In preclinical radiation research, it is challenging to localize soft tissue targets based on cone beam computed tomography (CBCT) guidance. As a more effective method to localize soft tissue targets, we developed an online bioluminescence tomography (BLT) system for small-animal radiation research platform (SARRP). We demonstrated BLT-guided radiation therapy and validated targeting accuracy based on a newly developed reconstruction algorithm.
Zhang B, Wang KK, Yu J, Eslami S, Iordachita I, Reyes J, Malek R, Tran PT, Patterson MS, Wong JW.
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microRNA-34a promotes DNA damage and mitotic catastrophe.
Efficient and error-free DNA repair is critical for safeguarding genome integrity, yet it is also linked to radio- and chemoresistance of malignant tumors. miR-34a, a potent tumor suppressor, influences a large set of p53-regulated genes and contributes to p53-mediated apoptosis. However, the effects of miR-34a on the processes of DNA damage and repair are not entirely understood. We explored tet-inducible miR-34a-expressing human p53 wild-type and R273H p53 mutant GBM cell lines, and found that miR-34a influences the broad spectrum of 53BP1-mediated DNA damage response. It escalates both post-irradiation and endogenous DNA damage, abrogates radiation-induced G 2/M arrest and drastically increases the number of irradiated cells undergoing mitotic catastrophe. Furthermore, miR-34a downregulates 53BP1 and inhibits its recruitment to the sites of DNA double-strand breaks. We conclude that whereas miR-34a counteracts DNA repair, it also contributes to the p53-independent elimination of distressed cells, thus preventing the rise of genomic instability in tumor cell populations. These properties of miR-34a can potentially be exploited for DNA damage-effecting therapies of malignancies.
Kofman AV, Kim J, Park SY, Dupart E, Letson C, Bao Y, Ding K, Chen Q, Schiff D, Larner J, Abounader R.
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Selective Inhibition of Parallel DNA Damage Response Pathways Optimizes Radiosensitization of Glioblastoma Stem-like Cells.
Glioblastoma is the most common form of primary brain tumor in adults and is essentially incurable. Despite aggressive treatment regimens centered on radiotherapy, tumor recurrence is inevitable and is thought to be driven by glioblastoma stem-like cells (GSC) that are highly radioresistant. DNA damage response pathways are key determinants of radiosensitivity but the extent to which these overlapping and parallel signaling components contribute to GSC radioresistance is unclear. Using a panel of primary patient-derived glioblastoma cell lines, we confirmed by clonogenic survival assays that GSCs were significantly more radioresistant than paired tumor bulk populations. DNA damage response targets ATM, ATR, CHK1, and PARP1 were upregulated in GSCs, and CHK1 was preferentially activated following irradiation. Consequently, GSCs exhibit rapid G2-M cell-cycle checkpoint activation and enhanced DNA repair. Inhibition of CHK1 or ATR successfully abrogated G2-M checkpoint function, leading to increased mitotic catastrophe and a modest increase in radiation sensitivity. Inhibition of ATM had dual effects on cell-cycle checkpoint regulation and DNA repair that were associated with greater radiosensitizing effects on GSCs than inhibition of CHK1, ATR, or PARP alone. Combined inhibition of PARP and ATR resulted in a profound radiosensitization of GSCs, which was of greater magnitude than in bulk populations and also exceeded the effect of ATM inhibition. These data demonstrate that multiple, parallel DNA damage signaling pathways contribute to GSC radioresistance and that combined inhibition of cell-cycle checkpoint and DNA repair targets provides the most effective means to overcome radioresistance of GSC.
Shafiq U Ahmed, Ross Carruthers, Lesley Gilmour, Salih Yildirim, Colin Watts and Anthony J Chalmers
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Identification of suitable endogenous controls for gene and miRNA expression studies in irradiated prostate cancer cells.
This study aimed to to evaluate the stability of commonly used endogenous control genes for messenger RNA (mRNA) (N = 16) and miRNAs (N = 3) expression studies in prostate cell lines following irradiation. The stability of endogenous control genes expression in irradiated (6 Gy) versus unirradiated controls was quantified using NormFinder and coefficient of variation analyses. HPRT1 and 18S were identified as most and least stable endogenous controls, respectively, for mRNA expression studies in irradiated prostate cells. SNORD48 and miR16 miRNA endogenous controls tested were associated with low coefficient of variations following irradiation (6 Gy). This study highlights that commonly used endogenous controls can be responsive to radiation and validation is required prior to gene/miRNAs expression studies.
H Lawlor, Armelle Meunier, Niamh McDermott, Thomas Lynch and Laure Marignol
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Xstrahl medical to showcase RADiant at UKRO, June 8th to 10th.
