Changes in net charge of glucocorticoid receptors by activation, and evidence for a biphasic activation kinetics

Recent advances in active targeting of nanomaterials for anticancer drug delivery

One of the challenges in cancer chemotherapy is the low target to non-target ratio of therapeutic agents which incur severe adverse effect on the healthy tissues. In this regard, nanomaterials have tremendous potential for impacting cancer therapy by altering the toxicity profile of the drug. Some of the striking advantages provided by the nanocarriers mediated targeted drug delivery are relatively high build-up of drug concentration at the tumor site, improved drug content in the formulation and enhanced colloidal stability. Further, nanocarriers with tumor-specific moieties can be targeted to the cancer cell through cell surface receptors, tumor antigens and tumor vasculatures with high affinity and accuracy. Moreover, it overcomes the bottleneck of aimless drug biodistribution, undesired toxicity and heavy dosage of administration. This review discusses the recent developments in active targeting of nanomaterials for anticancer drug delivery through cancer cell surface targeting, organelle specific targeting and tumor microenvironment targeting strategies. Special emphasis has been given towards cancer cell surface and organelle specific targeting as delivery of anticancer drugs through these routes have made paradigm change in cancer management. Further, the current challenges and future prospects of nanocarriers mediated active drug targeting are also demonstrated.

How successful is nuclear targeting by nanocarriers?

The nucleus is ultimately the final target for many therapeutics treating various disorders including cancers, heart dysfunction and brain disorders. Owing to their specialized cell uptake and trafficking mechanisms, nanoparticles (NPs) allow drug targeting where degradation sensitive therapeutics could be delivered to their target tissues and cell in active form and sufficient concentration. However, it has recently become increasingly obvious that cytosolic internalization of a drug molecule does not entail its interaction with its subcellular target and hence careful nanoparticle design and optimization is required to enable nuclear targeting. This review, discusses the barriers to NP nuclear delivery; crossing the cell membrane, endo/lysosomal escape, cytoplasmic trafficking and finally nuclear entry focusing on how NP synthesis and modification could allow for bypassing each of the aforementioned barriers and successfully reaching the nucleus. Examples of nuclear targeted NPs are also discussed, stressing on the critical aspects of nuclear targeting and pointing out how the disease state might change the normal NP path and how such change could be exploited to increase efficiency of nuclear targeting. Finally, the criteria set for the evaluation of nanocarriers for nuclear delivery are discussed highlighting that quantitative rather than qualitative evaluation is required to evaluate how successful nanocarriers for nuclear delivery are, particularly with regards to the amount of drug delivered and released in the nucleus.

Activation of glucocorticoid-type II receptor complexes in brain cytosol leads to an increase in surface hydrophobicity as determined by hydrophobic interaction chromatography

Hydrophobic interaction chromatography has been used to demonstrate an increase in the surface hydrophobicity of [3H]triamcinolone acetonide ([3H]TA)-labeled type II receptors in mouse brain cytosol following transformation of these receptor complexes to the activated DNA-binding form. After removing unbound [3H]TA and molybdate (which prevents activation) by gel filtration, [3H]TA-type II receptors were activated by incubation at 22 degrees C for 20 min. Gel filtration was then used to remove newly dissociated steroid and to readjust the molybdate and/or KCl concentration. Unactivated and activated receptors were then added to propyl, butyl, pentyl, hexyl, octyl, decyl, and dodecyl alkyl agarose, phenyl agarose, or unmodified agarose columns equilibrated and eluted with buffers of various molybdate and KCl concentrations and/or other additions, including glycerol, ethylene glycol, and urea. Under high-salt conditions, activated receptors were retained longer than unactivated receptors run on butyl, pentyl, hexyl, and phenyl agaroses. With the longer alkyl chain columns, essentially none of the [3H]TA was eluted in association with receptor macromolecules. Removal of the remaining steroid required receptor denaturation with urea. Under low-salt conditions, both receptor forms were retained more avidly on all alkyl agarose columns; however, on phenyl agarose only activated receptors displayed this increased retention. Further studies revealed that optimal separation and subsequent recovery of unactivated and activated [3H]TA-type II receptor complexes were achieved on pentyl agarose columns equilibrated and eluted with buffers containing 50 mM molybdate and 600-1,200 mM KCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Conformational and electrostatic properties of unoccupied and liganded estrogen receptors determined by aqueous two-phase partitioning

