Synergistic Antitumor Activity of Cetuximab and Namitecan in Human Squamous Cell Carcinoma Models Relies on Cooperative Inhibition of EGFR Expression and Depends on High EGFR Gene Copy Number

Abstract

Purpose: Despite the frequent overexpression of epidermal growth factor receptor (EGFR) in squamous cell carcinoma (SCC), the efficacy of cetuximab alone is limited. Given the marked activity of namitecan, a hydrophilic camptothecin, against SCC models, the present study was performed to explore the efficacy of the cetuximab-namitecan combination in a panel of SCC models.Experimental Design: We examined the antiproliferative and antitumor activities of the cetuximabnamitecan combination in four SCC models characterized by a different EGFR gene copy number/EGFR protein level. We also assessed the effects of the combination on EGFR expression at both mRNA and protein levels and investigated the molecular basis of the interaction between the two agents.Results: Cetuximab and namitecan exhibited synergistic effects, resulting in potentiation of cell growth inhibition and, most importantly, enhanced therapeutic efficacy, with high cure rates in three SCC models characterized by high EGFR gene copy number, without increasing toxicity. The synergistic antitumor effect was also observed with the cetuximab-irinotecan combination. At the molecular level, the two agents produced a cooperative effect resulting in complete downregulation of EGFR. Interestingly, when singly administered, the camptothecin was able to strongly decrease EGFR expression mainly by transcriptional inhibition.Conclusions: Our results (i) demonstrate a marked efficacy of the cetuximab-namitecan combination, which reflects a complete abrogation of EGFR expression as a critical determinant of the therapeutic improvement, in SCC preclinical models, and (ii) suggest EGFR gene copy number as a possible marker to be used for patient selection in the clinical setting.

PLK1 is a critical determinant of tumor cell sensitivity to CPT11 and its inhibition enhances the drug antitumor efficacy in squamous cell carcinoma models sensitive and resistant to camptothecins

“…Next, we exploited the availability of a human SCC experimental model of acquired drug resistance consisting of the pair of isogenic cell lines A431 and the TPT-resistant variant (A431/TPT) cross-resistant to SN38 in vitro ([ 24 ] and Fig. 4C ) and to CPT11 in vivo [ 37 ]. Again, in this system, the sequential exposure to SN38 and BI2536 resulted in a synergistic interaction ( Suppl.…”

“…Next, we tested the antitumor efficacy of the CPT11-BI2536 combined treatment against the couple of A431 and A431/TPT tumor xenografts. Given the known hypersensitivity of A431 to CPTs [ 24 , 25 , 37 ], CPT11 was delivered at the 20 mg/kg dose which produced in this model 87% TVI with 4/8 cured mice at the end of experiment (Table 1 and Fig. 5B ).…”

Antitumor activity of miR-34a in peritoneal mesothelioma relies on c-MET and AXL inhibition: persistent activation of ERK and AKT signaling as a possible cytoprotective mechanism

“…Proteins were obtained as described previously [16] from frozen s.c. tumors derived from two additional mice sacrified at different time points. Briefly, samples were pulverized by Mikro-Dismembrator II (B.…”

“…Brown Biotech International, Melsungen, Germany) and suspended in lysis buffer supplemented with protease and phosphatase inhibitors. Proteins were processed as described [16]. …”

Patient-derived solitary fibrous tumour xenografts predict high sensitivity to doxorubicin/dacarbazine combination confirmed in the clinic and highlight the potential effectiveness of trabectedin or eribulin against this tumour

“…Lysates from frozen PDX tumours obtained at the end of the last eribulin treatment were prepared [11]. Proteins were separated by SDS-PAGE, transferred onto nitrocellulose membranes and incubated with primary monoclonal antibodies, anti-MPM2, anti-cyclin B1, anti-phospho Cdk1 (Tyr15) and anti-b-actin [12].…”