Radiation resistance of cancer stem cells: the 4 R's of radiobiology revisited

Voxel based comparison and texture analysis of 18F-FDG and 18F-FMISO PET of patients with head-and-neck cancer

Background

Hypoxia can induce radiation resistance and is an independent prognostic marker for outcome in head and neck cancer. As ¹⁸F-FMISO (FMISO), a hypoxia tracer for PET, is far less common than ¹⁸F-FDG (FDG) and two separate PET scans result in doubled cost and radiation exposure to the patient, we aimed to predict hypoxia from FDG PET with new techniques of voxel based analysis and texture analysis.

Methods

Thirty-eight patients with head-and-neck cancer underwent consecutive FDG and FMISO PET scans before any treatment. ROIs enclosing the primary cancer were compared in a voxel-by-voxel manner between FDG and FMISO PET. Tumour hypoxia was defined as the volume with a tumour-to-muscle ratio (TMR) > 1.25 in the FMISO PET and hypermetabolic volume was defined as >50% SUVmax in the FDG PET. The concordance rate was defined as percentage of voxels within the tumour which were both hypermetabolic and hypoxic. 38 different texture analysis (TA) parameters were computed based on the ROIs and correlated with presence of hypoxia.

Results

Within the hypoxic tumour regions, the FDG uptake was twice as high as in the non-hypoxic tumour regions (SUVmean 10.9 vs. 5.4; p<0.001). A moderate correlation between FDG and FMISO uptake was found by a voxel-by-voxel comparison (r = 0.664 p<0.001). The average concordance rate was 25% (± 22%). Entropy was the TA parameter showing the highest correlation with hypoxia (r = 0.524 p<0.001).

Conclusion

FDG uptake was higher in hypoxic tumour regions than in non-hypoxic regions as expected by tumour biology. A moderate correlation between FDG and FMISO PET was found by voxel-based analysis. TA yielded similar results in FDG and FMISO PET. However, it may not be possible to predict tumour hypoxia even with the help of texture analysis.

Y90 Radioembolization Dosimetry: Concepts for the Interventional Radiologist

Transarterial radioembolization (TARE) with beta particle emitting microspheres via Yttrium-90 decay has become a fundamental component of the contemporary Interventional Oncology practice. TARE continues to advance as a result of increased utilization, clinical study, technological improvements, and evolving applications. To maximize TARE safety and efficacy, a core understanding of dosimetry is essential. The intent of this overview is to provide the reader with a general survey of radiation physics and biology, device differentiation, patient selection, anatomic assessment, activity administration models, and procedural techniques involved with TARE dosimetry.

Therapeutic Effects of Human Adipose-Derived Products on Impaired Wound Healing in Irradiated Tissue

BACKGROUND

Clinical sequelae of irradiation result in tissue devitalization (e.g., ischemia, fibrosis, and atrophy) where wound healing capacity is impaired. Fat-derived products may work to treat such pathology.

METHODS

Nonlethal irradiation at various doses (5, 10, and 15 Gy) and frequencies (one to three times on sequential days) was delivered to dorsal skin of nude mice, and subsequent gross and microscopic changes were evaluated for up to 4 weeks. Cutaneous punch wounds were then created to compare wound healing in irradiated and nonirradiated states. Wounds were also locally injected with vehicle, cultured adipose-derived stem cells, centrifuged fat tissue, or micronized cellular adipose matrix, and the therapeutic impact was monitored for up to 15 days.

RESULTS

Nude mice given total doses greater than 15 Gy spontaneously developed skin ulcers, and radiation damage was dose-dependent; however, a fractionated irradiation protocol was able to reduce the damage. Histologic assessment revealed dose-dependent dermal fibrosis/thickening and subcutaneous atrophy. Dose-dependent (5 to 15 Gy) impairment of wound healing was also evident. At the highest dosage (15 Gy three times), open wounds persisted on day 15. However, wounds injected with cultured adipose-derived stem cells were nearly healed on day 12, and those treated with injection of centrifuged fat or micronized tissue healed faster than untreated controls (p < 0.05). There was no significant differences between treated groups.

CONCLUSIONS

Tissue devitalization by irradiation was dose-dependent, although fractionated protocols helped to reduce it. Adipose-derived stem cells and other fat-derived products harboring adipose-derived stem cells successfully revitalized irradiated tissues and accelerated wound healing.

Moving Breast Cancer Therapy up a Notch

Breast cancer is the second most common malignancy, worldwide. Treatment decisions are based on tumor stage, histological subtype, and receptor expression and include combinations of surgery, radiotherapy, and systemic treatment. These, together with earlier diagnosis, have resulted in increased survival. However, initial treatment efficacy cannot be guaranteed upfront, and these treatments may come with (long-term) serious adverse effects, negatively affecting a patient's quality of life. Gene expression-based tests can accurately estimate the risk of recurrence in early stage breast cancers. Disease recurrence correlates with treatment resistance, creating a major need to resensitize tumors to treatment. Notch signaling is frequently deregulated in cancer and is involved in treatment resistance. Preclinical research has already identified many combinatory therapeutic options where Notch involvement enhances the effectiveness of radiotherapy, chemotherapy or targeted therapies for breast cancer. However, the benefit of targeting Notch has remained clinically inconclusive. In this review, we summarize the current knowledge on targeting the Notch pathway to enhance current treatments for breast cancer and to combat treatment resistance. Furthermore, we propose mechanisms to further exploit Notch-based therapeutics in the treatment of breast cancer.

Enhancement of radiotherapeutic efficacy for esophageal cancer by paclitaxel-loaded red blood cell membrane nanoparticles modified by the recombinant protein anti-EGFR-iRGD

Paclitaxel is widely used as a radiosensitizer for various tumors, including esophageal cancer, but its therapeutic effect remains to be improved. In this study, we constructed a novel nano-radiosensitizer, anti-EGFR-iRGD-conjugated (iE)-PRNPs, by conjugating the recombinant protein anti-epidermal growth factor receptor (EGFR)-internalizing arginine-glycine-aspartic (iRGD) to the surface of paclitaxel-loaded red blood cell membrane nanoparticles (PRNPs). The iE-PRNPs were confirmed to possess tumor-targeting, high penetrability, and sustained release properties that free paclitaxel does not possess. Compared with that of paclitaxel, the sensitizer enhancement ratio of iE-PRNPs was significantly increased (1.32-fold and 1.25-fold) in esophageal cancer cells with high and low expression levels of EGFR, respectively. Additionally, compared with that of unmodified PRNPs, the sensitizer enhancement ratio of iE-PRNPs in EGFR-overexpressing esophageal cancer cells was significantly increased (1.27-fold), while that of PRNPs in esophageal cancer cells with a low EGFR expression level increased slightly (1.06-fold). The improved radiosensitization effect was associated with enhanced G2/M arrest, increased reactive oxygen species, and more effective induction of DNA double-strand breaks. In summary, iE-PRNPs appear to be a novel type of radiosensitizer with the potential to overcome the bottleneck of esophageal cancer radiotherapeutic efficacy.

