Small molecule Mcl-1 inhibitors for the treatment of cancer

Molecular insights and clinical implications for the tumor suppressor role of SCFFBXW7 E3 ubiquitin ligase

FBXW7 is one of the most well-characterized F-box proteins, serving as substrate receptor subunit of SKP1-CUL1-F-box (SCF) E3 ligase complexes. SCFFBXW7 is responsible for the degradation of various oncogenic proteins such as cyclin E, c-MYC, c-JUN, NOTCH, and MCL1. Therefore, FBXW7 functions largely as a major tumor suppressor. In keeping with this notion, FBXW7 gene mutations or downregulations have been found and reported in many types of malignant tumors, such as endometrial, colorectal, lung, and breast cancers, which facilitate the proliferation, invasion, migration, and drug resistance of cancer cells. Therefore, it is critical to review newly identified FBXW7 regulation and tumor suppressor function under physiological and pathological conditions to develop effective strategies for the treatment of FBXW7-altered cancers. Since a growing body of evidence has revealed the tumor-suppressive activity and role of FBXW7, here, we updated FBXW7 upstream and downstream signaling including FBXW7 ubiquitin substrates, the multi-level FBXW7 regulatory mechanisms, and dysregulation of FBXW7 in cancer, and discussed promising cancer therapies targeting FBXW7 regulators and downstream effectors, to provide a comprehensive picture of FBXW7 and facilitate the study in this field.

Modeling the Binding of Anticancer Peptides and Mcl-1

Mcl-1 (myeloid cell leukemia 1), a member of the Bcl-2 family, is upregulated in various types of cancer. Peptides representing the BH3 (Bcl-2 homology 3) region of pro-apoptotic proteins have been demonstrated to bind the hydrophobic groove of anti-apoptotic Mcl-1, and this interaction is responsible for regulating apoptosis. Structural studies have shown that, while there is high overall structural conservation among the anti-apoptotic Bcl-2 (B-cell lymphoma 2) proteins, differences in the surface groove of these proteins facilitates binding specificity. This binding specificity is crucial for the mechanism of action of the Bcl-2 family in regulating apoptosis. Bim-based peptides bind specifically to the hydrophobic groove of Mcl-1, emphasizing the importance of these interactions in the regulation of cell death. Molecular docking was performed with BH3-like peptides derived from Bim to identify high affinity peptides that bind to Mcl-1 and to understand the molecular mechanism of their interactions. The interactions of three identified peptides, E2gY, E2gI, and XXA1_F3dI, were further evaluated using 250 ns molecular dynamics simulations. Conserved hydrophobic residues of the peptides play an important role in their binding and the structural stability of the complexes. Understanding the molecular basis of interaction of these peptides will assist in the development of more effective Mcl-1 specific inhibitors.

BCL-2 inhibition in haematological malignancies: Clinical application and complications

B-cell lymphoma-2 (BCL-2) family proteins are fundamental regulators of the intrinsic apoptotic pathway which modulate cellular fate. In many haematological malignancies, overexpression of anti-apoptotic factors (BCL-2, BCL-XL and MCL-1) circumvent apoptosis. To address this cancer hallmark, a concerted effort has been made to induce apoptosis by inhibiting BCL-2 family proteins. A series of highly selective BCL-2 homology 3 (BH3) domain mimetics are in clinical use and in ongoing clinical trials for acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM). These inhibitors serve as promising candidates, both as single agents or in combination therapy to improve patient outcomes. In other diseases such as follicular lymphoma, efficacy has been notably limited. There are also clinical problems with BCL-2 family inhibition, including drug resistance, disease relapse, tumour lysis syndrome, and clinically relevant cytopenias. Here, we provide a balanced view on both the clinical benefits of BCL-2 inhibition as well as the associated challenges.

Discovery and optimization of (2-naphthylthio)acetic acid derivative as selective Bfl-1 inhibitor

Bcl-2 anti-apoptotic protein family suppresses cell death by deploying a surface groove to capture the critical BH3 α-helix of pro-apoptotic members. Bfl-1 is a relatively understudied member of this family, though it has been implicated in the pathogenesis and chemoresistance of a variety of human cancers. Reported small molecular Bfl-1 inhibitors encountered the issue of either lack in potency or poor selectivity against its most homologous member Mcl-1. In order to tackle this issue, compound library was screened and a hit compound UMI-77 was identified. We modified its chemical structure to remove the characteristic of PAINS (pan-assay interference compounds), demonstrated the real binding affinity and achieved selectivity against Mcl-1 under the guidance of computational modeling. After optimization 15 was obtained as leading compound to block Bfl-1/BIM interaction in vitro with more than 10-fold selectivity over Mcl-1. We believe 15 is of great value for the exploration of Bfl-1 biological function and its potential as therapeutic target.

Targeting MCL-1 protein to treat cancer: opportunities and challenges

Evading apoptosis has been linked to tumor development and chemoresistance. One mechanism for this evasion is the overexpression of prosurvival B-cell lymphoma-2 (BCL-2) family proteins, which gives cancer cells a survival advantage. Mcl-1, a member of the BCL-2 family, is among the most frequently amplified genes in cancer. Targeting myeloid cell leukemia-1 (MCL-1) protein is a successful strategy to induce apoptosis and overcome tumor resistance to chemotherapy and targeted therapy. Various strategies to inhibit the antiapoptotic activity of MCL-1 protein, including transcription, translation, and the degradation of MCL-1 protein, have been tested. Neutralizing MCL-1's function by targeting its interactions with other proteins via BCL-2 interacting mediator (BIM)S2A has been shown to be an equally effective approach. Encouraged by the design of venetoclax and its efficacy in chronic lymphocytic leukemia, scientists have developed other BCL-2 homology (BH3) mimetics-particularly MCL-1 inhibitors (MCL-1i)-that are currently in clinical trials for various cancers. While extensive reviews of MCL-1i are available, critical analyses focusing on the challenges of MCL-1i and their optimization are lacking. In this review, we discuss the current knowledge regarding clinically relevant MCL-1i and focus on predictive biomarkers of response, mechanisms of resistance, major issues associated with use of MCL-1i, and the future use of and maximization of the benefits from these agents.

