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Supplementary Table III: AML patient samples tested with HDM2 inhibitor, CGM097: IC50 values for CGM097.

The tumor suppressor p53 is a key regulator of apoptosis and functions upstream in the apoptotic cascade by both indirectly and directly regulating Bcl-2 family proteins. In cells expressing wild-type (WT) p53, the HDM2 protein binds to p53 and blocks its activity. Inhibition of HDM2:p53 interaction activates p53 and causes apoptosis or cell-cycle arrest. Here, we investigated the ability of the novel HDM2 inhibitor CGM097 to potently and selectively kill WT p53-expressing AML cells. The antileukemic effects of CGM097 were studied using cell-based proliferation assays (human AML cell lines, primary AML patient cells, and normal bone marrow samples), apoptosis, and cell-cycle assays, ELISA, immunoblotting, and an AML patient–derived in vivo mouse model. CGM097 potently and selectively inhibited the proliferation of human AML cell lines and the majority of primary AML cells expressing WT p53, but not mutant p53, in a target-specific manner. Several patient samples that harbored mutant p53 were comparatively unresponsive to CGM097. Synergy was observed when CGM097 was combined with FLT3 inhibition against oncogenic FLT3-expressing cells cultured both in the absence as well as the presence of cytoprotective stromal-secreted cytokines, as well as when combined with MEK inhibition in cells with activated MAPK signaling. Finally, CGM097 was effective in reducing leukemia burden in vivo. These data suggest that CGM097 is a promising treatment for AML characterized as harboring WT p53 as a single agent, as well as in combination with other therapies targeting oncogene-activated pathways that drive AML. Mol Cancer Ther; 14(10); 2249–59. ©2015 AACR.

Supplementary Figures 1-7 Supplementary Figure 1. Amplification and sequencing primers used for genotyping of p53 in AML patient samples. Supplementary Figure 2. Apoptosis data corresponding to representative bar graphs shown in Figure 1C. Supplementary Figure 3. Cell cycle analysis data corresponding to representative bar graphs shown in Figure 1D. Supplementary Figure 4. Inhibition of growth of mutant FLT3-positive AML cells by CGM097. Supplementary Figure 5. Potentiation of effects of PKC412 by CGM097 against mutant FLT3-positive AML cells. Supplementary Figure 6. Potentiation of effects of AC220 by CGM097 against mutant FLT3-positive AML cells cultured in the absence and the presence of cytoprotective SCM. Supplementary Figure 7 (A-F). Apoptosis data corresponding to representative bar graphs shown in Figure 5C. Supplementary Figure 7 (G-L). Apoptosis data corresponding to representative bar graphs shown in Figure 5C. Supplementary Figure 7 (M-R). Apoptosis data corresponding to representative bar graphs shown in Figure 5C.

Supplementary Figure from Co-Targeting of MDM2 and CDK4/6 with Siremadlin and Ribociclib for the Treatment of Patients with Well-Differentiated or Dedifferentiated Liposarcoma: Results from a Proof-of-Concept, Phase Ib Study

Description of additional methods and procedures used in the study. Also includes Supplementary References.

Purpose:This phase I, dose-escalation study investigated the recommended dose for expansion (RDE) of siremadlin, a p53–MDM2 inhibitor, in patients with wild-type TP53 advanced solid or hematologic cancers.Patients and Methods:Initial dosing regimens were: 1A (day 1; 21-day cycle; dose 12.5–350 mg) and 2A (days 1–14; 28-day cycle; dose 1–20 mg). Alternative regimens included 1B (days 1 and 8; 28-day cycle) and 2C (days 1–7; 28-day cycle). The primary endpoint was incidence of dose-limiting toxicities (DLT) during cycle 1.Results:Overall, 115 patients with solid tumors and 93 with hematologic malignancies received treatment. DLTs occurred in 8/92 patients with solid tumors and 10/53 patients with hematologic malignancies. In solid tumors, an RDE of 120 mg was defined in 1B. In hematologic tumors, RDEs were defined in 1A: 250 mg, 1B: 120 mg, and 2C: 45 mg. More patients with hematologic malignancies compared with solid tumors experienced grade 3/4 treatment-related adverse events (71% vs. 45%), most commonly resulting from myelosuppression. These were more frequent and severe in patients with hematologic malignancies; 22 patients exhibited tumor lysis syndrome. Overall response rates at the RDEs were 10.3% [95% confidence interval (CI), 2.2–27.4] in solid tumors and 4.2% (95% CI, 0.1–21.1), 20% (95% CI, 4.3–48.1), and 22.2% (95% CI, 8.6–42.3) in acute myeloid leukemia (AML) in 1B, 1A, and 2C, respectively.Conclusions:A common safety profile was identified and preliminary activity was noted, particularly in AML. Comprehensive investigation of dosing regimens yielded recommended doses/regimens for future combination studies.

Like classical chemotherapy regimens used to treat cancer, targeted therapies will also rely upon polypharmacology, but tools are still lacking to predict which combinations of molecularly targeted drugs may be most efficacious. In this study, we used image-based proliferation and apoptosis assays in colorectal cancer cell lines to systematically investigate the efficacy of combinations of two to six drugs that target critical oncogenic pathways. Drug pairs targeting key signaling pathways resulted in synergies across a broad spectrum of genetic backgrounds but often yielded only cytostatic responses. Enhanced cytotoxicity was observed when additional processes including apoptosis and cell cycle were targeted as part of the combination. In some cases, where cell lines were resistant to paired and tripled drugs, increased expression of antiapoptotic proteins was observed, requiring a fourth-order combination to induce cytotoxicity. Our results illustrate how high-order drug combinations are needed to kill drug-resistant cancer cells, and they also show how systematic drug combination screening together with a molecular understanding of drug responses may help define optimal cocktails to overcome aggressive cancers. Cancer Res; 76(23); 6950–63. ©2016 AACR.

Activation of p53 by inhibitors of the p53–MDM2 interaction is being pursued as a therapeutic strategy in p53 wild-type cancers. Here, we report distinct mechanisms by which the novel, potent, and selective inhibitor of the p53–MDM2 interaction HDM201 elicits therapeutic efficacy when applied at various doses and schedules. Continuous exposure of HDM201 led to induction of p21 and delayed accumulation of apoptotic cells. By comparison, high-dose pulses of HDM201 were associated with marked induction of PUMA and a rapid onset of apoptosis. shRNA screens identified PUMA as a mediator of the p53 response specifically in the pulsed regimen. Consistent with this, the single high-dose HDM201 regimen resulted in rapid and marked induction of PUMA expression and apoptosis together with downregulation of Bcl-xL in vivo. Knockdown of Bcl-xL was identified as the top sensitizer to HDM201 in vitro, and Bcl-xL was enriched in relapsing tumors from mice treated with intermittent high doses of HDM201. These findings define a regimen-dependent mechanism by which disruption of MDM2–p53 elicits therapeutic efficacy when given with infrequent dosing. In an ongoing HDM201 trial, the observed exposure–response relationship indicates that the molecular mechanism elicited by pulse dosing is likely reproducible in patients. These data support the clinical comparison of daily and intermittent regimens of p53–MDM2 inhibitors.Significance: Pulsed high doses versus sustained low doses of the p53-MDM2 inhibitor HDM201 elicit a proapoptotic response from wild-type p53 cancer cells, offering guidance to current clinical trials with this and other drugs that exploit the activity of p53. Cancer Res; 78(21); 6257–67. ©2018 AACR.

Compounds used in this study.

Median of the shRNAs and RSA values. File containing median counts and log fold changes of each gene from Supplementary Data File S1. According significance values of each gene as activator or sensitizer compared to DMSO control (see Methods) are included.

