Thirty-seven patients with treatment-naïve metastatic NSCLC were reviewed. Patients received SBRT to doses of 30-50 Gy in 3-5 fractions to 1-6 metastases, as well as concurrent (immunotherapy with SBRT) or sequential (immunotherapy after completion of SBRT) nivolumab/ipilimumab on a phase I clinical trial at a single institution. All metastatic lesions were evaluated and the sites of initial disease, including liver, bone, or thoracic only metastases, were evaluated to determine if those sites influenced OS or PFS. Treated metastases control (TMC) was defined as lack of progression for irradiated metastases. Landmark analysis was used to assess correlation of TMC and OS. The Kaplan-Meier method was used to analyze OS and PFS.Thirty-seven patients with 120 evaluable metastases were enrolled with a median follow-up of 17.0 months. Patients who had liver metastases at baseline (n = 8) were found to have a worse PFS (log-rank P = 0.048), but no difference in OS (log-rank P = 0.243) when compared to patients who did not have liver metastases at baseline (n = 29). There was a trend toward significance for better PFS in patients who had thoracic only metastases at baseline (n = 6) compared to patients that had extra-thoracic metastases (n = 31) at baseline (Gehan-Breslow-Wilcoxon P = 0.061); however, there was no difference in OS. There was no statistically significant difference in PFS or OS for patients with bone metastases (n = 9) at baseline compared to patients who did not have bone metastases at baseline (n = 28). One- and two-year TMC were 93.8% and 91.7%, respectively. TMC corresponded to better OS (log-rank P = 0.040).Liver metastases present at diagnosis in metastatic NSCLC correlate with worse PFS. Treated metastases control rates also correlate with OS. These metrics may help predict outcomes and inform whether additional aggressive therapy is required for patients with metastatic NSCLC.

Intermittent radiotherapy as alternative treatment for recurrent high grade glioma: a modeling study based on longitudinal tumor measurements

Recurrent high grade glioma patients face a poor prognosis for which no curative treatment option currently exists. In contrast to prescribing high dose hypofractionated stereotactic radiotherapy (HFSRT, ge 6 Gy times 5 in daily fractions) with debulking intent, we suggest a personalized treatment strategy to improve tumor control by delivering high dose intermittent radiation treatment (iRT, ge 6 Gy times 1 every 6 weeks). We performed a simulation analysis to compare HFSRT, iRT and iRT plus boost (ge 6 Gy times 3 in daily fractions at time of progression) based on a mathematical model of tumor growth, radiation response and patient-specific evolution of resistance to additional treatments (pembrolizumab and bevacizumab). Model parameters were fitted from tumor growth curves of 16 patients enrolled in the phase 1 NCT02313272 trial that combined HFSRT with bevacizumab and pembrolizumab. Then, iRT +/− boost treatments were simulated and compared to HFSRT based on time to tumor regrowth. The modeling results demonstrated that iRT + boost(− boost) treatment was equal or superior to HFSRT in 15(11) out of 16 cases and that patients that remained responsive to pembrolizumab and bevacizumab would benefit most from iRT. Time to progression could be prolonged through the application of additional, intermittently delivered fractions. iRT hence provides a promising treatment option for recurrent high grade glioma patients for prospective clinical evaluation.

Oxygen-Sensitive MRI: A Predictive Imaging Biomarker for Tumor Radiation Response?