Co-culture of dendritic cells and cytokine-induced killer cells effectively suppresses liver cancer stem cell growth by inhibiting pathways in the immune system

BACKGROUND

Application of dendritic cells (DC) for cancer immunotherapy involves tumor-associated immunogenic antigens for effective therapeutic strategies. The present study investigated whether DC co-cultured with autologous cytokine-induced killer cells (CIK) could induce a more specific immune response against liver cancer stem cells (LCSC) generated from human hepatocellular carcinoma (HCC) cells in vitro and in vivo.

METHODS

Human DC and CIK were generated from peripheral blood mononuclear cells (PBMCs) taken from consenting liver cancer patients. Flow cytometry was used to determine the phenotypes of DC and CIK, and cell proliferation. The tumor growth and anti-tumor activity of these cells were further evaluated using a nude mouse tumor model.

RESULTS

We demonstrated that DC and CIK significantly enhanced the apoptosis ratio, depending on DC-CIK cell numbers, by increasing caspase-3 protein expression and reducing proliferating cell nuclear antigen (PCNA) protein expression against LCSC. The in vivo data indicated that DC-CIK exhibited significant LCSC cell-induced tumor growth inhibition in nude mice, which was most significant with LCSC antigen loaded DCs.

CONCLUSIONS

The results showed, that DC-CIK cells could inhibit HCC and LCSC growths in vitro and in vivo and the most successful DC triggering of cell cytotoxic activity could be achieved by their LCSC antigen loading.

Differential Inhibitory Effects of Curcumin Between HPV+ve and HPV-ve Oral Cancer Stem Cells

Aim: To investigate the role of a herbal antioxidative compound curcumin on cell proliferation, orosphere formation and miRNA-21 expression in HPV16+ve/–ve oral cancer stem cells.

Materials and Methods: Oral cancer stem cells were isolated from HPV+ve/HPV–ve oral cancer cell lines by FACS and stemness markers. MTT, spheroid assay and qRT-PCR were employed to examine the effects of curcumin.

Results: Curcumin treatment in micromolar concentration (0–50 μM) demonstrated significant differential inhibition in CSC proliferation, orosphere formation and miRNA-21 expression in a dose dependent manner, the effect being highly pronounced in HPV positive CSCs.

Conclusion: The strong and dose-dependent inhibitory effects of curcumin on cell proliferation, stemness and miRNA appear to be due to its chemosensitizing and anticancer effects on OSCC-CSCs.

DNA Repair Deficient Chinese Hamster Ovary Cells Exhibiting Differential Sensitivity to Charged Particle Radiation under Aerobic and Hypoxic Conditions

It has been well established that hypoxia significantly increases both cellular and tumor resistance to ionizing radiation. Hypoxia associated radiation resistance has been known for some time but there has been limited success in sensitizing cells to radiation under hypoxic conditions. These studies show that, when irradiated with low linear energy transfer (LET) gamma-rays, poly (ADP-ribose), polymerase (PARP), Fanconi Anemia (FANC), and mutant Chinese Hamster Ovary (CHO) cells respond similarly to the non-homologous end joining (NHEJ) and the homologous recombination (HR) repair mutant CHO cells. Comparable results were observed in cells exposed to 13 keV/μm carbon ions. However, when irradiated with higher LET spread out Bragg peak (SOBP) carbon ions, we observed a decrease in the oxygen enhancement ratio (OER) in all the DNA of repair mutant cell lines. Interestingly, PARP mutant cells were observed as having the largest decrease in OER. Finally, these studies show a significant increase in the relative biological effectiveness (RBE) of high LET SOBP carbon and iron ions in HR and PARP mutants. There was also an increase in the RBE of NHEJ mutants when irradiated to SOBP carbon and iron ions. However, this increase was lower than in other mutant cell lines. These findings indicate that high LET radiation produces unique types of DNA damage under hypoxic conditions and PARP and HR repair pathways play a role in repairing this damage.

New physical approaches to treat cancer stem cells: a review

Cancer stem cells (CSCs) have been identified as the main center of tumor therapeutic resistance. They are highly resistant against current cancer therapy approaches particularly radiation therapy (RT). Recently, a wide spectrum of physical methods has been proposed to treat CSCs, including high energetic particles, hyperthermia (HT), nanoparticles (NPs) and combination of these approaches. In this review article, the importance and benefits of the physical CSCs therapy methods such as nanomaterial-based heat treatments and particle therapy will be highlighted.

Precision Medicine with Imprecise Therapy: Computational Modeling for Chemotherapy in Breast Cancer

Medical oncology is in need of a mathematical modeling toolkit that can leverage clinically-available measurements to optimize treatment selection and schedules for patients. Just as the therapeutic choice has been optimized to match tumor genetics, the delivery of those therapeutics should be optimized based on patient-specific pharmacokinetic/pharmacodynamic properties. Under the current approach to treatment response planning and assessment, there does not exist an efficient method to consolidate biomarker changes into a holistic understanding of treatment response. While the majority of research on chemotherapies focus on cellular and genetic mechanisms of resistance, there are numerous patient-specific and tumor-specific measures that contribute to treatment response. New approaches that consolidate multimodal information into actionable data are needed. Mathematical modeling offers a solution to this problem. In this perspective, we first focus on the particular case of breast cancer to highlight how mathematical models have shaped the current approaches to treatment. Then we compare chemotherapy to radiation therapy. Finally, we identify opportunities to improve chemotherapy treatments using the model of radiation therapy. We posit that mathematical models can improve the application of anticancer therapeutics in the era of precision medicine. By highlighting a number of historical examples of the contributions of mathematical models to cancer therapy, we hope that this contribution serves to engage investigators who may not have previously considered how mathematical modeling can provide real insights into breast cancer therapy.

Repositioning disulfiram as a radiosensitizer against atypical teratoid/rhabdoid tumor

Background

Atypical teratoid/rhabdoid tumor (AT/RT) is one of the most common malignant brain tumors in infants. Although cancer stem cells of AT/RT express aldehyde dehydrogenase (ALDH), effective chemotherapies against AT/RT have not been established. Here, we examined radiosensitizing effects of disulfiram (DSF), an irreversible inhibitor of ALDH against AT/RT for a novel therapeutic method.

Methods

Patient-derived primary cultured AT/RT cells (SNU.AT/RT-5 and SNU.AT/RT-6) and established AT/RT cell lines (BT-12 and BT-16) were used to assess therapeutic effects of combining DSF with radiation treatment (RT). Survival fraction by clonogenic assay, protein expression, immunofluorescence, and autophagy analysis were evaluated in vitro. Antitumor effects of combining DSF with RT were verified by bioluminescence imaging, tumor volume, and survival analysis in vivo.

Results

The results demonstrated that DSF at low concentration enhanced the radiosensitivity of AT/RT cells with reduction of survival fraction to 1.21‒1.58. DSF increased DNA double-strand break (γ-H2AX, p-DNA-PKcs, and p-ATM), apoptosis (cleaved caspase-3), autophagy (LC3B), and cell cycle arrest (p21) in irradiated AT/RT cells, while it decreased anti-apoptosis (nuclear factor-kappaB, Survivin, and B-cell lymphoma 2 [Bcl2]). In vivo, DSF and RT combined treatment significantly reduced tumor volumes and prolonged the survival of AT/RT mouse models compared with single treatments. The combined treatment also increased γ-H2AX, cleaved caspase-3, and LC3B expression and decreased ALDH1, Survivin, and Bcl2 expression in vivo.

