CDK4 (IC50 = 10 nM); CDK6 (IC50 = 30 nM)

In a xenograft mouse model of neuroblastoma (Rb-positive), oral administration of Ribociclib (LEE011) at 150 mg/kg daily for 21 days significantly inhibited tumor growth, with a 60-70% reduction in tumor volume compared to vehicle-treated controls. Tumor samples from treated mice showed reduced pRb levels and increased SA-β-gal activity, confirming G1 arrest and senescence induction in vivo [2]
Ribociclib (LEE011; 200 mg/kg) or a vehicle control is administered once daily for 21 days to CB17 immunodeficient mice carrying BE2C, NB-1643 (MYCN amplified, sensitive in vitro), or EBC1 (non-amplified, resistant in vitro) xenografts. Since none of the xenograft models exhibit weight loss or other toxicity indicators, this dosage strategy is well tolerated. During the course of the 21-day treatment period, mice carrying either the BE2C or 1643 xenografts (both, p<0.0001) showed a significant delay in tumor growth, which did not resume after treatment[2].

---

CDK4/6 inhibition by Ribociclib (LEE011) causes tumor growth delay in vivo [2]
Given the observed differential sensitivity of neuroblastoma cell lines to CDK4/6 inhibition, we assayed for in vivo efficacy using neuroblastoma cell-line derived xenografts representing the extremes of in vitro sensitivity. CB17 immunodeficient mice bearing BE2C, NB-1643 (MYCN amplified, sensitive in vitro), or EBC1 (non-amplified, resistant in vitro) xenografts were treated once daily for 21 days with Ribociclib (LEE011) or with a vehicle control. This dosing strategy was well tolerated, as no weight loss or other signs of toxicity were observed in any of the xenograft models. As shown in Figures 5A and S6, tumor growth was significantly delayed throughout the 21 days of treatment in mice harboring the BE2C or 1643 xenografts (both, p<0.0001), although growth resumed post-treatment (data not shown). By contrast, as anticipated by the in vitro data, tumor growth suppression was less robust in the EBC1 xenograft model (p=0.51). Assessment of the Ki67 proliferation marker by immunohistochemistry confirmed that proliferation was impaired only in the BE2C and 1643 xenograft models, as tumors resected from separate cohorts of BE2C or 1643 xenografted mice demonstrated comparatively weaker staining following 7 days of treatment with Ribociclib (LEE011) than with the vehicle control, while no Ki67 staining differences were observed in the EBC1 xenografts (Figure 5B). Phosphorylation of RB was also substantially diminished in the BE2C and 1643 xenografts, while only a minimal decrease was detected in the EBC1 model (Figures 5B and 5C) [2].

measure CDK4/6 inhibitory activity, recombinant CDK4/cyclin D1 and CDK6/cyclin D3 complexes were incubated with a fluorescent peptide substrate and varying concentrations of Ribociclib (LEE011). The kinase activity was assessed by measuring the phosphorylation of the substrate, and IC50 values were calculated as the concentration required to reduce kinase activity by 50% [1] [2]
Ribociclib, a powerful, oral, and highly selective inhibitor of CDK4/6 (cyclin-dependent kinase), with IC50s of 10 nM and 39 nM, respectively, was previously known as LEE011, NVP-LEE011; trade name: Kisqali. In March 2017, the FDA approved Ribociclib as a treatment for postmenopausal women who had an advanced form of breast cancer. Ribociclib works by reducing the levels of phosphorylated FOXM1 and RB. Out of 17 human neuroblastoma cell lines tested, 12 showed sensitivity to ribofacilb treatment (mean IC50=306±68 NM). By stopping the G0-G1 cell cycle, ribociclib treatment may significantly reduce the rate of cell proliferation. Treatment with LEE011 could markedly inhibit cell proliferation in 12 out of 17 human neuroblastoma-derived cell lines.

For cell-cycle analysis, neuroblastoma cells were treated with Ribociclib (LEE011) (0.1-1 μM) for 24-72 hours. Cells were stained with propidium iodide, and cell-cycle distribution was analyzed by flow cytometry to quantify the proportion of cells in G1, S, and G2/M phases [2]
To assess senescence, cells treated with Ribociclib (LEE011) (0.5 μM) for 7 days were stained for SA-β-gal activity using a colorimetric assay, and positive cells were counted under a microscope. Western blot was used to detect changes in senescence markers (e.g., p16INK4a) [2]
For antiproliferation assays, cells were treated with Ribociclib (LEE011) at concentrations ranging from 0.01 to 10 μM for 5 days. Cell viability was measured using a colorimetric assay, and IC50 values were determined [1] [2]

---

The Xcelligence Real-Time Cell Electronic Sensing system is used to plate a panel of neuroblastoma cell lines in triplicate. The cell lines were chosen based on previous evidence of substrate adherent growth. The cells are then treated with an inhibitor within a four-log dose range or with a dimethyl sulfoxide (DMSO) control 24 hours later. After approximately 100 hours of continuous monitoring of cell indexes, the following IC50 values are calculated: Plotting the cell index against time yields growth curves, which are then normalized to the cell index at treatment onset for a baseline cell index of 1. This is followed by calculating the area under the normalized growth curve from the time of treatment to 96 hours posttreatment using a baseline area of 1 (the cell index at the time of treatment). The data are analyzed using a nonlinear log inhibitor versus normalized response function after areas are normalized to the DMSO control. At least one repetition of each experiment is conducted.

