Depolarization and calcium entry in squid giant axons

1. Changes in ionized calcium in giant axons were followed by recording the light produced by injected aequorin.2. From the effect of injecting calcium buffers the internal concentration of ionized calcium was found to be about the same as in a mixture of 45 Ca EGTA:55 free EGTA, i.e. about 0.3 muM.3. After an axon had been exposed to cyanide for 50-100 min the velocity of the aequorin reaction increased about 500 times. This effect, which could be reversed rapidly by removing cyanide, was probably brought about by release of calcium from an internal store.4. Injecting 30 mumole ATP per litre of axoplasm into a cyanide-poisoned axon caused a transient lowering of light intensity; oligomycin blocked the effect.5. Raising external calcium or replacing external sodium by choline or lithium reversibly increased the light produced by axons injected with aequorin.6. Stimulation at 50-200 impulses/sec in a solution containing 112 mM-Ca caused the light intensity to increase to a new steady level; after stimulation the light intensity returned to its original level with a time constant of 10-30 sec. Similar but smaller effects were seen in solutions containing less external calcium. The recovery after stimulation is probably due to uptake of calcium by the internal store.7. Injecting 3 m-mole EGTA per litre axoplasm lowered the resting glow and abolished the aequorin response to stimulation.8. There was no light response to stimulation immediately after an axial injection of aequorin and the effect increased to a ;steady' level with a half-time of about 5 min. The conclusion is that the rise in calcium concentration resulting from stimulation is confined to the peripheral part of the axon and that the diffusion coefficient of aequorin in axoplasm is about 4 x 10(-7) cm(2)/sec.9. The increment in light per impulse often increased markedly during the course of a long experiment and there was also considerable variation between axons.10. If the light response to stimulation was small it was proportional to the frequency of stimulation; if large to the square of the frequency.11. Voltage-clamp experiments showed that the calcium entry associated with a depolarizing pulse could be divided into an early component which was abolished by tetrodotoxin (TTX), and a late component which was unaffected by this inhibitor.12. The time relations of the early calcium entry were consistent with its being a leak of calcium ions through the sodium channel; the permeability of the sodium channel to calcium was about 1% of the permeability to sodium.13. The late entry of calcium was little changed by injecting enough tetraethylammonium (TEA) to block the outward potassium current; it was greatly reduced by external concentrations of manganese which had little effect on the maximum potassium conductance.14. The voltage-response curve for the late entry of calcium had a well defined maximum and was similar in shape to the curve relating calcium entry to depolarization at the presynaptic ending (Katz & Miledi, 1969, 1970).

The effect of cyanide on the efflux of calcium from squid axons

1. The average rate constant for loss of (45)Ca from an unpoisoned squid axon was 1.8 x 10(-3) min(-1), corresponding to an efflux of 0.2 p-mole/cm(2) sec.2. The Ca efflux from unpoisoned axons was reduced if external calcium was replaced with magnesium, or external sodium with lithium, choline or dextrose. Replacing both sodium and calcium reduced the efflux to about 40%.3. Cyanide caused little immediate change in Ca efflux but after 1(1/2)-2(1/2) hr the efflux increased to 5-15 times its normal value. The effect was rapidly reversed when cyanide was removed.4. The large Ca efflux into cyanide was reduced by a factor of three when external calcium was replaced with magnesium and by a further factor of about six when external sodium was replaced with lithium.5. The Ca efflux from both poisoned and unpoisoned axons had a Q(10) of 2-3, was not affected by ouabain and was greatly reduced by injecting ethyleneglycol bis (aminoethylether)-N,N'-tetra-acetic acid (EGTA).6. After injecting (45)Ca along the axis, the efflux of calcium reached its maximum much more rapidly in a cyanide-treated axon than in an unpoisoned axon.7. Pre-treatment with cyanide greatly increased the rate at which calcium was lost from axoplasm extruded into flattened dialysis bags. A similar effect was observed when cyanide was applied after extrusion.8. Replacing external sodium glutamate with potassium glutamate greatly reduced the loss of (45)Ca from intact axons poisoned with cyanide but had little effect on the loss from extruded axoplasm.9. The rate constant for loss of the Ca EGTA complex was about 3 x 10(-5) min(-1) for intact axons and 2 x 10(-2) min(-1) for extruded axoplasm.10. A possible explanation of the cyanide effect is that, after poisoning, calcium ions are released from a store and can then exchange at a higher rate with external sodium or calcium.11. The experiments suggest that part of the calcium efflux may be coupled to sodium entry.12. Theoretical equations for ;diffusion and chemical reaction in a cylinder' are described in the Appendix.

