Effect of bisphosphonates and statins on the in vitro radiosensitivity of breast cancer cell lines

BACKGROUND

Early-stage breast cancer is usually treated with breast-conserving surgery followed by adjuvant radiation therapy. Acute skin toxicity is a common radiation-induced side effect experienced by many patients. Recently, a combination of bisphosphonates (zoledronic acid) and statins (pravastatin), or ZOPRA, was shown to radio-protect normal tissues by enhancing DNA double-strand breaks (DSB) repair mechanism. However, there are no studies assessing the effect of ZOPRA on cancerous cells. The purpose of this study is to characterize the in vitro effect of the zoledronic acid (ZO), pravastatin (PRA), and ZOPRA treatment on the molecular and cellular radiosensitivity of breast cancer cell lines.

MATERIALS

Two breast cancer cell lines, MDA MB 231 and MCF-7, were tested. Cells were treated with different concentrations of pravastatin (PRA), zoledronate (ZO), as well as their ZOPRA combination, before irradiation. Anti-γH2AX and anti-pATM immunofluorescence were performed to study DNA DSB repair kinetics. MTT assay was performed to assess cell proliferation and viability, and flow cytometry was performed to analyze the effect of the drugs on the cell cycle distribution. The clonogenic assay was used to assess cell survival.

RESULTS

ZO, PRA, and ZOPRA treatments were shown to increase the residual number of γH2AX foci for both cell lines. ZOPRA treatment was also shown to reduce the activity of the ATM kinase in MCF-7. ZOPRA induced a significant decrease in cell survival for both cell lines.

CONCLUSIONS

Our findings show that pretreatment with ZOPRA can decrease the radioresistance of breast cancer cells at the molecular and cellular levels. The fact that ZOPRA was previously shown to radioprotect normal tissues, makes it a good candidate to become a therapeutic window-widening drug.

Influence of the Hypersensitivity to Low Dose Phenomenon on the Tumor Response to Hypofractionated Stereotactic Body Radiation Therapy

Stereotactic body radiation therapy (SBRT) has made the hypofractionation of high doses delivered in a few sessions more acceptable. While the benefits of hypofractionated SBRT have been attributed to additional vascular, immune effects, or specific cell deaths, a radiobiological and mechanistic model is still needed. By considering each session of SBRT, the dose is divided into hundreds of minibeams delivering some fractions of Gy. In such a dose range, the hypersensitivity to low dose (HRS) phenomenon can occur. HRS produces a biological effect equivalent to that produced by a dose 5-to-10 times higher. To examine whether HRS could contribute to enhancing radiation effects under SBRT conditions, we exposed tumor cells of different HRS statuses to SBRT. Four human HRS-positive and two HRS-negative tumor cell lines were exposed to different dose delivery modes: a single dose of 0.2 Gy, 2 Gy, 10 × 0.2 Gy, and a single dose of 2 Gy using a non-coplanar isocentric minibeams irradiation mode were delivered. Anti-γH2AX immunofluorescence, assessing DNA double-strand breaks (DSB), was applied. In the HRS-positive cells, the DSB produced by 10 × 0.2 Gy and 2 Gy, delivered by tens of minibeams, appeared to be more severe, and they provided more highly damaged cells than in the HRS-negative cells, suggesting that more severe DSB are induced in the "SBRT modes" conditions when HRS occurs in tumor. Each SBRT session can be viewed as hyperfractionated dose delivery by means of hundreds of low dose minibeams. Under current SBRT conditions (i.e., low dose per minibeam and not using ultra-high dose-rate), the response of HRS-positive tumors to SBRT may be enhanced significantly. Interestingly, similar conclusions were reached with HRS-positive and HRS-negative untransformed fibroblast cell lines, suggesting that the HRS phenomenon may also impact the risk of post-RT tissue overreactions.

