Cutting-Edge Apoptosis-Based Therapeutics

Insights Into Amentoflavone: A Natural Multifunctional Biflavonoid

Amentoflavone is an active phenolic compound isolated from Selaginella tamariscina over 40 years. Amentoflavone has been extensively recorded as a molecule which displays multifunctional biological activities. Especially, amentoflavone involves in anti-cancer activity by mediating various signaling pathways such as extracellular signal-regulated kinase (ERK), nuclear factor kappa-B (NF-κB) and phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), and emerges anti-SARS-CoV-2 effect via binding towards the main protease (Mpro/3CLpro), spike protein receptor binding domain (RBD) and RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2. Therefore, amentoflavone is considered to be a promising therapeutic agent for clinical research. Considering the multifunction of amentoflavone, the current review comprehensively discuss the chemistry, the progress in its diverse biological activities, including anti-inflammatory, anti-oxidation, anti-microorganism, metabolism regulation, neuroprotection, radioprotection, musculoskeletal protection and antidepressant, specially the fascinating role against various types of cancers. In addition, the bioavailability and drug delivery of amentoflavone, the molecular mechanisms underlying the activities of amentoflavone, the molecular docking simulation of amentoflavone through in silico approach and anti-SARS-CoV-2 effect of amentoflavone are discussed.

Novel sulphonamide benzoquinazolinones as dual EGFR/HER2 inhibitors, apoptosis inducers and radiosensitizers

A series of sulphonamide benzoquinazolinones 5-18 was synthesized and evaluated for cytotoxic activity against MDA-MB-231 cell line. The compounds showed IC₅₀ ranging from 0.26 to 161.49 µM. The promising compounds were evaluated for their inhibitory profile against epidermal growth factor (EGFR) and HER2 enzymes. Compound 10 showed more potent activity on both EGFR and HER2 than erlotinib (IC₅₀ 3.90 and 5.40 µM versus 6.21 and 9.42 µM). The pro-apoptotic activity of 10 was evaluated against caspase-3, Bax, B-cell lymphoma protein 2 (Bcl-2) expression levels, and cell cycle analysis. Compound 10 increased the level of caspase-3 by 10 folds, Bax level by 9 folds, decreased the level of the Bcl-2 by 0.14 and arrested the cell cycle in the G2/M phase. The radio-sensitizing activity of 10 was measured using a single dose of 8 Gy gamma radiation (IC₅₀ decreased from 0.31 to 0.22 µM). Molecular docking was performed on EGFR and HER2 receptors.

Magnolol: A Neolignan from the Magnolia Family for the Prevention and Treatment of Cancer

The past few decades have witnessed widespread research to challenge carcinogenesis; however, it remains one of the most important health concerns with the worst prognosis and diagnosis. Increasing lines of evidence clearly show that the rate of cancer incidence will increase in future and will create global havoc, designating it as an epidemic. Conventional chemotherapeutics and treatment with synthetic disciplines are often associated with adverse side effects and development of chemoresistance. Thus, discovering novel economic and patient friendly drugs that are safe and efficacious is warranted. Several natural compounds have proved their potential against this dreadful disease so far. Magnolol is a hydroxylated biphenyl isolated from the root and stem bark of Magnolia tree. Magnolol can efficiently prevent or inhibit the growth of various cancers originating from different organs such as brain, breast, cervical, colon, liver, lung, prostate, skin, etc. Considering these perspectives, the current review primarily focuses on the fascinating role of magnolol against various types of cancers, and the source and chemistry of magnolol and the molecular mechanism underlying the targets of magnolol are discussed. This review proposes magnolol as a suitable candidate that can be appropriately designed and established into a potent anti-cancer drug.

Synthesis of novel dibenzoxanthene derivatives and observation of apoptosis in human hepatocellular cancer cells

We have synthesized dibenzoxanthene derivatives 2a-2i via nucleophilic substitution of methoxyl group and evaluated underlying antitumor molecular mechanism of target compounds. Compounds showed high cytotoxic activities against BEL-7402, A549, HeLa and MG-63 cancer cells in the µM range. These compounds inhibited the cell growth of BEL-7402 cells at S or G2/M phase. The compounds 2a-2i also induced the apoptosis of BEL-7402 cells. In addition, compounds enhanced the level of intramolecular ROS and decreased the mitochondrial membrane potential. Western blot analysis showed caspase-3 were activated and the expression of Bcl-2 and Bcl-xl was down-regulated. According to given results, these dibenzoxanthenes exhibited a broad spectrum of antiproliferative effects on various tumors and therapeutic efficacy. Molecular mechanism indicated that induction of apoptosis was associated with DNA fragmentation, ROS generation, mitochondria dysfunction. Compounds induced apoptosis in BEL-7402 cells through the intrinsic ROS-mediated mitochondrial pathway.

