Coordinated single-cell tumor microenvironment dynamics reinforce pancreatic cancer subtype

Bulk analyses of pancreatic ductal adenocarcinoma (PDAC) samples are complicated by the tumor microenvironment (TME), i.e. signals from fibroblasts, endocrine, exocrine, and immune cells. Despite this, we and others have established tumor and stroma subtypes with prognostic significance. However, understanding of underlying signals driving distinct immune and stromal landscapes is still incomplete. Here we integrate 92 single cell RNA-seq samples from seven independent studies to build a reproducible PDAC atlas with a focus on tumor-TME interdependence. Patients with activated stroma are synonymous with higher myofibroblastic and immunogenic fibroblasts, and furthermore show increased M2-like macrophages and regulatory T-cells. Contrastingly, patients with 'normal' stroma show M1-like recruitment, elevated effector and exhausted T-cells. To aid interoperability of future studies, we provide a pretrained cell type classifier and an atlas of subtype-based signaling factors that we also validate in mouse data. Ultimately, this work leverages the heterogeneity among single-cell studies to create a comprehensive view of the orchestra of signaling interactions governing PDAC.

A Novel Class of Ribosome Modulating Agents Exploits Cancer Ribosome Heterogeneity to Selectively Target the CMS2 Subtype of Colorectal Cancer

Ribosomes in cancer cells accumulate numerous patient-specific structural and functional modifications that facilitate tumor progression by modifying protein translation. We have taken a unique synthetic chemistry approach to generate novel macrolides, Ribosome modulating agents (RMA), that are proposed to act distal to catalytic sites and exploit cancer ribosome heterogeneity. The RMA ZKN-157 shows two levels of selectivity: (i) selective translation inhibition of a subset of proteins enriched for components of the ribosome and protein translation machinery that are upregulated by MYC; and (ii) selective inhibition of proliferation of a subset of colorectal cancer cell lines. Mechanistically, the selective ribosome targeting in sensitive cells triggered cell-cycle arrest and apoptosis. Consequently, in colorectal cancer, sensitivity to ZKN-157 in cell lines and patient-derived organoids was restricted to the consensus molecular subtype 2 (CMS2) subtype that is distinguished by high MYC and WNT pathway activity. ZKN-157 showed efficacy as single agent and, the potency and efficacy of ZKN-157 synergized with clinically approved DNA-intercalating agents which have previously been shown to inhibit ribogenesis as well. ZKN-157 thus represents a new class of ribosome modulators that display cancer selectivity through specific ribosome inhibition in the CMS2 subtype of colorectal cancer potentially targeting MYC-driven addiction to high protein translation.

Significance

This study demonstrates that ribosome heterogeneity in cancer can be exploited to develop selective ribogenesis inhibitors. The colorectal cancer CMS2 subtype, with a high unmet need for therapeutics, shows vulnerability to our novel selective ribosome modulator. The mechanism suggests that other cancer subtypes with high MYC activation could also be targeted.

Abstract D065: Investigating the Interplay of monocytes in the tumor microenvironment of glioblastomas

We are members of INDUCER- Increasing Diversity in Undergraduate Cancer Biology Education & Research. Our program strives to give opportunities to experience cancer research to underrepresented students interested in the biomedical sciences. We want to help bridge the gap in medicine between Caucasians and People of Color and combat racial disparity. We utilize the GL261 cell line in the murine model to study and understand glioblastomas and their tumor microenvironment, which includes microglia and macrophages. Microglia function as macrophages of the central nervous system, play a critical role in the innate and adaptive responses to pathogens and can take on a pro-inflammatory/anti-tumorigenic (M1) or anti-inflammatory/pro-tumorigenic (M2) phenotype. Our research introduces Colony Stimulating Factor 1 Receptor (CSF1R), which is expressed by both microglia and macrophages, whose signaling is critical for their proliferation and survival. Pexidartinib is a CSF1R inhibitor drug developed by Plexxikon Inc (PLX), a pharmaceutical company. They have generated PLX3397 and PLX5622. Each drug inhibits specific kinases, for example, PLX3397 inhibits c-KIT, CSF1R, and FLT3, which are key players in tumor proliferation, while PLX5622 is a specific inhibitor that only targets CSF1R signaling. Both PLX3397 and PLX5622, provided to mice in their chow, ablate microglia in the CNS of wild type mice, without affecting peripheral macrophages. Upon discontinuation of the diet, microglia repopulate the CNS. PLX73086 is a second generation CSF1R inhibitor, and little is known about its effects on microglia and macrophages. What is known is that it should only ablate macrophages in the periphery, not affecting the CNS because it is not expected to cross the Blood Brain Barrier. Upon the discontinuation of the diet, repopulation is similarly expected. In our research, we studied the effects of PLX73086 on macrophages and microglia of the murine glioma model, after being fed the diet for 7 days and 7 days off the diet. We compared the extent of ablation and repopulation of the tissue.

Citation Format: Maryam Tayyab, Maame Gyamfi, Michael Caponegro, Dr. Styliani-Anna (Stella) Tsirka. Investigating the Interplay of monocytes in the tumor microenvironment of glioblastomas [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr D065.