Conclusions

DSF and RT combination therapy has additive therapeutic effects on AT/RT by potentiating programmed cell death, including apoptosis and autophagy of AT/RT cells. We suggest that DSF can be applied as a radiosensitizer in AT/RT treatment.

Targeted alpha therapy using Radium-223: From physics to biological effects

With the advance of the use of ionizing radiation in therapy, targeted alpha therapy (TAT) has assumed an important role around the world. This kind of therapy can potentially reduce side effects caused by radiation in normal tissues and increased destructive radiobiological effects in tumor cells. However, in many countries, the use of this therapy is still in a pioneering phase. Radium-223 (²²³Ra), an alpha-emitting radionuclide, has been the first of its kind to be approved for the treatment of bone metastasis in metastatic castration-resistant prostate cancer. Nevertheless, the interaction mechanism and the direct effects of this radiopharmaceutical in tumor cells are not fully understood neither characterized at a molecular level. In fact, the ways how TAT is linked to radiobiological effects in cancer is not yet revised. Therefore, this review introduces some physical properties of TAT that leads to biological effects and links this information to the hallmarks of cancer. The authors also collected the studies developed with ²²³Ra to correlate with the three categories reviewed - properties of TAT, 5 R's of radiobiology and hallmarks of cancer- and with the promising future to this radiopharmaceutical.

Trends and outcomes of neoadjuvant radiotherapy compared with postoperative radiotherapy for malignant breast cancer

Background

Although neoadjuvant treatment has become the established approach for women with large primary tumors or locally advanced breast cancer for which immediate surgery is not the best approach, it may also stimulate cancer stem cell self-renewal and facilitate recurrence. We sought to determine the survival outcomes of preoperative radiotherapy (PRRT) compared with postoperative radiotherapy (PORT).

Materials and Methods

The Surveillance, Epidemiology, and End Results (SEER) registry was queried for patients who were diagnosed with breast cancer and underwent cancer-directed surgery. Survival analyses were performed with Cox proportional hazard regression for both overall survival (OS) and disease-specific survival (DSS), and 1:1 propensity score (PS) matching-adjusted competing risk analyses were conducted for DSS.

Results

We first identified 1,111,218 eligible patients in 18 registries from 1973 to 2013 and found that, outside of the Utah registry, sequence patterns other than PORT were rarely used. Thus, we next identified eligible patients registered in Utah (n = 7,042) from 1988 to 2007. The treatment trends shifted abruptly in 1988. Compared with the PORT group, the PRRT group showed significantly higher risks of overall mortality (absolute difference, 22.4%; P < 0.001), breast cancer-specific mortality (absolute difference, 8.6%; P < 0.001), and cardiovascular disease-specific mortality (absolute difference, 11.5%; P = 0.021). Survival differences in treatment sequences were correlated with stage.

Conclusions

Substantial shifts in treatment patterns for malignant breast cancer were identified in Utah. Compared with PORT, PRRT showed significantly worse outcomes. These results could inform future standardized options for radiation sequence with surgery and further clinical trials.

Breast cancer stem cell-like cells generated during TGFβ-induced EMT are radioresistant

Failure of conventional antitumor therapy is commonly associated with cancer stem cells (CSCs), which are often defined as inherently resistant to radiation and chemotherapeutic agents. However, controversy about the mechanisms involved in the radiation response remains and the inherent intrinsic radioresistance of CSCs has also been questioned. These discrepancies observed in the literature are strongly associated with the cell models used. In order to clarify these contradictory observations, we studied the radiosensitivity of breast CSCs using purified CD24^−/low/CD44⁺ CSCs and their corresponding CD24⁺/CD44^low non-stem cells. These cells were generated after induction of the epithelial-mesenchymal transition (EMT) by transforming growth factor β (TGFβ) in immortalized human mammary epithelial cells (HMLE). Consequently, these 2 cellular subpopulations have an identical genetic background, their differences being related exclusively to TGFβ-induced cell reprogramming. We showed that mesenchymal CD24^−/low/CD44⁺ CSCs are more resistant to radiation compared with CD24⁺/CD44^low parental cells. Cell cycle distribution and free radical scavengers, but not DNA repair efficiency, appeared to be intrinsic determinants of cellular radiosensitivity. Finally, for the first time, we showed that reduced radiation-induced activation of the death receptor pathways (FasL, TRAIL and TNF-α) at the transcriptional level was a key causal event in the radioresistance of CD24^−/low/^CD44+ cells acquired during EMT.

Adjuvant Chemotherapy Seemed Not to Have Survival Benefit in Rectal Cancer Patients with ypTis-2N0 After Preoperative Radiotherapy and Surgery from a Population-Based Propensity Score Analysis

BACKGROUND

Adjuvant chemotherapy is currently offered routinely, as standard, after radical resection for patients with rectal cancer receiving neo-adjuvant chemoradiation. However, the efficacy of adjuvant chemotherapy in patients with ypTis-2N0M0 has not been documented to the same extent, and the survival benefit remained controversial. The purpose of this work was to determine the role of chemotherapy in patients with ypTis-2N0M0 classification.

MATERIALS AND METHODS

Data were obtained from the Surveillance, Epidemiology, and End Results database (n = 4,217). A propensity score model was utilized to balance baseline covariates.

RESULTS

Of the 4,217 included patients, 335 with ypTis-2N0M0 did not receive adjuvant chemotherapy. There were comparable cancer-specific survivals (CSS) between those undergoing adjuvant chemotherapy or not (log-rank test = 0.136, p = .712) in the overall sample. After propensity score matching, the cancer-specific survival did not differ between the chemotherapy and observation groups (log-rank test = 0.089, p = .765). Additionally, the Cox model did not demonstrate adjuvant chemotherapy as the prognostic factor, with hazard ratio = 0.95 (95% confidence interval 0.69-1.32) for CSS. Furthermore, the 10-year cumulative CSS was 78.7% and 79.4% between the chemotherapy and observation groups, indicating no significance, and no impact of adjuvant chemotherapy on survival was observed in different subgroups stratified by T stage, histological grade, histology, lymph nodes, and tumor size.

CONCLUSION

Patients with ypTis-2N0 rectal cancer did not benefit from adjuvant chemotherapy after preoperative radiology and radical surgery in this cohort study. These results provided new insight into the routine use of adjuvant chemotherapy for patients with rectal cancer with completed neo-adjuvant radiotherapy and curative surgery.

IMPLICATIONS FOR PRACTICE

Inconsistent recommendations for patients with rectal cancer receiving neo-adjuvant chemoradiation are offered by clinical guidelines. Adjuvant chemotherapy had no cancer-specific survival benefit, not only in the whole cohort, but also in the propensity score-matched cohort. A Cox model also confirmed adjuvant chemotherapy was not a significant prognostic factor in ypTis-2N0 rectal cancer. No survival benefit conferred by adjuvant chemotherapy was observed, regardless of whether T stage, histological type, grade, lymph nodes and tumor size varied.

