Emerging evidence suggests the insulinlike growth factor-1 receptor (IGF-1R) to be an important mediator of tumor-cell survival and resistance to cytotoxic therapy in multiple myeloma (MM). Recently, members of the cyclolignan family have been shown to selectively inhibit the receptor tyrosine kinase (RTK) activity of the IGF-1R ␤-chain. The effects of the cyclolignan picropodophyllin (PPP) were studied in vitro using a panel of 13 MM cell lines and freshly purified tumor cells from 10 patients with MM. PPP clearly inhibited growth in all MM cell lines and primary MM samples cultured in the presence or absence of bone marrow stromal cells. PPP induced a profound accumulation of cells in the G 2 /M-phase and an increased apoptosis. Importantly, IGF-1, IGF-2, insulin, or IL-6 did not reduce the inhibitory effects of PPP. As demonstrated by in vitro kinase assays, PPP down-regulated the IGF-1 RTK activity without inhibiting the insulin RTK activity.This conferred decreased phosphorylation of Erk1/2 and reduced cyclin dependent kinase (CDK1) activity. In addition, the expression of mcl-1 and survivin was reduced. Taken IntroductionThe insulin-like growth factor-1 receptor (IGF-1R) is strongly suggested to play key roles in malignant transformation and in promoting survival of tumor cells from cancers of, for example, breast, prostate, and colon. 1,2 Also in multiple myeloma (MM) cells the IGF-1R has been shown by us and others to stimulate growth and potently mediate survival. [3][4][5][6][7][8][9][10][11] Some characteristic features of the MM disease include growth of tumor cells almost exclusively restricted to the bone marrow, complex genetic aberrations, the presence at a high frequency of illegitimate translocations of a few identified partner genes (ie, 11q13 [cyclin D1], 6p21 [cyclin D3], 4p16 [FGFR3/MMSET],, and 20q11 [mafB]) to the immunoglobulin heavy chain locus, and the altered expression of c-Myc and Bcl-2 family genes. 12 So far, genetic alterations of the IGF-1R in malignant cells, including MM, have not been reported. 13 However, in the bone marrow environment, the IGF-1R in MM cells may become hyperactive as a result of autocrine and/or paracrine stimulation, making molecules of the IGF-1R signaling pathway equally important targets for intervention as mutated oncogenes. Supporting the notion of the hyperactivated IGF-1R in MM is the recent finding that IGF-1 serum level is a prognostic factor in MM. 14 The fact that IGF-1R signaling seems not to be an absolute requirement for maintenance of normal cell homeostasis 13 would encourage the development of IGF-1R inhibitors for clinical use in MM, as they may not be associated with the severe side effects of conventional cytotoxic drugs.On ligand interaction with the IGF-1R ␣-subunit, tyrosine residues in the intracellular, membrane-bound ␤-subunit become autophosphorylated. 15 This enables docking and phosphorylation of the insulin receptor substrate (IRS) and Shc, thereby activating 2 important pathways mediating proliferation and survival, that is...

IntroductionMultiple myeloma (MM) is an incurable tumor, in which the malignant B cells, although often initially sensitive to treatment, inevitably develop resistance to cytotoxic drugs. Glucocorticoids, such as dexamethasone, are known as highly effective drugs against MM 1 and are mostly used in combination with chemotherapeutic agents. 2 Emerging evidence shows the potency of insulinlike growth factor-I receptor (IGF-IR) in mediating survival of MM cells [3][4][5][6] as well as their resistance to cytotoxic treatment. 7,8 The ligands for the IGF-IR (mainly IGF-I and IGF-II) are, besides being present in plasma, abundant in the bone matrix and also produced by several cell types within the bone marrow, such as osteoblasts. 9 Thus, the selective homing of the MM cells within the bone marrow close to the bone tissue will provide the tumor cells with a milieu enriched with IGFs.The rational of mapping and targeting the IGF-IR signaling pathway for use in improved MM therapy rests on 2 fundamental observations. The first is the modest use of IGF-IR signaling in the proliferation of healthy cells in the adult individual. 10 The second is the previously successful strategy of targeting cellular survival circuits in terms of selective kinase inhibitors such as Although several signaling molecules, such as the mitogenactivated protein kinase (MAPK), are activated downstream of the phosphatidylinositol-3-kinase (PI3-K), the Akt pathway is of particular interest because of its role in inhibiting apoptosis and promoting cell proliferation. 