A survey of changing trends in modelling radiation lung injury in mice: bringing out the good, the bad, and the uncertain.

Within this millennium there has been resurgence in funding and research dealing with animal models of radiation-induced lung injury to identify and establish predictive biomarkers and effective mitigating agents that are applicable to humans. Most have been performed on mice but there needs to be assurance that the emphasis on such models is not misplaced. We therefore considered it timely to perform a comprehensive appraisal of the literature dealing with radiation lung injury of mice and to critically evaluate the validity and clinical relevance of the research. A total of 357 research papers covering the period of 1970-2015 were extensively reviewed. Whole thorax irradiation (WTI) has become the most common treatment for studying lung injury in mice and distinct trends were seen with regard to the murine strain, radiation dose, intended pathology investigated, length of study, and assays. Recently, the C57BL/6 strain has been increasingly used in the majority of these studies with the notion that they are susceptible to pulmonary fibrosis. Nonetheless, many of these investigations depend on animal survival as the primary end point and neglect the importance of radiation pneumonitis and the anomaly of lethal pleural effusions. A relatively large variation in survival times of C5BL/6 mice is also seen among different institutions pointing to the need for standardization of radiation treatments and environmental conditions. An analysis of mitigating drug treatments is complicated by the fact that the majority of studies are limited to the C57BL/6 strain with a premature termination of the experiments and do not establish whether the treatment actually prevents or simply delays the progression of radiation injury. This survey of the literature has pointed to several improvements that need to be considered in establishing a reliable preclinical murine model of radiation lung injury. The lethality end point should also be used cautiously and with greater emphasis on other assays such as non-invasive lung functional and imaging monitoring in order to quantify specific pulmonary injury that can be better extrapolated to radiation toxicity encountered in our own species.

Dacomitinib and gedatolisib in combination with fractionated radiation in head and neck cancer.

BACKGROUND AND PURPOSE: There has been little success targeting individual genes in combination with radiation in head and neck cancer. In this study we investigated whether targeting two key pathways simultaneously might be more effective. MATERIALS AND METHODS: We studied the effect of combining dacomitinib (pan-HER, irreversible inhibitor) and gedatolisib (dual PI3K/MTOR inhibitor) with radiation in well characterized, low passage xenograft models of HNSCC in vitro and in vivo. RESULTS: Dacomitinib showed differential growth inhibition in vitro that correlated to EGFR expression whilst gedatolisib was effective in both cell lines. Neither agent radiosensitized the cell lines in vitro. In vivo studies demonstrated that dacomitinib was an effective agent alone and in combination with radiation whilst the addition of gedatolisib did not enhance the effect of these two modalities despite inhibiting phosphorylation of key genes in the PI3K/MTOR pathway. CONCLUSIONS: Our results showed that combining two drugs with radiation provided no added benefit compared to the single most active drug. Dacomitinib deserves more investigation as a radiation sensitizing agent in HNSCC.

Pulsed Radiation Therapy With Concurrent Cisplatin Results in Superior Tumor Growth Delay in a Head and Neck Squamous Cell Carcinoma Murine Model.

PURPOSE: To assess the efficacy of 3-week schedules of low-dose pulsed radiation treatment (PRT) and standard radiation therapy (SRT), with concurrent cisplatin (CDDP) in a head and neck squamous cell carcinoma xenograft model. METHODS AND MATERIALS: Subcutaneous UT-SCC-14 tumors were established in athymic NIH III HO female mice. A total of 30 Gy was administered as 2 Gy/d, 5 d/wk for 3 weeks, either by PRT (10 × 0.2 Gy/d, with a 3-minute break between each 0.2-Gy dose) or SRT (2 Gy/d, uninterrupted delivery) in combination with concurrent 2 mg/kg CDDP 3 times per week in the final 2 weeks of radiation therapy. Treatment-induced growth delays were defined from twice-weekly tumor volume measurements. Tumor hypoxia was assessed by (18)F-fluoromisonidazole positron emission tomography imaging, and calculated maximum standardized uptake values compared with tumor histology. Tumor vessel density and hypoxia were measured by quantitative immunohistochemistry. Normal tissues effects were evaluated in gut and skin. RESULTS: Untreated tumors grew to 1000 mm(3) in 25.4 days (±1.2), compared with delays of 62.3 days (±3.5) for SRT + CDDP and 80.2 days (±5.0) for PRT + CDDP. Time to reach 2× pretreatment volume ranged from 8.2 days (±1.8) for untreated tumors to 67.1 days (±4.7) after PRT + CDDP. Significant differences in tumor growth delay were observed for SRT versus SRT + CDDP (P=.04), PRT versus PRT + CDDP (P=.035), and SRT + CDDP versus PRT + CDDP (P=.033), and for survival between PRT versus PRT + CDDP (P=.017) and SRT + CDDP versus PRT + CDDP (P=.008). Differences in tumor hypoxia were evident by (18)F-fluoromisonidazole positron emission tomography imaging between SRT and PRT (P=.025), although not with concurrent CDDP. Tumor vessel density differed between SRT + CDDP and PRT + CDDP (P=.011). No differences in normal tissue parameters were seen. CONCLUSIONS: Concurrent CDDP was more effective in combination PRT than SRT at restricting tumor growth. Significant differences in tumor vascular density were evident between PRT and SRT, suggesting a preservation of vascular network with PRT.

Pulsed low-dose irradiation of orthotopic glioblastoma multiforme (GBM) in a pre-clinical model: effects on vascularization and tumor control.

BACKGROUND AND PURPOSE: To compare dose-escalated pulsed low-dose radiation therapy (PLRT) and standard radiation therapy (SRT). METHODS AND MATERIALS: Intracranial U87MG GBM tumors were established in nude mice. Animals received whole brain irradiation with daily 2-Gy fractions given continuously (SRT) or in ten 0.2-Gy pulses separated by 3-min intervals (PLRT). Tumor response was evaluated using weekly CT and [(18)F]-FDG-PET scans. Brain tissue was subjected to immunohistochemistry and cytokine bead array to assess tumor and normal tissue effects. RESULTS: Median survival for untreated animals was 18 (SE±0.5) days. A significant difference in median survival was seen between SRT (29±1.8days) and PLRT (34.2±1.9days). Compared to SRT, PLRT resulted in a 31% (p<0.01), 38% (p<0.01), and 53% (p=0.01) reduction in normalized tumor volume and a 48% (p<0.01), 51% (p<0.01), and 70% (p<0.01) reduction in tumor growth rate following the administration of 10Gy, 20Gy, and 30Gy, respectively. Compared to untreated tumors, PLRT resulted in similar tumor vascular density, while SRT produced a 40% reduction in tumor vascular density (p=0.05). Compared to SRT, PLRT was associated with a 28% reduction in degenerating neurons in the surrounding brain parenchyma (p=0.05). CONCLUSIONS: Compared to SRT, PLRT resulted in greater inhibition of tumor growth and improved survival, which may be attributable to preservation of vascular density.