Force measurements in skinned muscle fibres

1. Isometric force was measured in skinned segments of frog semitendinosus muscle fibres exposed to solutions in which the calcium ion concentration was controlled with EGTA.2. The threshold for force development, calculated from an apparent stability constant for the CaEGTA complex of 10(6.69)M(-1) at pH 7.0, was generally close to pCa 7.5. Maximum force was reached at about pCa 6.0.3. Maximum force is proportional to the cross-sectional area of the fibres.4. The rate of force development was slower than that expected from simple diffusion of a substance from the bathing solution into the fibre. The delay appears to be due to slow equilibration of the EGTA buffer system during calcium uptake by the sarcoplasmic reticulum.5. Addition of deoxycholate (DOC) to the bathing solution produced a reversible increase in the rate of force development. The steady force was also increased for values of pCa that gave less than maximum force, which shifted the force-pCa relation toward lower calcium concentrations by about 0.5 pCa unit.6. The length-force relation in partially activated preparations is similar to that reported for electrically activated intact fibres. This result suggests that in the region of myofilament overlap the affinity of the binding sites for calcium is uniform along the length of the calciumbinding myofilament.

The effect of calcium on the force-velocity relation of briefly glycerinated frog muscle fibres

1. Twitch fibres were isolated from the semitendinosus muscles of frogs. The sarcolemma was made more permeable by a 30 min soak in a solution containing 47.3% glycerine (v/v), 2 mM-EGTA and 10 mM phosphate buffer, pH 7. This was followed by a 30-60 min soak in a solution containing the non-ionic detergent Lubrol-WX. The fibres were then placed in a relaxing medium containing (in mM): KCl, 100; MgCl(2), 1; ATP, 4; EGTA, 2; imidazole buffer, 10; pH 7.0.2. A piece of fibre about 1-2 mm long treated as described in (1) was attached to a servo apparatus. This apparatus made it possible either to hold fibre length constant giving isometric conditions, or alternatively to hold the force constant while measuring isotonic length changes. A special network made it possible to switch control from isometric to isotonic conditions so that afterloaded contractions with a shortening stop could be carried out.3. Contractions were induced at about 4 degrees C by lowering the pCa in the relaxing solution to various levels determined by the ratio of calcium and EGTA added. Contractions were never observed above pCa 7. The steady force generated reached a maximum over the range of pCa 6.09 to 5.49. The relationship between steady force generated and pCa is S-shaped and very steep, implying that multiple interacting binding sites for calcium are involved in the force generating process.4. The relative force-velocity relation is the same at pCa 6.09 and 5.49 where the steady force is at a maximum. The data points can be well fitted by a hyperbola in which the extrapolated value for V(max) is 2.39 muscle lengths/sec. The values obtained for the Hill parameters a/P(0) and b are within the range of those reported for living electrically excited frog muscle.5. The relative force-velocity points obtained at higher pCa values at which the steady force was on average 37% of that developed at pCa 5.49 can also be fitted by a hyperbola. However, the extrapolated value for V(max) is only 1.12 muscle lengths/sec. The value for a/P(0) is increased slightly and the value for b is markedly decreased.6. Evidence is presented against the possibility that an unrecognized fixed internal load is responsible for the change in the relative force-velocity relation obtained at high pCa.7. The relative force-velocity relation does not change appreciably over at least part of the range of sarcomere lengths in which the force generated varies linearly with overlap provided the pCa is held constant.8. The results support the view that lowering the pCa produces a mechanical state equivalent to that produced by tetanic electrical stimulation.9. Some models for calcium activation are discussed. It is concluded that a model based on calcium binding to troponin on the thin filaments is difficult to reconcile with all of the experimental evidence. There is additional evidence for believing that activating calcium may directly influence the cross-bridges.

