The Translational Research Cycle – Example in Infectious Diseases
Topic: Adverse Drug-Drug Interactions in Treating Infectious Diseases
Co-infection with different organisms is a common problem in infectious diseases therapy. This is
especially true in HIV-AIDS populations, where immune suppression greatly increases opportunistic infections
from other organisms, such as tuberculosis (TB). In many parts of the developing world, TB is the most
common opportunistic infection in HIV-AIDS patients. For example, it has been estimated that 30% of HIVAIDS patients are co-infected with TB world wide (UNAIDS). Although different drugs are used to treat each
disease, in some instances the administration of one drug greatly alters the efficacy of the other.
Translational research cycle
T0 – Basic laboratory ‘discovery’ of a new mechanism for preventing certain
adverse drug-drug interactions. The isothiocyanate, sulforaphane (SFN), is a
common dietary constituent of broccoli and broccoli sprouts. It has been
extensively studied as a putative ‘chemopreventive’ agent, potentially reducing the
incidence of cancer via several pathways, including ‘up regulation’ of genes that
code for ‘antioxidant’ pathways. In the process of studying how SFN alters gene
expression in human liver cells in primary culture, a ‘microarray’ experiment
evaluated the effects of SFN on gene expression of ~20,000 genes. It was noted
that the mRNA levels for one particular gene, Cytochrome P450 3A4 (CYP3A4),
was largely absent. CYP3A4 is normally expressed at relatively high levels in
liver and small intestine, and plays a major role in metabolism of many drugs and
non-drug chemicals. CYP3A4 is ‘inducible’ by many drugs and dietary
constituents, but there were few, if any, studies showing how substances could
‘down regulate’ (inhibit gene expression) of CYP3A4, although it was known that
some dietary constituents, such as grapefruit juice, could inhibit the enzymatic
activity of CYP3A4. Thus, this observation led to additional studies to explore the
molecular mechanism by which SFN inhibited the expression of CYP3A4 mRNA
in human liver cells.
CTRI interaction
Translational
Technologies and
Resources Core (TTRC)
– Center for array
technologies
T1 –In vitro laboratory studies to establish the molecular mechanism by
which SFN inhibits CYP3A4 gene expression. Based on the initial observation
described above, additional laboratory studies were done to evaluate the
mechanism(s) by which SFN inhibited CYP3A4 gene expression in human liver
cells. Through a series of in vitro studies, it was demonstrated that SFN binds to,
but does not activate, a nuclear receptor called the ‘Pregnane X-Receptor’ (PXR,
also called SXR or NR1I2). SFN appeared to tightly, perhaps irreversibly, bind to
the ligand binding site of the receptor, thus preventing other ligands from binding
and activating the receptor. Ligand activation of PXR was known to be a major
contributor to both ‘constitutive’ (basal) and inducible expression of CYP3A4.
Thus, the apparent molecular mechanism by which SFN blocks CYP3A4 gene
expression in human hepatocytes is by inhibiting ligand activation of PXR. This
has immediate clinical relevance to adverse drug interactions, because it is known
that many drugs act as ligands for PXR, thereby inducing expression of CYP3A4,
which then enhances the clearance of other drugs that happen to be substrates for
CYP3A4. The best example of this is the anti-tuberculosis drug, rifampin.
Rifampin is a potent activating ligand for PXR, and increases the activity of
CYP3A4 many fold. For example, a normal therapeutic regiment with rifampin
TTR/CSR cores. Several
Technology Access
Facilities identified by
the TTRC could be
accessed, such as
Molecular Modeling,
Proteomics, and
pharmacokinetics/drug
metabolism Mass
Spectrometry facility.
Appropriate for
Technology Access
Grant via CSR.
CORT and CBS –
epidemiologic studies
documenting ARV
treatment failure with use
will increase the clearance of the sedative, midazolam, by 10-fold or more.
Midazolam is cleared almost exclusively through metabolism via CYP3A4. Most
first-line antiretroviral (ARV) drugs, including the non-nucleoside reverse
transcriptase inhibitor nevirapine and the protease inhibitor lopinavir/ritonavir are
also substrates for CYP3A4. Thus, ARV treatment options are limited when TB
therapy with rifampin is required because it will induce CYP3A4, thereby
increasing clearance and reducing the efficacy of the ARVs. Although some new
drugs have become available (at least in developed countries) to work around this
adverse drug-drug interaction, it remains a significant public health problem in
developing countries where co-infection with TB and HIV-AIDS are common, and
both rifampin and first generation ARV drugs are widely used for TB and HIVAIDS therapy, respectively. Based on these basic laboratory discoveries, a ‘use
patent’ was filed to protect the ‘intellectual property’ related to the use of
isothiocyanates to block ligand activation of PXR and subsequent changes in gene
expression.