Supplementary information containing six supplementary figures (Figure S1-S6), one supplementary table (Table S1) and supplementary materials and methods. Supplementary Figure S1. Flow cytometric gating strategies for analysis of intra-tumoral T cells in parental and p53KO Colon26 tumors. Supplementary Figure S2. Flow cytometric gating strategies for analysis of intra-tumoral myeloid cells in parental and p53KO Colon26 tumors. Supplementary Figure S3. Anti-tumor activity of HDM201 in Colon26 syngeneic tumor model requires intact immune system. Supplementary Figure S4. p53 knockout in Colon 26 cells results in loss of response to HDM201 in vitro and in vivo. Supplementary Figure S5. HDM201 in combination with PD-1/PD-L1 blockade enhances anti-tumor responses in p53 wild-type tumors, but not in KO tumors. Supplementary Figure S6. Flow cytometric analysis of CD80, GITR, PD-L1, and CD86 expression after HDM201 treatment in vitro. Supplementary Table S1. Antibodies for flow cytometry analysis.

Purpose:Well-differentiated (WDLPS) and dedifferentiated (DDLPS) liposarcoma are characterized by co-amplification of the murine double minute-2 (MDM2) and cyclin-dependent kinase-4 (CDK4) oncogenes. Siremadlin, a p53–MDM2 inhibitor, was combined with ribociclib, a CDK4/6 inhibitor, in patients with locally advanced/metastatic WDLPS or DDLPS who had radiologically progressed on, or despite, prior systemic therapy.Patients and Methods:In this proof-of-concept, phase Ib, dose-escalation study, patients received siremadlin and ribociclib across different regimens until unacceptable toxicity, disease progression, and/or treatment discontinuation: Regimen A [4-week cycle: siremadlin once daily (QD) and ribociclib QD (2 weeks on, 2 weeks off)], Regimen B [3-week cycle: siremadlin once every 3 weeks; ribociclib QD (2 weeks on, 1 week off)], and Regimen C [4-week cycle: siremadlin once every 4 weeks; ribociclib QD (2 weeks on, 2 weeks off)]. The primary objective was to determine the maximum tolerated dose (MTD) and/or recommended dose for expansion (RDE) of siremadlin plus ribociclib in one or more regimens.Results:As of October 16, 2019 (last patient last visit), 74 patients had enrolled. Median duration of exposure was 13 (range, 1–174) weeks. Dose-limiting toxicities occurred in 10 patients, most of which were Grade 3/4 hematologic events. The RDE was siremadlin 120 mg every 3 weeks plus ribociclib 200 mg QD (Regimen B). Three patients achieved a partial response, and 38 achieved stable disease. One patient (Regimen C) died as a result of treatment-related hematotoxicity.Conclusions:Siremadlin plus ribociclib demonstrated manageable toxicity and early signs of antitumor activity in patients with advanced WDLPS or DDLPS.

From images to synergies (S1); Reproducibility of data from two screens (S2); Single agent responses and selectivity (S3); Screen-wide comparison of Caspase 3/7 activation and growth inhibition (S4); Heatmaps of growth inhibition and Capase 3/7 activation, and examples of broadly synergistic combinations targeting RAS/MAPK and/or PI3K/AKT pathways (S5); Combinations targeting RAS/MAPK and PI3K/AKT pathways at different nodes show similar efficacies (S6); Combinations involving RTKs (S7); Heatmaps of growth inhibition and Capase 3/7 activation, and examples of combinations targeting RAS/MAPK or PI3K/AKT pathways and other cellular processes (S8); Synergies of triple combination increase with synergies of underlying drug pairs (S9); Heatmap of synergies, growth inhibition, and Caspase 3/7 activation for triple combinations after hierarchical clustering (S10); Triple combinations targeting RAS/MAPK and PI3K/AKT pathways (S11); Triple combinations targeting RAS/MAPK and/or PI3K/AKT pathways and other cellular processes (S12); Combination targeting MDM2 and MEK in p53 wild-type models (S13); Sequential treatment of p53 wild-type lines with triple combination targeting MDM2, MEK, and BCL-2/-XL (S14); High order combinations to kill 'robust' cell lines (S15).

Supplementary Data from Co-Targeting of MDM2 and CDK4/6 with Siremadlin and Ribociclib for the Treatment of Patients with Well-Differentiated or Dedifferentiated Liposarcoma: Results from a Proof-of-Concept, Phase Ib Study

p53 is a transcription factor that plays a central role in guarding the genomic stability of cells through cell-cycle arrest or induction of apoptosis. However, the effects of p53 in antitumor immunity are poorly understood. To investigate the role of p53 in controlling tumor-immune cell cross-talk, we studied murine syngeneic models treated with HDM201, a potent and selective second-generation MDM2 inhibitor. In response to HDM201 treatment, the percentage of dendritic cells increased, including the CD103+ antigen cross-presenting subset. Furthermore, HDM201 increased the percentage of Tbet+Eomes+ CD8+ T cells and the CD8+/Treg ratio within the tumor. These immunophenotypic changes were eliminated with the knockout of p53 in tumor cells. Enhanced expression of CD80 on tumor cells was observed in vitro and in vivo, which coincided with T-cell–mediated tumor cell killing. Combining HDM201 with PD-1 or PD-L1 blockade increased the number of complete tumor regressions. Responding mice developed durable, antigen-specific memory T cells and rejected subsequent tumor implantation. Importantly, antitumor activity of HDM201 in combination with PD-1/PD-L1 blockade was abrogated in p53-mutated and knockout syngeneic tumor models, indicating the effect of HDM201 on the tumor is required for triggering antitumor immunity. Taken together, these results demonstrate that MDM2 inhibition triggers adaptive immunity, which is further enhanced by blockade of PD-1/PD-L1 pathway, thereby providing a rationale for combining MDM2 inhibitors and checkpoint blocking antibodies in patients with wild-type p53 tumors.Significance:This study provides a mechanistic rationale for combining checkpoint blockade immunotherapy with MDM2 inhibitors in patients with wild-type p53 tumors.

Supplementary material and methods include the description for the bioanalytical method for HDM201 detection in plasma and tumor, the human and mouse gene expression analysis in vitro and in vivo, the live-cell quantification of cleaved-caspase activation, the western blot analysis, the immunohistochemistry, the splinkerette PCR for the amplification of transposon integration sites and the tumor sequencing, mapping of insertion sequences to the mouse genome and identification of common integration site, additional information on the shRNA screen and the tumor models and supplementary references. Supplementary figures include: • Fig S1: the SJSA-1 inhibition growth curves when treated with HDM201 at different doses and for different times and the data for MOLM-3. • Fig S2: the cumulative percentage of cleaved-caspase-3/7 positive cells over the time, the GI50 of HDM201, CGM097 or nutlin-3a on SJSA-1 cells and the cellular apoptosis, as judged by AUC of cleaved-caspase-3/7 positive cells, induced by these compounds. • Fig S3: the PK profile in plasma and tumor of HDM201 in SJSA-1 tumors-bearing rat after p.o. and i.v. treatment, the Bcl-xl mRNA levels in tumors after HDM201 treatment, representative images of SJSA-1 tumors stained with p53 and cleaved-caspase 3 antibodies after HDM201 treatment and the individual data for the efficacy experiment in SJSA-1 tumor-bearing rats. • Fig S4: the PD of HDM201 in PB tumor bearing nude mice after single dose administration. Supplementary tables include: • Table S1: Biochemical profile of HDM201. • Table S2: List of cell lines tested for their sensitivity to HDM201 (n=291) • Table S3: Contingency table indicating association between sensitivity to HDM201 and TP53 wild-type status. • Table S4: List of cell lines tested for their sensitivity to both MDM2 knock-down by shRNA and HDM201 (n=261) • Table S5: Contingency table indicating association between sensitivity to HDM201 and sensitivity to MDM2 shRNA. • Table S6: List of significant rescuer and sensitizer genes following both HDM201 treatment types • Table S7: Pharmacokinetic parameters for HDM201 after p.o. and i.v. dosing in rat. • Table S8: Summary of primary PK parameters for HDM201 daily regimen after single dose (Day 1) in patients. • Table S9: Summary of primary PK parameters for HDM201 daily regimen on Day 14 in patients. • Table S10: Summary of primary PK parameters for HDM201 q3w regimen after single dose in patients.

