CHICAGO --A downtown arts festival is losing a sponsor.Crain's Chicago Business says the Bank of America is dropping the LaSalle Bank's sponsorship of Looptopia. That may force organizers of the all-night, downtown arts festival to cut some costs and scramble to reach their fundraising goals. LaSalle was the primary corporate sponsor of the first Looptopia last year. LaSalle was then bought by Bank of America. This year, Looptopia starts May 2.