SBP-101, a polyamine metabolic inhibitor, administered in combination with gemcitabine and nab-paclitaxel, shows signals of efficacy as first-line treatment for subjects with metastatic pancreatic ductal adenocarcinoma.
Authors: Singhal Nimit , Sigal Darren , Tebbutt Niall C. , Hezel Aram F , Nagrial Adnan , Lumba Sumit , George Thomas J. , Smith Sheri Lynn , Gagnon Suzanne , Walker Michael , Cullen Michael T. 
Published: June 2021

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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/m2) and A (125 mg/m2) 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 fourth 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. Interim Results: Fifty patients were enrolled (N=25, phase 1a and N=25, phase 1b) and have received up to 12 treatment cycles. SBP-101 plasma Cmax and AUC0-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=15), LFT/transaminase abnormalities (N=15), vision abnormalities (N=6), injection site pain (N=13), dehydration (N=7), diarrhea (N=7) and nausea (N=6). Serious adverse events related to SBP-101 observed in some subjects include hepatic toxicity (N= 6) and retinal toxicity (N=6) both occurring after prolonged treatment and requiring dose reduction or discontinuation. There is no evidence of SBP-101-related bone marrow suppression or peripheral neuropathy. At the recommended dose and schedule (N=30), CA19-9 levels decreased 60-99% in 19 of 29 evaluable patients, with 12/28 evaluable patients achieving partial responses (43%) and 11/28 achieving stable disease at 8 weeks (39%). Nine subjects are ongoing. PFS was confounded by SBP-101 dosing holds implemented to investigate potential toxicity. Median OS has not been reached. 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. Retinal toxicity that occurred in some subjects is under investigation. Clinical trial information: NCT03412799.