MUC1-C: The Occam Razor of Osimertinib Resistance?

The use of tyrosine kinase inhibitors (TKIs) in NSCLC with activating EGFR mutations has transformed the treatment of lung cancer and significantly improved survival in both the metastatic1Ramalingam S.S. Vansteenkiste J. Planchard D. et al.Overall survival with osimertinib in untreated, EGFR-mutated advanced NSCLC.N Engl J Med. 2020; 382: 41-50Crossref PubMed Scopus (1496) Google Scholar and adjuvant2Tsuboi M. Herbst R.S. John T. et al.Overall survival with osimertinib in resected EGFR-mutated NSCLC.N Engl J Med. 2023; 389: 137-147Crossref PubMed Scopus (76) Google Scholar settings. It was also the herald of using molecular targets in the approach to treating lung cancer. Tumors treated with first-generation TKIs, such as gefitinib and erlotinib, generally developed resistance through EGFR-dependent mechanisms, mainly a secondary EGFR T790M mutation.3Sequist L.V. Waltman B.A. Dias-Santagata D. et al.Genotypic and histological evolution of lung cancers acquiring resistance to EGFR inhibitors.Sci Transl Med. 2011; 3: 75ra26Crossref PubMed Scopus (0) Google Scholar Originally, it was thought that T790M is an expansion of a preexisting clone; however, more evidence supports an acquired event.4Hata A.N. Niederst M.J. Archibald H.L. et al.Tumor cells can follow distinct evolutionary paths to become resistant to epidermal growth factor receptor inhibition.Nat Med. 2016; 22: 262-269Crossref PubMed Google Scholar Efforts to overcome the T790M "gatekeeper" mutation culminated in the development of osimertinib, which has both a higher affinity for and faster reaction kinetics with L858R-mutant or L858R/T790M-mutant EGFR over wild-type EGFR.5Zhai X. Ward R.A. Doig P. Argyrou A. Insight into the therapeutic selectivity of the irreversible EGFR tyrosine kinase inhibitor osimertinib through enzyme kinetic studies.Biochemistry. 2020; 59: 1428-1441Crossref PubMed Scopus (29) Google Scholar Nevertheless, acquired osimertinib resistance inevitably occurs, often requiring changing treatment to traditional cytotoxic chemotherapy. EGFR-dependent resistance mechanisms only account for up to 20% of osimertinib resistance. Approximately 40% of osimertinib resistance occurs by means of EGFR-independent mechanisms, and approximately 40% occurs by means of unknown mechanisms. EGFR-independent mechanisms are diverse and include amplifications of MET, HER2, AXL, or PI3K, fusions in ALK, RET, or BRAF, mutations along the MAPK-PI3K pathway, cell cycle gene alterations, histologic transformations, or epithelial-to-mesenchymal transitions (EMTs).6Leonetti A. Sharma S. Minari R. Perego P. Giovannetti E. Tiseo M. Resistance mechanisms to osimertinib in EGFR-mutated non-small cell lung cancer.Br J Cancer. 2019; 121: 725-737Crossref PubMed Scopus (638) Google Scholar,7Ríos-Hoyo A. Moliner L. Arriola E. Acquired mechanisms of resistance to osimertinib—the next challenge.Cancers. 2022; 14: 1931Crossref PubMed Scopus (0) Google Scholar Mucin1 (MUC1) is a transmembrane glycoprotein normally found on the apical surface of luminal epithelial cells, which along with other members of the mucin family protect the underlying epithelia. Nevertheless, during times of stress, it separates into the MUC1-N and MUC1-C moieties, which both play separate roles in the transduction of survival signals by means of activation of tyrosine kinases such as EGFR and regulation of Wnt, p53, and NF-kB pathways by means of nuclear translocation.8Jin W. Zhang M. Dong C. Huang L. Luo Q. The multifaceted role of MUC1 in tumor therapy resistance.Clin Exp Med. 2022; 23: 1441-1474Crossref Scopus (4) Google Scholar MUC1 has been implicated in resistance to