U.S. stock index futures were slightly lower Wednesday morning.At around 02:25 a.m. ET, Dow futures dipped 43 points, indicating a negative open of more than 16 points. Futures on the S&P and Nasdaq were both marginally lower.The pre-market moves come as investors closely monitor Brexit developments. Officials and diplomats said that differences over the terms of the U.K.’s split from the European Union had narrowed significantly on Tuesday.It has raised hopes that a deal can be agreed by leaders at a key summit on Thursday. Sterling initially jumped above $1.28 on the news, a level not seen since late May, before paring gains as uncertainties remained.A crucial two-day summit of EU leaders begins in Brussels on Thursday. It is the last such meeting currently scheduled before the fast-approaching Brexit deadline.The world’s fifth-largest economy is due to leave the EU on October 31 and Prime Minister Boris Johnson has repeatedly insisted he will not request another delay.Elsewhere, China’s Foreign Ministry said Wednesday that it would take countermeasures against the U.S. in response to a bill that favors Hong Kong protesters.It comes less than 24 hours after the U.S. House of Representatives passed a bill that requests various government departments to consider whether political developments in Hong Kong require the U.S. to change the region’s special trading status.Data, earningsOn the data front, retail sales for September and a business leaders survey for October will be released at around 8:30 a.m. ET. Business inventories for August and the latest monthly survey from the National Association of Home Builders (NAHB) will follow slightly later in the session.In corporate news, Abbott Labs, Bank of America and U.S. Bancorp are among the major companies scheduled to report earnings before the opening bell.IBM, Netflix and CSX are among those expected to report their latest quarterly figures after market close.