EGFR Resisters / LUNGevity Research Award

EGFR mutations render lung cancer tumors resistant to immunotherapy via checkpoint blockade. Fortunately, the development of EGFR tyrosine kinase inhibitors (EGFRi) such as Osimertinib has provided impressive clinical responses in a majority of patients. However, many of these patients eventually recur. Studies by our group and others have identified some of the mechanisms associated with resistance to EGFRi. Although EGFRi eliminate the overwhelming proportion of tumor cells, a limited number of cells persist and have thus been termed DTPCs (drug-tolerant persister cells). Importantly, it is these DTPCs which eventually become resistant and are to blame for patient recurrence, highlighting the importance of eradicating these cells before they become fully resistant. Resistance to EGFR TKIs can emerge via two main mechanisms: oncogene-dependent and independent. While oncogene-dependent mechanisms include accumulation of additional mutations in EGFR such as T790M and C797S, oncogene-independent mechanisms include epithelial to mesenchymal transition (EMT) and small cell transformation. Despite their lack of responsiveness to EGFRi at this juncture, each of these mechanisms offers a unique opportunity to leverage cellular immunotherapy to eradicate EGFR mutant DTPCs before they become resistant, thereby improving clinical outcomes. Over the last few years, we have built a library of T cell receptors (TCRs) which confer the ability to recognize epitopes derived from common EGFR mutations including L858R, T790M, and C797S, as well as from the tumor-associated antigen (TAA) FOXM1 which is overexpressed in tumors, and upregulated upon resistance to EGFRi through EMT and small cell transformation. Therefore, we hypothesize that engineering T cells with receptors targeting these EGFR- and FOXM1-derived antigens allows the destruction of DTPCs following treatment with EGFRi, thereby preventing the emergence of resistance. We propose the following specific aims: Aim 1. Assess the impact of drug-tolerant persister cells on CD8 T cell phenotype and function. In this aim, we will identify immune suppressive mechanisms deployed by DTPCs to inhibit T cell response and function. Aim 2. Evaluate the potential of T cell engineering to eliminate DTPCs. In this aim, we will test the ability of TCR-engineered T cells recognizing epitopes derived from EGFR(L858R) and EGFR(T790M) and from the FOXM1 TAA to eradicate DTPCs in vitro and in vivo. Overall, our proposal aims to demonstrate for the first time that TCR engineering can be used in combination with EGFRi to eradicate EGFR-mutant DTPCs. As a result, this work lays the foundation for use of TCR-engineered T cells in this treatment setting. Most importantly, MD Anderson is currently running a clinical trial employing TCR engineering for the treatment of lung cancer with Alaunos Therapeutics which could provide a clear pathway towards the clinic.

The development of tyrosine kinase inhibitors (TKIs) revolutionized treatment of advanced/metastatic non-small-cell lung cancer with EGFR mutations. Osimertinib is one of several third-generation EGFR TKIs and shows improvement in progression-free survival and overall survival compared to first- and second-generation EGFR TKIs. However, intrinsic or acquired resistance to osimertinib emerges in essentially all patients, which prevents a cure for EGFR-mutated lung cancer. Therefore, it is necessary to develop better strategies to improve clinical outcomes. Recent evidence suggests that drug-tolerant persister (DTP) populations of cancer cells, which survive and adapt to TKIs during early phases of therapy, play an important role in the emergence of resistance to targeted therapies. Such DTP cells give rise to resistant cells via diverse mechanisms and contribute to spatial and temporal heterogeneity of tumors. Therefore, targeting DTP cells may be an efficient strategy to prevent resistance to EGFR TKIs. Using lung cancer cell line models and clinical specimens, we recently identified CD74 as a novel gene that plays a critical role in the drug-tolerant state. In vitro and in vivo experiments demonstrate that CD74 upregulation signals osimertinib resistance and blocks apoptosis, enabling tumor regrowth. Based on preliminary evidence, we hypothesize that CD74 increases tumor cell survival in the presence of TKIs and that elimination of CD74 positive cells by CD74-antibody-drug conjugates (ADCs) may suppress the emergence of DTP cells, which underlie relapse. In this proposal, we will test this hypothesis by: 1) confirming that CD74-positive cells are tolerant to EGFR TKIs; 2) investigating the mechanisms by which osimertinib induces CD74 expression; and 3) evaluating a combination of CD74-ADCs and osimertinib to prevent the emergence of acquired resistance. We will address these questions using cell culture systems and animal models. These experiments should unveil the mechanisms underlying resistance to EGFR-TKIs and the emergence of DTP cells, and provide preclinical evidence that a combination of CD74-ADC and EGFR TKIs is a rational and efficacious treatment strategy for EGFR-mutated lung cancer.