RG7128, a prodrug of PSI-6130

RG7128, a prodrug of PSI-6130

RG7128 is being developed by Pharmasset and Roche through our collaboration to develop nucleoside polymerase inhibitors for the treatment of chronic hepatitis C virus (HCV) infections. RG7128 is a pro-drug of a molecule we discovered named PSI-6130, an oral cytidine nucleoside analog. A pro-drug is a chemically modified form of a molecule designed to enhance the absorption, distribution and metabolic properties of that molecule. PSI-6130 is the active component of RG7128. At low concentrations, PSI-6130 was shown to be an inhibitor of HCV replication, specifically targeting the HCV RNA polymerase.

Phase 2b Trial (ongoing)

On April 24, 2009, Roche and we began dosing in a Phase 2b study with RG7128. The Phase 2b trial is anticipated to enroll about 400 treatment-naive, genotype-1 or genotype-4 HCV-infected patients. The trial will evaluate the dose and duration of treatment of RG7128 in combination with Pegasys plus Copegus. The primary efficacy endpoint of the trial will be the proportion of patients that achieve an SVR. Patients are expected to be enrolled into one of 5 arms:

* 24 weeks of total treatment, with RG7128 500mg BID in combination with Pegasys plus Copegus for 12 weeks, followed by 12 weeks of Pegasys plus Copegus
* 24 weeks of total treatment, with RG7128 1000mg BID in combination with Pegasys plus Copegus for 12 weeks, followed by 12 weeks of Pegasys plus Copegus
* 24 weeks of total treatment, with RG7128 1000mg BID in combination with Pegasys plus Copegus for 8 weeks, followed by a further 16 weeks of Pegasys plus Copegus
* 48 weeks of total treatment, with RG7128 1000mg BID in combination with Pegasys plus Copegus for 12 weeks, followed by a further 36 weeks of Pegasys plus Copegus.
* A control arm with only Pegasys plus Copegus for 48 weeks.

Patients in the 24 week arms will discontinue treatment at week 24 if they achieved an RVR. Patients who do not achieve an RVR will continue on the standard of care, Pegasys plus Copegus, until week 48. Patients are expected to be enrolled as two cohorts, with randomization of the second cohort, of about 300 patients, being initiated based on 12 week safety data of the first 100 patient cohort.

INFORM-1 Trial (ongoing)

On April 25, 2009, Roche, InterMune, Inc., and we announced the first results from our initial study of an interferon-free regimen for the treatment of patients chronically infected with HCV. This study, INFORM-1, combined for the first time in patients two oral, direct acting antiviral drugs, RG7128 and RG7227, an inhibitor of the HCV NS3/4 protease, which is being developed by InterMune, Inc., in collaboration with Roche. INFORM-1 is a randomized, double-blind, ascending dose Phase I trial. Patients receiving the combination of RG7227 and RG7128 for 14 days, without pegylated interferon or ribavirin, experienced a median reduction in HCV RNA of -4.8 to -5.2 log 10 IU/mL in the highest doses tested to date. The addition of RG7128 to RG7227 resulted in sustained HCV RNA reductions over the dosing period, with approximately 63% of patients having levels of virus in their blood below the limit of the quantification of the diagnostic assay (less than 40 IU/mL). Furthermore, 25% of patients in the highest dosage groups were below the limit of detection of the virus in their blood (less than 15 IU/mL) on the 14th day of dosing.

The combination was well tolerated over 14 days, with no treatment-related serious adverse events (SAEs), dose reductions or discontinuations. Pharmacokinetic analysis confirmed that there were no drug-drug interactions between the compounds.

The companies are now exploring combinations of RG7128 dosed twice-daily at 1000mg with RG7227 dosed twice-daily at 600mg and 900mg. In this expanded study, the companies also plan to explore this combination in treatment-experienced patients with HCV, or those who did not achieve SVR with a previous interferon-based treatment.

