Genetic and epigenetic mechanisms of multiple myeloma

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Drug Discovery Today: Disease Mechanisms

DRUG DISCOVERY

TODAY

Editors-in-Chief Toren Finkel – National Heart, Lung and Blood Institute, National Institutes of Health, USA Tamas Bartfai – Harold L. Dorris Neurological Research Center and The Scripps Research Institute, USA

DISEASE Autoimmune diseases MECHANISMS

Genetic and epigenetic mechanisms of multiple myeloma Angelo Vaccaz,*, Claudio Scavelliz, Aldo M Roccaro, Giulia Di Pietro, Franco Dammacco Department of Internal Medicine and Human Oncology, University of Bari Medical School, Policlinico – Piazza Giulio Cesare, 11, I-70124 Bari, Italy

Despite advances in systemic and supportive treatments multiple myeloma remains an incurable disease, and approaches are needed to improve the quality of response to therapy and hopefully overall survival. The pathophysiology of multiple myeloma is complex and still poorly characterised. It entails features of the malignant clone and interactions with bone marrow microenvironment. Multiple myeloma begins when different pathways induce dysregulation of cyclin D and transformation of plasma cells. Evolving mutations and epigenetic mechanisms (angiogenesis, cytokines) lead to progression of disease.

Introduction Multiple myeloma (MM) is a malignant haematological disease characterised by the accumulation of clonal plasma cells in several bone marrow (BM) sites, presence of monoclonal protein in the blood and/or urine, and osteolytic lesions. It represents approximately 1% of all cancers, 2% of all cancer deaths and 20% of deaths due to haematological malignancies [1]. The incidence of MM is age-dependent, and significantly higher in black males [1]. The role of various factors in the pathogenesis of MM, including the immune system, certain occupations, exposure to chemicals and radiation, and, most recently, the human herpes virus 8 (HHV-8) is far from certain, although there is evidence of clustering within *Corresponding author: (A. Vacca) [email protected] z The first two authors contributed equally to this work. 1740-6765/$ ß 2004 Elsevier Ltd. All rights reserved.

DOI: 10.1016/j.ddmec.2004.11.002

Section Editor: Alberto Mantovani – Istituto di Ricerche Farmacologiche Mario Negri, University of Milan, Italy Multiple myeloma (MM) represents a paradigmatic example for tumor progression and for the role of the microenvironment in neoplasia. Here, Angelo Vacca reviews the molecular basis of transformation in MM, MM classification and how the complex interplay between transformed cells and stroma propels growth and progression. The author has a strong background in the field, having in particular discovered the role of angiogenesis in MM, an aspect emphasised in this review.

families [2]. Susceptibility might increase with age and reduction in immune surveillance in step with a lifelong accumulation of toxic insults or antigenic challenges. The microenvironment and inflammatory cells seem to have a paradigmatic role in the development of MM and contribute to tumour growth and progression [3].

B-cell development and malignant clone origin Physiologically, an immature B lymphocyte differentiates in the BM and its heavy (H) and light (L) chain immunoglobulin (Ig) genes are rearranged (VDJ recombination) to create surface IgM molecules, which are receptors for antigen recognition. Naive B lymphocytes migrate to secondary lymphatic tissues, where stimulation with antigen leads to proliferation of the B cells and differentiation into lymphoblasts. Further maturation produces short-lived plasma cells, which secrete IgM (low-affinity antibody response). Antigen-activated cells also enter the germinal centres (GCs) of lymph nodes, where active hypermutation of the IgH and IgL gene sequences (somatic hypermutation) selects a clone expressing a highaffinity IgM. Some clone cells enter the blood as memory cells www.drugdiscoverytoday.com

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(lymphoplasmocytes), some differentiate into post-GC plasmablasts that switch Ig production from IgM to IgG and IgA (occasionally to IgD or IgE) ([IgH]-switch recombination), and migrate to the BM to complete their differentiation into long-lived plasma cells [4]. The normal precursor of MM plasma cells is believed to be a post-GC B-cell, as suggested both by the typical plasmablast and plasma cell habitus, and by molecular evidence of successfully completed somatic hypermutation and IgH switching [5]. However, molecular analysis of peripheral blood mononuclear cells has clearly demonstrated the presence of pre-switch circulating B cells that are clonally identical to the marrow plasma cells (clonotypic B cells) [6]. These cells are probably precursor cells in the context of neoplastic transformation, even if isotype switch variants have been observed as a result of downstream switching or trans-switching to sister chromatids [7]. The clinical role of clonotypic B cells in MM progression is unknown, though they have been correlated with decreased survival [8] insofar as they reflect tumour bulk or are a reservoir of drug-resistant cells.

