Antiviral activity and safety of 873140, a novel CCR5 antagonist, during short-term monotherapy in HIV-infected adults

Objective: 873140 is a spirodiketopiperazine CCR5 antagonist with prolonged receptor binding and potent antiviral activity in vitro. This study evaluated plasma HIV RNA, safety, and pharmacokinetics following short-term monotherapy in HIV-infected adults.

Design: Double-blind, randomized, placebo-controlled multi-center trial.

Methods: Treatment-naive or experienced HIV-infected subjects with R5-tropic virus, CD4 cell count nadir > 200 × 10⁶ cells/l, viral load > 5000 copies/ml and not receiving antiretroviral therapy for the preceding 12 weeks were enrolled. Forty subjects were randomized to one of four cohorts (200 mg QD, 200 mg BID, 400 mg QD, 600 mg BID) with 10 subjects (eight active, two placebo) in each cohort, and received treatment for 10 days. Serial HIV RNA, pharmacokinetics, and safety evaluations were performed through day 24.

Results: Of the 40 subjects, 21 were treatment-experienced; 35 were male, 20 were non-white, and eight were coinfected with hepatitis C virus. Median baseline HIV RNA ranged from 4.26log₁₀ to 4.46 log₁₀. 873140 was generally well tolerated with no drug-related discontinuations. The most common adverse events were grade 1 gastrointestinal complaints that generally resolved within 1-3 days on therapy. No clinically significant abnormalities were observed on electrocardiogram or in laboratory parameters. Mean log changes in HIV RNA at nadir, and the percentage of subjects with > 1 log₁₀ decrease were -0.12 (0%) for placebo, -0.46 (17%) for 200 mg once daily, -1.23 (75%) for 200 mg twice daily, -1.03 (63%) for 400 mg once daily, and -1.66 (100%) for 600 mg twice daily. An E_max relationship was observed between the area under the 873140 plasma concentration-time curve and change in HIV RNA.

Conclusions: 873140 demonstrated potent antiretroviral activity and was well tolerated. These results support further evaluation in Phase 2b/3 studies.

Introduction

The identification of new targets and novel agents against HIV infection remains a critical undertaking due to the widespread prevalence of drug resistant strains ^[1,2]. The cellular cc chemokine receptor 5 (CCR5) antagonists represent a new class of agents aimed at inhibiting viral entry. Following binding of gp120 to the CD4 receptor, CCR5 antagonists inhibit the interaction of gp120 to the co-receptor, an integral step in the fusion of HIV to the host cell ^[3,4].

873140 is a CCR5 antagonist of the spirodiketopiperazine class that is in late stage clinical development for the treatment of HIV infection. 873140 demonstrates potent in vitro antiviral activity with a 50% inhibitory concentration (IC₅₀) against CCR5-tropic HIV-1 in the subnanomolar range and demonstrates a slow receptor offset rate with no appreciable dissociation over 150 h in vitro ^[5,6]. This study represents the first administration of this agent to HIV-infected subjects to compare the antiviral effect, safety, tolerability, and pharmacokinetics of 873140 versus placebo during 10 days of monotherapy.

Methods

Study design

This was a randomized, double-blinded, placebo-controlled, multi-center study in HIV-infected adults. The study was approved by the Institutional Review Boards at each site and subjects signed an informed consent. Subjects underwent a screening evaluation within 30 days of dosing. Inclusion criteria included a positive HIV test, CCR5-using virus as determined by the PhenoSense HIV Entry assay (ViroLogic, Inc., South San Francisco, California, USA), CD4 cell nadir > 200 × 10⁶ cells/l, HIV RNA > 5000 copies/ml, and stable viral load defined by being within 0.5 log₁₀ over the previous 30-90 days. Patients could have been naive to previous antiretroviral therapy or have taken up to two previous highly active antiretroviral therapy regimens. Treatment-experienced subjects could not have received any antiretroviral therapy in the preceding 90 days prior to screening. Upon enrollment, subjects were randomized to one of the following four groups and received blinded treatments (n = 10 per arm) for 10 days: treatment group A, 873140 200 mg per oral (p.o.) once daily (q.d.) or placebo; treatment group B, 873140 200 mg p.o. twice daily (b.i.d.) or placebo; treatment group C, 873140 400 mg p.o. q.d. or placebo; treatment group D, 873140 600 mg p.o. b.i.d. or placebo.

