ABCB1 and melanoma: melanoma cells resistant to CHB due to GSTM1 and resistant to vincristine due to the synergy between GSTM1 and multidrug resistance protein 1;CAL1 human melanoma cells engineered to overexpress GSTM1 to study resistance to chlorambucil (via GSTM1) and vincristine (via GSTM1 synergy with MRP1)