Differential pattern of HIF-1α expression in HNSCC cancer stem cells after carbon ion or photon irradiation: one molecular explanation of the oxygen effect.

BACKGROUND: Head and neck squamous cell carcinoma (HNSCC) are resistant to standard treatments, partly due to cancer stem cells (CSCs) localised in hypoxic niches. Compared to X-rays, carbon ion irradiation relies on better ballistic properties, higher relative biological effectiveness and the absence of oxygen effect. Hypoxia-inducible factor-1α (HIF-1α) is involved in the resistance to photons, whereas its role in response to carbon ions remains unclear. METHODS: Two HNSCC cell lines and their CSC sub-population were studied in response to photons or carbon ion irradiation, in normoxia or hypoxia, after inhibition or not of HIF-1α. RESULTS: Under hypoxia, compared to non-CSCs, HIF-1α is expressed earlier in CSCs. A combined effect photons/hypoxia, less observed with carbon ions, results in a synergic and earlier HIF-1α expression in both subpopulations. The diffuse ROS production by photons is concomitant with HIF-1α expression and essential to its activation. There is no oxygen effect in response to carbon ions and the ROS localised in the track might be insufficient to stabilise HIF-1α. Finally, in hypoxia, cells were sensitised to both types of radiations after HIF-1α inhibition. CONCLUSIONS: Hypoxia-inducible factor-1α plays a main role in the response of CSCs and non-CSCs to carbon ion and photon irradiations, which makes the HIF-1α targeting an attractive therapeutic challenge.

Telomerase inhibition improves tumor response to radiotherapy in a murine orthotopic model of human glioblastoma.

BACKGROUND: Glioblastoma (GBM) is the most frequent and aggressive type of adult brain tumor. Most GBMs express telomerase; a high level of intra-tumoral telomerase activity (TA) is predictive of poor prognosis. Thus, telomerase inhibitors are promising options to treat GBM. These inhibitors increase the response to radiotherapy (RT), in vitro as well as in vivo. Since typical treatments for GBM include RT, our objective was to evaluate the efficiency of Imetelstat (TA inhibitor) combined with RT. FINDINGS: We used a murine orthotopic model of human GBM (N = 8 to11 mice per group) and µMRI imaging to evaluate the efficacy of Imetelstat (delivered by intra-peritoneal injection) alone and combined with RT. Using a clinically established protocol, we demonstrated that Imetelstat significantly: (i) inhibited the TA in the very center of the tumor, (ii) reduced tumor volume as a proportion of TA inhibition, and (iii) increased the response to RT, in terms of tumor volume regression and survival increase. CONCLUSIONS: Imetelstat is currently evaluated in refractory brain tumors in young patients (without RT). Our results support its clinical evaluation combined with RT to treat GBM.

p53-independent early and late apoptosis is mediated by ceramide after exposure of tumor cells to photon or carbon ion irradiation.

BACKGROUND: To determine whether ceramide is responsible for the induction of p53-independent early or late apoptosis in response to high- and low-Linear-Energy-Transfer (LET) irradiation. METHODS: Four cell lines displaying different radiosensitivities and p53-protein status were irradiated with photons or 33.4 or 184 keV/µm carbon ions. The kinetics of ceramide production was quantified by fluorescent microscopy or High-Performance-Liquid-Chromatogaphy and the sequence of events leading to apoptosis by flow cytometry. RESULTS: Regardless of the p53-status, both low and high-LET irradiation induced an early ceramide production in radiosensitive cells and late in the radioresistant. This production strongly correlated with the level of early apoptosis in radiosensitive cells and delayed apoptosis in the radioresistant ones, regardless of radiation quality, tumor type, radiosensitivity, or p53-status. Inhibition of caspase activity or ceramide production showed that, for both types of radiation, ceramide is essential for the initiation of early apoptosis in radiosensitive cells and late apoptosis following mitotic catastrophe in radioresistant cells. CONCLUSIONS: Ceramide is a determining factor in the onset of early and late apoptosis after low and high-LET irradiation and is the mediator of the p53-independent-apoptotic pathway. We propose that ceramide is the molecular bridge between mitotic catastrophe and the commitment phase of delayed apoptosis in response to irradiation.

