Amos, you messed up Mom's front page with all of that unwrapped text a few messages back! What were you thinking?

Many chemotherapy drugs work by interfering with the cell-division cycle. The drugs reach healthy cells and cancer cells alike, but they do most of their damage to the cancer cells. Unfortunately, some types of healthy cells divide as rapidly as cancer cells and are badly damaged as well. Such cells are found in bone marrow, the lining of the digestive tract, and hair follicles, so chemotherapy patients often lose their hair and are susceptible to infection. The damage to healthy cells limits the drug dose that a patient can tolerate and therefore limits the treatment's effectiveness.

Yoram Palti, of the Technion–Israel Institute of Technology in Haifa, and his colleagues have demonstrated another way to disrupt cell division: alternating electric fields with intensities of just 1–2 V/cm. The fields they use, with frequencies in the hundreds of kilohertz, were previously thought to do nothing significant to living cells other than heating them. But Palti and colleagues have conducted a small clinical trial showing that the fields have an effect in slowing the growth of tumors.1

In studies of tumor cells in vitro, Palti and colleagues observed two distinct effects, both of which depend on the direction of cell division with respect to the applied field.2 First, they found that cells in the electric field take longer than usual to divide, as shown in figure 1a. Second, they found that dividing cells sometimes disintegrate just before the division process is complete, as shown in figure 1, panels b and c. They offer an explanation for each effect.

The researchers suggest that cell division is slowed because the electric field hinders the formation and function of the mitotic spindle, the structure that guides the newly replicated chromosomes as they separate into the two daughter cells. The mitotic spindle is made up of microtubules, formed by the polymerization of dimers of the protein tubulin. (Microtubules and other cellular structures are illustrated in PHYSICS TODAY, September 2006, page 80.)

The tubulin dimers and polymers have large dipole moments, so they are affected by the electric field. But most other biochemical processes also involve polar molecules and structures, and small oscillating electric forces don't appear to have much of an effect on them. The difference, says Palti, is that when the tubulin dimers assemble into the mitotic spindle, they all line up in the same direction. If that direction happens to be orthogonal to the direction of the electric field, the microtubules are less likely to function normally.

That looks better, but it's too late for the page now. These 50 will always be out of whack once we move onto the next 50. Be more careful next time!