scholarly journals The Tubulin Inhibitor VERU-111 in Combination With Vemurafenib Provides an Effective Treatment of Vemurafenib-Resistant A375 Melanoma

2021 ◽  
Vol 12 ◽  
Author(s):  
Hongmei Cui ◽  
Qinghui Wang ◽  
Duane D. Miller ◽  
Wei Li
Keyword(s):  
Critical Role ◽  
Single Agent ◽  
Braf Inhibitor ◽  
Inhibitory Effect ◽  
Braf V600e ◽  
Akt Pathway ◽  
Great Promise ◽  
Tubulin Inhibitor

Melanoma is one of the deadliest skin cancers having a five-year survival rate around 15–20%. An overactivated MAPK/AKT pathway is well-established in BRAF mutant melanoma. Vemurafenib (Vem) was the first FDA-approved BRAF inhibitor and gained great clinical success in treating late-stage melanoma. However, most patients develop acquired resistance to Vem within 6–9 months. Therefore, developing a new treatment strategy to overcome Vem-resistance is highly significant. Our previous study reported that the combination of a tubulin inhibitor ABI-274 with Vem showed a significant synergistic effect to sensitize Vem-resistant melanoma both in vitro and in vivo. In the present study, we unveiled that VERU-111, an orally bioavailable inhibitor of α and β tubulin that is under clinical development, is highly potent against Vem-resistant melanoma cells. The combination of Vem and VERU-111 resulted in a dramatically enhanced inhibitory effect on cancer cells in vitro and Vem-resistant melanoma tumor growth in vivo compared with single-agent treatment. Further molecular signaling analyses demonstrated that in addition to ERK/AKT pathway, Skp2 E3 ligase also plays a critical role in Vem-resistant mechanisms. Knockout of Skp2 diminished oncogene AKT expression and contributed to the synergistic inhibitory effect of Vem and VERU-111. Our results indicate a treatment combination of VERU-111 and Vem holds a great promise to overcome Vem-resistance for melanoma patients harboring BRAF (V600E) mutation.

scholarly journals Hydroxychloroquine Synergizes With The PI3K Inhibitor BKM120 to Exhibit Antitumor Efficacy Independent of Autophagy

2021 ◽  
Author(s):  
Xin Peng ◽  
Shaolu Zhang ◽  
Wenhui Jiao ◽  
Zhenxing Zhong ◽  
Yuqi Yang ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Cell Biology ◽  
Molecular Mechanisms ◽  
Critical Role ◽  
Single Agent ◽  
Antitumor Efficacy ◽  
Antitumor Effects ◽  
Autophagy Inhibitor

Abstract Background: The critical role of phosphoinositide 3-kinase (PI3K) activation in tumor cell biology has prompted massive efforts to develop PI3K inhibitors (PI3Kis) for cancer therapy. However, recent results from clinical trials have shown only a modest therapeutic efficacy of single-agent PI3Kis in solid tumors. Targeting autophagy has controversial context-dependent effects in cancer treatment. As a FDA-approved lysosomotropic agent, hydroxychloroquine (HCQ) has been well tested as an autophagy inhibitor in preclinical models. Here, we elucidated the novel mechanism of HCQ alone or in combination with PI3Ki BKM120 in the treatment of cancer.Methods: The antitumor effects of HCQ and BKM120 on three different types of tumor cells were assessed by in vitro PrestoBlue assay, colony formation assay and in vivo zebrafish and nude mouse xenograft models. The involved molecular mechanisms were investigated by MDC staining, LC3 puncta formation assay, immunofluorescent assay, flow cytometric analysis of apoptosis and ROS, qRT-PCR, Western blot, comet assay, homologous recombination (HR) assay and immunohistochemical staining. Results: HCQ significantly sensitized cancer cells to BKM120 in vitro and in vivo. Interestingly, the sensitization mediated by HCQ could not be phenocopied by treatment with other autophagy inhibitors (Spautin-1, 3-MA and bafilomycin A1) or knockdown of the essential autophagy genes Atg5/Atg7, suggesting that the sensitizing effect might be mediated independent of autophagy status. Mechanistically, HCQ induced ROS production and activated the transcription factor NRF2. In contrast, BKM120 prevented the elimination of ROS by inactivation of NRF2, leading to accumulation of DNA damage. In addition, HCQ activated ATM to enhance HR repair, a high-fidelity repair for DNA double-strand breaks (DSBs) in cells, while BKM120 inhibited HR repair by blocking the phosphorylation of ATM and the expression of BRCA1/2 and Rad51. Conclusions: Our study revealed that HCQ and BKM120 synergistically increased DSBs in tumor cells and therefore augmented apoptosis, resulting in enhanced antitumor efficacy. Our findings provide a new insight into how HCQ exhibits antitumor efficacy and synergizes with PI3Ki BKM120, and warn that one should consider the “off target” effects of HCQ when used as autophagy inhibitor in the clinical treatment of cancer.

