E. Aubrey Thompson Ph.D.

Recipient of the Laura Geller Research Grant.

Lay Description

Mutations of the epidermal growth factor receptor (EGFR) gene are relatively uncommon among non-small cell lung cancer (NSCLC) patients. However, such mutations are observed with high frequency in a particular subset of NSCLC patients—women who have never smoked. The recent development of specific EGFR inhibitors has been highly beneficial to such, and about 75% of these individuals undergo initial response when treated with Iressa or Tarceva, the two most commonly used EGFR inhibitors. Mechanistic studies have revealed that tumors with EGFR mutations appear to require a higher level of EGFR activity than tumors with normal EGFR. Such tumors are said to be ‘addicted’ to EGFR, and the cells within these tumors die when EGFR function is inhibited. Unfortunately, many individuals with EGFR-addicted tumors ultimately relapse due to secondary mutations that cause EGFR to become resistant to the inhibitors. This unfortunate outcome emphasizes the need to learn more about how EGFR works, and figure out how to inhibit EGFR signaling downstream of the mutated receptor. Our preliminary data indicate that an enzyme called phospholipase D1 (PLD1) forms a nodal point of integration of EGFR signaling to downstream pathways that control proliferation, invasion, and survival. We have observed that inhibition of PLD1 results in death of EGFR-addicted cells, even those that are resistant to EGFR inhibitors. Our objective is to obtain pre-clinical proof-of-principle in support of the use of PLD1 inhibitors in the treatment of individuals whose tumors have EGFR mutations. We believe that such drugs, in combination with EGFR inhibitors, may have greater efficacy in treating EGFR-addicted lung cancer. Furthermore, PLD1 inhibitors should be effective in treating individuals who have acquired resistance to EGFR inhibitors. Our objectives are to confirm these hypothetical predictions and to develop models to test the efficacy of PLD1 inhibitor in future experiments.

Scientific Abstract

Phospholipase D1 (PLD1) converts phosphatidyl choline to phosphatidic acid (PA), an important signaling lipid that regulates processes related to proliferation, migration and motility, and survival. PLD1 activity is stimulated by EGFR activation, and inhibition of PLD1 blocks EGFR-mediated transformation of fibroblasts. Recent studies indicate that PA is required for activation of Ras downstream of EGFR, for activation of Raf1 downstream of Ras, and for activation of mTOR downstream of PI3K/Akt. Our preliminary data indicate that shRNA-mediated knockdown of PLD1 in cells with mutationally activated EGFR (H1975) results in cell death. PLD1 knockdown in cells with wild type EGFR (H1703 or H1299 engineered to overexpress WT EGFR) results in inhibition of invasion but not cell death. These data suggest that PLD1 constitutes a critical signaling node which integrates EGFR signaling to pathways that control proliferation and invasion (Ras/Raf1/MAPK) or survival (PI3K/Akt/mTOR/Mdm2). Our objective is to test this hypothesis. To this end, we will knock down PLD1 in a series of NSCLC cell lines that express WT or mutant EGFR. We will determine if PLD1 knockdown kills cells with mutationally activated EGFR, the so-called EGFR-addicted cells. We will test the hypothesis that PLD1 is required for EGFR activation of Ras, Raf1, and mTOR. In addition, we will use an orthotopic lung injection model to determine if the effects of PLD1 knockdown that we observe in culture are recapitulated in vivo. Our long term goal is to obtain pre-clinical proof-of-principle for the development of PLD inhibitors as chemotherapeutic agents. In this pilot project, we will develop the assay protocols and obtain the preliminary data that will be required to support a major application to support our studies of the role of PLD1 in lung cancer and of the evaluation and/or development of PLD1 inhibitors as tools to treat individuals with EGFR mutations, particularly those with drug-resistant tumors.