Phase 1 Clinical Trial of NPI-0052 in Patients With Advanced Solid Tumor Malignancies or Refractory Lymphoma

NPI-0052 (also known as marizomab) is a second generation proteasome inhibitor being developed as an anticancer agent. Proteasomes are responsible for degrading substrates such as damaged and aged proteins, tumor suppressors, and cell cycle regulators, and for regulating NF-κB activation by degrading its inhibitor, IκB. Blocking the proteasome pathway results in accumulation of proteins, which can cause cell death, particularly in tumor cells (Kisselev, 2001). The Food and Drug Administration (FDA) approved the first proteasome inhibitor (bortezomib; Velcade®) in 2003 for the treatment of patients with multiple myeloma (MM) and subsequently for treatment of patients with mantle cell lymphoma in 2006. Although this compound has demonstrated efficacy in both of those indications, resistance and toxicity develop with continued therapy. Resistance may result from a variety of mechanisms. Bortezomib toxicity (primarily neurological with peripheral neuropathy and neuralgia, and also thrombocytopenia and neutropenia) can result in treatment discontinuation (about 25% of patients in a clinical trial conducted in patients at time of first relapse required cessation of therapy due to adverse events). NPI-0052 inhibits the chymotrypsin-like (CT-L), caspase-like (C-L), and trypsin-like (T-L) activity of human erythrocyte-derived 20S proteasomes. Also known as salinosporamide A, NPI-0052 is a novel chemical entity discovered during the fermentation of Salinispora tropica NPS021184, a marine actinomycete, and is manufactured by saline fermentation. NPI-0052 was shown in nonclinical studies to have increased potency and duration of biological effects compared with bortezomib and may provide a significant therapeutic advantage, particularly if toxicity is less at therapeutic doses. This was the first-in-human study of NPI-0052, and was conducted in cancer patients.