scholarly journals KIF15 Promotes Proliferation and Growth of Hepatocellular Carcinoma

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Yue-Feng Sun ◽  
Hong-Li Wu ◽  
Rui-Fang Shi ◽  
Lin Chen ◽  
Chao Meng
Keyword(s):  
Hepatocellular Carcinoma ◽  
Liver Cancer ◽  
Critical Role ◽  
Great Promise ◽  
Cell Processes ◽  
Multiple Cell ◽  
Molecular Therapeutic ◽  
Molecular Therapeutic Targets

Liver cancer is thought as the most common human malignancy worldwide, and hepatocellular carcinoma (HCC) accounts for nearly 90% liver cancer. Due to its poor early diagnosis and limited treatment, HCC has therefore become the most lethal malignant cancers in the world. Recently, molecular targeted therapies showed great promise in the treatment of HCC, and novel molecular therapeutic targets is urgently needed. KIF15 is a microtubule-dependent motor protein involved in multiple cell processes, such as cell division. Additionally, KIF15 has been reported to participate in the growth of various types of tumors; however, the relation between KIF15 and HCC is unclear. Herein, our study investigated the possible role of KIF15 on the progression of HCC and found that KIF15 has high expression in tumor samples from HCC patients. KIF15 could play a critical role in the regulation of cell proliferation of HCC, which was proved by in vitro and in vivo assays. In conclusion, this study confirmed that KIF15 could be a novel therapeutic target for the treatment of HCC.

scholarly journals PERK mediates resistance to BRAF inhibition in melanoma with impaired PTEN

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Yifei Qin ◽  
Qiang Zuo ◽  
Lei Huang ◽  
Liping Huang ◽  
Glenn Merlino ◽  
...  
Keyword(s):  
Critical Role ◽  
Acquired Resistance ◽  
Braf Inhibitor ◽  
Treatment Needs ◽  
Braf Inhibition ◽  
Melanoma Treatment ◽  
Pten Inhibition ◽  
Mutant Braf

AbstractTargeting mutant BRAF in patients with melanomas harboring this oncogene has been highly successful as a first-line treatment, but other mutations may affect its efficacy and alter the route of acquired resistance resulting in recurrence and poor prognosis. As an evolving strategy, melanoma treatment needs to be expanded to include targets based on newly discovered emerging molecules and pathways. We here show that PERK plays a critical role in BRAF inhibitor-acquired resistance in melanoma with impaired PTEN. Inhibition of PERK by either shRNA or a pharmacological inhibitor blocked the growth of BRAF inhibitor-resistant melanoma with impaired PTEN in vitro and in vivo, suggesting an effective approach against melanomas with mutant BRAF and PTEN deficiency. Our current findings, along with our previous discovery that the AXL/AKT axis mediates resistance to BRAF inhibition in melanoma with wild-type PTEN, provide new insights toward a strategy for combating BRAF inhibition-acquired resistance in BRAF mutant melanoma with different PTEN statuses.

