The Multi-Kinase Inhibitor Sorafenib Blocks Migration, BCR Survival Signals, Protein Translation and Stroma-Mediated Bortezomib Resistance in Mantle Cell Lymphoma

Abstract 1647

Mantle cell lymphoma (MCL) is an incurable B-lymphoid neoplasm harboring the t(11;14)(q13;q32) translocation which leads to the overexpression of cyclin D1, with the consequent cell cycle deregulation. Typically, MCL is characterized by bad prognosis and an aggressive course of the disease. Unfortunately, current therapies have shown limited efficacy and relapses occur early, thus our purpose was to evaluate the antitumoral properties of the multikinase inhibitor sorafenib in MCL. Sorafenib is an oral multikinase inhibitor that targets several cancer-specific pathways and directly affects tumor cell proliferation, cell survival and neovascularization.

We analyzed the sensitivity to sorafenib in 9 MCL cell lines and 17 primary MCL cells by flow cytometry after annexin V staining. Sorafenib induced apoptosis in MCL cell lines with a mean LD50 of 11.5 ± 5.0 μM at 24 hours, while at 48 hours decreased to 7.1 ± 2.7 μM. In primary MCL cells, the mean LD50 was 13.0 ± 3.6 μM at 24 hours, while at 48 hours it notably decreased to 9.4 ± 3.4 μM. These data indicated that sorafenib exerted a time- and dose-dependent cytotoxic effect in MCL cells. Both in cell lines and primary MCL cells, sorafenib induces rapid dephosphorylation of the BCR (B-Cell Receptor)-associated tyrosine kinases, SYK and LYN, as well as of FAK, a downstream SRC target involved in focal adhesion. In line with this, we demonstrate a strong synergy when combining sorafenib with the SYK inhibitor, R406. In parallel, we show that sorafenib also blocks Mcl-1 and cyclin D1 translation, which promotes an unbalance between pro- and anti-apoptotic proteins and facilitates the release of Bax from cyclin D1. This process leads to the induction of the mitochondrial apoptotic pathway and caspase-dependent and independent mechanisms. Moreover, sorafenib inhibits MCL cell migration as well as actin polymerization in response to CXCL12. FAK siRNA-mediated knockdown partially prevents this inhibitory effect, indicating that FAK is a relevant target for the action of sorafenib in MCL cells. Importantly, this compound resensitizes MCL cells cocultured with bone marrow-derived stromal and follicular dendritic-like cells to bortezomib-induced apoptosis indicating that sorafenib was able to antagonize stroma-mediated resistance in MCL.

In conclusion, we provide first evidence on the molecular mechanism of action of the multikinase inhibitor sorafenib in MCL. We propose that this compound inhibits cell migration and stroma-mediated bortezomib resistance by interfering BCR signaling and protein translation. All these results suggest that sorafenib, alone or in combination with bortezomib-based therapies, may represent a promising approach for the treatment of MCL patients.