CDK4 and non-small cell lung carcinoma: Similar reductions in Hsp90 and CDK4 were observed in the A549 and H460 non-small-cell lung cancer (NSCLC) lines at 7.8 μM; below the median clinical serum concentration (Cmax) of 27 μM, it is suggested that clinical doses of ritonavir could potentially inhibit Hsp90 function.