Efficacy of SBP-101, a polyamine metabolic inhibitor, administered in combination with gemcitabine and nab-paclitaxel, as a first-line treatment for patients with metastatic pancreatic ductal adenocarcinoma.

575 Background: SBP-101, a polyamine metabolic inhibitor, inhibited growth in 6 human pancreatic ductal adenocarcinoma (PDA) cell lines and 3 murine xenograft tumor models of human PDA. SBP-101 monotherapy in heavily pre-treated PDA patients (> 2 prior regimens) showed a median survival of 5.9 months at the optimal dose level. Purpose: To assess the PK, safety and efficacy of SBP-101 in combination with gemcitabine (G) and nab-paclitaxel (A) in patients with previously untreated metastatic PDA. Methods: In a modified 3+3 dose escalation scheme, subcutaneous injections of SBP-101 were dosed at 0.2, 0.4 or 0.6 mg/kg days 1-5 of each 28-day cycle. G (1000 mg/m 2 ) and A (125 mg/m 2 ) were administered intravenously on Days 1, 8, and 15 of each cycle. PK was evaluated on day 1 of cycle 1 in cohorts 1-3. Safety was evaluated by clinical and laboratory assessments. Efficacy was assessed by CA19-9 levels, objective response using RECIST criteria, progression-free survival (PFS) and overall survival (OS). A 4th cohort using a modified dosing schedule of 0.4 mg/kg SBP-101 days 1-5 for cycles 1-2 and days 1, 8, and 15 every cycle thereafter was added to mitigate hepatic toxicity, and that dose and schedule were recommended for Phase 1b expansion. Results: Fifty patients were enrolled (N=25, Phase 1a and N=25, Phase 1b) and received up to 13 treatment cycles. SBP-101 plasma C max and AUC 0-t increased in a slightly more than dose proportional manner and were unchanged by the addition of G and A. PK parameters of G and A were unaltered by increasing doses of SBP-101. The most common nonserious adverse events related to SBP-101 (>10%) are fatigue (N=14), LFT/transaminase abnormalities (N=15), vision abnormalities (N=10), injection site pain (N=13), dehydration (N=7), nausea (N=7). Serious adverse events related to SBP-101 observed in some subjects include hepatic toxicity (N=6) and retinal toxicity (N=8) both occurring after prolonged treatment and requiring dose reduction or discontinuation. At the recommended dose and schedule (N=30), CA19-9 levels decreased 60-99% in 19 of 29 evaluable patients, with 1/29 (3%) achieving a complete remission 13/29 achieving partial responses (45%) and 10/29 achieving stable disease at 8 weeks (35%). PFS was confounded by SBP-101 dosing holds implemented to investigate potential toxicity. Sixteen subjects are in survival follow-up. Median OS is 10.1 months and is not final. Conclusions: Interim results suggest SBP-101 may enhance first-line treatment with G and A in patients with metastatic PDA. Hepatic toxicity can be mitigated with dose reduction or discontinuation. A vision screening program will be used in future studies to mitigate retinal toxicity. Clinical trial information: NCT03412799.