Pan-BH3 mimetic S1 exhibits broad-spectrum antitumour effects by cooperation between Bax and Bak

Small molecule S1 is a pan-BH3 mimetic that can bind antiapoptotic Bcl-2, Bcl-xL and Mcl-1 proteins. Herein, different Bcl-2 member expression cancer cell lines (NCI-H345, MCF-7, SMMC-7721 and Hela) and cells deficient in Bax and/or Bak by shRNA were used to unravel the cascade of events by which S1 promotes apoptosis compared with Bcl-2/Bcl-xL inhibitor ABT-737. We identified that S1 exhibited broader antitumour spectrum than ABT-737 through disruption of more Bcl-2 interactions including Mcl-1/Bak interaction. Moreover, the individual and combined roles of Bax and Bak in S1-induced apoptosis were revealed. Our results showed that S1 induced a Bak-mediated apoptosis. Bak played a predominant role in either S1 or ABT-737-induced apoptosis through the cooperation with Bax on the formation of large oligomers on mitochondrial membrane.

Diterpenylhydroquinones from natural ent-labdanes induce apoptosis through decreased mitochondrial membrane potential

In this study, we examined the cytotoxic effects of seven ent-labdane derivatives 1–7 (0–100 μM) in different human cancer cell lines. Our results showed that compounds 1–3 exhibited significant dose-dependent inhibition on the growth of the three different human cell lines, according to the sulphorhodamine B assay and produced morphological changes consistent with apoptosis, as confirmed by Hoestch 3342 staining analysis. They induced apoptosis in various cancer cell lines, as shown by nuclear condensation and fragmentation and caspase 3 activation. Such induction was associated with the depletion of mitochondrial membrane potential. These activities led to the cleavage of caspases and the trigger of cell death process. Overall, the compounds showed potent proapoptotic effects on the two different cancer cell lines, suggesting that the compounds deserve more extensive investigation of their potential medicinal applications.

Mitochondria in cancer: at the crossroads of life and death

Mitochondrial processes play an important role in tumor initiation and progression. In this review, we focus on three critical processes by which mitochondrial function may contribute to cancer: through alterations in glucose metabolism, the production of reactive oxygen species (ROS) and compromise of intrinsic apoptotic function. Alterations in cancer glucose metabolism include the Warburg effect, leading to a shift in metabolism away from aerobic respiration toward glycolysis, even when sufficient oxygen is present to support respiration. Such alterations in cellular metabolism may favor tumor cell growth by increasing the availability of biosynthetic intermediates needed for cellular growth and proliferation. Mutations in specific metabolic enzymes, namely succinate dehydrogenase, fumarate hydratase and the isocitrate dehydrogenases, have been linked to human cancer. Mitochondrial ROS may contribute to cancer via DNA damage and the activation of aberrant signaling pathways. ROS-dependent stabilization of the transcription factor hypoxia-inducible factor (HIF) may be a particularly important event for tumorigenesis. Compromised function of intrinsic apoptosis removes an important cellular safeguard against cancer and has been implicated in tumorigenesis, tumor metastasis, and chemoresistance. Each of the major mitochondrial processes is linked. In this review, we outline the connections between them and address ways these mitochondrial pathways may be targeted for cancer therapy.

Oxidative stress in apoptosis and cancer: an update

The oxygen paradox tells us that oxygen is both necessary for aerobic life and toxic to all life forms. Reactive oxygen species (ROS) touch every biological and medical discipline, especially those involving proliferative status, supporting the idea that active oxygen may be increased in tumor cells. In fact, metabolism of oxygen and the resulting toxic byproducts can cause cancer and death. Efforts to counteract the damage caused by ROS are gaining acceptance as a basis for novel therapeutic approaches, and the field of prevention of cancer is experiencing an upsurge of interest in medically useful antioxidants. Apoptosis is an important means of regulating cell numbers in the developing cell system, but it is so important that it must be controlled. Normal cell death in homeostasis of multicellular organisms is mediated through tightly regulated apoptotic pathways that involve oxidative stress regulation. Defective signaling through these pathways can contribute to both unbalance in apoptosis and development of cancer. Finally, in this review, we discuss new knowledge about recent tools that provide powerful antioxidant strategies, and designing methods to deliver to target cells, in the prevention and treatment of cancer.

