An albumin-based tumor-targeted oxaliplatin prodrug with distinctly improved anticancer activity in vivo

An oxaliplatin-based platinum(iv) drug which specifically binds to albumin after i.v. application led to several complete responses in tumor-bearing mice.

The design of targeted platinum(iv) prodrugs is a very promising approach to enhance the low selectivity of platinum(ii) drugs towards cancerous tissue in order to reduce the impact on healthy tissue and, consequently, the often severe side-effects. Herein, we report a set of mono-functionalized cis- and oxaliplatin-based platinum(iv) complexes bearing a maleimide moiety, which allows selective binding to serum albumin in the bloodstream. This leads not only to a prolonged plasma half-life by avoidance of fast renal clearance, but also to preferential accumulation of the drug in the tumor tissue due to the EPR-effect. Additionally, analogous succinimide-functionalized derivatives were prepared to verify the influence of the maleimide moiety. First experiments showed that all the maleimide compounds are stable and also possess good albumin-binding properties in whole serum. Further analytical studies on in vivo samples proved the highly increased plasma half-life, as well as tumor accumulation of the maleimide-functionalized substances. In vivo antitumor experiments with CT-26-bearing mice showed that, in contrast to the cisplatin derivatives, the oxaliplatin-based complexes had exceptionally better activity than the free drug resulting in the cure of the majority of treated mice. Subsequent analysis suggested that a distinctly faster reduction as well as reduced tumor accumulation of the cisplatin derivative might explain the worse performance compared to the oxaliplatin(iv) complexes. Taken together, a novel lead platinum(iv) complex with outstanding antitumor activity is presented, which will now be further developed towards clinical phase I trials.

Genomic manipulations in alkaliphilic haloarchaea demonstrated by a gene disruption in Natrialba magadii

Alkaliphilic haloarchaea, a distinct physiological group from the closely related neutrophilic haloarchaea, represent an underutilized resource for basic research and industrial applications. In contrast to the neutrophilic haloarchaea, no reports on genomic manipulations in haloalkaliphiles have been published until now. Genomic manipulations via homologous recombination are useful for basic research. In this study, we demonstrate the possibility for this strategy in alkaliphilic haloarchaea for the first time. In a previous study, we developed a PEG-mediated transformation technique for alkaliphilic haloarchaea that was deployed in this study to deliver a gene disruption cassette into the model organism Natrialba magadii. The gene encoding for the well-studied Natrialba extracellular protease was successfully disrupted by a recombination marker gene, demonstrating a proof of principle for the usability of homologous recombination for genomic manipulations in alkaliphilic haloarchaea. Since halo(alkali)philic Archaea are polyploid, a selection process was applied in order to obtain a mutant strain containing exclusively disrupted genes. The resulting strain exhibited no proteolytic activity measurable by an azo-casein assay. Complementation was able to restore proteolytic activity. The expression pattern of the Natrialba extracellular protease was different in the complemented strain.

Abstract 2573: Investigation of factors involved in the hypersensitivity to KP1339-treatment

The ruthenium-based compound KP1339 (trans-(tetrachlorobis(1H-indazole)ruthenate(III)), which is currently in Phase I/II trial, is already known for its promising anticancer activity. In course of a recent screening using diverse cancer cell lines of different origin (n = 25), a small subgroup with exceptional sensitivity to KP1339-treatment was discovered. The aim of the here presented study was to identify factors that underlie this sensitivity or which are connected to resistance to KP1339. Due to the fact that KP1339 comprises a metal center, interpretations of it's mode of action tend towards either generation of ROS or DNA binding. To avoid a biased approach, whole genome expression arrays were performed with mRNA isolated from hypersensitive and normal responsive cells that were either untreated or treated with KP1339 for 3 h and 6 h. Subsequent bioinformatic analysis of the gained data indicated that while hypersensitive cell lines activated pathways indicative for response to chemical stimuli (“metal ion”, “organic compound”), in normal responsive ones preferentially genes involved in pathways controlling cell cycle, DNA repair and metabolism were found. Subsequent investigations confirmed that upon KP1339-treatment hypersensitive cell lines showed pronounced apoptosis induction (indicated by caspase-mediated PARP cleavage and appearance of apoptotic nuclei visualized by DAPI staining). In contrast, normal responsive cells rather reacted with prolonged duration of the G2 phase to KP1339 treatment (video evaluation). This was confirmed by FACS analysis of ethanol-fixed and propidium iodide-stained cells indicating a profound increase in the percentage of cells with double DNA content upon KP1339 treatment. Moreover, in accordance to previous studies, KP1339 induced strong phosphorylation of ERK, p38 and JNK especially in normal responsive cell lines. This is of interest as p38 and JNK activation are known to be pro-survival factors within the extrinsic pathway of apoptosis. The relevance of this particular pathway is supported by preliminary results of activation of caspase 8 upon KP1339 treatment in hypersensitive cells. This knowledge can help to better understand the mechanisms underlying the promising anticancer activity of KP1339.

Citation Format: Beatrix Alte, Christine Pirker, Thomas Mohr, Kushtrim Kryeziu, Bernhard K. Keppler, Petra Heffeter, Walter Berger. Investigation of factors involved in the hypersensitivity to KP1339-treatment. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2573. doi:10.1158/1538-7445.AM2015-2573

Structure-Related Mode-of-Action Differences of Anticancer Organoruthenium Complexes with β-Diketonates

A series of organoruthenium(II) chlorido complexes with fluorinated O,O-ligands [(η(6)-p-cymene)Ru(F3C-acac-Ar)Cl] (1a-6a) and their respective 1,3,5-triaza-7-phosphaadamantane (pta) derivatives [(η(6)-p-cymene)Ru(F3C-acac-Ar)pta]PF6 (1b-6b) were synthesized and fully characterized in both solution and solid state. All complexes were inactive against nonmalignant keratinocytes but displayed variable activity against cancer cell models (ovarian, osteosarcoma). Compounds with a ligand containing the 4-chlorophenyl substituent (6a and 6b) exhibited the strongest anticancer effects. Despite a marginally lower cellular Ru accumulation compared to the chlorido complexes, pta analogues showed higher activity especially in the osteosarcoma model. Reduction of glutathione levels by buthionine sulfoximine (BSO) significantly enhanced the activity of all compounds with the most pronounced effects being observed for the pta series resulting in IC50 values down to the nanomolar range. While all chlorido complexes potently induce reactive oxygen species, DNA damage, and apoptosis, the respective pta compounds widely lacked ROS production but blocked cell cycle progression in G0/G1 phase.