Abstract 2991: Survival reliability of Glioblastoma on CD38
Authors: Earp Leland , Kala Srishti , Aulakh Sonikpreet 
Published: June 2022

Abstract
Glioblastoma (GBM) is a fatal malignancy of the brain. Unfortunately, the current multimodality management approach does not lead to long term survival benefits. Several prognostic factors such as Blood Brain Barrier (BBB) & Blood Tumor Barrier (BTB), Glioma Stem-like Cells (GSCs), an immunosuppressive tumor microenvironment (TME) and genetic heterogeneity promotes GBM progression. To improve treatment efficacy, these factors should be addressed in a rational manner. Our pre-clinical investigations indicate that maintenance of CD38 expression, a type II transmembrane glycoprotein, is vital to GBM survival. CD38 could be an ideal biologically relevant target as it is homogeneously expressed on tumor cells and its TME elements. Furthermore, accessibility of FDA approved anti-CD38 therapies, non-overlapping toxicities and potential to cross the BBB has granted approval of our phase I study using Radiation/Temozolomide and Immunotherapy with Daratumumab to Improve Antitumor Efficacy in newly diagnosed Glioblastoma (PRIDE) (NCT04922723). In brief, we performed Western blot (WB), RT-qPCR, and flow cytometry to examine CD38 expression on human GBM cell lines and microglia (LN229, T98G, DI-321, SA21 and HMC3) including CD38 transfected cells. We used trans well assays to analyze changes in CD38 expression in several environments. MTS viability assay was used to study the viability of Temozolomide on GBM cells. Basal expression of CD38 on GBM cells was assessed, showing that CD38 expression varies amongst cell lines and components of its TME. CD38 negative (flow sorted) cells regain CD38 expression around Day 4 after sorting, indicating that CD38 is crucial for GBM survival. We then sorted cells into CD38 negative and positive and performed trans well experiments with overexpressing and knock down cells, revealing that CD38 expression changes based upon surrounding cells in its environment. Cells transfected with shRNA against CD38 have a slower proliferative rate compared to wild-type and CD38 overexpressing cells. We also saw that LN229 Temozolomide (TMZ) resistant (LN229-TR) cells also have a slower proliferative rate and show an increase in CD38 expression. We also observed that CD133, SOX2 and Nestin are significantly over expressed in LN229-TR compared to LN229 CD38 WT, while sharing similar CD38 expression as GSCs and malignant GBM cells. IC50 of TMZ on CD38 overexpressing cells was significantly higher than CD38 WT GBM cells suggesting that CD38 expression contributes towards treatment resistance. All experiments were performed in triplicate and p values less than 0.05 were considered significant. Our preliminary data suggests that CD38 is regulating the proliferation rate as well as stem cell like features of GBM cells. Moreover, overexpression of CD38 is leading to TMZ resistance in pre-clinical models. Our ongoing in vitro and in vivo gene deletion experiments will further solidify the biological importance of CD38 in GBM.
Citation Format: Leland Earp, Srishti Kala, Sonikpreet Aulakh. Survival reliability of Glioblastoma on CD38 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2991.