Selective Inhibitor Of Cyclin-dependent Kinases Research Articles

Cycling Toward Progress: Ribociclib, a CDK 4/6 Inhibitor for Breast Cancer.

Ribociclib is an orally active, highly selective inhibitor of cyclin-dependent kinase (CDK) 4 and 6. It is the second CDK 4/6 inhibitor approved for hormone receptor-positive breast cancer. The addition of ribociclib to an aromatase inhibitor has resulted in marked improvements in progression-free survival for patients with metastatic breast cancer. Clin Cancer Res; 24(13); 2981-3. ©2018 AACRSee related article by Shah et al., p. 2999.

Cyclin-dependent kinase 7 (CDK7)-mediated phosphorylation of the CDK9 activation loop promotes P-TEFb assembly with Tat and proviral HIV reactivation

The HIV trans-activator Tat recruits the host transcription elongation factor P-TEFb to stimulate proviral transcription. Phosphorylation of Thr-186 on the activation loop (T-loop) of cyclin-dependent kinase 9 (CDK9) is essential for its kinase activity and assembly of CDK9 and cyclin T1 (CycT1) to form functional P-TEFb. Phosphorylation of a second highly conserved T-loop site, Ser-175, alters the competitive binding of Tat and the host recruitment factor bromodomain containing 4 (BRD4) to P-TEFb. Here, we investigated the intracellular mechanisms that regulate these key phosphorylation events required for HIV transcription. Molecular dynamics simulations revealed that the CDK9/CycT1 interface is stabilized by intramolecular hydrogen bonding of pThr-186 by an arginine triad and Glu-96 of CycT1. Arginine triad substitutions that disrupted CDK9/CycT1 assembly accumulated Thr-186-dephosphorylated CDK9 associated with the cytoplasmic Hsp90/Cdc37 chaperone. The Hsp90/Cdc37/CDK9 complex was also present in resting T cells, which lack CycT1. Hsp90 inhibition in primary T cells blocked P-TEFb assembly, disrupted Thr-186 phosphorylation, and suppressed proviral reactivation. The selective CDK7 inhibitor THZ1 blocked CDK9 phosphorylation at Ser-175, and in vitro kinase assays confirmed that CDK7 activity is principally responsible for Ser-175 phosphorylation. Mutation of Ser-175 to Lys had no effect on CDK9 kinase activity or P-TEFb assembly but strongly suppressed both HIV expression and BRD4 binding. We conclude that the transfer of CDK9 from the Hsp90/Cdc37 complex induced by Thr-186 phosphorylation is a key step in P-TEFb biogenesis. Furthermore, we demonstrate that CDK7-mediated Ser-175 phosphorylation is a downstream nuclear event essential for facilitating CDK9 T-loop interactions with Tat.

A phase 1, open-label, multicenter, non-randomized study to assess the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of AZD4573, a potent and selective CDK9 inhibitor, in subjects with relapsed or refractory hematological malignancies.

TPS7588Background: Cyclin-dependent kinase 9 (CDK9) belongs to the group of transcription-regulating CDKs and promotes transcription elongation through phosphorylation of RNA Polymerase II at serin...

Abstract P5-21-27: Efficacy and safety of ribociclib plus letrozole in US patients enrolled in the MONALEESA-2 study

Abstract Background: Endocrine-based therapy is the standard of care for patients with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer (ABC), in whom delaying disease progression is the primary goal. In the randomized Phase 3 MONALEESA-2 study (ClinicalTrials.gov identifier, NCT01958021), first-line ribociclib (a selective inhibitor of cyclin-dependent kinases 4 and 6) + letrozole significantly prolonged progression-free survival (PFS) compared with placebo + letrozole in postmenopausal women with HR+, HER2− ABC (hazard ratio, 0.556; 95% confidence interval [CI], 0.429–0.720) at the interim analysis cutoff date. Here, we present safety and efficacy data from US patients who were enrolled in the MONALEESA-2 study. Methods: Postmenopausal women (N=668) with HR+, HER2− ABC who did not receive prior systemic treatment for ABC and had an Eastern Cooperative Oncology Group performance status score of ≤1, adequate bone marrow and organ function, and no history of active cardiac dysfunction were randomized 1:1 to receive either ribociclib (600 mg/d, 3 weeks on/1 week off) + letrozole (2.5 mg/d, continuous) or placebo + letrozole. The primary end point was locally assessed PFS. The data cutoff for this analysis was January 29, 2016. Results: Baseline demographics, patient disposition, and prior therapy were well balanced across treatment groups in the US subset (N=213; ribociclib group, n=100; placebo group, n=113). Median treatment duration was 16.3 months. In US patients, median PFS was significantly prolonged in the ribociclib group (median PFS, not reached [NR]; 95% CI, 17.1 months to NR) versus the placebo group (median PFS, 14.4 months [95% CI, 11.1–18.4 months]; hazard ratio, 0.451 [95% CI, 0.281–0.724]; P=0.000363), with a median follow-up of 11.0 months. In a subsequent preplanned analysis of overall survival, median PFS was 27.6 months in the ribociclib group versus 15.0 months in the placebo group (hazard ratio, 0.527; 95% CI, 0.351–0.793). The overall response rate (ORR) was significantly greater in the ribociclib group (ORR, 38.0%; 95% CI, 28.5–47.5%) versus the placebo group (ORR, 26.5%; 95% CI, 18.4–34.7%; P=0.040). A trend toward benefit was observed with ribociclib in all subgroups (including age, disease burden, prior therapy, and biomarker status), which was consistent with the overall population. No on-treatment deaths occurred. The most common all-grade adverse events, irrespective of causality, were neutropenia (ribociclib, 69.0%; placebo, 3.7%), nausea (ribociclib, 65.0%; placebo, 39.4%), fatigue (ribociclib, 56.0%; placebo, 46.8%), and diarrhea (ribociclib, 41.0%; placebo, 32.1%). The most common grade 3 (≥25% in either group) and grade 4 (≥10% in either group) AE was neutropenia (grade 3: ribociclib, 39.0%; placebo, 0%; grade 4: ribociclib, 14.0%; placebo, 0%). Two patients (2.0%) in the ribociclib group and none in the placebo group experienced febrile neutropenia. Conclusions: The US patients in the MONALEESA-2 study derived significant PFS benefit from ribociclib + letrozole compared with placebo + letrozole, with a 55% reduction in the relative risk of disease progression. The safety profile was consistent with and comparable to the global study population. Citation Format: Yardley DA, Hart L, Favret A, Blau S, Diab S, Richards D, Sparano J, Beck JT, Richards P, Ward P, Ramaswamy B, Tsai M, Pluard T, Tolaney S, Esteva F, Small T, Purkayastha D, Miller M, Hortobagyi G. Efficacy and safety of ribociclib plus letrozole in US patients enrolled in the MONALEESA-2 study [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-27.

