Therapy model for advanced intracerebral B16 mouse melanoma using radiation therapy combined with immunotherapy

In vivo characterization of brain tumor biomechanics: magnetic resonance elastography in intracranial B16 melanoma and GL261 glioma mouse models

Introduction

Magnetic Resonance Elastography (MRE) allows the non-invasive quantification of tumor biomechanical properties in vivo. With increasing incidence of brain metastases, there is a notable absence of appropriate preclinical models to investigate their biomechanical characteristics. Therefore, the purpose of this work was to assess the biomechanical characteristics of B16 melanoma brain metastases (MBM) and compare it to murine GL261 glioblastoma (GBM) model using multifrequency MRE with tomoelastography post processing.

Methods

Intracranial B16 MBM (n = 6) and GL261 GBM (n = 7) mouse models were used. Magnetic Resonance Imaging (MRI) was performed at set intervals after tumor implantation: 5, 7, 12, 14 days for MBM and 13 and 22 days for GBM. The investigations were performed using a 7T preclinical MRI with 20 mm head coil. The protocol consisted of single-shot spin echo-planar multifrequency MRE with tomoelastography post processing, contrast-enhanced T1- and T2-weighted imaging and diffusion-weighted imaging (DWI) with quantification of apparent diffusion coefficient of water (ADC). Elastography quantified shear wave speed (SWS), magnitude of complex MR signal (T2/T2*) and loss angle (φ). Immunohistological investigations were performed to assess vascularization, blood-brain-barrier integrity and extent of glucosaminoglucan coverage.

Results

Volumetric analyses displayed rapid growth of both tumor entities and softer tissue properties than healthy brain (healthy: 5.17 ± 0.48, MBM: 3.83 ± 0.55, GBM: 3.7 ± 0.23, [m/s]). SWS of MBM remained unchanged throughout tumor progression with decreased T2/T2* intensity and increased ADC on days 12 and 14 (p<0.0001 for both). Conversely, GBM presented reduced φ values on day 22 (p=0.0237), with no significant alterations in ADC. Histological analysis revealed substantial vascularization and elevated glycosaminoglycan content in both tumor types compared to healthy contralateral brain.

Discussion

Our results indicate that while both, MBM and GBM, exhibited softer properties compared to healthy brain, imaging and histological analysis revealed different underlying microstructural causes: hemorrhages in MBM and increased vascularization and glycosaminoglycan content in GBM, further corroborated by DWI and T2/T2* contrast. These findings underscore the complementary nature of MRE and its potential to enhance our understanding of tumor characteristics when used alongside established techniques. This comprehensive approach could lead to improved clinical outcomes and a deeper understanding of brain tumor pathophysiology.

Regulatory T Cells in Autoimmunity and Cancer: A Duplicitous Lifestyle

Regulatory T (Treg) cells, possess a strategic role in the maintenance of immune homeostasis, and their function has been closely linked to development of diverse pathologies including autoimmunity and cancer. Comprehensive studies in various disease contexts revealed an increased plasticity as a characteristic of Treg cells. Although Treg cell plasticity comes in various flavors, the major categories enclose the loss of Foxp3 expression, which is the master regulator of Treg cell lineage, giving rise to “ex-Treg” cells and the “fragile” Treg cells in which FOXP3 expression is retained but accompanied by the engagement of an inflammatory program and attenuation of the suppressive activity. Treg cell plasticity possess a tremendous therapeutic potential either by inducing Treg cell de-stabilization to promote anti-tumor immunity, or re-enforcing Treg cell stability to attenuate chronic inflammation. Herein, we review the literature on the Treg cell plasticity with lessons learned in autoimmunity and cancer and discuss challenges and open questions with potential therapeutic implications.

