By Jack Denton 

Crispr Therapeutics stock was tumbling Wednesday, after the results of an experimental treatment from the gene-based medicine specialist underwhelmed investors.

That is bad news for high-profile investor Cathie Wood, whose Ark Investment Management recently bought shares in the biotech company for two of its actively managed exchange-traded funds (ETFs).

The ARK Innovation ETF (ARKK) and ARK Genomic Revolution ETF (ARKG) cumulatively bought up hundreds of thousands of shares of Crispr (ticker: CRSP) in the week leading up to its release of trial data on its gene-edited cancer drug, CTX110.

Crispr said Tuesday that "encouraging" phase-one results of the drug meant the company planned to expand its trial, with the next stage potentially leading to data for submission to regulators for approval.

But investors appeared underwhelmed by the results, which showed that just 36% of the 26 patients who received the drug had a complete response with no detectable cancer.

Crispr stock was down 6% in U.S. premarket trading Wednesday, as investors fretted over how the drug may fare against competitors. Shares rose in rival gene-editing biotechs like Editas Medicine (EDIT), which was 0.3% higher in the premarket, and Allogene Therapeutics (ALLO), which ticked up 0.2%.

Leading up to the release of Crispr's results, Wood's investment group bought up more than 700,000 Crispr shares valued around $100 each, according to Cathie's Ark, a website tracking ARK trades.

ARKK snapped up more than 513,000 shares of Crispr in trades made Oct. 8, Oct. 11, and Oct. 12, while ARKG bought more than 201,000 shares in trades on Oct. 8 and Oct. 11, according to data from Cathie's Ark.

Ark's holdings in the biotech group represented a market capitalization of $7.8 billion based on the stock's closing price Tuesday of $102.59.

After stunning performances in 2020, when ARKK's net asset value (NAV) grew 152% and ARKG's NAV surged 180%, both funds have failed to match the performance in 2021. ARKK's NAV is up 5% so far this year, while ARKG's NAV has declined 0.8%.

Write to Jack Denton at jack.denton@dowjones.com