ALBERT

Description: Bortezomib, a therapeutic agent for multiple myeloma (MM) and mantle cell lymphoma, suppresses proteosomal degradation leading to substantial changes in cellular transcriptional programs and ultimately resulting in apoptosis. Transcriptional regulators required for bortezomib-induced apoptosis in MM cells are largely unknown. Using gene expression profiling, we identified 36 transcription factors that displayed altered expression in MM cells treated with bortezomib. Analysis of a publically available database identified Kruppel-like family factor 9 (KLF9) as the only transcription factor with significantly higher basal expression in MM cells from patients who responded to bortezomib compared with nonresponders. We demonstrated that KLF9 in cultured MM cells was up-regulated by bortezomib; however, it was not through the induction of endoplasmic reticulum stress. Instead, KLF9 levels correlated with bortezomib-dependent inhibition of histone deacetylases (HDAC) and were increased by the HDAC inhibitor LBH589 (panobinostat). Furthermore, bortezomib induced binding of endogenous KLF9 to the promoter of the proapoptotic gene NOXA. Importantly, KLF9 knockdown impaired NOXA up-regulation and apoptosis caused by bortezomib, LBH589, or a combination of theses drugs, whereas KLF9 overexpression induced apoptosis that was partially NOXA-dependent. Our data identify KLF9 as a novel and potentially clinically relevant transcriptional regulator of drug-induced apoptosis in MM cells.

Description: Abstract 2946 Multiple myeloma (MM) is a hematologic malignancy characterized by the aberrant proliferation of plasma cells. Myeloma cells retain most of the physiological characteristics of their normal counterpart – the long-lived plasma cell. Myeloma cells secrete immunoglobulin and reside in the bone marrow, where they rely heavily on interactions with the stroma for survival signals. While recent advances in therapeutics have led to an increase in median survival post-diagnosis, the disease remains incurable. Understanding the pathways which mediate growth and survival of these cells will help in identifying new targets that can potentially further improve patient outcomes. CD28 is a receptor better known for its role in T-cell signaling through interaction with its ligands, CD80 or CD86. Interaction between CD28 on T-cells and CD80/86 on antigen-presenting cells leads to survival and proliferation of T-cells. Recent work has shown that the CD80/86-CD28 pathway also plays an important role in normal plasma cell generation and survival. Interestingly, high expression of CD28 and CD86 are poor prognostic markers for myeloma patients. Previous work has shown that CD28 activation provides survival signals for myeloma cells in growth-factor deficient conditions. It has also been shown that CD28 on the myeloma cell interacts with CD80/86 on the dendritic cell, which induces secretion of IL-6 (by the DC), an important myeloma growth factor. However, it is not known if CD28 or CD86 play a role in steady state growth and survival of myeloma cells. In order to determine the role of each of these 2 molecules in myeloma physiology, we knocked-down either CD28 or CD86 on the myeloma cell via lentivirus-mediated shRNAs. We found that knockdown of CD86 leads to apoptosis in 3 myeloma cell lines (RPMI8226, MM1.s, and KMS18). Four days after infection with the lentivirus containing shCD86, 45.7±4.9 and 60.3±4.6 percent control apoptosis was observed in RPMI8226 and MM1.s respectively, while less death was observed in KMS18 (17.6±1.6). CD28-knockdown resulted in apoptosis as well (24.9±4.3 for RPMI8226, 26.8±4.1 for MM1s, 21.8±3.8 for KMS18, percent control apoptosis). Consistent with these findings, we were unable to establish a myeloma cell line with stable knockdown of either CD28 or CD86. Additionally, RPMI8226 cells stably transfected to over-express either Bcl-2, Bcl-xL, or Mcl-1 are protected from cell death induced by CD86 or CD28 silencing. These data suggest that CD28 and CD86 are essential to prevent apoptosis of myeloma cells in vitro. To confirm these findings we determined the effects of CTLA4-Ig on myeloma survival. CTLA4-Ig inhibits CD86-CD28 signaling by binding to CD86, blocking its interaction with CD28. We found that treatment of RPMI8226 and MM1.s cells with CTLA4-Ig caused apoptosis in the myeloma cells after 2 days (23.9±3.9 for RPMI8226 and 20.4±6.2 for MM1.s, percent control apoptosis). Thus like normal plasma cells, CD28 and CD86 are required for the survival of myeloma cells. To determine why silencing of CD86 has a more potent effect than CD28 silencing on myeloma cell survival in 2 out of 3 cell lines, we investigated the effects of silencing on cell surface expression of each of these proteins. CD28 and CD86 mRNA and protein levels were silenced to similar levels by their cognate hairpins. However, in MM.1s and RPMI8226 we found that silencing of CD28 resulted in an increase in CD86 surface expression. This increase was also observed at the mRNA level and in the cells over-expressing Bcl-2 family members, indicating that this is not simply due to the selection of the highest expressing cells. These data suggest a feedback loop exists to regulate CD28-CD86 signaling in myeloma cells. Surprisingly, in the KMS18 cell line, we observe the converse effect, where silencing of CD86 resulted in upregulation of CD28. This provides a likely explanation for why these cells are less susceptible to CD86 silencing than the other two lines. Interestingly, blocking CD86 with CTLA4-Ig treatment also resulted in a modest upregulation in CD28 surface expression of MM.1s and RPMI8226, which suggests that silencing CD86 and binding of CD86 with a soluble receptor are not equivalent, and that multiple signaling feedback pathways exist to regulate the expression of this receptor-ligand pair that is necessary for myeloma cell survival. Disclosures: No relevant conflicts of interest to declare.

