Normal Tissue Protection Research Articles

Abstract 811: Pharmacologic ascorbate opens a therapeutic window for ATM inhibition and radiotherapy in colorectal cancer

Abstract Purpose/Objective(s): The ATM protein is key to DNA double strand break (DSB) repair and ATM inhibitors are potent radiosensitizers. Clinical translation of these agents in combination with radiotherapy (RT) has been limited due to concerns for increased normal tissue toxicity. Pharmacologic Ascorbate (P-AscH-) radiosensitizes cancer cells via generation of a H2O2 flux while acting as a radioprotector in normal tissue via free radicle scavenging. We hypothesized that P-AscH- could open a therapeutic window for the combination of RT and ATM inhibition in colorectal cancer (CRC). Materials/Methods: Multiple human and murine CRC cell lines were used in vitro. Clonogenic survival was assessed after combinations of RT +/- P-AscH and DNA Repair Inhibitors (DRIs). Catalase expression was induced using HCT116 cells expressing a doxycycline-inducible catalase transgene. DSBs were quantified using neutral comet assays. Cell cycle distribution were assessed using flow cytometry. ATM localization/activation were assessed using IF. Normal tissue toxicity in vivo was assessed using IHC following whole-abdominal RT. Survival and tumor growth delay was assessed following 5Gyx3 +/- drug treatment to unilateral flank tumors in syngeneic/xenograft models. Results: DRIs were potent radiosensitizers in most CRC cell lines and the addition of P-AscH- further reduced clonogenic survival. In contrast, P-AscH- did not radiosensitize HUVEC or FHs-74int normal cell lines. P-AscH- significantly increased the number of DSBs in tumors after RT in vitro. P-AscH- simultaneously decreased nuclear localization and activation of pATM after RT and perturbed G2+M phase progression. In vivo, the addition of P-AscH- to RT + KU60019 significantly increased survival delayed tumor growth in syngeneic/xenograft models while ameliorating increased normal bowel toxicity as measured by jejunal crypt density, acute weight loss, rectal injury, and markers of oxidative stress following whole-abdominal RT. The effects of P-AscH were reversed by inducing the overexpression of catalase. Conclusion: P-AscH- improves both aspects of the therapeutic window of RT+ATM inhibition in CRC by simultaneously enhancing tumor efficacy while decreasing RT-mediated bowel toxicity. The effects of P-AscH- on clonogenic survival, initial and persistent DSBs, G2+M phase perturbations, ATM activation/localization, and in vivo survival and tumor growth delay were dependent on H202 flux. Normal tissue protection appears to be related to decreased oxidative stress. Citation Format: Cameron M. Callaghan, Ibrahim M. Abukhiran, Richard V. Van Rheeden, Amanda L. Kalen, Samuel N. Rodman, Michael S. Petronek, Kranti A. Mapuskar, Sarah L. Mott, Mitchell C. Coleman, Prabhat C. Goswami, John M. Buatti, Bryan G. Allen, Douglas R. Spitz, Joseph M. Caster. Pharmacologic ascorbate opens a therapeutic window for ATM inhibition and radiotherapy in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 811.

Abstract 3304: Gene expression profiling of full-thickness skin after FLASH proton radiotherapy

