In BRAF-mutated melanoma cells, the BRAF inhibitor, vemurafenib, induces phosphorylation of eukaryotic initiation factor 2α (eIF2α) and subsequent induction of activating transcription factor 4 ...(ATF4), the central regulation node of the integrated stress response (ISR). While the ISR supports cellular adaptation to various stresses, the role of vemurafenib-triggered ISR has not been fully characterized. Here, we showed that in response to vemurafenib, BRAF-mutated melanoma and colorectal cancer cells rapidly induced the ISR as a cytoprotective mechanism through activation of general control nonderepressible 2 (GCN2), an eIF2α kinase sensing amino acid levels. The vemurafenib-triggered ISR, an event independent of downstream MEK inhibition, was specifically prevented by silencing GCN2, but not other eIF2α kinases, including protein kinase-like endoplasmic reticulum kinase, which transmits endoplasmic reticulum (ER) stress. Consistently, the ER stress gatekeeper, GRP78, was not induced by vemurafenib. Interestingly, ATF4 silencing by siRNA rendered BRAF-mutated melanoma cells sensitive to vemurafenib. Thus, the GCN2-mediated ISR can promote cellular adaptation to vemurafenib-induced stress, providing an insight into the development of drug resistance.
•Vemurafenib rapidly induced ATF4 through GCN2 activation in BRAF-mutated cells.•Induction of the ISR by vemurafenib occurred independently of PERK.•ATF4 silencing sensitized BRAF-mutated cells to vemurafenib.
Recent progress in the development of molecular cancer therapeutics has revealed new types of antitumor drugs, such as Herceptin, Gleevec, and Iressa, as potent therapeutics for specific tumors. Our ...work has focused on molecular cancer therapeutics, mainly in the areas of drug resistance, apoptosis and apoptosis resistance, and survival‐signaling, which is related to drug resistance. In this review, we describe our research on molecular cancer therapeutics, including molecular mechanisms and therapeutic approaches. Resistance to chemotherapeutic drugs is a principal problem in the treatment of cancer. P‐Glycoprotein (P‐gp), encoded by the MDR1 gene, is a multidrug transporter and has a major role in multidrug resistance (MDR). Targeting of P‐gp by small‐molecular compounds and/or antibodies is an effective strategy to overcome MDR in cancer, especially hematologic malignancies. Several P‐gp inhibitors have been developed and are currently under clinical phased studies. In addition to the multi‐drug transporter proteins, cancer cells have several drug resistance mechanisms. Solid tumors are often placed under stress conditions, such as glucose starvation and hypoxia. These conditions result in topo II poison resistance that is due to proteasome‐mediated degradation of DNA topoisomerases. Proteasome inhibitors effectively prevent this stress‐induced drug resistance. Glyoxalase I, which is often elevated in drug‐ and apoptosis‐resistant cancers, offers another possibility for overcoming drug resistance. It plays a role in detoxification of methylglioxal, a side product of glycolysis, which is highly reactive with DNA and proteins. Inhibitors of glyoxalase I selectively kill drug‐resistant tumors that express glyoxalase I. Finally, the susceptibility of tumor cells to apoptosis induced by antitumor drugs appears to depend on the balance between pro‐apoptotic and survival (anti‐apoptotic) signals. PI3K‐Akt is an important survival signal pathway, that has been shown to be the target of various antitumor drugs, including UCN‐01 and geldanamycin, new anticancer drugs under clinical evaluation. Our present studies provide novel targets for future effective molecular cancer therapeutics. (Cancer Sci 2003; 94: 15–21)
The emergence of acquired resistance is a major concern associated with molecularly targeted kinase inhibitors. The C797S mutation in the epidermal growth factor receptor (EGFR) confers resistance to ...osimertinib, a third‐generation EGFR‐tyrosine kinase inhibitor (EGFR‐TKI). We report that the derivatization of the marine alkaloid topoisomerase inhibitor lamellarin N provides a structurally new class of EGFR‐TKIs. One of these, lamellarin 14, is effective against the C797S mutant EGFR. Bioinformatic analyses revealed that the derivatization transformed the topoisomerase inhibitor‐like biological activity of lamellarin N into kinase inhibitor‐like activity. Ba/F3 and PC‐9 cells expressing the EGFR in‐frame deletion within exon 19 (del ex19)/T790M/C797S triple‐mutant were sensitive to lamellarin 14 in a dose range similar to the effective dose for cells expressing EGFR del ex19 or del ex19/T790M. Lamellarin 14 decreased the autophosphorylation of EGFR and the downstream signaling in the triple‐mutant EGFR PC‐9 cells. Furthermore, intraperitoneal administration of 10 mg/kg lamellarin 14 for 17 days suppressed tumor growth of the triple‐mutant EGFR PC‐9 cells in a mouse xenograft model using BALB/c nu/nu mice. Thus, lamellarin 14 serves as a novel structural backbone for an EGFR‐TKI that prevents the development of cross‐resistance against known drugs in this class.
