Effect of nelfinavir on insulin metabolism, proteasome activity and protein degradation in HepG2 cells

Mammalian Ddi2 is a shuttling factor containing a retroviral protease domain that influences binding of ubiquitylated proteins and proteasomal degradation

Although several proteasome subunits have been shown to bind ubiquitin (Ub) chains, many ubiquitylated substrates also associate with 26S proteasomes via “shuttling factors.” Unlike the well-studied yeast shuttling factors Rad23 and Dsk2, vertebrate homologs Ddi2 and Ddi1 lack a Ub-associated domain; therefore, it is unclear how they bind Ub. Here, we show that deletion of Ddi2 leads to the accumulation of Ub conjugates with K11/K48 branched chains. We found using affinity copurifications that Ddi2 binds Ub conjugates through its Ub-like domain, which is also required for Ddi2 binding to proteasomes. Furthermore, in cell extracts, adding Ub conjugates increased the amount of Ddi2 associated with proteasomes, and adding Ddi2 increased the binding of Ub conjugates to purified proteasomes. In addition, Ddi2 also contains a retroviral protease domain with undefined cellular roles. We show that blocking the endoprotease activity of Ddi2 either genetically or with the HIV protease inhibitor nelfinavir increased its binding to Ub conjugates but decreased its binding to proteasomes and reduced subsequent protein degradation by proteasomes leading to further accumulation of Ub conjugates. Finally, nelfinavir treatment required Ddi2 to induce the unfolded protein response. Thus, Ddi2 appears to function as a shuttling factor in endoplasmic reticulum–associated protein degradation and delivers K11/K48-ubiquitylated proteins to the proteasome. We conclude that the protease activity of Ddi2 influences this shuttling factor activity, promotes protein turnover, and helps prevent endoplasmic reticulum stress, which may explain nelfinavir’s ability to enhance cell killing by proteasome inhibitors.

Inhibitors of neuropeptide peptidases engaged in pain and drug dependence

Owing to a broad spectrum of functions performed by neuropeptides, this class of signaling molecules attracts an increasing interest. One of the key steps in the regulation of biological activity of neuropeptides is proteolytic conversion or degradation by proteinases that change or terminate biological activity of native peptides. These enzymes, in turn, are regulated by inhibitors, which play integral role in controlling many metabolic pathways. Thus, the search for selective inhibitors and detailed knowledge on the mechanisms of binding of these substances to enzymes, could be of importance for designing new pharmacological approaches. The aim of this review is to summarize the current knowledge on the inhibitors of enzymes that convert selected groups of neuropeptides, such as dynorphins, enkephalins, substance P and NPFF fragments. The importance of these substances in pathophysiological processes involved in pain and drug addiction, have been discussed. This article is part of the special issue on Neuropeptides.

Extracellular Vesicles: A Possible Link between HIV and Alzheimer's Disease-Like Pathology in HIV Subjects?

The longevity of people with HIV/AIDS has been prolonged with the use of antiretroviral therapy (ART). The age-related complications, especially cognitive deficits, rise as HIV patients live longer. Deposition of beta-amyloid (Aβ), a hallmark of Alzheimer's disease (AD), has been observed in subjects with HIV-associated neurocognitive disorders (HAND). Various mechanisms such as neuroinflammation induced by HIV proteins (e.g., Tat, gp120, Nef), excitotoxicity, oxidative stress, and the use of ART contribute to the deposition of Aβ, leading to dementia. However, progressive dementia in older subjects with HIV might be due to HAND, AD, or both. Recently, extracellular vesicles (EVs)/exosomes, have gained recognition for their importance in understanding the pathology of both HAND and AD. EVs can serve as a possible link between HIV and AD, due to their ability to package and transport the toxic proteins implicated in both AD and HIV (Aβ/tau and gp120/tat, respectively). Given that Aß is also elevated in neuron-derived exosomes isolated from the plasma of HIV patients, it is reasonable to suggest that neuron-to-neuron exosomal transport of Aβ and tau also contributes to AD-like pathology in HIV-infected subjects. Therefore, exploring exosomal contents is likely to help distinguish HAND from AD. However, future prospective clinical studies need to be conducted to compare the exosomal contents in the plasma of HIV subjects with and without HAND as well as those with and without AD. This would help to find new markers and develop new treatment strategies to treat AD in HIV-positive subjects. This review presents comprehensive literatures on the mechanisms contributing to Aβ deposition in HIV-infected cells, the role of EVs in the propagation of Aβ in AD, the possible role of EVs in HIV-induced AD-like pathology, and finally, possible therapeutic targets or molecules to treat HIV subjects with AD.