Abstract Purpose: To investigate the transcriptomic changes induced by FLASH proton radiotherapy (F-PRT) that could be responsible for the protection of normal epithelial tissues by radiation-induced toxicities as have been previously shown by us and others. Methods: C57BL/6J mice received 30 Gy of F-PRT or S-PRT to the hind leg at respective dose rates of 69-124 Gy/sec or 0.39-0.65 Gy/sec. RNA sequencing was performed using full-thickness leg skin at 5 days after radiation revealing major pathways regulated by F-PRT and S-PRT. In an endeavor to identify the full repertoire of cells and gene expression profiles that are involved in the sparing effects of FLASH PRT, we expanded our studies to include single-cell RNA sequencing (sc-RNA seq) and examined additional time points such as Day 2 and Day 10 after radiation. Single-cell transcriptome libraries were generated on a 10X Genomics Chromium system. Datasets were acquired from cell samples derived and sequenced from pooled skin samples of three mice per group. Skin from the sequenced mice was also embedded for spatial analysis of gene expression. Results: RNA sequencing revealed that F-PRT uniquely upregulates almost four times more genes compared to S-PRT (F-PRT-uniquely upregulated 489 genes vs S-PRT-uniquely upregulated 129 genes). Also, F-PRT uniquely downregulated 178 genes, compared to the 125 genes uniquely downregulated by S-PRT. GO analysis demonstrates that the keratinization and apoptosis pathways are uniquely upregulated by S-PRT, whereas F-PRT uniquely upregulates genes involved in vascular development pathway. During submission of the abstract, analysis of sc-RNA seq samples was pending. Conclusion: Our comprehensive studies inform on the transcriptomic profiling of skin cell populations that are affected by F-PRT vs S-PRT; this insight will further spur discoveries on the biology of FLASH radiotherapy effects. Citation Format: Anastasia Velalopoulou, Ilias V. Karagounis, Giorgos Skoufos, Ioannis I. Verginadis, Michele Kim, Khayrullo Shoniyozov, Artemis G. Hatzigeorgiou, Eric Diffenderfer, Lei Dong, James Metz, Constantinos Koumenis, Keith A. Cengel, Amit Maity, Theresa M. Busch. Gene expression profiling of full-thickness skin after FLASH proton radiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3304.

Systems biology basis of permanent tumor regression with normal tissue protection: Experimentally validated signaling pathway framework.

e15066 Background: Clinicians generally deal with malignant tumors in progression phase only, but there is a reverse complimentary process, namely permanent spontaneous regression of tumors, a well-known phenomenon occurring across human populations at 22%-46% rate (Scandinavian and Wisconsin Screening Registries: 0.33 million and 2.95 million populace respectively; Lancet Oncol.12: 1118-24, 2011; J.Nat.Cancer.Inst.36: 37-47, 2006). Probing such a phenomenon can illuminate how one can induce a permanent regression process on human tumors therapeutically. Here we develop a systems biology approach for this process, that we validate by experimental findings. Methods: Mathematical System Biology Formulation: For permanent tumor regression, we develop a coupled differential equations-based cell kinetic analysis, keeping normal tissue protected. Thereby, we mathematically model the temporal variation of the level of three essential tumor-lysis components: DNA replication-blockade, Antitumor Lymphocyte, Cytokine interleukin-2. Experimental Investigation: We investigate the temporal process of spontaneous tumor regression of melanoma (in Liebechov pigs) and analyze the microarray signal using IPA platform Gene expression signature: Using IPA analysis, we find the signaling pathways associated with the permanent tumor regression. Results: Mathematical System Biology Formulation: We find the temporal behavior of tumor-lysis components are: (1) DNA replication-blockade activation: Unimodal inverted U function (2) Antitumor Lymphocyte activation: Bimodal M function; (3) Interleukin-2 activation as Stationary step function. Experimental findings: Our microarray analysis gives temporal pattern of gene-expression levels corresponding to above three components: G2/M DNA damage checkpoint regulation (genes CCNB1, CDC2), Chemokine signaling activation - Interleukin 2 ( GRB2, PIK3CG), T Lymphocyte Receptor Signaling (CCR5, PRF1). These three temporal components respectively show Unimodal, Bimodal, and Stationary activation. Validation: We show that the three mathematically-derived temporal activation functions are well corroborated by corresponding experimental temporal pathway activation data (Smirnov-Kolmogorov statistical test satisfied; α = 5%). Conclusions: A novel tri-phasic activation of three antitumor signaling pathways (DNA blockade, Interleukin 2, Cytotoxic T cell) can permanently regress melanoma tumor in the experimental setting if the pathways are activated at different time points and not simultaneously; These temporally orchestrated patterns are much different from conventional chemotherapy/ immunotherapy protocols where the temporal activations are simultaneous and empirically chosen. Optimal temporal profiling of administration of antitumor agents is thus crucial from a therapeutic standpoint.