Brain Metastasis Cell Lines Panel: A Public Resource of Organotropic Cell Lines

Spread of cancer to the brain remains an unmet clinical need in spite of the increasing number of cases among patients with lung, breast cancer, and melanoma most notably. Although research on brain metastasis was considered a minor aspect in the past due to its untreatable nature and invariable lethality, nowadays, limited but encouraging examples have questioned this statement, making it more attractive for basic and clinical researchers. Evidences of its own biological identity (i.e., specific microenvironment) and particular therapeutic requirements (i.e., presence of blood-brain barrier, blood-tumor barrier, molecular differences with the primary tumor) are thought to be critical aspects that must be functionally exploited using preclinical models. We present the coordinated effort of 19 laboratories to compile comprehensive information related to brain metastasis experimental models. Each laboratory has provided details on the cancer cell lines they have generated or characterized as being capable of forming metastatic colonies in the brain, as well as principle methodologies of brain metastasis research. The Brain Metastasis Cell Lines Panel (BrMPanel) represents the first of its class and includes information about the cell line, how tropism to the brain was established, and the behavior of each model in vivo. These and other aspects described are intended to assist investigators in choosing the most suitable cell line for research on brain metastasis. The main goal of this effort is to facilitate research on this unmet clinical need, to improve models through a collaborative environment, and to promote the exchange of information on these valuable resources.

Integration of stereotactic radiosurgery or whole brain radiation therapy with immunotherapy for treatment of brain metastases

The prognosis of brain metastases (BM) is traditionally poor. BM are mainly treated by local radiotherapy, including stereotactic radiosurgery (SRS) or whole brain radiation therapy (WBRT). Recently, immunotherapy (i.e., immune checkpoint inhibitors, ICI) has demonstrated a survival advantage in multiple malignancies commonly associated with BM. Individually, radiotherapy and ICI both treat BM efficiently; hence, their combination seems logical. In this review, we summarize the existing preclinical and clinical evidence that supports the applicability of radiotherapy as a sensitizer of ICI for BM. Further, we discuss the optimal timing at which radiotherapy and ICI should be administered and review the safety of the combination therapy. Data from a few clinical studies suggest that combining SRS or WBRT with ICI simultaneously rather than consecutively potentially enhances brain abscopal-like responses and survival. However, there is a lack of conclusion about the definition of "simultaneous"; the cumulative toxic effect of the combined therapies also requires further study. Thus, ongoing and planned prospective trials are needed to further explore and validate the effect, safety, and optimal timing of the combination of immunotherapy with radiotherapy for patients with BM.

Quality Assessment of Stereotactic Radiosurgery of a Melanoma Brain Metastases Model Using a Mouselike Phantom and the Small Animal Radiation Research Platform

PURPOSE

To establish a novel preclinical model for stereotactic radiosurgery (SRS) with combined mouselike phantom quality assurance in the setting of brain metastases.

METHODS AND MATERIALS

C57B6 mice underwent intracranial injection of B16-F10 melanoma cells. T1-weighted postcontrast magnetic resonance imaging (MRI) was performed on day 11 after injection. The MRI images were fused with cone beam computed tomography (CBCT) images using the Small Animal Radiation Research Platform (SARRP). The gross tumor volume (GTV) was contoured using the MRI. A single sagittal arc using the 3 × 3 mm² collimator was used to deliver 18 Gy prescribed to the isocenter. MRI was performed 7 days after radiation treatment, and the dose delivered to the mice was confirmed using 2 mouselike anthropomorphic phantoms: 1 in the axial orientation and the other in the sagittal orientation. The SARRP output was measured using a PTW Farmer type ionization chamber as per the American Association of Physicists in Medicine Task Group report 61, and the H-D curve was generated up to a maximum dose of 30 Gy. Irradiated films were analyzed based on optical density distribution and H-D curve.

RESULTS

The tumor volume on day 11, before intervention, was 2.48 ± 1.37 mm³ in the no-SRS arm versus 3.75 ± 1.19 mm³ in the SRS arm (NS). In the SRS arm, GTV maximum dose (Dmax) and mean dose were 2048 ± 207 and 1785 ± 14 cGy. Using the mouselike phantoms, the radiochromic film showed close precision in comparison with projected isodose lines, with a Dmax of 1903.4 and 1972.7 cGy, the axial and sagittal phantoms, respectively. Tumor volume 7 days after treatment was 7.34 ± 8.24 mm³ in the SRS arm and 60.20 ± 40.4 mm³ in the no-SRS arm (P=.009). No mice in the control group survived more than 22 days after implantation, with a median overall survival (mOS) of 19 days; mOS was not reached in the SRS group, with 1 death noted.

