PDT works via light- mediated energy transfer from a photosensitizer to cellular oxygen, forming free radical species that kill targeted microbes.

Now, PDT is being considered as a possible robust treatment for periodontal diseases, which are caused by the overgrowth of pathogenic microflora around teeth. The application of PDT to oral infections could prove to be a valuable alternative or supplement to traditional cleaning procedures and antibiotic therapy. New treatments are urgently needed in view of widespread drug resistance to antibiotics and the rising number of infections that recur after scaling and root planing.

Porphyrin photosensitizers show potential for use as PDT-active drugs. However, limitations have been observed in their effectiveness against some Gram-negative bacteria.

Peter Spacciapoli and colleagues at Periodontix, Inc. (Watertown, MA), recently proposed broadening the range of PDT activity of porphyrins by combining the photoreactive agent with a moiety that has higher affinity for bacterial cell surfaces. They designed a light-activated drug, denoted ce6-5K, composed of the porphyrin-type photosensitizer chlorin e6 conjugated to a bacteria-binding pentalysine (Antimicrob. Agents Chemother. 2000, 44, 3364– 3367).

In the presence of laser light, ce6-5K killed all 12 of the targeted Gram-positive and Gram-negative oral pathogens, whereas the parent molecule, chlorin e6, was active against only a few of the Gram-positive species.

Chlorin e6 derivatives that have been tested in clinical trials for cancer indications have shown no significant side effects. Thus, there is reason to believe that potent and selective agents such as ce6-5K are feasible options for treating patients with periodontal disease.