Biomarkers of neuronal injury and amyloid metabolism in the cerebrospinal fluid of patients infected with HIV-1 subtypes B and C

Based on prior reports that the HIV-1 Tat protein modulates amyloid-beta (Aβ) metabolism, this study aimed to compare CSF neural injury biomarkers between 27 patients with HIV subtype B, 26 patients with HIV subtype C, 18 healthy HIV-negative controls, and 24 patients with Alzheimer's disease (AD). Immunoassays were used to measure soluble amyloid precursor protein α and β (sAPPα, sAPPβ), Aβ oligomers 38, 40, 42, and Aβ-total; phosphorylated tau (P-tau181), and total tau (T-tau). Comparisons between HIV(+) and HIV(-) (including AD) were adjusted by linear regression for gender and age; HIV subtype comparisons were adjusted for nadir CD4 and plasma viral load suppression. The p values were corrected for multiple testing with the Benjamini-Hochberg procedure. CSF Aβ-42 and Hulstaert (P-tau181) index were lower in HIV1-C than B (p = 0.03, and 0.049 respectively); subtypes did not differ on other CSF biomarkers or ratios. Compared to AD, HIV(+) had lower CSF levels of T-tau, P-tau181 (p < 0.001), and sAPPα (p = 0.041); HIV(+) had higher CSF Aβ-42 (p = 0.002) and higher CSF indexes: [Aß-42/(240 + 1.18 T-tau)], P-tau181/Aβ-42, T-tau/Aβ-42, P-tau181/T-tau, sAPPα/β (all p ≤ 0.01) than AD. Compared to HIV(-), HIV(+) had lower CSF Aβ-42, and T-tau (all p ≤ 0.004). As conclusion, amyloid metabolism was influenced by HIV infection in a subtype-dependent manner. Aß-42 levels were lower in HIV1-C than B, suggesting that there may be greater deposition of Aß-42 in HIV1-C. These findings are supported by CSF Hulstaert (P-tau181) index. Differences between HIV and AD in the patterns of Aß and Tau biomarkers suggest that CNS HIV infection and AD may not share some of same mechanisms of neuronal injury.

An Overview of Human Immunodeficiency Virus Type 1-Associated Common Neurological Complications: Does Aging Pose a Challenge?

With increasing survival of patients infected with human immunodeficiency virus type 1 (HIV-1), the manifestation of heterogeneous neurological complications is also increasing alarmingly in these patients. Currently, more than 30% of about 40 million HIV-1 infected people worldwide develop central nervous system (CNS)-associated dysfunction, including dementia, sensory, and motor neuropathy. Furthermore, the highly effective antiretroviral therapy has been shown to increase the prevalence of mild cognitive functions while reducing other HIV-1-associated neurological complications. On the contrary, the presence of neurological disorder frequently affects the outcome of conventional HIV-1 therapy. Although, both the children and adults suffer from the post-HIV treatment-associated cognitive impairment, adults, especially depending on the age of disease onset, are more prone to CNS dysfunction. Thus, addressing neurological complications in an HIV-1-infected patient is a delicate balance of several factors and requires characterization of the molecular signature of associated CNS disorders involving intricate cross-talk with HIV-1-derived neurotoxins and other cellular factors. In this review, we summarize some of the current data supporting both the direct and indirect mechanisms, including neuro-inflammation and genome instability in association with aging, leading to CNS dysfunction after HIV-1 infection, and discuss the potential strategies addressing the treatment or prevention of HIV-1-mediated neurotoxicity.

Insulin-degrading enzyme: new therapeutic target for diabetes and Alzheimer's disease?