Flying rats and microbeam paths crossing: the beauty of international interdisciplinary science

Purpose Microbeam radiotherapy (MRT) is a still experimental radiotherapy approach. Two combined parameters contribute to an excellent normal tissue protection and an improved control of malignant tumors in small animal models, compared to conventional radiotherapy: dose deposition at a high dose rate and spatial fractionation at the micrometre level. The international microbeam research community expects to see clinical MRT trials within the next ten years. Physics-associated research is still widely regarded as a male domain. Thus, the question was asked whether this is reflected in the scientific contributions to the field of microbeam radiotherapy. Method A literature search was conducted using Pubmed, Semantic Scholar and other sources to look specifically for female contributors to the field of microbeam radiotherapy development. Conclusion The original idea for MRT was patented in 1994 by an all-male research team. In approximately 50% of all publications related to microbeam radiotherapy, however, either the first or the senior author is a woman. The contribution of those women who have been driving the development of both technical and biomedical aspects of MRT in the last two decades is highlighted.

The Role of Radioprotector Agents in the Protection of Normal tissue

The Role of Radioprotector Agents in the Protection of Normal tissue

Oxygen Depletion in Proton Spot Scanning: A Tool for Exploring the Conditions Needed for FLASH

FLASH radiotherapy is a rapidly developing field which promises improved normal tissue protection compared to conventional irradiation and no compromise on tumour control. The transient hypoxic state induced by the depletion of oxygen at high dose rates provides one possible explanation. However, studies have mostly focused on uniform fields of dose and there is a lack of investigation into the spatial and temporal variation of dose from proton pencil-beam scanning (PBS). A model of oxygen reaction and diffusion in tissue has been extended to simulate proton PBS delivery and its impact on oxygen levels. This provides a tool to predict oxygen effects from various PBS treatments, and explore potential delivery strategies. Here we present a number of case applications to demonstrate the use of this tool for FLASH-related investigations. We show that levels of oxygen depletion could vary significantly across a large parameter space for PBS treatments, and highlight the need for in silico models such as this to aid in the development and optimisation of FLASH radiotherapy.

Bibliometric analysis of research relating to radiation-induced lung injury [2001-2020

Radiotherapy is one of the common means of cancer treatment, especially in the treatment of lung cancer. However, radiation therapy can cause lung tissue radiation lung injury. The study of this disease can reduce its incidence and avoid the occurrence of radiation pulmonary fibrosis. In the past 20 years, the study of radiation-induced lung injury (RILI) has attracted more attention. This paper extracts the main text information of RILI-related literature from WOSCC database from 2001 to 2020, uses Citespace and VOSviewer for visual analysis, and presents the results. We found that in the past 20 years, there have been 4,665 articles on RILI, and the number of articles published reached a peak in 2017. The United States is the main leader in this research field, among which UNIV Texas MD Anderson Cancer Center has published many research results in this field. The most active author is Liao Zhongxing, and the most influential journal is Int J Radiat Oncol, which provides a platform for scholars in related fields to publish their articles. Current research focuses mainly on randomized controlled trials related to RILI, the relationship between dose-volume histogram analysis and RILI formation, the protection of normal lung tissue, the effect of stereoscopic radiotherapy on RILI and the pathogenesis of RILI. In the study of the formation mechanism of RILI, the main research directions include the apoptosis mechanism of epithelial and endothelial cells, cytokine cascade theory, immune mechanism regulation process, oxidative stress mechanism, etc.

FLASH radiotherapy: Considerations for multibeam and hypofractionation dose delivery

Current interest in ultra-high-dose-rate radiation therapy (FLASH) has arisen from the observed protection of various normal tissues exposed to high single doses in preclinical studies [1]. In this context ‘ultra-high-dose-rate’ is considered to be ≥40 Gy/s (c.f. a conventional (CONV) dose-rate ≥ 0.01 Gy/s) [2,3] (Fig. 1). While existing preclinical and clinical application of FLASH has used only a single beam, some proponents of FLASH have suggested the use of multiple beams to achieve the same conformal dose distributions obtainable using advanced radiotherapy techniques such as scanned beam proton therapy with conventional radiation dose-rates [4].

