The Role of TGF-ß3 in Radiation Response.

Transforming growth factor-beta 3 (TGF-ß3) is a ubiquitously expressed multifunctional cytokine involved in a range of physiological and pathological conditions, including embryogenesis, cell cycle regulation, immunoregulation, and fibrogenesis. The cytotoxic effects of ionizing radiation are employed in cancer radiotherapy, but its actions also influence cellular signaling pathways, including that of TGF-ß3. Furthermore, the cell cycle regulating and anti-fibrotic effects of TGF-ß3 have identified it as a potential mitigator of radiation- and chemotherapy-induced toxicity in healthy tissue. This review discusses the radiobiology of TGF-ß3, its induction in tissue by ionizing radiation, and its potential radioprotective and anti-fibrotic effects.

Low-Dose-Rate Radiation-Induced Secretion of TGF-ß3 Together with an Activator in Small Extracellular Vesicles Modifies Low-Dose Hyper-Radiosensitivity through ALK1 Binding.

Hyper-radiosensitivity (HRS) is the increased sensitivity to low doses of ionizing radiation observed in most cell lines. We previously demonstrated that HRS is permanently abolished in cells irradiated at a low dose rate (LDR), in a mechanism dependent on transforming growth factor ß3 (TGF-ß3). In this study, we aimed to elucidate the activation and receptor binding of TGF-ß3 in this mechanism. T-47D cells were pretreated with inhibitors of potential receptors and activators of TGF-ß3, along with addition of small extracellular vesicles (sEVs) from LDR primed cells, before their radiosensitivity was assessed by the clonogenic assay. The protein content of sEVs from LDR primed cells was analyzed with mass spectrometry. Our results show that sEVs contain TGF-ß3 regardless of priming status, but only sEVs from LDR primed cells remove HRS in reporter cells. Inhibition of the matrix metalloproteinase (MMP) family prevents removal of HRS, suggesting an MMP-dependent activation of TGF-ß3 in the LDR primed cells. We demonstrate a functional interaction between TGF-ß3 and activin receptor like kinase 1 (ALK1) by showing that TGF-ß3 removes HRS through ALK1 binding, independent of ALK5 and TGF-ßRII. These results are an important contribution to a more comprehensive understanding of the mechanism behind TGF-ß3 mediated removal of HRS.

Synthesis, radiosynthesis, and positron emission tomography neuroimaging using 5-[18 F]fluoro-L-amino suberate.

System xc- (Sxc -) has emerged as a new biological target for PET studies to detect oxidative and excitotoxic stress. Notably, applications have, thus far, been limited to tumour imaging although Sxc- ) may play a major role in neurodegeneration. The synthesis procedures of tosylate precursor and its translation to Sxc - PET tracer 5[18F]fluoro-L-amino suberate by manual and automated radiosyntheses are described. A brain-PET study has been conducted to evaluate the tracer uptake into brain in healthy mice.

Ultra-early changes in vascular parameters from dynamic contrast enhanced MRI of breast cancer xenografts following systemic therapy with doxorubicin and liver X receptor agonist.

BACKGROUND: Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) may be used to depict tumour vascular structure and for therapy response assessment in various tumour sites. The purpose of the current work is to examine whether ultra-early changes in tumour physiology following cytotoxic treatment with doxorubicin and liver X receptor (LXR) agonist GW3965 are detectable by DCE-MRI. METHODS: 36 female, athymic nude foxn1nu mice with bilaterally implanted breast cancer xenografts (17 with ER-positive HBCx34, 19 with triple-negative HBCx39) were randomised in the following treatment groups; control, GW3965 (40 mg/kg p.o.), doxorubicin (8 mg/kg i.v.) and a combination therapy of GW3965 and doxorubicin. DCE-MRI (3D FLASH on a 7 T preclinical scanner) was performed at baseline and one and six days after onset of treatment. Wash-in (30 s p.i.) and wash-out (300 s p.i.) enhancement were quantified from dynamic uptake curves, before voxel-by-voxel fitting to the pharmacokinetic Tofts model and generation of maps for the resulting parameters Ktrans, νe and νB. Treatment effect was evaluated by univariate repeated measures mixed-effects maximum likelihood regression models applied to median tumour data. RESULTS: We found no effects of any treatment 24 h post treatment. After 6 days, doxorubicin given as both mono- and combination therapy gave significant increases of ~ 30% in wash-in enhancement (p < 0.011) and Ktrans (p < 0.017), and 40-50% in νB (p < 0.024) for HBCx34, but not for HBCx39. No effects of GW3965 were observed at any time (p > 0.1). CONCLUSIONS: Twenty-four h after onset of treatment was too early to evaluate treatment effects by DCE-MRI. Early enhancement and Ktrans were approximately equally sensitive metrics to capture treatment effects six days pt. Pharmacokinetic modelling however allowed us to attribute the observed effect to changes in tumour perfusion rather than increased retention.