To develop a noninvasive prognostic imaging biomarker related to hypoxia to predict SABR tumor control. A total of 145 subcutaneous syngeneic Dunning prostate R3327-AT1 rat tumors were focally irradiated once using cone beam computed tomography guidance on a small animal irradiator at 225 kV. Various doses in the range of 0 to 100 Gy were administered, while rats breathed air or oxygen, and tumor control was assessed up to 200 days. Oxygen-sensitive magnetic resonance imaging (MRI) (T1-weighted, ΔR1, ΔR2*) was applied to 79 of these tumors at 4.7 T to assess response to an oxygen gas breathing challenge on the day before irradiation as a probe of tumor hypoxia. Increasing radiation dose in the range of 0 to 90 Gy enhanced tumor control of air-breathing rats with a TCD50 estimated at 59.6 ± 1.5 Gy. Control was significantly improved at some doses when rats breathed oxygen during irradiation (eg, 40 Gy; P < .05), and overall there was a modest left shift in the control curve: TCD50(oxygen) = 53.1 ± 3.1 Gy (P < .05 vs air). Oxygen-sensitive MRI showed variable response to oxygen gas breathing challenge; the magnitude of T1-weighted signal response (%ΔSI) allowed stratification of tumors in terms of local control at 40 Gy. Tumors showing %ΔSI >0.922 with O2-gas breathing challenge showed significantly better control at 40 Gy during irradiation while breathing oxygen (75% vs 0%, P < .01). In addition, increased radiation dose (50 Gy) substantially overcame resistance, with 50% control for poorly oxygenated tumors. Stratification of dose-response curves based on %ΔSI >0.922 revealed different survival curves, with TCD50 = 36.2 ± 3.2 Gy for tumors responsive to oxygen gas breathing challenge; this was significantly less than the 54.7 ± 2.4 Gy for unresponsive tumors (P < .005), irrespective of the gas inhaled during tumor irradiation. Oxygen-sensitive MRI allowed stratification of tumors in terms of local control at 40 Gy, indicating its use as a potential predictive imaging biomarker. Increasing dose to 50 Gy overcame radiation resistance attributable to hypoxia in 50% of tumors.

Immunostimulating, proapoptotic and synergistic effects of propolis and its main constituent (chrysin) on the tumor growth and the cell sensitivity to ionizing radiation in mice

The increased interest in new approaches to the immunotherapy of cancer and a considerable demand for therapeutic agents which can modulate the several forms of immunodeficiency have encouraged studies on the immunomodulatory mechanisms of natural and synthetic substances. The present work was an endeavor to evaluate the imunostimulating as well as proapoptotic and synergistic effects of Chrysin (Ch) and Propolis (P) on the tumor growth and the cell sensitivity to ionizing radiation targeting the improvement of cancer therapeutic protocols. Chrysin (20 mg/kg body weight/day) and Propolis (100 mg/kg body weight day) were injected intraperitoneal to mice bearing 1cm3 solid tumor of Ehrlich ascites carcinoma (EAC) for 21 consecutive days. Mice were whole body exposed to 1 Gy of gamma radiation (two fractionated doses at 11 and 25 days post EAC inoculation, respectively). Treatments with Ch or P markedly suppress the proliferation of tumor in mice bearing solid Ehrlich tumor (EAC mice). The activity of interferon-gamma (IFN-γ) was significantly decreased in the treated mice compared to EAC mice. The concentrations of m-RNA for angiogenic factor (tumor necrosis factor alpha -TNF-α), free radicals as well as nitric oxide (NO) concentration were significantly decreased collimated with improvements in apoptotic regulators (Caspase-3 activity) compared to EAC mice. Moreover, the histopathological investigation confirms the improvement exerted by Ch or P even in EAC mice group or mice bearing solid Ehrlich tumor and subjected to γ-irradiation (EAC+R group). Exposure to gamma radiation sustained the modulatory effect of Ch or P on tumor when compared with EAC mice and those injected with Ch (EAC+Ch) or EAC and injected with P (EAC+P). Hence, Ch or P might represent a potential therapeutic strategy for increasing the radiation response of solid tumor.