scholarly journals A Ral GAP complex links PI 3-kinase/Akt signaling to RalA activation in insulin action

2011 ◽  
Vol 22 (1) ◽  
pp. 141-152 ◽  
Author(s):  
Xiao-Wei Chen ◽  
Dara Leto ◽  
Tingting Xiong ◽  
Genggeng Yu ◽  
Alan Cheng ◽  
...  
Keyword(s):  
Glucose Transporter ◽  
Critical Role ◽  
Inhibitory Effect ◽  
Small Gtpase ◽  
Regulatory Subunit ◽  
Hydrolysis Of ◽  
Identification And Characterization

Insulin stimulates glucose transport in muscle  and adipose tissue by translocation of glucose transporter 4 (GLUT4) to the plasma membrane. We previously reported that activation of the small GTPase RalA downstream of PI 3-kinase plays a critical role in this process by mobilizing the exocyst complex for GLUT4 vesicle targeting in adipocytes. Here we report the identification and characterization of a Ral GAP complex (RGC) that mediates the activation of RalA downstream of the PI 3-kinase/Akt pathway. The complex is composed of an RGC1 regulatory subunit and an RGC2 catalytic subunit (previously identified as AS250) that directly stimulates the guanosine triphosphate hydrolysis of RalA. Knockdown of RGC proteins leads to increased RalA activity and glucose uptake in adipocytes. Insulin inhibits the GAP complex through Akt2-catalyzed phosphorylation of RGC2 in vitro and in vivo, while activated Akt relieves the inhibitory effect of RGC proteins on RalA activity. The RGC complex thus connects PI 3-kinase/Akt activity to the transport machineries responsible for GLUT4 translocation.

scholarly journals ROS-mediated inactivation of the PI3K/AKT pathway is involved in the antigastric cancer effects of thioredoxin reductase-1 inhibitor chaetocin

2019 ◽  
Vol 10 (11) ◽  
Author(s):  
Chuangyu Wen ◽  
Huihui Wang ◽  
Xiaobin Wu ◽  
Lu He ◽  
Qian Zhou ◽  
...  
Keyword(s):  
Critical Role ◽  
Thioredoxin Reductase ◽  
Akt Pathway ◽  
Ros Generation ◽  
In Vivo Models ◽  
M Phase ◽  
Tumorigenesis And Progression ◽  
Induced Apoptosis

Abstract Novel drugs are urgently needed for gastric cancer (GC) treatment. The thioredoxin-thioredoxin reductase (TRX-TRXR) system has been found to play a critical role in GC tumorigenesis and progression. Thus, agents that target the TRX-TRXR system may be highly efficacious as GC treatments. In this study, we showed that chaetocin, a natural product isolated from the Chaetomium species of fungi, inhibited proliferation, induced G2/M phase arrest and caspase-dependent apoptosis in both in vitro and in vivo models (cell xenografts and patient-derived xenografts) of GC. Chaetocin inactivated TRXR-1, resulting in the accumulation of reactive oxygen species (ROS) in GC cells; overexpression of TRX-1 as well as cotreatment of GC cells with the ROS scavenger N-acetyl-L-cysteine attenuated chaetocin-induced apoptosis; chaetocin-induced apoptosis was significantly increased when GC cells were cotreated with auranofin. Moreover, chaetocin was shown to inactivate the PI3K/AKT pathway by inducing ROS generation; AKT-1 overexpression also attenuated chaetocin-induced apoptosis. Taken together, these results reveal that chaetocin induces the excessive accumulation of ROS via inhibition of TRXR-1. This is followed by PI3K/AKT pathway inactivation, which ultimately inhibits proliferation and induces caspase-dependent apoptosis in GC cells. Chaetocin therefore may be a potential agent for GC treatment.

