ALBERT

Description: The authors studied the role that interleukin (IL)-11 plays during the early stages of megakaryocyte (MK) development by investigating its in vitro effects on cell subpopulations enriched for bone marrow primitive progenitor cells and early and late committed progenitor cells. Progenitor subpopulations were isolated from bone marrow of normal or 5-fluorouracil (5FU)-treated mice and separated by sorting based on the surface antigens Sca-1, c-kit, and CD34. Functional analysis of the cell subpopulations, 5FU Lin−Sca-1+c-kit+ or normal bone marrow (NBM) Lin−Sca-1+c-kit+CD34−cells, indicated that exposure of these cells to recombinant human (rh)IL-11 in combination with steel factor (SF) stimulates the formation of colonies in methylcellulose and their proliferation in single cell-containing liquid cultures. Kinetic studies of MK progenitor generation, in response to SF and rhIL-11, demonstrated that a significant number of the progenitors produced are committed to the MK lineage. RhIL-11 also synergized with both SF and IL-3 to stimulate MK colony growth from NBM Lin−Sca-1+c-kit+ cells (early progenitors) and NBM Lin−Sca-1−c-kit+ cells (committed late progenitors). In the presence of IL-3, NBM, Lin−Sca-1−c-kit+ cells responded more strongly to rhIL-11 than SF. Consistent with these results is the observation that IL-11 receptor  chain mRNA is present in all the progenitor cells from which the MKs are derived. This cell culture and RNA analysis suggest that murine bone marrow primitive progenitor cells and early and late progenitor cells are direct targets of rhIL-11 and that rhIL-11 has the potential to promote megakaryocyte development at several very early stages. (Blood, 2000;95:503-509)

Description: Abstract 3835 Poster Board III-771 Introduction The first generation proteasome inhibitor VELCADE® (bortezomib) is indicated for the treatment of patients with multiple myeloma (MM), a form of plasma cell malignancy (PCM). MLN9708 is our novel proteasome inhibitor that selectively and reversibly binds to, and potently inhibits the b5 site of the 20s proteasome in preclinical studies. We have recently demonstrated that MLN9708 significantly prolongs tumor-free survival of double transgenic iMycCa/Bcl-XL mice, a genetically-engineered mouse model of de novo PCM. Here we describe the in vivo evaluation of cell lines derived from double transgenic iMycCa/Bcl-XL mice and the antitumor activity of MLN9708 in a disseminated mouse model of iMycCa/Bcl-XL PCM. Materials MLN9708 immediately hydrolyzes to MLN2238, the biologically active form, upon exposure to aqueous solutions or plasma. MLN2238 was used for all preclinical studies described below. Double transgenic iMycCa/Bcl-XL mice develop de novo PCM, in which neoplastic plasma cell development is driven by the targeted expression of the oncoprotein Myc and anti-apoptotic Bcl-XL (J. Clin. Invest. 113:1763-1773, 2004). DP54 and DP42 are plasma cell tumor cell lines isolated from the bone marrow and lymph nodes, respectively, of syngeneic mice previously inoculated with iMycCa/Bcl-XL tumors (Cancer Res. 67:4069-4078, 2007). In vitro, DP54 and DP42 cells express both the Myc and Bcl-XL transgenes, various plasma cell and B-cell markers including CD38, CD138 and B220, and have gene expression profiles very similar to human MM. Methods Cell viability studies were performed to determine the antiproliferative effects of MLN2238 in DP54 and DP42 cells in vitro. To evaluate DP54 and DP42 cells in vivo, these cells were aseptically inoculated into the tail vein of NOD-SCID mice. Progressions of the resultant PCM were monitored and tumor burdens were evaluated by magnetic resonance imaging (MRI), ex vivo mCT imaging, and histopathology. Mouse plasma samples were collected at the end of the studies and levels of immunoglobulin were assessed. To establish a preclinical disseminated mouse model of iMycCa/Bcl-XL PCM, freshly dissociated DP54-Luc cells (constitutively expressing firefly luciferase under a mouse Ig-k promoter) were aseptically inoculated into the tail vein of NOD-SCID mice. Once tumor growth has been established, mice were randomized into treatment groups and then treated with vehicle, bortezomib (at 0.7mg/kg intravenously [IV] twice weekly [BIW]) or MLN2238 (at 11 mg/kg IV BIW) for 3 consecutive weeks. Tumor burden was measured by bioluminescent imaging. Results In vitro, both DP54 and DP42 cells were sensitive to MLN2238 treatment (LD50 values of 14 and 25 nM, respectively). In vivo, NOD-SCID mice rapidly succumbed to PCM after being inoculated with DP54 and DP42 cells (25 and 14 days post-inoculation, respectively), where the disease was accompanied by marked elevation of plasma immunoglobulins. MRI scans revealed the presence of multiple lesions and several abnormalities were found including: cranial deformation, bowel distortion, splenomegaly and renal edema. Tumor infiltrates, ranging from minor to extensive, were identified in multiple organ compartments (brain