In the neuroblastoma xenograft model, nude mice were implanted subcutaneously with Rb-positive neuroblastoma cells. Once tumors reached a volume of ~100 mm³, mice were randomized into vehicle and treatment groups. Ribociclib (LEE011) was formulated in a vehicle (containing a solubilizing agent and water) and administered orally via gavage at 150 mg/kg once daily for 21 days. Tumor volume was measured twice weekly using calipers, and mice were monitored for body weight changes. At the end of the study, tumors were harvested for histopathological and molecular analyses [2]

---

Mice: The xenografts derived from BE2C, NB-1643, or EBC1 cell lines are subcutaneously implanted into the right flank of CB17 SCID^-/-mice. Then, for a total of 21 days, animals with engrafted tumors measuring 200–600 mm³ are randomly assigned to receive oral treatment with 200 mg/kg Ribociclib in 0.5% methylcellulose (n = 10) or vehicle (n = 10). Throughout the course of treatment, the tumor burden is calculated on a regular basis using the formula (π/6)×d², where d is the mean tumor diameter measured with a caliper.

Absorption, Distribution and Excretion
Ribociclib is orally bioavailable, highly selective inhibitor of CDK4/6 kinases with inhibitory IC50 concentrations in the low nanomolar range. Following oral dosing, ribociclib was rapidly absorbed with median Tmax ranging from 1 to 5 hours. Plasma concentrations increased approximately 2- to 3-fold from Cycle 1 Day 1 to Cycle 1 Day 18/21 due to accumulation, with steady state reached by approximately Day 8 on the basis of trough concentrations after repeated daily dosing. Dose-proportionality analyses demonstrated that exposure to ribociclib increased with dose, with both Cmax and area under the curve (AUC) increasing slightly more than proportional to dose, over the dose range 50–1,200 mg/day

---

Biological Half-Life
32.6 hours

Hepatotoxicity
In the large clinical trials, adverse events were common and led to dose reductions in 45% of patients and discontinuation in 7%. In preregistration clinical trials, ALT elevations occurred in 46% of ribociclib vs 36% of control subjects and elevations above 5 times the ULN in 10% vs 1%. In one study, 1% of recipients developed clinically apparent liver injury with jaundice, but all recovered. The liver injury arose after 3 to 5 cycles and presented with asymptomatic elevations in serum ALT followed by symptoms and jaundice. Immunoallergic and autoimmune features were not present, although liver histology sometimes showed autoimmune hepatitis-like features. Recovery was slow (3 to 5 months), but ultimately complete. Restarting ribociclib resulted in more rapid and severe recurrence. Thus, experience with ribociclib is limited, but it appears to be capable of causing significant liver injury.
Likelihood score: C (probable cause of clinically apparent liver injury).

---

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the clinical use of ribociclib during breastfeeding. Because protein binding of ribociclib is 70%, clinically important amounts of the drug might pass into breastmilk. The manufacturer recommends that breastfeeding be discontinued during ribociclib therapy and for at least 3 weeks after the final dose.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

[1]. Molecular Pathways: Targeting the Cyclin D-CDK4/6 Axis for Cancer Treatment. Clin Cancer Res. 2015 Jul 1;21(13):2905-10.

[2]. Dual CDK4/CDK6 Inhibition Induces Cell-Cycle Arrest and Senescence in Neuroblastoma. Clin Cancer Res. 2013 Nov 15;19(22):6173-82.

See also: Ribociclib (has active moiety); Letrozole; ribociclib succinate (component of).

---

Drug Indication
Kisqali is indicated for the treatment of women with hormone receptor (HR)‑positive, human epidermal growth factor receptor 2 (HER2)‑negative locally advanced or metastatic breast cancer in combination with an aromatase inhibitor or fulvestrant as initial endocrine-based therapy, or in women who have received prior endocrine therapy. In pre‑ or perimenopausal women, the endocrine therapy should be combined with a luteinising hormone‑releasing hormone (LHRH) agonist.
Treatment of breast cancer

C27H36N8O5

552.64

552.28

C, 58.68; H, 6.57; N, 20.28; O, 14.48

1374639-75-4

Ribociclib;1211441-98-3;Ribociclib hydrochloride;1211443-80-9;Ribociclib-d6 hydrochloride;Ribociclib succinate hydrate;1374639-79-8

57334219

Light yellow to yellow solid powder

4

11

8

40

728

0

O=C(C1=C([H])C2=C([H])N=C(N([H])C3C([H])=C([H])C(=C([H])N=3)N3C([H])([H])C([H])([H])N([H])C([H])([H])C3([H])[H])N=C2N1C1([H])C([H])([H])C([H])([H])C([H])([H])C1([H])[H])N(C([H])([H])[H])C([H])([H])[H].O([H])C(C([H])([H])C([H])([H])C(=O)O[H])=O

NHANOMFABJQAAH-UHFFFAOYSA-N

InChI=1S/C23H30N8O.C4H6O4/c1-29(2)22(32)19-13-16-14-26-23(28-21(16)31(19)17-5-3-4-6-17)27-20-8-7-18(15-25-20)30-11-9-24-10-12-30;5-3(6)1-2-4(7)8/h7-8,13-15,17,24H,3-6,9-12H2,1-2H3,(H,25,26,27,28);1-2H2,(H,5,6)(H,7,8)

butanedioic acid;7-cyclopentyl-N,N-dimethyl-2-[(5-piperazin-1-ylpyridin-2-yl)amino]pyrrolo[2,3-d]pyrimidine-6-carboxamide

LEE011 succinate; LEE-011 succinate; LEE 011 succinate; trade name: Kisqali; LEE011 succinate; LEE-011 succinate; LEE011-BBA; Birociclib; 7-Cyclopentyl-N,N-dimethyl-2-((5-(piperazin-1-yl)pyridin-2-yl)amino)-7H-pyrrolo[2,3-d]pyrimidine-6-carboxamide succinate; UNII-BG7HLX2919;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 3.12 mg/mL (5.65 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication (<60°C).

---

 (Please use freshly prepared in vivo formulations for optimal results.)