Date of Award

8-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Biomedical Sciences

Track

Genetics, Functional Genomics, and Proteomics

Research Advisor

Mary V. Relling, Pharm.D.

Committee

Cheng Cheng, Ph.D. Laura J. Janke, Ph.D. David R. Nelson, Ph.D. Jun Yang, Ph.D

Abstract

Acute lymphoblastic leukemia (ALL) is the most common type of childhood cancer. Asparaginase is a critical treatment component for ALL. However, its use is complicated by adverse effects, such as hypersensitivity, osteonecrosis and pancreatitis.

Hypersensitivity to asparaginase typically requires discontinuation of current formulation and substitution with other formulations, but the differential diagnosis can be challenging, and the diagnostic utility of antibody tests is unclear. We comprehensively analyzed anti-Elspar (native E.coli asparaginase) IgG antibodies in 410 pediatric patients treated on an asparaginaseintensive front-line clinical trial. Of 169 patients (41.2%) who exhibited clinical allergy, 147 (87.0%) were positive for anti-Elspar antibody. Of 241 patients without clinical allergy, 89 (36.9%) had detectable antibody. Among those positive for antibody, the antibody titers were higher in those who developed allergy than in those who did not (P < 1.0 × 10-15). Antibody measures at week 7 of continuation therapy had a sensitivity of 87%-88% and a specificity of 68%-69% for predicting or confirming clinical reactions. Antibodies were inversely associated with serum asparaginase activity (P = 7.0 × 10-6 ). Interestingly, high antibodies were associated with a lower risk of osteonecrosis (odds ratio = 0.83; 95% confidence interval, 0.78-0.89; P = 0.007), which is a dose-limiting adverse effect of glucocorticoids but has also been linked to asparaginase treatment. We conclude that antibodies were related to clinical allergy and to low systemic exposure to asparaginase, leading to lower risk of other adverse effects of therapy. Measures of serum antibodies to asparaginase can be useful in patients with ALL.

Osteonecrosis is a common dose-limiting toxicity of glucocorticoids. Data from clinical trials suggest that other medications can increase the risk of glucocorticoid-induced osteonecrosis. Here we utilized a mouse model to study the effect of asparaginase treatment on dexamethasone-induced osteonecrosis. After 6 weeks of treatment, mice receiving asparaginase along with dexamethasone had a higher rate of osteonecrosis than those receiving only dexamethasone (44% vs. 10%, P = 0.006). Primary epiphyseal arteriopathy, an initiating event for osteonecrosis, was observed in 58% of mice receiving asparaginase and dexamethasone compared to 17% of mice receiving dexamethasone only (P = 0.007). As in the clinic, greater exposure to asparaginase was associated with greater plasma exposure to dexamethasone (P = 0.0001). This model also recapitulated other clinical risk factors for osteonecrosis, including age at start of treatment, and association with the systemic exposure to dexamethasone (P = 0.027) and asparaginase (P = 0.036). We conclude that asparaginase can potentiate the osteonecrotic effect of glucocorticoids.

Acute pancreatitis is a serious complication of asparaginase with no definitive treatment. Risk factors for asparaginase-induced pancreatitis, especially the genetic predisposition, have not been clearly identified. We studied 5398 pediatric patients with ALL and showed that older age, higher exposure to asparaginase, higher Native American ancestry or African ancestry were independent clinical risk factors for pancreatitis. To determine genetic risk factors, we performed a genome-wide association study. A rare nonsense variant rs199695765 in CPA2, a pancreatic enzyme, was highly associated with pancreatitis (odds ratio = 588, 95% confidence interval 66.8- 5166, P = 9.0 ×10-9 ). A gene-level analysis showed an excess of additional CPA2 variants in those who did versus did not develop pancreatitis (P = 0.018). Furthermore, common variants in genes critical to purine metabolism and cytoskeleton function were also associated with development of pancreatitis. Our findings are consistent with a mixed genetic architecture underlying serious adverse drug effects, wherein a combination of rare but highly penetrant and common but weakly penetrant genetic risk factors contribute to genetic risk. For the patients carrying the highly penetrant variants, consideration should be given to treatment with a nonasparaginase containing ALL chemotherapy regimens.

Overall, we studied the major adverse effects of asparaginase in patients treated for ALL. These findings will provide important guidance for precision medicine.

DOI

10.21007/etd.cghs.2015.0185

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