Utilization of Quantitative In Vivo Pharmacology Approaches to Assess Combination Effects of Everolimus and Irinotecan in Mouse Xenograft Models of Colorectal Cancer

<div><p>Purpose</p><p>The PI3K/AKT/mTOR pathway is frequently dysregulated in cancers and inhibition of mTOR has demonstrated the ability to modulate pro-survival pathways. As such, we sought to determine the ability of the mTOR inhibitor everolimus to potentiate the antitumor effects of irinotecan in colorectal cancer (CRC).</p> <p>Experimental Design</p><p>The combinatorial effects of everolimus and irinotecan were evaluated <i>in vitro</i> and <i>in vivo</i> in CRC cell lines harboring commonly found mutations in <i>PIK3CA</i>, <i>KRAS</i> and/or <i>BRAF</i>. Pharmacokinetically-directed dosing protocols of everolimus and irinotecan were established and used to assess the in vivo antitumor effects of the agents. At the end of treatment, 3–6 tumors per treatment arm were harvested for biomarker analysis by NMR metabolomics.</p> <p>Results</p><p>Everolimus and irinotecan/SN38 demonstrated synergistic anti-proliferative effects in multiple CRC cell lines <i>in vitro</i>. Combination effects of everolimus and irinotecan were determined in CRC xenograft models using clinically-relevant dosing protocols. Everolimus demonstrated significant tumor growth inhibition alone and when combined with irinotecan in HT29 and HCT116 tumor xenografts. Metabolomic analysis showed that HT29 tumors were more metabolically responsive than HCT116 tumors. Everolimus caused a decrease in glycolysis in both tumor types whilst irinotecan treatment resulted in a profound accumulation of lipids in HT29 tumors indicating a cytotoxic effect.</p> <p>Conclusions</p><p>Quantitative analysis of tumor growth and metabolomic data showed that the combination of everolimus and irinotecan was more beneficial in the <i>BRAF/PIK3CA</i> mutant HT29 tumor xenografts, which had an additive effect, than the <i>KRAS/PIK3CA</i> mutant HCT116 tumor xenografts, which had a less than additive effect.</p>