A dose-escalation phase I study of a first-in-class cancer stemness inhibitor in patients with advanced malignancies.

2542 Background: Cancer Stem Cells (CSC) are considered to be fundamentally responsible for malignant growth, relapse, metastasis, and resistance to conventional therapies. BBI608 is an orally-administered first-in-class cancer stemness inhibitor which blocks CSC self-renewal and induces cell death in CSC as well as non-stem cancer cells by inhibition of the Stat3, Nanog and b-catenin pathways, and has shown potent anti-tumor and anti-metastatic activities pre-clinically. Methods: A phase 1 dose escalation studyin adult patients with advanced cancer who had failed standard therapies was conducted to determine the safety, tolerability, recommended phase 2 dose (RP2D), pharmacokinetics and preliminary anti-tumor activity of BBI608. A modified Simon accelerated titration scheme was used for dose escalation, with a cycle consisting of twice-daily oral administration of BBI608 for 4 weeks. Cycles were repeated every 4 weeks (28 days) until progression of disease, unacceptable toxicity, or other discontinuation criteria were met. Results: Fourteen cohorts (N=41) were dosed from 20 mg to 2000 mg/day with adverse events being generally mild; the most common being grade 1-2 diarrhea, nausea, anorexia and fatigue. Four grade 3 events included diarrhea (n=3) and fatigue (n=1). MTD was not reached and further dose escalation was limited by pill burden. By the 400 mg/day dose level the plasma concentration of BBI608 was sustained for over 8 hours at a concentration above 1.5 uM (several fold above the IC 50 ). 17/26 patients evaluable for tumor response achieved SD, for a DCR of 65%. Prolonged TTP was observed in 12/26 evaluable patients (46%), including patients with colorectal (CRC), head and neck, gastric, ovarian, melanoma, and breast cancer. In the subset of patients with CRC (N=18), SD was seen in 8/12 evaluable (67%). A median PFS of 14 weeks and median OS of 47 weeks were observed in evaluable CRC patients. Conclusions: Dose escalation of BBI608, a first-in-class cancer stem cell pathway inhibitor, has been achieved without dose limiting toxicity. BBI608 has shown an excellent safety profile, favorable pharmacokinetics, and encouraging signs of clinical activity particularly in CRC Clinical trial information: NCT01775423.