Insulin-degrading enzyme (IDE) is a major enzyme responsible for insulin degradation. In addition to insulin, IDE degrades many targets including glucagon, atrial natriuretic peptide, and beta-amyloid peptide, regulates proteasomal degradation and other cell functions. IDE represents a pathophysiological link between type 2 diabetes (T2DM) and late onset Alzheimer's disease (AD). Potent and selective modulators of IDE activity are potential drugs for therapies of both diseases. Acute treatment with a novel IDE inhibitor was recently tested in a mouse study as a therapeutic approach for the treatment of T2DM. In contrast, effective IDE activators can be used for the AD treatment. However, because of the pleiotropic IDE action, the sustained treatment with systemic IDE modulators should be carefully tested in animal studies. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets. KEY MESSAGES Insulin-degrading enzyme (IDE) represents a pathophysiological link between type 2 diabetes (T2DM) and Alzheimer's disease (AD). Selective modulators of IDE activity are potential drugs for both T2DM and AD treatment. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets.

The radiosensitizing effects of Nelfinavir on pancreatic cancer with and without pancreatic stellate cells

AIMS

We have previously shown in a phase I trial that nelfinavir (NFV) is safe with chemoradiation in PDAC with good signs for efficacy. Reverse translationally, we aimed to test the influence of PSCs on nelfinavir mediated radiosensitization to PDAC preclinically, because PDAC is very rich in desmoplasia and PSCs are known to mediate radioresistance.

METHODS

In a direct co-culture model of several PDAC cell lines with PSC we performed clonogenic assays +/- nelfinavir. This was repeated exposing cells to hypoxic conditions. In xenograft PDAC tumors we tested radiation +/- nelfinavir +/- PSC.

RESULTS

NFV sensitized both, PDAC only and PDAC cocultured with PSC (PDAC: Panc-1, MiaPaCa-2, PSN-1). In Panc-1 and PSN-1 this effect was larger +PSC compared to -PSC. Human pancreatic stellate cells (hPSC) were also sensitized by NFV which reduced p-FAK levels in hPSC, an effect that we previously found to sensitize specifically PDAC/PSC coculture. Contrarily, LY294002 reduced p-Akt in PSC (hPSC and LTC-14) but had no impact on PSC radiation survival. In vitro, nelfinavir sensitized Panc-1 and PSN-1 under normoxic and hypoxic conditions. In PSN-1 xenografts, +PSC led to faster tumor regrowth after radiation vs -PSC. The regrowth delay effect of nelfinavir after radiation was dramatically larger +PSC vs -PSC (time to reach 250mm(3) 183% vs 22%).

CONCLUSION

NFV mediated radiosensitization in PDAC with stroma is partly mediated by p-FAK inhibition (Chen et al., 2013). In vitro, NFV sensitizes both normoxic and hypoxic PDAC +/- PSC to a roughly similar extent. The dramatic increased effect of xenograft regrowth inhibition by nelfinavir in tumors with PSC is attributed to vascular normalization (Brunner et al., 2014) rather than direct modification of hypoxia as shown by the tumor regrowth after gemcitabine with NFV.

HIV protease inhibitors: a review of molecular selectivity and toxicity

Highly active antiretroviral therapy (HAART) is recognized as the most effective treatment method for AIDS, and protease inhibitors play a very important role in HAART. However, poor bioavailability and unbearable toxicity are their common disadvantages. Thus, the development of safer and potentially promising protease inhibitors is eagerly needed. In this review, we introduced the chemical characteristics and associated side effects of HIV protease inhibitors, as well as the possible off-target mechanisms causing the side effects. From the chemical structures of HIV protease inhibitors and their possible off-target molecules, we could obtain hints for optimizing the molecular selectivity of the inhibitors, to provide help in the design of new compounds with enhanced bioavailability and reduced side effects.

Recent advances in drug repositioning for the discovery of new anticancer drugs

Drug repositioning (also referred to as drug repurposing), the process of finding new uses of existing drugs, has been gaining popularity in recent years. The availability of several established clinical drug libraries and rapid advances in disease biology, genomics and bioinformatics has accelerated the pace of both activity-based and in silico drug repositioning. Drug repositioning has attracted particular attention from the communities engaged in anticancer drug discovery due to the combination of great demand for new anticancer drugs and the availability of a wide variety of cell- and target-based screening assays. With the successful clinical introduction of a number of non-cancer drugs for cancer treatment, drug repositioning now became a powerful alternative strategy to discover and develop novel anticancer drug candidates from the existing drug space. In this review, recent successful examples of drug repositioning for anticancer drug discovery from non-cancer drugs will be discussed.

