Emergence of tumor regenerative states during neoadjuvant therapy in locally advanced rectal cancer: selection or adaptation?

Locally advanced rectal cancer (LARC) is commonly treated with total neoadjuvant therapy (TNT), which consists of radiation therapy (RT), chemotherapy, and either total mesorectal excision (TME) or watch-and-wait based on tumor response. Most tumors treated with TNT show a spectrum of response ranging from minimal regression to complete tumor eradication, and some patients (~20%) with a clinical complete response (cCR) after TNT develop local tumor regrowth that may compromise their survival. Only ~50% of patients are able to forgo total mesorectal excision and achieve organ preservation. In addition, ~15% of patients develop distant metastatic recurrence, which is ultimately lethal. Given this data, there is an unmet need to understand mechanisms of resistance to TNT and local and distant metastatic tumor regeneration after therapy, and to develop strategies to improve local and distant disease control. Using genomic and transcriptomic analysis of pre-treatment LARC, mechanistic studies in patient-derived organoid and novel mouse models of LARC, and single cell transcriptomic analysis of metastatic colorectal cancer, we have identified that resistance to TNT and metastatic relapse are driven by a population of tumor regenerative cells (TRCs) that ectopically express the neuronal cell adhesion molecule L1CAM. L1CAM+ cells pre-existing in untreated rectal tumors are selected for during therapy, while L1CAM- cells can also dynamically enter into L1CAM+ TRC states through phenotypic plasticity. We have developed novel L1CAM targeting antibody drug conjugates (ADCs), and will test them in highly clinically relevant patient-derived organoid and organoid-derived orthotopic intraluminal rectal xenograft mouse models. The elimination of quiescence-capable tumor regenerative cells with an L1CAM targeting ADCs is expected to be complementary to chemotherapy and therapies that target rapidly proliferating cells. This represents a novel concept in cancer therapeutics that addresses the plasticity of cancer driving tumor relapse after therapy. We propose: (1) to interrogate the dynamics of clonal selection and phenotypic adaptation that govern entry into the L1CAM+ TRC state in rectal cancer. (2) Using novel L1CAM-targeting antibody drug conjugates (ADCs) that we have generated, we will determine the actionability of therapeutically targeting L1CAM+ TRCs before, during or after TNT to improve clinical outcomes. Together, these studies will inform the design of first- in human clinical trials to target tumor phenotypic plasticity using L1CAM-targeting ADCs, and define the optimal timing of targeting L1CAM+ TRCs during TNT for LARC. Through this work, our impact goals are two-fold: i) decrease the incidence of distant metastatic recurrence, and ii) increase organ preservation to maximize quality of life in patients with LARC. Project Number: 1R01CA299865-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Karuna Ganesh (+1 co-PI) | Institution: SLOAN-KETTERING INST CAN RESEARCH, NEW YORK, NY | Award Amount: $730,398 | Activity Code: R01 | Study Section: Clinical Oncology Study Section[CONC] View on NIH RePORTER: https://reporter.nih.gov/project-details/11297726