Influx rate of 18F-fluoroaminosuberic acid reflects cystine/glutamate antiporter expression in tumour xenografts.

PURPOSE: 18F-fluoroaminosuberic acid (18F-FASu) is a recently developed amino acid tracer for positron emission tomography (PET) of oxidative stress that may offer improved tumour assessment over the conventional tracer 18F-fluorodeoxyglucose (18F-FDG). Our aim was to evaluate and relate dynamic 18F-FASu and 18F-FDG uptake with pharmacokinetic modelling to transporter protein expression levels in a panel of diverse tumour xenograft lines. METHODS: Four different tumour xenograft lines were implanted in female athymic nude mice: MAS98.12 and HBCx3 (breast), TPMX (osteosarcoma) and A549 (lung). Dynamic PET over 60 min was performed on a small animal unit. The time-activity curves (TACs) for 18F-FASu and 18F-FDG in individual tumours were used to extract early (SUVE; 2 min p.i.) and late (SUVL; 55 min p.i.) standardised uptake values. Pharmacokinetic two-tissue compartment models were applied to the TACs to estimate rate constants K1-k4 and blood volume fraction vB. Relative levels of cystine/glutamate antiporter subunit xCT were assessed by western blotting, and expression of GLUT1 and CD31 by immunohistochemistry. RESULTS: 18F-FASu showed higher SUVE, whilst 18F-FDG exhibited higher SUVL. Influx rate K1 for 18F-FASu was significantly correlated with xCT levels (p = 0.001) and was significantly higher than K1 for 18F-FDG (p < 0.001). K1 for 18F-FDG was significantly correlated with GLUT1 levels (p = 0.002). vB estimated from 18F-FASu and 18F-FDG TACs was highly consistent and significantly correlated (r = 0.85, p < 0.001). Two qualitatively different 18F-FASu uptake profiles were identified: type α with low xCT expression and low K1 (A549 and HBCx3), and type ß with high xCT expression and high K1 (MAS98.12 and TPMX). CONCLUSION: The influx rate of 18F-FASu reflects xCT activity in tumour xenografts. Dynamic PET with pharmacokinetic modelling is needed to fully appraise 18F-FASu distribution routes.

Variability of dynamic 18F-FDG-PET data in breast cancer xenografts.

BACKGROUND: A murine breast cancer xenograft model was employed to evaluate inter- and intra-variability of various parameters derived from dynamic positron emission tomography with [18F]-fluorodeoxyglucose as tracer (FDG-PET). MATERIAL AND METHODS: Seventeen female athymic nude foxn1/nu mice with bilaterally implanted triple-negative basal-like ductal carcinoma (MAS98.12) breast cancer xenografts underwent a dynamic PET scan over an hour after injection of approximately 10 MBq FDG. Inter-animal data were obtained from the entire animal cohort, while intra-animal data were from four mice receiving an additional scan after one or two days. Standardised uptake values (SUVmax, SUVmean and SUVmedian) were estimated for all tumours at different time points. Tumour uptake was analysed with a kinetic two-compartment model for estimation of pharmacokinetic parameters. The coefficient of variation (CV) was calculated for all PET-derived metrics. RESULTS: The CVs for SUVmean and SUVmedian were typically 10-20% for the tumours, depending on the time post-injection and group (intra vs. inter). The CV for SUVmax was mostly higher. The variability in the pharmacokinetic parameters ranged from 23 to almost 150%. CONCLUSIONS: SUVmean and SUVmedian show less variability than SUVmax. The pharmacokinetic tumour metrics again display much greater variability than the SUV-based metrics. However, it is generally not known which of these metrics that best represents cancer aggressiveness and their use may still depend on the research questions addressed.