Anti-Angiogenic Effect of Bortezomib in Multiple Myeloma Patients.

Bortezomib is a proteasome inhibitor, which is an effective treatment for multiple myeloma (MM). Bortezomib inhibits NF-κB and thus enhances apoptosis and leads to reduced levels of growth factors, angiogenic factors and cell adhesion molecules, which are crucial for the growth and survival of myeloma. The aim of this study was to investigate whether bortezomib has an anti-angiogenic effect in MM patients and whether that effect correlates with response to treatment. We have studied the effect of bortezomib on angiogenesis in bone marrow biopsies and serum samples of nine patients with MM, who were treated with bortezomib. The patients studied (6M/3F median age 59 years, range 35–71 years) had received more than 4 lines of treatment before bortezomib administration. Six patients had IgG, one IgA, one non-secretory and one light-chain MM. Bortezomib was given at a dose of 1.3 mg/m², iv, in 3-week cycles, on days 1, 4, 8, and 11 of each cycle.

Microvessel density (MVD) was assessed in bone marrow trephine biopsies before and after 8 cycles of treatment by immunohistochemistry with monoclonal mouse antibodies to CD34 (QBEND-10, DAKO, Denmark). Serum samples were assessed for VEGF and angiogenin levels before and after every cycle of treatment with an ELISA (R&D systems). Five out of 9 patients achieved a partial response (PR), two patients had a minimal response (MR),one achieved a good partial response (GPR) and one a complete response (CR) to bortezomib administration, according to EBMT criteria. In six out of 9 patients there was a decrease of the MVD. More specifically in two of the patients with PR (P2,P4) and the two patients with MR (P5 and P7) there was a significant decrease in the MVD ( 1.7, 3.8, 4.2 and 1.4 fold decrease respectively). Patient 9, who achieved GPR had also a 2.3 fold decrease in MVD. In patients P2,P4,P5 and P6, who received 8 cycles of treatment, further reduction of MVD was noticed with further treatment. In patient 1, who achieved a PR, MVD did not show any significant change after 8 cycles of treatment. The patient relapsed soon after he has completed the treatment. In patient 5, the MVD increased over 2-fold and she relapsed very soon after the 4^th cycle and died of disease progression.

There was a significant reduction in mean angiogenin levels by cycle 4 (380 ng/ml) when compared with cycle 1 (537ng/ml) (p=0.028). On the contrary, there was no significant difference between the levels of VEGF at cycles 1 and 4 (122.5 pg/ml and 127.2 pg/ml respectively) (p=0.173).All data are shown in Table 1. We conclude that PS-341 may exert its anti-myeloma effect partly through anti- angiogenic mechanisms. Whether Bortezomib acts directly on endothelial cells or indirectly through modulation of the expression of angiogenic factors and angiopoetins which influence endothelial cell proliferartion and survival is unclear.