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The root of Croton crassifolius has been used as a traditional Chinese medicine (TCM), called Radix Croton Crassifolius, and commonly known as "Ji Gu Xiang" in Chinese. Its medicinal value has been recorded in several medical books or handbooks, such as "Sheng Cao Yao Xing Bei Yao", "Ben Cao Qiu Yuan" and "Zhong Hua Ben Cao". It has been traditional employed for treating sore throat, stomach-ache, rheumatism and cancer. At present, there are limited studies on the evaluation of low-polarity extracts of roots in C. crassifolius. Consequently, the aim of this study was to evaluate the antitumor effect of the low-polarity extract of C. crassifolius root. Extracts were obtained by supercritical fluid extraction. The extracts were tested for antitumor effects in vitro on several cancer cell lines. A CCK-8 kit was used for further analysis of cell viability. A flow cytometer and propidium iodide staining were used to evaluate the cell cycle and apoptosis. Hoechst staining, JC-1 staining and the fluorescence probe DCFH-DA were used to evaluate apoptotic cells. Molecular mechanisms of action were analyzed by quantitative RT‒PCR and Western blotting. Immunohistochemistry was used for the evaluation of xenograft tumors in male BALB/c mice. Finally, molecular docking was employed to predict the bond between the desired bioactive compound and molecular targets. Eleven diterpenoids were isolated from low-polarity C. crassifolius root extracts. Among the compounds, chettaphanin II showed the strongest activity (IC 50 = 8.58 μM) against A549 cells. Evaluation of cell viability and the cell cycle showed that Chettaphanin II reduced A549 cell proliferation and induced G2/M-phase arrest. Chttaphanin II significantly induced apoptosis in A549 cells, which was related to the level of apoptosis-related proteins. The growth of tumor tissue was significantly inhibited by chettaphanin II in experiments performed on naked mice. The antitumor mechanism of chettaphanin II is that it can obstruct the mTOR/PI3K/Akt signaling pathway in A549 cells. Molecular docking established that chettaphanin II could bind to the active sites of Bcl-2 and Bax. Taken together, the natural diterpenoid chettaphanin II was identified as the major antitumor active component, and its potential for developing anticancer therapies was demonstrated for the first time by antiproliferation evaluation in vitro and in vivo. [Display omitted] • Eleven diterpenoids were obtained from the SFE extract of C. crassifolius roots. • Chettaphanin II showed the strongest antitumor activity against A549 cells. • Chettaphanin II inhibited A549 cell proliferation and arrested cells in G2/M-phase. • Chettaphanin II induced A549 cell apoptosis by inhibiting PI3K/AKT/mTOR pathway. • Chettaphanin II significantly inhibited the growth of tumor tissue in nude mice. [ABSTRACT FROM AUTHOR]

• A new anthrahydrazone ligand (9-THA) and its three metal complexes were synthesized. • The tested cancer cell lines were most sensitive to the Cu(II) complex, 9-THA-Cu. • 9-THA-Cu could bind with DNA in an intercalative mode by its planar structure. • The Cu(II) center play a key role to exert anticancer activity and induce apoptosis. In the present study, we synthesized and extensively characterized a novel ligand, 9-THA, based on 9-benzothiazolanthrahydrazone, along with its three corresponding transition metal complexes: 9-THA-Co (1), 9-THA-Ni (2), and 9-THA-Cu (3). The crystallographic analysis revealed distinct coordination geometries - six-coordinate for 9-THA-Co and 9-THA-Ni, binding three and two 9-THA ligands, respectively, and four-coordinate for 9-THA-Cu, binding one 9-THA ligand. In vitro anticancer screening demonstrated that 9-THA-Cu exhibited significant growth inhibition in HeLa-229, NCI-H460, and SK-OV-3 cancer cells with IC 50 values of 12.10 ± 0.54, 12.12 ± 0.58, and 17.65 ± 0.66 μM, respectively. Moreover, it displayed comparable cytotoxicity to cisplatin on HL-7702 normal liver cells. In contrast, 9-THA and 9-THA-Co/9-THA-Ni did not exhibit significant growth inhibition in the tested cancer cells, suggesting that Cu(II) played a pivotal role in its anticancer mechanism. Further investigation revealed the intercalative DNA binding mode of 9-THA-Cu by UV–Vis and fluorescent spectral analyses. It also exhibited competitive binding with two typical DNA intercalators, Gel-red (GR) and ethidium bromide (EB). Cell cycle and cell apoptosis experiments indicated that 9-THA-Cu at a concentration of 22 μM could induce cell cycle arrest in the S phase in 40 % of HeLa-229 cancer cells. Simultaneously, it induced 33.2 % apoptosis in HeLa-229 cells, suggesting that 9-THA-Cu may employ multiple mechanisms to exert its anticancer effects. [Display omitted] [ABSTRACT FROM AUTHOR]