M2 isoform of pyruvate kinase rewires glucose metabolism during radiation therapy to promote an antioxidant response and glioblastoma radioresistance

BACKGROUND

Resistance to existing therapies is a significant challenge in improving outcomes for glioblastoma (GBM) patients. Metabolic plasticity has emerged as an important contributor to therapy resistance, including radiation therapy (RT). Here, we investigated how GBM cells reprogram their glucose metabolism in response to RT to promote radiation resistance.

METHODS

Effects of radiation on glucose metabolism of human GBM specimens were examined in vitro and in vivo with the use of metabolic and enzymatic assays, targeted metabolomics, and FDG-PET. Radiosensitization potential of interfering with M2 isoform of pyruvate kinase (PKM2) activity was tested via gliomasphere formation assays and in vivo human GBM models.

RESULTS

Here, we show that RT induces increased glucose utilization by GBM cells, and this is accompanied with translocation of GLUT3 transporters to the cell membrane. Irradiated GBM cells route glucose carbons through the pentose phosphate pathway (PPP) to harness the antioxidant power of the PPP and support survival after radiation. This response is regulated in part by the PKM2. Activators of PKM2 can antagonize the radiation-induced rewiring of glucose metabolism and radiosensitize GBM cells in vitro and in vivo.

CONCLUSIONS

These findings open the possibility that interventions designed to target cancer-specific regulators of metabolic plasticity, such as PKM2, rather than specific metabolic pathways, have the potential to improve the radiotherapeutic outcomes in GBM patients.

Adaptation of the Tumor Antigen Presentation Machinery to Ionizing Radiation

Ionizing radiation (IR) can reprogram proteasome structure and function in cells and tissues. In this article, we show that IR can promote immunoproteasome synthesis with important implications for Ag processing and presentation and tumor immunity. Irradiation of a murine fibrosarcoma (FSA) induced dose-dependent de novo biosynthesis of the immunoproteasome subunits LMP7, LMP2, and Mecl-1, in concert with other changes in the Ag-presentation machinery (APM) essential for CD8+ T cell-mediated immunity, including enhanced expression of MHC class I (MHC-I), β2-microglobulin, transporters associated with Ag processing molecules, and their key transcriptional activator NOD-like receptor family CARD domain containing 5. In contrast, in another less immunogenic, murine fibrosarcoma (NFSA), LMP7 transcripts and expression of components of the immunoproteasome and the APM were muted after IR, which affected MHC-I expression and CD8+ T lymphocyte infiltration into NFSA tumors in vivo. Introduction of LMP7 into NFSA largely corrected these deficiencies, enhancing MHC-I expression and in vivo tumor immunogenicity. The immune adaptation in response to IR mirrored many aspects of the response to IFN-γ in coordinating the transcriptional MHC-I program, albeit with notable differences. Further investigations showed divergent upstream pathways in that, unlike IFN-γ, IR failed to activate STAT-1 in either FSA or NFSA cells while heavily relying on NF-κB activation. The IR-induced shift toward immunoproteasome production within a tumor indicates that proteasomal reprogramming is part of an integrated and dynamic tumor-host response that is specific to the stressor and the tumor and therefore is of clinical relevance for radiation oncology.

Abstract 2325: IRF1 displays opposing tumor cell-intrinsic and -extrinsic roles in anti-tumor immunity

Interferons (IFNs), including IFN-α/β and IFN-γ, are multifaceted cytokines critical for antitumor immunity but contribute to T cell exhaustion through immune checkpoints. Recently, tumor cell expression of IRF1 was shown to enhance antitumor immunity, but a comprehensive evaluation of how IRF1 regulates IFN responses in the tumor and host has not been performed. Here, we show that Irf1-/- mice display enhanced tumor growth of WT and Irf1-/- tumors, as they fail to recruit sufficient NK cells and cytotoxic T cell (CTL). However, Irf1-/- tumors in wild-type mice displayed rapid immunogenic control, expansion of intratumoral lymphoid cells with enhanced effector programs and diminished exhaustion programs when compared to WT tumors. Mechanistically, IRF1 positively regulates the expression of distinct subsets of anti-tumor immunity suppression genes including the CD274/PD-L1, TRAIL, and IDO-1 checkpoints but not the IFN-inducible chemokines CXCL9-11. Surprisingly, control of Irf1-/- tumors required host IFN-α/β signaling but not IFN-γ signaling, while PD-L1 overexpression only weakly restored tumor growth. Thus, IRF1 selectively regulates the effects of IFNs on tumor cells and the tumor microenvironment and may be targeted to boost anti-tumor immunity.

Citation Format: Prabhat Kumar Purbey, Manash K. Paul, Keisuke S. Iwamoto, Allison Daly, Joowon Seo, Ameya S. Champhekar, Katie Campbell, Dorthe Schaue, William H. McBride, Steven M. Dubinett, Antoni Ribas, Stephen T. Smale, Philip O. Scumpia. IRF1 displays opposing tumor cell-intrinsic and -extrinsic roles in anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2325.

NRF2 Mediates Cellular Resistance to Transformation, Radiation, and Inflammation in Mice

Nuclear factor erythroid 2-related factor 2 (NRF2) is recognized as a master transcription factor that regulates expression of numerous detoxifying and antioxidant cytoprotective genes. In fact, models of NRF2 deficiency indicate roles not only in redox regulation, but also in metabolism, inflammatory/autoimmune disease, cancer, and radioresistancy. Since ionizing radiation (IR) generates reactive oxygen species (ROS), it is not surprising it activates NRF2 pathways. However, unexpectedly, activation is often delayed for many days after the initial ROS burst. Here, we demonstrate that, as assayed by γ-H2AX staining, rapid DNA double strand break (DSB) formation by IR in primary mouse Nrf2-/- MEFs was not affected by loss of NRF2, and neither was DSB repair to any great extent. In spite of this, basal and IR-induced transformation was greatly enhanced, suggesting that NRF2 protects against late IR-induced genomic instability, at least in murine MEFs. Another possible IR- and NRF2-related event that could be altered is inflammation and NRF2 deficiency increased IR-induced NF-κB pro-inflammatory responses mostly late after exposure. The proclivity of NRF2 to restrain inflammation is also reflected in the reprogramming of tumor antigen-specific lymphocyte responses in mice where Nrf2 k.o. switches Th2 responses to Th1 polarity. Delayed NRF2 responses to IR may be critical for the immune transition from prooxidant inflammation to antioxidant healing as well as in driving cellular radioresistance and survival. Targeting NRF2 to reprogram immunity could be of considerable therapeutic benefit in radiation and immunotherapy.

Classes of Drugs that Mitigate Radiation Syndromes

We previously reported several vignettes on types and classes of drugs able to mitigate acute and, in at least one case, late radiation syndromes in mice. Most of these had emerged from high throughput screening (HTS) of bioactive and chemical drug libraries using ionizing radiation-induced lymphocytic apoptosis as a readout. Here we report the full analysis of the HTS screen of libraries with 85,000 small molecule chemicals that identified 220 "hits." Most of these hits could be allocated by maximal common substructure analysis to one of 11 clusters each containing at least three active compounds. Further screening validated 23 compounds as being most active; 15 of these were cherry-picked based on drug availability and tested for their ability to mitigate acute hematopoietic radiation syndrome (H-ARS) in mice. Of these, five bore a 4-nitrophenylsulfonamide motif while 4 had a quinoline scaffold. All but two of the 15 significantly (p < 0.05) mitigated H-ARS in mice. We had previously reported that the lead 4-(nitrophenylsulfonyl)-4-phenylpiperazine compound (NPSP512), was active in mitigating multiple acute and late radiation syndromes in mice of more than one sex and strain. Unfortunately, the formulation of this drug had to be changed for regulatory reasons and we report here on the synthesis and testing of active analogs of NPSP512 (QS1 and 52A1) that have increased solubility in water and in vivo bioavailability while retaining mitigator activity against H-ARS (p < 0.0001) and other radiation syndromes. The lead quinoline 057 was also active in multiple murine models of radiation damage. Taken together, HTS of a total of 150,000 bioactive or chemical substances, combined with maximal common substructure analysis has resulted in the discovery of diverse groups of compounds that can mitigate H-ARS and at least some of which can mitigate multiple radiation syndromes when given starting 24 h after exposure. We discuss what is known about how these agents might work, and the importance of formulation and bioavailability.

