In vitro activity: CEP-18770 demonstrates marginal prevention of the tryptic and peptidyl gultamyl activities of the protesome. The IC50 values of CEP-18770 are similar to those of bortezomib, with the chymotryptic and caspase-like activities being inhibited at low-nanomolar concentrations. CEP-18770 inhibits A2780 ovarian cancer cells, PC3 prostate cancer, H460, LoVo colon cancer, RPMI8226 multiple myeloma cancer and HS-Sultan anaplastic non-Hodgkin lymphoma with IC50 values of 13.7, 22.2, 34.2 11.3, 5.6 and 8.2 nM, respectively. CEP-18770 blocks the ubiquitin-proteasome pathway in several MM and in the chronic myelogenous leukemia cell line, K562. CEP-18770 causes an accumulation of ubiquitinated proteins over 4 to 8 hours with a profile similar to that observed after bortezomib treatment. IκBα degradation is completely blocked by pretreatment with CEP-18770. CEP-18770 significantly inhibits high levels of NF-κB activity in both RPMI-8226 and U266 cells. The time- and concentration-dependent suppression of NF-kB DNA-binding activity in MM cell lines by CEP-18770 leads to a decrease of expression of several NF-κB-modulated genes mediating the growth and survival of tumor cells including IkBα itself, the X-chromosome-linked inhibitor-of-apoptosis protein (XIAP), the pro-inflammatory cytokines TNF-α and interleukin-1β (IL-1β), the intracellular adhesion molecule (ICAM1), and the pro-angiogeneic factor vascular endothelial growth factor. The expression of these NF-κB–mediated genes and their modulation by bortezomib are associated with more favorable clinical responsiveness to this agent, highlighting their potential prognostic value in response to CEP-18770 exposure. The proapoptotic activity of CEP-18770 against MM is not limited solely to tumor-derived MM cell lines, but extends to primary MM explants from relapsed or refractory patients including those previously treated with bortezomib. In addition, the combination of CEP-18770 with melphalan or bortezomib produces synergistic inhibition of MM cell viability in vitro.

Kinase Assay: Human multiple myeloma cells are washed twice with cold phosphate-buffered saline, pelleted and lysed with one volume of glass beads (<106 microns, acid-washed) and an equal volume of homogenization buffer (50 mM Tris (pH 7.4), 1 mM dithiothreitol, 5 mM MgCl2, 2 mM ATP and 250 mM sucrose) by vortexing at high speed for 15-30 min at 4 °C. Beads, membrane fractions, nuclei and cell debris are then removed from the supernatant by centrifugation at 16,000g for 5 min. The protein content of extracts is quantitated using the Bradford assay. Proteasome activity is assayed as described below. Equal amounts (typically 60 g) of protein are denatured by boiling in reducing sample buffer, separated by 12.5% SDS-PAGE and electrotransferred onto polyvinylidene difluoride (PVDF) membranes. Immunoblotting is performed using a dansyl-sulfonamidohexanoyl polyclonal antibody (1:7,500, rabbit) and horseradish peroxidase–coupled goat or swine anti-rabbit secondary antibody followed by enhanced chemiluminescence.

Cell Assay: HMEC and TEC cells are seeded into 24-well plates at a density of 104 cells/well in DMEM supplemented with 5% FCS. After incubation with proteasome inhibitors (48 hours), cells are washed, air dried, and stained with crystal violet as described. Cell number is determined, in duplicate samples, on the basis of a standard curve obtained with known cell numbers. All experiments are performed in triplicate. In vitro formation of capillary-like structures is studied on cells (4 × 104 cells/well in DMEM supplemented with 5% FCS. After incubation with proteasome inhibitors (48 hours), cells are washed (cells/well in 24-well plates) and seeded onto Matrigel-coated wells in DMEM containing 0.25% BSA. HMEC and TEC cells (5 × 103 per well), suspended in 200 μL DMEM with 5% FCS (positive control), serum-free medium (negative control), are layered onto the Matrigel surface in the presence or absence of proteasome inhibitor CEP-18770. Cells are observed with a inverted microscope and experimental results are then recorded after a 6-hour incubation at 37 °C. Data is analyzed, as the mean (× 1 SD) of total length of capillary-like structures, by the Micro-Image system and is expressed as mm/field by the computer analysis system in 5 different fields at 100 × magnification in duplicated wells for 4 different experiments.