The emergence of acquired resistance is a major concern associated with molecularly targeted kinase inhibitors. We report that the derivatization of the marine alkaloid topoisomerase inhibitor lamellarin N provides a structurally new class of epidermal growth factor receptor (EGFR)‐tyrosine kinase inhibitors (TKIs). One of these EGFR‐TKIs, lamellarin 14, is effective against the C797S mutant EGFR.
Abstract
The unfolded protein response (UPR) is an adaptive stress response pathway that is essential for cancer cell survival under endoplasmic reticulum stress such as during glucose starvation. In ...this study, we identified spautin-1, an autophagy inhibitor that suppresses ubiquitin-specific peptidase 10 (USP10) and USP13, as a novel UPR inhibitor under glucose starvation conditions. Spautin-1 prevented the induction of UPR-associated proteins, including glucose-regulated protein 78, activating transcription factor 4, and a splicing variant of x-box-binding protein-1, and showed preferential cytotoxicity in glucose-starved cancer cells. However, USP10 and USP13 silencing and treatment with other autophagy inhibitors failed to result in UPR inhibition and preferential cytotoxicity during glucose starvation. Using transcriptome and chemosensitivity-based COMPARE analyses, we identified a similarity between spautin-1 and mitochondrial complex I inhibitors and found that spautin-1 suppressed the activity of complex I extracted from isolated mitochondria. Our results indicated that spautin-1 may represent an attractive mitochondria-targeted seed compound that inhibits the UPR and cancer cell survival during glucose starvation.
As a branch of the unfolded protein response, protein kinase R-like endoplasmic reticulum kinase (PERK) represses global translation in response to endoplasmic reticulum (ER) stress. This ...pathophysiological condition is associated with the tumor microenvironment in cancer. Previous findings in our lab have suggested that PERK selectively represses translation of some mRNAs, but this possibility awaits additional investigation. In this study, we show that a stem-cell marker protein, leucine-rich repeat-containing G-protein–coupled receptor 5 (LGR5), is rapidly depleted in colon cancer cells during ER stress, an effect that depended on the PERK-mediated translational repression. Indeed, the PERK inhibition led to the accumulation of premature, underglycosylated forms of LGR5, which were produced only at low levels during proper PERK activation. Unlike the mature LGR5 form, which is constitutively degraded regardless of PERK activation, the underglycosylated LGR5 exhibited a prolonged half-life and accumulated inside the cells without being expressed on the cell surface. We also found that Erb-B2 receptor tyrosine kinase 3 (ERBB3) is subjected to a similarly-regulated depletion by PERK, whereas the epidermal growth factor receptor (EGFR), stress-inducible heat-shock protein family A (Hsp70) member 5 (HSPA5), and anterior gradient 2 protein-disulfide isomerase family member (AGR2) were relatively. insensitive to the PERK-mediated repression of translation. These results indicate that LGR5 and ERBB3 are targets for PERK-mediated translational repression during ER stress
This case report introduces a rare occurrence of transverse colon volvulus associated with persistent descending mesocolon (PDM), a congenital anomaly characterized by the medial positioning of the ...descending colon due to a failed fusion with the dorsal abdominal wall. We detail the case of an 18-year-old female, with a medical history of surgically corrected coarctation of the aorta and anal atresia, who presented with recurrent transverse colon volvulus despite having undergone a laparoscopic colopexy three years earlier. Physical examination revealed abdominal distension and metallic colic sounds while imaging studies confirmed the recurrence of the volvulus. Laparoscopic partial resection of the transverse colon was performed, which revealed a medially positioned descending colon due to PDM. Postoperative complications included anastomotic failure, necessitating a second operation. The patient was successfully discharged without further complications after seven days. This case underscores the clinical significance of recognizing PDM, highlighting its potential role in causing transverse colon volvulus and increasing the risk of anastomotic failure. It emphasizes the need for surgeons to remain vigilant regarding this congenital anomaly to mitigate unexpected outcomes such as recurrent volvulus and postoperative complications.
