Evaluation of prediction of in vivo activity from in vitro combinations: Examples using a MEK1/2 inhibitor combined with docetaxel in NSCLC models.

In an attempt to combat the resistance of tumors to chemotherapy, we have already described at this year9s AACR, the systematic evaluation of over 11,000 different compound combinations using the human cancer cell line encyclopedia. Correlations of synergy with genetic features were identified and some novel synergies discovered. Here, we describe the efficacy, tolerability and PK-PD of 23 different in vivo combinations selected from the screens to determine the predictability of in vitro screening, including two examples from the combination of a MEK1/2-inhibitor (MEK162) with the taxane, docetaxel. In vitro screens were conducted as previously described using 3-day viability assays, and inhibition of proliferation determined relative to untreated samples, and the degree of synergy scored using different types of analyses: Gaddum, Bliss, Loewe. Only those combinations showing synergy over a wide range of concentrations were chosen for in vivo study. For in vivo studies, cells were injected s.c. in the flank of athymic nude mice, and once tumors reached a mean size of at least 100 mm 3 were treated for 2-4 weeks with the appropriate dose and schedule of the compounds either as monotherapy, or in combination. Efficacy and tolerability were determined at the endpoint using the T/C TVol and T/C BW respectively to derive a combination-index as previously described by Clarke (1997), where a negative-value (-CCI) indicated synergy. In most cases, PK-PD was also measured in plasma and tumour either at steady-state and/or the endpoint to study the mechanism of the interaction and to check for drug-drug interactions and their eventual impact on PD and efficacy. Thus far, we have studied in vivo 13 different molecular targets across 6 different histotypes to give 23 different combinations. No antagonism was seen in vivo (+CCI), and 19/23 were deemed synergistic (CCI ≤-0.1), of which 8 showed regression which was not seen with the individual monotherapies. Of the 4 combinations showing no interaction, 2 were predicted by the in vitro score and the other 2 showed negative drug-drug interactions. There were no significant correlations between the CCI and the different types of in vitro score (p>0.35), but perhaps more importantly, cut-offs could be identified suggesting synergy could be predicted (p≤0.02) although not the extent of the interaction. Several novel combinations were identified for clinical investigation, including MEK162 combined with docetaxel in KRAS-mutant NSCLC, which in two different models in vivo had a CCI≤ -0.1, with PD-analyses showing that cytotoxic doses of the taxane activated the MAPK-pathway which was blocked by the combination. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A140. Citation Format: Paul Martin J. Mcsheehy, Alex Cao, Giordi Caponigro, David Duhl, Brant Firestone, Tom Gesner, Daniel Guthy, Jocelyn Holash, Fred King, Joseph Lehar, Christopher Leroy, Manway Liu, Lilli Petruzzelli, Dale Porter, Daniel Menezes, Anupama Reddy, Johannes Roesel, Christian Schnell, Timothy Smith, Mark Stump, Markus Wartmann, Marion Wiesmann. Evaluation of prediction of in vivo activity from in vitro combinations: Examples using a MEK1/2 inhibitor combined with docetaxel in NSCLC models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A140.