Bimoclomol: a nontoxic, hydroxylamine derivative with stress protein-inducing activity and cytoprotective effects

Preservation of the chemical architecture of a cell or of an organism under changing and perhaps stressful conditions is termed homeostasis. An integral feature of homeostasis is the rapid expression of genes whose products are specifically dedicated to protect cellular functions against stress. One of the best known mechanisms protecting cells from various stresses is the heat-shock response which results in the induction of the synthesis of heat-shock proteins (HSPs or stress proteins). A large body of information supports that stress proteins--many of them molecular chaperones--are crucial for the maintenance of cell integrity during normal growth as well as during pathophysiological conditions, and thus can be considered "homeostatic proteins." Recently emphasis is being placed on the potential use of these proteins in preventing and/or treating diseases. Therefore, it would be of great therapeutic benefit to discover compounds that are clinically safe yet able to induce the accumulation of HSPs in patients with chronic disorders such as diabetes mellitus, heart disease or kidney failure. Here we show that a novel cytoprotective hydroxylamine derivative, [2-hydroxy-3-(1-piperidinyl) propoxy]-3-pyridinecarboximidoil-chloride maleate, Bimoclomol, facilitates the formation of chaperone molecules in eukaryotic cells by inducing or amplifying expression of heat-shock genes. The cytoprotective effects observed under several experimental conditions, including a murine model of ischemia and wound healing in the diabetic rat, are likely mediated by the coordinate expression of all major HSPs. This nontoxic drug, which is under Phase II clinical trials, has enormous potential therapeutic applications.

Polyimides as biomaterials: preliminary biocompatibility testing

A number of commercially available polyimide materials were evaluated in vitro using a selected battery of levels I and II testing protocols prescribed by the National Institutes of Health Guidelines for Blood-Material Interactions. These procedures consisted of electron spectroscopy for chemical analysis and contact angle characterization surface studies, and protein adsorption, cell culture cytotoxicity, clotting time and haemolysis biocompatibility testing. The polyimide surfaces were invariant from the bulk composition with 60-80% C, 10-20% O and 2-5% N, producing advancing contact angles in the hydrophobic range (80-100 degrees). Consequently, they adsorbed significant amounts of albumin (2-3 micrograms/cm2) and fibrinogen (0.5-0.8 microgram/cm2). The polyimides also displayed an insignificant level of cytotoxicity and haemolysis, and clotting times ranged from 63 to 98% of normal. These clotting times and haemolytic index values were intermediate between the values observed for Teflon and Silastic controls. These factors, along with the strong adherence of polyimides to metal oxide substrates, indicate that polyimide materials are good candidates for further testing as encapsulants for implantable biosensors.

Mobility and transport of magnesium in squid giant axons

1. The Mg content of axons obtained from Loligo forbesi averaged 6.4 +/- 0.8 m-mole/kg axoplasm.2. A small patch of radioactive (28)Mg injected into an axon broadened considerably. A similar patch of (45)Ca showed hardly any broadening. The self-diffusion coefficient of Mg in axoplasm is about 2 x 10(-6) cm(2)/sec which is at least twenty times greater than that of Ca.3. Under the influence of an applied electric field Mg migrated towards the cathode. Its mobility was about half of that of Mg in free solution. This suggests that the concentration of ionized Mg in squid axoplasm is between 2 and 3 m-mole/kg axoplasm. The mobility of Mg was not changed by poisoning the axon fully.4. Mg influx and Mg efflux were roughly the same and equal to about 1 p-mole/cm(2) sec. Mg efflux was reduced by poisoning with cyanide and by replacement of external Na by choline. Removal of external K or Ca had little effect and removal of external Mg tended to increase the efflux.5. The dependence of Mg efflux on Na seems not to be secondary to changes in Ca because it persists in the absence of external Ca and in axons pre-injected with EGTA. The form of the dependence on Na ions approximates to a simple rectangular hyperbola.6. Replacement of external Na by Li or choline increased Mg influx. Mg influx was unaffected by cyanide.7. Mg efflux was reduced to an average of 15% by poisoning with cyanide or DNP. The efflux could be recovered by injection of ATP. Inhibition persisted in axons pre-injected with EGTA, showing that it is not secondary to a rise in Ca(i).8. During nervous activity there is an extra entry of Mg. For axons immersed in sea water this extra Mg entry per impulse is roughly the same as the extra Ca entry per impulse.