Weak Magnetic Fields Enhance the Efficacy of Radiation Therapy

Purpose

The clinical efficacy of radiation therapy is mechanistically linked to ionization-induced free radicals that cause cell and tissue injury through direct and indirect mechanisms. Free radical reaction dynamics are influenced by many factors and can be manipulated by static weak magnetic fields (WMF) that perturb singlet-triplet state interconversion. Our study exploits this phenomenon to directly increase ionizing radiation (IR) dose absorption in tumors by combining WMF with radiation therapy as a new and effective method to improve treatment.

Methods and Materials

Coils were custom made to produce both homogeneous and gradient magnetic fields. The gradient coil enabled simultaneous in vitro assessment of free radical/reactive oxygen species reactivity across multiple field strengths from 6 to 66 G. First, increases in IR-induced free radical concentrations using oxidant-sensitive fluorescent dyes in a cell-free system were measured and verified. Next, human and murine cancer cell lines were evaluated in in vitro and in vivo models after exposure to clinically relevant doses of IR in combination with WMF.

Results

Cellular responses to IR and WMF were field strength and cell line dependent. WMF was able to enhance IR effects on reactive oxygen species formation, DNA double-strand break formation, cell death, and tumor growth.

Conclusions

We demonstrate that the external presence of a magnetic field enhances radiation-induced cancer cell injury and death in vitro and in vivo. The effect extends beyond the timeframe when free radicals are induced in the presence of radiation into the window when endogenous free radicals are produced and therefore extends the applicability of this novel adjunct to cancer therapy in the context of radiation treatment.

Identification of miRNA signatures associated with radiation-induced late lung injury in mice

Acute radiation exposure of the thorax can lead to late serious, and even life-threatening, pulmonary and cardiac damage. Sporadic in nature, late complications tend to be difficult to predict, which prompted this investigation into identifying non-invasive, tissue-specific biomarkers for the early detection of late radiation injury. Levels of circulating microRNA (miRNA) were measured in C3H and C57Bl/6 mice after whole thorax irradiation at doses yielding approximately 70% mortality in 120 or 180 days, respectively (LD70/120 or 180). Within the first two weeks after exposure, weight gain slowed compared to sham treated mice along with a temporary drop in white blood cell counts. 52% of C3H (33 of 64) and 72% of C57Bl/6 (46 of 64) irradiated mice died due to late radiation injury. Lung and heart damage, as assessed by computed tomography (CT) and histology at 150 (C3H mice) and 180 (C57Bl/6 mice) days, correlated well with the appearance of a local, miRNA signature in the lung and heart tissue of irradiated animals, consistent with inherent differences in the C3H and C57Bl/6 strains in their propensity for developing radiation-induced pneumonitis or fibrosis, respectively. Radiation-induced changes in the circulating miRNA profile were most prominent within the first 30 days after exposure and included miRNA known to regulate inflammation and fibrosis. Importantly, early changes in plasma miRNA expression predicted survival with reasonable accuracy (88-92%). The miRNA signature that predicted survival in C3H mice, including miR-34a-5p, -100-5p, and -150-5p, were associated with pro-inflammatory NF-κB-mediated signaling pathways, whereas the signature identified in C57Bl/6 mice (miR-34b-3p, -96-5p, and -802-5p) was associated with TGF-β/SMAD signaling. This study supports the hypothesis that plasma miRNA profiles could be used to identify individuals at high risk of organ-specific late radiation damage, with applications for radiation oncology clinical practice or in the context of a radiological incident.

Radiation-induced tissue damage and response

Normal tissue responses to ionizing radiation have been a major subject for study since the discovery of X-rays at the end of the 19th century. Shortly thereafter, time-dose relationships were established for some normal tissue endpoints that led to investigations into how the size of dose per fraction and the quality of radiation affected outcome. The assessment of the radiosensitivity of bone marrow stem cells using colony-forming assays by Till and McCulloch prompted the establishment of in situ clonogenic assays for other tissues that added to the radiobiology toolbox. These clonogenic and functional endpoints enabled mathematical modeling to be performed that elucidated how tissue structure, and in particular turnover time, impacted clinically relevant fractionated radiation schedules. More recently, lineage tracing technology, advanced imaging and single cell sequencing have shed further light on the behavior of cells within stem, and other, cellular compartments, both in homeostasis and after radiation damage. The discovery of heterogeneity within the stem cell compartment and plasticity in response to injury have added new dimensions to the consideration of radiation-induced tissue damage. Clinically, radiobiology of the 20th century garnered wisdom relevant to photon treatments delivered to a fairly wide field at around 2 Gy per fraction, 5 days per week, for 5-7 weeks. Recently, the scope of radiobiology has been extended by advances in technology, imaging and computing, as well as by the use of charged particles. These allow radiation to be delivered more precisely to tumors while minimizing the amount of normal tissue receiving high doses. One result has been an increase in the use of schedules with higher doses per fraction given in a shorter time frame (hypofractionation). We are unable to cover these new technologies in detail in this review, just as we must omit low-dose stochastic effects, and many aspects of dose, dose rate and radiation quality. We argue that structural diversity and plasticity within tissue compartments provides a general context for discussion of most radiation responses, while acknowledging many omissions. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Tumor Size Matters-Understanding Concomitant Tumor Immunity in the Context of Hypofractionated Radiotherapy with Immunotherapy

The purpose of this study was to determine the dynamic contributions of different immune cell subsets to primary and abscopal tumor regression after hypofractionated radiation therapy (hRT) and the impact of anti-PD-1 therapy. A bilateral syngeneic FSA1 fibrosarcoma model was used in immunocompetent C3H mice, with delayed inoculation to mimic primary and microscopic disease. The effect of tumor burden on intratumoral and splenic immune cell content was delineated as a prelude to hRT on macroscopic T1 tumors with 3 fractions of 8 Gy while microscopic T2 tumors were left untreated. This was performed with and without systemic anti-PD-1. Immune profiles within T1 and T2 tumors and in spleen changed drastically with tumor burden in untreated mice with infiltrating CD4+ content declining, while the proportion of CD4+ Tregs rose. Myeloid cell representation escalated in larger tumors, resulting in major decreases in the lymphoid:myeloid ratios. In general, activation of Tregs and myeloid-derived suppressor cells allow immunogenic tumors to grow, although their relative contributions change with time. The evidence suggests that primary T1 tumors self-regulate their immune content depending on their size and this can influence the lymphoid compartment of T2 tumors, especially with respect to Tregs. Tumor burden is a major confounding factor in immune analysis that has to be taken into consideration in experimental models and in the clinic. hRT caused complete local regression of primary tumors, which was accompanied by heavy infiltration of CD8+ T cells activated to express IFN-γ and PD-1; while certain myeloid populations diminished. In spite of this active infiltrate, primary hRT failed to generate the systemic conditions required to cause abscopal regression of unirradiated microscopic tumors unless PD-1 blockade, which on its own was ineffective, was added to the RT regimen. The combination further increased local and systemically activated CD8+ T cells, but few other changes. This study emphasizes the subtle interplay between the immune system and tumors as they grow and how difficult it is for local RT, which can generate a local immune response that may help with primary tumor regression, to overcome the systemic barriers that are generated so as to effect immune regression of even small abscopal lesions.

Time-Dependent Measurement of Nrf2-Regulated Antioxidant Response to Ionizing Radiation Toward Identifying Potential Protein Biomarkers for Acute Radiation Injury

PURPOSE

Potential acute exposure to ionizing radiation in nuclear or radiological accidents presents complex mass casualty scenarios that demand prompt triage and treatment decisions. Due to delayed symptoms and varied response of radiation victims, there is an urgent need to develop robust biomarkers to assess the extent of injuries in individuals.

