C# how to convert an object to Interface which from dymamic loaded dll

here are my question: --in x.dll version 1.0 we have logic:

IRunKCT iRun; = business as IRunKCT;
if (iRun != null)
{
    //dosomething
}

--now in x.dll version2.0(which is dymamic loaded by assembll) after I have got the object "business", how to convert it to "IRunKCT"?