The BET bromodomain inhibitor ZEN-3365 targets the Hedgehog signaling pathway in acute myeloid leukemia

GANT61 surmounts drug resistance of ADR by upregulating lysosome activities and reducing BCL2 expression in HL-60/ADR cells

BACKGROUND

Drug resistance remains a significant obstacle to Acute myeloid leukemia (AML) successful treatment, often leading to therapeutic failure. Our previous studies demonstrated that Glioma-associated oncogene-1 (GLI1) reduces chemotherapy sensitivity and promotes cell proliferation in AML cells. GANT61, an inhibitor of GLI1, emerges as a promising candidate in AML treatment. This study aims to explore the effects of the combination of GANT61 and Adriamycin (ADR) on AML cells resistance and elucidate the mechanisms through which GANT61 may potentiate the sensitivity of AML cells to ADR.

METHODS

AML cell lines and AML primary cells were studied to evaluate effects and mechanisms of GANT61. Flow cytometry assays were used to verify apoptosis. Cell Counting Kit-8 (CCK-8) and EDU+ staining were used to observe changes in cell viability and the cytotoxic effect to different drugs. The transcriptomic profiles of HL-60/ADR cells with or without GANT61 treatment were compared via RNA-Seq analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses and Gene Set Enrichment Analysis (GSEA) were performed for differentially expressed genes (DEGs) to reveal the underlying mechanisms of GANT61 in AML cells. GLI1, BCL2, Bax protein and mRNA expression levels were assessed by Western blot and Real-time polymerase chain reaction (RT-PCR).

RESULTS

Our studies found that the combination of GANT61 and ADR synergistically inhibits proliferation while enhancing apoptosis in HL-60/ADR cells, and does not significantly exacerbate myelosuppression. Mechanistically, GSEA revealed enrichment of the gene set associated with the KEGG term "Apoptosis" and "Lysosome" in GANT61 treated cells. Meanwhile, "Apoptosis" was identified as the third most relevant pathway enriched by lysosomal DEGs, and BCL2 expression showed a negative correlation with these lysosomal DEGs in AML patients. RT-PCR and Western blot analysis disclosed that GANT61 significantly restrained BCL2 expression in AML cells. Lastly, we proved that venetoclax, a BCL2 inhibitor, co-treatment with GANT61 improved ADR sensitivity in HL-60/ADR cells.

CONCLUSIONS

GANT61 effectively reversed ADR resistance in HL-60/ADR cells by upregulating lysosome activities and downgrading BCL2 expression, providing a new treatment strategy with acceptable toxicity for AML-resistant patients.

Targeting cancer hallmark vulnerabilities in hematologic malignancies by interfering with Hedgehog/GLI signaling

Understanding the genetic alterations, disrupted signaling pathways, and hijacked mechanisms in oncogene-transformed hematologic cells is critical for the development of effective and durable treatment strategies against liquid tumors. In this review, we focus on the specific involvement of the Hedgehog (HH)/GLI pathway in the manifestation and initiation of various cancer features in hematologic malignancies, including multiple myeloma, T- and B-cell lymphomas, and lymphoid and myeloid leukemias. By reviewing canonical and noncanonical, Smoothened-independent HH/GLI signaling and summarizing preclinical in vitro and in vivo studies in hematologic malignancies, we elucidate common molecular mechanisms by which HH/GLI signaling controls key oncogenic processes and cancer hallmarks such as cell proliferation, cancer stem cell fate, genomic instability, microenvironment remodeling, and cell survival. We also summarize current clinical trials with HH inhibitors and discuss successes and challenges, as well as opportunities for future combined therapeutic approaches. By providing a bird's eye view of the role of HH/GLI signaling in liquid tumors, we suggest that a comprehensive understanding of the general oncogenic effects of HH/GLI signaling on the formation of cancer hallmarks is essential to identify critical vulnerabilities within tumor cells and their supporting remodeled microenvironment, paving the way for the development of novel and efficient personalized combination therapies for hematologic malignancies.

BRD4 as a potential target for human papillomaviruses associated cancer

Around 99% of cervical cancer and 5%-10% of human cancer are associated with human papillomaviruses (HPV). Notably, the life-cycle of HPV begins by low-level infection of the basal cells of the stratified epithelium, where the viral genomes are replicated and passed on to the daughter proliferating basal cells. The production of new viral particles remains restricted to eventually differentiated cells. HPVs support their persistent infectious cycle by hijacking pivotal pathways and cellular processes. Bromodomain-containing protein 4 (BRD4) is one of the essential cellular factors involved in multiple stages of viral transcription and replication. In this review, we demonstrate the role of BRD4 in the multiple stages of HPV infectious cycle. Also, we provide an overview of the intense research about the cellular functions of BRD4, the mechanism of action of bromodomain and extra terminal inhibitors, and how it could lead to the development of antiviral/anticancer therapies.

Multiprotein GLI Transcriptional Complexes as Therapeutic Targets in Cancer

The Hedgehog signaling pathway functions in both embryonic development and adult tissue homeostasis. Importantly, its aberrant activation is also implicated in the progression of multiple types of cancer, including basal cell carcinoma and medulloblastoma. GLI transcription factors function as the ultimate effectors of the Hedgehog signaling pathway. Their activity is regulated by this signaling cascade via their mRNA expression, protein stability, subcellular localization, and ultimately their transcriptional activity. Further, GLI proteins are also regulated by a variety of non-canonical mechanisms in addition to the canonical Hedgehog pathway. Recently, with an increased understanding of epigenetic gene regulation, novel transcriptional regulators have been identified that interact with GLI proteins in multi-protein complexes to regulate GLI transcriptional activity. Such complexes have added another layer of complexity to the regulation of GLI proteins. Here, we summarize recent work on the regulation of GLI transcriptional activity by these novel protein complexes and describe their relevance to cancer, as such GLI regulators represent alternative and innovative druggable targets in GLI-dependent cancers.

Hedgehog/GLI signaling in hematopoietic development and acute myeloid leukemia-From bench to bedside

While the underlying genetic alterations and biology of acute myeloid leukemia (AML), an aggressive hematologic malignancy characterized by clonal expansion of undifferentiated myeloid cells, have been gradually unraveled in the last decades, translation into clinical treatment approaches has only just begun. High relapse rates remain a major challenge in AML therapy and are to a large extent attributed to the persistence of treatment-resistant leukemic stem cells (LSCs). The Hedgehog (HH) signaling pathway is crucial for the development and progression of multiple cancer stem cell driven tumors, including AML, and has therefore gained interest as a therapeutic target. In this review, we give an overview of the major components of the HH signaling pathway, dissect HH functions in normal and malignant hematopoiesis, and specifically elaborate on the role of HH signaling in AML pathogenesis and resistance. Furthermore, we summarize preclinical and clinical HH inhibitor studies, leading to the approval of the HH pathway inhibitor glasdegib, in combination with low-dose cytarabine, for AML treatment.