Working to develop new treatments for osteoarthritis, researchers at Washington University School of Medicine in St. Louis have harnessed synthetic biology and tissue engineering technologies to generate genetically engineered cartilage that can deliver an anti-inflammatory drug in response to activity similar to the bending of a knee or other movements that put stress on joints.

“Drugs such as ibuprofen and naproxen that ease joint pain and lower systemic inflammation are the main treatments for osteoarthritis pain, but there are no therapies that actually prevent damage in the joints of patients with this debilitating form of arthritis,” said senior investigator Farshid Guilak, PhD, the Mildred B. Simon professor of orthopedic surgery. “We’ve developed a new field of research called mechanogenetics, where we can engineer cartilage cells to respond to the mechanical loading of the joint. Every time cells are under that stress, they produce an anti-inflammatory, biologic drug to reduce inflammation and limit arthritis-related damage.”

Guilak and colleagues reported on their developments and lab tests, in Science Advances. Their paper is titled, “A synthetic mechanogenetic gene circuit for autonomous drug delivery in engineered tissues.”

Smart biomaterials or bioartificial tissues that autonomously respond to biological signals and drive therapeutic or restorative responses in the body represent promising approaches for treating both chronic and acute diseases, the authors wrote. “Mechanotherapeutics, in particular, are a rapidly growing class of smart biomaterials that use mechanical signals or mechanical changes within diseased tissues to elicit a therapeutic response and ameliorate the defective cellular mechanical environment.” However, current mechanotherapeutic technologies rely on exogenous protein drug delivery or use ultrasound stimulation or synthetic polymer implants, and so only offer “a finite life span for drug delivery,” the team continued. “Creating systems with cellular-scale resolution of mechanical forces that offer long-term, feedback-controlled synthesis of biologic drugs could provide a completely new approach for therapeutic delivery.”

Osteoarthritis is a chronic joint disease for which there are no available disease-modifying drugs, the investigators further pointed out. The disease may ultimately result in the patient requiring a total joint replacement, when the diseased and degraded cartilage and surrounding joint tissues cause so much pain and loss of function that the condition becomes incapacitating.

Among the early symptoms of osteoarthritis is pain in response to movements that involve the so-called mechanical loading of a joint. The joint pain that typically accompanies bending or lifting can make it difficult for patients with osteoarthritis to perform normal activities.

Like the touch sensor on a smartphone, cartilage cells sense when stress is being applied, and the inflammation associated with the excessive stress of arthritis causes cartilage to break down. The cells developed by Guilak’s team, however, have been engineered to respond to that stress by secreting an anti-inflammatory drug that blocks cartilage damage.

Initial experiments conducted in the lab used cartilage cells from pigs to figure out how the cells sense when they are being mechanically stressed. “Studying these cells in the lab, we were able to identify key pathways in the cells that respond to stress from loading and the gene circuits in cartilage that are activated by mechanical loading,” said co-first author Robert J. Nims, PhD, a postdoctoral researcher in the lab of Guilak, and who is a co-director of the Washington University Center of Regenerative Medicine and director of research at Shriners Hospitals for Children, St. Louis laboratory.

The Guilak team then altered genes in cartilage cells in the laboratory. “… we engineered a mechanically responsive bioartificial tissue construct for therapeutic drug delivery by using the signaling pathways downstream of the mechano/osmosensitive ion channel TRPV4 to drive synthetic mechanogenetic gene circuits,” they explained. The researchers ultimately programmed the cells to respond to the mechanical stress associated with movement and weight-bearing by producing a drug to combat inflammation. “We engineered synthetic gene circuits to respond to mechanical TRPV4 activation for driving transgene production of an anti-inflammatory molecule, interleukin-1 receptor antagonist (IL-1Ra).”

Guilak further explained, “We altered snippets of DNA in the cells to tell them to do something different than normal when they sense a load. That is, to make an arthritis-fighting drug.” The cells were engineered to release an interleukin-1 receptor antagonist—a drug called anakinra—which is used to treat rheumatoid arthritis and has shown promise for treating post-traumatic osteoarthritis that occurs following joint injury. “By combining synthetic biology and tissue engineering, we developed a novel class of bioartificial material that is mechanogenetically sensitive,” the investigators stated. “This system functions by redirecting endogenous mechanically sensitive ion channels to drive synthetic genetic circuits for converting mechanical inputs into programmed expression of a therapeutic transgene.”

“It’s kind of like turning on a light,” said co-first author Lara Pferdehirt, a biomedical engineer and graduate research assistant in Guilak’s lab. “With a light, you flip a switch, and a light bulb turns on. But in this case, the switch is the mechanical loading of a joint, and the bulb is the anti-inflammatory drug.”

Prior studies of anakinra in patients with osteoarthritis have shown it to be safe, but ineffective when only injected into a joint one time. Guilak believes that is because if it is to work well, the drug must be released in arthritic joints over longer periods, while mechanical loading is occurring. “While IL-1Ra (drug name anakinra) is approved as a therapy for rheumatoid arthritis and has successfully attenuated osteoarthritis progression in preclinical models, clinical trials of IL-1Ra therapy in patients with established osteoarthritis have not shown efficacy, suggesting that controlled long-term delivery may be necessary for disease modification,” the team wrote.

“This drug doesn’t seem to work unless it’s delivered continuously for years, which may be why it hasn’t worked well in clinical trials involving patients with osteoarthritis,” he said. “In our experiments in cells in the lab, we used existing signaling systems in the cartilage cells that we engineered so that they would release the drug whenever it’s needed. Here, we are using synthetic biology to create an artificial cell type that we can program to respond to what we want it to respond to.”

In addition to reducing inflammation in arthritic joints, having specific cartilage cells deliver the drug only when and where it’s needed should make it possible to avoid side effects associated with long-term delivery of a strong anti-inflammatory drug to the entire body. Such side effects can include stomach pain, diarrhea, fatigue, and hair loss.

Guilak’s team in addition plans to use the same technique to alter other types of cells to make different drugs. “While we developed mechanogenetic cartilage tissues based on TRPV4 activation here, the use of other native, mechanically sensitive ion channels and receptors provides an attractive source of mechanosensors that can be elicited to provoke synthetic outputs,” they stated. “Together, this framework for developing mechanically responsive engineered tissues is a novel approach for establishing new autonomous therapeutics and drug delivery systems for mechanotherapeutics.”

“We can create cells that automatically produce pain-relieving drugs, anti-inflammatory drugs, or growth factors to make cartilage regenerate,” Guilak added. “We think this strategy could be a framework for doing what we might need to do to program cells to deliver therapies in response to a variety of medical problems.”

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