By David N. Leff
A person who goes in for a nose job comes out with a bill for rhinoplasty.
"Rhino," of course, means the nose. And "plasty" is the Greek word for "repair."
As the kerzillion cells in a human body undergo ceaseless division and multiplication, repair enzymes, found in every cell, bar none, stand by to do a job on any DNA that can't pass its quality control test.
Chimeriplasty is the name its inventors give to a new technology which dragoons those repair enzymes into altering genomic DNA to order. It deploys a synthetic double-helix molecule of DNA and RNA strands, with their sequence designed to match the target sequence, but with one exception: it introduces a single mismatch.
When such an obvious error pops up in the genome, the cell's repair machinery corrects the mismatch. This results in making the synthetic sequence, the chimeriplast, rewrite the new sequence of the genome.
An article in the March 1998 issue of Nature Medicine reports that "for the first time in medical history, alteration of genes within live animals can be efficiently accomplished by intravenous injection of a synthetic drug that targets and changes a preselected section of DNA."
Those are the words of clinical and research hepatologist Clifford Steer, the paper's senior author. The paper's title: "In vivo site-directed mutagenesis of the Factor IX gene by chimeric RNA/DNA oligonucleotides." Steer is a professor of medicine and cell biology at the University of Minnesota, Minneapolis.
The animals that received injections of the DNA-modifying chimeriplast into their tail veins were normal, healthy rats. The aim of the demonstrator-model treatment was not to cure them of some condition, but the contrary: To render the rats hemophilic by mutilating the gene encoding Factor IX in their blood-clotting cascade.
It did the job neatly and well.
The paper in Nature Medicine reported slowing down blood coagulation rates from 45 or 50 seconds to a sluggish clotting time of 90 seconds. And as Steer told BioWorld Today, "Since then, we've actually improved those frequencies up to 50 and 60 percent."
The package he and his co-authors injected, Steer explained, "was a very simple complex of two different components: The chimeric RNA/DNA molecule, compacted by a polymer vector, polyethylene amine, or PEI."
He continued: "The reason we had such high conversion from wild-type to mutant is that we tagged the PEI with a lactose disaccharide, galactose and glucose. There is a receptor on liver cells that recognizes the galactose molecule." Hence, the injection beelined for the liver, where it found and partially degraded the Factor IX gene.
"What we're hoping to do eventually," Steer observed, "is to cure hemophilia in human patients. Now that we've been able to induce it in rats, the next step is to cure it in a larger animal model." He is collaborating with a group at the University of North Carolina, Chapel Hill, that has a strain of dogs that express a single point mutation in the Factor IX gene, which means they have hemophilia B.
"Those studies are under way," Steer said, "and our preliminary isolating of hepatocytes from those hemophilic dogs is very encouraging. We've been able, in vitro, to convert from the abnormal mutant to the normal wild-type sequence of the Factor IX gene." He expects to initiate chimeriplast injections to the canine subjects "in the latter part of April."
Steer is lead inventor of a pending patent on the chimeriplast technology. It is held jointly by the University of Minnesota and Kimeragen Inc., of Newtown, Pa., to which the invention is licensed.
"The basis of the technology," said the company's president and CEO, Gerald Messerschmidt, "is the invention of molecular biologist and geneticist Eric Kmiec, who founded Kimeragen in 1996. (See BioWorld Today, Sept. 6, 1996, p. 1.)
The firm's chief scientific officer and president of its molecular pharmaceutical division is Michael Blaese, a founding father of modern gene therapy. He, together with W. French Anderson and Kenneth Culver, at the National Institutes of Health (NIH), in Bethesda, Md., on Sept. 14, 1990, infused genetically altered cells into the veins of a four-year-old girl with adenosine deaminase deficiency.
Now, Blaese is in transition between his laboratory at NIH and eventually moving full-time to his new post at Kimeragen.
Genes Corrected, Not Replaced
He pointed out that chimeriplasty "is distinct from gene therapy. We do not put genes into those cells," he pointed out. "The molecule itself is a drug that corrects the mutation, metabolizes and eliminates it from the cell. So it's a distinct process from gene therapy."
Steer is focusing on another disease besides hemophilia — a rare, horrendous, inherited liver disorder called Crigler-Najjar syndrome. Babies with the syndrome are born with an intensely yellow coloration.
"There are probably 300 patients known throughout the world," Steer observed, "and many more not identified. If the kids don't get therapy," he added, "they die. Intense light treatment degrades the bilirubin, which causes tremendous jaundice. And the bilirubin gets deposited in the brain and causes a neurological brain death called kernicterus. Ultimately, these patients will require a liver transplant.
"Crigler-Najjar is not caused by a point mutation," Steer observed. "It's a base that's actually gone, and has to be replaced. We've been successful in replacing it in an animal model — the Gunn rat — which exists in that particular disease state. Our results are encouraging and we hope to have data very soon. We'll be filing our first INDs [investigational new drug applications] by this fall."
Besides a broad spectrum of other diseases that are likely candidates for the technology, Blaese pointed to a separate opportunity now in the works — antimicrobial therapies. "This will be reported shortly in the literature," he noted. "It will have effects against bacteria and other microbes."
Blaese explained: "The DNA of microbes has sequences that differ from the DNA of humans. We can target those and alter a microbial gene that becomes lethal to the microbe, but would not cross-react with a human cell."
Then he came to the main payoff: "Many antibiotics kill off not only the bad bacteria but also some of the good bacteria. Our goal is to play a role in eliminating bacterial drug resistance." *