Neurite outgrowth and cell cycle kinetic changes induced by cis-diamminedichloroplatinum II and retinoic acid in a human neuroblastoma cell line

Inhibition of PIM Kinases Promotes Neuroblastoma Cell Differentiation to a Neuronal Phenotype

BACKGROUND

Neuroblastoma arises from aberrancies in neural stem cell differentiation. PIM kinases contribute to cancer formation, but their precise role in neuroblastoma tumorigenesis is poorly understood. In the current study, we evaluated the effects of PIM kinase inhibition on neuroblastoma differentiation.

METHODS

Versteeg database query assessed the correlation between PIM gene expression and the expression of neuronal stemness markers and relapse free survival. PIM kinases were inhibited with AZD1208. Viability, proliferation, motility were measured in established neuroblastoma cells lines and high-risk neuroblastoma patient-derived xenografts (PDXs). qPCR and flow cytometry detected changes in neuronal stemness marker expression after AZD1208 treatment.

RESULTS

Database query showed increased levels of PIM1, PIM2, or PIM3 gene expression were associated with higher risk of recurrent or progressive neuroblastoma. Increased levels of PIM1 were associated with lower relapse free survival rates. Higher levels of PIM1 correlated with lower levels of neuronal stemness markers OCT4, NANOG, and SOX2. Treatment with AZD1208 resulted in increased expression of neuronal stemness markers.

CONCLUSIONS

Inhibition of PIM kinases differentiated neuroblastoma cancer cells toward a neuronal phenotype. Differentiation is a key component of preventing neuroblastoma relapse or recurrence and PIM kinase inhibition provides a potential new therapeutic strategy for this disease.

9-cis-UAB30, a novel rexinoid agonist, decreases tumorigenicity and cancer cell stemness of human neuroblastoma patient-derived xenografts

Retinoic acid (RA) therapy has been utilized as maintenance therapy for high-risk neuroblastoma, but over half of patients treated with RA relapse. Neuroblastoma stem cell-like cancer cells (SCLCCs) are a subpopulation of cells characterized by the expression of the cell surface marker CD133 and are hypothesized to contribute to drug resistance and disease relapse. A novel rexinoid compound, 9-cis-UAB30 (UAB30), was developed having the same anti-tumor effects as RA but a more favorable toxicity profile. In the current study, we investigated the efficacy of UAB30 in neuroblastoma patient-derived xenografts (PDX). Two PDXs, COA3 and COA6, were utilized and alterations in the malignant phenotype were assessed following treatment with RA or UAB30. UAB30 significantly decreased proliferation, viability, and motility of both PDXs. UAB30 induced cell-cycle arrest as demonstrated by the significant increase in percentage of cells in G1 (COA6: 33.7 ± 0.7 vs. 43.3 ± 0.7%, control vs. UAB30) and decrease in percentage of cells in S phase (COA6: 44.7 ± 1.2 vs. 38.6 ± 1%, control vs. UAB30). UAB30 led to differentiation of PDX cells, as evidenced by the increase in neurite outgrowth and mRNA abundance of differentiation markers. CD133 expression was decreased by 40% in COA6 cells after UAB30. The ability to form tumorspheres and mRNA abundance of known stemness markers were also significantly decreased following treatment with UAB30, further indicating decreased cancer cell stemness. These results provide evidence that UAB30 decreased tumorigenicity and cancer cell stemness in neuroblastoma PDXs, warranting further exploration as therapy for high-risk neuroblastoma.

Novel retinoic acid derivative induces differentiation and growth arrest in neuroblastoma

INTRODUCTION

Retinoic acid (RA) is a differentiating agent utilized as maintenance therapy for high-risk neuroblastoma (NB), but associated toxicities limit its use. We have previously shown that a non-toxic, novel rexinoid, 9-cis-UAB30 (UAB30), decreased NB cell proliferation and in vivo tumor growth. A second generation, mono-methylated compound, 6-Methyl-UAB30 (6-Me), has been recently designed having greater potency compared with UAB30. In the current study, we hypothesized that 6-Me would inhibit NB cell proliferation and survival and induce differentiation and cell-cycle arrest.

METHODS

Proliferation and viability were measured in four human NB cell lines following treatment with UAB30 or 6-Me. Cell-cycle was analyzed and tumor cell stemness was evaluated with extreme limiting dilution assays and immunoblotting for expression of stem cell markers. A xenograft murine model was utilized to study the effects of 6-Me in vivo.

