Impact of the overexpression of the tyrosine kinase receptor RET in the hematopoietic potential of induced pluripotent stem cells (iPSCs)

INTRODUCTION

Previous studies have suggested that the tyrosine kinase receptor RET plays a significant role in the hematopoietic potential in mice and could also be used to expand cord-blood derived hematopoietic stem cells (HSCs). The role of RET in human iPSC-derived hematopoiesis has not been tested so far.

METHODS

To test the implication of RET on the hematopoietic potential of iPSCs, we activated its pathway with the lentiviral overexpression of RETWT or RETC634Y mutation in normal iPSCs. An iPSC derived from a patient harboring the RETC634Y mutation (iRETC634Y) and its CRISPR-corrected isogenic control iPSC (iRETCTRL) were also used. The hematopoietic potential was tested using 2D cultures and evaluated regarding the phenotype and the clonogenic potential of generated cells.

RESULTS

Hematopoietic differentiation from iPSCs with RET overexpression (WT or C634Y) led to a significant reduction in the number and in the clonogenic potential of primitive hematopoietic cells (CD34+/CD38-/CD49f+) as compared to control iPSCs. Similarly, the hematopoietic potential of iRETC634Y was reduced as compared to iRETCTRL. Transcriptomic analyses revealed a specific activated expression profile for iRETC634Y compared to its control with evidence of overexpression of genes which are part of the MAPK network with negative hematopoietic regulator activities.

CONCLUSION

RET activation in iPSCs is associated with an inhibitory activity in iPSC-derived hematopoiesis, potentially related to MAPK activation.

miR-495-3p sensitizes BCR-ABL1-expressing leukemic cells to tyrosine kinase inhibitors by targeting multidrug resistance 1 gene in T315I mutated cells

Chronic myeloid leukemia (CML) is a clonal hematopoietic malignancy driven by the BCR-ABL1 fusion oncoprotein. The development of tyrosine kinase inhibitors (TKIs) has deeply increased long-term survival of CML patients. Nonetheless, one patient out of four will switch TKI off owing either to drug intolerance or resistance partly due to amplification or mutations of BCR-ABL1 oncogene and alteration in ATP-binding cassette (ABC) transporters. Increasing evidence suggests the involvement of the microRNA miR-495-3p in cancer-associated chemoresistance through multidrug resistance 1 (MDR1) gene, which encodes an ATP-dependent efflux pump. Our study aimed at investigating the potential role of miR-495-3p in CML TKI chemo-sensitivity and determining the underlying molecular circuitry involved. We first observed that miR-495-3p expression was lower in BCR-ABL1-expressing cellular models in vitro. Notably, loss-of-function experiments showed increased proliferation associated with a decreased number of nondividing cells (G0/G1) and resistance to Imatinib. Conversely, our data showed that miR-495-3p overexpression hindered leukemic cell growth and TKI resistance in Imatinib-resistant T315I-mutant cells, as well as drug efflux activity through MDR1 regulation. Further investigating the role of miR-495-3p in CML patients, we found that predicted miR-495-3p targets were upregulated in patients in blast crisis that were involved in protein phosphorylation and associated with the worst prognosis. Taken together, our results demonstrate that downregulation of miR-495-3p expression is important in the malignant phenotype of CML and TKI resistance mechanisms and could be a useful biomarker and a potential therapeutic target to eradicate CML.

Frequent altered distribution of peripheral B-lymphocyte subsets in pediatric and adolescent patients with classical Hodgkin lymphoma

Peripheral lymphopenia is a well-known negative prognostic marker in classical Hodgkin lymphoma (cHL). We characterized the peripheral B-cell compartment in a prospective cohort of 83 pediatric cHL patients. We observed significantly low total B-cell counts (<100 cells/µl) in 31 of 83 patients (37%). More specifically, there was a smaller peripheral IgD^highCD27^- naïve B-cell pool among B-cell lymphopenic patients than for non-B-cell lymphopenic patients (p < 0.01). The B-cell count was lower in patients without in situ Epstein Barr Virus (EBV) expression than among those with in situ EBV expression (p = 0.03). Peripheral B-cell lymphopenia was associated with the presence of poor prognostic features, such as advanced lymphoma stage (p < 0.01) and the presence of B symptoms (p = 0.04). Of interest, B-cell lymphopenia resolved in all six studied patients in long-term remission. Our findings support that cHL tumor-associated factors interfere with the distribution of peripheral B-cell subsets.

