Background: Aryl hydrocarbon receptor (AHR), commonly known as an environmental sensor involved in the metabolism and elimination of xenobiotic substances, is also an important modulator in the development and functioning of the immune system. AHR expression is varied in the T cell subsets with the highest expression in T-helper 17 and T regulatory cells. It has been reported that AHR can act as a tumor promoter or a tumor suppressor, depending on the tumor type. Methods: In an effort to understand the role played by AHR in tumor growth, the MC38 syngeneic colon carcinoma tumor model was used on C57BL/6 or ahr knockout (KO, -/-) mice with or without AHR antagonist (CH223191) treatment. Tumor sizes were measured, and biomarkers were quantified in tumor microenvironment and draining lymph nodes using flow cytometry. Enzyme-linked immunosorbent assay was used to determine the amount of cytokines in tumors. Results: In ahr deficient mice, MC38 tumors progress more rapidly than in wild-type mice, accompanied by an increase in tumor-associated macrophages and M2 macrophages and a decrease in CD8a positive cytotoxic lymphocytes. Analysis of cytokines in the tumor microenvironment reveals a pro-inflammatory phenotype. Similar changes were observed by pharmacologic blockade of the receptor using CH223191. Conclusion: AHR acts as a tumor suppressor in mice implanted with MC38 colon carcinoma cells as evidenced by either a blockade or deficiency of AHR.

The aryl hydrocarbon receptor (AHR) is a ligand-activated signaling molecule which controls tumor growth and metastasis, T cell differentiation, and liver development. Expression levels of this receptor protein is sensitive to the cellular p23 protein levels in immortalized cancer cell lines. As little as 30% reduction of the p23 cellular content can suppress the AHR function. Here we reported that down-regulation of the p23 protein content in normal, untransformed human bronchial tracheal epithelial cells to 56% of its content also suppresses the AHR protein levels to 59% of the wild-type content. This p23-mediated suppression of AHR is responsible for the suppression of (1) the ligand-dependent induction of the cyp1a1 gene transcription; (2) the benzo[a]pyrene- or cigarette smoke condensate-induced CYP1A1 enzyme activity and (3) the benzo[a]pyrene and cigarette smoke condensate-mediated production of reactive oxygen species. Reduction of the p23 content does not alter expression of oxidative stress genes and production of PGE2. Down regulation of p23 suppresses the AHR protein levels in two other untransformed cell types, namely human breast MCF-10A and mouse immune regulatory Tr1 cells. Collectively, down-regulation of p23 suppresses the AHR protein levels in normal and untransformed cells and can in principle protect our lung epithelial cells from AHR-dependent oxidative damage caused by exposure to agents from environment and cigarette smoking.

No abstract

Rituximab-containing treatment regimens are the standard of care for patients with non-Hodgkin’s lymphoma (NHL). However, the majority of patients ultimately experience disease relapse or progression indicating resistance to rituximab therapy. IGM-2323 is an engineered high-affinity, high-avidity anti-CD20 pentameric IgM antibody with an anti-CD3 scFv fused to the joining chain. IGM-2323 offers a novel treatment strategy in NHL through two mechanisms: 1) the recruitment of T cells to kill CD20-expressing tumor cells through T cell dependent cellular cytotoxicity (TDCC) and, 2) complement-dependent cytotoxicity (CDC). We evaluated the activity of IGM-2323 in the presence of rituximab since rituximab can persist in patients after treatment discontinuation, and it can bind to an overlapping epitope on CD20 as IGM-2323. We hypothesized that the high valency of IGM-2323 could displace rituximab, thus enabling potent B cell killing by IGM-2323 even in the presence of high concentrations of rituximab. The affinity of IGM-2323 and its corresponding bivalent anti-CD20 IgG antibody to recombinant human CD20 protein were measured by surface plasmon resonance. IGM-2323 bound to human CD20 with an apparent 300-fold higher binding affinity (KD) and ~100-fold slower off-rate (kdis) than the bivalent anti-CD20 IgG. Human B cell lines with a range of CD20 expression levels, including a CD20-low rituximab-resistant Ramos cell variant, were pre-treated with escalating concentrations of rituximab, and subsequently evaluated in vitro for cell binding, TDCC, and CDC by IGM-2323. At high concentrations of rituximab, which correspond to reported peak serum concentrations (Cmax) found in rituximab-treated patients, IGM-2323 displaced the binding of rituximab on human B cell lines. In contrast, binding of a bispecific CD20xCD3 IgG was severely inhibited by the Cmax of rituximab. In TDCC assays with healthy donor effector T cells, pre-treatment with high concentrations of rituximab only modestly inhibited IGM-2323 activity. Furthermore, only a minor impact to the maximum killing activity (Emax) of IGM-2323 was observed at the Cmax of rituximab. In contrast, rituximab pre-treatment resulted in a distinctly lower Emax of a bispecific CD20xCD3 IgG. Live cell imaging of CDC kinetics was utilized to quantify the extent of CDC by IGM-2323 with or without rituximab. Pre-treatment with rituximab enhanced CDC of IGM-2323 compared to single agent activity. Our preclinical data indicate that IGM-2323 maintains activity in the presence of rituximab. IGM-2323 is currently being studied in a phase 1 clinical trial in relapsed/refractory NHL, where it has been generally well tolerated, with both complete and partial responses observed (NCT04082936). Clinical studies will continue to evaluate these findings, including the treatment of patients with circulating serum levels of rituximab. Citation Format: Kevin C. Hart, Kathryn Logronio, Mandy Li, Poonam Yakkundi, Marigold Manlusoc, Keyu Li, Paul R. Hinton, Dean Ng, Maya K. Leabman, Genevive Hernandez, Thomas Manley, Angus M. Sinclair, Stephen F. Carroll, Bruce A. Keyt, Maya F. Kotturi. High valency of IGM-2323, a CD20xCD3 IgM bispecific T cell engager, displaces rituximab binding and induces potent B lymphoma cell killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4179.

Hodgkin lymphoma, marginal zone lymphomas and aggressive anaplastic and angioimmunoblastic T-cell lymphomas, among other histologies (Table ). All of them mimic the histology of the tumor there were derived and showed genetic match with their respective patient tumor. From 10 of these orthotopic PDX, we have derived cell lines to have paired in vitro and in vivo models. These models are now molecularly characterized using a targeted next generation sequencing assay. In vivo massive pharmacologic screening in this models are ongoing.Conclusions: To our knowledge, these are one of the first orthotopic PDX lymphoma models generated, that can allow us to expand patients' refractory tumors in order to extensively study molecular features of them and target effective drug profiles.