Academic Background and Problem

Pancreatic Ductal Adenocarcinoma (PDAC) is an aggressive cancer with an extremely low five-year survival rate, primarily due to late diagnosis and limited treatment options. Approximately 95% of PDAC patients harbor KRAS mutations, with the KRAS-G12D mutation being the most common. Although KRAS mutations have long been considered “undruggable,” recent breakthroughs in inhibitors targeting KRAS-G12C mutations (e.g., Adagrasib) have been achieved, and the KRAS-G12D inhibitor MRTX1133 is currently under clinical development. However, MRTX1133 still faces the challenge of drug resistance in treating PDAC. This study aims to elucidate the molecular mechanisms of resistance to the KRAS-G12D inhibitor MRTX1133 and propose potential solutions.

Source of the Study

This study was conducted by Changfeng Li, Yuanda Liu, Chang Liu, and others, affiliated with the Endoscopy Center of China-Japan Union Hospital of Jilin University, DAMP Laboratory of the Third Affiliated Hospital of Guangzhou Medical University, Department of Oncology of the Second Xiangya Hospital, Central South University, and the Department of Surgery at UT Southwestern Medical Center. The paper was published on January 29, 2025, in the journal Science Translational Medicine, titled “Age-dependent macropinocytosis drives resistance to KRAS-G12D–targeted therapy in advanced pancreatic cancer.”

Research Process and Results

Research Process

1. Correlation Between Drug Resistance and AGER Expression
   Researchers implanted human PDAC cell lines (PANC-1 and PANC 04.03) into immunodeficient mice (NSG). Once tumors reached 150-250 mm³, the mice were treated with MRTX1133 or a control drug for three weeks. The results showed that 53.3% of the PANC-1 group was sensitive to MRTX1133, while 46.7% exhibited resistance. Through mRNA expression analysis, researchers found that AGER (Advanced Glycosylation End Product-Specific Receptor) expression was significantly upregulated in resistant tumors. This result was validated in PANC-1, PANC 04.03, and KPC mouse models.

2. Mechanism of AGER in MRTX1133 Resistance
   To validate the role of AGER in resistance, researchers overexpressed AGER (AGERki) in PANC 04.03 cells, which showed resistance to MRTX1133 both in vitro and in vivo. Conversely, knocking out AGER using CRISPR-Cas9 technology significantly increased the sensitivity of PANC-1 cells to MRTX1133. Further experiments revealed that AGER interacts with Diaphanous-related Formin 1 (Diaph1), driving Rac1-dependent macropinocytosis, thereby promoting intracellular amino acid uptake and the synthesis of the antioxidant glutathione (GSH), leading to MRTX1133 resistance.

3. Relationship Between Macropinocytosis and GSH Synthesis
   Researchers found that MRTX1133-treated resistant tumors exhibited higher uptake of fluorescein-labeled dextran (FITC-dextran), indicating enhanced macropinocytosis. Inhibiting macropinocytosis (using EIPA) or blocking the AGER-Diaph1 interaction (using RAGE229) significantly enhanced the anticancer activity of MRTX1133. Additionally, the study showed that macropinocytosis facilitates GSH synthesis by uptaking serum albumin (BSA), and GSH production further inhibits apoptosis, thereby enhancing resistance.

4. Impact of High Glucose and High-Fat Diets on AGER Expression and MRTX1133 Efficacy
   In high-glucose and high-fat diet models, AGER expression was significantly upregulated, and the efficacy of MRTX1133 was diminished. In high-fat diet-induced diabetic mice, AGER knockout restored the efficacy of MRTX1133. This finding reveals that high-glucose and high-fat diets upregulate AGER expression, thereby affecting the efficacy of MRTX1133.

5. Combination Therapy Targeting AGER-Dependent Macropinocytosis
   Researchers found that the combination of MRTX1133 with RAGE229 or EIPA significantly enhanced anticancer effects and prolonged survival in PDAC patient-derived xenograft (PDX) and KPC mouse models. Furthermore, the combination therapy induced the release of High Mobility Group Box 1 (HMGB1), activating an anti-tumor immune response mediated by CD8+ T cells.

Main Results and Logical Relationships

• AGER Expression Correlates with Resistance: The study first confirmed the high expression of AGER in MRTX1133-resistant tumors through in vivo experiments and further validated the direct role of AGER in resistance using CRISPR-Cas9 and overexpression experiments.
  
• AGER-Diaph1 Complex Drives Macropinocytosis: AGER interacts with Diaph1 to activate Rac1-dependent macropinocytosis, promoting amino acid uptake and GSH synthesis, thereby inhibiting apoptosis.
  
• Link Between Macropinocytosis and GSH Synthesis: Inhibiting macropinocytosis or GSH synthesis significantly enhanced the efficacy of MRTX1133, indicating that macropinocytosis is a key mechanism of resistance.
  
• High-Glucose and High-Fat Diets Enhance AGER-Dependent Resistance: Through high-glucose and high-fat diet experiments, researchers revealed that environmental factors (e.g., obesity and diabetes) exacerbate MRTX1133 resistance by upregulating AGER expression.
  
• Potential of Combination Therapy: The combination of MRTX1133 with RAGE229 or EIPA not only enhanced anticancer effects but also activated anti-tumor immune responses by inducing HMGB1 release.

Conclusion and Significance

This study reveals AGER-dependent macropinocytosis as a novel mechanism of resistance to the KRAS-G12D inhibitor MRTX1133. By targeting the AGER-Diaph1 complex or inhibiting macropinocytosis, researchers provide new therapeutic strategies for overcoming PDAC resistance. Additionally, the study reveals the mechanism by which high-glucose and high-fat diets affect MRTX1133 efficacy by upregulating AGER expression, offering important insights for the treatment of patients with metabolic disorders. This study not only holds significant scientific value but also provides new perspectives for the clinical treatment of PDAC.

Research Highlights

1. Discovery of a Novel Resistance Mechanism: The first to identify AGER-dependent macropinocytosis as a key mechanism of resistance to the KRAS-G12D inhibitor MRTX1133.
   
2. Potential of Targeted Therapy: Inhibiting the AGER-Diaph1 complex or macropinocytosis significantly enhances the efficacy of MRTX1133, providing a new target for PDAC treatment.
   
3. Impact of Environmental Factors: Reveals the mechanism by which high-glucose and high-fat diets affect MRTX1133 efficacy by upregulating AGER expression, offering important implications for the treatment of patients with metabolic disorders.
   
4. Activation of Immune Responses: Combination therapy induces HMGB1 release, activating anti-tumor immune responses mediated by CD8+ T cells, providing new insights for PDAC immunotherapy.

Other Valuable Information

This study also found that AGER-dependent macropinocytosis is not limited to KRAS-G12D inhibitors but may also play a role in KRAS-G12C inhibitors and other targeted therapies. Additionally, the high-throughput screening and gene-editing techniques used in the study provide important methodological support for future cancer research.