Efficacy and safety of the hypoxia-activated prodrug TH-302 in combination with gemcitabine and nab-paclitaxel in human tumor xenograft models of pancreatic cancer

Tumors often contain hypoxic regions resistant to chemo- and radiotherapy. TH-302 (T) is an investigational hypoxia-activated prodrug that selectively releases the DNA cross-linker bromo-isophosphoramide mustard under hypoxic conditions. This study evaluated the efficacy and safety profile of combining T with gemcitabine (G) and nab-paclitaxel (nP) in human pancreatic ductal adenocarcinoma (PDAC) xenograft models in mice. Antitumor activity of the G + nP + T triplet was assessed and compared with T-alone or the G + nP doublet in the Hs766t, MIA PaCa-2, PANC-1, and BxPC-3 PDAC xenograft models. Efficacy was assessed by tumor growth kinetic analysis. Body weight, blood cell counts, blood chemistry, and the von Frey neuropathy assay were analyzed to evaluate safety profiles. Pharmacodynamic changes after the treatment were determined by immunohistochemistry of cell proliferation, DNA damage, apoptosis, hypoxia, and tumor stroma density. The G + nP + T triplet exhibited enhanced efficacy compared with T-alone or the G + nP doublet. Compared with vehicle (V), G + nP induced body weight loss, reduced neutrophil and lymphocyte counts, increased the levels of liver function parameters, and induced neurotoxicity. However, when T was added to G + nP, there was no statistically increased impairment compared to G + nP. The triplet significantly increased DNA damage, apoptosis, and tumor necrosis. Furthermore, the triplet further inhibited cell proliferation and reduced stroma density and intratumoral hypoxia. The triplet combination of G + nP + T exhibited superior efficacy but additive toxicity was not evident compared to the G + nP doublet in this study. This study provides a translational rationale for combining G, nP, and T in the clinical setting to assess efficacy and safety. A Phase I clinical trial of the triplet combination is currently underway (NCT02047500).

Abstract C287: Efficacy and safety of the TH-302, gemcitabine, and nab-paclitaxel combination in xenograft models of pancreatic cancer

Background: Tumors often consist of hypoxic regions which are resistant to chemo- and radiotherapy. TH-302 (T) is an investigational hypoxia-targeted drug that selectively releases the DNA cross-linker bromo-isophosphoramide mustard under hypoxic conditions. A randomized Phase 2 clinical trial in pancreatic ductal adenocarcinoma (PDAC) demonstrated a significant increase in progression-free survival from the addition of T to gemcitabine (G) vs. G only (NCT01144455). A Phase 3 trial of G + T compared to G + placebo is currently underway (NCT01746979). G + nab-Paclitaxel (nP) significantly prolonged overall survival in a recent Phase 3 trial (NCT00844649). We investigated the efficacy and safety profile of combining T with G and nP in PDAC xenograft models.

Methods: Four PDAC xenograft models were established by s.c. implantation of Hs766t, MIA PaCa-2, PANC-1 and BxPC-3 cells into the flank of nude mice. A ‘same day’ administration of T, nP and G with a Q3Dx5 regimen was employed: T, 50mg/kg, ip; nP: 30mg/kg, iv; and G: 60mg/kg ip. Saline treated animals served as vehicle control (V). Antitumor activity of the G + nP + T triplet was assessed, and compared with the G + nP doublet. Hematological, blood chemistry, and immunohistochemical-based analyses were also performed in PANC-1 bearing nude and/or CD-1 mice. Samples were collected 24 hours after the last treatment. Neuropathy assays were performed in CD-1 mice.

Results: Using tumor growth inhibition, and Kaplan-Meier analysis of median time to tumor size of 1000mm3 to evaluate antitumor activity, G + nP + T triplet exhibited enhanced efficacy compared with T-alone or the G + nP in all four models. Of note, the complete response rate (CR) of G + nP + T in the PANC-1 model reached 100%, compared to 10% and 50% in the T-alone and G + nP, respectively. G + nP or T-alone treatment reduced neutrophils or lymphocytes compared with V, but there was no additional decrease in neutrophil or lymphocyte count when T was added to G + nP compared to G + nP. Plasma ALT and AST levels were elevated after G + nP treatment, and G + nP + T did not further increase the levels of these liver function parameters. By immunostaining, Ki67-positive cells (a marker of cell proliferation) were significantly reduced after the drug treatment in the PANC-1 xenograft, and to a greater magnitude in G + nP + T. The necrotic region in G + nP + T was increased compared with all other groups. Employing the von Frey neuropathy assay, G + nP treated mice exhibited mechanical allodynia in the hind paw 9 days after initiation of treatment whereas mice treated with T did not, and there was no additive neuropathy in G + nP + T.

Conclusions: The triplet combination of G + nP + T exhibited superior efficacy but additive toxicity was not evident compared to G + nP. These studies provide a translational rationale for combining G, nP, and T in the clinical setting to assess efficacy and safety.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C287.

Citation Format: Jessica D. Sun, Qian Liu, Dharmendra Ahluwalia, Wenwu Li, Yan Wang, Ayesha S. Ruprell, Charles P. Hart. Efficacy and safety of the TH-302, gemcitabine, and nab-paclitaxel combination in xenograft models of pancreatic cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C287.