Novel gold(I) complexes induce apoptosis in leukemia cells via the ROS-induced mitochondrial pathway with an upregulation of Harakiri and overcome multi drug resistances in leukemia and lymphoma cells and sensitize drug resistant tumor cells to apoptosis in vitro.

Gold complexes could be promising for tumor therapy because of their cytotoxic and cytostatic properties. We present novel gold(I) complexes and clarify whether they also show antitumor activity by studying apoptosis induction in different tumor cell lines in vitro, comparing the compounds on resistant cells and analyzing the mechanism of action. We particularly highlight one gold complex that shows cytostatic and cytotoxic effects on leukemia and lymphoma cells already in the nanomolar range, induces apoptosis via the intrinsic signaling pathway, and plays a role in the production of reactive oxygen species. Furthermore, not only did we demonstrate a large number of resistance overcomes on resistant cell lines, but some of these cell lines were significantly more sensitive to the new gold compound. Our results show promising properties for the gold compound as anti-tumor drug and suggest that it can subvert resistance mechanisms and thus targets resistant cells for killing.

Ruthenium Complex HB324 Induces Apoptosis via Mitochondrial Pathway with an Upregulation of Harakiri and Overcomes Cisplatin Resistance in Neuroblastoma Cells In Vitro.

Ruthenium(II) complexes with N-heterocyclic carbene (NHC) ligands have recently attracted attention as novel chemotherapeutic agents. The complex HB324 was intensively studied as an apoptosis-inducing compound in resistant cell lines. HB324 induced apoptosis via mitochondrial pathways. Of particular interest is the upregulation of the Harakiri resistance protein, which inhibits the anti-apoptotic and death repressor proteins Bcl-2 (B-cell lymphoma 2) and BCL-xL (B-cell lymphoma-extra large). Moreover, HB324 showed synergistic activity with various established anticancer drugs and overcame resistance in several cell lines, such as neuroblastoma cells. In conclusion, HB324 showed promising potential as a novel anticancer agent in vitro, suggesting further investigations on this and other preclinical ruthenium drug candidates.

The gallium complex KP46 sensitizes resistant leukemia cells and overcomes Bcl-2-induced multidrug resistance in lymphoma cells via upregulation of Harakiri and downregulation of XIAP in vitro.

Tris-(8-quinolinolato)gallium(III) (KP46, AP-002) is an orally administered investigational anticancer and bone-protective drug currently being evaluated in patients with advanced solid tumors with bone involvement. Despite the clinical efficacy of other gallium compounds in non-Hodgkin's lymphoma, effects of KP46 in hematological tumor settings have not been studied systematically before. We report here intriguing activities in various human cell lines, including such with multidrug resistance (MDR): In Nalm-6 lymphoblastic leukemia cell sublines, KP46 was capable of overcoming P-gp-related as well as P-gp-unrelated MDR. Apoptosis induction by KP46 was unaffected by bcl2-mediated vincristine-induced MDR in a BJAB lymphoma cell subline and even enhanced in a K562 leukemia subline with daunorubicin-induced MDR, which could be re-sensitized to daunorubicin by KP46. As the latter resistance is associated with lowered Harakiri (HRK) protein levels, a modulating effect of KP46 on HRK expression is suggested. This is consistent with the significant high upregulation of HRK on RNA and protein levels observed in KP46-treated parental BJAB cells according to qPCR and Western blot analysis, respectively. Furthermore, KP46 significantly reduces the protein level of X-linked inhibitor of apoptosis (XIAP) in BJAB cells, the most potent known inhibitor of apoptosis. Overall, these results indicate both a higher potential of HRK and XIAP as cellular targets for cancer therapy and a broader therapeutic potential of KP46 than hitherto envisaged.

B-nor-methylene Colchicinoid PT-100 Selectively Induces Apoptosis in Multidrug-Resistant Human Cancer Cells via an Intrinsic Pathway in a Caspase-Independent Manner.

Colchicine, the main active alkaloid from Colchicum autumnale L., is a potent tubulin binder and represents an interesting lead structure for the development of potential anticancer chemotherapeutics. We report on the synthesis and investigation of potentially reactive colchicinoids and their surprising biological activities. In particular, the previously undescribed colchicinoid PT-100, a B-ring contracted 6-exo-methylene colchicinoid, exhibits extraordinarily high antiproliferative and apoptosis-inducing effects on various types of cancer cell lines like acute lymphoblastic leukemia (Nalm6), acute myeloid leukemia (HL-60), Burkitt-like lymphoma (BJAB), human melanoma (MelHO), and human breast adenocarcinoma (MCF7) cells at low nanomolar concentrations. Apoptosis induction proved to be especially high in multidrug-resistant Nalm6-derived cancer cell lines, while healthy human leukocytes and hepatocytes were not affected by the concentration range studied. Furthermore, caspase-independent initiation of apoptosis via an intrinsic pathway was observed. PT-100 also shows strong synergistic effects in combination with vincristine on BJAB and Nalm6 cells. Cocrystallization of PT-100 with tubulin dimers revealed its (noncovalent) binding to the colchicine-binding site of ß-tubulin at the interface to the α-subunit. A pronounced effect of PT-100 on the cytoskeleton morphology was shown by fluorescence microscopy. While the reactivity of PT-100 as a weak Michael acceptor toward thiols was chemically proven, it remains unclear whether this contributes to the remarkable biological properties of this unusual colchicinoid.

Gold(I) Bis(1,2,3-triazol-5-ylidene) Complexes as Promising Selective Anticancer Compounds.

The synthesis and antiproliferative activity of Mes- and iPr-substituted gold(I) bis(1,2,3-triazol-5-ylidene) complexes in various cancer cell lines are reported, showing nanomolar IC50 values of 50 nM (lymphoma cells) and 500 nM (leukemia cells), respectively (Mes < iPr). The compounds exclusively induce apoptosis (50 nM to 5 µM) instead of necrosis in common malignant blood cells (leukemia cells) and do not affect non-malignant leucocytes. Remarkably, the complexes not only overcome resistances against the well-established cytostatic etoposide, cytarabine, daunorubicin, and cisplatin but also promote a synergistic effect of up to 182% when used with daunorubicin. The present results demonstrate that gold(I) bis(1,2,3-triazol-5-ylidene) complexes are highly promising and easily modifiable anticancer metallodrugs.

A metal-free salalen ligand with anti-tumor and synergistic activity in resistant leukemia and solid tumor cells via mitochondrial pathway.

PURPOSE: Since the discovery of the well-known cis-platin, transition metal complexes are highly recognized as cytostatic agents. However, toxic side effects of the metal ions present in the complexes may pose significant problems for their future development. Therefore, we investigated the metal-free salalen ligand WQF 044. METHODS: DNA fragmentations in leukemia (Nalm6) and solid tumor cells (BJAB, MelHO, MCF-7, RM82) proved the apoptotic effects of WQF 044, its overcoming of resistances and the cellular pathways that are affected by the substance. The apoptotic mechanisms finding were supported by western blot analysis, measurement of the mitochondrial membrane potential and polymerase chain reactions. RESULTS: A complex intervention in the mitochondrial pathway of apoptosis with a Bcl-2 and caspase dependence was observed. Additionally, a wide range of tumors were affected by the ligand in a low micromolar range in-vitro. The compound overcame multidrug resistances in P-gp over-expressed acute lymphoblastic leukemia and CD95-downregulated Ewing's sarcoma cells. Quite remarkable synergistic effects with vincristine were observed in Burkitt-like lymphoma cells. CONCLUSION: The investigation of a metal-free salalen ligand as a potential anti-cancer drug revealed in promising results for a future clinical use.