The requirement for cyclin D function in tumor maintenance

Abstract

D-cyclins represent components of cell cycle machinery. To test the efficacy of targeting D-cyclins in cancer treatment, we engineered mouse strains that allow acute and global ablation of individual D-cyclins in a living animal. Ubiquitous shutdown of cyclin D1 or inhibition of cyclin D-associated kinase activity in mice bearing ErbB2-driven mammary carcinomas triggered tumor cell senescence, without compromising the animals' health. Ablation of cyclin D3 in mice bearing Notch1-driven T cell acute lymphoblastic leukemias (T-ALL) triggered tumor cell apoptosis. Such selective killing of leukemic cells can also be achieved by inhibiting cyclin D associated kinase activity in mouse and human T-ALL models. Inhibition of cyclin D-kinase activity represents a highly-selective anticancer strategy that specifically targets cancer cells without significantly affecting normal tissues.

Figure 1. Acute Ablation of Cyclin D1 Blocks Tumor Progression and Triggers Senescence in ErbB2-driven Tumors

(A) Schematic representation of the experimental design. (B) Total tumor burden per mouse in cyclin D1^F/+/Esr1-Cre/MMTV-ErbB2 (D1^Δ/+) and in D1^F/−/Esr1-Cre/MMTV-ErbB2 (D1^Δ/−) mice. Deletion of cyclin D1 was induced (by tamoxifen administration) upon detection of palpable tumors; mice were sacrificed after 6 weeks. In the top panel, each dot represents the total tumor burden (grams) for a given mouse upon sacrifice, horizontal lines represent mean values. Lower panel: mean total tumor burden (grams) per mouse, error bars, SD, n=10. (C) Representative SA-β-galactosidase staining of sections of ErbB2-driven mammary tumors following acute cyclin D1 shutdown (cyclin D1^Δ/−), or in control animals (cyclin D1^Δ/+). Scale bar represents 50 μm. (D) Mean percentage of SA-β-galactosidase-positive area in tumor sections. For each section, three independent areas were scanned and quantified using software from Aperio Technologies. Error bars, SEM. (E) Total tumor burden per animal in MMTV-ErbB2 mice treated daily with vehicle only (VO) or PD 0332991 (PD, 150 mg/kg body weight) for 6 weeks after detection of palpable tumors. Upper panel shows tumor burden for each mouse, lower panel shows mean values ± SD, n=7. (F) Representative SA-β-galactosidase staining of sections of ErbB2-driven mammary carcinomas from mice treated with vehicle only or PD 0332991 for 6 weeks after detection of palpable tumors. Scale bar represents 50 μm. (G) Percentage of area staining positive for SA-β-galactosidase, analyzed as in (D). Error bars, SEM. See also Figure S1.

Figure 2. Acute Ablation of Cyclin D3 in Mouse Model of Notch1-ICD-driven T-cell Acute Lymphoblastic Leukemia

(A) Schematic representation of the experimental design. After T-ALL formation in the recipient mice, cyclin D3 ablation was induced at two weeks post BMT. (B) Representative FACS profiles showing percentage of Notch1-ICD-overexpressing GFP⁺ cells in peripheral blood right after completion of pI-pC administration (started 2 weeks post BMT) to cyclin D3^F/F/Mx1-Cre⁺(D3^Δ/Δ) or D3^F/F/Mx1-Cre⁻ (D3^F/F) mice. SSC, side scatter. (C) Mean percentages of GFP⁺ cells in peripheral blood in mice treated as in (B). Error bars, SD, n=7 (D) Kaplan-Meier analysis of survival time in each group, n=7. See also Figure S2.

Figure 3. Cyclin D3 Is Required for Maintenance of Notch1-ICD-driven T-ALL In Vivo

(A) Schematic representation of the experimental design. After T-ALL formation in the recipient mice, cyclin D3 ablation was induced at six and a half weeks post BMT. (B) Representative FACS analysis showing percentage of Notch1-ICD-overexpressing GFP⁺ cells in spleens right after completion of pI-pC administration (started 6.5 weeks post BMT) in cyclin D3^F/F/Mx1-Cre⁺ (D3^Δ/Δ) or D3^F/F/Mx1-Cre⁻ (D3^F/F) mice. SSC, side scatter. (C) Mean percentages of GFP+ cells in spleens in mice treated as in (B). Error bars, SD, n=4. (D) Kaplan-Meier analysis of survival time in each group, n=6. See also Figure S3.

Figure 4. Cyclin D3 Ablation Triggers Apoptosis of Notch1-ICD-driven T-ALL Cells

(A–E) Mice received Notch1-ICD-GFP-transduced cyclin D3^F/F/Mx1-Cre⁺ (D3^Δ/Δ) or D3^F/F/Mx1-Cre⁻ (D3^F/F) bone marrow cells, and were treated five times with pI-pC, starting at 6.5 weeks following BMT. (A) Representative FACS profiles of peripheral blood stained for Annexin V/7-AAD and gated on GFP⁺ cells. (B) Mean percentages of apoptotic (Annexin V⁺) cells from peripheral blood (gated on GFP⁺ cells) and analyzed as in (A). Error bars, SD, n=4. (C) Representative FACS profiles of cells from the spleen stained for Annexin V/7-AAD and gated on GFP⁺. (D) Mean percentages of apoptotic (Annexin V⁺) cells from spleens (gated on GFP⁺ cells) and analyzed as in (C). Error bars, SD, n=4. (E) TUNEL staining of spleen sections. Scale bar represents 50 μm. See also Figure S4.

