High endoplasmic reticulum activity renders multiple myeloma cells hypersensitive to mitochondrial inhibitors

Thiazolidinedione Use Is Associated with a Borderline Lower Risk of Multiple Myeloma and a Significantly Lower Risk of Death in Patients with Type 2 Diabetes Mellitus in Taiwan

BACKGROUND

Thiazolidinedione (TZD) exerts anti-proliferative effects on multiple myeloma (MM) cells. However, there has not been any human study investigating the risk of MM associated with TZD use.

METHODS

We used Taiwan's National Health Insurance database to identify 423,949 patients who had been newly diagnosed with diabetes mellitus between 1999 and 2005. After excluding ineligible patients, 86,999 pairs of patients with and without the use of TZD (rosiglitazone or pioglitazone) that had been matched based on propensity score were selected for a follow-up for MM until 31 December 2011. The hazard ratios for MM were estimated using Cox regression and weighted using a propensity score.

RESULTS

After a median follow-up of 4.6 years and 4.7 years in ever users and never users of TZD, 32 and 47 cases were diagnosed with MM, respectively. A 35% lower risk (though not statistically significant) was observed among ever users (hazard ratio 0.652, 95% confidence interval: 0.416-1.023, p = 0.0625). When ever users were divided by the median (15 months) cumulative duration of TZD therapy, the hazard ratios (95% confidence interval) for the lower and upper medians were 0.706 (0.394-1.264) and 0.603 (0.346-1.051), respectively. When treated as a continuous variable, the hazard ratio for every 1-month increment of the cumulative duration was 0.980 (95% confidence interval: 0.963-0.997, p = 0.0185). In the age subgroup analysis, a significantly lower risk could be seen in the older age subgroup of ≥65 years (hazard ratio 0.550, 95% confidence interval: 0.305-0.992, p = 0.0468). Additional analyses suggested that there were no interactions between TZD and some medications and between TZD and some clinical diagnoses, and that the use of TZD as a preventive drug for MM might not be cost-effective because a number-needed-to-treat of 5800 was too large. Survival analyses suggested that ever users had a significantly lower risk of death when all patients were analyzed (hazard ratio: 0.84, 95% confidence interval: 0.81-0.87, p < 0.0001 via a log-rank test) or when patients who developed MM were analyzed (hazard ratio: 0.40, 95% confidence interval: 0.19-0.86, p = 0.0153 via a log-rank test).

CONCLUSIONS

In Taiwanese patients with type 2 diabetes mellitus, TZD use is associated with a borderline lower risk of MM, which is more remarkable in patients aged ≥65 years. Because of the low incidence of MM, the use of TZD for the prevention of MM may not be cost-effective. Patients who have been treated with TZD may have a survival advantage. Future research is required to confirm the findings.

Multiple Myeloma: Possible Cure from the Sea

Simple Summary

Multiple myeloma (MM) is a complex white blood cell (plasma cell, PC) cancer. The aetiology of MM is still unknown, and it is still an incurable disease despite efforts by the scientific community. The high level of PC genetic heterogeneity renders MM a complex puzzle to be solved. Combinations of drugs are generally used to treat MM patients, with a general increase in overall survival. Relapsed and refractory MM patients are the generation of patients who resist or do not respond to first-line therapy and need additional treatments. Exploring new sources, such as marine organisms, for drug discovery is fundamental to fighting MM. Various studies have shown that marine natural products (MNPs) might have antiproliferative and cancer-specific cytotoxic properties, giving MNPs a pivotal role in anticancer drug discovery. This review recaps updated frontline treatment options, including new ones developed from MNP research.

Abstract

Multiple myeloma (MM) is a blood cancer that occurs in the plasma cells (PCs), a type of white blood cell. Despite the progress of several current treatments that prolong the overall patient’s survival, most MM cases are incurable. For this reason, many efforts have been undertaken by the scientific community in the search for new treatments. BLENREP^TM and Aplidin^® are two marine-derived drugs currently in use for MM. In addition, other natural products have been identified from marine organisms, tested for their possible anticancer properties, and are in preclinical or clinical trials for MM, including cytarabine, a compound in use for leukaemia treatment. Between the most successful marine compounds in fighting MM, there are molecules with specific targets, such as the elongation factor 1-alpha 2 and proteasome inhibitors, and compounds conjugated with antibodies that recognise specific cell types and direct the drug to the correct cell target. Active compounds belong to different chemical classes, from cyclic peptides to alkaloids, highlighting the importance of screening the plethora of compounds produced by marine organisms. In this review, we summarise the current state of art of MM therapies focusing on the marine natural product emerging roles.

