fadraciclib (CYC065)

P1, N=8, Completed, Cyclacel Pharmaceuticals, Inc. | Active, not recruiting --> Completed | Trial completion date: Feb 2024 --> May 2024 | Trial primary completion date: Mar 2023 --> Feb 2024

P1/2, N=210, Suspended, Cyclacel Pharmaceuticals, Inc. | Recruiting --> Suspended

P1, N=60, Completed, Cyclacel Pharmaceuticals, Inc. | Active, not recruiting --> Completed

P1/2, N=330, Recruiting, Cyclacel Pharmaceuticals, Inc. | Trial completion date: Dec 2023 --> Jun 2025 | Trial primary completion date: Oct 2023 --> Apr 2025

P1, N=8, Active, not recruiting, Cyclacel Pharmaceuticals, Inc. | Trial completion date: Oct 2023 --> Jan 2024 | Trial primary completion date: Aug 2023 --> Mar 2023

P1, N=14, Completed, Cyclacel Pharmaceuticals, Inc. | Active, not recruiting --> Completed | N=25 --> 14 | Trial completion date: Sep 2023 --> Apr 2023

P1, N=5, Completed, Cyclacel Pharmaceuticals, Inc. | Active, not recruiting --> Completed | N=25 --> 5

CDK2/9 antagonism with CYC065 (Fadraciclib)-treatment disordered centrosome stoichiometry in aneuploid cancer cells, preventing centrosome clustering...Thus, CDK2 inhibition preferentially disorders centrosome stoichiometry in cancer cells. Engaging this disruption is a strategy to explore against aneuploid cancers in future clinical trials.

Therefore, SUPT11 cells (used as a model of T-PLL) were exposed to venetoclax (25 and 50nM; BCL-2inh), fadraciclib (25 and 50nM; CDK2/9inh – indirect inhibitor of MCL-1 as it decreases mRNAs with high decay rates including MCL1 and MYC) or a combination of venetoclax and fadraciclib. In conclusion, preclinical evaluation of a T-PLL cell line and primary patient samples demonstrate BCL2-family dependency that can be effectively targeted with small molecule inhibitors of BCL2 and CDK2/9. In vivo studies in PDX models of T-PLL are underway to form the basis for clinical trials to study these combinations.

Material & Three NB cell lines (LAN-1, CHLA-90, CHLA-172) were treated with IC50 doses of abemaciclib, dinaciclib or fadraciclib. We describe the successful induction of NB differentiation by selective CDK inhibitors, which is enhanced by sequential administration of RA. Two of the three cell lines included in this study are representative of GD2-negative tumors. Therefore, we propose this approach as an alternative for NB cases ineligible for GD-directed immunotherapy.

NVP-2, MC180295, fadraciclib, KB-0742, LZT-106, and 21e have been developed mainly for treating solid tumors, and most of them work only on certain genotypes of solid tumors. Only VIP152 has been proven to benefit the patients with advanced high-grade lymphoma (HGL) and solid tumors in clinical trials. Continued efforts to explore the molecular mechanisms underlying the inhibitory effects, and to identify suitable tumor genotypes and combination treatment strategies, are crucial to demonstrate the efficacy of selective CDK9 inhibitors and degraders in tumor therapy.

P1/2, N=460, Recruiting, Gustave Roussy, Cancer Campus, Grand Paris | Trial completion date: Jan 2022 --> Aug 2027 | Trial primary completion date: Jan 2022 --> Aug 2027

To elucidate engaged mechanisms focused ion beam scanning electron microscope (FIB-SEM) and immunofluorescent staining were each used to interrogate the ultrastructure of multipolar mitosis after CDK2 inhibition by CYC065-treatment (a CDK2/9 inhibitor)...This is a clinically-tractable pharmacologic mechanism that conferring cancer cell death. Current work determines if similar mechanisms are engaged in vivo in syngeneic mouse lung cancer models undergoing CDK2 antagonism.

Fadraciclib (CYC065) is a second-generation aminopurine CDK2/9 inhibitor with increased potency and selectivity toward CDK2 and CDK9 compared to seliciclib (R-roscovitine). The best combination effects were achieved when both drugs were maintained together. Altogether, this study provides a rationale for the clinical development of fadraciclib in CLL, either alone or in combination with a Bcl-2 antagonist.

Further evaluation of this role has been hampered by the lack of selective pharmacological inhibitors. Herein, we provide a comprehensive overview about the therapeutic potential of targeting CDK3 in cancer.

