Abstract. Osteosarcoma, which is the most common primary bone tumor, occurs most frequently in adolescents. A number of studies have indicated that plumbagin (PL) (5-hydroxy-2-methyl-1, 4-naphthoquinone), a compound found in the plants of the Plumbaginaceae and Droseraceae families, possesses anticancer activity. However, its anticancer effects and mechanisms against osteosarcoma have not been explored. To determine the anticancer effect of PL on osteosarcoma cell lines MG-63 and U2OS, cell viability, apoptosis, cell cycle distribution, caspase-3 and caspase-9 activity and intracellular reactive oxygen species (ROS) generation were measured, and Western blot analyses were performed. PL significantly inhibited the growth of osteosarcoma cells, particularly U2OS cells. PL up-regulated the expression of p53 in U2OS cells and p21 in the two osteosarcoma cell lines causing cell cycle arrest by decreasing the expression of murine double minute 2 (MDM2)/ cyclin B1 and cyclin D1. Furthermore, PL altered the ratio of Bax/Bcl-2, and may have triggered the mitochondrial apoptotic pathway, resulting in caspase-3 and caspase-9 activation. We also found that PL induced the generation of ROS in osteosarcoma cell lines. To conclude, PL exerted anticancer activity on osteosarcoma cells by inducing pro-apoptotic signaling and modulating the intracellular ROS that causes induction of apoptosis. These effects may relate to the p53 status.

Purpose: To investigate the antitumor activity of a mitochondrial-localized HSP90 inhibitor, Gamitrinib, in multiple glioma models, and to elucidate the antitumor mechanisms of Gamitrinib in gliomas. Experimental Design: A broad panel of primary and temozolomide (TMZ)-resistant human glioma cell lines were screened by cell viability assays, flow cytometry, and crystal violet assays to investigate the therapeutic efficacy of Gamitrinib. Seahorse assays were used to measure the mitochondrial respiration of glioma cells. Integrated analyses of RNA sequencing (RNAseq) and reverse phase protein array (RPPA) data were performed to reveal the potential antitumor mechanisms of Gamitrinib. Neurospheres, patient-derived organoids (PDO), cell line–derived xenografts (CDX), and patient-derived xenografts (PDX) models were generated to further evaluate the therapeutic efficacy of Gamitrinib. Results: Gamitrinib inhibited cell proliferation and induced cell apoptosis and death in 17 primary glioma cell lines, 6 TMZ-resistant glioma cell lines, 4 neurospheres, and 3 PDOs. Importantly, Gamitrinib significantly delayed the tumor growth and improved survival of mice in both CDX and PDX models in which tumors were either subcutaneously or intracranially implanted. Integrated computational analyses of RNAseq and RPPA data revealed that Gamitrinib exhibited its antitumor activity via (i) suppressing mitochondrial biogenesis, OXPHOS, and cell-cycle progression and (ii) activating the energy-sensing AMP-activated kinase, DNA damage, and stress response. Conclusions: These preclinical findings established the therapeutic role of Gamitrinib in gliomas and revealed the inhibition of mitochondrial biogenesis and tumor bioenergetics as the primary antitumor mechanisms in gliomas.