Atu027 prevents pulmonary metastasis in experimental and spontaneous mouse metastasis models.

PURPOSE: Atu027, a novel RNA interference therapeutic, has been shown to inhibit lymph node metastasis in orthotopic prostate cancer mouse models. The aim of this study is to elucidate the pharmacologic activity of Atu027 in inhibiting hematogenous metastasis to the target organ lung in four different preclinical mouse models. EXPERIMENTAL DESIGN: Atu027 compared with vehicle or control small interfering RNA lipoplexes was tested in two experimental lung metastasis models (Lewis lung carcinoma, B16V) and spontaneous metastasis mouse models (MDA-MB-435, MDA-MB-231, mammary fat pad). Different dosing schedules (repeated low volume tail vein injections) were applied to obtain insight into effective Atu027 treatment. Primary tumor growth and lung metastasis were measured, and tissues were analyzed by immunohistochemistry and histology. In vitro studies in human umbilical vein endothelial cells were carried out to provide an insight into molecular changes on depletion of PKN3, in support of efficacy results. RESULTS: Intravenous administration of Atu027 prevents pulmonary metastasis. In particular, formation of spontaneous lung metastasis was significantly inhibited in animals with large tumor grafts as well as in mice with resected primary mammary fat pad tumors. In addition, we provide evidence that an increase in VE-cadherin protein levels as a downstream result of PKN3 target gene inhibition may change endothelial function, resulting in reduced colonization and micrometastasis formation. CONCLUSION: Atu027 can be considered as a potent drug for preventing lung metastasis formation, which might be suitable for preventing hematogenous metastasis in addition to standard cancer therapy.

Atu027, a liposomal small interfering RNA formulation targeting protein kinase N3, inhibits cancer progression.

We have previously described a small interfering RNA (siRNA) delivery system (AtuPLEX) for RNA interference (RNAi) in the vasculature of mice. Here we report preclinical data for Atu027, a siRNA-lipoplex directed against protein kinase N3 (PKN3), currently under development for the treatment of advanced solid cancer. In vitro studies revealed that Atu027-mediated inhibition of PKN3 function in primary endothelial cells impaired tube formation on extracellular matrix and cell migration, but is not essential for proliferation. Systemic administration of Atu027 by repeated bolus injections or infusions in mice, rats, and nonhuman primates results in specific, RNAi-mediated silencing of PKN3 expression. We show the efficacy of Atu027 in orthotopic mouse models for prostate and pancreatic cancers with significant inhibition of tumor growth and lymph node metastasis formation. The tumor vasculature of Atu027-treated animals showed a specific reduction in lymph vessel density but no significant changes in microvascular density.

Intracellular localization of lipoplexed siRNA in vascular endothelial cells of different mouse tissues.

Liposomally formulated siRNA can be used for RNAi applications in vivo. Intravenous bolus administration of lipoplexed siRNA has been shown to reduce gene expression in the vascular endothelium. Here, we applied immunofluorescence staining for different endothelial markers (PECAM-1, CD34, laminin) on paraffin sections to compare the respective expression pattern with the intracellular localization of intravenously administered, fluorescently labeled siRNA (siRNA-Cy3-lipoplex). By confocal microscopy, lipoplexed siRNA-Cy3 was detected inside vascular endothelial cells in vivo, which where identified with co-staining of endothelial markers. Consequently, the finding of intracellular siRNA uptake by vascular endothelial cells correlated with RNAi based specific protein reduction in situ as revealed by PECAM-1 specific immunofluorescence staining in lung tissue sections. Therefore, by using a cell biological approach these in situ data emphasize the functional uptake of liposomal siRNA molecules in vascular endothelial cells of different mouse tissues as indicated in our previous molecular study.

Inducible shRNA expression for application in a prostate cancer mouse model.

RNA interference (RNAi) is a powerful tool to induce loss-of-function phenotypes by inhibiting gene expression post-transcriptionally. Synthetic short interfering RNAs (siRNAs) as well as vector-based siRNA expression systems have been used successfully to silence gene expression in a variety of biological systems. We describe the development of an inducible siRNA expression system that is based on the tetracycline repressor and eukaryotic RNA polymerase III promoters (U6 and 7SK). For proof of concept we selectively inhibited expression of two catalytic subunits of the phosphatidylinositol 3-kinase (PI 3-kinase), p110alpha and p110beta, by using vector-derived short hairpin RNAs (shRNAs). Stable pools of human prostate cancer cells (PC-3) exhibiting reduced levels of both PI 3-kinase catalytic subunits due to the expression of corresponding shRNAs in an inducible fashion were established and analyzed for their invasive potential in vitro as well as in an orthotopic metastatic mouse model. This inducible system for RNAi allows an unbiased and comparable analysis of loss-of-function phenotypes by comparing selected isogenic cell populations on the induced and non-induced level. In addition, conditional RNAi allows the study of essential and multifunctional genes involved in complex biological processes by preventing inhibitory and compensatory effects caused by constitutive knockdown.