Cell experiment:

SupT1, Daudi, MCF7, ZR-75-1, A2058, WM2664, and H69 cells are seeded at 1000 cells per well; MV-4-11 and BV173 cells are plated at 4000 cells per well; Tom-1 cells are plated at 8,000 cells per well; NALM-1 cells are plated at 20,000 cells per well in Costar 3903 96 well plates. After 24 hours, plates are dosed with Lerociclib (G1T38) at a nine-point dose concentration from 10 μM to 1 nM. Cell viability is determined after four or six days. Plates are processed on BioTek Synergy2 multi-mode plate reader and data analyzed using GraphPad Prism 5 statistical software[1].

Animal experiment:

Mice[1]Female MMTV-NEU mice are used to test the efficacy of Lerocyclib (G1T38) (100 mpk, medicated diet). At time of treatment, body composition is assessed and weight measurements (in grams) are recorded and used as a measure of gross toxicity. Female nude mice are implanted with NSCLC PDX CTG0159 tumor. Mice are then randomized into treatment groups and dosing initiated once tumors reached a volume that fell within the range of 150-300 mm3. 100 mg/kg Lerociclib (G1T38) or vehicle is orally administered for 28 consecutive days. Female NCI Ath/nu mice are implanted with H1975 NSC lung adenocarcinoma model. Once tumors reach an average size of 100-150 mm3, mice are randomized into treatment cohorts. Mice are orally administered daily afatinib (20 mg/kg), erlotinib (70 mg/kg), or Lerociclib (50 or 100 mg/kg), as single agents or in combination (Lerociclib+erlotinib or Lerociclib+afatinib) for the duration of the study. All tumors are measured twice weekly until mice reach tumor burden of 1500 mm3.

Lerociclib (G1T38) is a potent and selective inhibitor of CDK4/6, with IC50s of 1 nM, 2 nM for CDK4/CyclinD1 and CDK6/CyclinD3, respectively.

Within the CDK family, Lerociclib is least selective against CDK9/cyclin T, ~30 fold between CDK4/cyclin D1 and CDK9/ cyclin T at the biochemical IC50. Lerociclib produces a robust and sustained G1 arrest in CDK4/6 dependent cells with an EC50 of ~20 nM. A dose dependent increase of cells in the G1 phase of the cell cycle is observed when CDK4/6 dependent WM2664 cells are treated with Lerociclib for 24 hours. This arrest is maintained through 300 nM, more than 300x the biochemical IC50. WM2664 cells treated with 30-1000 nM of Lerociclib for 24 hours exhibits a complete inhibition of RB phosphorylation compared to vehicle controls. Treatment with Lerociclib reduces RB phosphorylation within 1 hour post-treatment and generates near complete inhibition of RB phosphorylation by 16 hours post-treatment. Lerociclib produces a robust inhibition of proliferation in a diverse array of tumor cell lines including breast, melanoma, leukemia and lymphoma with EC50 concentrations as low as 23 nM[1].

In this HER2+ breast cancer model, Mice treated with Lerociclib elicits 8% tumor regression after 21 days of treatment while control animals have a 577% increase in tumor burden over the same treatment period. Compared to the vehicle-treated mice, daily treatment with 100 mg/kg of Lerocyclib or palbociclib shows tumor regression within 10 days in the MCF7 xenograft model. After 27 days of treatment, tumor growth inhibition is observed in the 10, 50, and 100 mg/kg Lerociclib cohorts (approximately 12%, 74%, and 90% inhibition, respectively). Daily oral palbociclib treatment causes an 18%, 66%, and 87% tumor growth inhibition in the 10, 50, and 100 mg/kg dosage cohorts, respectively. Interestingly, at 50 mg/kg, Lerociclib is significantly more efficaciou than palbociclib. Similar results are seen in the ER+ZR-75-1 breast cancer xenograft model when comparing Lerocyclib and palbociclib at the 50 mg/kg dose. Lerociclib treated mice exhibits 77% TGI with an overall 60% tumor growth delay demonstrating Lerocyclib alone is highly efficacious in this NSCLC tumor model.

[1]. Bisi JE, et al. Preclinical development of G1T38: A novel, potent and selective inhibitor of cyclin dependent kinases 4/6 for use as an oral antineoplastic in patients with CDK4/6 sensitive tumors. Oncotarget. 2017 Jun 27;8(26):42343-42358.