Description: Multiple myeloma is an incurable hematological malignancy of transformed plasma cells. Many cellular interactions and soluble factors have been demonstrated to play a role in myeloma pathogenesis; however, novel targets to enhance therapeutic intervention are needed. We have demonstrated that CD28 signaling in myeloma cells supports their survival during chemotherapeutic challenge in vitro and in vivo. However, the cellular mechanisms by which CD28 confers this survival advantage to myeloma cells are not completely understood. CD28 is best characterized as the canonical T cell co-stimulatory molecule. During T cell activation, CD28 signaling induces glycolysis, a metabolic program required for T cell proliferation and functional maturation. In the absence of glycolysis, T cells utilize fatty acid oxidation for energy production through the mitochondria. However, the way in which CD28 regulates metabolism in multiple myeloma is not well understood. Here we present evidence that CD28 signaling induces glut1 expression, and that poisoning the glycolytic pathway inhibits proliferation and survival of myeloma cells. AMPK, an energy sensitive kinase known to regulate metabolism by driving fatty acid oxidation, is normally activated when cellular energy levels are low. Interestingly, poisoning glycolysis with a glucose analogue that cannot be processed (2DG) leads to AMPK inhibition in myeloma cells. Furthermore, pharmacological activation of AMPK by AICAR, an AMP analogue, is not sufficient to rescue myeloma cell proliferation from glycolytic inhibition and in fact increases cell death (p

Description: Key Points CD28 delivers a pro-survival signal to MM cells via regulation of PI3K/Akt, FoxO3a, and Bim. Blockade of CD28:CD80/CD86 in vivo resensitizes MM cells to chemotherapy and significantly reduces tumor burden.

Description: Abstract 1111 Multiple myeloma is a neoplasm of bone marrow resident plasma cells characterized by its dependence on the bone marrow microenvironment (BME) for production of survival factors including IL-6, a prototypic cytokine in myeloma biology. However, little is known about the molecular and cellular components of the BME involved in IL-6 production. At the cellular level, we and others have previously shown that dendritic cells (DC)-expressing CD80/CD86 (ligands with short cytoplasmic tails and signaling partners of CD28 expressed on myeloma cells) - in the bone marrow microenvironment have been implicated as being an important component. At the molecular level, the CD28-CD80/86 and Notch1-Jagged2 pathways were separately implicated by us (in DC) and others (in stromal cells) in myeloma induced IL-6 production. Blocking either of the pathways causes significant decrease in IL-6 production suggesting crosstalk between the two pathways. To test our hypothesis, DC were stimulated with CD28-Ig (a soluble form of CD28 which mimicks myeloma cell-bound CD28) in the presence or absence of an inhibitor of Notch signaling -DAPT. DC treated with CD28-Ig and DAPT significantly downregulated IL-6 production when compared to DC treated with CD28-Ig alone. This decrease was not due to the decrease in CD80/86 expression on DC. Our results suggest that CD28 mediated IL-6 production is dependent on Notch signaling and crosstalk between the Notch1-Jagged2 and CD28-CD80/86 pathways leads to IL-6 production by DC. Crosstalk between CD28-CD80/86 and Notch1-Jagged2 pathways was also observed in murine bone marrow derived dendritic cells (BMDC), where a significant down regulation of IL-6 was observed upon blocking Notch signaling. One possible mechanism of crosstalk involves direct effect of CD80/86 crosslinking by CD28-Ig on Notch expression/signaling leading to increase in IL-6 production. We tested for this possibility in DC and found no significant change in Notch expression/signaling. We thus hypothesized that the mechanism of crosstalk involves molecules downstream of Notch and/or CD80/86. Notch signaling has been reported to be involved in the regulation of PTEN (a negative regulator of the PI3K/Akt pathway). Previous studies have also shown the importance of FoxO3a-a transcription factor tightly regulated by Akt- in regulating IL-6 production in BMDC upon CD80/86 crosslinking. We therefore tested the possible involvement of PTEN (molecule downstream of Notch signaling), PI3K-Akt-FoxO3a axis (downstream of CD80/86) in crosstalk between the two pathways aforementioned by testing the effect of GSI on their regulation at the protein level. Blocking PI3K causes significant decrease in IL-6 production by DC and also decreases phosphorylation of Akt and FoxO3a. Similarly results were observed with blocking Akt activation. Blocking Notch signaling downregulates activation of p-Akt and p-FoxO3a suggesting that crosstalk between Notch-CD80/86 signaling involves PI3K-Akt-FoxO3a axis. Additionally, Notch regulates PI3K pathway via inactivation of PTEN and activation of casein kinase II (a molecule known to phosphorylate PTEN). We propose a model of crosstalk between Notch and CD80/86 signaling involving negative regulation of PTEN (which in turn is regulated by casein kinase II) which drives IL-6 production by PI3K-Akt-FoxO3a upon crosslinking CD80/86 by CD28-Ig. We have previously reported that in the myeloma BME, DC backsignaling via CD80/86 is also involved in production of indoleamine 2, 3 dioxygenase (IDO), an immunosuppressive enzyme which breaks down tryptophan to L-kynurenine rendering T cells inactive. To test if the model of crosstalk between Notch and CD80/86 signaling is similar in IDO activity, we treated DC with CTLA4-Ig with DAPT/PI3K inhibitor and found significant downregulation of IDO activity suggesting the involvement of PI3K pathway in crosstalk. Though the median survival and progression-free survival of myeloma patients has doubled over the past decade, it remains incurable prompting the need for finding new targets. Our work helps decipher molecules involved in IL-6 and IDO (important cytokines in myeloma biology) production in the BME of myeloma thus providing novel therapeutic targets. Furthermore, expression of CD28 on T cells and long lived plasma cells (as shown by us previously) helps extend our model of crosstalk to understanding their biology as well. Disclosures: No relevant conflicts of interest to declare.

