Rhythm, a Boston-based biotechnology company developing peptide therapeutics that for metabolic diseases, has raised an additional $8 million to complete a $33 million Series B financing.

The additional $8 million comes from new investor, Pfizer Venture Investments, the venture capital arm of Pfizer. Pfizer joins existing investors MPM Capital, New Enterprise Associates, Third Rock Ventures and Ipsen, which all participated in a first closing of the Series B financing earlier this year.

Rhythm will use the proceeds to further develop its small-peptide therapeutics for metabolic diseases. RM-131 is a ghrelin agonist currently in phase II clinical trials for diabetic gastroparesis and GI functional disorders. RM-493 is a melanocortin 4 receptor (MC4R) agonist that is completing phase I clinical trials for the treatment of obesity and diabetes. This additional financing brings the total capital raised by Rhythm to $73 million.

"We are excited to have the support of Pfizer Ventures as we advance both metabolic programs through phase II trials," said Bart Henderson, co-founder and president of Rhythm. "The Pfizer team has deep commercial and development experience that we intend to leverage as we expand the clinical trial program for these two important new therapeutics."

Barbara Dalton, vice president of venture capital, Pfizer Venture Investments, said, "The obesity and diabetes epidemics represent one of the largest medical challenges confronting society today. Rhythm's metabolic programs are compelling because of the initial proof-of-concept data from ongoing clinical programs, along with the fact that peptide therapeutics have delivered high success rates in clinical development. We are pleased to help Rhythm capitalize on their opportunities."