CONCLUSIONS

Single-fraction SRS of 18 Gy delivered in a single arc can be delivered accurately with MRI T1-weighted postcontrast-based treatment planning. The mouse like phantom allows for verification of dose delivery and accuracy.

The Role of Lymphocytes in Radiotherapy-Induced Adverse Late Effects in the Lung

Radiation-induced pneumonitis and fibrosis are dose-limiting side effects of thoracic irradiation. Thoracic irradiation triggers acute and chronic environmental lung changes that are shaped by the damage response of resident cells, by the resulting reaction of the immune system, and by repair processes. Although considerable progress has been made during the last decade in defining involved effector cells and soluble mediators, the network of pathophysiological events and the cellular cross talk linking acute tissue damage to chronic inflammation and fibrosis still require further definition. Infiltration of cells from the innate and adaptive immune systems is a common response of normal tissues to ionizing radiation. Herein, lymphocytes represent a versatile and wide-ranged group of cells of the immune system that can react under specific conditions in various ways and participate in modulating the lung environment by adopting pro-inflammatory, anti-inflammatory, or even pro- or anti-fibrotic phenotypes. The present review provides an overview on published data about the role of lymphocytes in radiation-induced lung disease and related damage-associated pulmonary diseases with a focus on T lymphocytes and B lymphocytes. We also discuss the suspected dual role of specific lymphocyte subsets during the pneumonitic phase and fibrotic phase that is shaped by the environmental conditions as well as the interaction and the intercellular cross talk between cells from the innate and adaptive immune systems and (damaged) resident epithelial cells and stromal cells (e.g., endothelial cells, mesenchymal stem cells, and fibroblasts). Finally, we highlight potential therapeutic targets suited to counteract pathological lymphocyte responses to prevent or treat radiation-induced lung disease.

Radiotherapy and immunotherapy: Can this combination change the prognosis of patients with melanoma brain metastases?

Brain metastases are a common occurrence in patients with melanoma. Prognosis is poor. Radiotherapy is the main local treatment for brain metastases. Recently, immunotherapy (i.e. immune checkpoints inhibitors) showed a significant impact on the prognosis of patients with metastatic melanoma, also in the setting of patients with brain metastases. Despite various possible treatments, survival of patients with melanoma brain metastases is still unsatisfactory; new treatment modalities or combination of therapies need to be explored. Being immunotherapy and radiotherapy alone both efficient in the treatment of melanoma brain metastases, the combination of these two therapies seems logical. Moreover radiotherapy can improve the efficacy of immunotherapy and the immune system plays a relevant role in the action of radiotherapy. Preclinical data support this combination. Clinical data are more contradictory. In this review, we will discuss available therapies for melanoma brain metastases, focusing on the preclinical and clinical available data supporting the possible synergism between radiotherapy and immunotherapy.

Increasing radiation dose improves immunotherapy outcome and prolongation of tumor dormancy in a subgroup of mice treated for advanced intracerebral melanoma

Previously, we developed a clinically relevant therapy model for advanced intracerebral B16 melanomas in syngeneic mice combining radiation and immunotherapies. Here, 7 days after B16-F10-luc2 melanoma cells were implanted intracerebrally (D7), syngeneic mice with bioluminescent tumors that had formed (1E10(5) to 7E10(6) photons per minute (>1E10(6), large; <1E10(6), small) were segregated into large-/small-balanced subgroups. Then, mice received either radiation therapy alone (RT) or radiation therapy plus immunotherapy (RT plus IT) (single injection of mAbPC61 to deplete regulatory T cells followed by multiple injections of irradiated granulocyte macrophage colony stimulating factor transfected B16-F10 cells) (RT plus IT). Radiation dose was varied (15, 18.75 or 22.5 Gy, given on D8), while immunotherapy was provided similarly to all mice. The data support the hypothesis that increasing radiation dose improves the outcome of immunotherapy in a subgroup of mice. The tumors that were greatly delayed in beginning their progressive growth were bioluminescent in vivo-some for many months, indicating prolonged tumor "dormancy," in some cases presaging long-term cures. Mice bearing such tumors had far more likely received radiation plus immunotherapy, rather than RT alone. Radiotherapy is a very important adjunct to immunotherapy; the greater the tumor debulking by RT, the greater should be the benefit to tumor immunotherapy.