ESR1 and breast cancer: To further explore the molecular mechanisms through which FASN blockade might interrupt E2-dependent mitogenic ERα signaling, we first evaluated the effects of C75 on the expression of p21WAF1/CIP1 and p27Kip1 CDK inhibitors (CDKIs), two key players in the E2-induced regulation of cell cycle progression and critical mediators of the therapeutic effects of antiestrogen in breast cancer.40, 41, 42, 43, 44 The expression of p21WAF1/CIP1 and p27Kip1 proteins after E2 depletion were not drastically altered by C75 treatment (Figure 6a).