Biological stepwise course of MM MM develops through several sequential and interrelated steps [9] leading to the progressive acquisition of mutations or dysregulation of genes that control the cell cycle, programmed death (apoptosis) or alter tumour microenvironment interactions. The initial event is the immortalisation of a plasma cell to form a clone that is quiescent, non-accumulating within the BM (<10%), does not end-organ damage, and is usually – but not always – revealed by a stable low production of monoclonal component (monoclonal gammopathy of undetermined significance [MGUS]). Progression to MM then depends on the evolving mutations and microenvironment interactions, leading to plasma cell accumulation inside the BM (>10%) and end-organ damage (intramedullary myeloma). The disease is usually chemosensitive and enters a quiescent phase of variable duration (plateau phase). Finally, MM is characterised by resistance to drugs, and

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independence from growth factors and the BM microenvironment (extramedullary myeloma). At this stage, cells can occasionally be propagated in vitro as MM cell lines [9].

Cytogenetic and molecular mechanisms The intrinsic genetic instability of plasma cells might account for the wide array of karyotypic abnormalities that occur in MGUS and that increase as MM progresses [10]. IgH translocations (also known as ‘‘primary translocations’’; Table 1), which juxtapose as a result of illegitimate switch recombination, an oncogene to the IgH locus (14q32) and monosomy or deletion of chromosome 13, which is the site of a putative tumour-suppressor gene, are all thought to be early hallmarks of myeloma genesis, as suggested by their occurrence in nearly 50% of MGUS [11]. Trisomies of chromosomes 3, 5, 7, 9, 11, 15, 19, 21 are also frequent in MGUS [12]. These cytogenetic patterns indicate that the transformation of MGUS proceeds along a non-hyperdiploid and a hyperdiploid pathway [9]. These pathways might overlap, but are themselves incapable of triggering progression to MM. Gene expression profiling (GEP) has now provided a clearer molecular distinction between normal and malignant plasma cells. Altered expression of 120 genes involved in different activities discriminates normal from both malignant cells and allows stratification of MM patients into four subgroups [13]. The most significant changes that differentiate MM1 (similar to MGUS) from MM4 (similar to MM cell lines) are the expression of cell cycle control and DNA metabolism genes that clearly confer a highly proliferative and autonomous phenotype on MM4. Specifically, expression levels of cyclin D1, cyclin D2 or cyclin D3 in MM and MGUS are distinctly higher than in normal plasma cells, and overlap with the cyclin D2 levels expressed in normal proliferating plasmablasts. Cyclins are important cell cycle regulators that render plasma cells more susceptible to proliferative stimuli. The result is selective clonal expansion. GEP evaluation of IgH translocations and cyclin D expression led to another classification, which stratifies patients into five subgroups.

Table 1. Recurrent IgH switch translocations Chromosomal partner

Candidate oncogene

Function

11q13

Cyclin D1

Cell cycle regulator

myeov

Unknown

FGFR-3

Growth factor receptor tyrosine kinase

MMSET

Epigenetic regulator of transcription (chromatin remodelling)

16q23

c-maf

Transcription factor

6p21

Cyclin D3

Cell cycle regulator

6p25

MUM1or IRF4

Transcriptional regulator of IFN and IFN-stimulated genes

20q11

MaF-B

Transcription factor

4p16

Abbreviations: FGFR-3, fibroblast growth factor receptor-3; IFN, interferon; IRF4, interferon regulatory factor 4; MMSET, multiple myeloma nuclear set domain protein; MUM1, multiple myeloma oncogene 1; myeov, myeloma overexpressed gene.

