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Melanoma-derived brain metastases (MBM) represent an unmet clinical need because central nervous system progression is frequently an end stage of the disease. Immune checkpoint inhibitors (ICI) provide a clinical opportunity against MBM; however, the MBM tumor microenvironment (TME) has not been fully elucidated in the context of ICI. To dissect unique elements of the MBM TME and correlates of MBM response to ICI, we collected 32 fresh MBM and performed single-cell RNA sequencing of the MBM TME and T-cell receptor clonotyping on T cells from MBM and matched blood and extracranial lesions. We observed myeloid phenotypic heterogeneity in the MBM TME, most notably multiple distinct neutrophil states, including an IL8-expressing population that correlated with malignant cell epithelial-to-mesenchymal transition. In addition, we observed significant relationships between intracranial T-cell phenotypes and the distribution of T-cell clonotypes intracranially and peripherally. We found that the phenotype, clonotype, and overall number of MBM-infiltrating T cells were associated with response to ICI, suggesting that ICI-responsive MBMs interact with peripheral blood in a manner similar to extracranial lesions. These data identify unique features of the MBM TME that may represent potential targets to improve clinical outcomes for patients with MBM.

Supplementary Figure from Microenvironmental Landscape of Human Melanoma Brain Metastases in Response to Immune Checkpoint Inhibition

Supplementary Data from Microenvironmental Landscape of Human Melanoma Brain Metastases in Response to Immune Checkpoint Inhibition

Melanoma-derived brain metastases (MBM) represent an unmet clinical need because central nervous system progression is frequently an end stage of the disease. Immune checkpoint inhibitors (ICI) provide a clinical opportunity against MBM; however, the MBM tumor microenvironment (TME) has not been fully elucidated in the context of ICI. To dissect unique elements of the MBM TME and correlates of MBM response to ICI, we collected 32 fresh MBM and performed single-cell RNA sequencing of the MBM TME and T-cell receptor clonotyping on T cells from MBM and matched blood and extracranial lesions. We observed myeloid phenotypic heterogeneity in the MBM TME, most notably multiple distinct neutrophil states, including an IL8-expressing population that correlated with malignant cell epithelial-to-mesenchymal transition. In addition, we observed significant relationships between intracranial T-cell phenotypes and the distribution of T-cell clonotypes intracranially and peripherally. We found that the phenotype, clonotype, and overall number of MBM-infiltrating T cells were associated with response to ICI, suggesting that ICI-responsive MBMs interact with peripheral blood in a manner similar to extracranial lesions. These data identify unique features of the MBM TME that may represent potential targets to improve clinical outcomes for patients with MBM.

Metastases are the most common malignancy of the adult central nervous system and are becoming an increasingly troubling problem in oncology largely due to the lack of successful therapeutic options. The limited selection of treatments is a result of the currently poor understanding of the biological mechanisms of metastatic development, which in turn is difficult to achieve because of limited preclinical models that can accurately represent the clinical progression of metastasis. Described in this article are in vitro and in vivo model systems that are used to enhance the understanding of metastasis and to identify new therapies for the treatment of brain metastasis. © 2021 Wiley Periodicals LLC.

Melanoma-derived brain metastases (MBM) represent an unmet clinical need due to central nervous system (CNS) progression as a frequent, end-stage site of disease. Immune checkpoint inhibition (ICI) represents a clinical opportunity against MBM; however, the MBM tumor microenvironment (TME) has not been fully elucidated in the context of ICI. To dissect unique MBM-TME elements and correlates of MBM-ICI response, we collected 32 fresh MBM and performed single cell RNA sequencing of the MBM-TME and T cell receptor clonotyping on T cells from MBM and matched blood and extracranial lesions. We observed myeloid phenotypic heterogeneity, most notably multiple distinct neutrophil states including an IL-8 expressing population that correlated with malignant cell epithelial-to-mesenchymal transition. Additionally, we observe significant relationships between intracranial T cell phenotypes and the distribution of T cell clonotypes intracranially and peripherally. We found that the phenotype, clonotype, and overall number of MBM-infiltrating T cells were associated with response to ICI, suggesting that ICI-responsive MBMs interact with peripheral blood in a manner similar to extracranial lesions. These data demonstrate unique features of the MBM-TME, which may represent potential targets to improve clinical outcomes for patients with MBM.

