Buprenorphine for opioid dependence

Targeting the A3 adenosine receptor to treat hepatocellular carcinoma: anti-cancer and hepatoprotective effects

The A3 adenosine receptor (A3AR) is over-expressed in human hepatocellular carcinoma (HCC) cells. Namodenoson, an A3AR agonist, induces de-regulation of the Wnt and NF-kB signaling pathways resulting in apoptosis of HCC cells. In a phase I healthy volunteer study and in a phase I/II study in patients with advanced HCC, namodenoson was safe and well tolerated. Preliminary evidence of antitumor activity was observed in the phase I/II trial in a subset of patients with advanced disease, namely patients with Child-Pugh B (CPB) hepatic dysfunction, whose median overall survival (OS) on namodenoson was 8.1 months. A phase II blinded, randomized, placebo-controlled trial was subsequently conducted in patients with advanced HCC and CPB cirrhosis. The primary endpoint of OS superiority over placebo was not met. However, subgroup analysis of CPB7 patients (34 namodenoson-treated, 22 placebo-treated) showed nonsignificant differences in OS/progression-free survival and a significant difference in 12-month OS (44% vs 18%, p = 0.028). Partial response was achieved in 9% of namodenoson-treated patients vs 0% in placebo-treated patients. Based on the positive efficacy signal in HCC CPB7 patients and the favorable safety profile of namodenoson, a phase III study is underway.

Intravenous misuse of buprenorphine: characteristics and extent among patients undergoing drug maintenance therapy

Sublingual buprenorphine [Subutex(R)] is used to treat opioid dependence. However, illicit intravenous (IV) injection of buprenorphine is a widespread problem. This survey investigated the IV misuse of buprenorphine among patients receiving drug replacement therapy at the Drug Addiction Centre in Udine, Italy. All patients who were receiving treatment with buprenorphine or methadone at the Drug Addiction Centre were invited to fill in a voluntary and anonymous questionnaire consisting of five questions. The questions asked if the patient had ever misused buprenorphine intravenously, when the misuse had occurred, the patient's reasons for misusing buprenorphine, the patient's perception of their experience, and the patient's perception of how widespread IV misuse of buprenorphine is. 307 patients completed the questionnaire, 93 and 214 of whom, respectively, were receiving buprenorphine and methadone. In total, 23.12% of patients admitted an IV misuse of buprenorphine, with a significantly greater prevalence among patients currently receiving buprenorphine (35.48%) than those receiving methadone (17.75%; p < 0.001). Younger patients were also more likely to have misused buprenorphine, and tended to have done so before coming to the Drug Addiction Centre. The most frequent motivation for IV misuse was treatment of heroin addiction or withdrawal symptoms (50.71%), while only 12.67% of patients reported that their motivation was to experience pleasure or euphoria. The majority of patients who had misused buprenorphine intravenously (53.52%) had a negative experience, and methadone recipients were significantly more likely to find the experience negative than buprenorphine recipients (68.42% vs 36.36%; p = 0.007). Almost half of the patients (45.93%) thought that at least 50% of patients had taken buprenorphine by IV injection. The results of our study confirm the widespread IV misuse of buprenorphine. Misuse was most common among patients currently receiving buprenorphine treatment and younger patients. For the majority of patients, the reason for IV misuse was to treat their dependence. We believe that the prevalence of buprenorphine misuse could be reduced by adopting appropriate clinical practices and treating patients with the buprenorphine/naloxone combination rather than buprenorphine alone.

Differential activation of pregnane X receptor and constitutive androstane receptor by buprenorphine in primary human hepatocytes and HepG2 cells

Buprenorphine is a partial μ-opioid receptor agonist used for the treatment of opioid dependence that has several advantages over methadone. The principal route of buprenorphine disposition has been well established; however, little is known regarding the potential for buprenorphine to influence the metabolism and clearance of other drugs by affecting the expression of drug-metabolizing enzymes (DMEs). Here, we investigate the effects of buprenorphine on the activation of pregnane X receptor (PXR) and constitutive androstane receptor (CAR), as well as the induction of DMEs, in both HepG2 cells and human primary hepatocytes (HPHs). In HepG2 cells, buprenorphine significantly increased human PXR-mediated CYP2B6 and CYP3A4 reporter activities. CYP2B6 reporter activity was also enhanced by buprenorphine in HepG2 cells cotransfected with a chemical-responsive human CAR variant. Real-time reverse transcription-polymerase chain reaction analysis revealed that buprenorphine strongly induced CYP3A4 expression in both PXR- and CAR-transfected HepG2 cells. However, treatment with the same concentrations of buprenorphine in HPHs resulted in literally no induction of CYP3A4 or CYP2B6 expression. Further studies indicated that buprenorphine could neither translocate human CAR to the nucleus nor activate CYP2B6/CYP3A4 reporter activities in transfected HPHs. Subsequent experiments to determine whether the differential response was due to buprenorphine's metabolic stability revealed a dramatically differential rate of elimination for buprenorphine between HPHs and HepG2 cells. Taken together, these studies indicate that metabolic stability of buprenorphine defines the differential induction of DMEs observed in HepG2 and HPHs, and the results obtained from PXR and CAR reporter assays in immortalized cell line require cautious interpretation.