Evaluation of the Cell Invasion and Migration Process: A Comparison of the Video Microscope-based Scratch Wound Assay and the Boyden Chamber Assay.

The invasion and migration abilities of tumor cells are main contributors to cancer progression and recurrence. Many studies have explored the migration and invasion abilities to understand how cancer cells disseminate, with the aim of developing new treatment strategies. Analysis of the cellular and molecular basis of these abilities has led to the characterization of cell mobility and the physicochemical properties of the cytoskeleton and cellular microenvironment. For many years, the Boyden chamber assay and the scratch wound assay have been the standard techniques to study cell invasion and migration. However, these two techniques have limitations. The Boyden chamber assay is difficult and time consuming, and the scratch wound assay has low reproducibility. Development of modern technologies, especially in microscopy, has increased the reproducibility of the scratch wound assay. Using powerful analysis systems, an "in-incubator" video microscope can be used to provide automatic and real-time analysis of cell migration and invasion. The aim of this paper is to report and compare the two assays used to study cell invasion and migration: the Boyden chamber assay and an optimized in vitro video microscope-based scratch wound assay.

Dual "mAb" HER family blockade in head and neck cancer human cell lines combined with photon therapy.

Head and neck cancer stem cells (CSCs) are highly resistant to treatment. When EGFR is overexpressed in head and neck squamous cell carcinoma (HNSCC), HER2 and HER3 are also expressed. The aim of the present study was to investigate the effect of HER1/2/3 blockade through a combination of cetuximab and pertuzumab, with or without photon irradiation, on the proliferation and migration/invasion capabilities of an HNSCC chemo- and radioresistant human cell line (SQ20B) and its corresponding stem cell subpopulation. Cell proliferation, migration and invasion were studied after treatment with cetuximab +/- pertuzumab +/- 10 Gy photon irradiation. EGFR, phospho-EGFR, HER2 and HER3 protein expression levels were studied. Activation or inhibition of the RAS/MAPK and AKT-mTOR downstream signalling cascades was investigated through phospho-AKT and phospho-MEK1/2 expression. Cetuximab strongly inhibited SQ20B and FaDu cell proliferation, migration and invasion, whereas it had little effect on SQ20B-CSCs. Cetuximab-pertuzumab combined with radiation significantly inhibited SQ20B and FaDu cell and SQ20B-CSC proliferation, migration and invasion. Cetuximab-pertuzumab with 10 Gy photon irradiation switched off both phospho-AKT and phospho-MEK1/2 expression in the three populations. The triple therapy is therefore thought to inhibit SQ20B cells, SQ20B-CSCs and FaDu cells through an AKT-mTOR and Ras-MAPK downstream signalling blockade.

Isolation and Characterization of a Head and Neck Squamous Cell Carcinoma Subpopulation Having Stem Cell Characteristics.

Despite advances in the understanding of head and neck squamous cell carcinomas (HNSCC) progression, the five-year survival rate remains low due to local recurrence and distant metastasis. One hypothesis to explain this recurrence is the presence of cancer stem-like cells (CSCs) that present inherent chemo- and radio-resistance. In order to develop new therapeutic strategies, it is necessary to have experimental models that validate the effectiveness of targeted treatments and therefore to have reliable methods for the identification and isolation of CSCs. To this end, we present a protocol for the isolation of CSCs from human HNSCC cell lines that relies on the combination of two successive cell sortings performed by fluorescence activated cell sorting (FACS). The first one is based on the property of CSCs to overexpress ATP-Binding Cassette (ABC) transporter proteins and thus exclude, among others, vital DNA dyes such as Hoechst 33342. The cells sorted with this method are identified as a "side population" (SP). As the SP cells represent a low percentage (<5%) of parental cells, a growing phase is necessary in order to increase their number before the second cell sorting. The next step allows for the selection of cells that possess two other HNSCC stem cell characteristics i.e. high expression level of the cell surface marker CD44 (CD44(high)) and the over-expression of aldehyde dehydrogenase (ALDH(high)). Since the use of a single marker has numerous limitations and pitfalls for the isolation of CSCs, the combination of SP, CD44 and ALDH markers will provide a useful tool to isolate CSCs for further analytical and functional assays requiring viable cells. The stem-like characteristics of CSCs was finally validated in vitro by the formation of tumorispheres and the expression of ß-catenin.

