Targeting the IGF-Axis Potentiates Immunotherapy for Pancreatic Ductal Adenocarcinoma Liver Metastases by Altering the Immunosuppressive Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy, resistant to chemotherapy and associated with high incidence of liver metastases and poor prognosis. Using murine models of aggressive PDAC, we show here that in mice bearing hepatic metastases, treatment with the IGF-Trap, an inhibitor of type I insulin-like growth factor receptor (IGF-IR) signaling, profoundly altered the local, immunosuppressive tumor microenvironment in the liver, curtailing the recruitment of myeloid-derived suppressor cells, reversing innate immune cell polarization and inhibiting metastatic expansion. Significantly, we found that immunotherapy with anti-PD-1 antibodies also reduced the growth of experimental PDAC liver metastases, and this effect was enhanced when combined with IGF-Trap treatment, resulting in further potentiation of a T-cell response. Our results show that a combinatorial immunotherapy based on dual targeting of the prometastatic immune microenvironment of the liver via IGF blockade, on one hand, and reversing T-cell exhaustion on the other, can provide a significant therapeutic benefit in the management of PDAC metastases.

Design, Synthesis, and Characterization of 4-Aminoquinazolines as Potent Inhibitors of the G Protein-Coupled Receptor Kinase 6 (GRK6) for the Treatment of Multiple Myeloma

Both previous and additional genetic knockdown studies reported herein implicate G protein-coupled receptor kinase 6 (GRK6) as a critical kinase required for the survival of multiple myeloma (MM) cells. Therefore, we sought to develop a small molecule GRK6 inhibitor as an MM therapeutic. From a focused library of known kinase inhibitors, we identified two hits with moderate biochemical potencies against GRK6. From these hits, we developed potent (IC₅₀ < 10 nM) analogues with selectivity against off-target kinases. Further optimization led to the discovery of an analogue (18) with an IC₅₀ value of 6 nM against GRK6 and selectivity against a panel of 85 kinases. Compound 18 has potent cellular target engagement and antiproliferative activity against MM cells and is synergistic with bortezomib. In summary, we demonstrate that targeting GRK6 with small molecule inhibitors represents a promising approach for MM and identify 18 as a novel, potent, and selective GRK6 inhibitor.

Abstract 5076: Pancreatic ductal adenocarcinoma associated stellate cells promote a pro-metastatic microenvironment in the liver

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease associated with a 5-year survival rate of ~9%. The most notable clinical features of PDAC are its propensity for aggressive invasion, metastasis (mainly to the liver) and an inherent resistance to conventional therapies. A better understanding of the biology of PDAC metastasis is critical to improving the clinical management of this disease. PDAC is characterized by a dense desmoplastic reaction with up to 50% of the tumor mass consisting of stroma. The major cellular component of the PDAC stroma is the activated pancreatic stellate cell (aPSC). These cells contribute to PDAC progression through extracellular matrix deposition and the secretion of soluble factors. The objective of this study was to determine whether the aPSCs also play a role in PDAC metastasis by contributing to a pro-metastatic microenvironment in the liver.

Methods: We used a syngeneic cell line, LMP-derived from the KPC PDAC mouse model-that recapitulates the clinical course of the disease. When implanted in the pancreas, LMP cells grow rapidly and metastasize aggressively to the liver, and this is associated with PSC activation and expansion. We investigated the ability of PSC and aPSC-derived exosomes to activate hepatic stellate cells (HSC) using a co-culture system in vitro and analyzed the effect of aPSC-derived exosomes on LMP liver metastasis in vivo. Moreover, the protein cargo of PSC-derived exosomes was analyzed by mass spectrometry, in order to identify molecular mediators of PSC-HSC communication that can promote liver colonization by disseminating PDAC cells.

Results: In mice orthotopically implanted with LMP cells, we observed a rapid activation of HSC, an event that preceded tumor cell entry into the liver, as assessed by confocal microscopy and PCR. Similarly, the injection of aPSC-derived exosomes into tumor-naive mice resulted in a liver stromal response, involving HSC and liver-associated fibroblasts. Cultured HSC could be activated by co-culture with aPSCs or by uptake of aPSC-derived exosomes. Moreover, in mice injected with aPSC-derived exosomes, spontaneous liver metastasis was accelerated, resulting in increased metastatic burden. Mass spectometry identified several potential mediators of HSC activation in the aPSC-derived exosomes, including the IGF-2 mRNA binding protein-1 (IMP-1)-an oncofetal, RNA-binding protein involved in the regulation of cytoplasmic mRNA-fate. Finally, IMP-1 silencing in aPSCs reduced HSC activation and the pro-metastatic effect of aPSC-derived exosomes.

