Mcl-1 and Bcl-xL cooperatively maintain integrity of hepatocytes in developing and adult murine liver

BH3 mimetics targeting BCL-XL have efficacy in solid tumors with RB1 loss and replication stress

BH3 mimetic drugs that inhibit BCL-2, BCL-XL, or MCL-1 have limited activity in solid tumors. Through assessment of xenograft-derived 3D prostate cancer models and cell lines we find that tumors with RB1 loss are sensitive to BCL-XL inhibition. In parallel, drug screening demonstrates that disruption of nucleotide pools by agents including thymidylate synthase inhibitors sensitizes to BCL-XL inhibition, together indicating that replication stress increases dependence on BCL-XL. Mechanistically we establish that replication stress sensitizes to BCL-XL inhibition through TP53/CDKN1A-dependent suppression of BIRC5 expression. Therapy with a BCL-2/BCL-XL inhibitor (navitoclax) in combination with thymidylate synthase inhibitors (raltitrexed or capecitabine) causes marked and prolonged tumor regression in prostate and breast cancer xenograft models. These findings indicate that BCL-XL inhibitors may be effective as single agents in a subset of solid tumors with RB1 loss, and that pharmacological induction of replication stress may be a broadly applicable approach for sensitizing to BCL-XL inhibitors.

Mechanisms of drug resistance in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent form of primary liver cancer, associated with high morbidity and mortality worldwide. Despite advancements in diagnostic methods and systemic treatments, including tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (ICIs), the development of drug resistance remains a significant challenge in HCC management. Traditional treatments such as surgical resection and transarterial chemoembolization offer limited efficacy, especially in advanced stages. Although novel therapies like lenvatinib, sorafenib, regorafenib, and ICIs have shown promise, their effectiveness is often hindered by primary and acquired resistance, leading to poor long-term survival outcomes. This review focuses on the molecular mechanisms underlying resistance to targeted therapies and immunotherapies in HCC. Key factors contributing to resistance include alterations in the tumor microenvironment (TME), immune evasion, hypoxia, changes in cellular metabolism, and genetic mutations. Additionally, molecular players such as ferroptosis, autophagy, apoptosis, endoplasmic reticulum stress, ABC transporters, and non-coding RNAs(ncRNAs) are discussed as contributors to drug resistance. Understanding these mechanisms is critical for the development of novel therapeutic strategies aimed at overcoming resistance, improving patient outcomes, and ultimately enhancing survival rates in HCC patients.

USP13 inhibition exacerbates mitochondrial dysfunction and acute kidney injury by acting on MCL-1

Acute kidney injury (AKI) is a globally recognized public health issue that lacks satisfactory therapeutic strategies. Deubiquitinase ubiquitin-specific protease 13 (USP13) regulates various pathophysiological processes via the deubiquitination of multiple substrates. However, its role in AKI remains unclear. To illustrate the role and underlying mechanism of USP13 in AKI, we subjected Usp13 knockdown mice, and mice treated with the USP13 inhibitor spautin-1, and mice with USP13 overexpression plasmids to cisplatin challenge. Renal tubular epithelial cell injury and mitochondrial disturbances were determined in vitro. Immunoprecipitation and deubiquitylation assays were performed to verify the interactions between USP13 and myeloid cell leukemia (MCL-1). We observed a significant decrease of USP13 expression in cisplatin-challenged AKI mice and renal tubular epithelial cells. Overexpression of USP13 alleviated kidney injury, whereas knockdown or inhibition of USP13 further exacerbated AKI. Mechanistically, USP13 downregulation resulted in increased degradation of MCL-1 which is a key regulator of cell survival and mitochondrial function, and the resultant MCL-1 reduction disrupted mitochondrial homeostasis and aggravated renal tubular epithelial cell injury and death, contributing to AKI progression. In conclusion, our findings demonstrated that inhibition of USP13 could exacerbate mitochondrial dysfunction and AKI through its effects on MCL-1, and USP13 may serve as a target for AKI prevention and treatment.

Collaborative orchestration of BH3-only proteins governs Bak/Bax-dependent hepatocyte apoptosis under antiapoptotic protein-deficiency in mice

The fine-tuned balance between anti-apoptotic Bcl-2 family proteins, such as Bcl-xL and Mcl-1, and pro-apoptotic Bcl-2 family proteins, like Bak and Bax, is crucial for maintaining hepatocyte integrity. BH3-only proteins, including Bid, Bim, Puma, Noxa, Bad, Bmf, Bik and Hrk, serve as apoptosis initiators. They are activated by various stimuli, which leads to Bak/Bax activation. We previously reported that Bid and Bim contributed to hepatocyte apoptosis through Bak/Bax activation in the absence of anti-apoptotic proteins Bcl-xL and/or Mcl-1. However, the comprehensive involvement of all eight BH3-only proteins in Bak/Bax-dependent hepatocyte apoptosis remains unclear. Puma disruption suppressed hepatocyte apoptosis in hepatocyte-specific Bcl-xL or Mcl-1 knockout (Bcl-xLΔHep/ΔHep or Mcl-1ΔHep/ΔHep) mice. Disruption of Bid and Bim partially prevented lethality in Mcl-1ΔHep/+ Bcl-xLΔHep/ΔHep mice, although severe hepatocyte apoptosis persisted, which was suppressed by additional Puma disruption. However, hepatocyte apoptosis was still induced compared to that in Mcl-1ΔHep/+ Bcl-xLΔHep/ΔHep BaxΔHep/ΔHep Bak-/- mice. Triple disruption of Bid, Bim and Puma did not prevent induction of hepatocyte apoptosis in tamoxifen-induced Mcl-1iΔHep/iΔHep Bcl-xLiΔHep/iΔHep mice. Primary hepatocytes, isolated from Mcl-1fl/fl Bcl-xLfl/fl Bid-/- Bim-/- Puma-/- mice and immortalized, underwent apoptosis with doxycycline-dependent Cre recombination. Among the remaining five BH3-only proteins, Bik and Hrk were not expressed in these cells, and Noxa knockdown, but not Bad or Bmf knockdown, reduced apoptosis. Noxa disruption alleviated hepatocyte apoptosis in Mcl-1ΔHep/ΔHep mice and tamoxifen-induced Mcl-1iΔHep/iΔHep Bcl-xLiΔHep/iΔHep Bid-/- Bim-/- Puma-/- mice, prolonging survival. Apoptosis persisted in immortalized primary hepatocytes isolated from Mcl-1fl/fl Bcl-xLfl/fl Bid-/- Bim-/- Puma-/- Noxa-/- mice where doxycycline-dependent Cre recombination was induced, but was completely suppressed by Bak/Bax knockdown, while Bad or Bmf knockdown had no effect. In conclusion, among the eight BH3-only proteins, Puma and Noxa, alongside Bid and Bim, contributed to Bak/Bax-dependent hepatocyte apoptosis, but not indispensably, in the absence of Mcl-1 and Bcl-xL.

Short-Term Fasting Induces Hepatocytes' Stress Response and Increases Their Resilience

Fasting leads to a range of metabolic adaptations that have developed through evolution, as humans and other mammals have unequal access to food over the circadian cycle and are therefore adapted to fasting and feeding cycles. We have investigated the role of a single fasting episode in rats in triggering the stress response of liver hepatocytes. Since the stress responses were observed in both animals and isolated cells, we investigated whether the effects of the animal stressor could persist in the cells after isolation. By measuring staurosporine-induced apoptosis, stress signalling, and oxidative and antioxidant responses in hepatocytes from fasted and ad libitum-fed animals, we found that only fasting animals elicited a stress response that prevented caspase-9 activation and persisted in isolated cells. The addition of glucose oxidase, a hydrogen peroxide-producing enzyme, to the cells from ad libitum-fed animals also led to a stress response phenotype and prevented the activation of caspase-9. A single fasting episode thus leads to a stress response in normal hepatocytes, with hydrogen peroxide as a second messenger that reduces the initiation of apoptosis. This finding is the first characterisation of a mechanism underlying the effects of fasting and provides a basis for the development of methods to increase the resilience of cells. These findings need to be taken into account when interpreting the results obtained in animal and cell research models to account for the effects of overnight fasting used in many laboratory protocols. The research results also form the basis for the development of clinical applications to increase the resistance of transplants and to improve the fitness of hepatocytes under acute stress conditions in liver and some metabolic diseases.