Influence of Dose Rate on the Cellular Response to Low- and High-LET Radiations.

Nowadays, head and neck squamous cell carcinoma (HNSCC) treatment failure is mostly explained by locoregional progression or intrinsic radioresistance. Radiotherapy (RT) has recently evolved with the emergence of heavy ion radiations or new fractionation schemes of photon therapy, which modify the dose rate of treatment delivery. The aim of the present study was then to evaluate the in vitro influence of a dose rate variation during conventional RT or carbon ion hadrontherapy treatment in order to improve the therapeutic care of patient. In this regard, two HNSCC cell lines were irradiated with photons or 72 MeV/n carbon ions at a dose rate of 0.5, 2, or 10 Gy/min. For both radiosensitive and radioresistant cells, the change in dose rate significantly affected cell survival in response to photon exposure. This variation of radiosensitivity was associated with the number of initial and residual DNA double-strand breaks (DSBs). By contrast, the dose rate change did not affect neither cell survival nor the residual DNA DSBs after carbon ion irradiation. As a result, the relative biological efficiency at 10% survival increased when the dose rate decreased. In conclusion, in the RT treatment of HNSCC, it is advised to remain very careful when modifying the classical schemes toward altered fractionation. At the opposite, as the dose rate does not seem to have any effects after carbon ion exposure, there is less need to adapt hadrontherapy treatment planning during active system irradiation.

Corrigendum: Influence of Dose Rate on the Cellular Response to Low- and High-LET Radiations.

[This corrects the article on p. 58 in vol. 6, PMID: 27014633.].

MiR-422a promotes loco-regional recurrence by targeting NT5E/CD73 in head and neck squamous cell carcinoma.

At the time of diagnosis, 60% of patients with head and neck squamous cell carcinoma (HNSCC) present tumors in an advanced stage (III-IV) of disease and 80% will relapse within the first two years post-treatment, due to their frequent radio(chemo)resistance. To identify new molecular targets and companion biomarkers, we have investigated the miRNome of 75 stage III-IV oropharynx tumors without relapse (R) or with loco-regional relapse (non-responder, NR) within two years post-treatment. Interestingly, miR-422a was significantly downregulated in NR tumors, in agreement with the increase in cell proliferation and adhesion induced by miR-422a inhibition in vitro. Furthermore, we identified CD73/NT5E oncogene as target of miR-422a. Indeed, modulation of the endogenous level of miR-422a inversely influences the expression and the enzymatic activity of CD73. Moreover, knocking down CD73 mimics the effects of miR-422a upregulation. Importantly, in tumors, miR-422a and CD73 expression levels are inversely correlated, and both are predictive of relapse free survival - especially considering loco(regional) recurrence - in vitro two independent cohorts of advanced oropharynx or HNSCC (N=255) tumors. In all, we reported, for the first time, that MiR-422a and its target CD73 are involved in early loco(regional) recurrence of HNSCC tumors and are new targets for personalized medicine.

Targeting head and neck cancer stem cells to overcome resistance to photon and carbon ion radiation.

Although promising new radiation therapy techniques such as hadrontherapy are currently being evaluated in the treatment of head and neck malignancies, local control of head and neck squamous cell carcinoma (HNSCC) remains low. Here, we investigated the involvement of cancer stem-like cells (CSCs) in a radioresistant HNSCC cell line (SQ20B). Stem-like cells SQ20B/SidePopulation(SP)/CD44(+)/ALDH(high) were more resistant to both photon and carbon ion irradiation compared with non-CSCs. This was confirmed by a BrdU labeling experiment, which suggests that CSCs were able to proliferate and to induce tumorigenicity after irradiation. SQ20B/SP/CD44(+)/ALDH(high) were capable of an extended G2/M arrest phase in response to photon or carbon ion irradiation compared with non-CSCs. Moreover, our data strongly suggest that resistance of CSCs may result from an imbalance between exacerbated self-renewal and proliferative capacities and the decrease in apoptotic cell death triggering. In order to modulate these processes, two targeted pharmacological strategies were tested. Firstly, UCN-01, a checkpoint kinase (Chk1) inhibitor, induced the relapse of G2/M arrest and radiosensitization of SQ20B-CSCs. Secondly, all-trans retinoic acid (ATRA) resulted in an inhibition of ALDH activity, and induction of the differentiation and radiosensitization of SQ20B/SP/CD44(+)/ALDH(high) cells. The combination of ATRA and UCN-01 treatments with irradiation drastically decreased the surviving fraction at 2Gy of SQ20B-CSCs from 0.85 to 0.38 after photon irradiation, and from 0.45 to 0.21 in response to carbon ions. Taken together, our results suggest that the combination of UCN-01 and ATRA represent a promising pharmacological-targeted strategy that significantly sensitizes CSCs to photon or carbon ion radiation.

