ASH Annual Meeting
Photo courtesy of ASH
ORLANDO, FL—ABL001, an allosteric inhibitor of BCR-ABL1, has shown early evidence of single-agent activity in a multicenter, first-in-human, first-in-class trial of heavily treated patients with chronic myeloid leukemia (CML) that is resistant to or intolerant of prior tyrosine kinase inhibitors (TKIs), even at the lowest dose evaluated.
ABL001 and classical TKIs exhibit complementary mutation profiles, with ABL001 showing activity against TKI resistance mutations.
When combined with nilotinib in a mouse model of CML, ABL001 prevented the emergence of resistant disease even after treatment was discontinued.
“This produces a new therapeutic concept—that of allosteric inhibition,” said Oliver G. Ottmann, MD, of Cardiff University in the UK.
The ABL001 binding site is located in a region remote from the kinase domain and has the potential to combine with TKIs for greater pharmacologic control of BCR-ABL1.
“This obviously has the opportunity both for combining different treatments and for overcoming resistance to one or the other,” Dr Ottmann added.
Based on preliminary pharmacokinetic data and preclinical evidence, investigators proceeded to evaluate ABL001 in a phase 1 dose-escalation and dose-expansion study.
Their primary objective was to determine the maximum tolerated dose (MTD) in humans and the recommended dose for expansion (RDE). Secondary objectives were to evaluate the safety, tolerability, preliminary anti-CML activity, and pharmacokinetic and pharmacodynamic profile.
Dr Ottmann presented the findings during the 2015 ASH Annual Meeting as abstract 138.*
Study design
Patients received ABL001 orally as a single agent twice a day (BID) continuously until disease progression, unacceptable toxicity, consent withdrawal, or death.
The dose-escalation schema followed a Bayesian logistic regression model based on dose-limiting toxicities during cycle 1. Doses ranged from 10 mg to 200 mg BID.
A subsequent dose-expansion phase was planned to augment the data generated in the dose-escalation phase and to include patients with Ph-positive acute lymphoblastic leukemia resistant or intolerant to prior TKI therapy.
Dr Ottmann noted that there were 2 protocol amendments. The first amendment was made to include a once-daily (QD) dosing of ABL001 at 120 mg and 200 mg. The second amendment was made to evaluate the combination of 40 mg of ABL001 BID with nilotinib at 300 mg BID.
Inclusion/exclusion criteria
Patients had to be at least 18 years old with CML in chronic or accelerated phase. They had to have failed at least 2 prior TKIs or be intolerant of TKIs. Their performance status had to be 0–2.
Patients were excluded from the trial if they had an absolute neutrophil count less than 500/mm3, a platelet count less than 50,000/mm3, bilirubin level more than 1.5 x the upper limit of normal (ULN) or more than 3.0 x ULN in patients with Gilberts syndrome.
Their aspartate aminotransferase or alanine aminotransferase could not be above 3 x ULN, and creatinine could not be above 1.5 x ULN.
Patients were also excluded if they needed treatment with strong inhibitors or inducers of CYP3A4 or its substrates with narrow therapeutic index.
Patient demographics
Fifty-nine patients were enrolled on the trial at the time of the presentation and they had “typical” characteristics of patients at this stage, Dr Ottmann said.
Their median age was 56 (range, 23–78). Almost two-thirds (61%) were male and 39% female.
All but 1 patient had an ECOG performance status of 0, and patients had a median of 3.5 (range, 2–5) prior lines of therapy. Twenty-four patients (41%) had 2 prior TKIs, and 35 (59%) had 3 or more TKIs. Forty-five patients (76%) were resistant and 14 (24%) were intolerant to their prior TKI.
All but 1 patient had chronic phase CML, 18 (31%) were TKD nonmutated, 14 (24%) were mutated, and 17 (46%) were not evaluable.
Patient disposition
Of the 43 patients in the monotherapy BID cohort, 1 was treated at the 10 mg dose level, 5 at the 20 mg level, 12 at the 40 mg level, 12 at the 80 mg level, 8 at the 150 mg level, and 5 at the 200 mg level. They had a median duration of drug exposure ranging from 25 weeks to 67 weeks.
Of the 11 patients in the monotherapy QD group, 5 were treated at the 120 mg dose level and 6 at the 200 mg level. Their drug exposure was a median of 26 weeks for those receiving 120 mg and 9.8 weeks for those receiving the 200 mg dose.
And the 5 patients in the ABL001-plus-nilotinib group had a median of 6.3 weeks of drug exposure.
“We had a remarkably low rate of discontinuation to date,” Dr Ottmann pointed out.
Ten patients discontinued therapy, all in the monotherapy BID group, 1 at 10 mg, 2 at 40 mg, 2 at 80 mg, 3 at 150 mg, and 2 at 200 mg.
Seven patients discontinued for adverse events. Two patients withdrew consent, and 1 patient in the 40 mg group had disease progression, which is “quite remarkable in a phase 1,” Dr Ottmann said.
Pharmacokinetic profile
ABL001 is rapidly absorbed in a median of 2 to 3 hours, and there is a dose-proportional increase in exposure following single and repeated dosing.
The drug has an approximately 2-fold or lower accumulation on repeated dosing and a short elimination half-life of 5 to 6 hours.
Safety
“We have excellent tolerability,” Dr Ottmann said, with a small number of grade 3/4 adverse events (AEs).
Grade 3/4 AEs considered to be drug-related were mostly associated with hematologic suppression. Four patients (7%) had thrombocytopenia, 4 (7%) neutropenia, 3 (5%) anemia, 4 (7%) lipase increase, and 1 (2%) hypercholesterolemia.
AEs of all grades suspected of being related to the study drug and occurring in 5% or more of patients included thrombocytopenia (19%), neutropenia (15%), anemia (10%), nausea/vomiting/diarrhea (29%), arthralgia/myalgia (20%), rash (17%), fatigue (15%), lipase increase (14%), headache (14%), pruritus (10%), dry skin (7%), hypophosphatemia (7%), and acute pancreatitis (5%).
“The pancreatitis was reversible upon interruption or discontinuation of the drug,” Dr Ottmann explained.
There were 5 dose-limiting toxicities. Two patients had grade 3 lipase elevation in the 40 mg BID and 200 mg QD cohorts. One patient had grade 2 myalgia/arthralgia at 80 mg BID, 1 patient had a grade 3 acute coronary event at 150 mg BID, and 1 patient had a grade 3 bronchospasm at 200 mg BID.
No deaths occurred on the study, and the dose escalation is still ongoing.
Response
Twenty-nine patients with 3 months or more of follow-up were evaluable for response.
Twelve patients, who at baseline had hematologic relapse, achieved complete hematologic response within 2 months, and 8 who had cytogenetic relapse at baseline achieved a complete cytogenetic response within 3 to 6 months.
Of the 29 patients who had molecular relapse at baseline, 10 (34.5%) achieved a molecular response within 6 months, 7 (24.1%) had 1 log or more reduction in BCR-ABL1, 9 (31.0%) had less than a log reduction, and 3 (10.3%) had no reduction.
“The obvious question from the preclinical data,” Dr Ottmann said, “is do the mutations respond?”
And ABL001 has shown clinical activity across TKI-resistant mutations, such as V299L, F317L, and Y253H.
“So to conclude,” he said, “we have a new class, a new therapeutic category of drug, ABL001, which is quite well tolerated in extremely heavily treated patients with CML. We do consider this a promising approach.”
The trial was sponsored by Novartis.
*Data in the abstract differ from the presentation.