Oncolytic Virotherapy versus Cancer Stem Cells: A Review of Approaches and Mechanisms

A growing body of evidence suggests that a subset of cells within tumors are resistant to conventional treatment modalities and may be responsible for disease recurrence. These cells are called cancer stem cells (CSC), which share properties with normal stem cells including self-renewal, pluripotency, drug resistance, and the ability to maintain quiescence. While most conventional therapies can efficiently destroy rapidly dividing cancer cells comprising the bulk of a tumor, they often fail to kill the less abundant and quiescent CSCs. Furthermore, killing of only differentiated cells in the tumor may actually allow for enrichment of CSCs and thereby portend a bad prognosis. Therefore, targeting of CSCs is important to achieve long-term success in cancer therapy. Oncolytic viruses represent a completely different class of therapeutics that can kill cancer cells in a variety of ways, which differ from those of conventional therapies. Hence, CSCs that are inherently resistant to conventional therapies may be susceptible to oncolytic virus-mediated killing. Recent studies have shown that oncolytic viruses can efficiently kill CSCs in many types of cancer. Here, we discuss the mechanism through which CSCs can escape conventional therapies and how they may still be susceptible to different classes of oncolytic viruses. Furthermore, we provide a summary of recent studies that have tested oncolytic viruses on CSCs of different origins and discuss possible future directions for this fascinating subset of oncolytic virus research.

Multi-Scale Modeling and Oxygen Impact on Tumor Temporal Evolution: Application on Rectal Cancer During Radiotherapy

We present a multi-scale approach of tumor modeling in order to predict its evolution during radiotherapy. Within this context we focus on three different scales of tumor modeling: microscopic (individual cells in a voxel), mesoscopic (population of cells in a voxel) and macroscopic (whole tumor), with transition interfaces between these three scales. At the cellular level, the description is based on phase transfer probabilities in the cellular cycle. At the mesoscopic scale we represent populations of cells according to different stages in a cell cycle. Finally, at the macroscopic scale, the tumor description is based on the use of FDG PET image voxels. These three scales exist naturally: biological data are collected at the macroscopic scale, but the pathological behavior of the tumor is based on an abnormal cell-cycle at the microscopic scale. On the other hand, the introduction of a mesoscopic scale is essential in order to reduce the gap between the two extreme, in terms of resolution, description levels. It also reduces the computational burden of simulating a large number of individual cells. As an application of the proposed multi-scale model, we simulate the effect of oxygen on tumor evolution during radiotherapy. Two consecutive FDG PET images of 17 rectal cancer patients undergoing radiotherapy are used to simulate the tumor evolution during treatment. The simulated results are compared with those obtained on a third FDG PET image acquired two weeks after the beginning of the treatment.

Proteomic identification of the lactate dehydrogenase A in a radioresistant prostate cancer xenograft mouse model for improving radiotherapy

Radioresistance is a major challenge for prostate cancer (CaP) metastasis and recurrence after radiotherapy. This study aimed to identify potential protein markers and signaling pathways associated with radioresistance using a PC-3 radioresistant (RR) subcutaneous xenograft mouse model and verify the radiosensitization effect from a selected potential candidate. PC-3RR and PC-3 xenograft tumors were established and differential protein expression profiles from two groups of xenografts were analyzed using liquid chromatography tandem-mass spectrometry. One selected glycolysis marker, lactate dehydrogenase A (LDHA) was validated, and further investigated for its role in CaP radioresistance. We found that 378 proteins and 51 pathways were significantly differentially expressed between PC-3RR and PC-3 xenograft tumors, and that the glycolysis pathway is closely linked with CaP radioresistance. In addition, we also demonstrated that knock down of LDHA with siRNA or inhibition of LDHA activity with a LDHA specific inhibitor (FX-11), could sensitize PC-3RR cells to radiotherapy with reduced epithelial-mesenchymal transition, hypoxia, DNA repair ability and autophagy, as well as increased DNA double strand breaks and apoptosis. In summary, we identified a list of potential RR protein markers and important signaling pathways from a PC-3RR xenograft mouse model, and demonstrate that targeting LDHA combined with radiotherapy could increase radiosensitivity in RR CaP cells, suggesting that LDHA is an ideal therapeutic target to develop combination therapy for overcoming CaP radioresistance.

Targeting and killing glioblastoma with monoclonal antibody to O-acetyl GD2 ganglioside

There are still unmet medical needs in the treatment of glioblastoma, the most common and the most aggressive glioma of all brain tumors. Here, we found that O-acetyl GD2 is expressed in surgically resected human glioblastoma tissue. In addition, we demonstrated that 8B6 monoclonal antibody specific for O-acetylat GD2 could effectively inhibit glioblastoma cell proliferation in vitro and in vivo. Taken together, these results indicate that O-acetylated GD2 represents a novel antigen for immunotherapeutic-based treatment of high-grade gliomas.

High chloride channel accessory 1 expression predicts poor prognoses in patients with rectal cancer receiving chemoradiotherapy

Background: Concurrent chemoradiotherapy (CCRT) has now become the standard of treatments for advanced rectal cancer before surgery. To search the biological molecules with prognostic and therapeutic potential of CCRT could be beneficial for these patients. Recently, aberrant expression of chloride channels has been linked to radio-resistance in glioblastoma; however, its clinical implication has not been well-studied in rectal cancers. Therefore, we examined the clinical significance of targetable drivers associated with chloride channel activity in patients with rectal cancer receiving CCRT. Methods: After datamining from a published transcriptome of rectal cancers, upregulation of CLCA1 gene was recognized to be significantly correlated with non-responders of CCRT. In validation cohort of rectal cancers, the expression levels of CLCA1 were accessed by using immunohistochemistry assays in 172 tumor specimens that were obtained before any treatment. Expression levels of CLCA1 were statistically analyzed with principal clinicopathological features and survival outcomes in this substantial cohort. Results: In validation cohort, high expression of CLCA1 was significantly associated with higher pre-treatment tumor nodal stages (P=0.032), vascular invasion (P=0.028), and inferior tumor regression grade (P=0.042). In survival evaluations, high expression of CLCA1 was significantly correlated with worse local recurrence-free survival (LRFS; P=0.0012), metastasis-free survival (MeFS; P =0.0114), and disease-specific survival (DSS; P=0.0041). Furthermore, high expression of CLCA1 remained an independent prognosticator of shorter LRFS (P=0.029, hazard ratio=2.555), MeFS (P=0.044, hazard ratio=2.125) and DSS (P=0.044, hazard ratio=2.172). Conclusions: High expression of CLCA1 is significantly associated with poor therapeutic response and survival outcomes in rectal cancer patients with CCRT treatment before surgery. With the development of specific inhibitors, our findings indicate not only prognostic but also therapeutic potential of CLCA1 in rectal cancers.

Fractionation enhances acute oligodendrocyte progenitor cell radiation sensitivity and leads to long term depletion

Ionizing radiation (IR) is commonly used to treat central nervous system (CNS) cancers and metastases. While IR promotes remission, frequent side effects including impaired cognition and white matter loss occur following treatment. Fractionation is used to minimize these CNS late side effects, as it reduces IR effects in differentiated normal tissue, but not rapidly proliferating normal or tumor tissue. However, side effects occur even with the use of fractionated paradigms. Oligodendrocyte progenitor cells (OPCs) are a proliferative population within the CNS affected by radiation. We hypothesized that fractionated radiation would lead to OPC loss, which could contribute to the delayed white matter loss seen after radiation exposure. We found that fractionated IR induced a greater early loss of OPCs than an equivalent single dose exposure. Furthermore, OPC recovery was impaired following fractionated IR. Finally, reduced OPC differentiation and mature oligodendrocyte numbers occurred in single dose and fractionated IR paradigms. This work demonstrates that fractionation does not spare normal brain tissue and, importantly, highlights the sensitivity of OPCs to fractionated IR, suggesting that fractionated schedules may promote white matter dysfunction, a point that should be considered in radiotherapy.