paclitaxel in mouse models by means of up-regulation of adenosine triphosphate-binding cassette transporter B19Jin W. Liao X. Lv Y. et al.MUC1 induces acquired chemoresistance by upregulating ABCB1 in EGFR-dependent manner.Cell Death Dis. 2017; 8e2980–e2980Crossref Scopus (58) Google Scholar and also been found to aid in the development of resistance to trastuzumab10Hosseinzadeh A. Merikhian P. Naseri N. Eisavand M.R. Farahmand L. MUC1 is a potential target to overcome trastuzumab resistance in breast cancer therapy.Cancer Cell Int. 2022; 22: 110Crossref PubMed Scopus (0) Google Scholar and tamoxifen11Merikhian P. Ghadirian R. Farahmand L. Mansouri S. Majidzadeh A.K. MUC1 induces tamoxifen resistance in estrogen receptor-positive breast cancer.Expert Rev Anticancer Ther. 2017; 17: 607-613Crossref Scopus (32) Google Scholar in HER2+ and ER+ breast cancer cells, respectively. Given its involvement in modulation of multiple signaling pathways, both at the transcriptional and translational levels, Haratake et al.12Haratake N. Ozawa H. Morimoto Y. et al.MUC1-C is a common driver of acquired osimertinib resistance in non-small cell lung cancer.J Thorac Oncol. 2024; 19: 434-450Google Scholar sought to evaluate its role in the diverse mechanisms of osimertinib resistance. In this study, the authors exposed a NSCLC cell line harboring both the L858R and T790M EGFR mutations to high-dose osimertinib either instantly or gradually, to generate populations of drug-tolerant persister cells and osimertinib-resistant cells, respectively. In both cases, the cells had increased MUC1-C expression and its inhibition with either a MUC1-C short hairpin RNA or small molecule inhibitor led to suppression of phospho(p-)EGFR, p-ERK, p-AKT, and p-MET expression and decreased colony-forming capacity. The osimertinib-resistant cells were found to have mesenchymal characteristics with up-regulation of ZEB1, TWIST1, and N-cadherin. Suppression of MUC1-C down-regulated mediators of both proliferation p-EGFR, p-ERK, and p-AKT and mediators of EMT, ZEB1, TWIST1, and AXL. This caused an increase in sensitivity to osimertinib. In contrast, co-treatment with the AXL inhibitor bemcentinib down-regulated mediators of EMT but had no effect on proliferation mediators and little effect on osimertinib sensitivity. Furthermore, the authors used two cell lines containing well-known osimertinib resistance mechanisms in MET amplification and EGFR T790M/C797S compound mutation, respectively, and found increased expression of MUC1-C in both. Suppression of MUC1-C down-regulated p-MET in the first cell line and p-EGFR, p-ERK, and p-AKT in both. This resulted in decreased colony formation and increased osimertinib sensitivity. In the MET-amplified cell line, suppression of MUC1-C also inhibited p-SHP2 activation, which itself is thought to promote osimertinib resistance.13Xia L. Yang F. Wu X. et al.SHP2 inhibition enhances the anticancer effect of osimertinib in EGFR T790M mutant lung adenocarcinoma by blocking CXCL8 loop mediated stemness.Cancer Cell Int. 2021; 21: 337Crossref PubMed Scopus (7) Google Scholar The authors also revealed that treatment with a MUC1-C inhibitor along with osimertinib decreased self-renewal capacity of cell lines in both tumorsphere formation and in mouse xenografts than either drug alone. Finally, the authors sought to evaluate the relationship between MUC1 expression and clinical outcomes. In an analysis of The Cancer Genome Atlas patients with EGFR-mutant lung cancer, those with highly expressed MUC1 in RNA sequencing had shorter survival than those with low expressing MUC1. In a cohort of patient who were planned to receive osimertinib, those who had high