Leukemia stem cells: the root of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by a chromosome translocation that generates the Bcr-Abl oncogene encoding a constitutive kinase activity. Despite remarkable success in controlling CML at chronic phase by Bcr-Abl tyrosine kinase inhibitors (TKIs), a significant proportion of CML patients treated with TKIs develop drug resistance due to the inability of TKIs to kill leukemia stem cells (LSCs) that are responsible for initiation, drug resistance, and relapse of CML. Therefore, there is an urgent need for more potent and safer therapies against leukemia stem cells for curing CML. A number of LSCassociated targets and corresponding signaling pathways, including CaMKII-γ, a critical molecular switch for co-activating multiple LSC-associated signaling pathways, have been identified over the past decades and various small inhibitors targeting LSC are also under development. Increasing evidence shows that leukemia stem cells are the root of CML and targeting LSC may offer a curable treatment option for CML patients. This review summarizes the molecular biology of LSC and itsassociated targets, and the potential clinical application in chronic myeloid leukemia.     

针对T315I 突变的Bcr-Abl 酪氨酸激酶抑制剂研究进展

BCR-ABL 是一种由bcr 基因和c-abl 原癌基因融合产生的致癌基因。该基因表达的Bcr–Abl 癌蛋白是慢性粒细胞白血病的病理学基础。因此研发选择性的Bcr–Abl 酪氨酸激酶抑制剂成为治疗慢性粒细胞白血病的一种有效策略。目前已有数个Bcr–Abl 酪氨酸激酶抑制剂获准上市。然而,Abl 激酶结构域的突变或其他原因导致肿瘤耐药性的出现,其中T315I 突变是最重要的突变之一,引发的耐药性更是难以克服。重点介绍了针对T315I 突变的Bcr–Abl 酪氨酸激酶抑制剂的研究进展。     

Pigment epithelium‐derived factor peptide promotes limbal stem cell proliferation through hedgehog pathway

Expansion of limbal epithelial stem cells (LSCs) is crucial for the success of limbal transplantation. Previous studies showed that pigment epithelium‐derived peptide (PEDF) short peptide 44‐mer could effectively expand LSCs and maintain them in a stem‐cell state, but the mechanism remained unclear. In the current study, we found that pharmacological inhibition of Sonic Hedgehog (SHh) activity reduced the LSC holoclone number and suppressed LSC proliferation in response to 44‐mer. In mice subjected to focal limbal injury, 44‐mer facilitated the restoration of the LSC population in damaged limbus, and such effect was impeded by the SHh or ATGL (a PEDF receptor) inhibitor. Furthermore, we showed that 44‐mer increased nuclear translocation of Gli1 and Gli3 in LSCs. Knockdown of Gli1 or Gli3 suppressed the ability of 44‐mer to induce cyclin D1 expression and LSC proliferation. In addition, ATGL inhibitor suppressed the 44‐mer‐induced phosphorylation of STAT3 at Tyr705 in LSC. Both inhibitors for ATGL and STAT3 attenuated 44‐mer‐induced SHh activation and LSC proliferation. In conclusion, our data demonstrate that SHh‐Gli pathway driven by ATGL/STAT3 signalling accounts for the 44‐mer‐mediated LSC proliferation.     

Interference with SMO increases chemotherapy drug sensitivity of A2780/DDP cells by inhibiting the Hh/Gli signaling pathway

Aberrant activation of the Hedgehog (Hh)/Gli pathway contributes to the tumorigenesis of several human cancers, including ovarian cancers. We investigated the function of SMO on cell growth, drug resistance, and invasive ability in A2780/DDP cells. Moreover, we also tested the levels of the downstream target genes of the Hh/Gli pathway in SMO short hairpin RNA (shRNA) lentivirus-infected A2780/DDP cells. Western blot analysis results revealed that the Hh/Gli pathway was activated in cisplatin-resistant A2780/DDP cells. After infection by SMO shRNA lentivirus, the colony formation rate and invasive rate of cisplatin-resistant A2780/DDP cells were decreased. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that upon transfection with SMO shRNA, cell growth was decreased and drug sensitivity to cisplatin was upregulated. Moreover, interference with SMO decreased the expression of MMP-2, MMP-9, VEGF, and Snail in cisplatin-resistant cells. Thus, the Hh/Gli signaling pathway was aberrantly activated in A2780/DDP cells. The colony formation rate and invasive rate were decreased in SMO shRNA lentivirus–infected A2780/DDP cells. All results showed that inhibiting Hh/Gli signaling may negatively regulate the proliferation, invasion, and metastasis of cisplatin-resistant A2780/DDP cells, as well as increase the sensitivity of A2780/DDP to the chemotherapeutic drug of cisplatin.     

Hedgehog pathway activation in chronic myeloid leukemia: A promise for a novel combination therapeutic approach?

