Radiation Effects and Radioprotection in MC3T3-E1 Mouse Calvarial Osteoblastic Cells:

Modeling bystander effects that cause growth delay of breast cancer xenografts in bone marrow of mice treated with radium-223

RATIONALE

The role of radiation-induced bystander effects in cancer therapy with alpha-particle emitting radiopharmaceuticals remains unclear. With renewed interest in using alpha-particle emitters to sterilize disseminated tumor cells, micrometastases, and tumors, a better understanding of the direct effects of alpha particles and the contribution of the bystander responses they induce is needed to refine dosimetric models that help predict clinical benefit. Accordingly, this work models and quantifies the relative importance of direct effects (DE) and bystander effects (BE) in the growth delay of human breast cancer xenografts observed previously in the tibiae of mice treated with ²²³RaCl₂.

METHODS

A computational model of MDA-MB-231 and MCF-7 human breast cancer xenografts in the tibial bone marrow of mice administered ²²³RaCl₂ was created. A Monte Carlo radiation transport simulation was performed to assess individual cell absorbed doses. The responses of the breast cancer cells to direct alpha particle irradiation and gamma irradiation were needed as input data for the model and were determined experimentally using a colony-forming assay and compared to the responses of preosteoblast MC3T3-E1 and osteocyte-like MLO-Y4 bone cells. Using these data, a scheme was devised to simulate the dynamic proliferation of the tumors in vivo, including DE and BE propagated from the irradiated cells. The parameters of the scheme were estimated semi-empirically to fit experimental tumor growth.

RESULTS

A robust BE component, in addition to a much smaller DE component, was required to simulate the in vivo tumor proliferation. We also found that the relative biological effectiveness (RBE) for cell killing by alpha particle radiation was greater for the bone cells than the tumor cells.

CONCLUSION

This modeling study demonstrates that DE of radiation alone cannot explain experimental observations of ²²³RaCl₂-induced growth delay of human breast cancer xenografts. Furthermore, while the mechanisms underlying BE remain unclear, the addition of a BE component to the model is necessary to provide an accurate prediction of the growth delay. More complex models are needed to further comprehend the extent and complexity of ²²³RaCl₂-induced BE.

Amifostine Suppresses the Side Effects of Radiation on BMSCs by Promoting Cell Proliferation and Reducing ROS Production

This study is aimed at investigating the effect of amifostine (AMI) on rat bone marrow stromal stem cells (BMSCs) exposed to 2 Gy radiation. The BMSCs were divided into four groups, namely, group A that received 0 Gy radiation, group B that received 0 Gy radiation and AMI, group C that received 2 Gy radiation, and group D that received 2 Gy radiation and AMI. The proliferation, apoptosis, and distribution of BMSCs in the cell cycle, along with their osteogenesis ability, adipogenesis ability, and ROS production, were subsequently examined. The levels of ALP, PPARγ, P53, and TNFα were determined by Western blotting. The results demonstrated that the proliferation of BMSCs and the levels of ALP in group C were much lower than those in group A. The production of ROS and levels of PPARγ, P53, and TNFα in the group that received 2 Gy radiation were much higher than those in group A. Furthermore, the production of ROS and the levels of PPARγ, P53, and TNFα were much lower in group D than in group C. Additionally, the levels of ALP and extent of cell proliferation were much higher in group D than in group C. The results demonstrated the potential of AMI in reducing the side effects of radiation in BMSCs and in treatment of bone diseases caused by radiation.

Radioprotection With Amifostine Enhances Bone Strength and Regeneration and Bony Union in a Rat Model of Mandibular Distraction Osteogenesis

BACKGROUND

Using distraction osteogenesis (DO) to regenerate robust endogenous bone could greatly enhance postoncologic reconstruction of head and neck cancer. However, radiation (XRT) corrosive effects still preclude DO's immense potential. We posit that adjunctive pretreatment with the radioprotectant amifostine (AMF) can optimize wound healing and allow for successful DO with quantifiable enhancements in bony union and strength despite previous surgical bed irradiation.