Dysfunction of the TP53 tumor suppressor gene in lymphoid malignancies

Mutations of the TP53 gene and dysregulation of the TP53 pathway are important in the pathogenesis of many human cancers, including lymphomas. Tumor suppression by p53 occurs via both transcription-dependent activities in the nucleus by which p53 regulates transcription of genes involved in cell cycle, DNA repair, apoptosis, signaling, transcription, and metabolism; and transcription-independent activities that induces apoptosis and autophagy in the cytoplasm. In lymphoid malignancies, the frequency of TP53 deletions and mutations is lower than in other types of cancer. Nonetheless, the status of TP53 is an independent prognostic factor in most lymphoma types. Dysfunction of TP53 with wild-type coding sequence can result from deregulated gene expression, stability, and activity of p53. To overcome TP53 pathway inactivation, therapeutic delivery of wild-type p53, activation of mutant p53, inhibition of MDM2-mediated degradation of p53, and activation of p53-dependent and -independent apoptotic pathways have been explored experimentally and in clinical trials. We review the mechanisms of TP53 dysfunction, recent advances implicated in lymphomagenesis, and therapeutic approaches to overcoming p53 inactivation.

Increase of reduced nicotinamide adenine dinucleotide fluorescence lifetime precedes mitochondrial dysfunction in staurosporine-induced apoptosis of HeLa cells

In vivo noninvasive detection of apoptosis represents a new tool that may yield a more definite diagnosis, a more accurate prognosis, and help improve therapies for human diseases. The intrinsic fluorescence of reduced nicotinamide adenine dinucleotide (NADH) may be a potential optical biomarker for the apoptosis detection because NADH is involved in the respiration for the mitochondrial membrane potential (ΔΨ) formation and adenosine-5'-triphosphate (ATP) synthesis, and the depletion of ΔΨ and ATP level is the hallmark of apoptosis. We have previously observed the NADH fluorescence lifetime change is associated with staurosporine (STS)-induced mitochondria-mediated apoptosis. However, its relationship with mitochondrial functions such as ΔΨ, ATP, and oxygen consumption rate is not clear. In this study, we investigated this relationship. Our results indicate that the NADH fluorescence lifetime increased when ΔΨ and ATP levels were equal to or higher than their values of controls and decreased before the depletion of ΔΨ and ATP, and the oxygen consumption rate did not change. These findings suggest that the increased NADH fluorescence lifetime in STS-induced cell death occurred before the depletion of ΔΨ and ATP and activation of caspase 3, and was not simply caused by cellular metabolic change. Furthermore, the NADH fluorescence lifetime change is associated with the pace of apoptosis.

Therapeutic applications of compounds in the Magnolia family

The bark and/or seed cones of the Magnolia tree have been used in traditional herbal medicines in Korea, China and Japan. Bioactive ingredients such as magnolol, honokiol, 4-O-methylhonokiol and obovatol have received great attention, judging by the large number of investigators who have studied their pharmacological effects for the treatment of various diseases. Recently, many investigators reported the anti-cancer, anti-stress, anti-anxiety, anti-depressant, anti-oxidant, anti-inflammatory and hepatoprotective effects as well as toxicities and pharmacokinetics data, however, the mechanisms underlying these pharmacological activities are not clear. The aim of this study was to review a variety of experimental and clinical reports and, describe the effectiveness, toxicities and pharmacokinetics, and possible mechanisms of Magnolia and/or its constituents.

Inclusion complex of a Bcl-2 inhibitor with cyclodextrin: characterization, cellular accumulation, and in vivo antitumor activity

Small molecule inhibitors always exhibit poor water solubility due to the inherent hydrophobic property. It is an important challenge when they are developed as a real drug. S1, a structure-specific Bcl-2 inhibitor encountered this issue when moved forward in preclinical development. Herein, we prepared a 1:1 type of S1-gamma-cyclodextrin (S1-gamma-CD) inclusion complex to enhance the solubility. Bioevaluation of this new formulation was carried out totally in water solution. The cell internalization and cellular accumulation of S1-gamma-CD was illustrated by its fluorescence analogue S2. Disruption of Bcl-2/Bax heterodimerization in MCF-7 cells further revealed S1-gamma-CD could reach the subcellular function site. Moreover, the even stronger disruption by S1-gamma-CD than free S1 was found due to the higher local concentrations. Furthermore, the in vivo antitumor activity of S1-gamma-CD was evaluated in the H22 xenograft model. Results showed it exhibited significant antitumor activity with a decrease of tumor size (average tumor volume = 234 +/- 76 mm(3) vs control group, 398 +/- 121 mm(3), P < 0.01, and S1 group, 296 +/- 65 mm(3), P < 0.05), and a much longer survival time (the median time to the end point = 39.9 days vs control group, 29.2 days, P < 0.01). More importantly, the similar disruption of Bcl-2/Bax was found in S1-gamma-CD treated mice and free S1 treated ones. It demonstrated that S1-gamma-CD not only obtains a pharmaceutical level in vivo but also maintains the mechanism-based antitumor ability of S1 itself. It has been identified that cyclodextrin is appropriate to deliver a structure-specific molecule to its subcellular function site without any adverse effects on its mechanism-based potency, in either cultured cells or animals.

