Evolution of HER2-positive mammary carcinoma: HER2 loss reveals claudin-low traits in cancer progression

HER2-positive breast cancers may lose HER2 expression in recurrences and metastases. In this work, we studied cell lines derived from two transgenic mammary tumors driven by human HER2 that showed different dynamics of HER2 status. MamBo89HER2stable cell line displayed high and stable HER2 expression, which was maintained upon in vivo passages, whereas MamBo43HER2labile cell line gave rise to HER2-negative tumors from which MamBo38HER2loss cell line was derived. Both low-density seeding and in vitro trastuzumab treatment of MamBo43HER2labile cells induced the loss of HER2 expression. MamBo38HER2loss cells showed a spindle-like morphology, high stemness and acquired in vivo malignancy. A comprehensive molecular profile confirmed the loss of addiction to HER2 signaling and acquisition of an EMT signature, together with increased angiogenesis and migration ability. We identified PDGFR-B among the newly expressed determinants of MamBo38HER2loss cell tumorigenic ability. Sunitinib inhibited MamBo38HER2loss tumor growth in vivo and reduced stemness and IL6 production in vitro. In conclusion, HER2-positive mammary tumors can evolve into tumors that display distinctive traits of claudin-low tumors. Our dynamic model of HER2 status can lead to the identification of new druggable targets, such as PDGFR-B, in order to counteract the resistance to HER2-targeted therapy that is caused by HER2 loss

ADK-VR2, a cell line derived from a treatment-naïve patient with SDC4-ROS1 fusion-positive primarily crizotinib-resistant NSCLC: a novel preclinical model for new drug development of ROS1- rearranged NSCLC

(NSCLCs). Several tyrosine kinase inhibitors (TKIs) have shown high efficacy in patients whose tumors harbour a ROS1 fusion. However, the limited availability of preclinical models of ROS1-positive NSCLC hinders the discovery of new drugs and the understanding of the mechanisms underlying drug resistance and strategies to overcome it. Methods: The ADK-VR2 cell line was derived from the pleural effusion of a treatment-naïve NSCLC patient bearing SDC4-ROS1 gene fusion. The sensitivity of ADK-VR2 and its crizotinib-resistant clone ADK-VR2 AG143 (selected in 3D culture in the presence of crizotinib) to different TKIs was tested in vitro, in both 2D and 3D conditions. Tumorigenic and metastatic ability was assessed in highly immunodeficient mice. In addition, crizotinib efficacy on ADK-VR2 was evaluated in vivo. Results: 2D-growth of ADK-VR2 cells was partially inhibited by crizotinib. On the contrary, the treatment with other TKIs, such as lorlatinib, entrectinib and DS-6051b, did not result in cell growth inhibition. TKIs showed dramatically different efficacy on ADK-VR2 cells, depending on the cell culture conditions. In 3D culture, ADK-VR2 growth was indeed almost totally inhibited by lorlatinib and DS-6051b. The clone ADK VR2 AG143 showed higher resistance to crizotinib treatment in vitro, compared to its parental cell line, in both 2D and 3D cultures. Similarly to ADK-VR2, ADK-VR2 AG143 growth was strongly inhibited by lorlatinib in 3D conditions. Nevertheless, ADK-VR2 AG143 sphere formation was less affected by TKIs treatment, compared to the parental cell line. In vivo experiments highlighted the high tumorigenic and metastatic ability of ADK-VR2 cell line, which, once injected in immunodeficient mice, gave rise to both spontaneous and experimental lung metastases while the crizotinib-resistant clone ADK-VR2 AG143 showed a slower growth in vivo. In addition, ADK-VR2 tumor growth was significantly reduced but not eradicated by crizotinib treatment. Conclusions: The ADK-VR2 cell line is a promising NSCLC preclinical model for the stud