Long-Term Outcomes of NRG Oncology/RTOG 0529: A Phase 2 Evaluation of Dose-Painted Intensity Modulated Radiation Therapy in Combination With 5-Fluorouracil and Mitomycin-C for the Reduction of Acute Morbidity in Anal Canal Cancer

A multi-institutional phase 2 trial assessed long-term outcomes of dose-painted intensity modulated radiation therapy (IMRT) with 5-fluorouracil (5FU) and mitomycin-C (MMC) for anal canal cancer. T2-4N0-3M0 anal cancers received 5FU (1000 mg/m2/d, 96-hour infusion) and MMC (10 mg/m2 bolus) on days 1 and 29 of dose-painted IMRT prescribed as follows: T2N0=42 Gy elective nodal and 50.4 Gy anal tumor planning target volumes, 28 fractions; T3-4N0-3=45Gy elective nodal, 50.4 Gy ≤3 cm and 54 Gy >3cm metastatic nodal and 54 Gy anal tumor planning target volumes, 30 fractions. Local-regional failures, distant metastases, and colostomy failures were assessed using the cumulative incidence method, and disease-free survival, overall survival, and colostomy-free survival were assessed using the Kaplan-Meier method. Late effects were scored using National Cancer Institute-Common Terminology Criteria for Adverse Events v3. Of 52 patients, 54% were stage II, 25% were stage IIIA, and 21% were stage IIIB. Median follow-up was 7.9 years (min-max, 0.02-9.2 years). Local-regional failure, colostomy failures, distant metastases, overall survival, disease-free survival, and colostomy-free survival at 5 years are 16% (95% confidence interval [CI], 7%-27%), 10% (95% CI, 4%-20%), 16% (95% CI, 7%-27%), 76% (95% CI, 61%-86%), 70% (95% CI, 56%-81%), and 74% (95% CI, 59%-84%); and at 8 years they are 16% (95% CI, 7%-27%), 12% (95% CI, 5%-23%), 22% (95% CI, 12%-34%), 68% (95% CI, 53%-79%), 62% (95% CI, 47%-74%) and 66% (95% CI, 51%-77%), respectively. Eight patients experienced local-regional failure, with 5 patients having persistent disease at 12 weeks. No isolated nodal failures occurred in the microscopic elective nodal volumes. Six patients required colostomy-5 for local-regional salvage and 1 for a temporary ostomy for anorectal dysfunction. Rates of late adverse events included: 28 patients (55%) with grade 2, 8 patients (16%) with grade 3, 0 patients with grade 4, and 2 patients (4%) with grade 5 events (sinus bradycardia and myelodysplasia, possibly owing to chemotherapy). Only 11 patients reported grade 1 to 3 sexual dysfunction. Dose-painted IMRT with 5FU/MMC for the treatment of anal canal cancer yields comparable long-term efficacy as conventional radiation cohorts. Enhanced normal tissue protection lowered rates of grade 3 and higher late effects without compromising pelvic tumor control.

Doxorubicin-Loaded Platelets Conjugated with Anti-CD22 Mabs: A Novel Targeted Delivery System for B-Cell Lymphoma Treatment with Cardiac Avoidance

