Thrombopoietin mimetic stimulates bone marrow vascular and stromal niches to mitigate acute radiation syndrome.

Background: Acute radiation syndrome (ARS) manifests after exposure to high doses of radiation in the instances of radiologic accidents or incidents. Facilitating the regeneration of the bone marrow (BM), namely the hematopoietic stem and progenitor cells (HSPCs), is a key in mitigating ARS and multi-organ failure. JNJ-26366821, a PEGylated thrombopoietin mimetic (TPOm) peptide, has been shown as an effective medical countermeasure (MCM) to treat hematopoietic-ARS (H-ARS) in mice. However, the activity of TPOm on regulating BM vascular and stromal niches to support HSPC regeneration has not yet been elucidated. Methods: C57BL/6J mice (9-14 weeks old) received sublethal or lethal total body irradiation (TBI), a model for H-ARS, by 137Cs or X-rays. At 24 hours post-irradiation, mice were subcutaneously injected with a single dose of TPOm (0.3 mg/kg or 1.0 mg/kg) or PBS (vehicle). At homeostasis and on days 4, 7, 10, 14, 18, and 21 post-TBI with and without TPOm treatment, BM was harvested for histology, BM flow cytometry of HSPCs, endothelial (EC) and mesenchymal stromal cells (MSC), and whole-mount confocal microscopy. For survival, irradiated mice were monitored and weighed for 30 days. Lastly, BM triple negative cells (TNC; CD45-, TER-119-, CD31-) were sorted for single-cell RNA-sequencing to examine transcriptomics after TBI with or without TPOm treatment. Results: At homeostasis, TPOm expanded the number of circulating platelets and HSPCs, ECs, and MSCs in the BM. Following sublethal TBI, TPOm improved BM architecture and promoted recovery of HSPCs, ECs, and MSCs. Furthermore, TPOm elevated VEGF-C levels in normal and irradiated mice. Following lethal irradiation, mice improved body weight recovery and 30-day survival when treated with TPOm after 137Cs and X-ray exposure. Additionally, TPOm reduced vascular dilation and permeability. Finally, single-cell RNA-seq analysis indicated that TPOm increased the expression of collagens in MSCs to enhance their interaction with other progenitors in BM and upregulated the regeneration pathway in MSCs. Conclusions: TPOm interacts with BM vascular and stromal niches to locally support hematopoietic reconstitution and systemically improve survival in mice after TBI. Therefore, this work warrants the development of TPOm as a potent radiation MCM for the treatment of ARS.

Preclinical models of radiation-induced cardiac toxicity: Potential mechanisms and biomarkers.

Radiation therapy (RT) is an important modality in cancer treatment with >50% of cancer patients undergoing RT for curative or palliative intent. In patients with breast, lung, and esophageal cancer, as well as mediastinal malignancies, incidental RT dose to heart or vascular structures has been linked to the development of Radiation-Induced Heart Disease (RIHD) which manifests as ischemic heart disease, cardiomyopathy, cardiac dysfunction, and heart failure. Despite the remarkable progress in the delivery of radiotherapy treatment, off-target cardiac toxicities are unavoidable. One of the best-studied pathological consequences of incidental exposure of the heart to RT is collagen deposition and fibrosis, leading to the development of radiation-induced myocardial fibrosis (RIMF). However, the pathogenesis of RIMF is still largely unknown. Moreover, there are no available clinical approaches to reverse RIMF once it occurs and it continues to impair the quality of life of long-term cancer survivors. Hence, there is an increasing need for more clinically relevant preclinical models to elucidate the molecular and cellular mechanisms involved in the development of RIMF. This review offers an insight into the existing preclinical models to study RIHD and the suggested mechanisms of RIMF, as well as available multi-modality treatments and outcomes. Moreover, we summarize the valuable detection methods of RIHD/RIMF, and the clinical use of sensitive radiographic and circulating biomarkers.

Orthovoltage X-Rays Exhibit Increased Efficacy Compared with γ-Rays in Preclinical Irradiation.

Radionuclide irradiators (137Cs and 60Co) are commonly used in preclinical studies ranging from cancer therapy to stem cell biology. Amidst concerns of radiological terrorism, there are institutional initiatives to replace radionuclide sources with lower energy X-ray sources. As researchers transition, questions remain regarding whether the biological effects of γ-rays may be recapitulated with orthovoltage X-rays because different energies may induce divergent biological effects. We therefore sought to compare the effects of orthovoltage X-rays with 1-mm Cu or Thoraeus filtration and 137Cs γ-rays using mouse models of acute radiation syndrome. Following whole-body irradiation, 30-day overall survival was assessed, and the lethal dose to provoke 50% mortality within 30-days (LD50) was calculated by logistic regression. LD50 doses were 6.7 Gy, 7.4 Gy, and 8.1 Gy with 1-mm Cu-filtered X-rays, Thoraeus-filtered X-rays, and 137Cs γ-rays, respectively. Comparison of bone marrow, spleen, and intestinal tissue from mice irradiated with equivalent doses indicated that injury was most severe with 1-mm Cu-filtered X-rays, which resulted in the greatest reduction in bone marrow cellularity, hematopoietic stem and progenitor populations, intestinal crypts, and OLFM4+ intestinal stem cells. Thoraeus-filtered X-rays provoked an intermediate phenotype, with 137Cs showing the least damage. This study reveals a dichotomy between physical dose and biological effect as researchers transition to orthovoltage X-rays. With decreasing energy, there is increasing hematopoietic and intestinal injury, necessitating dose reduction to achieve comparable biological effects. SIGNIFICANCE: Understanding the significance of physical dose delivered using energetically different methods of radiation treatment will aid the transition from radionuclide γ-irradiators to orthovoltage X-irradiators.

