UK's main FTSE 100 stock index opened slightly up on Wednesday led by pharmaceuticals and insurers, with the market outlook hinging on key economic data for expectations around interest rate cuts from the U.S. Federal Reserve.

The blue-chip FTSE 100 index was up 0.1% by 0710 GMT, after rising for the fourth straight session on Tuesday, while the domestically-focused mid-cap FTSE 250 was largely unchanged.

The pharma sector was up 0.4%, led by 2% gains in GSK. Delaware's highest court will hear an appeal by GSK and other drugmakers seeking to end over 70,000 lawsuits claiming discontinued heartburn drug Zantac caused cancer.

Direct Line Insurance rose 1.2%, boosting non-life insurers, after Citigroup upgraded the stock to "buy" from "neutral".

Meanwhile, Kingfisher dropped 2% to the bottom of the FTSE 100 after Citigroup downgraded the home improvement retailer's shares to "neutral" from "buy".

On the earnings front, Prudential fell 1% following its quarterly results, weighed by a slowdown in China and Indonesia businesses.

Caution also loomed ahead of Nvidia's quarterly results due after market close, as investors eagerly await the fate of the global AI-driven equity rally. Owing to its back-to-back blockbuster results, market participants have sharply ramped up their expectations for the chip giant.

Further, this week's U.S. Personal Consumption Expenditure data will also provide investors additional hints on the pace of likely Federal Reserve rate cuts.

(Reporting by Ankika Biswas in Bengaluru; Editing by Varun H K)