Cloning experiment shows cancer reversible

The results of a cloning experiment show that the body may have the ability to reverse cancer, U.S.-based researchers said on Saturday.

They cloned mouse embryos from a melanoma skin cancer cell, and created healthy adult mice using some of the cloned cancer cells, showing that malignancy is not the inevitable fate of a cancer cell.

"This settles a principal biological question," said Dr. Rudolf Jaenisch, of the Whitehead Institute at the Massachusetts Institute of Technology, one of the country's leading experts in cloning.

He said while the genetic elements of cancer cannot be reversed, the epigenetics - how the genes are actually turned on and off - can be.

The finding, published in the journal Genes and Development, point to a new way to treat cancer, said Lynda Chin of the Dana-Farber Cancer Institute and Harvard Medical School, who worked on the study.

"Drugs that target the cancer epigenome may prove to be a key therapeutic opportunity for diverse cancers," she said in a statement. In other words, it might be possible to silence a cancer gene.

Cancer begins when certain genes mutate, or when a certain, inherited version of a gene somehow gets turned on.

This can happen through various so-called epigenetic processes - when other molecules in a cell affect genes without actually altering the sequence of DNA.

In the experiment, Konrad Hochedlinger and Robert Blelloch, both researchers in Jaenisch's lab, took the nucleus from a melanoma cell and injected it into a hollowed-out mouse egg cell.

This started the egg growing as if it had been fertilized by sperm.

They did not allow this embryonic mouse to develop, but harvested from it embryonic stem cells - immature cells that have the potential to become any cell in the body at all.

They put these stem cells into healthy mouse blastocysts - very early embryos only a few days old. Some of these developed into healthy, normal mice.

"It's important to note that the stem cells from the cloned melanoma were incorporated into most, if not all, tissues of adult mice, showing that they can develop into normal, healthy cells," Blelloch said. They included skin pigmentation cells, immune cells and connective tissue.

This could only have happened if the cancer cells had lost their malignant properties, at least temporarily, the researchers said.

But when certain cancer-related genes in these mice were activated, they developed malignant tumors at a much faster rate than normal mice, the researchers added.

Many researchers want to try similar experiments with human cancer cells, but the administration of President Bush forbids the use of federal funds for such study because it would involve the creation of what is technically a human embryo.