Src knockout mice are viable; and 3) it is unlikely that complete knock-down of Src would be required to elicit a cellular effect on cancer cells, as low levels of Src activity are present in most normal cell types. As a model system, we chose to examine MDA-MB-435S, a highly metastatic cancer cell line that we previously had shown to possess high Src activity. This cell line has been utilized in over 780 scientific papers as a model breast cancer cell line, but some controversy has arisen in the literature over the last few years regarding its classification, as it possesses some melanocytic characteristics. More recently, considerable evidence has been provided by several laboratories supporting the breast cancer origin of these cells as well 
as the classification of the MDA-MB-435S cells into the basal subset of human breast cancers that often express melanocyte-related genes. The MDA-MB-435S cells have also been characterized to fall within the claudin-low subtype of breast cancer cells which are enriched in epithelial-to-mesenchymal transition and stem-cell like features. The basal subtype of human breast cancer is typically triplenegative, and as a consequence 15322237 has a poor prognosis, as it is most often poorly responsive to many of the current treatment strategies. Basal subtype tumors can also be particularly aggressive, and often more likely to recur than other subtypes of breast cancer. Therefore, it is very important that we develop alternate methods of treatment that target this particular subtype of cancer. Cancer therapies targeting specific proteins are relatively new, and include antibodies, chemical inhibitors, and 9671117 now, siRNA. As compared to inhibitors targeting the protein products of various genes, siRNA shifts the focus of the targeting strategy from the protein that contributes to the malignancy to the mRNA that produces the protein. This is made possible by the use of siRNAs and their utilization of the RNA interference pathway to degrade specific cellular mRNAs, thereby modifying protein expression levels and activities. This strategy provides the opportunity to pick key genes in the malignant process irrespective of whether it may be difficult to develop traditional pharmaceutical agents that target these proteins. siRNAs also possess additional features which make them highly 58-63-9 attractive as pharmaceuticals, including 1) their high degree of specificity, 2) the ease with which multiple siRNAs targeting a single proteins can be designed, thereby reducing the likelihood of drug resistance, and 3) the ability to simultaneously target two or more gene products. siRNAs are introduced into cultured cells directly by transfection or by utilizing plasmid or viral vectors, and similar techniques have been utilized in whole animals, where ��naked��siRNA can be delivered to tissues/organs to treat certain disease conditions. In humans, the administration of siRNA using various carrier molecules is in its early stages of testing, but promising early results have been obtained. With perhaps the greatest relevance to cancer treatment, investigators have now begun phase I clinical trials involving the systemic administration of siRNA to patients with solid cancers. Their data demonstrate that the siRNA is delivered to the tumors and is capable of knocking down specific mRNAs, which is very encouraging news for laboratories currently developing siRNAbased therapeutics for human cancers. We wished to test the feasibility of the direct