RESULTS

Treatment with 6-Me led to decreased proliferation and viability, induced cell cycle arrest, and increased neurite outgrowth, indicating differentiation of surviving cells. Furthermore, treatment with 6-Me decreased tumorsphere formation and expression of stem cell markers. Finally, inhibition of tumor growth and increased animal survival was observed in vivo following treatment with 6-Me.

CONCLUSION

These results indicate a potential therapeutic role for this novel rexinoid in neuroblastoma treatment.

UAB30, a novel RXR agonist, decreases tumorigenesis and leptomeningeal disease in group 3 medulloblastoma patient-derived xenografts

BACKGROUND

Group 3 tumors account for approximately 25-30% of medulloblastomas and have the worst prognosis. UAB30 is a novel synthetic rexinoid shown to have limited toxicities in humans and significant efficacy in the pediatric neuroectodermal tumor, neuroblastoma. We hypothesized that treatment with UAB30 would decrease tumorigenicity in medulloblastoma patient-derived xenografts (PDXs).

METHODS

Three group 3 medulloblastoma PDXs (D341, D384 and D425) were utilized. Cell viability, proliferation, migration and invasion assays were performed after treatment with UAB30 or 13-cis-retinoic acid (RA). Cell cycle analysis was completed using flow cytometry. A flank model, a cerebellar model, and a model of leptomeningeal metastasis using human medulloblastoma PDX cells was used to assess the in vivo effects of UAB30 and RA.

RESULTS

UAB30 treatment led to cell differentiation and decreased medulloblastoma PDX cell viability, proliferation, migration and invasion and G1 cell cycle arrest in all three PDXs similar to RA. UAB30 and RA treatment of mice bearing medulloblastoma PDX tumors resulted in a significant decrease in tumor growth and metastasis compared to vehicle treated animals.

CONCLUSIONS

UAB30 decreased viability, proliferation, and motility in group 3 medulloblastoma PDX cells and significantly decreased tumor growth in vivo in a fashion similar to RA, suggesting that further investigations into the potential therapeutic application of UAB30 for medulloblastoma are warranted.

Preclinical Evaluation of UAB30 in Pediatric Renal and Hepatic Malignancies

Rare tumors of solid organs remain some of the most difficult pediatric cancers to cure. These difficult tumors include rare pediatric renal malignancies, such as malignant rhabdoid kidney tumors (MRKT) and non-osseous renal Ewing sarcoma, and hepatoblastoma, a pediatric liver tumor that arises from immature liver cells. There are data in adult renal and hepatic malignancies demonstrating the efficacy of retinoid therapy. The investigation of retinoic acid therapy in cancer is not a new strategy, but the widespread adoption of this therapy has been hindered by toxicities. Our laboratory has been investigating a novel synthetic rexinoid, UAB30, which exhibits a more favorable side-effect profile. In this study, we hypothesized that UAB30 would diminish the growth of tumor cells from both rare renal and liver tumors in vitro and in vivo We successfully demonstrated decreased cellular proliferation, invasion and migration, cell-cycle arrest, and increased apoptosis after treatment with UAB30. Additionally, in in vivo murine models of human hepatoblastoma or rare human renal tumors, there were significantly decreased tumor xenograft growth and increased animal survival after UAB30 treatment. UAB30 should be further investigated as a developing therapeutic in these rare and difficult-to-treat pediatric solid organ tumors. Mol Cancer Ther; 15(5); 911-21. ©2016 AACR.

Preclinical Evaluation of a Novel RXR Agonist for the Treatment of Neuroblastoma

Neuroblastoma remains a common cause of pediatric cancer deaths, especially for children who present with advanced stage or recurrent disease. Currently, retinoic acid therapy is used as maintenance treatment to induce differentiation and reduce tumor recurrence following induction therapy for neuroblastoma, but unavoidable side effects are seen. A novel retinoid, UAB30, has been shown to generate negligible toxicities. In the current study, we hypothesized that UAB30 would have a significant impact on multiple neuroblastoma cell lines in vitro and in vivo. Cellular survival, cell-cycle analysis, migration, and invasion were studied using AlamarBlue assays, FACS, and Transwell assays, respectively, in multiple cell lines following treatment with UAB30. In addition, an in vivo murine model of human neuroblastoma was utilized to study the effects of UAB30 upon tumor xenograft growth and animal survival. We successfully demonstrated decreased cellular survival, invasion, and migration, cell-cycle arrest, and increased apoptosis after treatment with UAB30. Furthermore, inhibition of tumor growth and increased survival was observed in a murine neuroblastoma xenograft model. The results of these in vitro and in vivo studies suggest a potential therapeutic role for the low toxicity synthetic retinoid X receptor selective agonist, UAB30, in neuroblastoma treatment.

