Lung cancer is the leading cause of cancer-related death worldwide, mainly due to its highly metastatic properties. Previously, we reported an inverse correlation between RhoB expression and the progression of the lung cancer, occurring between preinvasive and invasive tumors. Herein, we mimicked the loss of RhoB observed throughout lung oncogenesis with RNA interference in nontumoral bronchial cell lines and analyzed the consequences on both cell transformation and invasion. Down-regulation of RhoB did not modify the cell growth properties but did promote migration and invasiveness. Furthermore, RhoB depletion was accompanied by modifications of actin and cell adhesion. The specific activation of the Akt1 isoform and Rac1 was found to be critical for this RhoB-mediated regulation of migration. Lastly, we showed that RhoB down-regulation consecutive to KRasV12 cell transformation is critical for cell motility but not for cell proliferation. We propose that RhoB loss during lung cancer progression relates to the acquisition of invasiveness mediated by the phosphatidylinositol 3-kinase (PI3K)/AKT and Rac1 pathways rather than to tumor initiation. [Cancer Res 2009;69(15):6092-9]

Epidermal growth factor receptor (EGFR) mutations identify patients with lung cancer who derive benefit from kinase inhibitors. However, most patients eventually develop resistance, primarily due to the T790M second‐site mutation. Irreversible inhibitors (e.g., osimertinib/AZD9291) inhibit T790M‐EGFR, but several mechanisms, including a third‐site mutation, C797S, confer renewed resistance. We previously reported that a triple mixture of monoclonal antibodies, 3×mAbs, simultaneously targeting EGFR, HER2, and HER3, inhibits T790M‐expressing tumors. We now report that 3×mAbs, including a triplet containing cetuximab and trastuzumab, inhibits C797S‐expressing tumors. Unlike osimertinib, which induces apoptosis, 3×mAbs promotes degradation of the three receptors and induces cellular senescence. Consistent with distinct mechanisms, treatments combining 3×mAbs plus sub‐inhibitory doses of osimertinib synergistically and persistently eliminated tumors. Thus, oligoclonal antibodies, either alone or in combination with kinase inhibitors, might preempt repeated cycles of treatment and rapid emergence of resistance.

Non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide, which is mainly due to its high risk of metastatic dissemination. One critical point of this process is the ability of cancer cells to detach from the primary tumor and migrate through the extracellular matrix; however, the underlying molecular mechanisms are not yet fully understood. In the present study, we identified the small GTPase RhoB as a key regulator of bronchial cell morphology in a three-dimensional (3D) matrix. RhoB loss, which is frequently observed during lung cancer progression, induced an epithelial-mesenchymal transition (EMT) characterized by an increased proportion of invasive elongated cells in 3D. The process was mediated by Slug induction and E-cadherin repression. In addition, downregulation of RhoB induced Akt1 activation, which in turn activated Rac1 through the guanine-exchange factor Trio to control cell shape rearrangement. Further, we provide evidence that RhoB interacted with and positively regulates phosphatase PP2A through the recruitment of its regulatory subunit B55, which was found to be crucial for Akt dephosphorylation. B55 inhibition completely suppressed RhoB-mediated PP2A regulation. Finally, we show that PP2A inactivation, by targeting either its catalytic or its regulatory B55 subunit, completely reversed RhoB-dependent morphological changes and also fully prevented the ability of RhoB to decrease the invasiveness of bronchial cells. Altogether, these results highlight a novel signaling axis and describe new molecular mechanisms that could explain the tumor suppressor role of RhoB in lung cancer. Therefore, we propose that RhoB could be responsible for early metastatic prevention by inhibiting the EMT-derived invasiveness of lung cells through the control of PP2A activity.