Sorafenib and SIAIS361034, a novel PROTAC degrader of BCL-xL, display synergistic antitumor effects on hepatocellular carcinoma with minimal hepatotoxicity

The overexpression of BCL-xL is closely associated with poor prognosis in hepatocellular carcinoma (HCC). While the strategy of combination of BCL-xL and MCL-1 for treating solid tumors has been reported, it presents significant hepatotoxicity. SIAIS361034, a novel proteolysis targeting chimera (PROTAC) agent, selectively induces the ubiquitination and subsequent proteasomal degradation of BCL-xL through the CRBN-E3 ubiquitin ligase. When combined with sorafenib, SIAIS361034 showed a potent synergistic effect in inhibiting hepatocellular carcinoma development both in vitro and in vivo. Since SIAIS361034 exhibits a high degree of selectivity for degrading BCL-xL in hepatocellular carcinoma, the hepatotoxicity typically associated with the combined inhibition of BCL-xL and MCL-1 is significantly reduced, thereby greatly enhancing safety. Mechanistically, BCL-xL and MCL-1 sequester the BH3-only protein BIM on mitochondria at baseline. Treatment with SIAIS361034 and sorafenib destabilizes BIM/BCL-xL and BIM/MCL1 association, resulting in the liberation of more BIM proteins to trigger apoptosis. Additionally, we discovered a novel compensatory regulation mechanism in hepatocellular carcinoma cells. BIM can rapidly respond to changes in the balance between BCL-xL and MCL-1 through their co-transcription factor MEF2C to maintain apoptosis resistance. In summary, the combination therapy of SIAIS361034 and sorafenib represents an effective and safe approach for inhibiting hepatocellular carcinoma progression. The novel balancing mechanism may also provide insights for combination and precision therapies in the treatment of hepatocellular carcinoma.

Osteosarcoma cells depend on MCL-1 for survival, and osteosarcoma metastases respond to MCL-1 antagonism plus regorafenib in vivo

Osteosarcoma is the most common form of primary bone cancer, which primarily afflicts children and adolescents. Chemotherapy, consisting of doxorubicin, cisplatin and methotrexate (MAP) increased the 5-year osteosarcoma survival rate from 20% to approximately 60% by the 1980s. However, osteosarcoma survival rates have remained stagnant for several decades. Patients whose disease fails to respond to MAP receive second-line treatments such as etoposide and, in more recent years, the kinase inhibitor regorafenib. BCL-2 and its close relatives enforce cellular survival and have been implicated in the development and progression of various cancer types. BH3-mimetics antagonize pro-survival members of the BCL-2 family to directly stimulate apoptosis. These drugs have been proven to be efficacious in other cancer types, but their use in osteosarcoma has been relatively unexplored to date. We investigated the potential efficacy of BH3-mimetics against osteosarcoma cells in vitro and examined their cooperation with regorafenib in vivo. We demonstrated that osteosarcoma cell lines could be killed through inhibition of MCL-1 combined with BCL-2 or BCL-xL antagonism. Inhibition of MCL-1 also sensitized osteosarcoma cells to killing by second-line osteosarcoma treatments, particularly regorafenib. Importantly, we found that inhibition of MCL-1 with the BH3-mimetic S63845 combined with regorafenib significantly prolonged the survival of mice bearing pulmonary osteosarcoma metastases. Together, our results highlight the importance of MCL-1 in osteosarcoma cell survival and present a potential therapeutic avenue that may improve metastatic osteosarcoma patient outcomes.

Don't fear the reaper: The role of regulated cell death in tumorigenesis and BH3-mimetics for cancer therapy

From its earliest characterization, it has been recognized that there is a role for regulated (programmed) cell death in cancer. As our understanding of the different types of programmed cell death processes and their molecular control has advanced, so have the technologies that allow us to manipulate these processes to, for example, fight against cancer. In this review, we describe the roles of the different forms of regulated cell death in the development of cancer as well as their potential therapeutic exploitation. In that vein, we explore the development and use of BH3-mimetics, a unique class of drugs that can directly activate the apoptotic cell death machinery to treat cancer. Finally, we address key challenges that face the field to improve the use of these therapeutics and the efforts that are being undertaken to do so.

The Role of Bcl-2 Family Proteins and Sorafenib Resistance in Hepatocellular Carcinoma

Liver cancer has been reported to be one of the most malignant diseases in the world. It is late diagnosis consequently leads to a difficult treatment, as the cancer reached an advanced stage. Hepatocellular carcinoma (HCC) is the primary type of cancer diagnosed in the liver, with deadly characteristics and a poor prognosis. The first-in-line treatment for advanced HCC is sorafenib. Sorafenib acts by inhibiting cell proliferation and by inducing apoptosis as well as blocks receptors associated with these mechanisms. Due to its constant use, sorafenib resistance has been described, especially to proteins of the Bcl-2 family, and their overexpression of Bcl-XL and Mcl-1. This review focuses on the role of the Bcl-2 proteins in relation to sorafenib resistance as a consequence of first-in-line treatment in HCC.

MDM2 Is Essential to Maintain the Homeostasis of Epithelial Cells by Targeting p53

INTRODUCTION

MDM2 is known as the primary negative regulator of p53, and MDM2 promotes lung cancer fibrosis and lung injury through p53-dependent and p53-independent pathways. However, the mechanism by which MDM2 influences the pathogenesis of asthma is unknown. In this study, we investigated the function of MDM2 in lung epithelial cells in type 2 lung inflammation.

METHODS

We used type II alveolar epithelial cell-specific heterozygous knockout of Mdm2 mice to validate its function. Then papain-induced asthma model was established, and changes in inflammation were observed by measuring immunohistochemistry and flow cytometry analysis.

RESULTS

In this study, we knockdown the mouse Mdm2 gene in type 2 alveolar epithelial cells. We demonstrated that heterozygous Mdm2 gene-deleted mice were highly susceptible to protease allergen papain-induced pulmonary inflammation characterized by increased ILC2 numbers, IL-5 and IL-13 cytokine levels, and lung pathology. A mechanistic study showed that following the decreased expression of Mdm2 in lung epithelial cells and A549 cell line, p53 was overactivated, and the expression of its downstream genes p21, Puma, and Noxa was elevated, which resulted in apoptosis. After Mdm2 knockdown, the mRNA expression of inflammation-related gene IL-25, HMGB1, and TNF-α were increased, which further amplified the downstream ILC2 response and lung inflammation.

CONCLUSION

These results indicate that Mdm2 maintains the homeostasis of lung epithelial cells by targeting P53 and regulates the function of lung epithelial cells under type 2 lung inflammation.

AMPK inhibition sensitizes acute leukemia cells to BH3 mimetic-induced cell death

BH3 mimetics, including the BCL2/BCLXL/BCLw inhibitor navitoclax and MCL1 inhibitors S64315 and tapotoclax, have undergone clinical testing for a variety of neoplasms. Because of toxicities, including thrombocytopenia after BCLXL inhibition as well as hematopoietic, hepatic and possible cardiac toxicities after MCL1 inhibition, there is substantial interest in finding agents that can safely sensitize neoplastic cells to these BH3 mimetics. Building on the observation that BH3 mimetic monotherapy induces AMP kinase (AMPK) activation in multiple acute leukemia cell lines, we report that the AMPK inhibitors (AMPKis) dorsomorphin and BAY-3827 sensitize these cells to navitoclax or MCL1 inhibitors. Cell fractionation and phosphoproteomic analyses suggest that sensitization by dorsomorphin involves dephosphorylation of the proapoptotic BCL2 family member BAD at Ser75 and Ser99, leading BAD to translocate to mitochondria and inhibit BCLXL. Consistent with these results, BAD knockout or mutation to BAD S75E/S99E abolishes the sensitizing effects of dorsomorphin. Conversely, dorsomorphin synergizes with navitoclax or the MCL1 inhibitor S63845 to induce cell death in primary acute leukemia samples ex vivo and increases the antitumor effects of navitoclax or S63845 in several xenograft models in vivo with little or no increase in toxicity in normal tissues. These results suggest that AMPK inhibition can sensitize acute leukemia to multiple BH3 mimetics, potentially allowing administration of lower doses while inducing similar antineoplastic effects.