METHODS

Two groups of murine left hemimandibles were exposed to a human equivalent radiation dosage fractionated over 5 daily doses of 7 Gy. AMF-XRT-DO (n = 30) received AMF before radiation, whereas XRT-DO (n = 22) was untreated. All animals underwent left hemimandibular osteotomy and external fixator placement, followed by distraction to a 5.1-mm gap. Left hemimandibles were harvested and mechanically tested for parameters of strength, yield, and breaking load.

RESULTS

Radiation-related complications such as severe alopecia were significantly increased in XRT-DO compared with the AMF-treated group (P = 0.001), whereas infection and death were comparable (P = 0.318). Upon dissection, bony defects were grossly visible in XRT-DO distraction gap compared with AMF-XRT-DO, which exhibited significantly more complete unions (P = 0.004). Those results were significantly increased in the specimens prophylactically treated with AMF (yield: 39.41 N vs 21.78 N, P = 0.023; breaking load: 61.74 N vs 34.77 N, P = 0.044; respectively).

CONCLUSIONS

Our study revealed that AMF enhances biomechanical strength, regeneration, and bony union after radiation in a murine model of DO. The use of prophylactic AMF in combination with DO offers the promise of an alternative reconstructive option for patients afflicted with head and neck cancer.

Therapeutic ionizing radiation induced bone loss: a review of in vivo and in vitro findings

Radiation therapy is one of the routine treatment modalities for cancer patients. Ionizing radiation (IR) can induce bone loss, and consequently increases the risk of fractures with delayed and nonunion of the bone in the cancer patients who receive radiotherapy. The orchestrated bone remodeling can be disrupted due to the affected behaviors of bone cells, including bone mesenchymal stem cells (BMSCs), osteoblasts and osteoclasts. BMSCs and osteoblasts are relatively radioresistant compared with osteoclasts and its progenitors. Owing to different radiosensitivities of bone cells, unbalanced bone remodeling caused by IR is closely associated with the dose absorbed. For doses less than 2 Gy, osteoclastogenesis and adipogenesis by BMSCs are enhanced, while there are limited effects on osteoblasts. High doses (>10 Gy) induce disrupted architecture of bone, which is usually related to decreased osteogenic potential. In this review, studies elucidating the biological effects of IR on bone cells (BMSCs, osteoblasts and osteoclasts) are summarized. Several potential preventions and therapies are also proposed.

Amifostine protects vascularity and improves union in a model of irradiated mandibular fracture healing

BACKGROUND

Pathologic fractures of the mandible can be devastating to cancer patients and are due in large part to the pernicious effects of irradiation on bone vascularity. The authors' aim was to ascertain whether amifostine, a radioprotective drug, will preserve vascularity and improve bone healing in a murine model of irradiated mandibular fracture repair.

METHODS

Rats were randomized into three groups: nonirradiated fracture (n = 9), irradiation/fracture (n = 5), and amifostine/irradiation/fracture (n = 7). Animals in the irradiation groups underwent a human equivalent dose of radiation directed at the left hemimandible. Animals treated in the amifostine group received amifostine concomitantly with radiation. All animals underwent unilateral left mandibular osteotomy with external fixation set to a 2.1-mm fracture gap. Fracture healing was allowed for 40 days before perfusion with Microfil. Vascular radiomorphometrics were quantified with micro-computed tomography.

RESULTS

When compared with the irradiated/fractured group, amifostine treatment more than doubled the rate of fracture unions to 57 percent. Amifostine treatment also resulted in an increase in vessel number (123 percent; p < 0.05) and a corresponding decrease in vessel separation (55.5 percent; p < 0.05) there was no statistical difference in the vascularity metrics between the amifostine/irradiation/fracture group and the nonirradiated/fracture group.

CONCLUSIONS

Amifostine prophylaxis during radiation maintains mandibular vascularity at levels observed in nonirradiated fracture specimens, corresponding to improved unions. These results set the stage for clinical exploration of this targeted therapy alone and in combination with other treatments, to mitigate the effects of irradiation on bone healing and fracture repair.