The role of microRNA-21 (miR-21) in pathogenesis, diagnosis, and prognosis of gastrointestinal cancers: A review

MicroRNAs (miRNAs) are small non-coding RNAs regulating the expression of several target genes. miRNAs play a significant role in cancer biology, as they can downregulate their corresponding target genes by impeding the translation of mRNA (at the mRNA level) as well as degrading mRNAs by binding to the 3'-untranslated (UTR) regions (at the protein level). miRNAs may be employed as cancer biomarkers. Therefore, miRNAs are widely investigated for early detection of cancers which can lead to improved survival rates and quality of life. This is particularly important in the case of gastrointestinal cancers, where early detection of the disease could substantially impact patients' survival. MicroRNA-21 (miR-21 or miRNA-21) is one of the most frequently researched miRNAs, where it is involved in the pathophysiology of cancer and the downregulation of several tumor suppressor genes. In gastrointestinal cancers, miR-21 regulates phosphatase and tensin homolog (PTEN), programmed cell death 4 (PDCD4), mothers against decapentaplegic homolog 7 (SMAD7), phosphatidylinositol 3-kinase /protein kinase B (PI3K/AKT), matrix metalloproteinases (MMPs), β-catenin, tropomyosin 1, maspin, and ras homolog gene family member B (RHOB). In this review, we investigate the functions of miR-21 in pathogenesis and its applications as a diagnostic and prognostic cancer biomarker in four different gastrointestinal cancers, including colorectal cancer (CRC), pancreatic cancer (PC), gastric cancer (GC), and esophageal cancer (EC).

Bone marrow microenvironment- induced regulation of Bcl-2 family members in multiple myeloma (MM): Therapeutic implications

In Multiple Myeloma (MM) the finely tuned homeostasis of the bone marrow (BM) microenvironment is disrupted. Evasion of programmed cell death (apoptosis) represents a hallmark of cancer. Besides genetic aberrations, the supportive and protective MM BM milieu, which is constituted by cytokines and growth factors, intercellular and cell: extracellular matrix (ECM) interactions and exosomes, in particular, plays a key role in the abundance of pro-survival members of the Bcl-2 family (i.e., Mcl-1, Bcl-2, and Bcl-xL) in tumor cells. Moreover, microenvironmental cues have also an impact on stability- regulating post-translational modifications of anti-apoptotic proteins including de/phosphorylation, polyubiquitination; on their intracellular binding affinities, and localization. Advances of our molecular knowledge on the escape of cancer cells from apoptosis have informed the development of a new class of small molecules that mimic the action of BH3-only proteins. Indeed, approaches to directly target anti-apoptotic Bcl-2 family members are among today's most promising therapeutic strategies and BH3-mimetics (i.e., venetoclax) are currently revolutionizing not only the treatment of CLL and AML, but also hold great therapeutic promise in MM. Furthermore, approaches that activate apoptotic pathways indirectly via modification of the tumor microenvironment have already entered clinical practice. The present review article will summarize our up-to-date knowledge on molecular mechanisms by which the MM BM microenvironment, cytokines, and growth factors in particular, mediates tumor cell evasion from apoptosis. Moreover, it will discuss some of the most promising science- derived therapeutic strategies to overcome Bcl-2- mediated tumor cell survival in order to further improve MM patient outcome.

Single-cell RNA analysis to identify five cytokines signaling in immune-related genes for melanoma survival prognosis

Melanoma is one of the deadliest skin cancers. Recently, developed single-cell sequencing has revealed fresh insights into melanoma. Cytokine signaling in the immune system is crucial for tumor development in melanoma. To evaluate melanoma patient diagnosis and treatment, the prediction value of cytokine signaling in immune-related genes (CSIRGs) is needed. In this study, the machine learning method of least absolute selection and shrinkage operator (LASSO) regression was used to establish a CSIRG prognostic signature of melanoma at the single-cell level. We discovered a 5-CSIRG signature that was substantially related to the overall survival of melanoma patients. We also constructed a nomogram that combined CSIRGs and clinical features. Overall survival of melanoma patients can be consistently predicted with good performance as well as accuracy by both the 5-CSIRG signature and nomograms. We compared the melanoma patients in the CSIRG high- and low-risk groups in terms of tumor mutation burden, infiltration of the immune system, and gene enrichment. High CSIRG-risk patients had a lower tumor mutational burden than low CSIRG-risk patients. The CSIRG high-risk patients had a higher infiltration of monocytes. Signaling pathways including oxidative phosphorylation, DNA replication, and aminoacyl tRNA biosynthesis were enriched in the high-risk group. For the first time, we constructed and validated a machine-learning model by single-cell RNA-sequencing datasets that have the potential to be a novel treatment target and might serve as a prognostic biomarker panel for melanoma. The 5-CSIRG signature may assist in predicting melanoma patient prognosis, biological characteristics, and appropriate therapy.

Micro RNA 148a induces apoptosis and prevents angiogenesis with bevacizumab in colon cancer through direct inhibition of ROCK1/c-Met via HIF-1α under hypoxia

Angiogenesis and antiapoptosis effects are the major factors influencing malignancy progression. Hypoxia induces multiple mechanisms involving microRNA (miRNA) activity. Vascular endothelial growth factor (VEGF) is correlated with angiogenesis. An antiapoptotic factor, myeloid leukemia 1 (Mcl-1) is the main regulator of cell death. This study examined the role of miR-148a in inhibiting VEGF and Mcl-1 secretion by directly targeting ROCK1/c-Met by downregulating HIF-1α under hypoxia. The protein expression of ROCK1 or Met/HIF-1α/Mcl-1 in HCT116 and HT29 cells (all P < 0.05) was significantly reduced by miR-148a. The tube-formation assay revealed that miR-148a significantly suppressed angiogenesis and synergistically enhanced the effects of bevacizumab (both P < 0.05). The MTT assay revealed the inhibitory ability of miR-148a in HCT116 and HT29 cells (both P < 0.05). miR-148a and bevacizumab exerted synergistic antitumorigenic effects (P < 0.05) in an animal model. Serum miR-148a expression of metastatic colorectal cancer (mCRC) patients with a partial response was higher than that of mCRC patients with disease progression (P = 0.026). This result revealed that miR-148a downregulated HIF-1α/VEGF and Mcl-1 by directly targeting ROCK1/c-Met to decrease angiogenesis and increase the apoptosis of colon cancer cells. Furthermore, serum miR-148a levels have prognostic/predictive value in patients with mCRC receiving bevacizumab.

