Asparaginase Levels Fall Short in Indian Children With High-Risk Leukemia, Pilot Study Finds

Acute lymphoblastic leukemia is the most common childhood malignancy in India, and it is also one of the most curable cancers anywhere in the world — provided the drugs actually work the way they are supposed to. A new pilot study from New Delhi suggests that for some of India’s sickest young leukemia patients, a cornerstone chemotherapy drug may be falling silently short of its therapeutic target, raising questions about whether standard dosing protocols deliver adequate drug exposure in resource-limited settings.

The research, published in Frontiers in Hematology, represents the first systematic assessment of serum asparaginase activity during induction therapy in Indian children with high-risk B-cell acute lymphoblastic leukemia. Asparaginase is an enzyme that depletes circulating asparagine by catalyzing its hydrolysis to aspartic acid and ammonia. Unlike normal cells, leukemic lymphoblasts have limited capacity to synthesize asparagine de novo because they express little or no asparagine synthetase, the enzyme needed for autonomous asparagine production. This metabolic dependency makes them vulnerable to asparaginase-induced cell death, which is why the drug remains a critical component of virtually every modern ALL treatment protocol worldwide.

But asparaginase has a narrow therapeutic window with substantial interpatient pharmacokinetic variability. When enzyme activity is excessively high, the overproduction of aspartic acid and ammonia can exacerbate systemic toxicity. When activity is insufficient, asparagine is not adequately depleted, allowing leukemic cells to survive and proliferate. The drug’s half-life of approximately 1.2 days for native Escherichia coli preparations necessitates repeated dosing every few days to maintain therapeutic enzyme activity, and even then, individual patients metabolize and clear the enzyme at markedly different rates.

The study, conducted at Vardhman Mahavir Medical College and Safdarjung Hospital, enrolled thirty treatment-naive children aged one to twelve years with newly diagnosed B-cell ALL between March and July 2024. Nine patients were classified as high risk according to the modified ICiCLe protocol and selected for therapeutic drug monitoring. During induction, three died from sepsis and one was transferred, leaving five patients for final pharmacokinetic analysis. These five completed induction therapy with native E. coli L-asparaginase, contributing a total of forty-two serial samples, approximately eight per patient.

Researchers measured serum asparaginase activity using a spectrophotometric assay at pre-dose trough and twenty-four-hour post-dose peak time points. The results were striking. All five evaluable patients had subtherapeutic trough asparaginase activity below 0.5 IU/mL, the institutional target. Trough levels ranged from 0.43 to 0.47 IU/mL with a median of 0.44 IU/mL. Peak levels showed marked interpatient variability, ranging from 0.52 to 1.97 IU/mL with a median of 1.15 IU/mL, and peaks occurred at widely different time points from day one to day twenty-one after treatment initiation.

Higher enzyme activity correlated with biochemical toxicities across the cohort. Hepatotoxicity was evident in all five patients, with elevated lactate dehydrogenase levels in 100 percent and increased AST and ALT in 80 percent. Blood urea nitrogen was elevated in four of five patients, likely reflecting increased urea production from corticosteroid-induced catabolism, chemotherapy-related protein turnover, and ammonia generation from asparaginase rather than renal dysfunction, as serum creatinine and estimated glomerular filtration rate remained normal. Hypertriglyceridemia was universal, and subclinical pancreatitis — elevated amylase and lipase without symptoms — was observed in half of the patients.

The most insidious concern raised by the uniformly low trough levels is the phenomenon of silent inactivation. This occurs when anti-asparaginase antibodies develop and neutralize enzyme activity without producing observable allergic symptoms such as urticaria or anaphylaxis. Patients appear clinically asymptomatic despite loss of therapeutic drug effect, leading to inadequate asparagine depletion and subtherapeutic exposure. Silent inactivation has been reported in 4.5 to 7 percent of patients and is associated with higher relapse rates when undetected. Unlike overt hypersensitivity reactions, it can only be identified through laboratory measurement of serum asparaginase activity, making routine therapeutic drug monitoring essential for treatment efficacy.

International expert consensus now recommends routine measurement of serum asparaginase activity to identify both clinical hypersensitivity and silent inactivation, with timely switching to alternative preparations when therapeutic activity is compromised. In the United States and Europe, the Children’s Oncology Group and the European Organization for Research and Treatment of Cancer include specific protocols for asparaginase activity monitoring. However, in resource-limited settings including India, routine therapeutic drug monitoring is rarely implemented due to limited laboratory infrastructure, assay availability, and cost constraints. The absence of monitoring may contribute to suboptimal outcomes, as undetected silent inactivation can result in inadvertent omission of effective asparaginase exposure during critical phases of therapy.

The survival disparity between India and high-income countries is multifactorial, involving differences in disease biology, treatment protocols, supportive care, drug availability, and chemotherapeutic regimen. Pediatric ALL survival in India stands at 60 to 70 percent, significantly lower than the 85 to 90 percent observed in high-income countries. The annual incidence of ALL in India is estimated at 1.5 per 100,000 children. Whether the therapeutic range of asparaginase in serum as decided by published studies in the West is actually applicable for Indian patients remains an open question, given geographic, environmental, nutritional, and other diverse cohort factors that may affect pharmacokinetics and overall chemotherapy outcome.

The authors emphasize that their findings should be interpreted in an exploratory and hypothesis-generating manner. The small sample size of five patients, the single-center design, and the attrition from early mortality all limit generalizability. Survivor bias is a key limitation, as only patients who completed induction were included in the pharmacokinetic analysis, potentially skewing findings toward clinically stable individuals. The research-use-only assay introduces potential background signal interference from endogenous metabolites such as aspartate, oxaloacetate, and pyruvate. Additionally, target activity thresholds remain a subject of international debate, with different protocols using values ranging from 0.05 to 0.5 IU/mL. Despite these constraints, the study demonstrates the feasibility of conducting pharmacokinetic and toxicity-related investigations in an Indian pediatric population, paving the way for larger, multicentric investigations aimed at optimizing asparaginase-based therapy and improving treatment safety in resource-limited settings.

Subject of Research: Therapeutic drug monitoring of asparaginase in Indian pediatric ALL

Article Title: A pilot study on therapeutic drug monitoring of asparaginase in Indian children with high-risk ALL: evidence for suboptimal exposure

Article References: Dhanda, H., Zaman, S., Rishi, B., Kamal, R., Kaur, M., Anand, N., Noor, B., Tanwar, P., Zaheer, S., Prabhakar, P., Siraj, F., Singh, A., & Misra, A. (2026). A pilot study on therapeutic drug monitoring of asparaginase in Indian children with high-risk ALL: evidence for suboptimal exposure. Frontiers in Hematology, 5, Article 1779396. https://doi.org/10.3389/frhem.2026.1779396

Image Credits: AI Generated

DOI: 10.3389/frhem.2026.1779396

Keywords: asparaginase, acute lymphoblastic leukemia, therapeutic drug monitoring, pediatric oncology, silent inactivation, pharmacokinetics, India, drug exposure, pilot, therapeutic, drug, monitoring