Multifaceted anticancer activity of BH3 mimetics: Current evidence and future prospects

Maximizing Anticancer Response with MPS1 and CENPE Inhibition Alongside Apoptosis Induction

Antimitotic compounds, targeting key spindle assembly checkpoint (SAC) components (e.g., MPS1, Aurora kinase B, PLK1, KLP1, CENPE), are potential alternatives to microtubule-targeting antimitotic agents (e.g., paclitaxel) to circumvent resistance and side effects associated with their use. They can be classified into mitotic blockers, causing SAC-induced mitotic arrest, or mitotic drivers, pushing cells through aberrant mitosis by overriding SAC. These drugs, although advancing to clinical trials, exhibit unsatisfactory cancer treatment outcomes as monotherapy, probably due to variable cell fate responses driven by cyclin B degradation and apoptosis signal accumulation networks. We investigated the impact of inhibiting anti-apoptotic signals with the BH3-mimetic navitoclax in lung cancer cells treated with the selective CENPE inhibitor GSK923295 (mitotic blocker) or the MPS1 inhibitor BAY1217389 (mitotic driver). Our aim was to steer treated cancer cells towards cell death. BH3-mimetics, in combination with both mitotic blockers and drivers, induced substantial cell death, mainly through apoptosis, in 2D and 3D cultures. Crucially, these synergistic concentrations were less toxic to non-tumor cells. This highlights the significance of combining BH3-mimetics with antimitotics, either blockers or drivers, which have reached the clinical trial phase, to enhance their effectiveness.

Technologies of targeting histone deacetylase in drug discovery: Current progress and emerging prospects

Histone deacetylases (HDACs) catalyze the hydrolysis of acetyl-l-lysine side chains in histones and non-histones, which are key to epigenetic regulation in humans. Targeting HDACs has emerged as a promising strategy for treating various types of cancer, including myeloma and hematologic malignancies. At present, numerous small molecule inhibitors targeting HDACs are actively being investigated in clinical trials. Despite their potential efficacy in cancer treatment, HDAC inhibitors suffer from multi-directional selectivity and preclinical resistance issues. Hence, developing novel inhibitors based on cutting-edge medicinal chemistry techniques is essential to overcome these limitations and improve clinical outcomes. This manuscript presents an extensive overview of the properties and biological functions of HDACs in cancer, provides an overview of the current state of development and limitations of clinical HDAC inhibitors, and analyzes a range of innovative medicinal chemistry techniques that are applied. These techniques include selective inhibitors, dual-target inhibitors, proteolysis targeting chimeras, and protein-protein interaction inhibitors.

The novel small molecule BH3 mimetic nobiletin synergizes with vorinostat to induce apoptosis and autophagy in small cell lung cancer

Small cell lung cancer (SCLC) is a highly lethal subtype of lung cancer with few therapeutic options; therefore, the identification of new targets and drugs with potent combination therapy is desirable. We previously screened BH3 mimetics from a natural product library, and in this study, we validated nobiletin as a BH3 mimetic. Specifically, we observed its combination potential and mechanism with vorinostat in SCLC in vitro and in vivo. The results showed that combination treatment with nobiletin and vorinostat reduced the proliferation of SCLC H82 cells and increased the levels of apoptotic proteins such as cleaved caspase-9 and cleaved PARP. The combination treatment increased LC3-II expression and induced autophagic cell death. In addition, this treatment significantly inhibited H82 cell xenograft SCLC tumor growth in nude mice. The combination treatment with nobiletin and vorinostat efficiently increased autophagy by inhibiting the PI3K-AKT-mTOR pathway and promoting dissociation of the BCL-2 and Beclin 1 complex, increasing the level of isolated Beclin 1 to stimulate autophagy. Molecular docking and surface plasmon resonance analysis showed that nobiletin stably bound to the BCL-2, BCL-XL and MCL-1 proteins with high affinity in a concentration-dependent manner. These results suggest that nobiletin is a BH3-only protein mimetic. Furthermore, the combination of nobiletin with vorinostat increased histone H3K9 and H3K27 acetylation levels in SCLC mouse tumor tissue and enhanced the expression of the BH3-only proteins BIM and BID. We conclude that nobiletin is a novel natural BH3 mimetic that can cooperate with vorinostat to induce apoptosis and autophagy in SCLC.

Involvement of necroptosis in the selective toxicity of the natural compound (±) gossypol on squamous skin cancer cells in vitro

Cutaneous basal and squamous cell carcinoma reflect the first and second most common type of non-melanoma skin cancer, respectively. Especially cutaneous squamous cell carcinoma has the tendency to metastasize, finally resulting in a rather poor prognosis. Therapeutic options comprise surgery, radiation therapy, and a systemic or targeted chemotherapy. There are some good treatment results, but overall, the response rate of newly developed drugs is still modest. Drug repurposing represents an alternative approach where already available and clinically approved substances are used, which originally intended for other clinical benefits. In this context, we tested the effect of the naturally occurring polyphenolic aldehyde (±) gossypol with concentrations between 1 and 5 µM on the invasive squamous cell carcinoma cell line SCL-1 and normal human epidermal keratinocytes. Gossypol treatment up to 96 h resulted in a selective cytotoxicity of SCL-1 cells (IC50: 1.7 µM, 96 h) compared with normal keratinocytes (IC50: ≥ 5.4 µM, 96 h) which is mediated by mitochondrial dysfunction and finally leading to necroptotic cell death. Taken together, gossypol shows a high potential as an alternative anticancer drug for the treatment of cutaneous squamous cell carcinoma.

Sequential Treatment with Temozolomide Plus Naturally Derived AT101 as an Alternative Therapeutic Strategy: Insights into Chemoresistance Mechanisms of Surviving Glioblastoma Cells

Glioblastoma (GBM) is a poorly treatable disease due to the fast development of tumor recurrences and high resistance to chemo- and radiotherapy. To overcome the highly adaptive behavior of GBMs, especially multimodal therapeutic approaches also including natural adjuvants have been investigated. However, despite increased efficiency, some GBM cells are still able to survive these advanced treatment regimens. Given this, the present study evaluates representative chemoresistance mechanisms of surviving human GBM primary cells in a complex in vitro co-culture model upon sequential application of temozolomide (TMZ) combined with AT101, the R(-) enantiomer of the naturally occurring cottonseed-derived gossypol. Treatment with TMZ+AT101/AT101, although highly efficient, yielded a predominance of phosphatidylserine-positive GBM cells over time. Analysis of the intracellular effects revealed phosphorylation of AKT, mTOR, and GSK3ß, resulting in the induction of various pro-tumorigenic genes in surviving GBM cells. A Torin2-mediated mTOR inhibition combined with TMZ+AT101/AT101 partly counteracted the observed TMZ+AT101/AT101-associated effects. Interestingly, treatment with TMZ+AT101/AT101 concomitantly changed the amount and composition of extracellular vesicles released from surviving GBM cells. Taken together, our analyses revealed that even when chemotherapeutic agents with different effector mechanisms are combined, a variety of chemoresistance mechanisms of surviving GBM cells must be taken into account.

