Antitumor Activity of Phosphoinositide 3-Kinases Inhibitor, Copanlisib in Multiple Myeloma Cells
Authors: Tanaka Yuko , Okabe Seiichi , Tauchi Tetsuzo , Ito Yoshikazu , Ohyashiki Kazuma 
Published: October 2019

Abstract
Multiple myeloma (MM) is one of the common hematological malignancies and is a uniformly fatal disorder of B cells characterized by accumulation of abnormal plasma cells in the bone marrow. Proteasome inhibitor, bortezomib, and immunomodulatory drugs such as thalidomide and lenalidomide play important roles in the treatment of MM patients. Although novel agents including, e.g. bortezomib, have significantly improved the response and survival of patients with MM, a large number of patients eventually have relapsed. For the patients who relapse after treatment with novel agents, the prognosis is still poor. Thus circumstanced, alternative strategies are required for continued disease control. Phosphoinositide 3-kinases (PI3Ks) are a family of proteins involved in the regulator of cell growth, metabolism and proliferation. PI3K signaling pathway also plays a critical regulatory role in MM pathology, including survival, cellular proliferation, migration and angiogenesis. Therefore, PI3K signaling pathway may present attractive targets for MM treatment. Copanlisib also known as BAY80-6946 is a potent and highly selective reversible PI3K inhibitor. Copnalisib is currently investigated in a pivotal phase 2 clinical trial against hematological malignancy such as malignant lymphoma.
We hypothesized that treatment with PI3K inhibitor and proteasome inhibitors together would result in enhanced therapeutic activity in MM cells. In this study, we investigated the efficacy of copanlisib by using the MM cell lines, RPMI8226, MM1.S and MM1.R and primary sample.
72 h treatment of copanlisib exhibits cell growth inhibition of MM cell lines in a dose dependent manner. The treatment of proteasome inhibitors, bortezomib and carfilzomib exhibits cell growth inhibition partially against RPMI8226 cells in the presence of feeder cell line, HS-5. We examined the intracellular signaling in the presence of HS-5. Phosphorylation of Akt and activation of caspase 3 and poly (ADP-ribose) polymerase (PARP) was partially reduced by carfilzomib or bortezomib in the presence of HS-5. We found that the treatment of copanlisib abrogated the protective effects of HS-5 in RPMI8226 cells. We examined the intracellular signaling after treatment of copanlisib. Activity of caspase 3 and poly (ADP-ribose) polymerase (PARP) was increased after copnlisib treatment in a dose dependent manner. Because PI3K signaling pathway regulates MM cell migration, we next evaluated the chemotactic response of MM cells to stromal cell-derived factor 1α (SDF-1α). We found that 4 h treatment of SDF-1α significantly induced the migration of MM cells compared to control medium. Treatment of copanlisib inhibited SDF-1α-stimulated chemotaxis in a dose dependent manner. We found that phosphorylation of Akt was reduced after copanlisib treatment suggesting that intracellular PI3K signaling pathway may play the important role in SDF-1α induced chemotaxis of MM cells. We investigated the copanlisib activity against MM cells. Combined treatment of MM cells with proteasome inhibitor, carfilzomib or bortezomib, and copanlisib caused significantly more cytotoxicity than each drugs alone. Phosphorylation of Akt was reduced and cleaved PARP was increased after copanlisib with or without proteasome inhibitor. We also found that copanlisib which was combinaed with carfilzomib or borteomib exhibited cell growth inhibition against MM primary sample.
Data from this study suggested that administration of the PI3K inhibitor, copanlisib may be a powerful strategy against stroma-associated drug resistance of MM cells and enhance cytotoxic effects of proteasome inhibitors in those residual MM cells.

Disclosures
No relevant conflicts of interest to declare.