BCL-XL inhibitors enhance the apoptotic efficacy of BRAF inhibitors in BRAFV600E colorectal cancer

Metastatic BRAFV600E colorectal cancer (CRC) carries an extremely poor prognosis and is in urgent need of effective new treatments. While the BRAFV600E inhibitor encorafenib in combination with the EGFR inhibitor cetuximab (Enc+Cet) was recently approved for this indication, overall survival is only increased by 3.6 months and objective responses are observed in only 20% of patients. We have found that a limitation of Enc+Cet treatment is the failure to efficiently induce apoptosis in BRAFV600E CRCs, despite inducing expression of the pro-apoptotic protein BIM and repressing expression of the pro-survival protein MCL-1. Here, we show that BRAFV600E CRCs express high basal levels of the pro-survival proteins MCL-1 and BCL-XL, and that combining encorafenib with a BCL-XL inhibitor significantly enhances apoptosis in BRAFV600E CRC cell lines. This effect was partially dependent on the induction of BIM, as BIM deletion markedly attenuated BRAF plus BCL-XL inhibitor-induced apoptosis. As thrombocytopenia is an established on-target toxicity of BCL-XL inhibition, we also examined the effect of combining encorafenib with the BCL-XL -targeting PROTAC DT2216, and the novel BCL-2/BCL-XL inhibitor dendrimer conjugate AZD0466. Combining encorafenib with DT2216 significantly increased apoptosis induction in vitro, while combining encorafenib with AZD0466 was well tolerated in mice and further reduced growth of BRAFV600E CRC xenografts compared to either agent alone. Collectively, these findings demonstrate that combined BRAF and BCL-XL inhibition significantly enhances apoptosis in pre-clinical models of BRAFV600E CRC and is a combination regimen worthy of clinical investigation to improve outcomes for these patients.

Anticancer effects of rutin from Fagopyrum tataricum (tartary buckwheat) against osteosarcoma cell line

BACKGROUND

The present study is analysisof the seeds of buckwheat (Fagopyrum sp.),member of the Polygonaceae family for isolation of rutin and its anticancer property againstOsteosarcoma celllines (SAOS2). The selected plant is traditionally used for diabetes and cancer. It has several biological properties such as antibacterial, antioxidant and anti-aging.

PURPOSE

Thirty-five buckwheat cultivars were obtained from Nepal Agriculture Genetic Resources Centre (NAGRC) Khumaltar, Kathmandu, Nepal, and Kumrek Sikkim. These plant varieties are scientifically evaluated their biological properties.

METHODS

Rutin wasfractionated from buckwheat seeds using methanol fraction and analysed for quality by HPLC method. The rutin fraction of the cultivar NGRC03731 a tartary buck wheat and standard rutin was used against Osteosarcoma cell lines (SAOS2) and human gingival fibroblast cells (hGFs) for anticancer activity. The cell viability using rutin fraction and standard rutin treated with SAOS2 cells were assessed by MTT assay. For further research, the best doses (IC-50: 20 g/ml) were applied. By using AO/EtBr dual staining, the effects of Rutin fraction on SAOS2 cell death were analysed. The scratch wound healing assay was used to analyse cell migration. Real-time PCR was used to analyse the pro-/anti-apoptotic gene expression.

RESULTS

The seeds with the highest rutin content, NGRC03731 seeds, had 433 mg/100 g of rutin.The rutin fraction treatment and standard rutin significantly reduced cell viability in the MTT assay, and osteosarcoma cells were observed on sensitive to the IC-50 dose at a concentration of 20 g/ml after 24 h.The SAOS2 cells exposed to rutin fraction at 20 g/ml and standard rutin at 10 g/ml exhibited significant morphological alterations, cell shrinkage and decreased cell density, which indicate apoptotic cells.Rutin-fraction treated cells stained with acridine orange/ethidium bromide (AO/EtBr) dual staining cells turned yellow, orange, and red which indicatesto measure apoptosis.The anti-migration potential of rutin fraction, results prevented the migration of SAOS2 cancer cells.Rutin-fraction significantly increased the expression of pro-apoptotic proteinsBad, using real-time PCR analysis (mRNA for Bcl-2 family proteins) resulted Bcl-2's expression is negatively regulated.

CONCLUSION

Osteosarcoma (SAOS2) cell lines' proliferation, migration, and ability to proliferate were reduced markedly by rutin fraction and it also causes apoptosis of Osteosarcoma cell lines (SAOS2).

CD1d protects against hepatocyte apoptosis in non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis, a well-defined form of cell death in non-alcoholic steatohepatitis (NASH), is considered the primary cause of liver inflammation and fibrosis. However, the mechanisms underlying the regulation of hepatocyte apoptosis in NASH remain largely unclear. We explored the anti-apoptotic effect of hepatocyte CD1d in NASH.

METHODS

Hepatocyte CD1d expression was analyzed in patients with NASH and mouse models. Hepatocyte-specific gene overexpression or knockdown and anti-CD1d crosslinking were used to investigate the anti-apoptotic effect of hepatocyte CD1d on lipotoxicity-, Fas-, and concanavalin (ConA)-mediated liver injuries. A high-fat diet, a methionine-choline-deficient diet, a Fas agonist, and ConA were used to induce lipotoxic and/or apoptotic liver injuries. Palmitic acid was used to mimic lipotoxicity-induced apoptosis in vitro.

RESULTS

We identified a dramatic decrease in CD1d expression in hepatocytes of patients with NASH and mouse models. Hepatocyte-specific CD1d overexpression and knockdown experiments collectively demonstrated that hepatocyte CD1d protected against hepatocyte apoptosis and alleviated hepatic inflammation and injuries in NASH mice. Furthermore, decreased JAK2-STAT3 signaling was observed in NASH patient livers. Mechanistically, anti-CD1d crosslinking on hepatocytes induced tyrosine phosphorylation of the CD1d cytoplasmic tail, leading to the recruitment and phosphorylation of JAK2. Phosphorylated JAK2 activated STAT3 and subsequently reduced apoptosis in hepatocytes, which was associated with an increase in anti-apoptotic effectors (Bcl-xL and Mcl-1) and a decrease in pro-apoptotic effectors (cleaved-caspase 3/7). Moreover, anti-CD1d crosslinking effectively protected against Fas- or ConA-mediated hepatocyte apoptosis and liver injury in mice.

CONCLUSIONS

Our study uncovered a previously unrecognized anti-apoptotic CD1d-JAK2-STAT3 axis in hepatocytes that conferred hepatoprotection and highlighted the potential of hepatocyte CD1d-directed therapy for liver injury and fibrosis in NASH, as well as in other liver diseases associated with hepatocyte apoptosis.

IMPACT AND IMPLICATIONS

Excessive and/or sustained hepatocyte apoptosis is critical in driving liver inflammation and injury. The mechanisms underlying the regulation of hepatocyte apoptosis in non-alcoholic steatohepatitis (NASH) remain largely unclear. Here, we found that CD1d expression in hepatocytes substantially decreases and negatively correlates with the severity of liver injury in patients with NASH. We further revealed a previously unrecognized anti-apoptotic CD1d-JAK2-STAT3 signaling axis in hepatocytes, which confers significant protection against liver injury in NASH and acute liver diseases. Thus, hepatocyte CD1d-targeted therapy could be a promising strategy to manipulate liver injury in both NASH and other hepatocyte apoptosis-related liver diseases.