In each dosing group, eight of 10 subjects were randomized to receive active dose and two received placebo. All doses were administered after a meal containing approximately 30% fat. Doses were observed on the morning of each clinic visit (days 1, 2, 4, 5, 8, 10) and all other doses were self-administered on an outpatient basis. After completion of the dosing period, subjects had a 14-day (day 11-24) post-treatment period to assess the postdose antiviral effect of 873140. Safety and tolerability were assessed by adverse events (AE), clinical and laboratory evaluations, vital signs, and 12-lead electrocardiograms (ECG). Efficacy evaluations included plasma HIV-1 RNA and lymphocyte subsets. Serial pharmacokinetic sampling for 873140 plasma concentrations was performed on days 1 and 10. Plasma concentrations were determined by a validated LC/MS/MS method with a lower limit of quantification of 0.5 ng/ml.

Pharmacokinetic and pharmacokinetic/pharmacodynamic analyses

Pharmacokinetic parameters were determined using noncompartmental methods. Pharmacokinetic parameter estimation and pharmacokinetic/pharmacodynamic modeling were performed with WinNonlin 4.1 (Pharsight, Mountain View, California, USA). The following E_max model was used to fit the pharmacokinetic-antiviral effect data:

E = (E_max AUC)/(AUC₅₀ + AUC)

where E_max is the maximum reduction in HIV RNA, AUC is the area under the 873140 plasma concentration-time curve and AUC₅₀ is the 873140 AUC that achieves an effect that is 50% of the E_max.

Viral tropism

Viral tropism was determined at screening and on study days 1, 5, 10, and 24 by the PhenoSense HIV Entry assay.

Statistical analysis

Safety parameters including adverse events, laboratory evaluations, vital signs, and 12-lead ECG were listed by subject and summarized by treatment. Antiviral activity was assessed as the plasma HIV-1 RNA change from baseline on day 11 and at nadir (maximum reduction). CD4 cell count change from baseline on day 11 was summarized by treatment. Dose-proportionality of 873140 pharmacokinetic parameters was assessed with an analysis of variance (ANOVA) model using PROC MIXED based on dose-normalized pharmacokinetic parameters. Investigation of accumulation ratio and time invariant pharmacokinetics was assessed by ANOVA with terms for subject as random effect and day as fixed effect for each treatment. All statistical analyses were conducted with SAS Version 8.2 (SAS Institute, Cary, North Carolina, USA).

Results

Subject accountability

A total of 40 subjects were enrolled and 39 subjects completed the study. One subject in the 200 mg q.d. dose group discontinued therapy for a reason unrelated to study drug. Demographics are given in Table 1. Twenty subjects were Caucasian, 11 Hispanic, and nine were African-American.

Table 1

Efficacy

The median change in HIV RNA from baseline is shown in Fig. 1. The log₁₀ decline at nadir and the percentage of subjects achieving a 1 log drop is shown in Table 2. A dose-dependent decrease in HIV RNA was observed with the greatest effect of a mean 1.66 log₁₀ decline seen at the highest dose of 600 mg b.i.d. with all subjects in this cohort achieving at least a 1 log₁₀ decline. The nadir HIV RNA most commonly occurred on day 12, but ranged between day 5 and 24 (14 days postdosing) for subjects receiving 873140. No differences were noted in antiviral response between subjects who were naive to therapy or those having previously received antiretroviral drugs. CD4 lymphocyte counts on day 11 were not significantly different from baseline.

Fig. 1

Table 2

Safety

There were no deaths, serious adverse events, or grade 4 AE reported. Twenty-eight of 40 subjects (70%) experienced 69 AE that were considered by the investigator to be related to the study drug. The most commonly reported drug-related AE were gastrointestinal in nature. Diarrhea was reported more frequently in subjects receiving 873140 (25-57%) compared to placebo (0%). The incidence of loose stools was similar in subjects taking 873140 (13-38%) and in those taking placebo (33%). Nausea and abdominal pain occurred in 13-38% of subjects in the 873140 groups and 11% in subjects receiving placebo. The incidence of gastrointestinal AE was 57% at 200 mg q.d., 50% at 200 mg b.i.d., 75% in the 400 mg q.d. and 600 mg b.i.d. groups, and 44% in the placebo group. Gastrointestinal AE usually occurred on day 1 and generally resolved within 1-3 days while subjects continued on therapy. Two subjects received supportive medications for gastrointestinal AE: one received a single dose of loperamide and one received two doses of promethazine. Other AE included minor central nervous system complaints such as headache and dizziness and occurred with low frequency in only one or two subjects in both the active treatments and placebo groups. One subject experienced grade 3 fatigue 4 days after his first dose of 873140 (200 mg b.i.d.) which resolved 14 days after onset. All other drug-related AE were mild or moderate in intensity. There were no clinically significant changes in vital signs or ECG interval in subjects treated with 873140. In eight subjects with hepatitis C virus (HCV) coinfection, serum HCV RNA was not significantly altered between day 1 and day 11.