Telomere profiling: toward glioblastoma personalized medicine.

Despite a standard of care combining surgery, radiotherapy (RT), and temozolomide chemotherapy, the average overall survival (OS) of glioblastoma patients is only 15 months, and even far lower when the patient cannot benefit from this combination. Therefore, there is a strong need for new treatments, such as new irradiation techniques. Against this background, carbon ion hadrontherapy, a new kind of irradiation, leads to a greater biological response of the tumor, while minimizing adverse effects on healthy tissues in comparison with RT. As carbon ion hadrontherapy is restricted to RT-resistant patients, photon irradiation resistance biomarkers are needed. Long telomeres and high telomerase activity have been widely associated with photon radioresistance in other cancers. Moreover, telomere protection, telomere function, and telomere length (TL) also depend on the shelterin protein complex (TRF1, TRF2, TPP1, POT1, TIN2, and hRAP1). We thus decided to evaluate an enlarged telomeric status (TL, telomerase catalytic subunit, and the shelterin component expression level) as a potential radioresistance biomarker in vitro using cellular models and ex vivo using patient tumor biopsies. In addition, nothing was known about the role of telomeres in carbon ion response. We thus evaluated telomeric status after both types of irradiation. We report here a significant correlation between TL and the basal POT1 expression level and photon radioresistance, in vitro, and a significant increase in the OS of patients with long telomeres or a high POT1 level, in vivo. POT1 expression was predictive of patient response irrespective of the TL. Strikingly, these correlations were lost, in vitro, when considering carbon irradiation. We thus propose (1) a model of the implications of telomeric damage in the cell response to both types of irradiation and (2) assessment of the POT1 expression level and TL using patient tumor biopsies to identify radioresistant patients who could benefit from carbon hadrontherapy.

Different mechanisms of cell death in radiosensitive and radioresistant p53 mutated head and neck squamous cell carcinoma cell lines exposed to carbon ions and x-rays.

PURPOSE: We initiated studies on the mechanisms of cell death in head and neck squamous cell carcinoma cell lines (HNSCC) since recent clinical trials have shown that local treatment of HNSCC by carbon hadrontherapy is less efficient than it is in other radioresistant cancers. METHODS AND MATERIALS: Two p53-mutated HNSCC cell lines displaying opposite radiosensitivity were used. Different types of cell death were determined after exposure to carbon ions (33.6 and 184 keV/microm) or X-rays. RESULTS: Exposure to radiation with high linear energy transfer (LET) induced clonogenic cell death for SCC61 (radiosensitive) and SQ20B (radioresistant) cells, the latter systematically showing less sensitivity. Activation of an early p53-independent apoptotic process occurred in SCC61 cells after both types of irradiation, which increased with time, dose and LET. In contrast, SQ20B cells underwent G2/M arrest associated with Chk1 activation and Cdc2 phosphorylation. This inhibition was transient after X-rays, compared with a more prolonged and LET-dependent accumulation after carbon irradiation. After release, a LET-dependent increase of polyploid and multinucleated cells, both typical signs of mitotic catastrophe, was identified. However, a subpopulation of SQ20B cells was able to escape mitotic catastrophe and continue to proliferate. CONCLUSIONS: High LET irradiation induced distinct types of cell death in HNSCC cell lines and showed an increased effectiveness compared with X-rays. However, the reproliferation of SQ20B may explain the potential locoregional recurrence observed among some HNSCC patients treated by hadrontherapy. An adjuvant treatment forcing the tumor cells to enter apoptosis may therefore be necessary to improve the outcome of radiotherapy.