Cell death

Cell death supports morphogenesis during development and homeostasis after birth by removing damaged or obsolete cells. It also curtails the spread of pathogens by eliminating infected cells. Cell death can be induced by the genetically programmed suicide mechanisms of apoptosis, necroptosis, and pyroptosis, or it can be a consequence of dysregulated metabolism, as in ferroptosis. Here, we review the signaling mechanisms underlying each cell-death pathway, discuss how impaired or excessive activation of the distinct cell-death processes can promote disease, and highlight existing and potential therapies for redressing imbalances in cell death in cancer and other diseases.

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.

Targeting YAP-mediated HSC death susceptibility and senescence for treatment of liver fibrosis

BACKGROUND AND AIMS

Liver fibrosis results from the accumulation of myofibroblasts (MFs) derived from quiescent HSCs, and yes-associated protein (YAP) controls this state transition. Although fibrosis is also influenced by HSC death and senescence, whether YAP regulates these processes and whether this could be leveraged to treat liver fibrosis are unknown.

APPROACH AND RESULTS

YAP activity was manipulated in MF-HSCs to determine how YAP impacts susceptibility to pro-apoptotic senolytic agents or ferroptosis. Effects of senescence on YAP activity and susceptibility to apoptosis versus ferroptosis were also examined. CCl 4 -treated mice were treated with a ferroptosis inducer or pro-apoptotic senolytic to determine the effects on liver fibrosis. YAP was conditionally disrupted in MFs to determine how YAP activity in MF-HSC affects liver fibrosis in mouse models. Silencing YAP in cultured MF-HSCs induced HSC senescence and vulnerability to senolytics, and promoted ferroptosis resistance. Conversely, inducing HSC senescence suppressed YAP activity, increased sensitivity to senolytics, and decreased sensitivity to ferroptosis. Single-cell analysis of HSCs from fibrotic livers revealed heterogeneous sensitivity to ferroptosis, apoptosis, and senescence. In mice with chronic liver injury, neither the ferroptosis inducer nor senolytic improved fibrosis. However, selectively depleting YAP in MF-HSCs induced senescence and decreased liver injury and fibrosis.

CONCLUSION

YAP determines whether MF-HSCs remain activated or become senescent. By regulating this state transition, Yap controls both HSC fibrogenic activity and susceptibility to distinct mechanisms for cell death. MF-HSC-specific YAP depletion induces senescence and protects injured livers from fibrosis. Clarifying determinants of HSC YAP activity may facilitate the development of novel anti-fibrotic therapies.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Discovery of an Oral, Beyond-Rule-of-Five Mcl-1 Protein-Protein Interaction Modulator with the Potential of Treating Hematological Malignancies

Avoidance of apoptosis is critical for the development and sustained growth of tumors. The pro-survival protein myeloid cell leukemia 1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family of proteins which is overexpressed in many cancers. Upregulation of Mcl-1 in human cancers is associated with high tumor grade, poor survival, and resistance to chemotherapy. Therefore, pharmacological inhibition of Mcl-1 is regarded as an attractive approach to treating relapsed or refractory malignancies. Herein, we disclose the design, synthesis, optimization, and early preclinical evaluation of a potent and selective small-molecule inhibitor of Mcl-1. Our exploratory design tactics focused on structural modifications which improve the potency and physicochemical properties of the inhibitor while minimizing the risk of functional cardiotoxicity. Despite being in the "non-Lipinski" beyond-Rule-of-Five property space, the developed compound benefits from exquisite oral bioavailability in vivo and induces potent pharmacodynamic inhibition of Mcl-1 in a mouse xenograft model.

Histomorphological study of hepatic lobules of adult Wistar rats administered with aqueous extracts of leaves of cassia singueana

OBJECTIVES

Cassia singueana is widely used in northern Nigeria as an herb for the treatment of enamors ailments. Nevertheless the toxicity of the herb on liver architecture; the hepatic lobule and body weight is yet to be authenticated.

METHODS

A total of 24 male Wistar rats with an average weight of 150 g were randomly placed into four groups. Each group consisted of 6 rats. Group A served as the control group while groups B, C and D were given 150, 300, and 450 mg of Cassia singueana leaves extract respectively for 14 days. The animals were weighed before, during and after the treatment phase subsequently, they were sacrificed and the liver tissues were processed and stained using hematoxylin and eosin (H&E) stain, Masson's and Trichrome Stain, Gordon and Sweet's Stain, and Periodic Acid Schiff (PAS)Stain.

RESULTS

There was no significant change in the animal's body weight of in all the groups when compared to the control group. Our histology result showed that Cassia singueana induced vascular lesion and hepatocytes degeneration putatively though mechanism of cell death (apoptosis and necrosis). It was also found that Cassia singueana has no toxic effect on the reticular fibers of the liver. High dose of Cassia singueana was found to induce the deposition of PAS positive materials in hepatocytes.

CONCLUSIONS

The Cassia singueana leaves extract induce hepatocyte degeneration and vascular lesion in the hepatic lobules of the wistar rats, without affecting the animals' body weight.

Co-targeting BCL-XL and MCL-1 with DT2216 and AZD8055 synergistically inhibit small-cell lung cancer growth without causing on-target toxicities in mice

Small-cell lung cancer (SCLC) is an aggressive malignancy with limited therapeutic options. The dismal prognosis in SCLC is in part associated with an upregulation of BCL-2 family anti-apoptotic proteins, including BCL-X_L and MCL-1. Unfortunately, the currently available inhibitors of BCL-2 family anti-apoptotic proteins, except BCL-2 inhibitors, are not clinically relevant because of various on-target toxicities. We, therefore, aimed to develop an effective and safe strategy targeting these anti-apoptotic proteins with DT2216 (our platelet-sparing BCL-X_L degrader) and AZD8055 (an mTOR inhibitor) to avoid associated on-target toxicities while synergistically optimizing tumor response. Through BH3 mimetic screening, we identified a subset of SCLC cell lines that is co-dependent on BCL-X_L and MCL-1. After screening inhibitors of selected tumorigenic pathways, we found that AZD8055 selectively downregulates MCL-1 in SCLC cells and its combination with DT2216 synergistically killed BCL-X_L/MCL-1 co-dependent SCLC cells, but not normal cells. Mechanistically, the combination caused BCL-X_L degradation and suppression of MCL-1 expression, and thus disrupted MCL-1 interaction with BIM leading to an enhanced apoptotic induction. In vivo, the DT2216 + AZD8055 combination significantly inhibited the growth of cell line-derived and patient-derived xenografts and reduced tumor burden accompanied by increased survival in a genetically engineered mouse model of SCLC without causing appreciable thrombocytopenia or other normal tissue injuries. Thus, these preclinical findings lay a strong foundation for future clinical studies to test DT2216 + mTOR inhibitor combinations in a subset of SCLC patients whose tumors are co-driven by BCL-X_L and MCL-1.

BCL-2 protein family: attractive targets for cancer therapy

Acquired resistance to cell death is a hallmark of cancer. The BCL-2 protein family members play important roles in controlling apoptotic cell death. Abnormal over-expression of pro-survival BCL-2 family members or abnormal reduction of pro-apoptotic BCL-2 family proteins, both resulting in the inhibition of apoptosis, are frequently detected in diverse malignancies. The critical role of the pro-survival and pro-apoptotic BCL-2 family proteins in the regulation of apoptosis makes them attractive targets for the development of agents for the treatment of cancer. This review describes the roles of the various pro-survival and pro-apoptotic members of the BCL-2 protein family in normal development and organismal function and how defects in the control of apoptosis promote the development and therapy resistance of cancer. Finally, we discuss the development of inhibitors of pro-survival BCL-2 proteins, termed BH3-mimetic drugs, as novel agents for cancer therapy.