Small molecule-mediated directed differentiation of human embryonic stem cells toward ventricular cardiomyocytes

The generation of human ventricular cardiomyocytes from human embryonic stem cells and/or induced pluripotent stem cells could fulfill the demand for therapeutic applications and in vitro pharmacological research; however, the production of a homogeneous population of ventricular cardiomyocytes remains a major limitation. By combining small molecules and growth factors, we developed a fully chemically defined, directed differentiation system to generate ventricular-like cardiomyocytes (VCMs) from human embryonic stem cells and induced pluripotent stem cells with high efficiency and reproducibility. Molecular characterization revealed that the differentiation recapitulated the developmental steps of cardiovascular fate specification. Electrophysiological analyses further illustrated the generation of a highly enriched population of VCMs. These chemically induced VCMs exhibited the expected cardiac electrophysiological and calcium handling properties as well as the appropriate chronotropic responses to cardioactive compounds. In addition, using an integrated computational and experimental systems biology approach, we demonstrated that the modulation of the canonical Wnt pathway by the small molecule IWR-1 plays a key role in cardiomyocyte subtype specification. In summary, we developed a reproducible and efficient experimental platform that facilitates a chemical genetics-based interrogation of signaling pathways during cardiogenesis that bypasses the limitations of genetic approaches and provides a valuable source of ventricular cardiomyocytes for pharmacological screenings as well as cell replacement therapies.

Novel and versatile methodology for synthesis of cyclic imides and evaluation of their cytotoxic, DNA binding, apoptotic inducing activities and molecular modeling study

Versatile method has been developed for synthesis of N-substituted imides. Thus, acid anhydrides, imides and dicarboxylic acids were successfully subjected to dehydrative cyclization with substituted amines using DPPOx and Et(3)N to afford N-substituted imides under mild conditions. The DNA binding and apoptosis induction were investigated with regard to their potential utility as cytotoxic agents. Molecular modeling methods are used to study the cytotoxic activity of the active compounds by means of molecular and quantum mechanics.

2,2,2-Trichloro-N-({2-[2-(dimethylamino)ethyl]-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin- 5-yl}carbamoyl)acetamide (UNBS3157), a Novel Nonhematotoxic Naphthalimide Derivative with Potent Antitumor Activity

Amonafide (1), a naphthalimide which binds to DNA by intercalation and poisons topoisomerase IIalpha, has demonstrated activity in phase II breast cancer trials, but has failed thus far to enter clinical phase III because of dose-limiting bone marrow toxicity. Compound 17 (one of 41 new compounds synthesized) is a novel anticancer naphthalimide with a distinct mechanism of action, notably inducing autophagy and senescence in cancer cells. Compound 17 (2,2,2-trichloro-N-({2-[2-(dimethylamino)ethyl]-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-5-yl}carbamoyl)acetamide (UNBS3157)) was found to have a 3-4-fold higher maximum tolerated dose compared to amonafide and not to provoke hematotoxicity in mice at doses that display significant antitumor effects. Furthermore, 17 has shown itself to be superior to amonafide in vivo in models of (i) L1210 murine leukemia, (ii) MXT-HI murine mammary adenocarcinoma, and (iii) orthotopic models of human A549 NSCLC and BxPC3 pancreatic cancer. Compound 17, therefore, merits further investigation as a potential anticancer agent.

Synthesis of chalcone-imide derivatives and investigation of their anticancer and antimicrobial activities, carbonic anhydrase and acetylcholinesterase enzymes inhibition profiles

The new 1-(4-(3-(aryl)acryloyl)phenyl)-1H-pyrrole-2,5-diones (5a-g) were prepared from 4'-aminchalcones (3a-g) and screened for biological activities. All compounds (3a-g and 5a-g), except 3d and 3e displayed good cytotoxic activities with IC₅₀ values in the range of 7.06-67.46 μM. IC₅₀ value of 5-fluorouracil (5-FU) was 90.36 μM. Moreover, most of compounds 5a-g showed high antibacterial activity with 8-20 mm of inhibition zone (19-25 mm of Sulbactam-Cefoperazone (SCF)). In addition, they showed good inhibitory action against acetylcholinesterase (AChE), and human carbonic anhydrase I, and II (hCA I and hCA II) isoforms. Also, these compounds demonstrated effective inhibition profiles with Ki values of 426.47-699.58 nM against hCA I, 214.92-532.21 nM against hCA II, and 70.470-229.42 nM against AChE. On the other hand, acetazolamide, clinically used drug, showed a Ki value of 977.77 ± 227.4 nM against CA I, and 904.47 ± 106.3 nM against CA II, respectively. Also, tacrine inhibited AChE showed a Ki value of 446.56 ± 58.33 nM.