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This classification was named translocation-cyclin classification (TC; [14]). TC1 tumours (18% of patients) express high D1 or D3 levels as a result of t(11;14) and t(6;14) translocations, respectively; TC2 (43%) and TC3 tumours (17%) ectopically express low to moderate levels of D1 and high levels of D2, respectively, but no IgH translocation; TC4 tumours (15%) express high levels of D2 and multiple myeloma nuclear set domain protein (MMSET) and, in most cases, fibroblast growth factor receptor-3 (FGFR-3) as a result of a t(4;14) translocation; TC5 tumours (7%) express the highest levels of D2, together with high levels of either c-maf or MaF-B as a result of t(14;16) and t(14;20) translocations. Interestingly, this model provides a unifying molecular pathogenesis of MM transformation based on dysregulation of a cyclin D independently of the underlying mechanism (IgH translocation [TC1, TC4 and TC5] or ectopic increased expression produced ab initio by aberrant interactions with the microenvironment [TC2, TC3], see below). Finally, other genic events promoted by increased proliferation, such as ‘‘secondary translocations’’ involving c-MYC oncogene, and activating mutations of N, K-RAS, p53 and p18 oncogenes are associated with progression [10].

Role of the BM microenvironment The BM microenvironment consists of the extracellular matrix (ECM) wrapping several stromal cell types, including fibroblasts, osteoblasts, osteoclasts, endothelial cells and leukocytes, which are intimately involved in all biological stages of intramedullary growth [10]. Selective homing of MM cells to BM occurs via the release of specific chemokines (Table 2) from BM stromal cells, selective adhesion to endothelial cells and trans-endothelial migration. When in loco, adhesion molecules mediate homotypic interactions between MM cells as well as heterotypic interactions between MM cells and the ECM or stromal cells, resulting in enhanced expression and release of cytokines and growth factors needed for the survival of MM plasma cells (Table 2). This tumour–host interplay highlights a reciprocal relationship that sustains disease development and promotes progression through the induction of pathological phenomena, such as neovascularisation (angiogenesis and vasculogenesis) and bone disruption (osteoclastogenesis) [10]. The BM microenvironment certainly supports MM progression, and there is increasing evidence [14] that the earliest phases (initiating events) of the TC2 subtype are solely dependent on aberrant microenvironment interactions and apparently not preceded by MGUS. Corroboration is also provided by preliminary data obtained by GEP of microenvironment-associated genes (MAGs) [15], showing upregulation of MAG1 and MAG2, which code for adhesion proteins engaged in heterotypic interactions. Their similar expression levels in MGUS, and the highest levels in MM (which were

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consensual to the percentage of plasma cells) suggested that a de novo microenvironment-induced form of MM might exist.

Myeloma cell pathways: growth and apoptosis The survival of MM cells depends on the proper balance between growth and apoptotic pathways [14]. IL-6 is the most important growth factor MM cells. It acts primarily via a paracrine growth loop, but can also exert an autocrine effect. Several cytokines, such as IL-1a, IL-1b, tumour necrosis factor-a (TNF-a), macrophage-colony stimulating factor (M-CSF), vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), upregulate IL-6 through activation of the transcription factor NF-kB [16]. In resting cells, NF-kB is bound to its inhibitor (IkB) in the cytosol. When cells are stimulated, IkB is degraded via the ubiquitin-proteasome pathway, and NF-kB translocates to the nucleus, where it stimulates the transcription of several genes that regulate cell growth and survival. IL-6 activates Janus kinases (JAKs), which stimulate the Ras-mitogen-activated protein kinase (MAPK) growth pathways and trigger MM cell growth. JAKs also induce the phosphorylation of proteins known as signal transducer and activator of transcription (STAT) proteins (STAT-1 and STAT-3). Activation of the JAK–STAT pathway prevents apoptosis of MM cells and mediates drug resistance [14]. Apoptosis occurs via the sequential activation of initiator (procaspase-8, -9, -10) and effector (caspase-3, -6, -7) caspases, which lead to cell death by proteolytic cleavage of various targets [13]. Two upstream mechanisms trigger caspases: first, cross-linking of death receptors by their ligands (e.g. FAS– FASL); and second, the release of mitochondrial apoptogenic proteins, such as cyt-c and Smac. The adhesion of b1-integrin-bearing MM cells to fibronectin expressed on stromal cells and the ECM allows escape from immune surveillance through dysregulation of FAS–FASL-mediated apoptosis. BM cytokines [e.g. IL-6, vascular endothelial growth factor (VEGF)] prevent apoptosis by stimulating the release of antiapoptotic family members (Bcl-2, Bcl-XL, Mcl-1) [14] located on the outer mitochondrial membrane, where apoptotic inducers (e.g. Bax and Bak) reside in an inactive form. When activated, they oligomerise and bind transiently to specific proteins (BH3-only proteins, e.g. Bid, Bim) to form pores, thus permitting the efflux of apoptogenic proteins. When Mcl-1 and Bcl-XL are overexpressed, they sequester BH3-only proteins and prevent their interaction with Bak or Bax, thus overcoming apoptotic signals.

