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MDM2 turnover and expression of ATRX determine the choice between quiescence and senescence in response to CDK4 inhibition.

Kovatcheva M, Liu DD, Dickson MA, Klein ME, O'Connor R, Wilder FO, Socci ND, Tap WD, Schwartz GK, Singer S, Crago AM, Koff A - Oncotarget (2015)

Bottom Line: Failure to reduce MDM2 does not prevent CDK4i-induced withdrawal from the cell cycle but the cells remain in a reversible quiescent state.CDK4i-induced senescence associated with loss of MDM2 is also observed in some breast cancer, lung cancer and glioma cell lines indicating that this is not limited to WD/DDLS cells in which MDM2 is overexpressed or in cells that contain wild type p53.Interestingly, in seven patients the changes in MDM2 expression were correlated with outcome.

View Article: PubMed Central - PubMed

Affiliation: The Louis V. Gerstner Graduate School of Biomedical Sciences, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, USA.

ABSTRACT
CDK4 inhibitors (CDK4i) earned Breakthrough Therapy Designation from the FDA last year and are entering phase III clinical trials in several cancers. However, not all tumors respond favorably to these drugs. CDK4 activity is critical for progression through G1 phase and into the mitotic cell cycle. Inhibiting this kinase induces Rb-positive cells to exit the cell cycle into either a quiescent or senescent state. In this report, using well-differentiated and dedifferentiated liposarcoma (WD/DDLS) cell lines, we show that the proteolytic turnover of MDM2 is required for CDK4i-induced senescence. Failure to reduce MDM2 does not prevent CDK4i-induced withdrawal from the cell cycle but the cells remain in a reversible quiescent state. Reducing MDM2 in these cells drives them into the more stable senescent state. CDK4i-induced senescence associated with loss of MDM2 is also observed in some breast cancer, lung cancer and glioma cell lines indicating that this is not limited to WD/DDLS cells in which MDM2 is overexpressed or in cells that contain wild type p53. MDM2 turnover depends on its E3 ligase activity and expression of ATRX. Interestingly, in seven patients the changes in MDM2 expression were correlated with outcome. These insights identify MDM2 and ATRX as new regulators controlling geroconversion, the process by which quiescent cells become senescent, and this insight may be exploited to improve the activity of CDK4i in cancer therapy.

No MeSH data available.


Related in: MedlinePlus

MDM2 loss is associated with patient response to PalbociclibSeven patients with measurable advanced WD/DDLS confirmed positive for CDK4 amplification and Rb protein expression, and whom had progressed on at least one systemic therapy prior to enrollment (clinicaltrials.gov identifier NCT01209598), consented to pre-treatment biopsies taken prior to therapy and post-treatment biopsies taken after receiving one dose of oral PD0332991 (125mg daily for 21 days). Tumor response was assessed with CT scan by a reference radiologist every 6 weeks for 36 weeks, and every 12 weeks thereafter. Patients were followed up until March 2014. Three patients (red bars) did not derive clinical benefit and stopped treatment within 84 days. Two of these patients (#2 and #3, triangles) died on study and are indicated with a triangle. The third patient, #8, came off study as their disease progressed. Four patients (blue bars) had demonstrable clinical benefit, remaining on treatment for more than 84 days. Two of these progressed after 168 (#8) and 376 (#7) days respectively, while two remained on treatment with ongoing benefit (arrows), one achieving a complete response (star). (Inset) Extracts were prepared from pre- and post-treatment biopsies of protein expression measured by immunoblot. GAPDH was a loading control.
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Figure 8: MDM2 loss is associated with patient response to PalbociclibSeven patients with measurable advanced WD/DDLS confirmed positive for CDK4 amplification and Rb protein expression, and whom had progressed on at least one systemic therapy prior to enrollment (clinicaltrials.gov identifier NCT01209598), consented to pre-treatment biopsies taken prior to therapy and post-treatment biopsies taken after receiving one dose of oral PD0332991 (125mg daily for 21 days). Tumor response was assessed with CT scan by a reference radiologist every 6 weeks for 36 weeks, and every 12 weeks thereafter. Patients were followed up until March 2014. Three patients (red bars) did not derive clinical benefit and stopped treatment within 84 days. Two of these patients (#2 and #3, triangles) died on study and are indicated with a triangle. The third patient, #8, came off study as their disease progressed. Four patients (blue bars) had demonstrable clinical benefit, remaining on treatment for more than 84 days. Two of these progressed after 168 (#8) and 376 (#7) days respectively, while two remained on treatment with ongoing benefit (arrows), one achieving a complete response (star). (Inset) Extracts were prepared from pre- and post-treatment biopsies of protein expression measured by immunoblot. GAPDH was a loading control.

Mentions: The specifics of the trial, treatment regimen, and timing of biopsy as well as the criteria for patient outcome are described in the methods. Three of these patients had stable disease for more than 1 year, one had a complete remission by RECIST 1.1 criteria, and three did poorly on the drug. To measure MDM2 we extracted protein from pre- and post-treatment biopsies and performed immunoblots. We also blotted GAPDH as a loading control and phosphorylated Rb to confirm that the drug had hit the target. MDM2 was reduced in all four post-treatment samples from patients who performed well, and was not reduced, and even increased in patients who performed poorly (Figure 8). phospho-Rb diminished in all the PD0332991-treated tissues relative to the pre-treatment biopsy. Because of the limited amount of material we could not look at ATRX reactivity with the Bethyl antibody. Thus, PD0332991-induced down regulation of MDM2 associates with a positive response to therapy.


