Role of Obesity in Regulation of Cell Surface GRP78 (C4289)

Letter of Intent for New FY 23/24 PCRTF Funding ABSTRACT Acute myeloid leukemia (AML) accounts for 15-20 percent of childhood leukemia. Although improved treatment options have increased the overall survival for AML, approximately 30% of the cases tend to relapse. The management of AML patients is an ongoing challenge due to the relapse rates and treatment related mortality. Clinical outcome is linked to the degree of genetic heterogeneity of AML and higher body mass index (BMI) at diagnosis; these underlying factors are associated with poor survival for AML. It is important to note that Kentucky has one of the highest prevalence of childhood obesity, ranking 3rd in the nation. Recent studies have suggested that cell surface GRP78 (csGRP78) is elevated in AML. The ER (endoplasmic reticulum)-stres s response protein GRP78 promotes cell survival and csGRP78 is associated with increased malignant behavior and resistance to chemotherapy and radiotherapy. csGRP78 is also a targetable receptor on AML cells, and is not expressed on most normal cells. Consistently, CAR-T cells directed against csGRP78 in AML in mouse models induce remarkable inhibition of the tumor cells but do not affect normal tissues. Interestingly, the adipocyte-derived cytokine leptin, which is usually elevated in obese individuals, induces GRP78 levels in cancer cells. However, the precise relationship between obesity, csGRP78, and treatment response in AML patients has not been elucidated. We propose to address this question by studying the effect of obesity on AML growth and treatment response in obese mouse models, so as to extend the findings to pediatric AML. We hypothes ize that although obesity may impede conventional treatment of AML, targeting csGRP78 elevated in AML especially in obese mice, will overcome treatment resistance and prevent relapse. We will use fluorescent activated cell sorting (FACS) analysis to quantify cells expressing csGRP78 and CD33, a reliable leukemic cell marker, on AML cells and determine whether the ratio of csGRP78+ cells to CD33+ cells is elevated by obesity associated factors. We realize that CD33 is expressed on 85-90% of AML cells, but may also be expressed on monocytes and granulocytes. However, leukemic mice will have depleted monocytes and granulocytes percentage-wis e, and the co-expression of csGRP78 with CD33 will be specific for the leukemic cells. As csGRP78+/CD33+ cells are expected to represent AML in mice injected AML cells, we will use an antagonistic csGRP78 antibody or the pro-apoptotic protein Par-4 that binds to its receptor csGRP78 to signal apoptosis and growth inhibition of AML. These studies will be performed in immunodeficient NOD Scid gamma (NSG) mice injected with human AML cells and fed either normal chow diet or high fat diet to induce obesity, or in immunocompetent mice that are obesity-prone (i.e., ob/ob or db/db mice) injected with mouse AML cells in order to interrogate the effect of obesity and leptin on AML growth, csGRP78 expression and response to csGRP78-targeted treatment. The findings will have translational relevance in treating obese children with AML by targeting csGRP78.