Exportin 1 inhibition prevents neuroendocrine transformation through SOX2 downregulation in lung and prostate cancers [ATAC-seq]
In lung and prostate adenocarcinomas, neuroendocrine (NE) transformation to an aggressive derivative resembling small cell lung cancer (SCLC) is associated with poor prognosis. We previously described dependency of SCLC on the nuclear transporter exportin 1. Here we explored the role of exportin 1 in NE transformation. We observed upregulated exportin 1 in lung and prostate pre-transformation adenocarcinomas. Exportin 1 was induced upregulated following genetic inactivation of TP53 and RB1 in lung and prostate adenocarcinoma cell lines, accompanied by increased sensitivity to the exportin 1 inhibitor selinexor in vitro. Exportin 1 inhibition prevented NE transformation and extended response to targeted therapies in both lung anddifferent TP53/RB1-inactivated prostate adenocarcinoma xenograft models that acquire NE features upon treatment with the AR inhibitor enzalutamide, and extended response to the EGFR inhibitor osimertinib in a lung cancer transformation patient-derived xenograft (PDX) model exhibiting combined adenocarcinoma/SCLC histology. Ectopic SOX2 expression restored the enzalutamide-promoted NE transformationNE phenotype on adenocarcinoma-to-NE transformation xenograft models despite selinexor treatment. Selinexor sensitized NE-transformed lung and prostate small cell carcinoma PDXs tumors after NE transformation to standard cytotoxics.   Together these data nominate exportin 1 inhibition as a novel  potential therapeutic approach target to constrain lineage plasticity and prevent or treat NE transformation in lung and prostate adenocarcinoma. Overall design: 4-10 female 6-week-old NOD.Cg-Prkdc<scid> Il2rg<tm1Wjl>/SzJ (NSG) mice were subcutaneously engrafted per treatment arm and until tumors reached 100-150 mm3. At that point, mice were randomized into groups and treated with either vehicle, cisplatin (2 mg/kg intraperitoneally (i.p.) once/week), etoposide (3 mg/kg i.p. QDx3), selinexor (10 mg/kg p.o. QDx3), enzalutamide (10 mg/kg per os (p.o). QDx5), osimertinib (25 mg/kg p.o. QDx5) or the combinations of cisplatin + etoposide, cisplatin + selinexor, enzalutamide + selinexor or osimertinib + selinexor at the previously mentioned doses. 3-4 tumors per treatment group were collected at day 56 (day 31 for the control condition). Mice weights and tumor volumes were measured twice a week and mice were sacrificed when tumors reached humane endpoint (volume = 1000 mm3). The number of mice per treatment arm were selected according to previous experience with the models and response to treatments. Blinding was not performed. All animal experiments were approved by the Memorial Sloan Kettering Cancer Center (MSKCC) Animal Care and Use Committee (#13-07-007). Frozen tissues were weighed and homogenized in RLT and nucleic acids were extracted using the AllPrep DNA/RNA Mini Kit (QIAGEN, #80204) according to the manufacturer's instructions. RNA was eluted in nuclease-free water.