JUPITER, Fla.—While keeping its focus on finding a cure, scientists from the Florida campus of The Scripps Research Institute (TSRI) have discovered new targets for potentially increasing the effectiveness of current treatments for breast cancer and reducing the undesirable side effects.
This discovery represents a small piece of the puzzle of how to eradicate breast cancer, yet is a bit of good news for the thousands of breast cancer survivors, family, friends and supporters who have run and walked marathons across the United States this past summer and previous years to raise funds and awareness toward ultimately finding a cure—among other public awareness and fundraising efforts.
The TSRI findings appeared in a paper published online ahead of print on June 5 for the journal Structure.
Patrick R. Griffin, a TSRI professor who led the study, explained that approximately two out of three breast cancers are driven by receptors that bind the hormones estrogen and progesterone and, when the hormones bind to these receptors in cancer cells, they signal the cancer cells to grow. What makes the progesterone receptor (PR) therapeutically interesting is that it has two activation domains—AF1 and AF2. Normally, both are needed for full activation of the receptor.
“These findings potentially open up a new avenue and target (AF1-coactivator interaction surface) for breast cancer therapy/drug discovery,” Griffin tells DDNews.
“Using hydrogen-deuterium exchange technology, our study pinpoints just how AF2 communicates with AF1—the first evidence of the long-range interaction between these two functional domains,” says Griffin, who is chairman of the Department of Molecular Therapeutics at TSRI’s Jupiter, Fla., campus. “These findings support further research to look for promising small molecules that block that interaction. Being able to detect how certain activators interact with the AF1 region of PR may provide insight into targeting these interactions. The current therapies target the C-terminal AF2, which only contributes to part of the function of PR, and in hormone-resistant PR, they are no longer useful.”
“It has been speculated for a very long time that the N-terminal AF1 regions of nuclear receptors interact or influence the C-terminal ligand binding domain that contains AF2,” Griffin adds. “The reason for this is the apparent synergy between these two regions as detected using mutagenesis.”
The findings are especially important because in some mutations AF2 is deleted, yet the receptor still drives the cancer using its AF1 domain, Griffin explains. Current drugs used for treating these cancers only target the AF2 domain, and so with nothing to bind to, they do not work at all. While several studies have shown the importance of AF1, its binding domain is remarkably dynamic, frequently shifting shape and making it difficult to target with drugs.
In the new study, the scientists used an advanced technology known as hydrogen-deuterium exchange (HDX) mass spectrometry to measure the intricate interactions between the AF1 and AF2 domains of the progesterone receptor.
“HDX mass spectrometry is defined as a high-precision, high-sensitivity mapping technique that enabled the scientists to determine the specific regions of the receptor that are altered upon interaction, along with the finding that transcriptional co-activators such as TBPc influence receptor activity by linking AF1 to AF2 functionally,” Griffin says.
This information was used to infer structural changes that result from the interaction and to probe the conformational flexibility of intact multidomain proteins.
“Long term, we are looking at the influence of different DNA response elements on the ternary complex, as well as profiling other key co-regulators of PR, particularly those that function via interaction with AF1,” he adds. “We are thinking that this information would provide insight on how to construct functional screens that would then go to the HTS lab to screen 400,000 compounds to find small molecules that are disrupters of these interactions.”
In addition to exploring potential new drugs for breast cancer, TSRI researchers also hope to investigate the implications for prostate cancer, another hormone-driven disease.
“Many features of the androgen receptor are similar to the progesterone receptor, as they belong to the same subfamily of steroid receptors,” stated Devrishi Goswami, the first author of the study and a member of the Griffin laboratory, in a news release about the work. “It could work the very same way. So these new insights may also help in finding new approaches to treating hormone-therapy-resistant prostate cancer.”
In addition to Goswami and Griffin, other authors of the study, “Influence of Domain Interactions on Conformational Mobility of the Progesterone Receptor as Detected by Hydrogen/Deuterium Exchange Mass Spectrometry,” include Bruce Pascal of TSRI, Celetta Callaway and Dean P. Edwards of the Baylor College of Medicine in Houston and Raj Kumar of The Commonwealth Medical College in Scranton, Pa.
Despite the nation’s unsuccessful decades-long war to beat cancer, TSRI remains committed to its Anti-Cancer Campaign goals, Griffin said.
“In the past several decades of our war on cancer, there have been victories, large and small, and advances in detection, prevention and treatment,” the TSRI campaign states. “While these triumphs are worth celebrating, there is still much left to learn about the large cluster of diseases we call cancer.”
When the United States boosted its government funding to beat back cancer 40 years ago, cancer mortality rates began to decline; between 1991 and 2006, they fell about 21 percent for men and 12 percent for women. But, while cancer is still a widespread problem, over the past several years federal funding for critical basic biomedical research has decreased in real dollars—by 25 percent over the past 10 years.
What is especially important for scientific breakthroughs, though, are high-risk, high-reward endeavors—the kind that are particularly difficult to fund through conventional government grants.
TSRI states the company has long had a broad and active program on both campuses in the field of cancer research. In terms of breast cancer, TSRI has had a number of important findings, including the most recent study by the Pat Griffin laboratory.
Last year, the Kendall Nettles laboratory in Florida uncovered a class of novel compounds that can alter cell signaling activity, resulting in a variety of responses including a strong anti-inflammatory effect, and these findings could lead to new strategies for treating diseases such as breast cancer.
Also in 2013, Associate Prof. Brunhilde H. Fielding from TSRI’s La Jolla, Calif., campus identified a mechanism through which mitochondria, the powerhouses of a cell, control tumor aggressiveness in breast cancer.
Based on these findings, the team developed a simple treatment that inhibits cancer progression and prolongs life when tested in mice. In 2012, Assistant Prof. Jun-Li Luo from the Florida campus shed new light on exactly how the activation of a pair of inflammatory signaling pathways leads to the transformation of normal breast cells to cancer cells. TSRI has also designated cancer research as one of its six initiatives, each focusing on areas of excellence and promising pathways for the future.
