Novel Treatment Strategies for Brain metastases of Breast Cancer

About 20-40% of advanced breast cancer patients will develop symptomatic brain metastases. Once the patients diagnosed with metastatic brain tumors, there is 80% mortality rate within one year. The presence of blood-brain barrier makes it difficult for drugs to reach the site of action in brain-related ailments. To overcome we came up with two strategies: First, we encapsulated the chemotherapy in a liposome and thereby significantly improving the plasma pharmacokinetics of chemotherapy. We also observed that tumor drug exposure significantly improved by liposomal formulation. This improvement in plasma drug pharmacokinetics and tumor drug accumulation after administration of the liposomal formulation decreased the tumor burden and significantly increased the median survival by 40% when compared to vehicle group in an experimental model of brain metastases. In another strategy, we want to modulate blood-brain barrier in brain metastases to increase permeation. Notch-4 signaling pathway plays an important role in angiogenesis and inhibition of Notch-4 by DAPT will increase the expression of vascular endothelial growth factor receptor-2 ultimately leading to leaky vasculature in metastatic brain tumor. In our studies, we found that inhibition of Notch-4 by DAPT increased the permeation 14C- Aminoisobutyric acid specifically in the brain metastases. We also observed that the progression of tumor burden was decreased when animals were administered both Notch-4 inhibitor and chemotherapy. We also found that median survival is increased by 20% in animals treated with chemotherapy with concurrent Notch-4 inhibition by DAPT. Finally, we evaluated the effect of chemotherapy on normal brain region adjacent to brain metastases. We found that the permeation of fluorescent tracers and 14C-paclitaxel increased in brain adjacent to the tumor. We also found that the expression of activated astrocytes increased in brain adjacent to tumors after chronic chemotherapy treatment in our brain metastases model. Together these results suggest that novel strategies improved survival in brain metastases of breast cancer. Future studies should aim at combining these individual strategies to further increase survival in a preclinical model. At the same time care should be taken not increase chemotherapy permeation into the normal brain as it may lead to unwanted effects like chemo-fog

P-glycoprotein Mediated Efflux Limits Substrate and Drug Uptake in a Preclinical Brain Metastases of Breast Cancer Model

The blood-brain barrier (BBB) is a specialized vascular interface that restricts the entry of many compounds into brain. This is accomplished through the sealing of vascular endothelial cells together with tight junction proteins to prevent paracellular diffusion. In addition, the BBB has a high degree of expression of numerous efflux transporters which actively extrude compounds back into blood. However, when a metastatic lesion develops in brain the vasculature is typically compromised with increases in passive permeability (blood-tumor barrier; BTB). What is not well documented is to what degree active efflux retains function at the BTB despite the changes observed in passive permeability. In addition, there have been previous reports documenting both increased and decreased expression of P-gp in lesion vasculature. Herein, we simultaneously administer a passive diffusion marker (14C-AIB) and a tracer subject to P-gp efflux (rhodamine 123) into a murine preclinical model of brain metastases of breast cancer. We observed that the metastatic lesions had similar expression (p>0.05; n=756-1214 vessels evaluated) at the BBB and the BTB. Moreover, tissue distribution of R123 was not significantly (p>0.05) different between normal brain and the metastatic lesion. It is possible that the similar expression of P-gp on the BBB and the BTB contribute to this phenomenon. Additionally we observed P-gp expression at the metastatic cancer cells adjacent to the vasculature which may also contribute to reduced R123 uptake into the lesion. The data suggest that despite the disrupted integrity of the BTB, efflux mechanisms appear to be intact, and may be functionally comparable to the normal BBB. The BTB is a significant hurdle to delivering drugs to brain metastasis