EXPERIMENTAL DESIGN

The transcription factor Nrf2 is the master of redox homeostasis and there is transcriptional evidence of Nrf2-dependent antioxidant response activation upon radiation. The biomarker potential of Nrf2-dependent downstream target enzymes is investigated by measuring their response in bone marrow extracted from C57Bl/6 and C3H mice of both genders for up to 4 days following 6 Gy total body irradiation using targeted MS.

RESULTS

Overall, C57Bl/6 mice have a stronger proteomic response than C3H mice. In both strains, male mice have more occurrences of upregulation in antioxidant enzymes than female mice. For C57Bl/6 male mice, three proteins show elevated abundances after radiation exposure: catalase, superoxide dismutase 1, and heme oxygenase 1. Across both strains and genders, glutathione S-transferase Mu 1 is consistently decreased.

CONCLUSIONS AND CLINICAL RELEVANCE

This study provides the basis for future development of organ-specific protein biomarkers used in diagnostic blood test for radiation injury.

Baseline T cell dysfunction by single cell network profiling in metastatic breast cancer patients

Background

We previously reported the results of a multicentric prospective randomized trial of chemo-refractory metastatic breast cancer patients testing the efficacy of two doses of TGFβ blockade during radiotherapy. Despite a lack of objective responses to the combination, patients who received a higher dose of TGFβ blocking antibody fresolimumab had a better overall survival when compared to those assigned to lower dose (hazard ratio of 2.73, p = 0.039). They also demonstrated an improved peripheral blood mononuclear cell (PBMC) counts and increase in the CD8 central memory pool. We performed additional analysis on residual PBMC using single cell network profiling (SCNP).

Methods

The original trial randomized metastatic breast cancer patients to either 1 or 10 mg/kg of fresolimumab, every 3 weeks for 5 cycles, combined with radiotherapy to a metastatic site at week 1 and 7 (22.5 Gy given in 3 doses of 7.5 Gy). Trial immune monitoring results were previously reported. In 15 patients with available residual blood samples, additional functional studies were performed, and compared with data obtained in parallel from seven healthy female donors (HD): SCNP was applied to analyze T cell receptor (TCR) modulated signaling via CD3 and CD28 crosslinking and measurement of evoked phosphorylation of AKT and ERK in CD4 and CD8 T cell subsets defined by PD-1 expression.

Results

At baseline, a significantly higher level of expression (p < 0.05) of PD-L1 was identified in patient monocytes compared to HD. TCR modulation revealed dysfunction of circulating T-cells in patient baseline samples as compared to HD, and this was more pronounced in PD-1⁺ cells. Treatment with radiotherapy and fresolimumab did not resolve this dyfunctional signaling. However, in vitro PD-1 blockade enhanced TCR signaling in patient PD-1⁺ T cells and not in PD-1^- T cells or in PD-1⁺ T cells from HD.

Conclusions

Functional T cell analysis suggests that baseline T cell functionality is hampered in metastatic breast cancer patients, at least in part mediated by the PD-1 signaling pathway. These preliminary data support the rationale for investigating the possible beneficial effects of adding PD-1 blockade to improve responses to TGFβ blockade and radiotherapy.

Trial registration

NCT01401062.

Position of lipidation influences anticancer activity of Smac analogs

A small group of lipid-conjugated Smac mimetics was synthesized to probe the influence of the position of lipidation on overall anti-cancer activity. Specifically, new compounds were modified with lipid(s) in position 3 and C-terminus. Previously described position 2 lipidated analog M11 was also synthesized. The resulting mini library of Smacs lipidated in positions 2, 3 and C-terminus was screened extensively in vitro against a total number of 50 diverse cancer cell lines revealing that both the position of lipidation as well as the type of lipid, influence their anti-cancer activity and cancer type specificity. Moreover, when used in combination therapy with inhibitor of menin-MLL1 protein interactions, position 2 modified analog SM2 showed strong synergistic anti-cancer properties. The most promising lipid-conjugated analogs SM2 and SM6, showed favorable pharmacokinetics and in vivo activity while administered subcutaneously in the preclinical mouse model. Collectively, our findings suggest that lipid modification of Smacs may be a viable approach in the development of anti-cancer therapeutic leads.

Interleukin 32 expression in human melanoma

Background

Various proinflammatory cytokines can be detected within the melanoma tumor microenvironment. Interleukin 32 (IL32) is produced by T cells, NK cells and monocytes/macrophages, but also by a subset of melanoma cells. We sought to better understand the biology of IL32 in human melanoma.

Methods

We analyzed RNA sequencing data from 53 in-house established human melanoma cell lines and 479 melanoma tumors from The Cancer Genome Atlas dataset. We evaluated global gene expression patterns associated with IL32 expression. We also evaluated the impact of proinflammatory molecules TNFα and IFNγ on IL32 expression and dedifferentiation in melanoma cell lines in vitro. In order to study the transcriptional regulation of IL32 in these cell lines, we cloned up to 10.5 kb of the 5′ upstream region of the human IL32 gene into a luciferase reporter vector.

Results

A significant proportion of established human melanoma cell lines express IL32, with its expression being highly correlated with a dedifferentiation genetic signature (high AXL/low MITF). Non IL32-expressing differentiated melanoma cell lines exposed to TNFα or IFNγ can be induced to express the three predominant isoforms (α, β, γ) of IL32. Cis-acting elements within this 5′ upstream region of the human IL32 gene appear to govern both induced and constitutive gene expression. In the tumor microenvironment, IL32 expression is highly correlated with genes related to T cell infiltration, and also positively correlates with high AXL/low MITF dedifferentiated gene signature.

Conclusions

Expression of IL32 in human melanoma can be induced by TNFα or IFNγ and correlates with a treatment-resistant dedifferentiated genetic signature. Constitutive and induced expression are regulated, in part, by cis-acting sequences within the 5′ upstream region.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1862-y) contains supplementary material, which is available to authorized users.

The Aftermath of Surviving Acute Radiation Hematopoietic Syndrome and its Mitigation

Intensive research is underway to find new agents that can successfully mitigate the acute effects of radiation exposure. This is primarily in response to potential counterthreats of radiological terrorism and nuclear accidents but there is some hope that they might also be of value for cancer patients treated with radiation therapy. Research into mitigation countermeasures typically employs classic animal models of acute radiation syndromes (ARS) that develop after whole-body irradiation (WBI). While agents are available that successfully mitigate ARS when given after radiation exposure, their success raises questions as to whether they simply delay lethality or unmask potentially lethal radiation pathologies that may appear later in time. Life shortening is a well-known consequence of WBI in humans and experimental animals, but it is not often examined in a mitigation setting and its causes, other than cancer, are not well-defined. This is in large part because delayed effects of acute radiation exposure (DEARE) do not follow the strict time-dose phenomena associated with ARS and present as a diverse range of symptoms and pathologies with low mortality rates that can be evaluated only with the use of large cohorts of subjects, as in this study. Here, we describe chronically increased mortality rates up to 660 days in large numbers of mice given LD_70/30 doses of WBI. Systemic myeloid cell activation after WBI persists in some mice and is associated with late immunophenotypic changes and hematopoietic imbalance. Histopathological changes are largely of a chronic inflammatory nature and variable incidence, as are the clinical symptoms, including late diarrhea that correlates temporally with changes in the content of the microbiome. We also describe the acute and long-term consequences of mitigating hematopoietic ARS (H-ARS) lethality after LD_70/30 doses of WBI in multiple cohorts of mice treated uniformly with radiation mitigators that have a common 4-nitro-phenylsulfonamide (NPS) pharmacophore. Effective NPS mitigators dramatically decrease ARS mortality. There is slightly increased subacute mortality, but the rate of late mortalities is slowed, allowing some mice to live a normal life span, which is not the case for WBI controls. The study has broad relevance to radiation late effects and their potential mitigation and epitomizes the complex interaction between radiation-damaged tissues and immune homeostasis.

