Molecular staples shape a cancer killer

September 02, 2004

Howard Hughes Medical Institute (HHMI) researchers have successfully designed and improved a new type of cancer-killing compound by performing molecular surgery to stabilize the molecule so that it selectively triggers cell death.

The idea for developing the compound emerged from the HHMI laboratory of Stanley J. Korsmeyer, who leads one of the hottest research teams currently studying programmed cell death, or apoptosis, a genetic program that executes cells that are no longer needed. Using the biologically active portion of a protein that triggers apoptosis, Korsmeyer's team successfully inserted non-natural amino acids into the peptide sequence and then performed a chemical reaction that created a "staple" within the molecule, resulting in its stabilization. Korsmeyer and the paper's lead author, Loren D. Walensky, who are at the Dana-Farber Cancer Institute at Harvard Medical School, reported their studies in the September 3, 2004, issue of the journal Science.

The chemical approach they applied, called hydrocarbon stapling, was developed by their collaborator Gregory L. Verdine of Harvard University, and permitted the researchers to overcome the tendency of short peptides to lose their critical three-dimensional structure - and their ability to kill cells -- when removed from the context of the complete protein. This has been one of the greatest obstacles associated with using short peptides as therapeutic agents, and has hindered their legitimacy as pharmaceutical lead compounds. By making the peptides more resistant to degradation and enabling their cellular uptake, the hydrocarbon staple overcomes classic shortcomings of peptide therapeutics.

As the molecular events that lead to execution and death have become clearer during the last decade, researchers speculated that it would not be long before biotechnology and pharmaceutical companies were racing to develop novel compounds that could be used to hasten or prevent the demise of cells.

"Academic and industrial laboratories are engaged in a Herculean effort to develop new molecules that reactivate the apoptotic program in tumor cells," wrote HHMI investigator Steven F. Dowdy of the University of California, San Diego, in a Perspectives article that was published in the same issue of Science.

Korsmeyer, Walensky, and their colleagues aimed to construct a key regulatory segment of an apoptosis-triggering protein called BID that could induce apoptosis in cancer cells. Their objective was to create a short peptide that functionally mimicked the specific region of the BID protein that elicits cell death. Theoretically, such a small molecule -- basically a short string of amino acids -- could insinuate itself into cancer cells to trigger their suicide.

"Our goal was to modify the natural peptide sequence only enough to stabilize or reinforce its shape to improve its pharmacological properties," said Walensky. The researchers used the hydrocarbon stapling strategy to brace the peptide from within.

"We substituted non-natural amino acids for natural amino acids in selected positions," he said. "The non-natural amino acids look very similar to the natural ones, except that they include hydrocarbons that can be cross-linked to one another. This cross-linking provides a constraint, which doesn't allow the peptide to unfold." The researchers dubbed the engineered peptide "stabilized alpha-helix of BCL-2 domains" (SAHB). The BCL-2 family of proteins regulates apoptosis.

When the researchers examined SAHB's properties, they found that it assumed a stable alpha-helical shape, bound to the right protein to trigger apoptosis, and resisted degradation by proteases. They also found that SAHB specifically triggered the cell's power plants, the mitochondria, to release a protein that participates in launching apoptotic destruction.

Their experiments with leukemia cells cultured in the laboratory revealed that SAHB could enter, and, more importantly, inhibit the growth of those cells.

"When we saw that we could activate cell death in a specific way in whole cells, we were eager to conduct animal studies," said Walensky. So, the researchers tested the effects of SAHB on mice that harbored human leukemia cells. "We found that SAHB treatment effectively suppressed leukemia in these mice," he said.

According to Walensky, the experiments are the first steps in a broader effort to construct hydrocarbon-stapled alpha-helical peptides that affect many control points of apoptosis. These are necessary because different cancers may have thwarted the apoptotic machinery in different ways, he said.

"The goal would be to use the natural sequences of these pro-apoptotic peptides to try to specifically activate the cell death program in a resistant cell," said Walensky. "For example, certain lymphomas are specifically driven by BCL-2 overexpression. So, if you could knock down some of the impact of that BCL-2, you would tip that lymphoma cell over the edge toward death."

Korsmeyer, Walensky, and their colleagues are now developing and testing different hydrocarbon-stapled BH3 domains against a range of cancer cells. Ultimately, they believe that further development of these peptides could broaden the arsenal of compounds used to kill different cancers.

Walensky said he would not be surprised to see hydrocarbon stapling of alpha-helices applied to control many interactions between proteins. "The alpha-helix plays a pivotal role in many biological interactions," said Walensky. "So if we could target protein-protein interactions at critical biological control points using the natural, evolutionarily derived sequence for that protein target -- with just this minor modification of hydrocarbon stapling -- then we might have a whole new set of tools to study and manipulate protein interactions within cells."
-end-


Howard Hughes Medical Institute

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.