Doxorubicin-mediated bone loss in breast cancer bone metastases is driven by an interplay between oxidative stress and induction of TGFβ

Breast cancer patients, who are already at increased risk of developing bone metastases and osteolytic bone damage, are often treated with doxorubicin. Unfortunately, doxorubicin has been reported to induce damage to bone. Moreover, we have previously reported that doxorubicin treatment increases circulating levels of TGFβ in murine pre-clinical models. TGFβ has been implicated in promoting osteolytic bone damage, a consequence of increased osteoclast-mediated resorption and suppression of osteoblast differentiation. Therefore, we hypothesized that in a preclinical breast cancer bone metastasis model, administration of doxorubicin would accelerate bone loss in a TGFβ-mediated manner. Administration of doxorubicin to 4T1 tumor-bearing mice produced an eightfold increase in osteolytic lesion areas compared untreated tumor-bearing mice (P = 0.002) and an almost 50% decrease in trabecular bone volume expressed in BV/TV (P = 0.0005), both of which were rescued by anti-TGFβ antibody (1D11). Doxorubicin, which is a known inducer of oxidative stress, decreased osteoblast survival and differentiation, which was rescued by N-acetyl cysteine (NAC). Furthermore, doxorubicin treatment decreased Cu-ZnSOD (SOD1) expression and enzyme activity in vitro, and treatment with anti-TGFβ antibody was able to rescue both. In conclusion, a combination therapy using doxorubicin and anti-TGFβ antibody might be beneficial for preventing therapy-related bone loss in cancer patients.

Quantitative histologic evidence of amifostine-induced cytoprotection in an irradiated murine model of mandibular distraction osteogenesis

BACKGROUND

Head and neck cancer management requires adjuvant radiotherapy. The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation on a murine mandibular model of distraction osteogenesis. Using quantitative histomorphometry, the authors' specific aim was to objectively measure amifostine radioprotection of the cellular integrity and tissue quality of an irradiated and distracted regenerate.

METHODS

Sprague-Dawley rats were assigned randomly into two groups: radiotherapy/distraction osteogenesis and amifostine/radiotherapy/distraction osteogenesis, which received amifostine before radiotherapy. Both groups received a fractionated human equivalent dose of radiation prior to left mandibular osteotomy with fixator placement. Distraction to 5.1 mm was followed by a 28-day consolidation period. Quantitative histomorphometry was performed on left hemimandibles for osteocytes, empty lacunae, bone volume-to-tissue volume ratio, and osteoid volume-to-tissue volume ratio.

RESULTS

Amifostine/radiotherapy/distraction osteogenesis exhibited bony bridging as opposed to radiotherapy/distraction osteogenesis fibrous unions. Quantitative histomorphometry analysis revealed statistically significant higher osteocyte count and bone volume-to-tissue volume ratio in amifostine-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in empty lacunae and the ratio of osteoid volume-to-tissue volume between both groups.

CONCLUSIONS

The authors have successfully established the significant osseous cytoprotective and histoprotective capacity of amifostine for distraction osteogenesis in the face of radiotherapy. The amifostine-sparing effect on bone cellularity correlated with increased bony unions and elimination of fibrous union. The authors posit that the demonstration of similar efficacy of amifostine in the clinic may allow the successful implementation of distraction osteogenesis as a viable reconstructive option for head and neck cancer in the future.

Effects of irradiation on osteoblast-like cells on different titanium surfaces in vitro

The aim of this study was to investigate the effects of irradiation on adhesion ability, proliferation, and differentiation of MC3T3-E1 cells on microarc oxidation (MAO) titanium surfaces and polished titanium (PT) surfaces. MC3T3-E1 cells were exposed to a single dose at 2, 4, 6, 8, or 10 Gy using a (60) Co source, with tissue culture polystyrene plates chosen as controls. On all surfaces, irradiation resulted in a dose-dependent decrease in cellular proliferation. At 4 Gy dose, the cell proliferation of cells decreased by 17.8% on MAO and 18.6% on PT surfaces, respectively, compared with nonirradiated controls. Cells exposed to 8 Gy dose showed significant inhibition in collagen secretion and osteogenesis-related genes expression (OSX, COL-Iα1, and OCN). In contrast, irradiation increased cell adhesion to three surfaces dose dependently. It was also demonstrated that cells on MAO surface showed higher adhesion and collagen secretion than on PT surface at different radiation doses. This study revealed the effects of irradiation on osteoblasts in vitro on two titanium surfaces. MAO surface could be used in dental implants in irradiated bone due to enhanced adhesion ability and collagen secretion in osteoblasts.