Single-Cell Transcriptome in Chronic Myeloid Leukemia: Pseudotime Analysis Reveals Evidence of Embryonic and Transitional Stem Cell States

Recent experimental data suggest that the heterogeneity of chronic myeloid leukemia (CML) stem cells may be the result of the development of unique molecular events generating functional consequences in terms of the resistance and persistence of leukemic stem cells. To explore this phenomenon, we designed a single-cell transcriptome assay evaluating simultaneously the expression of 87 genes. Highly purified CD34+ cells from three CML patients at diagnosis were immobilized in microfluidic chips, and the expression of 87 genes was evaluated in each cell. This analysis identified a group of 13 highly connected genes including NANOG, POU5F1, LIN28A, and SOX2, representing on average 8.59% of the cell population analyzed. Bioinformatics analysis with the corrected matrix and t-distributed stochastic neighbor embedding (tSNE) algorithm identified four distinct clusters, and the pseudotime analysis confirmed the presence of seven stem cell states in the four clusters identified. ALOX5 expression was associated with the group of cells expressing the pluripotency markers. In in vitro analyses, two genes that were predicted to undergo similar regulation using pseudotime analysis (ALOX5 and FGFR) were found to be similarly inhibited by ponatinib, an FGFR inhibitor. Finally, in an independent cohort of CML patients, we found that pluripotency gene expression is a common feature of CD34+ CML cells at diagnosis. Overall, these experiments allowed identification of individual CD34+ cells expressing high levels of pluripotency genes at diagnosis, in which a continuum of transitional states were identified using pseudotime analysis. These results suggest that leukemic stem cell persistence in CML needs to be targeted simultaneously rather than using a single pathway.

Aryl hydrocarbon receptor (AHR) is a novel druggable pathway controlling malignant progenitor proliferation in chronic myeloid leukemia (CML)

Aryl Hydrocarbon Receptor (AHR) is an ubiquitous basic helix-loop-helix transcription factor, which is ligand-activated and involved in numerous biological processes including cell division, cell quiescence and inflammation. It has been shown that AHR is involved in normal hematopoietic progenitor proliferation in human cells. In addition, loss of AHR in knockout mice is accompanied by a myeloproliferative syndrome-like disease, suggesting a role of AHR in hematopoietic stem cell (HSC) maintenance. To study the potential role of AHR pathway in CML progenitors and stem cells, we have first evaluated the expression of AHR in UT-7 cell line expressing BCR-ABL. AHR expression was highly reduced in UT-7 cell expressing BCR-ABL as compared to controls. AHR transcript levels, quantified in primary peripheral blood CML cells at diagnosis (n = 31 patients) were found to be significantly reduced compared to healthy controls (n = 15). The use of StemRegenin (SR1), an AHR antagonist, induced a marked expansion of total leukemic cells and leukemic CD34+ cells by about 4- and 10-fold respectively. SR1-treated CML CD34+ cells generated more colony-forming cells and long-term culture initiating cell (LTC-IC)-derived progenitors as compared to non-SR1-treated counterparts. Conversely, treatment of CML CD34+ cells with FICZ, a natural agonist of AHR, induced a 3-fold decrease in the number of CD34+ cells in culture after 7 days. Moreover, a 4-day FICZ treatment was sufficient to significantly reduce the clonogenic potential of CML CD34+ cells and this effect was synergized by Imatinib and Dasatinib treatments. Similarly, a 3-day FICZ treatment contributed to hinder significantly the number of LTC-IC-derived progenitors without synergistic effect with Imatinib. The analysis of molecular circuitry of AHR signaling in CML showed a transcriptional signature in CML derived CD34+ CD38- primitive cells with either low or high levels of AHR, with an upregulation of myeloid genes involved in differentiation in the "AHR low" fraction and an upregulation of genes involved in stem cell maintenance in the "AHR high" fraction. In conclusion, these findings demonstrate for the first time that down-regulation of AHR expression, a major cell cycle regulator, is involved in the myeloproliferative phenotype associated with CML. AHR agonists inhibit clonogenic and LTC-IC-derived progenitor growth and they could be used in leukemic stem cell targeting in CML.

