The article describes the structural analysis of P-glycoprotein (Pgp), a key enzyme involved in multidrug resistance (MDR) in cancer treatment. Pgp is known for its broad substrate specificity, capable of recognizing and transporting hundreds of chemically unrelated toxins. The x-ray structure of apo-Pgp at 3.8 Å resolution reveals an internal cavity of approximately 6,000 ų, with two nucleotide binding domains (NBDs) separated by about 30 Å. Two additional structures of Pgp complexed with cyclic peptide inhibitors show distinct drug binding sites within the internal cavity, capable of stereo-selective binding based on hydrophobic and aromatic interactions. The inward-facing conformation of Pgp, which is competent for drug binding, is characterized by two portals open to the cytoplasm and the inner leaflet of the lipid bilayer. This structure provides insights into the molecular basis for Pgp's poly-specific drug binding and its role in MDR. The study also highlights the potential for designing anticancer drugs and MDR inhibitors by understanding the structural mechanisms of Pgp.The article describes the structural analysis of P-glycoprotein (Pgp), a key enzyme involved in multidrug resistance (MDR) in cancer treatment. Pgp is known for its broad substrate specificity, capable of recognizing and transporting hundreds of chemically unrelated toxins. The x-ray structure of apo-Pgp at 3.8 Å resolution reveals an internal cavity of approximately 6,000 ų, with two nucleotide binding domains (NBDs) separated by about 30 Å. Two additional structures of Pgp complexed with cyclic peptide inhibitors show distinct drug binding sites within the internal cavity, capable of stereo-selective binding based on hydrophobic and aromatic interactions. The inward-facing conformation of Pgp, which is competent for drug binding, is characterized by two portals open to the cytoplasm and the inner leaflet of the lipid bilayer. This structure provides insights into the molecular basis for Pgp's poly-specific drug binding and its role in MDR. The study also highlights the potential for designing anticancer drugs and MDR inhibitors by understanding the structural mechanisms of Pgp.