Cdk4/cyclin D3 (IC50 = 9 nM); Cdk4/cyclin D1 (IC50 = 11 nM); Cdk6/cyclin D2 (IC50 = 16 nM); DYRK1A (IC50 = 2000 nM); MAPK (IC50 = 8000 nM)

Palbociclib is a CKD4/6 inhibitor, dramatically lowers the viability of HR+/HER2+ tumor cells when combined with fulvestrant and tucatinib.[2]

Palbociclib a CKD4/6 inhibitor, exhibits superior efficacy in suppressing tumor growth in vivo when combinates with tucatinib and fulvestrant.[2]

In DMSO, a stock solution of PD0332991 is made. CDK assays are run on filter plates with 96 wells. By infecting insect cells with baculovirus, all CDK-cyclin kinase complexes are expressed and purified. A portion of pRb fused to GST (GST·RB-Cterm) spanning amino acids 792–928 serves as the substrate for the assays. Each well has a total volume of 0.1 mL and contains the following final concentrations: 20 mM Tris-HCl, pH 7.4, 50 mM NaCl, 1 mM dithiothreitol, 10 mM MgCl2, 25 μM ATP (for CDK4-cyclin D1, CDK6-cyclin D2, and CDK6-cyclin D3), or 12 μM ATP (for CDK2-cyclin E, CDK2-cyclin A, and CDC2-cyclin B). This mixture also contains 0.25 μCi of [γ-32P]ATP, 20 ng of enzyme, 1 μg of GST·RB-Cterm, and PD 0332991 (0.001-0.1μM). The plate is placed on a plate mixer for two minutes after all ingredients—aside from the [γ-32P]ATP—are added to the wells. The plate is incubated at 25°C for 15 minutes after the addition of [γ-32P]ATP to initiate the reaction. The plate is kept at 4 °C for at least an hour to allow the substrate to precipitate before the reaction is stopped by adding 0.1 mL of 20% trichloroacetic acid. Next, 0.2 mL of 10% trichloroacetic acid is used to wash the wells five times, and a β plate counter is used to measure the radioactive incorporation.

Cell viability is assessed using the Cell Titer Glo assay following a 72-hour vehicle or medication treatment. Prior to fulvestrant treatment, cells are grown in conditions free of estrogen and estradiol is added to a final concentration of 10^-8 M. For every cell line, the IC30 values for palbociclib, fulvestrant, and tucatinib are determined; the IC30 concentrations are then utilized in the ensuing studies.

NCG mice injected with MDA-MB-361 cells
50mg/kg
o.g.

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Oral administration of PD 0332991 to mice bearing the Colo-205 human colon carcinoma produces marked tumor regression. Therapeutic doses of PD 0332991 cause elimination of phospho-Rb and the proliferative marker Ki-67 in tumor tissue and down-regulation of genes under the transcriptional control of E2F. The results indicate that inhibition of Cdk4/6 alone is sufficient to cause tumor regression and a net reduction in tumor burden in some tumors.[1]

Absorption, Distribution and Excretion
Palbociclib presents a linear pharmacokinetic profile and its peak plasma concentration was observed 6-12 hours after oral administration. The oral bioavailability is reported to be of 46% with a steady-state reached after 8 days and a median accumulation ratio of 2.4. The absorption of palbociclib is significantly reduced under fasting conditions and hence, food intake is recommended when this drug is administered.
The main route of elimination of palbociclib is through feces after hepatic metabolism while renal clearance seems to play a minor role accounting only for 17.5% of the eliminated dose.
The mean apparent distribution of palbociclib is 2583 L which suggests that palbociclib penetrates extensively into peripheral tissues.
The mean apparent oral clearance of palbociclib is of 63.1 L/h.

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Metabolism / Metabolites
Palbociclib is mainly hepatically transformed. the metabolism is mainly performed by the activities of the cytochrome P450 isoenzyme 3A and the sulfotransferase 2A1. The metabolism of palbociclib is represented mainly by reactions of oxidation and sulfonation followed by acylation and glucuronidation as minor reactions. After its metabolism, palbociclib forms mainly inactive glucuronide and sulfamic acid conjugates. The major circulating metabolite, accounting for 1.5% of the dose in excreta is is the glucuronide conjugate.

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Biological Half-Life
The mean plasma elimination half-life of palbociclib is 29 hours.