Phase 1 Studies

During September 2008, we completed the clinical activities in Part 3 of a Phase 1 clinical trial with RG7128 that was initiated by Roche and us in October 2006 under an IND filing. This expanded Phase 1 trial was a multiple center, observer-blinded, randomized and placebo-controlled study designed to investigate the pharmacokinetics, pharmacodynamics, safety, tolerability and food effect of RG7128 in healthy volunteers and in patients chronically infected with HCV genotype 1, 2 or 3. This Phase 1 trial also provided antiviral potency data over 14 and 28 days in patients chronically infected with HCV genotype 1 and following 28 days of treatment in patients chronically-infected with HCV genotypes 2 or 3. This adaptive Phase 1 study was comprised of three parts:

Part 1 was a single ascending dose study conducted in 46 healthy volunteers. The primary objective of Part 1 was to assess the safety, tolerability and pharmacokinetics of RG7128 following single ascending doses under fasting conditions. The secondary objective of Part 1 was to explore the effect of food on the pharmacokinetics of RG7128. Single oral doses of RG7128 were administered to 46 healthy volunteers in five sequential dose groups (500 mg, 1500 mg, 4500 mg, 6000 mg and 9000 mg) and one food effect group (1500 mg). Results from the single ascending dose portion of the study indicated:

* All doses of RG7128 studied (500 mg to 9000 mg) were generally safe and well-tolerated.
* All patients completed the study, and none experienced gastrointestinal adverse events or serious adverse events during the study.
* No hematologic or other safety laboratory abnormalities of clinical significance were noted.
* No maximum tolerated dose was identified.

Part 2 was a multiple ascending dose study conducted in 40 patients chronically infected with HCV genotype 1 who had previously failed interferon therapy. The primary objective of Part 2 was to assess the safety, tolerability and pharmacokinetics of RG7128 after once-daily (“QD”) or twice-daily (“BID”) dosing for 14 days. The secondary objective was to assess antiviral efficacy by measuring the change in HCV RNA. Results from the multiple ascending dose portion of the study indicated:

* RG7128 demonstrated potent, dose-dependent antiviral activity in four patient cohorts (8 active, 2 placebo per cohort) receiving 750 mg or 1500 mg administered either QD or BID for 14 days as monotherapy. The maximum decrease in HCV RNA from baseline was demonstrated in the patient cohort that received 1500 mg BID. RG7128 demonstrated mean HCV RNA decreases from baseline of 0.9 log (87.4% reduction), 1.5 log (96.8% reduction), 2.1 log (99.2% reduction) and 2.7 log (99.8% reduction) in patients receiving 750 mg QD, 1500 mg QD, 750 mg BID and 1500 mg BID, respectively. Based on the mean data, all four dose groups reached nadir values at Day 15. A maximum 4.2 log (99.9% reduction) HCV RNA decrease was demonstrated in a patient following 14 days of monotherapy with 1500 mg BID of RG7128, a value also below the level of detection, which was less than 15 International Units per milliliter (IU/ml).
* There was no evidence of viral rebound in any dose cohort during the 14 days of dosing.
* RG7128 was generally safe and well tolerated over 14 days of treatment of patients chronically infected with HCV genotype 1 who had previously failed interferon therapy. There were no serious adverse events, no adverse events requiring dose modification, and no dose-related gastrointestinal adverse events.

Part 3 was a 4-week study of RG7128 in combination with the current standard of care for chronic HCV infection, Pegasys (pegylated interferon) plus Copegus (ribavirin) in 81 treatment-naïve patients chronically infected with HCV genotype 1, and additionally, in 25 prior treatment non-responders, or patients who did not achieve an SVR with previous interferon-based therapy, who were chronically infected with HCV genotypes 2 or 3. The primary objective of this study was to assess the safety, tolerability, and pharmacokinetics of RG7128 in the clinically-relevant setting of combination therapy with the current standard of care for chronic HCV infection. The secondary objective of Part 3 was to evaluate the short-term change in HCV RNA. The study included three oral dose regimens of RG7128 (500 mg, 1500 mg and 1000 mg—cohorts 1,2 and 3, respectively) in patients chronically infected with HCV genotype 1 and one oral dose regimen of RG7128 (1500 mg—cohort 4) in patients chronically infected with HCV genotypes 2 or 3. All four dose regimens were administered twice-daily with Pegasys plus Copegus for 4 weeks. Dose cohorts 1, 2 and 4 enrolled 25 patients, with 20 patients randomized to receive RG7128 and five patients randomized to receive placebo, and cohort 3 enrolled 31 patients, with 25 patients randomized to receive RG7128 and six patients randomized to receive placebo, all administered in combination with standard of care. After completing four weeks of the triple combination regimen and a follow-up of four weeks of Pegasys plus Copegus, all patients are scheduled to receive up to 40 weeks of open-label standard of care dosing under a separate protocol.

