Glutaminase as a metabolic target of choice to counter acquired resistance to Palbociclib by colorectal cancer cells

Therapeutic resistance in cancer results from genetic or epigenetic mechanisms that enable cell survival under drug pressure. While several resistance mechanisms to cyclin-dependent kinase inhibitors have been identified, acquired resistance is still a therapeutic challenge. Here, we have systematically analyzed metabolic reprogramming in colorectal cancer cells exposed to Palbociclib, a CDK4/6 inhibitor, or Telaglenestat, a glutaminase inhibitor. Through multiple approaches, we show that Palbociclib and Telaglenestat elicit complementary metabolic responses and are thus uniquely suited to counter the metabolic reprogramming induced by the reciprocal drug. As such, while Palbociclib induced reduced tumor growth in vivo, and Telaglenestat did not show a significant effect, the drug combination displayed a strong synergistic effect on tumor growth. Likewise, initial responses to Palbociclib were followed by signs of adaptation and resistance, which were prevented by combining Palbociclib with Telaglenestat. The combination of Palbociclib and Telaglenestat may effectively forestall acquired resistance to Palbociclib. We have quantified transcript abundance in residual tumors from a mouse xenograft model of HCT116 human colorectal cancer cells exposed to Palbociclib, a CDK4/6 inhibitor, or Telaglenestat, a glutaminase inhibitor. Gene expression was also profiled in two-dimensional monolayer cell cultures explanted from the residual tumors.