CDK4/6 inhibition as maintenance and combination therapy for high grade serous ovarian cancer

The Clinicopathological Significance of the Cyclin D1/E1-Cyclin-Dependent Kinase (CDK2/4/6)-Retinoblastoma (RB1/pRB1) Pathway in Epithelial Ovarian Cancers

Cyclin-dependent kinases (CDK2, CDK4, CDK6), cyclin D1, cyclin E1 and phosphorylated retinoblastoma (pRB1) are key regulators of the G1/S cell cycle checkpoint and may influence platinum response in ovarian cancers. CDK2/4/6 inhibitors are emerging targets in ovarian cancer therapeutics. In the current study, we evaluated the prognostic and predictive significance of the CDK2/4/6-cyclin D1/E1-pRB1 axis in clinical ovarian cancers (OC). The CDK2/4/6, cyclin D1/E1 and RB1/pRB1 protein expression were investigated in 300 ovarian cancers and correlated with clinicopathological parameters and patient outcomes. CDK2/4/6, cyclin D1/E1 and RB1 mRNA expression were evaluated in the publicly available ovarian TCGA dataset. We observed nuclear and cytoplasmic staining for CDK2/4/6, cyclins D1/E1 and RB1/pRB1 in OCs with varying percentages. Increased nuclear CDK2 and nuclear cyclin E1 expression was linked with poor progression-free survival (PFS) and a shorter overall survival (OS). Nuclear CDK6 was associated with poor OS. The cytoplasmic expression of CDK4, cyclin D1 and cyclin E1 also has predictive and/or prognostic significance in OCs. In the multivariate analysis, nuclear cyclin E1 was an independent predictor of poor PFS. Tumours with high nuclear cyclin E1/high nuclear CDK2 have a worse PFS and OS. Detailed bioinformatics in the TCGA cohort showed a positive correlation between cyclin E1 and CDK2. We also showed that cyclin-E1-overexpressing tumours are enriched for genes involved in insulin signalling and release. Our data not only identified the prognostic/predictive significance of these key cell cycle regulators but also demonstrate the importance of sub-cellular localisation. CDK2 targeting in cyclin-E1-amplified OCs could be a rational approach.

CDK4/6 Inhibition With Lerociclib is a Potential Therapeutic Strategy for the Treatment of Pediatric Sarcomas

BACKGROUND

Sarcomas are a heterogenous collection of bone and soft tissue tumors. The heterogeneity of these tumors makes it difficult to standardize treatment. CDK 4/6 inhibitors are a family of targeted agents which limit cell cycle progression and have been shown to be upregulated in sarcomas. In the current preclinical study, we evaluated the effects of lerociclib, a CDK4/6 inhibitor, on pediatric sarcomas in vitro and in 3D bioprinted tumors.

METHODS

The effects of lerociclib on viability, proliferation, cell cycle, motility, and stemness were assessed in established sarcoma cell lines, U-2 OS and MG-63, as well as sarcoma patient-derived xenografts (PDXs). 3D printed biotumors of each of the U-2 OS, MG-63, and COA79 cells were utilized to study the effects of lerociclib on tumor growth ex vivo.

RESULTS

CDK 4/6, as well as the intermediaries retinoblastoma protein (Rb) and phosphorylated Rb were identified as targets in the four sarcoma cell lines. Lerociclib treatment induced cell cycle arrest, decreased proliferation, motility, and stemness of sarcoma cells. Treatment with lerociclib decreased sarcoma cell viability in both traditional 2D culture as well as 3D bioprinted microtumors.

CONCLUSIONS

Inhibition of CDK 4/6 activity with lerociclib was efficacious in traditional 2D sarcoma cell culture as well as in 3D bioprints. Lerociclib holds promise and warrants further investigation as a novel therapeutic strategy for management of these heterogenous groups of tumors.

The effects of chitosan-loaded JQ1 nanoparticles on OVCAR-3 cell cycle and apoptosis-related gene expression

Background and purpose

Ovarian cancer is the deadliest gynecological cancer. Bromodomain and extra terminal domain (BET) proteins play major roles in the regulation of gene expression at the epigenetic level. Jun Qi (JQ1) is a potent inhibitor of BET proteins. Regarding the short half-life and poor pharmacokinetic profile, JQ1 was loaded into newly developed nano-carriers. Chitosan nanoparticles are one of the best and potential polymers in cancer treatment. The present study aimed to build chitosan-JQl nanoparticles (Ch-J-NPs), treat OVCAR-3 cells with Ch-J-NPs, and evaluate the effects of these nanoparticles on cell cycle and apoptosis-associated genes.

Experimental approach

Ch-J-NPs were synthesized and characterized. The size and morphology of Ch-J-NPs were defined by DLS and FE-SEM techniques. OVCAR-3 cells were cultured and treated with Ch-J-NPs. Then, IC50 was measured using MTT assay. The groups were defined and cells were treated with IC50 concentration of Ch-J-NPs, for 48 h. Finally, cells in different groups were assessed for the expression of genes of interest using quantitative RT-PCR.

Findings/Results

IC50 values for Ch-J-NPs were 5.625 μg/mL. RT-PCR results demonstrated that the expression of genes associated with cell cycle activity (c-MYC, hTERT, CDK1, CDK4, and CDK6) was significantly decreased following treatment of cancer cells with Ch-J-NPs. Conversely, the expression of caspase-3, and caspase-9 significantly increased. BAX (pro-apoptotic) to BCL2 (anti-apoptotic) expression ratio, also increased significantly after treatment of cells with Ch-J-NPs.

