BackgroundImmune checkpoint inhibitors (ICIs) to date have demonstrated limited activity in advanced ovarian cancer (OC). Folate receptor alpha (FRα) is overexpressed in the majority of OCs and presents an attractive target for a combination immunotherapy to potentially overcome resistance to ICI in OCs. The current study sought to examine clinical and immunologic responses to TPIV200, a multiepitope FRα vaccine administered with programmed death ligand 1 (PD-L1) inhibitor durvalumab in patients with advanced platinum-resistant OC.MethodsFollowing Simon two-stage phase II trial design, 27 patients were enrolled. Treatment was administered in 28-day cycles (intradermal TPIV200 and granulocyte-macrophage colony-stimulating factor (GM-CSF) for 6 cycles and intravenous durvalumab for 12 cycles). Primary endpoints included overall response rate and progression-free survival at 24 weeks. Translational parameters focused on tumor microenvironment, PD-L1 and FRα expression, and peripheral vaccine-specific immune responses.ResultsTreatment was well tolerated, with related grade 3 toxicity rate of 18.5%. Increased T cell responses to the majority of peptides were observed in all patients at 6 weeks (p<0.0001). There was one unconfirmed partial response (3.7%) and nine patients had stable disease (33.3%). Clinical benefit was not associated with baseline FRα or PD-L1 expression. One patient with prolonged clinical benefit demonstrated loss of FRα expression and upregulation of PD-L1 in a progressing lesion. Despite the low overall response rate, the median overall survival was 21 months (13.5–∞), with evidence of benefit from postimmunotherapy regimens.ConclusionsCombination of TPIV200 and durvalumab was safe and elicited robust FRα-specific T cell responses in all patients. Unexpectedly durable survival in this heavily pretreated population highlights the need to investigate the impact of FRα vaccination on the OC biology post-treatment.

The lectin, galectin-3 (Gal3), has been implicated in a variety of inflammatory and oncogenic processes, including tumor growth, invasion, and metastasis. The interactions of Gal3 and MUC16 represent a potential targetable pathway for the treatment of MUC16-expressing malignancies. We found that the silencing of Gal3 in MUC16-expressing breast and ovarian cancer cells in vitro inhibited tumor cell invasion and led to attenuated tumor growth in murine models. We therefore developed an inhibitory murine monoclonal anti–Gal3 carbohydrate-binding domain antibody, 14D11, which bound human and mouse Gal3 but did not bind human Galectins-1, -7, -8 or -9. Competition studies and a docking model suggest that the 14D11 antibody competes with lactose for the carbohydrate binding pocket of Gal3. In MUC16-expressing cancer cells, 14D11 treatment blocked AKT and ERK1/2 phosphorylation, and led to inhibition of cancer cell Matrigel invasion. Finally, in experimental animal tumor models, 14D11 treatment led to prolongation of overall survival in animals bearing flank tumors, and retarded lung specific metastatic growth by MUC16 expressing breast cancer cells. Our results provide evidence that antibody based Gal3 blockade may be a viable therapeutic strategy in patients with MUC16-expressing tumors, supporting further development of human blocking antibodies against Gal3 as potential cancer therapeutics.

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Objective: Galectin-3 (LGALS3) regulates the interaction of surface proteins with the extracellular membrane domain and mediates a signal cascade leading to invasion, oncogene activation and growth. We targeted LGALS3 cancer promotion by developing high-affinity anti-galectin-3 antibodies directed either at the carbohydrate recognition domain (CRD) of the galectin-3 carboxyl-terminus (to block sugar binding) or at the N-terminus (NT) (to inhibit N-terminal mediated oligomerization of galectin-3) in order to prevent formation of the cell surface galectin lattice and suppress the oncogenic effects of the glycoprotein. Methods: Two distinct types of murine monoclonal antibodies (MAb) were generated by creating hybridomas from mice immunized either with a fusion protein derived from the 128-amino acid LGALS3 carboxyl-terminus fused to a human IgG1-Fc backbone followed by immunization with a recombinant human LGALS3 protein, or the mice were further immunized with a 25-amino acid peptide derived from the LGALS3-N-terminus conjugated to KLH. The resulting antibodies were confirmed to recognize either the LGALS3 CRD or NT by ELISA. Functional assays (Matrigel invasion, inhibition of laminin binding, and oncogene expression) and cell surface expression by FACS analysis were utilized to confirm MAb binding and activity. Mice bearing A2780 and SKOV3 ovarian cancer cell lines were treated with purified MAb to determine the effects of MAb on tumor growth in vivo. Data were analyzed for statistical significance using Student's t-test. Results: Initial screening yielded two candidate antibodies, of which one (named 14D11.2D2) had superior binding to galectin-3 by ELISA and Surface Plasmon Resonance (SPR). The antibody dissociation constant was 14.6 nM by SPR. At a concentration as low as 150 nM, the 14D11.2D2 MAb decreased galectin-3 binding to laminin by 36.6% compared to untreated control. In a Matrigel invasion assay, the anti-CRD MAb significantly inhibited invasion by MUC16 expressing SKOV3 cells and by wild-type MUC16 positive OVCAR3 cells. MUC16 expressing A2780 cells showed a statistically nonsignificant decrease in invasion. In vivo experiments with MUC16 expressing A2780 or SKOV3 tumors showed a significant inhibition of tumor growth in mice treated with anti-CRD MAb. Six candidate antibodies directed against the LGALS3-N-terminus have been identified. Characterization of two NT antibodies (1F5.D4 and 7D4.A1) is under way via in in vitro and in vivo experiments. Conclusion: High-affinity CRD and NT anti-galectin-3 antibodies inhibit MUC16-induced cellular invasion and growth. Anti-LGALS3 MAbs hold therapeutic potential for inhibition of glycosylation-dependent invasion. Citation Format: Dharmarao Thapi, Marina Stasenko, Thomas White, Sven J. Walderich, Noah Feit, Frances Weis-Garcia, David R. Spriggs. High-affinity anti-galectin-3 antibodies targeting oncogenic properties in serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1776.

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