Endocrine Abstracts

JOINT1256

Background: Adrenocortical carcinomas (ACC) are highly aggressive malignancies with limited treatment options. Polo-like kinase 1 (PLK1) and cyclin-dependent kinases (CDKs) 1/2/4 are among the most overexpressed genes in ACC human samples. We have previously demonstrated the efficacy of PBD-targeting PLK1 inhibitor (PLK1i) poloxin in ACC cell lines (H295R, MUC-1, CU-ACC2).

Aims and methods: We tested the efficacy of 1) two PLK1i, i.e. the polo-box domain (PBD)-targeting poloxin and the kinase domain (KD)-targeting plogosertib; 2) two CDK inhibitors (CDKi), i.e. dinaciclib (targeting preferentially CDK1/2) and the CDK1-cyclin B1 inhibitor cucurbitacin E (CurE); 3) the combination of plogosertib and dinaciclib. Their efficacy was evaluated in four ACC cell lines, including H295R, MUC-1, and the newly generated TVBF-7 and JIL-2266. Increasing drug concentrations for 72 h. Cell proliferation and apoptosis were assessed by BrdU incorporation and caspase 3/7 activity, respectively, compared to basal condition. The “SynergyFinder” tool was used to analyse two-drugs combinations.

Results: PLK1i poloxin reduced proliferation at very high doses, achieving a maximum effect at 100μM (P<0.01 in MUC-1 and TVBF-7; P<0.001 in H295R and JIL-2266), and increased apoptosis at 10μM (P<0.05 for all). At considerably lower concentrations, plogosertib dose-dependently reduced cell proliferation (P<0.05 at 100 nM in MUC-1 and JIL-2266; P<0.01 at 750 nM in H295R and TVBF-7) and increased apoptosis (P<0.05 for H295R, TVBF-7, and JIL-2266 at 1μM). CDKi dinaciclib markedly reduced cell proliferation at low nanomolar doses (P<0.05 at 20 nM in MUC-1 and JIL-2266, and at 100 nM in TVBF-7; P<0.01 at 100 nM in H295R), and increased apoptosis (P<0.05 in MUC-1, TVBF-7, and JIL-2266 at 200 nM). CurE dose-dependently reduced proliferation in all ACC cells, but its effects were less pronounced than dinaciclib (P<0.05 at 100 nM in MUC-1 and TVBF-7; P<0.01 at 100 nM in H295R and JIL-2266). In line with the observed differences in treatment sensitivity among cell lines, qRT-PCR analysis showed that CDK1/2 and PLK1 mRNA expression was particularly high in MUC-1 and JIL-2266. Synergistic suppression of cell proliferation by combined treatment with PLK1i plogosertib and CDKi dinaciclib was observed in H295R (P<0.05) and TVBF-7 (P<0.01) cell lines.

Conclusion: Plogosertib and dinaciclib were the most effective inhibitors in all cell lines, representing interesting novel targeted treatment options for ACC. Moreover, the combination of these drugs showed a synergistic effect, suggesting a potential benefit of using both PLK1i and multi CDKi that need to be further investigated in vivo.