Overcoming chemo/radio-resistance of pancreatic cancer by inhibiting STAT3 signaling

Chemo/radio-therapy resistance to the deadly pancreatic cancer is mainly due to the failure to kill pancreatic cancer stem cells (CSCs). Signal transducer and activator of transcription 3 (STAT3) is activated in pancreatic CSCs and, therefore, may be a valid target for overcoming therapeutic resistance. Here we investigated the potential of STAT3 inhibition in sensitizing pancreatic cancer to chemo/radio-therapy. We found that the levels of nuclear pSTAT3 in pancreatic cancer correlated with advanced tumor grade and poor patient outcome. Liposomal delivery of a STAT3 inhibitor FLLL32 (Lip-FLLL32) inhibited STAT3 phosphorylation and STAT3 target genes in pancreatic cancer cells and tumors. Consequently, Lip-FLLL32 suppressed pancreatic cancer cell growth, and exhibited synergetic effects with gemcitabine and radiation treatment in vitro and in vivo. Furthermore, Lip-FLLL32 reduced ALDH1-positive CSC population and modulated several potential stem cell markers. These results demonstrate that Lip-FLLL32 suppresses pancreatic tumor growth and sensitizes pancreatic cancer cells to radiotherapy through inhibition of CSCs in a STAT3-dependent manner. By targeting pancreatic CSCs, Lip-FLLL32 provides a novel strategy for pancreatic cancer therapy via overcoming radioresistance.

Natural Forms of Vitamin E as Effective Agents for Cancer Prevention and Therapy

Initial research on vitamin E and cancer has focused on α-tocopherol (αT), but recent clinical studies on cancer-preventive effects of αT supplementation have shown disappointing results, which has led to doubts about the role of vitamin E, including different vitamin E forms, in cancer prevention. However, accumulating mechanistic and preclinical animal studies show that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol (δT), γ-tocotrienol (γTE), and δ-tocotrienol (δTE), have far superior cancer-preventive activities than does αT. These vitamin E forms are much stronger than αT in inhibiting multiple cancer-promoting pathways, including cyclo-oxygenase (COX)- and 5-lipoxygenase (5-LOX)-catalyzed eicosanoids, and transcription factors such as nuclear transcription factor κB (NF-κB) and signal transducer and activator of transcription factor 3 (STAT3). These vitamin E forms, but not αT, cause pro-death or antiproliferation effects in cancer cells via modulating various signaling pathways, including sphingolipid metabolism. Unlike αT, these vitamin E forms are quickly metabolized to various carboxychromanols including 13'-carboxychromanols, which have even stronger anti-inflammatory and anticancer effects than some vitamin precursors. Consistent with mechanistic findings, γT, δT, γTE, and δTE, but not αT, have been shown to be effective for preventing the progression of various types of cancer in preclinical animal models. This review focuses on cancer-preventive effects and mechanisms of γT, δT, γTE, and δTE in cells and preclinical models and discusses current progress in clinical trials. The existing evidence strongly indicates that these lesser-known vitamin E forms are effective agents for cancer prevention or as adjuvants for improving prevention, therapy, and control of cancer.

The 150 most important questions in cancer research and clinical oncology series: questions 67-75 : Edited by Chinese Journal of Cancer

Since the beginning of 2017, Chinese Journal of Cancer has published a series of important questions in cancer research and clinical oncology, which sparkle diverse thoughts, interesting communications, and potential collaborations among researchers all over the world. In this article, 9 more questions are presented as followed. Question 67. How could we overcome the resistance of hepatocellular carcinoma against chemotherapeutics? Question 68. Is pursuit of non-covalent small-molecule binders of RAS proteins viable as a strategy of cancer drug discovery? Question 69. In what oligomeric structures do RAS proteins signal? Question 70. How can we achieve non-invasive early detection and diagnosis of lung cancer? Question 71. Does genetic information influence the volatolome enabling diagnosis of lung cancer with genetic mutations via cell headspace or breath analysis? Question 72. Is heavy ion beam radiotherapy effective to kill cancer stem cells? Question 73. Is there any diversity among different types of cancer in terms of sensitivity to heavy ion beam radiotherapy? Question 74. Can targeted alpha-particle therapy augment the effect of carbon ion radiotherapy on malignancies? Question 75. How does chromosomal instability drive tumor progression?

Opportunities for Radiosensitization in the Stereotactic Body Radiation Therapy (SBRT) Era

Stereotactic body radiation therapy (SBRT) utilizing a small number of high-dose radiation therapy fractions continues to expand in clinical application. Although many approaches have been proposed to radiosensitize tumors with conventional fractionation, how these radiosensitizers will translate to SBRT remains largely unknown. Here, we review our current understanding of how SBRT eradicates tumors, including the potential contributions of endothelial cell death and immune system activation. In addition, we identify several new opportunities for radiosensitization generated by the move toward high dose per fraction radiation therapy.

Radiosensitization by gold nanoparticles: Will they ever make it to the clinic?

The utilization of gold nanoparticles (AuNPs) as radiosensitizers has shown great promise in pre-clinical research. In the current review, the physical, chemical, and biological pathways via which AuNPs enhance the effects of radiation are presented and discussed. In particular, the impact of AuNPs on the 5 Rs in radiobiology, namely repair, reoxygenation, redistribution, repopulation, and intrinsic radiosensitivity, which determine the extent of radiation enhancement effects are elucidated. Key findings from previous studies are outlined. In addition, crucial parameters including the physicochemical properties of AuNPs, route of administration, dosing schedule of AuNPs and irradiation, as well as type of radiation therapy, are highlighted; the optimal selection and combination of these parameters enable the achievement of a greater therapeutic window for AuNP sensitized radiotherapy. Future directions are put forward as a means to provide guidelines for successful translation of AuNPs to clinical applications as radiosensitizers.

Cancer Cell Death-Inducing Radiotherapy: Impact on Local Tumour Control, Tumour Cell Proliferation and Induction of Systemic Anti-tumour Immunity

Radiotherapy (RT) predominantly is aimed to induce DNA damage in tumour cells that results in reduction of their clonogenicity and finally in tumour cell death. Adaptation of RT with higher single doses has become necessary and led to a more detailed view on what kind of tumour cell death is induced and which immunological consequences result from it. RT is capable of rendering tumour cells immunogenic by modifying the tumour cell phenotype and the microenvironment. Danger signals are released as well as the senescence-associated secretory phenotype. This results in maturation of dendritic cells and priming of cytotoxic T cells as well as in activation of natural killer cells. However, RT on the other hand can also result in immune suppressive events including apoptosis induction and foster tumour cell proliferation. That's why RT is nowadays increasingly combined with selected immunotherapies.