Identification of bicyclic compounds that act as dual inhibitors of Bcl-2 and Mcl-1

Elevated expression of anti-apoptotic proteins, such as Bcl-2 and Mcl-1 contributes to poor prognosis and resistance to current treatment modalities in multiple cancers. Here, we report the design, synthesis and characterization of benzimidazole chalcone and flavonoid scaffold-derived bicyclic compounds targeting both Bcl-2 and Mcl-1 by optimizing the structural differences in the binding sites of both these proteins. Initial docking screen of Bcl-2 and Mcl-1 with pro-apoptotic protein Bim revealed possible hits with optimal binding energies. All the optimized bicyclic compounds were screened for their in vitro cytotoxic activity against two oral cancer cell lines (AW8507 and AW13516) which express high levels of Bcl-2 and Mcl-1. Compound 4d from the benzimidazole chalcone series and compound 6d from the flavonoid series exhibited significant cytotoxic activity (IC₅₀ 7.12 μM and 17.18 μM, respectively) against AW13516 cell line. Time Resolved-Fluorescence Resonance Energy Transfer (TR-FRET) analysis further demonstrated that compound 4d and compound 6d could effectively inhibit the Bcl-2 and Mcl-1 proteins by displacing their BH3 binding partners. Both compounds exhibited potent activation of canonical pathway of apoptosis evident from appearance of cleaved Caspase-3 and PARP. Further, treatment of oral cancer cells with the inhibitors induced dissociation of the BH3 only protein Bim from Mcl-1 and Bak from Bcl-2 but failed to release Bax from Bcl-xL thereby confirming the nature of compounds as BH3-mimetics selectively targeting Bcl-2 and Mcl-1. Our study thus identifies bicyclic compounds as promising candidates for anti-apoptotic Bcl-2/Mcl-1 dual inhibitors with a potential for further development.

Targeting cancer stemness mediated by BMI1 and MCL1 for non-small cell lung cancer treatment

Lung cancer is the leading cause of cancer‐associated death, with a global 5‐year survival rate <20%. Early metastasis and recurrence remain major challenges for lung cancer treatment. The stemness property of cancer cells has been suggested to play a key role in cancer plasticity, metastasis and drug‐resistance, and is a potential target for drug development. In this study, we found that in non‐small cell lung cancer (NSCLC), BMI1 and MCL1 play crucial roles of cancer stemness including invasion, chemo‐resistance and tumour initiation. JNK signalling serves as a link between oncogenic pathway or genotoxicity to cancer stemness. The activation of JNK, either by mutant EGFR or chemotherapy agent, stabilized BMI1 and MCL1 proteins through suppressing the expression of E3‐ubiquitin ligase HUWE1. In lung cancer patient samples, high level of BMI1 is correlated with poor survival, and the expression of BMI1 is positively correlated with MCL1. A novel small‐molecule, BI‐44, was developed, which effectively suppressed BMI1/MCL1 expressions and inhibited tumour formation and progression in preclinical models. Targeting cancer stemness mediated by BMI1/MCL1 with BI‐44 provides the basis for a new therapeutic approach in NSCLC treatment.

Metformin Enhancement of Therapeutic Effects of 5-Fluorouracil and Oxaliplatin in Colon Cancer Cells and Nude Mice

Studies have demonstrated that metformin has antitumor effects in addition to therapeutic effects on hyperglycemia; however, few studies have explored the effects of metformin in chemotherapy. Therefore, we hypothesized that the administration of metformin would enhance the therapeutic effects of 5-fluorouracil and oxaliplatin (FuOx) to inhibit the growth of colorectal cancer (CRC) cells in vitro and in vivo. The results of our in vitro experiments demonstrated that metformin significantly increased the effects of FuOx with respect to cell proliferation (p < 0.05), colony formation (p < 0.05), and migration (p < 0.01) and induced cell cycle arrest in the G0/G1 phase in HT29 cells and the S phase in SW480 and SW620 cells (p < 0.05). Flow cytometry analysis revealed that metformin combined with FuOx induced late apoptosis (p < 0.05) by mediating mitochondria-related Mcl-1 and Bim protein expression. Furthermore, in vivo, metformin combined with FuOx more notably reduced tumor volume than FuOx or metformin alone did in BALB/c mice (p < 0.05). These findings demonstrate that metformin may act as an adjunctive agent to enhance the chemosensitivity of CRC cells to FuOx. However, further clinical trials are warranted to validate the clinical implications of the findings.

Anti-apoptotic MCL1 Protein Represents Critical Survival Molecule for Most Burkitt Lymphomas and BCL2-negative Diffuse Large B-cell Lymphomas

The pro-survival MCL1 protein is overexpressed in many cancers, including B-cell non-Hodgkin lymphomas (B-NHL). S63845 is a highly specific inhibitor of MCL1. We analyzed mechanisms of sensitivity/resistance to S63845 in preclinical models of diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma. Annexin V-based cytotoxic assays, Western blot analysis, protein co-immunoprecipitation, and cell clones with manipulated expression of BCL2 family proteins were used to analyze mechanisms of sensitivity to S63845. Experimental in vivo therapy with S63845 and/or venetoclax was performed using patient-derived xenografts (PDX) of treatment-refractory B-NHL. A subset of DLBCL and majority of Burkitt lymphoma cell lines were sensitive to S63845. The level of BCL2 protein expression was the major determinant of resistance to S63845: BCL2 serves as a buffer for pro-apoptotic proteins released from MCL1 upon exposure to S63845. While BCL2-negative lymphomas were effectively eliminated by single-agent S63845, its combination with venetoclax was synthetically lethal in BCL2-positive PDX models. Concerning MCL1, both, the level of MCL1 protein expression, and its occupational status represent key factors mediating sensitivity to S63845. In contrast to MCL1-BIM/BAK1 complexes that prime lymphoma cells for S63845-mediated apoptosis, MCL1-NOXA complexes are associated with S63845 resistance. In conclusion, MCL1 represents a critical survival molecule for most Burkitt lymphomas and a subset of BCL2-negative DLBCLs. The level of BCL2 and MCL1 expression and occupational status of MCL1 belong to the key modulators of sensitivity/resistance to S63845. Co-treatment with venetoclax can overcome BCL2-mediated resistance to S63845, and enhance efficacy of MCL1 inhibitors in BCL2-positive aggressive B-NHL.

Synthesis and biological evaluation of FJ-809, a compound originally described as MIM1 and an inhibitor of the anti-apoptotic protein Mcl-1

The development of inhibitors of anti-apoptotic proteins, such as Mcl-1, is currently a very active area in the field of cancer research.

Drug Repurposing: Deferasirox Inhibits the Anti-Apoptotic Activity of Mcl-1

Introduction

With the aim of repositioning commercially available drugs for the inhibition of the anti-apoptotic myeloid cell leukemia protein, Mcl-1, implied in various cancers, five molecules, highlighted from a published theoretical screening, were selected to experimentally validate their affinity toward Mcl-1.

Results

A detailed NMR study revealed that only two of the five tested drugs, Torsemide and Deferasirox, interacted with Mcl-1. NMR data analysis allowed the complete characterization of the binding mode of both drugs to Mcl-1, including the estimation of their affinity for Mcl-1. Biological assays evidenced that the biological activity of Torsemide was lower as compared to the Deferasirox, which was able to efficiently and selectively inhibit the anti-apoptotic activity of Mcl-1. Finally, docking and molecular dynamics led to a 3D model for the Deferasirox:Mcl-1 complex and revealed the positioning of the drug in the Mcl-1 P2/P3 pockets as well as almost all synthetic Mcl-1 inhibitors. Interestingly, contrary to known synthetic Mcl-1 inhibitors which interact through Arg263, Deferasirox, establishes a salt bridge with Lys234.

