Abstract 458: Targeting p27Kip1 to inhibit CDK4/6/2 as a novel therapeutic strategy to treat pancreatic ductal adenocarcinoma

Abstract

Abstract CDK4/6 inhibitors are powerful tools used clinically to treat metastatic, HR+ BC patients. While combined CDK4/6i treatment in combination with Estrogen modulation significantly extends Progression Free Survival (PFS) in metastatic HR+ breast cancer patients, those treated invariably develop aquired resistance, which results in only marginal improvement in Overall Survival (OS). The drug resistance seen in the presence of CDK4/6i, such as palbociclib, has been shown to be attributed to activation and compensation by CDK2. Pancreatic ductal adenocarcinoma (PDAC) is characterized by aberrant activation of the CyclinD-CDK4/6 signaling pathway and inactivation of the CDKN2A locus encoding the CDK4/6 inhibitor, p16INK4A, and was initially thought to be a good candidate for CDK4/6i use. Surprisingly, CDK4/6i do not show response in most PDAC lines and have not been used clinically in this tumor type. We hypothesized that PDAC may be intrinsically resistant to CDK4/6 inhibition due to activation of CDK2 and as such inhibition of both CDK4/6 and CDK2 may be required. We have developed a novel strategy to kill drug-resistant tumor cells using a therapeutic liposomal:peptide formulation, IpY.1, to inhibit the tyrosine phosphorylation of p27Kip1(CDKN1B), which in turn inhibits both CDK4/6 and CDK2. IpY.1 is specific for p27, and this reduces toxicity relative to that seen with the small molecule ATP-competitive CDK4/6i or CDK2i. IpY.1 blocks DNA replication in HR+ breast cancer (BC) cells and mouse models, but unlike CDK4/6i or CDK2i treatment, it induces ROS-dependent necroptosis to kill the tumor cells. Palbociclib did not have a significative effect on ATP levels or proliferation of PDAC cell lines. In contrast, we found that IpY.1 was able to block proliferation and reduce viability in palbociclib-resistant PDAC lines, suggesting that dual CDK4/6 and CDK2 inhibition via p27 targeting was required. Some PDAC lines were “super sensitive” and responded with IC50 values ~10X less than seen with the ER+ BC lines, and we are currently screening for biomarkers of response. CDK2 activity was reduced in IpY.1 treated lines and markers of necroptosis were detected. Immunoblot analysis showed decreased pY88 phosphorylation of p27 (the target of IpY) demonstrating target engagement. We have demonstrated that unlike palbociclib, IpY.1 blocks proliferation and viability in all PDAC lines tested, suggesting that targeting p27 may be a viable approach to treat PDAC. Citation Format: Carolina Guido, Susan RS Gottesman, Stacy W. Blain. Targeting p27Kip1 to inhibit CDK4/6/2 as a novel therapeutic strategy to treat pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 458.