Letter pubs.acs.org/chemneuro
Estrogen Receptor Beta Selective Agonists as Agents to Treat Chemotherapeutic-Induced Neuropathic Pain Jian-Nong Ma,† Krista McFarland,† Roger Olsson,‡ and Ethan S. Burstein*,† †
ACADIA Pharmaceuticals Inc., 3611 Valley Center Drive, Ste. 300, San Diego, California 92130, United States Chemical Biology & Therapeutics, Department of Experimental Medical Science, Lund University, S-221 84 Lund, Sweden
‡
ABSTRACT: Chemotherapy-induced neuropathic pain (CINP) remains a major unmet medical need. Estrogen receptor beta (ERβ)selective agonists represent a novel strategy for treating CINP because they are neuroprotective and may also have anticancer activity. We confirmed that ERβ-selective agonists have antiallodynic effects in the spinal nerve ligation model of neuropathic pain. We then showed that structurally diverse ERβ-selective agonists also relieved allodynia in CINP caused by taxol, oxaliplatin, and vincristine. These effects were receptor subtype specific and mediated by ERβ receptors as ERαselective and nonselective estrogen agonists were inactive, a mixture of an ERβ and ERα agonist was inactive, and ERβ-selective antagonists blocked the effects of the ERβ-selective agonists. The efficacy and potency of ERβ-agonists was greater in male rats than females. To address the possibility that AC-186 might stimulate proliferation of cancers, rendering it unsuitable for treating CINP, we evaluated proliferative effects of AC-186 on prostate cancer cells and found it inhibited growth (LNCaP cells) or had no effect (PC3 cells) on these cells. Thus, ERβ-selective agonists exhibit potential for treating CINP. KEYWORDS: Neuropathic pain, estrogen receptor beta, chemotherapy, taxol, oxaliplatin, vincristine
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europathic pain is a debilitating disorder caused by damage or dysfunction of the nervous system and is estimated to affect 1% or more of the general population.1 Neuropathic pain originates from diverse sources including diabetic and hereditary neuropathies, herpes, physical traumas, and surgery, and is a frequent dose-limiting side effect of chemotherapy.2,3 First-line medications for treating neuropathic pain include gabapentin, duloxetine, lidocaine patch, opioids, tramadol, and tricyclic antidepressants (TCAs); all are limited by variable efficacy and adverse effects.4 The treatment options are even more limited for chemotherapy-induced neuropathic pain (CINP).5,6 Thus, there exists a major unmet medical need for drugs to treat CINP. ERβ-selective agonists represent a novel strategy for treating CINP. ERβ-selective agonists have shown the potential to be highly efficacious drugs for treating a wide array of pain modalities including chronic inflammatory pain states.7 ERβ receptors modulate a number of physiological effects that impact neuropathic pain including antinociceptive8 and anti-inflammatory9 effects. Recently, we described a novel ERβ-selective agonist that showed efficacy in a variety of neuropathic pain and chronic inflammatory models.10,11 Subsequently, we demonstrated that structurally similar compounds exhibit neuroprotective properties.12 In addition to their analgesic properties, ERβ agonists may also have anticancer activity.13 The combination of analgesic, anti-inflammatory, neuroprotective, and anticancer properties of ERβ-selective agonists suggests such compounds might be particularly useful for treating CINP. © 2016 American Chemical Society
RESULTS
We have previously reported that ERβ-selective agonists are effective in rodent models of neuropathic pain.10 Recently, we described a novel ERβ-selective agonist called AC-186 which displays neuroprotective properties in a rat model of Parkinson’s disease.12 Like our prototype ERβ-selective agonist AC-131,10,12 and DPN,14 AC-186 is selective for ERβ receptors over ERα receptors (Table 1). The current studies confirmed that AC-186 was active in a standard model of neuropathic pain, the spinalnerve ligation (SNL) or Chung model of neuropathic pain, with similar efficacy to Gabapentin (Figure 1A). Importantly, in a screen for behavioral toxicity (modified Irwin neurotoxicity screen15), we found no effects of AC-186 at doses up to 300 mg/ kg on motility that could have confounded our allodynia measurements (unpublished observations). To determine if the antiallodynic effects of AC-186 were ERβmediated, we tested AC-186 in the presence and absence of PHTPP, an ERβ-selective antagonist.16 PHTPP completely blocked the effects of AC-186 (Figure 1B), but had no effect alone. We employed a series of ERβ-, ERα-, and nonselective agonists and antagonists to assess whether ERβ receptors mediated analgesic effects in the SNL pain model. To determine if ERα-activation contributed to the antiallodynic effects we Received: June 23, 2016 Accepted: July 19, 2016 Published: July 26, 2016 1180