Conclusion

Deferasirox could be a potential candidate for drug repositioning as Mcl-1 inhibitor.

Co-Delivery of Paclitaxel and shMCL-1 by Folic Acid-Modified Nonviral Vector to Overcome Cancer Chemotherapy Resistance

Acquired chemoresistance presents a major clinical impediment, which is an urgent problem to be solved. Interestingly, myeloma cell leukemia-1 (MCL-1) and folate receptor expression levels are higher in chemotherapy-resistant patients than in pretreatment patients. In this study, a multifunctional folic acid (FA)-targeting core-shell structure is presented for simultaneous delivery of shMCL-1 and paclitaxel (PTX). The transfection efficiency of shMCL-1 with the FA-targeting delivery system is higher than with a nontargeting delivery system in Skov3 and A2780T cells. The FA-targeting system significantly inhibits cell growth, blocks cell cycles, and promotes apoptosis of cancer cells in vitro. The mechanisms involved in inhibiting growth are related to Bcl-2/Bax and cdc2/Cyclin B1 pathways. An analysis of RNA sequencing suggests that shMCL-1 reverses chemoresistance through regulating genes such as regulator of chromosome condensation 2 (RCC2). The synergetic effect of shMCL-1 and PTX effectively inhibits tumor growth in both PTX-resistant and normal cancer models by inducing tumor apoptosis, inhibiting proliferation, and limiting tumor angiogenesis. The study results indicate that a FA-targeting delivery system combining shMCL-1 with PTX can simultaneously target tumor sites and restore the sensitivity of chemotherapy-resistant cancer to PTX. These findings have important implications for patients with normal or PTX-resistant cancer.

Synthesis and biological studies of new piperidino-1,2,3-triazole hybrids with 3-aryl isoxazole side chains

A small library of new piperidine-triazole hybrids with 3-aryl isoxazole side chains has been designed and synthesized. Their cytotoxicity against a panel of seven cancer cell lines has been established. For the most promising compound, an IC₅₀ value of 3.8 μM on PUMA/Bcl-xL interaction in live cancer cells was established through BRET analysis. A rationale was proposed for these results through complete molecular modelling studies.

Kidney cancer biomarkers and targets for therapeutics: survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, p53, KRAS and AKT in renal cell carcinoma

The incidence of renal cell carcinoma (RCC) is increasing worldwide with an approximate 20% mortality rate. The challenge in RCC is the therapy-resistance. Cancer resistance to treatment employs multiple mechanisms due to cancer heterogeneity with multiple genetic and epigenetic alterations. These changes include aberrant overexpression of (1) anticancer cell death proteins (e.g., survivin/BIRC5), (2) DNA repair regulators (e.g., ERCC6) and (3) efflux pump proteins (e.g., ABCG2/BCRP); mutations and/or deregulation of key (4) oncogenes (e.g., MDM2, KRAS) and/or (5) tumor suppressor genes (e.g., TP5/p53); and (6) deregulation of redox-sensitive regulators (e.g., HIF, NRF2). Foci of tumor cells that have these genetic alterations and/or deregulation possess survival advantages and are selected for survival during treatment. We will review the significance of survivin (BIRC5), XIAP, MCL-1, HIF1α, HIF2α, NRF2, MDM2, MDM4, TP5/p53, KRAS and AKT in treatment resistance as the potential therapeutic biomarkers and/or targets in RCC in parallel with our analized RCC-relevant TCGA genetic results from each of these gene/protein molecules. We then present our data to show the anticancer drug FL118 modulation of these protein targets and RCC cell/tumor growth. Finally, we include additional data to show a promising FL118 analogue (FL496) for treating the specialized type 2 papillary RCC.

Role of 1q21 in Multiple Myeloma: From Pathogenesis to Possible Therapeutic Targets

Multiple myeloma (MM) is characterized by an accumulation of malignant plasma cells (PCs) in the bone marrow (BM). The amplification of 1q21 is one of the most common cytogenetic abnormalities occurring in around 40% of de novo patients and 70% of relapsed/refractory MM. Patients with this unfavorable cytogenetic abnormality are considered to be high risk with a poor response to standard therapies. The gene(s) driving amplification of the 1q21 amplicon has not been fully studied. A number of clear candidates are under investigation, and some of them (IL6R, ILF2, MCL-1, CKS1B and BCL9) have been recently proposed to be potential drivers of this region. However, much remains to be learned about the biology of the genes driving the disease progression in MM patients with 1q21 amp. Understanding the mechanisms of these genes is important for the development of effective targeted therapeutic approaches to treat these patients for whom effective therapies are currently lacking. In this paper, we review the current knowledge about the pathological features, the mechanism of 1q21 amplification, and the signal pathway of the most relevant candidate genes that have been suggested as possible therapeutic targets for the 1q21 amplicon.

Berberine Exerts Anti-cancer Activity by Modulating Adenosine Monophosphate- Activated Protein Kinase (AMPK) and the Phosphatidylinositol 3-Kinase/ Protein Kinase B (PI3K/AKT) Signaling Pathways

Background

The antagonistic relationship between adenosine monophosphate-activated protein kinase (AMPK) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling play a vital role in cancer development. The anti-cancer effects of berberine have been reported as a main component of the traditional Chinese medicine Rhizoma coptidis, although the roles of these signaling pathways in these effects have not been systematically reviewed.

METHODS

We searched the PubMed database for studies with keywords including ["berberine"] and ["tumor" or "cancer"] and ["AMPK"] or ["AKT"] published between January 2010 and July 2020, to elucidate the roles of the AMPK and PI3K/AKT pathways and their upstream and downstream targets in the anti-cancer effects of berberine.

RESULTS

The anti-cancer effects of berberine include inhibition of cancer cell proliferation, promotion of apoptosis and autophagy in cancer cells, and prevention of metastasis and angiogenesis. The mechanism of these effects involves multiple cell kinases and signaling pathways, including activation of AMPK and forkhead box transcription factor O3a (FOXO3a), accumulation of reactive oxygen species (ROS), and inhibition of the activity of PI3K/AKT, rapamycin (mTOR) and nuclear factor-κB (NF-κB). Most of these mechanisms converge on regulation of the balance of AMPK and PI3K/AKT signaling by berberine.

CONCLUSION

This evidence supports the possibility that berberine is a promising anti-cancer natural product, with pharmaceutical potential in inhibiting cancer growth, metastasis and angiogenesis via multiple pathways, particularly by regulating the balance of AMPK and PI3K/AKT signaling. However, systematic preclinical studies are still required to provide scientific evidence for further clinical studies.

