Sulforaphane as an Antagonist to Human PXR-mediated Drug-drug Interactions

Adverse drug-drug interactions (DDIs) are responsible for approximately 3% of all hospitalizations in the US, perhaps costing more than $1.3 billion per year. One of the most common causes of DDIs is the when one drug alters the metabolism of another. A key enzyme in the liver and intestine, called "cytochrome P450 3A4 (CYP3A4) is generally considered to be the most important drug metabolizing enzyme. The gene for CYP3A4 can be 'turned on' by the presence of certain other drugs, resulting in much higher levels of CYP3A4 in the liver and intestine. Thus, when a drug that induces CYP3A4 is given with or before another drug that is metabolized by 3A4, a 'drug-drug' interaction occurs because the first drug (the inducer) greatly changes the rate at which the second drug (CYP3A4 substrate) is removed from the body. Many drugs increase CYP3A4 activity by binding to a receptor called the Pregnane-X-Receptor (PXR), which is a major switch that controls the expression of the CYP3A4 gene. Using human liver cells we have demonstrated that sulforaphane (SFN), found in broccoli, can block drugs from activating the PXR receptor, thereby inhibiting the switch that causes CYP3A4 induction. The purpose of this project is to determine if SFN can be used to block adverse DDIs that occur when drugs bind to and activate the PXR receptor and subsequently induce CYP3A4 activity. We will recruit 24 human volunteers to participate in the study. This project will determine whether SFN can prevent the drug Rifampin from binding to PXR and increasing CYP3A4 activity in humans following oral administration of SFN (broccoli sprout extract). The rate of removal of a small dose of the drug midazolam will be used to determine the enzymatic activity of CYP3A4 before and following treatment with Rifampin, in the presence or absence of SFN, since midazolam is only eliminated from the bloodstream by CYP3A4. . We predict that SFN will prevent the increase in midazolam clearance (metabolism) that normally follows treatment with the antibiotic, rifampicin.

This research is important because it could potentially lead to a simple, cost-effective way of preventing one of the most common causes of adverse drug-drug interactions that occurs today. For example, rifampicin, which is a cheap and effective antibiotic used to treat TB, cannot be used in HIV/AIDS patients because it increases the metabolism of many of the antiretroviral drugs used to treat HIV/AIDS. TB is a major opportunistic infection in AIDS patients, so this is a serious clinical problem, especially in developing countries where more expensive alternative drug therapies are not available. We hypothesize that co-formulation of rifampicin with SFN could block this drug-drug interaction without altering its efficacy, thereby allowing its use in HIV/AIDS patients infected with TB. This is but one example of numerous drug-drug interactions that occur via this mechanism.

• Drug: Rifampicin
  Rifampicin, an antibiotic used to treat TB, is administered at a dose of 300 mg day x 7 days to induce CYP3A5.
  Other Names:

  • Rifampin
  • Rifampicin
  • rifamycin
  • Rimactane
  • Rifadin
• Dietary Supplement: sulforaphane plus rifampicin
  Sulforaphane (SFN) is an isothiocyanate derived from the plant phytochemical, glucoraphinin. It appears to inhibit ligand binding to the ligand activated nuclear transcription factor, Pregnane X-Receptor (PXR). This arm tests the hypothesis that SFN can block ligand binding to the PXR, thereby inhibiting transcriptional activation of PXR-regulated genes. Sulforaphane is administered daily for 7 days as a broccoli sprout extract, at a dose rate of 75 mg (~420 umoles)per day for 7 days. Rifampicin is also administered once per day at a dose rate of 300 mg/day for 7 days.
  Other Names:

  • sulforaphane: glucoraphinin (precursor); 1-Isothiocyanato-4-methylsulfinyl-butane
  • Rifampicin: Rifampin, Rifadin, Rimactane
• Dietary Supplement: sulforaphane alone
  Sulforaphane (SFN) is an isothiocyanate derived from the plant phytochemical, glucoraraphinin. It appears to inhibit ligand binding to the ligand activated nuclear transcription factor, Pregnane X-Receptor (PXR). This arm tests the hypothesis that SFN can block ligand binding to the PXR, thereby inhibiting transcriptional activation of PXR-regulated genes
  Other Name: 1-isothiocyanato-4-(methylsulphinyl)butane

• Active Comparator: 1
  Subjects are given 300 mg / 7 days of rifampicin to induce CYP3A4. Midazolam clearance is measured on the 8th day.
  Intervention: Drug: Rifampicin
• Active Comparator: 2
  Sulforaphane (SFN), a natural product derived from broccoli sprouts, is utilized as a putative inhibitor of ligand (Rifampin) activation of the Pregnane X-receptor. In this arm, both SFN (putative inhibitor of ligand binding to PXR) and Rifampin (strong activating ligand of PXR) are given together.
  Intervention: Dietary Supplement: sulforaphane plus rifampicin
• Active Comparator: 3
  This arm involves the administration of Sulforaphane (SFN) alone, in the absence of the PXR ligand, rifampicin. The hypothesis is that SFN will have no effect on the expression of PXR-regulated genes. Alternatively, it is possible that SFN could inhibit as yet unidentified endogenous ligands to the PXR receptor, thereby causing down-regulations of genes regulated wholely or in part by PXR. SFN is administered as a broccoli sprout extract at a dose rate of 75 mg (~420 umoles) per day for 7 days.
  Intervention: Dietary Supplement: sulforaphane alone

Inclusion Criteria:

• Adults from all ethnicities will be encouraged to participate, with our recruitment efforts we expect similar profile as that of the greater Seattle area.

Exclusion Criteria:

Exclusion criteria address a mix of medical and practical issues and include:

• Medical history of gastrointestinal, hepatic, or renal disorders
• Pregnancy or lactation
• Known allergies/intolerances to any foods used in the feeding trial
• Weight loss or gain greater than 4.5 kg within the past year
• Major changes in eating habits within the past year (e.g. adoption of a faddish diet)
• Antibiotic use within the past 3 months
• Body weight greater than 150% of desirable
• Exercise patterns that require or result in major changes in diet
• Current use of prescription medication (including oral contraceptives)
• Current use of over-the-counter medications and herbal supplements
• Regular exposure to passive smoke
• Occupational exposure to smoke or organic solvents
• Food dislikes that would preclude participation in the feeding trial
• Alcohol intake of greater than 2 drinks/day (2 drinks=720 mL beer, 240 mL wine, or 9 mL spirits). Additionally, before the trial, participants will have a blood draw to be sent to the UW Medical Center Lab for liver and kidney functions profile and pregnancy test for women. Those with abnormal test results will be excluded as well as pregnant women.

• Fred Hutchinson Cancer Research Center
• National Institute of General Medical Sciences (NIGMS)