Clinical trials of R-(-)-gossypol (AT-101) in newly diagnosed and recurrent glioblastoma: NABTT 0602 and NABTT 0702

Abstract

Purpose: AT-101 is an oral bcl-2 family protein inhibitor (Bcl-2, Bcl-XL, Mcl-1, Bcl-W) and potent inducer of proapoptotic proteins. A prior study of the parent compound, racemic gossypol, demonstrated objective and durable responses in patients with malignant glioma. AT-101 has demonstrated synergy with radiation in animal models. The objectives of trial NABTT 0602 were to determine the MTD of AT-101 concurrent with temozolomide (TMZ) and radiation therapy (RT) (Arm I) and to determine the MTD of AT-101 when given with adjuvant TMZ after completion of standard chemoradiation (Arm 2). Separately in trial NABTT 0702, the survival and response rates of single agent AT-101 were evaluated in patients with recurrent glioblastoma.

Methods: In NABTT 0602 Phase I, a 3+3 design was used to define MTDs after maximal safe resection, patients with newly diagnosed glioblastoma received standard concurrent RT (60 Gy) and TMZ 75 mg/m2/day followed by adjuvant TMZ 150-200 mg/m2 days 1-5 in 28-day cycles (Stupp regimen). In Arm I, AT-101 was administered M-F during the six weeks of RT beginning 20 mg qd. In Arm 2, concurrent with each adjuvant cycle of TMZ, AT-101 was administered at a starting dose of 20 mg, days 1-21 followed by 7-day break for a maximum of 6 cycles. The PK blood samples were collected in the first three patients in each cohort of arm 1. In NABTT 0702 patients with recurrent glioblastoma received 20 mg p.o. per day for 21 of 28 days in repeated cycles to assess overall survival (OS).

Results: A total of sixteen patients were enrolled on the two study arms of NABTT 0602. In Arm 1 AT-101 was escalated from 20 to 30 mg where one of six patients experienced DLT (grade 3 GI ulcer). On Arm 2 one patient treated at 20 mg experienced DLT (grade 3 ileus, nausea and diarrhea). The cohort was expanded to include seven patients without observation of DLT. PK results were consistent with drug levels from non-CNS studies. At study closure six patients are still alive. The median survival times for Arm I and Arm II are 15.2 months and 18.2 months, respectively. In NABTT 0702 fifty-six patients were enrolled and forty-three were eligible for imaging response. Sixteen patients (29%) had stable disease as best response and one partial response was observed. The median OS with single agent AT-101 was 5.7 months (95%CI: 3.8-7.6 months) for patients with rGBM.

Conclusions: AT-101 can be safely administered with radiation therapy and TMZ in patients with newly diagnosed glioblastoma without toxicity unique to patients with CNS tumors. Because of toxicity observed in non-CNS AT-101 clinical trials, further dose-escalation was not attempted. The recommended dose for future studies that utilize continual AT-101 exposure is 20 mg days M-F concurrent with RT/TMZ and 20 mg days 1-21 for each 28-day cycle of TMZ. AT-101 has limited activity as a single agent in unselected patients with recurrent glioblastoma. Future trials should attempt to better understand resistance mechanisms and consider combination therapy.

Fig 1. Treatment schemas for NABTT 0602 arm I and arm II.

In arm I AT-101 was given five days per week during RT and concurrent with temozolomide for six weeks. In arm II enrollment and treatment with AT-101 started four weeks after completion of RT. AT-101 was administered concurrently with each adjuvant cycle of temozolomide.

Fig 2. Treatment schema for NABTT 0702 testing the single agent activity of AT-101 in patients with recurrent glioblastoma.

AT-101 administered 20 mg p.o. per day on days 1–21 of 28-day cycles until progression.

Fig 3. CONSORT diagram for NABTT 0602 and NABTT 0702.

Fig 4. Overall survival for entire cohort including arm I and arm II (NABTT 0602).

Fig 5. Overall survival for arm I and arm II separately (NABTT 0602).

Fig 6. AT-101 single agent objective response in patient with recurrent glioblastoma.

The MRI on the left is the post-contrast coronal image before treatment with AT-101. The MRI on the was performed with similar technique after seven months of AT-101 and demonstrates marked reduction in the enhancing abnormality.

Fig 7. Progression-free and overall survival for AT-101 monotherapy in patients with recurrent glioblastoma (NABTT 0702).