Conclusions: Our data identify a novel PSC-HSC crosstalk mechanism that contributes to generating a pro-metastatic microenvironment in the liver and implicate aPSC-derived exosomal IMP-1 in this inter-cellular communication. Our results identify IMP-1 as a potential target for curtailing the metastatic spread of PDAC.

Citation Format: John David Konda, Masakazu Hashimoto, Jian Zhang, Maria Celia Fernandez, Ni Wang, Stephanie Perrino, Laura Montermini, Janusz Rak, Jean-Sebastien Pelletier, Andrew M. Lowy, Pnina Brodt. Pancreatic ductal adenocarcinoma associated stellate cells promote a pro-metastatic microenvironment in the liver [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 5076.

Heat-shock protein 27 (HSP27, HSPB1) is up-regulated by MET kinase inhibitors and confers resistance to MET-targeted therapy

The tyrosine kinase encoded by the MET oncogene is activated by gene mutation or amplification in tumors, which in most instances maintain addiction, i.e., dependency, to MET activation. This makes MET an attractive candidate for targeted therapies. Here we show that, in 3/3 MET-addicted human gastric cancer cell lines, MET kinase inhibition resulted in a 3- to 4-fold increased expression of the antiapoptotic small heat-shock protein of 27 kDa (HSP27, HSPB1). HSP27 increase depended on the inhibition of the MEK/ERK pathway and on heat-shock factor 1 (HSF1) and hypoxia-inducible factor-1α (HIF-1α) regulation. Importantly, HSP27-silenced MET-addicted cells underwent 2- and 3-fold more apoptosis following MET inhibition in vitro and in vivo, respectively. Likewise, in human cancer cells susceptible to epidermal growth factor receptor (EGFR) inhibition, EGFR inhibitors induced HSP27 expression and were strengthened by HSP27 suppression. In control cell lines that were not affected by drugs targeting MET or EGFR, these drugs did not induce HSP27 increase. Therefore, in cancer therapies targeting the MET pathway, the induction of HSP27 might limit the efficacy of anti-MET agents. As HSP27 increase also impairs the effectiveness of EGFR inhibitors and is known to protect cells from chemotherapeutics, the induction of HSP27 by targeted agents might strongly affect the success of combination treatments.

Abstract B42: Heat Shock Protein 27 (HSP27, HSPB1) is up-regulated by MET kinase inhibition and limits the effectiveness of inhibitors

The receptor for the hepatocyte growth factor (HGF) is encoded by the MET oncogene and its activation results in cell growth, survival, motility and invasiveness. Deregulated HGF/MET signaling is observed in many tumors and both HGF and MET are attractive candidates for targeted therapies. Unexpectedly, we found that in ovarian cancer cells the activation of the MET receptor downmodulated the expression of the small heat shock protein 27 (HSP27), which functions as a molecular chaperone and as an antiapoptotic protein. In MET addicted gastric carcinoma cells, where MET is constitutively active, MET kinase inhibition by JNJ-38877605 up-regulated HSP27 expression. More importantly, in these gastric carcinoma cells suppression of HSP27 was alone able to induce cell death and increased cell susceptibility to MET inhibition. HSP27 suppression did not affect MET stability and phosphorylation, but increased activation of caspase 3, which is a known HSP27 client protein. Regulation of HSP27 expression by MET signaling occurred at transcriptional level, as confirmed by the use of HSP27 promoter in a reporter assay. It was not due to the engagement of HSF1, the master key transcription factor regulating HSPs expression, but depended on MEK activation and resulting HIF 1alpha stabilization. MEK inhibition and HIF 1 alpha silencing resulted in the induction of HSP27, suggesting a direct or indirect transcriptional repression. Altogether data show that MET activation down-regulates and MET inhibition up-regulates HSP27 expression, and that HSP27 increased expression protects cells from death induced by MET inhibitors. Therefore, in therapies with MET targeting agents, HSP27 increase might impair the effectiveness of MET inhibitors. As it is known that HSP27 protects cells for chemotherapeutics, data suggest that HSP27 might strongly affect combinatorial treatments.