The effects of low dose X-irradiation on osteoblastic MC3T3-E1 cells in vitro

BACKGROUND

It has been indicated that moderate or high dose of X-irradiation could delay fracture union and cause osteoradionecrosis, in part, mediated by its effect on proliferation and differentiation of osteoblasts. However, whether low dose irradiation (LDI) has similar roles on osteoblasts is still unknown. In this study, we investigated whether and to what extent LDI could affect the proliferation, differentiation and mineralization of osteoblasts in vitro.

METHODS

The MC3T3-E1 cells were exposed to single dose of X-irradiation with 0, 0.1, 0.5, 1.0 Gy respectively. Cell proliferation, apoptosis, alkaline phosphatase (ALP) activity, and mineralization was evaluated by methylthiazoletetrazolium (MTT) and bromodeoxyuridine (BrdU) assay, flow cytometry, ALP viability kit and von Kossa staining, respectively. Osteocalcin (OCN) and core-binding factor α1 (Cbfα1) expressions were measured by real time-PCR and western blot, respectively.

RESULTS

The proliferation of the cells exposed to 2.0 Gy was significantly lower than those exposed to ≤1.0 Gy (p < 0.05) from Day 4 to Day 8, measured by MTT assay and BrdU incorporation. For cells exposed to ≤1.0 Gy, increasing dosages of X-irradiation had no significant effect on cell proliferation and apoptosis. Importantly, LDI of 0.5 and 1 Gy increased ALP activities and mineralized nodules of MC3T3-E1 cells. In addition, mRNA and protein expressions of OCN and Cbfα1 were also markedly increased after treatment with LDI at 0.5 and 1 Gy.

CONCLUSIONS

LDI have different effects on proliferation and differentiation of osteoblasts from those of high dose of X-irradiation, which might suggest that LDI could lead to promotion of fracture healing through enhancing the differentiation and mineralization of osteoblasts.

Quantitative histomorphometric assessment of regenerate cellularity and bone quality in mandibular distraction osteogenesis after radiation therapy

BACKGROUND

The use of mandibular distraction osteogenesis (MDO) for tissue replacement after oncologic resection in head and neck cancer could have immense therapeutic ramifications. We have previously demonstrated significantly decreased mechanical and microdensitomeric metrics of our MDO regenerate after 36-Gy radiation. Quantitative histomorphometry, a third metric, would permit objective investigation of the effects of radiation on tissue and cellular composition. Our hypothesis is that radiation-induced cellular depletion and diminution in function impair optimal bone regeneration.

METHODS

Five rats received radiation to the left mandible; 5 received none. All animals underwent surgical placement of external fixators, creation of mandibular osteotomies, distraction to a 5.1-mm gap width, and consolidation. Point counting and color thresholding were performed.

RESULTS

There was a significant increase in empty lacunae and a corresponding diminution in osteocytes after radiation. Whereas the volume fraction of mineralized, mature bone was not different, that of nonmineralized, immature osteoid was significantly increased in the radiated group compared with that in the nonradiated group.

CONCLUSIONS

Our findings confirm our prior 2 metrics. Actually, all 3 diverse metrics--microdensitometry, biomechanical analysis, and histomorphometry--corroborate our hypothesis of cellular depletion and diminution of function as the potential mechanism of radiation-induced attenuation in the distracted regenerate. Furthermore, our findings of tissue and cellular changes in the irradiated regenerate elucidate the pathophysiology of decreased bone quality when amalgamated with our previous results. Therapeutic agents may now be introduced, and their effects on the irradiated regenerate critically measured, so that MDO may be used as a viable reconstructive option in patients with head and neck cancer.

