Tumourigenicity and radiation resistance of mesenchymal stem cells

Direct ionizing radiation and bystander effect in mouse mesenchymal stem cells

Purpose: This study aimed to evaluate the radiation-induced direct and bystander (BYS) responses of mesenchymal stem cells (MSCs) and to characterize these cells radiobiologically.Methods and materials: MSCs were irradiated (IR) and parameters related to DNA damage and cellular signaling were verified in a dose range from 0.5 to 15 Gy; also a transwell insert co-culture system was used to study medium-mediated BYS effects.Results: The main effects on directly IR cells were seen at doses higher than 6 Gy: induction of cell death, cell cycle arrest, upregulation of p21, and alteration of redox status. Irrespective of a specific dose, induction of micronuclei formation, H2AX phosphorylation, and decreased Akt expression also occurred. Thus, mTOR expression, cell senescence, nitric oxide generation, and calcium levels, in general were not significantly modulated by radiation. Data from the linear-quadratic model showed a high alpha/beta ratio, which is consistent with a more exponential survival curve. BYS effects from the unirradiated MSCs placed into companion wells with the directly IR cells, were not observed.Conclusions: The results can be interpreted as a positive outcome, meaning that the radiation damage is restricted to the directed IR MSCs not leading to off-target cell responses.

Nicotinamide N-Methyltransferase: An Emerging Protagonist in Cancer Macro(r)evolution

Nicotinamide N-methyltransferase (NNMT) has progressed from being considered merely a Phase II metabolic enzyme to one with a central role in cell function and energy metabolism. Over the last three decades, a significant body of evidence has accumulated which clearly demonstrates a central role for NNMT in cancer survival, metastasis, and drug resistance. In this review, we discuss the evidence supporting a role for NNMT in the progression of the cancer phenotype and how it achieves this by driving the activity of pro-oncogenic NAD+-consuming enzymes. We also describe how increased NNMT activity supports the Warburg effect and how it promotes oncogenic changes in gene expression. We discuss the regulation of NNMT activity in cancer cells by both post-translational modification of the enzyme and transcription factor binding to the NNMT gene, and describe for the first time three long non-coding RNAs which may play a role in the regulation of NNMT transcription. We complete the review by discussing the development of novel anti-cancer therapeutics which target NNMT and provide insight into how NNMT-based therapies may be best employed clinically.

Intraoperative radiotherapy for breast cancer treatment efficiently targets the tumor bed preventing breast adipose stromal cell outgrowth

OBJECTIVES

Mesenchymal stromal cells (MSC) in bone marrow have been shown to be radioresistant, which is related to pronounced DNA repair mechanisms. Intraoperative radiotherapy (IORT) during breast-conserving surgery for early breast cancer is an innovative technique applying low energy x‑ray to the tumor bed immediately after removal of the tumor. IORT is considered to reduce the risk of local tumor recurrence by directly targeting cells of the tumor bed and altering the local microenvironment. Aim of this study was to investigate whether IORT affects the outgrowth potential of breast adipose tissue-derived MSC (bASC) as part of the tumor bed.

MATERIALS AND METHODS

After surgical tumor resection, biopsies of the tumor bed were taken before (pre IORT) and after IORT (post IORT) and processed applying well-established protocols for ASC isolation and characterization.

RESULTS

In all, 95% of pre IORT tumor bed samples yielded persistently outgrowing bASC with typical ASC characteristics: fibroblastoid morphology, proliferation, adipogenic and osteogenic differentiation and ASC surface marker expression. However, none of the post IORT samples yielded persistent outgrowth of bASC.

CONCLUSIONS

After breast-conserving surgery, approximately 90% of local recurrences emerge in close proximity to the initial tumor bed, potentially reflecting a significant contribution of the tumor bed to relapse. Our data show that IORT, besides the proven effect on breast cancer cells, efficiently modifies the tumor environment by having an impact on tumor bed bASC. This effect on tumor bed stromal cells might contribute to reduce the risk of tumor relapse and metastases.

