Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Highlights d Analysis of TRAP1 dynamics allows discovery of paralogselective allosteric inhibitors d Small molecules targeting TRAP1 revert TRAP1-dependent succinate dehydrogenase inhibition d Allosteric TRAP1 inhibitors abolish tumorigenic growth of neoplastic cells d Selective targeting of TRAP1 activity provides new antagonists of chaperones

Mitochondria are dynamic organelles that exchange a multiplicity of signals with other cell compartments, in order to finely adjust key biological routines to the fluctuating metabolic needs of the cell. During neoplastic transformation, cells must provide an adequate supply of the anabolic building blocks required to meet a relentless proliferation pressure. This can occur in conditions of inconstant blood perfusion leading to variations in oxygen and nutrient levels. Mitochondria afford the bioenergetic plasticity that allows tumor cells to adapt and thrive in this ever changing and often unfavorable environment. Here we analyse how mitochondria orchestrate the profound metabolic rewiring required for neoplastic growth.

We rationally designed allosteric compounds that stimulate Hsp90 ATPase activity and show anticancer potencies in the low micromolar to nanomolar range. In parallel, we clarified their mode of action and developed a quantitative model that links the dynamic ligand-protein cross-talk to observed cellular and in vitro activities. Our results support the potential of using dynamicsbased approaches to develop original mechanism-based cancer therapeutics.Heat Shock Protein 90 (Hsp90) is a chaperone that controls the folding of more than 200 client proteins and constitutes a central node in many signaling pathways [1] . Overexpression and dysregulation of Hsp90 have been linked with cancer and neurodegeneration. It is thus not surprising that this chaperone has become an important drug-target: in principle its inhibition can result in the simultaneous degradation of multiple clients associated with different pathological hallmarks [2] . Inhibitors targeting the N-terminal ATP-binding site have been developed and some reached clinical trials [3] . However, they all showed problems due to the induction of the HSF1 mediated heat shock response and of Hsp70 overexpression, leading to drug resistance and toxicity [3a-c, 4] .A viable alternative to interfering with Hsp90 is represented by allosteric ligands, which perturb the chaperone by targeting sites alternative to the ATP-site. Novobiocin was shown to inhibit Hsp90 by binding the C-terminal region without inducing the heat shock response. Based on this observation, a number of new derivatives with promising activities against a variety of cancers were developed [5] .Correspondence to: Giorgio Colombo. HHMI Author Manuscript HHMI Author Manuscript HHMI Author ManuscriptIn this context, we have developed a method for the identification of allosteric pockets via the analysis of residue-pair distance fluctuations in the structural ensemble around the active state of the chaperone. Such analysis unveiled an allosteric pocket at 65Å from the active site, located at the MD:CTD border in a region overlapping with the client binding site [6] . This facilitated the design of modulators showing promising anticancer activities and a novel molecular mechanism of perturbation of Hsp90 functions: the ligands in fact proved to be activators of closure kinetics and ATPase of the chaperone in vitro, induce cancer cell death, and interfere with client maturation. We developed a first Quantitative-Structure-DynamicsActivity-Relationship (QSDAR) model correlating the structures of an initial set of modulators to observed activation effects [6c] .Here, based on this initial model, we report the rational design of new allosteric ligands, reaching low micromolar to nanomolar anticancer activities, which supports their potential in the development of anticancer therapeutics. On the computational side, we further develop a model to evaluate the potency of allosteric modulators by taking into account the dynamic cross-talk that exists between the protein and the ligand.The conform...