Figure 5. Pharmacological Inhibition of Cdk4/6 Activity in Notch1-ICD-driven T-ALL

(A to F) Mice received Notch1-ICD-GFP-transduced C57BL/6 wild-type bone marrow cells, and were fed daily with either vehicle only (VO) or CDK4/6 inhibitor, PD 0332991 (PD, 100–150mg/kg body weight). (A) PD 0332991 treatment was started at 6.5 weeks post bone marrow transplantation. Shown are representative FACS profiles depicting percentage of GFP⁺ cells in peripheral blood after 7 days of PD 0332991 administration. SSC, side scatter. (B) Mean percentages of GFP+ cells in peripheral blood, in mice treated as in (A). Error bars, SD, n=7. (C and D) Kaplan-Meyer survival curves. In (C), treatment was started at 2 weeks post-BMT (following detection of GFP⁺ cells in peripheral blood), n = 10 mice per group. In (D) treatment started at 6.5 weeks post-BMT, after animals had developed tumors, n=10 mice per group. (E and F) Splenocytes from vehicle-treated moribund mice were cultured in vitro and treated with vehicle only (VO) or 1uM of PD 0332991 (PD) for 4 days. Cells were then stained for Annexin V/7-AAD, and analyzed by FACS. (E) Shown is a representative FACS profile of Annexin V/7-AAD staining gated on GFP⁺ splenic tumor cells. (F) Mean percentage of apoptotic (Annexin V⁺) tumor cells following treatment with vehicle only or 1uM of PD. Error bars, SD, n=4.

Figure 6. Pharmacological Inhibition of CDK4/6 Kinase Triggers Apoptosis of Human T-ALL Cell Lines

(A and B) Human T-ALL cell lines were cultured and treated with vehicle only (VO) or 1uM of PD 0332991 (PD) for 4 days, stained for Annexin V/7-AAD and analyzed by FACS. (A) Shown are representative FACS profiles of KOPTK1, DND41, MOLT-16 and RPMI-8402 cells stained with Annexin V/7-AAD. (B) Quantification of the apoptotic (Annexin V⁺) cells, analyzed as above. Shown are mean values. Error bars, SD, n=4. See also Figure S5.

Figure 7. Effects of Pharmacological Inhibition of CDK4/6 on Human T-ALL In Vivo

(A–J) Human KOPTK1-Luc⁺ or DND41-Luc⁺ cells were engrafted by tail vein injection into NSG mice and treated daily with vehicle only (VO) or PD 0332991 (PD, 150mg/kg body weight). (A) Animals with established KOPTK1-Luc⁺ leukemia were treated daily, for 5 days, with vehicle or PD 0332991. Tumor burden is expressed as relative bioluminescence, normalized to the baseline bioluminescence on treatment day 1. Shown are mean values, error bars, SEM. (B) After 5 days of treatment, peripheral blood and bone marrow were collected from KOPTK1-Luc⁺ xenografted animals, and apoptosis of human leukemic cells determined by FACS analysis of Annexin V/7-AAD staining, gated on human CD45⁺ cells. Graphs represent mean percentages of apoptotic (Annexin V⁺) cells. Error bars, SD. (C) Animals with established DND41-Luc⁺ leukemia were treated daily, for 7 days, with vehicle or PD 0332991. Tumor burden is expressed as relative bioluminescence, normalized to the baseline bioluminescence on treatment day 1. Shown are mean values, error bars, SEM. (D) After 7 days of treatment, peripheral blood and bone marrow were collected from DND41-Luc⁺ xenografted animals, and apoptosis of human leukemic cells determined by FACS analysis of Annexin V/7-AAD staining, gated on human CD45⁺ cells. Graphs represent mean percentages of apoptotic (Annexin V⁺) cells. Error bars, SD. (E) Bioluminescence imaging of representative vehicle- and PD 0332991-treated KOPTK1-Luc⁺ xenografted animals. (F) Total body bioluminescence (photons s⁻¹ ROI⁻¹) in vehicle- and PD 0332991-treated recipients of KOPTK1-Luc⁺ cells was monitored over time to determine tumor burden. Shown are mean values, error bars, SEM. (G) Kaplan-Meier survival curves of KOPTK1-Luc⁺ recipients treated with vehicle or PD 0332991. (H) Bioluminescence imaging of representative vehicle- and PD 0332991-treated DND41-Luc⁺ xenografted animals. (I) Total body bioluminescence (photons s⁻¹ ROI⁻¹) in vehicle- and PD 0332991-treated recipients of DND41-Luc⁺ cells was monitored over time to determine tumor burden. Shown are mean values, error bars, SEM. (J) Kaplan-Meier survival curves of DND41-Luc⁺ recipients treated with vehicle only or PD 0332991. n=8 for all groups. See also Figure S6.

Figure 8. Response of KOPTK1 T-ALL Cells and V720 Breast Cancer Cells to Inhibition of Cyclin D-CDK Kinase

(A) KOPTK1 and V720 cells were treated with PD 0332991 (PD) or vehicle (VO) for 48 hrs and 24 hrs, respectively. Experiment was done in triplicate. Genes which show changes in expression levels after PD treatment were selected based on an absolute fold-change >1.5, absolute mean difference >50 and p-value <0.05, and were classified into three groups: genes with altered expression levels in both cell types (Group 1), in KOPTK1 cells only (Group 2) or in V720 cells only (Group 3). Each row corresponds to one gene and is normalized across the row. (B) Heatmap images representing relative expression levels of cell cycle-related genes that showed significant expression change after PD treatment in KOPTK1 cells (top) or V720 cells (bottom). (C) A heatmap image representing relative expression levels of apoptosis-related genes that showed significant expression change after PD treatment in KOPTK1 cells. (D) Expression levels of seven apoptosis-related genes in KOPTK1 cells. Shown are mean values ± SD, n=3 per group. See also Table S1–S4.