Phase i pharmacokinetic and pharmacodynamic study of the pan-PI3K/mTORC vascular targeted pro-drug SF1126 in patients with advanced solid tumours and B-cell malignancies

Background: SF1126 is a peptidic pro-drug inhibitor of pan-PI3K/mTORC. A first-in-human study evaluated safety, dose limiting toxicities (DLT), maximum tolerated dose (MTD), pharmacokinetics (PK), pharmacodynamics (PD) and efficacy of SF1126, in patients with advanced solid and B-cell malignancies. Patients and methods: SF1126 was administered IV days 1 and 4, weekly in 28 day-cycles. Dose escalation utilised modified Fibonacci 3+3. Samples to monitor PK and PD were obtained. Results: Forty four patients were treated at 9 dose levels (90-1110 mg/m²/day). Most toxicity was grade 1 and 2 with a single DLT at180 mg/m² (diarrhoea). Exposure measured by peak concentration (C _max) and area under the time-concentration curve (AUC _0-t) was dose proportional. Stable disease (SD) was the best response in 19 of 33 (58%) evaluable patients. MTD was not reached but the maximum administered dose (MAD) was 1110 mg/m². The protocol was amended to enrol patients with CD20+ B-cell malignancies at 1110 mg/m ². A CLL patient who progressed on rituximab [R] achieved SD after 2 months on SF1126 alone but in combination with R achieved a 55% decrease in absolute lymphocyte count and a lymph node response. PD studies of CLL cells demonstrated SF1126 reduced p-AKT and increased apoptosis indicating inhibition of activated PI3K signalling. Conclusion: SF1126 is well tolerated with SD as the best response in patients with advanced malignancies.