Abstract 2633: Vitamin D3 analog inecalcitol synergizes with tyrosine kinase inhibitors (TKI) and selectively inhibit the growth of chronic myeloid leukemia (CML) progenitors: Development of a clinically applicable leukemic stem cell targeting strategy

Tyrosine kinase inhibitor (TKI) therapies have profoundly changed the natural history of chronic myeloid leukemia (CML) and prolonged survival. However, in vitro and in vivo data suggest strongly that the eradication of the most primitive CML stem cells will not be possible by the use of TKI therapies alone. The mechanisms of this inefficiency might involve cell autonomous (activation of alternate signaling, reduced BCR-ABL expression) or non-cell autonomous (niche-related) pathways. It would therefore be of major interest to determine if compounds targeting CML progenitors and stem cells can be used in combination with TKI. Few targeted therapies have been so far shown to be clinicaly acceptable.

We have used for this purpose Inecalcitol (19, nor 14 epi 23-yne-1,25 (OH)2D3) (ICC),a vitamin D3 analog, which has been shown to exert antiproliferative effects in several types of cancer cell lines. CD34+ cells isolated from CML patients at diagnosis (n = 15) were tested in clonogenic assays (500 CD34+ cells / dish in triplicate). Interestingly, ICC alone is highly efficient to inhibit the clonogenic growth in the majority of the CML patients at diagnosis (10/ 15 patients). The combination of ICC with either Imatinib Mesylate (IM), Dasatinib (DA) or Nilotinib (NIL) in clonogenic assays showed a synergistic effect for the inhibition of CFC growth (10 - 25% CFC survival) using IM (n = 15 patients). In the same conditions, we have not observed any significant inhibitory effect of IM and ICC combination in cord-blood derived progenitors (n = 3).

To determine the effects of these combinations in the most primitive stem cells, we have performed long-term cultures initiating cell (LTC-IC) assays using purified CD34+ cells (4.104 cells / dish) from CML patients with half medium changes each week for 5 weeks. The combination was tested in 6 (ICC+ IM) and 4 (ICC + DA / NIL) CML samples. As a control, CD34+ cells from cord blood were used. In CML samples tested with the combination of either IM / ICC (n = 6) or DA/ NIL and ICC (n = 4), CML LTC-IC derived progenitors were highly inhibited (ICC and IM) or undetectable (ICC and DA or NIL).

Short-term cultures of CML CD34+ cells in the presence of 5 growth factors with or without ICC showed that ICC induced the expression of myeloid markers and highly favored the appearance of double positive CD14/CD15 cells. Experiments are underway to determine if ICC interferes with the expression of the components of SHH pathway (Smo, Ptched, Gli). as well as the gene expression profiling of CML cells treated with ICC. Thus, these results establish that ICC, a clinically used derivative of vitamin D3 has a clear activity in CML progenitors by itself and a major synergistic effect with TKI. A clinical phase 2 trial aiming to confirm the synergistic effect of ICC and TKI is ongoing in CML patients treated with imatinib.

Citation Format: Ali G. Turhan, Hyacinthe Johnson Ansah, Patricia Hugues, Camille Debord, Remi Delansorne, Agnes Guerci-Bresler, Jean Francois Dufour Lamartinie, Annelise Bennaceur-Griscelli. Vitamin D3 analog inecalcitol synergizes with tyrosine kinase inhibitors (TKI) and selectively inhibit the growth of chronic myeloid leukemia (CML) progenitors: Development of a clinically applicable leukemic stem cell targeting strategy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2633. doi:10.1158/1538-7445.AM2015-2633

Using e-learning to train dentists in the development of standardised oral health promotion interventions for persons with disability

BACKGROUND

This study aims to evaluate whether an e-learning curriculum was sufficient to impart the necessary knowledge to dentists to allow them to implement an oral health promotion intervention in an institution for persons with disability.

MATERIALS AND METHODS

Participants were asked to complete a 10-module online training course and to implement a standardised intervention in an institution. The outcome measures were as follows: online tracking of progress; multiple choice questionnaires completed at the end of most modules; self-efficacy questionnaire completed before and after online training; completion of training and calibration in the use of a standardised risk assessment form; initiation and full completion of an oral health promotion intervention in an institution; satisfaction of participants with the online training experience; and evaluation of the impact of the intervention by the institution staff.