1-(4-nitrobenzenesulfonyl)-4-penylpiperazine increases the number of Peyer's patch-associated regenerating crypts in the small intestines after radiation injury

OBJECTIVE

Exposure to lethal doses of radiation has severe effects on normal tissues. Exposed individuals experience a plethora of symptoms in different organ systems including the gastrointestinal (GI) tract, summarized as Acute Radiation Syndrome (ARS). There are currently no approved drugs for mitigating GI-ARS. A recent high-throughput screen performed at the UCLA Center for Medical Countermeasures against Radiation identified compounds containing sulfonylpiperazine groups with radiation mitigation properties to the hematopoietic system and the gut. Among these 1-[(4-Nitrophenyl)sulfonyl]-4-phenylpiperazine (Compound #5) efficiently mitigated gastrointestinal ARS. However, the mechanism of action and target cells of this drug is still unknown. In this study we examined if Compound #5 affects gut-associated lymphoid tissue (GALT) with its subepithelial domes called Peyer's patches.

METHODS

C3H mice were irradiated with 0 or 12 Gy total body irradiation (TBI). A single dose of Compound #5 or solvent was administered subcutaneously 24 h later. 48 h after irradiation the mice were sacrificed, and the guts examined for changes in the number of visible Peyer's patches. In some experiments the mice received 4 daily injections of treatment and were sacrificed 96 h after TBI. For immune histochemistry gut tissues were fixed in formalin and embedded in paraffin blocks. Sections were stained with H&E, anti-Ki67 or a TUNEL assay to assess the number of regenerating crypts, mitotic and apoptotic indices. Cells isolated from Peyer's patches were subjected to immune profiling using flow cytometry.

RESULTS

Compound #5 significantly increased the number of visible Peyer's patches when compared to its control in non-irradiated and irradiated mice. Additionally, assessment of total cells per Peyer's patch isolated from these mice demonstrated an overall increase in the total number of Peyer's patch cells per mouse in Compound #5-treated mice. In non-irradiated animals the number of CD11b^high in Peyer's patches increased significantly. These Compound #5-driven increases did not coincide with a decrease in apoptosis or an increase in proliferation in the germinal centers inside Peyer's patches 24 h after drug treatment. A single dose of Compound #5 significantly increased the number of CD45⁺ cells after 12 Gy TBI. Importantly, 96 h after 12 Gy TBI Compound #5 induced a significant rise in the number of visible Peyer's patches and the number of Peyer's patch-associated regenerating crypts.

CONCLUSION

In summary, our study provides evidence that Compound #5 leads to an influx of immune cells into GALT, thereby supporting crypt regeneration preferentially in the proximity of Peyer's patches.

Defenses against Pro-oxidant Forces - Maintenance of Cellular and Genomic Integrity and Longevity

There has been enormous recent progress in understanding how human cells respond to oxidative stress, such as that caused by exposure to ionizing radiation. We have witnessed a significant deciphering of the events that underlie how antioxidant responses counter pro-oxidant damage to key biological targets in all cellular compartments, including the genome and mitochondria. These cytoprotective responses include: 1. The basal cellular repertoire of antioxidant capabilities and its supporting cast of facilitator enzymes; and 2. The inducible phase of the antioxidant response, notably that mediated by the Nrf2 transcription factor. There has also been frenetic progress in defining how reactive electrophilic species swamp existing protective mechanisms to augment DNA damage, events that are embodied in the cellular "DNA-damage response", including cell cycle checkpoint activation and DNA repair, which occur on a time scale of hours to days, as well as the implementation of cellular responses such as apoptosis, autophagy, senescence and reprograming that extend the time period of damage sensing and response into weeks, months and years. It has become apparent that, in addition to the initial oxidative insult, cells typically undergo further waves of secondary reactive oxygen/nitrogen species generation, DNA damage and signaling and that these may reemerge long after the initial events have subsided, probably being driven, at least in part, by persisting DNA damage. These reactive oxygen/nitrogen species are an integral part of the pathological consequences of radiation exposure and may persist across multiple cell divisions. Because of the pervasive nature of oxidative stress, a cell will manifest different responses in different subcellular compartments and to different levels of stress injury. Aspects of these compartmentalized responses can involve the same proteins (such as ATM, p53 and p21) but in different functional guises, e.g., in cytoplasmic versus nuclear responses or in early- versus late-phase events. Many of these responses involve gene activation and new protein synthesis as well as a plethora of post-translational modifications of both basal and induced response proteins. It is these responses that we focus on in this review.

[Inflammatory and immune biomarkers of radiation response]

In radiotherapy, the treatment is adapted to each individual to protect healthy tissues but delivers most of time a standard dose according to the tumor histology and site. The only biomarkers studied to individualize the treatment are the HPV status with radiation dose de-escalation strategies, and tumor hypoxia with dose escalation to hypoxic subvolumes using FMISO- or FAZA-PET imaging. In the last decades, evidence has grown about the contribution of the immune system to radiation tumor response. Many preclinical studies have identified some of the mechanisms involved. In this context, we have realised a systematic review to highlight potential inflammatory and immune biomarkers of radiotherapy response. Some are inside the tumor microenvironment, as lymphocyte infiltration or PD-L1 expression, others are circulating biomarkers, including different types of hematological cells, cytokines and chemokines.

Focal Irradiation and Systemic TGFβ Blockade in Metastatic Breast Cancer

Purpose: This study examined the feasibility, efficacy (abscopal effect), and immune effects of TGFβ blockade during radiotherapy in metastatic breast cancer patients.Experimental Design: Prospective randomized trial comparing two doses of TGFβ blocking antibody fresolimumab. Metastatic breast cancer patients with at least three distinct metastatic sites whose tumor had progressed after at least one line of therapy were randomized to receive 1 or 10 mg/kg of fresolimumab, every 3 weeks for five cycles, with focal radiotherapy to a metastatic site at week 1 (three doses of 7.5 Gy), that could be repeated to a second lesion at week 7. Research bloods were drawn at baseline, week 2, 5, and 15 to isolate PBMCs, plasma, and serum.Results: Twenty-three patients were randomized, median age 57 (range 35-77). Seven grade 3/4 adverse events occurred in 5 of 11 patients in the 1 mg/kg arm and in 2 of 12 patients in the 10 mg/kg arm, respectively. Response was limited to three stable disease. At a median follow up of 12 months, 20 of 23 patients are deceased. Patients receiving the 10 mg/kg had a significantly higher median overall survival than those receiving 1 mg/kg fresolimumab dose [hazard ratio: 2.73 with 95% confidence interval (CI), 1.02-7.30; P = 0.039]. The higher dose correlated with improved peripheral blood mononuclear cell counts and a striking boost in the CD8 central memory pool.Conclusions: TGFβ blockade during radiotherapy was feasible and well tolerated. Patients receiving the higher fresolimumab dose had a favorable systemic immune response and experienced longer median overall survival than the lower dose group. Clin Cancer Res; 24(11); 2493-504. ©2018 AACR.

4-(Nitrophenylsulfonyl)piperazines mitigate radiation damage to multiple tissues

Our ability to use ionizing radiation as an energy source, as a therapeutic agent, and, unfortunately, as a weapon, has evolved tremendously over the past 120 years, yet our tool box to handle the consequences of accidental and unwanted radiation exposure remains very limited. We have identified a novel group of small molecule compounds with a 4-nitrophenylsulfonamide (NPS) backbone in common that dramatically decrease mortality from the hematopoietic acute radiation syndrome (hARS). The group emerged from an in vitro high throughput screen (HTS) for inhibitors of radiation-induced apoptosis. The lead compound also mitigates against death after local abdominal irradiation and after local thoracic irradiation (LTI) in models of subacute radiation pneumonitis and late radiation fibrosis. Mitigation of hARS is through activation of radiation-induced CD11b⁺Ly6G⁺Ly6C⁺ immature myeloid cells. This is consistent with the notion that myeloerythroid-restricted progenitors protect against WBI-induced lethality and extends the possible involvement of the myeloid lineage in radiation effects. The lead compound was active if given to mice before or after WBI and had some anti-tumor action, suggesting that these compounds may find broader applications to cancer radiation therapy.