Effects of osteopontin inhibition on radiosensitivity of MDA-MB-231 breast cancer cells

Background

Osteopontin (OPN) is a secreted glycophosphoprotein that is overexpressed in various tumors, and high levels of OPN have been associated with poor prognosis of cancer patients. In patients with head and neck cancer, high OPN plasma levels have been associated with poor prognosis following radiotherapy. Since little is known about the relationship between OPN expression and radiosensitivity, we investigated the cellular and radiation induced effects of OPN siRNA in human MDA-MB-231 breast cancer cells.

Methods

MDA-MB-231 cells were transfected with OPN-specific siRNAs and irradiated after 24 h. To verify the OPN knockdown, we measured the OPN mRNA and protein levels using qRT-PCR and Western blot analysis. Furthermore, the functional effects of OPN siRNAs were studied by assays to assess clonogenic survival, migration and induction of apoptosis.

Results

Treatment of MDA-MB-231 cells with OPN siRNAs resulted in an 80% decrease in the OPN mRNA level and in a decrease in extracellular OPN protein level. Transfection reduced clonogenic survival to 42% (p = 0.008), decreased the migration rate to 60% (p = 0.15) and increased apoptosis from 0.3% to 1.7% (p = 0.04). Combination of OPN siRNA and irradiation at 2 Gy resulted in a further reduction of clonogenic survival to 27% (p < 0.001), decreased the migration rate to 40% (p = 0.03) and increased apoptosis to 4% (p < 0.005). Furthermore, OPN knockdown caused a weak radiosensitization with an enhancement factor of 1.5 at 6 Gy (p = 0.09) and a dose modifying factor (DMF₁₀) of 1.1.

Conclusion

Our results suggest that an OPN knockdown improves radiobiological effects in MDA-MB-231 cells. Therefore, OPN seems to be an attractive target to improve the effectiveness of radiotherapy.

Short-term effects of whole-body exposure to (56)fe ions in combination with musculoskeletal disuse on bone cells

Space travel and prolonged bed rest cause bone loss due to musculoskeletal disuse. In space, radiation fields may also have detrimental consequences because charged particles traversing the tissues of the body can elicit a wide range of cytotoxic and genotoxic lesions. The effects of heavy-ion radiation exposure in combination with musculoskeletal disuse on bone cells and tissue are not known. To explore this, normally loaded 16-week-old male C57BL/6 mice were exposed to (56)Fe ions (1 GeV/nucleon) at doses of 0 cGy (sham), 10 cGy, 50 cGy or 2 Gy 3 days before tissue harvest. Additional mice were hindlimb unloaded by tail traction continuously for 1 week to simulate weightlessness and exposed to (56)Fe-ion radiation (0 cGy, 50 cGy, 2 Gy) 3 days before tissue harvest. Despite the short duration of this study, low-dose (10, 50 cGy) irradiation of normally loaded mice reduced trabecular volume fraction (BV/TV) in the proximal tibiae by 18% relative to sham-irradiated controls. Hindlimb unloading together with 50 cGy radiation caused a 126% increase in the number of TRAP(+) osteoclasts on cancellous bone surfaces relative to normally loaded, sham-irradiated controls. Together, radiation and hindlimb unloading had a greater effect on suppressing osteoblastogenesis ex vivo than either treatment alone. In sum, low-dose exposure to heavy ions (50 cGy) caused rapid cancellous bone loss in normally loaded mice and increased osteoclast numbers in hindlimb unloaded mice. In vitro irradiation also was more detrimental to osteoblastogenesis in bone marrow cells that were recovered from hindlimb unloaded mice compared to cells from normally loaded mice. Furthermore, irradiation in vitro stimulated osteoclast formation in a macrophage cell line (RAW264.7) in the presence of RANKL (25 ng/ml), showing that heavy-ion radiation can stimulate osteoclast differentiation even in the absence of osteoblasts. Thus heavy-ion radiation can acutely increase osteoclast numbers in cancellous tissue and, under conditions of musculoskeletal disuse, can enhance the sensitivity of bone cells, in particular osteoprogenitors, to the effects of radiation.