Way more complex than "closed to out" or "open to out" conformation on DAT binding...

[Nagelfar]

Way more complex than "closed to out" or "open to out" conformation on DAT binding...

Novel C-1 Substituted Cocaine Analogs Unlike Cocaine
or Benztropine

apparently, they have been able to render C1 position analogues of cocaine that bind in an open-to-out fashion, but are non-stimulating like the closed-to-out kind. I edited WP with thus:

Final energy-minimized poses of the model hDAT/ligand complexes are shown in Fig. 8. After flexible docking, cocaine was oriented such that the protonated tropane amine faced the S1 site residues of TM1 and exhibited strong molecular interactions with residues Asp79 (via a hydrogen bond) and Phe76 (via a cation-pi interaction with the aromatic side chain of Phe76).

The 3-beta-benzoyloxy and 2-beta-carbomethoxy moieties were positioned toward TMs 3 and 8, enveloped by the side chains of residues Val152, Gly153, Tyr156, and Asn157, as well as Ser422 and Ala423 (Fig. 8A). The docking orientation of cocaine and the binding-pocket residues found were to be consistent with those reported by Beuming et al. (2008) in their docking model of cocaine at the DAT S1 site.

The docking model of 2 (1-methyl-cocaine) suggested that the analog binds in a similar manner as cocaine, with the extra methyl group oriented toward Asp79 and surrounding residues of TM1 (Ph76, Ala77, and Val78), but still readily accommodated within the binding pocket (Fig. 8B).

In contrast, the additional steric heft of the C-1 phenyl substituent of 6 (1-phenyl-cocaine) was not as readily accepted, and the compound adopted an entirely different binding orientation than cocaine and 2 (Fig. 8c). The extra C-1 phenyl group was positioned downward (toward the cytosolic vestibule), adjacent to the aromatic side chains of residues Phe76 and Phe326. In addition, the 3-beta-benzoyloxy moiety was oriented upward, slightly above the extra-cellular vestibule gating network residues Arg85, Phe320, and Asp476, enabling formation of a cation-pi interaction between the benzoyloxy aromic ring and Arg85

A=cocaine, B=C1-methyl-cocaine, C=C1-phenyl-cocaine & D=benztropine

(I really want to put an acetoxy group at C1!!!!! )

 

[serotonin2A]

It may have something to do with the kinetics of binding. The 1-substituted analogs may be preferentially interacting with the outward facing conformation but the residence time may not be long enough to produce locomotor stimulant effects. 1-Methylcocaine did induce a CPP, so it does have some degree of cocaine-like effects.

 

[Nagelfar]

It may have something to do with the kinetics of binding. The 1-substituted analogs may be preferentially interacting with the outward facing conformation but the residence time may not be long enough to produce locomotor stimulant effects. 1-Methylcocaine did induce a CPP, so it does have some degree of cocaine-like effects.

They were saying they have anti-depressant but non-stimulant like effects.

It looks like the phenyl analog comes close to interacting with D476, but these kind of binding depictions always appear to me like looking through a haze of confetti at a birthday surprise party, and since the skeletal structure is translucent grey to solid grey in some parts, it's hard to tell.

 

[serotonin2A]

They were saying they have anti-depressant but non-stimulant like effects.

It looks like the phenyl analog comes close to interacting with D476, but these kind of binding depictions always appear to me like looking through a haze of confetti at a birthday surprise party, and since the skeletal structure is translucent grey to solid grey in some parts, it's hard to tell.

1-Methylcocaine produced CPP, which indicates euphoric effects and not simply anti-depressant effects.

What type of interaction would you reasonably anticipate occurring between a charged/hydrophilic Asp and a lipophilic benzene ring?

DAT was subsequently crystallized from Drosophila , so it would be interesting to see them repeat the docking studies.

 

[Nagelfar]

1-Methylcocaine produced CPP, which indicates euphoric effects and not simply anti-depressant effects.

