Brevetoxin derivatives that inhibit toxin activity

BACKGROUND

The brevetoxins are marine neurotoxins that interfere with the normal functions of the voltage-gated Na(+) channel. We have identified two brevetoxin derivatives that do not exhibit pharmacological properties typical of the brevetoxins and that function as brevetoxin antagonists.

RESULTS

PbTx-3 and benzoyl-PbTx-3 elicited Na(+) channel openings during steady-state depolarizations; however, two PbTx-3 derivatives retained their ability to bind to the receptor, but did not elicit Na(+) channel openings. alpha-Naphthoyl-PbTx-3 acted as a PbTx-3 antagonist but did not affect Na(+) channels that were not exposed to PbTx-3. beta-Naphthoyl-PbTx-3 reduced openings of Na(+) channels that were not exposed to PbTx-3.

CONCLUSIONS

Some modifications to the brevetoxin molecule do not alter either the binding properties or the activity of these toxins. Larger modifications to the K-ring sidechain do not interfere with binding but have profound effects on their pharmacological properties. This implies a critical function for the K-ring sidechain of the native toxin.

Comparison of annamycin to adriamycin in cardiac and MDR tumor cell systems

Based on the response of a wide variety of tumors to the anthracycline, Adriamycin, numerous studies have been initiated to find an even more effective analog. In this pursuit two of the obstacles that have been necessary to overcome are a unique dose dependent Adriamycin-induced cardiotoxicity reported in patients treated with this chemotherapeutic agent as well as p-gp-mediated multi drug resistance (MDR) which has been found in tumor cells exposed to Adriamycin in vitro and in vivo as well as in human tumor samples. Using an in vitro cardiac cell system and MDR+ and MDR- Friend leukemia cell lines we find that a relatively new anthracycline, Annamycin, has reduced cardiotoxic activity but is more effective in inhibiting the growth of MDR+ cells than Adriamycin. The reduced cardiotoxicity of Annamycin is approximately 10 fold lower than Adriamycin whereas the increased efficacy against the MDR+ Friend leukemia tumor cell line is about 2 fold. The observation that Adriamycin preferentially accumulates in cardiac-muscle (CM) but not in cardiac non-muscle (NM) cells while Annamycin accumulates equally in both, may explain in part the reduced cardiotoxicity of Annamycin. Moreover, the cytosolic accumulation of Annamycin vs the nuclear localization of Adriamycin suggests a different target site for each drug.

Pyridothiadiazinedioxides structurally related to quinazolinones cholecystokinin/gastrin receptor ligands: synthesis and biological evaluation

The synthesis of 3-aralkyl-4-aryl-4H-, 3-aralkylamino-4-aryl-4H- and 3-aralkylsulfanyl-4-aryl-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1, 1-dioxides is described. Moreover, the affinity of the different compounds towards the cholecystokinin CCK-A and CCK-B receptors was evaluated. For selected compounds, affinity on the two receptor subtypes was expressed in the micromolar range. This was comparable to the affinity observed with the naturally occurring CCK receptor antagonist asperlicin.

4H-1,2,4-Pyridothiadiazine 1,1-dioxides and 2,3-dihydro-4H-1,2, 4-pyridothiadiazine 1,1-dioxides chemically related to diazoxide and cyclothiazide as powerful positive allosteric modulators of (R/S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid receptors: design, synthesis, pharmacology, and structure-activity relationships