The effect of HIV protease inhibitors on amyloid-β peptide degradation and synthesis in human cells and Alzheimer's disease animal model

Combined antiretroviral therapy (ART) tremendously improved the lifespan and symptoms associated with AIDS-defining illness in affected individuals. However, chronic ART-treated patients frequently develop age-dependent complications, including dementia, diabetes, and hyperlipidemia: all risk factors of Alzheimer's disease. Importantly, the effect of ART compounds on amyloid generation and clearance has never been systematically examined. Nine prescribed HIV protease inhibitors were tested for their effect on amyloid-β peptide (Aβ) clearance in primary cultured human monocyte-derived macrophages. Atazanavir, ritonavir, and saquinavir modestly inhibited of Aβ degradation, while lopinavir, nelfinavir, and ritonavir enhanced secretion of undigested Aβ after phagocytosis. Lopinavir, nelfinavir, ritonavir, and saquinavir inhibited endogenous Aβ40 production from primary cultured human cortical neurons, which were associated with reduction in Beta-site APP Converting Enzyme 1 (BACE1) and γ-secretase enzyme activities. However, ART compounds showed little inhibition of purified BACE1 activity in vitro, suggesting the indirect effect of ART compounds on BACE1 activity in neurons. Finally, nefinavir or lopinavir/ritonavir (Kaletra) were orally administered for 30 days into APP SCID mice expressing a double mutant form of APP 695 (KM670/671NL + V717F) in homozygosity for the scid allele of Prkdc. There was no difference in beta-amyloidosis by ART drug administration as determined by both immunohistochemistry and ELISA measurements although the therapeutic doses of the ART compounds was present in the brain. These data demonstrated that ART drugs can inhibit Aβ clearance in macrophages and Aβ production in neurons, but these effects did not significantly alter Aβ accumulation in the mouse brain.

Insulin metabolism in human adipocytes from subcutaneous and visceral depots

Subjects with the metabolic syndrome (insulin resistance, glucose intolerance, dyslipidemia, hypertension, etc.) have a relative increase in abdominal fat tissue compared to normal individuals and obesity has also been shown to be associated with a decrease in insulin clearance. The majority of the clearance of insulin is due to the action of insulin-degrading enzyme (IDE) and IDE is present throughout all tissues. Since abdominal fat is increased in obesity we hypothesized that IDE may be altered in the different fat depots. Adipocytes were isolated from fat samples obtained from subjects during elective abdominal surgery. Fat samples were taken from subcutaneous (SQ) and visceral (VIS) sites. Insulin metabolism was compared in adipocytes isolated from SQ and VIS fat tissue. Adipocytes from the VIS site degraded more insulin that those from SQ fat tissue. Inhibitors of cathepsins B and D has no effect on the degradation of insulin, while bacitracin, an inhibitor of IDE, inhibited degradation by approx. 33% in both SQ and VIS adipocytes. These data show that insulin metabolism is relatively greater in VIS than in SQ fat tissue and potentially due to IDE.

HIV-1-induced amyloid beta accumulation in brain endothelial cells is attenuated by simvastatin

HIV-1-infected brains are characterized by increased amyloid deposition. To study the influence of HIV-1 on amyloid beta (Abeta) homeostasis at the blood-brain barrier (BBB) level, we employed a model of brain microvascular endothelial cells exposed to HIV-1 in the presence or absence of Abeta. HIV-1 markedly increased endogenous Abeta levels and elevated accumulation of exogenous Abeta. Simvastatin, the HMG-CoA reductase inhibitor, blocked these effects. We next evaluated the effects of HIV-1 and/or simvastatin on expression of the receptor for lipoprotein related protein (LRP1) and the receptor for advanced glycation end products (RAGE), known to regulate Abeta transport across the BBB. LRP1 expression was not affected by HIV-1; however, it was increased by simvastatin. Importantly, simvastatin attenuated HIV-1-induced RAGE expression. These results suggest that HIV-1 may directly contribute to Abeta accumulation at the BBB level. In addition, statins may protect against increased Abeta levels associated with HIV-1 infection in the brain.

