NK-012

Objective Multiple myeloma (MM) is the second most common hematological cancer. An attempt to treat MM using a topoisomerase I inhibitor was made based on our previous non-clinical studies suggesting the usefulness of an SN-38 derivative. Our aim was to conduct a phase I/II study of NK012, a micelle-forming SN-38 conjugate, in patients with relapsed/refractory multiple myeloma (RRMM). Methods NK012 was administered at doses of 12-24 mg/m² and the safety, pharmacokinetics and preliminary efficacy were evaluated. Results Neutropenia was the most common grade 3 or 4 adverse drug reaction. Grade 4 neutropenia accounted for the majority of dose-limiting toxicities and only appeared at a dose of 24 mg/m². The maximum concentrations and the area under the concentration-time curves from time zero to infinity for both NK012 and its active metabolite SN-38 increased in a dose-dependent manner. The best overall response was stable disease, which was achieved in 12 out of 16 patients. Conclusion The recommended dose of NK012 monotherapy for RRMM patients was concluded to be 20 mg/m². However, this phase I/II study was terminated at the end of the phase I stage because no patients showed an objective response. Additional clinical studies of combination therapy with NK012 and other agents are warranted.

To evaluate the pharmacokinetics of intraarterial (IA) administration of micellar nanoparticles incorporating SN-38 injection compared with intravenous (IV) administration in a rabbit liver tumor model.

In this animal care committee-approved study, 18 rabbits (mean weight, 3.89 kg; range, 3.20-4.70 kg) with VX2 liver tumors were divided into two groups (IA and IV). Micellar nanoparticles incorporating SN-38 (30 mg/kg) were injected through the left hepatic artery in the IA group and the right femoral vein in the IV group. NK012 and free SN-38 in the plasma, liver parenchyma, and tumors were measured within 24 hours. Histologic examinations were conducted at 2 and 24 hours.

There were no significant differences in the serum area under the concentration-time curve (0-24 h) for free SN-38, at 1,500 and 1,310 μg∙min/mL in the IA and IV groups, respectively (P = .152). The IA group showed significantly higher free SN-38 concentrations in tumor tissues at all time points compared with the IV group (P = .002 at 3 min, P = .011 at 2 h, and P = .047 at 24 h). Histologic findings showed that significantly higher tumor necrosis ratios were observed in the IA group compared with the IV group at 24 hours (P = .028).

Micellar nanoparticles could be a promising IA drug delivery system to achieve high tumor tissue concentrations of SN-38.