A perspective on the impact of radiation therapy on the immune rheostat

The advent and success of immune checkpoint inhibitors (ICIs) in cancer treatment has broadened the spectrum of tumours that might be considered "immunogenic" and susceptible to immunotherapeutic (IT) intervention. Not all cancer types are sensitive, and not all patients with any given type respond. Combination treatment of ICIs with an established cytotoxic modality such as radiation therapy (RT) is a logical step towards improvement. For one, RT alone has been shown to be genuinely immunomodulatory and secondly pre-clinical data generally support combined ICI-RT approaches. This new integrated therapy for cancer treatment holds much promise, although there is still a lot to be learned about how best to schedule the treatments, manage the toxicities and determine what biomarkers might predict response, as well as many other issues. This review examines how RT alters the immune rheostat and how it might best be positioned to fully exploit IT.

Abstract B86: Radiation and TGFβ blockade bring back memories in metastatic breast cancer patients

Purpose: This is a pilot study combining focal irradiation and systemic TGFβ blockade in metastatic breast cancer. The rationale for using TGFβ blockade was to limit tumor growth and further spread as well as to curb systemic immune suppression. Combining this systemic approach with hypofractionated radiation of selective tumor metastasis aimed at vaccinating each patient in vivo with her own, relevant tumor antigens by local radiation damage and allow T cells to reach their full potential while escaping TGFβ's grip.

Experimental Design: Serial blood samples from 22 patients undergoing treatment with 1mg or 10mg Fresolimumab and Radiation at the New York University School of Medicine (n=15) and at the David Geffen School of Medicine, University of California, Los Angeles (n=7) were immunophenotyped based on flow cytometric analysis of 21 surface antigens.

Results: There were significant differences between the 1mg and 10mg groups with respect to several immune parameters, especially the rise in circulating central memory CD8s at the higher dose level (relative increase at 2 weeks 10mg vs 1mg, p=0.027). Regulatory networks responded to the 10mg treatment regime with a consistent expansion in CD4 Tregs while mMDSCs declined (ratio Tregs/mMDSC rising in 10mg vs 1mg, p=0.026). An overall survival benefit was seen in the 10mg Fresolimumab arm (median OS 64.1 weeks versus 20 weeks, p=0.015 log rank test) albeit not striking. CART analysis allowed accurate survival classification based on 2-week changes in CD8/mMDSC ratios and plasma Tryptophan (ROC AUC 0.979).

Conclusion: Inhibiting TGFβ in the context of focal irradiation seems to create a favorable systemic immune landscape that drives T cell memory differentiation while limiting myeloid suppression.

Citation Format: Dörthe Schaue, Michael W. Xie, Josephine A. Ratikan, Ewa D. Micewicz, Lin Hwang, Kym F. Faull, James W. Sayre, Percy P. Lee, John A. Glaspy, Sandra Demaria, Silvia C. Formenti, William H. McBride. Radiation and TGFβ blockade bring back memories in metastatic breast cancer patients. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B86.

Plasticity of Myeloid Cells during Oral Barrier Wound Healing and the Development of Bisphosphonate-related Osteonecrosis of the Jaw

Injury to the barrier tissue initiates a rapid distribution of myeloid immune cells from bone marrow, which guide sound wound healing. Bisphosphonates, a widely used anti-bone resorptive drug with minimal systemic side effects, have been linked to an abnormal wound healing in the oral barrier tissue leading to, in some cases, osteonecrosis of the jaw (ONJ). Here we report that the development of ONJ may involve abnormal phenotypic plasticity of Ly6G+/Gr1+ myeloid cells in the oral barrier tissue undergoing tooth extraction wound healing. A bolus intravenous zoledronate (ZOL) injection to female C57Bl/6 mice followed by maxillary first molar extraction resulted in the development of ONJ-like lesion during the second week of wound healing. The multiplex assay of dissociated oral barrier cells exhibited the secretion of cytokines and chemokines, which was significantly modulated in ZOL mice. Tooth extraction-induced distribution of Ly6G+/Gr1+ cells in the oral barrier tissue increased in ZOL mice at week 2. ONJ-like lesion in ZOL mice contained Ly6G+/Gr1+ cells with abnormal size and morphology as well as different flow cytometric staining intensity. When anti-Ly6G (Gr1) antibody was intraperitoneally injected for 5 days during the second week of tooth extraction, CD11b+GR1(hi) cells in bone marrow and Ly6G+ cells in the oral barrier tissue were depleted, and the development of ONJ-like lesion was significantly attenuated. This study suggests that local modulation of myeloid cell plasticity in the oral barrier tissue may provide the basis for pathogenesis and thus therapeutic as well as preventive strategy of ONJ.

Abstract 4987: Role of the PD-1/PDL-1 pathway in resistance of patients with metastatic breast cancer to treatment with radiotherapy and TGFβ neutralization

Experimental data and clinical observations indicate that local radiation therapy (RT) converts the irradiated tumor into an in situ vaccine and improves responses to immunotherapy. Preclinical breast cancer models show that TGFb neutralization was required to achieve CD8+ T cell priming specific for multiple tumor antigens, and rejection of the irradiated tumor and non-irradiated metastases (Vanpouille-Box et al., Cancer Res 2015). Tumor response and survival were improved by PD-1 blockade. We explored the role of the PD-1/PDL-1 pathway in resistance to combined RT + TGFβ neutralizing antibody (fresolimumab) in metastatic breast cancer patients (pts).

22 pts were treated in a prospective trial at NYU and UCLA (NCT01401062, supported by DOD MTA BC100481). Pts were randomly assigned to 2 doses of fresolimumab (freso) (1mg/kg and 10 mg/kg, q 3 weeks). Image guided RT was delivered to one metastasis on weeks 2 and 7, 7.5 GyX3. 1 pt achieved objective response, with 28% reduction of tumor burden. The response lasted 11 months, anthracycline-induced acute myelogenous leukemia developed. Pts randomized to the higher freso dose had a hazard ratio of 2.17 (95% CI: 0.753-6.272) for risk of death at 1 year follow up. Currently, at a median follow up of 2 years, 20/22 pts have died.

To explore reasons for the limited response, peripheral blood mononuclear cells collected at baseline, 5 and 15 weeks into treatment, were analyzed. Responses to survivin, as a tumor antigen, were assessed using tetramers. Single cell network profiling (SCNP) was used to evaluate expression of 6 immunomodulatory receptors plus immune signaling in T cells collected from 7 healthy donors (HD) and 15 breast cancer pts (6 at 1mg/kg, 9 at 10mg/kg fresolimumab). In vitro activation of p-AKT and p-Erk was quantified following in vitro T cell receptor (TCR) modulation with anti-CD3/αnti-CD28.

6/12 HLA-A2.1+ pts had pre-existing survivin-specific CD8+ T cells, and 3 showed an increase over time. 2 pts who were negative generated modest responses after RT and 10 mg/kg freso. Prior to treatment, PDL-1 expression was increased in monocytes (p = 0.01) and CD4+ T cells (p = 0.037) compared to HD. Elevated PD-1 (p = 0.054) and OX-40 (p = 0.014) expression were identified on CD4+ T cells of pts. Upon TCR modulation, CD4+ and CD8+ T cells from pts showed reduced signaling through p-AKT and, to a lesser extent, p-Erk, compared to HD. Signaling was lower in PD-1+ vs PD-1- CD8+ and CD4+ T cells. Addition of anti-PD-1 pembrolizumab partially restored TCR-mediated signaling through p-AKT and p-Erk in PD-1+ but not PD-1- T cells.