Abstract OT3-05-05: MonarchE: A randomized, open-label, phase 3 study of abemaciclib combined with standard adjuvant endocrine therapy versus standard adjuvant endocrine therapy alone in patients with high risk, node positive, early stage, HR+, HER2- breast cancer

Abstract Background: Abemaciclib, an oral, selective inhibitor of cyclin-dependent kinases 4 and 6 dosed on a twice daily continuous schedule, has demonstrated clinical efficacy and tolerability in patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer when administered as monotherapy (MONARCH 1) and in combination with endocrine therapy (ET) in MONARCH 2 and MONARCH 3. In neoMONARCH, abemaciclib plus anastrozole as neoadjuvant therapy reduced the breast tumor cell proliferation marker Ki67 to a greater extent than anastrozole alone after 2 weeks of treatment. Endocrine monotherapy is the current standard of care in the adjuvant setting. However, a proportion of pts relapse despite this therapy. A population with a higher risk of recurrence (15% at 5 years) may be identified based on the clinical and pathological characteristics of disease. Optimizing adjuvant therapy for these pts is an important need. Trial Design: MonarchE (NCT03155997) is a multicenter, randomized, open-label Phase 3 trial that will evaluate the potential for abemaciclib to enhance adjuvant ET. Pts will be randomized 1:1 to abemaciclib 150 mg twice daily continuous schedule plus standard of care (SOC) adjuvant ET versus SOC adjuvant ET alone and stratified by prior chemotherapy (neoadjuvant, adjuvant, or none), menopausal status (pre- or post-), and region (N. America/Europe, Asia, or other). Pts may have started ET within 8 weeks prior to randomization. Pts will receive abemaciclib for up to 2 years in combination with ET per physician's choice (such as tamoxifen or an aromatase inhibitor, +/- ovarian suppression). ET alone will be continued as clinically indicated. All randomized pts will be followed for a total of 10 years. Eligibility Criteria: Eligible pts (male or female) must have early stage resected HR+, HER2- invasive breast cancer with either ≥ 4 positive pathological axillary lymph nodes (pALNs), or 1 to 3 positive pALNs and at least one of the following high risk markers: primary tumor size ≥5 cm, histological grade 3 tumor, or centrally assessed Ki67 index of ≥20% (in a subset of pts). Pts must have completed definitive locoregional therapy (+/- (neo)adjuvant chemotherapy) and be randomized no more than 12 weeks after completion of last non-ET (surgery, chemotherapy, or radiotherapy). Pts must have tumor tissue available for biomarker analysis prior to randomization. Specific Aims: The primary objective of monarchE is to evaluate invasive disease-free survival (IDFS) per the STEEP System.1 Secondary objectives include evaluation of IDFS in pts with Ki67 index of ≥20%, distant relapse-free survival, overall survival, safety, pharmacokinetics, and pt health outcomes. Statistical Methods: Assuming an IDFS hazard ratio of .73, the study is powered to approximately 80% to test the superiority of abemaciclib plus standard ET at a 1-sided α=0.025 using a stratified log-rank test. Target accrual: Approximately 3580 pts Contact information: 1-877-285-4559 Reference: 1. Hudis et al. J Clin Oncol. 2007;25(15):2127-2132. Citation Format: Rastogi P, Toi M, Harbeck N, Bourayou N, Frenzel M, Johnston S. MonarchE: A randomized, open-label, phase 3 study of abemaciclib combined with standard adjuvant endocrine therapy versus standard adjuvant endocrine therapy alone in patients with high risk, node positive, early stage, HR+, HER2- breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT3-05-05.

Abstract P5-21-02: Efficacy and safety of abemaciclib in patients with liver metastases in the MONARCH 1, 2, and 3 studies