A series of 4H-1,2,4-pyridothiadiazine 1,1-dioxides and 2, 3-dihydro-4H-1,2,4-pyridothiadiazine 1,1-dioxides bearing various alkyl and aryl substituents on the 2-, 3-, and 4-positions was synthesized and tested as possible positive allosteric modulators of the (R/S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors. Many compounds were found to be more potent than the reference compounds diazoxide and aniracetam as potentiators of the AMPA current in rat cortex mRNA-injected Xenopus oocytes. The most active compound, 4-ethyl-2,3-dihydro-4H-pyrido[3,2-e]-1,2, 4-thiadiazine 1,1-dioxide (31b), revealed an in vitro activity on Xenopus oocytes not far from that of cyclothiazide, the most potent allosteric modulator of AMPA receptors reported to date. Moreover, 31b, but not cyclothiazide, was found to potentiate the duration and the amplitude of the excitatory postsynaptic field potentials induced by electric stimulation in rat hippocampal slices. Such an effect could indicate, for 31b, but not for cyclothiazide, a possible interaction with postsynaptic AMPA receptor binding sites located on hippocampal CA1 neurons. Structure-activity relationships indicated that the structural requirements responsible for a biological activity on AMPA receptors are different from those responsible for an inhibitory activity on the insulin releasing process (putative ATP-sensitive K+-channel openers). For instance, 31b and other related dihydropyridothiadiazines were found to be ineffective as inhibitors of insulin release from rat pancreatic B-cells, in contrast to diazoxide and known pyridothiadiazines reported as ATP-sensitive K+-channel openers. Conversely, the pyridothiadiazines active on B-cells were found to be ineffective as potentiators of the AMPA currents in Xenopus oocytes. Thus, 31b appeared to be more specific than diazoxide as an AMPA receptor modulator. This compound may be considered as a new pharmacological tool, different from diazoxide and cyclothiazide, for studying AMPA receptors. Moreover, 31b can also constitute a new therapeutic agent for the treatment of cognitive disorders.

Synthesis and biological evaluation of new 3-aralkylamino-2-aryl-2H-1, 2,4-pyridothiadiazine 1,1-dioxides as potential CCK-receptor ligands

A series of 2-aralkyl-4H-pyridothiadiazine 1,1-dioxides and 3-aralkylamino-2-aryl-2H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides structurally related to quinazolinone CCK receptor antagonists were synthesized and evaluated as CCK-A and CCK-B receptor ligands. The compounds were effective as cholecystokinin-ligands in the micromolar range of concentration, c.f. the cholecystokinin receptor antagonists asperlicin, lorglumide or benzotript, and were thus less potent than the best quinazolinones previously reported. Although the compounds were unsuitable for drug use, the work contributed to our understanding of the chemistry of unusual 2,3-disubstituted pyridothiadiazinedioxides.

Circumvention of P-GP MDR as a function of anthracycline lipophilicity and charge

From a number of studies it has been suggested that positive charge and degree of lipophilicity dictate, or at least influence, whether anthracyclines are recognized by the apparently clinical important mechanism of tumor cell resistance, i.e., P-gp-mediated multidrug resistance. Using a selected series of analogs in which lipophilicity and or positive charge are altered we find the following: (1) Positively-charged anthracyclines as compared to their neutral counterparts are better recognized by MDR+ cells. (2) With increasing lipophilicity charge becomes less important for MDR recognition. (3) In MDR+ cells with a resistance index to Adriamycin (ADR) of 4534, as compared to an MDR- parental line, almost all of the resistance is circumvented (resistance index = 3) with an anthracycline which does not contain a protonatable nitrogen and is highly lipophilic (partition coefficient, log p = > 1.99). (4) As lipophilicity is increased to log p > 1.99 and nuclear binding is decreased, anthracycline localization switches from nuclear to cytoplasmic which most likely indicates a different cytotoxic target and mechanism of action. (5) Cytoplasmically localized anthracyclines appear to distribute also in mitochondria which suggests these organelles as possible new anthracycline targets. In contrast, ADR shows no mitochondrial localization. (6) Photoaffinity analysis suggests that the highly lipophilic analogs, regardless of charge, interfere with NASV-Vp binding to P-gp. This is consistent with the idea that highly lipophilic anthracyclines act as modulators of MDR which may contribute to their mechanism of overcoming this form of resistance. The possible clinical significance of these data is that highly lipophilic anthracyclines are shown to circumvent MDR which most likely reflects their ability to localize in the cytoplasm and affect targets other than nuclear DNA, i.e., mitochondria, and to act as self modulators of MDR. Thus, a new approach to circumventing MDR and other mechanisms of resistance which involve nuclear targets is the use of active anthracyclines which are highly lipophilic and localize in the cytoplasm/mitochondria.

