Investigating transcriptional regulation of cisplatin sensitivity in small cell lung cancer using a functional overexpression screen.

e20162 Background: Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine malignancy characterized by initial sensitivity to platinum-etoposide chemotherapy, yet patients commonly experience early relapse and the development of drug resistance. In the absence of recurrent actionable genomic alterations, accumulating evidence points to epigenetic dysregulation as a central driver of progression and therapy resistance. SCLC exhibits remarkable molecular heterogeneity and phenotypic plasticity, with recent classification systems defining distinct molecular subtypes based on differential expression of lineage-defining transcription factors. Dynamic changes in subtype identity during treatment have emerged as a potential mechanism of acquired resistance and differential responses to platinum-based chemotherapy. Defining the transcriptional programs that govern these patterns of chemoresistance therefore represents a critical unmet need in SCLC. Methods: To identify transcriptional regulators that confer cisplatin resistance, we performed a pooled, barcoded open reading frame (ORF) overexpression screen in an SCLC cell line model under prolonged cisplatin treatment. This unbiased functional genomics approach revealed selective enrichment of members of the Forkhead box (FOX) family of transcription factors. FOX proteins are an evolutionarily conserved family defined by a characteristic winged helix DNA binding domain that regulate diverse cellular processes, including stress responses, cell cycle control, DNA damage repair, and cell fate determination. Across cancer types, FOX factor dysregulation has been linked to drug resistance through regulation of DNA repair pathways, apoptotic signaling, and pro-survival pathways. Results: We have confirmed that FOX transcription factors emerging from the ORF overexpression screen are mediators of cisplatin resistance. We are systematically characterizing resistance phenotypes across major SCLC molecular subtypes using a comprehensive panel of cell line models. Integrating transcriptomic analysis with functional assays, we will delineate the FOX-driven transcriptional programs and assess whether resistance is mediated through shared or subtype-specific mechanisms, including validation in patient-derived datasets. Conclusions: The impact of these findings could inform SCLC management by identifying transcriptional biomarkers predictive of cisplatin response and early drug resistance. Mechanistic insights into FOX-mediated resistance programs may also support rational combination strategies that pair platinum chemotherapy with targeted inhibition of key resistance pathways.