Neovascularisation Angiogenesis, the formation of new blood vessels from an existing vascular network, is a stepwise course of events leading to the activation of endothelial cells, degradation of the ECM, and the proliferation and migration of endothelial cells towards the angiogenic stimulus (‘sprouting’) [17]. www.drugdiscoverytoday.com

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Table 2. Molecules active in the bone marrow microenvironment Chemokine

Receptor

Other functions

MIP-1a

CCR1, CCR3, CCR5

Bone resorption

SDF-1

CXCR4

Plasma cell growth, migration and survival

MCP-1

CCR2

Recruitment of macrophages

Adhesion molecule

Ligand

Main interactions

VLA-4 (a4 b1)

Fibronectin

Plasma cell–ECM adhesion

VCAM-1

Plasma cell–vessel and stroma adhesion

VLA-5 (a5 b1)

Fibronectin

Plasma cell–ECM adhesion

Syndecan-1 (CD138)

Collagen 1

Plasma cell–ECM adhesion

LFA-1 (CD11a or CD18)

ICAM-1 (CD54), ICAM-2

Homotypic cell aggregation (plasma cells, endothelial cells); B lymphocyte–dendritic cell adhesion

CD40

CD40Rc

Proliferation, differentiation, Ig secretion and isotype switching

NCAM (CD56)

NCAM (CD56)

Homotypic cell aggregation (plasma cells, osteoblasts)

CD44

Hyaluronate Collagen Fibronectin

Plasma cell–lymphocyte interactions; plasma cell–ECM adhesion and trafficking into the peripheral blood

Factor

Origin

Function

IL-6

Stromal cells, plasma cells

Stimulation of plasma cell growth, survival, drug resistance and bone resorption

IL-1a or -1b

Stromal cells, plasma cells

Stimulation of IL-6 secretion and bone resorption

TNF-a

Stromal cells, plasma cells

Stimulation of IL-6 secretion, bone resorption and expression of adhesion molecules

TNF-b

Plasma cells

Stimulation of IL-6 secretion and bone resorption

M-CSF

Stromal cells

Stimulation of IL-6 secretion and bone resorption

IL-11

Stromal cells

Stimulation of IL-6 secretion and bone resorption

VEGF

Plasma cells, stromal cells

Stimulation of IL-6 secretion, plasma cell growth and migration, angiogenesis

bFGF

Plasma cells, stromal cells

Stimulation of IL-6 secretion and angiogenesis

HGF

Plasma cells

Stimulation of IL-11 secretion, plasma cell survival and angiogenesis

IGF-1

Stromal cells

Stimulation of plasma cell growth, survival, migration and angiogenesis

HB-EGF

Stromal cells, plasma cells

Stimulation of plasma cell growth and survival

IL-21

Stromal cells

Stimulation of plasma cell growth and survival

Abbreviations: bFGF, basic fibroblast growth factor; CCR, CC chemokine receptor; CD, cell determinant; CXCR, CXC chemOKine receptor; HB-EGF, heparin-binding epidermal growth factor; HGF, hepatocyte growth factor; ICAM, intercellular cell adhesion molecule; IGF-1, insulin-like growth factor-1; IL, interleukin; LFA, lymphocyte function-associated antigen; MCP-1, monocyte chemotactic protein-1; M-CSF, macrophage-colony stimulating factor; MIP, macrophage inflammatory protein-1; NCAM, neural cell adhesion molecule; SDF-1, stromal cellderived factor-1; TNF, tumour necrosis factor; VCAM, vascular cell adhesion molecule; VEGF, vascular endothelial growth factor; VLA, very late-activating antigen.

