PDE4 Differential Expression Is a Potential Prognostic Factor and a Therapeutic Target in Myelodysplastic Syndromes

Inflammation and innate immunity have an essential role in the pathogenesis of myelodysplastic syndromes (MDS). One of the key inflammatory cytokines that is upregulated in MDS and acute myeloid leukemia (AML) is IL-8. [Schinke C et al, 2015]. The expression of IL-8 and other inflammatory cytokines is controlled by phosphodiesterase 4 (PDE4), which has yet to be studied in MDS and AML. Furthermore PDE4 inhibitors may be useful therapeutic targets for MDS. Based on this, we evaluated the expression of PDE4 and examined its potential impact on clinical outcomes in MDS. Transcriptomic profiling was obtained from the Illumina Genome Analyzer IIx platform, using the NuGEN Ovation RNA sequencing (RNA-seq) system. Total RNA was extracted from CD34+ bone marrow hematopoietic cells from healthy individuals (n=10) and patients with MDS (n=24) or CMML (n=19). We interrogated the RNA-seq dataset to analyze expression levels of each isoform of the PDE4 (A, B, C and D) using Z-score to normalize the results. Median overall survival (OS) was estimated using Kaplan-Meier methods with the log-rank test. Survival rates for each isoform of the PDE4 were stratified by negative or positive Z-scores (low or high expression groups, respectively). The study cohort had a median follow-up of 21.2 months (range: 0.2-68). Median age at diagnosis was 69 years (range: 43-87) with 67.5 % of diagnosed patients being ≥65 years. Most of patients (72%) were male, and 21% had a prior chemotherapy and/or radiotherapy. The median count (x 10⁹/L) for white blood cells and platelets was 12.2 (range: 0.7-67) and 97.2 (range: 11-331), respectively. IPSS risk was low and int-1 in 51.2% of patients, int-2 in 37.2%, high in 6.9%, and not available in 4.7%. The cytogenetic groups of risk were: very good and good in 53.5% of patients, intermediate in 30.2%, poor in 14% and not available in 2.3%. The overall response rate (ORR) to hypomethylation agents (HMA) was 51.1%, with 37.2% having complete response (CR), 6.9% having bone marrow CR, and 6.9% having hematologic improvement. Median OS for the whole cohort was 17.6 months (95% confidence interval [CI]: 9.6-25.6). Detailed PDE4 isoform-specific analyses are presented in Table1. Importantly, there appears to be an impact on OS depending on PDE4 isoform expression levels, which should be confirmed in a larger patient cohort. PDE4 expression may be useful as both a prognostic factor and a potential therapeutic target for patients with MDS. The effects of PDE4 inhibitors should be investigated in vitro against MDS cell lines and in preclinical mouse models of MDS. One potential application for this study is to exploit the blockade of the PDE4 pathway on the IL8 expression, which may be a good therapeutic strategy against MDS and AML stem cells [Schinke C et al, 2015]. PDE4 inhibitors could also be included in our therapeutic arsenal in the context of the HMA failure in selected patients with MDS.