I have a dataset of RNA-seq samples for testing different drugs on the presence of another drug. One of my samples is the normal cells with no drugs (control negative) and another is the cells with just the base drug (control positive). All of the other samples are cells with the base drug and another testing drug. So, my question is how to do design a proper Design Matrix for comparing these samples. I can separately compare with control negative and control positive. But, my intention is to somehow neutralize the effect of one of the controls in all the samples and compare to the other one. Is that possible? How should I design the matrix?