Inclusion of Nitrofurantoin into the Realm of Cancer Chemotherapy via Biology-Oriented Synthesis and Drug Repurposing

Structural modifications of the antibacterial drug nitrofurantoin were envisioned, employing drug repurposing and biology-oriented drug synthesis, to serve as possible anticancer agents. Eleven compounds showed superior safety in non-cancerous human cells. Their antitumor efficacy was assessed on colorectal, breast, cervical, and liver cancer cells. Three compounds induced oxidative DNA damage in cancer cells with subsequent cellular apoptosis. They also upregulated the expression of Bax while downregulated that of Bcl-2 along with activating caspase 3/7. The DNA damage induced by these compounds, demonstrated by pATM nuclear shuttling, was comparable in both MCF7 and MDA-MB-231 (p53 mutant) cell lines. Mechanistic studies confirmed the dependence of these compounds on p53-mediated pathways as they suppressed the p53-MDM2 interaction. Indeed, exposure of radiosensitive prostatic cancer cells to low non-cytotoxic concentrations of compound 1 enhanced the cytotoxic response to radiation indicating a possible synergistic effect. In vivo antitumor activity was verified in an MCF7-xenograft animal model.

Influence of cellular models and individual factor in the biological response to head CT scan exams

BACKGROUND

While computed tomography (CT) exams are the major cause of medical exposure to ionising radiation, the radiation-induced risks must be documented. We investigated the impact of the cellular models and individual factor on the deoxyribonucleic acid double-strand breaks (DSB) recognition and repair in human skin fibroblasts and brain astrocytes exposed to current head CT scan conditions.

METHOD

Nine human primary fibroblasts and four human astrocyte cell lines with different levels of radiosensitivity/susceptibility were exposed to a standard head CT scan exam using adapted phantoms. Cells were exposed to a single-helical (37.4 mGy) and double-helical (37.4 mGy + 5 min + 37.4 mGy) examination. DSB signalling and repair was assessed through anti-γH2AX and anti-pATM immunofluorescence.

RESULTS

Head CT scan induced a significant number of γH2AX and pATM foci. The kinetics of both biomarkers were found strongly dependent on the individual factor. Particularly, in cells from radiosensitive/susceptible patients, DSB may be significantly less recognised and/or repaired, whatever the CT scan exposure conditions. Similar conclusions were reached with astrocytes.

CONCLUSIONS

Our results highlight the importance of both individual and tissue factors in the recognition and repair of DSB after current head CT scan exams. Further investigations are needed to better define the radiosensitivity/susceptibility of individual humans.

Influence of cellular models and individual factor in the biological response to chest CT scan exams

Background

While computed tomography (CT) exams are the major cause of medical exposure to ionising radiation, there is increasing evidence that the potential radiation-induced risks must be documented. We investigated the impact of cellular models and individual factor on the deoxyribonucleic acid double-strand breaks (DSB) recognition and repair in human fibroblasts and mammary epithelial cells exposed to current chest CT scan conditions.

Method

Twelve human primary fibroblasts and four primary human mammary epithelial cell lines with different levels of radiosensitivity/susceptibility were exposed to a standard chest CT scan exam using adapted phantoms. Cells were exposed to a single helical irradiation (14.4 mGy) or to a topogram followed, after 1 min, by one single helical examination (1.1 mGy + 14.4 mGy). DSB signalling and repair was assessed through anti-γH2AX and anti-pATM immunofluorescence.

Results

Chest CT scan induced a significant number of γH2AX and pATM foci. The kinetics of both biomarkers were found strongly dependent on the individual factor. The topogram may also influence the biological response of radiosensitive/susceptible fibroblasts to irradiation. Altogether, our findings show that a chest CT scan exam may result in 2 to 3 times more unrepaired DSB in cells from radiosensitive/susceptible patients.

Conclusions

Both individual and tissue factors in the recognition and repair of DSB after current CT scan exams are important. Further investigations are needed to better define the radiosensitivity/susceptibility of individual humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41747-022-00266-0.

Radiation-Induced Fibrosis in Patients with Head and Neck Cancer: A Review of Pathogenesis and Clinical Outcomes

Radiotherapy-related fibrosis remains one of the most challenging treatment related side effects encountered by patients with head and neck cancer. Several established and ongoing novel therapies have been studied with paucity of data in how to best treat these patients. This review aims to provide researchers and health care providers with a comprehensive review on the presentation, etiology, and therapeutic options for this serious condition.