Snail maintains metastatic potential, cancer stem-like properties, and chemoresistance in mesenchymal mouse breast cancer TUBO‑P2J cells

Snail, a zinc-finger transcriptional repressor of E-cadherin expression, is one of the key inducers of epithelial-mesenchymal transition (EMT) in epithelial cancer. In breast cancer, EMT has been associated with malignancies, including metastasis, cancer stem-like properties, and resistance to chemotherapy and radiotherapy. In this study, we analysed the role of Snail in the highly metastatic mesenchymal TUBO‑P2J mouse breast cancer cells, by loss of function using short hairpin RNA. Though silencing Snail did not restore the E-cadherin expression or induce morphological changes, Snail silencing significantly ablated in vitro and in vivo metastatic potentials. In addition, Snail silencing also reduced resistance to chemotherapy drugs and cancer stem-like properties, such as CD44 expression, aldehyde dehydrogenase (ALDH) activity, colony formation, and in vivo tumour formation and growth. However, radioresistance was not decreased by silencing Snail. Collectively, this study suggested that Snail is a main regulator of the maintenance of malignancy potentials and is a good target to prevent cancer metastasis and to increase chemotherapy susceptibility.

Epigenetic Mechanisms of Tamoxifen Resistance in Luminal Breast Cancer

Breast cancer is one of the most common cancers and the second leading cause of cancer death in the United States. Estrogen receptor (ER)-positive cancer is the most frequent subtype representing more than 70% of breast cancers. These tumors respond to endocrine therapy targeting the ER pathway including selective ER modulators (SERMs), selective ER downregulators (SERDs) and aromatase inhibitors (AIs). However, resistance to endocrine therapy associated with disease progression remains a significant therapeutic challenge. The precise mechanisms of endocrine resistance remain unclear. This is partly due to the complexity of the signaling pathways that influence the estrogen-mediated regulation in breast cancer. Mechanisms include ER modifications, alteration of coregulatory function and modification of growth factor signaling pathways. In this review, we provide an overview of epigenetic mechanisms of tamoxifen resistance in ER-positive luminal breast cancer. We highlight the effect of epigenetic changes on some of the key mechanisms involved in tamoxifen resistance, such as tumor-cell heterogeneity, ER signaling pathway and cancer stem cells (CSCs). It became increasingly recognized that CSCs are playing an important role in driving metastasis and tamoxifen resistance. Understanding the mechanism of tamoxifen resistance will provide insight into the design of novel strategies to overcome the resistance and make further improvements in breast cancer therapeutics.

Cervical cancer stem cells manifest radioresistance: Association with upregulated AP-1 activity

Transcription factor AP-1 plays a central role in HPV-mediated cervical carcinogenesis. AP-1 has also been implicated in chemo-radio-resistance but the mechanism(s) remained unexplored. In the present study, cervical cancer stem-like cells (CaCxSLCs) isolated and enriched from cervical cancer cell lines SiHa and C33a demonstrated an elevated AP-1 DNA-binding activity in comparison to non-stem cervical cancer cells. Upon UV-irradiation, CaCxSLCs showed a UV exposure duration-dependent higher proliferation and highly increased AP-1 activity whereas it was completely abolished in non-stem cancer cells. CaCxSLCs also showed differential overexpression of c-Fos and c-Jun at transcript as well as in protein level. The loss of AP-1 activity and expression was accompanied by decrease in cell viability and proliferation in UV-irradiated non-stem cancer cells. Interestingly, CaCxSLCs treated with curcumin prior to UV-irradiation abolished AP-1 activity and a concomitant reduction in SP cells leading to abrogation of sphere forming ability, loss of proliferation, induction of apoptosis and the cells were poorly tumorigenic. The curcumin pre-treatment abolished the expression of c-Fos and c-Jun but upregulated Fra-1 expression in UV-irradiated CaCxSLCs. Thus, the study suggests a critical role of AP-1 protein in the manifestation of radioresistance but targeting with curcumin helps in radiosensitizing CaCxSLCs through upregulation of Fra-1.

Tumor-initiating cells contribute to radiation resistance in primary human renal clear cell carcinomas by activating the DNA damage checkpoint response

The use of radiotherapy in patients with clear cell renal carcinoma (ccRCC) is predominantly limited to palliation of metastases or control of local growth, because ccRCC cells readily develop radioresistance. The mechanisms underlying ccRCC resistance remain elusive. The present study demonstrated that ccRCC cells that survive fractionated radiation treatment display tumor-initiating cell (TIC) characteristics, such as high self-renewal and tumorigenic capacities, and overexpress stemness genes. ccRCC cells that survived fractionated radiation exhibited increased activation of the DNA damage checkpoint response and G2/M phase arrest compared with sham-irradiated cells. The results of the present study suggest that ionizing radiation destroys the bulk of tumor cells within ccRCC, but spares TICs; this subpopulation confers ccRCC radioresistance and may cause tumor recurrence or relapse following radiotherapy. Furthermore, these findings indicate that the DNA damage checkpoint response may serve as a potential therapeutic target for overcoming resistance of TICs in patients with ccRCC.

Targetable T-type Calcium Channels Drive Glioblastoma

Glioblastoma (GBM) stem-like cells (GSC) promote tumor initiation, progression, and therapeutic resistance. Here, we show how GSCs can be targeted by the FDA-approved drug mibefradil, which inhibits the T-type calcium channel Cav3.2. This calcium channel was highly expressed in human GBM specimens and enriched in GSCs. Analyses of the The Cancer Genome Atlas and REMBRANDT databases confirmed upregulation of Cav3.2 in a subset of tumors and showed that overexpression associated with worse prognosis. Mibefradil treatment or RNAi-mediated attenuation of Cav3.2 was sufficient to inhibit the growth, survival, and stemness of GSCs and also sensitized them to temozolomide chemotherapy. Proteomic and transcriptomic analyses revealed that Cav3.2 inhibition altered cancer signaling pathways and gene transcription. Cav3.2 inhibition suppressed GSC growth in part by inhibiting prosurvival AKT/mTOR pathways and stimulating proapoptotic survivin and BAX pathways. Furthermore, Cav3.2 inhibition decreased expression of oncogenes (PDGFA, PDGFB, and TGFB1) and increased expression of tumor suppressor genes (TNFRSF14 and HSD17B14). Oral administration of mibefradil inhibited growth of GSC-derived GBM murine xenografts, prolonged host survival, and sensitized tumors to temozolomide treatment. Our results offer a comprehensive characterization of Cav3.2 in GBM tumors and GSCs and provide a preclinical proof of concept for repurposing mibefradil as a mechanism-based treatment strategy for GBM. Cancer Res; 77(13); 3479-90. ©2017 AACR.

Role of ATP as a Key Signaling Molecule Mediating Radiation-Induced Biological Effects

Adenosine triphosphate (ATP) serves as a signaling molecule for adaptive responses to a variety of cytotoxic agents and plays an important role in mediating the radiation stress-induced responses that serve to mitigate or repair the injurious effects of γ radiation on the body. Indeed, low doses of radiation may have a net beneficial effect by activating a variety of protective mechanisms, including antitumor immune responses. On the other hand, ATP signaling may be involved in the radiation resistance of cancer cells. Here, focusing on our previous work, we review the evidence that low-dose γ irradiation (0.25-0.5 Gy) induces release of extracellular ATP, and that the released ATP mediates multiple radiation-induced responses, including increased intracellular antioxidant synthesis, cell-mediated immune responses, induction of DNA damage repair systems, and differentiation of regulatory T cells.

