Clinical efficacy and toxicity data on phase I study of fosbretabulin in combination with everolimus in neuroendocrine tumors.

Abstract

4114 Background: Fosbretabulin, a synthetic, water-soluble, phosphorylated prodrug of the natural product combretastatin A4 (CA4P), initially isolated from the bark of the South African bush willow, Combretum caffrum, is the lead compound in a class of agents termed vascular disrupting agents (VDAs). Everolimus, an mTOR inhibitor, is FDA approved for the management of well-differentiated NETs. A Phase I trial combining fosbretabulin and everolimus to determine the recommended Phase II trial dose (RP2D), safety data and early clinical efficacy in metastatic GEPNET patients was conducted. Methods: An investigator-initiated, single center, open-label, phase I study involving GEPNETs incorporated partial order continual reassessment method (PO-CRM) to define the dose escalation. The primary objective was to establish the maximum tolerated dose (MTD) of the combination of everolimus and fosbretabulin in NETs that have progressed after at least one prior regimen for metastatic disease. Secondary objective included identifying the safety profile of the combination using NCI CTCAE4 reporting criteria. Patients received daily oral everolimus (2.5 mg, 5 mg, 7.5 mg, and 10 mg). Fosbretabulin was administered IV 60 mg/m2 either q3 weekly or q weekly based on PO-CRM. Patients were treated for 12 weeks with all combinations. RECIST 1.1 was used to evaluate radiological responses at 3 month. Results: Of the 17 patients enrolled, 16 completed the 12-week trial. One patient was not evaluable due to noncompliance. No DLTs were observed at day 21. The highest dose of 10 mg daily oral everolimus in combination with weekly 60mg/m2 IV fosbretabulin is the RP2D. No grade 4 or 5 toxicities were noted. Grade 3 toxicities were seen in 5 patients; abdominal pain and hyperglycemia (not related to study drug), fatigue (possibly related), decreased lymphocyte count and anemia (related). Several patients had delay in treatment due to grade 2 AE’s (GI symptoms, rash, thrombocytopenia) and one patient was unable to complete treatment due to pneumonitis. All evaluable patients except one had stable disease at 3 months. One patient showed SD but non target lesion demonstrated PD. One patient had > 30% decrease in tumor size but overall sum of lesions showed SD. A detailed table with all grade toxicities and waterfall plot of RR will be presented at the meeting. Conclusions: Ten mg PO daily everolimus plus 60 mg/m2 fosbretabulin IV weekly is the RP2D. Early clinical data suggests clinical activity and stable disease in all but one patient at 3 months. Clinical trial information: NCT0301429.