Individual Response to Radiation of Individuals with Neurofibromatosis Type I: Role of the ATM Protein and Influence of Statins and Bisphosphonates

Neurofibromatosis type 1 (NF1) is a disease characterized by high occurrence of benign and malignant brain tumours and caused by mutations of the neurofibromin protein. While there is an increasing evidence that NF1 is associated with radiosensitivity and radiosusceptibility, few studies have dealt with the molecular and cellular radiation response of cells from individuals with NF1. Here, we examined the ATM-dependent signalling and repair pathways of the DNA double-strand breaks (DSB), the key-damage induced by ionizing radiation, in skin fibroblast cell lines from 43 individuals with NF1. Ten minutes after X-rays irradiation, quiescent NF1 fibroblasts showed abnormally low rate of recognized DSB reflected by a low yield of nuclear foci formed by phosphorylated H2AX histones. Irradiated NF1 fibroblasts also presented a delayed radiation-induced nucleoshuttling of the ATM kinase (RIANS), potentially due to a specific binding of ATM to the mutated neurofibromin in cytoplasm. Lastly, NF1 fibroblasts showed abnormally high MRE11 nuclease activity suggesting a high genomic instability after irradiation. A combination of bisphosphonates and statins complemented these impairments by accelerating the RIANS, increasing the yield of recognized DSB and reducing genomic instability. Data from NF1 fibroblasts exposed to radiation in radiotherapy and CT scan conditions confirmed that NF1 belongs to the group of syndromes associated with radiosensitivity and radiosusceptibility.

Radiosensitizing Effect of Curcumin on Human Bladder Cancer Cell Lines: Impact on DNA Repair Mechanisms

Chemo-radiotherapy is one of the promising approaches to treat bladder cancer, but its effectiveness is limited to sensitive patients. Polyphenol curcumin has shown anticancer and radiosensitizing potentials, but the mechanism is not fully understood. Here, the In Vitro response of UM-UC5 and UM-UC6 bladder cell lines to curcumin and radiation treatments was evaluated. The effect of curcumin on the DNA double-strand breaks repair system after treatment with ionizing radiation (2 Gy) was determined by immunofluorescence. Cell viability, proliferation, and survival were performed using trypan blue, MTT, clonogenic, and sphere-forming assays. The migratory ability of both cells was assessed by wound healing. We showed that curcumin treatment increased the radiosensitivity by modifying the DNA double-strand breaks repair kinetics of the most radioresistant cells UM-UC6 without affecting the radiosensitive UM-UC5. Moreover, UM-UC6 cell survival and proliferation was significantly decreased after the combination of curcumin with radiation. Bladder cell migration was also inhibited considerably. Curcumin was also shown to reduce the number and the volume of bladder cancer spheres of both cell lines. This study revealed that curcumin was able to radiosensitize resistant bladder cell line without affecting the sensitive one with minimal side effects through enhancing DNA damage signaling and repair pathway.

Assessing Radiosensitivity of Bladder Cancer in vitro: A 2D vs. 3D Approach

Background: Bladder cancer is the fourth most commonly diagnosed cancer among males worldwide. Current treatment strategies established for bladder cancer mainly consist of cystectomy yet advances in radiation therapy have pointed to the value of organ-preserving strategies in preserving patients' quality of life. Aim: To study and compare the radiosensitivity in two-dimension (2D) and physiologically-relevant three-dimension (3D) in vitro culture of three human bladder cancer cell lines, RT4, T24, and UM-UC-3. Materials and Methods: Clonogenic assay was performed to assess cells' radiosensitivity in 2D. Employing the 3D Matrigel™-based cultures to enrich for cancer stem cells (CSCs) allowed us to assess the survival of this subpopulation of cells via evaluating the number, i.e., sphere forming unit (SFU), and the sizes of cultured spheres, formed from cells exposed to different radiation doses compared to non-irradiated cells. Results: Irradiating cells with increasing radiation doses revealed highest survival rates with RT4 cells in 2D, followed by T24 and UM-UC-3. In 3D, however, UM-UC-3 cells were shown to be the most radio-resistant as evidenced by the number of spheres formed, yet they displayed the least efficient volume reduction/regression (VR), whilst the volume decreased significantly for both RT4 and T24 cells. Sphere VR and sphere ratio (SR) values were then plotted against each other demonstrating a linear correlation between volume and number with RT4 and UM-UC-3 cell lines, but not T24. Lastly, multiple regression model was employed to evaluate the possibility of obtaining a function combining both 3D parameters, SR and VR, with the surviving fraction (SF) in 2D, and showed a linear regression for T24 cells only, with a correlation coefficient of 0.97 for the combined parameters. Conclusion: We were able to radiobiologically characterize 3 human bladder cancer cell lines showing differential effects of radiation between 2D and 3D culture systems, paving the way for achieving better assessment of radiosensitivity of bladder cancer in vitro.

