Drug developing startup Moderna Inc. (MRNA) - Get Report  has raised $604.3 million for an initial public offering running up to its Nasdaq debut Friday -- but trading was down from the start, falling 5% to $21.84 by noon.

The valuation is reportedly the largest for a biotechnology company since 2016. Moderna, which has no approved drugs yet, is working on personalized therapies for cancer and infectious and rare diseases.

The startup's IPO was priced on Thursday at $23 for a total of nearly 26.3 million common shares. Trading of all the common stock began on the Nasdaq Global Select Market on Friday with the offering slated for closure on Dec. 11.

With more than 650 employees, Moderna has raised about $2.4 billion in investment from Merck, Fidelity Management and Research Company and other companies and venture and private equity firms since forming in 2010. 

Based in Cambridge, Massachusetts -- considered a hub of biotechnology research -- Moderna has several therapies and vaccines in early stage clinical trials, with at least one a stage 2 clinical trial. The company is investigating so-called messenger RNA therapeutics and vaccines that would in theory direct cells in patients' bodies to produce intracellular or secreted proteins that play a role in treating or preventing diseases such as Zika, Chikungunya, types of influenza, and various cancerous tumors such as those of the pancreas. Two of its drugs in development are being bankrolled by Merck.