Comparison of the efficacy of gossypol acetate enantiomers in rats with uterine leiomyoma

Gossypol acetate (GA), as the product of racemic gossypol and acetic acid conjugated by hydrogen bond, is hydrolyzed into gossypol to exert its effect on treating uterine leiomyoma (UL), which has been listed in China. But hypokalemia and mild changes of liver function limit its clinical application. It had been reported that the biological activities of gossypol optical isomers were different. In this study, we aimed to clarify whether there were differences in the efficacy of gossypol enantiomers and whether a single gossypol optical isomer could alleviate adverse reactions in the treatment of UL. The results indicated that (-)-GA and (+)-GA had significant therapeutic effect on rats with UL. Interestingly, (-)-GA could better significantly ameliorate the pathological structure, inhibit the secretion of estrogen, and downregulate the expression of estrogen receptor-alpha (ER-α) and progesterone receptor (PR) than (+)-GA. Additionally, (-)-GA could better evidently decrease the symptoms of abnormally elevated inflammatory factors caused by UL. In contrast, (-)-GA and (+)-GA had certain effects on potassium ion concentration in serum, liver and kidney function, and the effects of (+)-GA on liver function were more obvious than (-)-GA. These findings will be of great significance to the drug development of gossypol optical isomers.

The role of BCL-2 family proteins in regulating apoptosis and cancer therapy

Apoptosis, as a very important biological process, is a response to developmental cues or cellular stress. Impaired apoptosis plays a central role in the development of cancer and also reduces the efficacy of traditional cytotoxic therapies. Members of the B-cell lymphoma 2 (BCL-2) protein family have pro- or anti-apoptotic activities and have been studied intensively over the past decade for their importance in regulating apoptosis, tumorigenesis, and cellular responses to anticancer therapy. Since the inflammatory response induced by apoptosis-induced cell death is very small, at present, the development of anticancer drugs targeting apoptosis has attracted more and more attention. Consequently, the focus of this review is to summarize the current research on the role of BCL-2 family proteins in regulating apoptosis and the development of drugs targeting BCL-2 anti-apoptotic proteins. Additionally, the mechanism of BCL-2 family proteins in regulating apoptosis was also explored. All the findings indicate the potential of BCL-2 family proteins in the therapy of cancer.

Hypericin, a potential new BH3 mimetic

Many types of cancer such as prostate cancer, myeloid leukemia, breast cancer, glioblastoma display strong chemo resistance, which is supported by enhanced expression of multiple anti-apoptotic Bcl-2, Bcl-XL and Mcl-1 proteins. The viable anti-cancer strategies are based on developing anti-apoptotic Bcl-2 proteins inhibitors, BH3 mimetics. Our focus in past years has been on the investigating a new potential BH3 mimetic, Hypericin (Hyp). Hyp is a naturally occurring photosensitive compound used in photodynamic therapy and diagnosis. We have demonstrated that Hyp can cause substantial effects in cellular ultrastructure, mitochondria function and metabolism, and distribution of Bcl2 proteins in malignant and non-malignant cells. One of the possible mechanisms of Hyp action could be the direct interactions between Bcl-2 proteins and Hyp. We investigated this assumption by in silico computer modelling and in vitro fluorescent spectroscopy experiments with the small Bcl2 peptide segments designed to correspond to Bcl2 BH3 and BH1 domains. We show here that Hyp interacts with BH3 and BH1 peptides in concentration dependent manner, and shows the stronger interactions than known BH3 mimetics, Gossypol (Goss) and ABT-263. In addition, interactions of Hyp, Goss and ABT263, with whole purified proteins Bcl-2 and Mcl-1 by fluorescence spectroscopy show that Hyp interacts stronger with the Bcl-2 and less with Mcl-1 protein than Goss or ABT-263. This suggest that Hyp is comparable to other BH3 mimetics and could be explore as such. Hyp cytotoxicity was low in human U87 MG glioma, similar to that of ABT263, where Goss exerted sufficient cytotoxicity, suggesting that Hyp acts primarily on Bcl-2, but not on Mcl-1 protein. In combination therapy, low doses of Hyp with Goss effectively decreased U87 MG viability, suggesting a possible synergy effect. Overall, we can conclude that Hyp as BH3 mimetic acts primarily on Bcl-2 protein and can be explored to target cells with Bcl-2 over-expression, or in combination with other BH3 mimetics, that target Mcl-1 or Bcl-XL proteins, in dual therapy.

All-Trans-Retinoic Acid Combined With Valproic Acid Can Promote Differentiation in Myeloid Leukemia Cells by an Autophagy Dependent Mechanism

Acute myeloid leukemia (AML) is an aggressive blood cancer with an overall survival of 30%. One form of AML, acute promyelocytic leukemia (APL) has become more than 90% curable with differentiation therapy, consisting of all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO). Application of differentiation therapy to other AML subtypes would be a major treatment advance. Recent studies have indicated that autophagy plays a key role in the differentiation of ATRA-responsive APL cells. In this study, we have investigated whether differentiation could be enhanced in ATRA resistant cells by promoting autophagy induction with valproic acid (VPA). ATRA sensitive (NB4) and resistant leukemia cells (NB4R and THP-1) were co-treated with ATRA and valproic acid, followed by assessment of autophagy and differentiation. The combination of VPA and ATRA induced autophagic flux and promoted differentiation in ATRA-sensitive and -resistant cell lines. shRNA knockdown of ATG7 and TFEB autophagy regulators impaired both autophagy and differentiation, demonstrating the importance of autophagy in the combination treatment. These data suggest that ATRA combined with valproic acid can promote differentiation in myeloid leukemia cells by mechanism involving autophagy.

Induction of multiple subroutines of regulated necrosis in murine macrophages by natural BH3-mimetic gossypol

Macrophages are critical sentinel cells armed with multiple regulated necrosis pathways, including pyroptosis, apoptosis followed by secondary necrosis, and necroptosis, and are poised to undergo distinct form(s) of necrosis for tackling dangers of pathogenic infection or toxic exposure. The natural BH3-mimetic gossypol is a toxic phytochemical that can induce apoptosis and/or pyroptotic-like cell death, but what exact forms of regulated necrosis are induced remains largely unknown. Here we demonstrated that gossypol induces pyroptotic-like cell death in both unprimed and lipopolysaccharide-primed mouse bone marrow-derived macrophages (BMDMs), as evidenced by membrane swelling and ballooning accompanied by propidium iodide incorporation and lactic acid dehydrogenase release. Notably, gossypol simultaneously induces the activation of both pyroptotic and apoptotic (followed by secondary necrosis) pathways but only weakly activates the necroptosis pathway. Unexpectedly, gossypol-induced necrosis is independent of nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, as neither inhibitor for the NLRP3 pathway nor NLRP3 deficiency protects the macrophages from the necrosis. Furthermore, necrotic inhibitors or even pan-caspase inhibitor alone does not or only partly inhibit such necrosis. Instead, a combination of inhibitors composed of pan-caspase inhibitor IDN-6556, RIPK3 inhibitor GSK'872 and NADPH oxidase inhibitor GKT137831 not only markedly inhibits the necrosis, with all apoptotic and pyroptotic pathways being blocked, but also attenuates gossypol-induced peritonitis in mice. Lastly, the activation of the NLRP3 pathway and apoptotic caspase-3 appears to be independent of each other. Collectively, gossypol simultaneously induces the activation of multiple subroutines of regulated necrosis in macrophages depending on both apoptotic and inflammatory caspases.

