Cell experiment:

The effect of CYC065 on the viability and IC50 of USC-ARK-1, USC-ARK-2, USC-ARK-7, USC-ARK-4 and USC-ARK-6 USC primary cell lines is determined in flow-cytometry assay. Briefly, tumour cells are plated in six-well plates and treated with a titration of CYC065 concentrations (i.e., ranging from 100 to 500 nM). After 72 h, cells are harvested, washed and stained with propidium iodide (PI; 5 μg/mL) for flow cytometric counts. The percentage of viable cells is then normalised considering the vehicle-treated cells as 100% viable. Half-maximal inhibitory concentration values are determined using GraphPad Prism5 version 6. For drug combination studies, USC-ARK-1 and USC-ARK-2 cell lines are incubated with the combination of Taselisib and CYC065 at multiple paired concentrations including the IC50, the IC50/2 and the IC50*2 of each cell line to the corresponding drug (i.e., 10 nM of Taselisib and 198 nM of CYC065 for USC-ARK-1 and 50 nM of Taselisib and 62.5 nM of CYC065 for USC-ARK-2). Synergism is assessed by the combination index (CI). CI values<1 define a synergistic activity of the combination treatment. The CI values are calculated using the CompuSyn software[1].

Animal experiment:

Mice[1] The in vivo efficacy of CYC065 used as a single agent is evaluated on xenograft mouse models derived from the CCNE1-amplified USC-ARK-2 USC cell line. Xenografts derived from the CCNE1-amplified, PIK3CA-mutated USC-ARK-1 cell line are used for evaluating the in vivo combination of CYC065 and Taselisib. Briefly, 5-7-week-old SCID mice are injected into the subcutaneous region with USC cells. A minimum of five animals per group are used. Treatments are administrated by oral gavage starting 1 week after tumor implantation when the size of the tumor is 0.125-0.150 cm3. Uterine serous carcinoma-ARK-2-derived xenografts are divided into two groups: one group of animal receive the vehicle, whereas the experimental group receive CYC065 (22.5 mg/kg daily for 3 weeks). Uterine serous carcinoma-ARK-1-derived xenografts are instead divided into four groups: one group receive the vehicle (0.5% methylcellulose-0.2% Tween-80), one group receive CYC065 (22.5 mg/kg daily for 3 weeks), one group receive Taselisib (10 mg/kg daily, 5 days per week per 3 weeks) and the last group receive the combination of CYC065 and Taselisib. The size of the tumor at the initiation of treatment is 0.125-0.150 cm3. Mouse weight and tumor size is recorded two times a week for the entire experimental period. Tumor volume is calculated.

CYC065 is a second-generation, orally available ATP-competitive inhibitor of CDK2/CDK 9 kinases.

CYC065 blocks cells in the G1 phase of the cell cycle and inhibits cell growth specifically in cyclin E1 (CCNE1)-overexpressing uterine serous carcinomas (USCs). USC cell lines expressing high CCNE1 mRNA and protein levels to be significantly more sensitive to treatment with CYC065 in vitro when compared with low CCNE1-expressing cell lines (IC50: mean±s.d.=124.1±57.8 nM in CCNE1-overexpressing USC cell lines vs 415±117.5 nM in CCNE1 low expressors, respectively; P=0.0003). Importantly, low concentrations of CYC065 (i.e., 100 nM) causes an arrest in the G1 phase of the cell cycle only in the CCNE1-overexpressing USC cell lines (i.e., USC-ARK-2, USC-ARK-7) [1].

To evaluate the therapeutic potential of CYC065 as a single agent, USC-ARK-2-derived xenografts are treated daily with CYC065 (22.5 mg/kg) for a 3-week period. Tumor size and mouse weight are recorded two times a week. The daily administration of CYC065 results in a significant reduction of tumor growth compared with the vehicle-treated mice (P=0.012 starting at day 9 of the treatment). No significant weight loss is reported during the entire treatment period[1].

[1]. Cocco E, et al. Dual CCNE1/PIK3CA targeting is synergistic in CCNE1-amplified/PIK3CA-mutated uterine serous carcinomas in vitro and in vivo. Br J Cancer. 2016 Jul 26;115(3):303-11.