Chronic Myeloid Leukemia (CML) is a hematopoietic stem cell malignancy that is driven by the oncogenic BCR-ABL fusion protein, and for which treatment with ABL tyrosine kinase inhibitors (TKI) has yielded great success. While this is the case, BCR-ABL leukemic stem cells can persist despite TKI therapy, and efforts have intensified towards determining the molecular pathways that are critical for the maintenance of such cells. Recent studies indicate that aberrant Hedgehog (Hh) signaling plays a crucial role in the survival of the leukemic stem cell population. The Hh pathway displays crucial roles during embryonic development, tissue regeneration and repair in adults. Several mechanisms that lead to the aberrant activation of the Hh pathway have been identified in various cancers. Here we review in detail the discovery that Hh signaling governs the maintenance of the critical leukemia initiating cells or leukemic stem cells (LSCs) in BCR-ABL-induced CML as well as discuss investigations on the role of Hh signaling in normal hematopoeisis. As inhibitors that directly target the positive Hh signal transducer Smoothened (SMO) have entered clinical trials, these findings offer a unique opportunity to potentially target the LSC population that is not eliminated with ABL tyrosine kinase inhibition therapy in CML.     

Design and synthesis of 3-substituted benzamide derivatives as Bcr-Abl kinase inhibitors

A series of 3-substituted benzamide derivatives structurally related to STI-571 (imatinib mesylate), a Bcr-Abl tyrosine kinase inhibitor used to treat chronic myeloid leukemia (CML), was prepared and evaluated for antiproliferative activity against the Bcr-Abl-positive leukemia cell line K562. About ten 3-halogenated and 3-trifluoromethylated benzamide derivatives were identified as highly potent Bcr-Abl kinase inhibitors. One of these, NS-187 (9b), is a promising new candidate Bcr-Abl inhibitor for the therapy of STI-571-resistant chronic myeloid leukemia.     

Repression of Hedgehog signal transduction in T-lineage cells increases TCR-induced activation and proliferation

Hedgehog proteins signal for differentiation, survival and proliferation of the earliest thymocyte progenitors, but their functions at later stages of thymocyte development and in peripheral T-cell function are controversial. Here we show that repression of Hedgehog (Hh) pathway activation in T-lineage cells, by expression of a transgenic repressor form of Gli2 (Gli2δC2), increased T-cell differentiation and activation in response to TCR signalling. Expression of the Gli2δC2 transgene increased differentiation from CD4+CD8+ to single positive thymocyte, and increased peripheral T cell populations. Gli2δC2 T-cells were hyper-responsive to activation by ligation of CD3 and CD28: they expressed cell surface activation markers CD69 and CD25 more quickly, and proliferated more than wild-type T-cells. These data show that Hedgehog pathway activation in thymocytes and T-cells negatively regulates TCR-dependent differentiation and proliferation. Thus, as negative regulators of TCR-dependent events, Hh proteins provide an environmental influence on T-cell fate.     

Gankyrin activates the hedgehog signalling to drive metastasis in osteosarcoma

Gankyrin is a regulatory subunit of the 26-kD proteasome complex and promotes the occurrence and progression of many malignancies. However, the role of gankyrin in osteosarcoma (OS) metastasis remains unclear. Hedgehog signalling has been shown to regulate stem cell homeostasis and cancer metastasis, but the mechanisms that activate this pathway in OS are still poorly understood. Here, a series of in vitro and in vivo assays were carried out to explore the function and mechanism of gankyrin regulating Hedgehog signalling in OS. We demonstrated that gankyrin promotes migration, invasion and regulates the expression of some stemness factors by up-regulating Gli1 in OS. Importantly, our data showed an interaction between gankyrin and Gli1. Moreover, gankyrin suppresses the ubiquitin-mediated degradation of Gli1 protein in OS. Gankyrin also significantly promotes the lung metastasis of OS in vivo. Our findings suggest that gankyrin drives metastasis and regulates the expression of some stemness factors in osteosarcoma by activating Hedgehog signalling, indicating that drug screening for compounds targeting gankyrin may contribute to the development of novel and effective therapies for OS.     

A novel synthetic smoothened antagonist transiently inhibits pancreatic adenocarcinoma xenografts in a mouse model

Background

Hedgehog (Hh) signaling is over-activated in several solid tumors where it plays a central role in cell growth, stroma recruitment and tumor progression. In the Hh signaling pathway, the Smoothened (SMO) receptor comprises a primary drug target with experimental small molecule SMO antagonists currently being evaluated in clinical trials.

Principal Findings

Using Shh-Light II (Shh-L2) and alkaline phosphatase (AP) based screening formats on a “focused diversity” library we identified a novel small molecule inhibitor of the Hh pathway, MS-0022 (2-bromo-N-(4-(8-methylimidazo[1,2-a]pyridin-2-yl)phenyl)benzamide). MS-0022 showed effective Hh signaling pathway inhibition at the level of SMO in the low nM range, and Hh pathway inhibition downstream of Suppressor of fused (SUFU) in the low µM range. MS-0022 reduced growth in the tumor cell lines PANC-1, SUIT-2, PC-3 and FEMX in vitro. MS-0022 treatment led to a transient delay of tumor growth that correlated with a reduction of stromal Gli1 levels in SUIT-2 xenografts in vivo.

Significance

We document the in vitro and in vivo efficacy and bioavailability of a novel small molecule SMO antagonist, MS-0022. Although MS-0022 primarily interferes with Hh signaling at the level of SMO, it also has a downstream inhibitory effect and leads to a stronger reduction of growth in several tumor cell lines when compared to related SMO antagonists.