BCL-xL/MCL-1 inhibition and RARγ antagonism work cooperatively in human HL60 leukemia cells

Novel indole retinoid derivative induces apoptosis and cell cycle arrest and modulates AKT and ERK signaling in HL-60 cells

Chemotherapy with targeted drugs is the first line therapy option for acute and chronic myeloid leukemia. However, hematopoietic stem cell transplantation may be used in high-risk patients or patients with failed responses to chemo drugs. Discovery and development of more effective new agents with lower side effects is the main aim of leukemia treatment. In this study, a novel retinoid compound with tetrahydronaphthalene ring was synthesized and evaluated for anticancer activity in human chronic and acute myeloid leukemia cell lines K562 and HL-60. Novel N-(1H-indol-1-yl)-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2-carboxamide was synthesized based on molecular hybridization of the two different bioactive structures retinoid head and indole. The effects of the synthesized carboxamide compound, which was referred to as compound 5, were determined in K562 chronic myeloid leukemia and HL-60 acute myeloid leukemia cell lines and L929 fibroblast cell line, which served as a control. Colorimetric MTT and caspase3 activity tests, flow cytometry, western blot, and microscopic examinations were used to evaluate biological activity. Compound 5 more effectively induced cell death in HL60 cells in comparison to K562 cells and L929 fibroblast cells. Therefore, further mechanism of cell death was investigated in HL60 cell line. It was found that compound 5 induced remarkable cytotoxicity, caspase3 activation, and PARP fragmentation in HL60 cells. Flow cytometric staining showed that the percentage of cells arrested in G0/G1 was also increased with compound 5 treatment. Important modulator proteins of cell proliferation p-ERK, p-AKT, and p-m-TOR were also found to be inhibited with compound 5 treatment. Collectively, our results reveal compound 5, which is a novel indole retinoid compound as a potential active agent for the treatment of acute promyelocytic leukemia.

Roles and Regulation of BCL-xL in Hematological Malignancies

Members of the Bcl-2 family are proteins that play an essential role in the regulation of apoptosis, a crucial process in development and normal physiology in multicellular organisms. The essential mechanism of this family of proteins is given by the role of pro-survival proteins, which inhibit apoptosis by their direct binding with their counterpart, the effector proteins of apoptosis. This family of proteins was named after the typical member Bcl-2, which was named for its discovery and abnormal expression in B-cell lymphomas. Subsequently, the structure of one of its members BCL-xL was described, which allowed one to understand much of the molecular mechanism of this family. Due to its role of BCL-xL in the regulation of cell survival and proliferation, it has been of great interest in its study. Due to this, it is important to research its role regarding the development and progression of human malignancies, especially in hematologic malignancies. Due to its variation in expression in cancer, it has been suggested that BCL-xL can or cannot play a role in cancer depending on the cellular or tissue context. This review discusses recent advances in its transcriptional regulation of BCL-xL, as well as the advances regarding the activities of BCL-xL in hematological malignancies, its possible role as a biomarker, and its possible clinical relevance in these malignancies.

Alternative splicing of BCL-X and implications for treating hematological malignancies

BCL-X is a member of the BCL-2 family. It regulates apoptosis and plays a critical role in hematological malignancies. It is well-known that >90% of human genes undergo alternative splicing. A total of 10 distinct splicing transcripts of the BCL-X gene have been identified, including transcript variants 1–9 and ABALON. Different transcripts from the same gene have different functions. The present review discusses the progress in understanding the different alternative splicing transcripts of BCL-X, including their characteristics, functions and expression patterns. The potential use of BCL-X in targeted therapies for hematological malignancies is also discussed.

The application of BH3 mimetics in myeloid leukemias

Execution of the intrinsic apoptotic pathway is controlled by the BCL-2 proteins at the level of the mitochondrial outer membrane (MOM). This family of proteins consists of prosurvival (e.g., BCL-2, MCL-1) and proapoptotic (e.g., BIM, BAD, HRK) members, the functional balance of which dictates the activation of BAX and BAK. Once activated, BAX/BAK form pores in the MOM, resulting in cytochrome c release from the mitochondrial intermembrane space, leading to apoptosome formation, caspase activation, and cleavage of intracellular targets. This pathway is induced by cellular stress including DNA damage, cytokine and growth factor withdrawal, and chemotherapy/drug treatment. A well-documented defense of leukemia cells is to shift the balance of the BCL-2 family in favor of the prosurvival proteins to protect against such intra- and extracellular stimuli. Small molecule inhibitors targeting the prosurvival proteins, named 'BH3 mimetics', have come to the fore in recent years to treat hematological malignancies, both as single agents and in combination with standard-of-care therapies. The most significant example of these is the BCL-2-specific inhibitor venetoclax, given in combination with standard-of-care therapies with great success in AML in clinical trials. As the number and variety of available BH3 mimetics increases, and investigations into applying these novel inhibitors to treat myeloid leukemias continue apace the need to evaluate where we currently stand in this rapidly expanding field is clear.