Overall, data indicate impaired T cell signaling in PD-1+ T cells of metastatic breast cancer pts, which may explain the inability to respond to RT + TGFβ blockade. In vitro addition of anti-PD-1 improved T cell signaling through p-AKT and p-Erk. Together with the preclinical data, this supports adding anti-PD-1 to the combination of RT +TGFβ blockade.

Citation Format: Sandra Demaria, Claire Vanpouille-Box, Rachael E. Hawtin, Christie Fanton, Andy Conroy, Erik Evensen, Neha Dixit, Alan Barber, Dorthe Schaue, William H. McBride, Mary Helen Barcellos-Hoff, Silvia C. Formenti. Role of the PD-1/PDL-1 pathway in resistance of patients with metastatic breast cancer to treatment with radiotherapy and TGFβ neutralization. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4987.

Changes in Imaging and Cognition in Juvenile Rats After Whole-Brain Irradiation

Purpose

In pediatric cancer survivors treated with whole-brain irradiation (WBI), long-term cognitive deficits and morbidity develop that are poorly understood and for which there is no treatment. We describe similar cognitive defects in juvenile WBI rats and correlate them with alterations in diffusion tensor imaging and magnetic resonance spectroscopy (MRS) during brain development.

Methods and Materials

Juvenile Fischer rats received clinically relevant fractionated doses of WBI or a high-dose exposure. Diffusion tensor imaging and MRS were performed at the time of WBI and during the subacute (3-month) and late (6-month) phases, before behavioral testing.

Results

Fractional anisotropy in the splenium of the corpus callosum increased steadily over the study period, reflecting brain development. WBI did not alter the subacute response, but thereafter there was no further increase in fractional anisotropy, especially in the high-dose group. Similarly, the ratios of various MRS metabolites to creatine increased over the study period, and in general, the most significant changes after WBI were during the late phase and with the higher dose. The most dramatic changes observed were in glutamine-creatine ratios that failed to increase normally between 3 and 6 months after either radiation dose. WBI did not affect the ambulatory response to novel open field testing in the subacute phase, but locomotor habituation was impaired and anxiety-like behaviors increased. As for cognitive measures, the most dramatic impairments were in novel object recognition late after either dose of WBI.

Conclusions

The developing brains of juvenile rats given clinically relevant fractionated doses of WBI show few abnormalities in the subacute phase but marked late cognitive alterations that may be linked with perturbed MRS signals measured in the corpus callosum. This pathomimetic phenotype of clinically relevant cranial irradiation effects may be useful for modeling, mechanistic evaluations, and testing of mitigation approaches.

Bone morphogenetic protein 7 sensitizes O6-methylguanine methyltransferase expressing-glioblastoma stem cells to clinically relevant dose of temozolomide

Background

Temozolomide (TMZ) is an oral DNA-alkylating agent used for treating patients with glioblastoma. However, therapeutic benefits of TMZ can be compromised by the expression of O6-methylguanine methyltransferase (MGMT) in tumor tissue. Here we used MGMT-expressing glioblastoma stem cells (GSC) lines as a model for investigating the molecular mechanism underlying TMZ resistance, while aiming to explore a new treatment strategy designed to possibly overcome resistance to the clinically relevant dose of TMZ (35 μM).

Methods

MGMT-expressing GSC cultures are resistant to TMZ, and IC50 (half maximal inhibitory concentration) is estimated at around 500 μM. Clonogenic GSC surviving 500 μM TMZ (GSC-500 μM TMZ), were isolated. Molecular signatures were identified via comparative analysis of expression microarray against parental GSC (GSC-parental). The recombinant protein of top downregulated signature was used as a single agent or in combination with TMZ, for evaluating therapeutic effects of treatment of GSC.

Results

The molecular signatures characterized an activation of protective stress responses in GSC-500 μM TMZ, mainly including biotransformation/detoxification of xenobiotics, blocked endoplasmic reticulum stress-mediated apoptosis, epithelial-to-mesenchymal transition (EMT), and inhibited growth/differentiation. Bone morphogenetic protein 7 (BMP7) was identified as the top down-regulated gene in GSC-500 μM TMZ. Although augmenting BMP7 signaling in GSC by exogenous BMP7 treatment did not effectively stop GSC growth, it markedly sensitized both GSC-500 μM TMZ and GSC-parental to 35 μM TMZ treatment, leading to loss of self-renewal and migration capacity. BMP7 treatment induced senescence of GSC cultures and suppressed mRNA expression of CD133, MGMT, and ATP-binding cassette drug efflux transporters (ABCB1, ABCG2), as well as reconfigured transcriptional profiles in GSC by downregulating genes associated with EMT/migration/invasion, stemness, inflammation/immune response, and cell proliferation/tumorigenesis. BMP7 treatment significantly prolonged survival time of animals intracranially inoculated with GSC when compared to those untreated or treated with TMZ alone (p = 0.0017), whereas combination of two agents further extended animal survival compared to BMP7 alone (p = 0.0489).

Conclusions

These data support the view that reduced endogenous BMP7 expression/signaling in GSC may contribute to maintained stemness, EMT, and chemoresistant phenotype, suggesting that BMP7 treatment may provide a novel strategy in combination with TMZ for an effective treatment of glioblastoma exhibiting unmethylated MGMT.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0459-1) contains supplementary material, which is available to authorized users.

Lipid-conjugated Smac analogues

A small library of monovalent and bivalent Smac mimics was synthesized based on 2 types of monomers, with general structure NMeAla-Xaa-Pro-BHA (Xaa=Cys or Lys). Position 2 of the compounds was utilized to dimerize both types of monomers employing various bis-reactive linkers, as well as to modify selected compounds with lipids. The resulting library was screened in vitro against metastatic human breast cancer cell line MDA-MB-231, and the two most active compounds selected for in vivo studies. The most active lipid-conjugated analogue M11, showed in vivo activity while administered both subcutaneously and orally. Collectively, our findings suggest that lipidation may be a viable approach in the development of new Smac-based therapeutic leads.

Bridged Analogues for p53-Dependent Cancer Therapy Obtained by S-Alkylation

A small library of anticancer, cell-permeating, stapled peptides based on potent dual-specific antagonist of p53-MDM2/MDMX interactions, PMI-N8A, was synthesized, characterized and screened for anticancer activity against human colorectal cancer cell line, HCT-116. Employed synthetic modifications included: S-alkylation-based stapling, point mutations increasing hydrophobicity in key residues as well as improvement of cell-permeability by introduction of polycationic sequence(s) that were woven into the sequence of parental peptide. Selected analogue, ArB14Co, was also tested in vivo and exhibited potent anticancer bioactivity at the low dose (3.0 mg/kg). Collectively, our findings suggest that application of stapling in combination with rational design of polycationic short analogues may be a suitable approach in the development of physiologically active p53-MDM2/MDMX peptide inhibitors.

Radiation and inflammation

The immune system has the power to modulate the expression of radiation-induced normal and tumor tissue damage. On the one hand, it can contribute to cancer cure, and on the other hand, it can influence acute and late radiation side effects, which in many ways resemble acute and chronic inflammatory disease states. The way radiation-induced inflammation feeds into adaptive antigen-specific immune responses adds another dimension to the tumor-host cross talk during radiation therapy and to possible radiation-driven autoimmune responses. Understanding how radiation affects inflammation and immunity is therefore critical if we are to effectively manipulate these forces for benefit in radiation oncology treatments.

Opportunities and challenges of radiotherapy for treating cancer

The past 20 years have seen dramatic changes in the delivery of radiation therapy, but the impact of radiobiology on the clinic has been far less substantial. A major consideration in the use of radiotherapy has been on how best to exploit differences between the tumour and host tissue characteristics, which in the past has been achieved empirically by radiation-dose fractionation. New advances are uncovering some of the mechanistic processes that underlie this success story. In this Review, we focus on how these processes might be targeted to improve the outcome of radiotherapy at the individual patient level. This approach would seem a more productive avenue of treatment than simply trying to increase the radiation dose delivered to the tumour.

