Naim Chabaytah

@article{nokey,

title = {Assessing radiosensitivity through sublethal damage recovery: a comparison of survival-based and molecular repair kinetics},

author = {Naim Chabaytah and Mirta Dumančić and Emmanuel C. Asante and Tanner Connell and Michael Witcher and Shirin Abbasinejad Enger},

url = {https://iopscience.iop.org/article/10.1088/1361-6560/ade221},

doi = {10.1088/1361-6560/ade221},

issn = {1361-6560},

year  = {2025},

date = {2025-06-16},

urldate = {2025-06-16},

journal = {Physics in Medicine & Biology},

volume = {70},

number = {125009},

issue = {12},

abstract = {Objective. This study aimed to determine whether the kinetics of sublethal damage recovery after x-ray irradiation, quantified as the repair half time (TrepairSLD) derived from split-dose clonogenic survival, correlates with intrinsic radiosensitivity across four human cancer cell lines: HeLa (cervical), PC3 (prostate), and HCT116 and HT29 (colorectal). In addition, the study compared this survival-based indicator with molecular repair kinetics assessed throughγH2AX and 53BP1 foci clearance.Approach. By using a phenomenological approach, we assessed sublethal damage recovery kinetics, aiming to determine whether this recovery rate could serve as a biomarker for cancer-specific intrinsic radiosensitivity. Cells were subjected to split-dose 4 Gy irradiation delivered in two fractions of 2 Gy across a 0 to 10 h inter-fraction interval range using a Multi-Rad x-ray irradiator with a peak tube voltage of 225 kV. The clonogenic assay was performed following split-dose irradiation of the experimental groups to assess cell survival. Colonies were fixed, stained, and counted (⩾50 cells/colony viable threshold) to calculate survival fractions (SFs) from the four independent experimental runs completed for each cell line. Unirradiated control cells were used to calculate plating efficiency. The measured SF as a function of inter-fraction time was fitted with the Lea-Catcheside modified linear-quadratic model with a half-life of sublethal damage repair,TrepairSLD, as a free parameter. To compare this approach to molecular DNA repair kinetics, immunofluorescence-based ionizing radiation-induced foci (IRIF) clearance experiments were performed following single 2 Gy irradiation using the same x-ray source.γH2AX and 53BP1 foci were quantified from 0.5 to 24 h post-irradiation, and foci clearance half-lives (TrepairγH2AXandTrepair53BP1) were determined by single-phase exponential decay fitting.Main results. For all measured cell lines, an increase in SF was observed with increasing inter-fraction time. The estimatedTrepairSLDvaried across cell lines, from1.07±0.35 h in HT29, to1.98±0.94 h in HeLa,2.00±0.30 h in PC3, and3.58±1.45 h in HCT116, indicating different capacities for sublethal damage repair. A negative correlation was measured betweenTrepairSLDand clonogenic survival at 2 Gy (SF2Gy) by performing orthogonal distance regression, with a slope of-350±50 min (p = 0.02).TrepairγH2AXandTrepair53BP1ranged from 3 to 11 h, with HT29 showing the fastest foci resolution. However, these molecular repair kinetics times did not significantly correlate withSF2Gy(p > 0.05) or follow the same trend asTrepairSLDacross cell lines. For example, PC3 cells exhibited the slowest foci clearance, whereas HCT116 displayed the slowestTrepairSLD, suggesting that IRIF-based measurements do not reliably reflect functional sublethal damage repair.Significance. Clonogenic survival assays capture the integrated biological outcome of radiation exposure, reflecting not only DNA damage recognition and repair but also downstream processes such as checkpoint activation, chromatin context, and long-term proliferative capacity. In contrast, molecular readouts likeγH2AX and 53BP1 foci clearance, though rapid and widely used, may not fully account for defects in damage response pathways. The observed discrepancy between foci clearance kinetics and survival-based repair rates in this study highlights the limitations of foci quantification as a surrogate for radiosensitivity. These findings underscore the value of survival-based sublethal damage recovery measurements as functionally rich indicators of intrinsic radiosensitivity, which may inform future biomarker development or predictive modeling frameworks.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cyr2024-me,

title = {Establishing a standardized murine orthotopic intra-rectal model for the study of colorectal adenocarcinoma},

author = {Mélodie Cyr and Naim Chabaytah and Joud Babik and Behnaz Behmand and Guillaume St-Jean and Shirin A. Enger},

url = {https://jgo.amegroups.org/article/view/93989},

doi = {10.21037/jgo-24-515},

isbn = {2078-6891},

year  = {2024},

date = {2024-12-31},

urldate = {2024-12-31},

journal = {Journal of Gastrointestinal Oncology},

volume = {15},

issue = {6},

pages = {2578-2587},

abstract = {Background: Orthotopic models offer a more accurate representation of colorectal cancer (CRC) compared to subcutaneous models. Despite promising results from the reported intra-rectal models, establishing a standardized method for CRC research remains challenging due to model variability, hindering comprehensive studies on CRC pathogenesis and treatment modalities, such as brachytherapy. This study aimed to establish a standardized workflow for an orthotopic intra-rectal animal model to induce the growth of colorectal adenocarcinoma in male and female mice.



Methods: HT-29 colorectal adenocarcinoma cells were injected into the rectal mucosa of female (n=21) and male (n=26) non-obese diabetic severe combined immunodeficiency (NOD SCID) gamma (NSG) mice. Mice were placed on a 45° wedge elevating their pelvis for better visualization of the anus. Tumor growth and localization were monitored using a 7-T magnetic resonance imaging (MRI) scanner with rapid acquisition with relaxation echo (RARE) sequence at weeks 1, 2, and 3 post-cell instillation. Once tumors reached 5-8 mm in diameter, the mice were euthanized. Histopathology and immunohistochemical analyses confirmed the tumors' morphology, including necrosis, vascularity (CD-31) and apoptosis (cleaved caspase-3).