Results from cohorts 1, 2 and 3 in 81 treatment-naïve patients chronically infected with HCV genotype 1 indicated:

* Following 4 weeks of treatment with RG7128 500mg BID with Pegasys plus Copegus (cohort 1), patients achieved a mean 3.8 log10 IU/mL decrease in HCV RNA and 30% (6 of 20) achieved undetectable levels of HCV RNA (<15 IU/ml), or rapid virologic response (“RVR”).
* Following 4 weeks of treatment with RG7128 1500mg BID with Pegasys plus Copegus (cohort 2), patients achieved a mean 5.1 log10 IU/mL decrease in HCV RNA and 85% (17 of 20) achieved RVR.
* Following 4 weeks of treatment with RG7128 1000mg BID with Pegasys plus Copegus (cohort 3), preliminary results indicated patients achieved a mean 5.1 log10 IU/mL decrease in HCV RNA and 88% (22 of 25) patients achieved RVR.
* Following 4 weeks of treatment with placebo with Pegasys plus Copegus, patients achieved a mean 2.9 log10 IU/mL decrease in HCV RNA and 18.75% (3 of 16) achieved RVR.

For cohorts 1, 2 and 3 in treatment-naïve genotype 1 patients, safety and tolerability for the 4-week treatment period were similar for RG7128 with Pegasys plus Copegus compared to placebo with Pegasys plus Copegus. There were no serious adverse events reported during the 4-week treatment periods of triple therapy, and most of the adverse events reported were of mild to moderate intensity. Headache and fatigue were the most frequently reported adverse events in patients who received active RG7128 plus Pegasys plus Copegus, with an overall frequency of 66% and 42% reporting at least one of these events, respectively. These events were also the most frequently reported adverse events in patients who received placebo with Pegasys and Copegus. In general, the adverse events reported were consistent with the clinical safety profile for Pegasys and Copegus, including the frequency and severity of these adverse events, as well as any general body system observations. Grade 3/4 neutropenia was observed in 31% of the placebo patients and in 12% to 30% of the RG7128 patients in each active dosing cohort. Grade 3 changes in hemoglobin were observed in 19% of the placebo patients and in 31% of the RG7128 patients. There were no clinically significant changes in hepatic, renal, or other safety laboratory parameters, vital signs, or electrocardiograms. Overall, there was no clinical evidence of any major organ toxicities related to RG7128. One patient in the active treatment group discontinued the study during the 4 week treatment period due to lower-gastrointestinal adverse events. At the time of study discontinuation, this patient had undetectable HCV RNA. RG7128 was generally safe and well-tolerated when administered for 4 weeks in combinations with Pegasus plus Copegus in patients with HCV genotype 1.

Results from the 1500 mg dose cohort (cohort 4) in 25 prior treatment non-responders, or patients who did not achieve an SVR with previous interferon-based therapy, and who were chronically infected with HCV genotypes 2 or 3 indicated:

* Following 4 weeks of treatment with RG7128 1500mg BID with Pegasys plus Copegus (cohort 4), preliminary results indicated patients achieved a mean 5.0 log 10 IU/mL decrease in HCV RNA and 90% (18 of 20) patients achieved RVR.
* Following 4 weeks of treatment with placebo with Pegasys plus Copegus, patients achieved a mean 3.7 log 10 IU/mL decrease in HCV RNA and 60.0% (3 of 5) achieved RVR.
* Safety and tolerability during the 4-week treatment period were similar for RG7128 with Pegasys plus Copegus compared to placebo with Pegasys plus Copegus. There were no serious adverse events reported during the 4-week treatment period, and most of the adverse events reported were of mild to moderate intensity. One subject discontinued RG7128, Pegasys and Copegus due to protocol specified stopping criteria (not treatment-emergent), and ECG changes. Adverse events reported in cohort 4 were similar to those reported in Cohorts 1-3. Grade 3/4 neutropenia was observed in 0% of the 5 placebo patients and in 20% of the 20 RG7128 patients in the active dosing cohort. Grade 3 changes in hemoglobin were observed in 20% of the placebo patients and in 25% of the RG7128 patients. There were no clinically significant changes in hepatic, renal, or other safety laboratory parameters, vital signs, or electrocardiograms. As seen in the patients infected with HCV genotype 1, there was no clinical evidence of any major organ toxicities related to RG7128. RG7128 was generally safe and well-tolerated when administered for 4 weeks in combination with Pegasus plus Copegus in patients with HCV genotypes 2 and 3.