Photo by Larry Young
LUGANO—Updated phase 1 results with TGR-1202 suggest this next-generation PI3kδ inhibitor lacks the hepatotoxicity associated with other PI3Kδ inhibitors.
Investigators also confirmed that no case of colitis has been reported to date with TGR-1202, and only 2% of evaluable patients on this trial have experienced grade 3-4 diarrhea.
The study is an ongoing, first-in-human trial in patients with relapsed or refractory hematologic malignancies.
Owen O’Connor, MD, PhD, of Columbia University Medical Center in New York, New York, shared results from this trial at the 13th International Congress on Malignant Lymphoma (abstract 038*). The trial is sponsored by TG Therapeutics, Inc., the company developing TGR-1202.
“TGR-1202 is a radically different sort of PI3kδ inhibitor,” Dr O’Connor said. “[I]t’s really a unique chemical entity that is different from the previous 2 structures [idelalisib and duvelisib] that you’ve probably heard something about.”
Study design
This ongoing trial of TGR-1202 is open to patients with hematologic malignancies who relapsed after or were refractory to at least 1 prior treatment regimen. Patients are eligible if they have an ECOG performance status of 2 or less with adequate organ system function, including absolute neutrophil count of 750/μL or greater and platelets of 50,000/μL or greater.
TGR-1202 is dosed orally, once a day in continuous, 28-day cycles. The original dose-escalation portion of the study was a classic 3+3 design, starting at 50 mg and increasing to 1800 mg. Patients who received prior therapy with a PI3K and/or mTOR inhibitor were excluded from the dose-escalation cohorts but were allowed in the expansion cohorts.
Dr O’Connor pointed out that, through cohort 5, TGR-1202 was taken in the fasting state. However, pharmacokinetic studies performed in the fed state revealed that the area under the curve (AUC) and Cmax could be doubled by taking the drug with food. So the expansions in the ongoing 800 mg and 1200 mg cohorts are being conducted in the fed state.
Dr O’Connor also noted that a subsequent, micronized version of TGR-1202 was developed. The micronization “essentially increases the surface area of the formulation, allowing for better bioavailability and markedly increases the AUC and Cmax exposure,” he said.
So the investigators conducted a second escalation with the micronized formulation, starting at 200 mg and increasing to 800 mg. At present, they are enrolling patients to the 800 mg and 1200 mg cohorts conducted in the fed state with the micronized formulation.
Demographics
Dr O’Connor presented data on 66 patients who were evaluable for safety and 51 for efficacy. The patients’ median age was 66 (range, 22–85), and 46 were male.
In all, there were 20 patients with chronic lymphocytic leukemia (CLL), 17 with follicular lymphoma, 10 with diffuse large B-cell lymphoma, 9 with Hodgkin lymphoma, 5 with mantle cell lymphoma, 3 with marginal zone lymphoma, 1 with Waldenström’s macroglobulinemia, and 1 with hairy cell leukemia.
Patients had received a median of 3 prior therapies (range, 1–14), and 36 (55%) had 3 or more prior therapies. Thirty-four patients (52%) were refractory to their prior therapy.
Efficacy
Dr O’Connor reported that higher doses of TGR-1202—1200 mg of the initial formulation and 600 mg or more of the micronized version—demonstrated rapid and profound responses in CLL, follicular lymphoma, and marginal zone lymphoma.
Responses have been limited in diffuse large B-cell lymphoma, Hodgkin lymphoma, and mantle cell lymphoma.
Eighty-eight percent of CLL patients achieved a nodal partial remission, and 63% achieved a response according to iwCLL criteria (Hallek 2008).
Safety and tolerability
Adverse events occurring in more than 10% of patients included nausea (41%), diarrhea (32%), fatigue (32%), headache (23%), vomiting (23%), cough (21%), decreased appetite (17%), rash (17%), constipation (14%), hypokalemia (14%), anemia, dizziness, dyspnea, neutropenia, and pyrexia (12% each), and abdominal pain (11%).
The most common grade 3-4 toxicity was neutropenia, occurring in 11% of patients.
“But other than that, the bulk of the toxicities in terms of grade 3-4 events were relatively modest,” Dr O’Connor said. “[I]t’s worth pointing out that diarrhea grade 3-4 only occurred in about 2% of patients in the population.”
Approximately 50% of patients (n=31) have been on study for more than 6 months, and approximately 30% taking a higher dose level have been on study for 6 months or more. Twenty-five of 37 patients exposed to 800 mg or more of the micronized formulation currently remain on study.
“So this gives you a sense that it is a very well-tolerated drug, with patients staying on for extended periods of time,” Dr O’Connor said.
He added that time on study becomes relevant in assessing some of the gastrointestinal toxicities seen with other PI3Kδ inhibitors, where it seems the median time to gastrointestinal toxicity is beyond 6 months.
“So far, and I’m willing to concede it’s early, but with half the patients being treated for over 6 months, [diarrhea/colitis] seems to be much lower than the experience with the other PI3 kinase inhibitors,” Dr O’Connor said.
“I think one of the more important features of [TGR-1202], and one that allows me to think we might be able to integrate this drug a little more readily into various combination regimens, are the discontinuations due to other adverse events.”
“Only 4% treated with [TGR-1202] had discontinuations secondary to adverse events. [A]nd it looks like the efficacy is in line with what we’d expect with some of the other drugs, but this [study] is actively accruing still.”
*Information in the abstract differs from that presented at the meeting.