Signature of acquired resistance to fluvastatin

Background: Cholesterol pathway inhibition by statins prevents breast cancer development in mouse models of breast cancer but their efficacy is not very high (about 50%) . Therefore, the goal of this study is to investigate if the fluvastatin mediated upregulation in the steroid biosynthesis pathway genes limit the efficacy of statin chemoprevention. Methods: A published gene signature of statin resistance was validated in cell line-based models of inherent and acquired resistance during breast cancer. These signatures were next validated in a mouse model of hormone receptor negative breast cancer. Results: We found more than 70% of a published multi-gene fluvastatin resistance signature to be significantly upregulated in an inherently resistant cell line relative to fluvastatin sensitive cell line. We found this inherent statin resistance gene signature to be also shared with the signature of acquired resistance to fluvastatin (13 / 23 total genes). These 13 inherent resistance genes and 10 additional genes mapped to 2 of the top 3 deregulated pathways that are steroid-, and terpenoid backbone- biosynthesis pathway. Next, we tested if one or multiple genes of statin resistance signature, could predict efficacy of statin chemoprevention in the SV40 C3TAg transgenic mouse model. We found upregulation of a large number (19/24) of genes in the tumor bearing mammary glands, suggesting that upregulation of these pathways drives resistance to statin chemoprevention. A subset of 13-genes from this panel was significantly associated with response to statin treatment, as was the expression level of HMGCR alone in a mouse model of breast cancer. Lastly, we studied if a 10-day period of fluvastatin treatment to SV40C3 TAg mice, can also trigger the upregulation of these genes and provide an early signal of statin resistance. These experiments showed that a 10-day period is insufficient to cause a feedback upregulation in steroid biosynthesis pathway genes and thus cannot be used as an early biomarker to detect resistance to fluvastatin. Conclusions: High basal or restorative upregulation in the steroid biosynthesis pathway gene expression after fluvastatin treatment appears to be strongly associated with resistance to statin chemoprevention for breast cancer and may serve as a biomarker to identify patients that are most likely to respond to statins or develop resistance. Three replicates of the untreated MCF10.AT1 and three replicates of the MCF10.AT1-resistant cells were used for the clariom D array analysis.