Abstract Background: Abemaciclib is an oral, selective inhibitor of cyclin-dependent kinases 4 & 6 that is dosed on a twice daily continuous schedule. In patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC), abemaciclib has demonstrated clinical efficacy with a tolerable safety profile when administered as monotherapy in MONARCH 1 (NCT02102490), in combination with fulvestrant in MONARCH 2 (NCT02107703), and in combination with non-steroidal aromatase inhibitors (NSAI) in MONARCH 3 (NCT02246621). Inducing tumor response and delaying disease progression is of critical need in pts with liver metastases (mets). Methods: An exploratory subgroup analysis was conducted in pts with liver mets at baseline across the MONARCH 1, 2, and 3 studies. All pts had HR+, HER2- ABC. The primary endpoint of MONARCH 1 was objective response rate (ORR), and the primary endpoint of MONARCH 2 and 3 was investigator-assessed progression-free survival (PFS). Analysis methods for these endpoints were previously described. Key enrollment criteria and dosing information are listed in Table 1. Table 1. Eligibility criteria and dosing information for the MONARCH 1, 2, and 3 studiesKey enrollment criteriaMONARCH 1MONARCH 2MONARCH 3Prior endocrine therapyProgressed on or after ETProgressed while receiving adjuvant or first-line ET, or ≤ 12 months from the end of adjuvant ETET naïve or disease relapse >12 months after (neo)adjuvant ETChemotherapy regimens in advanced setting1 or 200Visceral crisisNo restrictionNot permittedNot permittedDose and Schedule abemaciclib200 mg, twice daily, continuous150 mg1, twice daily, continuous150 mg, twice daily, continuousfulvestrant-500 mg, per label-anastrozole2--1 mg, dailyletrozole2--2.5 mg, daily1post-amendment; 2physician's choice of NSAI (anastrozole or letrozole); ET: endocrine therapy Results: Efficacy results of pts with liver mets are described in Table 2. The most frequent adverse events observed in pts with liver mets in MONARCH 1 were diarrhea, nausea, and fatigue and in the abemaciclib arms of MONARCH 2 and 3 were diarrhea, neutropenia, and nausea. Table 2. PFS and response rates of pts with liver mets in MONARCH 1, 2, and 3 MONARCH 1MONARCH 2 abemaciclib armMONARCH 2 placebo armMONARCH 3 abemaciclib armMONARCH 3 placebo armPts with liver mets, n93115594830PFS, HR (95% CI)N/A.45 (.31, .64).47 (.25, .87)Median PFS, months5.611.63.115.07.2ORR, n (%)20 (21.5)54 (47.0)9 (15.3)26 (54.2)6 (20.0)CBR, n (%)39 (41.9)77 (67.0)21 (35.6)32 (66.7)12 (40.0)CBR: clinical benefit rate (complete response [CR] + partial response [PR] + stable disease ≥6 months); HR: hazard ratio; ORR: objective response rate (CR+PR); PFS: progression-free survival; pts: patients Conclusions: The results suggest that the combination of abemaciclib and endocrine therapy was an effective treatment option in pts with liver metastases, a population deriving modest benefit from single-agent endocrine therapy. Tolerability results were generally consistent with the safety populations previously reported for each study. Citation Format: Di Leo A, Dickler M, Sledge GW, Toi M, Forrester T, Nanda S, Koustenis A, Bourayou N, Johnston S. Efficacy and safety of abemaciclib in patients with liver metastases in the MONARCH 1, 2, and 3 studies [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-02.

Abstract GS6-02: The benefit of abemaciclib in prognostic subgroups: An exploratory analysis of combined data from the MONARCH 2 and 3 studies

Abstract Background: Abemaciclib is an orally administered, selective inhibitor of cyclin-dependent kinases 4 & 6 that is dosed on a twice daily continuous schedule. Abemaciclib has demonstrated clinical efficacy with a generally tolerable safety profile in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer in combination with fulvestrant in MONARCH 2 (NCT02107703) and in combination with non-steroidal aromatase inhibitors (NSAI) in MONARCH 3 (NCT02246621). These analyses were conducted to evaluate if patient and disease characteristics may better inform in whom and when abemaciclib should be initiated to define optimal treatment strategies. Methods: MONARCH 2 and 3 enrolled patients with HR+, HER2- advanced breast cancer. In MONARCH 2, patients whose disease had progressed while receiving endocrine therapy were treated with abemaciclib/placebo plus fulvestrant. In MONARCH 3, patients were treated with abemaciclib/placebo plus NSAI as initial therapy for advanced disease. An exploratory pooled analysis of the two studies was performed to determine significant prognostic factors. Efficacy results (progression-free survival [PFS] and objective response rate [ORR] in patients with measurable disease) were examined for patient subgroups corresponding to each of the identified significant prognostic factors. Subpopulation treatment effect pattern plot (STEPP) methodology was performed to examine the association between treatment-free interval (TFI) following adjuvant endocrine therapy and outcomes of endocrine therapy alone or in combination with abemaciclib in MONARCH 3. Results: Analyses of clinical factors in over 1000 patients confirmed the following to have prognostic value: bone-only disease, liver metastases, tumor grade, progesterone receptor (PgR) status, and ECOG performance status. Prognosis was poor in patients with liver metastases, PgR-negative tumors, and high-grade tumors. While all subpopulations benefited from the addition of abemaciclib to endocrine therapy regardless of prognosis, substantial benefit of abemaciclib was observed in poor prognosis subgroups, characterized by large increases in PFS (hazard ratios = 0.4 to 0.5) and ORR (over 30%). In addition, STEPP analysis of TFI on a subset of the MONARCH 3 population showed that patients with the shortest TFI appeared to have a poorer prognosis and received more benefit from the addition of abemaciclib compared to patients with longer TFI. Conclusions: This exploratory analysis has provided data that could help optimize treatment strategies by identifying that patients with poor prognostic factors may receive greater benefit from the addition of abemaciclib to endocrine therapy. Citation Format: Goetz MP, O'Shaughnessy J, Sledge Jr. GW, Martin M, Lin Y, Forrester T, Mockbee C, Smith IC, Di Leo A, Johnston S. The benefit of abemaciclib in prognostic subgroups: An exploratory analysis of combined data from the MONARCH 2 and 3 studies [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr GS6-02.

