DNA-incorporated thioguanine to detect potential non-adherence to maintenance therapy in acute lymphoblastic leukemia

Adherence to 6-mercaptopurine (6-MP)/methotrexate maintenance treatment for acute lymphoblastic leukemia (ALL) is pivotal to preventing relapse, and the 6-MP metabolite DNA-incorporated thioguanine (DNA-TG) is associated with relapse risk. In the ALLTogether-1 (A2G1) Maintenance sub-study (EU CT nr 2022-501050-11-01), DNA-TG, thioguanine nucleotides (TGN), and methylated mercaptopurine metabolites (MeMP) are analyzed regularly. Upon levels below preset limits (TGN < 50, or MeMP < 200 or < 100 nmol/mmol hemoglobin for thiopurine S-methyltransferase (TPMT) wild type and heterozygous patients, respectively), the treating physician is informed of potential non-adherence. We investigated the feasibility of using DNA-TG as the primary flagging of potential non-adherence.

We analyzed 6-MP metabolites in 3,074 blood samples from 368 children enrolled in the A2G1 Maintenance sub-study.

In 6% of samples, TGN (median 212, 95% range 40–642), MeMP (median 4,959, 95% range 135–23,880) or both were below the flagging potential non-adherence limits. DNA-TG was associated with TGN (estimate = 1.72, p < 0.0001), MeMP (estimate = 1.10, p < 0.0001), and prescribed 6-MP dose (estimate = 1.083 and 1.132, p < 0.0001, for TPMT wild type and heterozygous patients) in linear effects models, and the predicted probability of treatment interruption in logistic regression models. DNA-TG was below 200 fmol TG/µg DNA (13th percentile of all measurements, median 569, 95% range 73–1,823) in all samples with both TGN and MeMP below the flagging potential non-adherence limits.

DNA-TG can provide a cost-effective guidance on when to measure TGN and MeMP to determine whether non-adherence should be suspected, which is an additional benefit to monitoring DNA-TG during maintenance therapy.