102P MicroRNAs in urine and saliva as non-invasive biomarkers of minimal residual disease in pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia is the most common type of cancer among children. Around 20% of patients relapse after remission. Minimal residual disease (MRD) is used as a predictor of relapse. MDR is measured by flow cytometry in bone marrow samples. MicroRNAs are small non-coding RNAs that regulate gene expression, acting as oncogenic or tumor suppressor biomolecules. MicroRNAs are secreted in various biofluids, including urine or saliva, at levels that reflect the homeostatic state of an individual. These secreted microRNAs might be useful as non-invasive biomarkers of MRD and treatment follow up in leukemia. This study aims to identify and evaluate the usefulness of urinary and salivary microRNAs as biomarkers of MRD in children diagnosed with acute lymphoblastic leukemia. Saliva and urine samples, from high (MRD≥10) and standard intermediate (MDR<10) risk of relapse children, were collected on day 15 of chemotherapy. MicroRNAs were extracted using a commercial kit and sequenced to identify differences in secretion patterns. Differential expression analysis was carried out using the DeSeq2 algorithm. The mean MRD on day 15 was 52.23 % ± 38.42 and 1.03 % ± 0.53 in the high risk and standard intermediate risk children, respectively. Twenty-three microRNAs were differentially secreted (adjusted p-value < 0.01 and log 2 fold change > 1) between the high risk and standard intermediate children in saliva (12 upregulated and 11 downregulated). In contrast, only 3 sequences were differentially secreted (all downregulated) in urine samples. The miR-1246 and miR-3976 showed the highest increase (log 2 fold change = 7.53) and decrease (log 2 fold change = -5.52), respectively, in saliva samples. In urine miR-4783-5p showed the highest decrease (log 2 fold change = -3.15). However, these results need to be validated using PCR techniques. In conclusion, miR-1246, miR-3976 and miR-4783-5p show promising utility as MRD biomarkers for monitoring MRD and treatment follow up in children diagnosed with ALL. With the additional advantage that microRNAs are more stable than other molecular markers and urine and saliva samples are non-invasive and easy to collect.