RESULTS

The study sample included 26 dentists. The 10 modules were passed by 24 dentists, and the mean value of the highest overall score recorded in the multiple questionnaires was 88.4% (± 4.0). Twenty participants completed the self-efficacy questionnaire before and after training; the mean values of scores after training were statistically different and higher than those at baseline. Questionnaire regarding satisfaction with the online training experience was completed by 22 participants; all of them stated that they were satisfied with the online training experience.

CONCLUSIONS

The results indicate that the online training course helped participants to increase self-efficacy and to provide interventions in institutions. This study could have implications for both undergraduate and postgraduate dental education in France.

[Nasal fossae hemangiopericytoma revealed by acute dacryocystitis]

We report a 42-year-old woman with a hemangiopericytoma tumor located in nasal fossae, revealed by acute dacryocystitis. Clinical rhinoscopic examination and orbitofacial tomodensitometry showed tumefaction of the lacrimal sac and nasolacrimal duct. We removed the tumor by endonasal surgery. The anatomopathology examination confirmed the diagnosis of hemangiopericytoma. The internal canthus area and the maxillary sinus roof were treated with complementary irradiation.

[Syphilitic uveitis]

The incidence of syphilitic uveitis is reportedly increasing, up to 1% uveitis in general, with often polymorphic and atypical manifestations. Three cases of syphilitic uveitis are reported here, at different stages (secondary, latent, late). The bacteriologic sterilization is often unlikely in ocular syphilis, and recurrence is frequent; therefore a high-dose intravenous penicillin G treatment is then to recommend. HIV serology must be systematically associated with syphilitic tests.

Incorporation and turnover of phospholipid precursors in normal and tumoral glial cells in culture

The incorporation and turnover of phospholipid precursors in cultured normal and tumoral glial cells was investigated during the plateau phase of growth. Glycerol was incorporated similarly by all cell types, and was renewed with a half-life of 19-37 hr. Acetate had a much longer half-life in primary cultures (50-75 hr) than in proliferative tumor cells (20-40 hr). Phosphate had a more rapid turnover rate in primary cultures (25 hr) than in proliferative tumor cells (50 hr). For all precursors, inositol- and choline phosphoglycerides had a faster turnover rate than other phospholipids.

Incorporation and metabolism of exogenous fatty acids by cultured normal and tumoral glial cells

We have investigated the transformation of exogenous radioactive free fatty acids by cultured glial cells and their incorporation into complex lipids. The cells were either tumor lines (C6 and NN) or primary cultures from newborn rat hemispheres. The tumor lines could undergo morphological differentiation with dibutyryl cyclic AMP or bromodeoxyuridine. The fatty acid precursors used were palmitic, stearic, oleic, linoleic and linolenic acids. Tumor cells presented a higher incorporation of the precursors in the cell lipid acyl groups than did normal cells. Tumor cells desaturated and/or elongated palmitic, stearic and oleic acid to a higher extent than did normal cells. In contrast, tumor cells transformed linoleic and linolenic acids to their polyunsaturated derivatives to a lower extent than did normal cells. In differentiated tumor cells, these patterns of metabolism were shifted toward the patterns of normal cells. Tumor cells did not exhibit delta 4-desaturase activity, but such activity was restored in the C6 line upon dibutyryl cyclic AMP-induced differentiation. Transformation of linoleic and linolenic acid is likely to proceed through initial delta 6 desaturation. Phospholipids were preferentially labelled with the radioactive fatty acids, and only a little radioactivity was found in the neutral lipid fraction, mainly in diacylglycerols. Each fatty acid precursor label was incorporated in individual phospholipids to a proportion which reflected the typical acyl group composition of glycerophospholipids; we observed high levels of incorporation of palmitic acid and its derivatives into choline glycerophospholipids, and high levels of incorporation of linolenic acid and its derivatives into ethanolamine glycerophospholipids. This pattern was more marked in tumor cells than in normal cells, and the differentiation of tumor cells partially restored the normal pattern, mainly in bromodeoxyuridine-treated NN cells. Both types of differentiation of glial cell lines can be useful as models for the understanding of membrane physiology in normal and tumor cells.