Abstract LB-B24: Targeting transcriptional addiction for the treatment of TSC

Abstract Introduction: Tuberous sclerosis complex (TSC) is characterized by tumor development in the brain, heart, skin, kidney and lungs. While everolimus is approved for treatment of TSC angiomyolipoma and TSC subependymal giant cell astrocytoma, responses are not complete and tumor regrowth occurs after treatment cessation. Therapies for TSC that induce a selective cytocidal response in TSC-null cells are not currently available, and are highly desirable for TSC patients. In TSC tumors loss of the TSC1/TSC2 protein complex leads to activation of mTORC1 with downstream effects on anabolism and cell growth. We hypothesized that mTORC1 activation would also enhance mRNA transcription and that this effect might create a therapeutic vulnerability. In addition, we hypothesized that rapamcyin treatment of TSC-null cells would lead to complex compensatory effects on transcription, and that synergy might be seen in co-treatment with a transcriptional inhibitor. Cyclin-dependent kinase 7 (CDK7) plays a critical role in phosphorylation of RNA polymerase II, thus regulating RNA transcription. Recent screens have identified THZ1, a selective and covalent CDK7 inhibitor, as a cytocidal compound for several cancer types. We hypothesized that THZ1 and inhibitors of CDK7 might be selectively lethal to TSC-null cells in TSC-associated tumors. Methods: Drug sensitivity assay was performed using Quant-it PicoGreen. FACS and assays of apoptosis, such as Propidium Iodide/Annexin V staining and immunoblot for cleaved caspase 3 were used to assess apoptosis. We used RNA-sequencing and metabolome profiling to assess metabolomics and transcriptional effects of THZ1, and investigate the novel hypothesis that targeting transcription triggers selective cell death in TSC-null cells. To further assess the therapeutic potential of THZ1+/-Rapamycin in TSC, In vivo treatment studies were performed using xenografts in athymic nude mice. Results: Drug sensitivity assays to THZ1+/- Rapamycin revealed selective lethality for both the TSC1-null HCV29 bladder cancer derived cell line vs. addback TSC1-HCV29 and the TSC2-null 621-101 angiomyolipoma cell line vs. TSC2 addback 621-103. The IC50 of each of TSC1/TSC2 null cells was 6-10 fold lower vs. addback lines. FACS assay of apoptosis showed 37% of HCV29 cells Annexin V+ in comparison to 3% of TSC1-HCV29 cells. IB showed cleaved Caspase 3 only in THZ1-treated TSC1-null cells. RNA-seq on samples treated with THZ1(30nm) for 6 hours identified many genes with markedly different expression: e.g. 1128 genes showed a > 5-fold lower expression in THZ1-treated HCV29 compared with THZ1-treated TSC1-HCV29 cells. Genes involved in glutathione biosynthesis pathway such as GCLC (glutamate-cysteine ligase catalytic subunit) showed an 82% reduction in mRNA levels in THZ1-treated HCV29 cells vs. TSC1-HCV 29. Metabolite analyzes confirmed that THZ1 caused a marked decrease (4 fold) in glutathione levels, and supplemental GSH-MEE rescued cell death induction in response to THZ1.THZ1(10mg/kg/twice daily) +/- Rapamycin (3mg/kg/3 days week) for 30 days markedly reduced the tumor growth rate in the in vivo TSC1-null xenograft model and prevented tumor regrowth compared to either Rapamycin or vehicle. Conclusions: These findings reveal that targeting transcriptional addiction will selectively induce cell death of TSC-null cells. We hypothesize that targeting transcription with a covalent CDK7 inhibitor has novel therapeutic benefit for patients with TSC. Citation Format: Mahsa zarei, Heng Du, Rachel E. Yan, Yubao Wang, Thingu Zhang, John M. Asara, David J. Kwiatkowski. Targeting transcriptional addiction for the treatment of TSC [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B24.

Pharmacological perturbation of CDK9 using selective CDK9 inhibition or degradation.

Cyclin-dependent kinase 9 (CDK9), an important regulator of transcriptional elongation, is a promising target for cancer therapy, particularly for cancers driven by transcriptional dysregulation. We characterized NVP-2, a selective ATP-competitive CDK9 inhibitor, and THAL-SNS-032, a selective CDK9 degrader consisting of a CDK-binding SNS-032 ligand linked to a thalidomide derivative that binds the E3 ubiquitin ligase Cereblon (CRBN). To our surprise, THAL-SNS-032 induced rapid degradation of CDK9 without affecting the levels of other SNS-032 targets. Moreover, the transcriptional changes elicited by THAL-SNS-032 were more like those caused by NVP-2 than those induced by SNS-032. Notably, compound washout did not significantly reduce levels of THAL-SNS-032-induced apoptosis, suggesting that CDK9 degradation had prolonged cytotoxic effects compared with CDK9 inhibition. Thus, our findings suggest that thalidomide conjugation represents a promising strategy for converting multi-targeted inhibitors into selective degraders and reveal that kinase degradation can induce distinct pharmacological effects compared with inhibition.

Combined Inhibition of CDK4/6 and PI3K/AKT/mTOR Pathways Induces a Synergistic Anti-Tumor Effect in Malignant Pleural Mesothelioma Cells

Malignant pleural mesothelioma (MPM) is a progressive malignancy associated to the exposure of asbestos fibers. The most frequently inactivated tumor suppressor gene in MPM is CDKN2A/ARF, encoding for the cell cycle inhibitors p16INK4a and p14ARF, deleted in about 70% of MPM cases. Considering the high frequency of alterations of this gene, we tested in MPM cells the efficacy of palbociclib (PD-0332991), a highly selective inhibitor of cyclin-dependent kinase (CDK) 4/6. The analyses were performed on a panel of MPM cell lines and on two primary culture cells from pleural effusion of patients with MPM. All the MPM cell lines, as well as the primary cultures, were sensitive to palbociclib with a significant blockade in G0/G1 phase of the cell cycle and with the acquisition of a senescent phenotype. Palbociclib reduced the phosphorylation levels of CDK6 and Rb, the expression of myc with a concomitant increased phosphorylation of AKT. Based on these results, we tested the efficacy of the combination of palbociclib with the PI3K inhibitors NVP-BEZ235 or NVP-BYL719. After palbociclib treatment, the sequential association with PI3K inhibitors synergistically hampered cell proliferation and strongly increased the percentage of senescent cells. In addition, AKT activation was repressed while p53 and p21 were up-regulated. Interestingly, two cycles of sequential drug administration produced irreversible growth arrest and senescent phenotype that were maintained even after drug withdrawal. These findings suggest that the sequential association of palbociclib with PI3K inhibitors may represent a valuable therapeutic option for the treatment of MPM.

Abstract LB-297: In vivo anti-tumor efficacy of UD-017, a novel highly selective & orally available CDK7 inhibitor, in colorectal cancer cells xenograft models

