To assess the safety of atopaxar, the Japanese Lessons from Antagonizing the Cellular Effect of Thrombin (J-LANCELOT) Trial [
29] consisting of two multicenter, randomized, double-blind, placebo-controlled phase II studies in Japanese patients with ACS or high-risk artery disease was conducted. In this trial 241 patients with NSTEMI or UA were randomized to 50, 100, or 200 mg atopaxar for 12 weeks including a 400 mg loading dose compared to placebo and placebo loading dose [
29].
In the CAD study, 263 patients were randomized to receive the same doses of atopaxar as in the ACS study. In contrast, they did not receive a loading dose and were treated for 24 weeks [
29]. The primary safety endpoint was the incidence of bleeding events adjudicated according to the Clopidogrel in Unstable Angina to Prevent Recurrent Events CURE [
32] and TIMI [
33] definitions. The secondary endpoint was the incidence of major cardiovascular adverse events (MACE), defined as cardiovascular death, MI, stroke, or recurrent ischemia. Compared to placebo TIMI minor bleeding was not increased in atopaxar treated patients [ACS: 6.6% placebo vs. 5.0% atopaxar (all dose groups); CAD: 1.5% placebo vs. 1.5% atopaxar (all dose groups)] without the occurrence of any TIMI major bleeding [
29]. A numerical increase in any TIMI bleeding with the dose of 200 mg atopaxar was observed (ACS: 16.4% placebo vs. 23.0% atopaxar,
P = 0.398; CAD: 4.5% placebo vs. 13.2% atopaxar,
P = 0.081) [
29]. The rate of MACE in the combined atopaxar groups was not different from placebo [ACS: 6.6% placebo vs. 5.0% atopaxar (all dose groups),
P = 0.73; CAD: 4.5% placebo vs. 1.0% atopaxar (all dose groups),
P = 0.066] [
29]. TRAP-induced platelet aggregation assessed in 42 ACS patients and 80 CAD patients showed inhibition by 20–60% with 50 mg atopaxar and by 90% with 100 and 200 mg atopaxar in agreement with the results of phase I studies [
28,
29]. The most common adverse event (AE) was hepatic function disorder [ACS: 11.5% placebo vs. 23.3% atopaxar (all dose groups),
P = 0.064; CAD: 1.5% placebo vs. 10.2% atopaxar (all dose groups),
P = 0.032] [
29]. In detail, in the ACS patients hepatic function disorder was seen in 9.3%, 29.2%, and 29.5% in the 50, 100, and 200 mg atopaxar groups, respectively (100 mg atopaxar vs. placebo,
P = 0.015; 200 mg atopaxar vs. placebo,
P = 0.023). The rate of hepatic function disorder in CAD patients was lower. It was observed in 3.2%, 7.6%, and 19.1% in the 50, 100, and 200 mg atopaxar groups, respectively (200 mg atopaxar vs. placebo,
P = 0.001). Remarkably, a prolongation of QTc in the 100 mg (
P = 0.015) and 200 mg (
P = 0.037) groups in comparison with the placebo group was also observed.
Based on the same study design LANCELOT ACS and LANCELOT CAD studies have recently been completed to evaluate the safety of atopaxar outside of Japan in 603 and 720 patients, respectively [
30,
31]. Although no difference in any TIMI bleeding was observed in LANCELOT ACS [ACS: 10.1% placebo vs. 9.3% atopaxar (all dose groups),
P = 0.77], a trend towards increased TIMI bleeding in the atopaxar groups was seen in LANCELOT CAD [CAD: 6.8% placebo vs. 10.3% atopaxar (all dose groups),
P = 0.17]. Differences in bleeding rates reached significant levels when analyzed according to the CURE criteria [CAD: 0.6% placebo vs. 3.9% atopaxar (all dose groups),
P = 0.03]. TRAP-induced platelet aggregation was inhibited 74% at 1–3 h up to 92% at 3–6 h after loading dose corresponding to the results of J-LANCELOT and results of phase I studies [
28,
29]. Similar to the results from the J-LANCELOT trial, a dose-dependent hepatic enzyme elevation and a prolongation of the QTc interval at higher doses were seen. In LANCELOT ACS atopaxar significantly reduced ischemia on continuous electrocardiography (ECG) monitoring at 48 h compared with placebo [relative risk (RR) 0.67,
P = 0.02] defined as horizontal or down-sloping ST-segment depression ≥0.1 mV or upward ST-segment elevation ≥0.1 mV [
30]. The trial was not powered for differences in ischemic clinical endpoints.
The combined results of the phase II clinical trials would have been sufficiently positive to start phase III trials. However, the numerically greater incidence in safety endpoints and AE, such as QTc prolongation and liver enzyme elevation, as well as the lack of a convincing dose-related trend for safety and efficacy of atopaxar, limit the encouraging results of these clinical trials. Currently, the development of atopaxar by Eisai is discontinued.