Palbociclib is an oral, reversible, selective, small-molecule inhibitor of CDK4 and CDK6 indicated in combination with letrozole for the treatment of postmenopausal women with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer as initial endocrine-based therapy for their metastatic disease. CDK4 and CDK6 along with their regulatory partner cyclin D1 play a key role in regulating the G1- to S-phase cell-cycle transition via regulation of phosphorylation of the retinoblastoma (Rb) protein. Inhibition of these proteins leads to reduced phosphorylation of Rb, inhibition of downstream signalling, and increased tumor growth arrest. Palbociclib received an accelerated approval from the Food and Drug Administration on February 3, 2015. Palbociclib is marketed under the trade name Ibrance. IBRANCE is a kinase inhibitor indicated in combination with letrozole for the treatment of postmenopausal women with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer as initial endocrine-based therapy for their metastatic disease.

Cobimetinib is an orally active, potent and highly selective small molecule inhibiting mitogen-activated protein kinase kinase 1 (MAP2K1 or MEK1), and central components of the RAS/RAF/MEK/ERK signal transduction pathway. It has been approved in Switzerland and the US, in combination with vemurafenib for the treatment of patients with unresectable or metastatic BRAF V600 mutation-positive melanoma. Preclinical studies have demonstrated that Cobimetinib is effective in inhibiting the growth of tumor cells bearing a BRAF mutation, which has been found to be associated with many tumor types. A threonine-tyrosine kinase and a key component of the RAS/RAF/MEK/ERK signalling pathway that is frequently activated in human tumors, MEK1 is required for the transmission of growth-promoting signals from numerous receptor tyrosine kinases. Cobimetinib is used in combination with vemurafenib because the clinical benefit of a BRAF inhibitor is limited by intrinsic and acquired resistance. Reactivation of the MAPK pathway is a major contributor to treatment failure in BRAF-mutant melanomas, approximately ~80% of melanoma tumors becomes BRAF-inhibitor resistant due to reactivation of MAPK signalling. BRAF-inhibitor resistant tumor cells are sensitive to MEK inhibition, therefore cobimetinib and vemurafenib will result in dual inhibition of BRAF and its downstream target, MEK. Cobimetinib specifically binds to and inhibits the catalytic activity of MEK1, resulting in inhibition of extracellular signal-related kinase 2 (ERK2) phosphorylation and activation and decreased tumor cell proliferation. Cobimetinib and vemurafenib target two different kinases in the RAS/RAF/MEK/ERK pathway. Cobimetinib is used for the treatment of patients with unresectable or metastatic melanoma with a BRAF V600E or V600K mutation. Cobimetinib is used in combination with vemurafenib, a BRAF inhibitor. Cobimetinib is marketed under the trade name Cotellic.