Objective: B-cell lymphoma accounts for approximately 85% of all adult non-Hodgkin's lymphoma cases. Chemotherapy remains the first-line treatment for B-cell lymphoma. However, cytotoxic drugs cause various adverse reactions in normal tissues and cells, thus limiting the applied dosage of chemotherapeutic agents and hampering their effects on tumor cells. Therefore, crucial requirements for effective cancer treatment include tumor-specific drug accumulation and the protection of normal tissues from cytotoxic effects.Methods: In this study, we developed a novel drug delivery system for lymphoma treatment: doxorubicin-loaded platelets that were conjugated with anti-CD22 monoclonal antibodies (mAbs) (DOX-platelet-CD22). Platelets are bio- and immune-compatible drug carriers that can prolong the circulation time of drugs. Anti-CD22 mAb-labeled platelets can precisely deliver doxorubicin to tumor cells. The conjugation of anti-CD22 mAbs and encapsulation of doxorubicin in platelets were confirmed using fluorescence microscopy. Scanning electron microscopy and platelet aggregation assay were used to analyze the potential changes in platelet morphology and function. The cytotoxicity of DOX-platelet-CD22 on myocardial cell was evaluated by CCK-8 assay and its anti-tumour effects were determined by CCK-8 assay, flow cytometry and DAPI staining. The possible mechanism was further investigated by reverse transcription-polymerase chain reaction (RT-PCR) and western blotting.Results: Anti-CD22 mAbs were successfully coupled to platelets loaded with doxorubicin with high drug loading and encapsulation efficiency. No significant changes in morphology and function were observed between native platelets and DOX-platelet-CD22. Further, doxorubicin in DOX-platelet-CD22 was released most rapidly in an acidic condition. In Raji cells treated with DOX-platelet-CD22, the intracellular DOX concentration significantly increased, the cell viability remarkably decreased and apoptosis was obviously induced. These results indicate that platelets conjugated anti-CD22 mAbs can improve the therapeutic effects of doxorubicin. Moreover, the viability of myocardial cells treated with DOX-platelet-CD22 were significantly increased compared with those treated with free doxorubicin, demonstrating that DOX-platelet-CD22 can reduce cardiotoxicity caused by doxorubicin. Compared with other groups, the expression levels of Bax, caspase-3, and caspase-9 were notably upregulated while the Bcl-2 expression was downregulated in Raji cells treated with DOX-platelet-CD22. These findings indicate that DOX-platelet-CD22 can improve the antitumor activity of doxorubicin through bcl-2/caspase-mediated apoptosis pathway.Conclusion: DOX-platelet-CD22 drug delivery system enhances the anti-tumor effects and reduces the adverse effects of doxorubicin, thus proposing a promising option for B-cell lymphoma treatment. DisclosuresNo relevant conflicts of interest to declare.

Technical Note: 4D robust optimization in small spot intensity-modulated proton therapy (IMPT) for distal esophageal carcinoma.

To compare the dosimetric performances of small-spot three-dimensional (3D) and four-dimensional (4D) robustly optimized intensity-modulated proton (IMPT) plans in the presence of uncertainties and interplay effect simultaneously for distal esophageal carcinoma. Thirteen (13) patients were selected and re-planned with small-spot ( ~2-6mm) 3D and 4D robust optimization in IMPT, respectively. The internal clinical target volumes (CTVhigh3d , CTVlow3d ) were used in 3D robust optimization. Different CTVs (CTVhigh4d , CTVlow4d ) were generated by subtracting an inner margin of the motion amplitudes in three cardinal directions from the internal CTVs and used in 4D robust optimization. All patients were prescribed the same dose to CTVs (50Gy[RBE] for CTVhigh3d /CTVhigh4d and 45Gy[RBE] for CTVlow3d /CTVlow4d ). Dose-volume histogram (DVH) indices were calculated to assess plan quality. Comprehensive plan robustness evaluations that consisted of 300 perturbed scenarios (10 different motion patterns to consider irregular motion (sampled from a Gaussian distribution) and 30 different uncertainties scenarios (sampled from a 4D uniform distribution) combined), were performed to quantify robustness to uncertainties and interplay effect simultaneously. Wilcoxon signed-rank test was used for statistical analysis. Compared to 3D robustly optimized plans, 4D robustly optimized plans had statistically improved target coverage and better sparing of lungs and heart (heart Dmean , P=0.001; heart V30Gy[RBE] , P=0.001) in the nominal scenario. 4D robustly optimized plans had better robustness in target dose coverage (CTVhigh4d V100% , P=0.002) and the protection of lungs and heart (heart Dmean , P=0.001; heart V30Gy[RBE] , P=0.001) when uncertainties and interplay effect were considered simultaneously. Even with small spots in IMPT, 4D robust optimization outperformed 3D robust optimization in terms of normal tissue protection and robustness to uncertainties and interplay effect simultaneously. Our findings support the use of 4D robust optimization to treat distal esophageal carcinoma with small spots in IMPT.

