# Simultaneous targeting of KRAS and CDK4 synergistically induces durable growth arrest in pancreatic cancer cells

## TL;DR

Combining KRAS and CDK4 inhibitors effectively stops pancreatic cancer cell growth and may improve cancer treatment.

## Contribution

A novel combination therapy using KRAS and CDK4 inhibitors shows synergistic anti-cancer effects in preclinical models.

## Key findings

- Sotorasib and Palbociclib synergistically induce durable growth arrest in KRAS-G12C-mutant pancreatic cancer cells.
- KRAS-G12D inhibition with MRTX1133 and Palbociclib also suppresses growth of KRAS-G12D-mutant PDAC cells.
- Palbociclib failed to enhance MRTX1133 effects in vivo, possibly due to increased tumor vascularization.

## Abstract

Mutant Ras oncoproteins, particularly KRAS, are among the most prevalent drivers of cancer. Small-molecule KRAS inhibitors have emerged as promising cancer therapeutics, yet resistance development remains a major hurdle. To overcome this challenge, we explored rational combination strategies aimed at enhancing therapeutic efficacy and durability. We show that the KRAS-G12C inhibitor Sotorasib synergizes with the CDK4/6 inhibitor Palbociclib to eliminate pancreatic ductal adenocarcinoma (PDAC) cells and organoids harboring KRAS-G12C mutations. This synergy was especially pronounced following drug washout, indicating a durable cellular response. Similar synergistic effects were observed in non-small-cell lung cancer (NSCLC) cells. Additionally, the KRAS-G12D inhibitor MRTX1133 cooperated with Palbociclib to suppress growth of KRAS-G12D-mutant PDAC cells. Mechanistically, the combinations induced sustained cell cycle arrest, marked by reduced RB phosphorylation, decreased E2F1 expression, and increased levels of CDKN1B/p27. Deletion of CDKN1B largely reversed the growth-inhibitory effect, highlighting its essential role in mediating the observed synergy. In an orthotopic, immunocompetent mouse model of PDAC, MRTX1133 significantly reduced tumor growth and extended survival; however, despite its ability to suppress RB phosphorylation, Palbociclib failed to enhance these effects. Single-cell RNA sequencing suggested that Palbociclib treatment induces tumor vascularization, perhaps contributing to the lack of drug synergy observed in vivo. In summary, our findings demonstrate the therapeutic potential of enhancing cell cycle restriction point activation in KRAS inhibitor-based therapies, while emphasizing the importance of placing combination therapies into a suitable context.