Distinct Levels of Radioresistance in Lgr5+ Colonic Epithelial Stem Cells versus Lgr5+ Small Intestinal Stem Cells

Although small and large intestines possess seemingly similar Wnt-driven leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)⁺ adult epithelial stem cells, we report here that the two organs exhibit distinct mechanisms of tissue response to ionizing radiation. Employing Lgr5-lacZ transgenic mice and Lgr5 in situ hybridization, we found colonic epithelial stem cells (CESC) markedly more radioresistant in vivo than small intestinal crypt base columnar stem cells (CBC; D₀ = 6.0 ± 0.3 Gy vs. 1.3 ± 0.1, respectively; P < 0.01). Accordingly, CESCs survived 30 Gy exposure, while CBCs were completely depleted after 15 Gy. EdU incorporation studies indicated that after 19 Gy, CBCs exited growth arrest at 12 hours, resuming normal mitotic activity despite 60% of this population displaying residual γH2AX foci, indicative of persistent unrepaired DNA damage. Checkpoint recovery before complete double-strand break (DSB) repair represents the sine qua non of a newly defined potentially lethal pathophysiology termed checkpoint adaptation. In the small intestinal mucosa, checkpoint adaptation resulted in CBCs succumbing to an 8-fold increase in the incidence of highly lethal chromosomal aberrations and mitotic catastrophe by 48 hours postradiation. In contrast, Lgr5⁺ CESCs displayed delayed checkpoint recovery at 48 hours post-19 Gy, coordinated with complete DSB repair and regeneration of colonic mucosa originating, at least in part, from surviving CESCs. The discovery that small intestinal CBCs succumb to checkpoint adaptation is the first demonstration that this aberrant cell-cycle response may drive mammalian tissue radiosensitivity. Cancer Res; 77(8); 2124-33. ©2017 AACR.

A novel rat fibrosarcoma cell line from transformed bone marrow-derived mesenchymal stem cells with maintained in vitro and in vivo stemness properties

Increasing evidence suggests a possible relationship between mesenchymal stem cells (MSCs) and sarcoma. MSCs are hypothesized to be the cells initiating sarcomagenesis, and cancer stem cells (CSCs) sharing features of MSCs have been identified in sarcomas. Here, we report on the characteristics of a bone marrow-derived rat mesenchymal stem cell line that spontaneously transformed in long-term culture. The rat transformed mesenchymal stem cells (rTMSCs) produced soft-tissue fibrosarcomas in immunocompromised mice and immunocompetent rats. In vitro, the rTMSCs displayed increased proliferation capacity compared to the untransformed cell line. The transformed MSCs maintained the mesenchymal phenotype by expression of the stem cell marker CD 90 and the lack of hematopoietic and endothelial markers. Cytogenetic analysis detected trisomy 6 in the rTMSCs. Side population (SP) isolation and tumorsphere cultivation of the transformed cells confirmed the presence of CSCs among the rTMSCs. Importantly, the rTMSCs retained their differentiation capacity towards osteogenic and adipogenic lineages. This transformed MSC-based cell line may be valuable in examining the balance in a mixed cell population between cancer stem cell properties and the ability to differentiate to specific non-transformed cell populations. Moreover, it may also be a useful tool to evaluate the efficacy of novel targeted immunotherapies in vivo.

TCN, an AKT inhibitor, exhibits potent antitumor activity and enhances radiosensitivity in hypoxic esophageal squamous cell carcinoma in vitro and in vivo

The aim of the present study was to investigate the radiosensitization effect of triciribine (TCN) on human esophageal squamous cell carcinoma (ESCC) in normoxia or hypoxia and its mechanism. The cytotoxicity and radiosensitization mechanism of TCN were investigated by Cell Counting Kit 8, clonogenic assay, flow cytometry, western blotting (WB) and immunofluorescence staining of phospho-histone H2A.X, Ser139 (γ-H2AX) in ESCC in vitro, while the protein expression levels of AKT, phosphorylated (p)-AKT, hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) were evaluated by WB in vivo. The cytotoxicity of TCN was dose dependent. Upon exposure to TCN, ESCC cells in hypoxia treated with 4-Gy radiotherapy exhibited an evidently higher apoptotic rate than cells subjected to other treatments. TCN could significantly inhibit the protein expression of p-AKT, HIF-1α and VEGF in vitro and in vivo. The present results suggested that TCN can effectively inhibit AKT, p-AKT, HIF-1α and VEGF, thus conferring radiosensitivity to ESCC in vitro and vivo. TCN is considered as an adjuvant in radiotherapy of ESCC in clinical application.

Fast and high temperature hyperthermia coupled with radiotherapy as a possible new treatment for glioblastoma

Background

A new transcranial focused ultrasound device has been developed that can induce hyperthermia in a large tissue volume. The purpose of this work is to investigate theoretically how glioblastoma multiforme (GBM) can be effectively treated by combining the fast hyperthermia generated by this focused ultrasound device with external beam radiotherapy.

Methods/Design

To investigate the effect of tumor growth, we have developed a mathematical description of GBM proliferation and diffusion in the context of reaction–diffusion theory. In addition, we have formulated equations describing the impact of radiotherapy and heat on GBM in the reaction–diffusion equation, including tumor regrowth by stem cells. This formulation has been used to predict the effectiveness of the combination treatment for a realistic focused ultrasound heating scenario.

Our results show that patient survival could be significantly improved by this combined treatment modality.

Discussion

High priority should be given to experiments to validate the therapeutic benefit predicted by our model.

Electronic supplementary material

The online version of this article (doi:10.1186/s40349-016-0078-3) contains supplementary material, which is available to authorized users.

Targeting the AKT/cyclin D1 pathway to overcome intrinsic and acquired radioresistance of tumors for effective radiotherapy

PURPOSE

Radiotherapy (RT) is a powerful tool in the treatment of cancer, having the advantage of preserving normal tissues. Clinical outcomes of RT are significantly improved by technological advances, enabling increased radiation doses directed very specifically to a tumor. However, tumor radioresistance remains a major impediment to effective RT. We have shown that human tumor cells surviving after repeated exposure to fractionated radiation (FR) of X-rays for 1 month have acquired radioresistance through constitutive activation of AKT and downstream cyclin D1 nuclear retention. Tumor radioresistance is also proposed to be an intrinsic characteristic of cancer stem cells (CSC), whose efficient DNA repair is thought to confer this phenotype. We have isolated radioresistant CD133-positive cells following exposure to long-term FR. These cells exhibited the CSC phenotype with activation of the AKT/cyclin D1 pathway. In this review, I summarize our current understanding of the molecular mechanisms underlying tumor radioresistance and propose a strategy for overcoming radioresistance by targeting the AKT/cyclin D1 pathway.

CONCLUSION

Two different mechanisms: acquired radioresistance of surviving tumor cells after RT and intrinsic radioresistance of CSC are associated with tumor radioresistance. Inhibition of the AKT pathway results in radiosensitization of both types of tumor radioresistance.

