Pazopanib inhibits the activation of PDGFRß-expressing astrocytes in the brain metastatic microenvironment of breast cancer cells.

Brain metastases occur in more than one-third of metastatic breast cancer patients whose tumors overexpress HER2 or are triple negative. Brain colonization of cancer cells occurs in a unique environment, containing microglia, oligodendrocytes, astrocytes, and neurons. Although a neuroinflammatory response has been documented in brain metastasis, its contribution to cancer progression and therapy remains poorly understood. Using an experimental brain metastasis model, we characterized the brain metastatic microenvironment of brain tropic, HER2-transfected MDA-MB-231 human breast carcinoma cells (231-BR-HER2). A previously unidentified subpopulation of metastasis-associated astrocytes expressing phosphorylated platelet-derived growth factor receptor ß (at tyrosine 751; p751-PDGFRß) was identified around perivascular brain micrometastases. p751-PDGFRß(+) astrocytes were also identified in human brain metastases from eight craniotomy specimens and in primary cultures of astrocyte-enriched glial cells. Previously, we reported that pazopanib, a multispecific tyrosine kinase inhibitor, prevented the outgrowth of 231-BR-HER2 large brain metastases by 73%. Here, we evaluated the effect of pazopanib on the brain neuroinflammatory microenvironment. Pazopanib treatment resulted in 70% (P = 0.023) decrease of the p751-PDGFRß(+) astrocyte population, at the lowest dose of 30 mg/kg, twice daily. Collectively, the data identify a subpopulation of activated astrocytes in the subclinical perivascular stage of brain metastases and show that they are inhibitable by pazopanib, suggesting its potential to prevent the development of brain micrometastases in breast cancer patients.

Hypertension and hand-foot skin reactions related to VEGFR2 genotype and improved clinical outcome following bevacizumab and sorafenib.

BACKGROUND: Hypertension (HT) and hand-foot skin reactions (HFSR) may be related to the activity of bevacizumab and sorafenib. We hypothesized that these toxicities would correspond to favorable outcome in these drugs, that HT and HFSR would coincide, and that VEGFR2 genotypic variation would be related to toxicity and clinical outcomes. METHODS: Toxicities (> or = grade 2 HT or HFSR), progression-free survival (PFS), and overall survival (OS) following treatment initiation were evaluated. Toxicity incidence and VEGFR2 H472Q and V297I status were compared to clinical outcomes. RESULTS: Individuals experiencing HT had longer PFS following bevacizumab therapy than those without this toxicity in trials utilizing bevacizumab in patients with prostate cancer (31.5 vs 14.9 months, n = 60, P = 0.0009), and bevacizumab and sorafenib in patients with solid tumors (11.9 vs. 3.7 months, n = 27, P = 0.052). HT was also linked to a > 5-fold OS benefit after sorafenib and bevacizumab cotherapy (5.7 versus 29.0 months, P = 0.0068). HFSR was a marker for prolonged PFS during sorafenib therapy (6.1 versus 3.7 months respectively, n = 113, P = 0.0003). HT was a risk factor for HFSR in patients treated with bevacizumab and/or sorafenib (OR(95%CI) = 3.2(1.5-6.8), P = 0.0024). Carriers of variant alleles at VEGFR2 H472Q experienced greater risk of developing HT (OR(95%CI) = 2.3(1.2 - 4.6), n = 170, P = 0.0154) and HFSR (OR(95%CI) = 2.7(1.3 - 5.6), n = 170, P = 0.0136). CONCLUSIONS: This study suggests that HT and HFSR may be markers for favorable clinical outcome, HT development may be a marker for HFSR, and VEGFR2 alleles may be related to the development of toxicities during therapy with bevacizumab and/or sorafenib.