Lipids modulate the BH3-independent membrane targeting and activation of BAX and Bcl-xL

Regulation of apoptosis is tightly linked with the targeting of numerous Bcl-2 proteins to the mitochondrial outer membrane (MOM), where their activation or inhibition dictates cell death or survival. According to the traditional view of apoptotic regulation, BH3-effector proteins are indispensable for the cytosol-to-MOM targeting and activation of proapoptotic and antiapoptotic members of the Bcl-2 protein family. This view is challenged by recent studies showing that these processes can occur in cells lacking BH3 effectors by as yet to be determined mechanism(s). Here, we exploit a model membrane system that recapitulates key features of MOM to demonstrate that the proapoptotic Bcl-2 protein BAX and antiapoptotic Bcl-xL have an inherent ability to interact with membranes in the absence of BH3 effectors, but only in the presence of cellular concentrations of Mg²⁺/Ca²⁺ Under these conditions, BAX and Bcl-xL are selectively targeted to membranes, refolded, and activated in the presence of anionic lipids especially the mitochondrial-specific lipid cardiolipin. These results provide a mechanistic explanation for the mitochondrial targeting and activation of Bcl-2 proteins in cells lacking BH3 effectors. At cytosolic Mg²⁺ levels, the BH3-independent activation of BAX could provide localized amplification of apoptotic signaling at regions enriched in cardiolipin (e.g., contact sites between MOM and mitochondrial inner membrane). Increases in MOM cardiolipin, as well as cytosolic [Ca²⁺] during apoptosis could further contribute to its MOM targeting and activity. Meanwhile, the BH3-independent targeting and activation of Bcl-xL to the MOM is expected to counter the action of proapoptotic BAX, thereby preventing premature commitment to apoptosis.

Advances in autophagy as a target in the treatment of tumours

Autophagy is a multi-step lysosomal degradation process, which regulates energy and material metabolism and has been used to maintain homeostasis. Autophagy has been shown to be involved in the regulation of health and disease. But at present, there is no consensus on the relationship between autophagy and tumour, and we consider that it plays a dual role in the occurrence and development of tumour. That is to say, under certain conditions, it can inhibit the occurrence of tumour, but it can also promote the process of tumour. Therefore, autophagy could be used as a target for tumour treatment. The regulation of autophagy plays a synergistic role in the radiotherapy, chemotherapy, phototherapy and immunotherapy of tumour, and nano drug delivery system provides a promising strategy for improving the efficacy of autophagy regulation. This review summarised the progress in the regulatory pathways and factors of autophagy as well as nanoformulations as carriers for the delivery of autophagy modulators.

Celecoxib Analogues for Cancer Treatment: An Update on OSU-03012 and 2,5-Dimethyl-Celecoxib

Cyclooxygenase-2 (COX-2) is an important enzyme involved in prostaglandins biosynthesis from arachidonic acid. COX-2 is frequently overexpressed in human cancers and plays a major tumor promoting function. Accordingly, many efforts have been devoted to efficiently target the catalytic site of this enzyme in cancer cells, by using COX-2 specific inhibitors such as celecoxib. However, despite their potent anti-tumor properties, the myriad of detrimental effects associated to the chronic inhibition of COX-2 in healthy tissues, has considerably limited their use in clinic. In addition, increasing evidence indicate that these anti-cancerous properties are not strictly dependent on the inhibition of the catalytic site. These findings have led to the development of non-active COX-2 inhibitors analogues aiming at preserving the antitumor effects of COX-2 inhibitors without their side effects. Among them, two celecoxib derivatives, 2,5-Dimethyl-Celecoxib and OSU-03012, have been developed and suggested for the treatment of viral (e.g., recently SARS-CoV-2), inflammatory, metabolic diseases and cancers. These molecules display stronger anti-tumor properties than celecoxib and thus may represent promising anti-cancer molecules. In this review, we discuss the impact of these two analogues on cancerous processes but also their potential for cancer treatment alone or in combination with existing approaches.

Aberrant Bcl-x splicing in cancer: from molecular mechanism to therapeutic modulation

Bcl-x pre-mRNA splicing serves as a typical example to study the impact of alternative splicing in the modulation of cell death. Dysregulation of Bcl-x apoptotic isoforms caused by precarious equilibrium splicing is implicated in genesis and development of multiple human diseases, especially cancers. Exploring the mechanism of Bcl-x splicing and regulation has provided insight into the development of drugs that could contribute to sensitivity of cancer cells to death. On this basis, we review the multiple splicing patterns and structural characteristics of Bcl-x. Additionally, we outline the cis-regulatory elements, trans-acting factors as well as epigenetic modifications involved in the splicing regulation of Bcl-x. Furthermore, this review highlights aberrant splicing of Bcl-x involved in apoptosis evade, autophagy, metastasis, and therapy resistance of various cancer cells. Last, emphasis is given to the clinical role of targeting Bcl-x splicing correction in human cancer based on the splice-switching oligonucleotides, small molecular modulators and BH3 mimetics. Thus, it is highlighting significance of aberrant splicing isoforms of Bcl-x as targets for cancer therapy.

Intrinsically Connected: Therapeutically Targeting the Cathepsin Proteases and the Bcl-2 Family of Protein Substrates as Co-regulators of Apoptosis

Taken with the growing importance of cathepsin-mediated substrate proteolysis in tumor biology and progression, the focus and emphasis placed on therapeutic design and development is coming into fruition. Underpinning this approach is the invariable progression from the direction of fully characterizing cathepsin protease members and their substrate targets, towards targeting such an interaction with tangible therapeutics. The two groups of such substrates that have gained much attention over the years are the pro- and anti- apoptotic protein intermediates from the extrinsic and intrinsic signaling arms of the apoptosis pathway. As proteins that are central to determining cellular fate, some of them present themselves as very favorable candidates for therapeutic targeting. However, considering that both anti- and pro- apoptotic signaling intermediates have been reported to be downstream substrates for certain activated cathepsin proteases, therapeutic targeting approaches based on greater selectivity do need to be given greater consideration. Herein, we review the relationships shared by the cathepsin proteases and the Bcl-2 homology domain proteins, in the context of how the topical approach of adopting 'BH3-mimetics' can be explored further in modulating the relationship between the anti- and pro- apoptotic signaling intermediates from the intrinsic apoptosis pathway and their upstream cathepsin protease regulators. Based on this, we highlight important future considerations for improved therapeutic design.

Effects of the Anti-Tumorigenic Agent AT101 on Human Glioblastoma Cells in the Microenvironmental Glioma Stem Cell Niche

Glioblastoma (GBM) is a barely treatable disease due to its profound chemoresistance. A distinct inter- and intratumoral heterogeneity reflected by specialized microenvironmental niches and different tumor cell subpopulations allows GBMs to evade therapy regimens. Thus, there is an urgent need to develop alternative treatment strategies. A promising candidate for the treatment of GBMs is AT101, the R(-) enantiomer of gossypol. The present study evaluates the effects of AT101, alone or in combination with temozolomide (TMZ), in a microenvironmental glioma stem cell niche model of two GBM cell lines (U251MG and U87MG). AT101 was found to induce strong cytotoxic effects on U251MG and U87MG stem-like cells in comparison to the respective native cells. Moreover, a higher sensitivity against treatment with AT101 was observed upon incubation of native cells with a stem-like cell-conditioned medium. This higher sensitivity was reflected by a specific inhibitory influence on the p-p42/44 signaling pathway. Further, the expression of CXCR7 and the interleukin-6 receptor was significantly regulated upon these stimulatory conditions. Since tumor stem-like cells are known to mediate the development of tumor recurrences and were observed to strongly respond to the AT101 treatment, this might represent a promising approach to prevent the development of GBM recurrences.

