Abstract C167: An SN38 dendrimer nanoparticle, DEP irinotecan (SN38-SPL9111), demonstrates efficacy in mouse models of gastrointestinal cancer and augments anti-tumor effects of immune checkpoint blockade and PARP inhibition
Authors: Blyth Benjamin J , Kelly Brian D , Giannis Michael , Cargill Anne , Seta Aynaz , Heery Graham P , Eglezos Anthony , Johnstone Cameron N , Paull Jeremy R A 
Published: December 2023

Background: Irinotecan is a topoisomerase 1 inhibitor pro-drug used to treat gastrointestinal (GI) cancers including as first line for colorectal cancer (CRC) as part of the FOLFIRI plus monoclonal antibody (mAb) regimen, and for pancreatic cancer in the FOLFIRINOX regimen. However, irinotecan causes severe and dose-limiting side effects, including diarrhea and neutropenia. Starpharma has developed a highly optimized polylysine dendrimer enhanced (DEP) nanoparticle conjugate of the irinotecan active metabolite, SN38 (DEP SN38 or DEP irinotecan). DEP SN38 avoids the need for liver conversion of irinotecan to SN38 and achieves preferential tumor targeting. DEP SN38 is in phase 2 clinical investigation as monotherapy or combination therapy in patients with solid tumors (EudraCT no: 2019-001318-40). SN38 is known to enhance the efficacy of immune checkpoint blockade (ICB) via effects on immune cells in the tumor microenvironment. Here, we evaluated the anti-tumor effects of DEP SN38 alone or in combination with either ICB (anti- programmed cell death-1 [PD1] mAb) or poly adenosine diphosphate (ADP) ribose polymerase (PARP) inhibition (olaparib) in mouse models of GI cancer.

Methods: HT29 (human CRC) and CAPAN-1 (human pancreatic cancer) cell line xenografts were established subcutaneously in BALB/c nude or NOD-scid-Gamma immunodeficient mice, respectively. Three doses of DEP SN38 (at 5-10mg/kg SN38) or irinotecan (35-80 mg/kg) were administered intravenously (IV) on days 1, 8, 15. Olaparib (50 mg/kg) was delivered by daily IV injection for 5 days/week over 3 weeks. DEP SN38 (IV on days 1, 8, 15 at 18-35 mg/kg SN38) or irinotecan (75 mg/kg) plus rat anti-PD1 mAb therapy or control mAb (intraperitoneally, 100 mg/kg then 50 mg/kg on days 5, 8, 12) was evaluated in both MC38 (C57BL/6) and CT26 (BALB/c) allograft models of CRC. Toleration of drug was bodyweight loss ≤15%.

Results: DEP SN38 treatment of HT29 or CAPAN-1 xenografts led to tumor regressions, prolonged control of tumor growth and improved survival. In contrast, conventional irinotecan had minimal effect on tumor growth versus vehicle control. DEP SN38 was well tolerated by mice with minimal bodyweight loss. Administration of anti-PD1 mAb alone confirmed the known modest sensitivity of MC38, and resistance of CT26 syngeneic tumors, to ICB. DEP SN38 plus anti-PD1 mAb, enhanced anti-tumor responses in the MC38 model beyond those seen for each agent alone and also resulted in tumor eradication and prolonged survival. In the CT26 model, anti-PD1 mAb was also augmented by addition of DEP SN38 but not irinotecan alone, despite resistance of CT26 tumors to anti-PD1 mAb alone. The HT29 CRC model was resistant to Olaparib alone. In contrast, anti-tumor effects and prolonged survival were observed with olaparib plus DEP SN38.

Conclusions: DEP SN38 demonstrated superior efficacy compared to irinotecan when used in models of GI cancer. The anti-tumor efficacy of both ICB and PARP inhibition was augmented by DEP SN38 in models of CRC, and these combinations should be investigated clinically.

Citation Format: Benjamin J Blyth, Brian D Kelly, Michael Giannis, Anne Cargill, Aynaz Seta, Graham P Heery, Anthony Eglezos, Cameron N Johnstone, Jeremy R A Paull. An SN38 dendrimer nanoparticle, DEP irinotecan (SN38-SPL9111), demonstrates efficacy in mouse models of gastrointestinal cancer and augments anti-tumor effects of immune checkpoint blockade and PARP inhibition [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C167.