Understanding MCL1: from cellular function and regulation to pharmacological inhibition

Myeloid cell leukemia-1 (MCL1), an antiapoptotic member of the BCL2 family characterized by a short half-life, functions as a rapid sensor that regulates cell death and other relevant processes that include cell cycle progression and mitochondrial homeostasis. In cancer, MCL1 overexpression contributes to cell survival and resistance to diverse chemotherapeutic agents; for this reason, several MCL1 inhibitors are currently under preclinical and clinical development for cancer treatment. However, the nonapoptotic functions of MCL1 may influence their therapeutic potential. Overall, the complexity of MCL1 regulation and function represent challenges to the clinical application of MCL1 inhibitors. We now summarize the current knowledge regarding MCL1 structure, regulation, and function that could impact the clinical success of MCL1 inhibitors.

Insight into the interplay between mitochondria-regulated cell death and energetic metabolism in osteosarcoma

Osteosarcoma (OS) is a pediatric malignant bone tumor that predominantly affects adolescent and young adults. It has high risk for relapse and over the last four decades no improvement of prognosis was achieved. It is therefore crucial to identify new drug candidates for OS treatment to combat drug resistance, limit relapse, and stop metastatic spread. Two acquired hallmarks of cancer cells, mitochondria-related regulated cell death (RCD) and metabolism are intimately connected. Both have been shown to be dysregulated in OS, making them attractive targets for novel treatment. Promising OS treatment strategies focus on promoting RCD by targeting key molecular actors in metabolic reprogramming. The exact interplay in OS, however, has not been systematically analyzed. We therefore review these aspects by synthesizing current knowledge in apoptosis, ferroptosis, necroptosis, pyroptosis, and autophagy in OS. Additionally, we outline an overview of mitochondrial function and metabolic profiles in different preclinical OS models. Finally, we discuss the mechanism of action of two novel molecule combinations currently investigated in active clinical trials: metformin and the combination of ADI-PEG20, Docetaxel and Gemcitabine.

No time to die? Intrinsic apoptosis signaling in hematopoietic stem and progenitor cells and therapeutic implications

PURPOSE OF REVIEW

Dysregulated apoptosis contributes to the pathogenesis of many hematologic malignancies. BH3-mimetics, antagonists of antiapoptotic BCL-2 proteins, represent novel, and promising cancer drugs. While the acute myelosuppressive effects of Venetoclax, the first Food and Drug Administration approved BCL-2 inhibitor, are fairly well described, little is known about side effects of novel BH3-mimetics and effects of chronic Venetoclax treatment.

RECENT FINDINGS

Highly relevant publications focused on the effects of acute and chronic Venetoclax therapy, with focus on cell-type specific adaptive mechanisms, the emergence of clonal hematopoiesis, and the selection of BAX-mutated hematopoietic cells in patients treated with Venetoclax for a long period. Important advances were made in understanding primary and secondary Venetoclax resistance and prediction of Venetoclax response. Combination therapies of BH3-mimetics targeting different BCL-2 proteins are highly anticipated. However, human stem and progenitors require both MCL-1 and BCL-XL for survival, and serious myelosuppressive effects of combined MCL-1/BCL-XL inhibition can be expected.

SUMMARY

Long-term studies are indispensable to profile the chronic side effects of Venetoclax and novel BH3-mimetics and better balance their risk vs. benefit in cancer therapy. Combination therapies will be powerful, but potentially limited by severe myelosuppression. For precision medicine, a better knowledge of BCL-2 proteins in the healthy and diseased hematopoietic system is required.

BH3 mimetic drugs cooperate with Temozolomide, JQ1 and inducers of ferroptosis in killing glioblastoma multiforme cells

Glioblastoma multiforme (GBM) is the most common and aggressive form of brain cancer, with treatment options often constrained due to inherent resistance of malignant cells to conventional therapy. We investigated the impact of triggering programmed cell death (PCD) by using BH3 mimetic drugs in human GBM cell lines. We demonstrate that co-targeting the pro-survival proteins BCL-XL and MCL-1 was more potent at killing six GBM cell lines compared to conventional therapy with Temozolomide or the bromodomain inhibitor JQ1 in vitro. Enhanced cell killing was observed in U251 and SNB-19 cells in response to dual treatment with TMZ or JQ1 combined with a BCL-XL inhibitor, compared to single agent treatment. This was reflected in abundant cleavage/activation of caspase-3 and cleavage of PARP1, markers of apoptosis. U251 and SNB-19 cells were more readily killed by a combination of BH3 mimetics targeting BCL-XL and MCL-1 as opposed to dual treatment with the BCL-2 inhibitor Venetoclax and a BCL-XL inhibitor. The combined loss of BAX and BAK, the essential executioners of intrinsic apoptosis, rendered U251 and SNB-19 cells refractory to any of the drug combinations tested, demonstrating that apoptosis is responsible for their killing. In an orthotopic mouse model of GBM, we demonstrate that the BCL-XL inhibitor A1331852 can penetrate the brain, with A1331852 detected in both tumour and healthy brain regions. We also investigated the impact of combining small molecule inducers of ferroptosis, erastin and RSL3, with BH3 mimetic drugs. We found that a BCL-XL or an MCL-1 inhibitor potently cooperates with inducers of ferroptosis in killing U251 cells. Overall, these findings demonstrate the potential of dual targeting of distinct PCD signalling pathways in GBM and may guide the utility of BCL-XL inhibitors and inducers of ferroptosis with standard of care treatment for improved therapies for GBM.

What can we learn from mice lacking pro-survival BCL-2 proteins to advance BH3 mimetic drugs for cancer therapy?

In many human cancers the control of apoptosis is dysregulated, for instance as a result of the overexpression of pro-survival BCL-2 proteins. This promotes tumorigenesis by protecting nascent neoplastic cells from stress and renders malignant cells resistant to anti-cancer agents. Therefore, several BH3 mimetic drugs targeting distinct pro-survival proteins have been developed. The BCL-2 inhibitor Venetoclax/ABT-199, has been approved for treatment of certain blood cancers and tens of thousands of patients have already been treated effectively with this drug. To advance the clinical development of MCL-1 and BCL-XL inhibitors, a more detailed understanding of their distinct and overlapping roles in the survival of malignant as well as non-transformed cells in healthy tissues is required. Here, we discuss similarities and differences in pro-survival BCL-2 protein structure, subcellular localisation and binding affinities to the pro-apoptotic BCL-2 family members. We summarise the findings from gene-targeting studies in mice to discuss the specific roles of distinct pro-survival BCL-2 family members during embryogenesis and the survival of non-transformed cells in healthy tissues in adults. Finally, we elaborate how these findings align with or differ from the observations from the clinical development and use of BH3 mimetic drugs targeting different pro-survival BCL-2 proteins.

Overcoming Gemcitabine Resistance in Pancreatic Cancer Using the BCL-XL-Specific Degrader DT2216

Pancreatic cancer is the third most common cause of cancer-related deaths in the United States. Although gemcitabine is the standard of care for most patients with pancreatic cancer, its efficacy is limited by the development of resistance. This resistance may be attributable to the evasion of apoptosis caused by the overexpression of BCL-2 family antiapoptotic proteins. In this study, we investigated the role of BCL-XL in gemcitabine resistance to identify a combination therapy to more effectively treat pancreatic cancer. We used CRISPR-Cas9 screening to identify the key genes involved in gemcitabine resistance in pancreatic cancer. Pancreatic cancer cell dependencies on different BCL-2 family proteins and the efficacy of the combination of gemcitabine and DT2216 (a BCL-XL proteolysis targeting chimera or PROTAC) were determined by MTS, Annexin-V/PI, colony formation, and 3D tumor spheroid assays. The therapeutic efficacy of the combination was investigated in several patient-derived xenograft (PDX) mouse models of pancreatic cancer. We identified BCL-XL as a key mediator of gemcitabine resistance. The combination of gemcitabine and DT2216 synergistically induced cell death in multiple pancreatic cancer cell lines in vitro In vivo, the combination significantly inhibited tumor growth and prolonged the survival of tumor-bearing mice compared with the individual agents in pancreatic cancer PDX models. Their synergistic antitumor activity is attributable to DT2216-induced degradation of BCL-XL and concomitant suppression of MCL-1 by gemcitabine. Our results suggest that DT2216-mediated BCL-XL degradation augments the antitumor activity of gemcitabine and their combination could be more effective for pancreatic cancer treatment.