The technique of aqueous two-phase partitioning (ATPP) has been used to characterize conformational and electrostatic properties of unoccupied and liganded rat uterine estrogen receptors. The adaptation of the hydroxylapatite receptor assay with ATPP systems has permitted estrogen receptor (ER) partition coefficients to be accurately determined, even when the partitioning process results in significant loss of ER binding capacity. The pH and salt dependences of estrogen receptor partition coefficients indicate that the theory governing partitioning behavior can be accurately applied to partitioning data obtained with crude cytosols. This technique has revealed a ligand-induced change in the properties of the unoccupied receptor that precedes the process of heat-induced transformation in vitro. The difference in partitioning behavior between unoccupied and nontransformed estrogen receptor is observed in all combinations of buffers and salts tested and is of equal magnitude as the difference between partition coefficients of nontransformed and transformed ER. The partition coefficients of both unoccupied and nontransformed ER are constant over the ER concentration range in which binding cooperativity has been previously demonstrated. The combined effects of salt and pH on ER partition coefficients indicate a pI of approximately 5.5 for both unoccupied and nontransformed estrogen receptors. However, the partition coefficients at the pI differ. It is concluded that estradiol binding to its unoccupied receptor results in a change in surface properties of the ER monomer that is independent of receptor transformation and makes the receptor less hydrophobic.

Mechanism of action of an antiprogesterone, RU486, in the rabbit endometrium. Effects of RU486 on the progesterone receptor and on the expression of the uteroglobin gene

RU486 is a recently described antiprogesterone. In order to be able to understand its mechanism of action it is necessary to analyze its effect on a discrete gene product. We show here that the induction of uteroglobin mRNA by progesterone in the rabbit endometrium may be a suitable model for such studies since RU486 totally inhibits this effect without itself exerting any agonistic activity. Moreover, RU486, which does not bind to the estrogen receptor and is devoid of general antiestrogenic activity, partially inhibits the induction by estradiol of uteroglobin mRNA. Studies of the interaction between [3H]RU486 and the progesterone receptor have been undertaken with the aim of understanding the antagonistic effect of this compound. The binding to DNA-cellulose of heat-activated [3H]RU486-receptor complexes was slightly decreased (37%) when compared with that of the agonist [3H]R5020-receptor complexes (47%). Detailed analysis of this difference showed that it was due to both a decreased activation of complexes and to a diminished affinity of activated complexes towards DNA. The change in activation was shown by the fact that at high concentrations of DNA, where all activated complexes are bound, agonist-receptor complexes were bound to DNA in higher proportion than antagonist-receptor complexes. Moreover a difference was also observed when studying the binding of agonist-receptor and antagonist-receptor complexes to charged resins (phosphocellulose, DEAE-cellulose) which are known to discriminate between activated and non-activated complexes. Decreased affinity to DNA of antagonist-receptor complexes was shown by studying their binding at various concentrations of DNA, either in crude cytosol or after isolating a homogenous population of activated-receptor complexes by DNA-cellulose chromatography and by comparing the salt extraction from DNA-cellulose of agonist-receptor and antagonist-receptor complexes. Both effects (decreased activation and diminished affinity towards DNA) were relatively moderate and could account only for a small decrease in the agonistic activity of RU486. Thus, the fact that this compound is a complete antagonist without any agonistic activity can only be explained by a defect in some further step of hormone action as, for instance in the specific interaction with the regulatory regions of the uteroglobin gene. No immunological difference could be detected between [3H]R5020-receptor and [3H]RU486-receptor complexes, both interacted with the five monoclonal antibodies raised against purified R5020-receptor complexes.(ABSTRACT TRUNCATED AT 400 WORDS)

ATP-dependent activation of glucocorticoid-receptor complexes from the rat's heart

The effect of ATP on the cytosolic rat heart glucocorticoid receptor was studied by employing different methods for evaluation of the changes in molecular properties of the receptor, induced by activation. Incubation of triamcinolone acetonide labelled cytosol at 25 degrees C or with 10 mM ATP at 4 degrees C leads to the increase in the partition coefficient of the receptor in the aqueous dextran-polyethylene glycol two-phase system and also nuclear uptake of the complexes. The effect of ATP on the partition coefficient was more pronounced, compared with that of thermal treatment or dilution of the cytosol and totally inhibited by 10 mM sodium molybdate. The activating effect of ATP on the glucocorticoid-receptor complexes and sensitivity of this activation to sodium molybdate was also confirmed by DEAE-cellulose chromatography of cytosolic receptor preparations. The results suggest that ATP may be involved in the glucocorticoid receptor activation and through this regulates the translocation of complexes into the nucleus under in vivo conditions.

Lithium inhibits the cytolytic glucocorticoid effect on S49 mouse lymphoma cells

Cytolysis is the end point of receptor-mediated effects of glucocorticoids on S49 mouse lymphoma cells of wild-type. In the presence of 5 mM LiCl this effect of triamcinolone or dexamethasone was markedly delayed. The cytoprotective effect of Li+ against 10(-7) M triamcinolone acetonide was already manifest after 24 h of steroid incubation, and on the fifth day 50-fold more Li+-treated than control cells were viable. This effect of Li+ was not exerted through changes of the doubling time of the cells, and thus could not be ascribed to an overall reduction of protein- or RNA synthesis. Data on accumulation and effect of cyclic AMP indicated that the cytoprotective effect was independent on cyclic AMP. Furthermore Li+ did not affect the amount or affinity of glucocorticoid receptors in intact cells. By use of aqueous 2-phase partitioning and DNA-Sepharose binding of [3H]triamcinolone acetonide labelled cytosols we demonstrate that Li+ inhibits the in vitro salt-activation of the glucocorticoid-receptor complexes by 60-100%. The nuclear bound fraction of hormone-receptor complexes in intact cells at 37 degrees C was not affected by Li+. The data suggest that Li+ inhibits the cytolytic glucocorticoid effect by interacting with the hormone-receptor complexes.