Allosteric regulation of protease activity by small molecules

Proteases regulate a plethora of biological processes. Because they irreversibly cleave peptide bonds, the activity of proteases is strictly controlled. While there are many ways to regulate protease activity, an emergent mechanism is the modulation of protease function by small molecules acting at allosteric sites. This mode of regulation holds the potential to allow for the specific and temporal control of a given biological process using small molecules. These compounds also serve as useful tools for studying protein dynamics and function. This review highlights recent advances in identifying and characterizing natural and synthetic small molecule allosteric regulators of proteases and discusses their utility in studies of protease function, drug discovery and protein engineering.

A novel BH3 mimetic S1 potently induces Bax/Bak-dependent apoptosis by targeting both Bcl-2 and Mcl-1

Broad spectrum Bcl-2 small molecule inhibitors act as BH3 mimetics are effective antitumor agents. Herein, we have identified S1, a previously discovered small molecule Bcl-2 inhibitor, as the first authentic BH3 mimetic as well as a dual, nanomolar inhibitor of Bcl-2 and Mcl-1 (K(i) = 310 nM and 58 nM, respectively). The results of fluorescence polarization assays, coimmunoprecipitation, fluorescent resonance energy transfer, and shRNA indicated that S1 can disrupt Bcl-2/Bax, Mcl-1/Bak and Bcl-2/Bim heterodimerization in multiple cell lines, activate Bax accompanied by its translocation to mitochondrial, activate caspase 3 completely dependent on Bax/Bak, and in turn induce a Bim-independent apoptosis. Moreover, S1 could induce apoptosis on the primary acute lymphoblastic leukemia cells regardless of Mcl-1 level. Mechanism-based single agent antitumor activity in a mouse xenograft H22 (mouse liver carcinoma) model ascertain its therapeutic potential. S1 represents a novel chemical class of antitumor leads that function solely as BH3 mimetics and pan-Bcl-2 inhibitors. In the meanwhile, S1 could become a unique tool for interactions between Bcl-2 family proteins.

A new class of naphthalimide-based antitumor agents that inhibit topoisomerase II and induce lysosomal membrane permeabilization and apoptosis

Based on the advantages of multitarget drugs for cancer treatment, a new class of naphthalimides was designed, synthesized, and proved to inhibit topoisomerase II (topo II), induced lysosomal membrane permeabilization (LMP), and ultimately caused apoptosis and cell death. The majority of compounds 7a-d and 8a-d potently inhibited the growth of the five tested cancer cell lines with IC(50) values ranging from 2 to 10 microM and are more active than amonafide, a naphthalimide that was in phase III clinical trials. These compounds were tested for their interactions with DNA and their cell-free topo II inhibition activities, which demonstrated these compounds were weak DNA binders but modest topo II inhibitors. Furthermore, compounds 7b-d were found to notably induce LMP and exhibited better antiproliferative activity compared with their single-target analogues. All of the newly synthesized compounds were demonstrated to efficiently induce apoptosis via a mitochondrial pathway. Accordingly, a new paradigm was suggested for the design of novel multitarget anticancer drugs.

Targeting AAC-11 in cancer therapy

IMPORTANCE OF THE FIELD

Since its discovery in 1997, the antiapoptotic factor AAC-11 has rapidly gained attention due to its potential use in cancer therapy. Indeed, most cancer cells express elevated levels of AAC-11, which is now known to be involved in both tumor cells growth as well as sensitivity to chemotherapeutic drugs.

AREAS COVERED IN THIS REVIEW

In this review, we examine the most recent evidence about the role of AAC-11 in cancer biology and the therapeutic perspectives associated with its specific targeting. For that purpose, literature dealing with AAC-11 in the PubMed database was reviewed from 1997 up to date.

