The Novel Autophagy Inhitibor Elaiophylin Exerts Antitumor Activity Against Multiple Myeloma With Mutant TP53 In Part Through Endoplasmic Reticulum Stress-induced Apoptosis

Aim: This study aimed to assess the effect of elaiophylin on multiple myeloma(MM)cells,especially with TP53 mutant,and investigate the possible molecular mechanism.Methods: The cell viability,colony formation ability,proliferation and apoptosis in vitro were evaluated by Cell Counting Kit-8(CCK8),colony formation assay,Edu and AnnexinV/PI flow cytometry analysis,respectively.To confirm the blockage of autophagy flux,cells were studied by western blotting,immunofluorescence staining,and tandem mRFP-GFP-tagged LC3(tfLC3)fluorescence microscopy.The relative expression of ER stress canonical targets was determined by Western blots and qRT-PCR.To exclude the "off-target" effect,we performed a rescue experiment by adding TUDCA,a common ER stress inhibitor.Additionally,we evaluated elaiophylin sensitivity and relative safety on multiple myeloma cells in a well-established zebrafish/tumor xenograft model and further in a NOD/SCID subcutaneous xenograft model.Results: The results suggested that elaiophylin exerted anti-myeloma activity by causing apoptosis and proliferation arrest in vitro.Further study confirmed that elaiophylin expectedly blocked the autophagy flux at the late stage.Intriguingly,elaiophylin-induced apoptosis related to sequential and persistent activation of endoplasmic reticulum(ER)stress pathway,at least in PERK/ATF4/CHOP and XBP1 s branches,as evidenced by the effect of the common ER stress inhibitor tauroursodeoxycholic acid(TUDCA)to ameliorate the cell death to some extent.Our further findings thus provided evidence that elaiophylin is of paramount efficacy and safety both in zebrafish and NOD/SCID mouse MM xenograft models.Conclusion: Taken together,our data demonstrated,for the first time,that elaiophylin exposure to human multiple myeloma cells with TP53 mutant resulted in blockage of autophagy flux and thus induced cell death partly involved in ER stress-associated apoptosis.Targeting disruption of the cellular protein handling system by elaiophylin is therefore considered as a promising therapeutic strategy to overcome incurable multiple myeloma even with TP53 mutations.