Glucose deprivation, a cell condition that occurs in solid tumors, activates the unfolded protein response (UPR). A key feature of the UPR is the transcription program activation, which allows the ...cell to survive under stress conditions. Here, we show that the UPR transcription program is disrupted by the antidiabetic biguanides metformin, buformin, and phenformin depending on cellular glucose availability. These drugs inhibit production of the UPR transcription activators XBP1 and ATF4 and induce massive cell death during glucose deprivation as did the antitumor macrocyclic compound versipelostatin. Gene expression profiling shows remarkable similarity in the modes of action of biguanides and versipelostatin determined by the broad range of glucose deprivation-inducible genes. Importantly, during glucose deprivation, most of the biguanide suppression genes overlap with the genes induced by tunicamycin, a chemical UPR inducer. Gene expression profiling also identifies drug-driven signatures as a tool for discovering pharmacologic UPR modulators. Our findings show that disrupting the UPR during glucose deprivation could be an attractive approach for selective cancer cell killing and could provide a chemical genomic basis for developing UPR-targeting drugs against solid tumors.
The integrated stress response (ISR) is a cellular process that is characterized by activation of eukaryotic initiation factor (eIF)2α kinases and subsequent induction of activating transcription ...factor (ATF)4. The ISR plays an important role in protecting cells from tumor-related metabolic stresses, such as nutrient deprivation and perturbed proteostasis. Here, we showed that disruption of the ISR, together with increased cellular stress vulnerability, was produced by pharmacological inhibition of BCR-ABL, the oncogenic driver in chronic myeloid leukemia (CML). Treatment of CML-derived K562 cells with BCR-ABL tyrosine kinase inhibitors, including imatinib, dasatinib, nilotinib and ponatinib, prevented activation of eIF2α kinases, protein kinase-like endoplasmic reticulum kinase (PERK) and general control nonderepressible 2, and downstream ATF4 induction during metabolic stress. Prevention of ATF4 induction likely occurred as a result of the combinatorial suppression of the eIF2α kinase and phosphoinositide 3-kinase/mammalian target of rapamycin signaling pathways. In addition, we found that pharmacological inhibition of PERK mimicked BCR-ABL inhibition to enhance apoptosis induction under stress conditions. These findings indicate that the ISR is under the control of BCR-ABL and may foster adaptation to tumorigenic stresses in CML cells.
•BCR-ABL inhibitors prevent activation of PERK and GCN2.•BCR-ABL inhibitors suppress ATF4 induction, possibly through multiple mechanisms.•Metabolic stress conditions enhance apoptosis induction by BCR-ABL inhibitors.
Under hypoxia, HIF-1α binds to aryl hydrocarbon receptor nuclear translocator (ARNT, also called HIF-1β) to activate expression of genes important for cell survival. Alternatively, HIF-1α can bind to ...the tumor suppressor p53 and promote p53-dependent apoptosis. Here we show that the opposite functions of HIF-1α are distinguished by its phosphorylation status. Two distinguishable forms of HIF-1α, phosphorylated and dephosphorylated, were induced during hypoxia-induced apoptosis. The phosphorylated HIF-1α was the major form that bound to ARNT. Ectopically expressed ARNT was consistently able to enhance HIF-1α phosphorylation in a binding-dependent manner. In contrast, the dephosphorylated HIF-1α was the major form that bound to p53. Depletion of the dephosphorylated HIF-1α, by using the Hsp90 inhibitor geldanamycin A that had little effect on the phosphorylated HIF-1α expression, suppressed p53 induction and subsequent apoptosis. Depletion of dephosphorylated HIF-1α also prevented hypoxia-induced nuclear accumulation of HDM2, a negative regulator of p53. Our results indicate that the functions of HIF-1α varied with its phosphorylation status and that dephosphorylated HIF-1α mediated apoptosis by binding to and stabilizing p53.
PDF