The BH3 mimetic (±) gossypol induces ROS-independent apoptosis and mitochondrial dysfunction in human A375 melanoma cells in vitro

A major challenge in current cancer therapy is still the treatment of metastatic melanomas of the skin. BH3 mimetics represent a novel group of substances inducing apoptosis. In this study, we investigated the cytotoxic effect of (±) gossypol (GP), a natural compound from cotton seed, on A375 melanoma cells and the underlying biochemical mechanisms. To prevent undesired side effects due to toxicity on normal (healthy) cells, concentrations only toxic for tumor cells have been elaborated. Viability assays were performed to determine the cytotoxicity of GP in A375 melanoma and normal (healthy) cells. For the majority of experiments, a concentration of 2.5 µM GP was used resulting in a ROS-independent but caspase-dependent cell death of A375 melanoma cells. At this level, GP was non-toxic for normal human epidermal melanocytes. GP has a very short half-life, however, it was demonstrated that only the “parent” compound and not decomposition products are responsible for the cytotoxic effect in A375 melanoma cells. GP significantly decreased mitochondrial membrane potential accompanied by a Drp1-dependent loss of mitochondrial integrity (fragmentation) in tumor cells. Taken together, GP induced a ROS-independent intrinsic apoptosis leading to the conclusion that within a specific concentration range, GP may work as effective anticancer drug without harmful side effects.

Lytic and sublytic effects of gossypol on red blood cells and thymocytes

Gossypol is a natural polyphenol presently considered as a promising biological phytochemical with a range of activities including anticancer. We examined volume regulation-dependent effects of gossypol using erythrocytes and thymic lymphocytes. Gossypol effectively lysed human red blood cells (RBC) with a half-maximal concentration of 67.4 ± 1.6 μmol/L and in a non-colloid osmotic manner. Sublytic gossypol doses of 1-10 μmol/L significantly protected RBC from osmotic hemolysis, but potentiated their sensitivity to the colloid-osmotic lysis induced by a pore-former nystatin. When added to the thymocytes suspension, gossypol caused a strong depression of the ability of cells to restore their volume under hypoosmotic stress with a half-maximal activity at 2.1 ± 0.3 μmol/L. Gossypol suppressed regulatory volume decrease under experimental conditions, when cationic permeability was controlled by gramicidin D, and volume recovery depended mainly on anionic conductance, suggesting that the polyphenol inhibits the swelling-induced anion permeability. In direct patch-clamp experiments, gossypol inhibited the volume-sensitive outwardly rectifying (VSOR) chloride channel in thymocytes and in human HCT116 and HeLa cells, possibly by a mechanism when gossypol molecule with a radius close to the size of channel pore plugs into the narrowest portion of the native VSOR chloride channel. Micromolar gossypol suppressed proliferation of thymocytes, HCT116 and HeLa cells. VSOR blockage may represent new mechanism of anticancer activity of gossypol in addition to its action as a BH3-mimetic.

AT101-Loaded Cubosomes as an Alternative for Improved Glioblastoma Therapy

Introduction

AT101, the R-(-)-enantiomer of the cottonseed-derived polyphenol gossypol, is a promising drug in glioblastoma multiforme (GBM) therapy due to its ability to trigger autophagic cell death but also to facilitate apoptosis in tumor cells. It does have some limitations such as poor solubility in water-based media and consequent low bioavailability, which affect its response rate during treatment. To overcome this drawback and to improve the anti-cancer potential of AT101, the use of cubosome-based formulation for AT101 drug delivery has been proposed. This is the first report on the use of cubosomes as AT101 drug carriers in GBM cells.

Materials and Methods

Cubosomes loaded with AT101 were prepared from glyceryl monooleate (GMO) and the surfactant Pluronic F-127 using the top-down approach. The drug was introduced into the lipid prior to dispersion. Prepared formulations were then subjected to complex physicochemical and biological characterization.

Results

Formulations of AT101-loaded cubosomes were highly stable colloids with a high drug entrapment efficiency (97.7%) and a continuous, sustained drug release approaching 35% over 72 h. Using selective and sensitive NMR diffusometry, the drug was shown to be efficiently bound to the lipid-based cubosomes. In vitro imaging studies showed the high efficiency of cubosomal nanoparticles uptake into GBM cells, as well as their marked ability to penetrate into tumor spheroids. Treatment of GBM cells with the AT101-loaded cubosomes, but not with the free drug, induced cytoskeletal rearrangement and shortening of actin fibers. The prepared nanoparticles revealed stronger in vitro cytotoxic effects against GBM cells (A172 and LN229 cell lines), than against normal brain cells (SVGA and HMC3 cell lines).

Conclusion

The results indicate that GMO-AT101 cubosome formulations are a promising basic tool for alternative approaches to GBM treatment.

Putting the Brakes on Tumorigenesis with Natural Products of Plant Origin: Insights into the Molecular Mechanisms of Actions and Immune Targets for Bladder Cancer Treatment

Bladder cancer is the 10th most commonly diagnosed cancer worldwide. Although the incidence in men is 4 times higher than that in women, the diagnoses are worse for women. Over the past 30 years, the treatment for bladder cancer has not achieved a significant positive effect, and the outlook for mortality rates due to muscle-invasive bladder cancer and metastatic disease is not optimistic. Phytochemicals found in plants and their derivatives present promising possibilities for cancer therapy with improved treatment effects and reduced toxicity. In this study, we summarize the promising natural products of plant origin with anti-bladder cancer potential, and their anticancer mechanisms—especially apoptotic induction—are discussed. With the developments in immunotherapy, small-molecule targeted immunotherapy has been promoted as a satisfactory approach, and the discovery of novel small molecules against immune targets for bladder cancer treatment from products of plant origin represents a promising avenue of research. It is our hope that this could pave the way for new ideas in the fields of oncology, immunology, phytochemistry, and cell biology, utilizing natural products of plant origin as promising drugs for bladder cancer treatment.

Therapeutic Potential of Autophagy Modulation in Cholangiocarcinoma

Autophagy is a multistep catabolic process through which misfolded, aggregated or mutated proteins and damaged organelles are internalized in membrane vesicles called autophagosomes and ultimately fused to lysosomes for degradation of sequestered components. The multistep nature of the process offers multiple regulation points prone to be deregulated and cause different human diseases but also offers multiple targetable points for designing therapeutic strategies. Cancer cells have evolved to use autophagy as an adaptive mechanism to survive under extremely stressful conditions within the tumor microenvironment, but also to increase invasiveness and resistance to anticancer drugs such as chemotherapy. This review collects clinical evidence of autophagy deregulation during cholangiocarcinogenesis together with preclinical reports evaluating compounds that modulate autophagy to induce cholangiocarcinoma (CCA) cell death. Altogether, experimental data suggest an impairment of autophagy during initial steps of CCA development and increased expression of autophagy markers on established tumors and in invasive phenotypes. Preclinical efficacy of autophagy modulators promoting CCA cell death, reducing invasiveness capacity and resensitizing CCA cells to chemotherapy open novel therapeutic avenues to design more specific and efficient strategies to treat this aggressive cancer.