Kinetic analyses of activation-induced changes in the hydrodynamic and surface properties of the glucocorticoid-receptor complex in mouse brain

Unactivated, molybdate-stabilized, [3H]triamcinolone acetonide-labeled, glucocorticoid receptors from mouse whole brain were activated by removal of the molybdate and incubation at 22 degrees C for 1.5 to 24 min and then rapidly quenched at 0 degrees C with molybdate. The loss of the 9.2 S (unactivated) form of the [3H]TA-receptor complex and the concomitant formation of the 3.8 S (activated) form displayed first-order kinetics with a half-time of less than two min. The increase in the 3.8 S form correlated nearly perfectly with an increased binding to DNA-cellulose, and with a decreased and increased adsorption to DEAE-cellulose and glass fiber filters, respectively. The changes in adsorption to these filters, which occurred at a faster rate than did the changes in binding to DNA-C, are thought to reflect an increase in the relative number of positive charges and hydrophobic groups on the surface of the activated complex.

Hydrodynamic and biochemical correlates of the activation of the glucocorticoid-receptor complex

Possible changes in the size and shape of the glucocorticoid-receptor complex (GRC) following activation remain poorly documented, due to the lability and possible activation of the receptor during the determination of these hydrodynamic parameters. In the present study molybdate was used to stabilize the GRC, thus preventing these uncontrolled transformations. Cytosol prepared from mouse whole brains was incubated for 18 h at 0-2 degrees C with [3H]triamcinolone acetonide (+/- molybdate). Activation was then initiated by incubation at 22 degrees C for variable times and quenched at 0 degree C by adding molybdate. The Stokes radius and sedimentation coefficient of the GRC declined from 77 A and 9.2 S before activation to 58 A and 3.8 S after activation. These measurements remained consistent after recycling GRC between sedimentation and gel filtration procedures and correspond to a 3-fold reduction in the relative molecular mass. The loss and formation of the 297 and 92 kDa species, respectively, after different durations of activation correlated nearly perfectly with increased binding of GRC to DNA-cellulose (DNA-C). The observed size change also correlated well with decreased adsorption to DEAE-cellulose filters (DE-81) and increased adsorption to glass fiber filters (GF/C). The increased adsorption to GF/C may reflect an increase in hydrophobicity which, with extended durations of activation, leads to increased aggregation and reduced binding to DNA-C, but not to a change in adsorption to DE-81. We propose that during activation the 297 kDa form of the GRC splits to form a 92 kDa species that displays an increased affinity for DNA.

Aqueous two-phase partition studies of glucocorticoid receptors exposed to limited trypsination

In a previous investigation the properties of glucocorticoid receptors exposed to partial proteolysis by chymotrypsin were studied by aqueous two-phase partitioning (Andreasen, P.A. and Gehring, U. (1981) Eur. J. Biochem. 120, 443-449). This paper describes studies of the properties of cytosolic glucocorticoid receptors submitted to limited trypsination, employing phase partitioning of rat thymocyte cytosol labelled with tritiated triamcinolone acetonide. Trypsin treatment of labelled cytosol at 0 degrees C does not result in any dissociation of steroid from the receptor. The partition properties of the trypsin-treated receptors exposed to receptor-activating conditions are indistinguishable from those of the activated native and chymotrypsin-treated receptors, although the trypsin-treated receptors have lost the affinity for DNA and dextran sulphate. Trypsin treatment of cytosol not exposed to receptor-activating conditions results in a rapid change in the receptor partition coefficients identical to that following chymotrypsin treatment. However, during incubations under conditions at which activation of native and chymotrypsin-treated receptors is very slow, the trypsin-treated receptor is converted to a form with partition properties indistinguishable from those of the activated receptors. During exposure of the cytosol to activating conditions, the time-course of the partition coefficient of the trypsin-treated receptors is only slightly different from that of the native and chymotrypsin-treated receptors, but the trypsin-treated receptors are far less susceptible to the activation inhibitors ATP, Li+ and MoO42-. We conclude that the proteolytic cleavages induced by trypsin in the non-activated receptor do not lead to any immediate changes in the charge and surface properties of the receptor different from those following chymotrypsin treatment, but that the trypsin-treated receptor is not able to maintain a non-activated state and a normal susceptibility to activation inhibitors.