To demonstrate the utility of a selective CDK9 inhibitor for treatment of hematologic patients with an unmet medical need such as high-grade B cell lymphoma (HGBL) and chronic lymphocytic leukemia who relapse or are refractory to ibrutinib and venetoclax (R/R CLL)...Differential expression (DE) analysis from VIP152, atuveciclib and KB-0742 treatment of 2 lymphoma cell lines by RNA seq is compared to DE of samples from 7 VIP152 treated HGBL patients...With high ATP, VIP152, AZD4573 and alvocidib maintain potency in low nM range, while fadraciclib and KB-0742 have 760 nM-1.7 µM IC50s...Selective transcriptional downregulation is observed with 30mg IV weekly. Samples from patients with DLBCL or CLL are sensitive to VIP152 and updated PK, PD and ctDNA dynamics from the ongoing phase 1 trials (NCT02635672, NCT04978779) will be presented.

P1, N=25, Active, not recruiting, Cyclacel Pharmaceuticals, Inc. | Recruiting --> Active, not recruiting | Trial completion date: Dec 2020 --> Sep 2023 | Trial primary completion date: Jun 2020 --> Apr 2023

P1, N=25, Active, not recruiting, Cyclacel Pharmaceuticals, Inc. | Recruiting --> Active, not recruiting | Trial completion date: May 2020 --> Jul 2023 | Trial primary completion date: Jan 2020 --> Jan 2023

P1/2, N=210, Recruiting, Cyclacel Pharmaceuticals, Inc.

Patient resistance to the current standard of care, temozolomide and radiotherapy, is common and highlights the need to discover more effective treatment strategies. Collectively, these data demonstrate that CYC065 and THZ1 display high anti-cancer activity in primary and recurrent GBM and provide scientific rationale for the further development of CDK inhibitors to potentiate their clinical utilization in the future.

However, 10–50% of newly diagnosed patients with AML may not respond to venetoclax and HMA or LDAC, and 3–15% patients may not respond to venetoclax with intensive or non-intensive chemotherapy.1–6 In addition, up to 40% of responding patients may relapse with low rates of response of 20% to salvage therapy and poor overall survival of 2 months after relapse.7 Clinical and biological factors associated with primary and acquired resistance to venetoclax include secondary AML, monocytic differentiation, complex cytogenetics, mutations in TP53, BAX, dependence on other anti- apoptotic proteins, altered metabolism of nicotinamide, fatty acids, and oxidative phosphortylation.3,8–14 Several novel inhibitors of BCL-2 are currently being tested in clinic, including BGB 11417, APG-2575, LP-108 and others...There is strong pre-clinical rationale for targeting MCL-1 alone as well as in conjunction with BCL-2 inhibition in AML.15 Recently several selective and highly potent MCL-1 inhibitors have entered pre-clinical and clinical development including S63845, AZD5991, AMG397, and others. Questions remain regarding the therapeutic window of these inhibitors given the important physiologic role of MCL-1 in vital organs and early reports of cardiac adverse events from the AMG176 phase 1 trial.15,16 Multiple pre-clinical studies have expectedly shown synergism between BCL- 2 and MCL-1 inhibition making it a promising path for clinical development of these agents.17,18 Multifactorial challenges in design of specific MCL-1 inhibitors also led to interest in compounds which downregulate MCL-1 expression. Cyclin dependent kinase (CDK) inhibitors including alvocidib, dinaciclib, voruciclib are in various stages of evaluation. Although addition of alvocidib to intensive chemotherapy improved response rates but failed to improve event-free or overall survival.19 Novel CDK inhibitors are currently in early phase trials including AZD4573, CYC065, TG02-101, and others. Inhibition of Nedd8 activating enzyme has complex repercussions for the intrinsic apoptotic pathway with eventual increase in Noxa leading to MCL-1 neutralization.20 Pevonedistat has shown promising early results in AML and myelodysplastic syndrome and is being investigated multiple clinical trials for solid tumors as well. BCL-xL Inhibition Another anti-apoptotic protein BCL-xL had been long recognized as a potential therapeutic target in AML, in particular AML from preceding MPN and AML recurrent post venetoclax failure, but toxicity of earlier inhibitors precluded clinical development.21–23 Recently, AZD0466, a dual BCL-2/xL inhibitor with a favorable therapeutic index and robust activity has been developed and is undergoing pre-clinical development and planned for phase iin hematological malignancies.24 Targeting the Extrinsic Apoptosis Pathway Inhibitor of apoptosis protein (IAP) inhibition: X-linked IAP (XIAP), cellular IAP (cIAP) and survivin have been of long- standing interest in AML. Prior clinical trials with XIAP inhibitor AEG35156, cIAP targeting agent birinapant, and survivin targeting agent LY2181308 have not succeeded in clinc.16,25 ASTX660 is a dual antagonist of XIAP and cIAP which is currently being investigated in phase 1/2 trials in solid tumors and in combination with HMA in relapsed or refractory AML.26,27 TRAIL Agonism Agonists of the TNF-related apoptosis-inducing ligand (TRAIL) receptors have been tested in AML with low response rates.28,29 Previous agents have had limited success in part due to suboptimal clustering of TRAIL receptors.30 Novel antibodies against TRAILR1 and TRAILR2 including an IgM molecule IGM-8444, a tetravalent compound INBRX-109, and HLX56 are currently in phase 1 trials and preclinical data suggests potential synergy with venetoclax.31 FLIP Inhibition FLICE-like inhibitor protein (FLIP or CFLAR) is a key regulator of the death-inducing signaling complex (DISC) involved in the extrinsic apoptotic pathway...This can be augmented by inhibiting p53 degradation via MDM2, which is often upregulated in AML.34 Idasanutlin in combination with venetoclax showed anti- Figure 1 leukemic activity in the dose finding stage in R/R AML.35 Several other inhibitors of MDM2 and dual MDM2/X inhibitors are currently in various stages of pre-clinical and clinical development including HDM-201, KRT-232, BI-9078282, and others.34 Conclusions Opportunities to target the apoptosis machinery in AML has considerably evolved in the last decade. While venetoclax heralded a paradigm shift for patients, we are now faced with challenges in patients who relapse or remain refractory. We have novel clinical stage compounds to methodologically target different facets of the apoptotic pathway and optimize novel combinations with the goal to improve the cure rates in AML patients.