Competitive glucose metabolism as a target to boost bladder cancer immunotherapy

Bladder cancer - the tenth most frequent cancer worldwide - has a heterogeneous natural history and clinical behaviour. The predominant histological subtype, urothelial bladder carcinoma, is characterized by high recurrence rates, progression and both primary and acquired resistance to platinum-based therapy, which impose a considerable economic burden on health-care systems and have substantial effects on the quality of life and the overall outcomes of patients with bladder cancer. The incidence of urothelial tumours is increasing owing to population growth and ageing, so novel therapeutic options are vital. Based on work by The Cancer Genome Atlas project, which has identified targetable vulnerabilities in bladder cancer, immune checkpoint inhibitors (ICIs) have arisen as an effective alternative for managing advanced disease. However, although ICIs have shown durable responses in a subset of patients with bladder cancer, the overall response rate is only ~15-25%, which increases the demand for biomarkers of response and therapeutic strategies that can overcome resistance to ICIs. In ICI non-responders, cancer cells use effective mechanisms to evade immune cell antitumour activity; the overlapping Warburg effect machinery of cancer and immune cells is a putative determinant of the immunosuppressive phenotype in bladder cancer. This energetic interplay between tumour and immune cells leads to metabolic competition in the tumour ecosystem, limiting nutrient availability and leading to microenvironmental acidosis, which hinders immune cell function. Thus, molecular hallmarks of cancer cell metabolism are potential therapeutic targets, not only to eliminate malignant cells but also to boost the efficacy of immunotherapy. In this sense, integrating the targeting of tumour metabolism into immunotherapy design seems a rational approach to improve the therapeutic efficacy of ICIs.

The Role of the BCL-2 Family of Proteins in HIV-1 Pathogenesis and Persistence

Advances in HIV-1 therapy have transformed the once fatal infection into a manageable, chronic condition, yet the search for a widely applicable approach to cure remains elusive. The ineffectiveness of antiretroviral therapy (ART) in reducing the size of the HIV-1 latent reservoir has prompted investigation into the mechanisms of HIV-1 latency and immune escape. One of the major regulators of apoptosis, the BCL-2 protein, alongside its homologous family members, is a major target of HIV-1-induced change. Recent studies have now demonstrated the association of this protein with cells that support proviral forms in the setting of latency and have helped identify BCL-2 as a novel and promising therapeutic target for HIV-1 therapy directed at possible cure. This review aims to systematically review the interactions of HIV-1 with BCL-2 and its homologs and to examine the possibility of using BCL-2 inhibitors in the study and elimination of the latent reservoir.

Combined treatment of AT101 and demethoxycurcumin yields an enhanced anti-proliferative effect in human primary glioblastoma cells

PURPOSE

Glioblastoma multiforme (GBM) is a poorly curable disease due to its profound chemoresistance. Despite recent advances in surgery, radiotherapy and chemotherapy, the efficient treatment of GBMs is still a clinical challenge. Beside others, AT101, the R-(-) enantiomer of gossypol, and demethoxycurcumin (DMC), a curcumin-related demethoxy compound derived from Curcuma longa, were considered as possible alternative drugs for GBM therapy.

METHODS

Using different human primary GBM cell cultures in a long-term stimulation in vitro model, the cytotoxic and anti-proliferative effects of single and combined treatment with 5 µM AT101 and 5 µM or 10 µM DMC were investigated. Furthermore, western blots on pAkt and pp44/42 as well as JC-1 staining and real-time RT-PCR were performed to understand the influence of the treatment at the molecular and gene level.

RESULTS

Due to enhanced anti-proliferative effects, we showed that combined therapy with both drugs was superior to a single treatment with AT101 or DMC. Here, by determination of the combination index, a synergism of the combined drugs was detectable. Phosphorylation and thereby activation of the kinases p44/42 and Akt, which are involved in proliferation and survival processes, were inhibited, the mitochondrial membrane potential of the GBM cells was altered, and genes involved in dormancy-associated processes were regulated by the combined treatment strategy.

CONCLUSION

Combined treatment with different drugs might be an option to efficiently overcome chemoresistance of GBM cells in a long-term treatment strategy.

Mimicking Strategy for Protein-Protein Interaction Inhibitor Discovery by Virtual Screening

As protein–protein interactions (PPIs) are highly involved in most cellular processes, the discovery of PPI inhibitors that mimic the structure of the natural protein partners is a promising strategy toward the discovery of PPI inhibitors. In this review, we discuss recent advances in the application of virtual screening for identifying mimics of protein partners. The classification and function of the mimicking protein partner inhibitor discovery by virtual screening are described. We anticipate that this review would be of interest to medicinal chemists and chemical biologists working in the field of protein–protein interaction inhibitors or probes.

MCL1 regulates cell death, tumor growth and chemosensitivity to sabutoclax in ovarian adenocarcinoma

This research was conducted to study the role of MCL1 in ovarian adenocarcinoma cell death and survival as well as chemosensitivity to sabutoclax. Both in vitro and in vivo assays including qRT-PCR, Western blot, CCK-8, caspase 3/7 activation, colony foci formation assay and xenograft assay were conducted. Except for the xenograft assay, the other experiments were conducted at the cellular level and they were carried out to assess cell activities such as viability, programmed death and proliferation. SKOV3 and OVCAR3 cell lines were used as the cell models for all experiments. It was proved that MCL1 was overexpressed in ovarian adenocarcinoma (tissues and cells) at RNA and protein levels. MCL1 knockdown was also discovered to suppress the viability and proliferation of ovarian adenocarcinoma cells in vivo and in vitro. Lastly, it was found that MCL1 knockdown significantly promoted ovarian carcinoma cell death and the sensitivity to sabutoclax. Thus, we concluded that MCL1 acted as a cancer facilitator in ovarian adenocarcinoma and it is also a suppressor of sabutoclax sensitivity.

Proteasome-Independent Protein Knockdown by Small-Molecule Inhibitor for the Undruggable Lung Adenocarcinoma

Therapeutic target identification and corresponding drug development is a demanding task for the treatment of lung adenocarcinoma, especially the most malignant proximal-proliferative subtype without druggable protein kinase mutations. Using a cell-SELEX-generated aptamer, we discovered a new tumor driver protein, leucine-rich pentatricopeptide repeat-containing protein (LRPPRC), which is specifically overexpressed in the most lethal subtype of lung adenocarcinoma. Targeted LRPPRC protein knockdown is a promising therapeutic strategy for the undruggable LUAD (lung adenocarcinoma). Nevertheless, LRPPRC is mainly located in mitochondria and degraded by protease. Current protein knockdown approaches, such as proteolysis-targeting chimeras (PROTACs), have limitations in their applications to the proteins degraded through proteasome-independent ways. Here, we designed an aptamer-assisted high-throughput method to screen small molecules that could bind to LRPPRC directly, disrupt the interaction of LRPPRC with its stabilizing chaperon protein, and lead to LRPPRC degradation by mitochondrial protease. The screened compound, gossypolacetic acid (GAA), is an old medicine that can accomplish the new function for targeted LRPPRC knockdown. It showed significant antitumor effects even with the LRPPRC-positive patient-derived tumor xenograft (PDX) model. This work not only extended the application of aptamers to screen small-molecule inhibitors for the undruggable lung cancers, but more importantly provided a new strategy to develop protein knockdown methods beyond the proteasome system.