Description: Despite major advances in chemotherapy, multiple myeloma remains incurable and in need of new therapies that target novel pathways. Insufficient understanding of the molecular pathways that regulate survival in myeloma is a major impediment towards designing better therapies to prolong survival in patients or even cure the disease. This necessitates the identification of new protein targets that are crucial for the growth and survival of multiple myeloma. Just like normal plasma cells, MM cells also depend on their interactions with bone marrow stromal cells (BMSC) for survival and production of essential growth factors. We have previously shown that MM cells interact with dendritic cells (DC) in the microenvironment and in vitro can stimulate DC to produce IL-6 (ASH2010#132, ASH2011 #147, ASH2012#722). Our recent publications show that when MM cells are not in direct contact with DC, the IL-6 produced by DC can protect MM cells against dexamethasone induced cell death, while neutralizing the IL-6 with antibodies can reverse that effect (Nair et al., 2011). Unfortunately, exactly how this survival response is mediated in MM is not very clear. PIM2, a serine threonine kinase, part of the proto-oncogene group of PIM kinases has been implicated in survival in several types of cancers including prostate cancer and multiple myeloma. In our lab, microarray gene expression analysis of publicly available datasets (Figure 1) show a trend towards increased expression of PIM2 in plasma cells from myeloma patients (left panel), and significantly in the poor prognosis subgroup MAF (Zhan et al., 2006) (right panel). For the first time we show that IL-6 produced by DC may be protecting myeloma cells by up regulating PIM2 and inactivating a major protein translation inhibitor 4EBP1, which also happens to be a PIM2 target. We show that silencing PIM2 with siRNA down regulates PIM2 activity and reverses the inactivation of 4EBP1, while the latter is known to cause cell death in myeloma. We also demonstrate that neutralizing IL-6 in MM cells that either don’t produce IL-6 on their own (MM.1S) or those that do (U266), abrogates extraneous DC-IL6 ability to induce PIM2 and its downstream target 4EBP1. Recombinant IL-6 also provided similar induction of PIM2 in myeloma and increased 4EBP1 phosphorylation, which was again reversed by neutralizing the antibody against IL-6. In myeloma patients, the use of dexamethasone in frontline therapies is often complicated by the ability of the bone marrow environment to produce IL-6 that not only induce increased proliferation of MM but also help resist dexamethasone mediated cell death in myeloma. Interestingly, when we used a novel PIM2 inhibitor, JP_11646 (kindly provided by Jasco Pharmaceuticals, LLC), it not only arrested IL-6 induced proliferation even at sub-lethal doses, but also prevented IL-6 mediated rescue of myeloma cells (Figure 2). This suggests that PIM2 might be a major player in IL-6 mediated drug resistance in myeloma and targeting it may help to subvert IL-6 mediated survival in myeloma. Through RT-PCR and westerns, we also show that IL-6 modulates PIM2 expression and activity resulting in increased 4EBP1 phosphorylation (Figure 3). This was abrogated when PIM2 activity was inhibited by JP_11646 (Figure 3). We also present data that suggests IL-6 via PIM2 may be regulating other anti-apoptotic molecules downstream of IL-6 receptors including MCL-1, that is vital to MM survival. Developing PIM2 targeted therapies provides an exciting opportunity to affect the myeloma tumor microenvironment where MM induced IL-6 production from BM could be inducing drug resistance. Figure 1: Microarray expression ofPIM2 in myeloma and MAF Figure 1:. Microarray expression ofPIM2 in myeloma and MAF Figure 2: PIM2 inhibition abrogates IL-6 induced MM proliferation (A) and protection (B). Figure 2:. PIM2 inhibition abrogates IL-6 induced MM proliferation (A) and protection (B). Figure 3: Inhibiting PIM2 activity prevents PIM2 induced phosphorylation of 4EBP1 by IL-6 in myeloma Figure 3:. Inhibiting PIM2 activity prevents PIM2 induced phosphorylation of 4EBP1 by IL-6 in myeloma Disclosures Caserta: Jasco Pharmaceuticals LLC: Equity Ownership. Baldino:Jasco Pharmaceuticals LLC: Equity Ownership.

