As Ruth Nussinov, Ph.D., and her team watched a mutated, cancer-causing protein twist and bend across their computer screen in a simulation, two things quickly became evident.
First, it was clear how the mutation paved the way for cancers to form. Second, the twisting and bending created a pocket—a gap in the protein’s proverbial armor—no one had seen before.
This discovery of the heretofore-unknown pocket and the computer simulations illuminating how mutated versions of that protein, mTOR, contribute to cancer at a molecular level offer an opportunity to target mutant mTOR for enhanced cancer treatment.
“Exploring these structural details could lead to more targeted and effective therapeutic strategies for cancer treatment,” Nussinov said.
Nussinov leads the Frederick National Laboratory for Cancer Research’s Computational Structural Biology Section, which is embedded in the National Cancer Institute’s Center for Cancer Research.
Nussinov’s team published their findings in the Journal of Chemical Information and Modeling.
mTOR helps regulate essential survival functions in our cells. But some mutations allow it to become overactive. In those scenarios, cells multiply too fast, live too long, and are harder to kill—hallmarks of cancer.
Mutant mTOR is implicated in the biology of melanoma and in malignant tumors in no fewer than six different organs in the human body.
The protein is a high-profile candidate for cancer treatment, yet few drugs exist that specifically target its mutant forms.
mTOR’s structure—the configuration of its molecules, including folds, bends, and pockets—tells scientists how it functions and interacts with other proteins, both in cancer and in normal cells and tissues. This information can guide efforts to develop new drugs, yet there’s still much unknown.
“This gap in understanding motivated us to investigate mTOR’s molecular architecture," Nussinov said.
Nussinov’s team selected several cancer-causing mTOR mutants and put them through molecular dynamics simulations, computer models that use existing chemical and biological data to predict how proteins behave under given conditions.
The method let them render versions of mTOR with individual mutations and see how the mutations changed the protein’s structure, if at all.
“This approach also allows us to probe the effects of mutations or changes in environmental conditions on mTOR’s function, which would be difficult to observe directly with experimental methods,” Nussinov said. “Computational molecular dynamics gives us a powerful tool to gain a deeper understanding of mTOR’s behavior in a way that complements experimental work and helps guide further investigation.”
The simulations revealed that most of the mutations shift mTOR’s structure in a way that favors cancer-causing conditions.
With these mutants, a portion of mTOR unfolds such that other proteins can more frequently interact with it to trigger cells to multiply, extend their normal life spans, and form tumors. Two other mutations stopped short of doing so but created conditions that make the shift likely.
“That was both exciting and surprising, as it suggested that small, previously overlooked changes in mTOR’s structure could have significant functional consequences,” Nussinov said, adding that some of the shifts aligned with known cancer-causing mutations.
The finding underscores the relationship between mTOR’s structure and its role in cancer.
Potential treatments could aim to re-fold mTOR mutants or block their interactions while unfolded.
The new pocket the team discovered has potential for that. The same mutations that contort mTOR protein into its cancer-driving shape also create the pocket in its structure, and the simulations suggest at least two existing drugs can hit it.
The compounds, RLY-2608 and STX-478, were designed to disable a protein that commonly interacts with PI3Ka (a critical drug target for cancer), but they cleanly fit into the mutant mTOR’s pocket, the team found.
Equally valuable, the drugs fit better with mutant mTOR than normal mTOR, suggesting that future treatments targeting the pocket may be better at zeroing in on the cancer cells with the mutants and less harmful to cancer patients’ healthy cells.
“Our discovery opens up new avenues for designing therapeutic strategies targeting mTOR,” Nussinov said.
While Nussinov and her team are encouraged by the outcome of the study, they’re balancing it with a healthy dose of realism. The work was done on the computer, and like any experimental method, molecular dynamics has limitations.
The findings are cause for optimism and testify molecular dynamics’ power and utility, Nussinov said. However, she added they need to be validated in laboratory and microscopy studies so scientists can be certain the simulations align with reality.
“By integrating both, we expect to gain a deeper understanding of mTOR’s druggable potential,” she said. “Looking ahead, we are excited about collaborating to integrate our molecular dynamics simulations with experimental data.”
Mary Ellen Hackett Manager, Communications Office 301-401-8670