Antitumoral effect of PLK-1-inhibitor BI2536 in combination with cisplatin and docetaxel in squamous cell carcinoma cell lines of the head and neck

Abstract

Inhibition of the polo-like-kinase-1 (PLK-1) has been shown to be effective in several haematological and solid tumor models. In this systemic in vitro study, the antitumor effect of BI2536, a small molecule inhibitor of PLK-1, in combination with cisplatin and docetaxel was examined in nine squamous cell carcinoma cell lines, most of which had a head and neck origin (SCCHN). Dose escalation studies were conducted with nine SCCHN cell lines using BI2536, cisplatin and docetaxel in cell line-specific concentrations. Growth inhibitory and proapoptotic effects were measured quantitatively using cytohistology and a Human Apoptose Array kit. BI2536 in combination with cisplatin and docetaxel showed a markedly higher antiproliferative and apoptotic activity in the SCCHN cell lines investigated (P≤0.008), compared with single agent cisplatin or docetaxel alone. The findings of this study showed that the addition of PLK-1-inhibitor BI2536 to conventional chemotherapeutic drugs led to a statistically higher antiproliferative and apoptotic effect in SCCHN cell lines compared with cisplatin or docetaxel alone. Inaugurating BI2536 in the clinical setting might enhance the antitumoral activity of conventional drugs, possibly leading to less toxic side effects of cancer therapy.

Keywords: BI2536; apoptosis; cisplatin; docetaxel; growth inhibition; squamous cell head and neck carcinoma cell lines.

Figure 1

Growth-inhibitory effect of single agent cisplatin (blue column) and docetaxel (red column), as well as the combination of BI2536/cisplatin (yellow column) and BI2536/docetaxel (black column) at a fixed cell line-specific concentration as shown in Table I after 72 h treatment in PE/CA-PJ 41 cell line. The results of the other cell lines treated were similar to these. The corresponding untreated tumor cell line (grey column) served as the control and was incubated, according to the manufacturer’s instructions, only with antibiotics at 37°C in the cell type-specific medium Quantum 263 with L-glutamine. The absolute tumor cell numbers in the treated and control cell lines were determined in a Rosenthal chamber at 72 h after treatment or incubation with Quantum 263 (controls), respectively. Mean values of three independent experiments with standard deviation are shown. Single agent differences vs. combin ation treatment and untreated controls are indicated by asterisks. Combination treatment of BI2536 with cisplatin- or docetaxel-inhibited cell proliferation significantly higher compared to therapy with cisplatin or docetaxel alone (P≤0.015).

Figure 2

Growth-inhibitory effect of single agent cisplatin (blue column) and docetaxel (red column), as well as the combination of BI2536/cisplatin (yellow column) and BI2536/docetaxel (black column) at a fixed cell line-specific concentration, as shown in Table I after 72 h treatment in PE/CA-PJ 49 cell line. The results of the other cell lines treated were similar to these. The corresponding untreated tumor cell line (grey column) served as the control and was incubated, according to the instructions of the suppliers, only with antibiotics at 37°C in the cell type-specific medium Quantum 263 with L-glutamine. The absolute tumor cell numbers in treated and control cell lines were determined in a Rosenthal chamber at 72 h after treatment or incubation with Quantum 263 (controls), respectively. Mean values of three independent experiments with standard deviation are shown. Single agent differences vs. combin ation treatment and untreated controls are indicated by asterisks. Combination treatment of BI2536 with cisplatin or docetaxel inhibited cell proliferation significantly higher than therapy with cisplatin or docetaxel alone (P≤0.015).

Figure 3

Detection of pro-caspase-3 as a typical apoptosis marker by Human Apoptose Array kit. Besides other cell markers (data not shown) we detected the typical apoptosis marker pro-caspase-3 in nine different squamous carcinoma cell lines treated with BI2536 in combination with cisplatin and docetaxel. Fig. 2 shows the results received when treating PE/CA-PJ 49 cells with BI2536 in combination with cisplatin and docetaxel.