Description: Abstract 473 Multiple myeloma (MM) is the second most common hematologic malignancy and remains incurable for most patients. Myeloma cells are the transformed counterpart of the normal, bone marrow-resident long lived plasma cells (LLPC) that can survive for years to decades and are also responsible for long-term production of protective antibody titers. Critical interactions between MM and their bone marrow stromal cells (BMSC), that are important for their long term survival and chemotherapy resistance (in MM) identifies potential therapeutic targets, and are often the target for many IMIDs (thalidomide, lenalidomide). However, the specific molecular and cellular components of these interactions remain poorly characterized. These interactions directly transduce pro-survival signals to the myeloma cells as well as induce niche production of supportive soluble factors, the prototypic example being MM induction of stromal IL-6 - a key pro-MM survival cytokine. Despite this importance, the specific molecular and cellular components involved in these interactions remain poorly characterized. We have previously shown that CD28 expressed on human myeloma cells directly transduces a survival signal to MM cells upon binding its CD80/CD86 ligands on conventional (myeloid) dendritic cells (DC), and that DC preferentially co-localize with myeloma cells in the patient bone marrow niche. In our previous presentation at ASH (2010), we showed that myeloma cells interact with DCs to produce immunosuppressive factors such as IDO, and protects myeloma cells against cell death via a CD28-B7 mediated interaction. We now show that DC-IDO not only suppresses T-cell proliferation in invitro assays, but also contributes to the immunosuppressive milieu by inducing naïve T-cells to form T-regs (Fig 1). We hypothesize that while IDO activity by itself can suppress T-cell proliferation and induce T-cell growth arrest and apoptosis, the generation of T-regs by these immunosuppressive DCs (previous studies have shown a close association of T-regs with myeloma cells) form two facets of an immunosuppressive defense that myeloma cells mount against the body's anti-myeloma immune response.Figure 1Figure 1. As we have shown in our earlier presentations at ASH, on the myeloma side, the activation of CD28 induces pro-survival responses that can be extinguished by blocking CD28-B7 interactions between myeloma cells and DCs. Now we show that CD28 activation is accompanied by rapid tyrosine phosphorylation of CD28, association of p85 (PI3K), activation of Vav-1 and increase in CD28 associated tyrosine kinase activity, as shown by immunoprecipitation, western and kinase activity assays. Our data suggests a role for SLP76 downstream of Vav1 in CD28 mediated survival of myeloma cells. Immunoassays with protein extracts from myeloma cells that were previously co-cultured with DCs and isolated using positive magnetic selection show a decrease in BLIMP1 expression (Fig 2) that correlates with published data by other groups that indicates that DC mediated increase in myeloma clonogenicity/tumorigenicity is accompanied by increases in BCL6 (a negative regulator of BLIMP1). Blocking CD28-B7 interactions between myeloma and dendritic cells reversed this decrease in BLIMP1 expression. The implications of this to myeloma survival is currently under study in our lab.Figure 2Figure 2. In summary, we propose that CD28 expressed by myeloma cells serves as a central molecular bridge within a complex and integrated cellular and soluble factor microenvironment necessary for MM cell survival. CD28 directly delivers a pro-survival signal to the myeloma cell, and by ligating CD80/CD86 on conventional DC backsignals to these stromal cells to elicit immunosuppressive enzyme IDO and inducing immunosuppressive T-regulatory cells. Although undoubtedly incomplete, this model begins to point to novel therapeutic targets for the treatment of multiple myeloma. Disclosures: No relevant conflicts of interest to declare.