Optimizing Antiretroviral Therapy in HIV-Infected Children and Adolescents

Although, the use of protease inhibitors (PI) containing highly active antiretroviral
therapy (HAART) has led to a remarkable improvement in the prognosis and outcome of HIV
infection, only 45% to 70% of treatment-naïve patients who commence HAART achieve complete
virological suppression. The emergence of HIV resistance to antiretroviral drugs is one of
the main obstacles to the successful long-term suppression of HIV replication. Poor
adherence and unfavorable pharmacokinetics (PK) caused by altered absorption, genetic
variations in metabolism and drug-drug interactions frequently lead to antiretroviral drug
concentrations below the inhibitory concentration for 50% of the viral quasispecies (IC50)
and loss of viral suppression.

Enzymes of the cytochrome (CYP) P450 (CYP2C19, CYP3A4, CYP3A5) family located in the liver
and small intestine are responsible for the metabolism of PIs. The absence of expression of
certain enzymes from this family was recently correlated with a genetic polymorphism, which
may have a major role in variation of cytochrome P450-mediated drug metabolism. Results of
these studies suggest significant differences in the distribution of the polymorphism
associated alleles between ethnic groups, in particular between Caucasians and African
Americans. Detection of cytochrome P450 variant alleles and more detailed data on their
allelic frequency in various ethnic groups is critical to assess their impact on PK of
antiretroviral agents, in particular PIs.

This research proposal is aimed at the development of a novel multidisciplinary approach to
optimize HAART in HIV infected children. It is increasingly clear that inter-individual
variation in drug metabolism and responsiveness has a strong genetic component. The
metabolic pathways leading to drug clearance, bio-availability, and cellular responses are
complex, and only beginning to be understood. Key to our understanding of inter-individual
responses is identification of the genetic polymorphisms that contribute to this
variability, the relative contribution of different genes/SNPs, and the possible
interactions between the corresponding protein products or pathways. We propose to develop a
dosing regimen of PIs in HIV-infected children that takes into account genetic variability
in drug metabolism and transport, and resistance of the dominant viral strain (as determined
by virtual phenotype).

In order to do so, the protocol address the following Specific Aims:

- Specific Aim 1 (completed previously): Determine the prevalence of genetic variations
in CYP2C19, CYP3A4, CYP3A5, and MDR-1 genes in a cohort of children and adolescents
with HIV infection.

- Specific Aim 2 (completed previously): Evaluate the relationship of this genetic
variability to the pharmacokinetic parameters (Cmin, Cmax, AUC) and toxicity (graded by
the Division of AIDS [DAIDS] classification) of protease inhibitors in pediatric
patients with HIV infection.

- Specific Aim 3 (THIS STUDY): Evaluate the impact of dose adjustment of protease
inhibitors based on pharmacogenetic profile and virtual inhibitory quotient (VIQ) on
clinical outcome (measured by HIV-RNA viral load and CD4+ cell count changes) and
toxicity (graded by the DAIDS classification) in pediatric patients with HIV infection.

Inclusion criteria:

- Evidence of HIV infection confirmed by positive culture or PCR on at least two
occasions, or a positive ELISA and a confirmatory Western Blot. At least one of these
tests must be done in an ACTG certified laboratory which is approved to perform the
assay for protocol testing

- Age 4-21 years

- Current use of HAART regimen (NRTI or/and NNRTI based) containing a PI

- HIV-RNA levels above 1,000 copies/mL (Stage II)

- vIQ<1 for Kaletra

- Signed informed consent and, if indicated, signed informed assent or waiver of
assent.

Exclusion criteria:

- Grade 3-4 DAIDS defined toxicity

- Use of cimetidine (used as the internal standard for the HPLC-MS/MS assay)

- Any active opportunistic infection

- Any of the following laboratory findings at entry: absolute neutrophil count <750
cells/mm3; platelet count <75,000 cells/mm3; AST >3 times upper limit of age adjusted
normal values; ALT >3 times upper limit of age adjusted normal values; serum
creatinine >1.2mg/dL.

- Patients on dual PI regimen (except when second PI is given for boosting) at the time
of enrollment