BOSTON — Six pioneering women are speaking at an International Women's Day celebration in downtown Boston.The Thursday event is being organized by 261 Fearless Inc., a women's running non-profit organization founded by Kathrine Switzer, the first woman to officially run the Boston Marathon.Switzer will join a panel discussion with four other women, including Ayanna Pressley, the first woman of color elected to the Boston City Council, and Zahra Arabzada, an Afghan student who founded "The Hijabi Runner" blog.