Abstract Background: Cyclin dependent kinase 7 (CDK7) is an attractive target for cancer drugs due to its dual roles, cell cycle regulation & gene transcription/RNA procession. Recent studies show that transcription of some oncogene is highly sensitive to inhibition of transcription such as inhibition by CDK7. The dependence of cancer cells on transcription can be therefore advantageous to CDK7 inhibitors as effective anti-cancer drugs. We synthesized a novel small molecule highly selective reversible CDK7 inhibitor, UD-017. In this study, we evaluated anti-cancer activity of UD-017 in the colorectal cancer cells, HCT-116, xenograft models in mice & investigated the rationale for CDK7 inhibition as anti-cancer drugs. Experimental procedures: We first examined the pharmacokinetics profile of UD-017 after an oral administration in mice. We then evaluated the anti-tumor efficacy of UD-017 in HCT-116 xenograft models in mice. We further investigated the pharmacodynamics of UD-017 by detecting the phosphorylation levels of the retinoblastoma (cell cycle) & RNA polymerase II (transcription) & expression levels of c-myc in the tumor tissues in the same model after oral administration of UD-017. Results: UD-017 was identified as an orally available inhibitor of CDK7. The bioavailability was approximately 50% in BALB/c mice. In the HCT-116 xenograft model in mice, UD-017 inhibited the cancer growth by 33%, 64% & 88% at 25, 50 & 100 mg/kg, respectively, with clear dose-dependence by once daily administration for 14 days. Throughout the experiment, UD-017 was well tolerated with no reduction in body weights & no myelosuppression. In order to evaluate the effect of UD-017 in combination with chemotherapeutics, UD-017 was administrated with 5-fluorouracil (5-FU) to HCT-116 xenografted mice with either 50 mg/kg of UD-017 alone, or 15 mg/kg ip of 5-FU alone, or in combination of UD-017 plus 5-FU. UD-017 showed clear combination effect with 5-FU without further affecting the side effects of 5-FU. Phosphorylation of the retinoblastoma was inhibited after oral administration of UD-017 time-dependently in the tumor tissues. Phosphorylation of RNA polymerase II COOH-terminal domain (CTD) was also inhibited & expression of c-myc was decreased. PPAP cleavage was subsequently induced, causing apoptotic death of the cancer cells. Conclusion: We propose UD-017 as a novel type of anti-cancer drug that shows favorable oral pharmacokinetics profile & complete anti-tumor responses in xenograft models of colorectal cancer cells, & also shows in vivo synergy in combination with chemotherapy. These data support the rationale for further advancing towards clinical development. IND-enabling studies are in progress. Citation Format: Yasuhiro Aga, Sayaka Ogi, Yasunori Tokunaga, Ayumi Ogawa, Kazuhiro Onuma, Takashi Matsushita, Hidetoshi Sunamoto, Toru Hasegawa, Shigeru Ushiyama. In vivo anti-tumor efficacy of UD-017, a novel highly selective & orally available CDK7 inhibitor, in colorectal cancer cells xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-297. doi:10.1158/1538-7445.AM2017-LB-297

Abstract LB-111: In vitro anti-cancer activity of UD-017, a novel potent & highly selective CDK7 reversible inhibitor

Abstract Background: Cyclin dependent kinase 7 (CDK7) is a member of the CDK family, & has a dual function relating to the cell cycle progression & gene transcription/ RNA processing. Recently CDK7 has been emerged as an attractive target for anticancer drugs due to its dual role. We synthesized UD-017, a small molecule, highly selective CDK7 inhibitor with a novel chemotype. In this study, we characterized in vitro antiproliferative profile of UD-017 & elucidated underlying mechanism how CDK7 inhibition contributes to the antiproliferation of cancer cells. Experimental procedures: We conducted a large panel of 9 CDKs & 313 other kinases assay of UD-017 to determine its selectivity & analyzed kinetics for CDK7 enzyme inhibition. We evaluated the antiproliferative activity of UD-017 in over 100 multiple types of cancer cell lines. We then investigated the mechanism of antiproliferative activity of UD-017 using human colorectal cancer cell line, HCT-116, & human multiple myeloma cell line, NCI-H929. We also explored biomarker candidates mainly using colorectal cancer cell lines. Results: UD-017 inhibited CDK7 enzyme with an IC50 value of 16 nM, which is at least 300-fold more selective against other CDKs, CDK1 through CDK9. Inhibition of UD-017 was reversible & ATP-competitive. In a panel of 313 kinases assay, the compound inhibited CDK7 almost mono-specifically. In antiproliferative panel assays using over 100 cancer cell lines, UD-017 broadly inhibited a wide range of cancer cells from colon, breast, lung, kidney, blood, pancreas & urinary bladder cancers. Specifically, it inhibited the growth of HCT-116 & NCI-H929 with GI50 values of 29 nM and 6.8 nM, respectively. In the mechanism study of the antiproliferative activity, UD-017 inhibited phosphorylation of CDK1, CDK2 & the retinoblastoma (RB) & arrested the cell-cycle. Phosphorylation of RNA polymerase II c-terminal domain was also inhibited & expression levels of c-Myc and XIAP decreased & the cleavage of PARP increased, which were followed by significant induction of apoptosis. UD-017 showed both cell cycle arrest & induction of apoptosis. In the biomarker study, c-Myc & cyclin H showed good correlation with antiproliferative activities in 6 colorectal cancer cell lines and will be candidate biomarkers of UD-017. Conclusion: UD-017 is a potent & highly selective CDK7 inhibitor, & significantly inhibits the proliferation of human cancer cells with concomitant cell cycle arrest & induction of apoptosis. In vivo anti-tumor efficacy for UD-017 is warranted. Citation Format: Takashi Matsushita, Kazuhiro Onuma, Hidetoshi Sunamoto, Ayumi Ogawa, Sayaka Ogi, Toru Hasegawa, Shigeyuki Kono, Noriaki Iwase, Yasuhiro Aga, Shigeru Ushiyama. In vitro anti-cancer activity of UD-017, a novel potent & highly selective CDK7 reversible inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-111. doi:10.1158/1538-7445.AM2017-LB-111

Preclinical in vitro and in vivo study of UD-017, a novel highly selective and orally available CDK7 inhibitor, in a variety of cancers.

