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Other names | DA-Phe; DA-PHEN; Dopamine–phenylalanine conjugate |
Drug class | Monoamine precursor; Dopamine receptor agonist |
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Chemical and physical data | |
Formula | C17H20N2O3 |
Molar mass | 300.358 g·mol−1 |
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DA-Phen, also known as dopamine–phenylalanine conjugate, is a synthetic dopamine prodrug which is under preclinical evaluation. [1] [2] [3] [4] [5] [6] [7] Dopamine itself is hydrophilic and is unable to cross the blood–brain barrier, thus showing peripheral selectivity. [2] DA-Phen was developed as a dopamine prodrug that would allow for entry into the central nervous system via passive diffusion and/or active transport. [1] [2]
DA-Phen is a conjugate of dopamine and the amino acid phenylalanine (Phe or Phen). [1] [2] It is slowly cleaved by brain enzymes (t½ = 460 minutes) to yield free dopamine but is also rapidly hydrolyzed in human blood plasma (t½ = 28 minutes). [2] The drug was intended as a prodrug but may also directly interact with the dopamine D1-like and/or D2-like receptors. [1] [5] [4] [6] DA-Phen has shown centrally mediated effects in animals, including increased cognitive flexibility, improved spatial learning and memory, antidepressant- and anxiolytic-like effects, and decreased ethanol intake. [1] [7] [5]
Other analogues, such as DA-Trp and DA-Leu, have also been developed and studied. [4]
Recently, DA has been conjugated with Phe (DA-Phen, Fig 2A) and other Phe mono substituted moieties obtaining related neurotransmitter derivatives capable of carrying DA into the CNS [35,36]. In particular, the physicochemical properties of DA-Phen, e.g. molecular weight and LogD, are favourable for its ability in crossing biological membranes [35]. The aptitude of DA-Phen to reach the CNS has been assessed in a combined approach in vitro, using the PAMPA-BBB and Caco-2 models. Transport across the BBB substantially occurred through transcellular permeation, involving carrier-mediated processes. Molecular docking analysis evidenced that this conjugate interacts with the deep pocket of the identified D1 binding site of the human brain receptor [37]. Following administration on rats, DA-Phen showed a consistent enhancement in cognitive flexibility in naïve subjects, whereas in rats who are trained to alcohol self-administration the conjugate is able to reduce both ethanol intake and forced abstinence signs [38].
1.5. Peptide Transport-Mediated Prodrugs Giannola et al. [80] have proposed a 2-amino-N-[2-(3,4-dihydroxyphenyl)-ethyl]-3-phenyl-propionamide dopamine prodrug (DA-PHEN) (Figure 10) [81]. It was synthesized by condensation of dopamine with a neutral amino acid to interact with the BBB endogenous transporters and readily enter the CNS. DA-PHEN undergoes slow cleavage by cerebral enzymes (t 1/2 460 min) and yields free dopamine in the brain, but it is rapidly hydrolyzed in human plasma (t 1/2 28 min). Chemical stability studies on DA-PHEN proved that no DA release happened in the gastrointestinal tract, also the prodrug can cross through a simulated intestinal mucosal membrane. Recently, De Caro et al. [81] studied in vitro the ability of DA-PHEN to penetrate the CNS. The team used in their study parallel artificial permeability assay (PAMPA) and Caco-2 models. Despite the relatively low molecular weight (300.35 Da) and the estimated experimental value [80] of log DPh 7.4 (0.76) of DA-PHEN which indicates good potential for passage through biological membranes, they noticed very limited transport through PAMPA-BBB [81]. In fact, the apparent permeability was 3.2 × 107 cm/s, indicating low capacity of DA-PHEN to penetrate BBB by passive transcellular route. Transport trials via Caco-2 cells showed marked increase of DA-PHEN flux with regard to that calculated in PAMPA-BBB system. However, high penetration rates seen in DA-PHEN cannot be obtained only by the simple diffusion, but may also involve carrier mediated transport [82].
DA-PHEN (XXXXI): can be classified as a dopamine prodrug, belonging to the group of peptide transport-mediated prodrugs. It can easily cross the BBB and reach the CNS; it has been proposed that the molecule can also act as a per se drug which modulates cognitive performances correlated with dopaminergic neurotransmission. Preclinical studies will be the next step to be performed.