While immune checkpoint inhibitors (ICI) have revolutionized treatment of advanced cancers, few of the 30% of cancer patients who develop brain metastases benefit from immunotherapy. Inhibition of CDK4/6 pathway - altered in >50% of brain metastatic patients - can reportedly increase tumor inflammation and sensitize extracranial tumors to ICI. To determine whether intracranial tumors can be similarly sensitized, we studied efficacy of combination CDK4/6 inhibitor Abemaciclib and ICI in immunocompetent mouse models of brain metastasis bearing concurrent intracranial and extracranial murine tumors that are ICI-resistant. 8-week-old female C57BL/6 mice received subcutaneous injections of 2x105 YUMM1.7 or B16-F10 melanoma cells 3 days prior to intracranial injections of 1x104 YUMM1.7-FmC (firefly luciferase-tagged) cells or 5x103 B16-F10 cells respectively. 8-week-old female BALB/C mice similarly received 2x105 4T1 mammary carcinoma cells in mammary fat pad 3 days prior to intracranial injections with 2x104 4T1-FmC cells. Mice were randomized into 4 treatment groups (n=5-7/group): Abemaciclib monotherapy (administered daily), anti-PD-1 monotherapy (every 3 days), Abemaciclib and anti-PD-1 (combination therapy), and treatment with vehicle and isotype-matched antibody as control. In all 3 tumor models, extracranial tumor growth was significantly reduced compared to control mice following combination therapy (P Citation Format: Naema Nayyar, Mohini Singh, Magali de Sauvage, Nazanin Ijad, Ashish Dahal, Jane Chuprin, Michael Brehm, Priscilla Brastianos. CDK4/6 inhibition with Abemaciclib improves intracranial and extracranial response to checkpoint blockade in pre-clinical models of brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4181.

Brain metastases (BM) are the most common neoplasm to affect the adult central nervous system. BM develop in 40-50% of advanced lung adenocarcinoma (LUAD), but the lack of durable response to chemotherapy, immunotherapy, or targeted therapy results in death within a year of BM diagnosis. Several advances have been made in identifying genetic drivers of primary cancers. The cell cycle, RAS and ERK pathways have all been implicated in as critical oncogenic regulators, with aberrations linked to driving the progression and metastasis of LUAD. Abemaciclib is a targeted CDK4/6 inhibitor, and LY3214996 is selective ERK1/2 inhibitor, and have shown efficacy in preclinical tumor models as well as in clinical trials. Furthermore, both therapeutics can interfere with the cell cycle, abemaciclib through targeting CDK4/6 and LY3214996 through cyclinD1. Here we present data assessing abemaciclib and LY3214996, as single and combined agents, in cell lines across different KRAS and CDKN2A mutational backgrounds. Seven days post-intracranial inoculation of NSCLC and NSCLC-BM line, mice received either abemaciclib, LY3214996, or a combination P.O. daily for 21 days, and were monitored pre- and post-treatment for tumor growth with bioluminescent imaging. In vitro we demonstrated a dose-dependent reduction in cell growth with each treatment, as well as cell arrest in G1 phase. In vivo, whereas cell lines with a combined KRAS mutation and CDKN2A mutation/deletion had no significant reduction in BM growth, cell lines with a CDKN2A del or BRAF mutation had significant BM reduction, with single agents and combined treatment. Further research is necessary to elucidate under what genetic contexts abemaciclib, LY3214996 or the combination are most effective. Nonetheless, this work highlights that abemaciclib and LY3214996 should be further explored for CDKN2A or BRAF mutant BM.

While immune checkpoint inhibitors (ICI) have revolutionized treatment of metastatic melanoma, few of the 75% of patients who develop brain metastases benefit from immunotherapy. Inhibition of CDK4/6 pathway – altered in ~90% of melanoma patients – can reportedly increase tumor inflammation and sensitize extracranial tumors to ICI. To determine whether intracranial melanoma can be similarly sensitized, we studied efficacy of combination CDK4/6 inhibitor Abemaciclib and ICI in immunocompetent mouse models of melanoma brain metastases bearing concurrent intracranial and extracranial tumors. 8-week-old female C57BL/6 mice received subcutaneous injections of 2x105 YUMM1.7 or B16-F10 melanoma cells 3 days prior to intracranial injections of 5x104 YUMM1.7 cells or 5x103 B16-F10 cells respectively. Mice were randomized into 6 treatment groups (n=5-7/group): Abemaciclib alone, anti-PD-1 monotherapy, anti-PD-1 and anti-CTLA4 combined (combination ICI), Abemaciclib and anti-PD-1, Abemaciclib combined with anti-PD-1 and anti-CTLA4 (triple therapy), and treatment with vehicle and isotype-matched antibodies as control. In mice bearing YUMM1.7 tumors, subcutaneous tumor growth was significantly reduced compared to control in mice treated with Abemaciclib alone (p< 0.05), combination ICI (p< 0.05) and triple therapy (p< 0.05). However, improvement in survival was only observed with triple therapy (p=0.039) compared to control group. In mice bearing B16-F10 tumors, we observed striking reduction in subcutaneous tumor growth in mice treated with Abemaciclib and anti-PD-1 compared to control-treated mice (p=0.0016) or to mice receiving anti-PD-1 monotherapy (p=0.000056). This further corresponded to a significant increase in survival of Abemaciclib and anti-PD-1 treated mice compared to control (p=0.02). Additionally, we observed improved survival in mice treated with combination ICI (p=0.006) or triple therapy (p=0.01). These results indicate CDK4/6 inhibition with Abemaciclib can improve both extracranial and intracranial responses to ICI and sensitize melanoma brain metastases to immunotherapy. Our pre-clinical findings warrant further investigation to determine whether this combination approach can improve patient outcomes.