Discovery of RRx-001, a Myc and CD47 Downregulating Small Molecule with Tumor Targeted Cytotoxicity and Healthy Tissue Cytoprotective Properties in Clinical Development.

After extensive screening of aerospace compounds in an effort to source a novel anticancer agent, RRx-001, a first-in-class dinitroazetidine small molecule, was selected for advancement into preclinical and clinical development. RRx-001 is a minimally toxic small molecule with a distinct chemical structure and mechanism of action. The paradox of RRx-001 is that it mediates both antitumor cytotoxicity and normal tissue protection. The question of exactly how RRx-001 does this, and by means of what mechanism(s), depending on the route of delivery, intravenous or intratumoral, are explored. RRx-001 is currently in phase 2 and 3 clinical trials for the treatment of multiple solid tumor malignancies and as a supportive care drug.

Cage-like radiotherapy system for noncoplanar radiotherapy

The aim of this study was to design a cage-like radiotherapy system (CRTS) to further promote the clinical application of noncoplanar radiotherapy. The CRTS comprises two stands, two O-rings, several arc girders, an X-ray head, an imaging subsystem, and a treatment couch. The X-ray head rotates with O-rings around the patient’s body and slides along the arc girder. Compared with the C-arm linear accelerator (C-Linac), the clinically available spatial irradiation angle ranges (SIARs) of the CRTS for the head, chest, and abdomen were 33%, 63.6%, and 62.6% larger, respectively. Moreover, according to a preliminary planning comparison based on the dose distribution simulation method, the CRTS achieved much better protection of normal tissue than the C-Linac. Furthermore, the CRTS enabled accurate noncoplanar irradiation without movement of the body being irradiated, allowed automatic control of the movements of different parts without risk of collisions, and provided continuous radiation over an angle that considerably exceeded a full turn. These advantages make CRTS very promising for noncoplanar radiotherapy.

Pharmacological Ascorbate Promotes the Tumor Radiosensitization of Au@Pd Nanoparticles with Simultaneous Protection of Normal Tissues

Nanoradiosensitizers containing high-Z elements hold great potential in radiotherapy owing to the increasing energy deposition effect on X-ray irradiation. However, their potential clinical application is limited by the irradiation damage in nontarget tissues surrounding the tumor site, as well as the safety concerns for nanomaterials. Our findings demonstrate that pharmacological ascorbate displays a synergistic radiosensitizing effect in combination with nanoradiosensitizers. By engineering the Au@Pd core-shell nanostructures and precisely regulating their shell thickness, the obtained Au@Pd nanomaterials exhibit excellent ascorbate oxidase-like activity. Along with the accelerating generation of H2O2, pharmacological ascorbate significantly enhances the radiosensitizing effect of Au@Pd-PEG nanoparticles on both cancer cells and solid tumor. Interestingly, pharmacological ascorbate effectively protects normal tissues from X-ray-induced injury. The present work demonstrates that pharmacological ascorbate is an ideal agent for selectively improving the radiosensitizing effect of nanomaterials, providing a promising strategy to facilitate the clinical translation of nanoradiosensitizers.

Early Toxicities After High Dose Rate Proton Therapy in Cancer Treatments.