Bimoclomol, a heat shock protein co-inducer, acts by the prolonged activation of heat shock factor-1

The novel hydroxylamine derivative, bimoclomol, has been shown previously to act as a co-inducer of several heat shock proteins (Hsp-s), enhancing the amount of these proteins produced following a heat shock compared to heat shock alone. Here we show that the co-inducing effect of bimoclomol on Hsp expression is mediated via the prolonged activation of the heat shock transcription factor (HSF-1). Bimoclomol effects are abolished in cells from mice lacking HSF-1. Moreover, bimoclomol binds to HSF-1 and induces a prolonged binding of HSF-1 to the respective DNA elements. Since HSF-1 does not bind to DNA in the absence of stress, the bimoclomol-induced extension of HSF-1/DNA interaction may contribute to the chaperone co-induction of bimoclomol observed previously. These findings indicate that bimoclomol may be of value in targeting HSF-1 so as to induce up-regulation of protective Hsp-s in a non-stressful manner and for therapeutic benefit.

Characterization of a selective and potent antagonist of human P2X(7) receptors, AZ11645373

BACKGROUND AND PURPOSE

The ATP-gated P2X(7) receptor has been shown to play a role in several inflammatory processes, making it an attractive target for anti-inflammatory drug discovery. We have recently identified a novel set of cyclic imide compounds that inhibited P2X(7) receptor-mediated dye uptake in human macrophage THP-1 cells. In this study the actions and selectivity of one of these compounds, AZ11645373, were characterized.

EXPERIMENTAL APPROACH

We measured membrane currents, calcium influx, and YOPRO-1 uptake from HEK cells expressing individual P2X receptors, and YOPRO1 uptake and interleukin-1beta release from THP-1 cells in response to ATP and the ATP analogue benzoylbenzoyl ATP (BzATP).

KEY RESULTS

AZ11645373 up to 10 microM, had no agonist or antagonist actions on membrane currents due to P2X receptor activation at human P2X(1), rat P2X(2), human P2X(3), rat P2X(2/3), human P2X(4), or human P2X(5) receptors expressed in HEK cells. AZ11645373 inhibited human P2X(7) receptor responses in HEK cells in a non-surmountable manner with K (B) values ranging from 5 - 20 nM, with mean values not significantly different between assays. K (B) values were not altered by removing extracellular calcium and magnesium. ATP-evoked IL-1beta release from lipopolysaccharide-activated THP-1 cells was inhibited by AZ11645373, IC(50) = 90 nM. AZ11645373 was > 500-fold less effective at inhibiting rat P2X(7) receptor-mediated currents with less than 50% inhibition occurring at 10 microM.

CONCLUSIONS AND IMPLICATIONS

AZ11645373 is a highly selective and potent antagonist at human but not rat P2X(7) receptors and will have much practical value in studies of human cells.

Esterase-sensitive nitric oxide donors of the diazeniumdiolate family: in vitro antileukemic activity

We have designed a novel prodrug class that is stable in neutral aqueous media but releases bioactive nitric oxide (NO) on metabolism by esterase. Diazeniumdiolates of structure R(2)N-N(O)=N-OR', in which R' = Na, were reacted with BrCH(2)OAc to convert the spontaneously NO-releasing salts 1a (R(2)N = diethylamino) and 1b (R(2)N = pyrrolidino) to prodrugs 2a (AcOM-DEA/NO) and 2b (AcOM-PYRRO/NO), respectively, where R' = CH(2)OAc. In contrast to anions 1a and 1b (half-lives in pH 7.4 phosphate at 37 degrees C of 2 min and 3 s, respectively), 2a and 2b showed only minimal decomposition after 16 h under these conditions. Very rapid hydrolysis occurred in the presence of porcine liver esterase, however, with free anion 1a being observed as an intermediate in the esterase-induced generation of NO from 2a. The potential utility of this prodrug class is illustrated with a comparison of 1 and 2 as antiproliferative agents in NO-sensitive human leukemia cell lines HL-60 and U937. While the 72-h IC(50)'s for 1a and 1b (which generate NO throughout the medium) in HL-60 cell cultures were >600 microM, those of 2a and 2b were 8.3 and 6.4 microM, respectively. This result is consistent with our hypothesis that 2 is selectively hydrolyzed to 1 and thence to NO intracellularly. For U937 cells, the 72-h IC(50) for both 2a and 2b was 53 microM. By contrast, relatively high antiproliferative IC(50)'s (>100 microM in U937 cells) were observed for analogues in which R' = CH(2)CH(2)SC(O)Me, from which acetyl and 2-mercaptoethyl groups must be successively cleaved to free the NO-releasing diazeniumdiolate function. Within 24 h at initial concentrations of 50 microM, 2a and 2b induced apoptosis in 50% and 57% of the HL-60 cells, respectively (35% and 40% of the U937 cells, respectively). The data reveal significant in vitro antileukemic activity on the part of these novel compounds. Moreover, their substantial ease-of-handling advantages over the anionic diazeniumdiolates from which they are derived suggest their use as convenient agents for probing the biological roles of NO.

