Nab-Paclitaxel + Gemcitabine + Cisplatin Combination Treatment Modulates Pancreatic Tumor Stroma
Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer which is the third leading cause of cancer related deaths in the United States. It has a dismal five-year survival rate of <9%. PDAC is characterized by its dense desmoplastic stroma, supportive tumor microenvironment, and deficiency in DNA repair mechanisms. Current treatments for advanced PDAC have a relatively low response rate (31.6% for FOLFIRINOX; 23% for nab-paclitaxel + gemcitabine). Recently, a phase Ib/II study demonstrated that the nab-paclitaxel + gemcitabine + cisplatin (triple combination) had a significantly higher response rate of 70.8% in patients with advanced PDAC.
To understand the biological effects of the triple combination, we used single cell RNA sequencing (scRNA-seq) to investigate the gene expression and cell population changes upon drug treatment in the LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) transgenic mouse model for PDAC. Mice were treated with saline or the triple combination (3 mice each) and tumors were harvested and sequenced using the 10X genomics scRNA-Seq platform. Analyses of the scRNA-Seq data revealed that, compared to saline controls, triple combination treated tumors showed a decrease in the numbers of multiple cell types within the tumor including cancer-associated fibroblasts which were reduced by 9.8%, tumors undergone epithelial mesenchymal transition by 17%, and epithelial tumor cells ETCs by 25.8%. On the other hand, immune cells were increased in the triple combination treated tumors including tumor associated macrophages by 18.2% and tumor infiltrating lymphocytes (TILs) by 34.4%. To verify the findings from the scRNA-Seq study, we performed immunohistochemistry (IHC) on the formalin-fixed paraffin-embedded samples from the same saline or drug treated tumor tissues to evaluate the changes in individual cell types. Quantification of IHC signals suggested a decrease in desmoplasia and an increase in cell death/apoptosis of cancer cells after triple treatment, which is consistent with the scRNA-Seq data. CD31, a marker for endothelial cells (blood vessels), showed significantly increased staining in triple treated tumors. Staining with CD3 and CD8, which are markers for subsets of TILs, did not generate conclusive results. We are currently performing staining with additional immune cell markers such as CD68 (macrophages) and CD45 (TILs) to further verify the findings.
Overall, our data suggests that the triple combination treatment significantly reduces tumor burden and modulates the tumor stroma including reduced desmoplasia, increased cell death/apoptosis and microvasculature, and potentially increased immune cell infiltration in the KPC mouse PDAC tumors.