Werewolf Therapeutics, Inc. Werewolf Therapeutics (HOWL) was one of the market's biggest pre-market movers on Friday after announcing a merger with Ambros Therapeutics.

The rally — shares soared by about 75% in premarket trading — marks a dramatic turnaround for a biotech that spent much of this year exploring strategic options, including a sale. It also shines a spotlight on one of billionaire investor Israel Englander's lesser-known biotech holdings.

A $500 Million Deal

The all-stock transaction values San Diego-based Ambros at $500 million and assigns Werewolf an implied equity value of $47.5 million.

The companies also secured an oversubscribed $150 million private placement led by healthcare-focused investors, providing fresh capital to advance Ambros' lead drug candidate through late-stage development. Once the deal closes, the combined company will operate under the Ambros Therapeutics name, with existing Werewolf shareholders owning approximately 6.8% of the business.

The agreement culminates a process that began in February when Werewolf hired Piper Sandler to explore either a sale or a merger to boost shareholder value. After months of uncertainty, the market rewarded the outcome with one of the day's strongest biotech rallies.

Israel Englander Trimmed His Stake Before the Breakthrough

The merger also casts fresh light on Millennium Management's latest regulatory filing.

According to the firm's second-quarter Form 13F, billionaire Israel Englander reduced Millennium's position in Werewolf Therapeutics by 53%, leaving the fund with roughly 62,000 shares at the end of June. The reduction came before the merger announcement that ignited Friday's rally.

However, investors should be careful not to overinterpret that move. Form 13F filings are backward-looking snapshots that disclose holdings as of quarter-end and do not capture subsequent trading activity. Nor do they reveal why a fund increased or reduced a position. In other words, the filing provides context—but not a verdict on Englander's current view of the stock.

The bigger story is not that a billionaire investor trimmed a small biotech position. It's that Werewolf is off the block.

By combining with Ambros Therapeutics and securing $150 million in fresh capital, the Watertown, Massachusetts-based company expects to shift from a cash-constrained biotech to a better-funded, late-stage drug developer.