Defining biomarkers and overcoming resistance to DLL3-targeting immune therapies in lung cancer - Project Summary Small cell lung cancer (SCLC) is a highly aggressive, neuroendocrine malignancy that has seen limited gains with a “one-size-fits all” approach with immune checkpoint inhibition (ICI). Specifically, despite the approval of anti-PDL1 for all extensive-stage SCLC patients, ICI only provides approximately two months of overall survival benefit across an unselected population. There remains a major, unmet need for strategies that engage the immune system in the “immune-cold” SCLC populations (~80% of patients) that do not derive benefit from ICI. New therapeutics designed to overcome the barriers posed by SCLC to cytotoxic immune cells include T-cell engagers (TCEs). Of these, the most advanced target Delta-like ligand 3 (DLL3) – a target highly expressed in non-inflamed SCLC and, thus, may serve as a beacon for delivery of cytotoxic T-cells to the SCLC immune desert. In 2024, a DLL3-targeting TCE (tarlatamab) was FDA approved, offering a glimpse of the potential of this approach with unprecedented durability of responses, but also revealing the inherent limitations of current strategies (~60% of patients do not benefit). Reversing or bypassing the immunologic inertness that typifies the majority of SCLC is a critical, unmet need. The proposed experiments are intended to gain a greater understanding of tumor-intrinsic and immune-related mechanisms of response and resistance to TCEs with a goal to expand the application of, and depth and durability of response to, DLL3-targeting immune. To address these research gaps, we have assembled a multidisciplinary team with scientific, clinical, translational, and computational expertise in SCLC preclinical models, intra-tumoral heterogeneity, biomarker analyses, surface targeting therapies, and SCLC surface-targeting therapy clinical trials. Based on our data, we hypothesize that 1) inter- and intra-tumoral heterogeneity in DLL3 expression and a minimal immune response, particularly in previously treated SCLC tumors, limit the efficacy of DLL3 TCEs and 2) combination targeting to activate immune responses will enhance the frequency, depth, and durability of responses. To address these hypotheses among non-inflamed SCLC subtypes, we propose the following Aims: in Aim 1, we will characterize markers of response and resistance to the approved DLL3 TCE using both preclinical and patient models. In Aim 2, we will characterize adaptive tumor-intrinsic resistance mechanisms following DLL3-targeted immune therapies in preclinical tumor models and patients. In Aim 3, we will explore innovative strategies to combine DLL3 TCEs with therapies intended to enhance inflammation and/or immune cell infiltration to ensure that responses are durable and benefit a broader population. In alignment with NIH guidance to reduce, replace, and refine animal testing we include significant in vitro work (cell lines, PDX derived organoids) and several computational analyses of patient samples to minimize animal use. There are, however, experiments in this proposal that utilize animal models that are essential as no other available approach replicates immune cell infiltration and cytotoxicity
