Enanta Pharmaceuticals Inc. raised $18 million in Series E financing to further the development of macrolide antibiotics and immunosuppressants.

"We plan at least one additional closing, and the goal is to raise approximately $25 million," said Enanta President and CEO Spiros Jamas.

The Watertown, Mass.-based firm is developing improved versions of existing drugs through its Drug Morphing and Peptide Morphing chemistry technology.

Enanta plans to use the money to advance research and development by taking its macrolide antibiotic candidate based on erythromycin into Phase I studies and through Phase II trials, Jamas said.

"We have a very active program for respiratory infections," he said.

Jamas noted that there are a number of macrolides on the market, such as Abbott Park, Ill.-based Abbott Laboratories Inc.'s Biaxin (clarithromycin), which is a derivative of erythromycin.

"Erythromycin is a good starting point for this type of antibiotic," he said, noting that it has a very good safety record and has been on the market for about 50 years. "It is also used in pediatric populations quite frequently for ear infections, sinusitis and strep throat, and it has good oral availability."

Unfortunately, Jamas said, "bacteria are always learning new ways to resist antibiotics over time. We're always in a race to outwit the bacteria. We have insights into how the bacteria develop resistance as to what changes they make to themselves or to antibiotics to create resistance," he said.

Enanta started with the core structure of erythromycin, and, as with any macrolide, worked to improve its stability, efficacy and safety profile. The company expects to take the macrolide into clinical trials in early 2003, Jamas said, and will continue internal development until Phase II, when it hopes to partner the drug.

A similar approach is being taken by Enanta to cyclosporine A analogues (CsAs), which have an anti-inflammatory effect and can be delivered topically to the target organ, such as the lungs, skin or colon. In asthma, for example, the drug is inhaled and designed to treat severe and steroid-resistant asthma patients. Cyclosporine is a cyclic-peptide, and it also can be used to suppress the immune system, for example, to alleviate organ transplant rejection.

"One of the unique capabilities Enanta has is its cyclic-ring structure compounds," Jamas said. "They require fairly complex chemistry to handle and modify these compounds." The privately held company plans to take the CsAs through preclinical development and then seek a partner.

Jamas said the funding is expected to last the company through the next two years. Enanta has raised $43 million to date. The new funding also will allow it to add more positions, although Enanta has been busily adding staff for a while now.

"We still have some key hires to make, but [we're] tapering off," he said.