of rifampin or other antiTB drugs
T2 - Clinical investigations of Sulforaphane as a clinically effective antagonist
to ligand activation of PXR. A phase I, ‘proof of principle’ clinical trial was
funded by NIH to test the hypothesis that co-administration of SFN with rifampin
would block rifampin-mediated induction of CYP3A4, measured by assessment of
midazolam clearance before and after 7 days of treatment with rifampin. The
study is being performed in the CTRI CRC, via collaboration between the UW
CRC and FHCRC Prevention Center. The design is an open label, cross-over
study with 3 arms – 1) sulforaphane alone, 2) rifampin alone, and 3) sulforaphane
plus rifampin. Twenty four healthy volunteers who meet study requirements
receive 7 days of treatment for each arm, with at least two weeks between each
arm to allow for a return to equilibrium of CYP3A4 activity. CYP3A4 activity
was assessed prior to and following the 7 day treatment regiment by
pharmacokinetic analysis of midazolam ‘AUC’. Previous clinical studies with
rifampin and midazolam have demonstrated that rifampin treatment will reduce the
AUC of midazolam by 90-95%. If the proof of principle study demonstrates
significant efficacy of SFN in preventing rifampin-mediated increase in
midazolam clearance, then further clinical studies would be warranted.
IND submission support
(Pre-clinical core) and
IRB submission,
regulatory consultation
(RSB), protocol
development and
database systems
(CBS/BMI), potential
pilot funding (CSR),
conduct the study
(CRCN) and research
coordinators for
implementation (RSB).
Based on positive results in the early Phase I clinical trial discussed above, a trial
in normal, healthy volunteers will be conducted to demonstrate that coadministration of SFN with rifampin will prevent the enhanced clearance of
ritonavir normally associated with rifampin treatment. The design would be
similar to the Phase I study above, but would look directly at clearance of
ritonavir. A further Phase II trial investigating the rifampin/SFN interaction with
other ARVs would then be conducted in HIV-infected patients taking a variety of
ARV medications. HIV-infected adults on a stable ARV regimen including either
a protease inhibitor (PI) or a non-nucleoside reverse transcriptase inhibitor
(NNRTI) would participate in an open-label study of the effect of rifampin/SFN
administration on the pharmacokinetics of the PI or NNRTI.
If these Phase II clinical trials proved successful, a Phase III clinical trial would
then be designed to determine if SFN co-formulation with rifampin is effective in
preventing the rifampin – ARV interaction, and does not alter efficacy of either
drug in the treatment of their targeted diseases. (Prior to this step could be a return
to T1 activities to develop rifampin/SFN co-formulated into a single
Entrepreneurial Law
Clinic, pre-clinical
research consulting
Preclinical core’s drug
and device consultation
group. RSB, BMI and
CBS’s assistance in
setting up a clinical
development plan and
databases to follow and
track the data.
Continued input from
RSB, CBS, preclinical
cores with the PI to
review the initial results
and decide on the next
steps. Can the project
move forward or must
there be more preclinical
formulation work?
The development of a
Phase 3 protocol will
require multiple cores,
RSB for IRB
applications, IND and
regulatory issues and
bioethics issues that may
arise, CBS/BMI for
protocol development,
CRCN for study conduct,
CORT for use of practice
tablet/capsule.)
T3- Dissemination and implementation of SFN co-formulations to prevent
drug-drug interactions.
If the Phase III trial confirms the efficacy of the rifampin/SFN co-formulation in
mitigating the rifampin-ARV drug-drug interaction, thus allowing the concurrent
treatment of TB and HIV, further work would be done to revise guidelines. In
addition, further studies would be warranted investigating the use of SFN in other
clinical situations where significant drug interactions due to drug metabolism via
the CYP3A4 enzymatic pathway confound optimal therapy.
T4 – Evaluation of the public health impact of preventing adverse drug-drug
interactions via antagonism of PXR activation.
Further work would be done to evaluate the uptake of the revised TB-HIV
treatment guidelines and investigate drug distribution to the areas of the world
most affected by the TB-HIV epidemic and the effects on TB-HIV mortality.
based networks for study
conduct, TTRC for
potential assay
development for clinical
trial safety or efficacy
endpoints, Preclinical for
industry partnerships to
financially support and
potentially run such a
trial.
Collaboration with
external groups such as
the Center for AIDS
Research
CORT for work through
the practice based
networks to study
utilization of therapy
working with CBS/BMI.
Bioethics
CORT, BMI, CBS