Description: In response to thrombin and other extracellular activators, platelets secrete molecules from large intracellular vesicles (granules) to initiate thrombosis. Little is known about the molecular machinery responsible for vesicle docking and secretion in platelets and the linkage of that machinery to cell activation. We found that platelet membranes contain a full complement of interacting proteins—VAMP, SNAP-25, and syntaxin 4—that are necessary for vesicle docking and fusion with the plasma membrane. Platelets also contain an uncharacterized homologue of the Sec1p family that appears to regulate vesicle docking through its binding with a cognate syntaxin. This platelet Sec1 protein (PSP) bound to syntaxin 4 and thereby excluded the binding of SNAP-25 with syntaxin 4, an interaction critical to vesicle docking. As predicted by its sequence, PSP was detected predominantly in the platelet cytosol and was phosphorylated in vitro by protein kinase C (PKC), a secretion-linked kinase, incorporating 0.87 ± 0.11 mol of PO4 per mole of protein. PSP was also specifically phosphorylated in permeabilized platelets after cellular stimulation by phorbol esters or thrombin and this phosphorylation was blocked by the PKC inhibitor Ro-31-8220. Phosphorylation by PKC in vitro inhibited PSP from binding to syntaxin 4. Taken together, these studies indicate that platelets, like neurons and other cells capable of regulated secretion, contain a unique complement of interacting vesicle docking proteins and PSP, a putative regulator of vesicle docking. The PKC-dependent phosphorylation of PSP in activated platelets and its inhibitory effects on syntaxin 4 binding provide a novel functional link that may be important in coupling the processes of cell activation, intracellular signaling, and secretion.

Description: Abstract 2709 Poster Board II-685 Introduction: The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal manner by which cells regulate protein homeostasis. The successful development of bortezomib for multiple myeloma and previously treated mantle cell lymphoma has validated the proteasome as a therapeutic target for hematological malignancies. MLN9708 was identified in screens for a proteasome inhibitor with greater antitumor activity than bortezomib in preclinical xenograft models. MLN9708 immediately hydrolyzes to MLN2238, the biologically active form, upon exposure to aqueous solutions or plasma. MLN2238 was used for all preclinical studies described below. Results: MLN2238 inhibited the 20S proteasome b5 site (IC50 of 3.4 nM), an engineered proteasome substrate (4x ubiquitin-luciferase reporter) and blocked TNFa-induced activation of the NFkB pathway. Cell viability studies confirmed that MLN2238 has potent activity against both myeloma and lymphoma cell lines. The proteasome dissociation half life of MLN2238 was determined to be approximately 6-fold faster than bortezomib, consistent with data generated from Proteasome-Glo wash out experiments where proteasome activity recovered more quickly in MLN2238-treated cells compared to bortezomib. In immunocompromised mice MLN2238 achieved exposures that resulted in significant blood and tumor proteasome inhibition and had increased plasma and tumor exposure compared to bortezomib (when dosed at MTD). In Sprague-Dawley rats, MLN2238 had improved plasma exposure, lower plasma clearance, higher blood Vdss, better oral F% and higher plasma protein binding than bortezomib. In WSU-DLCL2 xenografts, a model of diffuse large B cell lymphoma, greater antitumor activity was seen in mice treated with IV or SC doses of MLN2238 compared to bortezomib. For example, MLN2238 dosed SC QD at its MTD resulted in a T/C of 0.29 compared to bortezomib dosed SC QD at its MTD which resulted in a T/C of 0.79. Pharmacodynamic (PD) responses (in mice) were assessed by evaluating tumor 20S b5 site-specific activity and expression levels of GADD34, an unfolded protein response (UPR) pathway gene shown to be upregulated in response to proteasome inhibition. Consistent with the efficacy difference between MLN2238 and bortezomib in WSU-DLCL2 xenografts, MLN2238 demonstrated an improved PD response compared to bortezomib, showing higher levels of tumor proteasome inhibition and pathway marker elevation. MLN2238 and bortezomib were then evaluated for their ability to reduce tumor burden and improve overall survival in a disseminated model of lymphoma. Tumor burden was tracked over time via bioluminescent scans in NOD-SCID mice inoculated with OCI-Ly7-luciferase cells. The strongest antitumor response was seen in mice treated with MLN2238 SC QD at its MTD, and this dosing regimen also significantly prolonged overall survival compared to vehicle treated controls (median survival was 54 vs. 33 days). Weaker antitumor responses were seen following treatment with bortezomib (either at its SC QD MTD or weekly IV MTD) and these dose regimens did not significantly prolong survival in this study. Conclusions: MLN2238 is a potent, reversible and orally bioavailable proteasome inhibitor with improved pharmacokinetics, pharmacodynamics and antitumor activity in preclinical xenograft models compared to bortezomib. MLN9708 is currently in clinical development for a variety of oncology indications. Disclosures: Kupperman: Milllennium: Employment. Lee:Milllennium: Employment, Equity Ownership. Cao:Milllennium: Employment, Equity Ownership. Bannerman:Milllennium: Employment. Fitzgerald:Millennium Pharmaceuticals: Employment. Berger:Millennium Pharmaceuticals: Employment. Yu:Millennium Pharmaceuticals: Employment. Zhang:Millennium Pharmaceuticals: Employment. Hales:Millennium Pharmaceuticals: Employment. Bruzzese:Millennium Pharmaceuticals: Employment. Liu:Millennium Pharmaceuticals: Employment. Blank:Millennium Pharmaceuticals: Employment. Garcia:Millennium Pharmaceuticals: Employment. Tsu:Millennium Pharmaceuticals: Employment. Dick:Millennium Pharmaceuticals: Employment. Fleming:Millennium Pharmaceuticals: Employment. Yu:Millennium Pharmaceuticals: Employment. Manfredi:Millennium Pharmaceuticals: Employment. Rolfe:Millennium Pharmaceuticals: Employment. Bolen:Millennium Pharmaceuticals: Employment.

