Annual Report for Fiscal Year 2005. My laboratory research program focuses on the development of novel targeted molecular therapy for thoracic cancers. The main approach of the research effort is to design clinically applicable strategies to efficiently and selectively induce apoptosis of cancer cells by targeting either the receptor-mediated growth/survival signaling pathways or the receptor-mediated death signaling pathways. This report summarizes the research achievement and progress in my laboratory in FY2005. 1.Targeting receptor-mediated mitogenic/survival pathways to downregulate expression of prometastasis malignant phenotypes in cultured thoracic cancer cells. Since 2001, my laboratory has focused on evaluating the biologic effects of blocking EGFR-dependent signal transductions by the selective EGFR tyrosine kinase inhibitor (EGFR-TKI) PD153035 (PD) in a panel of 12 cultured thoracic cancer cells (esophageal cancers - EsC and malignant pleural mesothelioma - MPM) expressing different levels of EGFR, ranging from levels comparable to those of normal skin keratinocytes to levels many fold higher. The rationale behind this study is to demonstrate that EGFR-TKI is only effective in cancer cells over-expressing EGFR because of their dependence on EGFR-regulated signal pathways for growth/survival, a view not commonly shared by other investigators in the field citing initial preclinical studies and small volume phase I/II clinical trials using gefitinib (Iressa) or erlotinib (Tarceva). Clinical evidence stemming from a recently published study of a large phase III study indicates that there exists a correlation between response and survival benefit and the levels of EGFR expression in patients taking elortinib for stage IV NSCLC (Tsao M et al. NEJM 2005; 353(2):133-44.). There are no known activating EGFR mutations in EsC or MPM. We observed that the EGFR-TKI PD is very efficient in mediating cell cycle arrest (but no apoptosis), in suppressing clonogenic activity as well as the production of pro-angiogenic cytokine (VEGF, IL-8) only in EGFR overexpressing MPM (H513, H2595) or EsC (TE2, TE3, TE12) cells. Western blots analysis of phosphorylated EGFR, ERK1/2 and AKT in PD-treated MPM cell lines H211 (mildly elevated EGFR) and H513 (high EGFR) indicated that while PD was very efficient in inhibiting phosphorylation EGFR in both H513 and H211 cells, yet abrogation of ERK1/2 and AKT phosphorylation was only observed in H513 and not in H211 cells. This differential effect of PD on downstream pathways signaling in these cells correlates with their distinct biological responses following PD treatment. We postulated that the lack of PD effect on EGFR-dependent downstream signaling pathways in tumor cells like H211 cells with normal levels of EGFR is due to the presence of other growth factor receptors that, in parallel with EGFR, transduce their mitogenic signals to similar set of intracellular signaling cascades, while in EGFR overexpressing cancer cells like H513, EGFR is the predominant mitogenic receptor. A potentially more efficient strategy is to selectively target the intracellular signal transduction pathways downstream of the membrane growth factor receptor repertoire. The theoretical advantage of targeting the intracellular pathways such as PI3K/PDK/AKT or Ras/Raf/MEK is the ability to collectively block inputs from multiple upstream receptors which converge to that particular pathway and the potential disadvantage of this approach is that this would only alter biologic responses mediated by that single pathway alone.
Showing the most recent 10 out of 21 publications
