DDDR-02. CDK4/6 INHIBITION WITH ABEMACICLIB SENSITIZES INTRACRANIAL TUMORS TO CHECKPOINT BLOCKADE IN PRE-CLINICAL MODELS OF BRAIN METASTASIS

Abstract Although immune checkpoint inhibitors (ICI) have become a useful tool in the management of central nervous system (CNS) metastases, only subset patients experience durable clinical responses and prognosis continues to remain poor. In particular, role ICI for CNS metastases from breast cancer has also not been adequately explored. CDK4/6 inhibition shown sensitize extracranial tumors ICI, we previously reported intracranial efficacy combination with abemaciclib anti-PD-1 preclinical models melanoma brain metastasis. We now investigated this strategy further mouse model triple negative 4T1 mammary carcinoma cells were first injected into fat pad then intracranially 3 days later. While single agent antibody or both ineffective at reducing tumor growth, found significant reduction burden when was combined anti-PD-1. Immunofluorescence CD8 CD3 revealed increase tumor-infiltrating CD8+ T monotherapy as well therapy tumors. observed similar two metastasis models, YUMM1.7 B16-F10, following therapy. conclude that can improve by driving cell infiltration Future work will focus on investigating additional treatment-induced changes microenvironment dissecting effect activation function.