AZD5991 is a highly selective BH3-mimetic that demonstrates high in vitro potency in MCL1-dependent cell lines with an IC50 <1 nM.7 We have demonstrated that direct MCL1 inhibition with AZD5991 disrupts survival of neoplastic B-cells in lymph-node mimicking conditions, induces mitochondrial dysfunction and cooperates with BCL2/X inhibitors in vitro and in vivo.8 A phase 1 clinical trial of AZD5991 alone or in combination with venetoclax in hematologic malignancies is ongoing (NCT03218683)...AMG-176 demonstrated synergy with venetoclax in AML models; however, it also caused cytopenias.9 AMG-176 was shown to induce apoptosis of CLL cells independent of prognostic markers and overcame the protective effect of stromal microenvironment.10 However, suppressive effects on hematopoiesis will likely become the dose- limiting factor in clinical trials of MCL1-targeting agents. The effect of MCL1 inhibition on cord blood-derived CD34+ cells was studied using a small-molecule inhibitor, S63845,11 resulting in almost complete depletion of human hematopoietic stem and progenitor cells, while mature blood cells survived normally...We have shown that SYK inhibition with entospletinib leads to downmodulation of MCL1 protein in CLL both in vitro and in the clinic.12,13 Treatment of CLL cells with entospletinib, but not other BCR-signaling inhibitors, led to a disruption of BAFF-BCR cross-talk and downmodulation of MCL1 mRNA and protein, thus implicating SYK in transduction of multiple pro-survival signals emanating from the tumor microenvironment.13 Entospletinib has shown promising clinical activity in CLL.12,14 It is currently being developed in myeloid malignancies.15 A novel dual SYK/BTK inhibitor luxeptinib also was shown to downregulate MCL1 and other pro-survival BCL2 proteins in CLL.16 Transcriptional cyclin-dependent kinases (CDK7/9) regulate activity of RNA polymerase, thereby controlling production of mRNA. Downmodulation of MCL1 has been considered a key mechanistic event accounting for the pro-apoptotic activity of CDK inhibitors in neoplastic B-cells.17,18 Pan-CDK inhibitors (flavopiridol, dinaciclib) demonstrate clinical efficacy in lymphoid malignancies. We and others reported that preclinical efficacy of AZ5576, a selective inhibitor of CDK9, and its clinical congener AZD4573 in lymphoid tumors depended on rapid downmodulation of MCL1, BFL1, and MYC.19–21 CDK9 inhibition can increase efficacy of BH3-mimetics, but safety of this combination will need to be explored.22,23 CDK9 inhibitors in development, in addition to AZD4573, include VIP152, CYC065, and voruciclib...Navitoclax is a small-molecule inhibitor of BCL2, BCLX, and BCL2L2; however, its use in CLL has been plagued by thrombocytopenia.24 AZD4320 is an alternative agent that co-targets BCL2/X...ABBV-155, an antibody-drug conjugate targeting BCLX, where BCLX is being used as a payload to avoid “off-tumor” effects, demonstrated promise in solid tumor models.26 Finally, as many microenvironment-driven pro-survival pathways converge on NFB, leading to induction of chemokines, cell cycle regulators, and BCL2 family proteins themselves, this transcription factor continues to be an attractive target in CLL...When combined with ibrutinib in murine CLL models, VAY-736 produced prolonged survival compared with either therapy alone.28 Alternative targets for therapeutic antibodies include ROR1 (cirmtuzumab), CD19 (tafasitamab), and others.29 As resistance to novel agents is becoming an unmet need in CLL, exploration of novel targets is of paramount importance...Multiple CDK inhibitors are currently being explored and have anti-tumor effects not restricted to MCL1 inhibition. CAR T cells and bi-specific antibodies have exceptional efficacy in lymphoid malignancies and thus are of high relevance in CLL.

