Synthesis and X-ray structure analysis of cytotoxic heptacoordinated Salan hafnium(IV) complexes stabilized with 2,6-dipicolinic acid

Anti-tumor and cellular mechanisms of HfIVtetra-(8-hydroxyquinolinato) complexes

Three 8-hydroxyquinoline-stabilized hafnium complexes, [HfIV(oxinate)4], were synthesized with good aqueous stability and solubility by reacting HfIVCl4 with 8-hydroxyquinoline (HL1), 2-methyl-8-hydroxyquinoline (HL2) and 5-chloro-8-hydroxyquinoline (HL3) in THF, achieving high yields. Among the synthesized complexes, [HfIV(L1)4] and [HfIV(L3)4] exhibited potent inhibitory activity against human liver (Hep G2), cervical (HeLa S3) and lung (PC9) cancer cell lines, while showing low toxicity against non-tumorigenic murine epithelial AML12 cells. Notably, [HfIV(L1)4] demonstrated the most potent activity, with an IC50 value of 0.8 ± 0.3 μM against Hep G2 cells, which is 17 times lower than that of cisplatin (IC50 = 13.8 ± 1.3 μM). Mechanistic cell studies revealed that [HfIV(L1)4] could effectively inhibit cell migration, induce reactive oxygen species generation and cause mitochondrial membrane potential disruption. Furthermore, [HfIV(L1)4] blocked the cell cycle progression at the G2/M phase and led almost exclusively to early apoptosis in Hep G2 cells. Western blot analysis revealed that in Hep G2 cells [HfIV(L1)4] could upregulate the expression of caspase-3 and Bax proteins while downregulating the expression of the anti-apoptotic Bcl-2 protein, highlighting the apoptotic pathway as a key mechanism of action. Comparisons are made with previously reported [ZrIV(L1)4], which shows higher cytotoxicity, cellular uptake, reactive oxygen species generation, mitochondrial damage and stronger inhibition of antioxidant enzymes' activity. However, [HfIV(L1)4] induces primarily early apoptosis, which is advantageous. Overall, these rare earth complexes, particularly [HfIV(L1)4] and [ZrIV(L1)4], demonstrate promising potential as novel anticancer agents with significant efficacy against human liver cancer cells and favourable selectivity profiles for further therapeutic development.

Synthesis and X-ray structure analysis of cytotoxic 2-picolylamino-type HfIV-bis-chelated complexes

Eight novel heteroleptic HfIV complexes containing differently substituted 2-picolylamino-bis-phenolate and 2,6-dipicolinic acid (Dipic) groups as chelating ligands were synthesized and characterized with yields higher than 80%. These [ONON] type HfIV complexes have good aqueous stability and potent anti-tumor activity against HeLa S3 (human cervical adenocarcinoma) and Hep G2 (human derived hepatoma) cells. In particular, the complexes demonstrated selective inhibitory activity against Hep G2 cells. The IC50 value of the most cytotoxic complex [L1HfIVDipic4-Cl] (0.9 ± 0.4 μM) was ten-fold higher than that of cisplatin (11.2 ± 2.1 μM) on Hep G2 cells, being the most cytotoxic anti-tumor HfIV complex to date. Furthermore, [L1HfIVDipic4-Cl] could inhibit tumor cell migration, induce reactive oxygen species generation (particularly HO˙), loss of mitochondrial membrane potential and almost exclusive early apoptosis in HeLa S3 cells. [L1HfIVDipic4-Cl] exhibited rapid cellular uptake by HeLa S3 cells, and when in aqueous media, these HfIV complexes slowly hydrolyzed, releasing non-toxic phenolato ligands as the product of hydrolysis. Overall, these rare earth complexes, particularly [L1HfIVDipic4-Cl], show promising potential as novel anticancer agents with significant efficacy against human liver cancer cells and favorable selectivity profiles for further therapeutic development.

Synthesis, in vitro antitumor evaluation and structure activity relationship of heptacoordinated amino-bis(Phenolato) Ti(IV) complexes stabilized by 2,6-dipicolinic acid

Eighteen novel Ti(IV) complexes stabilized by different chelating amino-bis(phenolato) (ONNO, ONON, ONOO) ligands and 2,6-dipicolinic acid as a second chelator were synthesized with isolated yields ranging from 79 to 93%. Complexes were characterized by 1H and 13C-NMR spectroscopy, as well as by HRMS and X-Ray diffraction analysis. The good to excellent aqueous stability of these Ti(IV) complexes can be modulated by the substitutions on the 2-position of the phenolato ligands. Most of the synthesized Ti(IV) complexes demonstrated potent inhibitory activity against Hela S3 and Hep G2 tumor cells. Among them, the naphthalenyl based Salan type 2j, 2-picolylamine based [ONON] type 2n and N-(2-hydroxyethyl) based [ONOO] type 2p demonstrated up to 40 folds enhanced cytotoxicity compared to cisplatin together with a significantly reduced activity against healthy AML12 cells. The three Ti(IV) complexes exhibited fast cellular uptake by Hela S3 cells and induced almost exclusively apoptosis. 2j could trigger higher level of ROS generation than 2p and 2n.

Anticancer Metallocenes and Metal Complexes of Transition Elements from Groups 4 to 7

With the progression in the field of bioinorganic chemistry, the role of transition metal complexes as the most widely used therapeutics is becoming a more and more attractive research area. The complexes of transition metals possess a great variety of attractive pharmacological properties, including anticancer, anti-inflammatory, antioxidant, anti-infective, etc., activities. Transition metal complexes have proven to be potential alternatives to biologically active organic compounds, especially as antitumor agents. The performance of metal coordination compounds in living systems is anticipated to differ generally from the action of non-metal-containing drugs and may offer unique diagnostic and/or therapeutic opportunities. In this review, the rapid development and application of metallocenes and metal complexes of elements from Groups 4 to 7 in cancer diagnostics and therapy have been summarized. Most of the heavy metals discussed in the current review are newly discovered metals. That is why the use of their metal-based compounds has attracted a lot of attention concerning their organometallic and coordination chemistry. All of this imposes more systematic studies on their biological activity, biocompatibility, and toxicity and presupposes further investigations.