Attenuation of signal flow from P2Y6 receptor by protein kinase C-alpha in SK-N-BE(2)C human neuroblastoma cells

Extracellular nucleotides exert a variety of biological actions through several kinds of P2 receptors in many tissues and cell types. We found that treatment with nucleotides increases intracellular Ca2+ concentration ([Ca2+]i) in SK-N-BE(2)C human neuroblastoma cells with a following order of potency: UDP > UTP > ADP >> ATP. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that specific mRNAs coding for human P2Y1, P2Y4, and P2Y6 receptors were expressed in the cells, but Northern blot analysis revealed that P2Y6 receptors were the predominant type. Activation of protein kinase C-alpha by treatment with 1 micro m phorbol 12-myristate 13-acetate dramatically inhibited both the UDP-induced [Ca2+]i rise and inositol 1,4,5-trisphosphate (IP3) generation, whereas incubation with pertussis toxin had little effect on the responses. The UDP-induced [Ca2+]i rise and IP3 production were maintained up to 30 min after stimulation, while bradykinin-induced responses rapidly decreased to the basal level within 5 min of stimulation. Pretreatment of cells with the maximal effective concentration of UDP reduced the subsequent carbachol- or bradykinin-induced [Ca2+]i rise without inhibition of IP3 generation. Neuronal differentiation of the cells by treatment with retinoic acid for 7 days did not change the expression level of P2Y6 receptors. Taken together, the data indicate that P2Y6 receptors highly responsive to diphosphonucleotide UDP are endogenously expressed in the human neuroblastoma SK-N-BE(2)C cells and that they are involved in the modulation of other phospholipase C-coupled receptor-mediated Ca2+ mobilization by depleting the IP3-sensitive Ca2+ stores.

Retinoic acid-induced differentiation in a human neuroblastoma cell line is associated with an increase in nitric oxide synthesis

The human neuroblastoma cell line SK-N-BE, after incubation with 10 microM retinoic acid (RA) or 20 nM phorbol 12-myristate 13-acetate (PMA), underwent biochemical and morphological signs of differentiation within 10-14 days. In parallel, SK-N-BE cells produced significantly higher amounts of nitric oxide (NO) in comparison with controls, as assessed by the measurement of nitrite and nitrate in the culture supernatant and of NO synthase (NOS) activity in the cell lysates (measured as ability to convert [3H]arginine into [3H]citrulline and as NADPH diaphorase activity). Nitrite/nitrate production was abolished by adding the NO scavenger hemoglobin in the culture medium and was inhibited by aminoguanidine (AG, a selective inhibitor of the inducible NOS isoform) but not by the less selective inhibitor NG-nitro-L-arginine methylester (NAME). Western blotting experiments with monoclonal antibodies against the ncNOS and iNOS isoforms suggest that RA-elicited NOS activation is not attributable to an increased expression of the protein. NAME and AG were not able to revert inhibition of proliferation induced by RA, and the NO donor sodium nitroprusside did not mimic the effect of RA and PMA. These data indicate that increased NO synthesis does not mediate RA- or PMA-induced differentiation but may be an additional marker of differentiation into sympathetic-like neuronal cells.

Differentiation of U-937 promonocytic cells with mitomycin C or cis-diamminedichloroplatinum II

Administration of 0.3 microM mitomycin C (MMC) or 2.0 microM cis-diamminedichloroplatinum II (CDDP) decreased the growth activity and induced the differentiation of U-937 human promonocytic cells, as shown by nitroblue tetrazolium reduction and an increase in surface expression of the leukocyte integrins CD11b/CD18 and CD11c/CD18. Expression of these differentiation markers started to be significant at 48 hr of treatment. These concentrations resulted in little cell damage (determined by Trypan blue exclusion) and slightly induced apoptosis (determined by DNA degradation and changes in nuclear morphology). The treatments induced a transient increase in c-fos and c-jun mRNA levels, with maximum values at 1-6 hr; a transient increase in collagenase mRNA level, with a maximum value at 48 hr; and a progressive increase in vimentin and lamin A and C mRNA levels. These changes were qualitatively similar to those produced by 12-0-tetradecanoylphorbol 13-acetate. CDDP and MMC also caused a transient increase of total AP-1 binding activity, as determined by gel retardation assays. The drugs produced an early transient activation (3-6 hr) of membrane-bound protein kinase C, followed by a later activation (48 hr) of both the membrane and the cytosolic enzyme. These results suggest that protein kinase C and AP-1-dependent gene expression could be involved in myeloid cell differentiation by alkylating agents.

