THE DEVELOPMENT OF A MOUSE MODEL TO DETERMINE THE RELATION BETWEEN ASPARAGINASE-INDUCED PANCREATITIS AND GENETIC RISK FACTORS

Abstract

Acute lymphoblastic leukemia is the most common childhood cancer. Treatment protocols include the essential biologic drug asparaginase, which has helped to dramatically improve survival rates. Unfortunately, asparaginase causes several adverse drug reactions (ADRs) including pancreatitis, which afflicts up to 18% of children. Pancreatitis can be life- threatening and severe cases can result in the retraction of crucial asparaginase treatment, which can lead to a greater risk of cancer relapse. The reason why asparaginase-induced pancreatitis (AIP) develops remains unclear, but it needs to be understood to optimize the therapeutic management of individuals at a higher risk for pancreatitis development. This thesis work was conducted in the ongoing effort to understand AIP pathogenesis. Preliminary clinical data suggested that AIP risk and/or development may be related to genetic variants of PITX2 and RAR . The main objective was to establish an AIP mouse model to investigate the functional roles of PITX2 and RAR in AIP development. In the first experiment, three mice strains, BALB/cByJ, A/J, and C57BL/6J, were intraperitoneally injected with either control PBS or 1.5 IU/g of pegylated asparaginase (peg-asp) and dissected on Day 5 post- injection for evaluation of pancreatitis development. Histological evidence suggestive of pancreatitis including mild edema, inflammatory infiltrate, fat necrosis, and islet hyperplasia were observed in pancreatic samples of some but not all peg-asp-treated mice. This suggests that some mice may have reached the AIP disease threshold but were in a state of recovery when samples were analysed. A/J mice had the most severe reaction to peg-asp via excessive weight loss and hepatotoxicity, another ADR category of asparaginase that is often linked to pancreatitis. Thus, A/J mice were chosen for a second experiment in which additional doses (0.750 or 0.375 IU/g peg-asp) and endpoints (Day 3 or 5) were evaluated. Histological signs of AIP were absent when mice were treated with the lower peg-asp doses, while some of their livers demonstrated mild toxicity. Peg-asp-treated mice serum amylase and lipase activity levels remained statistically the same as controls. No changes were observed in PITX2 and RAR mRNA expression. Although an AIP mouse model was not successfully developed, novel insights were made that will propel the next wave of research. For the first time it was shown that different strains of mice, BALB/cByJ, A/J, and C57BL/6J, react differently to asparaginase via different degrees of weight loss and hepatotoxicity. This further solidified the idea that genetic differences are likely at play in producing variable asparaginase-induced ADRs. The role of PITX2 and RAR in AIP development requires further investigation as it was not explored at the protein level and may be influenced by other factors not identified in this study. To further optimize the AIP mouse model, earlier endpoints and multiple asparaginase injections, intramuscular or intravenous administration routes, and diet interventions such as vitamin A supplementation or depletion will be explored.