High Plasma Lysyloxidase Concentration Is Associated with Inferior Outcome and Extramedullary Disease in Patients with Acute Myeloid Leukemia

Previous work of our group led to the identification of several differentially regulated microRNAs in patients with acute myeloid Leukemia (AML) harboring a mutation of the Nucleophosmin 1 gene (NPM1) – amongst these was miR-149 which is reported to regulate Lysyloxidase (LOX). LOX is described as necessary for premetastatic niche formation in various epithelium-derived malignancies and its expression level correlates with distant metastasis free- and overall survival (OS). Animal models have demonstrated that inhibition of LOX sufficiently eliminates metastasis. Therefore, we were interested to investigate whether the LOX-concentration in AML plasma samples is of prognostic relevance and whether it is associated with certain characteristics such as extramedullary disease.

Patients and methods: Plasma samples of 156 patients with AML (n=63 with reported extramedullary manifestation and n=93 without reported extramedullary manifestation; age 17–60 years) who were treated within the prospective AML2003 trial (NCT00180102) of the SAL study group were analyzed for LOX concentration using the Amplite Fluorimetric LOX Assay Kit (AAT Bioquest, Sunnyvale, CA, USA). All fluorescence reads were performed in triplicate with recombinant human LOXL2 (R&D Systems, Minneapolis, MN, USA) for standard curve estimation. Signals were read by a fluorescence microplate reader at Ex/Em 540/590 nm. Supernatant of the NPM1 mutated AML cell line OCI/AML3 served as internal control. LOX values were compared for statistical significance using the two tailed t test for continuous variables and chi-square test for dichotomized variables. The method of Kaplan-Meier was used to estimate OS and event-free survival (EFS). Survival distributions were compared using the log-rank test.

The mean LOX concentration for all patients was 58 ng/mL (standard error of the mean (SEM) 12). Dichotomizing at the mean LOX level (n=29 patients > mean = LOX-high; n=126 ≤ mean = LOX-low), survival comparing LOX-high and LOX-low patients in a univariate analysis revealed a 3-year OS of 22% (95% CI: 6–39%) and 53% (95% CI: 43–62%, p=.004), and 2-year EFS of 14% (95% CI: 2–28%) and 43% (95% CI: 34–52%, p=.001), respectively. In the Lox-high group 79% of patients exposed extramedullary AML compared to 32% in the Lox-low group, p<0.001. The mean LOX concentration in AML patients with extramedullary disease (n=63) was 131 ng/mL (SEM 26) as compared to 9 ng/mL (SEM 4) in patients without reported extramedullary AML manifestation (n=93), p<0.001.

This analysis is the first study so far investigating the role of LOX in AML. High LOX levels are associated with statistically significant worse OS and EFS in AML patients. The positive correlation between high LOX levels and extramedullary AML suggests a potentially pathophysiological relevant mechanism involved in extramedullary homing and growth of AML and may offer further insights into AML biology. Future studies will need to address the functional modalities of how LOX is regulated and how it contributes to migratory and adhesion properties in AML.

No relevant conflicts of interest to declare.