What type of interaction would you reasonably anticipate occurring between a charged/hydrophilic Asp and a lipophilic benzene ring?

DAT was subsequently crystallized from Drosophila , so it would be interesting to see them repeat the docking studies.

Yeah, I remember reading about the effects of crack smoke on fruit flies. ;-P

 

[Nagelfar]

1-Methylcocaine produced CPP, which indicates euphoric effects and not simply anti-depressant effects.

Did you read the whole thing sero? It said even analog 2, the C1-methyl, did not produce behavioral stimulation despite producing CPP. The paper postulates it has to do with differing affinity for the sigma 1 & 2 receptors, that is the only other affinity these compounds possess besides MAT.

What is also interesting is I remember people saying that cocaine cut with lidocaine would be apparent, because it numbs you a lot more, that cocaine was a "subtler" numbing, but according to the values in this page, lidocaine was the weakest local anesthetic of all compounds tested and cocaine was by far superior at blocking sodium channels (reasonable why its still used in certain oral surgeries). I think most people are in contrast used to the cut not being a local anesthetic; if that was the question of street potency.

 

[serotonin2A]

Did you read the whole thing sero? It said even analog 2, the C1-methyl, did not produce behavioral stimulation despite producing CPP. The paper postulates it has to do with differing affinity for the sigma 1 & 2 receptors, that is the only other affinity these compounds possess besides MAT.

I read over it. In terms of what they wrote about the sigma-1, they are basically proposing that there is effectively no difference between how cocaine and these analogs interact with DAT. They are saying that the analogs can potentially induce CPP like cocaine but they fail to stimulate locomotor activity (LMA) due to lack of sigma-1 affinity.

In terms of whether that explanation is correct, it is true that sigma-1 antagonists block cocaine-induced LMA. However, interpreting that finding is complicated by the fact that selective sigma-1 agonists don't increase LMA on their own, and also because sigma-1 is a chaperone protein and is necessary for the function of some membrane-bound ion channels. So it has always seemed like the sigma-1 blockade effect on cocaine LMA may reflect a constitutive interaction, where sigma-1 activation is necessary for transduction of the LMA response to cocaine but does not actually mediate the response.

In any event, it is important to consider that the goal of these studies is to identify potential treatments for cocaine dependence. The studies were not designed to probe the mechanism of action of cocaine at DAT. Based on their evidence, there isn't anyway to know whether the behavioral pharmacology differences are due to differences in their interaction with DAT vs some other factor. Even if the former explanation is correct, something like residence time could be the underlying explanation. So I wouldn't walk away from this study thinking it calls into question the current thinking about DAT function.

What is also interesting is I remember people saying that cocaine cut with lidocaine would be apparent, because it numbs you a lot more, that cocaine was a "subtler" numbing, but according to the values in this page, lidocaine was the weakest local anesthetic of all compounds tested and cocaine was by far superior at blocking sodium channels (reasonable why its still used in certain oral surgeries). I think most people are in contrast used to the cut not being a local anesthetic; if that was the question of street potency.

EDIT: I missed you comment about numbing. Cocaine is more potent than lidocaine. But it makes sense to think that cocaine cut with lidocaine would produce more numbing. Say someone had cocaine that was 50% pure. If it was cut with lidocaine, then 100% of the mixture would be a local anesthetic. If it was cut with a sugar, only 50% of the mixture would be a local anesthetic.

 

[Nagelfar]

Stimulation without preferred placement: could always be something to do with the likes of other new research such as this (Dopamine Regulation of Lateral Inhibition between Striatal Neurons Gates the Stimulant Actions of Cocaine.)

In Brief: Dobbs et al. uncover a novel synaptic mechanism by which cocaine exerts its stimulant effect on locomotion. They show that cocaine suppresses the lateral inhibition between neurons in the nucleus accumbens to disinhibit striatal neurons and promote locomotion

^This is 2016

 

[Nagelfar]

Conformational changes in dopamine transporter intracellular regions upon cocaine binding and dopamine translocation