New Analogues of Amonafide and Elinafide, Containing Aromatic Heterocycles: Synthesis, Antitumor Activity, Molecular Modeling, and DNA Binding Properties

Amonafide- and elinafide-related mono and bisintercalators, modified by the introduction of a pi-excedent furan or thiophene ring fused to the naphthalimide moiety, have been synthesized. These compounds have shown an interesting antitumor profile. The best compound, 9, was 2.5-fold more potent than elinafide against human colon carcinoma cells (HT-29). Molecular dynamic simulations and physicochemical experiments have demonstrated that these compounds are capable of forming stable DNA complexes. These results, together with those previously reported by us for imidazo- and pyrazinonaphthalimide analogues, have prompted us to propose that the DNA binding process does not depend on the electronic nature of the fused heterocycle.

The effect of membrane potential on the mammalian sodium-potassium pump reconstituted into phospholipid vesicles

1. We have studied effects of electrical diffusion potentials on active Na+-K+ exchange in phospholipid vesicles reconstituted with pig kidney Na+, K+-ATPase. 2. Diffusion potentials, negative inside, were established using outwardly directed K+ gradients plus valinomycin or Li+ gradients plus a Li+ ionophore, AS701. Measurement of fluorescence changes of the carbocyanine dye DiS-C3-(5) showed that the ionophores generated potentials of the expected orientation and of sufficient stability for their effects on active transport to be assessed. Measurement of rates of passive 22Na+ fluxes, over a wide range of diffusion potentials, were consistent with the quantitative predictions of the constant-field flux equation. This result demonstrates that values of diffusion potentials calculated from the Nernst or constant-field equation are accurate. 3. In some conditions, the inside-negative potential (-130 to -180 mV) accelerated the rate of ATP-dependent Na+-K+ exchange on inside-out-oriented pumps, compared to 'control' without the ionophores. Reduction in the size of the diffusion potentials by addition to the medium of Li+ with AS701 or Cs+ with the valinomycin progressively annulled the acceleratory effects, consistent with these being true effects of a change in membrane potentials. 4. At saturating cytoplasmic Na+ and ATP concentrations, the diffusion potential accelerated ATP-dependent Na+-K+ exchange by up to about 30% compared to control but this effect disappeared at rate-limiting ATP concentrations (approximately 1 microM). 5. Using prior knowledge of rate-limiting steps, we interpret this finding to mean that the conformational transition E2(2K)----E12K associated with transport of two K+ ions is voltage insensitive while E1P(3Na)----E2P3Na associated with transport of three Na+ ions is voltage sensitive. The simplest explanation is that the net charge in the transport domain of the protein when no ions, 2K+ or 3Na+ are bound is -2, 0 and +1 respectively. 6. The accelerating effect of the negative-inside diffusion potential on Na+-K+ exchange is greater at limitingly low cytoplasmic Na+ concentrations than at saturating cytoplasmic Na+ concentrations. Cytoplasmic Na+ activation curves show that the diffusion potential increases the apparent cytoplasmic Na+ affinity and reduces the sigmoidicity of cytoplasmic Na+ activation. 7. A kinetic analysis reveals that this effect on apparent affinity is due to an increase in intrinsic Na+ binding and occurs in addition to the effect on a transport rate constant.(ABSTRACT TRUNCATED AT 400 WORDS)

A G-quadruplex-binding compound showing anti-tumour activity in an in vivo model for pancreatic cancer