The Phosphorylated ATM Immunofluorescence Assay: A High-performance Radiosensitivity Assay to Predict Postradiation Therapy Overreactions

PURPOSE

The ability to identify, before treatment, those patients who will overreact to radiation therapy would have sound positive clinical implications. By focusing on DNA double-strand breaks recognition and repair proteins after irradiation, we recently demonstrated that the maximal number of phosphorylated ATM (pATM) nuclear foci in the first hour (pATMmax) after ex vivo irradiation correlated with postradiation therapy toxicity severity. We performed additional analyses of our whole collection of fibroblast lines to refine the predictive performance of our assay.

METHODS AND MATERIALS

Immunofluorescence experiments were performed on 117 primary skin fibroblast lines irradiated at 2 Gy. The toxicity response was split into 2 binary classes: 0 if the toxicity grade was <2 and 1 otherwise. To assess the relationship between the quantity of pATMmax foci and toxicity grade, we applied a correlation and then a supervised classification analysis. Training data sets from 13 radiosensitive patients randomly drawn using a random undersampling technique were constituted. Receiver operating characteristic analyses were performed using a Monte-Carlo method to estimate the optimal threshold and discriminate the responses for each data set. The discrimination cutoff was estimated as the maximum value of the 10⁴ thresholds computed from each training subset.

RESULTS

As expected, we confirmed a quasi-linear dependence between toxicity and pATMmax (Pearson correlation coefficient -0.85; P < 2.2e^-16). When taken as a binary predictive assay with the optimal cutoff value of 34.5 pATM foci/cell, our assay showed outstanding predictive performance (sensitivity, specificity, negative predictive value, positive predictive value, and area under the curve: 100%, 92%, 100%, 99%, and 0.987, respectively).

CONCLUSIONS

The results of these experiments allowed us to identify pATMmax as a high-performance predictive parameter of patients with postradiation therapy overreactions. Additional studies are in progress to confirm that this radiosensitivity assay reaches the same performance level in any condition to adapt clinical practice.

Fast and Binary Assay for Predicting Radiosensitivity Based on the Theory of ATM Nucleo-Shuttling: Development, Validation, and Performance

PURPOSE

To examine the possibility of predicting clinical radiosensitivity by quantifying the nuclear forms of autophosphorylated ATM protein (pATM) via a specific enzyme-linked immunosorbent assay (ELISA).

METHODS AND MATERIALS

This study was performed on 30 skin fibroblasts from 9 radioresistant patients and 21 patients with adverse tissue reaction events. Patients were divided into 2 groups: radioresistant (toxicity grade <2) and radiosensitive (toxicity grade ≥2). The quantity of nuclear pATM molecules was assessed by the ELISA method at 10 minutes and 1 hour after 2 Gy and compared with pATM immunofluorescence data.

RESULTS

The pATM ELISA data were in quantitative agreement with the immunofluorescence data. A receiver operating characteristic analysis was applied first to 2 data sets (a training set [n=14] and a validating [n=16] set) and thereafter to all the data with a 2-fold cross-validation method. The assay showed an area under the curve value higher than 0.8, a sensitivity of 0.8, and a specificity ranging from 0.75 to 1, which strongly documents the predictive power of the pATM ELISA.

CONCLUSION

This study showed that the assessment of nuclear pATM quantity after 2 Gy via an ELISA technique can be the basis of a predictive assay with the highest statistical performance among the available predictive approaches.

Optimizing tumor immune response through combination of radiation and immunotherapy

Radiation therapy and immunotherapy are two highly evolving modalities for the treatment of solid tumors. Immunotherapeutic drugs can either stimulate the immune system via immunogenic pathways or target co-inhibitory checkpoints. An augmented tumor cell recognition by host immune cells can be achieved post-irradiation, as irradiated tissues can release chemical signals which are sensed by the immune system resulting in its activation. Different strategies combining both treatment modalities were tested in order to achieve a better therapeutic response and longer tumor control. Both regimens act synergistically to one another with complimentary mechanisms. In this review, we explore the scientific basis behind such a combination, starting initially with a brief historical overview behind utilizing radiation and immunotherapies for solid tumors, followed by the different types of these two modalities, and the biological concept behind their synergistic effect. We also shed light on the common side effects and toxicities associated with radiation and immunotherapy. Finally, we discuss previous clinical trials tackling this multimodality combination and highlight future ongoing research.