Description: Abstract 1834 Poster Board I-860 Introduction The clinical success of VELCADE® (bortezomib) for Injection has validated the proteasome as a therapeutic target for the treatment of human cancer. The novel proteasome inhibitor MLN9708 is a potent, reversible, and specific inhibitor of the b5 site of the 20S proteasome identified in preclinical studies. MLN9708 is currently in human clinical development for both hematological and non-hematological malignancies. Here we describe the pharmacodynamic (PD) response of MLN9708 in the murine bone marrow compartment and its strong antitumor activity in an intraosseous xenograft model of plasma cell malignancy. Materials MLN9708 immediately hydrolyzes to MLN2238, the biologically active form, upon exposure to aqueous solutions or plasma. MLN2238 was used for all preclinical studies described below. Methods It has been previously shown that double transgenic iMycCa/Bcl-XL mice develop de novo plasma cell malignancies (J. Clin. Invest. 113:1763-1773, 2004) in which neoplastic plasma cell development is driven by the targeted expression of the transgene Myc (c-myc; myelocytomatosis oncogene) and Bcl-x (Bcl2l1; encodes the oncoprotein Bcl-XL). DP54 is a plasma cell tumor cell line derived from the bone marrow of a syngeneic mouse previously inoculated with an iMycCa/Bcl-XL tumor (Cancer Res. 67:4069-4078, 2007). In vitro, DP54 cells express both the Myc and Bcl-XL transgenes, various plasma cell and B-cell markers including CD38, CD138 and B220, and has gene expression profile very similar to human multiple myeloma. To establish a preclinical intraosseous model of plasma cell malignancy for efficacy studies, freshly dissociated DP54-Luc cells (constitutively expressing firefly luciferase under a mouse Ig-k promoter) were aseptically injected into the bone marrow space of the upper shaft of the right tibia of NOD-SCID mice. Once tumor growth has been established, mice were randomized into treatment groups and then treated intravenously (IV) with vehicle, bortezomib (at 0.8 mg/kg twice weekly [BIW]) or MLN2238 (at 11 mg/kg BIW) for 3 consecutive weeks. Tumor burden was measured by bioluminescent imaging. Results MLN2238 strongly inhibited proteasome activity in the blood and bone marrow compartments of mice (maximum b5 inhibition of 84% and 83%, respectively). In vivo, when DP54 cells were aseptically injected into the bone marrow space of the mouse tibia, signs of bone erosion in the tibia, femur and cranial sagittal sultures (as determined by ex-vivo mCT imaging) were observed which resembled osteolytic lesions frequently seen in human multiple myeloma. Dissemination of DP54-Luc cells after intratibia inoculations were detected by in vivo bioluminescent and confirmed by ex vivo imaging where luminescent tumor nodules were detected in the spleen, kidneys, intestine, lymph nodes and bones including right tibia, spine and cranium. To assess the antitumor activity of MLN2238 in the bone marrow compartment, an efficacy study was performed using the DP54-Luc intraosseous xenograft model of plasma cell malignancy. Tumor burden (bioluminescence), osteolytic lesions (mCT) and overall survival after treatment with bortezomib and MLN2238 will be presented. Conclusion The novel proteasome inhibitor MLN9708 demonstrates strong activity in the bone marrow compartment in vivo. MLN9708 is currently in human clinical development for both hematological and solid tumor indications. Disclosures Lee: Milllennium: Employment, Equity Ownership. Bannerman:Milllennium: Employment. Terkelsen:Milllennium: Employment. Bradley:Milllennium: Employment, Equity Ownership, Research Funding. Li:Milllennium: Employment. Li:Milllennium: Employment. Janz:Milllennium: Research Funding. Van Ness:Milllennium: Research Funding. Manfredi:Milllennium: Employment. Kupperman:Milllennium: Employment.