Overexpression of KDM4D promotes acute myeloid leukemia cell development by activating MCL-1

Acute myeloid leukemia (AML) is regarded as a fatal cancer in the world. The overall survival in adult patients with AML is still poor. As lysine demethylases, the KDM4 family is found highly expressed in many kinds of tumors. In this study, we demonstrate that KDM4D is overexpressed in AML and knockdown of KDM4D not only inhibits the proliferation of AML cells, but also induces cell cycle arrest and apoptosis. Furthermore, our research shows that KDM4D can regulate the expression of MCL-1 by demethylating H3K9me3 at the promoter region in AML cells. Besides, we find that high expression of KDM4D is correlated with poor overall survival in AML patients. Taken together, our study demonstrated that KDM4D can promote MCL-1 expression in AML and may serve as a novel target for the treatment of AML.

Synergistic Effect of Doxorubicin and siRNA-Mediated Silencing of Mcl-1 Using Cationic Niosomes against 3D MCF-7 Spheroids

Chemotherapy is a vital option for cancer treatment; however, its therapeutic outcomes are limited by dose-dependent toxicity and the occurrence of chemoresistance. siRNAs have emerged as an attractive therapeutic option enabling specific interference with target genes. Combination therapy using chemotherapeutic agents along with gene therapy could be a potential strategy for cancer management, which not only improves therapeutic efficacy but also decreases untoward effects from dose reduction. In this study, a cationic niosome containing plier-like cationic lipid B was used to convey siRNA against anti-apoptotic mRNA into MCF-7 and MDA-MB-231 cells. Mcl-1 silencing markedly decreased the viability of MCF-7 cells and triggered apoptosis. Moreover, computer modeling suggested that the combination of doxorubicin (Dox) and Mcl-1 siRNA exhibited a synergistic relationship and enabled a dose reduction of each agent at 1.71 and 3.91 folds, respectively, to reach a 90% inhibitory effect when compared to single-agent treatments. Synergistic antitumor activity was further verified in a 3D spheroid culture which revealed, in contrast to single-agent treatment, the combination markedly decreased spheroid volume over time. Together, the combination therapy between Mcl-1 silencing and Dox exhibits a synergistic effect that may be exploited for novel breast cancer treatment.

Myeloid cell leukemia-1 is an important predictor of survival and progression of small cell lung cancer

Background

Small cell lung cancer (SCLC) is the most fatal malignancy for which more effective therapies are urgently needed. Overexpression of myeloid cell leukemia-1 (Mcl-1) has been demonstrated to be one of the most common genetic alterations among different types of tumor/cancer, which induces resistance against various anti-cancer therapies including cisplatin. The study aimed to explore the role of Mcl-1 in the prognosis and resistance to anti-cancer therapy in patients with SCLC.

Methods

Patients with SCLC were recruited from those enrolled/treated in Sun Yat-sen University Cancer Center. Their specimens were collected for immunohistochemical evaluation. We compared the baseline characteristics, response to chemotherapy and overall survival (OS) of the patients with different expression levels of Mcl-1.

Results

The expression level of Mcl-1 was significantly lower in patients with limited stage SCLC than in those with extensive stage SCLC (P=0.014). Based on the median value of Mcl-1 expression level, the patients were divided into high and low Mcl-1 groups, respectively. Univariate analysis revealed that low Mcl-1 expression was associated with a significant improvement in OS, with a hazard ratio (HR) of 0.538. Multivariate analysis confirmed the independent prognostic value of Mcl-1 expression level (P=0.014). Moreover, we found a significantly close relationship between higher Mcl-1 expression level and shorter time to progression (TTP) of the patients received chemotherapy (P=0.040).

Conclusions

Our findings demonstrated that Mcl-1 expression level was a prognostic biomarker for survival outcomes and cancer progression in the patients with SCLC. Thus, it could be used as a valuable biomarker in identifying those patients with high risk of treatment failure.

Recent Advances in the Development of Selective Mcl-1 Inhibitors for the Treatment of Cancer (2017-Present)

Background:

Myeloid cell leukemia-1 (Mcl-1) protein, as a critical pro-survival member of the B-cell lymphoma 2 (Bcl-2) protein family, plays an important role in apoptosis, carcinogenesis and resistance to chemotherapies. Hence, potently and selectively inhibiting Mcl-1 to induce apoptosis has become a widely accepted anticancer strategy.

Objective:

This review intends to provide a comprehensive overview of patents and primary literature, published from 2017 to present, on small molecule Mcl-1 inhibitors with various scaffolds. By analyzing the modes of compound-protein interactions, the similarities and differences of those structures are discussed, which could provide guidance for future drug design.

Methods:

The primary accesses for patent searching are SciFinder and Espacenet®. Besides the data disclosed in patents, some results published in the follow-up research papers will be included in this review.

Results:

The review covers dozens of patents on Mcl-1 inhibitors in the past three years, and the scaffolds of compounds are mainly divided into indole scaffolds and non-indole scaffolds. The compounds described here are compared with the relevant inhibitors disclosed in previous patents, and representative compounds, especially those launched in clinical trials, are emphasized in this review.

Conclusion:

For most of the compounds in these patents, analyses of the binding affinity to Mcl-1 and studies in multiple cell lines were conducted, wherein some compounds were tested in preclinical cancer models or were included in other biological studies. Some compounds showed promising results and potential for further study.

Using NMR Spectroscopy in the Fragment-Based Drug Discovery of Small-Molecule Anticancer Targeted Therapies

Against the challenge of providing personalized cancer care, the development of targeted therapies stands as a promising approach. The discovery of these agents can benefit from fragment-based drug discovery (FBDD) methods that help guide ligand design and provide key structural information on the targets of interest. In particular, nuclear magnetic resonance spectroscopy is a promising biophysical tool in fragment discovery due to its detection capabilities and versatility. This review provides an overview of FBDD, describes the basis of NMR-based fragment screening, summarizes some exciting technical advances reported over the past decades, and closes with a discussion of selected case studies where this technique has been used as part of drug discovery campaigns to produce lead compounds towards the design of anti-cancer targeted therapies.

