Mechanisms of resistance to EGFR inhibitors

5-aminolaevulinic acid/photo-dynamic therapy and gefitinib in non-small cell lung cancer cell lines: a potential strategy to improve gefitinib therapeutic efficacy

OBJECTIVES

Often, non-small cell lung cancers (NSCLC) respond only poorly to the tyrosine kinase inhibitor (TKI) gefitinib, which targets the epidermal growth factor receptor (EGFR), these poor responders EGFRs lacking activating mutations. In this study, we have attempted to improve TKI response of NSCLC cell lines (A549 and H1299) devoid of EGFR mutations, by combination of gefitinib and 5-ALA/photodynamic therapy (PDT).

MATERIALS AND METHODS

Cells of the two lines were incubated with gefitinib (from 0.5 to 50 mm, for 48 h) then irradiated at doses ranging from 4 to 20 J/cm(2) ; 5-ALA concentration and incubation time were kept constant (1 mm for 3 h). We analysed cell viability, colony-forming efficiency, cell cycle parameters, proteasome and NF-κB activity and expression patterns of specific proteins, after individual or combined treatments.

RESULTS

Effects (antagonistic, additive or synergistic) of combination treatment were evaluated using a predictive model (combination index) for expected interactive effects and results are consistent with mutual potentiation exceeding simple additivity. Investigation of molecular mechanisms underlying cytotoxic effects indicated that combination treatment impaired proteasome function, inhibited NF-κB transcriptional activity and hampered AKT pro-survival signalling.

CONCLUSIONS

The results of this study show that poor response of cells devoid of EGFR activating mutations to TKIs, can be overcome by combining gefitinib with 5-ALA/photodynamic therapy (PDT).

Targeted therapies for advanced non-small-cell lung cancer: current status and future implications

Lung cancer remains the leading cause of malignancy-related mortality worldwide, with over one million cases diagnosed yearly. Non-small-cell lung cancer (NSCLC) accounts for >80% of all lung cancers. Because lung cancer is typically diagnosed at an advanced stage, chemotherapy (CT) is the mainstay of management. Conventional treatment of NSCLC has apparently reached a plateau of effectiveness in improving survival of patients, and treatment outcomes must still be considered disappointing. Hence, considerable efforts have been made in order to identify novel targeted agents that interfere with other dysregulated pathways in advanced NSCLC patients. In order to further improve the results of targeted therapy, we should not forget that lung cancer is a heterogeneous disease with multiple mutations, and it is unlikely that any single signaling pathway drives the oncogenic behaviour of all tumours. The relative failure of some targeted therapies may be a result of multilevel cross-stimulation among the targets of the new biological agents along several pathways of signal transduction that lead to neoplastic events. Thus, blocking only one of these pathways allows others to act as salvage or escape mechanisms for cancer cells. We summarize the most promising research approaches to the treatment of NSCLC, with particular attention to drugs with multiple targets or combining targeted therapies.

The potential role of mTOR inhibitors in non-small cell lung cancer

The mammalian target of rapamycin (mTOR), a serine/threonine kinase, is a downstream mediator in the phosphatidylinositol 3-kinase/Akt signaling pathway, which plays a critical role in regulating basic cellular functions including cellular growth and proliferation. Currently, the mTOR inhibitor rapamycin and its analogues (CCI-779, RAD001, AP23573), which induce cell-cycle arrest in the G(1) phase, are being evaluated in cancer clinical trials. The mTOR inhibitors appear to be well tolerated, with skin reactions, stomatitis, myelosuppression, and metabolic abnormalities the most common toxicities seen. These adverse events are transient and reversible with interruption of dosing. Several pieces of evidence suggest a certain antitumor activity, including tumor regressions and prolonged stable disease, which has been reported among patients with a variety of malignancies, including non-small cell lung cancer (NSCLC). These promising preliminary clinical data have stimulated further research in this setting. Here, we review the basic structure of the pathway together with current results and future developments of mTOR inhibitors in the treatment of NSCLC patients.