DOI: 10.1021/acschemneuro.6b00183 ACS Chem. Neurosci. 2016, 7, 1180−1187
Letter
ACS Chemical Neuroscience Table 1. In Vitro Profiles of Estrogen Receptor Agonistsa
a Data for AC-131, AC-186, and 17β-estradiol (E2) were reported previously.12 Data for DPN and PPT were obtained using the RSAT functional assay.10 Efficacy was expressed as a percentage of the maximum response to E2. *Antagonist data for PHTPP are reported as relative binding affinity and are from ref 16. DPN, diarylpropionitrile or 2,3-bis(4-hydroxyphenyl)-propionitrile.14 PPT, 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5triyl)trisphenol.17 PHTPP, 2-phenyl-3-(4-hydroxyphenyl)-5,7-bis(trifluoromethyl)-pyrazolo[1,5-a]pyrimidine.16
observed, we tested an ERα-selective agonist (PPT17), another ERβ-selective agonist called AC-13110,12 or the nonselective estrogen 17β-estradiol (E2) in the SNL model. Only AC-131 had antiallodynic effects suggesting ERα does not mediate antiallodynic effects of estrogen ligands (Figure 1C). Because E2 has equipotent agonist activity at ERα and ERβ receptors, and did not have antiallodynic effects, we tried treating SNL-rats with a combination of an ERα-selective agonist (PPT, see Table 1) and AC-186. As shown in Figure 1D, coadministration of PPT nullified the antiallodynic effects of AC-186. Previously, we reported gender-specific neuroprotective effects of AC-186 and related compounds in models of Parkinson’s disease.12 Therefore, we tested AC-186 in female rats that underwent SNL. As shown in Figure 1E, the observed maximum analgesic effect of AC-186 was lower in female rats than it was in males, even at higher doses, whereas the efficacy of gabapentin was similar in both genders. The efficacy of AC-186 was not improved in ovariectomized rats compared to intact females (Figure 1F). Next we tested AC-186 in chemotherapy-induced neuropathic pain (CINP) models. These models were appealing because CINP represents a large, unmet medical need and because ERβagonists are potentially useful anticancer agents in their own right.13 Paclitaxel (Taxol) is a member of the taxane family of chemotherapeutic drugs and is widely prescribed.18 In male rats,
AC-186 provided essentially complete reversal of Taxol-induced allodynia at doses of 10 and 30 mg/kg (Figure 2A). Repeat dosing experiments showed that no tolerance or desensitization to the effects of AC-186 occurred over 5 days (Figure 2B). The analgesic effects of AC-186 were blocked by the ERβ-selective antagonist PHTPP, and coadministration of an ERα-selective agonist (PPT) (Figure 2C). Similar to the SNL model, ERβselective agonists (DPN, see Table 1) were active, whereas ERαselective (PPT) and nonselective estrogen receptor agonists (E2) were not (Figure 2D). The maximum analgesic effect of AC-186 in female rats was less than half of what it was in males (see Figure 2E, compare to Figure 2A), whereas the efficacy of gabapentin was slightly higher in females (MPE = 58 ± 21) than in males (MPE = 47 ± 17). Subsequently, we explored other models of CINP. Oxaliplatin is a member of the platinum-based group of chemotherapeutic drugs. As shown in Figure 3A, AC-186 reversed oxaliplatininduced allodynia in a dose-dependent manner, providing significant reversal a dose of 30 mg/kg. Repeat dosing experiments demonstrated that no tolerance or desensitization to the effects of AC-186 occurred over 5 days (Figure 3B). The antiallodynic effect of AC-186 was blocked by PHTPP, and by coadministration of PPT (Figure 3C). Another ERβ-selective agonist (DPN, see Table 1) was active in this model, whereas the PPT was not (Figure 3D). Similar to the Taxol experiments, we 1181
DOI: 10.1021/acschemneuro.6b00183 ACS Chem. Neurosci. 2016, 7, 1180−1187
Letter
ACS Chemical Neuroscience
Figure 1. Efficacy of ERβ-selective agonists in the spinal nerve ligation model. Spinal nerve ligation (SNL) of the L5/L6 nerve was done as described previously,10 using male (A−D) or female (E, F) Sprague−Dawley (SD) rats. Allodynia was assessed by applying a light tactile stimulus (von Frey hairs) to the plantar surface of the surgical paw until the 50% threshold was established. A positive response was recorded if the paw was sharply withdrawn. Eight von Frey hairs were used (0.4, 0.6, 1, 2, 4, 6, 8, and 15 g). The percent maximum possible effect (MPE %) was calculated as [(Rdrug − Rveh)/(Rsham − Rveh)] × 100%, where Rdrug was the response in SNL animals receiving drug, Rveh was the response in SNL animals receiving vehicle, and Rsham was the response in animals that did not under SNL-induced neuropathy. Rveh was 3, and Rsham was 14. The presence of tactile allodynia (von Frey filament 50% response threshold of