Development of Mcl-1 inhibitors for cancer therapy

The myeloid leukemia cell differentiation protein (Mcl-1) is an anti-apoptotic protein of the B-cell lymphoma 2 (Bcl-2) family, which regulates cellular apoptosis. Mcl-1 expression plays a key role in survival of cancer cells and therefore serves as a promising target in cancer therapy. Besides, its importance as a cancer target, various peptides and small-molecule inhibitors have been successfully designed and synthesized, yet no Mcl-1 inhibitor is approved for clinical use. However, recent development on the understanding of Mcl-1's role in key cellular processes in cancer and an upsurge of reports highlighting its association in various anticancer drug resistance supports the view that Mcl-1 is a key target in various cancers, especially hematological cancers. This review compiles structures of a variety of inhibitors of Mcl-1 reported to date. These include inhibitors based on a diverse range of heterocycles (e.g. indole, imidazole, thiophene, nicotinic acid, piperazine, triazine, thiazole, isoindoline), oligomers (terphenyl, quaterpyridine), polyphenol, phenalene, anthranilic acid, anthraquinone, macrocycles, natural products, and metal-based complexes. In addition, an effort has been made to summarize the structure activity relationships, based on a variety of assays, of some important classes of Mcl-1 inhibitors, giving affinities and selectivities for Mcl-1 compared to other Bcl-2 family members. A focus has been placed on categorizing the inhibitors based on their core frameworks (scaffolds) to appeal to the chemical biologist or medicinal chemist.

Targeting MCL-1 in hematologic malignancies: Rationale and progress

Myeloid cell leukemia sequence 1 (MCL-1) is an antiapoptotic protein that plays a key role in promoting cell survival in multiple myeloma (MM), acute myeloid leukemia (AML), and non-Hodgkin lymphoma (NHL). Overexpression of MCL-1 is associated with treatment resistance and poor prognosis; thus, MCL-1 inhibitors are rational therapeutic options for malignancies depending on MCL-1. Several MCL-1 inhibitors have entered clinical trials, including AZD5991, S64315, AMG 176, and AMG 397. A key area of investigation is whether MCL-1 inhibitors will complement the activity of BCL-2 inhibitors, such as venetoclax, and synergistically enhance anti-tumor efficacy when given in combination with other anti-cancer drugs. Another important question is whether a safe therapeutic window can be found for this new class of inhibitors. In summary, inhibition of MCL-1 shows potential as a treatment for hematologic malignancies and clinical evaluation of MCL-1 inhibitors is currently underway.

Lycorine hydrochloride inhibits cell proliferation and induces apoptosis through promoting FBXW7-MCL1 axis in gastric cancer

Background

Lycorine hydrochloride (LH), an alkaloid extracted from the bulb of the Lycoris radiata, is considered to have anti-viral, anti-malarial, and anti-tumorous effects. At present, the underlying mechanisms of LH in gastric cancer remain unclear. MCL1, an anti-apoptotic protein of BCL2 family, is closely related to drug resistance of tumor. Therefore, MCL1 is considered as a potential target for cancer treatment.

Methods

The effect of LH on gastric cancer was assessed in vitro (by MTT, BrdU, western blotting…) and in vivo (by immunohistochemistry).

Results

In this study, we showed that LH has an anti-tumorous effect by down-regulating MCL1 in gastric cancer. Besides, we unveiled that LH reduced the protein stability of MCL1 by up-regulating ubiquitin E3 ligase FBXW7, arrested cell cycle at S phase and triggered apoptosis of gastric cancer cells. Meanwhile, we also demonstrated that LH could induce apoptosis of the BCL2-drug-resistant-cell-lines. Moreover, PDX (Patient-Derived tumor xenograft) model experiment proved that LH combined with HA14–1 (inhibitor of BCL2), had a more significant therapeutic effect on gastric cancer.

Conclusions

The efficacy showed in our data suggests that lycorine hydrochloride is a promising anti-tumor compound for gastric cancer.

MUC1 Aptamer-Capped Mesoporous Silica Nanoparticles for Navitoclax Resistance Overcoming in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. In the last years, navitoclax has emerged as a possible treatment for TNBC. Nevertheless, rapid navitoclax resistance onset has been observed thorough Mcl-1 overexpression. As a strategy to overcome Mcl-1-mediated resistance, herein we present a controlled drug co-delivery system based on mesoporous silica nanoparticles (MSNs) targeted to TNBC cells. The nanocarrier is loaded with navitoclax and the Mcl-1 inhibitor S63845 and capped with a MUC1-targeting aptamer (apMUC1-MSNs(Nav/S63845)). The apMUC1-capped nanoparticles effectively target TNBC cell lines and successfully induce apoptosis, overcoming navitoclax resistance. Moreover, navitoclax encapsulation protects platelets against apoptosis. These results point apMUC1-gated MSNs as suitable BH3 mimetics nanocarriers in the targeted treatment of MUC1-expressing TNBC.

Resistance Mechanisms to Targeted Agents in Chronic Lymphocytic Leukemia

Agents that specifically target pathologic mechanisms of survival have now been approved for the treatment of chronic lymphocytic leukemia in both the treatment-naive and relapsed/refractory settings. These 4 agents include the Bruton tyrosine kinase inhibitor ibrutinib, the B-cell leukemia/lymphoma-2 inhibitor venetoclax, and the phosphatidylinositol-3 kinase inhibitors idelalisib and duvelisib. Although clinical outcomes are improved with all of these inhibitors, acquired resistance does occur and leads to progression of disease. Resistance to targeted therapy can occur through direct mutations of the target or through the overexpression of alternative cell survival pathways not affected by the specific inhibitor. Determining which patients will develop resistance, why resistance occurs, how to overcome resistance, and when to test for resistance are all subjects of ongoing research. In this review, we describe the current data relative to the development of resistance to targeted therapies in CLL.

Ruthenium Dendrimers against Human Lymphoblastic Leukemia 1301 Cells

Ruthenium atoms located in the surfaces of carbosilane dendrimers markedly increase their anti-tumor properties. Carbosilane dendrimers have been widely studied as carriers of drugs and genes owing to such characteristic features as monodispersity, stability, and multivalence. The presence of ruthenium in the dendrimer structure enhances their successful use in anti-cancer therapy. In this paper, the activity of dendrimers of generation 1 and 2 against 1301 cells was evaluated using Transmission Electron Microscopy, comet assay and Real Time PCR techniques. Additionally, the level of reactive oxygen species (ROS) and changes of mitochondrial potential values were assessed. The results of the present study show that ruthenium dendrimers significantly decrease the viability of leukemia cells (1301) but show low toxicity to non-cancer cells (peripheral blood mononuclear cells-PBMCs). The in vitro test results indicate that the dendrimers injure the 1301 leukemia cells via the apoptosis pathway.

Harnessing big 'omics' data and AI for drug discovery in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of primary adult liver cancer. After nearly a decade with sorafenib as the only approved treatment, multiple new agents have demonstrated efficacy in clinical trials, including the targeted therapies regorafenib, lenvatinib and cabozantinib, the anti-angiogenic antibody ramucirumab, and the immune checkpoint inhibitors nivolumab and pembrolizumab. Although these agents offer new promise to patients with HCC, the optimal choice and sequence of therapies remains unknown and without established biomarkers, and many patients do not respond to treatment. The advances and the decreasing costs of molecular measurement technologies enable profiling of HCC molecular features (such as genome, transcriptome, proteome and metabolome) at different levels, including bulk tissues, animal models and single cells. The release of such data sets to the public enhances the ability to search for information from these legacy studies and provides the opportunity to leverage them to understand HCC mechanisms, rationally develop new therapeutics and identify candidate biomarkers of treatment response. Here, we provide a comprehensive review of public data sets related to HCC and discuss how emerging artificial intelligence methods can be applied to identify new targets and drugs as well as to guide therapeutic choices for improved HCC treatment.