Hepatotoxicity
In the large clinical trials, adverse events were common and led to dose reductions in one-third of patients and discontinuation in 8%. Publications on the efficacy and safety of palbociclib rarely mentioned serum ALT elevations or hepatotoxicity. In a study of women with refractory, metastatic breast cancer, serum ALT elevations occurred in 6% [2% over 5 times ULN] receiving palbociclib and fulvestrant compared to 3% [none over 5 times ULN] on fulvestrant alone. Since its approval and more widescale use, there have been several reports of prominent ALT elevations arising after 2 or 3 cycles of palbociclib, that improved on discontinuation and recurred rapidly when restarted. Serum bilirubin and alkaline phosphatase levels were normal and symptoms were not mentioned. In addition, there have been rare reports of patients with refractory metastatic breast cancer who developed pseudocirrhosis within 2 to 3 months of starting palbociclib presenting with fatigue, jaundice and ascites with only modest elevations in serum aminotransferase and alkaline phosphatase levels. Imaging revealed a severely nodular liver, but liver histology showed desmoplastic changes in areas of necrotic metastatic tumor without cirrhosis. The liver also had vascular changes suggestive of sinusoidal obstruction syndrome, changes possibly caused by the dramatic involution of the metastatic tumor tissue combined with vascular damage. Pseudocirrhosis has been reported with other highly successful antineoplastic therapies of cancer metastatic to the liver, but the frequency is rare.
Likelihood score: C (probable rare cause of clinically apparent liver injury that may represent pseudocirrhosis from nodular transformation of the liver in response to necrosis of hepatic metastases).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
No information is available on the clinical use of palbociclib during breastfeeding. Because palbociclib is 85% bound to plasma proteins, the amount in milk is likely to be low. However, its half-life is about 29 hours and it might accumulate in the infant. It is also given in combination with letrozole or fulvestrant, which may increase the risk to the infant. The manufacturer recommends that breastfeeding be discontinued during palbociclib therapy and for 3 weeks after the last 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.

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Protein Binding
Binding of palbociclib to human plasma proteins in vitro accounts for approximately 85% of the administered dose.

[1]. Mol Cancer Ther . 2004 Nov;3(11):1427-38.

[2]. Mol Cancer Ther. 2022 Jan 1; 21(1): 48–57. Published online 2021 Nov 2.

Pharmacodynamics
Due to its mechanism of action, palbociclib inhibits cell growth and suppresses DNA replication in retinoblastoma tumor suppressor gene (RB) proficient cancer cells. As expected, these RB cells present a significant increase in the proportion of cells in G1 state and the presence of palbociclib produces effective dephosphorylation of RB, reduce proliferation and induce senescence causing cell-cycle arrest. In vitro studies showed the potential for palbociclib to reduce cellular proliferation of estrogen receptor-positive breast cancer cell lines through the inhibition of the cell-cycle progression from G1 to S phase. In this study, it was demonstrated that the sensitivity of the cells significantly increased with the expression of _RB1_ and _CCND1_ and low expression of _CDKN2A_. As well, palbociclib, combined with antiestrogens, enhanced _in vivo_ antitumor activity in estrogen receptor-positive breast cancer mouse models. In clinical trials, palbociclib, in combination with letrozole, was shown to significantly increase the progression-free survival (PFS) in patients with metastatic breast cancer without prior endocrine treatment. In the results, the PFS increased from 4.5 to 9.5 months with an overall response rate (ORR) of 24.6%.

C24H29N7O2

447.54

447.238

C, 64.41; H, 6.53; N, 21.91; O, 7.15

571190-30-2

Palbociclib monohydrochloride;827022-32-2;Palbociclib hydrochloride;571189-11-2;Palbociclib-d8;1628752-83-9;Palbociclib isethionate;827022-33-3;Palbociclib dihydrochloride;Palbociclib orotate;2757498-64-7;Palbociclib-d4 hydrochloride

5330286

Yellow solid powder

1.3±0.1 g/cm3

711.5±70.0 °C at 760 mmHg

200ºC

384.1±35.7 °C

0.0±2.3 mmHg at 25°C

1.648

0.99

2

8

5

33

775

0

O=C1C(C(C([H])([H])[H])=O)=C(C([H])([H])[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]

AHJRHEGDXFFMBM-UHFFFAOYSA-N

InChI=1S/C24H29N7O2/c1-15-19-14-27-24(28-20-8-7-18(13-26-20)30-11-9-25-10-12-30)29-22(19)31(17-5-3-4-6-17)23(33)21(15)16(2)32/h7-8,13-14,17,25H,3-6,9-12H2,1-2H3,(H,26,27,28,29)

6-acetyl-8-cyclopentyl-5-methyl-2-[(5-piperazin-1-ylpyridin-2-yl)amino]pyrido[2,3-d]pyrimidin-7-one;hydrochloride

PD0332991; Palbociclib free base; UNII-G9ZF61LE7G; 6-acetyl-8-cyclopentyl-5-methyl-2-((5-(piperazin-1-yl)pyridin-2-yl)amino)pyrido[2,3-d]pyrimidin-7(8H)-one; PD-0332991; PD 0332991; Trade name: Ibrance.

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

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: ≥ 2 mg/mL (4.47 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2 mg/mL (4.47 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: 6.67 mg/mL (14.90 mM) in 0.5% CMC/saline water (add these co-solvents sequentially from left to right, and one by one), suspension solution; Need ultrasonic and warming and heat to 42°C.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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