The BLAZE high-dose arm showed increasing
separation over time of the curves of decline on ADAS-Cog 12 for placebo (dashed line) and intravenous crenezumab (solid line)
in the mild subgroup of patients (MMSE 20-26). In a post-hoc analysis of a group of patients with mild AD (MMSE 20-26) treated
with high-dose intravenous crenezumab, there was a 52.0% reduction in cognitive decline (p=0.29). In patients with mild-to-moderate
AD (MMSE 18-26) treated with high-dose intravenous crenezumab, there was a 10.3% reduction in cognitive decline (p=0.84). Importantly,
the sample size of the study was not expected to have adequate power to detect a modest but clinically significant difference between
active medication and placebo at the 5% significance level (as is commonly the case in Phase 2 studies in AD). Effect sizes and
p-values were not adjusted for multiplicity.
In the BLAZE study, patients in the high-dose
crenezumab arm showed less cognitive decline on the measure of global function, CDR-Sum of boxes, as compared to placebo. In mild-to-moderate
AD (MMSE 18-26), a 7.4% reduction in global functional decline (p=0.84) was observed. In a post-hoc analysis in patients with mild
AD (MMSE 20-26), treatment with high-dose intravenous crenezumab resulted in a 41.5% reduction in global functional decline (p=0.44).
Although the results were not statistically significant, the sample size of the study was not expected to have adequate power to
detect a modest but clinically significant difference between active medication and placebo at the 5% significance level (as is
commonly the case in Phase 2 studies in AD).
Safety Data from ABBY and
Crenezumab demonstrated favorable safety
and tolerability in Phase 2 clinical studies even at high doses. Crenezumab’s safety profile is especially reflected in a
low incidence of ARIA-E (0.3%) in Phase 2 clinical studies. ARIA-E was observed in only one patient who received high-dose intravenous
crenezumab in the ABBY study. No case of ARIA-E was reported in the placebo arm or the BLAZE study. Favorable pharmacokinetic properties
coupled with a favorable safety and tolerability profile enables crenezumab to penetrate the brain more readily at therapeutically
relevant doses. Since dose limiting toxicities are a potential reason for the failure of other antibodies to demonstrate efficacy,
crenezumab’s potential safety at high doses is a distinguishing product feature.
There was no imbalance in the overall rate
of AEs. AEs were observed in 91.3% of patients treated with crenezumab versus 90.3% of patients who received placebo. AEs were
generally mild-to-moderate and transient. AEs did not appear to be related to crenezumab exposure. Five deaths occurred during
ABBY and BLAZE, all in patients who received crenezumab during the randomized placebo-controlled period (1.4% of the crenezumab-treated
population). The overall rate of deaths is consistent with the background rate of death in the elderly AD population. There was
no consistent pattern for the cause of death and none were considered by the investigators to be related to crenezumab. It was
reported that 3.2% of crenezumab-treated patients developed pneumonia versus 0.6% in placebo-treated patients in ABBY and BLAZE,
but the rate of pneumonia cases in crenezumab-treated patients is consistent with the expected rate in the elderly population (2.5%–4.4%)
and no drug-related mechanism for pneumonia was identified.
Genentech has not disclosed detailed information
about serious adverse events associated with crenezumab either publicly or to us. However, at the 2014 Alzheimer’s Association
International Conference, it was reported that in the combined Phase 2 study populations, serious adverse events occurred at similar
rates in patients treated with crenezumab (16.5%) and in patients given a placebo (11.9%).
Phase 1b Study to explore
To explore safety at higher doses, crenezumab
was tested in a Phase 1b dose escalation clinical study (NCT02353598) conducted in the United States. This randomized, placebo-controlled,
double-blind, four parallel-arm study evaluated the safety and tolerability of at least four doses of intravenous crenezumab in
77 patients with mild to moderate AD (MMSE 18-28) between the ages of 50 to 90. An optional open-label extension stage was offered
to patients after completion of the double-blind stage of the study. At the 2017 AAIC meeting, Genentech presented the results
of the four cohorts with mild-to-moderate Alzheimer’s disease. No dose-limiting toxicities were observed at 30, 45, 60 and
120 mg/kg doses of crenezumab. No events of ARIA-E were observed in the Phase 1b study and only few patients (6 of 75) showed asymptomatic
Amyloid Related Imaging Abnormality-Hemsiderin (ARIA-H).The pharmacokinetic profile of crenezumab is dose proportional up to the
60 mg/kg dose and is consistent with historical data. The serum concentrations at this dose are four times higher than in the 15mg/kg
dose used in the Phase 2 trials. These safety and pharmacokinetic data of the Phase 1b dose escalation study support the continued
treatment of patients with crenezumab at the higher dose of 60 mg/kg.