Adarx Pharmaceuticals Inc., a late-stage gene therapy developer, raised $446.3 million in an upsized initial public offering, pricing its shares at the top of its marketed range.

According to a statement on Thursday, the San Diego-based company, whose backers include OrbiMed Advisors, sold 26.25 million shares at $17 each.

The company's regulatory filings show that Adarx initially planned to offer 21.875 million shares at a price range of $15 to $17 each.

Based on the outstanding shares listed in the filings, this pricing values Adarx at approximately $1.8 billion.

Adarx is developing small interfering RNA (siRNA) drugs to treat a range of conditions, from eye diseases and kidney disorders to obesity and Alzheimer's disease.

These therapies address diseases at the genetic level while avoiding permanent changes to a patient's genome or DNA.

The company currently has three candidate therapies in clinical development and two others in preclinical stages.

According to its filings, for the six months ended June 30, Adarx reported collaboration revenue of $2.9 million and a net loss of $48.4 million, compared with collaboration revenue of $208,000 and a net loss of $33.6 million in the same period last year.