Abstract PO-020: The NRF2-redox-metabolism axis protects pancreatic cancer cells from radiation toxicity

Abstract More than 90% of pancreatic ductal adenocarcinomas (PDAC) are driven by activating KRAS mutations (mKRAS), which promote a remarkable resistance to all non-surgical therapies, including radiation therapy (RT). Unfortunately, mKRAS remains undruggable for the vast majority of PDAC tumors. This necessitates the discovery of downstream targets, which most likely govern the oxidative stress response and promote the acquisition of radiation resistance. Notably, the master orchestrator of oxidative stress response, the transcription factor NRF2, is upregulated by mKRAS and in some models, NRF2 is activated by irradiation (IR). This suggests that IR may amplify the already heightened, mKRAS-driven activation of NRF2 in PDAC. NRF2 targets include genes involved in restoring redox balance, likely promoting survival during RT. However, the involvement of NRF2 in PDAC radioresistance remains unknown. To fill this knowledge gap, we have systematically investigated the role of the NRF2 pathway in regulating radiation response in PDAC tumors. Our studies show that depletion of NRF2 via CRISPR/Cas9 targeted gene deletion (NRF2-ko) results in the accumulation of significantly higher levels of reactive oxygen species in irradiated PDAC cells. Importantly, this correlates with increased radiosensitivity of NRF2-ko cells in vitro, compared to NRF2-wt controls. Interestingly, irradiation of PDAC cells upregulates the expression of metabolic genes that drive the generation of various antioxidant species, in a NRF2-dependent manner. At the metabolite level, IR induces re-routing of glycolytic metabolites towards the antioxidant pentose phosphate pathway and the depletion of NRF2 abrogates these changes. Together, these findings suggest that part of the mechanism via which NRF2 promotes radiation survival of PDAC cells is by reprogramming cellular metabolism to drive a metabolic antioxidant response. Altogether, these findings support a crucial role for the NRF2-redox-metabolism axis in driving RT resistance in PDAC. This further suggests that inhibition of the NRF2 pathway would be followed by a failure to resist IR-induced oxidative stress, and subsequently sensitize mKRAS pancreatic cancer to RT. Citation Format: Justine Bailleul, Taha Yazal, David Sung, Juan Nathaniel, Daisy Palomera, Anahita Sehgal, Rachel Ruan, Erina Vlashi. The NRF2-redox-metabolism axis protects pancreatic cancer cells from radiation toxicity [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-020.

Abstract PO-033: The angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient tumour hypoxia and improves response to ionizing radiation therapy

Abstract Poorly oxygenated (hypoxic) cells are key components of the solid tumour microenvironment that drive tumour heterogeneity. Hypoxia regulates a variety of processes that promote tumour cell survival and metastasis, and hypoxic tumour cells are resistant to therapy. Patients with tumours that contain hypoxic cells have worse outcome after radiotherapy, chemotherapy, and even surgery, underscoring the therapeutic relevance of hypoxia in driving more aggressive tumour phenotypes. Hypoxic tumour cells result from deficiencies in the delivery of oxygen relative to the high oxygen demand of tumour cells. “Chronic” hypoxia develops due to the limited diffusion distance of oxygen through tumour tissue, while “transient” hypoxia occurs due to fluctuations in microregional tumour perfusion and oxygen delivery over time. Transiently hypoxic cells are more resistant to radiation therapy and are more metastatic than chronically hypoxic cells although, despite decades of work in this area, there are no effective long-term strategies to specifically target transiently hypoxic cells in solid tumours. Angiotensin II type 1 receptor (AT1R) blockers (ARBs) are widely prescribed anti-hypertensive agents that can also exhibit anti-fibrotic activity. Recent evidence indicates that the ARB losartan can inhibit collagen I (Col1) deposition in tumours by cancer-associated fibroblasts (CAFs), reduce blood vessel constriction, and increase net tumour blood flow, although the influence of losartan or other ARBs on transient hypoxia and tumour radiation response is unknown. We hypothesized that ARB-mediated inhibition of Col1 deposition from CAFs increases tumour blood flow by stabilizing microregional fluctuations in tumour perfusion and that ARBs will reduce transient tumour hypoxia. We tested the ARBs losartan and telmisartan in human tumour xenografts using positron emission tomography and intravenously injected fluorescent perfusion dyes to quantify tumour perfusion, and a combination of exogenous hypoxia markers and the hemorheological agent pentoxifylline to assess transient tumour hypoxia. We found that CAF-containing tumours had reduced Col1 levels in response to telmisartan, but not losartan, consistent with the improved pharmacokinetics and AT1R binding affinity of telmisartan. Telmisartan increased net tumour blood flow and stabilized microregional fluctuations in tumour perfusion. Importantly, telmisartan decreased overall hypoxia in the tumours by specifically targeting transient tumour hypoxia, which translated into a significant improvement in radiation response. These data indicate that telmisartan reduces a therapeutically-relevant population of transiently hypoxic tumour cells. Understanding how the solid tumour microenvironment influences cancer therapy is central to improving treatment outcome. Our work underscores the importance of transient tumour hypoxia and supports future clinical studies to evaluate telmisartan as a neoadjuvant for radiation therapy. Citation Format: Brennan J. Wadsworth, Rachel A. Cederberg, Che-Min Lee, Natalie S. Firmino, S. Elizabeth Franks, Jinhe Pan, Nadine Colpo, Kuo-Shyan Lin, Francois Benard, Kevin L. Bennewith. The angiotensin II type 1 receptor blocker telmisartan inhibits the development of transient tumour hypoxia and improves response to ionizing radiation therapy [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-033.

