BACKGROUND: The phosphatidylinositol-3-kinase/mammalian target of rapamycin 
(PI3K/mTOR) pathway is commonly deregulated in human cancer, hence many PI3K and 
mTOR inhibitors have been developed and have now reached clinical trials. 
Similarly, CDKs have been investigated as cancer drug targets.
METHODS: We have synthesised and characterised a series of 6-aminopyrimidines 
identified from a kinase screen that inhibit PI3K and/or mTOR and/or CDK2. 
Kinase inhibition, tumour cell growth, cell cycle distribution, cytotoxicity and 
signalling experiments were undertaken in HCT116 and HT29 colorectal cancer cell 
lines, and in vivo HT29 efficacy studies.
RESULTS: 2,6-Diaminopyrimidines with an O(4)-cyclohexylmethyl substituent and a 
C-5-nitroso or cyano group (1,2,5) induced cell cycle phase alterations and were 
growth inhibitory (GI50<20 μM). Compound 1, but not 2 or 5, potently inhibits 
CDK2 (IC50=0.1 nM) as well as PI3K, and was cytotoxic at growth inhibitory 
concentrations. Consistent with kinase inhibition data, compound 1 reduced 
phospho-Rb and phospho-rS6 at GI50 concentrations. Combination of NU6102 (CDK2 
inhibitor) and pictilisib (GDC-0941; pan-PI3K inhibitor) resulted in synergistic 
growth inhibition, and enhanced cytotoxicity in HT29 cells in vitro and HT29 
tumour growth inhibition in vivo.
CONCLUSIONS: These studies identified a novel series of mixed CDK2/PI3K 
inhibitors and demonstrate that dual targeting of CDK2 and PI3K can result in 
enhanced antitumour activity.