Angiogenesis is mandatory to MM plasma cell growth, because without neovascularisation oxygen and nutrients are lacking. Growth is halted and a ‘dormancy state’ or an ‘avascular phase’ (such as MGUS and non-active MM) [18] are induced. With clone expansion and epigenetic modifications (hypoxia, shear stress) of the microenvironment, subsets of tumour plasma cell switch to an angiogenic phenotype that generates the ‘vascular phase’ (active MM) [18]. It involves a change in the local balance between pro- and anti-angiogenic factors [17] (Table 3). The events that initiate the angiogenic cascade are not well defined. Adhesive interactions between plasma cells and stromal cells might promote the release of angiogenic growth factors (VEGFs, FGFs, hepatocyte growth factor [HGF]), mobilise insulin-like growth factors (IGFs) and 360

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matrix metalloproteinases (MMPs) from the ECM (where they are present in a latent form) and recruit inflammatory cells (monocytes, mast cells) to produce other angiogenic molecules. Rapid growth of plasma cells ever further away from capillaries results in hypoxia, and this induces VEGF expression via hypoxia-inducible factor-a (HIF-a). Oncogenes, such as K-ras, src and fos can induce the upregulation of angiogenic factors, (e.g. VEGF, IGF-1 and TGF-a) or the production of cytokines and proteolytic enzymes. Oncogene products also act directly as angiogenic factors (e.g. FGF-4 or hst-1, IgH translocations involving FGFR-3 gene). In addition, activated endothelial cells can proliferate through autocrine loops (VEGF or VEGFR-2 pathway) [19]. The demonstration of CD34+AC133+ angioblasts within BM endothelial cells from

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Table 3. Inducers and inhibitors of angiogenesis Function Inducers VEGF isoforms

Regulators of angiogenesis via autocrine and paracrine loops

PlGF

Homologue of VEGF, triggers angiogenesis via amplification of VEGF activity

NP1

Receptor for the VEGF165 isoform; co-receptor of VEGFR-2

bFGF

Promotes growth, survival and migration of endothelial cells

HGF

Promotes growth, survival and migration of endothelial cells

IGF-1

Promotes growth and survival of endothelial cells

Ang1

Stabilises nascent vessels by tightening endo–periendothelial cell interactions

Ang2

Angiogenic in the presence of VEGF via loosening of periendothelial cells

PDGF-BB

Recruits smooth muscle cells around nascent endothelial channels

TGF-b1

Stabilises nascent vessels by stimulating ECM production

aVb3, aVb5

Cellular receptors for matrix components and proteinases

VE-cadherin

Mediates adhesion and the VEGF endothelial survival effect

PECAM

Cell surface glycoprotein on endothelial cells, mediating homotypic adhesion

MMPs

Proteinases that degrade matrix proteins, thereby promoting cellular migration

TIMPs

MMP inhibitors

u-PA

Activator of plasminogen; promotes cellular migration and matrix remodelling

PAI-1

Inhibitor of u-PA and activator of MMPs. Stabilises nascent vessels via preventing proteolytic breakdown of the vessel matrix

Ephrins

Regulate arterial or venous specification

NOS

Promotes angiogenesis through generation of nitric oxide

Cox2

Generates inflammatory and angiogenic prostaglandins

AC133

Orphan receptor involved in angioblast differentiation

Inhibitors Thrombospondin-1 Angiostatin

A 180 kDa modular ECM protein Fragment of plasminogen

Endostatin

A 20 kDa zinc-binding fragment of type XVIII collagen

Vasostatin

An amino-terminal fragment of calreticulin

VEGF inhibitor (VEGI)

A 174 amino acid protein with 20–30% homology to TNF family

Fragment of platelet factor 4 (PF4)

A amino-terminal fragment of PF4

Derivative of prolactin

A 16 kDa fragment of the hormone prolactin

Restin

A domain of human collagen XV

Meth-1 and Meth-2

Proteins containing MMPs and thrombospondin domains

SPARC cleavage product

Fragments of secreted protein, acid and rich in cysteine

Osteopontin cleavage product

Thrombin-generated fragment containing an RGD sequence

Interferon a, b, g; IP-10, IL-4, IL-12

Cytokines and chemokines involved in several steps of angiogenesis

Inhibitors of differentiation (Id1 or Id3)

Inhibitory helix–loop–helix transcription factors

PEX

Fragment of MMP2, blocking binding of MMP2 to aVb3

Maspin

Tumour suppressor gene product, encoding a serpin member

Canstatin

Fragment of the a2-chain of collagen type IV

Anti-thrombin III fragment

A fragment missing carboxy-terminal loop of anti-thrombin III

Abbreviations: Ang1, angiopoietin-1; Ang2, angiopoietin-2; bFGF, basic fibroblast growth factor; Cox2, cyclooxygenase-2; ECM, extracellular matrix; HGF, hepatocyte growth factor; IGF-1, insulin-like growth factor-1; IL, interleukin; IP-10, inducible protein-10; MMPs, matrix metalloproteinases; NOS, nitric oxide synthase; NP1, neuropilin-1; PAI-1, plasminogen activator inhibitor-1; PDGF-BB, platelet-derived growth factor-BB; PECAM, platelet endothelial cell adhesion molecule; PlGF, placental growth factor; TGF-b1, transforming growth factor-b1; TIMPs, tissue-inhibitors of MMP; u-PA, urokinase-type plasminogen activators; VE, vascular endothelial; VEGF, vascular endothelial growth factor.

