Abstract P2-21-05: Vascular effects of Platelet-derived growth factor-B (PDGFB) in breast cancer metastasis to the brain

Brain metastases are associated with shortened survival and poorer quality of life in breast cancer patients. Recently, the importance of platelet-derived growth factor-B (PDGFB) and its stromally localized cognate receptor, platelet-derived growth factor receptor-beta (PDGFRβ) in promoting breast cancer metastasis to the brain was identified by our group. Historically, PDGFB-to-PDGFRβ signaling is known to promote angiogenesis and vessel maturation both in normal physiology and in cancer, but the mechanism(s) behind this tumor stromal interplay in brain metastasis is poorly understood. Based on our previous work and the work of others, we hypothesized that breast tumor-derived PDGFB directly modulates both brain endothelial and blood brain barrier (BBB) function by altering angiogenesis and endothelial permeability. To test this directly, we over-expressed PDGFB ligand in MDA-MB-231 and HCC1187 triple negative breast cancer cell lines and compared the angiogenic potential of the conditioned medium (CM) from these cells. We utilized both a 3D in vitro (human brain microvascular endothelial cell, HBMEC) spheroid angiogenesis model and a tri-culture BBB system (HBMECs in direct interaction with human astrocytes and human pericytes) to test the BBB vasculature. CM harvested from PDGFB overexpressing cells significantly increased the sprouting angiogenesis potential of 3D HBMECs and the migration of 3D tri-culture BBB spheroids compared to CM obtained from parental cells. In addition, CM from PDGFB overexpressing cells caused the surface of BBB spheroids to exhibit significantly increased permeability to high molecular weight dextran compared to CM from parental cells. In agreement with these findings, the tight junction protein ZO1 was diminished. Importantly, in vivo BBB permeability was also tested upon intracardiac injection of MDA-MB-231 cells with and without PDGFB overexpression. These studies revealed that Evans blue dye fluorescence intensity was significantly higher in the brains of mice injected with PDGFB overexpressing cells compared to parental cells. Overall, these studies reveal a previously unrecognized role for PDGFB-to-PDGFRβ signaling in brain vascular remodeling and BBB permeability, which has clinical implications for women with PDGFB-positive breast cancer.

Citation Format: Sajita Shah, Rebecca Packard, Sarah Steck, Alexis Mossing, Yalini Ramamoorthy, Katie Thies, Alexander Didier, Jonathan Spehar, Dillon Richardson, Tasneem Arsiwala, Jonathan Godbout, Steven Sizemore, Paul Lockman, Gina Sizemore. Vascular effects of Platelet-derived growth factor-B (PDGFB) in breast cancer metastasis to the brain [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-21-05.

BCL-xL inhibition potentiates cancer therapies by redirecting the outcome of p53 activation from senescence to apoptosis

Cancer therapies trigger diverse cellular responses, ranging from apoptotic death to acquisition of persistent therapy-refractory states such as senescence. Tipping the balance toward apoptosis could improve treatment outcomes regardless of therapeutic agent or malignancy. We find that inhibition of the mitochondrial protein BCL-xL increases the propensity of cancer cells to die after treatment with a broad array of oncology drugs, including mitotic inhibitors and chemotherapy. Functional precision oncology and omics analyses suggest that BCL-xL inhibition redirects the outcome of p53 transcriptional response from senescence to apoptosis, which likely occurs via caspase-dependent down-modulation of p21 and downstream cytostatic proteins. Consequently, addition of a BCL-2/xL inhibitor strongly improves melanoma response to the senescence-inducing drug targeting mitotic kinase Aurora kinase A (AURKA) in mice and patient-derived organoids. This study shows a crosstalk between the mitochondrial apoptotic pathway and cell cycle regulation that can be targeted to augment therapeutic efficacy in cancers with wild-type p53.