2-Methoxyestradiol in Combination with Velcade® Results in an Augmentation of NFκB Inhibition, In Vitro Antiproliferative Activity and In Vivo Antitumor Efficacy in the RPMI-8226 Myeloma Model.

2-Methoxyestradiol (2ME2, Panzem^®) is an endogenous metabolite of estradiol with antiproliferative, proapoptotic, and antiangiogenic activity. Some of these activities are mediated through the downregulation of HIF1-α. Panzem^® capsules have been evaluated in several oncology clinical trials, including multiple myeloma where some patients have been on therapy for more than 4 years with stable disease. A new formulation of 2ME2 with enhanced absorption, Panzem^® NCD, is currently in Phase 1 and 2 clinical studies in oncology. In anticipation of combination studies with Panzem^® NCD, we evaluated the effectiveness of 2ME2 alone or with the proteosome inhibitor, Velcade^® (bortezomib), in the RPMI-8226 myeloma xenograft tumor model. Preliminary in vitro studies indicated significantly increased antiproliferative activity when 2ME2 (1.5μM) was combined with Velcade^® (5nM) compared to Velcade^® alone (p<0.05 ANOVA). Additionally, 2ME2 in combination with Velcade^® also resulted in decreased nuclear NFκB in response to TNFα, as compared to either agent alone. Subsequent to these studies, female CB17 SCID mice were injected subcutaneously with 1 x 10⁶ RPMI-8226 tumor cells. Starting 10 days after tumor cell inoculation when mean tumor volume was approximately 100–200 mm³, cohorts of mice (n=8/group) began treatment with (a) vehicle alone ad libitum in the drinking water; (b) 2ME2 300 mg/kg ad libitum in the drinking water; (c) Velcade^® 1.5 mg/kg i.p., biw; or (d) 2ME2 (300 mg/kg) in combination with Velcade^® (1.5 mg/kg). On study day 27, mean tumor volume in vehicle-treated, control mice was approximately 3400 mm³. Under these experimental conditions, treatment with either 2ME2 alone or Velcade^® alone generated a treatment/control (T/C) value of 0.66 and 0.64, respectively. In comparison, 2ME2 in combination with Velcade^® resulted in a T/C value of 0.35. Velcade^® is a well recognized and commonly used antineoplastic agent in multiple myeloma. The degradation of HIF1-α is accomplished through the proteosome. These studies demonstrate that a combination strategy using Velcade^® and 2ME2 can enhance the antitumor effectiveness of either agent alone in the treatment of a xenograft model of human multiple myeloma.