e14086 Background: Cyclin dependent kinase 7 (CDK7) modulates mRNA transcription and some oncogenes are reported to be sensitive to inhibition of transcription in certain cancer cells. CDK7 inhibitors have been considered as an intriguing approach to treat cancers that depend on transcriptional regulation of their oncogenes. We synthesized a novel highly selective CDK7 inhibitor, UD-017, and found that the compound showed antitumor potency in a variety of cancers in vitro and in vivo. We therefore explored underlying mechanisms especially focusing on an oncogenic driver, c-Myc. Methods: We examined CDK7 selectivity of UD-017 against the other CDKs and kinases. We evaluated an antiproliferative activity of UD-017 in over 200 multiple types of cancer cell lines including patients-derived cancer cells. We then investigated the correlation between c-Myc expression levels and an antiproliferative activity of UD-017 in cancer cells. Antitumor efficacy of UD-017 was assessed in multiple types of cancer xenograft models and patients-derived xenograft model. We determined whether an intratumoral c-Myc expression levels correlated with in vivo antitumor efficacy of UD-017 in xenograft models. Results: UD-017 inhibited CDK7 enzyme (IC50= 16 nM) highly selectively among the CDKs (over 300-fold) and almost mono-specifically in a panel of 313 kinases assay. In a cellular antiproliferative panel assay, UD-017 broadly inhibited the proliferation of a variety of cancer cells and c-Myc expression levels showed the good correlation with antiproliferative activity. UD-017 showed favorable PK profile and good oral absorbability and showed the potent antitumor activity in multiple types of cancer xenograft models in mice. In correlation with the PK, UD-017 reduced the intratumoral c-Myc mRNA levels time-dependently after dosing of UD-017 in the colorectal cancer xenograft model. Conclusions: We identified a highly selective and orally available CDK7 inhibitor that showed the broad in vitro and in vivo antitumor activity in a variety of cancers, modulating c-Myc as an oncogenic driver. These data support the rationale for further advancing towards clinical development.

Preclinical in vitro and in vivo evaluation of antitumor activity of UD-017, a novel selective and orally available CDK7 inhibitor, in colorectal cancer.

e14085 Background: Cyclin dependent kinase 7 (CDK7) is an attractive target for cancer drugs due to its dual roles, cell cycle regulation and gene transcription/RNA procession. We synthesized UD-017, a small molecule, highly selective CDK7 inhibitor with a novel chemotype. In this study, we characterize antitumor activity of UD-017 in vitro and in vivo, and try to elucidate underlying mechanisms by which CDK7 inhibition contributes to the antitumor efficacy in colorectal cancer cells. Methods: We examined CDK7 selectivity of UD-017 against the other CDKs and kinases. We evaluated the antitumor activity in a variety of human cancer cell lines including colorectal cancer cells. We investigated the mechanism of antitumor activity of UD-017 using a human colorectal cancer cell line, HCT-116. In vivo antitumor efficacy of UD-017 was assessed in HCT-116 xenograft models and patient derived xenograft (PDX) model. Results:UD-017 inhibited CDK7 enzyme (IC50 = 16 nM), which is at least 300-fold more selective against other CDKs. In a panel of 313 kinases assay, UD-017 inhibited CDK7 almost mono-specifically. UD-017 potently inhibited the growth of human cancer cells including the patient-derived colorectal cancer cells.In the mechanism study, UD-017 inhibited phosphorylation of CDK1, 2 and retinoblastoma, which was followed by cell-cycle arrest. Inhibition of both RNA polymerase II phosphorylation and c-Myc expression was observed followed by apoptosis induction. HCT-116 xenograft model and PDX model demonstrated the potent antitumor activity of UD-017 with dose-dependence by daily oral administration for 2 weeks. Furthermore, UD-017 showed the combination effect with 5-FU without further affecting the side effects of the chemotherapy. Conclusions:UD-017 is a potent and highly selective CDK7 inhibitor, and significantly inhibits the growth of human cancer cell lines with cell-cycle arrest and apoptosis induction. UD-017 showed potent and dose-dependent antitumor response in the HCT-116 xenograft model and PDX model. Further investigation towards clinical development is warranted.

Palbociclib: A Review in HR-Positive, HER2-Negative, Advanced or Metastatic Breast Cancer.

Oral palbociclib (Ibrance®) is a first-in-class, highly selective inhibitor of cyclin-dependent kinases 4 and 6 (i.e. a CDK4/6 inhibitor). It is indicated for the treatment of women with HR-positive, HER2-negative advanced or metastatic breast cancer, in combination with an aromatase inhibitor as initial endocrine-based therapy, and in combination with fulvestrant (with or without a luteinizing hormone-releasing hormone agonist) in those previously treated with endocrine therapy. In clinical trials, palbociclib in combination with letrozole as initial endocrine-based therapy in postmenopausal women (PALOMA-1 and PALOMA-2), or in combination with fulvestrant in pre-, peri-, or postmenopausal women with disease progression after endocrine therapy (PALOMA-3), significantly prolonged progression-free survival (PFS) and improved clinical benefit response (CBR) rates. Neutropenia was the most commonly reported any-grade and grade≥3 adverse event. It was infrequently associated with febrile neutropenia (<2%) and generally manageable with a palbociclib dose delay, interruption or reduction, without the routine use of growth factors, and without affecting efficacy. In conclusion, oral palbociclib combination therapy is a valuable emerging option for use in patients with HR-positive, HER2-negative advanced or metastatic breast cancer.

КАРБОНИЛИРОВАНИЕ БЕЛКОВ КАК МЕХАНИЗМ РЕГУЛЯЦИИ ПРОЛИФЕРАЦИИ ОПУХОЛЕВЫХ КЛЕТОК ЛИНИИ МCF-7

Tumor progression is accompanied by dysregulation of cell proliferation and apoptosis, which plays an essential role in breast cancer pathogenesis and cell resistance to chemotherapy. The role of protein carbonylation in molecular mechanisms of regulating MCF-7 breast cancer cell proliferation under the effect of roscovitine, a selective inhibitor of cyclin-dependent kinases, was evaluated. The cells were grown in adherent cell culture with or without roscovitine. The levels of reduced/oxidized glutathione and the concentration of protein carbonyl derivatives were determined by spectrophotometry. The cell cycle was evaluated by the flow cytometry; the same technique was used to measure the reactive oxygen species (ROS) concentration. Cell culture with roscovitine resulted in a decrease in the redox potential of the glutathione system and a rise in the ROS and protein carbonyl derivative concentrations. Roscovitine contributed to the G 0 /G 1 and G 2 /М phase arrest due to its interaction with ATP-binding sites of cyclin-dependent kinases. Roscovitine could also promote enzyme carbonylation. The obtained results can be further used for development of personalized approaches to breast cancer therapy.

