Calpain-Mediated Integrin Deregulation as a Novel Mode of Action for the Anticancer Gallium Compound KP46

Abstract

On the basis of enhanced tumor accumulation and bone affinity, gallium compounds are under development as anticancer and antimetastatic agents. In this study, we analyzed molecular targets of one of the lead anticancer gallium complexes [KP46, Tris(8-quinolinolato)gallium(III)] focusing on colon and lung cancer. Within a few hours, KP46 treatment at low micromolar concentrations induced cell body contraction and loss of adhesion followed by prompt cell decomposition. This rapid KP46-induced cell death lacked classic apoptotic features and was insensitive toward a pan-caspase inhibitor. Surprisingly, however, it was accompanied by upregulation of proapoptotic Bcl-2 family members. Furthermore, a Bax-but not a p53-knockout HCT-116 subline exhibited significant KP46 resistance. Rapid KP46-induced detachment was accompanied by downregulation of focal adhesion proteins, including several integrin subunits. Loss of integrin-b1 and talin plasma membrane localization corresponded to reduced binding of RGD (Arg-Gly-Asp) peptides to KP46-treated cells. Accordingly, KP46-induced cell death and destabilization of integrins were enhanced by culture on collagen type I, a major integrin ligand. In contrast, KP46-mediated adhesion defects were partially rescued by Mg 2þ ions, promoting integrin-mediated cell adhesion. Focal adhesion dynamics are regulated by calpains via cleavage of multiple cell adhesion molecules. Cotreatment with the cell-permeable calpain inhibitor PD150606 diminished KP46-mediated integrin destabilization and rapid cell death induction. KP46 treatment distinctly inhibited HCT-116 colon cancer xenograft in vivo by causing reduced integrin plasma membrane localization, tissue disintegration, and intense tumor necrosis. This study identifies integrin deregulation via a calpainmediated mechanism as a novel mode of action for the anticancer gallium compound KP46. Mol Cancer Ther; 13(10); 2436-49. Ó2014 AACR.

Three-dimensional and co-culture models for preclinical evaluation of metal-based anticancer drugs

“…Cells grown in spheroids are known to produce increased amounts of adhesion molecules [49], which in general mediate invasiveness. KP46 has been reported recently to down-regulate focal adhesion proteins, in particular integrin-b1, causing deregulation of cell-matrix adhesion [50]. In good agreement with these findings, we showed that KP46 inhibits contraction of collagen I gels by fibroblasts and fibroblast invasion into collagen I, corroborating the impact on stroma interactions caused by treatment with this compound.…”

“…In good agreement with these findings, we showed that KP46 inhibits contraction of collagen I gels by fibroblasts and fibroblast invasion into collagen I, corroborating the impact on stroma interactions caused by treatment with this compound. We showed further that KP46 down-regulates α-SMA in monolayer culture of fibroblasts in a dosedependent manner, which can be an additional reason not only for the anti-invasive activity of the compound, but also for cell morphology changes and cell detachment observed in fibroblasts (see Electronic supplementary material) and cancer cell lines [50]. Data obtained from HCT116/fibroblast co-culture in a 3D matrix, however, showed that KP46 selectively targets cancer cells but has no discernible impact on fibroblast viability.…”

Coordination compounds in cancer: Past, present and perspectives

“…The cytotoxicity mechanism involves p53 activation mediated by Ca 2+ -signalling and ROS production (Gogna et al, 2012;Madan et al, 2013). Recently, new insights onto the mechanism of action have been highlighted (Jungwirth et al, 2014). KP46 has been tested in various phase II clinical trials and no dose-limiting toxicity was found.…”

Loss of phosphodiesterase 4D mediates acquired triapine resistance via Epac-Rap1-Integrin signaling

“…For histological evaluations, 3 μm formalin-fixed and paraffin-embedded tumor sections were deparaffinised and rehydrated. Sections were stained with hematoxylin and eosin (H&E), Ki-67 (clone MiB-1; DAKO, Glostrup, Denmark) 1:100, and integrin β1 (CD29, #610467; BD Bioscience, NJ, USA) 1:400 as described previously [80]. …”