Development and Validation of a Small Animal Immobilizer and Positioning System for the Study of Delivery of Intracranial and Extracranial Radiotherapy Using the Gamma Knife System

Technical note: Multi-MATE, a high-throughput platform for automated image-guided small-animal irradiation

BACKGROUND

Small animal irradiation is essential to study the radiation response of new interventions before or parallel to human therapy. Image-guided radiotherapy (IGRT) and intensity-modulated radiotherapy (IMRT) are recently adopted in small animal irradiation to more closely mimic human treatments. However, sophisticated techniques require exceedingly high time, resources, and expertize that are often impractical.

PURPOSE

We propose a high throughput and high precision platform named Multiple Mouse Automated Treatment Environment (Multi-MATE) to streamline image-guided small animal irradiation.

METHODS

Multi-MATE consists of six parallel and hexagonally arranged channels, each equipped with a transfer railing, a 3D-printed immobilization pod, and an electromagnetic control unit, computer-controlled via an Arduino interface. The mouse immobilization pods are transferred along the railings between the home position outside the radiation field and the imaging/irradiation position at the irradiator isocenter. All six immobilization pods are transferred to the isocenter in the proposed workflow for parallel CBCT scans and treatment planning. The immobilization pods are then sequentially transported to the imaging/therapy position for dose delivery. The positioning reproducibility of Multi-MATE are evaluated using CBCT and radiochromic films.

RESULTS

While parallelizing and automating the image-guided small animal radiation delivery, Multi-MATE achieved the average pod position reproducibility of 0.17 ± 0.04 mm in the superior-inferior direction, 0.20 ± 0.04 mm in the left-right direction, and 0.12 ± 0.02mm in the anterior-posterior direction in repeated CBCT tests. Additionally, in image-guided dose delivery tasks, Multi-MATE demonstrated the positioning reproducibility of 0.17 ± 0.06 mm in the superior-inferior direction, 0.19 ± 0.06 mm in the left-right direction.

CONCLUSIONS

We designed, fabricated, and tested a novel automated irradiation platform, Multi-MATE to accelerate and automate image-guided small animal irradiation. The automated platform minimizes human operation and achieves high setup reproducibility and image-guided dose delivery accuracy. Multi-MATE thus removes a major barrier to implementing high-precision preclinical radiation research.

Comparison of 3 Positioning Techniques for Fractionated High-precision Radiotherapy in an Orthotopic Mouse Model of Pancreatic Cancer

Small-animal irradiators are widely used in oncologic research, and many experiments use mice to mimic radiation treatments in humans. To improve fractionated high-precision irradiation in mice with orthotopic pancreatic tumors, we evaluated 3 positioning methods: no positioning aid, skin marker, and immobilization devices (immobilization masks). We retrospectively evaluated the translation vector needed for optimal tumor alignment (by shifting the mouse in left-right, in cranio-caudal, and in anterior-posterior direction) on cone-beam CT from our small-animal radiotherapy system. Of the 3 methods, the skin marker method yielded the smallest mean translation vector (3.8 mm) and was the most precise method overall for most of the mice. In addition, the skin marker method required supplemental rotation (that is, roll, pitch, and yaw) for optimal tumor alignment only half as often as positioning without a positioning aid. Finally, the skin marker method had the highest scores for the quality of the fusion results. Overall, we preferred the skin marker method over the other 2 positioning methods with regard to optimal treatment planning and radiotherapy in an orthotopic mouse model of pancreatic cancer.

MCT4 regulates de novo pyrimidine biosynthesis in GBM in a lactate-independent manner

Background

Necrotic foci with surrounding hypoxic cellular pseudopalisades and microvascular hyperplasia are histological features found in glioblastoma (GBM). We have previously shown that monocarboxylate transporter 4 (MCT4) is highly expressed in necrotic/hypoxic regions in GBM and that increased levels of MCT4 are associated with worse clinical outcomes.

Methods

A combined transcriptomics and metabolomics analysis was performed to study the effects of MCT4 depletion in hypoxic GBM neurospheres. Stable and inducible MCT4-depletion systems were used to evaluate the effects of and underlining mechanisms associated with MCT4 depletion in vitro and in vivo, alone and in combination with radiation.

Results

This study establishes that conditional depletion of MCT4 profoundly impairs self-renewal and reduces the frequency and tumorigenicity of aggressive, therapy-resistant, glioblastoma stem cells. Mechanistically, we observed that MCT4 depletion induces anaplerotic glutaminolysis and abrogates de novo pyrimidine biosynthesis. The latter results in a dramatic increase in DNA damage and apoptotic cell death, phenotypes that were readily rescued by pyrimidine nucleosides supplementation. Consequently, we found that MCT4 depletion promoted a significant prolongation of survival of animals bearing established orthotopic xenografts, an effect that was extended by adjuvant treatment with focused radiation.

Conclusions

Our findings establish a novel role for MCT4 as a critical regulator of cellular deoxyribonucleotide levels and provide a new therapeutic direction related to MCT4 depletion in GBM.

The Ig superfamily protein PTGFRN coordinates survival signaling in glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most malignant primary brain tumor with a median survival of approximately 14 months. Despite aggressive treatment of surgical resection, chemotherapy and radiation therapy, only 3-5% of GBM patients survive more than 3 years. Contributing to this poor therapeutic response, it is believed that GBM contains both intrinsic and acquired mechanisms of resistance, including resistance to radiation therapy. In order to define novel mediators of radiation resistance, we conducted a functional knockdown screen, and identified the immunoglobulin superfamily protein, PTGFRN. In GBM, PTGFRN is found to be overexpressed and to correlate with poor survival. Reducing PTGFRN expression radiosensitizes GBM cells and potently decreases the rate of cell proliferation and tumor growth. Further, PTGFRN inhibition results in significant reduction of PI3K p110β and phosphorylated AKT, due to instability of p110β. Additionally, PTGFRN inhibition decreases nuclear p110β leading to decreased DNA damage sensing and DNA damage repair. Therefore overexpression of PTGFRN in glioblastoma promotes AKT-driven survival signaling and tumor growth, as well as increased DNA repair signaling. These findings suggest PTGFRN is a potential signaling hub for aggressiveness in GBM.