Targeting Autophagy for Cancer Treatment and Tumor Chemosensitization

Autophagy is a tightly regulated catabolic process that facilitates nutrient recycling from damaged organelles and other cellular components through lysosomal degradation. Deregulation of this process has been associated with the development of several pathophysiological processes, such as cancer and neurodegenerative diseases. In cancer, autophagy has opposing roles, being either cytoprotective or cytotoxic. Thus, deciphering the role of autophagy in each tumor context is crucial. Moreover, autophagy has been shown to contribute to chemoresistance in some patients. In this regard, autophagy modulation has recently emerged as a promising therapeutic strategy for the treatment and chemosensitization of tumors, and has already demonstrated positive clinical results in patients. In this review, the dual role of autophagy during carcinogenesis is discussed and current therapeutic strategies aimed at targeting autophagy for the treatment of cancer, both under preclinical and clinical development, are presented. The use of autophagy modulators in combination therapies, in order to overcome drug resistance during cancer treatment, is also discussed as well as the potential challenges and limitations for the use of these novel therapeutic strategies in the clinic.

The Incomplete Puzzle of the BCL2 Proteins

The proteins of the BCL2 family are key players in multiple cellular processes, chief amongst them being the regulation of mitochondrial integrity and apoptotic cell death. These proteins establish an intricate interaction network that expands both the cytosol and the surface of organelles to dictate the cell fate. The complexity and unpredictability of the BCL2 interactome resides in the large number of family members and of interaction surfaces, as well as on their different behaviours in solution and in the membrane. Although our current structural knowledge of the BCL2 proteins has been proven therapeutically relevant, the precise structure of membrane-bound complexes and the regulatory effect that membrane lipids exert over these proteins remain key questions in the field. Here, we discuss the complexity of BCL2 interactome, the new insights, and the black matter in the field.

The novel small molecular BH3 mimetics SM3 and its regulation of cell apoptosis and autophagy

Bcl-2 family proteins play an important role in regulation of the cell survival and death. The inhibition of the anti-apoptotic proteins of Bcl-2 family leads to the apoptosis of cancer. BH3 mimetics have been developed targeting anti-apoptotic proteins of Bcl-2 family as small molecular drugs. It has been proved that BH3 mimetics has effect on apoptosis and proliferation in leukemia and some of them has been used in phase one or two clinical trials. Besides, with the development of the research on autophagic cell death, the antagonism and the synergism of autophagy and apoptosis is significant in cell death. As a hub of these two pathways of cell death, Bcl-2 protein is a potential target in basic research and clinical applications. In our studies, we found 32 potential BH3 mimetics compounds from 140,000 small molecular compounds via pharmacophore-based virtual screening. Furthermore, we demonstrated SM3, one of the 32 potential BH3 mimetics, induced autophagy and apoptosis simultaneously in dose-time dependence in A549 cell. SM3 induced apoptosis by intrinsic apoptosis pathway and induced autophagy by weakening the interaction between Beclin-1 and Bcl-2 complex. We wish to provide evidences and clues for the structural optimizing and further study of new compounds in the future.

Importance of Hypericin-Bcl2 interactions for biological effects at subcellular levels

Hypericin (Hyp) is a naturally occurring compound used as photosensitizer in photodynamic therapy and diagnosis. Recently, we have shown that Hyp presence alone, without illumination, resulted in substantial biological effects at several sub-cellular levels. Hyp induced changes in cellular ultrastructure, mitochondria function and metabolism, and distribution of Bcl2 proteins in malignant and non-malignant cells. The molecular mechanisms that underlie Hyp light-independent effects are still elusive. We have hypothesized that Bcl2-Hyp interactions might be one possible mechanism. We performed molecular docking studies to determine the Hyp-Bcl2 interaction profile. Based on the interaction profiles small Bcl2 peptide segments were selected for further study. We designed small peptides corresponding to Bcl2 BH3 and BH1 domains and tested the binding of Hyp and Bcl2 known inhibitor, ABT263, to the peptides in computer modeling and in vitro binding studies. We employed endogenous tryptophan and tyrosine in the BH3 and BH1 peptides, respectively, and their fluorescent properties to show interaction with Hyp and ABT263. Overall, our results indicate that Hyp can interact with Bcl2 protein at its BH3-BH1 hydrophobic groove, and this interaction may trigger changes in intracellular distribution of Bcl2 proteins. In addition, our computer modeling results suggest that Hyp also interacts with other anti-apoptotic members of Bcl2 family similar to the known BH3 mimetics. Our findings are novel and might contribute to understanding Hyp light-independent effects. In addition, they may substantiate the therapeutic use of Hyp as a BH3 mimetic molecule to enhance other cancer treatments.

A phase I study of AT-101, a BH3 mimetic, in combination with paclitaxel and carboplatin in solid tumors

Background AT-101 is a BH3 mimetic that inhibits the heterodimerization of Bcl-2, Bcl-xL, Bcl-W, and Mcl-1 with pro-apoptotic proteins, thereby lowering the threshold for apoptosis. This phase I trial investigated the MTD of AT-101 in combination with paclitaxel and carboplatin in patients with advanced solid tumors. Methods Patients were treated with AT-101 (40 mg) every 12 h on days 1, 2 and 3 of each cycle combined with varying dose levels (DL) of paclitaxel and carboplatin [DL1: paclitaxel (150 mg/m²) and carboplatin (AUC 5) on day 1 of each cycle; DL2: paclitaxel (175 mg/m²) and carboplatin (AUC 6) on day 1 of each cycle]. Secondary objectives included characterizing toxicity, efficacy, pharmacokinetics, and pharmacodynamics of the combination. Results Twenty-four patients were treated across two DLs with a planned expansion cohort. The most common tumor type was prostate (N = 11). Two patients experienced DLTs: grade 3 abdominal pain at DL1 and grade 3 ALT increase at DL2; however, the MTD was not determined. Moderate hematologic toxicity was observed. One CR was seen in a patient with esophageal cancer and 4 patients achieved PRs (1 NSCLC, 3 prostate). PD studies did not yield statistically significant decreases in Bcl-2 and caspase 3 protein levels, or increased apoptotic activity induced by AT-101. Conclusion The combination of AT-101 at 40 mg every 12 h on days 1, 2 and 3 combined with paclitaxel and carboplatin was safe and tolerable. Based on the modest clinical efficacy seen in this trial, this combination will not be further investigated. Clinical Trial Registration: NCT00891072, CTEP#: 8016.