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patients with active MM [19] provides evidence that ongoing neovascularisation is also supported by vasculogenesis. The overall features of endothelial cells, however, resemble tumour phenotype [19] as shown in lymphoma [20]. This raises questions about the endothelial cell origin: plasma cells and endothelial cells might derive from a common clonogenic cell (a Ferrata’s [tumour] haemangioblast?) that undergoes differentiation into the various phenotypes (but conserving molecular hallmark of transformation). However, close interactions in the BM might generate hybrids between plasma cells and existing (normal) endothelial cells. New studies are warranted for clarifying this subject.

Mechanisms of osteolytic lesions: osteoclastogenesis Plasma cell accumulation is associated with increased rates of bone turnover and osteolytic lesions as a result of unbalanced bone remodelling. A significant increase in both the recruitment of new osteoclasts and single osteoclast activity occurs

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in the close vicinity of MM cells, suggesting that bone disease results from local production of osteoclast activating factors (OAF) secreted by either MM cells or stromal cells (Table 2). Additional molecules involved in osteoclastogenesis have recently been discovered [21], including the receptor activator of nuclear factor ligand (RANKL), the decoy receptor osteoprotegerin (OPG), and the chemokine macrophage inflammatory protein-1a (MIP-1a). RANK ligand (RANKL) is expressed by stromal cells and binds to its receptor (RANK), which is present on osteoclasts, triggering differentiation and activation signals in osteoclast precursors, and thus promoting bone resorption. OPG is a naturally occurring factor that antagonises the effects of RANKL and so preserves bone integrity. Therefore, the ratio between RANKL and OPG is crucial to the regulation of osteoclast activity and bone resorption. The binding of MM cells to stromal cells is mediated by b1 integrins, and VCAM1 induces overexpression of RANKL in both cell types

Figure 1. Stepwise course of multiple myeloma formation. (a) The process of multiple myeloma (MM) begins when partially overlapping pathways induce dysregulation of cyclin D. This results in transformation of plasma cells and the generation of a non-proliferating clone (b) called monoclonal gammopathy of undetermined significance (MGUS). Evolving mutations and interactions with bone marrow stromal cells promote proliferation of plasma cells corresponding to disease progression (c). A complex cytokine network mediates the induction of angiogenesis, MM plasma cell survival and activation of osteoclasts which produce bone resorption (d). Lastly, plasma cell leukaemia is generated (e).

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Target(s)

Effects

Status

Company and/or working group

Website/reference

VelcadeTM, bortezomib (PS-341)

Proteasome

Inhibition of NF-kB activity: # IL-6-dependent signalling " apoptosis # adhesion molecules

Recently FDA approved

Millennium Pharmaceuticals, Inc; T. Hideshima et al.

http://www.mlnm.com/; [email protected]

Thalidomide

Angiogenesis, NF-kB, TNF-a, apoptosis

Inhibition of angiogenesis Antiapoptosis in MM cells Downregulation of adhesion molecules Immunomodulation

Phase III

A. Vacca et al.; T. Hideshima et al.

;;[email protected]; [email protected]

RevlimidTM, CC-5013

T cells, TNF-a, apoptosis

Immunomodulation antiapoptosis in MM cells

Phase III

Celgene Corporation; T. Hideshima et al.

http://www.celgene.com; [email protected]

Genasense, oblimersen (G3139)

Bcl-2 (antisense oligonucleotide)

Induction of apoptosis

Phase III

Genta Incorporated

http://www.genta.com

TrisenoxW, Arsenic trioxide

Bcl-2, VEGF, LAK cells

Antiapoptosis in MM cells Inhibition of angiogenesis Upregulation of immune response

Phase II

Cell Therapeutics, Inc; T. Hideshima et al.

http://www.cticseattle.com; [email protected]

