Cytotoxic stress caused by azalamellarin D (AzaD) interferes with cellular protein translation by targeting the nutrient-sensing kinase mTOR.

Analogs of pyrrole alkaloid lamellarins exhibit anticancer activity by modulating multiple cellular events. Lethal doses of several lamellarins were found to enhance autophagy flux in HeLa cells, suggesting that lamellarins may modulate protein homeostasis through the interference of proteins or kinases controlling energy and nutrient metabolism. To further delineate molecular mechanisms and their targets, our results herein show that azalamellarin D (AzaD) cytotoxicity could cause translational attenuation, as indicated by a change in eIF2α phosphorylation. Intriguingly, acute AzaD treatment promoted the phosphorylation of GCN2, a kinase that transduces the integrated stress response (ISR), and prolonged exposure to AzaD could increase the levels of the phosphorylated forms of eIF2α and the other ISR kinase protein kinase R (PKR). However, the effects of AzaD on ISR signalling were marginally abrogated in cells with genetic deletion of GCN2 and PKR, and evaluation of protein target engagement by cellular thermal shift assay (CETSA) revealed no significant interaction between AzaD and ISR kinases. Further investigation revealed that acute AzaD treatment negatively affected mechanistic target of rapamycin (mTOR) phosphorylation and signalling. The analyses by CETSA and computational modelling indicated that mTOR may be a possible protein target for AzaD. These findings indicate the potential for developing lamellarins as novel agents for cancer treatment.

Synthesis and Anticancer Activity of Pentafluorobenzenesulfonamide Derivatives as Caspase-Dependent Apoptosis-Inducing Agents.

Arylsulfonamides are ubiquitous in a number of anticancer agents, and fluorine substitution on aromatic rings often improves drug profile. Herein, a series of novel pentafluorobenzenesulfonamide derivatives with different molecular scaffolds were readily synthesized and assessed for their antitumor activities against multiple cancer cell lines, including A549, HepG2, HuCCA-1, and MOLT-3. Dihydroimidazoline-containing analogue and its Diels-Alder cycloadducts exhibited enhanced cytotoxicity at micromolar range while the incorporation of other heterocyclic cores via nucleophilic substitution reaction resulted in diminished potency. Selected analogues were shown to induce the accumulation of cleaved forms of Casp-9, Casp-7 and PARP in cancer cells, indicating intrinsic apoptosis via a caspase-dependent process.

Melatonin Attenuates High Glucose-Induced Changes in Beta Amyloid Precursor Protein Processing in Human Neuroblastoma Cells.

Diabetes mellitus (DM), one of metabolic diseases, has been suggested as a risk factor for Alzheimer's disease (AD). However, how the metabolic pathway activates amyloid precursor protein (APP) processing enzymes then contributes to the increase of amyloid-beta (Aß) production, is not clearly understood. In the present study, we aimed to examine the protective effect of melatonin against hyperglycemia-induced alterations in the amyloidogenic pathway. High concentration of glucose was used to induce hyperglycemia in human neuroblastoma SH-SY5Y cells. We found that 30 mM glucose affected the expression of insulin receptors and glucose transporters, which indicated the disruption of glucose sensing. High glucose induced the activation of the phosphorylated protein kinase B (pAkt)/GSK-3ß signaling pathway and a significant increase in the expression of ß-site beta APP cleaving enzyme (BACE1), presenilin1 (PS1) and Aß42. Pretreatment with melatonin significantly reversed these parameters. We also showed that these effects are similar to those effects in the presence of the GSK-3ß blocker, N-(4-methoxybenyl)-N'-(5-nitro-1,3-thiazol-2-yl) urea (ARA) in glucose-treated hyperglycemic cells. These suggested that melatonin exerted an inhibitory effect on the activation of APP-cleaving enzymes via the GSK-3ß signaling pathway. Pretreatment with luzindole, a melatonin receptor MT1 antagonist, significantly prevented the effect of melatonin on the glucose-induced increase level of APP processing enzymes. This suggested that melatonin attenuated the toxic effect on hyperglycemia involving the amyloidogenic pathway partially mediated via melatonin receptor. Taken together the present results suggested that melatonin has a beneficial role in preventing Aß generation in a cellular model of hyperglycemia-induced DM.

Roles of autophagy in relation to mitochondrial stress responses of HeLa cells to lamellarin cytotoxicity.

