Silencing HoxA1 by Intraductal Injection of siRNA Lipidoid Nanoparticles Prevents Mammary Tumor Progression in Mice

Silencing of HoxA1 with nanoparticle siRNA prevented loss of hormone receptor expression, suppressed cell proliferation, and reduced mammary tumor incidence in mice. Silencing Breast Cancer with Nanoparticle siRNA Cancer drives researchers crazy. But what drives cancer? In a new study by Brock and colleagues, the researchers modeled the gene network of mice and found HoxA1 to be a putative driver of early breast cancer progression. Silencing this gene using nanoparticle-packaged small interfering RNA (siRNA) led to tumor reduction in mice. Ductal carcinoma in situ (DCIS) is a noninvasive lesion of the breast that progresses to invasive breast cancer in an estimated 14 to 53% of cases. However, current prognostic methods are unable to predict whether DCIS will indeed become invasive. Brock et al. used a computational gene network inference approach to look at early gene expression changes in mammary tumor progression, and identified HoxA1 as a likely candidate. The authors then confirmed that HoxA1 was overexpressed in human breast lesions by looking at patient gene expression data. To verify the role of this candidate gene in cancer progression, HoxA1 siRNA was formulated into lipidoid nanoparticles and administered to transgenic mice that develop tumors much like people do. The HoxA1-silencing nanoparticles were delivered locally (through the nipple), to avoid any systemic immune response, and led to a decrease in tumor formation, as compared to mice that received control siRNA. Notably, the HoxA1 siRNA prevented the loss of hormone (estrogen and progesterone) receptors in the treated mammary glands—a loss that is one hallmark of breast cancer progression. This study demonstrates how computational methods can generate viable oncogene candidates for RNA interference (RNAi) therapy. Brock et al. discovered and preliminarily validated HoxA1 as a driver of breast cancer progression in mice, but additional human cell and tissue testing will be needed to verify the role of this gene in human DCIS and mammary tumorigenesis. With advances in screening, the incidence of detection of premalignant breast lesions has increased in recent decades; however, treatment options remain limited to surveillance or surgical removal by lumpectomy or mastectomy. We hypothesized that disease progression could be blocked by RNA interference (RNAi) therapy and set out to develop a targeted therapeutic delivery strategy. Using computational gene network modeling, we identified HoxA1 as a putative driver of early mammary cancer progression in transgenic C3(1)-SV40TAg mice. Silencing this gene in cultured mouse or human mammary tumor spheroids resulted in increased acinar lumen formation, reduced tumor cell proliferation, and restoration of normal epithelial polarization. When the HoxA1 gene was silenced in vivo via intraductal delivery of nanoparticle-formulated small interfering RNA (siRNA) through the nipple of transgenic mice with early-stage disease, mammary epithelial cell proliferation rates were suppressed, loss of estrogen and progesterone receptor expression was prevented, and tumor incidence was reduced by 75%. This approach that leverages new advances in systems biology and nanotechnology offers a novel noninvasive strategy to block breast cancer progression through targeted silencing of critical genes directly within the mammary epithelium.