A Novel WNT5A-Mimicking Peptide Affects Leukemia Cell Survival in the Bone Marrow Microenvironment

Background: The crosstalk between hematopoietic cells and bone marrow (BM) microenvironment in hematological malignancies is related to disease initiation, maintenance and relapse. BM niche sustains a protective response against currently available treatments that have shown unwanted adverse effects and high levels of toxicity for patients. WNT5a is a glycoprotein secreted by mesenchymal stromal cells (MSC) that activates the WNT non-canonical pathway in hematopoietic cells, modulating important biological processes related to neoplasia development.

Aims: To investigate WNT5a mRNA expression, protein levels and methylation pattern in Myelodysplastic Syndrome (MDS) and de novo Acute Myeloid Leukemia (AML) patients and their impact on clinical outcomes, and to analyze effects of Foxy-5 (WNTResearch), a new WNT5a-mimicking compound.

Methods: WNT5a mRNA expression was analyzed in mononuclear cells (MC) from 371 AML patients (212 male, median age 61 years [range: 2-87]) (Ohsu, Nature 2018). BMMSC and BM biopsies from 5 healthy donors (HD), 6 MDS and 13 AML patients at diagnosis were submitted to analysis of WNT5a mRNA expression and methylation after Azacytidine (1μM) treatment by real-time PCR, and WNT5a protein levels by immunohistochemistry and immunofluorescence (IF). A panel of myeloid leukemia cell lines (U937, HL60, THP1, KG1a, K562) were treated with Foxy-5 (1 to 100μM) for 72h in monoculture, coculture and 3D-coculture (with MSC) and evaluated for ROS production (DCFDA dye), cell proliferation (Ki-67 stain), autophagy (acridine orange dye), chemotaxis (Transwell), actin polymerization (phalloidin stain), cell cycle (PI/RNAse stain), cell viability (MTT assay), apoptosis (Annexin-V stain) and protein expression (Western blot, WB). MC and CD34+ cells from HD were submitted to cytotoxic assays. Statistical analyzes were performed using ANOVA or Mann-Whitney tests, as appropriate.

Results: WNT5a gene expression was reduced in MC from AML patients with adverse cytogenetic risk compared to favorable and intermediate cytogenetic risk (fold-decrease [FD]: 42.9; 18.8, respectively) (P<.05) and in BMMSC from AML compared to HD (FD: 53.3) (P<.05). Accordingly, WNT5a gene expression in MDS and AML BMMSC treated with Azacytidine was restored (fold-increase [FI]: 3.99; 1.50, respectively). WNT5a protein expression were diminished in BMMSC from MDS and AML patients compared to HD onto a 3D-coculture (IF)(P<.05) and immunohistochemically detected in all BM hematopoietic lineages. Foxy-5 reduced ROS production in U937 (FD of mean fluorescence intensity [MFI]: 48.2; 46.6), HL60 (FD: 47.1; 115.0), KG1a (FD: 34.9; 20.7) and K562 (FD: 19.0; 24.3) at 100μM in monoculture and coculture, respectively (P<.05). Foxy-5 also significantly decreased proliferation in U937 (FD: 41.0), HL60 (FD: 18.0), THP1 (FD: 36.0) and K562 (FD: 68.0) at 100μM (P<.05), confirmed by a 3D-coculture containing these cell lines and MSC. Foxy-5 reduced monocyte differentiation and inhibited CD11b expression in U937 (FD: 16.4) and THP1 (FD: 14.4). Cell cycle progression was blocked in sub G0/G1 phase in all cell lines (P<.05) after Foxy-5 treatment, probably mediated by the reduction of cyclin D1 protein levels, as verified by WB. Further, Foxy-5 reduced AKT1/2/3 and ERK1/2 phosphorylation levels, possibly by beta-catenin inhibition, with disruption of actin polymerization (U937 (FD: 65.3), HL60 (FD: 35.9), THP1 (FD: 58.5), K562 (FD: 15.0)) at 100μM (P<.05) and consequent impairment of CXCL12-induced chemotaxis (U937 (FD: 27.9), HL60 (FD: 42.5), THP1 (FD: 82.4), K562 (FD: 45.1)) at 100μM (P<.05). In coculture, cell autophagy was reduced in U937 (FD: 27.8), HL60 (FD: 35.9), KG1a (FD: 16.4) and K562 (FD: 35.8) when treated with Foxy-5 at 100μM (P<.05). Finally, Foxy-5 treatment did not affect cytotoxicity in MC and CD34+ cells from HD.

Conclusion: WNT5a downregulation in MDS and AML patients occurs probably by methylation and contributes to poor prognosis. Foxy-5, by restoring WNT5a levels, could represent a strategy to counterbalance several oncogenic processes present in leukemia by reducing ROS production and, consequently, inhibiting cell growth and differentiation, downregulating PI3K and MAPK pathways, disrupting actin polymerization and decreasing autophagy. Thus, Foxy-5 treatment may be an important approach to impair leukemia growth and maintenance and arises as a promising therapeutic target.