Bone Effect of Bortezomib in Patients With Relapsed/Refractory Multiple Myeloma

Multiple myeloma (MM) accounts for approximately 1% of all malignancies and 10% of
hematological tumors, representing the second most frequently occurring hematological
malignancy in the United States. At any one time, 50,000 people suffer from MM, and
approximately 15,000 are diagnosed each year. The median age is approximately 65 years,
although occasionally MM occurs in the second decade of life. Myeloma is a disease of
neoplastic plasma cells that synthesize abnormal amounts of immunoglobulin or immunoglobulin
fragments. Myeloma is the only hematological malignancy associated with bone disease.
Myeloma is a B-cell neoplasia characterized by clonal expansion of plasma cells in the bone
marrow. It is the most malignant stage of plasma cell dyscrasias, which also include the
precursor stages of MGUS and indolent or smoldering myeloma. Myeloma is frequently
associated with lytic bone disease that is responsible for the most debilitating
manifestations of the disease, including bone pain and fractures.

Bone disease in myeloma results from the activation of osteoclast and suppression of
osteoblast activity in the myelomatous bone marrow. Change in bone turnover rates, expressed
as increased osteoblastic and osteoclastic activity, precede the progression pf MGUS or
smoldering myeloma to overt myeloma by as long as three years.

Treatment with bisphosphonates reduces bone resorption and also to some degree, bone
formation, and over the long-term moderately increases bone density. Other approved
antiresorptive therapies have been shown to reduce the risk of fracture in osteoporotic
women, but none have been shown to restore normal bone mass or strength. As a result,
treatments that directly stimulate bone formation may overcome these limitations, increase
bone mass, and improve the quality of life of myeloma patients. Bone disease is responsible
for the most severe complications associated with multiple myeloma. As treatment and
survival of myeloma patients improve, new therapies to improve complications are important
and vitally needed VELCADEâ„¢ (bortezomib) for Injection is a small molecule proteasome
inhibitor developed by Millennium Pharmaceuticals, Inc., (Millennium) as a novel agent to
treat human malignancies. VELCADE is currently approved by the United States Food and Drug
Administration (US FDA) and it is registered in Europe for the treatment of multiple myeloma
patients who have received at least one prior therapy.

The clinical response to bortezomib observed in a 63-year-old woman with multiple myeloma
and the parallel increase in alkaline phosphatase (ALP) has led us and other groups to
evaluate the correlation between bone anabolism and myeloma response to bortezomib. After
similar elevations were noted in patients responding to bortezomib, thalidomide,
dexamethasone combination, ALP levels were analysed in two large bortezomib trials (Roodman,
2008). Giuliani and coworkers (2007) found that bortezomib significantly increased the
activity of the critical osteoblast transcription factor, RUNX2, in human osteoblast
precursors and stimulated bone nodule formation in vitro. Importantly, they found a
significant increase in the number of osteoblasts per mm2 of bone tissue and the number of
RUNX2 positive osteoblastic cells in marrow biopsies from myeloma patients that responded to
bortezomib. Again, the effect on osteoblasts was only seen in patients whose myeloma
responded to bortezomib, making it difficult to distinguish if the increase in osteoblast
activity was due to the anti-myeloma effects of bortezomib or direct effects on osteoblasts
or both. Terpos and colleagues (2006) have reported that bortezomib also decreased DKK1 and
RANKL concentrations and normalized bone remodeling indices in the serum of patients with
relapsed myeloma. However, the majority of patients that showed an increase in bone
formation markers also showed an antitumor response to bortezomib, making it unclear if the
stimulatory effects on bone formation were secondary to the effects of bortezomib on myeloma
or due to direct effects on osteoblast differentiation After similar elevations were noted
in patients responding to bortezomib, thalidomide, dexamethasone combination, ALP levels
were analysed in two large bortezomib trials.

We first completed a retrospective analysis of large Phase 3 trials comparing ALP levels in
responders (≥PR) vs nonresponders (≤PR) patients.

Data obtained from the APEX Crest and Summit protocols, have shown that a total of 85
myeloma patients were treated with bortezomib at the dose of 0.7 mg/m2 for different reasons
with significant antimyeloma efficacy for multiple cycles. This dose (0.7 mg/m2) will be
used in this trial to test if the antimyeloma activity of bortezomib is still associated to
bone anabolic effect. Data for the APEX, summit, and CREST trials is on file at Millennium
Pharmaceuticals.

Given that this study is a continuation of a previous protocol (UARK 2004-22) when at the
dose of 1.3 and 1.0 mg/m2 an antimyeloma effect and associated bone formation were observed.
This trial will test the effect of 0.7 mg/m2 (which has been shown to be effective on
antimyeloma treatment) on bone formation to determine the minimal dose associated to bone
effect.