MUC1 RNA expression at baseline had shorter overall survival. Finally, in a cohort of patients with resected EGFR-mutant cancer, those that expressed higher MUC1-C by immunohistochemistry were found to have more advanced pathologic stage, more aggressive pathologic features, and shorter overall survival. Overall, the authors propose the involvement of MUC1 in a number of known resistance mechanisms to osimertinib, including MET amplification, EGFR C797S mutation, EMT, and other mutations, which may converge on the AKT and ERK signaling pathways. Osimertinib resistance has also been found to develop through activation of NF-kB by means of the IKK pathway, resulting in up-regulation of a number of resistance-inducing proteins.14Shostak K. Chariot A. Chariot A. EGFR and NF-κB: partners in cancer.Trends Mol Med. 2015; 21: 385-393Abstract Full Text Full Text PDF PubMed Google Scholar Apolipoprotein B mRNA editing catalytic polypeptides (APOBEC) are a family of cytidine deaminases known to drive carcinogenesis by activating oncogenes or inactivating tumor suppressors.15Butler K. Banday A.R. APOBEC3-mediated mutagenesis in cancer: causes, clinical significance and therapeutic potential.J Hematol Oncol. 2023; 16: 31Crossref Scopus (3) Google Scholar Patients with EGFR-mutant NSCLC treated with TKIs who went on to acquire resistance were found to have an enrichment in APOBEC mutational signatures.16Selenica P. Marra A. Choudhury N.J. et al.APOBEC mutagenesis, kataegis, chromothripsis in EGFR-mutant osimertinib-resistant lung adenocarcinomas.Ann Oncol. 2022; 33: 1284-1295Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar APOBEC3A in particular was found to be up-regulated in cell lines exposed to osimertinib which was sustained in the subsequently induced drug-tolerant persister cells. The key transcription factor mediating TKI-induced APOBEC up-regulation was then identified to be NF-kB.17Isozaki H. Sakhtemani R. Abbasi A. et al.Therapy-induced APOBEC3A drives evolution of persistent cancer cells.Nature. 2023; 620: 393-401Crossref PubMed Scopus (2) Google Scholar NF-kB has also been found to promote cell survival and residual disease in cell lines and murine models of EGFR-mutant lung cancer treated with TKIs.18Blakely C.M. Pazarentzos E. Olivas V. et al.NF-κB-activating complex engaged in response to EGFR oncogene inhibition drives tumor cell survival and residual disease in lung cancer.Cell Rep. 2015; 11: 98-110Abstract Full Text Full Text PDF PubMed Scopus (142) Google Scholar These mechanisms are similar to a previously described pathway leading to resistance to first-generation EGFR TKIs, in which TKI exposure led to activation of NF-kB which subsequently up-regulated activation-induced cytidine deaminase which generated the T790M mutation.19El Kadi N. Wang L. Davis A. et al.The EGFR T790M mutation is acquired through AICDA-mediated deamination of 5-methylcytosine following TKI treatment in lung cancer.Cancer Res. 2018; 78: 6728-6735Crossref PubMed Scopus (24) Google Scholar Activation of NF-kB after exposure to osimertinib has also been found to result in an immunosuppressive tumor immune microenvironment20Wang C. Fei K. Liu L. et al.Abnormal activation of NF-κB and MAPK signaling pathways affect osimertinib resistance and influence the recruitment of myeloid-derived suppressor cells to shape the immunosuppressive tumor immune microenvironment.Thorac Cancer. 