Molecular model of hexokinase binding to the outer mitochondrial membrane porin (VDAC1): Implication for the design of new cancer therapies Camillo Rosano National Institute for Cancer Research (IST), L.go Rosanna Benzi 10, 16129 Genova, Italy abstract article info Article history: Received 6 August 2010 Received in revised form 25 January 2011 Accepted 28 January 2011 Available online 20 February 2011 Keywords: Hexokinase VDAC1 Mitochondrial outer membrane permeabilization Protein modeling Docking simulations Apoptosis Cancer A key feature of many cancers is the capacity and the propensity to metabolize glucose to lactic acid at a very high rate even in the presence of oxygen. This characteristic was first discovered in 1924 by Otto Heinrich Warburg. Hexokinase, the first enzyme in the glycolytic pathway, not only improves the cell's energy supply in malignant cells, but also protects cancer cells against apoptosis through direct interaction with mitochondria and with the Voltage Dependent Anion Channel 1 (VDAC1). The rupture of HK:VDAC1 protein complex provides a therapeutic opportunity, as this association appears to protect tumor cells from mitochondrial outer membrane permeabilization, an event that marks the point of no return in multiple pathways leading to cell death. In the absence of a crystallographic structure and in order to perform an in silico screening of possible small molecules able to inhibit the protein association, we are presenting a computational model of HK-I:VDAC1 complex. It appears as evident how the first 15 N-terminal residues of HK-I interact with the inner part of the barrel of VDAC1 and not with the outside walls, within the mitochondrial membrane as previously believed. This finding is in agreement with the existence of a secondary ATP binding site in the same N-terminal region of HK-I which seems to have a crucial role in HK-I interaction with VDAC1. This evidence appears to be in accord also with the high levels of ATP that are found in cancer cells. Eventually such arrangements may contribute to stabilize the tertiary structure of VDAC1 while shielding from pro-apoptotic factor binding, protecting in a synergic way the tumoral cell from programmed death. © 2011 Elsevier B.V. and Mitochondria Research Society. All rights reserved. I think that only daring speculation can lead us further and not just accumulation of facts. Albert Einstein 1. Introduction Strategies to fight cancer have been created on the basis that this disease is caused by genetic alterations and, as a result, it can be treatable by reversing or targeting these changes. However, the clinical applications of this approach have been limited up to now. Tumors, in fact, are very complex and heterogeneous displaying a very high degree of robustness against therapeutic drugs. These character- istics render cancer a system able to keep its functionality despite any possible environmental change: heterogeneity indeed confers tumor cells elevated chances to grow and survive also in presence of various endogen and hexogen perturbations. Despite this complex array of genetic changes, all the cancer cells develop an alteration in the metabolism of oxygen which is not subjected to the genetic variability of tumors. The altered metabolism, characterized by an increased glucose uptake and elevated rate of glycolysis, was first recognized by Otto Warburg in the early '30s of last century. In this context, a potential point of fragility of cancer cells has been already identified (Bustamante and Pedersen, 1977; Bustamante et al., 1981; Pedersen et al., 2002). Different from most normal tissues in fact, cancer cell mitochondria show a very tight association between hexokinases (HKs) and a porin belonging to the mitochondrial outer mem- brane (MOM), the Voltage Dependent Anion Channel 1 (VDAC1) (Nakashima et al., 1986). This association, stabilizing the porin, protects the tumoral cells from MOM permeabilization (MOMP), a non-return point in the pathways leading to cell death (Ferri and Kroemer, 2001). VDAC1 acts as a gatekeeper for the entry and exit of mitochondrial metabolites, thus controlling the cross-talk between mitochondria and the cytosol (Blachly-Dyson and Forte, 2001) by switching between an “open” and a “closed” state. This control is important in both maintaining normal mitochondria respiration and triggering apoptosis when cytochrome c and other apoptogenic factors are released from the intermembrane space into the cytosol (Shoshan-Barmatz et al., 2006). VDAC1 also serves as a site for the docking of some cytosolic proteins, such as HKs, and it is recognized as a key protein in mitochondria-mediated apoptosis (Bernardi, 1998; Mitochondrion 11 (2011) 513–519 E-mail address: camillo.rosano@istge.it. 1567-7249/$ – see front matter © 2011 Elsevier B.V. and Mitochondria Research Society. All rights reserved. doi:10.1016/j.mito.2011.01.012 Contents lists available at ScienceDirect Mitochondrion journal homepage: www.elsevier.com/locate/mito