HIV protease inhibitors block oral epithelial cell DNA synthesis

OBJECTIVES

Anti-retroviral therapy regimens that include HIV protease inhibitors (PIs) are associated with diverse adverse effects including increased prevalence of oral warts, oral sensorial deficits and gastrointestinal toxicities suggesting that PIs may perturb epithelial cell biology. To test the hypothesis that PIs could affect specific biological processes of oral epithelium, the effects of these agents were evaluated in several oral epithelial cell-lines.

DESIGN

Primary and immortalized oral keratinocytes and squamous carcinoma cells of oropharyngeal origin were cultured in the presence of pharmacologically relevant concentrations of PIs. Their affects on cell viability, cytotoxicity and DNA synthesis were assessed by enzymatic assays and incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA.

RESULTS

Viability of primary and immortalized oral keratinocytes as well as squamous carcinoma cells of oropharyngeal origin was significantly reduced by select PIs at concentrations found in plasma. Of the seven PIs evaluated, nelfinavir was the most potent with a mean 50% inhibitory concentration [IC(50)] of 4.1 microM. Lopinavir and saquinavir also reduced epithelial cell viability (IC(50) of 10-20 microM). Atazanavir and ritonovir caused minor reductions in viability, while amprenavir and indinavir were not significant inhibitors. The reduced cell viability, as shown by BrdU incorporation assays, was due to inhibition of DNA synthesis rather than cell death due to cytotoxicity.

CONCLUSION

Select PIs retard oral epithelial cell proliferation in a drug and dose-dependent manner by blocking DNA synthesis. This could account for some of their adverse effects on oral health.

HIV protease inhibitors and insulin resistance: lessons from in-vitro, rodent and healthy human volunteer models

PURPOSE OF REVIEW

Although the use of HIV protease inhibitors is linked to the development of insulin resistance and other metabolic changes that greatly increase the risk for cardiovascular disease, the molecular mechanisms responsible remain incompletely understood. This review summarizes recent advances that have been made in understanding the relative contributions of individual protease inhibitors to both acute and chronic insulin resistance together with newly identified cellular mediators.

RECENT FINDINGS

Individual protease inhibitors, alone and in combination, have differing propensities to induce insulin resistance, reflecting relative differences in both affinities for identified molecular targets and pharmacokinetic profiles. Several of the most recent protease inhibitors approved for clinical use or in development appear to be less likely to induce insulin resistance. In addition to direct effects on glucose transporter-4 activity, induction of oxidative stress, proteosome inhibition, alteration of adipokine levels, and changes in suppressors of cytokine signaling-1 have been implicated.

SUMMARY

A better understanding of the propensity of individual HIV protease inhibitors to produce insulin resistance will allow the tailoring of individual treatment plans based upon overall risk for diabetes. The elucidation of the molecular mechanisms for alterations in glucose homeostasis will facilitate the development of newer generations of HIV protease inhibitors that maintain their clinical efficacy without contributing to the development of diabetes mellitus and other proatherogenic effects.

Tumor vascular changes mediated by inhibition of oncogenic signaling

Many inhibitors of the epidermal growth factor receptor (EGFR)-RAS-phosphatidylinositol 3-kinase (PI3K)-AKT signaling pathway are in clinical use or under development for cancer therapy. Here, we show that treatment of mice bearing human tumor xenografts with inhibitors that block EGFR, RAS, PI3K, or AKT resulted in prolonged and durable enhancement of tumor vascular flow, perfusion, and decreased tumor hypoxia. The vessels in the treated tumors had decreased tortuosity and increased internodal length accounting for the functional alterations. Inhibition of tumor growth cannot account for these results, as the drugs were given at doses that did not alter tumor growth. The tumor cell itself was an essential target, as HT1080 tumors that lack EGFR did not respond to an EGFR inhibitor but did respond with vascular alterations to RAS or PI3K inhibition. We extended these observations to spontaneously arising tumors in MMTV-neu mice. These tumors also responded to PI3K inhibition with decreased tumor hypoxia, increased vascular flow, and morphologic alterations of their vessels, including increased vascular maturity and acquisition of pericyte markers. These changes are similar to the vascular normalization that has been described after the antiangiogenic treatment of xenografts. One difficulty in the use of vascular normalization as a therapeutic strategy has been its limited duration. In contrast, blocking tumor cell RAS-PI3K-AKT signaling led to persistent vascular changes that might be incorporated into clinical strategies based on improvement of vascular flow or decreased hypoxia. These results indicate that vascular alterations must be considered as a consequence of signaling inhibition in cancer therapy.

