BACKGROUND Breast cancer is a common disease found among women and has been a serious issue for last two decades. Although various kinds of heat shock proteins (Hsp's) have strong implications in cancer, heat shock protein 90 alpha (Hsp90α) has attracted highest attention for the cause and therapy of breast cancer. It regulates approximately 200 numbers of proteins known as client proteins including large number of oncoproteins found to be upregulated in many cancer cells. Therefore, inhibition of Hsp90α is a common therapeutic approach pursued in many cancers. However, Hsp90α inhibitors both natural and chemical, reported so far are plagued with problems related to toxicity, bioavailability and solubility including geldanamycin, the most common Hsp90α inhibitor. Therefore, search for a suitable Hsp90α inhibitor is an urgent need. HYPOTHESIS Here we hypothesize that Hsp organizing protein (HOP) helps in the interaction of Hsp90α with Hsp70, which is the key to appropriate chaperonin function of Hsp90α and therefore, inhibiting such interaction might lead to the disruption of Hsp90α-client protein complex, which in turn destabilize and degrade client proteins. We further hypothesize that considering the residues involved in the reaction we can design novel peptide based Hsp90α inhibitor. EXPERIMENTAL DESIGN In our present in silico investigation, we hypothesized that the chaperone function of Hsp90α requires the complex formation with HOP and co-chaperones Hsp70, Hsp40. We performed the docking interaction between Hsp90α and HOP. Based on the key residues involved in the interaction between Hsp90α and HOP, we designed ten peptides having twelve amino acids each. We docked the designed peptides with Hsp90α using docking software Hex 6.1 and the peptide with the highest binding energy value was identified. Using the online FOLDAMYLOID program, we assessed their amyloidogenic propensity. Amylodegenic properties were also considered and based on that five different peptides were again redesigned. Several modifications incorporated onto the peptide led to the design of five different peptides. RESULTS The peptide with the lowest amyloidogenic properties and highest binding energy for Hsp90α was the criteria laid for selection as an Hsp90α-inhibitor. Its potential to bind Hsp90α and disrupt Hsp90α-HOP complex was subsequently investigated using both wild as well as mutant p53 as a client protein. CONCLUSION The predicted binding energy values showed that our designed novel peptide demonstrated strong binding affinity for Hsp90α. Subsequently, the binding affinity of Hsp90α for mutant p53 was shown to be reduced substantially indicating a strong inhibitory potential of the designed peptide PEP73 (INSAYKLKYARG) for Hsp90α.