As a promising class of bioactive marine pyrrole alkaloids, lamellarins reportedly act on multiple targets to suppress the vitality of various cancer cell lines. Nevertheless, an in-depth understanding of the molecular mechanisms governing their cytotoxicity is still in demand. Here we report that while activating intrinsic apoptosis, up to 5 µM of lamellarins and their lactam-containing analogs, azalamellarins, also induced mitochondrial stress responses and autophagy in HeLa cervical cancer cells. Detailed characterization of the mitochondria in the treated cells revealed shifted abundance of the two optic atrophy protein 1 (Opa1) isoforms, disturbed morphology, and dissipated membrane potential, leading to PTEN-induced kinase-1 (PINK1) and microtubule-associated protein 1 light chain 3-II (LC3-II) accumulation as a molecular signature of mitophagy. Furthermore, an acute treatment with lamellarins also modulated cellular autophagy flux as evidenced by elevated LC3-II levels, LC3 puncta formation, and p62 degradation. Surprisingly, clustered regularly interspaced short palindromic repeats (CRISPR)-based suppression of autophagy transiently affected the number of apoptotic cells induced by these compounds. Our findings illustrate the potential of these alkaloids for further development into prospective anti-cancer agents.

An Expeditious Modular Hybrid Strategy for the Diversity-Oriented Synthesis of Lamellarins/Azalamellarins with Anticancer Cytotoxicity.

A modular hybrid strategy has been developed for the diversity-oriented synthesis of lamellarins/azalamellarins. The common pentacyclic pyrrolodihydroisoquinoline lactone/lactam core was formed via the Michael addition/ring closure (Mi-RC) and the copper(I) thiophene-2-carboxylate (CuTC)-catalyzed C-O/C-N Ullmann coupling. Subsequent direct functionalization at C1, DDQ-mediated C5═C6 oxidation, and global deprotection of all benzyl-type O- and N-protecting groups furnished the desired lamellarins/azalamellarins. The late-stage functionalization at C1 provided a handle to accommodate a wider scope of functional groups as they need to tolerate only the DDQ oxidation and global deprotection. Moreover, with the C1-H pyrrole as the late-stage common intermediate, it was also possible to divergently exploit not only its nucleophilic nature to react with some electrophilic species but also some transition-metal-catalyzed cross-coupling reactions (via the intermediacy of the C1-iodopyrrole) to incorporate diversity at this position. Overall, this strategy simplifies the preparation of lamellarins/azalamellarins; including the Mi-RC, these C1-structurally diverse analogues could be prepared efficiently in 6-7 steps from the easily accessed 1-acetoxymethyldihydroisoquinoline and ß-nitrocinnamate. Some selected azalamellarins were evaluated for their inhibitory effect against HeLa cervical cancer cells. An acute induction of intrinsic apoptosis was detected and may lead to growth suppression of or cytotoxicity against cancer cells.

Synthesis and antitumor activity of bis(arylsulfonyl)dihydroimidazolinone derivatives.

A series of novel bis(arylsulfonyl)dihydroimidazolinones with different aryl substitution patterns were readily synthesized and evaluated for their antitumor activities. Some of the newly synthesized compounds exhibited cytotoxicity at micromolar range against multiple cancer cell lines, including A549, HepG2, HuCCA-1, and MOLT-3. The most potent analogue contained pentafluorobenzenesulfonyl groups, which could be chemically elaborated to serve as a potential pharmacophore.

Endoplasmic reticulum stress-induced degradation of DNAJB12 stimulates BOK accumulation and primes cancer cells for apoptosis.

DNAJB12 (JB12) is an endoplasmic reticulum (ER)-associated Hsp40 family protein that recruits Hsp70 to the ER surface to coordinate the function of ER-associated and cytosolic chaperone systems in protein quality control. Hsp70 is stress-inducible, but paradoxically, we report here that JB12 was degraded by the proteasome during severe ER stress. Destabilized JB12 was degraded by ER-associated degradation complexes that contained HERP, Sel1L, and gp78. JB12 was the only ER-associated chaperone that was destabilized by reductive stress. JB12 knockdown by siRNA led to the induction of caspase processing but not the unfolded protein response. ER stress-induced apoptosis is regulated by the highly labile and ER-associated BCL-2 family member BOK, which is controlled at the level of protein stability by ER-associated degradation components. We found that JB12 was required in human hepatoma cell line 7 (Huh-7) liver cancer cells to maintain BOK at low levels, and BOK was detected in complexes with JB12 and gp78. Depletion of JB12 during reductive stress or by shRNA from Huh-7 cells was associated with accumulation of BOK and activation of Caspase 3, 7, and 9. The absence of JB12 sensitized Huh-7 to death caused by proteotoxic agents and the proapoptotic chemotherapeutic LCL-161. In summary, JB12 is a stress-sensitive Hsp40 whose degradation during severe ER stress provides a mechanism to promote BOK accumulation and induction of apoptosis.

Restoration of R117H CFTR folding and function in human airway cells through combination treatment with VX-809 and VX-770.