Results: There was a 92% and 95% tumor growth success rate in male and female mice, respectively. Tumors grew to 5-8 mm in diameter within ~20 days. No significant difference in tumor size was observed between genders. Tumor morphology was consistent across cases. Most tumors exhibited a lack of central blood vessels, accompanied by varying degrees of necrosis and apoptosis, whereas external portions were highly vascularized.



Conclusions: An orthotopic intra-rectal model was successfully developed. This model will be used in future studies to evaluate the efficacy of CRC treatments.



Keywords: Colorectal adenocarcinoma; HT-29; animal model; orthotopic intra-rectal.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Relative biological effectiveness of clinically relevant photon energies for the survival of human colorectal, cervical, and prostate cancer cell lines},

author = {Joanna Li and Naim Chabaytah and Joud Babik and Behnaz Behmand and Hamed Bekerat and Tanner Connell and Michael D C Evans and Russell Ruo and Te Vuong and Shirin A Enger 6},

doi = {10.1088/1361-6560/ad7d5a},

year  = {2024},

date = {2024-09-19},

journal = {Physics in Medicine and Biology },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Assessing radiosensitivity through sublethal damage recovery: a comparison of survival-based and molecular repair kinetics},

author = {Naim Chabaytah and Mirta Dumančić and Emmanuel C. Asante and Tanner Connell and Michael Witcher and Shirin Abbasinejad Enger},

url = {https://iopscience.iop.org/article/10.1088/1361-6560/ade221},

doi = {10.1088/1361-6560/ade221},

issn = {1361-6560},

journal = {Physics in Medicine & Biology},

volume = {70},

number = {125009},

issue = {12},

abstract = {Objective. This study aimed to determine whether the kinetics of sublethal damage recovery after x-ray irradiation, quantified as the repair half time (TrepairSLD) derived from split-dose clonogenic survival, correlates with intrinsic radiosensitivity across four human cancer cell lines: HeLa (cervical), PC3 (prostate), and HCT116 and HT29 (colorectal). In addition, the study compared this survival-based indicator with molecular repair kinetics assessed throughγH2AX and 53BP1 foci clearance.Approach. By using a phenomenological approach, we assessed sublethal damage recovery kinetics, aiming to determine whether this recovery rate could serve as a biomarker for cancer-specific intrinsic radiosensitivity. Cells were subjected to split-dose 4 Gy irradiation delivered in two fractions of 2 Gy across a 0 to 10 h inter-fraction interval range using a Multi-Rad x-ray irradiator with a peak tube voltage of 225 kV. The clonogenic assay was performed following split-dose irradiation of the experimental groups to assess cell survival. Colonies were fixed, stained, and counted (⩾50 cells/colony viable threshold) to calculate survival fractions (SFs) from the four independent experimental runs completed for each cell line. Unirradiated control cells were used to calculate plating efficiency. The measured SF as a function of inter-fraction time was fitted with the Lea-Catcheside modified linear-quadratic model with a half-life of sublethal damage repair,TrepairSLD, as a free parameter. To compare this approach to molecular DNA repair kinetics, immunofluorescence-based ionizing radiation-induced foci (IRIF) clearance experiments were performed following single 2 Gy irradiation using the same x-ray source.γH2AX and 53BP1 foci were quantified from 0.5 to 24 h post-irradiation, and foci clearance half-lives (TrepairγH2AXandTrepair53BP1) were determined by single-phase exponential decay fitting.Main results. For all measured cell lines, an increase in SF was observed with increasing inter-fraction time. The estimatedTrepairSLDvaried across cell lines, from1.07±0.35 h in HT29, to1.98±0.94 h in HeLa,2.00±0.30 h in PC3, and3.58±1.45 h in HCT116, indicating different capacities for sublethal damage repair. A negative correlation was measured betweenTrepairSLDand clonogenic survival at 2 Gy (SF2Gy) by performing orthogonal distance regression, with a slope of-350±50 min (p = 0.02).TrepairγH2AXandTrepair53BP1ranged from 3 to 11 h, with HT29 showing the fastest foci resolution. However, these molecular repair kinetics times did not significantly correlate withSF2Gy(p > 0.05) or follow the same trend asTrepairSLDacross cell lines. For example, PC3 cells exhibited the slowest foci clearance, whereas HCT116 displayed the slowestTrepairSLD, suggesting that IRIF-based measurements do not reliably reflect functional sublethal damage repair.Significance. Clonogenic survival assays capture the integrated biological outcome of radiation exposure, reflecting not only DNA damage recognition and repair but also downstream processes such as checkpoint activation, chromatin context, and long-term proliferative capacity. In contrast, molecular readouts likeγH2AX and 53BP1 foci clearance, though rapid and widely used, may not fully account for defects in damage response pathways. The observed discrepancy between foci clearance kinetics and survival-based repair rates in this study highlights the limitations of foci quantification as a surrogate for radiosensitivity. These findings underscore the value of survival-based sublethal damage recovery measurements as functionally rich indicators of intrinsic radiosensitivity, which may inform future biomarker development or predictive modeling frameworks.



Keywords: DNA repair kinetics; intrinsic radiosensitivity; photon therapy; sublethal damage recovery.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}