Based on the immunophenotype, acute lymphoblastic leukemia (ALL) can be categorized into B-cell or T-cell lineages. B-cell precursor ALL (BCP-ALL) cases show various genetic/molecular abnormalities, and varying frequencies of chimeric fusion transcripts in BCP-ALL cases are reported from different parts of the world. We studied the immunophenotypic aberrancy profiles of a large number of BCP-ALL cases with respect to various common chimeric fusion transcripts. Flow cytometric immunophenotyping and multiplex reverse-transcription polymerase chain reaction assays were performed for 986 BCP-ALL cases. Among 986 BCP-ALL cases, the incidence of various fusion transcripts was 38.36% in adult cases and 20.68% in pediatric cases. Adult BCP-ALL patients with t(9;22)(BCR-ABL1) fusion transcripts and expression of aberrant myeloid markers were significantly older at presentation (p=0.0218) with male preponderance (p=0.0246) compared to those without aberrant myeloid expression. In pediatric patients with the t(12;21)(ETV6-RUNX1) chimeric fusion transcript, aberrant expression of CD13 was observed in 39.13%, CD33 in 36.95%, and CD117 in 8.69% of patients, respectively. Pediatric BCP-ALL patients with the ETV6-RUNX1 fusion transcript and expression of aberrant myeloid markers were not significantly different compared to those without with respect to demographic and clinical/hematological characteristics (p=0.5955). Aberrant myeloid markers were rarely or never expressed in pediatric and adult BCP-ALL patients with the t(4;11)(KTM2A-AF4) and t(1;19)(TCF3-PBX1) fusion transcripts. Aberrant myeloid markers were frequently expressed among BCP-ALL patients with the t(9;22)(BCR-ABL1) and t(12;21)(ETV6-RUNX1) fusion transcripts. However, BCP-ALL patients with the t(4;11)(KTM2A-AF4) and t(1;19)(TCF3-PBX1) fusion transcripts rarely or never expressed aberrant myeloid markers. Aberrant myeloid CD markers can be used in predicting chimeric fusion transcripts at baseline so as to plan appropriate tyrosine kinase inhibitor therapy in cases of BCP-ALL with specific chimeric fusion transcripts. This study has delineated the relationship of chimeric fusion transcripts with the aberrant expression of myeloid markers in a large cohort of BCP-ALL cases.

MYC is a key driver in many aggressive and therapy-resistant cancers. We have developed and characterized a small-molecule MYC inhibitor named MYCi975. To uncover combination strategies for MYC inhibitors, we conducted a genome-wide CRISPR screen using MYCi975. This screen revealed a notable synthetic lethality when MYC inhibition was paired with disruption of mitochondrial complex I components, but not other complexes. Mechanistically, MYC inhibition reduced oxidative phosphorylation and glycolysis, triggering a compensatory up-regulation of complex I genes. Consequently, genetic or pharmacological targeting of complex I sensitized tumors to MYCi975 treatment, leading to increased purine catabolism and infiltration of CD8 ⁺ T cells and macrophages into tumors. Additionally, a wide range of tumor cells with lower complex I expression showed increased MYC dependency. These results indicate that metabolic adaptation to MYC inhibition exposes a targetable weakness at complex I and provide a rational strategy for combination therapy with emerging MYC inhibitors.