Biochemical pathways of copper complexes: progress over the past 5 years

Copper is an essential trace element with vital roles in many metalloenzymes; it is also prominent among nonplatinum anticancer metallodrugs. Copper-based complexes are endogenously biocompatible, tenfold more potent than cisplatin, exhibit fewer adverse effects, and have a wide therapeutic window. In cancer biology, copper acts as an antitumor agent by inhibiting cancer via multiple pathways. Herein, we present an overview of advances in copper complexes as 'lead' antitumor drug candidates, and in understanding their biochemical and pharmacological pathways over the past 5 years. This review will help to develop more efficacious therapeutics to improve clinical outcomes for cancer treatments.

Tuning isoform selectivity and bortezomib sensitivity with a new class of alkenyl indene PDI inhibitor

Protein disulfide isomerase (PDI, PDIA1) is an emerging therapeutic target in oncology. PDI inhibitors have demonstrated a unique propensity to selectively induce apoptosis in cancer cells and overcome resistance to existing therapies, although drug candidates have not yet progressed to the stage of clinical development. We recently reported the discovery of lead indene compound E64FC26 as a potent pan-PDI inhibitor that enhances the cytotoxic effects of proteasome inhibitors in panels of Multiple Myeloma (MM) cells and MM mouse models. An extensive medicinal chemistry program has led to the generation of a diverse library of indene-containing molecules with varying degrees of proteasome inhibitor potentiating activity. These compounds were generated by a novel nucleophilic aromatic ring cyclization and dehydration reaction from the precursor ketones. The results provide detailed structure activity relationships (SAR) around this indene pharmacophore and show a high degree of correlation between potency of PDI inhibition and bortezomib (Btz) potentiation in MM cells. Inhibition of PDI leads to ER and oxidative stress characterized by the accumulation of misfolded poly-ubiquitinated proteins and the induction of UPR biomarkers ATF4, CHOP, and Nrf2. This work characterizes the synthesis and SAR of a new chemical class and further validates PDI as a therapeutic target in MM as a single agent and in combination with proteasome inhibitors.

Inhibitors of the protein disulfide isomerase family for the treatment of multiple myeloma

Multiple Myeloma (MM) is highly sensitive to disruptions in cellular protein homeostasis. Proteasome inhibitors (PIs) are initially effective in the treatment of MM, although cures are not achievable and the emergence of resistance limits the durability of responses. New therapies are needed for refractory patients, and those that combat resistance to standard of care agents would be particularly valuable. Screening of multiple chemical libraries for PI re-sensitizing compounds identified E61 as a potent enhancer of multiple PIs and MM specific activity. Using a tandem approach of click chemistry and peptide mass fingerprinting, we identified multiple protein disulfide isomerase (PDI) family members as the primary molecular targets of E61. PDIs mediate oxidative protein folding, and E61 treatment induced robust ER and oxidative stress responses as well as the accumulation of ubiquitinylated proteins. A chemical optimization program led to a new structural class of indene (exemplified by lead E64FC26), which are highly potent pan-style inhibitors of PDIs. In mice with MM, E64FC26 improved survival and enhanced the activity of bortezomib without any adverse effects. This work demonstrates the potential of E64FC26 as an early drug candidate and the strategy of targeting multiple PDI isoforms for the treatment of refractory MM and beyond.

Combining 2-deoxy-D-glucose with fenofibrate leads to tumor cell death mediated by simultaneous induction of energy and ER stress

Unregulated growth and replication as well as an abnormal microenvironment, leads to elevated levels of stress which is a common trait of cancer. By inducing both energy and endoplasmic reticulum (ER) stress, 2-Deoxy-glucose (2-DG) is particularly well-suited to take advantage of the therapeutic window that heightened stress in tumors provides. Under hypoxia, blocking glycolysis with 2-DG leads to significant lowering of ATP resulting in energy stress and cell death in numerous carcinoma cell types. In contrast, under normoxia, 2-DG at a low-concentration is not toxic in most carcinomas tested, but induces growth inhibition, which is primarily due to ER stress. Here we find a synergistic toxic effect in several tumor cell lines in vitro combining 2-DG with fenofibrate (FF), a drug that has been safely used for over 40 years to lower cholesterol in patients. This combination induces much greater energy stress than either agent alone, as measured by ATP reduction, increased p-AMPK and downregulation of mTOR. Inhibition of mTOR results in blockage of GRP78 a critical component of the unfolded protein response which we speculate leads to greater ER stress as observed by increased p-eIF2α. Moreover, to avoid an insulin response and adsorption by the liver, 2-DG is delivered by slow-release pump yielding significant anti-tumor control when combined with FF. Our results provide promise for developing this combination clinically and others that combine 2-DG with agents that act synergistically to selectively increase energy and ER stress to a level that is toxic to numerous tumor cell types.