Fibrinolytic crosstalk with endothelial cells expands murine mesenchymal stromal cells

Tissue plasminogen activator (tPA), aside from its vascular fibrinolytic action, exerts various effects within the body, ranging from synaptic plasticity to control of cell fate. Here, we observed that by activating plasminogen and matrix metalloproteinase-9, tPA expands murine bone marrow-derived CD45(-)TER119(-)Sca-1(+)PDGFRα(+) mesenchymal stromal cells (PαS-MSCs) in vivo through a crosstalk between PαS-MSCs and endothelial cells. Mechanistically, tPA induces the release of Kit ligand from PαS-MSCs, which activates c-Kit(+) endothelial cells to secrete MSC growth factors: platelet-derived growth factor-BB (PDGF-BB) and fibroblast growth factor 2 (FGF2). In synergy, FGF2 and PDGF-BB upregulate PDGFRα expression in PαS-MSCs, which ultimately leads to PαS-MSC expansion. These data show a novel mechanism by which the fibrinolytic system expands PαS-MSCs through a cytokine crosstalk between niche cells.

Adipose mesenchymal stromal cells response to ionizing radiation

BACKGROUND AIMS

This study evaluates the biological response of adipose tissue-derived mesenchymal stromal cells (aMSCs) to ionizing radiation (IR).

METHODS

Irradiated BALB/c mice aMSCs were characterized for functionality and phenotype. The clonogenic capacity of irradiated aMSCs was assessed and compared with those of metastatic breast cancer cell line (4T1) and normal mouse fibroblasts (NIH3T3-wt). We investigated the IR-induced DNA damage response, apoptosis, changes in cell cycle (CC) dynamics and protein and gene expression.

RESULTS

Irradiated and non-irradiated aMSCs were able to differentiate into adipocytes, chondrocytes and osteocytes with no significant difference. Irradiated aMSCs maintained the expression of mesenchymal stromal cells (MSCs) surface antigens and, as expected, were negative for hematopoietic stem cells (HSCs) surface antigens when tested up to 7 days after IR for all irradiation doses with no significant difference. Clonogenically, irradiated aMSCs had higher relative survival fraction and plating efficiency than 4T1 and NIH3T3-wt. Irradiated aMSCs expressed higher □H2AX and significantly showed faster and more time-efficient IR-induced DNA damage response evident by up-regulated DNA-PKcs and RAD51. Two hours after IR, most of aMSCs DNA damage/repair-related genes showed up-regulation that disappeared within 6 h after IR. Irradiated aMSCs showed a significant rise and an earlier peak of p-ATM-dependent and -independent (p84/5E10-mediated) G2/M CC arrest compared with 4T1 and NIH3T3-wt.

CONCLUSIONS

After IR exposure, aMSCs showed a robust and time-efficient radiation-induced DNA damage repair response, stable phenotypical characteristics and multi-lineage differentiation potential, suggesting they may be reliable candidates for cell therapy in radiation oncology regenerative medicine.

Radiation responses of stem cells: targeted and non-targeted effects

Stem cells are fundamental to the development of any tissue or organism via their ability to self-renew, which is aided by their unlimited proliferative capacity and their ability to produce fully differentiated offspring, often from multiple lineages. Stems cells are long lived and have the potential to accumulate mutations, including in response to radiation exposure. It is thought that stem cells have the potential to be induced into a cancer stem cell phenotype and that these may play an important role in resistance to radiotherapy. For radiation-induced carcinogenesis, the role of targeted and non-targeted effects is unclear with tissue or origin being important. Studies of genomic instability and bystander responses have shown consistent effects in haematopoietic models. Several models of radiation have predicted that stem cells play an important role in tumour initiation and that bystander responses could play a role in proliferation and self-renewal.

From radioresistance to radiosensitivity: In vitro evolution of L5178Y lymphoma

PURPOSE

To discuss the possible reasons for the loss of tumourigenicity and the acquisition of new phenotypic features (among them, sensitivity to X and UVC radiations) as a result of in vitro cultivation of L5178Y lymphoma cells.

