By David N. Leff

Editor's note: Science Scan is a roundup of recently published biotechnology-relevant research.

A hole in the head is what many people - or their witch doctors - used to feel they needed. Anthropologists the world over have dug up thousands of human skeletal remains showing neat, round apertures in the skull that were obviously deliberate, not accidental. Even Hippocrates recommended trepanation for correcting certain lesions of the head. Further back in antiquity, this drastic surgery may have intended to drive out evil spirits that inflicted fits or migraine. The record shows that for many, if not most, trepanation cases, the operation was presumably a success - and the patient lived.

At the University of Michigan School of Dentistry, a number of laboratory rats have undergone trepanning of the skull at the hands of researchers bent on "trying to develop a gene therapy approach for regenerating bone." So said molecular biologist Renny Franceschi, of an investigative group at the school called the Center for Biorestoration of Oral Health. "We're 10 or 15 scientists," he told BioWorld Today, "trying to regenerate different kinds of tissues - bones, teeth, oral mucosa."

That's where half a dozen trepanned rats came in, as reported in the May 20, 2000, issue of Human Gene Therapy, under the title: "Gene therapy directed osteogenesis: BMP-7 transduced human fibroblasts from bone in vivo."

"We drilled a defect in the skulls of six rats," Franceschi, a co-author of the paper, told BioWorld Today, "put cells in, then closed the defect. Those cells were actually a gene delivery construct consisting of DNA sequences that expressed human bone morphogenic protein (BMP-7), inserted in an adenovirus vector. Our idea was that if we put these cells in, they'd be able to make enough of this BMP to recruit cells in the vicinity of the lesion, and make bones."

"The defects in the rats' skulls," he recounted, "were big enough, 1 or 2 centimeters in diameter, so they could not close by themselves. But within just four weeks this treatment was able to form new bone across the whole skull. It almost completely closed the wound, spanned the entire gap, and at least partially integrated with bone around it."

Franceschi explained: "The proteins start producing bone matrix with collagen, and mineralize it so it would actually form a vital bone. The new bone looks just like natural bone, with hard, outer, bony surface, spongy interior and marrow core."

In a separate set of ex vivo experiments, reported in the journal, the co-authors implanted engineered human gingival (gum) cells under the skin of mice unable to reject foreign tissue. To their surprise, the new bone that formed consisted of both murine and human cells. This suggests to them that the new cells were not only delivering BMP-7, but also responding to the protein, and themselves making bone - albeit at a subcutaneous site where no bone normally grew.

These results, Franceschi said, "raise the prospect of simpler, less painful bone grafts in human patients. Potential applications," he added, "would be any case where you would want to form new bone, such as long bones of limbs that won't heal by themselves, or cranial malformation as a result of trauma.

"Now," he pointed out, "orthopedic surgeons install plates or pins, or put in powdered bone to stimulate bone formation. With our genetic approach, we are trying to do the same thing, but hopefully more efficiently."

Franceschi and his co-authors at the School of Dentistry are planning to treat long-bone fractures in rats. "If it works at that stage," he predicted, "we'll probably go to dogs or primates, and if everything looks good, to clinical trials after that.

"We developed the initial idea of using AV vectors ex vivo as a way of delivering BMP," he observed, "and showed that the AV-BMP construct will also form bone when directly administered to animals at soft tissue sites. While still pursuing the ex vivo cell-based approach, where the viruses infect the cells in culture, we are now directly administering the virus to the animal in vivo. In both cases," Franceschi concluded, "we can get bone formation, and we have a paper in press on that in the Journal of Cellular Biochemistry."

Two Rare Genetic Disorders - Ataxia Telangiectasia, Nijmegen Breakage Syndrome - Share Symptoms

Ataxia telangiectasia (A-T) is a mercifully rare, but horrendously complex, recessive genetic disorder. By age 10, a child born with A-T is likely to be wheelchair-bound. Death intervenes in the victim's 20s. (See BioWorld Today, May 19, 1998, p. 1.)

Besides the slow degeneration of their brains' cerebellum, A-T patients - of whom only some 500 cases have been diagnosed in the U.S. - suffer immune deficiencies, heightened proneness to cancer, sterility and exquisite sensitivity to ionizing radiation, notably X-rays. All these afflictions trace back to a single mutated gene called ATM - "ataxia telangiectasia mutated." ATM resides on the long arm of human chromosome 11, and encodes ATM, one of the body's largest proteins.

Nijmegen breakage syndrome (NBS) has symptoms strangely similar to A-T, plus a congeries of other abnormalities, and is equally rare in occurrence. Its gene, NBS, lurks on the long arm of human chromosome 8, and expresses the protein nibrin, which is involved in repairing double-strand breaks in DNA. Among the striking similarities of ATM and nibrin is the increased breakage of their patients' chromosomes. Double-stranded DNA breaks are not unusual in healthy people. They are a necessary step in the embryonic formation of sperm and ova, as well as lymphocytes - immune-system cells. Normally, such breaks are routinely processed and mended. But A-T and NBS patients lack this DNA-repairing mechanism, which is thought to account for their protean symptoms.

Two papers back to back in Nature dated May 25, 2000, deal with the joined-at-the-hip similarities in these two maladies. Their authors found that the proteins produced by the genes of both diseases are essential for the successful repair of broken DNA strands. One article, from the University of Texas Health Science Center in San Antonio, bears the title: "Functional link between ataxia-telangiectasia and Nijmegen breakage syndrome gene products." The other report, by scientists at the Dana Farber Cancer Institute in Boston, is titled: "ATM phosphorylation of Nijmegen breakage syndrome protein is required in a DNA damage response."