Mechanism of antineoplastic activity of lonidamine

Lonidamine (LND) was initially introduced as an antispermatogenic agent. It was later found to have anticancer activity sensitizing tumors to chemo-, radio-, photodynamic-therapy and hyperthermia. Although the mechanism of action remained unclear, LND treatment has been known to target metabolic pathways in cancer cells. It has been reported to alter the bioenergetics of tumor cells by inhibiting glycolysis and mitochondrial respiration, while indirect evidence suggested that it also inhibited L-lactic acid efflux from cells mediated by members of the proton-linked monocarboxylate transporter (MCT) family and also pyruvate uptake into the mitochondria by the mitochondrial pyruvate carrier (MPC). Recent studies have demonstrated that LND potently inhibits MPC activity in isolated rat liver mitochondria (K(i) 2.5 μM) and cooperatively inhibits L-lactate transport by MCT1, MCT2 and MCT4 expressed in Xenopus laevis oocytes with K(0.5) and Hill Coefficient values of 36–40 μM and 1.65–1.85, respectively. In rat heart mitochondria LND inhibited the MPC with similar potency and uncoupled oxidation of pyruvate was inhibited more effectively (IC(50) ~7 μM) than other substrates including glutamate (IC(50) ~20 μM). LND inhibits the succinate-ubiquinone reductase activity of respiratory Complex II without fully blocking succinate dehydrogenase activity. LND also induces cellular reactive oxygen species through Complex II and has been reported to promote cell death by suppression of the pentose phosphate pathway, which resulted in inhibition of NADPH and glutathione generation. We conclude that MPC inhibition is the most sensitive anti-tumour target for LND, with additional inhibitory effects on MCT-mediated L-lactic acid efflux, Complex II and glutamine/glutamate oxidation

Identification of key binding site residues of MCT1 for AR-C155858 reveals the molecular basis of its isoform selectivity

The proton-linked monocarboxylate transporters (MCTs) are required for lactic acid transport into and out of all mammalian cells. Thus, they play an essential role in tumour cells that are usually highly glycolytic and are promising targets for anti-cancer drugs. AR-C155858 is a potent MCT1 inhibitor (K(i) ~2 nM) that also inhibits MCT2 when associated with basigin but not MCT4. Previous work [Ovens, M.J. et al. (2010) Biochem. J. 425, 523–530] revealed that AR-C155858 binding to MCT1 occurs from the intracellular side and involves transmembrane helices (TMs) 7–10. In the present paper, we generate a molecular model of MCT4 based on our previous models of MCT1 and identify residues in the intracellular substrate-binding cavity that differ significantly between MCT4 and MCT1/MCT2 and so might account for differences in inhibitor binding. We tested their involvement using site-directed mutagenesis (SDM) of MCT1 to change residues individually or in combination with their MCT4 equivalent and determined inhibitor sensitivity following expression in Xenopus oocytes. Phe(360) and Ser(364) were identified as important for AR-C155858 binding with the F(360)Y/S(364)G mutant exhibiting >100-fold reduction in inhibitor sensitivity. To refine the binding site further, we used molecular dynamics (MD) simulations and additional SDM. This approach implicated six more residues whose involvement was confirmed by both transport studies and [(3)H]-AR-C155858 binding to oocyte membranes. Taken together, our data imply that Asn(147), Arg(306) and Ser(364) are important for directing AR-C155858 to its final binding site which involves interaction of the inhibitor with Lys(38), Asp(302) and Phe(360) (residues that also play key roles in the translocation cycle) and also Leu(274) and Ser(278)

A new form of energy dissipation by a moving object in He II.

Despite the superfluid1 character of 4He below the lambda transition temperature, there are two distinct mechanisms by which an object moving through the liquid dissipates kinetic energy: (1) it can scatter the excitations (rotons, phonons, 3He isotopic impurities) that constitute the normal fluid component; and (2) for speeds in excess of the Landau critical velocity vL it can create rotons, apparently in pairs. The first process has been studied extensively, mostly by measurements of the zero-field mobilities of positive and negative ions. The second process, which is much rarer, has also been investigated in considerable detail by studies of the motion of negative ions in isotopically pure 4He at elevated pressures. Here, we report an attempt to extend the latter type of investigation to lower pressures. This yields unexpected results that can be accounted for satisfactorily only if we postulate the existence of a third dissipation mechanism

Vortex nucleation in ultradilute superfluid 3He/4He solutions.

A detailed investigation of vortex nucleation in He II containing traces of 3He isotopic impurity is reported. Systematic measurements of the nucleation rate due to negative ions were made at 23 bars. A model is proposed which, when fitted to the data, implies that a single 3He atom trapped on the surface of the ion has the dual effect of reducing the critical velocity for vortex nucleation by circa 4 m/s, while simultaneously increasing the corresponding rate constant by a factor of circa 10^3