The manipulation of apoptosis for cancer therapy using BH3-mimetic drugs

Apoptosis is a form of programmed cell death that is regulated by the balance between prosurvival and proapoptotic BCL-2 protein family members. Evasion of apoptosis is a hallmark of cancer that arises when this balance is tipped in favour of survival. One form of anticancer therapeutic, termed 'BH3-mimetic drugs', has been developed to directly activate the apoptosis machinery in malignant cells. These drugs bind to and inhibit specific prosurvival BCL-2 family proteins, thereby mimicking their interaction with the BH3 domains of proapoptotic BCL-2 family proteins. The BCL-2-specific inhibitor venetoclax is approved by the US Food and Drug Administration and many regulatory authorities worldwide for the treatment of chronic lymphocytic leukaemia and acute myeloid leukaemia. BH3-mimetic drugs targeting other BCL-2 prosurvival proteins have been tested in preclinical models of cancer, and drugs targeting MCL-1 or BCL-X_L have advanced into phase I clinical trials for certain cancers. As with all therapeutics, efficacy and tolerability need to be carefully balanced to achieve a therapeutic window whereby there is significant anticancer activity with an acceptable safety profile. In this Review, we outline the current state of BH3-mimetic drugs targeting various prosurvival BCL-2 family proteins and discuss emerging data regarding primary and acquired resistance to these agents and approaches that may overcome this. We highlight issues that need to be addressed to further advance the clinical application of BH3-mimetic drugs, both alone and in combination with additional anticancer agents (for example, standard chemotherapeutic drugs or inhibitors of oncogenic kinases), for improved responses in patients with cancer.

Targeting the BCL-2-regulated apoptotic pathway for the treatment of solid cancers

The deregulation of apoptosis is a key contributor to tumourigenesis as it can lead to the unwanted survival of rogue cells. Drugs known as the BH3-mimetics targeting the pro-survival members of the BCL-2 protein family to induce apoptosis in cancer cells have achieved clinical success for the treatment of haematological malignancies. However, despite our increasing knowledge of the pro-survival factors mediating the unwanted survival of solid tumour cells, and our growing BH3-mimetics armamentarium, the application of BH3-mimetic therapy in solid cancers has not reached its full potential. This is mainly attributed to the need to identify clinically safe, yet effective, combination strategies to target the multiple pro-survival proteins that typically mediate the survival of solid tumours. In this review, we discuss current and exciting new developments in the field that has the potential to unleash the full power of BH3-mimetic therapy to treat currently recalcitrant solid malignancies.

Discovery of 3,5-Dimethyl-4-Sulfonyl-1H-Pyrrole-Based Myeloid Cell Leukemia 1 Inhibitors with High Affinity, Selectivity, and Oral Bioavailability

Myeloid cell leukemia 1 (Mcl-1) protein is a key negative regulator of apoptosis, and developing Mcl-1 inhibitors has been an attractive strategy for cancer therapy. Herein, we describe the rational design, synthesis, and structure-activity relationship study of 3,5-dimethyl-4-sulfonyl-1H-pyrrole-based compounds as Mcl-1 inhibitors. Stepwise optimizations of hit compound 11 with primary Mcl-1 inhibition (52%@30 μM) led to the discovery of the most potent compound 40 with high affinity (K_d = 0.23 nM) and superior selectivity over other Bcl-2 family proteins (>40,000 folds). Mechanistic studies revealed that 40 could activate the apoptosis signal pathway in an Mcl-1-dependent manner. 40 exhibited favorable physicochemical properties and pharmacokinetic profiles (F% = 41.3%). Furthermore, oral administration of 40 was well tolerated to effectively inhibit tumor growth (T/C = 37.3%) in MV4-11 xenograft models. Collectively, these findings implicate that compound 40 is a promising antitumor agent that deserves further preclinical evaluations.

BCL2 inhibitors and MCL1 inhibitors for hematological malignancies

BCL2 and MCL1 are commonly expressed pro-survival (anti-apoptotic) proteins in hematological cancers and play important roles in their biology either through dysregulation or by virtue of intrinsic importance to the cell-of-origin of the malignancy. A new class of small molecule anti-cancer drugs, BH3-mimetics, now enable specific targeting of these proteins in patients. BH3-mimetics act by inhibiting the pro-survival BCL2 proteins to enable the activation of BAX and BAK, apoptosis effectors which permeabilize the outer mitochondrial membrane, triggering apoptosis directly in many cells and sensitizing others to cell death when combined with other anti-neoplastic drugs. Venetoclax, a specific inhibitor of BCL2, is the first approved in class, demonstrating striking single agent activity in chronic lymphocytic leukemia (CLL) and in other lymphoid neoplasms, as well as activity against acute myeloid leukemia (AML), especially when used in combination. Key insights from the venetoclax experience include that responses occur rapidly, with major activity as monotherapy proving to be the best indicator for success in combination regimens. This emphasizes the importance of adequate single agent studies for drugs in this class. Furthermore, secondary resistance is common with long-term exposure and often mediated by genetic or adaptive changes in the apoptotic pathway, suggesting that BH3-mimetics are better suited to limited-duration, rather than continuous, therapy. The success of venetoclax has inspired development of BH3-mimetics targeting MCL1. Despite promising preclinical activity against MYC-driven lymphomas, myeloma and AML, their success may particularly depend on their tolerability profile given physiological roles for MCL1 in several non-hematological tissues.

Gab1 in livers with persistent hepatocyte apoptosis has an antiapoptotic effect and reduces chronic liver injury, fibrosis, and tumorigenesis

Grb2-associated binder 1 (Gab1) is an adaptor protein that is important for intracellular signal transduction by receptor tyrosine kinases that are receptors for various growth factors and plays an important role in rapid liver regeneration after partial hepatectomy and during acute hepatitis. On the other hand, mild liver regeneration is induced in livers of individuals with chronic hepatitis, where hepatocyte apoptosis is persistent; however, the impact of Gab1 on such livers remains unclear. We examined the role of Gab1 in chronic hepatitis. Gab1 knockdown enhanced the decrease in cell viability and apoptosis induced by ABT-737, a Bcl-2/-xL/-w inhibitor, in BNL.CL2 cells, while cell viability and caspase activity were unchanged in the absence of ABT-737. ABT-737 treatment induced Gab1 cleavage to form p35-Gab1. p35-Gab1 was also detected in the livers of mice with hepatocyte-specific Mcl-1 knockout (KO), which causes persistent hepatocyte apoptosis. Gab1 deficiency exacerbated hepatocyte apoptosis in Mcl-1 KO mice with posttranscriptional downregulation of Bcl-XL. In BNL.CL2 cells treated with ABT-737, Gab1 knockdown posttranscriptionally suppressed Bcl-xL expression, and p35-Gab1 overexpression enhanced Bcl-xL expression. Gab1 deficiency in Mcl-1 KO mice activated STAT3 signaling in hepatocytes, increased hepatocyte proliferation, and increased the incidence of liver cancer with the exacerbation of liver fibrosis. In conclusion, Gab1 is cleaved in the presence of apoptotic stimuli and forms p35-Gab1 in hepatocytes. In chronic liver injury, the role of Gab1 in suppressing apoptosis and reducing liver damage, fibrosis, and tumorigenesis is more important than its role in liver regeneration.NEW & NOTEWORTHY Grb2-associated binder 1 (Gab1) is known to contribute to liver regeneration after acute liver injury. However, in chronic liver diseases, Gab1 plays a greater role in suppressing hepatocyte apoptosis than in liver regeneration, resulting in suppression of hepatocyte proliferation, liver fibrosis, and liver carcinogenesis.