Therapeutic potential of Bcl-xL/Mcl-1 synthetic inhibitor JY-1-106 and retinoids for human triple-negative breast cancer treatment

Overexpression of anti-apoptotic proteins belonging to the B cell lymphoma (Bcl)-2 family is observed in numerous cancer types and has been postulated to promote cancer cell survival and chemotherapy resistance. Bcl-extra large (x_L)/myeloid cell leukemia sequence (Mcl)-1 was demonstrated to be expressed at relatively high levels in clinically aggressive basal-like cancers and inhibiting Bcl-x_L overexpression could potentially provoke cell death. A molecule able to target Bcl-x_L/Mcl-1, JY-1-106, is herein under investigation. It is also known that vitamin A-derived compounds exhibit antitumor activity in a variety of in vitro experimental models, promoting their effects via nuclear receptor isoforms including retinoic acid receptors (RARs). Pre-clinical observation highlighted that triple negative (estrogen receptor/progesterone receptor/human epidermal growth factor receptor)-breast cancer cells displayed resistance to retinoids due to the RARγ high expression profile. The present study used the triple-negative human breast cancer cell line, MDA-MB-231, to analyze the effects of the Bcl-x_L/Mcl-1 synthetic inhibitor, JY-1-106, alone or in combination with retinoids on cell viability. The results revealed a synergistic effect in reducing cell viability primarily by using JY-1-106 with the selective RARγ antagonist SR11253, which induces massive autophagy and necrosis. Furthermore, the results highlighted that JY-1-106 alone is able to positively influence the gene expression profile of p53 and RARα, providing a therapeutic advantage in human triple-negative breast cancer treatment.

Retinoic acid receptors α and γ are involved in antioxidative protection in renal tubular epithelial cells injury induced by hypoxia/reoxygenation

Renal interstitial fibrosis (RIF) is a common outcome in various chronic kidney diseases. Injury to renal tubular epithelial cell (RTEC) is major link in RIF. Hypoxia is one of the common factors for RTEC damage. Retinoic acid receptors (RARs), RARα, RARβ and RARγ, are evolutionary conserved and pleiotropic proteins that have been involved in various cellular functions, including proliferation, differentiation, apoptosis, and transcription. Recently, we discovered that aberrant expression of RARs was involved in the development of RIF in rats. Here, we investigated the role of RARs in the hypoxia/reoxygenation (HR) damage model in RTEC with virus-based delivery vectors to knockdown or overexpress RARs. Relevant indicators were detected. Our results showed that HR inhibited RARα and RARγ expressions in a time-dependent manner in RTECs; however, the expression of RARβ was not changed obviously. RARα and RARγ overexpression could protect cells from oxidative stress-induced injury by inhibiting HR-induced intracellular superoxide anion (O2-) generation, cell viability and mitochondria membrane potential (MMP) decrease and transforming growth factor β1 (TGF-β1) expression and promoting endogenous antioxidant defense components, superoxide dismutase (SOD) and glutathione (GSH). Meanwhile, inhibition of RARα and RARγ expressions by small interference RNAs (siRNA) resulted in a less resistance of RTEC to HR as shown in increased O2- production and TGF-β1 expression and decreased cell viability, MMP, SOD and GSH levels. These data indicates that RARα and RARγ act as positive regulators to offset oxidative damage and profibrosis cytokine accumulation and therefore has an antioxidative effect.

Akacid medical formulation induces apoptosis in myeloid and lymphatic leukemic cell lines in vitro and in vivo

Akacid medical formulation (AMF) is an oligoguanidine that exerts biocidal activity against airborne and surface microorganisms including bacteria, viruses, fungi, and molds, while showing relatively low toxicity to humans. We have previously shown that AMF exerts antiproliferative effects on a variety of solid tumor cell lines. In this study we raised the question whether AMF could also substantially inhibit cell growth or induce apoptosis in cell lines derived from hematologic malignancies such as leukemia or lymphoma. We found that AMF has antiproliferative effects on various hematologic cell lines derived from human leukemia and lymphoma. Additionally, we show that AMF induces apoptosis in leukemia cell lines not only via the extrinsic and intrinsic pathway, but also in a caspase-independent manner. This effect was found also in G0-arrested cells. Finally, in our animal experiments utilizing male nu/nu Balb/c mice we found a significant growth retardation, which was immunohistochemically associated with a significantly lower number of KI67-positive cells and caspase-3 induction in AMF-treated mice.