Proteolysis-targeting chimera (PROTAC) therapies degrading SWI/SNF ATPases interfere with androgen receptor (AR) signaling in AR-dependent castration-resistant prostate cancer (CRPC-AR). To explore the utility of SWI/SNF therapy beyond AR-sensitive CRPC, we investigated SWI-/SNF-targeting agents in AR-negative CRPC. SWI-/SNF-targeting PROTAC treatment of cell lines and organoid models reduced the viability of not only CRPC-AR but also WNT signaling–dependent AR-negative CRPC (CRPC-WNT). The CRPC-WNT subgroup represents 11% of around 400,000 cases of CRPC worldwide that die yearly. SWI/SNF ATPase SMARCA4 depletion interfered with the master transcriptional regulator TCF7L2 in CRPC-WNT. Functionally, TCF7L2 maintained proliferation via the MAPK signaling axis in this subtype of CRPC. Together, these data provide a mechanistic rationale for interventions that perturb DNA binding of the proproliferative transcription factor TCF7L2 and/or direct MAPK signaling inhibition in the CRPC-WNT subclass of advanced prostate cancer. Significance: SWI/SNF-targeting agents interfere with a lineage-defining molecular axis in the WNT signaling–dependent, androgen receptor-negative subtype of prostate cancer, which accounts for around 10% of castration-resistant tumors.

Background: Atypical teratoid rhabdoid tumors (ATRTs) are highly aggressive pediatric central nervous system tumors defined by the inactivation of the SMARCB1 gene. Despite the identification of three distinct molecular subtypes, each defined by unique clinical and molecular characteristics, no subtype-specific therapeutic strategies are currently available. This highlights an urgent need to deepen our understanding of the cellular heterogeneity and developmental origins of ATRTs. Methods: We generated a comprehensive single-nucleus transcriptomic atlas of ATRT samples, integrated it with single-nucleus ATAC-seq and spatial transcriptomics data, and validated our findings experimentally using patient-derived ATRT tumoroid models. Results: Our analyses revealed distinct subtype-specific differentiation trajectories, each resembling different brain progenitor lineages. We identified key transcription factors that appear to drive these developmental pathways. Furthermore, a shared cycling, intermediate precursor cell (IPC)-like cell population, interspersed throughout tumors, was consistently present within all ATRT samples. We demonstrate that these subtype-specific differentiation pathways can be pharmacologically manipulated in patient-derived ATRT tumoroids. By directing tumor cells along their respective subtype-specific trajectories, we were able to induce a shift toward more differentiated, non-proliferative states. Conclusions: Collectively, our findings show that ATRTs recapitulate fetal brain signaling programs in a subtype-specific manner. This work provides a framework for understanding ATRT heterogeneity and supports the feasibility of maturation-based therapeutic strategies tailored to the molecular subtype of the tumor.

Proteolysis targeting chimera (PROTAC) therapies degrading SWI/SNF ATPases offer a novel approach to interfere with androgen receptor (AR) signaling in AR-dependent castration-resistant prostate cancer (CRPC-AR). To explore the utility of SWI/SNF therapy beyond AR-sensitive CRPC, we investigated SWI/SNF-targeting agents in AR-negative CRPC. SWI/SNF targeting PROTAC treatment of cell lines and organoid models reduced the viability of not only CRPC-AR but also WNT-signaling dependent AR- negative CRPC (CRPC-WNT). The CRPC-WNT subgroup represents 11% of around 400,000 cases of CRPC worldwide who die yearly of CRPC. We discovered that SWI/SNF ATPase SMARCA4 depletion interfered with the master transcriptional regulator TCF7L2 (TCF4) in CRPC-WNT. Functionally, TCF7L2 maintains proliferation via the MAPK signaling axis in this subtype of CRPC. These data suggest a mechanistic rationale for interventions that perturb the DNA binding of the pro-proliferative TCF7L2 transcription factor (TF) and/or direct MAPK signaling inhibition in the CRPC-WNT subclass of advanced prostate cancer. Statement of significance: Androgen receptor (AR)-negative prostate cancer (PCa) remains a clinical challenge due to the lack of targeted therapeutic options. Here, we identified a lineage-defining molecular axis in a subtype of AR- negative PCa, accounting for around 10% of castration-resistant PCa (CRPC) that can be interfered with by SWI/SNF-targeting agents.

Malignant rhabdoid tumors are highly aggressive pediatric malignancies with limited treatment options and poor outcomes. To expand therapeutic options, we employed mass spectrometry-based cell surface proteomics on malignant rhabdoid tumor and patient-matched normal kidney organoids to identify potential CAR T cell targets. Integrating these findings with transcriptomics and protein expression data, we revealed ROBO1 as a promising target, showing strong and uniform expression across malignant rhabdoid and other pediatric tumors. ROBO1-targeted CAR T cells displayed potent anti-tumor activity in vitro , effectively eliminating tumor cells in co-cultures with organoids from malignant rhabdoid tumors, rhabdomyosarcoma, and neuroblastoma. In vivo, ROBO1 CAR T cells infiltrated tumors, induced potent tumor regression and significantly increased survival in malignant rhabdoid tumor-bearing mice. These findings establish ROBO1 as a compelling therapeutic target for CAR T cell therapy and offer a promising approach to address the critical need for effective treatments in high-risk pediatric solid tumors. Statement of significance: This study identifies ROBO1 as a promising CAR T cell target for pediatric solid tumors. Using patient-derived tumor organoids and tissues, we demonstrate strong ROBO1 expression across several tumor entities and robust anti-tumor efficacy of ROBO1-targeted CAR T cells in vitro and in vivo , underscoring its potential for clinical translation.

TCF7L2 is not maintaining CRPC-WNT proliferation via traditional WNT signaling cues

CRPC-WNT organoids become deregulated in multiple proliferative pathways upon SMARCA2/4 degradation