CKIs reduced proliferation and promoted apoptosis also in chick embryo xenograft models of primary and recurrent GBM. Collectively, these studies highlight the potential of these novel CKIs to suppress growth and induce cell death of patient-derived GBM cultures in vitro and in vivo, warranting further clinical investigation.

Synergistic activity was demonstrated when fadraciclib was combined with the BCL-2 inhibitor venetoclax, or the conventional chemotherapy agents, cytarabine, or azacitidine, with the combination of fadraciclib and azacitidine having the most favorable therapeutic window. In summary, these results highlight the potential of fadraciclib as a novel therapeutic approach for AML.

Glioma stem cells (GSCs) are tumour initiating cells which contribute to treatment resistance, temozolomide (TMZ) chemotherapy and radiotherapy, in glioblastoma (GBM), the most aggressive adult brain tumour. Apoptotic cell death in GSC subpopulations and non-stem tumour cells resulted in sphere disruption. Collectively, our study highlights the potential of these novel CKIs to induce cell death in GSCs from recurrent tumours, warranting further clinical investigation.

Thus, induced anaphase catastrophe after CYC065-treatment can combat aneuploid cancers despite KRAS oncoprotein expression. These findings should guide future trials of this novel CDK2/9 inhibitor in the cancer clinic.

After treatment with trastuzumab, the NSG mice inoculated with BT474R2-5M cells developed significantly lower tumor volumes (p < .001), when compared to mice inoculated with BT474R2 cells. Taken together, these results indicate that for patients with HER2+ breast cancer, a mechanism of CCNE-mediated trastuzumab resistance, regulated through noncanonical SMAD3 phosphorylation, could be treated with CDK2 inhibition to help enhance the efficacy of trastuzumab therapy.

MYCN overexpression in mesenchymal neuroblastoma was sufficient to induce adrenergic identity and sensitize cells to CYC065. CYC065, used together with temozolomide, a reference therapy for relapsed neuroblastoma, caused long-term suppression of neuroblastoma growth in vivo, highlighting the clinical potential of CDK9/2 inhibition in the treatment of MYCN-amplified neuroblastoma.

Here, we provide the first disclosure of the chemical structure of fadraciclib (CYC065), a CDK inhibitor and clinical candidate designed by further optimization from the aminopurine scaffold of seliciclib. Fadraciclib preclinical pharmacology data support its therapeutic potential in CDK9- or CDK2-dependent cancers and as a rational combination with BCL2 inhibitors in hematological malignancies. Fadraciclib is currently in Phase 1 clinical studies in patients with advanced solid tumors (NCT02552953) and also in combination with venetoclax in patients with relapsed or refractory chronic lymphocytic leukemia (CLL) (NCT03739554) and relapsed refractory acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) (NCT04017546).

CYC065 pulse treatment effectively induced apoptosis in AML cell lines in vitro. Target inhibition was confirmed by analysis of gene and protein expression and was accompanied by induction of apoptosis and cell cycle arrest. A synergistic effect of CYC065 in combination with venetoclax, cytarabine, or azacitidine was seen in AML cell lines and primary AML cells.