Preclinical Evaluation of Folate Receptor-α Chimeric Antigen Receptor T Cells Exhibits Highly Efficient Antitumor Activity against Osteosarcoma.

UNLABELLED: Metastatic and relapsed osteosarcoma remains difficult to treat despite advanced surgical techniques, intensified chemotherapy, and targeted therapies. Adoptive immunotherapies such as chimeric antigen receptor (CAR) T cells are in their nascent stage but remain a viable therapeutic strategy for patients with aggressive solid tumors such as osteosarcoma. Folate receptor-α (FOLR1) has been functionally implicated in osteosarcoma pathophysiology, providing rationale as a potential therapeutic target. We recently advanced a FOLR1-specific CAR T-cell product (FH FOLR1-CART) into a trial in infant acute myeloid leukemia (NCT06609928) and now evaluate this CAR construct against osteosarcoma. We provide comprehensive FOLR1 transcript and protein expression profile in patients with osteosarcoma, cell lines, and patient-derived xenografts, substantiating its significance as a therapeutic target. We further evaluate the in vitro and in vivo efficacy of FH FOLR1-CART in both standard and patient-derived osteosarcoma cell lines and xenograft models. FOLR1 transcript is expressed in the overwhelming majority of osteosarcoma primary patient specimens, osteosarcoma cell lines, and patient-derived models. FH FOLR1-CART exhibits robust in vitro activation and potent cytotoxicity against FOLR1-expressing osteosarcoma cell lines and primary osteosarcoma patient samples. More importantly, FH FOLR1-CART demonstrates potent antitumor activity in both localized and metastatic in vivo cell-derived and patient-derived xenograft models, with complete tumor eradication. These results demonstrate a potential therapeutic option for patients with advanced osteosarcoma. FH FOLR1-CART is advancing to an early-phase trial in relapsed/refractory osteosarcoma at Fred Hutchinson Cancer Center and Seattle Children's Hospital.

SIGNIFICANCE: FOLR1 expression has previously been implicated in the pathogenesis of treatment-resistant osteosarcoma. This report demonstrates FOLR1 expression by most osteosarcoma tumors and provides preclinical evidence of robust antitumor activity both in vitro and in vivo against xenograft osteosarcoma models exhibited by FH FOLR1-CART. These data support ongoing efforts for clinical translation of FH FOLR1-CART to an early-phase clinical trial for patients with aggressive osteosarcoma.