Legend for Supplementary Tables S1-S6 and Supplementary Figures S1-S15.

Supplementary Methods, Figures 1-5 from PIK3CA Mutation Uncouples Tumor Growth and Cyclin D1 Regulation from MEK/ERK and Mutant KRAS Signaling

Mutational activation of KRAS is a common event in human tumors. Identification of the key signaling pathways downstream of mutant KRAS is essential for our understanding of how to pharmacologically target these cancers in patients. We show that PD0325901, a small-molecule MEK inhibitor, decreases MEK/ERK pathway signaling and destabilizes cyclin D1, resulting in significant anticancer activity in a subset of KRAS mutant tumors in vitro and in vivo. Mutational activation of PIK3CA, which commonly co-occurs with KRAS mutation, provides resistance to MEK inhibition through reactivation of AKT signaling. Genetic ablation of the mutant PIK3CA allele in MEK inhibitor–resistant cells restores MEK pathway sensitivity, and re-expression of mutant PIK3CA reinstates the resistance, highlighting the importance of this mutation in resistance to therapy in human cancers. In KRAS mutant tumors, PIK3CA mutation restores cyclin D1 expression and G1-S cell cycle progression so that they are no longer dependent on KRAS and MEK/ERK signaling. Furthermore, the growth of KRAS mutant tumors with coexistent PIK3CA mutations in vivo is profoundly inhibited with combined pharmacologic inhibition of MEK and AKT. These data suggest that tumors with both KRAS and phosphoinositide 3-kinase mutations are unlikely to respond to the inhibition of the MEK pathway alone but will require effective inhibition of both MEK and phosphoinositide 3-kinase/AKT pathway signaling. Cancer Res; 70(17); 6804–14. ©2010 AACR.

Supplementary Figures 1-3, Tables 1-9, Methods from Genomic and Biological Characterization of Exon 4 KRAS Mutations in Human Cancer

Supplementary Materials from Genetic Predictors of MEK Dependence in Non–Small Cell Lung Cancer

Mutations in RAS proteins occur widely in human cancer. Prompted by the confirmation of KRAS mutation as a predictive biomarker of response to epidermal growth factor receptor (EGFR)–targeted therapies, limited clinical testing for RAS pathway mutations has recently been adopted. We performed a multiplatform genomic analysis to characterize, in a nonbiased manner, the biological, biochemical, and prognostic significance of Ras pathway alterations in colorectal tumors and other solid tumor malignancies. Mutations in exon 4 of KRAS were found to occur commonly and to predict for a more favorable clinical outcome in patients with colorectal cancer. Exon 4 KRAS mutations, all of which were identified at amino acid residues K117 and A146, were associated with lower levels of GTP-bound RAS in isogenic models. These same mutations were also often accompanied by conversion to homozygosity and increased gene copy number, in human tumors and tumor cell lines. Models harboring exon 4 KRAS mutations exhibited mitogen-activated protein/extracellular signal-regulated kinase kinase dependence and resistance to EGFR-targeted agents. Our findings suggest that RAS mutation is not a binary variable in tumors, and that the diversity in mutant alleles and variability in gene copy number may also contribute to the heterogeneity of clinical outcomes observed in cancer patients. These results also provide a rationale for broader KRAS testing beyond the most common hotspot alleles in exons 2 and 3. Cancer Res; 70(14); 5901–11. ©2010 AACR.

Randomized trials in acute myeloid leukemia (AML) have demonstrated improved survival by the BCL-2 inhibitor venetoclax combined with azacitidine in older patients, and clinical trials are actively exploring the role of venetoclax in combination with intensive chemotherapy in fitter patients with AML. As most patients still develop recurrent disease, improved understanding of relapse mechanisms is needed. We find that 17% of patients relapsing after venetoclax-based therapy for AML have acquired inactivating missense or frameshift/nonsense mutations in the apoptosis effector gene BAX. In contrast, such variants were rare after genotoxic chemotherapy. BAX variants arose within either leukemic or preleukemic compartments, with multiple mutations observed in some patients. In vitro, AML cells with mutated BAX were competitively selected during prolonged exposure to BCL-2 antagonists. In model systems, AML cells rendered deficient for BAX, but not its close relative BAK, displayed resistance to BCL-2 targeting, whereas sensitivity to conventional chemotherapy was variable. Acquired mutations in BAX during venetoclax-based therapy represent a novel mechanism of resistance to BH3-mimetics and a potential barrier to the long-term efficacy of drugs targeting BCL-2 in AML.

Background CGM097 inhibits the p53-HDM2 interaction leading to downstream p53 activation. Preclinical in vivo studies support clinical exploration while providing preliminary evidence for dosing regimens. This first-in-human phase I study aimed at assessing the safety, MTD, PK/PD and preliminary antitumor activity of CGM097 in advanced solid tumour patients (NCT01760525). Methods Fifty-one patients received oral treatment with CGM097 10–400 mg 3qw (n = 31) or 300–700 mg 3qw 2 weeks on/1 week off (n = 20). Choice of dose regimen was guided by PD biomarkers, and quantitative models describing the effect of CGM097 on circulating platelet and PD kinetics. Results No dose-limiting toxicities were reported in any regimens. The most common treatment-related grade 3/4 AEs were haematologic events. PK/PD models well described the time course of platelet and serum GDF-15 changes, providing a tool to predict response to CGM097 for dose-limiting thrombocytopenia and GDF-15 biomarker. The disease control rate was 39%, including one partial response and 19 patients in stable disease. Twenty patients had a cumulative treatment duration of >16 weeks, with eight patients on treatment for >32 weeks. The MTD was not determined. Conclusions Despite delayed-onset thrombocytopenia frequently observed, the tolerability of CGM097 appears manageable. This study provided insights on dosing optimisation for next-generation HDM2 inhibitors. Translational relevance Haematologic toxicity with delayed thrombocytopenia is a well-known on-target effect of HDM2 inhibitors. Here we have developed a PK/PD guided approach to optimise the dose and schedule of CGM097, a novel HDM2 inhibitor, using exposure, platelets and GDF-15, a known p53 downstream target to predict patients at higher risk to develop thrombocytopenia. While CGM097 had shown limited activity, with disease control rate of 39% and only one patient in partial response, the preliminary data from the first-in-human escalation study together with the PK/PD modeling provide important insights on how to optimize dosing of next generation HDM2 inhibitors to mitigate hematologic toxicity.