Description: In response to thrombin and other extracellular activators, platelets secrete molecules from large intracellular vesicles (granules) to initiate thrombosis. Little is known about the molecular machinery responsible for vesicle docking and secretion in platelets and the linkage of that machinery to cell activation. We found that platelet membranes contain a full complement of interacting proteins—VAMP, SNAP-25, and syntaxin 4—that are necessary for vesicle docking and fusion with the plasma membrane. Platelets also contain an uncharacterized homologue of the Sec1p family that appears to regulate vesicle docking through its binding with a cognate syntaxin. This platelet Sec1 protein (PSP) bound to syntaxin 4 and thereby excluded the binding of SNAP-25 with syntaxin 4, an interaction critical to vesicle docking. As predicted by its sequence, PSP was detected predominantly in the platelet cytosol and was phosphorylated in vitro by protein kinase C (PKC), a secretion-linked kinase, incorporating 0.87 ± 0.11 mol of PO4 per mole of protein. PSP was also specifically phosphorylated in permeabilized platelets after cellular stimulation by phorbol esters or thrombin and this phosphorylation was blocked by the PKC inhibitor Ro-31-8220. Phosphorylation by PKC in vitro inhibited PSP from binding to syntaxin 4. Taken together, these studies indicate that platelets, like neurons and other cells capable of regulated secretion, contain a unique complement of interacting vesicle docking proteins and PSP, a putative regulator of vesicle docking. The PKC-dependent phosphorylation of PSP in activated platelets and its inhibitory effects on syntaxin 4 binding provide a novel functional link that may be important in coupling the processes of cell activation, intracellular signaling, and secretion.

Description: We have investigated the mechanism of action of the thrombopoietic cytokine, recombinant human interleukin-11 (rhIL-11), on megakaryocytopoiesis in vitro. We have shown that rhIL-11–induced murine and human megakaryocytopoiesis are not mediated by thrombopoietin (Tpo). Murine megakaryocytes (MKs) were produced from bone marrow (BM) mononuclear cells cultured with rhIL-11, IL-3, and a combination of the two cytokines. Conditioned media (CM) were collected and assayed for the presence of biologically active Tpo. Tpo activity was not detected in any of the CMs tested. Next, human BM CD34+ cells were cultured in serum-free fibrin clot medium with rhIL-11, IL-3, or rhIL-11 plus IL-3 and an antibody that neutralizes human Tpo activity. No inhibition of either burst-forming unit-MK– or colony-forming unit-MK–derived colony formation was observed. The antibody did partially inhibit steel factor-induced MK-colony formation, suggesting that the actions of this cytokine are mediated, in part, by Tpo. We determined that MKs can be direct targets of rhIL-11 by showing the expression of functional IL-11 receptor on these cells. Total RNA was prepared from cultured human BM CD41+CD14− cells (MKs) and IL-11 receptor α chain mRNA was detected in the MKs by reverse transcription-polymerase chain reaction. Analysis of single-sorted CD41+CD14− cells confirmed that the observed IL-11 receptor expression was not due to contaminating CD41− cells in the pool. The presence of rhIL-11 receptor α chain protein in the cells was established by Western blot analysis. After a short exposure of purified BM MKs to rhIL-11, enhanced phosphorylation of both its signal transduction subunit, gp130, and the transcription factor, STAT3 was detected, showing a direct activation of receptor signaling by the cytokine. Consistent with the lack of effect of rhIL-11 on platelets in vivo, IL-11 receptor α chain mRNA and protein were not detected in isolated human platelets. These data indicate that rhIL-11 acts directly on MKs and MK progenitors but not on platelets.