Systemic Delivery of the Cancer Gene Therapy Biologic, SNS01, Has Significant Anti-Tumoral Activity in a Murine Model of Multiple Myeloma.

Abstract 2462

Poster Board II-439

The eukaryotic translation initiation factor 5A (eIF5A) is highly conserved and the only known protein to contain the amino acid hypusine. Hypusinated eIF5A and deoxyhypusine synthase, one of the enzymes mediating eIF5A post-translational hypusination, have been identified as markers of neoplastic growth and metastasis, respectively. However, recent studies have indicated that, in its unhypusinated form, eIF5A is pro-apoptotic and thus functionally distinct from hypusine-modified eIF5A. SNS01 is a cancer gene therapy biologic targeted to the treatment of multiple myeloma. SNS01 is comprised of three components: a DNA vector containing a B-cell-specific (B29) promoter driving expression of a pro-apoptotic mutant of eIF5A (eIF5AK50R) that cannot be hypusinated; an siRNA that targets the native hypusinated eIF5A that promotes growth of cancer cells; and a synthetic polymer called polyethylenimine (PEI). RT-qPCR experiments demonstrated that treatment of the human myeloma cell line, KAS-6/1, with SNS01 results in a 90 % reduction in the expression of eIF5A mRNA (mediated by the siRNA) as well as the accumulation of ∼ 22,000 copies of the plasmid-derived eIF5AK50R mRNA per ng of total RNA. SNS01 was found to induce apoptosis in both IL-6-dependent (KAS-6/1) and IL-6-independent (U266) myeloma cell lines and was found to be more effective at inducing apoptosis than PEI nanoparticles carrying either the eIF5A siRNA or the eIF5AK50R plasmid alone. Apoptosis assays were used to optimize the ratio of DNA:siRNA in the nanoparticles and a ratio of 2:1 was found to be optimal for the induction of apoptosis in myeloma cells. The anti-tumoral activity of SNS01 was assessed in SCID mice bearing subcutaneous human multiple myeloma (KAS-6/1) tumors using twice-weekly intra-venous injections and a dose range between 0.15 mg/kg and 1.5 mg/kg. Control mice treated with PEI nanoparticles containing a non-expressing plasmid and a non-targeting siRNA had an average tumor volume of 284 mm3 at the time of sacrifice, whereas mice treated with 1.5 mg/kg or 0.75 mg/kg SNS01 exhibited significant tumor regression and had average tumor volumes of 13 mm3 (95 % inhibition; *p = 0.026) and 24.5 mm3 (91 % inhibition; *p = 0.03), respectively. In addition, for mice treated with 1.5 mg/kg SNS01, there was no evidence of tumors under the skin. Lower doses of SNS01 also demonstrated anti-tumoral activity with mice treated with 0.38 mg/kg and 0.15 mg/kg exhibiting a 73 % and 61 % inhibition of tumor growth, respectively. TUNEL-labeling revealed evidence of apoptotic cells in the treated tumors indicating that tumor regression occurs through the induction of apoptosis. Twice weekly dosing of SNS01 was found to be critical for effective tumor control. In a separate study, twice weekly dosing of SNS01 at 1.5 mg/kg was found to inhibit tumor growth by 88 % (p = 0.01) while once weekly dosing did not significantly reduce tumor burden. Since SNS01 is intended as a therapy for multiple myeloma, a bone marrow neoplasm, the biodistribution of PEI nanoparticles containing a GFP plasmid with the B-cell-specific B29 promoter and a fluorescently (DY547)-labeled siRNA was assessed following i.v. administration in Balb/c mice. The fluorescent siRNA was observed in the liver, lung, spleen, and bone marrow, while GFP expression was primarily observed in the bone marrow. In summary, our preclinical data indicate that systemic administration of SNS01 is an effective anti-cancer therapy in an animal model of multiple myeloma. Additionally, since PEI nanoparticles are taken up by cells of the bone marrow following systemic delivery, SNS01 may be an effective treatment option for multiple myeloma patients and is currently being evaluated for use in clinical trials.