RESULTS

Ten years ago the phenotypic differences between LY-R (original L5178Y maintained in vivo and examined in vitro) and LY-S lines were reviewed in detail by the author. The loss of tumourigenicity of LY-R cells upon in vitro cultivation accompanying the acquirement of the LY-S phenotype had been described earlier by Beer et al. (1983). In spite of their common origin, the sublines were shown to differ in their relative sensitivity to a number of DNA damaging agents and in numerous other features. Here, selected differences between LY-R and LY-S lines are briefly reviewed. It is proposed that Wallace's concept (2010a) that mitochondria are the interface between environmental conditions and the genome may explain the LY-R-LY-S conversion under prolonged in vitro cultivation.

CONCLUSION

The differences between the LY lines were probably of epigenetic rather than genetic character. The properties of LY-R cells changed as a result of exposure to an oxic in vitro milieu. The changes could be preconditioned by heteroplasmy and the selection of cells endowed with mitochondria best fitted to a high oxygen-low carbon dioxide environment.

Torc1/Torc2 inhibitor, Palomid 529, enhances radiation response modulating CRM1-mediated survivin function and delaying DNA repair in prostate cancer models

BACKGROUND

P529, a Torc1/Torc2 inhibitor, has demonstrated its potential as a radiosensitizer. However the molecular mechanisms underlying this phenomenon still need to be elucidated. Aim of this study is to dissect molecular mechanisms regulating the radiosensitizing properties of P529 in a wide panel of prostate cancer models.

METHODS

Six tumor cell lines and xenograft models were used for in vitro and in vivo studies. Clonogenic survival, apoptotic, autophagic, and senescence assays were used to examine the effects of ionizing radiation (IR) alone and in combination with P529. CRM1, survivin, GSK-3β, and DNA-DSBs expression and modulation, upon P529 and RT, were monitored by western blot. In vivo treatment response upon P529, irradiation or combination of P529 with IR was monitored by tumor volume, time to progression (TTP), and immunohistochemical analysis.

RESULTS

P529 treatment induced significantly more apoptosis and DNA double-strand break (DSB) when combined with radiotherapy resulting in cellular radiosensitization and growth delay of irradiated tumor xenografts. Upon P529 treatment Rad51, DNA-PKcs, and Ku70 protein expression was downregulated, indicating delayed DNA double-strand damage repair. The radiosensitizing properties of P529 were partially linked to GSK-3β, cyclin-D1, and c-myc modulation with associated inhibition of CRM1-mediated nuclear export of survivin. Importantly, autophagy and tumor senescence were involved in the enhanced P529 radioresponse.

CONCLUSIONS

Impaired DNA double-strand damage repair, inhibition of CRM1-mediated nuclear export of survivin, modulation of cyclin-D1 and c-myc with associated pro-apoptotic and autophagic and senescent events explain the radiosensitizing properties of P529 in preclinical models of prostate cancer.

Low dose effects of ionizing radiation on normal tissue stem cells

In recent years, there has been growing evidence for the involvement of stem cells in cancer initiation. As a result of their long life span, stem cells may have an increased propensity to accumulate genetic damage relative to differentiated cells. Therefore, stem cells of normal tissues may be important targets for radiation-induced carcinogenesis. Knowledge of the effects of ionizing radiation (IR) on normal stem cells and on the processes involved in carcinogenesis is very limited. The influence of high doses of IR (>5Gy) on proliferation, cell cycle and induction of senescence has been demonstrated in stem cells. There have been limited studies of the effects of moderate (0.5-5Gy) and low doses (<0.5Gy) of IR on stem cells however, the effect of low dose IR (LD-IR) on normal stem cells as possible targets for radiation-induced carcinogenesis has not been studied in any depth. There may also be important parallels between stem cell responses and those of cancer stem cells, which may highlight potential key common mechanisms of their response and radiosensitivity. This review will provide an overview of the current knowledge of radiation-induced effects on normal stem cells, with particular focus on low and moderate doses of IR.