Cystic fibrosis (CF) is a lethal recessive genetic disease caused primarily by the F508del mutation in the CF transmembrane conductance regulator (CFTR). The potentiator VX-770 was the first CFTR modulator approved by the FDA for treatment of CF patients with the gating mutation G551D. Orkambi is a drug containing VX-770 and corrector VX809 and is approved for treatment of CF patients homozygous for F508del, which has folding and gating defects. At least 30% of CF patients are heterozygous for the F508del mutation with the other allele encoding for one of many different rare CFTR mutations. Treatment of heterozygous F508del patients with VX-809 and VX-770 has had limited success, so it is important to identify heterozygous patients that respond to CFTR modulator therapy. R117H is a more prevalent rare mutation found in over 2,000 CF patients. In this study we investigated the effectiveness of VX-809/VX-770 therapy on restoring CFTR function in human bronchial epithelial (HBE) cells from R117H/F508del CF patients. We found that VX-809 stimulated more CFTR activity in R117H/F508del HBEs than in F508del/F508del HBEs. R117H expressed exclusively in immortalized HBEs exhibited a folding defect, was retained in the ER, and degraded prematurely. VX-809 corrected the R117H folding defect and restored channel function. Because R117 is involved in ion conductance, VX-770 acted additively with VX-809 to restore CFTR function in chronically treated R117H/F508del cells. Although treatment of R117H patients with VX-770 has been approved, our studies indicate that Orkambi may be more beneficial for rescue of CFTR function in these patients.

VX-809 corrects folding defects in cystic fibrosis transmembrane conductance regulator protein through action on membrane-spanning domain 1.

Cystic fibrosis (CF) is a fatal genetic disorder associated with defective hydration of lung airways due to the loss of chloride transport through the CF transmembrane conductance regulator protein (CFTR). CFTR contains two membrane-spanning domains (MSDs), two nucleotide-binding domains (NBDs), and a regulatory domain, and its channel assembly requires multiple interdomain contacts. The most common CF-causing mutation, F508del, occurs in NBD1 and results in misfolding and premature degradation of F508del-CFTR. VX-809 is an investigational CFTR corrector that partially restores CFTR function in people who are homozygous for F508del-CFTR. To identify the folding defect(s) in F508del-CFTR that must be repaired to treat CF, we explored the mechanism of VX-809 action. VX-809 stabilized an N-terminal domain in CFTR that contains only MSD1 and efficaciously restored function to CFTR forms that have missense mutations in MSD1. The action of VX-809 on MSD1 appears to suppress folding defects in F508del-CFTR by enhancing interactions among the NBD1, MSD1, and MSD2 domains. The ability of VX-809 to correct F508del-CFTR is enhanced when combined with mutations that improve F508del-NBD1 interaction with MSD2. These data suggest that the use of VX-809 in combination with an additional CFTR corrector that suppresses folding defects downstream of MSD1 may further enhance CFTR function in people with F508del-CFTR.

A novel mammalian ER-located J-protein, DNAJB14, can accelerate ERAD of misfolded membrane proteins.

Misfolded proteins in the endoplasmic reticulum (ER) are dislocated out of the ER to the cytosol, polyubiquitinated, and degraded by the ubiquitin-proteasome system in a process collectively termed ER-associated degradation (ERAD). Recent studies have established that a mammalian ER-localized transmembrane J-protein, DNAJB12, cooperates with Hsc70, a cytosolic Hsp70 family member, to promote the ERAD of misfolded membrane proteins. Interestingly, mammalian genomes have another J-protein called DNAJB14 that shows a high sequence similarity to DNAJB12. Yet, very little was known about this protein. Here, we report the characterization of DNAJB14. Immunofluorescence study and protease protection assay showed that, like DNAJB12, DNAJB14 is an ER-localized, single membrane-spanning J-protein with its J-domain facing the cytosol. We used co-immunoprecipitation assay to find that DNAJB14 can also specifically bind Hsc70 via its J-domain to recruit this chaperone to ER membrane. Remarkably, the overexpression of DNAJB14 accelerated the degradation of misfolded membrane proteins including a mutant of cystic fibrosis transmembrane conductance regulator (CFTRΔF508), but not that of a misfolded luminal protein. Furthermore, the DNAJB14-dependent degradation of CFTRΔF508 was compromised by MG132, a proteasome inhibitor, indicating that DNAJB14 can enhance the degradation of a misfolded membrane protein using the ubiquitin-proteasome system. Thus, the mammalian ER possesses two analogous J-proteins (DNAJB14 and DNAJB12) that both can promote the ERAD of misfolded transmembrane proteins. Compared with DNAJB12 mRNA that was widely expressed in mouse tissues, DNAJB14 mRNA was expressed more weakly, being most abundant in testis, implying its specific role in this tissue.