NT5C2 (5'-Nucleotidase Cytosolic II)

Protein-protein interaction networks indicate that these variations are involved in nucleotide metabolism and pharmacological responses, confirming their role in thiopurine resistance. In summary, NT5C2 and PRPS1 gene variations may act as potential biomarkers for resistance and hence require more experimental validation of VUS to determine their significance.

For ribavirin, adenosine kinase (ADK) and adenylsuccinate synthase (ADSS) were critical for nucleotide metabolism and bioactivation. Remdesivir uptake and activation depended on the transporter SLC29A3 and phosphoamidase HINT1, whereas favipiravir resistance was linked to NT5C2-mediated dephosphorylation. Viral replication assays in Huh7 cells validated that knockout of SLC29A3, HINT1, or NT5C2 significantly altered antiviral efficacy. This study delineates the genetic network governing nucleotide analog response, providing mechanistic insights and potential biomarkers for personalized antiviral therapy.

Recently, our laboratory reported the dephosphorylation action of these nucleotidases toward the metabolites of clinically used nucleoside analog drugs, including gemcitabine, emtricitabine, tenofovir, and acyclovir. Using in vitro incubations and enzyme kinetics, we demonstrate the involvement of NT5C3 in the dephosphorylation of an important antineoplastic agent, fludarabine. Furthermore, we employed mass spectrometry imaging to visualize peptides corresponding to NT5C3 and other major nucleotidases in the kidney cortex and colonic mucosa.

Here, we have demonstrated the importance of using RNA-seq to facilitate the differential diagnosis of B-ALL with successful detection of gene fusions and mutations. This will aid both patient risk stratification and precision medicine.

Tracking the NT5C2 variant by digital PCR confirm the expansion of the NT5C2 clone at maintenance treatment. Overall, our exploratory analysis suggests a role for these genetic events, most of which have already been described in pediatric cases, driving resistance associated to specific chemotherapeutic agents, contributing to the relapse of a high proportion of adult T-ALL patients (60%).

TP53 and CREBBP mutations, even as subclonal aberrations, were associated with shorter 3-year event-free survival among all patients with B-ALL (TP53 mutant vs wild-type: p=0.008, CREBBP mutant vs wild-type: p=0.010); and notably, B-ALL patients showing no measurable residual disease on day 33 could be further stratified based on TP53 mutational status (p<0.001). Our in-depth molecular characterization performed across all risk groups identified novel opportunities for molecularly targeted therapy in 55.9% of high-risk and in 31.6% of standard/intermediate-risk patients.

A total of seven major clones of NRAS [five] and NT5C2 [two] were noted in six out of 14 (43%) relapse patients, accounting for 44% of early relapses. In addition, 10 minor clones (PMS2 [two], NRAS [four], NT5C2 [three], and TP53 [one]) were noted in five out of 14 (36%) patients. In the 56 sequential therapy samples, six major clones were noted (NRAS [five], KRAS [one]) in four out of 14 (28.5%) patients, with two increasing in size in maintenance samples, leading to subsequent relapse in both cases. In addition, therapy-acquired minor clones in NT5C2 [four] and PMS2 [one] were seen to emerge in maintenance samples in four out of 14 (28.5%) patients, with concordant detection of such major and minor clones in unpaired relapse samples, indicating the need for their active surveillance during therapy. Overall, digital PCR validated NRAS and NT5C2 major clones in one-third (10 out of 27; 37%) of cases, driving nearly half of early relapses.

Among the polymorphisms examined, 14 across 13 genes showed significant associations with MTX-PG2-5 levels, even after adjusting for the false discovery rate (ABCC5, ATG16L1, CEP72, FSTL5, GMPS, HTR3A, IMPDH1, NT5C2, SLC28A3, SLCO1B3, SUCLA2, TPMT, and TYMS). This study enhances our understanding of genetic polymorphisms in MTX metabolism and therapeutic monitoring for MTX maintenance, promoting personalized medicine in acute lymphoblastic leukemia patients.

Incorporation of the 8-amino acid sequence SQVAVQKR into this enzyme created a putative phosphorylation site and resulted in elevated nucleosidase activity, which is a known consequence of gain-of-function mutations in NT5C2 and a common determinant of 6-mercaptopurine (6-MP) resistance. Furthermore, both the NT5C2ex6a and R238W variants induced collateral sensitivity to the inosine monophosphate dehydrogenase (IMPDH) inhibitor mizoribine. These results ascribe an important role for splicing perturbations in chemotherapy resistance in relapsed B-ALL and suggest that IMPDH inhibitors, including the commonly used immunosuppressive agent mycophenolate mofetil, could be a valuable therapeutic option for treating thiopurine-resistant leukemias.

Incorporation of the 8-amino acid sequence SQVAVQKR into this enzyme created a putative phosphorylation site and resulted in elevated nucleosidase activity, which is a known consequence of gain-of-function mutations in NT5C2 and a common determinant of 6-mercaptopurine (6-MP) resistance. Furthermore, both the NT5C2ex6a and R238W variants induced collateral sensitivity to the inosine monophosphate dehydrogenase (IMPDH) inhibitor mizoribine. These results ascribe an important role for splicing perturbations in chemotherapy resistance in relapsed B-ALL and suggest that IMPDH inhibitors, including the commonly used immunosuppressive agent mycophenolate mofetil, could be a valuable therapeutic option for treating thiopurine-resistant leukemias.

This systematic review strongly supports the further investigation of DNA-TG as a marker for monitoring thiopurine therapy. Its correlation with treatment outcomes, such as relapse-free survival in ALL and the risk of leukopenia in IBD, underscores its role in enhancing personalized treatment approaches. DNA-TG effectively identifies NUDT15 variants and predicts late leukopenia in patients with IBD, regardless of their NUDT15 variant status. The recommended threshold for late leukopenia prediction in patients with IBD with DNA-TG is suggested to be between 320 and 340 fmol/µg DNA. More clinical research on DNA-TG implementation is mandatory to improve patient care and to improve inclusivity in thiopurine treatment.

By contrast, early relapse ALL was characterized by a single diagnostic clone seeding relapse by a clonal sweep along with acquired mutations in chemoresistance-associated genes. To validate and extend these findings, we are currently analyzing 11 additional infant relapse samples with WGS.