scholarly journals hsa_circ_0023409 Accelerates Gastric Cancer Cell Growth and Metastasis Through Regulating the IRS4/PI3K/AKT Pathway

2021 ◽  
Vol 30 ◽  
pp. 096368972097539
Author(s):  
Jian Li ◽  
Yongjing Yang ◽  
Dequan Xu ◽  
Ling Cao
Keyword(s):  
Gastric Cancer ◽  
Histological Grade ◽  
Human Life ◽  
Critical Role ◽  
Luciferase Reporter ◽  
Akt Pathway ◽  
Migration And Invasion ◽  
Circular Rnas

Gastric cancer (GC) is a big threat to human life and health. Circular RNAs (circRNAs), a subclass of noncoding RNAs, were reported to play a critical role in GC progression. Here, we investigated the role of a novel circRNA named hsa_circ_0023409 in GC and its mechanism. Hsa_circ_0023409 expression in GC and adjacent tissues was examined by quantitative real-time polymerase chain reaction and in situ hybridization. The functions of hsa_circ_0023409 in GC cells were assessed both in vitro and in vivo. Immunofluorescence staining was performed for the localization of hsa_circ_0023409 and miR-542-3p in cells. The interaction between hsa_circ_0023409 and miR-542-3p, and miR-542-3p and insulin receptor substrate 4 (IRS4) was detected by dual-luciferase reporter assay. The effect of hsa_circ_0023409, miR-542-3p, and IRS4 on IRS4/phosphatidylinositol 3-kinase (PI3K)/AKT pathway was detected by western blot. The results showed that hsa_circ_0023409 was mainly located in cytoplasm and highly expressed in GC tissues and cells. Moreover, hsa_circ_0023409 showed positive correlation with tumor size, histological grade, and tumor–node–metastasis staging of GC patients. Functional studies showed that hsa_circ_0023409 promoted cell viability, proliferation, migration, and invasion and suppressed apoptosis in GC. Mechanism studies demonstrated that hsa_circ_0023409 upregulated IRS4 via sponging miR-542-3p in GC cells. Furthermore, IRS4 overexpression activated the PI3K/AKT pathway and reversed the inhibitory effect of hsa_circ_0023409 knockdown on the PI3K/AKT pathway. Taken together, we prove that hsa_circ_0023409 activates IRS4/PI3K/AKT pathway by acting as a sponge for miR-542-3p, thus promoting GC progression, indicating that hsa_circ_0023409 may serve as a potential target for treatment of GC and prognosis of GC patients.

Alpha Lipoic Acid (ALA) Inhibits the Anti-Myeloma Effects of Bortezomib.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3832-3832 ◽  
Author(s):  
Jeffrey A Steinberg ◽  
Jing Shen ◽  
Eric Sanchez ◽  
Haiming Chen ◽  
Zhi-Wei Li ◽  
...  
Keyword(s):  
Cell Viability ◽  
Cell Lines ◽  
Vascular Dysfunction ◽  
Single Agent ◽  
Inhibitory Effect ◽  
Control Group ◽  
Treatment Schedule ◽  
20 Nm

