This screen allows one to identify genes involved in cell survival, and more importantly, it is designed to identify which shRNAs (and therefore which genes) will assist in making a cell more sensitive, or more resistant, to paclitaxel (Figure 2). We identified several genes that lead to increased resistance to treatment. This correlates with published examples of cases in which patients carrying mutations or deletions of tumor suppressor genes have a lower rate of response to a variety of therapies. Prominent among those genes is p53, which was found to play a role in paclitaxel resistance in our screen as well.
More intriguing is the finding that some genes, when down-regulated by these shRNAs, lead to increased sensitivity of cells to paclitaxel (Figure 3). Again, there is evidence in the literature to support this finding. BRCA1 has been found to be mutated in breast and ovarian tumors, and patients with these mutations can be more responsive to chemotherapies than patients with this gene intact. Patients with renal cell carcinoma and a mutation or truncation in the VHL tumor suppressor gene have better response rates and a longer time to tumor progression when treated with a certain molecular therapy than patients with a functioning VHL. The gene VHL was also identified in our screen.
It is important to note that these experiments are preliminary and it is difficult to conclude the role of specific genes identified and their potential relevance to actual clinical outcomes, however, the implications are promising. Our experiments imply that by examining the molecular state of a tumor and determining the levels of certain tumor suppressor genes, one might be able to determine the likelihood of response to a therapy. P