It's time to die: BH3 mimetics in solid tumors

The removal of cells by apoptosis is an essential process regulating tissue homeostasis. Cancer cells acquire the ability to circumvent apoptosis and survive in an unphysiological tissue context. Thereby, the Bcl-2 protein family plays a key role in the initiation of apoptosis, and overexpression of the anti-apoptotic Bcl-2 proteins is one of the molecular mechanisms protecting cancer cells from apoptosis. Recently, small molecules targeting the anti-apoptotic Bcl-2 family proteins have been identified, and with venetoclax the first of these BH3 mimetics has been approved for the treatment of leukemia. In solid tumors the anti-apoptotic Bcl-2 family proteins Mcl-1 and Bcl-xL are frequently overexpressed or genetically amplified. In this review, we summarize the role of Mcl-1 and Bcl-xL in solid tumors and compare the different BH3 mimetics targeting Mcl-1 or Bcl-xL.

Persistent hepatocyte apoptosis promotes tumorigenesis from diethylnitrosamine-transformed hepatocytes through increased oxidative stress, independent of compensatory liver regeneration

Hepatocellular carcinoma highly occurs in chronic hepatitis livers, where hepatocyte apoptosis is frequently detected. Apoptosis is a mechanism that eliminates mutated cells. Hepatocyte apoptosis induces compensatory liver regeneration, which is believed to contribute to tumor formation. Hepatocyte-specific Mcl-1 knockout mice (Mcl-1^Δhep mice) developed persistent hepatocyte apoptosis and compensatory liver regeneration with increased oxidative stress in adulthood but had not yet developed hepatocyte apoptosis at the age of 2 weeks. When diethylnitrosamine (DEN) was administered to 2-week-old Mcl-1^Δhep mice, multiple liver tumors were formed at 4 months, while wild-type mice did not develop any tumors. These tumors contained the B-Raf V637E mutation, indicating that DEN-initiated tumorigenesis was promoted by persistent hepatocyte apoptosis. When N-acetyl-L-cysteine was given from 6 weeks of age, DEN-administered Mcl-1^Δhep mice had reduced oxidative stress and suppressed tumorigenesis in the liver but showed no changes in hepatocyte apoptosis or proliferation. In conclusion, enhanced tumor formation from DEN-transformed hepatocytes by persistent hepatocyte apoptosis is mediated by increased oxidative stress, independent of compensatory liver regeneration. For patients with livers harboring transformed cells, the control of oxidative stress may suppress hepatocarcinogenesis based on chronic liver injury.

The role of BCL-2 family proteins and therapeutic potential of BH3-mimetics in malignant pleural mesothelioma

Introduction: With limited recent therapeutic changes, malignant pleural mesothelioma (MPM) is associated with poor survival and death within 12 months, making it one of the most lethal malignancies. Due to unregulated asbestos use in developing countries and home renovation exposures, cases of MPM are likely to present for decades. As MPM is largely driven by dysregulation of tumor suppressor genes, researchers have examined other mechanisms of subverting tumor proliferation and spread. Over-expression of pro-survival BCL-2 family proteins impairs cells from undergoing apoptosis, and BH3-mimetics  targeting them are a novel treatment option across various cancers, though have not been widely investigated in MPM.Areas covered: This review provides an overview of MPM and its current treatment landscape. It summarizes the role of BCL-2 family proteins in tumorigenesis and the therapeutic potential of BH3-mimetics . Finally, it discusses the role of BCL-2 proteins in MPM and the pre-clinical rationale for investigating BH3-mimetics as a therapeutic strategy.Expert opinion: As a disease without readily actionable oncogene driver mutations and with modest benefit from immune checkpoint inhibition, novel therapeutic options are urgently needed for MPM. Hence, BH3-mimetics provide a promising treatment option, with evidence supporting dependence on pro-survival BCL-2 proteins for MPM cell survival.

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.

Myeloid cell leukemin-1 inhibitors: a growing arsenal for cancer therapy

B-cell lymphoma-2 (Bcl-2) family proteins, comprising proapoptotic proteins (Bax and Bak), antiapoptotic proteins (Bcl-2, Bcl-X_L, Bcl-w, Mcl-1, and A1) and BCL-2 homology domain 3 (BH3)-only proteins (Bid, Noxa, and Puma), have long been identified as pivotal apoptosis regulators. As an antiapoptotic member, myeloid cell leukemin-1 (Mcl-1) can bind with proapoptotic proteins and inhibit apoptosis. Mcl-1 is frequently overexpressed and closely associated with oncogenesis and poor prognosis in several cancers, posing a tremendous obstacle for cancer therapy. Recently, an increasing number of Mcl-1-selective small-molecule inhibitors have entered preclinical studies and advanced into clinical trials. In this review, we briefly introduce the role of Mcl-1 in apoptosis and highlight the recent development of Mcl-1 small-molecule inhibitors.

Ubiquitination and deubiquitination of MCL1 in cancer: deciphering chemoresistance mechanisms and providing potential therapeutic options

MCL1 is an important antiapoptotic member of the BCL-2 family that is distinguishable from other family members based on its relatively short half-life. Emerging studies have revealed the crucial role of MCL1 in the chemoresistance of cancer cells. The antiapoptotic function of MCL1 makes it a popular therapeutic target, although specific inhibitors have begun to emerge only recently. Notably, emerging studies have reported that several E3 ligases and deubiquitinases modulate MCL1 stability, providing an alternate means of targeting MCL1 activity. In addition, the emergence and development of proteolysis-targeting chimeras, the function of which is based on ubiquitination-mediated degradation, has shown great potential. In this review, we provide an overview of the studies investigating the ubiquitination and deubiquitination of MCL1, summarize the latest evidence regarding the development of therapeutic strategies targeting MCL1 in cancer treatment, and discuss the promising future of targeting MCL1 via the ubiquitin–proteasome system in clinical practice.

Roseotoxin B alleviates cholestatic liver fibrosis through inhibiting PDGF-B/PDGFR-β pathway in hepatic stellate cells

Identifying effective anti-fibrotic therapies is a major clinical need that remains unmet. In the present study, roseotoxin B was shown to possess an improving effect on cholestatic liver fibrosis in bile duct–ligated mice, as proved by histochemical and immunohistochemical staining, hepatic biochemical parameters, and TUNEL apoptotic cell detection in tissue sections. Using cellular thermal shift assay, computational molecular docking, microscale thermophoresis technology, and surface plasmon resonance biosensor, we confirmed that PDGFR-β was a direct target of roseotoxin B in fibrotic livers. Of note, human tissue microarrays detected pathologically high expression of p-PDGFR-β in liver samples of ~80% of patients with liver fibrosis and cirrhosis. PDGF-B/PDGFR-β pathway promotes transdifferentiation and excessive proliferation of hepatic stellate cells (HSCs), which is a very crucial driver for liver fibrosis. Meaningfully, roseotoxin B blocked the formation of PDGF-BB/PDGFR-ββ complex by targeting the D2 domain of PDGFR-β, thereby inhibiting the PDGF-B/PDGFR-β pathway in HSCs. In summary, our study provided roseotoxin B as a unique candidate agent for the treatment of liver fibrosis.