PanzemTM, 2-methoxy estradiol

VEGF, IL-6 apoptosis

Inhibition of angiogenesis Antiapoptosis in MM cells

Phase II

EntreMed, Inc; T. Hideshima et al.

http://www.entremed.com; [email protected]

ZarnestraTM, Tipifarnib (R115777)

Ras

Inhibition of Ras farnesylation, a post-translational modification required for activation

Phase II

Johnson & Johnson Pharmaceutical Research and Development

http://www.jnj.com/

AvastinTM, Bevacizumab

VEGF-VEGFR-2 pathway (anti-VEGF)

Inhibition of angiogenesis Inhibition of MM cell growth

Phase II

Genentech

http://www.gene.com/

ZD6474

VEGFR-2 (tyrosine kinase inhibitor)

Inhibition of angiogenesis Inhibition of MM cell growth

Phase II

Astra-Zeneca

http://www.astrazeneca.com/

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Atlizumab (Tocilizumab)

IL-6 (anti-IL-6 receptor)

Inhibition of MM growth

Phase II

Chugai Pharma

http://www.chugaibio.com/

Suberoylanilide hydroxamic acid

Histone deacetylase

Inhibition of gene transcription of the ubiquitin-proteasome pathway

Phase I

National Cancer Institute, Aton Pharma; T. Hideshima et al.

http://www.nci.nih.gov/; http://www.atonpharma.com/; [email protected]

TRAIL-R1 monoclonal antibody (TRM-1)

Extrinsic pathway apoptosis

Antiapoptosis in MM cells

Phase I

Human Genome Sciences

http://www.hgsi.com/

Mcl-1 antisense

Mcl-1 (antisense oligonucleotide)

Induction of apoptosis

Pre-clinical

Isis

http://www.isispharm.com/

PD173074

FGFR-3 inhibitor

Antiangiogenesis

Pre-clinical

Pfizer

http://www.pfizer.com/

Abbreviations: FDA, Food and Drug Administration; IL, interleukin; LAK, lymphokine activator killer; MM, multiple myeloma; NF-kB, nuclear factor-kB; TNF-a, tumour necrosis factor-a; TRAIL, tumor necrosis factor-related apoptosis-inducing ligand; VEGF, vascular endothelial growth factor; VEGFR, VEGF receptor.

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Drug

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Table 4. Novel drugs in clinical trials

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and suppresses OPG production by stromal cells. In addition, MM cells internalise and degrade OPG within their lysosomal compartment. This process is dependent on physical interactions between OPG and heparan sulphates present on syndecan-1. MIP-1a secreted by MM cells induces expression of RANKL in stromal cells and probably acts directly on osteoclast precursors that express CCR5 to induce recruitment, late-stage differentiation and ultimately activation [21].

Conclusion: evolution of a new treatment paradigm for MM Conventional therapy targeting only the MM plasma cell induces objective responses with a median survival of 24– 36 months; high-dose therapy improves response rates and overall survival, but patients invariably relapse and salvage therapy is often ineffective [14]. The emerging role of the BM microenvironment throughout all malignant processes (Fig. 1) has provided the framework for development of a new MM treatment paradigm targeting both the MM plasma cell and all components of the microenvironment. Novel therapeutic agents are currently under investigation (Table 4). The TC classification might predict prognosis and response to treatment and thus pave the way for patient-targeted management. TC1 patients appear to be ideal candidates for high-dose therapy, and TC2 and TC3 patients appear to be ideal candidates for microenvironment-directed therapy. TC4 and TC5 patients, who have a worse prognosis with either standard or intense therapy, might need a combination of novel treatments. A multi-target strategy is difficult because of the wide heterogeneity of MM and the lack of a clearly defined stepwise progression course. However, this appears to be the right way to enable patient-specific selection of targeted therapy, and possibly a successful cure. In this respect, the identification of the critical role of cyclin D dysregulation in the earliest phases of MM transformation is fostering new studies targeting patients with MGUS. Antiangiogenesis therapy in high-risk MGUS or non-active MM patients is also being investigated.

Acknowledgements Supported by Associazione Italiana per la Ricerca sul Cancro (AIRC, Milan) and Ministry for Education, the Universities and Research (Inter-University Funds for Basic Research

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Vol. 1, No. 3 2004

[FIRB], Rome, and a grant from the Foundation Cassa di Risparmio di Puglia, Barix), Italy.

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