Abstract B18: Blocking α4β1 integrin interaction with matrix metalloproteinase-9 overcomes stroma-induced resistance of chronic lymphocytic leukemia cells to fludarabine and arsenic trioxide

Abstract

Abstract Chronic lymphocytic leukemia (CLL) progression is determined by CLL cell accumulation in lymphoid organs, where they receive survival signals that impair therapeutic treatments. MMP-9 is a microenvironment component and we have shown that induces a signalling pathway that leads to CLL cell survival. We have now studied whether MMP-9 is involved in the response to cytotoxic agents such as fludarabine and arsenic trioxide (ATO). Both agents upregulated MMP-9 (mRNA and protein) and enhanced its binding to CLL cells. Cell-associated MMP-9 was restricted to early apoptotic cells and totally dependent on apoptosis onset, suggesting a role in the response to these drugs. Indeed, anti-MMP-9 antibodies accelerated apoptosis. Moreover, MEC-1 cells (CLL-derived) stably transfected with MMP-9 were more resistant to drug-induced apoptosis than Mock-transfected cells. Western blot analyses revealed that MMP-9 prevented down regulation of anti-apoptotic Bcl-2 family members. Therefore, MMP-9 likely represents a compensatory survival response that contributes to drug resistance. Additionally, culturing CLL cells with bone marrow stromal cells (BMSC) prevented the apoptotic effect of ATO and this was nearly completely reverted with anti-MMP-9 antibodies. Blocking α4β1 integrin (MMP-9 receptor) and/or αLβ2 integrin (ICAM-1 receptor) also overcame stroma-induced survival. This was also partially achieved by culturing CLL cells with BMSC-conditioned medium, indicating that both cell adhesion and soluble factors contributed to the observed drug resistance. To determine the mechanisms involved, the effect of blocking several signalling pathways was studied. Inhibiting the PI3K/Akt or focal adhesion pathways with specific inhibitors significantly restored the sensitivity of CLL cells to ATO. Therefore, our results highlight the role of MMP-9 in CLL drug resistance and indicate that concomitant targeting of MMP-9 may improve the CLL response to treatment. Supported by grants SAF2012-31613 and RD12/0036/0061 (AGP) from the Ministry of Economy and Innovation, Spain; S2010/BMD-2314 (AGP) from the Comunidad de Madrid/European Union, and by a grant from the Fundación Puerta de Hierro, Madrid (JAGM). Citation Format: Irene Amigo-Jiménez, Elvira Bailón, Estefanía Ugarte-Berzal, José Antonio García-Marco, Angeles Garcia-Pardo. Blocking α4β1 integrin interaction with matrix metalloproteinase-9 overcomes stroma-induced resistance of chronic lymphocytic leukemia cells to fludarabine and arsenic trioxide. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr B18. doi:10.1158/1538-7445.CHTME14-B18