Toward Targeting Antiapoptotic MCL-1 for Cancer Therapy

Apoptosis is critical for embryonic development, tissue homeostasis, and the removal of infected or otherwise dangerous cells. It is controlled by three subgroups of the BCL-2 protein family—the BH3-only proteins that initiate cell death; the effectors of cell killing, BAX and BAK; and the antiapoptotic guardians, including MCL-1 and BCL-2. Defects in apoptosis can promote tumorigenesis and render malignant cells refractory to anticancer therapeutics. Activation of cell death by inhibiting antiapoptotic BCL-2 family members has emerged as an attractive strategy for cancer therapy, with the BCL-2 inhibitor venetoclax leading the way. Large-scale cancer genome analyses have revealed frequent amplification of the locus encoding antiapoptotic MCL-1 in human cancers, and functional studies have shown that MCL-1 is essential for the sustained survival and expansion of many types of tumor cells. Structural analysis and medicinal chemistry have led to the development of three distinct small-molecule inhibitors of MCL-1 that are currently undergoing clinical testing.

Hepatoprotective effects of Shilajit on high fat-diet induced non-alcoholic fatty liver disease (NAFLD) in rats

Background Non-alcoholic fatty liver disease (NAFLD) is the main common cause of chronic liver disease. The aim of this study is to evaluate the effect of Shilajit, a medicine of Ayurveda, on the liver damage caused by NAFLD. Materials and methods Forty male Wistar rats, after being established as fatty liver models by feeding a high-fat diet (HFD, 12 weeks), were divided randomly into five groups as follows: control (standard diet), vehicle (HFD + distilled water), high-dose Shilajit (HFD + 250 mg/kg Shilajit), low-dose Shilajit (HFD + 150 mg/kg Shilajit) and pioglitazone (HFD + 10 mg/kg pioglitazone). The serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), triglycerides (TG), total cholesterol (TC), low-density lipoprotein (LDL), glucose and liver glutathione peroxidase (GPx), superoxide dismutase (SOD) activity, malondialdehyde (MDA) levels, liver weight, and histopathological manifestation outcomes were measured after the 2-week intervention. Results Shilajit treatment significantly reduced the values of AST and ALT, TG, TC, LDL, glucose, liver weight, and steatosis, and instead, increased high-density lipoprotein (HDL) compared with the vehicle group (p < 0.05). Further, Shilajit treatment improved the adverse effects of HFD-induced histopathological changes in the liver as compared with the vehicle group (p < 0.001). MDA level and GPx activity increased but SOD activity decreased in the vehicle group compared with the control group (p < 0.05), while treatment with Shilajit restored the antioxidant/oxidant balance toward a significant increase in the antioxidant system in the Shilajit group (p < 0.05). Conclusions These findings suggest that Shilajit improved the histopathological NAFLD changes in the liver and indicated the potential applicability of Shilajit as a potent agent for NAFLD treatment.

Hepatocyte apoptosis is tumor promoting in murine nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease is the most common chronic liver disease and may progress to nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). The molecular determinants of this pathogenic progression, however, remain largely undefined. Since liver tumorigenesis is driven by apoptosis, we examined the effect of overt hepatocyte apoptosis in a mouse model of NASH using mice lacking myeloid cell leukemia 1 (Mcl1), a pro-survival member of the BCL-2 protein family. Hepatocyte-specific Mcl1 knockout (Mcl1^∆hep) mice and control littermates were fed chow or FFC (high saturated fat, fructose, and cholesterol) diet, which induces NASH, for 4 and 10 months. Thereafter, liver injury, inflammation, fibrosis, and tumor development were evaluated biochemically and histologically. Mcl1^∆hep mice fed with the FFC diet for 4 months displayed a marked increase in liver injury, hepatocyte apoptosis, hepatocyte proliferation, macrophage-associated liver inflammation, and pericellular fibrosis in contrast to chow-fed Mcl1^∆hep and FFC diet-fed Mcl1-expressing littermates. After 10 months of feeding, 78% of FFC diet-fed Mcl1^∆hep mice developed liver tumors compared to 38% of chow-fed mice of the same genotype. Tumors in FFC diet-fed Mcl1^∆hep mice were characterized by cytologic atypia, altered liver architecture, immunopositivity for glutamine synthetase, and histologically qualified as HCC. In conclusion, this study provides evidence that excessive hepatocyte apoptosis exacerbates the NASH phenotype with enhancement of tumorigenesis in mice.

Type 1 Innate Lymphoid Cells Protect Mice from Acute Liver Injury via Interferon-γ Secretion for Upregulating Bcl-xL Expression in Hepatocytes

Although type 1 innate lymphoid cells (ILC1s) have been originally found as liver-resident ILCs, their pathophysiological role in the liver remains poorly investigated. Here, we demonstrated that carbon tetrachloride (CCl₄) injection into mice activated ILC1s, but not natural killer (NK) cells, in the liver. Activated ILC1s produced interferon-γ (IFN-γ) and protected mice from CCl₄-induced acute liver injury. IFN-γ released from activated ILC1s promoted the survival of hepatocytes through upregulation of Bcl-xL. An activating NK receptor, DNAM-1, was required for the optimal activation and IFN-γ production of liver ILC1s. Extracellular adenosine triphosphate accelerated interleukin-12-driven IFN-γ production by liver ILC1s. These findings suggest that ILC1s are critical for tissue protection during acute liver injury.

A selective BCL-XL PROTAC degrader achieves safe and potent antitumor activity

BCL-X_L is a well-validated cancer target. However, the on-target and dose-limiting thrombocytopenia limits the use of BCL-X_L inhibitors such as ABT263 as safe and effective anticancer agents. To reduce the toxicity of ABT263, we converted it into DT2216, a BCL-X_L proteolysis targeting chimera (PROTAC), that targets BCL-X_L to the Von Hippel-Lindau (VHL) E3 ligase for degradation. We found that DT2216 was more potent against various BCL-X_L-dependent leukemia and cancer cells but significantly less toxic to platelets than ABT263 in vitro because VHL is poorly expressed in platelets. In vivo, DT2216 effectively inhibits the growth of several xenograft tumors as a single agent or in combination with other chemotherapeutic agents, without causing significant thrombocytopenia. These findings demonstrate the potential to use PROTAC technology to reduce on-target drug toxicities and rescue the therapeutic potential of previously undruggable targets. Furthermore, DT2216 may be developed as a safe first-in-class anticancer agent targeting BCL-X_L.

Beneficial Role of ROS in Cell Survival: Moderate Increases in H2O2 Production Induced by Hepatocyte Isolation Mediate Stress Adaptation and Enhanced Survival

High levels of reactive oxygen species (ROS) can lead to impairment of cell structure, biomolecules' loss of function and cell death and are associated with liver diseases. Cells that survive increased ROS often undergo malignant transformation. Many cancer cells tolerate high levels of ROS. Here we report a transiently increased production of H₂O₂ and concomitant upregulation of antioxidative enzymes triggered by hepatocyte isolation; the H₂O₂ levels revert in about two days in culture. Three-day survival rate of the isolated cells in the presence of 2.5-fold increase of H₂O₂ is almost 80%. Apoptosis activation through the mitochondrial pathway is meanwhile reduced by inhibition of caspase-9 triggering. This reduction depends on the amount of H₂O₂ production, as decreased production of H₂O₂ in the presence of an antioxidant results in increased apoptosis triggering. These stress adaptations do not influence urea production, which is unchanged throughout the normal and stress adapted phases. We conclude that hepatocytes' stress adaptation is mediated by increased ROS production. In this case, high ROS improve cell survival.

Harmonized Autophagy Versus Full-Fledged Hepatitis B Virus: Victorious or Defeated

Autophagy is a finely tuned process in the regulation of innate immunity to avoid excessive inflammatory responses and inflammasome signaling. In contrast, the results of recent studies have shown that autophagy may disease-dependently contribute to the pathogenesis of liver diseases, such as fibrosis, cirrhosis, and hepatocellular carcinoma (HCC) during hepatitis B virus (HBV) infection. HBV has learned to subvert the cell's autophagic machinery to promote its replication. Given the great impact of the autophagy mechanism on the HBV infection and HCC, recognizing these factors may be offered new hope for human intervention and treatment of chronic HBV. This review focuses on recent findings viewing the dual role of autophagy plays in the pathogenesis of HBV infected hepatocytes.