Paratek Pharmaceuticals Inc. garnered $22 million in the first tranche of its $40 million Series H financing round. The second and final tranche, worth the remaining $18 million, is expected to close in early 2008.

John Dunphy, vice president, chief financial officer and treasurer of Boston-based Paratek, said the company received "a lot of interest" from investors due to its focus on anti-infectives. In particular, investors like the fact that the anti-infective market is growing and clinical trials "are very defined" and can be completed quickly, he said.

Aisling Capital led the round, joined by new investors D.E. Shaw and Boston Life Science Venture Corp. Existing investors Nomura Phase4 Ventures, Novartis BioVentures, BioFund Ventures, HBM BioVentures, Lombard Odier Darier Hentsch, BioVeda Fund and Hercules Technology Growth Capital also participated. The second tranche will come from the same group of investors.

Pacific Growth Equities served as the placement agent for the financing.

The money raised should carry Paratek through the end of 2008. But by the middle of next year, the company hopes to complete a public offering, which is why the Series H goal was to attract both venture and cross-over investors, Dunphy said.

Paratek has raised $116 million to date, $76 million from venture investors (Series A, C, D, F and H rounds) and $40 million through equity investments by partners (Series B, E and G rounds).

Proceeds from the current round will be used primarily to complete ongoing Phase II trials with the tetracycline derivative PTK 0796. The trials compare oral and intravenous formulations of the drug to Zyvox (linezolid, Pfizer Inc.) for the hospital-based treatment of complicated skin and skin structure infections (cSSSI). Paratek expects to advance into Phase III trials for cSSSI and community-acquired pneumonia (CAP) by mid-20008.

Moving into the clinic next year is a derivative of PTK 0796 specifically designed for community settings. Like the original, the derivative will be broad-spectrum and will address many common bacteria as well as resistant strains such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococci and penicillin-resistant Streptococcus pneumoniae. But the derivative also is engineered to treat bronchitis, flu and other diseases commonly found in community settings, Dunphy said.

Paratek partnered PTK 0796 with Bayer AG in 2003, but the partnership dissolved in 2005 as Bayer turned its focus to other indications. Last year, Paratek licensed the worldwide rights to the community derivative to Merck & Co. Inc. in a deal worth up to $127 million. (See BioWorld Today, Sept. 16, 2003, and March 10, 2006.)

Other tetracycline antibiotics in Paratek's pipeline include an agent for C. difficile currently in the lead optimization stage and a narrow-spectrum acne product licensed to Warner Chilcott Co. and expected to enter the clinic next year.

Tetracycline antibiotics have been in use for about 50 years, but resistance issues have driven them out of favor in many indications. Dunphy said Paratek has been able to use its chemistry expertise to modify the tetracycline molecule at any position. "We know where the resistance is, and we can modify around it," he said.

Paratek also has modified tetracycline to strip away its antibiotic properties and focus on its anti-inflammatory effects. The company licensed a program in multiple sclerosis to Merck Serono SA, which should be starting clinical trials next year. Preclinical programs in rheumatoid arthritis and stroke are also in development, as is an early stage program for spinal muscular atrophy. (See BioWorld Today, Oct. 28, 2004.)

Beyond tetracyclines, Paratek has a preclinical program studying multiple adaptation response (MAR) inhibitors against multiple types of bacteria. MAR is responsible for kicking off bacterial defense mechanisms, and Dunphy said Paratek's program "doesn't kill the bacteria but prevents them from infecting the host," which should prevent resistance problems.

Although it has many programs in development, Dunphy said Paratek plans to hold on to rights to PTK 0796 for hospital-based treatment and doesn't have "any specific plans" to partner its internal preclinical programs. But as those early stage programs move forward, Paratek might look for partners, probably starting with the rheumatoid arthritis compound, he added.