In Vivo Anti-Tumor Activity of Atiprimod on SCID Models of Multiple Myeloma.

Atiprimod (N-N-diethl-8, 8-dipropyl-2-azaspiro [4.5] decane-2-propanamine) is an orally bio-available cationic amphiphilic agent previously studied for its in vivo anti-inflammatory activity. We previously demonstrated that Atiprimod, in a time- and dose-dependent manner, inhibits myeloma cell growth and survival in IL-6 independent (OPM1) as well as dependent (INA-6) MM cell-lines with an IC₅₀ in the range of 0.5–2 μM. We have now further characterized the molecular changes in MM cells induced by Atiprimod, evaluating the gene expression profile of INA-6 and OPM-1 cells exposed to this drug. Following 24 h treatment, Atiprimod induced significant down-regulation of genes involved in growth and cell-cycle control (CDC14, CDC2-like 5, Cyclin-E binding protein 1 and MDM2), adhesion (ITGA-6, ITGA-X, ADAM-17, CDH-3, CDH-6, CTNND-1, PECAM-1 and MADCAM-1) cell-signalling pathways (PRKAB-1, Mapk-7, GPR-125 and GPR-32), up-regulation of genes implicated in apoptotic cascades (TNFAIP-3, TNFSF-10, TNFRSF-10c, CDKN2A and CDKN1A) and in negative regulation of signal transduction (RGS-4 and IGFBP-5). We next evaluated the in vivo activity of Atiprimod using three SCID mouse models of human MM: 1) To evaluate effects of Atiprimod directly on MM cells, we used SCID mice bearing subcutaneous OPM1 tumors and treated i.p. with Atiprimod or vehicle alone (PBS) on alternate days for 7 days. In this model 31%, 48% and 55% inhibition of tumor growth were observed in mice treated with Atiprimod at 20, 30 and 50 mg/kg, respectively, compared to control group. 2) To evaluate effects of Atiprimod on MM cells in the context of a human BM microenvironment, we used SCID mice implanted with a human fetal bone chip (SCID-hu) engrafted with IL-6-dependant INA-6 cells and treated i.p. with Atiprimod (40 mg/kg) or vehicle alone (PBS) for two weeks. The response was evaluated by detection of serum soluble human IL-6 receptor (shuIL-6R) released by MM cells in murine serum. We observed a 60% reduction in shuIL-6R level in mice treated with Atiprimod versus control group. 3) Finally, to evaluate effects of Atiprimod on primary patient cells in a human microenvironment, we used SCID-hu mice engrafted with patient MM cells (IgG λ) and treated i.p. with Atiprimod (50 mg/kg) or vehicle alone (PBS) for 4 weeks. Treatment with Atiprimod induced a reduction in both human IgG and λ light chain levels in mouse sera, whereas levels of both proteins continued to rise in mice treated with vehicle alone. Taken together these data demonstrate the in vivo anti-tumor activity of Atiprimod and provide a rational for its clinical evaluation in MM. Based on these data the drug is presently in a multi-site Phase I/IIa clinical trial in patients with relapsed or refractory multiple myeloma (MM).