p53 is a transcription factor that plays a central role in guarding the genomic stability of cells through cell-cycle arrest or induction of apoptosis. However, the effects of p53 in antitumor immunity are poorly understood. To investigate the role of p53 in controlling tumor-immune cell cross-talk, we studied murine syngeneic models treated with HDM201, a potent and selective second-generation MDM2 inhibitor. In response to HDM201 treatment, the percentage of dendritic cells increased, including the CD103+ antigen cross-presenting subset. Furthermore, HDM201 increased the percentage of Tbet+Eomes+ CD8+ T cells and the CD8+/Treg ratio within the tumor. These immunophenotypic changes were eliminated with the knockout of p53 in tumor cells. Enhanced expression of CD80 on tumor cells was observed in vitro and in vivo, which coincided with T-cell–mediated tumor cell killing. Combining HDM201 with PD-1 or PD-L1 blockade increased the number of complete tumor regressions. Responding mice developed durable, antigen-specific memory T cells and rejected subsequent tumor implantation. Importantly, antitumor activity of HDM201 in combination with PD-1/PD-L1 blockade was abrogated in p53-mutated and knockout syngeneic tumor models, indicating the effect of HDM201 on the tumor is required for triggering antitumor immunity. Taken together, these results demonstrate that MDM2 inhibition triggers adaptive immunity, which is further enhanced by blockade of PD-1/PD-L1 pathway, thereby providing a rationale for combining MDM2 inhibitors and checkpoint blocking antibodies in patients with wild-type p53 tumors. Significance: This study provides a mechanistic rationale for combining checkpoint blockade immunotherapy with MDM2 inhibitors in patients with wild-type p53 tumors.

Introduction: Uveal melanoma (UM) is a rare and malignant intraocular tumour with a dismal prognosis. Despite a good control of the primary tumour by radiation or surgery, up to 50% of patients subsequently develop metastasis for which no efficient treatment is yet available.Methodology: To identify therapeutic opportunities, we performed an in vitro screen of 30 combinations of different inhibitors of pathways that are dysregulated in UM. Effects of drug combinations on viability, cell cycle and apoptosis were assessed in eight UM cell lines. The best synergistic combinations were further evaluated in six UM patient-derived xenografts (PDXs).Results: We demonstrated that the Bcl-2/X-L/W inhibitor (ABT263) sensitised the UM cell lines to other inhibitors, mainly to mammalian target of rapamycin (mTOR), mitogen-activated protein kinase kinase (MEK) and murine double minute 2 (MDM2) inhibitors. mTOR (RAD001) and MEK1/2 (trametinib) inhibitors were efficient as single agents, but their combinations with ABT263 displayed no synergism in UM PDXs. In contrast, the combination of ABT263 with MDM2 inhibitor (HDM201) showed a trend for a synergistic effect.Conclusion: We showed that inhibition of Bcl-2/X-L/W sensitised the UM cell lines to other treatments encouraging investigation of the underlying mechanisms. Furthermore, our findings highlighted Bcl-2/X-L/W and MDM2 co-inhibition as a promising strategy in UM. (C) 2019 The Author(s). Published by Elsevier Ltd.

BackgroundResistance to endocrine therapy is a major clinical challenge in the management of oestrogen receptor (ER)-positive breast cancer. In this setting, p53 is frequently wildtype and its activity may be suppressed via upregulation of its key regulator MDM2. This underlies our rationale to evaluate MDM2 inhibition as a therapeutic strategy in treatment-resistant ER-positive breast cancer.MethodsWe used the MDM2 inhibitor NVP-CGM097 to treat in vitro and in vivo models alone and in combination with fulvestrant or palbociclib. We perform cell viability, cell cycle, apoptosis and senescence assays to evaluate anti-tumour effects in p53 wildtype and p53 mutant ER-positive cell lines (MCF-7, ZR75-1, T-47D) and MCF-7 lines resistant to endocrine therapy and to CDK4/6 inhibition. We further assess the drug effects in patient-derived xenograft (PDX) models of endocrine-sensitive and endocrine-resistant ER-positive breast cancer.ResultsWe demonstrate that MDM2 inhibition results in cell cycle arrest and increased apoptosis in p53-wildtype in vitro and in vivo breast cancer models, leading to potent anti-tumour activity. We find that endocrine therapy or CDK4/6 inhibition synergises with MDM2 inhibition but does not further enhance apoptosis. Instead, combination treatments result in profound regulation of cell cycle-related transcriptional programmes, with synergy achieved through increased antagonism of cell cycle progression. Combination therapy pushes cell lines resistant to fulvestrant or palbociclib to become senescent and significantly reduces tumour growth in a fulvestrant-resistant patient-derived xenograft model.ConclusionsWe conclude that MDM2 inhibitors in combination with ER degraders or CDK4/6 inhibitors represent a rational strategy for treating advanced, endocrine-resistant ER-positive breast cancer, operating through synergistic activation of cell cycle co-regulatory programmes.

BackgroundResistance to endocrine therapy is a major clinical challenge in the management of estrogen receptor (ER)-positive breast cancer. In this setting p53 is frequently wildtype and its activity may be suppressed via upregulation of its key regulator MDM2. This underlies our rationale to evaluate MDM2 inhibition as a therapeutic strategy in treatment resistant ER-positive breast cancer.MethodsWe used the MDM2 inhibitor NVP-CGM097 to treatin vitroandin vivomodels alone and in combination with fulvestrant or palbociclib. We perform cell viability, cell cycle, apoptosis and senescence assays to evaluate antitumor effects in p53 wildtype and p53 mutant ER positive cell lines (MCF-7, ZR75-1, T-47D) and MCF-7 lines resistant to endocrine therapy and to CDK4/6 inhibition. We further assess the drug effects in patient-derived xenograft (PDX) models of endocrine-sensitive and -resistant ER positive breast cancer.ResultsWe demonstrate that MDM2 inhibition results in cell cycle arrest and increased apoptosis in p53-wildtypein vitroandin vivobreast cancer models, leading to potent anti-tumour activity. We find that endocrine therapy or CDK4/6 inhibition synergises with MDM2 inhibition but does not further enhance apoptosis. Instead, combination treatments result in profound regulation of cell cycle-related transcriptional programmes, with synergy achieved through increased antagonism of cell cycle progression. Combination therapy pushes cell lines resistant to fulvestrant or palbociclib to become senescent and significantly reduces tumour growth in a fulvestrant resistant patient derived xenograft model.ConclusionsWe conclude that MDM2 inhibitors in combination with ER degraders or CDK4/6 inhibitors represent a rational strategy for treating advanced, endocrine resistant ER-positive breast cancer, operating through synergistic activation of cell cycle co-regulatory programs.

Activation of p53 by inhibitors of the p53–MDM2 interaction is being pursued as a therapeutic strategy in p53 wild-type cancers. Here, we report distinct mechanisms by which the novel, potent, and selective inhibitor of the p53–MDM2 interaction HDM201 elicits therapeutic efficacy when applied at various doses and schedules. Continuous exposure of HDM201 led to induction of p21 and delayed accumulation of apoptotic cells. By comparison, high-dose pulses of HDM201 were associated with marked induction of PUMA and a rapid onset of apoptosis. shRNA screens identified PUMA as a mediator of the p53 response specifically in the pulsed regimen. Consistent with this, the single high-dose HDM201 regimen resulted in rapid and marked induction of PUMA expression and apoptosis together with downregulation of Bcl-xL in vivo. Knockdown of Bcl-xL was identified as the top sensitizer to HDM201 in vitro, and Bcl-xL was enriched in relapsing tumors from mice treated with intermittent high doses of HDM201. These findings define a regimen-dependent mechanism by which disruption of MDM2–p53 elicits therapeutic efficacy when given with infrequent dosing. In an ongoing HDM201 trial, the observed exposure–response relationship indicates that the molecular mechanism elicited by pulse dosing is likely reproducible in patients. These data support the clinical comparison of daily and intermittent regimens of p53–MDM2 inhibitors. Significance: Pulsed high doses versus sustained low doses of the p53-MDM2 inhibitor HDM201 elicit a proapoptotic response from wild-type p53 cancer cells, offering guidance to current clinical trials with this and other drugs that exploit the activity of p53. Cancer Res; 78(21); 6257–67. ©2018 AACR.