The comorbidity of HIV-associated neurocognitive disorders and Alzheimer's disease: a foreseeable medical challenge in post-HAART era

Although the introduction of highly active antiretroviral therapy (HAART) has led to a strong reduction of HIV-associated dementia (HAD) incidence, the prevalence of minor HIV-1-associated neurocognitive disorder (HAND) is rising among AIDS patients. HAART medication has shifted neuropathology from a subacute encephalitic condition to a subtle neurodegenerative process involving synaptic and dendritic degeneration, particularly of hippocampal neurons that are spared prior to HAART medication. Considerable neuroinflammation coupled with mononuclear phagocyte activation is present in HAART-medicated brains, particularly in the hippocampus. Accumulating evidence suggests that the resultant elevated secretion of pro-inflammatory cytokines such as interferon-gamma, tumor necrosis factor-alpha, and interleukin-1beta can increase amyloid-beta peptide (Abeta) generation and reduce Abeta clearance. Recent advancements in Alzheimer's disease (AD) research identified Abeta biogenesis and clearance venues that are potentially influenced by HIV viral infection, providing new insights into beta-amyloidosis segregation in HIV patients. Our study suggests enhanced beta-amyloidosis in ART-treated HAD and HIV-associated encephalitis brains and suppression of Abeta clearance by viral infection of human primary macrophages. A growing awareness of potential convergent mechanisms leading to neurodegeneration shared by HIV and Abeta points to a significant chance of comorbidity of AD and HAND in senile HIV patients, which calls for a need of basic studies.

The role of protease inhibitors in the pathogenesis of HIV-associated lipodystrophy: cellular mechanisms and clinical implications

Metabolic complications associated with HIV infection and treatment frequently present as a relative lack of peripheral adipose tissue associated with dyslipidemia and insulin resistance. In this review we explain the connection between abnormalities of intermediary metabolism, observed either in vitro or in vivo, and this group of metabolic effects. We review molecular mechanisms by which the HIV protease inhibitor (PI) class of drugs may affect the normal stimulatory effect of insulin on glucose and fat storage. We then propose that both chronic inflammation from HIV infection and treatment with some drugs in this class trigger cellular homeostatic stress responses with adverse effects on intermediary metabolism. The physiologic outcome is such that total adipocyte storage capacity is decreased, and the remaining adipocytes resist further fat storage. The excess circulating and dietary lipid metabolites, normally "absorbed" by adipose tissue, are deposited ectopically in lean (muscle and liver) tissue, where they impair insulin action. This process leads to a pathologic cycle of lipotoxicity and lipoatrophy and a clinical phenotype of body fat distribution with elevated waist-to-hip ratio similar to the metabolic syndrome.

HIV-1 protease inhibitors nelfinavir and atazanavir induce malignant glioma death by triggering endoplasmic reticulum stress

HIV type 1 (HIV-1) protease inhibitors (PI) have been shown to have anticancer activity in non-HIV-associated human cancer cells. The underlying mechanism of this effect is unclear. Here, we show that the PIs nelfinavir and atazanavir cause cell death in various malignant glioma cell lines in vitro. The underlying mechanism of this antitumor effect involves the potent stimulation of the endoplasmic reticulum (ER) stress response (ESR), as indicated by increased expression of two ESR markers, GRP78 and CHOP, and activation of ESR-associated caspase-4. Induction of ESR seems to play a central role in PI-induced cell death because small interfering RNA-mediated knockdown of the protective ER chaperone GRP78 sensitizes cells; whereas knockdown of proapoptotic caspase-4 protects cells from PI-induced cell death. Furthermore, the treatment of cells with PIs leads to aggresome formation and accumulation of polyubiquitinated proteins, implying proteasome inhibition. Thus, our results support a model whereby PIs cause tumor cell death via triggering of the ESR, inhibition of proteasome activity, and subsequent accumulation of misfolded proteins. Inhibition of glioma growth via ESR takes place in the in vivo setting as well, as nelfinavir inhibits the growth of xenografted human malignant glioma, with concomitant induction of the proapoptotic ER stress marker CHOP. Because ER stress has also been reported as the mechanism for insulin resistance and diabetes, our ER stress model of PI function may also explain why these drugs may induce insulin resistance as one of their most common side effects.