ZIO-101, a Novel Organic Arsenic, Inhibits Human Myeloma Cell Growth in a SCID-hu Model.

Inorganic arsenics like arsenic trioxide (ATO) are novel anti-cancer drugs active in acute promyelocytic leukemia (APL) and multiple myeloma (MM). ATO induces apoptosis of plasma cells by several mechanisms including down-regulation of BCL-2 expression and inhibition of DNA-binding by NF-κB. The amount of ATO that can be safely given is low because of QTc-prolongation. ZIO-101, a new organic arsenic, is in phase-1/-2 trials. ZIO-101 can be safely given at much higher doses than ATO. We evaluated the in vivo anti-myeloma activity of ZIO-101 in a SCID-hu mouse model of human myeloma. LAGλ-1 was developed from a person with melphalan-resistant and LAGλ-1B from a person with bortezomib-resistant myeloma. Each severe combined immunodeficient (SCID) mouse was implanted with a 2–4 mm³ fragment of LAGλ-1B or LAGλ-1 into the left superficial gluteal muscle. Fragments were allowed to grow for 14 d when human IgG was first detectable. ZIO-101 was given IV 1 or 2 times/d using three different schedules: one day/w, 3 days/w or 5 days/w at doses of 50– 200 mg/kg/d. Tumor volume and human IgG were assessed weekly. Doses up to 200 mg/kg were well-tolerated. Anti-myeloma effects were observed in both models at doses of 100 – 200 mg/kg on all 3 schedules. Mice receiving 100 mg/kg twice daily thrice weekly and those receiving 200 mg/kg once weekly showed marked anti-myeloma activity (100 mg/kg, P = 0.03; 200 mg/kg, P = 0.001) and reduced human IgG levels (100 mg/kg, P < 0.001; 200 mg/kg, P = 0.01) compared to controls. We are evaluating ZIO-101 in other SCID-hu models of human myeloma and exploring different doses and schedules of ZIO-101 alone or combined with other anti-myeloma agents. In summary, these data show activity of ZIO-101 in human myeloma in vivo. These studies provide the bases for future clinical trials.