Improving outcomes in acute myeloid leukemia (AML) remains a major clinical challenge. Overexpression of pro-survival BCL-2 family members rendering transformed cells resistant to cytotoxic drugs is a common theme in cancer. Targeting BCL-2 with the BH3-mimetic venetoclax is active in AML when combined with low-dose chemotherapy or hypomethylating agents. We now report the pre-clinical anti-leukemic efficacy of a novel BCL-2 inhibitor S55746, which demonstrates synergistic pro-apoptotic activity in combination with the MCL1 inhibitor S63845. Activity of the combination was caspase and BAX/BAK dependent, superior to combination with standard cytotoxic AML drugs and active against a broad spectrum of poor risk genotypes, including primary samples from patients with chemoresistant AML. Co-targeting BCL-2 and MCL1 was more effective against leukemic, compared to normal hematopoietic progenitors, suggesting a therapeutic window of activity. Finally, S55746 combined with S63845 prolonged survival in xenograft models of AML and suppressed patient-derived leukemia but not normal hematopoietic cells in bone marrow of engrafted mice. In conclusion, a dual BH3-mimetic approach is feasible, highly synergistic, and active in diverse models of human AML. This approach has strong clinical potential to rapidly suppress leukemia, with reduced toxicity to normal hematopoietic precursors compared to chemotherapy.

Activating FLT3 internal tandem duplication (FLT3-ITD) mutations, present in ~30% of AML patients, are associated with poor prognosis. Given that efficacy of FLT3 inhibitors used as monotherapy is limited due to development of secondary FLT3 mutations or activation of alternative survival pathways, new combinatorial strategies are needed to improve outcome in FLT3-ITD AML patients. Constitutive activation of mutated FLT3 often leads to elevated expression of MCL-1, an anti-apoptotic member of the BCL-2 family. Upregulation of MCL-1 underlies the resistance of AML to initially successful targeted therapies, including Bcl-2 inhibition with venetoclax, placing MCL-1 as an attractive target for combinatorial therapies. We have recently shown for the first time that a novel MCL-1 inhibitor S63845 elicited synergistic activity with FLT3 inhibitors AC220, sorafenib and with a multi-kinase inhibitor midostaurin at nanomolar doses in pre-clinical in vitro models of FLT3-ITD AML, including cells resistant to venetoclax (Skwarska A, et al. Cancer Res 2019;79 Suppl 13, Abstract#342). Here, we further explored the therapeutic potential and mechanisms-of-action of dual targeting of FLT3-ITD and MCL-1 in vitro and in vivo. S63845 and midostaurin co-treatment significantly increased apoptosis in FLT3-ITD cells with caspase-3 activation and PARP cleavage within 6 hours of treatment. Analysis of drug combinations using Bliss independence model revealed strong synergistic effect of S63845/midostaurin combination in murine isogenic Ba/F3-FLT3-ITD, Ba/F3-FLT3-ITD-D835Y and Ba/F3-FLT3-ITD-F691L dual mutants with minimal effect in Ba/F3-wt FLT3 cells, suggesting that inhibition of FLT3-ITD could mechanistically contribute to the synergy between midostaurin and S63845. Midostaurin monotherapy caused de-phosphorylation of FLT3-ITD and its downstream targets STAT5, AKT and MAPK, known to upregulate MCL-1 expression and stability (Fig 1A). Consequently, midostaurin significantly reduced Mcl-1 T163 phosphorylation and protein levels exclusively in FLT3-ITD cells. Midostaurin also decreased inhibitory phosphorylation of GSK3, suggesting the involvement of ubiquitin/proteasome axis in MCL-1 degradation. Additionally, pre-treatment with pan-caspase inhibitor zVAD-fmk partially reversed MCL-1 downregulation, implying contribution of caspase-mediated degradation to overall decrease of MCL-1 after midostaurin treatment. While midostaurin alone enhanced degradation of MCL-1, it did not fully deplete the pool of MCL-1. Surprisingly, midostaurin also induced the loss of proapoptotic NOXA, an endogenous inhibitor of MCL-1, which can potentially increase a fraction of free MCL-1. These results provide a strong rationale for targeting residual MCL-1 with selective MCL-1 inhibitor S63845 with the goal to facilitate deeper therapeutic responses in FLT3-ITD AML. Mechanistically, midostaurin increased expression of apoptosis activator BIM and blocked BIM phosphorylation required for its inhibitory sequestration by MCL-1. BIM shRNA knockdown cells were less sensitive to midostaurin/S63845 combination. Similarly, CRISPR/Cas9-mediated knock-out of BAK, a BIM-activated executor of apoptosis, resulted in reduced efficacy of tested combination. These results indicate that activation of BIM/BAX axis has a functional role in the response of AML cells to dual FLT3-ITD and MCL-1 inhibition (Fig 1B). To validate the efficacy of combination in vivo, we used xenotransplantation model of MOLM-14 cells expressing luciferase. Mice were treated for 3 weeks with low doses of midostaurin (25 mg/kg/5 days per week) and with MIK665, structurally optimized version of S63845 Mcl-1 inhibitor with improved pharmacokinetics in mice (Halilovic E, et al. Cancer Res 2019;79 Suppl 13, Abstract#4477). Administration of MIK665 at 25 mg/kg or 35 mg/kg IV 2 days per week in combination with oral midostaurin resulted in a marked delay in the progression of MOLM-14 cell line-derived xenograft and significantly reduced leukemia tumor burden (Fig 1C). The long-term effect of combination on mice survival is currently being tested and will be reported. Altogether, our results indicate that efficacy of FLT3-ITD inhibitors can be enhanced through combination with low doses BH3 mimetics targeting MCL-1 and provide a rationale for the clinical evaluation of such combinations in FLT3 mutant AML patients. Figure 1 Figure 1. Disclosures Skwarska: Halilovich E, Wang Y, Morris E, Konopleva M, Skwarska A.: Patents & Royalties: Combination of a MCL-1 inhibitor and midostaurin, uses and pharmaceutical composition thereof.. Halilovic: Novartis: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Mistry: Novartis: Current Employment, Current holder of individual stocks in a privately-held company. Derréal: Servier: Current Employment. Banquet: Servier: Current Employment. Daver: Genentech: Consultancy, Research Funding; Trillium: Consultancy, Research Funding; Novimmune: Research Funding; Glycomimetics: Research Funding; Trovagene: Consultancy, Research Funding; FATE Therapeutics: Research Funding; Astellas: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Hanmi: Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Bristol Myers Squibb: Consultancy, Research Funding; Daiichi Sankyo: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; ImmunoGen: Consultancy, Research Funding; Sevier: Consultancy, Research Funding; Novartis: Consultancy; Jazz Pharmaceuticals: Consultancy, Other: Data Monitoring Committee member; Dava Oncology (Arog): Consultancy; Celgene: Consultancy; Syndax: Consultancy; Shattuck Labs: Consultancy; Agios: Consultancy; Kite Pharmaceuticals: Consultancy; SOBI: Consultancy; STAR Therapeutics: Consultancy; Karyopharm: Research Funding; Newave: Research Funding. Andreeff: Medicxi: Consultancy; ONO Pharmaceuticals: Research Funding; AstraZeneca: Research Funding; Reata, Aptose, Eutropics, SentiBio; Chimerix, Oncolyze: Current holder of individual stocks in a privately-held company; Karyopharm: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Glycomimetics: Consultancy; Novartis, Cancer UK; Leukemia & Lymphoma Society (LLS), German Research Council; NCI-RDCRN (Rare Disease Clin Network), CLL Foundation; Novartis: Membership on an entity's Board of Directors or advisory committees; Syndax: Consultancy; Aptose: Consultancy; Oxford Biomedica UK: Research Funding; Amgen: Research Funding; Breast Cancer Research Foundation: Research Funding; Senti-Bio: Consultancy. Wei: Novartis, Astellas, Pfizer, MacroGenics, AbbVie, Genentech, Servier, Celgene, Amgen, AstraZeneca, Janssen: Honoraria; Novartis, Celgene, AbbVie, Servier, AstraZeneca, and Amgen: Research Funding; Walter and Eliza Hall Institute: Ended employment in the past 24 months. Konopleva: Cellectis: Other: grant support; Stemline Therapeutics: Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; AstraZeneca: Other: grant support, Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support; Ascentage: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; Sanofi: Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; KisoJi: Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Calithera: Other: grant support, Research Funding; Rafael Pharmaceuticals: Other: grant support, Research Funding; Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding.