Cycling CD34 expression in subpopulations of head and neck squamous cell carcinoma cell lines is involved in radioresistance and change in cytokeratin expression profile

The expression of the hair follicle stem cell marker CD34 was analyzed in five different head and neck squamous cell carcinoma (HNSCC) cell lines with different antibodies. All HNSCC cell lines expressed CD34 on their cell surface. After cell cycle synchronization via serum starvation, we observed cyclic CD34 expression in HNSCC cells dependent on cell cycle progression via immunofluorescent staining and flow cytometric analysis. Investigation of the CD34(+) and CD34(-) HNSCC populations revealed most of the cells in S-phase and G2/M-Phase in CD34(+) cells in contrast to CD34(-) cells. Knockdown of CD34 in HNSCC cells led to diminished clonal expansion in a colony forming assay after subjecting the cells to ionizing radiation. Furthermore, knockdown of CD34 after cell cycle synchronization induced high CK1, CK4, and CK5 gene expression and downregulation of CK10 gene expression as shown by Taqman^® quantitative PCR analysis. The expression levels of CK1 and CK10 were verified via western blot analysis. In summary, our study shows that CD34 plays a role during cell cycle progression of head and neck squamous cell carcinoma and additionally is involved in irradiation resistance and differentiation of malignant oral keratinocytes.

Invasive oral cancer stem cells display resistance to ionising radiation

There is a significant amount of evidence to suggest that human tumors are driven and maintained by a sub-population of cells, known as cancer stem cells (CSC). In the case of head and neck cancer, such cells have been characterised by high expression levels of CD44 cell surface glycoprotein, while we have previously shown the presence of two diverse oral CSC populations in vitro, with different capacities for cell migration and proliferation. Here, we examined the response of oral CSC populations to ionising radiation (IR), a front-line measure for the treatment of head and neck tumors. We show that oral CSC initially display resistance to IR-induced growth arrest as well as relative apoptotic resistance. We propose that this is a result of preferential activation of the DNA damagerepair pathway in oral CSC with increased activation of ATM and BRCA1, elevated levels of DNA repair proteins RAD52, XLF, and a significantly faster rate of DNA double-strand-breaks clearance 24 hours following IR. By visually identifying CSC sub-populations undergoing EMT, we show that EMT-CSC represent the majority of invasive cells, and are more radio-resistant than any other population in re-constructed 3D tissues. We provide evidence that IR is not sufficient to eliminate CSC in vitro, and that sensitization of CD44^hi/ESA^low cells to IR, followed by secondary EMT blockade, could be critical in order to reduce primary tumor recurrence, but more importantly to be able to eradicate cells capable of invasion and distant metastasis.

Neoplastic human embryonic stem cells as a model of radiation resistance of human cancer stem cells

Studies have implicated that a small sub-population of cells within a tumour, termed cancer stem cells (CSCs), have an enhanced capacity for tumour formation in multiple cancers and may be responsible for recurrence of the disease after treatment, including radiation. Although comparisons have been made between CSCs and bulk-tumour, the more important comparison with respect to therapy is between tumour-sustaining CSC versus normal stem cells that maintain the healthy tissue. However, the absence of normal known counterparts for many CSCs has made it difficult to compare the radiation responses of CSCs with the normal stem cells required for post-radiotherapy tissue regeneration and the maintenance of tissue homeostasis. Here we demonstrate that transformed human embryonic stem cells (t-hESCs), showing features of neoplastic progression produce tumours resistant to radiation relative to their normal counterpart upon injection into immune compromised mice. We reveal that t-hESCs have a reduced capacity for radiation induced cell death via apoptosis and exhibit altered cell cycle arrest relative to hESCs in vitro. t-hESCs have an increased expression of BclXL in comparison to their normal counterparts and re-sensitization of t-hESCs to radiation upon addition of BH3-only mimetic ABT737, suggesting that overexpression of BclXL underpins t-hESC radiation insensitivity. Using this novel discovery platform to investigate radiation resistance in human CSCs, our study indicates that chemotherapy targeting Bcl2-family members may prove to be an adjuvant to radiotherapy capable of targeting CSCs.

Dendrimers as Innovative Radiopharmaceuticals in Cancer Radionanotherapy

Radiotherapy is one of the most commonly used cancer treatments, with an estimate of 40% success that could be improved further if more efficient targeting and retention of radiation at the tumor site were achieved. This review focuses on the use of dendrimers in radionanotherapy, an emerging technology aimed to improve the efficiency of radiotherapy by implementing nanovectorization, an already established praxis in drug delivery and diagnosis. The labeling of dendrimers with radionuclides also aims to reduce the dose of radiolabeled materials and, hence, their toxicity and tumor resistance. Examples of radiolabeled dendrimers with alpha, beta, and Auger electron emitters are commented, along with the use of dendrimers in boron neutron capture therapy (BNCT). The conjugation of radiolabeled dendrimers to monoclonal antibodies for a more efficient targeting and the application of dendrimers in gene delivery radiotherapy are also covered.

Targeting stem cells by radiation: From the biological angle to clinical aspects

Radiotherapy is a cornerstone of anticancer treatment. However in spite of technical evolutions, important rates of failure and of toxicity are still reported. Although numerous pre-clinical data have been published, we address the subject of radiotherapy-stem cells interaction from the clinical efficacy and toxicity perspective. On one side, cancer stem cells (CSCs) have been recently evidenced in most of solid tumor primary locations and are thought to drive radio-resistance phenomena. It is particularly suggested in glioblastoma, where CSCs were showed to be housed in the subventricular zone (SVZ). In recent retrospective studies, the radiation dose to SVZ was identified as an independent factor significantly influencing overall survival. On the other side, healthy tissue stem cells radio-destruction has been recently suggested to cause two of the most quality of life-impacting side effects of radiotherapy, namely memory disorders after brain radiotherapy, and xerostomia after head and neck radiotherapy. Recent publications studying the impact of a radiation dose decrease on healthy brain and salivary stem cells niches suggested significantly reduced long term toxicities. Stem cells comprehension should be a high priority for radiation oncologists, as this particular cell population seems able to widely modulate the efficacy/toxicity ratio of radiotherapy in real life patients.

Side population cells from long-term passage non-small cell lung cancer cells display loss of cancer stem cell-like properties and chemoradioresistance

The side population (SP) assay is a widely used method for isolating stem cell-like cells from cancer cell lines and primary cells. The cancer cells used in different laboratories have been passaged for different generations. Emerging evidence revealed that repeated passaging of cell lines for multiple generations frequently leads to change of characteristics. Thus, it is worth investigating the effects of repeated passaging on the biological and functional properties of the enriched SP fraction from early- and late-passage cells. The present study reports that the cancer stem cell (CSC) characteristics, including increased frequency of tumor-initiating and self-renewal capacity, and resistance to the chemotherapy agent doxorubicin and ionizing radiation, was diminished in SP cells from late-passage non-small cell lung cancer (NSCLC) cells. This finding revealed that the SP from long-term passage NSCLC cells was not consistently enriched for stem cell-like cancer cells, and low-passage cell lines and primary cancer cells are therefore recommended in the CSCs field.