We report here that a tetra-substituted naphthalene-diimide derivative (MM41) has significant in vivo anti-tumour activity against the MIA PaCa-2 pancreatic cancer xenograft model. IV administration with a twice-weekly 15 mg/kg dose produces ca 80% tumour growth decrease in a group of tumour-bearing animals. Two animals survived tumour-free after 279 days. High levels of MM41 are rapidly transported into cell nuclei and were found to accumulate in the tumour. MM41 is a quadruplex-interactive compound which binds strongly to the quadruplexes encoded in the promoter sequences of the BCL-2 and k-RAS genes, both of which are dis-regulated in many human pancreatic cancers. Levels of BCL-2 were reduced by ca 40% in tumours from MM41-treated animals relative to controls, consistent with BCL-2 being a target for MM41. Molecular modelling suggests that MM41 binds to a BCL-2 quadruplex in a manner resembling that previously observed in co-crystal structures with human telomeric quadruplexes. This supports the concept that MM41 (and by implication other quadruplex-targeting small molecules) can bind to quadruplex-forming promoter regions in a number of genes and down-regulate their transcription. We suggest that quadruplexes within those master genes that are up-regulated drivers for particular cancers, may be selective targets for compounds such as MM41.

A comparison of the effects of NN'-dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enrgy-linked reactions in mitochondria and submitochondrial particles

1. The effects of dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enzyme systems related to respiratory-chain phosphorylation were compared. Dicyclohexylcarbodi-imide and oligomycin A have very similar functional effects, giving 50% inhibition of ATP-utilizing and ATP-generating systems at concentrations below 0.8nmole/mg. of submitochondrial-particle protein. Aurovertin is a more potent inhibitor of ATP synthesis, giving 50% inhibition at 0.2nmole/mg. of protein. However, aurovertin is a less potent inhibitor of ATP-utilizing systems: the ATP-driven energy-linked nicotinamide nucleotide transhydrogenase is 50% inhibited at 3.0nmoles/mg. of protein and the ATP-driven reduction of NAD(+) by succinate is 50% inhibited at 0.95nmole/mg. of protein. 2. With EDTA-particles (prepared by subjecting mitochondria to ultrasonic radiation at pH9 in the presence of 2mm-EDTA) the maximum stimulation of the ATP-driven partial reactions is effected by similar concentrations of oligomycin A and dicylcohexylcarbodi-imide, but the latter is less effective. The stimulatory effects of suboptimum concentrations of dicyclohexylcarbodi-imide and oligomycin A are additive. Aurovertin does not stimulate these reactions or interfere with the stimulation by the other inhibitors. 3. Dicyclohexylcarbodi-imide and oligomycin A stimulate the aerobic energy-linked nicotinamide nucleotide transhydrogenase of EDTA-particles, but the optimum concentration is higher than that required for the ATP-driven partial reactions. Aurovertin has no effect on this reaction. 4. The site of action of dicyclohexylcarbodi-imide is in CF(0), the mitochondrial fraction that confers oligomycin sensitivity on F(1) mitochondrial adenosine triphosphatase.

PS-15: a potent, orally active antimalarial from a new class of folic acid antagonists

A new, orally-active inhibitor of dihydrofolic acid reductase (DHFR), PS-15 (N-(3-(2,4,5-trichlorophenoxy)propyloxy)-N'-(1-methylethyl)- imidocarbonimidic diamide hydrochloride), has significant activity against drug-resistant Plasmodium falciparum. It is not cross-resistant with other inhibitors of DHFR (e.g., pyrimethamine and cycloguanil). Although it bears similarities to proguanil, PS-15 represents a new antifolate class of drugs that we have named oxyguanils or hydroxylamine-derived biguanides. This compound displays intrinsic antimalarial activity and also is metabolized in vivo to WR99210, an extremely active triazine inhibitor of DHFR. When tested in vitro against drug-resistant clones of P. falciparum, PS-15 was more active than proguanil, and the putative metabolite, WR99210, was more active than the proguanil metabolite cycloguanil. The drug is also more active as well as less toxic than proguanil when administered orally to mice infected with P. berghei. When administered orally to Aotus monkeys infected with multidrug-resistant P. falciparum, PS-15 was more active than either proguanil or WR99210. In 1973, WR99210 underwent clinical trials for safety and tolerance in volunteers. The trials showed gastrointestinal intolerance and limited bioavailability; further development of the drug was abandoned. Because PS-15 has intrinsic antimalarial activity, is not cross-resistant with other DHFR inhibitors, and can be metabolized to WR99210 in vivo, oral administration of this new drug should circumvent the shortcomings and retain the advantages found with both proguanil and WR99210.