PRF1 and neoplasm: Similarly, NK-target cell conjugation requires calcium flux (64, 65); thus, the presence of EGTA (a potent chelating agent of divalent cations including Ca2+) abrogated the enhanced cytolysis observed for panobinostat pretreated tumor cells (Figures 4K–N) possibly by blocking the tight conjugation formation between NK and tumor cells as well as abolishing the granzymes/perforin exocytosis.