Objective: This work explores the mode of action of PB28, MC70 and MC18 three molecules that showed anti-tumoral properties by arresting cellular growth and inhibiting glycoprotein P. Methods: Here we conduct a microarray-based study and analyze the expression patterns associated with the action of drugs. An ontology based analysis has been conducted, and the individuated cellular processes have been analyzed with gene networks, examining the interactions among genes. A clustering analysis revealed mechanisms shared with other drugs. Results: The results indicate that this compounds have side effects that include inflammatory response and fever, induced by the interleukin signaling pathway. Other evidences related with known effects of the compounds were highlighted. Conclusions: The results indicate that the direct effects could be reached at a post-transcriptional level of P-gp or through other targets, further studies will address these hypothesis. The prediction of side effects will be useful in subsequent in vivo experiments.