Background: Treatment options for patients (pts) with relapsed/refractory (r/r) AML and HR-MDS who cannot tolerate standard therapy are limited, and innovative combination approaches are needed. Dysregulation of the tumor protein 53 [p53, (TP53 gene)], Murine Double Minute-2 (MDM2) interaction leads to uncontrolled cell proliferation and tumor growth (Chene 2003). Siremadlin is an orally administered small molecule inhibitor of the p53-MDM2 interaction, which has a well-characterized safety profile and shows antitumor activity in pts with AML (Stein 2021). Combination of siremadlin with BCL-2 inhibitors (eg, venetoclax [VEN]) results in synergistic activity in p53 wild-type AML cell lines and leads to complete and durable antitumor responses in a variety of p53wt AML patient-derived xenograft models (Wang 2019). Thus, combined MDM2 and BCL-2 inhibition may result in improved outcomes for pts with hematologic malignancies. Here we report the preliminary results of a phase Ib, open-label study of siremadlin in combination with VEN for the treatment of pts with AML and HR- MDS (NCT03940352). Methods: Pts were adults with r/r AML after ≥1 but ≤3 prior therapies who were not suited for standard therapy, or pts with AML who were unfit for standard chemotherapy. HR-MDS pts (per Revised International Prognostic Scoring System) who have previously failed hypomethylating agent therapy were also eligible. AML pts with TP53-mutant tumors (determined as the presence of any mutations in exons 5,6,7, and 8 at minimum) were excluded. Pts with prior treatment with an MDM2 or MDM4 inhibitor in combination with a BCL-2 inhibitor were excluded. Siremadlin (20 or 30 mg) was administered daily from day 1-5 during each 28-day cycle in combination with VEN at a starting dose of 50 mg daily, followed by a gradual ramp-up period over 4 days to a target daily dose of 400 mg (dose level [DL] 1: siremadlin 20 mg + VEN and DL2: siremadlin 30 mg + VEN]. Pts continued study treatment until unacceptable toxicity, disease progression, or investigator/patient decision. The primary objective is to evaluate safety/tolerability; secondary objectives are to test preliminary efficacy (per Cheson 2003) and pharmacokinetics (PK). Results: As of data cutoff March 1, 2021, 18 total pts underwent treatment. The median age was 72.5 y (range, 29-84). Most pts had an Eastern Cooperative Oncology Group performance status of 0 (n=13, 72%). Of the 17 (94%) pts with AML, 3 pts had first-line and 14 pts had r/r AML. One (6%) pt had HR-MDS (DL1); efficacy data for this pt are not presented. Eleven pts were treated at DL1 and 7 at DL2. Treatment is ongoing for 2 pts (both DL2). The mean treatment duration was 3.8 mo (range, 0.9-10.3; DL1) and 1.8 mo (range, 0-3.8; DL2). Two pts (DL1) had ≥9 mo treatment duration. The most common grade ≥3 adverse events (AEs) suspected to be treatment-related were neutropenia (n=5, 28%) and thrombocytopenia (n=4, 22%); 11 pts (61.1%) experienced grade ≥3 serious AEs regardless of study-treatment; only febrile neutropenia was experienced by >20% of pts (n=8, 44%). One case of tumor lysis syndrome was reported. Notably, gastrointestinal grade ≥3 serious AEs were uncommon (diarrhea [n=2, 11%] and nausea [n=1, 6%]). Dose modification or interruption due to an AE occurred in 10 (56%) pts, mostly due to febrile neutropenia (n=4) and neutropenia (n=3), and discontinuation due to an AE occurred in 4 (22%) pts, mostly due to febrile neutropenia (n=2). Among the 11 pts in the dose-determining set, 2 experienced dose limiting toxicities (1 with anemia, bone marrow failure, and thrombocytopenia and 1 with febrile neutropenia). Two on-treatment deaths occurred; however, none were treatment-related. Among 10 pts with AML in DL1, 1 had complete remission (CR), 3 had CR with incomplete blood count recovery (CRi) and had 1 partial remission. Among 7 pts with AML in DL2, 3 pts had CRi (Table). One pt in DL2 currently has an ongoing CRi. PK exposure and parameters for siremadlin and VEN for both cohorts were comparable to historical single-agent data. No drug-drug interaction between siremadlin and VEN was observed. Conclusions: Siremadlin + VEN is well-tolerated in pts with AML and shows promising antileukemic activity in r/r AML pts. These results validate the MDM2-p53 interaction as a therapeutic target and provide support for further development of siremadlin + VEN in pts with AML or HR-MDS. Dose escalation is ongoing to determine the recommended dose for expansion. Figure 1 Figure 1. Disclosures Wei: Astellas: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Genentech: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Membership on an entity's Board of Directors or advisory committees; Macrogenics: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Breccia: Pfizer: Honoraria; Novartis: Honoraria; Incyte: Honoraria; Abbvie: Honoraria; Bristol Myers Squibb/Celgene: Honoraria. Cedena Romero: Janssen: Honoraria; BMS: Honoraria. Ciceri: IRCCS Ospedale San Raffaele: Current Employment. Erba: AbbVie Inc; Agios Pharmaceuticals Inc; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Incyte Corporation; Jazz Pharmaceuticals Inc; Novartis: Speakers Bureau; AbbVie Inc: Other: Independent review committee; AbbVie Inc; Agios Pharmaceuticals Inc; Astellas; Bristol Myers Squibb; Celgene, a Bristol Myers Squibb company; Daiichi Sankyo Inc; Genentech, a member of the Roche Group; GlycoMimetics Inc; Incyte Corporation; Jazz Pharmaceuticals Inc; Kura Oncology; Nov: Other: Advisory Committee; AbbVie Inc; Agios Pharmaceuticals Inc; ALX Oncology; Amgen Inc; Daiichi Sankyo Inc; FORMA Therapeutics; Forty Seven Inc; Gilead Sciences Inc; GlycoMimetics Inc; ImmunoGen Inc; Jazz Pharmaceuticals Inc; MacroGenics Inc; Novartis; PTC Therapeutics: Research Funding. Gaur: Novartis: Current Employment. Sechaud: Novartis: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Halilovic: Novartis: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. Kuenzle: Novartis: Current Employment. Fabre: Novartis: Current Employment, Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company. OffLabel Disclosure: Siremadlin is a small molecule inhibitor of the p53-MDM2 interaction under investigation for the treatment of patients with myeloid malignancies.