Abstract Abstract 3832 Poster Board III-768 Introduction ALA is an antioxidant often used in the management of peripheral neuropathy (PN) for patients with multiple myeloma (MM). A clinical trial evaluating ALA in diabetic neuropathy showed this drug to be effective for patients with both somatic and autonomic neuropathies. It also normalized the endoneural blood flow, reduced oxidative stress and improved vascular dysfunction. Bortezomib (Velcade®), the first-in-class proteasome inhibitor (PI), which is approved for the treatment of patients with MM, may cause PN. As a result, patients are often treated empirically with ALA. In this study, we investigated whether ALA has any impact on the anti-MM effects of bortezomib. Methods First, cells from the MM cell lines RPMI8226 and MM1S (1×105 cells per 100μl) were treated with ALA alone to determine whether ALA had any effects on their growth as determined with an MTS assay. MM cells were plated in a 96-well plate using serum-free media. The cells were treated with either media alone or ALA at concentrations ranging from 1 to 1000 μM for 48 hours. The acidity of ALA at these doses was determined and if the pH was less than 7, we neutralized it using NaOH. Second, we measured the proliferation of cells exposed to bortezomib alone and combinations of a fixed concentration of bortezomib and escalating concentrations of ALA. Results The exposure of cells to ALA alone had a stimulatory effect on the growth of both MM cell lines in vitro. ALA alone at 1000 μM resulted in an increase in cell viability of MM1S cells by approximately 10% when compared to the control group. ALA alone also stimulated the growth of RPMI8226 cells but at much lower concentrations than observed for MM1S. Compared to untreated cells, there was an increase in cell viability with ALA at concentrations as low as 1 μM and a concentration dependent increase at concentrations of 1, 10, 100, and 1000 μM in RPMI8226 cells. At the highest concentration (1000 μM) of ALA, cell viability increased 150% when compared to RPMI8226 cells incubated with media alone. Next, we evaluated the effect of ALA on bortezomib's anti-MM activity. As a single agent, bortezomib reduced MM1S (20 nM) and RPMI8226 (5 nM) cell viability by 93% and 70% respectively. When ALA was added at a clinically achievable concentration (100 μM) to bortezomib (RPMI8226, 5 nM; MM1S, 20 nM), a reduction in the anti-MM effects of bortezomib on these cell lines was observed when compared to bortezomib treatment alone. Compared to bortezomib alone, the combination of ALA plus bortezomib doubled cell viability (increased RPMI8226 and MM1S cell viability from 32.5% to 65% and 7.5% to 15%, respectively). These negative effects of ALA on bortezomib's anti-MM activity were consistently observed in multiple experiments involving both of these cell lines evaluating concentrations of ALA ranging from 100 to 1000 μM and bortezomib ranging from 5 to 20 nM. Conclusions Our data suggest that ALA has the potential to antagonize the anti-MM effects of bortezomib based on our in vitro results using MM cell lines. Thus, it is possible that ALA could negatively impact the therapeutic benefit of bortezomib for MM patients and this requires further study especially if ALA is accepted as an intervention in bortezomib-related neuropathy. We are currently completing studies evaluating primary MM patients' tumor cells in vitro and our human MM xenograft models in vivo to further validate this impact of ALA on bortezomib's anti-MM activity and whether changes in treatment schedule of these drugs may prevent this inhibitory effect from occurring. In addition, because part of bortezomib's anti-tumor effects are related to reactive oxygen species (ROS) levels, we are evaluating whether the inhibitory effects of ALA on this PI may be overcome by increasing intracellular ROS levels. Disclosures: Hilger: Millennium Pharmaceutcals: Employment. Berenson:Millennium Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding, Speakers Bureau.

PTH- PTHR1 Axis Control on Anti-Myeloma Effect of Proteasome Inhibitors

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 5017-5017
Author(s):  
Maurizio Zangari ◽  
Fang Xiao ◽  
Ye Yang ◽  
Hongwei Xu ◽  
Guido J. Tricot ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Conflicts Of Interest ◽  
Single Agent ◽  
Proteasome Inhibitors ◽  
In Vitro Study ◽  
Inhibitory Effect ◽  
Tumor Burden ◽  
Control Group

