Introduction: Substantial preclinical evidence has indicated that inhibition of integrin linked-kinase (ILK) correlates with cytotoxic/cytostatic cellular effects, delayed tumor growth in animal models of cancer, and inhibition of angiogenesis. Widely anticipated to represent a very promising therapeutic target in several cancer indications, it is increasingly evident that optimal therapeutic benefits obtained using ILK targeting strategies will only be achieved in combination settings. The purpose of this study was to investigate the therapeutic potential of the ILK small molecule inhibitor, QLT0267 (267), alone or in combination with chemotherapies commonly used to treat breast cancer patients.
Methods: A single end-point metabolic assay was used as an initial screen for 267 interactions with selected chemotherapeutic agents. These in vitro assays were completed with seven breast cancer cell lines including several which over-expressed human epidermal growth factor receptor 2 (Her2). One agent, docetaxel (Dt), consistently produced synergistic interactions when combined with 267. Dt/267 interactions were further characterized by measuring therapeutic endpoints linked to phosphorylated protein kinase B (P-AKT) suppression, inhibition of vascular endothelial growth factor (VEGF) secretion and changes in cytoarchitecture. In vivo efficacy studies were completed in mice bearing orthotopic xenografts where tumor growth was assessed by bioluminescence and calliper methods.
Results: The combination of 267 and Dt resulted in increased cytotoxic activity, as determined using an assay of metabolic activity. Combinations of cisplatin, doxorubicin, vinorelbine, paclitaxel, and trastuzumab produced antagonistic interactions. Further endpoint analysis in cell lines with low Her2 levels revealed that the 267/Dt combinations resulted in: a three-fold decrease in concentration (dose) of 267 required to achieve 50% inhibition of P-AKT; and a dramatic disruption of normal filamentous-actin cellular architecture. In contrast to Her2-positive cell lines, three-fold higher concentrations of 267 were required to achieve 50% inhibition of P-AKT when the drug was used in combination with Dt. In vivo studies focusing on low Her2-expressing breast cancer cells (LCC6) implanted orthotopically demonstrated that treatment with 267/Dt engendered improved therapeutic effects when compared with mice treated with either agent alone.
Conclusions: The findings indicate that the 267/Dt drug combination confers increased (synergistic) therapeutic efficacy towards human breast cancer cells that express low levels of Her2.