Additional file 2: Fig. S1 MDM2 inhibition activates p53 and reduces tumour proliferation in vitro and in vivo. A. Full gel and blot scans for the Western blots shown in Fig. 1b. Total protein was visualised using BioRad stain-free imaging technology according to the manufacturer’s instructions. B. Analysis of cell cycle phase using flow cytometry to quantify propidium iodide staining of genomic DNA shows significant alterations to cell cycle phase distribution in p53wt models consistent with arrest in both G1 and G2 after incubation for 48 hours with 1μM NVP-CGM097. Red = G1 (bottom), blue = S (middle), green = G2/M (top). Statistical significance from χ2 test using the vehicle treated profile as the expected value is indicated. C. NVP-CGM097 (50mg/kg daily, red) significantly inhibited tumour volumes compared to vehicle (2% DMSO daily, green) at endpoint. Final tumour volumes were compared using two-tailed T test to determine significance. D. Representative images of Ki-67 quantification of endpoint tumours in Qupath software showing the classification of different tissue compartments: tumour (red and blue), stroma (green), and necrosis (black); and detection of Ki-67 negative and positive tumour cells. A single classifier was applied to all tumour sections. Fig. S2. NVP-CGM097 treatment causes gene expression changes in cell cycle and p53 pathways in vitro. A. Multidimensional scaling (MDS) plot showing the level of sample similarity between MCF-7 cell lines treated with vehicle, NVP-CGM097, fulvestrant and combination therapy (NVP-CGM097 plus fulvestrant). B. Venn diagram showing the overlap between differentially expressed genes (adjusted p-value < 0.05- and 2-fold change) induced by treatment in MCF-7 cell lines. C. KEGG pathway analysis using RNA-Seq transcriptomic data shows a significant negative enrichment of Cell Cycle regulation in MCF-7 cell lines following 48 hours of treatment with 1μM NVP-CGM097 and positive enrichment of p53 Signalling Pathway. D. KEGG enrichment analysis showing p53 Signalling Pathway activation in MCF-7 cell lines following treatment with NVP-CGM097. Fig. S3 Enrichment analysis of significant differentially expressed genes against curated gene sets. Fig. S4 MDM2 inhibition induces changes in gene and protein expression associated with the cell cycle in endocrine resistant models in vitro and in vivo. A. Incucyte analysis of cell numbers of parental MCF-7 cells (blue) and MCF-7 FasR cells (red) over time after treatment with 100 nM fulvestrant. Vehicle treated parental MCF-7 cell growth (grey) is shown for comparison. B. Full gel images for the Western blots shown in Fig. 4c. C. Quantification of ER staining in the nucleus and cytoplasm of three independent replicates per arm from PDX model Gar15-13 following 10 days of treatment with vehicle (2% DMSO daily, green), NVP-CGM097 (50mg/kg daily, red), fulvestrant (5 mg weekly, blue) or the combination of fulvestrant and NVP-CGM097 (purple). Tumours treated with fulvestrant alone or in combination had significantly reduced ER staining in both cellular compartments compared to tumours not treated with fulvestrant. Tumour cell identification and ER quantification were performed in QuPath software. D. Heat map of significant downregulated genes from the E2F Targets and G2/M Checkpoint gene sets in the Gar1513 PDX model. E. Normalised log2 expression levels of significant p53 target genes in in the Gar1513 PDX model induced by NVP-CGM097 (red), fulvestrant (blue) and the combination of NVP-CGM097 and fulvestrant (purple), averaged by condition, associated with cell cycle, apoptosis and senescence. Fig. S5. MDM2 inhibition in combination with CDK4/6 inhibition synergistically downregulates cell cycle markers in vitro. A. MDS plot of MCF-7 cell lines treated for 48 h with Vehicle (0.01% DMSO), 1 μM NVP-CGM097, 500 nM palbociclib, or the combination of NVP-CGM097 and palbociclib. B. Venn diagram showing the overlap between differentially expressed genes (adjusted p-value

Intrinsic resistance of unknown mechanism impedes the clinical utility of inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) in malignancies other than breast cancer. Here we used melanoma patient-derived xenografts (PDXs) to study the mechanisms for CDK4/6i resistance in pre-clinical settings. We observed that melanoma PDXs resistant to CDK4/6i frequently displayed activation of phosphatidyl inositol 3 kinase (PI3K)-AKT pathway, and inhibition of this pathway improved CDK4/6i response in a p21-dependent manner. We showed that a target of p21, CDK2, was necessary for proliferation in CDK4/6i-treated cells. Upon treatment with CDK4/6i, melanoma cells up-regulated cyclin D1, which sequestered p21 and another cyclin-dependent kinase inhibitor, p27, leaving a shortage of p21 and p27 available to bind and inhibit CDK2. Therefore, we tested whether induction of p21 in resistant melanoma cells would render them responsive to CDK4/6i. Because p21 is transcriptionally driven by p53, we coadministrated CDK4/6i with a murine double minute (MDM2) antagonist to stabilize p53, allowing p21 accumulation. This resulted in improved anti-tumor activity in PDXs and in murine melanoma. Furthermore, co-administration of CDK4/6 and MDM2 antagonists with standard of care therapy caused tumor regression. Notably, the molecular features associated with response to CDK4/6 and MDM2 inhibitors in PDXs were recapitulated by an ex vivo organotypic slice culture assay, which could potentially be adopted in clinic for patient stratification. Our findings provide a rationale for co-targeting CDK4/6 and MDM2 in melanoma.

This work was supported by the Spanish ISCIII-FIS and FEDER Funds (PI 15/00067 and PI 15/02156) and the Regional Health Council of Castilla y León (GRS 1604/A/17). EMA was supported by a grant from the Regional Education Council of Castilla y León co-financed by the European Social Fund.

Like classical chemotherapy regimens used to treat cancer, targeted therapies will also rely upon polypharmacology, but tools are still lacking to predict which combinations of molecularly targeted drugs may be most efficacious. In this study, we used image-based proliferation and apoptosis assays in colorectal cancer cell lines to systematically investigate the efficacy of combinations of two to six drugs that target critical oncogenic pathways. Drug pairs targeting key signaling pathways resulted in synergies across a broad spectrum of genetic backgrounds but often yielded only cytostatic responses. Enhanced cytotoxicity was observed when additional processes including apoptosis and cell cycle were targeted as part of the combination. In some cases, where cell lines were resistant to paired and tripled drugs, increased expression of antiapoptotic proteins was observed, requiring a fourth-order combination to induce cytotoxicity. Our results illustrate how high-order drug combinations are needed to kill drug-resistant cancer cells, and they also show how systematic drug combination screening together with a molecular understanding of drug responses may help define optimal cocktails to overcome aggressive cancers. Cancer Res; 76(23); 6950–63. ©2016 AACR.