WHAT THE READER WILL GAIN

AAC-11 is an antiapoptotic gene that has the potential to be a target for anti-cancer therapy, and warrants further investigation. As its expression seems to predict unfavorable prognosis, at least in some cancers, it also may become a potent prognostic marker.

TAKE HOME MESSAGE

Blocking AAC-11 function in cancer for therapeutic purposes might be of great interest. The recent report of efficient AAC-11 inhibiting peptides that sensitize tumor cells to chemotherapeutic drugs has raise the exciting notion that AAC-11 might be a druggable target and fueled the search for new therapeutic agents that could block AAC-11 function.

Synthesis and in vitro cytotoxic activity of compounds with pro-apoptotic potential

In our search for new anticancer therapies, some compounds synthesized in our lab were selected and their potential cytotoxic activity was evaluated in vitro against two cancer cells lines including a solid tumor (UACC-62, melanoma) and a human lymphoma (JURKAT). Compounds showing cytotoxic activity were subjected to an apoptosis assay. Two compounds showed promising results.

Inhibition of the ER Ca2+ pump forces multidrug-resistant cells deficient in Bak and Bax into necrosis

Tumor cells deficient in the proapoptotic proteins Bak and Bax are resistant to chemotherapeutic drugs. Here, we demonstrate that murine embryonic fibroblasts deficient for both Bak and Bax are, however, efficiently killed by thapsigargin, a specific inhibitor of ER Ca(2+) pumps that induces ER stress by depleting ER Ca(2+) stores. In the presence of Bak and Bax, thapsigargin eliminates cells by release of mitochondrial cytochrome c and subsequent caspase activation, which leads to the proteolytic inactivation of the molecular necrosis switch PARP-1 and results in apoptosis. By contrast, in the absence of Bak and Bax, a failure to activate caspases results in PARP-1-mediated ATP depletion. The subsequent necrosis is not prevented by autophagy as an alternative energy source. Moreover, in cells deficient for both Bak and Bax, thapsigargin induces permanent mitochondrial damage by Ca(2+) overload, permeability transition and membrane rupture. Thus, even though deficiency in Bak and Bax protects these cells against apoptosis, it does not compromise necrosis induced by SERCA inhibitors. Importantly, thapsigargin induces caspase-independent cell death also in colon and prostate carcinoma cells deficient in Bak and Bax expression. Therefore, targeted application of ER stressors such as thapsigargin might be a promising approach for the treatment of Bak- and Bax-deficient, drug-resistant tumors.

Targeting the apoptosome for cancer therapy

Apoptosis is a programmed mechanism of cell death that ensures normal development and tissue homeostasis in metazoans. Avoidance of apoptosis is an important contributor to the survival of tumor cells, and the ability to specifically trigger tumor cell apoptosis is a major goal in cancer treatment. In vertebrates, numerous stress signals engage the intrinsic apoptosis pathway to induce the release of cytochrome c from mitochondria. Cytochrome c binds to apoptosis protease activating factor-1, triggering formation of the apoptosome, a multisubunit protein complex that serves as a platform for caspase activation. In this review we summarize the mechanisms of apoptosome assembly and activation, and our current understanding of the regulation of these processes. We detail the evidence that loss-of-function of the apoptosome pathway may contribute to the development of specific cancers. Finally we discuss recent results showing enhanced sensitivity of some tumor cells to cytochrome c-induced apoptosis, suggesting that agents able to directly or indirectly trigger apoptosome-catalyzed caspase activation in tumor cells could provide new approaches to cancer treatment.

Noncanonical NF-kappaB activation requires coordinated assembly of a regulatory complex of the adaptors cIAP1, cIAP2, TRAF2 and TRAF3 and the kinase NIK

Recent studies suggest that nuclear factor kappaB-inducing kinase (NIK) is suppressed through constitutive proteasome-mediated degradation regulated by TRAF2, TRAF3 and cIAP1 or cIAP2. Here we demonstrated that the degradation of NIK occurs upon assembly of a regulatory complex through TRAF3 recruitment of NIK and TRAF2 recruitment of cIAP1 and cIAP2. In contrast to TRAF2 and TRAF3, cIAP1 and cIAP2 seem to play redundant roles in the degradation of NIK, as inhibition of both cIAPs was required for noncanonical NF-kappaB activation and increased survival and proliferation of primary B lymphocytes. Furthermore, the lethality of TRAF3 deficiency in mice could be rescued by a single NIK gene, highlighting the importance of tightly regulated NIK.