The Interplay of Autophagy and Tumor Microenvironment in Colorectal Cancer-Ways of Enhancing Immunotherapy Action

Autophagy as a primary homeostatic and catabolic process is responsible for the degradation and recycling of proteins and cellular components. The mechanism of autophagy has a crucial role in several cellular functions and its dysregulation is associated with tumorigenesis, tumor-stroma interactions, and resistance to cancer therapy. A growing body of evidence suggests that autophagy is also a key regulator of the tumor microenvironment and cellular immune response in different types of cancer, including colorectal cancer (CRC). Furthermore, autophagy is responsible for initiating the immune response especially when it precedes cell death. However, the role of autophagy in CRC and the tumor microenvironment remains controversial. In this review, we identify the role of autophagy in tumor microenvironment regulation and the specific mechanism by which autophagy is implicated in immune responses during CRC tumorigenesis and the context of anticancer therapy.

Therapeutic implications of novel peptides targeting ER-mitochondria Ca2+-flux systems

Intracellular Ca²⁺-flux systems located at the ER-mitochondrial axis govern mitochondrial Ca²⁺ balance and cell fate. Multiple yet incurable pathologies are characterized by insufficient or excessive Ca²⁺ fluxes toward the mitochondria, in turn leading to aberrant cell life or death dynamics. The discovery and ongoing molecular characterization of the main interorganellar Ca²⁺ gateways have resulted in a novel class of peptide tools able to regulate relevant protein-protein interactions (PPIs) underlying this signaling scenario. Here, we review peptides, molecularly derived from Ca²⁺-flux systems or their accessory proteins. We discuss how they alter Ca²⁺-signaling protein complexes and modulate cell survival in light of their forthcoming therapeutic applications.

Balancing Apoptosis and Autophagy for Parkinson's Disease Therapy: Targeting BCL-2

Apoptosis and autophagy are important intracellular processes that maintain organism homeostasis and promote survival. Autophagy selectively degrades damaged cellular organelles and protein aggregates, while apoptosis removes damaged or aged cells. Maintaining a balance between autophagy and apoptosis is critical for cell fate, especially for long-lived cells such as neurons. Conversely, their imbalance is associated with neurodegenerative diseases such as Parkinson's disease (PD), which is characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Restoring the balance between autophagy and apoptosis is a promising strategy for the treatment of PD. Some core proteins engage in cross talk between apoptosis and autophagy, including B cell lymphoma (BCL)-2 family members. This Review summarizes the role of BCL-2 members in the regulation of apoptosis and autophagy and discusses potential therapeutic approaches that target this balance for PD treatment.

Reversing platinum resistance in ovarian cancer multicellular spheroids by targeting Bcl-2

Purpose

Peritoneal metastasis is the most common pathway for the spread of ovarian cancer. Ovarian cancer cells in ascites prefer to aggregate into the more chemoresistant multicellular spheroids (MCSs), leading to treatment failure and disease recurrence. We previously established a suspension MCS model of ovarian cancer cells in vitro and found that the MCS cells acquired drug resistance to cisplatin. In the present study, we aimed to uncover the underlying mechanism of the platinum resistance of MCS and the potential targets to reverse the drug resistance.

Materials and methods

MCS models were established for the phenotypic studies, including proliferation, invasion, migration, drug resistance, apoptosis assays, and signaling pathway analysis. The key molecule, Bcl-2, was screened by profile analysis and validated by Western blotting. siRNA was used to verify the anti-cisplatin-induced apoptosis effect of Bcl-2. The Bcl-2 inhibitor, ABT-737, was used for improving the sensitivity of MCS to cisplatin. The 50% inhibitory concentrations (IC50) were measured by viability assays treated with different concentrations of cisplatin. Flow cytometry and Western blotting were used for quantification of drug-induced apoptosis.

Results

The ovarian cancer MCS showed a proliferation-stagnant but invasive phenotype when resuspended. When treated with cisplatin, MCS cells showed much higher viability, with significantly fewer apoptotic cells than the adherent cells. Levels of Bcl-2 were upregulated in ovarian cancer ascitic cells and MCS cells. Bcl-2 knockdown by siRNA or blockage by ABT-737 enhanced the cisplatin-induced apoptosis and reduced the 50% inhibitory concentrations of cisplatin for MCS by 58.5% and 88.2%, respectively.

Conclusion

The upregulated Bcl-2 contributes to cisplatin resistance in our MCS model and targeting it sensitizes the MCS to cisplatin treatment. This provides us a preliminary treatment method for ovarian cancer peritoneal metastasis.

Rapid Imaging of BCL-2 Family Interactions in Live Cells Using FLIM-FRET

The Bcl-2 proteins control cell death via interchanging interactions within the Bcl-2 family. Fluorescence lifetime imaging microscopy (FLIM) is used to detect Förster resonance energy transfer (FRET) between two fluorescent-fusion proteins in live cells. FLIM-FRET has been used to detect specific interactions and their disruption, for Bcl-2 family proteins. To date, this has been possible only in low throughput, due to the time required for serial data acquisition. We developed an automated optical system with eight parallel detectors for rapid and efficient data collection. Here we describe how to use this system for FLIM-FRET imaging of Bcl-2 family protein interactions in a 384-well plate format.

Effect of the BH3 Mimetic Polyphenol (-)-Gossypol (AT-101) on the in vitro and in vivo Growth of Malignant Mesothelioma

Malignant mesothelioma (MM) is a primary tumor arising from mesothelial cells. The survival of MM patients following traditional chemotherapy is poor, thus innovative treatments for MM are needed. (-)-gossypol (AT-101) is a BH3 mimetic compound which possesses anti-tumoral activity by targeting multiple signaling transduction pathways. Several clinical trials employing AT-101 have been performed and some of them are still ongoing. Accordingly, we investigated the in vitro effects of AT-101 on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis and autophagy of human (MM-B1, H-Meso-1, and MM-F1) and mouse (#40a) MM cell lines. In addition, we explored the in vivo anti-tumor activities of AT-101 in a mouse model, in which the transplantation of MM cells induces ascites in the peritoneal space. AT-101 inhibited in vitro MM cells survival in a dose- and time-dependent manner and triggered autophagy, but the process was then blocked and was coincident with apoptosis activation. To confirm the effect of AT-101 in inducing the apoptosis of MM cells, MM cells were simultaneously treated with AT-101 and with the caspase inhibitor, Z-VAD-FMK. Z-VAD-FMK was able to significantly reduce the number of cells in the subG1 phase compared to the treatment with AT-101 alone. This result corroborates the induction of cell death by apoptosis following treatment with AT-101. Indeed, Western blotting results showed that AT-101 increases Bax/Bcl-2 ratio, modulates p53 expression, activates caspase 9 and the cleavage of PARP-1. In addition, the treatment with AT-101 was able to: (a) decrease the ErbB2 protein expression; (b) increase the EGFR protein expression; (c) affect the phosphorylation of ERK1/2, p38 and AKT; (d) stimulate JNK1/2 and c-jun phosphorylation. Our in vivo results showed that the intraperitoneal administration of AT-101 increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM therapies by employing AT-101 as an anticancer agent in combination with standard therapies.

