mrk-003 and Multiple-Myeloma

To explore the tumor growth inhibition of gamma secretase inhibitor MRK003 on human multiple myeloma xenograft mice by inhibition of AKT and Notch1 expression.. NOD/SCID mice were injected with human multiple myeloma cell lines RPMI8226 to establish a xenograft mouse model. Mice were randomized into two groups：the experimental group were injected with MRK003 at a dose of 5 mg× kg⁻¹×d⁻¹ for 14 days; the inhibitor was replaced by an equal saline in the control group. Mice were sacrificed by cervical dislocation on the next day after the last injection and tumor tissue was removed to detect the expression of Notch1 and AKT by immunohistochemistry.. After subcutaneous injection with RPMI8226, mice had tumor formation in 5-7 days and the largest tumor block in 10-12 days. Before RPMI8226 injection, the mean sizes of tumor block in the experimental and the control groups were 509.2 mm³, 511.2 mm³(P>0.05). 9 days after injection, the mean sizes of tumor tissue in the experimental and the control groups were 636.6 mm³, 691.2 mm³(P<0.01). On the next day after the last injection, the tumor sizes of the experimental and the control groups were 683.5 mm³ and 1798.7 mm³(P<0.01). The size of tumor block in the experimental group was significantly smaller than that of the control group(P<0.01). Immunohistochemistry staining showed that the positive expression rates of Notch1(11.1%, P<0.01) and AKT(13.3%, P<0.01) in experimental group were significantly decreased compared with the control group(Notch1: 95.6%; AKT: 93.3%). Western blot results showed that Notch1 and AKT protein in experimental group were significantly lower than those in the control group.. MRK003 could inhibit the tumor growth of human multiple myeloma xenograft mice by downregulated expression of Notch1 signaling pathway.

Topics: Amyloid Precursor Protein Secretases; Animals; Cell Line, Tumor; Cyclic S-Oxides; Humans; Mice; Mice, Inbred NOD; Mice, SCID; Multiple Myeloma; Proto-Oncogene Proteins c-akt; Receptor, Notch1; Signal Transduction; Thiadiazoles; Xenograft Model Antitumor Assays

Notch-stimulated signaling cascade results in transcriptional regulation of genes involved in cell fate decision, apoptosis and proliferation and has been implicated in various malignancies. Here, we investigated the impact of MRK003, an inhibitor of this pathway, on myeloma and lymphoma cells. We first studied the expression patterns of notch receptors and ligands on multiple myeloma (MM) and non-Hodgkin's lymphoma (NHL) cell lines. Next, we used a γ-secretase inhibitor, MRK003 to test the importance of notch-stimulated pathways in MM and NHL disease biology. We observed expression of notch receptors and ligands on MM and NHL cell lines. MRK003 treatment induced caspase-dependent apoptosis and inhibited proliferation of MM and NHL cell lines and patient cells. Examination of signaling events after treatment showed time-dependent decrease in levels of the notch intracellular domain, Hes1 and c-Myc. MRK003 downregulated cyclin D1, Bcl-Xl and Xiap levels in NHL cells and p21, Bcl-2 and Bcl-Xl in MM cells. In addition, MRK003 caused an upregulation of pAkt, indicating crosstalk with the PI3K/Akt pathway. We evaluated MRK003 in combination with Akt1/2 kinase inhibitor and observed synergy in killing MM and NHL cell lines examined.

Topics: Amyloid Precursor Protein Secretases; Apoptosis; Base Sequence; Cell Line, Tumor; Cyclic S-Oxides; DNA Primers; Drug Screening Assays, Antitumor; Enzyme Inhibitors; Humans; Lymphoma, Non-Hodgkin; Multiple Myeloma; Reverse Transcriptase Polymerase Chain Reaction; Thiadiazoles