Mechanisms of malignancy in glioblastoma cells are linked to mitochondrial Ca2 + uniporter upregulation and higher intracellular Ca2+ levels

Glioblastoma (GBM) is one of the most malignant brain tumours and, despite advances in treatment modalities, it remains largely incurable. Ca²⁺ regulation and dynamics play crucial roles in different aspects of cancer, but they have never been investigated in detail in GBM. Here, we report that spontaneous Ca²⁺ waves in GBM cells cause unusual intracellular Ca²⁺ ([Ca²⁺]_i) elevations (>1 μM), often propagating through tumour microtubes (TMs) connecting adjacent cells. This unusual [Ca²⁺]_i elevation is not associated with the induction of cell death and is concomitant with overexpression of mitochondrial Ca²⁺ uniporter (MCU). We show that MCU silencing decreases proliferation and alters [Ca²⁺]_i dynamics in U87 GBM cells, while MCU overexpression increases [Ca²⁺]_i elevation in human astrocytes (HAs). These results suggest that changes in the expression level of MCU, a protein involved in intracellular Ca²⁺ regulation, influences GBM cell proliferation, contributing to GBM malignancy.This article has an associated First Person interview with the first author of the paper.

Cancer cell‑specific anticancer effects of Coptis chinensis on gefitinib‑resistant lung cancer cells are mediated through the suppression of Mcl‑1 and Bcl‑2

The epidermal growth factor receptor (EGFR)‑tyrosine kinase inhibitor (TKI), gefitinib, is an effective therapeutic drug used in the treatment of non‑small cell lung cancers (NSCLCs) harboring EGFR mutations. However, acquired resistance significantly limits the efficacy of EGFR‑TKIs and consequently, the current chemotherapeutic strategies for NSCLCs. It is, therefore, necessary to overcome this resistance. In the present study, the anticancer potential of natural extracts of Coptis chinensis (ECC) against gefitinib‑resistant (GR) NSCLC cells were investigated in vitro and in vivo. ECC inhibited the viability, migration and invasion, and effectively induced the apoptosis of GR cells. These effects were associated with the suppression of EGFR/AKT signaling and the expression of anti‑apoptotic proteins, Mcl‑1 and Bcl‑2, which were overexpressed in GR NSCLC cells. Combination treatment with ECC and gefitinib enhanced the sensitivity of GR cells to gefitinib in vitro, but not in vivo. However, ECC increased the survival of individual zebrafish without affecting the anticancer effect to cancer cells in vivo, which indicated a specific cytotoxic effect of ECC on cancer cells, but not on normal cells; this is an important property for the development of novel anticancer drugs. On the whole, the findings of the present study indicate the potential of ECC for use in the treatment of NSCLC, particularly in combination with EGFR‑TKI therapy, in EGFR‑TKI‑resistant cancers.

Discovery and Characterization of 2,5-Substituted Benzoic Acid Dual Inhibitors of the Anti-apoptotic Mcl-1 and Bfl-1 Proteins

Anti-apoptotic Bcl-2 family proteins are overexpressed in a wide spectrum of cancers and have become well validated therapeutic targets. Cancer cells display survival dependence on individual or subsets of anti-apoptotic proteins that could be effectively targeted by multimodal inhibitors. We designed a 2,5-substituted benzoic acid scaffold that displayed equipotent binding to Mcl-1 and Bfl-1. Structure-based design was guided by several solved cocrystal structures with Mcl-1, leading to the development of compound 24, which binds both Mcl-1 and Bfl-1 with K_i values of 100 nM and shows appreciable selectivity over Bcl-2/Bcl-xL. The selective binding profile of 24 was translated to on-target cellular activity in model lymphoma cell lines. These studies lay a foundation for developing more advanced dual Mcl-1/Bfl-1 inhibitors that have potential to provide greater single agent efficacy and broader coverage to combat resistance in several types of cancer than selective Mcl-1 inhibitors alone.

The Application of Arsenic Trioxide in Ameliorating ABT-737 Target Therapy on Uterine Cervical Cancer Cells through Unique Pathways in Cell Death

ABT-737, a B cell lymphoma-2 (Bcl-2) family inhibitor, activates apoptosis in cancer cells. Arsenic trioxide is an apoptosis activator that impairs cancer cell survival. The aim of this study was to evaluate the effect of a combination treatment with ABT-737 and arsenic trioxide on uterine cervical cancer cells. MTT (3-(4,5-dimethylthiazol-2-yl)-25-diphenyltetrazolium bromide) assay revealed that ABT-737 and arsenic trioxide induced a synergistic effect on uterine cervical cancer cells. Arsenic trioxide enhanced ABT-737-induced apoptosis and caspase-7 activation and the ABT-737-mediated reduction of anti-apoptotic protein Mcl-1 in Caski cells. Western blot assay revealed that arsenic trioxide promoted the ABT-737-mediated reduction of CDK6 and thymidylate synthetase in Caski cells. Arsenic trioxide promoted ABT-737-inhibited mitochondrial membrane potential and ABT-737-inhibited ANT expression in Caski cells. However, ABT-737-elicited reactive oxygen species were not enhanced by arsenic trioxide. The combined treatment induced an anti-apoptosis autophagy in SiHa cells. This study is the first to demonstrate that a combination treatment with ABT-737 and arsenic trioxide induces a synergistic effect on uterine cervical cancer cells through apoptosis. Our findings provide new insights into uterine cervical cancer treatment.

Antitumor effect of TW-37, a BH3 mimetic in human oral cancer

TW-37 is a small molecule B cell lymphoma-2 (Bcl-2) homology 3 mimetic with potential anticancer activities. However, the in vivo anti-cancer effect of TW-37 in human oral cancer has not been properly studied yet. Here, we attempted to confirm antitumor activity of TW37 in human oral cancer. TW-37 significantly inhibited cell proliferation and increased the number of dead cells in MC-3 and HSC-3 human oral cancer cell lines. TW-37 enhanced apoptosis of both cell lines evidenced by annexin V/propidium iodide double staining, sub-G₁ population analysis and the detection of cleaved poly (ADP-ribose) polymerase and caspase-3. In addition, TW-37 markedly downregulated the expression of Bcl-2 protein, while not affecting Bcl-xL or myeloid cell leukemia-1. In vivo, TW-37 inhibited tumor growth in a nude mice xenograft model without any significant liver and kidney toxicities. Collectively, these data reveal that TW-37 may be a promising small molecule to inhibit human oral cancer.

