CSIG-22. PHARMACOLOGIC INHIBITION AND KNOCKDOWN OF CAMK2 IMPAIR GROWTH OF PATIENT-DERIVED GLIOBLASTOMA CULTURES

Abstract INTRODUCTION Glioblastoma (GBM), a primary brain malignancy with a median survival of 15-18 months, presents a pressing challenge in neuro-oncology. Patient-derived GBM cultures (PDGCs) exhibit spontaneous calcium (Ca2+) waves, which are thought to drive tumor growth and represent a therapeutic target. The mechanisms underlying the generation and the effectors of these Ca2+ waves remain elusive. We hypothesize CAMK2, a Ca2+/calmodulin-dependent protein kinase expressed as four distinct isoforms, is a key effector of such Ca2+ waves by phosphorylating substrates that promote tumor growth. METHODS Using multiple PDGCs, CAMK2 isoform-specific mRNA levels were assessed via qRT-PCR both at baseline and after shRNA-mediated knockdown (KD). Tumorsphere formation and WST-8 assays were performed to assess PDGC clonogenic potential after either KD or pharmacologic inhibition with the cell-permeable CAMK2 inhibitor KN93. RESULTS The relative mRNA levels of CAMK2 isoforms across three PDGC lines were, in decreasing order: CAMK2D, CAMK2G, CAMK2B, and CAMK2A. Expression of CAMK2D- and CAMK2B-specific shRNAs significantly reduced tumorsphere growth compared to control shRNA. CAMK2D KD reduced sphere formation by 55.13 ± 3.54% (p=0.0001) and 47.72 ± 9.55% (p=0.008) in separate PDGC lines, while CAMK2B KD reduced sphere formation by 41.15 ± 11.51% (p=0.021) and sphere size by 41.78% ± 10.50% (p=0.049) (n=3/experiment). KN93 treatment reduced tumorsphere formation by 59.23 ± 1.40% (p=0.0006) and 42.94 ± 13.0% (p=0.032) in two PDGC lines (n=3) and PDGC viability, while CAMK2-inactive analogue KN92 and DMSO minimally impacted viability (p<0.0001, two-way ANOVA). CONCLUSION CAMK2D and CAMK2B KD, as well as KN93 treatment, reduce tumorsphere formation, suggesting CAMK2 has a tumorigenic role in GBM. Further investigation of CAMK2 isoforms and in vivo validation are underway. Future aims include directly testing the link between spontaneous Ca2+ waves and CAMK2 activation and identifying CAMK2 phosphorylation targets that mediate tumor growth.