2023; 14: 1843-1856Crossref Scopus (1) Google Scholar and is also suggested to be involved in a transforming growth factor-β2–mediated EMT.21lian X.Y. Wei Y.L. Yuan L.W. et al.TGFβ2-mediated epithelial–mesenchymal transition and NF-κB pathway activation contribute to osimertinib resistance.Acta Pharmacol Sin. 2021; 42: 451-459Crossref Scopus (29) Google Scholar MUC1 is known to directly promote NF-kB–mediated gene expression and EMT,22Hiraki M. Maeda T. Mehrotra N. et al.Targeting MUC1-C suppresses BCL2A1 in triple-negative breast cancer.Signal Transduct Target Ther. 2018; 3: 13Crossref PubMed Google Scholar and its silencing has been found to reduce NF-kB activity in cancer cell lines.23Ahmad R. Raina D. Trivedi V. et al.MUC1 oncoprotein activates the IκB kinase β complex and constitutive NF-κB signalling.Nat Cell Biol. 2007; 9: 1419-1427Crossref PubMed Scopus (160) Google Scholar At least three different mechanisms have been elucidated through which MUC1 activates NF-kB including binding to IKKβ-IKKγ complexes to trigger IκBα phosphorylation and prevent its inhibition of NF-kB,23Ahmad R. Raina D. Trivedi V. et al.MUC1 oncoprotein activates the IκB kinase β complex and constitutive NF-κB signalling.Nat Cell Biol. 2007; 9: 1419-1427Crossref PubMed Scopus (160) Google Scholar associating with transforming growth factor-β–activated kinase-1 to phosphorylate IKKβ24Takahashi H. Jin C. Rajabi H. et al.MUC1-C activates the TAK1 inflammatory pathway in colon cancer.Oncogene. 2015; 34: 5187-5197Crossref PubMed Scopus (83) Google Scholar and binding to the NF-kB p65 subunit to cause direct activation.25Ahmad R. Raina D. Joshi M.D. et al.MUC1-C oncoprotein functions as a direct activator of the nuclear factor-κB p65 transcription factor.Cancer Res. 2009; 69: 7013-7021Crossref PubMed Scopus (161) Google Scholar Though NF-kB activity is not directly evaluated in the present study, this interaction may have explained its findings of reduced p-ERK and p-AKT expression in a number of settings, given the crosstalk between the NF-kB and ERK/AKT pathways. Although the involvement of NF-kB as a transcription factor for mediators of cancer growth suggests that its inhibition is a good therapeutic target, its ubiquitous involvement in normal cellular function, especially in normal innate immunity by means of interleukin-1β secretion,26Greten F.R. Arkan M.C. Bollrath J. et al.NF-κB is a negative regulator of IL-1β secretion as revealed by genetic and pharmacological inhibition of IKKβ.Cell. 2007; 130: 918-931Abstract Full Text Full Text PDF PubMed Scopus (525) Google Scholar may make it difficult to avoid serious adverse effects such as infections. The close relationship between NF-kB and MUC1, without the ubiquitous involvement of MUC1 in as large a number of normal cellular functions, makes the latter appealing therapeutic target. Resistance to osimertinib is an active phenomenon where cells with cancer stem properties endure the initial insult to use several survival and proliferation pathways overcoming EGFR inhibition. In the present study, MUC1 represents the cornerstone of this dynamic process of resistance suggesting that a combination of EGFR TKI and MUC1 inhibitor is a reasonable therapeutic strategy. Anirudh Yalamanchali: Conceptualization, Roles/Writing—original draft. Khaled A. Hassan: Conceptualization, Supervision, Writing—review and editing. MUC1-C Is a Common Driver of Acquired Osimertinib Resistance in NSCLCJournal of Thoracic OncologyVol. 19Issue 3PreviewOsimertinib is an irreversible EGFR tyrosine kinase inhibitor approved for the first-line treatment of patients with metastatic NSCLC harboring EGFR exon 19 deletions or L858R mutations. Patients treated with osimertinib invariably develop acquired resistance by mechanisms involving additional EGFR mutations, MET amplification, and other pathways. There is no known involvement of the oncogenic MUC1-C protein in acquired osimertinib resistance. Full-Text PDF Open Access