Reversal of morphine tolerance by a compound with NPFF receptor subtype-selective actions

AbstractNeuropeptide FF (NPFF) modulates opiate actions. It has pro-nociceptive effects, primarily through the NPFF receptor 1 subtype, and anti-nociceptive effects, primarily through the NPFFR2 subtype. AC-263093 is a small l, organic, systemically active molecule that was previously shown to functionally activate NPFFR2, but not NPFFR1. It was hypothesized that AC-263093 would attenuate morphine tolerance. Rats were tested for radiant heat tail-flick latency before and after 5mg/kg morphine sulfate s.c. They were then rendered morphine-tolerant by continuous subcutaneous infusion of 17.52mg/kg/day morphine sulfate. On the seventh day of infusion, they were retested for analgesia 10 and 20min after 5mg/kg morphine sulfate s.c. Tolerance was indicated by reduction of morphine analgesia from the pre-infusion test. Fifty minutes prior to morphine challenge, rats received either 10mg/kg i.p. AC-263093 or injection vehicle alone. AC-2623093-treated rats had far smaller tolerance scores than control rats. This drug effect was significant, p=0.015. The same dose of AC-263093 had almost no analgesic effect in non-tolerant, saline-infused rats. In vitro experiments revealed that AC-263093 had equal affinity for NPFFR1 and NPFFR2, and functionally inactivated NPFFR1, in addition to its previously shown ability to activate NPFFR2. Thus, altering the balance between activation of NPFF receptor subtypes may provide one approach to reversing opiate tolerance

Bexarotene prodrugs: Targeting through cleavage by NQO1 (DT-diaphorase).

Bexarotene, a retinoid X receptor (RXR) agonist, is being tested as a potential disease modifying treatment for neurodegenerative conditions. To limit the peripheral exposure of bexarotene and release it only in the affected areas of the brain, we designed a prodrug strategy based on the enzyme NAD(P)H/quinone oxidoreductase (NQO1) that is elevated in neurodegenerative diseases. A series of indolequinones (known substrates of NQO1) was synthesized and coupled to bexarotene. Bexarotene-3-(hydroxymethyl)-5-methoxy-1,2-dimethyl-1H-indole-4,7-dione ester 7a was cleaved best by NQO1. The prodrugs are not cleaved by esterase

Low Dose Bexarotene Treatment Rescues Dopamine Neurons and Restores Behavioral Function in Models of Parkinson's Disease

Nurr1 is a nuclear hormone receptor (NucHR) strongly implicated in the growth, maintenance, and survival of dopaminergic neurons. Nurr1 may be unable to bind ligands directly, but it forms heterodimers with other NucHRs that do. Using bioluminescence resonance energy transfer (BRET) assays to directly monitor interactions of Nurr1 with other NucHRs, we found the cancer drug bexarotene (Targretin, also LGD1069) displayed biased interactions with Nurr1-RXR heterodimers compared with RXR-RXR homodimers. Remarkably, at doses up to 100-fold lower than those effective in rodent cancer models, bexarotene rescued dopamine neurons and reversed behavioral deficits in 6-hydroxydopamine (6-OHDA) lesioned rats. Compared to the high doses used in cancer therapy, low doses of bexarotene have significantly milder side effects including a reduced increase in plasma triglycerides and less suppression of thyroid function. On the basis of extrapolations from rat to human doses, we hypothesize that low oral doses of bexarotene may provide an effective and tolerated therapy for Parkinson's disease (PD)

The A-CD analogue of 16 beta,17 alpha-estriol is a potent and highly selective estrogen receptor beta agonist

Selective estrogen receptor beta (ER beta) agonists display neuroprotective properties in animal models and hold promise in the treatment of neurodegenerative diseases. In our quest to design, synthesize and evaluate potent and safe ER beta agonists, we focused on making an analogue of 16 beta,17 alpha-estriol (16,17-epiestriol), a potent and one of the most ER beta selective endogenous estrogens reported. Herein we disclose the synthesis and in vitro evaluation of an analogue based on the recently introduced A-CD scaffold. A 14-step synthesis based on the Hajos-Parrish ketone resulted in the discovery of (1S,2S,3aS,5S,7aS)-5-(4-hydroxyphenyl)-7a-methyloctahydro-1H-indene-1,2-diol (15). This A-CD analogue of 16 beta, 17 alpha-estriol is a highly selective (500-fold) ER beta full agonist over ER alpha with a pEC(50) of 7.7 at ER beta. Molecular modelling suggests that 15 turns around in the ligand-binding domain compared to estriol, thus the 7a-methyl occupies the alpha-face, which might explain the high selectivity