Combination radiotherapy in an orthotopic mouse brain tumor model

Verification of 5-Aminolevurinic Radiodynamic Therapy Using a Murine Melanoma Brain Metastasis Model

Melanoma is a highly aggressive cancer with a propensity for brain metastases. These can be treated by radiotherapy, but the radiation-resistant nature of melanoma makes the prognosis for melanoma patients with brain metastases poor. Previously, we demonstrated that treatment of mice with subcutaneous melanoma with 5-aminolevurinic acid (5-ALA) and X-rays in combination, (“radiodynamic therapy (RDT)”), instead of with 5-ALA and laser beams (“photodynamic therapy”), improved tumor suppression in vivo. Here, using the B16-Luc melanoma brain metastasis model, we demonstrate that 5-ALA RDT effectively treats brain metastasis. We also studied how 5-ALA RDT damages cells in vitro using a B16 melanoma culture. Cell culture preincubated with 5-ALA alone increased intracellular photosensitizer protoporphyrin IX. On X-ray irradiation, the cells enhanced their ∙OH radical generation, which subsequently induced γH2AX, a marker of DNA double-strand breaks in their nuclei, but decreased mitochondrial membrane potential. After two days, the cell cycle was arrested. When 5-ALA RDT was applied to the brain melanoma metastasis model in vivo, suppression of tumor growth was indicated. Therapeutic efficacy in melanoma treatment has recently been improved by molecular targeted drugs and immune checkpoint inhibitors. Treatment with these drugs is now expected to be combined with 5-ALA RDT to further improve therapeutic efficacy.

Ly6G+ inflammatory cells enable the conversion of cancer cells to cancer stem cells in an irradiated glioblastoma model

Most glioblastomas frequently recur at sites of radiotherapy, but it is unclear if changes in the tumor microenvironment due to radiotherapy influence glioblastoma recurrence. Here, we demonstrate that radiation-induced senescent glioblastoma cells exhibit a senescence-associated secretory phenotype that functions through NFκB signaling to influence changes in the tumor microenvironment, such as recruitment of Ly6G⁺ inflammatory cells and vessel formation. In particular, Ly6G⁺ cells promote conversion of glioblastoma cells to glioblastoma stem cells (GSCs) through the NOS2-NO-ID4 regulatory axis. Specific inhibition of NFκB signaling in irradiated glioma cells using the IκBα super repressor prevents changes in the tumor microenvironment and dedifferentiation of glioblastoma cells. Treatment with Ly6G-neutralizing antibodies also reduces the number of GSCs and prolongs survival in tumor-bearing mice after radiotherapy. Clinically, a positive correlation exists between Ly6G⁺ cells and the NOS2-NO-ID4 regulatory axis in patients diagnosed with recurrent glioblastoma. Together, our results illustrate important roles for Ly6G⁺ inflammatory cells recruited by radiation-induced SASP in cancer cell dedifferentiation and tumor recurrence.

Injectable Hydrogels for Localized Chemotherapy and Radiotherapy in Brain Tumors

Overall survival of patients with newly diagnosed glioblastoma (GBM) remains dismal at 16 months with state-of-the-art treatment that includes surgical resection, radiation, and chemotherapy. GBM tumors are highly heterogeneous, and mechanisms for overcoming tumor resistance have not yet fully been elucidated. An injectable chitosan hydrogel capable of releasing chemotherapy (temozolomide [TMZ]) while retaining radioactive isotopes agents (iodine, [¹³¹I]) was used as a vehicle for localized radiation and chemotherapy, within the surgical cavity. Release from hydrogels loaded with TMZ or ¹³¹I was characterized in vitro and in vivo and their efficacy on tumor progression and survival on GBM tumors was also measured. The in vitro release of ¹³¹I was negligible over 42 days, whereas the TMZ was completely released over the first 48 h. ¹³¹I was completely retained in the tumor bed with negligible distribution in other tissues and that when delivered locally, the chemotherapy accumulated in the tumor at 10-fold higher concentrations than when delivered systemically. We found that the tumors were significantly decreased, and survival was improved in both treatment groups compared to the control group. Novel injectable chemo-radio-hydrogel implants may potentially improve the local control and overall outcome of aggressive, poor prognosis brain tumors.

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.

Preclinical models in radiation oncology

As the incidence of cancer continues to rise, the use of radiotherapy has emerged as a leading treatment modality. Preclinical models in radiation oncology are essential tools for cancer research and therapeutics. Various model systems have been used to test radiation therapy, including in vitro cell culture assays as well as in vivo ectopic and orthotopic xenograft models. This review aims to describe such models, their advantages and disadvantages, particularly as they have been employed in the discovery of molecular targets for tumor radiosensitization. Ultimately, any model system must be judged by its utility in developing more effective cancer therapies, which is in turn dependent on its ability to simulate the biology of tumors as they exist in situ. Although every model has its limitations, each has played a significant role in preclinical testing. Continued advances in preclinical models will allow for the identification and application of targets for radiation in the clinic.