MDM2 turnover and expression of ATRX determine the choice between quiescence and senescence in response to CDK4 inhibition.

Kovatcheva M, Liu DD, Dickson MA, Klein ME, O'Connor R, Wilder FO, Socci ND, Tap WD, Schwartz GK, Singer S, Crago AM, Koff A - Oncotarget (2015)

MDM2 loss is associated with patient response to PalbociclibSeven patients with measurable advanced WD/DDLS confirmed positive for CDK4 amplification and Rb protein expression, and whom had progressed on at least one systemic therapy prior to enrollment (clinicaltrials.gov identifier NCT01209598), consented to pre-treatment biopsies taken prior to therapy and post-treatment biopsies taken after receiving one dose of oral PD0332991 (125mg daily for 21 days). Tumor response was assessed with CT scan by a reference radiologist every 6 weeks for 36 weeks, and every 12 weeks thereafter. Patients were followed up until March 2014. Three patients (red bars) did not derive clinical benefit and stopped treatment within 84 days. Two of these patients (#2 and #3, triangles) died on study and are indicated with a triangle. The third patient, #8, came off study as their disease progressed. Four patients (blue bars) had demonstrable clinical benefit, remaining on treatment for more than 84 days. Two of these progressed after 168 (#8) and 376 (#7) days respectively, while two remained on treatment with ongoing benefit (arrows), one achieving a complete response (star). (Inset) Extracts were prepared from pre- and post-treatment biopsies of protein expression measured by immunoblot. GAPDH was a loading control.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 8: MDM2 loss is associated with patient response to PalbociclibSeven patients with measurable advanced WD/DDLS confirmed positive for CDK4 amplification and Rb protein expression, and whom had progressed on at least one systemic therapy prior to enrollment (clinicaltrials.gov identifier NCT01209598), consented to pre-treatment biopsies taken prior to therapy and post-treatment biopsies taken after receiving one dose of oral PD0332991 (125mg daily for 21 days). Tumor response was assessed with CT scan by a reference radiologist every 6 weeks for 36 weeks, and every 12 weeks thereafter. Patients were followed up until March 2014. Three patients (red bars) did not derive clinical benefit and stopped treatment within 84 days. Two of these patients (#2 and #3, triangles) died on study and are indicated with a triangle. The third patient, #8, came off study as their disease progressed. Four patients (blue bars) had demonstrable clinical benefit, remaining on treatment for more than 84 days. Two of these progressed after 168 (#8) and 376 (#7) days respectively, while two remained on treatment with ongoing benefit (arrows), one achieving a complete response (star). (Inset) Extracts were prepared from pre- and post-treatment biopsies of protein expression measured by immunoblot. GAPDH was a loading control.
Mentions: The specifics of the trial, treatment regimen, and timing of biopsy as well as the criteria for patient outcome are described in the methods. Three of these patients had stable disease for more than 1 year, one had a complete remission by RECIST 1.1 criteria, and three did poorly on the drug. To measure MDM2 we extracted protein from pre- and post-treatment biopsies and performed immunoblots. We also blotted GAPDH as a loading control and phosphorylated Rb to confirm that the drug had hit the target. MDM2 was reduced in all four post-treatment samples from patients who performed well, and was not reduced, and even increased in patients who performed poorly (Figure 8). phospho-Rb diminished in all the PD0332991-treated tissues relative to the pre-treatment biopsy. Because of the limited amount of material we could not look at ATRX reactivity with the Bethyl antibody. Thus, PD0332991-induced down regulation of MDM2 associates with a positive response to therapy.

Bottom Line: Failure to reduce MDM2 does not prevent CDK4i-induced withdrawal from the cell cycle but the cells remain in a reversible quiescent state.CDK4i-induced senescence associated with loss of MDM2 is also observed in some breast cancer, lung cancer and glioma cell lines indicating that this is not limited to WD/DDLS cells in which MDM2 is overexpressed or in cells that contain wild type p53.Interestingly, in seven patients the changes in MDM2 expression were correlated with outcome.

View Article: PubMed Central - PubMed

Affiliation: The Louis V. Gerstner Graduate School of Biomedical Sciences, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, USA.

ABSTRACT
CDK4 inhibitors (CDK4i) earned Breakthrough Therapy Designation from the FDA last year and are entering phase III clinical trials in several cancers. However, not all tumors respond favorably to these drugs. CDK4 activity is critical for progression through G1 phase and into the mitotic cell cycle. Inhibiting this kinase induces Rb-positive cells to exit the cell cycle into either a quiescent or senescent state. In this report, using well-differentiated and dedifferentiated liposarcoma (WD/DDLS) cell lines, we show that the proteolytic turnover of MDM2 is required for CDK4i-induced senescence. Failure to reduce MDM2 does not prevent CDK4i-induced withdrawal from the cell cycle but the cells remain in a reversible quiescent state. Reducing MDM2 in these cells drives them into the more stable senescent state. CDK4i-induced senescence associated with loss of MDM2 is also observed in some breast cancer, lung cancer and glioma cell lines indicating that this is not limited to WD/DDLS cells in which MDM2 is overexpressed or in cells that contain wild type p53. MDM2 turnover depends on its E3 ligase activity and expression of ATRX. Interestingly, in seven patients the changes in MDM2 expression were correlated with outcome. These insights identify MDM2 and ATRX as new regulators controlling geroconversion, the process by which quiescent cells become senescent, and this insight may be exploited to improve the activity of CDK4i in cancer therapy.

No MeSH data available.


Related in: MedlinePlus