An Anti-VEGF Antibody, in Combination with Bortezomib, Markedly Inhibits Tumor Growth in SCID-hu Models of Human Multiple Myeloma.

Vascular endothelial growth factor (VEGF) is an important signaling protein that plays a critical role in vasculogenesis and angiogenesis, and serves as one of the contributors to physiological or pathological conditions that can stimulate the formation of new blood vessels. The uncontrolled growth of new blood vessels is an important contributor to a number of pathological conditions, including multiple myeloma (MM). In support of this, bone marrow angiogenesis has been shown to correlate with disease status and poor prognosis in MM. VEGF also directly induces myeloma cell proliferation. We previously evaluated the effects of single agent mouse/human anti-VEGF antibody G6.31 (Campbell et al, Blood (ASH Annual Meeting Abstracts), Nov 2006) in several of our mouse models of human MM. In this study, we evaluated the effects of the same anti-VEGF antibody in combination with bortezomib or lenalidomide. Severe combined immunodeficient (SCID) mice were implanted into the left superficial gluteal muscle with either a 2.0 – 4.0 mm³ fragment from a patient when she was bortezomib-sensitive, LAGκ-1A, or resistant, LAGκ-1B. The tumors were allowed to grow for 21 days at which time human IgG levels were detectable in the mouse serum, and mice were blindly assigned into treatment groups (n=10 mice/group). Treatment groups consisted of a control IgG antibody or anti-VEGF antibody administered via i.p. injection twice weekly at a dose of 2 mg/kg, bortezomib administered via intravenous injection at a dose of 0.25 or 0.5 mg/kg twice weekly, lenalidomide administered via i.p. injection at a dose of 50 mg/kg daily × 5 per week, anti-VEGF antibody (2 mg/kg) + bortezomib (0.25 or 0.5 mg/kg), and anti-VEGF (2 mg/kg) + lenalidomide (50 mg/kg). Mice receiving the combination therapy of anti-VEGF + bortezomib (0.5 mg//kg) antibody showed marked inhibition of tumor growth and reduction of paraprotein levels compared to mice receiving control antibody. Notably, this combination also produced much more marked anti-MM effects compared to bortezomib treatment alone, anti-VEGF antibody alone, or vehicle alone. This combination was well tolerated. In contrast, mice receiving the combination of anti-VEGF antibody + lenalidomide showed no significant differences in tumor volume or hIgG levels compared to single agent treatment or vehicle alone. The markedly improved anti-MM effects of the combination of bortezomib and anti-VEGF antibody compared to single agent treatment in this in vivo study of human MM is promising, and these results have provided the preclinical rationale for an ongoing randomized multi-center Phase II trial.