BackgroundThe conventional dose rate of radiation therapy is 0.01–0.05 Gy per second. According to preclinical studies, an increased dose rate may offer similar anti-tumoral effect while dramatically improving normal tissue protection. This study aims at evaluating the early toxicities for patients irradiated with high dose rate pulsed proton therapy (PT).Materials and MethodsA single institution retrospective chart review was performed for patients treated with high dose rate (10 Gy per second) pulsed proton therapy, from September 2016 to April 2020. This included both benign and malignant tumors with ≥3 months follow-up, evaluated for acute (≤2 months) and subacute (>2 months) toxicity after the completion of PT.ResultsThere were 127 patients identified, with a median follow up of 14.8 months (3–42.9 months). The median age was 55 years (1.6–89). The cohort most commonly consisted of benign disease (55.1%), cranial targets (95.1%), and were treated with surgery prior to PT (56.7%). There was a median total PT dose of 56 Gy (30–74 Gy), dose per fraction of 2 Gy (1–3 Gy), and CTV size of 47.6 ml (5.6–2,106.1 ml). Maximum acute grade ≥2 toxicity were observed in 49 (38.6%) patients, of which 8 (6.3%) experienced grade 3 toxicity. No acute grade 4 or 5 toxicity was observed. Maximum subacute grade 2, 3, and 4 toxicity were discovered in 25 (19.7%), 12 (9.4%), and 1 (0.8%) patient(s), respectively.ConclusionIn this cohort, utilizing high dose rate proton therapy (10 Gy per second) did not result in a major decrease in acute and subacute toxicity. Longer follow-up and comparative studies with conventional dose rate are required to evaluate whether this approach offers a toxicity benefit.

Quantitative Comparison of Knowledge-Based and Manual Intensity Modulated Radiation Therapy Planning for Nasopharyngeal Carcinoma.

Background and purposeTo validate the feasibility and efficiency of a fully automatic knowledge-based planning (KBP) method for nasopharyngeal carcinoma (NPC) cases, with special attention to the possible way that the success rate of auto-planning can be improved.Methods and materialsA knowledge-based dose volume histogram (DVH) prediction model was developed based on 99 formerly treated NPC patients, by means of which the optimization objectives and the corresponding priorities for intensity modulation radiation therapy (IMRT) planning were automatically generated for each head and neck organ at risk (OAR). The automatic KBP method was thus evaluated in 17 new NPC cases with comparison to manual plans (MP) and expert plans (EXP) in terms of target dose coverage, conformity index (CI), homogeneity index (HI), and normal tissue protection. To quantify the plan quality, a metric was applied for plan evaluation. The variation in the plan quality and time consumption among planners was also investigated.ResultsWith comparable target dose distributions, the KBP method achieved a significant dose reduction in critical organs such as the optic chiasm (p<0.001), optic nerve (p=0.021), and temporal lobe (p<0.001), but failed to spare the spinal cord (p<0.001) compared with MPs and EXPs. The overall plan quality evaluation gave mean scores of 144.59±11.48, 142.71±15.18, and 144.82±15.17, respectively, for KBPs, MPs, and EXPs (p=0.259). A total of 15 out of 17 KBPs (i.e., 88.24%) were approved by our physician as clinically acceptable.ConclusionThe automatic KBP method using the DVH prediction model provided a possible way to generate clinically acceptable plans in a short time for NPC patients.

Exploiting DNA repair pathways for tumor sensitization, mitigation of resistance, and normal tissue protection in radiotherapy.

More than half of cancer patients are treated with radiotherapy, which kills tumor cells by directly and indirectly inducing DNA damage, including cytotoxic DNA double-strand breaks (DSBs). Tumor cells respond to these threats by activating a complex signaling network termed the DNA damage response (DDR). The DDR arrests the cell cycle, upregulates DNA repair, and triggers apoptosis when damage is excessive. The DDR signaling and DNA repair pathways are fertile terrain for therapeutic intervention. This review highlights strategies to improve therapeutic gain by targeting DDR and DNA repair pathways to radiosensitize tumor cells, overcome intrinsic and acquired tumor radioresistance, and protect normal tissue. Many biological and environmental factors determine tumor and normal cell responses to ionizing radiation and genotoxic chemotherapeutics. These include cell type and cell cycle phase distribution; tissue/tumor microenvironment and oxygen levels; DNA damage load and quality; DNA repair capacity; and susceptibility to apoptosis or other active or passive cell death pathways. We provide an overview of radiobiological parameters associated with X-ray, proton, and carbon ion radiotherapy; DNA repair and DNA damage signaling pathways; and other factors that regulate tumor and normal cell responses to radiation. We then focus on recent studies exploiting DSB repair pathways to enhance radiotherapy therapeutic gain.

