Research

The endoplasmic reticulum (ER) is the major site for protein synthesis and folding. Tumor cells grow rapidly, develop decreased nutrition supplies, and increase reactive oxygen species (ROS) production. The adverse microenvironment and accumulation of improperly folded proteins in the ER of cancer cells induces ER stress, which in turn triggers the Unfolded Protein Response (UPR) as an adaptive mechanism to restore ER proteostasis. As this signaling pathway is differentially regulated during tumor growth and progression, modulating UPR signaling is a promising therapeutic strategy for cancer.

In mammalian cells, three major ER transmembrane proteins operate as ER stress sensors: inositol-requiring enzyme 1α (IRE1α), activating transcription factor 6 (ATF6) and PRKR-like ER kinase (PERK). Our lab focuses on the role of IRE1α signaling in regulating cancer progression. IRE1α, an evolutionary conserved ER stress sensor, consists of two enzymatic activities: a serine/threonine kinase and an RNase activity. When misfolded proteins accumulate in the ER, IRE1α dimerizes/oligomerizes and trans-auto phosphorylates, thereby activating its RNases activity (Figure 1). The RNase activity consists of: (i) The non-conventional splicing of the mRNA of XBP1 to allow production of XBP1s (XBP1 spliced), a transcription factor and (ii) RNase-mediated cleavage of target mRNAs, referred to as regulated IRE1-dependent decay (RIDD) of RNA.

Our group was the first to identify a critical role for the IRE1-XBP1 branch of the UPR in cancer. We showed that XBP1 mediated survival under hypoxia and was essential for tumor growth (Romero-Ramirez et al, Cancer Res 2004). Since demonstrating the therapeutic potential of inhibiting this target, we have focused on developing pharmacologic inhibitors of this pathway. We completed a high-throughput screening strategy and completed a screen of >120,000 compounds.

The Koong Lab was the first to identify a class of compounds that specifically and potently inhibit IRE1 in cell lines, tumor xenografts, and patient-derived specimens (Papandreou et al, Blood 2011). This study demonstrated the feasibility of targeting this pathway pharmacologically, leading to multiple pre-clinical and clinical development paradigms. Since then, we completed a whole genome siRNA screen to identify other genes that regulate this pathway with the overall goal of finding other therapeutic targets in cancer (Yang et al, MCR 2018).

Ongoing work in the laboratory is focused on developing novel classes of compounds to block the activity of IRE1 and other UPR targets as a therapeutic strategy. We have developed these targeted therapies alone and in combination with radiation therapy in relevant disease models to optimize translation into the clinic.

Check out our recent publication in Nature Communications titled: IRE1α determines ferroptosis sensitivity through regulation of glutathione synthesis.

Pancreatic cancer is currently the third-leading cause of cancer-related death in the United States. Despite aggressive combined modality therapies, the five-year overall average survival across all stages remains ~10%.

Therapeutic paradigms are hampered by the inability to detect pancreatic cancer until late stages. In addition, pancreatic cancer is relatively resistant to conventional chemotherapy and radiation therapy and to date, no effective targeted therapies or immunotherapies have been identified.

The Koong Lab is focused on understanding how pancreatic tumors develop and to develop therapeutic approaches that target molecular pathways regulated by the tumor microenvironment.

The pancreas consists of exocrine (acinar), ductal, and endocrine (α, β, δ, ε) cells. Pancreatic ductal adenocarcinoma (PDAC) has been shown to originate primarily from oncogenic transformation of acinar cells. Normal acinar cells transdifferentiate to ductal-like phenotypes when exposed to certain intracellular and environmental stimuli, a process known as acinar-to-ductal metaplasia (ADM).

During ADM, acinar cells acquire ‘progenitor cell-like’ characteristics which render them susceptible to oncogene induced pancreatic intra-epithelial neoplasias (PanINs) formation (see Figure 1).

Our research demonstrates that an endoplasmic reticulum (ER) stress induced protein, XBP1 drives ADM and PanIN development in mouse pancreatic cancer models, and that modulation of XBP1 signaling is a major driver of tumor progression and survival of tumor-bearing mice.

Pancreatic ductal adenocarcinoma (PDAC) develops and proliferates under very low oxygen conditions, or hypoxia (Koong et al., 2000). These conditions occur within tumors which may have an oxygen concentration of 0.5% or less. (For reference, room air contains 21% oxygen.)

This intratumoral hypoxia is at least partially due to the fibrotic and desmoplastic stroma (Stylianopoulos et al., 2012) that increases intratumoral pressure (Chauhan et al., 2014), which is thought to block blood flow and the delivery of oxygen, nutrients and even therapeutic drugs (Koay et al., 2014). This property makes the stroma a compelling therapeutic target, with the reasoning that reducing the physical barrier imposed by this desmoplasia would allow therapy to become more effective.

Unfortunately, Phase III clinical studies to disrupt pancreatic cancer stroma by inhibiting Sonic hedgehog protein (De Jesus-Acosta et al., 2020) or infusion with a recombinant pegylated human hyaluronidase (Hakim et al., 2019) failed to meet survival endpoints (Van Cutsem et al., 2020), despite promising Phase II results (Hingorani et al., 2018). These clinical data stimulated the pancreatic cancer research field to consider functional inhibition of the stromal elements as a therapeutic strategy.Since hypoxia is a universal feature of pancreatic cancer, we reasoned that hypoxia plays a critical role in cellular homeostasis of the PDAC tumor microenvironment. We focused our efforts on how low oxygen levels may enhance pro-tumor signaling between fibroblasts and the immune system.

We developed a novel dual recombinase system with collaborations with the Kirsch Lab at the Princess Margaret Cancer Centre and the Saur Lab at Technical University of Munich (TUM) and German Cancer Research Center (DKFZ).

For more information on this system, refer to our reviews (Fuentes et al., 2020; Huang et al., 2017). Ongoing projects in our laboratory indicate that hypoxia signaling within PDAC-associated fibroblasts promotes the immunosuppressive M2 polarization of macrophages.

These newly formed M2 macrophages suppress anti-tumor T cell responses, which leads to favorable conditions for tumor growth.This effect was HIF-2a (HIF2) dependent and could be reversed with a small molecule inhibitor of HIF-2a called PT2399, a preclinical version of belzutifan, an FDA-approved HIF-2a inhibitor for use in VHL-mutant renal cell carcinoma (Garcia et al., 2022). We are actively working to identify the paracrine factor(s) mediating this polarization effect on macrophages.

We envision that by using our combination of in vivo mouse modeling and in vitro cell/organoid culture systems we will determine the role of hypoxia in various cell types within the PDAC tumor microenvironment, with the goal to identify potentially druggable targets, such as the fibroblast-macrophage signaling axis.