Mitochondrial-Targeted Decyl-Triphenylphosphonium Enhances 2-Deoxy-D-Glucose Mediated Oxidative Stress and Clonogenic Killing of Multiple Myeloma Cells

Therapeutic advances have markedly prolonged overall survival in multiple myeloma (MM) but the disease currently remains incurable. In a panel of MM cell lines (MM.1S, OPM-2, H929, and U266), using CD138 immunophenotyping, side population staining, and stem cell-related gene expression, we demonstrate the presence of stem-like tumor cells. Hypoxic culture conditions further increased CD138^low stem-like cells with upregulated expression of OCT4 and NANOG. Compared to MM cells, these stem-like cells maintained lower steady-state pro-oxidant levels with increased uptake of the fluorescent deoxyglucose analog. In primary human MM samples, increased glycolytic gene expression correlated with poorer overall and event-free survival outcomes. Notably, stem-like cells showed increased mitochondrial mass, rhodamine 123 accumulation, and orthodox mitochondrial configuration while more condensed mitochondria were noted in the CD138^high cells. Glycolytic inhibitor 2-deoxyglucose (2-DG) induced ER stress as detected by qPCR (BiP, ATF4) and immunoblotting (BiP, CHOP) and increased dihydroethidium probe oxidation both CD138^low and CD138^high cells. Treatment with a mitochondrial-targeting agent decyl-triphenylphosphonium (10-TPP) increased intracellular steady-state pro-oxidant levels in stem-like and mature MM cells. Furthermore, 10-TPP mediated increases in mitochondrial oxidant production were suppressed by ectopic expression of manganese superoxide dismutase. Relative to 2-DG or 10-TPP alone, 2-DG plus 10-TPP combination showed increased caspase 3 activation in MM cells with minimal toxicity to the normal hematopoietic progenitor cells. Notably, treatment with polyethylene glycol conjugated catalase significantly reduced 2-DG and/or 10-TPP-induced apoptosis of MM cells. Also, the combination of 2-DG with 10-TPP decreased clonogenic survival of MM cells. Taken together, this study provides a novel strategy of metabolic oxidative stress-induced cytotoxicity of MM cells via 2-DG and 10-TPP combination therapy.

Protein Disulfide Isomerase Superfamily in Disease and the Regulation of Apoptosis

Cellular homeostasis requires the balance of a multitude of signaling cascades that are contingent upon the essential proteins being properly synthesized, folded and delivered to appropriate subcellular locations. In eukaryotic cells the endoplasmic reticulum (ER) is a specialized organelle that is the central site of synthesis and folding of secretory, membrane and a number of organelletargeted proteins. The integrity of protein folding is enabled by the presence of ATP, Ca++, molecular chaperones, as well as an oxidizing redox environment. The imbalance between the load and capacity of protein folding results in a cellular condition known as ER stress. Failure of these pathways to restore ER homeostasis results in the activation of apoptotic pathways. Protein disulfide isomerases (PDI) compose a superfamily of oxidoreductases that have diverse sequences and are localized in the ER, nucleus, cytosol, mitochondria and cell membrane. The PDI superfamily has multiple functions including, acting as molecular chaperones, protein-binding partners, and hormone reservoirs. Recently, PDI family members have been implicated in the regulation of apoptotic signaling events. The complexities underlying the molecular mechanisms that define the switch from pro-survival to pro-death response are evidenced by recent studies that reveal the roles of specific chaperone proteins as integration points in signaling pathways that determine cell fate. The following review discusses the dual role of PDI in cell death and survival during ER stress.

Conversion of 2-deoxyglucose-induced growth inhibition to cell death in normoxic tumor cells

BACKGROUND

Inhibition of glucose metabolism has recently become an attractive target for cancer treatment. Accordingly, since 2-deoxyglucose (2-DG) competes effectively with glucose, it has come under increasing scrutiny as a therapeutic agent. The initial response of tumor cells to 2-DG is growth inhibition, which is thought to conserve energy and consequently protect cells from its ATP-lowering effects as a glycolytic inhibitor. However, since 2-DG also mimics mannose and thereby interferes with N-linked glycosylation, the question is raised of how this sugar analog inhibits tumor cell growth and whether the mechanism by which it protects cells can be manipulated to convert 2-DG-induced growth inhibition to cell death.