Roscovitine Protects From Arterial Injury by Regulating the Expressions of c-Jun and p27 and Inhibiting Vascular Smooth Muscle Cell Proliferation.

Roscovitine (Rosc) is a selective inhibitor of cyclin-dependent kinases (CDKs) and a promising therapy for various cancers. However, limited information is available on the biological significance of Rosc in vascular smooth muscle cells (VSMCs), the cell type critical for the development of proliferative vascular diseases. In this study, we address the effects of Rosc in regulating VSMC proliferation, both in vitro and in vivo, exploring the underlying molecular mechanisms. The proliferations and cell-cycle distributions of in vitro cultured VSMCs, as well as several other cancer cell lines, were examined by cell-counting assay and flow cytometry, respectively. Molecular changes in various CDKs, cyclins, and other regulatory molecules were examined by reverse transcription polymerase chain reaction, Western blot, or immunocytochemistry. The in vivo effects of Rosc were examined on a carotid arterial balloon-injury model. Rosc significantly inhibited VSMC proliferation in response to serum or angiotensin II and arrested these cells at the G0/G1 phase. These changes were associated with a specific and robust decrease in CDK4, cyclin E, c-Jun, and a dramatic increase in p27kip1 in VSMCs, which was also translated in vivo and correlated with the protection of Rosc on injury-induced neointimal hyperplasia. Acting on distinct molecular targets in VSMCs versus cancer cells, Rosc inhibits VSMC proliferation and protects from proliferative vascular diseases.

Abstract P4-22-16: First-line ribociclib + letrozole in patients with HR+, HER2– advanced breast cancer (ABC) presenting with visceral metastases or bone-only disease: A subgroup analysis of the MONALEESA-2 trial

Abstract Background: Patients with ABC who present with visceral metastases have a worse outcome than patients with non-visceral disease, while patients with bone-only disease tend to have a better prognosis. Ribociclib (LEE011) is an oral, selective inhibitor of cyclin-dependent kinase (CDK) 4/6. In a Phase 3, placebo-controlled, randomized trial (MONALEESA-2; NCT01958021), first-line ribociclib (R) + letrozole (L) significantly prolonged progression-free survival (PFS) vs placebo (P) + L in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) ABC, with a hazard ratio of 0.556 (95% confidence interval [CI]: 0.429–0.720; p=0.00000329) at the interim analysis cut-off date (Jan 29, 2016). Here, we present subgroup analyses in patients with visceral metastases, and those with bone-only disease. Methods: Postmenopausal women with HR+, HER2– ABC were randomized 1:1 to receive R (600 mg/day; 3-weeks-on/1-week-off) + L (2.5 mg/day; continuous) or P+L, stratified by the presence of liver and/or lung metastases. No prior CDK4/6 inhibitors or systemic therapy for ABC were allowed. Eligible patients had Eastern Cooperative Oncology Group performance status ≤1, baseline alanine/aspartate aminotransferase levels &amp;lt;5× upper limit of normal (ULN) or &amp;lt;2.5× ULN for patients with or without liver metastases, respectively, and ≥1 predominantly lytic bone lesion at baseline for patients with bone-only disease. Locally assessed PFS was analyzed for all patients (primary endpoint), and for predefined patient subgroups. Results: Overall, 668 patients were randomized; 393 had visceral metastases and 147 had bone-only disease. Visceral metastasesBone-only disease n=393n=147 R+LP+LR+LP+L n=197n=196n=69n=78Median age, years (range)63 (23–91)63 (29–88)65 (37–85)63 (37–84)De novo metastatic disease, n (%)53 (27)55 (28)28 (41)24 (31)Non-de novo disease-free interval, n (%)≤24 months12 (6)15 (8)5 (7)6 (8)&amp;gt;24 months132 (67)126 (64)36 (52)48 (62)Discontinued treatment, n (%)83 (42)111 (57)29 (42)40 (51)Reason for discontinuation, n (%)Disease progression56 (28)93 (47)17 (25)31 (40)Patient/physician decision10 (5)15 (8)7 (10)6 (8)Adverse events16 (8)3 (2)4 (6)2 (3)Protocol deviation001 (1)1 (1)Death1 (&amp;lt;1)000 In patients with visceral metastases: Median PFS was not reached in the R+L arm (95% CI: 19.3–not estimable [NE]) vs 13.0 months (95% CI: 12.6 –16.5) in the P+L arm, with hazard ratio 0.535 (95% CI: 0.385–0.742). Median duration of exposure was 12.0 and 13.0 months (R and L, respectively) in the R+L arm, and 12.1 and 12.2 months (P and L, respectively) in the P+L arm. In patients with bone-only disease: Median PFS was not reached in the R+L arm (95% CI: NE–NE) vs 15.3 months (95% CI: 13.8–NE) in the P+L arm, with hazard ratio 0.690 (95% CI: 0.381–1.249). Median duration of exposure was 12.1 and 12.6 months (R and L, respectively) in the R+L arm, and 12.7 and 12.9 months (P and L, respectively) in the P+L arm. Conclusions: First-line R+L was well tolerated and significantly prolonged PFS vs P+L in postmenopausal women with HR+, HER2– ABC, both in patients with visceral metastases and those with bone-only disease. Keywords: Advanced breast cancer; CDK4/6 inhibitor; Letrozole; Ribociclib Citation Format: Burris HA, Chan A, Campone M, Blackwell KL, Winer EP, Janni W, Verma S, Burdaeva O, Alba E, Favret AM, Mondal S, Miller M, Germa C, Hirawat S, Yap YS. First-line ribociclib + letrozole in patients with HR+, HER2– advanced breast cancer (ABC) presenting with visceral metastases or bone-only disease: A subgroup analysis of the MONALEESA-2 trial [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-16.

Inhibitors of cyclin-dependent kinases as cancer therapeutics.