Avasopasem Manganese Protects Against Radiation Induced Oral Mucositis and Enhances the Response of Squamous Cell Carcinoma of the Head and Neck to Ionizing Radiation and Radioimmune Therapy

Locoregional recurrence (LRR) is the major cause of morbidity and mortality in patients with squamous cell carcinoma of the head and neck (HNSCC). For those patients that experience surgically unresectable LRR, median overall survival (OS) is less than one year. Approaches utilizing stereotactic ablative radiotherapy (SabR) and immuno-oncology agents such as Nivolumab (α-PD-1 inhibitor) in the salvage setting have become alternatives to conventional chemoradiation therapy. Despite improvements in OS, rates of acute oral mucositis (OM) and late toxicities (skin fibrosis) remain concerns with SabR in the context of re-irradiation. Here we present pre-clinical evidence that avasopasem manganese (GC4419), a highly selective superoxide dismutase mimetic that has received FDA Breakthrough Therapy Designation and is currently in a Phase III trial for reducing severe OM in patients undergoing chemoradiotherapy for locally advanced HNSCC (NCT03689712) also enhances the anti-tumor radiation response of HNSCC tumors. We demonstrate in pre-clinical animal models that avasopasem protects the normal mucosa of the mouse tongue from primary irradiation toxicity. We will also report the results of ongoing studies examining whether avasopasem protects murine mucosa from reirradiation as with SabR as a salvage therapy. Utilizing clonogenic survival assays, we demonstrate that avasopasem at physiologically achievable concentrations exhibits single agent anti-cancer activity and also enhances the response of HNSCC lines to irradiation. In tumor growth delay (TGD) experiments utilizing the syngeneic HNSCC tumor model, AT-84, when avasopasem is delivered in combination with biologically equivalent fractionation schedules of 17 Gy x 1 fxn, 10.24 Gy x 2 fxn, or 5 Gy x 5 fxn, an enhancement of the radiation response is achieved. This potentiation of the anti-tumor response with GC4419 is more pronounced at fraction doses exceeding the threshold considered for intensity modulated radiation therapy. In addition, when avasopasem is combined with radiation and an α-PD-1 inhibitor, a further enhancement of the radiation response is observed, indicating that it compliments radiotherapy combined with immunotherapy. The pre-clinical data strongly suggest that avasopasem should be combined with radio-immune therapy to not only enhance local tumor control, but also to provide normal tissue protection with SabR which may allow dose escalation and further improve treatment outcomes. Whether radiation combined with avasopasem and checkpoint inhibitor has an effect on metastasis is under examination.