Pak1 pathway hyper-activation mediates resistance to endocrine therapy and CDK4/6 inhibitors in ER+ breast cancer

by Selleckchem | Oct 23 2023

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have been approved in combination with endocrine therapy (ET) to treat estrogen receptor-positive (ER+) metastatic breast cancer (BC). However, drug resistance represents the leading cause of breast cancer patients mortality. This study aimed to identify novel resistance mechanisms to ER antagonists in combination with CDK4/6 inhibitors. We generated two ER+ BC cell lines, T47D and MCF7, resistant to the combination of the ER antagonist fulvestrant and CDK4/6i abemaciclib, named T47D-FAR and MCF7-FAR. Transcriptomic analysis revealed common up-regulation of genes involved in MAPK and epithelial to mesenchymal transition (EMT) pathways in FAR cells, sustaining their hyper-invasive phenotype and increased anchorage-independent growth, compared to sensitive cells. FAR cells showed higher p21-activated kinase 1 (Pak1) expression and phosphorylation levels than parental cells. PAK1 knockdown by siRNAs hampered cell proliferation, reduced anchorage-independent growth and invasive properties of T47D-FAR and MCF7-FAR, re-sensitizing them to fulvestrant and abemaciclib. Conversely, over-expression of PAK1 in MCF7 and T47D cells increased tumor spheroids' growth and invasion and reduced sensitivity to fulvestrant and abemaciclib, confirming its role in inducing drug resistance. Finally, treatment with Pak1 inhibitors, PF-3758309 (PF309) and NVS-PAK1-1, restored cell sensitivity to fulvestrant and abemaciclib of MCF7-FAR and T47D-FAR cells, both in vitro and in vivo. In conclusion, our data suggested a pivotal role for Pak1 in resistance to ET and CDK4/6i in ER+ breast cancers. These data might promote the rationale for the development of novel Pak1 inhibitors for treatment of patients with ER+ BC progressing on ET plus CDK4/6i.

Comments:

The study you described aimed to identify novel resistance mechanisms to estrogen receptor (ER) antagonists in combination with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) in the treatment of estrogen receptor-positive (ER+) metastatic breast cancer. The researchers generated two ER+ breast cancer cell lines, T47D-FAR and MCF7-FAR, which were resistant to the combination of the ER antagonist fulvestrant and CDK4/6i abemaciclib.

Transcriptomic analysis of the resistant cell lines revealed common up-regulation of genes involved in the MAPK (mitogen-activated protein kinase) pathway and epithelial to mesenchymal transition (EMT) pathway. These pathways are known to play important roles in cancer progression, invasion, and metastasis. The up-regulation of these genes in the FAR cells supported their hyper-invasive phenotype and increased anchorage-independent growth compared to the sensitive cells.

Further investigation showed that the FAR cells had higher expression and phosphorylation levels of p21-activated kinase 1 (Pak1) compared to the parental cells. Knockdown of Pak1 using small interfering RNAs (siRNAs) resulted in reduced cell proliferation, decreased anchorage-independent growth, and diminished invasive properties of the FAR cells. This knockdown also re-sensitized the FAR cells to fulvestrant and abemaciclib, suggesting that Pak1 plays a role in inducing drug resistance.

To further validate the role of Pak1 in drug resistance, the researchers overexpressed Pak1 in MCF7 and T47D cells, which increased tumor spheroid growth and invasion and reduced sensitivity to fulvestrant and abemaciclib. These findings confirmed that Pak1 contributes to the development of resistance to ER antagonists and CDK4/6 inhibitors.

Finally, the researchers treated the FAR cells with Pak1 inhibitors, PF-3758309 (PF309), and NVS-PAK1-1, and observed that these inhibitors restored cell sensitivity to fulvestrant and abemaciclib both in vitro and in vivo.

In conclusion, the study suggests that Pak1 plays a pivotal role in resistance to endocrine therapy (ET) and CDK4/6 inhibitors in ER+ breast cancers. The findings highlight the potential for developing novel Pak1 inhibitors as a treatment strategy for ER+ breast cancer patients who have progressed on ET plus CDK4/6i therapy. Further research and development of Pak1 inhibitors may provide new therapeutic options to overcome drug resistance in this patient population.