Radiosensitization of gliomas by intracellular generation of 5-fluorouracil potentiates prodrug activator gene therapy with a retroviral replicating vector

A tumor-selective non-lytic retroviral replicating vector (RRV), Toca 511, and an extended-release formulation of 5-fluorocytosine (5-FC), Toca FC, are currently being evaluated in clinical trials in patients with recurrent high-grade glioma (NCT01156584, NCT01470794 and NCT01985256). Tumor-selective propagation of this RRV enables highly efficient transduction of glioma cells with cytosine deaminase (CD), which serves as a prodrug activator for conversion of the anti-fungal prodrug 5-FC to the anti-cancer drug 5-fluorouracil (5-FU) directly within the infected cells. We investigated whether, in addition to its direct cytotoxic effects, 5-FU generated intracellularly by RRV-mediated CD/5-FC prodrug activator gene therapy could also act as a radiosensitizing agent. Efficient transduction by RRV and expression of CD were confirmed in the highly aggressive, radioresistant human glioblastoma cell line U87EGFRvIII and its parental cell line U87MG (U87). RRV-transduced cells showed significant radiosensitization even after transient exposure to 5-FC. This was confirmed both in vitro by a clonogenic colony survival assay and in vivo by bioluminescence imaging analysis. These results provide a convincing rationale for development of tumor-targeted radiosensitization strategies utilizing the tumor-selective replicative capability of RRV, and incorporation of radiation therapy into future clinical trials evaluating Toca 511 and Toca FC in brain tumor patients.

Abstract 633: Inhibition of TGFβ as a strategy to convert the irradiated tumor into in situ individualized vaccine

Accumulating data support the concept that ionizing radiation therapy (RT) has the potential to convert the tumor into an in situ, individualized vaccine; however this potential is rarely realized by RT alone. Transforming growth factor β (TGFβ) is an immunosuppressive cytokine that is activated by RT and inhibits the antigen-presenting function of dendritic cells and the differentiation of effector CD8+ T cells. Here we tested the hypothesis that TGFβ hinders the ability of RT to promote anti-tumor immunity. Development of tumor-specific immunity was examined in two pre-clinical models of metastatic breast cancer and analyzed in patients with metastatic breast cancer treated with local radiotherapy and the TGFβ-neutralizing antibody Fresolimumab.

Mice bearing established 4T1 and TSA mouse mammary carcinomas treated with pan-isoform specific TGFβ neutralizing antibody, 1D11, showed significantly improved control of the irradiated tumor and non-irradiated metastases, but no effect in the absence of RT. Notably, whole tumor transcriptional analysis demonstrated the selective upregulation of genes associated with immune-mediated rejection only in tumors of mice treated with RT+TGFβ blockade. Mice treated with RT+TGFβ blockade exhibited cross-priming of CD8+ T cells producing IFNγ in response to three tumor-specific antigens in tumor-draining lymph nodes, which was not evident for single modality treatment. Likewise, HLA-A2.1+ metastatic breast cancer patients (n=8) enrolled in NCT01401062 trial of local RT and fresolimumab were examined for CD8+ T cells specific for the tumor antigen survivin by tetramer staining. Three patients developed increased frequencies of survivin-specific CD8+ T cells in the blood during treatment, while two patients negative at baseline became positive.

Analysis of the immune infiltrate in mouse tumors showed a significant increase in CD4+ and CD8+ T cells only in mice treated with the combination of RT+TGFβ blockade. Depletion of CD4+ or CD8+ T cells abrogated the therapeutic benefit of RT+TGFβ blockade.

These data identify TGFβ as a master inhibitor of the ability of RT to generate an in situ tumor vaccine, which supports testing inhibition of TGFβ during radiotherapy to promote therapeutically effective anti-tumor immunity.

Supported by DOD BCRP Multi-Team Award BC100481.

Citation Format: Claire I. Vanpouille-Box, Julie M. Diamond, Jiri Zavadil, James Babb, Dörthe Schaue, Mary Helen Barcellos-Hoff, William H. McBride, Silvia C. Formenti, Sandra Demaria. Inhibition of TGFβ as a strategy to convert the irradiated tumor into in situ individualized vaccine. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 633. doi:10.1158/1538-7445.AM2014-633

Radiation biology in the context of changing patterns of radiotherapy

The last decade has witnessed a revolution in the clinical application of high-dose "ablative" radiation therapy. Initially this approach was limited to the treatment of brain tumors, but more recently we have seen its successful extension to tumors outside the brain, e.g., for small lung nodules. These advances have been driven largely by improvements in image-guided inverse treatment planning that allow the dose per fraction to the tumor to be increased over the conventional 2 Gy dose while keeping the late normal tissue complications at an acceptable level by dose limitation. Despite initial concerns about excessive late complications, as might be expected based on dose extrapolations using the linear-quadratic equation, these approaches have shown considerable clinical promise. Our knowledge of the biological consequences of high-doses of ionizing radiation in normal and cancerous tissues has lagged behind these clinical advances. Our intent here is to survey recent experimental findings from the perspective of better understanding the biological effects of high-dose therapy and whether they are truly different from conventional doses. We will also consider the implications of this knowledge for further refining and improving these approaches on the basis of underlying mechanisms.

Novel dimeric Smac analogs as prospective anticancer agents

A small library of monovalent Smac mimics with general structure NMeAla-Tle-(4R)-4-Benzyl-Pro-Xaa-cysteamide, was synthesized (Xaa=hydrophobic residue). The library was screened in vitro against human breast cancer cell lines MCF-7 and MDA-MB-231, and two most active compounds oligomerized via S-alkylation giving bivalent and trivalent derivatives. The most active bivalent analogue SMAC17-2X was tested in vivo and in physiological conditions (mouse model) it exerted a potent anticancer effect resulting in ∼23.4days of tumor growth delay at 7.5mg/kg dose. Collectively, our findings suggest that bivalent Smac analogs obtained via S-alkylation protocol may be a suitable platform for the development of new anticancer therapeutics.

Current status and recommendations for the future of research, teaching, and testing in the biological sciences of radiation oncology: report of the American Society for Radiation Oncology Cancer Biology/Radiation Biology Task Force, executive summary

In early 2011, a dialogue was initiated within the Board of Directors (BOD) of the American Society for Radiation Oncology (ASTRO) regarding the future of the basic sciences of the specialty, primarily focused on the current state and potential future direction of basic research within radiation oncology. After consideration of the complexity of the issues involved and the precise nature of the undertaking, in August 2011, the BOD empanelled a Cancer Biology/Radiation Biology Task Force (TF). The TF was charged with developing an accurate snapshot of the current state of basic (preclinical) research in radiation oncology from the perspective of relevance to the modern clinical practice of radiation oncology as well as the education of our trainees and attending physicians in the biological sciences. The TF was further charged with making suggestions as to critical areas of biological basic research investigation that might be most likely to maintain and build further the scientific foundation and vitality of radiation oncology as an independent and vibrant medical specialty. It was not within the scope of service of the TF to consider the quality of ongoing research efforts within the broader radiation oncology space, to presume to consider their future potential, or to discourage in any way the investigators committed to areas of interest other than those targeted. The TF charge specifically precluded consideration of research issues related to technology, physics, or clinical investigations. This document represents an Executive Summary of the Task Force report.

National Institutes of Health funding in radiation oncology: a snapshot

Currently, pay lines for National Institutes of Health (NIH) grants are at a historical low. In this climate of fierce competition, knowledge about the funding situation in a small field like radiation oncology becomes very important for career planning and recruitment of faculty. Unfortunately, these data cannot be easily extracted from the NIH's database because it does not discriminate between radiology and radiation oncology departments. At the start of fiscal year 2013 we extracted records for 952 individual grants, which were active at the time of analysis from the NIH database. Proposals originating from radiation oncology departments were identified manually. Descriptive statistics were generated using the JMP statistical software package. Our analysis identified 197 grants in radiation oncology. These proposals came from 134 individual investigators in 43 academic institutions. The majority of the grants (118) were awarded to principal investigators at the full professor level, and 122 principal investigators held a PhD degree. In 79% of the grants, the research topic fell into the field of biology, 13% in the field of medical physics. Only 7.6% of the proposals were clinical investigations. Our data suggest that the field of radiation oncology is underfunded by the NIH and that the current level of support does not match the relevance of radiation oncology for cancer patients or the potential of its academic work force.

