The Unfolded Protein Response As a Predictor of Chemosensitivity in Pediatric Acute Myeloid Leukemia

Background: Survival in newly diagnosed pediatric patients with acute myeloid leukemia (AML) is approximately 65% with a much lower survival in patients with relapsed disease. Leukemia cells are exposed to proteotoxic stress due to their rapid, inefficient metabolism and accumulation of reactive oxygen species. This proteotoxic stress results in the production of misfolded proteins, which leads to activation of cell stress pathways, such as the unfolded protein response (UPR). We hypothesized that UPR induction correlates with a better response to chemotherapy.

Methods: Peripheral blood samples from pediatric patients with AML were collected prior to initiation of induction chemotherapy, then at ~6 hours (h) and 24 h post initiation of chemotherapy. Peripheral blood mononuclear cells were frozen as pellets after depletion of non-tumor cells using magnetic bead selection (Miltenyi Biotech). The expression of UPR proteins was determined by chemiluminescence using an automated capillary electrophoresis system, ProteinSimple Wes^TM. The expressions of 5 UPR proteins were examined including Grp78, IRE1, total and phosphorylated (active) eIF2-α, and ATF6-α. Protein expression was normalized to actin expression and fold differences were compared between samples and within each sample at different time points.

Results: Within each group of UPR proteins, there was a wide variability in the level of baseline expression, with 6 of 38 samples expressing >4 fold increase in Grp78, compared to the median level in healthy pediatric and adult controls (Figure 1). Basal IRE1 levels were also significantly higher in pediatric controls vs. adult controls. A trend towards lower overall survival (OS) and event-free survival (EFS) was noted in patients who had a low baseline Grp78 and a low baseline IRE1 (low baseline IRE1 was defined as <2 x below the median level of healthy pediatric controls). Post chemotherapy, UPR induction (defined as >2 x above baseline level) was seen in a subset of patients, most notably for ATF6α. However, post chemotherapy UPR induction was not associated with differences in either event-free survival or overall survival.

Conclusion: UPR has a variable expression at baseline in pediatric AML patients, with a trend for lower overall survival in patients with a low basal Grp78 and IRE1 expression, suggesting chemoresistance in this subset of patients.

Figure 1

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Figure 1

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