Abstract B006: Complement downregulation promotes an inflammatory signature that renders colorectal cancer susceptible to immunotherapy

Background: The role of inflammatory immune responses in colorectal cancer (CRC) development and response to therapy is a matter of intense debate. While inflammation is a known driver of CRC, inflammatory immune infiltrates are a positive prognostic factor in CRC as inflammation can enhance response to immune checkpoint blockade (ICB) therapy. Yet, the majority of CRC are poorly infiltrated and even in presence of an inflammatory infiltrate half of these cancers become refractory to ICB. Therefore, there is a need to identify mechanisms to establish therapy supportive inflammation. We have previously reported that, irrespective of their MSI-H or MSS status, about 10% of patients with CRC down-regulate the receptor for the complement anaphylatoxin C3a (C3aR) via methylation-dependent mechanisms. The complement system is a well characterized first line of defense against pathogens and a central component of the immune response. Emerging evidence suggests that complement C3aR may play a role in intestinal homeostasis. However, to date, it is unknown how the C3a/C3aR axis can affect CRC development and influence response to therapy with ICB. Methods: We used here a comprehensive approach encompassing analysis of publicly available human CRC human datasets, inflammation-driven and newly generated spontaneous mouse models of CRC, and multi-platform high dimensional analysis of immune responses and microbiota sequencing, RNASeq and mass cytometry. Results: Using our novel mouse model of CRC (APCMin/+/C3aR-/-) we showed that loss of C3aR resulted in enhanced immune infiltration in typically “cold” tumors and changes in the intestinal microbiota. Similarly, we found that down-regulation of the complement C3aR in patients correlates with changes in specific tumor-infiltrating immune cells. Notably, when treated with a-PD1, APCMin/+/C3aR-/- mice showed a significant reduction in their tumor multiplicity and tumor load compared to untreated mice, suggesting that the loss of C3aR unleashes in the colon a microbiota-mediated favorable inflammatory infiltrate that can be exploited by the immunotherapy to reduce both de novo tumor development and the growth of already existing tumors. Conclusions: Our findings reveal that C3aR may act as a previously unrecognized checkpoint to enhance antitumor immunity in CRC. Our results suggest that C3aR may be exploited to overcome ICB resistance in a larger group of CRC patients.

Citation Format: Silvia Guglietta, Lukas M. Weber, Bruno Fosso, Marinella Marzano, Gary Hardiman, Monica Olcina, Mark D. Robinson, Carste Krieg. Complement downregulation promotes an inflammatory signature that renders colorectal cancer susceptible to immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr B006.

Abstract 5501: Evaluation of the first potent and highly selective inhibitor of ATR kinase: An approach to selectively sensitize cancer cells to ionizing radiation and hypoxia

DNA damaging agents, such as ionizing radiation (IR), have provided a basis for the treatment of solid tumors for decades, yet they provide only modest benefit for most patients. This reflects, in part, the efficient repair of DNA damage via a complex signaling and repair network known as the DNA damage response (DDR). The ATR, ATM and DNA-PK phosphoinositol 3-kinase-like serine/threonine protein kinases (PIKKs) are the key regulators of the DDR to IR-induced double-strand DNA breaks. This acts to detect the DNA lesions, enforce checkpoints to arrest cell cycle progression, and stimulate repair. Various components of the DDR have been shown to be commonly defective in cancer cells. These cells are widely hypothesized to become dependent on their remaining DDR pathways for survival from DNA damage. The tumor microenvironment has been reported to induce a DDR and in particular, ATR-mediated signaling in response to severe hypoxia.

While inhibitors of a number of DDR enzymes, including ATM, DNA-PK, Chk1 and PARP, have been reported, there have been no reports of drug-like ATR inhibitors. Using the first potent and selective ATR inhibitor (VE-821), we now characterize the effects of ATR inhibition on the cellular response to IR and hypoxia. VE-821 sensitizes many cancer cell lines to IR in both clonogenic and short-term (MTS) assays. For example, VE-821 reduced the surviving fraction of MiaPaca-2 cells treated with 6 Gy IR by 3-fold. Consistent with this, ATR inhibition ablated both RAD51 focus formation and phosphorylation of Chk1 (but not Chk2) after IR treatment, delayed the IR-induced G2/M arrest analyzed by flow cytometry and slowed down DNA replication rates measured using DNA fiber technology. Furthermore, we provide evidence that a basis for the sensitization of cancer cell lines to IR with VE-821 is a synthetic lethal interaction between loss of ATM signaling (a frequent event in cancer resulting from loss of function of proteins such as ATM or p53) and ATR inhibition when cells are treated with IR. In keeping with these results, normal cells (with functional ATM) do not appear sensitized to IR by ATR inhibition. In this case a compensatory DDR is activated, which in turn leads to checkpoint arrest and a strong survival response. Importantly, ATR inhibition also sensitized cancer cells to IR under hypoxic conditions, and to anoxia alone.

These studies show for the first time that a selective ATR inhibitor can preferentially sensitize cancer cells to ionizing radiation under both normoxic and hypoxic conditions and exploit a synthetic lethal interaction between ATM and ATR signaling. This underpins the broad potential of ATR inhibition as a highly promising new strategy to improve the efficacy of DNA damaging therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5501. doi:10.1158/1538-7445.AM2011-5501

Targeting hypoxic cells through the DNA damage response

Exposure to hypoxia-induced replication arrest initiates a DNA damage response that includes both ATR- and ATM-mediated signaling. DNA fiber analysis was used to show that these conditions lead to a replication arrest during both the initiation and elongation phases, and that this correlated with decreased levels of nucleotides. The DNA damage response induced by hypoxia is distinct from the classical pathways induced by damaging agents, primarily due to the lack of detectable DNA damage, but also due to the coincident repression of DNA repair in hypoxic conditions. The principle aims of the hypoxia-induced DNA damage response seem to be the induction of p53-dependent apoptosis or the preservation of replication fork integrity. The latter is of particular importance should reoxygenation occur. Tumor reoxygenation occurs as a result of spontaneous changes in blood flow and also therapy. Cells experiencing hypoxia and/or reoxygenation are, therefore, sensitive to loss or inhibition of components of the DNA damage response, including Chk1, ATM, ATR, and poly(ADP-ribose) polymerase (PARP). In addition, restoration of hypoxia-induced p53-mediated signaling may well be effective in the targeting of hypoxic cells. The DNA damage response is also induced in endothelial cells at moderate levels of hypoxia, which do not induce replication arrest. In this situation, phosphorylation of H2AX has been shown to be required for proliferation and angiogenesis and is, therefore, an attractive potential therapeutic target.