Tropism and phenotype

One subject randomized to the 200 mg q.d. group had a transient detection of both CCR5 and CXCR4-using viruses on day 10 of the study. CCR5-using virus only was detected in this subject at other timepoints on therapy (day 1 and 5) and at follow-up on day 24. This subject had a 0.5 log₁₀ decrease in HIV RNA during the study, consistent with the mean decrease for this dosing group. A preliminary analysis of this subject demonstrated that CCR5- and CXCR4-using virus was pre-existing prior to therapy but that is was below the assay detection limit. In all other subjects only CCR5-using virus was detected during the trial and at follow-up.

Pharmacokinetics

Pharmacokinetic parameters of 873140 on day 10 are shown in Table 3. 873140 was readily absorbed with a median t_max of 1.75-2.5 h on day 10 of dosing. AUC(0-∞) and AUC(0-τ) increased with total daily dose; the increase was slightly greater than dose-proportional on day 10. Some accumulation was observed with AUC(0-τ) values on day 10 that were 41%, 79%, and 80% higher than the AUC(0-τ) on day 1 for the 200 mg q.d., 200 mg b.i.d., and 600 mg b.i.d. regimens, respectively. This increase in AUC over time was not seen at 400 mg q.d.

Table 3

Pharmacokinetics/pharmacodynamics (PK/PD)

HIV-infected subjects with higher 873140 exposures tended to have a greater antiviral response. An E_max model described the relationship between the day 10 AUC(0-24) and day 11 HIV-1 RNA decline from baseline as shown in Fig. 2. Parameter values were 1.92 ± 0.32 copies/ml log₁₀ decline in HIV-RNA for E_max and 492 ± 229 ng/h/ml for AUC₅₀.

Fig. 2

Discussion

CCR5 represents a novel target for development of new antiretroviral drugs. This trial demonstrated that 873140 possesses potent activity against R5-tropic HIV strains during short-term monotherapy. The antiviral effect was similar between treatment naive and experienced subjects, which is expected for a compound directed toward a new target. The mean 1.6 copies/ml log₁₀ decline in HIV RNA is similar to other investigational drugs in this class, as well as to that seen with nucleoside reverse transcriptase inhibitors and protease inhibitors, further validating CCR5 as an important target for further drug development ^[7-10].

Of note, the HIV-RNA levels continued to decline after 873140 was discontinued with the nadir generally occurring on day 12, approximately 48 h after treatment was stopped (Fig. 1). This extended antiviral effect may be a consequence of the prolonged binding of 873140 to CCR5. In an in vitro assay using membrane preparations, various CCR5 antagonists were shown to have extended binding to the receptor ^[6]. 873140 demonstrated a half-life of receptor occupancy estimated to be in excess of 150 h ^[6]. This delay in achieving viral load nadir has also been observed in short-term clinical studies of other investigational CCR5 antagonists and in SIV-infected macaques receiving a CCR5 inhibitor ^[7,8,11]. Ongoing clinical trials including 873140 in combination with other antiretrovirals will determine both the activity and durability of 873140-based antiretroviral regimens.

A range of doses (200-1200 mg/day) was studied to allow examination of exposure-response relationships. In addition, the dose of 400 mg/day was administered either once daily or in divided doses twice daily to explore the effect of dosing frequency on the antiviral activity of 873140. PK/PD modeling of the relationship between various plasma PK parameters (total daily AUC, maximum and minimum concentrations-C_max, and C_min) and antiviral activity (HIV RNA day 11 or nadir change from baseline) demonstrated that overall exposure, as described by plasma AUC, provided the best fit of the PK/PD model shown in Fig. 2. A comparison of the 400 mg q.d. and 200 mg b.i.d. regimens supported the notion that plasma AUC and not C_max was the better PK parameter linked to efficacy in this study. An evaluation of the plasma C_min-antiviral effect relationship was limited because many C_min values were below the assay limit of detection for the q.d. regimens. The AUC-antiviral effect relationship was used to select doses for future studies, which will continue to explore the exposure-response relationship of various 873140 regimens in combination with other antiretrovirals.

873140 was well tolerated during this short term study with gastrointestinal complaints reported as the most common adverse event. When these events did occur, they generally began on day 1 and resolved in the majority of patients over 1-3 days. Adverse events were generally mild and supportive medications for nausea or diarrhea were only given to two subjects in the trial.

873140 has now progressed into larger late stage clinical trials. The availability of a new, potent class of drugs to the HIV clinician has numerous implications. The successful development of the CCR5 antagonist class will lead to new treatment options for HIV-infected subjects.

Acknowledgements

The authors acknowledge the valuable contributions of Thomas Murtaugh, Lei Fang, and Sara Sparks.