st-1968 and Carcinoma--Squamous-Cell

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.. We examined the antiproliferative and antitumor activities of the cetuximab-namitecan 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.. 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.. 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.

Topics: Animals; Antibodies, Monoclonal, Humanized; Antineoplastic Combined Chemotherapy Protocols; Camptothecin; Carcinoma, Squamous Cell; Cell Line, Tumor; Cetuximab; DNA Copy Number Variations; Drug Synergism; ErbB Receptors; Gene Dosage; Gene Expression; Gene Expression Regulation, Neoplastic; Humans; Inhibitory Concentration 50; Mice; Mice, Nude; Xenograft Model Antitumor Assays

ST1968 (namitecan), a novel 7-modified hydrophilic camptothecin, was found to be effective against tumor models relatively resistant to topotecan and irinotecan. Based on this observation, this study was designed to investigate the cellular and antitumor effects of ST1968 in a subline of A431, squamous cell carcinoma, selected for resistance to topotecan (A431/TPT). This model was characterized by a slow growth rate, associated with downregulation of EGFR and topoisomerase I. In contrast to other camptothecins (SN38 and gimatecan), ST1968 was able to overcome almost completely the resistance at cellular level. The cellular pharmacokinetics indicated a comparable accumulation and retention of ST1968 in sensitive and resistant cells, in spite of expression of the efflux transporter, P-glycoprotein, in resistant cells. The uptake and retention of topotecan were dramatically reduced in both tumor cell lines, but more evident in the resistant one. In contrast to topotecan, ST1968 retained an outstanding efficacy in vivo against the resistant tumor (A431/TPT). The results are consistent with the interpretation that ST1968 was able to overcome the most relevant mechanisms associated with the development of topotecan resistance (i.e., slow proliferation and target downregulation) owing to its peculiar pharmacokinetic behaviour.

Topics: Animals; Camptothecin; Carcinoma, Squamous Cell; Cell Line, Tumor; Drug Resistance, Neoplasm; Female; Humans; Mice; Mice, Nude; Topotecan; Xenograft Model Antitumor Assays

DNA damage response and checkpoint activation are expected to influence the sensitivity to DNA-damaging agents. This study was designed to investigate the DNA damage response to the novel camptothecin, ST1968, in two tumor cell lines with a different biological background (A2780 and KB), which underwent distinct cell cycle perturbations and cell death modalities. Following treatment with the camptothecin or ionizing radiation, both inducing double-strand DNA breaks, the ovarian carcinoma A2780 cells exhibited activation of the ATM-Chk2 pathway and early induction of apoptosis. In contrast, the squamous carcinoma KB cells exhibited activation of ATR-Chk1 pathway, a persistent G(2)/M-phase arrest, cellular senescence, mitotic catastrophe and delayed apoptosis, suggesting a defective ATM pathway. The cellular response to UV-induced DNA damage, which activates ATR-Chk1 pathway, was similar in the two cell lines exhibiting early apoptosis induction. Inhibition of ATM in A2780 cells, resulting in reduced phosphorylation of Chk2, enhanced ST1968-induced apoptosis, but had no effect in KB cells. The susceptibility to camptothecin-induced apoptosis of A2780 cells was likely p53-dependent but not related to the activation of the ATM pathway. In contrast, the inhibition of Chk1 enhanced apoptosis response in KB cell but not in A2780. Thus, depending on the biological context, the camptothecin activated ATM-Chk2 or ATR-Chk1 pathways, both having a protective role. In conclusion, our results are consistent with the interpretation that the modality of cell death response is not the critical determinant of sensitivity to camptothecins, and support the interest of inhibition of checkpoint kinases to improve the efficacy of camptothecins.

Topics: Ataxia Telangiectasia Mutated Proteins; Camptothecin; Carcinoma, Squamous Cell; Cell Cycle; Cell Cycle Proteins; Cell Line, Tumor; DNA Damage; DNA-Binding Proteins; Female; Humans; Infrared Rays; Ovarian Neoplasms; Protein Serine-Threonine Kinases; Tumor Suppressor Proteins; Ultraviolet Rays

ST1968, a novel hydrophilic camptothecin analogue of the 7-oxyiminomethyl series, is characterised by the formation of stable DNA-topoisomerase I cleavable complex and by a promising profile of antitumour activity. The present study was designed to extend preclinical evaluation of the novel camptothecin in human squamous cell carcinoma (SCC) models. ST1968 exhibited an impressive activity with a high cure rate in SCC models. ST1968 produced 100% of complete response without evidence of regrowth in tumours characterised by susceptibility to drug-induced apoptosis (FaDu, A431 and A2780). In contrast to irinotecan, ST1968 still showed an excellent, persisting activity in models less susceptible to apoptosis induction (KB, Caski and SiHa), in which drug treatment elicited a persistent DNA damage response, as documented by phosphorylation of p53, RPA-2 and histone H2AX, resulting in delayed apoptosis and senescence. This behaviour was associated with a marked cellular/tumour drug accumulation. In conclusion, ST1968 exhibited an outstanding antitumour activity superior to that of irinotecan against SCC. A high intracellular accumulation, resulting in fast apoptosis or DNA damage persistence, appeared to be a critical determinant of SCC sensitivity to ST1968.

Topics: Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Camptothecin; Carcinoma, Squamous Cell; Caspase 3; DNA Damage; Drug Evaluation; Female; Humans; Irinotecan; Male; Mice; Mice, Nude; Neoplasm Transplantation; Ovarian Neoplasms; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases; Prostatic Neoplasms; Transplantation, Heterologous; Tumor Cells, Cultured