3-amino-3,4-dihydro-2H-1-benzopyran derivatives as 5-HT1A receptor ligands and potential anxiolytic agents. 2. Synthesis and quantitative structure-activity relationship studies of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans]

In continuation of our work on 3-amino-3,4-dihydro-2H-1-benzopyran derivatives with high affinity for 5-HT1A receptors, we have prepared rigid spirobenzopyran analogues designed from the pharmacophore models of Mellin and selected via a quantitative structure-activity relationship approach mainly based on similarity indices. A series of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans] with various substitutions on the aromatic ring as well as on the extracyclic spiranic nitrogen atom were then synthesized and evaluated for their serotonergic and dopaminergic activities. Good correlation between the predicted and the experimental binding values was observed with an average difference of 0.2 unit on log(IC50). Affinities for the 5-HT1A receptors were in the nanomolar range for the best compounds ((+)-11a,23) with a high selectivity versus other 5-HT (5-HT1B, 5-HT2, 5-HT3) or dopamine (D1, D2) receptor subtypes. As for the 3-amino-3,4-dihydro-2H-1-benzopyran series, the dextrorotatory enantiomer (+)-11a showed better affinity and selectivity for 5-HT1A receptors than its levorotatory analogue (-)-11a. Compound (+)-11a proved in vitro to be a full agonist and in vivo to be active in various comportmental tests predictive of psychotropic activity, such as the forced swim test and the tail suspension test, and is currently under complementary investigations.

3-and 4-substituted 4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides as potassium channel openers: synthesis, pharmacological evaluation, and structure-activity relationships

4-N-Substituted and -unsubstituted 3-alkyl- and 3-(alkylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides were synthesized and tested vs diazoxide and selected 3-alykl- and 3-(alkylamino)-7-chloro-4H-1,2,4-benzothiadiazine 1,1-dioxides as potassium channel openers on pancreatic and vascular tissues. Several 4-N-unsubstituted 3-(alkylamino)pyridothiadiazines and some 3-(alkylamino)-7-chlorobenzothiadiazines were found to be more potent than diazoxide for the inhibition of the insulin-releasing process. Moreover, the 3-(alkylamino)pyridothiadiazines appeared to be more selective for the pancreatic than for the vascular tissue. By means of the pharmacological results obtained on pancreatic B-cells, structure--activity relationships were deduced and a pharmacophoric model for the interaction of these drugs with their receptor site associated to the pancreatic K(ATP) channel was proposed. According to their selectivity for the B-cell (endocrine tissue) vs the vascular (smooth muscle tissue) ionic channel, selected 3-(alkylamino)-4H-pyrido[4,3-e]-1,2,4,-thiadiazine 1,1-dioxides may serve as pharmacological tools in studying the K(ATP) channels ("pancreatic-like" K(ATP) channels) in other tissues.

3,4-Dihydro-3-amino-2H-1-benzopyran derivatives as 5-HT1A receptor ligands and potential anxiolytic agents. 1. Synthesis and structure--activity relationship studies

A series of 3,4-dihydro-3-amino-2H-1-benzopyran derivatives were prepared in order to determine the necessary structural requirements for good affinity for 5-HT1A receptors and high selectivity versus other receptors. Modifications of the extracyclic amino substituents, the length of the alkyl side chains, and their substituents were explored. The best compounds (9g, 9k, 15b, 15d) possess imido or sulfonamido functional groups with a preferential length of four methylenes for the side chain. After resolution, the dextrorotatory enantiomers showed better affinity and selectivity for 5-HT1A receptors. These compounds have been proven to be full agonists. 9g and its enantiomers showed anxiolytic activity in vivo in various comportemental models. The compound (+)-9g is currently under clinical investigation.