Purpose: A crucial event in lung adenocarcinoma progression is the switch from an aerogenous spread toward an infiltrating tumor. Loss of RhoB expression has been suggested to be critical for lung cancer invasion. Here, we tested RhoB expression as a prognostic biomarker in non-small cell lung cancer (NSCLC) with a special focus on lepidic pattern.Experimental Design: We analyzed RhoB expression using both IHC and RT-qPCR in two series of operated patients (n ¼ 100 and 48, respectively) and in a series of advanced lepidic adenocarcinoma (n ¼ 31) from different hospitals. Next, we examined the role of RhoB in lung cancer progression in transgenic mice that express inducible EGFR L858R crossed with Rhob null mice.Results: We identified that loss of RhoB expression was strongly associated with worse survival (P ¼ 0.0001) and progression-free survival (P < 0.001) in the first series. We then confirmed these results after multivariate analyses of the second series. In the series of adenocarcinoma with lepidic features issued from a clinical trial (IFCT-0401), we showed that loss of RhoB expression was associated with higher aggressiveness of stage IV. Finally, we showed that EGFR L858R /Rhob þ/þ mice developed mainly diffuse lung tumors with a lepidic pattern, whereas EGFR L858R /Rhob þ/À and EGFR L858R /Rhob À/À developed a greater number of tumors, and aggressive adenocarcinomas with invasive properties. Conclusions:We showed that RhoB is not only a strong prognostic factor in NSCLC but it is also critical for the acquisition of an aggressive phenotype of adenocarcinoma.

Overexpression and activation of TPM3-ALK tyrosine kinase fusion protein is a causal oncogenic event in the development of Anaplastic Large Cell Lymphoma and Inflammatory Myofibroblastic ALK-positive tumors. Thus, the development of ALK specific tyrosine kinase inhibitors is a current therapeutic challenge. Animal models are essential to assess, in vivo, the efficiency of ALK-oncogene inhibitors and to identify new and/or additional therapeutic targets in the ALK tumorigenesis pathway. Using the tetracycline system to allow conditional and concomitant TPM3-ALK and luciferase expression, we have developed a unique transplant model for bioluminescent TPM3-ALK-induced fibroblastic tumors in athymic nude mice. The reversible TPM3-ALK expression allowed us to demonstrate that this oncogene is essential for the tumor growth and its maintenance. In addition, we showed that this model could be used to precisely assess tumor growth inhibition upon ALK chemical inactivation. As proof of principle, we used the general tyrosine kinase inhibitor herbimycin A to inhibit ALK oncoprotein activity. As expected, herbimycin A treatment reduced tumor growth as assessed both by tumor volume measurement and bioluminescent imaging. We conclude that this transplant model for TPM3-ALK-induced tumors represents a valuable tool not only to accurately and rapidly evaluate in vivo ALK-targeted therapies but also to gain insight into the mechanism of ALK-positive tumor development.

Although lung cancer patients harboring EGFR mutations benefit from treatment with EGFR‐tyrosine kinase inhibitors (EGFR‐TKI), most of them rapidly relapse. RHOB GTPase is a critical player in both lung carcinogenesis and the EGFR signaling pathway; therefore, we hypothesized that it could play a role in the response to EGFR‐TKI. In a series of samples from EGFR‐mutated patients, we found that low RHOB expression correlated with a good response to EGFR‐TKI treatment while a poor response correlated with high RHOB expression (15.3 versus 5.6 months of progression‐free survival). Moreover, a better response to EGFR‐TKI was associated with low RHOB levels in a panel of lung tumor cell lines and in a lung‐specific tetracycline‐inducible EGFRL 858R transgenic mouse model. High RHOB expression was also found to prevent erlotinib‐induced AKT inhibition in vitro and in vivo. Furthermore, a combination of the new‐generation AKT inhibitor G594 with erlotinib induced tumor cell death in vitro and tumor regression in vivo in RHOB‐positive cells. Our results support a role for RHOB/AKT signaling in the resistance to EGFR‐TKI and propose RHOB as a potential predictor of patient response to EGFR‐TKI treatment.

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