THU495 Glutamate Metabolic Enzymes GLUD1/2 And GPX4 Are Associated with Tumor Size In Black Women With Invasive Lobular Breast Cancer
Authors: Young Todd , Abalum Theresa C , Hodgins Nicole , Persaud Sonali , Fernandez Aileen I , Olukoya Ayodeji Olajuwon , Rozeboom Aaron Mark , Riggins Rebecca Baab 
Published: October 2023

Abstract
Disclosure: T. Young: None. T.C. Abalum: None. N. Hodgins: None. S. Persaud: None. A.I. Fernandez: None. A.O. Olukoya: None. A.M. Rozeboom: None. R.B. Riggins: None.
Background and Objective: Invasive Lobular Breast Cancer (ILC) is a special histologic type of breast cancer with unique genetic and biological features. ILC may be less dependent on glucose metabolism than the more common histologic type, invasive ductal breast cancer (IDC), instead relying more on lipid and amino acid metabolism. Our lab has previously published that expression of metabotropic glutamate receptors is increased in more rapidly growing and therapy-resistant cell line models of ILC. We hypothesized that increased expression of glutamate transporters and regulatory enzymes is associated with poor prognostic features. Methods and Analysis: We used multispectral immunohistochemical staining to measure the expression of four functionally related proteins: CD98, GLUD1/2, GPX4, and SLC7A11 in a cohort of 72 women with ILC (23.5% Black, 64.7% White, 11.8% Other). The cohort was in a two-fold redundant tissue microarray (TMA) format comprised of primary tumors collected by the Georgetown University Histopathology and Tissue Shared Resource. SLC7A11 and CD98 form a heterodimer that exports glutamate from, and imports cystine to, the cell. GLUD1/2 are two isoenzymes that convert glutamate into α-ketoglutarate to replenish the TCA cycle, or recycle ammonia to support amino acid synthesis. GPX4 is an enzyme that protects cells from lipid peroxidation-induced death. We compared expression of these proteins with clinical, pathological, and demographic variables (overall survival, hormone receptor expression, tumor size, race, age) using t test/ANOVA, Kaplan-Meier survival analysis, and linear regression. Results: In the 68 evaluable cases, the percentage of ILC tumor cells stained positive for GLUD1/2 and GPX4 was significantly higher than for CD98 or SLC7A11 (P&lt;0.001), so further analyses focused on these. Women with a combination of high (above median) GLUD1/2+ (&gt;49%) and GPX4+ (&gt;54%) expression had a trend toward decreased survival (Hazard Ratio, HR 3.53, P=0.159). GPX4, GLUD1/2, and estrogen receptor (ER) expression were associated with tumor size in the entire cohort (R2 = 0.124, P = 0.041), but this relationship was markedly stronger in Black women (R2 = 0.487, P = 0.040). In univariate analyses, GLUD1/2 (R2 = 0.43, P&lt;0.01) and GPX4 (R2 = 0.27, P&lt;0.05) expression were each associated with tumor size in Black women, but not in the entire cohort. GPX4 expression and tumor size were both significantly higher (P&lt;0.05) in Black women over 60 years of age, compared to those under 60. Conclusion: GLUD1/2 and GPX4 expression may be prognostic in ILC, as our results show that tumor size increases with higher expression of these proteins (especially among Black women). Limitations of this study include small sample size and lack of an independent cohort for validation. Future studies will include analysis of these proteins in a TMA comprised of tissue from women with IDC.
Presentation: Thursday, June 15, 2023