Well, it turned out that the cancer cells began expressing a specific type of membrane protein within the membranes of those cancer cells. And what this membrane protein did was it used ATP to basically drive those molecules, the drugs, out of the cell. And it did that before the drugs could actually elicit their effects on the cancer cells. So these became known as MDR proteins or simply P glycoproteins. So actually they're not only proteins, they're glycoproteins because they have sugar components. So we see that multidrug resistance was shown to be a result of the expression of these membrane proteins that became known as multi drug resistant proteins.