Recently, there has been increased recognition of histologic subtype as a potential predictor of efficacy with first-line treatment of advanced NSCLC[
12,
13]. A retrospective analysis of the pivotal E4599 trial of first-line bevacizumab combined with carboplatin/paclitaxel in nonsquamous NSCLC showed that patients with adenocarcinoma (the most frequent histologic subtype) who received bevacizumab combined with carboplatin/paclitaxel had favorable overall survival compared with patients who received carboplatin/paclitaxel alone[
15]. Although the number of enrolled patients with other histologic subtypes was small, clinical benefits among these patients appeared more limited than among those with adenocarcinoma. Current multidisciplinary recommendations for changes in NSCLC classification[
33] support the potential value of histologic subtype in influencing treatment decisions in NSCLC. In addition to histology, research has revealed the importance of driver mutations in NSCLC, which are particularly prevalent among adenocarcinomas, presenting at different incidence rates in specific patient groups. Preclinical and clinical evidence has shown that these mutations may affect response to targeted therapy[
16,
22], suggesting that a further division of NSCLC into clinically relevant mutational subgroups may allow for a more tailored treatment approach. Targeted treatments that may be effective regardless of mutational status may be even more desirable.
Hence, it appears critical that preclinical studies assessing investigational agents should be designed to test activity in models that represent more than one NSCLC subtype. The antitumor activity of a number of VEGFR inhibitors either as single agents or combined with chemotherapy has been demonstrated in a variety of NSCLC xenograft models[
34‐
38]. However, few of these studies have assessed activity in more than one or two different models. The present study aimed to assess the antitumor activity of motesanib as a single agent or combined with chemotherapy in human NSCLC xenograft models with varying genetic backgrounds and histology[
36,
39‐
41]. When administered alone, motesanib inhibited the growth of all five NSCLC xenografts, A549, Calu-6, NCI-H358, NCI-H1299, and NCI-H1650, in a dose-dependent manner. Calu-6 tumors were relatively resistant to treatment compared with the other cell lines: only the highest motesanib dose administered (75 mg/kg BID) resulted in xenograft growth inhibition (66%). Decreased responsiveness to single-agent VEGFR inhibitors, including motesanib, and epidermal growth factor receptor (EGFR) inhibitors in the Calu-6 model (compared with other tumor xenograft models) have been described previously[
34,
35,
42]. The reasons for this differential responsiveness are not immediately evident, but based on the above studies, it is likely rooted in causes other than variations in experimental design, because it has been seen across independent studies and with various therapies focusing on different molecular targets. In all models, tumor xenograft growth inhibition increased when motesanib was combined with QW cisplatin or docetaxel, agents that are components of standard two-drug chemotherapies for NSCLC treatment[
4], compared with either single-agent treatment. The results from the experiment with the Calu-6 model are particularly noteworthy because of its relative resistance to treatment with angiogenesis inhibitors and EGFR-targeted agents alone. One possible explanation for the improved antitumor activity of the combination treatments is that angiogenesis inhibitors may modulate the tumor vasculature, resulting in enhanced delivery of chemotherapy to target cells[
43,
44], but we have not directly addressed this issue in the current study. Mutational status of the cells appeared to have had no influence on the antitumor activity of motesanib treatment. Regardless of whether cell lines had common driver mutations (ie,
KRAS) or less frequently occurring mutations (ie,
BRAF,
NRAS) or a combination of mutated genes, treatment with motesanib as monotherapy or in combination with chemotherapy resulted in tumor growth inhibition, albeit at different doses depending on the model. Targeted treatments that may be effective regardless of mutational status of the patient may be particularly desirable, particularly for agents targeting the stroma, where the mutational spectrum is not expected to be equivalent.
The antitumor activity that motesanib exhibited against the NSCLC xenograft models chosen for this study was mediated, at least in part, by an antiangiogenic mechanism rather than a direct effect on the tumor cells themselves. Unlike human medullary cancer cells that express VEGFR2[
26], VEGFR2 could not be detected in any of the cell lines and phosphorylated VEGFR2 could not be detected following exogenous administration of VEGF. Motesanib did not inhibit the proliferation of cells from any of the cell lines in vitro. The lack of inhibition of proliferation also suggests that other motesanib targets (eg, PDGFR and Kit) are not important in this context. It should be noted that some studies have reported that sorafenib and vandetanib (both of which inhibit VEGFR signalling) can attenuate the proliferation of lung cancer cells in vitro[
45‐
47]. However, both of these agents also inhibit EGFR signalling and, consequently, it is not possible to ascertain whether the observed effects were due to inhibition of VEGFR signalling, EGFR signalling, or both. Treatment with single-agent motesanib or motesanib plus cisplatin showed significant reductions in tumor blood vessel area compared with vehicle in NCI-H358 and NCI-H1650 xenografts. These results are consistent with those from previous studies reporting that motesanib alone or combined with chemotherapy had antitumor activity in xenograft models of breast, thyroid, and colorectal cancer, which was also associated with a significant decrease in tumor blood vessel area[
23‐
26]. Overall, our data support a predominant role for antiangiogenesis in inhibition of tumor growth by motesanib.