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Inhibition of eIF2alpha dephosphorylation maximizes bortezomib efficiency and eliminates quiescent multiple myeloma cells surviving proteasome inhibitor therapy.

ABSTRACT: The proteasome inhibitor bortezomib (Velcade) effectively eradicates multiple myeloma (MM) cells, partly by activating endoplasmic reticulum (ER) stress apoptotic signaling. However, MM recurrences in bortezomib-treated patients are invariable. We have shown that ER stress signaling can also induce growth arrest and survival in cancer cells. Thus, we hypothesized that bortezomib therapy could induce quiescence and survival of residual MM cells, contributing to disease recurrence. Here, we report that in MM cells, proteasome inhibition with MG-132 or bortezomib results in a surviving cell fraction that enters a prolonged quiescent state (G(0)-G(1) arrest). Mechanism analysis revealed that bortezomib-surviving quiescent cells attenuate eIF2alpha phosphorylation and induction of the ER stress proapoptotic gene GADD153. This occurs independently of the eIF2alpha upstream kinases PERK, GCN2, and PKR. In contrast, the prosurvival ER-chaperone BiP/Grp78 was persistently induced. The bortezomib-surviving quiescent fraction could be eradicated by a simultaneous or sequential combination therapy with salubrinal, an inhibitor of GADD34-PP1C phosphatase complex, and, in consequence, eIF2alpha dephosphorylation. This effect was mimicked by expression of a phosphorylated mimetic eIF2alpha-S51D mutant. Our data indicate that bortezomib can induce growth arrest in therapy-surviving MM cells and that attenuation of eIF2alpha phosphorylation contributes to this survival. Most importantly, this survival mechanism can be blocked by inhibiting eIF2alpha dephosphorylation. Thus, strategies that maintain eIF2alpha in a hyperphosphorylated state may be a novel therapeutic approach to maximize bortezomib-induced apoptosis and reduce residual disease and recurrences in this type of cancer.

SUBMITTER: Schewe DM

PROVIDER: S-EPMC2726651 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Inhibition of eIF2alpha dephosphorylation maximizes bortezomib efficiency and eliminates quiescent multiple myeloma cells surviving proteasome inhibitor therapy.

Schewe Denis M DM Aguirre-Ghiso Julio A JA

Cancer research 20090203 4

The proteasome inhibitor bortezomib (Velcade) effectively eradicates multiple myeloma (MM) cells, partly by activating endoplasmic reticulum (ER) stress apoptotic signaling. However, MM recurrences in bortezomib-treated patients are invariable. We have shown that ER stress signaling can also induce growth arrest and survival in cancer cells. Thus, we hypothesized that bortezomib therapy could induce quiescence and survival of residual MM cells, contributing to disease recurrence. Here, we report ...[more]

PMID: 19190324

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Project description:BackgroundThe ErbB2/Her2/Neu receptor tyrosine kinase is amplified in approximately 30% of human breast cancers. Phosphorylation of the translation initiation factor, eIF2alpha inhibits global protein synthesis and activates a stress signaling and growth suppressive program. We have shown that forced phosphorylation of eIF2alpha can suppress head and neck, colorectal carcinoma and multiple myeloma tumor growth and/or survival. Here we explore whether ErbB2 modulates eIF2alpha phosphorylation and whether forced phosphorylation of the latter can antagonize ErbB2 deregulation of mammary acinar morphogenesis.ResultsWe tested whether ErbB2 signaling influenced eIF2alpha signaling and whether enhanced phosphorylation of the latter affected ErbB2-deregulated mammary acinar development. We obtained stable MCF10A cells overexpressing wild-type (Wt) Neu/ErbB2 or a constitutively active (CA) variant via retroviral delivery or mammary tumor cells from MMTV-Neu tumors. Western blotting, RT-PCR and confocal microscopy were used to analyze the effects of ErbB2 activation on eIF2alpha signaling and the effect of the GADD34-PP1C inhibitor salubrinal. Wt- and MMTV-Neu cells formed aberrant acini structures resembling DCIS, while CA-ErbB2 overexpression induced invasive lesions. In these structures we found that CA-ErbB2 but not the Wt variant significantly down-regulated the pro-apoptotic gene CHOP. This occurred without apparent modulation of basal phosphorylation of PERK and eIF2alpha or induction of its downstream target ATF4. However, inhibition of eIF2alpha dephosphorylation with salubrinal was sufficient to inhibit Wt- and CA-ErbB2- as well as MMTV-Neu-induced deregulation of acinar growth. This was linked to enhanced CHOP expression, inhibition of proliferation, induction of apoptosis and luminal clearing in Wt-ErbB2 and to inhibition of cyclin D1 levels and subsequent proliferation in CA-ErbB2 cells.ConclusionDepending on the strength of ErbB2 signaling there is a differential regulation of CHOP and eIF2alpha phosphorylation. ErbB2 uncouples in basal conditions eIF2alpha phosphorylation from CHOP induction. However, this signal was restored by salubrinal treatment in Wt-ErbB2 expressing MCF10A cells as these DCIS-like structures underwent luminal clearing. In CA-ErbB2 structures apoptosis is not induced by salubrinal and instead a state of quiescence with reduced proliferation was achieved. Treatments that stabilize P-eIF2alpha levels may be effective in treating ErbB2 positive cancers without severely disrupting normal tissue function and structure.

Project description:BackgroundThe ongoing US MM-6 study is investigating in-class transition (iCT) from parenteral bortezomib-based induction to all-oral IRd (ixazomib-lenalidomide-dexamethasone) with the aim of increasing proteasome inhibitor (PI)-based treatment adherence and duration while maintaining patients' health-related quality of life (HRQoL) and improving outcomes.Patients and methodsUS community sites are enrolling non-transplant-eligible patients with newly diagnosed multiple myeloma (MM) with no evidence of progressive disease after 3 cycles of bortezomib-based therapy to receive IRd (up to 39 cycles or until progression or toxicity). The patients use mobile or wearable digital devices to collect actigraphy (activity and sleep) data and electronically complete HRQoL, treatment satisfaction and medication adherence questionnaires. The primary endpoint is progression-free survival. The key secondary endpoints include response rates and therapy duration.ResultsAt the data cutoff, 84 patients had been treated (median age 73 years; 44% aged ≥ 75 years; 49% men; 15% Black or African American; and 10% Hispanic or Latino). Of the 84 patients, 62% were continuing therapy. The mean duration of total PI therapy was 10.1 months and for the IRd regimen was 7.3 months. With an 8-month median follow-up, the 12-month progression-free survival rate was 86% (95% confidence interval, 73%-93%) from both the start of bortezomib-based treatment and the start of IRd. The overall response rate was 62% (complete response, 4%; very good partial response, 25%; partial response, 33%) after bortezomib-based induction and 70% (complete response, 26%; very good partial response, 29%; partial response, 15%) after iCT. The IRd safety profile was consistent with previous clinical trial data, and HRQoL and treatment satisfaction were maintained.ConclusionThe patients included in the US MM-6 study are representative of the real-world US MM population. The use of iCT might permit prolonged PI-based therapy with promising efficacy, without impacting patients' HRQoL or treatment satisfaction.

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Inhibition of eIF2alpha dephosphorylation maximizes bortezomib efficiency and eliminates quiescent multiple myeloma cells surviving proteasome inhibitor therapy.

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Inhibition of eIF2alpha dephosphorylation maximizes bortezomib efficiency and eliminates quiescent multiple myeloma cells surviving proteasome inhibitor therapy.

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