Journal of Neuro-Oncology

, Volume 100, Issue 3, pp 345–361

Receptor activation and inhibition in cellular response to chemotherapeutic combinational mimicries: the concept of divergent targeting

Laboratory Investigation - Human/Animal Tissue

DOI: 10.1007/s11060-010-0196-7

Cite this article as:
Watt, H.L., Rachid, Z. & Jean-Claude, B.J. J Neurooncol (2010) 100: 345. doi:10.1007/s11060-010-0196-7

Abstract

The antiproliferative effect of tandem somatostatin receptor (SSTR) activation, epidermal growth factor receptor (EGFR) inhibition, and induction of DNA damage was analyzed using octreotide (OCT), a SSTR agonist, the clinical DNA methylating agent temozolomide (TMZ), Iressa, an EGFR inhibitor, and dual EGFR-DNA targeting agents termed “combi-molecules”. Using SSTR-expressing glioma cells harbouring low levels of EGFR (U87MG) or transfected to overexpress EGFR (U87/EGFR) or a variant (U87/EGFRvIII), we showed that Iressa, alone or in combination with the DNA damaging agent TMZ, and combi-molecules RA2 and RA5 inhibited EGF-induced phosphorylation of EGFR in U87MG and more moderately in U87/EGFR and U87/EGFRvIII transfected cells. This translated into equivalent levels of Erk 1/2 inhibition. Activation of SSTRs with OCT did not modulate the effects of the various treatments on Erk 1/2 phosphorylation. Likewise, SSTR activation did not alter TMZ- or DNA-damaging combi-molecules, RA2 and RA5, induced p53 activation nor upregulation. However, SSTR activation significantly shifted TMZ-, RA2- and RA5-induced cell-cycle arrest to earlier phases (i.e., G2/M to late S, late S to S, S to G1). Further analysis showed that apoptosis was not induced. This was in agreement with the fact that p53 activation did not induce Bax upregulation nor did EGFR inhibition promote Bad dephosphorylation. Moreover, enhancement of survivin, an anti-apoptotic protein, expression was observed. The results in toto suggest that the combination of SSTR activation with EGFR inhibition and DNA damage affects cell-cycle progression but a disconnection between the targeted signalling pathways in these brain tumour cells precludes synergistic cell-killing by the triple growth inhibitory events.

Keywords

Binary targeting combi-molecule Cell-cycle analysis Epidermal growth factor receptor Somatostatin receptors Survivin Temozolomide 

Abbreviations

ATM

Ataxia-telangiectasia

ATR

ATM and Rad-3-related

BER

Base excision repair

DMSO

Dimethyl sulfoxide

EGF

Epidermal growth factor

ErbBs

Epidermal growth factor receptors

GPCR

G protein-coupled receptors

MAPK

Mitogen-activated protein kinase

NER

Nucleotide excision repair

OCT

Octreotide

PBST

0.1% Tween 20 (v/v) in phosphate-buffered saline

PGT

Poly(L-glutamic acid–L-tyrosine 4:1)

PI

Propidium iodide

PVDF

Poly(vinylidene difluoride)

RTK

Receptor tyrosine kinase

SST

Somatostatin

SSTR

Somatostatin receptor

TK

Tyrosine kinase

TKI

Tyrosine kinase inhibitor

TMB

Tetramethylbenzidine peroxidase substrate

TMZ

Temozolomide

Copyright information

© Springer Science+Business Media, LLC. 2010

Authors and Affiliations

  1. 1.Cancer Drug Research Laboratory, Department of MedicineMcGill University Health Centre/Royal Victoria HospitalMontrealCanada