The nucleo-shuttling of the ATM protein as a basis for a novel theory of radiation response: resolution of the linear-quadratic model

PURPOSE

For 50 years, cellular radiosensitivity has been defined in vitro as the lack of clonogenic capacity of irradiated cells and its mathematical link with dose has been described by the target theory. Among the numerous formulas provided from the target theory, the linear-quadratic (LQ) model empirically describes cell survival as a negative exponential of a second degree polynomial dose-function in which αD is the linear component and βD(2) is the quadratic one. The LQ model is extensively used in radiobiology (to describe survival curves) and in radiotherapy (the α/β ratio indicates whether tissue reactions can occur early or late after the treatment). However, no biological interpretation of the LQ parameters was proposed to explain together the radiation response in a wide dose range, the radiosensitivity of some genetic syndromes caused by the mutation of cytoplasmic proteins and the hyper-radiosensitivity phenomenon specific to low-dose.

THE MODEL

From a solid amount of experimental data, we hypothesized that the major forms of ataxia telangiectasia mutated (ATM) are cytoplasmic dimers and that ionizing radiation induce ATM monomerization. The resulting ATM monomers diffuse into nucleus to facilitate double-strand-breaks (DSB) recognition and repair. Such hypotheses lead to a coherent molecular interpretation of the LQ model by considering the yield of recognized but unrepaired (α-type) DSB and the non-recognized (β-type) DSB. The notion of cell tolerance to unrepaired DSB was introduced by considering that not all DSB are lethal. Cell survival and DSB repair and signaling immunofluorescence data from 42 normal skin fibroblast and 18 tumor human cell lines were used to verify the validity of this biomathematical model proposed.

RESULTS

Our model is validated at different levels by one of the widest spectrum of radiosensitivity. That mathematical developments of the present model imply that β is a Lorentzian function of α was confirmed experimentally. Our model is also relevant to describe the hypersensitivity to low-dose phenomenon.

CONCLUSIONS

Our model provides a very general picture of human radiosensitivity, independently of the dose, the cell type and the genetic status.

[Repeated radiation dose effect and DNA repair: Importance of the individual factor and the time interval between the doses]

The dose fractionation effect is a recurrent question of radiation biology research that remains unsolved since no model predicts the clinical effect only with the cumulated dose and the radiobiology of irradiated tissues. Such an important question is differentially answered in radioprotection, radiotherapy, radiology or epidemiology. A better understanding of the molecular response to radiation makes possible today a novel approach to identify the parameters that condition the fractionation effect. Particularly, the time between doses appears to be a key factor since it will permit, or not, the repair of certain radiation-induced DNA damages whose repair rates are of the order of seconds, minutes or hours: the fractionation effect will therefore vary according to the functionality of the different repair pathways, whatever for tumor or normal tissues.

Mutations of the Huntington's disease protein impact on the ATM-dependent signaling and repair pathways of the radiation-induced DNA double-strand breaks: corrective effect of statins and bisphosphonates

Huntington's disease (HD) is a neurodegenerative syndrome caused by mutations of the IT15 gene encoding for the huntingtin protein. Some research groups have previously shown that HD is associated with cellular radiosensitivity in quiescent cells. However, there is still no mechanistic model explaining such specific clinical feature. Here, we examined the ATM-dependent signaling and repair pathways of the DNA double-strand breaks (DSB), the key damage induced by ionizing radiation, in human HD skin fibroblasts. Early after irradiation, quiescent HD fibroblasts showed an abnormally low rate of recognized DSB managed by non-homologous end-joining reflected by a low yield of nuclear foci formed by phosphorylated H2AX histones and by 53BP1 protein. Furthermore, HD cells elicited a significant but moderate yield of unrepaired DSB 24 h after irradiation. Irradiated HD cells also presented a delayed nucleo-shuttling of phosphorylated forms of the ATM kinase, potentially due to a specific binding of ATM to mutated huntingtin in the cytoplasm. Our results suggest that HD belongs to the group of syndromes associated with a low but significant defect of DSB signaling and repair defect associated with radiosensitivity. A combination of biphosphonates and statins complements these impairments by facilitating the nucleo-shuttling of ATM, increasing the yield of recognized and repaired DSB.