Stromal Senescence following Treatment with the CDK4/6 Inhibitor Palbociclib Alters the Lung Metastatic Niche and Increases Metastasis of Drug-Resistant Mammary Cancer Cells.

BACKGROUND: CDK4/6 inhibitors (CDKi) have improved disease control in hormone-receptor-positive, HER2-negative metastatic breast cancer, but most patients develop progressive disease. METHODS: We asked whether host stromal senescence after CDK4/6 inhibition affects metastatic seeding and growth of CDKi-resistant mammary cancer cells by using the p16-INK-ATTAC mouse model of inducible senolysis. RESULTS: Palbociclib pretreatment of naïve mice increased lung seeding of CDKi-resistant syngeneic mammary cancer cells, and this effect was reversed by depletion of host senescent cells. RNA sequencing analyses of lungs from non-tumor-bearing p16-INK-ATTAC mice identified that palbociclib downregulates immune-related gene sets and gene expression related to leukocyte migration. Concomitant senolysis reversed a portion of these effects, including pathway-level enrichment of TGF-ß- and senescence-related signaling. CIBERSORTx analysis revealed that palbociclib alters intra-lung macrophage/monocyte populations. Notably, lung metastases from palbociclib-pretreated mice revealed senescent endothelial cells. Palbociclib-treated endothelial cells exhibit hallmark senescent features in vitro, upregulate genes involved with the senescence-associated secretory phenotype, leukocyte migration, and TGF-ß-mediated paracrine senescence and induce tumor cell migration and monocyte trans-endothelial invasion in co-culture. CONCLUSIONS: These studies shed light on how stromal senescence induced by palbociclib affects lung metastasis, and they describe palbociclib-induced gene expression changes in the normal lung and endothelial cell models that correlate with changes in the tumor microenvironment in the lung metastatic niche.

An evaluation of palbociclib as a breast cancer treatment option: a current update.

INTRODUCTION: Patients with hormone receptor-positive/HER2-negative (HR+/HER2-) metastatic breast cancer have benefitted from treatment with palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor capable of selectively targeting mechanisms of cell cycle progression that contribute to tumor cell proliferation. Palbociclib use in this setting demonstrates improved progression-free survival when given in combination with aromatase inhibitors or fulvestrant. AREAS COVERED: The authors describe the current state of research surrounding palbociclib use in breast cancer, present evidence supporting a role for palbociclib in additional subtypes of metastatic breast cancer such as HER2-positive (HER2+) and triple-negative, report ongoing clinical trials aimed at expanding the scope of use for palbociclib, and discuss expected clinical results that will better inform decisions on including palbociclib as a part of breast cancer treatment strategies. EXPERT OPINION: Preclinical and clinical studies have shown promising evidence for palbociclib use in metastatic HER2+ and androgen receptor-expressing triple-negative breast cancer but mixed results in the adjuvant/neoadjuvant setting, where differences may only be detectable in high-risk disease. Palbociclib combinations may constitute viable replacements for chemotherapy in the neoadjuvant setting as part of de-escalation strategies. Investigation into synergy of palbociclib with immunotherapies is also ongoing based on non-canonical effects of CDK4/6 inhibition on the tumor immune microenvironment.

Short- and Long-Term Effects of CDK4/6 Inhibition on Early-Stage Breast Cancer.

CDK4/6 inhibitors are used in the treatment of advanced estrogen receptor (ER)(+) breast cancer. Their efficacy in ER(-) and early-stage breast cancer is currently under investigation. Here, we show that palbociclib, a CDK4/6 inhibitor, can inhibit both progression of ductal carcinoma in situ (DCIS) and growth of invasive disease in both an ER(-) basal breast cancer model (MCFDCIS) and an ER(+) luminal model (MCF7 intraductal injection). In MCFDCIS cells, palbociclib repressed cell-cycle gene expression, inhibited proliferation, induced senescence, and normalized tumorspheres formed in Matrigel while the formation of acini by normal mammary epithelial cells (MCF10A) was not affected. Palbociclib treatment of mice with MCFDCIS tumors inhibited their malignant progression and reduced proliferation of invasive lesions. Transcriptomic analysis of the tumor and stromal cell compartments showed that cell cycle and senescence genes, and MUC16, an ovarian cancer biomarker gene, were repressed during treatment. Knockdown of MUC16 in MCFDCIS cells inhibited proliferation of invasive lesions but not progression of DCIS. After cessation of palbociclib treatment genes associated with differentiation, for example, P63, inflammation, IFNγ response, and antigen processing and presentation remained suppressed in the tumor and surrounding stroma. We conclude that palbociclib can prevent progression of DCIS and is antiproliferative in ER(-) invasive disease mediated in part via MUC16. Lasting effects of CDK4/6 inhibition after drug withdrawal on differentiation and the immune response could impact the approach to treatment of early-stage ER(-) breast cancer.

A novel BAP1 mutation is associated with melanocytic neoplasms and thyroid cancer.

Germline mutations in the tumor suppressor gene, BRCA-1 associated protein (BAP1), underlie a tumor predisposition syndrome characterized by increased risk for numerous cancers including uveal melanoma, melanocytic tumors and mesothelioma, among others. In the present study we report the identification of a novel germline BAP1 mutation, c.1777C>T, which produces a truncated BAP1 protein product and segregates with cancer. Family members with this mutation demonstrated a primary clinical phenotype of autosomal dominant, early-onset melanocytic neoplasms with immunohistochemistry (IHC) of these tumors demonstrating lack of BAP1 protein expression. In addition, family members harboring the BAP1 c.1777C>T germline mutation developed other neoplastic disease including thyroid cancer. IHC analysis of the thyroid cancer, as well, demonstrated loss of BAP1 protein expression. Our investigation identifies a new BAP1 mutation, further highlights the relevance of BAP1 as a clinically important tumor suppressor gene, and broadens the range of cancers associated with BAP1 inactivation. Further study will be required to understand the full scope of BAP1-associated neoplastic disease.