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.

Radiation intestinal injury in the era of precision radiotherapy

Radiation-induced intestinal injury is caused by radiotherapy of pelvic malignant tumors. The main symptoms include persistent blood in stool, tenesmus, perianal pain, and severe intestinal perforation. Compared to conventional radiotherapy, precision radiotherapy (PT) has a greater advantage in the protection of normal tissues by reducing radiation dose of intestinal tract. However, in the era of PT, we still need to face the balance between curative effect and side injury, especially for complex, recurrent or advanced tumors. In general, when making treatment decisions, we should give priority to radiotherapeutic efficacy and patient survival, then consider how to reduce radiotherapy injuries. Decision-making requires multidisciplinary team consultation, together with patients and their families. Due to the difficulty and complexity in the treatment of radiation-induced intestinal injury, its prevention is very important. PT is advised, including avoiding excessive intestinal doses, and controlling the irradiation area of the mucosa. Constipation prevention is important during and after radiotherapy, in order to avoid damage to the intestine. Diet education is necessary. Patient should not eat leftovers, cold dishes, pickles and other foods prone to cause intestinal infections. At present, there are still few researches in the field of radiation-induced intestinal injury. We expect that in the near future, there will be greater progress and breakthroughs in prevention, diagnosis and treatment of radiation-induced intestinal injury.

Abstract 6284: GC4419 protects again radiation induced oral mucositis, enhances the response of squamous cell carcinoma of the head and neck tumors to ionizing radiation, and enhances radioimmune therapy

Abstract 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 immune oncology agents such as Nivolumab (α-PD-1 agonist) 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 a concern with SAbR, particularly in the context of re-irradiation. Here we present pre-clinical evidence that GC4419 (Galera Therapeutics), a highly selective superoxide dismutase mimetic that recently received FDA Breakthrough therapy status following a Phase II, randomized, placebo controlled trial for reducing the duration and incidence of severe OM in patients undergoing chemoradiation therapy for locally advanced HNSCC (NCT02508389) also enhances the anti-tumor radiation response of HNSCC tumors to irradiation. We demonstrate in pre-clinical animal models that GC4419 protects the normal mucosa of the mouse tongue from radiation exposure. Utilizing clonogenic survival assays, GC4419 demonstrates single agent anti-cancer activity at physiologically achievable concentrations, while also enhancing the response of HNSCC lines to irradiation. In tumor growth delay (TGD) experiments utilizing the syngeneic HNSCC tumor model, AT-84, when GC4419 is delivered 30-60 minutes pre-irradiation 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. In tumor cure rate (TCD50) studies, GC4419 enhanced radiation exposure with a DEF of 1.25. Furthermore, when GC4419 is combined with radiation and an α-PD-1 inhibitor, a further enhancement of the radiation response is observed, indicating that GC4419 compliments radiotherapy combined with immune oncology. We will also report the results of ongoing studies examining the potency of GC4419 in protecting normal murine mucosa in the setting of reirradiation relevant to SAbR as a salvage therapy. This potentiation of the anti-tumor response with GC4419 is more pronounced at doses exceeding the threshold to be considered for intensity modulated radiation therapy (IMRT). The accompanying pre-clinical data strongly suggest that GC4419 should be combined with radio-immune therapy to not only enhance local tumor control, but that the potential for normal tissue protection with SAbR also creates the opportunity for dose escalation and may further improvement in treatment outcome. Citation Format: Brock James Sishc, Elizabeth Polsdofer, Debabrata Saha, Michael Story. GC4419 protects again radiation induced oral mucositis, enhances the response of squamous cell carcinoma of the head and neck tumors to ionizing radiation, and enhances radioimmune therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6284.