Radiotherapy is involved in 50% of all cancer treatments and 40% of cancer cures. Most of these treatments are delivered in fractions of equal doses of radiation (Fractional Equivalent Dosing (FED)) in days to weeks. This treatment paradigm has remained unchanged in the past century and does not account for the development of radioresistance during treatment. Even if under-optimized, deviating from a century of successful therapy delivered in FED can be difficult. One way of exploring the infinite space of fraction size and scheduling to identify optimal fractionation schedules is through mathematical oncology simulations that allow for in silico evaluation. This review article explores the evidence that current fractionation promotes the development of radioresistance, summarizes mathematical solutions to account for radioresistance, both in the curative and non-curative setting, and reviews current clinical data investigating non-FED fractionated radiotherapy.

To explore whether glycosuria induces virulence of uropathogens, in turn facilitating urinary tract infection (UTI), we exposed group B Streptococcus (GBS) strain 10/84 to human urine plain or with 300 mg/dL glucose (mimicking moderate glycosuria). Exposure to moderate glycosuria significantly augmented bacterial growth, kidney bacterial burden in a mouse model of ascending UTI, and virulence characteristics and expression of corresponding genes. Exposure to glycosuria increased GBS adherence to human bladder epithelial cell line and expression of corresponding PI2a fimbrial gene, antimicrobial peptide LL-37 resistance and bacterial surface charge modulating dltA, and GBS hemolytic ability and expression of genes encoding pore-forming toxins.

The gold standard assay for radiation response is the clonogenic assay, a normalized colony formation assay (CFA) that can capture a broad range of radiation-induced cell death mechanisms. Traditionally, this assay relies on two-dimensional (2D) cell culture conditions with colonies counted by fixing and staining protocols. While some groups have converted these to three-dimensional (3D) conditions, these models still utilize 2D-like media compositions containing serum that are incompatible with stem-like cell models such as brain tumor initiating cells (BTICs) that form self-aggregating spheroids in neural stem cell media. BTICs are the preferred patient-derived model system for studying glioblastoma (GBM) as they tend to better retain molecular and phenotypic characteristics of the original tumor tissue. As such, it is important that preclinical radiation studies should be adapted to BTIC conditions. In this study, we describe a series of experimental approaches for performing CFA experiments with BTIC cultures. Our results indicate that serum-free clonogenic assays are feasible for combination drug and radiation testing and may better facilitate translatability of preclinical findings.

Ultra-high dose rate (FLASH-RT) and conventional proton beam radiotherapy to intracranial glioblastoma PDX were compared for tumor control and normal tissue toxicity via DNA and RNA damage response markers. Both conventional and FLASH radiotherapy yielded similar survival benefits; however, conventional radiotherapy resulted in greater normal tissue DNA and RNA damage.

Glioblastoma (GBM) is the most common and deadly primary brain tumor in adults. While in vitro patient-derived xenografts (PDX) lines are useful for studying GBM, they often exclude astrocytes and macrophages, which contribute significantly to tumor growth, invasion, and chemoradioresistance. Integrating these cells into tumor models is difficult due to their need for serum, which triggers GBM-PDX lines to lose their stem-like properties. The aim of this study was to develop a serum-free triculture model of GBM-PDX lines, normal human astrocytes (NHAs), and macrophages. Serum-free media alternatives were formulated for NHAs and identified for THP-1 macrophages, then combined with GBM PDX media to establish “PSX,” an experimental maintenance media. Cells were transitioned to serum-free media alternatives and functionally assessed through several parameters unique to each cell type. In addition to assessing GBM “stemness,” a custom 350-gene NanoString chip was used to assess differential gene expression in monocultured PDX cells versus PDX cells exposed to NHAs and macrophages. PSX maintained canonical function in astrocytes and macrophages while preserving the stem-like properties of GBM-PDX cells. Tri-culturing all three cells increased the expression of stemness-associated transcription factors and increased the expression of genes related to stemness and hypoxia in GBM cells. GBM PDX cells exposed to NHAs and macrophages in direct triculture exhibit increases in markers of stemness and hypoxia. These findings suggest that the serum-free triculture model presented herein may better recapitulate the tumoral heterogeneity of GBM in vitro, providing a novel model to utilize in current research.