The HOTAIRM1-miR-222 Axis Regulates Venetoclax Resistance and Defines a High-Risk Subset in Pediatric t(8;21) Acute Myeloid Leukemia

Abstract Although acute myeloid leukemia (AML) with the RUNX1::RUNX1T1 fusion [t(8;21)(q22;q22.1)] defines a distinct cytogenetic subtype, differences in treatment response suggest additional molecular contributors beyond chromosomal abnormalities. Deregulated hematopoietic lineage-specific long non-coding RNAs (lncRNAs) contribute to leukemogenesis and therapy resistance. To investigate their role in t(8;21) AML, we performed whole-transcriptome sequencing of pediatric patients and age-matched healthy controls, identifying significant downregulation of lncRNA HOTAIRM1 , a regulator of myeloid differentiation (adjusted P < 0.05). This was confirmed in a single-cell RNA-sequencing dataset (GSE116256) and the Leukemia MILE dataset (GSE13159, P=0.03). Validation of expression in our study cohort using qPCR specifically demonstrated significant downregulation of the myeloid specific isoform, HOTAIRM1 – HM1V2 (P<0.0001). Analysis of downstream pathways activated by HM1V2 loss identified miR-222 , an oncomiR, as a de-repressed target (P=0.01). Elevated miR-222 expression was observed across AML cell lines (P<0.05), leukemic stem and progenitor cells (GSE117090, P<0.05), AML plasma-derived exosomes (GSE142699, P<0.0001), the current study dataset (P<0.0001), and the TARGET AML dataset (P<0.0001). Restoring HM1V2 expression with epigenetic agents azacytidine and panobinostat induced apoptosis in venetoclax-resistant Kasumi-1 cells (P < 0.01), through suppression of miR-222 (P < 0.01) and downregulation of anti-apoptotic proteins BCL-xL and MCL-1 (P < 0.05), key mediators of the venetoclax resistance mechanism. Machine learning based feature selection and Cox regression analysis showed that high miR-222 expression predicts poor outcome in pediatric t(8;21) AML, validated in both our institutional pediatric AML cohort (P < 0.05) and the multi-institutional TARGET cohort (P < 0.0001). Together, our findings highlight an epigenetic based approach to restore isoform-specific HM1V2 pathway function in venetoclax-resistant AML cells, and identifies miR-222 as a prognostic marker to refine risk stratification within the traditionally favorable-risk t(8;21) AML subgroup. Key Points Loss of myeloid lineage specific isoform of lncRNA HOTAIRM1 - HOTAIRM1 variant 2 , results in de-repression of microRNA miR-222 , and contributes to venetoclax resistance in pediatric AML patients harbouring the t(8;21)(q22;q22.1)/RUNX1::RUNX1T1 fusion. MicroRNA miR-222 shows potential as a single marker predictor that complements current risk stratification by identifying a subset of pediatric t(8;21) AML patients with poor prognosis. Abstract Figure