Richardson and Wang's laboratory team sifted the tumor DNA and spotted a region on chromosome 8 that contained many redundant, or amplified, copies in the drug-resistant tumors. They found that this small region, labeled 8q22, was associated with a poor outcome in the breast cancer patients. In parallel, they discovered that 12 genes in that region were consistently "overexpressed" making abnormal amounts of protein as a result of amplification. "This was the only region of the genome that was tightly associated with poor outcomes despite the adjuvant chemotherapy treatment," Wang noted.
Wang, Richardson, and colleagues singled out the genes in the region that might be involved in tumors' drug resistance, based on their structures and functions. They then experimentally narrowed the field to two likely candidates - LAPTM4B and YWHAZ.
When the researchers knocked out the two genes' function in cancer cells grown in the laboratory, the cells became vulnerable to anthracycline compounds. Conversely, when the genes were overexpressed, the cells resisted anthracycline compounds, but were killed by other agents, cisplatin and paclitaxel.
To clinch their case, the researchers needed to carry out a blind test in which they didn't know ahead of time which patients' tumors had responded well to drug therapy. Fortunately, they learned of a Belgian clinical trial in which breast cancer patients had been treated prior to surgery with epirubicin one of the anthracyclines and their tumors were studied to determine the drug's effectiveness. Among other things, the researchers had obtained gene expression data from the tumors. The Dana-Farber researchers used that data to predict the degree of patients' tumors' response to the drug by measuring the LAPTM4B and YWHAZ activity in the tumors.
When their predictions were matched with the Belgian outcome data, "it
|Contact: Bill Schaller|
Dana-Farber Cancer Institute