Pharmacogenomic Association with Neurotoxicity in Hispanic Children with Acute Lymphoblastic Leukemia (ALL)

Introduction

Vincristine is vital in the treatment of acute lymphoblastic leukemia (ALL), but is dose-limited by the development of disabling neuropathies. Vincristine is metabolized extensively by polymorphically expressed CYP3A4/5, which contributes to its 10-fold inter-patient pharmacokinetic variability. Further, there is more recent evidence that an inherited polymorphism in the CEP72 rs924607 gene contributes to vincristine sensitivity. Hispanic children have among the lowest rates of ALL survival when compared to other ethnicities, and pharmacogenomic variability among races is postulated to contribute. This is the first study to examine specifically both CYP3A5 polymorphisms and CEP72 gene expression in correlation with vincristine neurotoxicity in a large cohort of Hispanic ALL patients.

Methods

Banked germline blood samples from 300 self-identified Hispanic patients with ALL treated at Texas Children's Hospital between 1990 and 2015 were interrogated for allelic discrimination of CEP72 and at the CYP3A5*3, *6, and *7 polymorphic loci using TaqMan assays. Patient medical records were electronically searched for evidence of neuropathic events. Neuropathies were categorized as motor or sensory and graded using the Modified ("Balis") Pediatric Scale of Peripheral Neuropathies. Missing administered vincristine data was imputed using the patient's known treatment protocol and date of event coupled with protocol specifics retrieved from the literature. Multivariate analysis was run modeling the influences of CYP3A5 and CEP72 genotypes on the development and time to development of greater than or equal to Grade 3 neuropathies. Descriptive statistics were used to identify the prevalence of CYP3A5 and CEP72 genotypes and the associated phenotypes in this patient population. Time to neuropathy analysis was performed using the Kaplan-Meier failure estimates and log-rank test in Stata V.12.1 (College Station, TX).

Results

Based on CYP3A5 polymorphisms, overall, we found that 5% of our patients were extensive metabolizers of vincristine, 33% were intermediate metabolizers, and 62% were poor metabolizers. Additionally, we found that the TT risk CEP72 genotype is a rare finding in our cohort (9.3%). Clinically, we found that 18.4% of our patients experienced greater than or equal to Grade 3 neurotoxicity. Assessing the influence of being both a CYP3A5 intermediate or poor metabolizer and having the TT risk CEP72 genotype was limited by the paucity of patients with both genotypes (n=25). However, CYP3A5 poor metabolizers experienced neurotoxicity more often than intermediate or extensive metabolizers, although we did not find a statistically significant correlation between phenotype and incidence of neurotoxicity. Additionally, we found that there was a statistically significant difference in time to development of neurotoxicity within the first 100 days of treatment between intermediate and poor CYP3A5 metabolizers (P=0.036), with poor metabolizers experiencing greater than or equal to Grade 3 neurotoxicity sooner (Figure 1).

Conclusions

For the first time, we show that CYP3A5 poor metabolizers experienced greater than or equal to Grade 3 neurotoxicity significantly sooner than intermediate metabolizers within the first 100 days of treatment. We found a low prevalence of the minor allele of CEP72 rs924607TT in our Hispanic cohort. However, classification of CYP3A5 metabolizers and genotypes within our Hispanic population as well as our incidence of neurotoxicity are consistent with current literature. Further testing in a larger cohort should be performed but this study reinforces the significance of CYP3A5 metabolism of vincristine in leading to significant neurotoxicity and suggests that, at least in Hispanic patients, vigilance to early development of neurotoxicity should be performed by practitioners.

Figure 1

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Figure 1

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