High-Throughput Screens To Identify Autophagy Inducers That Function by Disrupting Beclin 1/Bcl-2 Binding

Autophagy, a lysosomal degradation pathway, plays a crucial role in cellular homeostasis, development, immunity, tumor suppression, metabolism, prevention of neurodegeneration, and lifespan extension. Thus, pharmacological stimulation of autophagy may be an effective approach for preventing or treating certain human diseases and/or aging. We sought to establish a method for developing new chemical compounds that specifically induce autophagy. To do this, we developed two assays to identify compounds that target a key regulatory node of autophagy induction-specifically, the binding of Bcl-2 (a negative regulator of autophagy) to Beclin 1 (an allosteric modulator of the Beclin 1/VPS34 lipid kinase complex that functions in autophagy initiation). These assays use either a split-luciferase assay to measure Beclin 1/Bcl-2 binding in cells or an AlphaLISA assay to directly measure direct Beclin 1/Bcl-2 binding in vitro. We screened two different chemical compound libraries, comprising ∼300 K compounds, to identify small molecules that disrupt Beclin 1/Bcl-2 binding and induce autophagy. Three novel compounds were identified that directly inhibit Beclin 1/Bcl-2 interaction with an IC₅₀ in the micromolar range and increase autophagic flux. These compounds do not demonstrate significant cytotoxicity, and they exert selectivity for disruption of Bcl-2 binding to the BH3 domain of Beclin 1 compared with the BH3 domain of the pro-apoptotic Bcl-2 family members, Bax and Bim. Thus, we have identified candidate molecules that serve as lead templates for developing potent and selective Beclin 1/Bcl-2 inhibitors that may be clinically useful as autophagy-inducing agents.

Effects of sequentially applied single and combined temozolomide, hydroxychloroquine and AT101 treatment in a long-term stimulation glioblastoma in vitro model

PURPOSE

Glioblastoma multiforme (GBM) is a poorly curable disease due to its heterogeneity that enables single cells to survive treatment regimen and initiate tumor regrowth. Although some progress in therapy has been achieved in the last years, the efficient treatment of GBMs is still a clinical challenge. Besides the standard therapeutic drug temozolomide (TMZ), quinoline-based antimalarial drugs such as hydroxychloroquine (HCQ) and BH3 mimetics such as AT101 were considered as possible drugs for GBM therapy.

METHODS

We investigated the effects of sequentially applied single and combined TMZ, HCQ and AT101 treatments in a long-term stimulation GBM in vitro model. We performed all investigations in parallel in human astrocytes and two differentially TMZ-responsive human GBM cell lines and adjusted used drug concentrations to known liquor/plasma concentrations in patients. We determined amounts of dead cells and still remaining growth rates and depicted our results in a heatmap-like summary to visualize which sequential long-term treatment schedule seemed to be most promising.

RESULTS

We showed that sequential stimulations yielded higher cytotoxicity and better tumor growth control in comparison to single TMZ treatment. This was especially the case for the sequences TMZ/HCQ and TMZ + AT101/AT101 which was as effective as the non-sequential combination TMZ + AT101. Importantly, those affected both less and more TMZ-responsive glioma cell lines, whilst being less harmful for astrocytes in comparison to single TMZ treatment.

CONCLUSIONS

Sequential treatment with mechanistically different acting drugs might be an option to reduce side effects in long-term treatment, for example in local administration approaches.

Autophagy inducers in cancer

Autophagy is a complex, physiological process devoted to degrade and recycle cellular components. Proteins and organelles are first phagocytized by autophagosomes, then digested in lysosomes, and finally recycled to be utilized again during cellular metabolism. Moreover, autophagy holds an important role in the physiopathology of several diseases. In cancer, excellent works demonstrated the dual functions of autophagy in tumour biology: autophagy activation can promote cancer cells survival (protective autophagy), or contribute to cancer cell death (cytotoxic/nonprotective autophagy). A better understanding of the dichotomy roles of autophagy in cancer biology can help to identify or design new drugs able to induce/enhance (or block) autophagic flux. These features will necessary be tissue-dependent and confined to a specific time of treatment. The intent of this review is to focus on the different potentialities of autophagy inducers in cancer prevention versus therapy in order to elicit a desirable clinical response. Few promising synthetic and natural compounds have been identified and the pros and cons of their role in autophagy regulation is reviewed here. In the complex framework of autophagy modulation, "connecting the dots" is not a simple work and the lack of clinical studies further complicates the scenario, but the final goal to obtain clinically relevant autophagy inducers can reveal an unexpected landscape.

Novel synthetic drugs currently in clinical development for chronic lymphocytic leukemia

INTRODUCTION

Over the last few years, several new synthetic drugs, particularly Bruton's tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K) and BCL-2 inhibitors have been developed and investigated in chronic lymphocytic leukemia (CLL). Areas covered: This review highlights key aspects of BTK, PI3K and BCL-2 inhibitors that are currently at various stages of preclinical and clinical development in CLL. A literature review of the MEDLINE database for articles in English concerning CLL, B-cell receptor, BCL-2 antagonists, BTK inhibitors and PI3K inhibitors, was conducted via PubMed. Publications from 2000 through July 2017 were scrutinized. The search terms used were acalabrutinib, ACP-196, BGB-3111, ONO-4059, GS-4059, duvelisib, IPI-145, TGR-1202, copanlisib, Bay 80-6946, buparlisib, BKM-120, BCL-2 inhibitors, venetoclax, ABT-263, navitoclax, CDK inhibitors, alvocidib, flavopiridol, dinaciclib, SCH 727,965, palbociclib, PD-0332991, in conjunction with CLL. Conference proceedings from the previous five years of the ASH and EHA Annual Scientific Meetings were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles. Expert opinion: The use of new synthetic drugs is a promising strategy for the treatment of CLL. Data from ongoing and future clinical trials will aid in better defining the status of new drugs in the treatment of CLL.

BH3 mimetics efficiently induce apoptosis in mouse basophils and mast cells

Basophil granulocytes and mast cells are recognized for their roles in immunity and are central effectors of diverse immunological disorders. Despite their similarities, there is emerging evidence for non-redundant roles of the circulating yet scarce basophils and tissue-resident mast cells, respectively. Because of their importance in allergic pathogenesis, specific induction of apoptosis in basophils and mast cells may represent an interesting novel treatment strategy. The pro-inflammatory cytokine interleukin-3 serves as a key factor for basophil and mouse mast cell survival. Interleukin-3 increases the expression of anti-apoptotic BCL-2 family members, such as BCL-2, BCL-X_L or MCL-1; however, little is known how strongly these individual proteins contribute to basophil survival. Here, we were applying small molecule inhibitors called BH3 mimetics, some of which show remarkable success in cancer treatments, to neutralize the function of anti-apoptotic BCL-2 family members. We observed that expression levels of anti-apoptotic BCL-2 proteins do not necessarily correlate with their respective importance for basophil survival. Whereas naive in vitro-differentiated mouse basophils efficiently died upon BCL-2 or BCL-X_L inhibition, interleukin-3 priming rendered the cells highly resistant toward apoptosis, and this could only be overcome upon combined targeting of BCL-2 and BCL-X_L. Of note, human basophils differed from mouse basophils as they depended on BCL-2 and MCL-1, but not on BCL-X_L, for their survival at steady state. On the other hand, and in contrast to mouse basophils, MCL-1 proved critical in mediating survival of interleukin-3 stimulated mouse mast cells, whereas BCL-X_L seemed dispensable. Taken together, our results indicate that by choosing the right combination of BH3 mimetic compounds, basophils and mast cells can be efficiently killed, even after stimulation with potent pro-survival cytokines such as interleukin-3. Because of the tolerable side effects of BH3 mimetics, targeting basophils or mast cells for apoptosis opens interesting possibilities for novel treatment approaches.