For compounds directed against molecular targets expressed in tumor cells, the ex vivo 3D tumor clonogenic assay (TCA) is a rapid and reliable ex vivo assay with a high predictive value for in vivo tumor sensitivity. Single cell suspensions prepared from patient-derived tumor xenografts (PDX) growing subcutaneously in nude mice or from cultured human tumor cell lines are seeded in semisolid medium and tumor colony formation is monitored in the presence or absence of test compounds over a period of one to three weeks.

Based on experiments with up to 70 PDX, we have demonstrated that the TCA accurately replicates the in vivo sensitivity of PDX towards cMet inhibitors across all major tumor histologies. More specifically, all three NSCLC PDX that regressed in response to cMet inhibition in in vivo efficacy tests were sensitive to several cMet inhibitors in the ex vivo TCA. By contrast, data obtained with a 2D cell proliferation and survival assay did not correlate with the 3D and in vivo situations, suggesting that cMet function does not affect cell survival and proliferation on plastic but confers the capacity for anchorage-independent growth. The correlation of 3D but not 2D data with in vivo sensitivity was confirmed using anti-cMet siRNAs in selected PDX-derived non-small cell lung cancer cell lines. Preliminary immunohistochemical analysis revealed that PDX sensitive to cMet inhibitors expressed high cMet levels while not all PDX expressing high cMet levels were sensitive to cMet inhibitors.

In conclusion, for cMet inhibitors the TCA replicates in vivo sensitivities of PDX to a high degree. Due to its short duration the TCA is an excellent tool for the screening of large numbers of cMet inhibitors and PDX. As all of the PDX qualified for use in the TCA (>200) have been extensively molecularly characterised (gene expression, gene copy number variation and mutation analysis) this assay is also an excellent tool for generating high quality biomarker hypotheses during the preclinical profiling of molecules intended for oncology indications.

Citation Format: Sabine Gorynia, Jianing Guo, Andreas Ackermann, Armin Maier, Rebekka Krumbach, Gerhard Kelter, Vincent Vuaroqueaux, Thomas Metz, Thomas Metcalfe, Heiner H. Fiebig. Ex vivo 3D assay: rapid and reliable replication of the in vivo anti-tumor efficacy of c-Met inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3835. doi:10.1158/1538-7445.AM2013-3835