Effects of 1,25-dihydroxyvitamin D3 and retinoic acid on the proliferation and cell cycle phase distribution of neuroblastoma SK-N-SH cells

The hormone 1,25-(OH)2D3 has been shown to modulate cell proliferation and induce differentiation in several normal and malignant cell lines. In this work, we examined the effect of the hormone on the neuroblastoma SK-N-SH cell line. The steroid did not influence cell growth and cell cycle distribution, while retinoic acid inhibited proliferation and induced an accumulation of the cells in the G0/G1 phase of the cell cycle. 1,25-(OH)2D3 did not alter cell morphology. The activities of the 1-alpha- and 24-hydroxylases were low and not regulated by the hormone. The level of the total 1,25-(OH)2D3 receptor was low. We conclude that the lack of effect of 1,25-(OH)2D3 on the SK-N-SH cell line is related to the low level of the 1,25-(OH)2D3 receptor.

Neuroblastoma: the result of multistep transformation?

Genetic and molecular abnormalities, in association with malignant phenotypes, have been previously demonstrated in a variety of human tumors. Although the multistep theory fits well for some cancers such as retinoblastoma and colon carcinoma, for many others it still remains to be proven. Neuroblastoma, a tumor found in pediatric patients, seems to fall into the multistep model. Nonrandom chromosome abnormalities have been found with 1p deletion, loss of heterozygosity for short arm of chromosome 1 and for chromosome 11q and 14q. Amplification of N-myc oncogene and an increased level of Ras protein have also been demonstrated. Therefore, even if it is not possible to show that these mutations happen as discrete events in their order of appearance, the multistep model seems involved in neuroblastoma development. Neuroblastoma has a peculiar aspect, however, that makes this tumor a natural model of defect of cell differentiation. In fact, there is a particular subset of metastatic tumors that show spontaneous regression. In vitro, neuroblastoma cell lines can be induced to differentiate along the neural pathway using retinoic acid. Other natural and chemical substances are also able to induce cell differentiation. During retinoic acid treatment, N-myc oncogene expression decreases and other genes are deregulated. p53 and MDR1 gene expression increases. These two different aspects, failure of cell differentiation pathway and genetic mutations, make the neuroblastoma one of the most difficult problems of modern molecular biology.

Nerve growth factor receptor expression in medulloblastomas and the potential role of nerve growth factor as a differentiating agent in medulloblastoma cell lines

Nerve growth factor (NGF) has the potential to induce cellular differentiation in various neoplastic and nonneoplastic cell lines. In this study, our aim was to determine NGF receptor (NGFr) status in medulloblastoma specimens and cell lines and to investigate whether NGF could act as a potential differentiating agent for this common pediatric brain tumor. Paraffin-embedded tumor tissue from 10 patients with the diagnosis of medulloblastoma was retrospectively analyzed to determine the frequency of NGFr expression. Of the 10 tumor specimens evaluated, 4 were positive for NGFr; however, NGFr staining was confined to only 5 to 8% of the cells in a randomly scattered pattern. No colocalization was present with neuronal, glial, or vascular structures. In addition, two medulloblastoma cell lines established in our laboratory were also evaluated for NGFr. In this study, we also examined the effects of retinoic acid, 12-O-tetradecanoyl-phorbol-13-acetate, and NGF on medulloblastoma cell lines to evaluate their effect on morphological differentiation and NGFr expression. Although these agents failed to cause NGFr expression in our cell lines, morphological alteration was noticed in only one of the cell lines with retinoic acid. Therefore, because of the lack of de novo or induced NGFr expression, it is unlikely that NGF will be useful as a potential therapeutic differentiating agent for medulloblastomas.

Expression of protein kinase C-alpha (PKC-alpha) and MYCN mRNAs in human neuroblastoma cells and modulation during morphological differentiation induced by retinoic acid

It is known that PKC is differently expressed in brain and the peripheral nervous system and is involved in cellular differentiation. We have analyzed 9 human neuronal-derived crest-cell lines for PKC-alpha mRNA. Seven out of nine expressed 9.0 kb and 4.0 kb PKC-alpha mRNAs, but three had high level of 9.0 kb transcription. The different expression of the two messenger RNAs may result from alternative splicing and a different degree of cell maturation. The same cell lines were studied for MYCN gene expression. A possible relation between the two genes is discussed. One cell line expressing high levels of both PKC-alpha mRNA was treated with 10(-5) M retinoic acid (RA). The expression of both messenger RNAs was suppressed when the cells achieved a morphological differentiation and showed neurite-like processes. A decrease of PKC-alpha gene expression was associated to down regulation of MYCN mRNA. These preliminary results suggest that PKC suppression of PKC-alpha mRNA is associated with reversion of the malignant phenotype.