NP-ALT, a liposomal: Peptide drug, blocks p27Kip1 phosphorylation to induce oxidative stress, necroptosis, and regression in therapy-resistant breast cancer cells

Resistance to cyclin D-CDK4/6 inhibitors (CDK4/6i) represents an unmet clinical need and is frequently caused by compensatory CDK2 activity. Here we describe a novel strategy to prevent CDK4i resistance by using a therapeutic liposomal:peptide formulation, NP-ALT, to inhibit the tyrosine phosphorylation of p27Kip1(CDKN1B), which in turn inhibits both CDK4/6 and CDK2. We find that NP-ALT blocks proliferation in HRþ breast cancer cells, as well as CDK4i-resistant cell types, including triple negative breast cancer (TNBC). The peptide ALT is not as stable in primary mammary epithelium, suggesting that NP-ALT has little effect in nontumor tissues. In HRþ breast cancer cells specifically, NP-ALT treatment induces ROS and RIPK1-dependent necroptosis. Estrogen signaling and ERa appear required. Significantly, NP-ALT induces necroptosis in MCF7 ESR^Y537S cells, which contain an ER gain of function mutation frequently detected in metastatic patients, which renders them resistant to endocrine therapy. Here we show that NP-ALT causes necroptosis and tumor regression in treatment na€1ve, palbociclib-resistant, and endocrine-resistant BC cells and xenograft models, demonstrating that p27 is a viable therapeutic target to combat drug resistance. Implications: This study reveals that blocking p27 tyrosine phosphorylation inhibits CDK4 and CDK2 activity and induces ROS-dependent necroptosis, suggesting a novel therapeutic option for endocrine and CDK4 inhibitor-resistant HRþ tumors.