Abstract Abstract 5017 Multiple myeloma (MM) is a plasma cell malignancy with high osteolytic capacity and impaired bone formation. Our recent studies have demonstrated that PTH serum increases are associated with Bortezomib responses in multiple myeloma patients, indicating a possible role of PTH in anti myeloma effect of Bortezomib. We first tested the 5TGM1 cell line for sensitivity to bortezomib, PTH, and [TYR34]bPTH-(7-34) bovine (a specific PTHR1 inhibitor) in various combinations. In an in vitro study, 5TGM1 cells were sensitive to cytotoxicity of bortezomib and PTH in a dose dependent fashion. TYR compound was found to have no effect as single agent on 5TGM1 cell survival, but was able to partially block the inhibitory effect of bortezomib on cell growth (Figure 1). In an in vivo study using the 5TGM1 C 57BL/KaLwRijmice, we tested PTH-PTHR1 axis on bortezomib anti-myeloma activity. As shown in Figure 1, mice survival was positively affected by bortezomib administration (P = 0.04), and the combination of PTH + bortezomib showed a trend to further improve survival (P = 0.09). Interestingly, the concomitant use of [TYR] compound with bortezomib completely abrogated the efficacy of the proteasome inhibitor on survival. Tumor burden assessed by M-protein levels decreased consistently in mice treated with bortezomib alone, PTH alone, or a combination of PTH + bortezomib compared with the control group treated with PBS (P = 0.003, P = 0.05, P = 0.01 respectively). Importantly the tumor burden in the mice treated with bortezomib was significantly lower than in mice treated with bortezomib plus the PTH inhibitor (TYR), again indicating that the PTHR inhibitor abrogates the effect of Bortezomib on tumor growth. Similar results were obtained using the same systems for other commercially available proteasome inhibitors. Thus, we conclude that the PTH- PTHR1 pathway appears essential for proteasome inhibition activity in myeloma. Our observations may lead to novel treatment approaches in myeloma. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Hydroxychloroquine synergizes with the PI3K inhibitor BKM120 to exhibit antitumor efficacy independent of autophagy

2021 ◽  
Vol 40 (1) ◽  
Author(s):  
Xin Peng ◽  
Shaolu Zhang ◽  
Wenhui Jiao ◽  
Zhenxing Zhong ◽  
Yuqi Yang ◽  
...  
Keyword(s):  
Tumor Cells ◽  
Cell Biology ◽  
Molecular Mechanisms ◽  
Critical Role ◽  
Single Agent ◽  
Antitumor Efficacy ◽  
Antitumor Effects ◽  
Autophagy Inhibitor

Abstract Background The critical role of phosphoinositide 3-kinase (PI3K) activation in tumor cell biology has prompted massive efforts to develop PI3K inhibitors (PI3Kis) for cancer therapy. However, recent results from clinical trials have shown only a modest therapeutic efficacy of single-agent PI3Kis in solid tumors. Targeting autophagy has controversial context-dependent effects in cancer treatment. As a FDA-approved lysosomotropic agent, hydroxychloroquine (HCQ) has been well tested as an autophagy inhibitor in preclinical models. Here, we elucidated the novel mechanism of HCQ alone or in combination with PI3Ki BKM120 in the treatment of cancer. Methods The antitumor effects of HCQ and BKM120 on three different types of tumor cells were assessed by in vitro PrestoBlue assay, colony formation assay and in vivo zebrafish and nude mouse xenograft models. The involved molecular mechanisms were investigated by MDC staining, LC3 puncta formation assay, immunofluorescent assay, flow cytometric analysis of apoptosis and ROS, qRT-PCR, Western blot, comet assay, homologous recombination (HR) assay and immunohistochemical staining. Results HCQ significantly sensitized cancer cells to BKM120 in vitro and in vivo. Interestingly, the sensitization mediated by HCQ could not be phenocopied by treatment with other autophagy inhibitors (Spautin-1, 3-MA and bafilomycin A1) or knockdown of the essential autophagy genes Atg5/Atg7, suggesting that the sensitizing effect might be mediated independent of autophagy status. Mechanistically, HCQ induced ROS production and activated the transcription factor NRF2. In contrast, BKM120 prevented the elimination of ROS by inactivation of NRF2, leading to accumulation of DNA damage. In addition, HCQ activated ATM to enhance HR repair, a high-fidelity repair for DNA double-strand breaks (DSBs) in cells, while BKM120 inhibited HR repair by blocking the phosphorylation of ATM and the expression of BRCA1/2 and Rad51. Conclusions Our study revealed that HCQ and BKM120 synergistically increased DSBs in tumor cells and therefore augmented apoptosis, resulting in enhanced antitumor efficacy. Our findings provide a new insight into how HCQ exhibits antitumor efficacy and synergizes with PI3Ki BKM120, and warn that one should consider the “off target” effects of HCQ when used as autophagy inhibitor in the clinical treatment of cancer.