Spinal cord tolerance to single-session uniform irradiation in pigs: implications for a dose-volume effect

BACKGROUND AND PURPOSE

This study was performed to test the hypothesis that spinal cord radiosensitivity is significantly modified by uniform versus laterally non-uniform dose distributions.

MATERIALS AND METHODS

A uniform dose distribution was delivered to a 4.5-7.0 cm length of cervical spinal cord in 22 mature Yucatan minipigs for comparison with a companion study in which a laterally non-uniform dose was given [1]. Pigs were allocated into four dose groups with mean maximum spinal cord doses of 17.5 ± 0.1 Gy (n=7), 19.5 ± 0.2 Gy (n=6), 22.0 ± 0.1 Gy (n=5), and 24.1 ± 0.2 Gy (n=4). The study endpoint was motor neurologic deficit determined by a change in gait within one year. Spinal cord sections were stained with a Luxol fast blue/periodic acid Schiff combination.

RESULTS

Dose-response curves for uniform versus non-uniform spinal cord irradiation were nearly identical with ED(50)'s (95% confidence interval) of 20.2 Gy (19.1-25.8) and 20.0 Gy (18.3-21.7), respectively. No neurologic change was observed for either dose distribution when the maximum spinal cord dose was ≤ 17.8 Gy while all animals experienced deficits at doses ≥ 21.8 Gy.

CONCLUSION

No dose-volume effect was observed in pigs for the dose distributions studied and the endpoint of motor neurologic deficit; however, partial spinal cord irradiation resulted in less debilitating neurologic morbidity and histopathology.

Cytokines in radiobiological responses: a review

Cytokines function in many roles that are highly relevant to radiation research. This review focuses on how cytokines are structurally organized, how they are induced by radiation, and how they orchestrate mesenchymal, epithelial and immune cell interactions in irradiated tissues. Pro-inflammatory cytokines are the major components of immediate early gene programs and as such can be rapidly activated after tissue irradiation. They converge with the effects of ionizing radiation in that both generate free radicals including reactive oxygen and nitrogen species (ROS/RNS). "Self" molecules secreted or released from cells after irradiation feed the same paradigm by signaling for ROS and cytokine production. As a result, multilayered feedback control circuits can be generated that perpetuate the radiation tissue damage response. The pro-inflammatory phase persists until such times as perceived challenges to host integrity are eliminated. Antioxidant, anti-inflammatory cytokines then act to restore homeostasis. The balance between pro-inflammatory and anti-inflammatory forces may shift to and fro for a long time after radiation exposure, creating waves as the host tries to deal with persisting pathogenesis. Individual cytokines function within socially interconnected groups to direct these integrated cellular responses. They hunt in packs and form complex cytokine networks that are nested within each other so as to form mutually reinforcing or antagonistic forces. This yin-yang balance appears to have redox as a fulcrum. Because of their social organization, cytokines appear to have a considerable degree of redundancy and it follows that an elevated level of a specific cytokine in a disease situation or after irradiation does not necessarily implicate it causally in pathogenesis. In spite of this, "driver" cytokines are emerging in pathogenic situations that can clearly be targeted for therapeutic benefit, including in radiation settings. Cytokines can greatly affect intrinsic cellular radiosensitivity, the incidence and type of radiation tissue complications, bystander effects, genomic instability and cancer. Minor and not so minor, polymorphisms in cytokine genes give considerable diversity within populations and are relevant to causation of disease. Therapeutic intervention is made difficult by such complexity; but the potential prize is great.

T lymphocytes and normal tissue responses to radiation

There is compelling evidence that lymphocytes are a recurring feature in radiation damaged normal tissues, but assessing their functional significance has proven difficult. Contradictory roles have been postulated in both tissue pathogenesis and protection, although these are not necessarily mutually exclusive as the immune system can display what may seem to be opposing faces at any one time. While the exact role of T lymphocytes in irradiated normal tissue responses may still be obscure, their accumulation after tissue damage suggests they may be critical targets for radiotherapeutic intervention and worthy of further study. This is accentuated by recent findings that pathologically damaged “self,” such as occurs after exposure to ionizing radiation, can generate danger signals with the ability to activate pathways similar to those that activate adoptive immunity to pathogens. In addition, the demonstration of T cell subsets with their recognition radars tuned to “self” moieties has revolutionized our ideas on how all immune responses are controlled and regulated. New concepts of autoimmunity have resulted based on the dissociation of immune functions between different subsets of immune cells. It is becoming axiomatic that the immune system has the power to regulate radiation-induced tissue damage, from failure of regeneration to fibrosis, to acute and chronic late effects, and even to carcinogenesis. Our understanding of the interplay between T lymphocytes and radiation-damaged tissue may still be rudimentary but this is a good time to re-examine their potential roles, their radiobiological and microenvironmental influences, and the possibilities for therapeutic manipulation. This review will discuss the yin and yang of T cell responses within the context of radiation exposures, how they might drive or protect against normal tissue side effects and what we may be able do about it.

Marrow-derived stromal cell delivery on fibrin microbeads can correct radiation-induced wound-healing deficits

Skin that is exposed to radiation has an impaired ability to heal wounds. This is especially true for whole body irradiation, where even moderate non-lethal doses can result in wound healing deficits. Our previous attempts to administer dermal cells locally to wounds to correct radiation-induced deficits were hampered by poor cell retention. Here we improve the outcome by using biodegradable fibrin microbeads (FMB) to isolate a population of mesenchymal marrow-derived stromal cells (MSC) from murine bone marrow by their specific binding to the fibrin matrix, culture them to high density in vitro and deliver them as MSC on FMB at the wound site. MSC are retained and proliferate locally and assist wounds gain tensile strength in whole body irradiated mice with or without additional skin only exposure. MSC-FMB were effective in 2 different mouse strains but were ineffective across a major histocompatability barrier. Remarkably, irradiated mice whose wounds were treated with MSC-FMB showed enhanced hair regrowth suggesting indirect effect on the correction of radiation-induced follicular damage. Further studies showed that additional wound healing benefit could be gained by administration of G-CSF and AMD3100. Collagen strips coated with haptides and MSCs were also highly effective in correcting radiation-induced wound healing deficits.

Regulatory T cells in radiotherapeutic responses

Radiation therapy (RT) can extend its influence in cancer therapy beyond what can be attributed to in-field cytotoxicity by modulating the immune system. While complex, these systemic effects can help tip the therapeutic balance in favor of treatment success or failure. Engagement of the immune system is generally through recognition of damage-associated molecules expressed or released as a result of tumor and normal tissue radiation damage. This system has evolved to discriminate pathological from physiological forms of cell death by signaling "danger." The multiple mechanisms that can be evoked include a shift toward a pro-inflammatory, pro-oxidant microenvironment that can promote maturation of dendritic cells and, in cancer treatment, the development of effector T cell responses to tumor-associated antigens. Control over these processes is exerted by regulatory T cells (Tregs), suppressor macrophages, and immunosuppressive cytokines that act in consort to maintain tolerance to self, limit tissue damage, and re-establish tissue homeostasis. Unfortunately, by the time RT for cancer is initiated the tumor-host relationship has already been sculpted in favor of tumor growth and against immune-mediated mechanisms for tumor regression. Reversing this situation is a major challenge. However, recent data show that removal of Tregs can tip the balance in favor of the generation of radiation-induced anti-tumor immunity. The clinical challenge is to do so without excessive depletion that might precipitate serious autoimmune reactions and increase the likelihood of normal tissue complications. The selective modulation of Treg biology to maintain immune tolerance and control of normal tissue damage, while releasing the "brakes" on anti-tumor immune responses, is a worthy aim with promise for enhancing the therapeutic benefit of RT for cancer.