A stromal Integrated Stress Response activates perivascular cancer-associated fibroblasts to drive angiogenesis and tumour progression.

Bidirectional signalling between the tumour and stroma shapes tumour aggressiveness and metastasis. ATF4 is a major effector of the Integrated Stress Response, a homeostatic mechanism that couples cell growth and survival to bioenergetic demands. Using conditional knockout ATF4 mice, we show that global, or fibroblast-specific loss of host ATF4, results in deficient vascularization and a pronounced growth delay of syngeneic melanoma and pancreatic tumours. Single-cell transcriptomics of tumours grown in Atf4Δ/Δ mice uncovered a reduction in activation markers in perivascular cancer-associated fibroblasts (CAFs). Atf4Δ/Δ fibroblasts displayed significant defects in collagen biosynthesis and deposition and a reduced ability to support angiogenesis. Mechanistically, ATF4 regulates the expression of the Col1a1 gene and levels of glycine and proline, the major amino acids of collagen. Analyses of human melanoma and pancreatic tumours revealed a strong correlation between ATF4 and collagen levels. Our findings establish stromal ATF4 as a key driver of CAF functionality, malignant progression and metastasis.

Rapid Mobilization of Medical Student Volunteers to Administer Vaccines During the COVID-19 Pandemic.

In December 2020, the first COVID-19 vaccines were approved for emergency use by the U.S. Food and Drug Administration, and vaccination efforts rapidly launched across the country. Concurrently, New York City experienced an increase in COVID-19 hospitalizations. This created an immediate need to inoculate frontline workers in a strained health system that lacked sufficient personnel to meet the demand. In response, New York State permitted medical students with appropriate clinical experience to administer vaccinations. Albert Einstein College of Medicine students rapidly stepped in to administer vaccines and serve as clinic navigators. Student leaders at Einstein collaborated with Montefiore Medical Center to rapidly implement a student vaccination initiative. Medical students underwent virtual and on-site training regarding COVID-19 vaccines and their administration. In January 2021, students began to staff vaccine clinics across the Bronx. By July 2021, 291 out of 830 eligible medical and Medical Scientist Training Program (MSTP) students (35.1%) had volunteered >2400 h. Of the 291 volunteers, 77 (26.5%) worked as vaccinators and administered approximately 2929 COVID-19 vaccines from January to May 2021. We demonstrate success using the concept of Entrustable Professional Activities (EPAs) in the context of training medical students in a specific clinical skill. Our framework resulted in the administration of approximately 2929 COVID-19 vaccines from January to May 2021. The authors believe that this framework can be implemented at peer institutions to alleviate the burden on hospital systems and outpatient clinics vaccinating their communities against COVID-19, or to meet future clinical needs.

Interleukin 6 Signaling Blockade Exacerbates Acute and Late Injury From Focal Intestinal Irradiation.

PURPOSE: To evaluate the acute changes in leukocyte populations after focal irradiation and to assess the role of interleukin 6 (IL-6) in acute and late radiation injury. METHODS AND MATERIALS: Mice were surgically implanted with a radiopaque marker on the surface of the small intestine. Mice were then imaged with cone beam computed tomography to locate the marker and irradiated with 18 Gy of 5 × 5 mm collimated x-rays onto the marked intestine using the Small Animal Radiation Research Platform. Intestinal sections and blood were harvested 1, 3.5, 7, and 14 days and 2 months postirradiation (post-IR) for histology and complete blood count, respectively. Immune cell populations were assessed by immunofluorescence in the acute phase. Collagen deposition was assessed 2 months post-IR. IL-6-/- intestinal sections were assessed post-IR for morphology, EdU, Ki67, and TUNEL in comparison to IL-6+/+ mice. Furthermore, a set of IL-6+/+ mice were treated with anti-IL-6R to assess the role of IL-6 in late intestinal injury. RESULTS: Intestinal radiation damage peaked 14 days post-IR, and fibrosis had developed by 60 days post-IR. There was a marked infiltration of immune cells into the irradiated intestine, with increased neutrophils, macrophages, B-cells, and CD4+ T cells maintained from 3.5 to 14 days post-IR. CD8+ T cells were decreased from days 7 to 14 post-IR. Systemically, leukocytes were increased in the peripheral blood 14 days post-IR with anemia being maintained from 14 days to 2 months. IL-6 was significantly increased in the serum post-IR. IL-6-/- mice demonstrated worsened intestinal injury acutely post-IR. Moreover, anti-IL-6R-treated mice presented with worsened intestinal fibrosis 2 months post-IR. CONCLUSIONS: Focal irradiation of the intestine produced a significant increase in immune cells in the irradiated area and systemic inflammation and anemia. Blockade of IL-6 signaling was found to exacerbate acute intestinal injury and late intestinal injury after focal irradiation.