Background/Aims: The tumor suppressor p53 is depleted in many tumor cells by the E3 ubiquitin ligase mouse double minute 2 homolog (MDM2) through MDM2/p53 interaction. A novel target for inhibiting p53 degradation and for causing reexpression of p53wild type is inhibition of MDM2. The small molecule NVP-CGM097 is a novel MDM2 inhibitor. We investigated MDM2 inhibition as a target in neuroendocrine tumor cells in vitro. Methods: Human neuroendocrine tumor cell lines from the pancreas (BON1), lung (NCI-H727), and midgut (GOT1) were incubated with the MDM2 inhibitor NVP-CGM097 (Novartis) at concentrations from 4 to 2,500 nM. Results: While p53wild type GOT1 cells were sensitive to NVP-CGM097, p53mutated BON1 and p53mutated NCI-H727 cells were resistant to NVP-CGM097. Incubation of GOT1 cells with NVP-CGM097 at 100, 500, and 2,500 nM for 96 h caused a significant decline in cell viability to 84.9 ± 9.2% (p < 0.05), 77.4 ± 6.6% (p < 0.01), and 47.7 ± 9.2% (p < 0.01). In a Western blot analysis of GOT1 cells, NVP-CGM097 caused a dose-dependent increase in the expression of p53 and p21 tumor suppressor proteins and a decrease in phospho-Rb and E2F1. Experiments of co-incubation of NVP-CGM097 with 5-fluorouracil, temozolomide, or everolimus each showed additive antiproliferative effects in GOT1 cells. NVP-CGM097 and 5-fluorouracil increased p53 and p21 expression in an additive manner. Conclusions: MDM2 inhibition seems a promising novel therapeutic target in neuroendocrine tumors harboring p53wild type. Further investigations should examine the potential role of MDM2 inhibitors in neuroendocrine tumor treatment.

// Guillaume Carita 1,* , Estelle Frisch-Dit-Leitz 2,* , Ahmed Dahmani 1 , Chloe Raymondie 1 , Nathalie Cassoux 3 , Sophie Piperno-Neumann 4 , Fariba Nemati 1 , Cecile Laurent 5 , Leanne De Koning 6 , Ensar Halilovic 7 , Sebastien Jeay 7 , Andrew Wylie 7 , Caroline Emery 7 , Sergio Roman-Roman 2 , Marie Schoumacher 2,* and Didier Decaudin 1,4,* 1 Laboratory of preclinical investigation, Department of Translational Research, PSL University, Institut Curie, Paris, France 2 Department of Translational Research, Institut Curie, PSL University, Paris, France 3 Department of Ophthalmological Oncology, Institut Curie, Paris, France 4 Department of Medical Oncology, Institut Curie, Paris, France 5 Residual Tumor & Response to Treatment Lab, Department of Translational Research, Institut Curie, PSL University, Paris, Paris, France 6 RPPA Platform, Department of Translational Research, Institut Curie, PSL University, Paris, France 7 Novartis Institutes for Biomedical Research, Cambridge, MA USA * These authors have contributed equally to this work Correspondence to: Didier Decaudin, email: // Keywords : xenograft models, cellular response to anticancer drugs, uveal melanoma, AEB071 combinations, synergy Received : April 04, 2016 Accepted : May 10, 2016 Published : May 22, 2016 Abstract Uveal melanoma (UM) is the most common cancer of the eye in adults. Many UM patients develop metastases for which no curative treatment has been identified. Novel therapeutic approaches are therefore urgently needed. UM is characterized by mutations in the genes GNAQ and GNA11 which activate the PKC pathway, leading to the use of PKC inhibitors as a rational strategy to treat UM tumors. Encouraging clinical activity has been noted in UM patients treated with PKC inhibitors. However, it is likely that curative treatment regimens will require a combination of targeted therapeutic agents. Employing a large panel of UM patient-derived xenograft models (PDXs), several PKC inhibitor-based combinations were tested in vivo using the PKC inhibitor AEB071. The most promising approaches were further investigated in vitro using our unique panel of UM cell lines. When combined with AEB071, the two agents CGM097 (p53-MDM2 inhibitor) and RAD001 (mTORC1 inhibitor) demonstrated greater activity than single agents, with tumor regression observed in several UM PDXs. Follow-up studies in UM cell lines on these two drug associations confirmed their combination activity and ability to induce cell death. While no effective treatment currently exists for metastatic uveal melanoma, we have discovered using our unique panel of preclinical models that combinations between PKC/mTOR inhibitors and PKC/p53-MDM2 inhibitors are two novel and very effective therapeutic approaches for this disease. Together, our study reveals that combining PKC and p53-MDM2 or mTORC1 inhibitors may provide significant clinical benefit for UM patients.

Background: Resistance to endocrine therapy is a major clinical challenge in the management of estrogen receptor (ER)-positive breast cancer. In this setting p53 is frequently wildtype and its activity may be suppressed via upregulation of its key regulator MDM2. This underlies our rationale to evaluate MDM2 inhibition as a therapeutic strategy in treatment resistant ER-positive breast cancer. Methods: We used the MDM2 inhibitor NVP-CGM097 to treat in vitro and in vivo models alone and in combination with fulvestrant or palbociclib. We perform cell viability, cell cycle, apoptosis and senescence assays to evaluate antitumor effects in p53 wildtype and p53 mutant ER positive cell lines (MCF-7, ZR75-1, T-47D) and MCF-7 lines resistant to endocrine therapy and to CDK4/6 inhibition. We further assess the drug effects in patient-derived xenograft (PDX) models of endocrine-sensitive and -resistant ER positive breast cancer. Results: We demonstrate that MDM2 inhibition results in cell cycle arrest and increased apoptosis in p53-wildtype in vitro and in vivo breast cancer models, leading to potent anti-tumour activity. We find that endocrine therapy or CDK4/6 inhibition synergises with MDM2 inhibition but does not further enhance apoptosis. Instead, combination treatments result in profound regulation of cell cycle-related transcriptional programmes, with synergy achieved through increased antagonism of cell cycle progression. Combination therapy pushes cell lines resistant to fulvestrant or palbociclib to become senescent and significantly reduces tumour growth in a fulvestrant resistant patient derived xenograft model. Conclusions: We conclude that MDM2 inhibitors in combination with ER degraders or CDK4/6 inhibitors represent a rational strategy for treating advanced, endocrine resistant ER-positive breast cancer, operating through synergistic activation of cell cycle co-regulatory programs. Citation Format: Neil Portman, Heloisa Milioli, Sarah Alexandrou, Rhiannon Coulson, Aliza Yong, Kristine Fernandez, KeeMing Chia, Ensar Halilovic, Davendra Segara, Andrew Parker, Sue Haupt, Ygal Haupt, Wayne Tilley, Alex Swarbrick, Liz Caldon, Elgene Lim. Mdm2 inhibition synergises with endocrine therapy or cdk4/6 inhibition for the treatment of estrogen receptor-positive breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-17.

The tumor suppressor p53 is a key regulator of apoptosis and functions upstream in the apoptotic cascade by both indirectly and directly regulating Bcl-2 family proteins. In cells expressing wild-type (WT) p53, the HDM2 protein binds to p53 and blocks its activity. Inhibition of HDM2:p53 interaction activates p53 and causes apoptosis or cell-cycle arrest. Here, we investigated the ability of the novel HDM2 inhibitor CGM097 to potently and selectively kill WT p53-expressing AML cells. The antileukemic effects of CGM097 were studied using cell-based proliferation assays (human AML cell lines, primary AML patient cells, and normal bone marrow samples), apoptosis, and cell-cycle assays, ELISA, immunoblotting, and an AML patient–derived in vivo mouse model. CGM097 potently and selectively inhibited the proliferation of human AML cell lines and the majority of primary AML cells expressing WT p53, but not mutant p53, in a target-specific manner. Several patient samples that harbored mutant p53 were comparatively unresponsive to CGM097. Synergy was observed when CGM097 was combined with FLT3 inhibition against oncogenic FLT3-expressing cells cultured both in the absence as well as the presence of cytoprotective stromal-secreted cytokines, as well as when combined with MEK inhibition in cells with activated MAPK signaling. Finally, CGM097 was effective in reducing leukemia burden in vivo. These data suggest that CGM097 is a promising treatment for AML characterized as harboring WT p53 as a single agent, as well as in combination with other therapies targeting oncogene-activated pathways that drive AML. Mol Cancer Ther; 14(10); 2249–59. ©2015 AACR.