Palbociclib

Breast Feeding; Lactation; Milk, Human; Antineoplastic Agents; Enzyme Inhibitors; Protein Kinase Inhibitors; Signal Transduction Inhibitors

FDA approved drugs -> Active ingredient

EMA approved medicines: Human medicine

EMA approved medicines: Human medicine

FDA approved drugs -> Active ingredient

Danger

H301 (100%): Toxic if swallowed [Danger Acute toxicity, oral]

P264, P270, P301+P316, P321, P330, P405, and P501 (click each P-code to see the statement)

Aggregated GHS information provided per 39 reports by companies from 1 notifications to the ECHA C&L Inventory.

Danger

H341 (94.9%): Suspected of causing genetic defects [Warning Germ cell mutagenicity]

Acute Tox. 3 (100%)

Muta. 2 (94.9%)

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.

L - Antineoplastic and immunomodulating agents

QL - Antineoplastic and immunomodulating agents

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%.

Palbociclib is a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor that acts by binding to the ATP pocket with an IC50 in the range of 9-15 nmol/L. It is important to consider that it presents low to absent activity against other kinases. The CDK4/6 kinase is involved, with coregulatory partner cyclin D, in the G1-S transition. Hence, inhibition of this step prevents cell cycle progression in cells in whose this pathway is functioning. This step includes the pathways of the phosphorylation of retinoblastoma protein and the E2F family of transcription factors.