METHODS

Cell growth and death were measured via counting viable and dead cells based on trypan blue exclusion. Markers of ATP reduction and the unfolded protein response (UPR) were detected by Western blot. Protein functions were manipulated through chemical compounds, siRNA and the use of gene-specific wild-type and knock-out mouse embryonic fibroblasts (MEFs).

RESULTS

At 2-DG concentrations that can be achieved in human plasma without causing significant side effects, we find (a) It induces growth inhibition predominantly by interference with glycosylation, which leads to accumulation of unfolded proteins in the endoplasmic reticulum activating the UPR; (b) Inhibition of PERK (but not ATF6 or IRE1), a major component of the UPR, leads to conversion of 2-DG-induced growth inhibition to cell death and (c) secondarily to PERK, inhibition of GCN2, a kinase that is activated in response to low intracellular glutamine, increases 2-DG's cytotoxic effects in PERK -/- MEFs.

CONCLUSIONS

Overall, these findings present a novel anticancer strategy that can be translated into therapeutic gain as they uncover the metabolic target PERK, and to a lesser degree GCN2, that when inhibited convert 2-DG's static effect to a toxic one in tumor cells growing under normoxia.

Synthesis and SAR of Lehualide B: a marine-derived natural product with potent anti-multiple myeloma activity

We report a concise and convergent laboratory synthesis of the rare marine natural product lehualide B that has led to the discovery that (1) this compound has low nanomolar activity against human multiple myeloma cells and (2) the anticancer effects of lehualide B and its analogues are selective (i.e., they are approximately 2-3 orders of magnitude less toxic to human breast cancer cells). Synthetic lehualide B is shown to be an effective inhibitor of complex I of the mitochondrial electron transport chain, with potency similar to that observed for the terrestrial natural products piericidin A1 and rotenone, an observation that led to the discovery that piericidin A1 is also selectively cytotoxic toward human multiple myeloma cells. Interestingly, synthetic derivatives of lehualide B that resemble verticipyrone (an established complex I inhibitor composed of a γ-pyrone and a simple monounsaturated hydrophobic chain) lack the potent antimyeloma activity of the natural product. Finally, the synthesis and evaluation of a collection of lehualide-inspired analogues led to the elucidation of structure-activity relationships for this rare natural product that established important roles for the substituted γ-pyrone headgroup and the skipped polyene side chain.

Retinoblastoma treatment: impact of the glycolytic inhibitor 2-deoxy-d-glucose on molecular genomics expression in LH(BETA)T(AG) retinal tumors

PURPOSE

The purpose of this study was to evaluate the effect of 2-deoxy-D-glucose (2-DG) on the spatial distribution of the genetic expression of key elements involved in angiogenesis, hypoxia, cellular metabolism, and apoptosis in LH(BETA)T(AG) retinal tumors.

METHODS

The right eye of each LH(BETA)T(AG) transgenic mouse (n = 24) was treated with either two or six subconjunctival injections of 2-DG (500 mg/kg) or saline control at 16 weeks of age. A gene expression array analysis was performed on five different intratumoral regions (apex, center, base, anterior-lateral, and posterior-lateral) using Affymetrix GeneChip Mouse Gene 1.0 ST arrays. To test for treatment effects of each probe within each region, a two-way analysis of variance was used.

RESULTS

Significant differences between treatment groups (ie, 0, 2, and 6 injections) were found as well as differences among the five retinal tumor regions evaluated (P < 0.01). More than 100 genes were observed to be dysregulated by ≥2-fold difference in expression between the three treatment groups, and their dysregulation varied across the five regions assayed. Several genes involved in pathways important for tumor cell growth (ie, angiogenesis, hypoxia, cellular metabolism, and apoptosis) were identified.

CONCLUSIONS

2-DG was found to significantly alter the gene expression in LH(BETA)T(AG) retinal tumor cells according to their location within the tumor as well as the treatment schedule. 2-DG's effects on genetic expression found here correlate with previous reported results on varied processes involved in its in vitro and in vivo activity in inhibiting tumor cell growth.

Mitochondrial proteome: toward the detection and profiling of disease associated alterations

Existing at the heart of cellular energy metabolism, the mitochondrion is uniquely positioned to have a major impact on human disease processes. Examples of mitochondrial impact on human pathology abound and include etiologies ranging from inborn errors of metabolism to the site of activity of a variety of toxic compounds. In this review, the unique aspects of the mechanisms related to the mitochondrial proteome are discussed along with an overview of the literature related to mitochondrial proteomic exploration. The review includes discussion of potential areas for exploration and advantages of applying proteomic techniques to the study of mitochondria.