First-in-Human Study of AT13148, a Dual ROCK-AKT Inhibitor in Patients with Solid Tumors

Abstract

Purpose: AT13148 is an oral AGC kinase inhibitor, which potently inhibits ROCK and AKT kinases. In preclinical models, AT13148 has been shown to have antimetastatic and antiproliferative activity.

Patients and methods: The trial followed a rolling six design during dose escalation. An intrapatient dose escalation arm to evaluate tolerability and a biopsy cohort to study pharmacodynamic effects were later added. AT13148 was administered orally three days a week (Mon-Wed-Fri) in 28-day cycles. Pharmacokinetic profiles were assessed using mass spectrometry and pharmacodynamic studies included quantifying p-GSK3β levels in platelet-rich plasma (PRP) and p-cofilin and p-MLC2 levels in tumor biopsies.

Results: Fifty-one patients were treated on study. The safety of 5-300 mg of AT13148 was studied. Further, the doses of 120-180-240 mg were studied in an intrapatient dose escalation cohort. The dose-limiting toxicities included hypotension (300 mg), pneumonitis, and elevated liver enzymes (240 mg), and skin rash (180 mg). The most common side effects were fatigue, nausea, headaches, and hypotension. On the basis of tolerability, 180 mg was considered the maximally tolerated dose. At 180 mg, mean C _max and AUC were 400 nmol/L and 13,000 nmol/L/hour, respectively. At 180 mg, ≥50% reduction of p-cofilin was observed in 3 of 8 posttreatment biopsies.

Conclusions: AT13148 was the first dual potent ROCK-AKT inhibitor to be investigated for the treatment of solid tumors. The narrow therapeutic index and the pharmacokinetic profile led to recommend not developing this compound further. There are significant lessons learned in designing and testing agents that simultaneously inhibit multiple kinases including AGC kinases in cancer.

Figure 1. The dose escalation scheme

Dose was doubled from 5 - 160 mg, following which a more conservative increase in dose to 240 mg and 300 mg was evaluated. Following grade 4 hypotension being seen at 300 mg an intra-patient dose escalation schedule was explored to evaluate if this improved tolerability of higher doses. The dose of 180 mg was considered tolerated pre- and post-treatment biopsies were conducted to evaluate pharmacodynamics effects.

Figure 2. Relationship of hypotension and pharmacokinetic parameters

The maximum drop in supine systolic blood pressure was measured and correlated with PK profiles of individual patients in patients where matched blood pressure and PK measurements were available at doses 160 mg, 240 mg and 300 mg. A) Relationship between AUC and drop in blood pressure r² = 0.17. B) Relationship between Cmax and maximal drop in blood pressure r² = 0.25.

Figure 3. Pharmacodynamic effects in platelet-rich plasma

Phosphorylation of GSK3β is a downstream event of AKT activation and reduction of p-GSK3β was quantified in platelet rich plasma before and after treatment with AT13148. A) The relationship of the plasma levels of AT13148 and p-GSK3β across the dose levels of 160 - 300 mg. There was a trend towards reduction of p-GSK3β and increasing plasma levels of AT13148, r² = 0.17, p = 0.0354. B) p-GSK3β normalized to total GSK3β levels were reduced between 2 - 24 hrs after treatment of AT3148 at the 300 mg cohort. The asterisk indicates significance in Dunnett’s test. The changes were not significant at doses lower than 300 mg.

Figure 4. Pharmacodynamic effects in tumor tissue

Biopsies were done at the dose level of 180 mg thrice a week. Phosphorylation of cofilin normalized to GAPDH at baseline and at 15 - 28 days of intermittent dosing was assayed using an immuno-chemiluminescence assays and results are presented as percentage of pre-dose levels (A) A reduction of more than 50% of p-cofilin levels were seen in 3/8 patients. (B) Phosphorylation of MLC2 was measured by IHC in pre- and post-treatment tumor specimens of patients treated with AT13148 showing reduction in phosphorylation in only 1/5 samples.