You can use a hidden field to bind..
write it below ur checkbox code.. this way..
<asp:checkbox id="chkbox1" runat="server" xmlns:asp="#unknown" />
<asp:hiddenfield id="HiddenB1" runat="server" xmlns:asp="#unknown" />
Write this in RowDataBound .cs
SAMPLEClass entity = (SAMPLEClass)e.Row.DataItem;
HiddenField Hidden1 = (HiddenField)e.Row.FindControl("Hidden1");
Hidden1.Value = entity.somecolumnvaluetobind.ToString();