SCIO-469, a Potent and Selective Inhibitor of p38a MAPK, Normalizes the Bone Marrow Microenvironment and Inhibits Multiple Myeloma Cell Proliferation in In Vitro and In Vivo Models.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1501-1501 ◽  
Author(s):  
Aaron N. Nguyen ◽  
Mamatha Reddy ◽  
Margaret Henson ◽  
Elizabeth G. Stebbins ◽  
Gilbert O’Young ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Bone Marrow ◽  
Cell Proliferation ◽  
Drug Resistance ◽  
Critical Role ◽  
Bone Destruction ◽  
Great Promise ◽  
In Vivo Models

Abstract Despite recent advances in the treatment of multiple myeloma (MM), this disease remains incurable. Accumulating evidence suggest that the bone marrow (BM) microenvironment of MM plays a critical role in tumor growth, survival, and drug resistance. A key aspect of this tumor-supportive environment is elevated levels of cytokines and other soluble factors. Most prominent among these is IL-6, which acts as a survival factor for MM cells and promotes their proliferation, migration, and drug resistance. Other mediators also implicated in the disease are VEGF and TNFa. The p38 MAPK is activated by a multitude of signals, including pro-inflammatory cytokines (e.g., TNFa and IL-1ß) and environmental stress. Furthermore, p38 activation has been shown to be important for the synthesis and secretion of IL-6, VEGF, and TNFa. Consequently, inhibition of p38 is postulated to reduce the production of these factors implicated in MM and to have therapeutic benefit by suppressing the tumor-supportive state of the BM microenvironment. Here, we demonstrate that SCIO-469, a specific and potent inhibitor of p38a MAPK, strongly inhibits MM cell proliferation by affecting MM cells directly as well as the BM microenvironment. SCIO-469 directly inhibits MM cell proliferation in long term culture. Importantly, SCIO-469 potently inhibits IL-6 and VEGF secretion from BM stromal cells (BMSC). To examine the effect of inhibiting BMSC-derived factors important in MM, we measured MM cell proliferation using transwell plates that separate BMSC from MM cells via a porous membrane. In transwell plates containing only MM cells, MM cell proliferation was modest and was inhibited by SCIO-469. In contrast, the presence of BMSC in transwell inserts dramatically increased the proliferation of MM cells over the course of the study. This result suggests that factors (e.g., IL-6) secreted by BMSC greatly stimulate MM cell proliferation. When SCIO-469 was added to these transwell cultures containing BMSC, MM cell proliferation was inhibited significantly. Consistent with these results, we show that levels of IL-6 under these conditions mirror exactly the proliferation of MM cells; IL-6 level is high in vehicle-treated cultures and is suppressed in SCIO-469-treated cultures. Finally, in a mouse xenograft plasmacytoma model of MM, we show that p38 inhibition significantly inhibited the increase in MM tumor volume. Collectively, our data indicate that SCIO-469 is a suppressor of the BM microenvironment and an effective inhibitor of MM cell proliferation in vitro and in vivo. Since SCIO-469 also inhibits secretion of osteoclast-stimulating factors (RANKL, IL-11, and MIP1a) in the microenvironment, SCIO-469 may not only inhibit MM cell survival but may also alleviate bone-related pathologies (bone destruction and osteolytic lesions) commonly associated with MM. Therefore, SCIO-469 may offer great promise for an improved outcome for patients with MM.

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