Abstract
The proteasome was validated as an oncology target following the clinical success of VELCADE (bortezomib) for injection for the treatment of multiple myeloma and recurring mantle cell lymphoma. Consequently, several groups are pursuing the development of additional small-molecule proteasome inhibitors for both hematologic and solid tumor indications. Here, we describe MLN9708, a selective, orally bioavailable, second-generation proteasome inhibitor that is in phase I clinical development. MLN9708 has a shorter proteasome dissociation half-life and improved pharmacokinetics, pharmacodynamics, and antitumor activity compared with bortezomib. MLN9708 has a larger blood volume distribution at steady state, and analysis of 20S proteasome inhibition and markers of the unfolded protein response confirmed that MLN9708 has greater pharmacodynamic effects in tissues than bortezomib. MLN9708 showed activity in both solid tumor and hematologic preclinical xenograft models, and we found a correlation between greater pharmacodynamic responses and improved antitumor activity. Moreover, antitumor activity was shown via multiple dosing routes, including oral gavage. Taken together, these data support the clinical development of MLN9708 for both hematologic and solid tumor indications.
Highlights
The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal manner by which cells regulate protein homeostasis
VELCADE is approved for the treatment of patients with multiple myeloma and previously treated mantle cell lymphoma [13,14,15,16,17,18,19,20,21]
MLN9708 was identified in screens for small-molecule proteasome inhibitors with an improved pharmacologic profile compared with bortezomib (Fig. 1)
Summary
The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal manner by which cells regulate protein homeostasis. The effect of MLN2238 or bortezomib on β5 activity was determined in situ using the Proteasome-Glo cell-based assay. Blood and tumor 20S proteasome inhibition versus time profiles were generated for MLN2238 and bortezomib from both CWR22 and WSU-DLCL2 xenografts (Fig. 2).
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