Despite initial benefit from tyrosine kinase inhibitors (TKIs), patients with advanced non-small cell lung cancer (NSCLC) harboring (ALK) and (ROS1) gene fusions ultimately progress. Here, we report on the potential resistance mechanisms in a series of patients with ALK and ROS1 NSCLC progressing on different types and/or lines of -targeted therapy. We used a combination of next-generation sequencing (NGS), multiplex mutation assay, direct DNA sequencing, RT-PCR, and FISH to identify fusion variants/partners and copy-number gain (CNG), kinase domain mutations (KDM), and copy-number variations (CNVs) in other cancer-related genes. We performed testing on 12 and 43 patients. One of 12 ROS1 (8%) and 15 of 43 (35%) ALK patients harbored KDM. In the ROS1 cohort, we identified and β-catenin mutations and HER2-mediated bypass signaling as non-ROS1-dominant resistance mechanisms. In the ALK cohort, we identified a novel gene fusion, a fusion, 2 , and 3 mutations, as well as mutations in , and In addition, we identified CNV in multiple proto-oncogenes genes including and others. We identified a putative TKI resistance mechanism in six of 12 (50%) ROS1 patients and 37 of 43 (86%) ALK patients. Our data suggest that a focus on KDMs will miss most resistance mechanisms; broader gene testing strategies and functional validation is warranted to devise new therapeutic strategies for drug resistance. .

Oncogenic rearrangements in RET are present in 1-2% of lung adenocarcinoma (LAD) patients. Ponatinib is a multi-kinase inhibitor with low-nanomolar potency against the RET kinase domain. Here, we demonstrate that ponatinib exhibits potent anti-proliferative activity in RET fusion positive LC-2/ad LAD cells and inhibits phosphorylation of the RET fusion protein and signaling through ERK1/2 and AKT. Using distinct dose-escalation strategies, two ponatinib-resistant LC-2/ad cell lines, PR1 and PR2, were derived. PR1 and PR2 cell lines retained expression, but not phosphorylation of the RET fusion and lacked evidence of a resistance mutation in the RET kinase domain. Both resistant lines retained activation of the MAPK pathway. Next-generation RNA sequencing revealed an oncogenic NRAS p.Q61K mutation in the PR1 cell. PR1 cell proliferation was preferentially sensitive to siRNA knockdown of NRAS compared to knockdown of RET, more sensitive to MEK inhibition than the parental line, and NRAS-dependence was maintained in the absence of chronic RET inhibition. Expression of NRAS p.Q61K in RET fusion expressing TPC1 cells conferred resistance to ponatinib. PR2 cells exhibited increased expression of EGFR and AXL. EGFR inhibition decreased cell proliferation and phosphorylation of ERK1/2 and AKT in PR2 cells but not LC-2/ad cells. Although AXL inhibition enhanced PR2 sensitivity to afatinib, it was unable to decrease cell proliferation by itself. Thus, EGFR and AXL cooperatively rescued signaling from RET inhibition in the PR2 cells. Collectively, these findings demonstrate that resistance to ponatinib in RET-rearranged LAD is mediated by bypass signaling mechanisms that result in restored RAS/MAPK activation.

Purpose: Approved therapies for EGFR exon 20, ERBB2 mutations, and NRG1 fusions are currently lacking for non–small cell lung cancer and other cancers. Tarloxotinib is a prodrug that harnesses tumor hypoxia to generate high levels of a potent, covalent pan-HER tyrosine kinase inhibitor, tarloxotinib-effector (tarloxotinib-E), within the tumor microenvironment. This tumor-selective delivery mechanism was designed to minimize the dose-limiting toxicities that are characteristic of systemic inhibition of wild-type EGFR. Experimental Design: Novel and existing patient-derived cell lines and xenografts harboring EGFR exon 20 insertion mutations, ERBB2 mutations and amplification, and NRG1 fusions were tested in vitro and in vivo with tarloxotinib to determine its impact on cancer cell proliferation, apoptosis, and cell signaling. Results: Tarloxotinib-E inhibited cell signaling and proliferation in patient-derived cancer models in vitro by directly inhibiting phosphorylation and activation of EGFR, HER2, and HER2/HER3 heterodimers. In vivo, tarloxotinib induced tumor regression or growth inhibition in multiple murine xenograft models. Pharmacokinetic analysis confirmed markedly higher levels of tarloxotinib-E in tumor tissue than plasma or skin. Finally, a patient with lung adenocarcinoma harboring an ERBB2 exon 20 p.A775_G776insYVMA mutation demonstrated a dramatic clinical response to tarloxotinib. Conclusions: Experimental data with tarloxotinib validate the novel mechanism of action of a hypoxia-activated prodrug in cancer models by concentrating active drug in the tumor versus normal tissue, and this activity can translate into clinical activity in patients.

The tumor suppressor protein p53 is central to the cellular stress response and may be a predictive biomarker for cancer treatments. Upon stress, wildtype p53 accumulates in the nucleus where it enforces cellular responses, including cell cycle arrest and cell death. p53 is so dominant in its effects, that p53 enforcement - or - restoration therapy is being studied for anti-cancer therapy. Two mechanistically distinct small molecules that act via p53 are the selective inhibitor of nuclear export, selinexor, and MDM2 inhibitor, nutlin-3a. Here, individual cells are studied to define cell cycle response signatures, which captures the variability of responses and includes the impact of loss of p53 expression on cell fates. The individual responses are then used to build the population level response. Matched cell lines with and without p53 expression indicate that while loss-of-function results in altered cell cycle signatures to selinexor treatment, it does not diminish overall cell loss. On the contrary, response to single-agent nutlin-3a shows a strong p53-dependence. Upon treatment with both selinexor and nutlin-3a there are combination effects in at least some cell lines - even when p53 is absent. Collectively, the findings indicate that p53 does act downstream of selinexor and nutlin-3a, and that p53 expression is dispensable for selinexor to cause cell death, but nutlin-3a response is more p53-dependent. Thus, TP53 disruption and lack of expression may not predict poor cell response to selinexor, and selinexor's mechanism of action potentially provides for strong efficacy regardless of p53 function.