An Alternatively Spliced Gain-of-Function NT5C2 Isoform Contributes to Chemoresistance in Acute Lymphoblastic...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Relapsed or refractory B-cell acute lymphoblastic leukemia (B-ALL) is a significant cause of pediatric cancer mortality.
• Chemotherapy failures in B-ALL are not fully explained by relapse-specific mutations, indicating other resistance mechanisms.
• Alternative splicing (AS) is an understudied area in acquired drug resistance.

Purpose of the Study:

• To investigate the role of alternative splicing in chemotherapy resistance in pediatric B-ALL.
• To identify novel AS events associated with relapse and drug resistance.
• To explore potential therapeutic strategies targeting AS-driven resistance.

Main Methods:

• RNA sequencing of paired diagnostic/relapse pediatric B-ALL samples.
• Analysis of alternative splicing patterns, including exon skipping, poison exon inclusion, and intron retention.
• Functional validation of novel splice variants in B-ALL cells in vitro and in vivo.

Main Results:

• Pervasive alternative splicing patterns were discovered in relapsed B-ALL, linked to resistance against multiple chemotherapies.
• A novel, relapse-associated alternative splicing event in NT5C2 mRNA produced an isoform (NT5C2ex6a) with elevated nucleosidase activity.
• NT5C2ex6a conferred resistance to 6-mercaptopurine, similar to known gain-of-function mutations, and induced collateral sensitivity to mizoribine.

Conclusions:

• Alternative splicing is a critical mechanism of acquired drug resistance in relapsed/refractory B-ALL.
• The NT5C2ex6a splice variant represents a novel driver of thiopurine resistance.
• Inosine monophosphate dehydrogenase inhibitors may offer a therapeutic avenue for thiopurine-resistant leukemias.