There is an optional overload for DataBinder.Eval to supply formatting:
<%# DataBinder.Eval(Container.DataItem, "expression"[, "format"]) %>
The format parameter is a String value, using the value placeholder replacement syntax (called composite formatting) like this:
<asp:Label id="lblNewsDate" runat="server" Text="<%# DataBinder.Eval(Container.DataItem, "publishedDate", "{0:dddd d MMMM}") %>"</label>