Xstrahl Medical (Booth 20) will introduce the exciting new Photoelectric Therapy system at the 8th UK Radiation Oncology (UKRO) Conference from the 8th to 10th of June at the Ricoh Arena, Coventry.
Xstrahl to showcase RADiant at DEGRO 2015 in Hamburg, Germany
Xstrahl will attend this year’s Deutschen Gesellschaft für Radioonkologie e.V. (DEGRO) in Hamburg, Germany from 25th – 28th June. There will be 4,000 attendees from around Europe looking to get the latest information and technology in the name of science.
Xstrahl introduces RADiant to the European market at ESTRO
Xstrahl Medical will introduce the exciting new Photoelectric Therapy system to the European Market at the start of the 3rd European Society for Radiotherapy and Oncology (ESTRO) forum in Barcelona, Spain on Friday 24th April. Xstrahl (Stand 3700) have worked with clinicians to develop a system that will allow an even greater number of patients to choose this surgery free, non-invasive treatment option.
MRI-Only Based Radiotherapy Treatment Planning for the Rat Brain on a Small Animal Radiation Research Platform (SARRP).
Computed tomography (CT) is the standard imaging modality in radiation therapy treatment planning (RTP). However, magnetic resonance (MR) imaging provides superior soft tissue contrast, increasing the precision of target volume selection. We present MR-only based RTP for a rat brain on a small animal radiation research platform (SARRP) using probabilistic voxel classification with multiple MR sequences. Six rat heads were imaged, each with one CT and five MR sequences. The MR sequences were: T1-weighted, T2-weighted, zero-echo time (ZTE), and two ultra-short echo time sequences with 20 μs (UTE1) and 2 ms (UTE2) echo times. CT data were manually segmented into air, soft tissue, and bone to obtain the RTP reference. Bias field corrected MR images were automatically segmented into the same tissue classes using a fuzzy c-means segmentation algorithm with multiple images as input. Similarities between segmented CT and automatic segmented MR (ASMR) images were evaluated using Dice coefficient. Three ASMR images with high similarity index were used for further RTP. Three beam arrangements were investigated. Dose distributions were compared by analysing dose volume histograms. The highest Dice coefficients were obtained for the ZTE-UTE2 combination and for the T1-UTE1-T2 combination when ZTE was unavailable. Both combinations, along with UTE1-UTE2, often used to generate ASMR images, were used for further RTP. Using 1 beam, MR based RTP underestimated the dose to be delivered to the target (range: 1.4%-7.6%). When more complex beam configurations were used, the calculated dose using the ZTE-UTE2 combination was the most accurate, with 0.7% deviation from CT, compared to 0.8% for T1-UTE1-T2 and 1.7% for UTE1-UTE2. The presented MR-only based workflow for RTP on a SARRP enables both accurate organ delineation and dose calculations using multiple MR sequences. This method can be useful in longitudinal studies where CT’s cumulative radiation dose might contribute to the total dose.
Shandra Gutierrez, Benedicte Descamps, Christian Vanhove
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Abrogation of radioresistance in glioblastoma stem-like cells by inhibition of ATM kinase.
Resistance to radiotherapy in glioblastoma (GBM) is an important clinical problem and several authors have attributed this to a subpopulation of GBM cancer stem cells (CSCs) which may be responsible for tumour recurrence following treatment. It is hypothesised that GBM CSCs exhibit upregulated DNA damage responses and are resistant to radiation but the current literature is conflicting. We investigated radioresistance of primary GBM cells grown in stem cell conditions (CSC) compared to paired differentiated tumour cell populations and explored the radiosensitising effects of the ATM inhibitor KU-55933. We report that GBM CSCs are radioresistant compared to paired differentiated tumour cells as measured by clonogenic assay. GBM CSC’s display upregulated phosphorylated DNA damage response proteins and enhanced activation of the G2/M checkpoint following irradiation and repair DNA double strand breaks (DSBs) more efficiently than their differentiated tumour cell counterparts following radiation. Inhibition of ATM kinase by KU-55933 produced potent radiosensitisation of GBM CSCs (sensitiser enhancement ratios 2.6-3.5) and effectively abrogated the enhanced DSB repair proficiency observed in GBM CSCs at 24 h post irradiation. G2/M checkpoint activation was reduced but not abolished by KU-55933 in GBM CSCs. ATM kinase inhibition overcomes radioresistance of GBM CSCs and, in combination with conventional therapy, has potential to improve outcomes for patients with GBM.
Ross Carruthers, Shafiq U Ahmed, Karen Strathdee, Natividad Gomez-Roman, Evelyn Amoah-Buahin, Colin Watts and Anthony J Chalmers
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