Induction of Autophagy Is an Early Response to Gefitinib and a Potential Therapeutic Target in Breast Cancer

Abstract

Gefitinib (Iressa®, ZD1839) is a small molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. We report on an early cellular response to gefitinib that involves induction of functional autophagic flux in phenotypically diverse breast cancer cells that were sensitive (BT474 and SKBR3) or insensitive (MCF7-GFPLC3 and JIMT-1) to gefitinib. Our data show that elevation of autophagy in gefitinib-treated breast cancer cells correlated with downregulation of AKT and ERK1/2 signaling early in the course of treatment. Inhibition of autophagosome formation by BECLIN-1 or ATG7 siRNA in combination with gefitinib reduced the abundance of autophagic organelles and sensitized SKBR3 but not MCF7-GFPLC3 cells to cell death. However, inhibition of the late stage of gefitinib-induced autophagy with hydroxychloroquine (HCQ) or bafilomycin A1 significantly increased (p<0.05) cell death in gefitinib-sensitive SKBR3 and BT474 cells, as well as in gefitinib-insensitive JIMT-1 and MCF7-GFPLC3 cells, relative to the effects observed with the respective single agents. Treatment with the combination of gefitinib and HCQ was more effective (p<0.05) in delaying tumor growth than either monotherapy (p>0.05), when compared to vehicle-treated controls. Our results also show that elevated autophagosome content following short-term treatment with gefitinib is a reversible response that ceases upon removal of the drug. In aggregate, these data demonstrate that elevated autophagic flux is an early response to gefitinib and that targeting EGFR and autophagy should be considered when developing new therapeutic strategies for EGFR expressing breast cancers.

mTORC1-independent autophagy regulates receptor tyrosine kinase phosphorylation in colorectal cancer cells via an mTORC2-mediated mechanism

“…EGFR targeted therapy has been characterised as a potent autophagy-inducing stimulus in cancer cells 17,19,42,44,45,[48][49][50] Interestingly, we found that all CRC cell lines utilised in this work exhibit basal autophagic flux irrespective of their PI3K or KRAS mutational status. Although earlier studies have suggested that autophagy can be regulated in an mTORC1-independent manner, [13][14][15][16][17][18][19] the role of basal autophagy in cancer remains elusive.…”

“…It has been proposed by us and others that in established tumours autophagy plays a pro-survival role, 28,39,41,42,45,46,57 in particular upon starvation or downstream inhibition of oncogenic kinase signalling, both of which result in inhibition of the main autophagy inhibitor, the PI3K/AKT/mTORC1 pathway. However, little is known on the role of autophagy and autophagy-like pathways in the presence of active PI3K/AKT/mTORC1 signalling in cancer cells, due to mutations in either PI3K or RAS pathway.…”

“…28,39,41,42,45,46 We set out to further investigate the RTK-autophagy pathway in the context of CRC, where RTK signalling is a factor implicated in tumour development and is being targeted clinically. In particular, several agents targeting EGFR and other members of the ErbB family are currently being tested in CRC trials.…”

“…In turn, pharmacological inhibition of autophagy potentiates OncTK/RTK targeted therapy. 2,28,[38][39][40][41] In particular, autophagy has been placed downstream of two RTKs with a known role in cancer, the Epidermal Growth Factor Receptor (EGFR) 17,19,[42][43][44][45][46][47][48][49][50] and the Hepatocyte Growth Factor Receptor (HGFR), c-MET. 51 EGFR has been suggested to regulate autophagy either directly 17,19 or indirectly through its downstream effectors.…”

Copolymer micelles function as pH-responsive nanocarriers to enhance the cytotoxicity of a HER2 aptamer in HER2-positive breast cancer cells

“…we examined whether cell viability and HER2 protein expression were affected when lysosomal function was compromised using bafilomycin A1, a macrolide antibiotic that passively permeates into lysosomes and increases lysosomal pH, which disrupts lysosomal activity. 50, 51 Figure 6C indicates that pretreatment with bafilomycin A1 followed by co-incubation with HApt-MNPs increased cell viability (by ~25%) and upregulated HER2 (by ~38%) compared to cells treated with the same concentration of HApt-MNPs without bafilomycin A1 to block lysosomal function ( Figure 6D). The increase in pH inside cells treated with bafilomycin A1 was confirmed by LysoTracker Red staining ( Figure S7).…”