Electra Therapeutics (ETRA) priced its upsized initial public offering of 23.3 million shares at $15 apiece for gross proceeds of about $350 million, the company said Thursday.

The underwriters were granted a 30-day option to purchase up to an additional 3.5 million shares at the public offering price, the company said.

The shares are expected to begin trading on Nasdaq on Friday under the ticker ETRA, with the offering expected to close Monday.