Impact of BMI1 expression on the apoptotic effect of paclitaxel in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers worldwide. Despite advances in treatment, no treatment modality specific for the different CRC phenotypes has been developed. BMI1 has been previously reported to play an important role in the regulation of cancer stem cells and cell cycle in CRC. However, the role of BMI1 in individualized treatment for CRC is largely unknown. In this study, we found that the apoptotic effect of paclitaxel is more profound in BMI1-depleted cells. The apoptotic effect is exerted by promoting caspase-8-independent apoptotic pathways after combination with paclitaxel in BMI1 knockdown cells. This effect could be totally recovered by pretreatment with caspase inhibitor compared with caspase-8 inhibitor alone. It has been reported that the levels of MCL-1 play a role in regulating cell resistance to paclitaxel treatment. Our data indicated that the downregulation of MCL-1 through the activation of GSK3beta and JNK is driven by BMI1 depletion. Consistent with in vitro data, a synergic anti-growth effect of BMI1 depletion with paclitaxel treatment was shown in vivo. In conclusion, paclitaxel has a stronger suppressive effect on tumor growth and proliferation in CRC with low BMI1 expression. Thus, in CRC patients, paclitaxel could be specifically indicated for patients with low BMI1 expression.

Binding mode of Pyridoclax to myeloid cell leukemia-1 (Mcl-1) revealed by nuclear magnetic resonance spectroscopy, docking and molecular dynamics approaches

Myeloid cell leukemia-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family proteins. Its amplification is one of the most frequent genetic aberrations found in human cancers. Pyridoclax, a promising BH3 mimetic inhibitor, interacts directly with Mcl-1 and induces massive apoptosis at a concentration of 15 µM in combination with anti-Bcl-x_L strategies in chemo-resistant ovarian cancer cell lines. In this study, a combined experimental and theoretical approach was used to investigate the binding mode of Pyridoclax to Mcl-1. The representative poses generated from dynamics simulations compared with NMR data revealed: (i) Pyridoclax bound to P1 and P2 pockets of Mcl-1 BH3 binding groove through its styryl and methyl groups establishing mainly hydrophobic contacts, (ii) one of the ending pyridines interacts through electrostatic interaction with K234 side chain, a negatively charged residue present only in this position in Mcl-1. Communicated by Ramaswamy H. Sarma.

H1, a derivative of tetrandrine, enhances the efficacy of 5-FU in Bel7402/5-FU cells via suppressing STAT3/MCL-1 and inducing PUMA

Currently, 5-fluorouracil (5-FU) resistance became a major obstacle to its clinical use for patients with hepatocellular carcinoma (HCC). It's urgent to develop a novel strategy for enhancing the therapeutic efficacy of 5-FU. Herein, we found that H1 (a derivative of Tetrandrine) exerted a potent anti-MDR effect on growth of 5-FU resistant HCC cells (Bel7402/5FU). The resistant fold (RF) of 5-FU is over 160-fold, while the RF of H1 is only 4.8-fold in Bel7402/5-FU cells. Further studies demonstrated that blockage of STAT3/MCL-1 signaling and induction of PUMA is responsible to anti-MDR activity of H1. Moreover, combination of H1 and 5-FU (Ratio = 1:2) could synergistically induce apoptosis of Bel7402/5-FU cells. Co-treatment of H1 enhances the suppression of p-STAT3 and MCL-1, and significantly increases PUMA expression. Finally, the combination of H1 and 5-FU results in an increase of cleaved PARP. Taken together, H1 effectively improve the cytotoxic effect of 5-FU against Bel7402/5-FU cells via blocking STAT3/MCL-1 pathway and inducing PUMA. Our findings suggested that combination 5-FU with anti-MDR agents might present a novel strategy to enhance the therapeutic efficacy of 5-FU in resistant HCC.

Targeting cancer's Achilles’ heel: role of BCL-2 inhibitors in cellular senescence and apoptosis

Members of the antiapoptotic BCL-2 proteins are involved in tumor growth, progression and survival, and are also responsible for chemoresistance to conventional anticancer agents. Early efforts to target these proteins yielded some active compounds; however, newer methodologies involving structure-based drug design, Nuclear Magnetic Resonance (NMR)-based screening and fragment-based screening yielded more potent compounds. Discovery of specific as well as nonspecific inhibitors of this class of proteins has resulted in great advances in targeted chemotherapy and decrease in chemoresistance. Here, we review the history and current progress in direct as well as selective targeting of the BCL-2 proteins for anticancer therapy.

Caspase cleavage of Mcl-1 impairs its anti-apoptotic activity and proteasomal degradation in non-small lung cancer cells

Global cleavage of cellular proteins by activated caspases is a hallmark of apoptosis, which causes biochemical collapse of the cell. Recent studies suggest that, rather than completely destroying a protein, caspase cleavage can confer novel characteristics or functions. In this respect, the post-caspase role of Bcl-2 family proteins remains uncharacterized. Here, we showed that Mcl-1, a pro-survival member of the Bcl-2 family, was cleaved by caspase-3 in non-small cell lung cancer (NSCLC) cells undergoing chemotherapeutic agent-triggered apoptosis. Caspase cleavage partially impaired the anti-apoptotic activity of Mcl-1 by reducing its mitochondrial localization and impeding its association with the permeability transition pore-forming protein Bak. However, the stability of cleaved Mcl-1 was markedly enhanced because it was more refractory to ubiquitination-dependent proteasomal degradation, thereby improving cell viability to a greater extent than full-length Mcl-1 when transiently expressed in NSCLC cells. These findings shed new light on the role of Mcl-1 in apoptosis and suggest potential novel targets for optimizing the tumoricidal capacity of chemotherapy.

The chemical biology of apoptosis: Revisited after 17 years

A balance of Bcl-2 family proteins dictates cell survival or death, as the interactions between these proteins regulate mitochondrial apoptotic signaling pathways. However, cancer cells frequently show upregulation of pro-survival Bcl-2 proteins and sequester activated pro-apoptotic BH3-only proteins driven by diverse cytotoxic stresses, resulting in tumor progression and chemoresistance. Synthetic molecules from either structure-based design or screening procedures to engage and inactivate pro-survival Bcl-2 proteins and restore apoptotic process represent a chemical biological means of selectively killing malignant cells. 17 years ago, one of us reviewed on the discovery of novel Bcl-2 targeted agents [1]. Here we revisit this area and examine the progress and current status of small molecule Bcl-2 inhibitor development, demonstrating the Bcl-2 family as a valid target for cancer therapy and providing successful examples for the discovery of inhibitors that target protein-protein interactions.