to be identified. Discovery that sildenafil inhibits phosphodiesterase-5 (PDE-5) proteins, for example, enabled this drug to be repurposed for pulmonary arterial hypertension treatment, since PDE-5 is expressed in pulmonary hypertensive lungs. Determination Microscopy-based methods Bioactive compounds induce phenotypic changes in target cells, changes that are observable by microscopy and that can give insight into the mechanism of action of the compound. With antibacterial agents, the conversion of target cells to spheroplasts can be an indication that peptidoglycan synthesis is being inhibited, and filamentation of target cells can be an indication that PBP3, FtsZ, or DNA synthesis is being inhibited. Other antibacterial agent-induced changes include ovoid cell formation, pseudomulticellular forms, localized swelling, bulge formation, blebbing, and peptidoglycan thickening. In the case of anticancer agents, bleb formation can be an indication that the compound is disrupting the plasma membrane. A current limitation of this approach is the time required to manually generate and interpret data, but advances in automated microscopy and image analysis software may help resolve this. Direct biochemical methods Direct biochemical methods include methods in which a protein or a small molecule, such as a drug candidate, is labeled and is traced throughout the body. This proves to be the most direct approach to find target protein that will bind to small targets of interest, such as a basic representation of a drug outline, in order to identify the pharmacophore of the drug. Due to the physical interactions between the labeled molecule and a protein, biochemical methods can be used to determine the toxicity, efficacy, and mechanism of action of the drug. Computation inference methods Typically, computation inference methods are primarily used to predict protein targets for small molecule drugs based on computer based pattern recognition. However, this method could also be used for finding new targets for existing or newly developed drugs. By identifying the pharmacophore of the drug molecule, the profiling method of pattern recognition can be carried out where a new target is identified. This provides an insight at a possible mechanism of action since it is known what certain functional components of the drug are responsible for when interacting with a certain area on a protein, thus leading to a therapeutic effect. Omics based methods Omics based methods use omics technologies, such as chemoproteomics, reverse genetics and genomics, transcriptomics, and proteomics, to identify the potential targets of the compound of interest. Reverse genetics and genomics approaches,