12 One candidate target molecule for antitumor therapy is represented by the phosphoprotein mammalian target of rapamycin, mTOR (also known as FRAP , , or RAPT), in which the PI3-K/Akt pathway has been suggested to affect the mTOR phosphorylation state and catalytic activity. 13 Rapamycin binds to its cellular receptor, the immunophilin FK506 binding protein 12 (FKBP12), to form a complex that interacts with mTOR, thereby blocking its activity. 14 Mitogenactivated signaling through mTOR phosphorylates the serine/ threonine kinase p70S6K and the translational repressor eukaryotic initiation factor (eIF) 4E binding protein (4EBP1) also known as PHAS-I. 15 Activated p70S6K directly phosphorylates the 40S ribosomal protein S6, which correlates with enhanced translation of transcripts with 5Ј-terminal oligo-pyrimidine sequences that encode components of the translational machinery. 16 Multisite phosphorylation of 4EBP1 results in its dissociation from eIF4E, thereby allowing eIF4E to participate in assembly of a translational initiation complex leading to translational up-regulation of proteins required for cell cycle progression from G 1 to S phase. 17 Currently, rapamycin is in clinical use because of its effect on preventing allograft rejection without showing the severe side effects usually associated with traditional immunosuppressive therapy. 18,19 Rapamycin has also shown activity against a variety of 20 In the National Cancer Institute (NCI) cell line screening panel, T-cell leuk...

IntroductionMultiple myeloma (MM) is a deadly B-cell malignancy, characterized by the proliferation of monoclonal plasma cells in the bone marrow (BM). There the MM cells secrete high levels of immunoglobulins, induce osteolysis, and activate angiogenesis. 1,2 We have reported that MM cells produce post-switch isotypes of immunoglobulins with clonally fixed hypervariable regions. 3 Whether this switch occurs in lymph nodes, circulation, or BM, the cells need to enter or re-enter the BM where they interact with the stromal cells and receive essential survival and proliferation signals. The homing process has been thoroughly described 4 and chemokines are required for the directed migration of the MM cells to the extravascular compartment of the BM. Once in the BM, MM cells activate osteoclasts, leading to MM-associated bone disease, and endothelial cells (ECs), leading to neovascularization. [5][6][7][8] The expression of vascular endothelial growth factor (VEGF), an EC-specific mitogen, stimulating vascular permeability, 9 has been reported in human 10 MM and by the murine 5TMM cells. 11 Insulin-like growth factor 1 (IGF-1) is an endocrine factor involved in metabolic control and normal growth, having crucial roles in many types of cancer cells. [12][13][14] It is known to be produced by different cell types including BM stromal cells. 15 IGF-1 has been acknowledged to be an important antiapoptotic and proliferation factor for MM cells, stimulating proliferation of both interleukin 6 (IL-6)-independent and -dependent cell lines. [16][17][18][19][20] We and others have shown that IGF-1 also acts as a chemoattractant for MM cells, thus playing a role in the homing of these cells to the BM. [21][22][23] Furthermore, we have previously demonstrated that IGF-1 stimulates VEGF secretion by MM cells, contributing to angiogenesis. 24 The principal pathways for transduction of the IGF-1 receptor (IGF-1R)-mediated signal are the ERK and the Akt pathways. 12,13,24 On ligand interaction with the IGF-1R␣ subunit, residues in the tyrosine kinase domain of the ␤ subunit are autophosphorylated. Additional phosphorylation sites adjacent to these tyrosine residues can serve as a docking site for the adaptor proteins (IRS proteins) mediating activity through the regulatory subunit of PI3K. The receptor can also recruit SHC, leading to activation of the MAPK pathway. 12 Because IGF-1 is a pleiotropic factor in different cancers, it is an attractive target for therapeutic intervention. A variety of strategies have been developed to inhibit the IGF-1R signaling pathways in tumor cells. Recently, a member of the cyclolignan family, picropodophyllin (PPP), was developed by molecular modeling to mimic the 3-dimensional structure of the IGF-1R tyrosine kinase domain. It was shown to potently and selectively inhibit the activity of the IGF-1R tyrosine kinase (IGF-1RTK) in solid tumors. 25 The aim of the present work was to investigate the in vitro and in vivo effects of PPP on MM using the 5T33MM model. This For personal use only. on May ...