Over the past two decades there has been a great deal of interest in the development of inhibitors of the cyclin-dependent kinases (CDKs). This attention initially stemmed from observations that different CDK isoforms have key roles in cancer cell proliferation through loss of regulation of the cell cycle, a hallmark feature of cancer. CDKs have now been shown to regulate other processes, particularly various aspects of transcription. The early non-selective CDK inhibitors exhibited considerable toxicity and proved to be insufficiently active in most cancers. The lack of patient selection biomarkers and an absence of understanding of the inhibitory profile required for efficacy hampered the development of these inhibitors. However, the advent of potent isoform-selective inhibitors with accompanying biomarkers has re-ignited interest. Palbociclib, a selective CDK4/6 inhibitor, is now approved for the treatment of ER+/HER2- advanced breast cancer. Current developments in the field include the identification of potent and selective inhibitors of the transcriptional CDKs; these include tool compounds that have allowed exploration of individual CDKs as cancer targets and the determination of their potential therapeutic windows. Biomarkers that allow the selection of patients likely to respond are now being discovered. Drug resistance has emerged as a major hurdle in the clinic for most protein kinase inhibitors and resistance mechanism are beginning to be identified for CDK inhibitors. This suggests that the selective inhibitors may be best used combined with standard of care or other molecularly targeted agents now in development rather than in isolation as monotherapies.

Selective Targeting Cyclin-Dependent Kinase-9 (CDK9) Downmodulates c-MYC and Induces Apoptosis in Diffuse Large B-Cell Lymphoma (DLBCL) Cells

DLBCL accounts for >10,000 deaths in the U.S. annually. Despite efficacy of upfront chemo-immunotherapy, up to 50% of patients die within 5 years. While inhibitors of B-cell receptor signaling transformed the therapeutic paradigm in indolent lymphomas, they show poor activity in DLBCL, which thus represents an unmet clinical need.MYC oncogene, a transcription factor which regulates cell proliferation and growth, is a key driver in lymphomagenesis. Myc overexpression is associated with chemoresistance in NHL, while "double-hit" lymphomas characterized by MYC and BCL2 rearrangement are most aggressive. Myc proteins have extraordinarily short half-life. To regulate transcription, Myc recruits pTEFb, an elongation factor whose catalytic core comprises CDK9/cyclin T complexes. Hence, Myc expression and function may be susceptible to CDK9 inhibition. Non-specific inhibitors of multiple CDKs have shown promise in B-cell malignancies, where their pro-apoptotic effect has been attributed to a reduction in transcription and downmodulation of short lived pro-survival proteins, e.g. MCL1. However, such inhibitors lack a therapeutic window or a refined mechanism of action. Here we selectively targeted CDK9 in a pre-clinical study in DLBCL and demonstrate that this therapeutic approach disrupts Myc oncogenic function.Experiments were conducted in activated B-cell(ABC)-type (OCI-LY3, U2932, NuDUL-1) and germinal center(GC)-type (OCI-LY18/19, SUDHL4/6/10/16, VAL) DLBCL cell lines and in primary lymph node-derived B-cells from patients with refractory DLBCL. Tumor xenografts were established in NSG mice. We used AZ5576, a novel selective CDK9 inhibitor (Astra Zeneca), pan-CDK inhibitors (flavopiridol, dinaciclib) and genetic knockdown of CDK9.Treatment with AZ5576 promoted rapid apoptosis induction (within 2 hours) in DLBCL cell lines and primary tumor cells, as evident by PARP cleavage. Quantification of Annexin V+ cells after 24 hour drug exposure rendered an IC50 of 300-500 nM in DLBCL cell lines independent of cell of origin and 100 nM in primary DLBCL cells. Loss of RNA polymerase phosphorylation at Ser2 residue, a CDK9-dependent site, preceded apoptosis. Contrary to pan-CDK inhibitors, AZ-5576 did not inhibit CDKs 2, 4/6, and 7 (as measured by pRb and pRNApol [Ser5]), confirming its selective effect.CDK9 inhibition resulted in rapid (within 1 hour) and dose-dependent downregulation of Myc and MCL1 mRNA and protein in DLBCL cell lines and primary cells. Cell cycle profiling demonstrated that treatment with AZ-5576 led to S phase reduction, consistent with loss of Myc, while pan-CDK inhibitors downmodulated S/G2/M, reflecting inhibition of multiple CDKs. Cyclohexamide chase experiments demonstrated enhanced degradation of Myc in DLBCL cells treated with AZ-5576. Myc protein degradation is tightly regulated: while phosphorylation at Ser62 enhances Myc stability, MycT58 is primed for degradation. CDK9 inhibition decreased pMycS62 prior to apoptosis induction in DLBCL cell lines. Raji cells, which carry a stabilizing MycT58A mutation, were less sensitive to AZ-5576. This suggests that CDK9 may govern Myc protein turnover, thus regulating its expression through multiple mechanisms.Overexpression of Myc was associated with enhanced sensitivity to CDK9 inhibition. Treatment with 300 nM AZ-5576 for 24 h induced apoptosis of 35-70% of Myc-high cells (e.g., U-2932, VAL), compared with 10-20% of Myc-low cells (e.g., OCI-LY3, SU-DHL10). CDK9 inhibition did not disrupt Myc-CDK9 complex formation. Despite this, it abrogated Myc transcriptional activity in a functional reporter assay. Meanwhile, sensitivity to AZ-5576 did not correlate with expression of MCL1, BCL2 or BCLX.Our findings were confirmed in a mouse xenograft model. VAL cells were inoculated subcutaneously and treatment with AZ-5576 (30 mg/kg orally twice weekly) or vehicle control began when tumors reached 10 mm in size. Treatment led to reduced tumor progression (Figure), prolonged survival, decreased cell proliferation (Ki-67), enhanced apoptosis (Annexin V), and reduction in Myc total and p-S62 levels and MCL1.Thus, our data suggests that targeting CDK9 is a promising therapeutic strategy poised to disrupt Myc oncogenic activity in DLBCL and provides rationale for clinical development of AZ-5576. [Display omitted] DisclosuresChen:Seattle Genetics: Consultancy. Drew:Astra Zeneca: Employment. Danilov:ImmunoGen: Consultancy; Pharmacyclics: Consultancy; Astra Zeneca: Research Funding; Prime Oncology: Honoraria; Dava Oncology: Honoraria; GIlead Sciences: Research Funding; Takeda: Research Funding.