The Role of Integrin Beta-1 in the Chemoresistance of Acute Myeloid Leukemia

Abstract

BACKGROUND: Acute myeloid leukemia (AML) is an aggressive disease that has a poor prognosis with a survival rate of 30-40%. The bone marrow microenvironment provides protection to AML cells from chemotherapy and thus confers cell adhesion-mediated drug resistance (CAM-DR) and promotes relapse. Integrins are key anchor molecules in CAM-DR of leukemia cells; they are heterodimeric adhesion molecules on the cell surface consisting of an alpha and a beta unit. Upregulated integrin alpha 4 and 6 expression is associated with poor survival in leukemias. We hypothesize that the targeting of integrin beta 1 (ITGB1, β1, or CD29) will also affect the integrin alpha units as they are heterodimer partners. This could be a superior approach to overcome CAM-DR in AML than just targeting the individual alpha units. METHODS: ITGB1 gene was knocked out via CRISPR-Cas9 using 2 guide RNAs in AML cell lines and expression of integrin subunits was profiled by flow cytometry. AML cell lines were treated in vitro with the anti-human ITGB1 monoclonal antibody OS2966 in combination with Ara-C chemotherapy and we determined effects on cell viability by flow cytometry and on cell signaling using RNA-sequencing. Using human patient-derived AML xenograft mouse models, we tested if blockade of ITGB1 combined with chemotherapy can overcome CAM-DR in vivo. Mice were treated with control total Ig (10 mg/kg), OS2966 (10 mg/kg), total Ig + Ara-C (600 mg/kg), or OS2966 + Ara-C twice a week for two weeks. RESULTS: Analysis of patient-derived AML cells at diagnosis and relapse, and of AML cell lines, showed high expression of ITGB1 and varying levels of other alpha and beta units. Loss-of-function studies of ITGB1 using CRISPR/Cas9-mediated knockout of ITGB1 in MLL-rearranged and FLT3-ITD+ AML cell lines MV4-11 and MOLM-13, and in AML cell line U937, revealed that surface expression of integrin alphas 3, 4, 5 and 6 were markedly decreased as determined by flow cytometry analysis. ITGB2 expression was high in all 3 AML cell lines and not affected by ITGB1 deletion. Remarkably, ITGB3 was downregulated upon ITGB1 deletion in 2 out of 3 AML cell lines, whereas the 3rd AML cell line did not express any ITGB3. As a result of the ITGB1 deletion, AML cells showed less adhesion to murine bone marrow stroma (OP9) cells and to extracellular matrix proteins. We found that inhibition of surface ITGB1 on human AML using OS2966 de-adhered the AML cells from OP9 cells. Moreover, ITGB1 blockade using OS2966 synergized with Ara-C in vitro and significantly decreased cell viability compared to single agent controls in human AML cell lines U937 and MV4-11. RNA sequencing data suggest that the NFkB pathway is significantly dysregulated in the combination treatment Ara-C and OS2966 compared to Ara-C alone. To test ITGB1 inhibition in vivo, a patient-derived AML sample, HEM279 (Fig. 1A), and AML cell line, U937 (Fig. 1B), were engrafted into NSG-SGM3 mice. Leukemic mice were treated with single agents including control total Ig, OS2966, or Ara-C; and with total Ig in combination with Ara-C or OS2966. In both xenograft models, the combination treatment of OS2966 with Ara-C significantly prolonged survival of leukemic mice compared to Ara-C only: HEM279: MST 115 +/- 15.4 days vs 73.1 +/- 5.2 days post-AML injection; p=0.0005; U937: MST 170 days vs 32 days post-AML injection; p=0.0004; 50% of the mice engrafted with U937 and treated with OS2966 with Ara-C survived until day 290 post-AML injection, which is when the experiment was terminated. CONCLUSIONS: Integrin alpha subunit expression is dependent on ITGB1 expression, supporting our hypothesis that targeting integrin beta 1 affects alpha integrin units. ITGB1 inhibition with OS2966 combined with chemotherapy significantly decreases cell viability of AML cell lines in vitro and prolongs survival of xenograft mice in vivo. Our findings will allow for better understanding of the role of ITGB1 in drug resistance of AML and of ITGB1 as a preclinical target in AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal