Supplemental figure 4: (A) Mia PaCa2 xenograft tumor volume plotted over time for mice that had no treatment or abemaciclib treatment daily for 9 days. (B) Graphical representation of tumor volume (left) in no treatment and abemaciclib treated mice with n=5, two tumors per mice. All mice, including one outlier mouse in the abemaciclib arm, shown for comparison to Figure 5. Graphical representation of tumor weights after sacrifice are shown, including one outlier mouse in the abemaciclib arm, shown for comparison to Figure 5 (right). (C) Xenograft tumors from all experimental arms were collected at day 69 at the end of the experiment and harvested for western blot analysis, and probed for pRb, ser 780. Quantification of the western blot is shown above the blot.
ARTICLE ABSTRACT
Mutation or promoter hypermethylation of CDKN2A is found in over 90% of pancreatic ductal adenocarcinomas (PDAC) and leads to loss of function of cell-cycle inhibitors p16 (INK4A) and p14 (ARF) resulting in unchecked proliferation. The CDK4/6 inhibitor, abemaciclib, has nanomolar IC50s in PDAC cell lines and decreases growth through inhibition of phospho-Rb (pRb), G1 cell-cycle arrest, apoptosis, and the senescent phenotype detected with β-galactosidase staining and relevant mRNA elevations. Daily abemaciclib treatments in mouse PDAC xenograft studies were safe and demonstrated a 3.2-fold decrease in tumor volume compared with no treatment (P < 0.0001) accompanying a decrease in both pRb and Ki67. We determined that inhibitors of HuR (ELAVL1), a prosurvival mRNA stability factor that regulates cyclin D1, and an inhibitor of Yes-Associated Protein 1 (YAP1), a pro-oncogenic, transcriptional coactivator important for CDK6 and cyclin D1, were both synergistic with abemaciclib. Accordingly, siRNA oligonucleotides targeted against HuR, YAP1, and their common target cyclin D1, validated the synergy studies. In addition, we have seen increased sensitivity to abemaciclib in a PDAC cell line that harbors a loss of the ELAVL1 gene via CRISP-Cas9 technology. As an in vitro model for resistance, we investigated the effects of long-term abemaciclib exposure. PDAC cells chronically cultured with abemaciclib displayed a reduction in cellular growth rates (GR) and coresistance to gemcitabine and 5-fluorouracil (5-FU), but not to HuR or YAP1 inhibitors as compared with no treatment controls. We believe that our data provide compelling preclinical evidence for an abemaciclib combination–based clinical trial in patients with PDAC.
Our data suggest that abemaciclib may be therapeutically relevant for the treatment in PDAC, especially as part of a combination regimen inhibiting YAP1 or HuR.
