By David N. Leff
From ordinary aspirin to non-steroidal pain-killers to salts of gold (oral or injectable) to total joint replacement, rheumatoid arthritis (RA) commands a gamut of current therapies. Yet one in ten of its fully treated victims ends up permanently disabled, despite this increasingly drastic medical arsenal.
A standard manual for physicians advises, "Food and diet quackery [for RA] is common, and should be discouraged."
The journal Arthritis & Rheumatism reports in its May 1998 issue: "Available data suggest that the overall prevalence of [definitely diagnosed] RA among U.S. adults is approximately ten per 1,000 (1 percent); rates for women are approximately 2.5 times higher than rates for men. These figures," the article adds, "translate into a total of approximately 2.1 million persons: 600,000 men and 1.5 million women."
Nor are these sufferers mainly found among the aged. As a rule, RA sets in, suddenly or insidiously, between the ages of 20 and 45. And these prime-of-life victims cost the U.S. economy 2.2 million lost work days a year.
Besides the array of drugs and devices designed to relieve the agonizing pain and disability of tender, inflamed and deformed RA synovial joints, academic and industrial researchers (among them many biotechnology companies) are focussed on finding and foiling the root causes of this devastating autoimmune disease.
The main bull's eye in their cross-hairs is the misnamed molecule tumor necrosis factor (TNF). Whatever its role in cancer may or may not be, TNF's main task as an immune defense cytokine is to generate protective inflammatory responses at the site of tissue damage or infection.
The trouble is that all too often, TNF doesn't know when to stop. Driven by the still-mysterious forces in the immune system that trigger autoimmune disease, TNF is strongly suspected of progressively ruining the joints — usually of hands and feet — that mark RA.
Therapy Targets Macrophages
Macrophages, best known as the phagocytic cells that engulf, digest and spit out harmful microbes and other noxious substances, are also the production centers that generate TNF.
"Macrophages are the main source of inflammatory cytokines, like TNF," observed biochemical immunologist Brian Foxwell, at the Kennedy Institute of Rhematology, in Hammersmith, London. And it's been shown by others that in RA they're major generators of inflammatory factors.
"People both here and in the U.S.," he added, "have showed that if you inhibit TNF with an antibody against it, you seem to ameliorate the effects of arthritis. So it appears that macrophages are major factories, if you like, in the production of the inflammatory mediators, which are pivotal to the autoimmune process, of which RA appears definitely to be a prime case."
Despite successes in recent clinical trials of such antibodies at cutting TNF off at the pass, Foxwell and his associates sought to stifle the cytokine at its very point of synthesis. For this, he turned to gene transfer.
Foxwell is lead author of a report in the current Proceedings of the National Academy of Sciences (PNAS), dated July 7, 1998. Its title is "Efficient adenoviral infection with IkBa reveals that macrophage tumor necrosis factor alpha production in rheumatoid arthritis is NF-kB dependant."
Foxwell explained that "NF-kB is a transcription factor essential for TNF production.
"IkB," he continued, "is a protein that normally keeps this NF-kB transcription factor in a dormant state. So it appears to be a naturally occurring specific inhibitor of NF-kB function. When the macrophage cell is activated, IkB is destroyed, thereby releasing this factor to do its job.
"What we've done," he told BioWorld Today, "is develop an improved technique to genetically modify primary human macrophages at very high efficiency. Using an adenoviral vector system in vitro," he went on, "we were able to deliver genes to more than 95 percent of normal human macrophages.
"From our point of view, it's an important tool with which to examine, and hopefully identify, key molecules in those cells. In the future they could become targets for new drugs or new therapeutic entities or modalities to treat RA. That's our real thrust.
"The big problem with macrophages," Foxwell explained, "is to introduce foreign genes so you can actually manipulate their function. People have tried it and have had some success, but what we've done is get nearly all cells — close to 100 percent."
He surmised macrophages resist accepting DNA sequences because they are programmed to oust intruders by phagocytosis and thus might degrade DNA.
Foxwell described how he and his co-authors went about their TNF search-and-destroy mission.
"As described in the paper," he recounted, "we asked the question a lot of people have skirted around: 'Is NF-kB — which is a DNA transcription factor that controls protein expression — important for expression of the inflammatory cytokine TNF? Or is it not?'"
Treatment Achieves 75 Percent TNF Inhibition
In the laboratory, the Hammersmith group asked that question of primary human macrophages, not cell lines or tumor cells. They also used their gene transfer technique in fresh, human rheumatoid synovial joint tissue, obtained from hip or knee replacement surgery.
The PNAS report stated that in spontaneous production of TNF from human rheumatoid joint cultures, the team achieved 75 percent inhibition, "indicating that the NF-kB pathway is an essential step for DNA synthesis in synovial macrophages, and. . . should be an effective therapeutic target in this disease."
"Therefore," Foxwell said, "we've come to the basic conclusion that NF-kB is indeed important in stimulating TNF. Not only in primary human cells, but even when you apply IkB* to diseased tissue, you see TNF suppression.
"So this finding," he pointed out, "would appear to validate NF-kB as a target for other forms of RA therapy. That's the implication."
In pursuit of that goal, Foxwell concluded, "There are many other molecules that we are now approaching in the same fashion, many sorts of kinases and mechanisms of control. And one can't disclose those." *