Conclusion and implications

Ch-J-NPs showed significant anti-cell cyclic and apoptotic effects on OVCAR-3 cells.

Therapy-induced senescence as a component of tumor biology: Evidence from clinical cancer

Therapy-Induced Senescence (TIS) is an established response to anticancer therapy in a variety of cancer models. Ample evidence has characterized the triggers, hallmarks, and functional outcomes of TIS in preclinical studies; however, limited evidence delineates TIS in clinical cancer (human tumor samples). We examined the literature that investigated the induction of TIS in samples derived from human cancers and highlighted the major findings that suggested that TIS represents a main constituent of tumor biology. The most frequently utilized approach to identify TIS in human cancers was to investigate the protein expression of senescence-associated markers (such as cyclins, cyclin-dependent kinase inhibitors, Ki67, DNA damage repair response markers, DEC1, and DcR1) via immunohistochemical techniques using formalin-fixed paraffin-embedded (FFPE) tissue samples and/or testing the upregulation of Senescence-Associated β-galactosidase (SA-β-gal) in frozen sections of unfixed tumor samples. Collectively, and in studies where the extent of TIS was determined, TIS was detected in 31-66% of tumors exposed to various forms of chemotherapy. Moreover, TIS was not only limited to both malignant and non-malignant components of tumoral tissue but was also identified in samples of normal (non-transformed) tissue upon chemo- or radiotherapy exposure. Nevertheless, the available evidence continues to be limited and requires a more rigorous assessment of in vivo senescence based on novel approaches and more reliable molecular signatures. The accurate assessment of TIS will be beneficial for determining its relevant contribution to the overall outcome of cancer therapy and the potential translatability of senotherapeutics.

Quiescent Ovarian Cancer Cells Secrete Follistatin to Induce Chemotherapy Resistance in Surrounding Cells in Response to Chemotherapy

PURPOSE

We recently reported that the transcription factor NFATC4, in response to chemotherapy, drives cellular quiescence to increase ovarian cancer chemoresistance. The goal of this work was to better understand the mechanisms of NFATC4-driven ovarian cancer chemoresistance.

EXPERIMENTAL DESIGN

We used RNA sequencing to identify NFATC4-mediated differential gene expression. CRISPR-Cas9 and FST (follistatin)-neutralizing antibodies were used to assess impact of loss of FST function on cell proliferation and chemoresistance. ELISA was used to quantify FST induction in patient samples and in vitro in response to chemotherapy.

RESULTS

We found that NFATC4 upregulates FST mRNA and protein expression predominantly in quiescent cells and FST is further upregulated following chemotherapy treatment. FST acts in at least a paracrine manner to induce a p-ATF2-dependent quiescent phenotype and chemoresistance in non-quiescent cells. Consistent with this, CRISPR knockout (KO) of FST in ovarian cancer cells or antibody-mediated neutralization of FST sensitizes ovarian cancer cells to chemotherapy treatment. Similarly, CRISPR KO of FST in tumors increased chemotherapy-mediated tumor eradication in an otherwise chemotherapy-resistant tumor model. Suggesting a role for FST in chemoresistance in patients, FST protein in the abdominal fluid of patients with ovarian cancer significantly increases within 24 hours of chemotherapy exposure. FST levels decline to baseline levels in patients no longer receiving chemotherapy with no evidence of disease. Furthermore, elevated FST expression in patient tumors is correlated with poor progression-free, post-progression-free, and overall survival.

CONCLUSIONS

FST is a novel therapeutic target to improve ovarian cancer response to chemotherapy and potentially reduce recurrence rates.

Novel pentacyclic derivatives and benzylidenes of the progesterone series cause anti-estrogenic and antiproliferative effects and induce apoptosis in breast cancer cells

The promising antitumor effects of progesterone derivatives have been identified in many studies. However, the specific mechanism of action of this class of compounds has not been fully described. Therefore, in this study, we investigated the antiproliferative and (anti)estrogenic activities of novel pentacyclic derivatives and benzylidenes of the progesterone series. The antiproliferative effects of the compounds were evaluated on hormone-dependent MCF7 breast cancer cells using the MTT test. Estrogen receptor α (ERα) activity was assessed by a luciferase-based reporter assay. Immunoblotting was used to evaluate the expression of signaling proteins. All benzylidenes demonstrated inhibitory effects with IC₅₀ values below 10 µM, whereas pentacyclic derivatives were less active. These patterns may be associated with the lability of the geometry of benzylidene molecules, which contributes to an increase in the affinity of interaction with the receptor. The selected compounds showed significant anti-estrogenic potency. Benzylidene 1d ((8 S,9 S,10R,13 S,14 S,17 S)-17-[(2E)-3-(4-fluorophenyl)prop-2-enoyl]-10,13-dimethyl-1,2,6,7,8,9,11,12,14,15-decahydrocyclopenta[a]phenanthren-3-one) was the most active in antiproliferative and anti-estrogenic assays. Apoptosis induced by compound 1d was accompanied by decreases in CDK4, ERα, and Cyclin D1 expression. Compounds 1d and 3d were characterized by high inhibitory potency against resistant breast cancer cells. Apoptosis induced by the leader compounds was confirmed by PARP cleavage and flow cytometry analysis. Compound 3d caused cell arrest in the G2/M phase. Further analysis of novel derivatives of the progesterone series is of great importance for medicinal chemistry, drug design, and oncology.

Targeting senescence as an anticancer therapy

Cellular senescence is a stress response elicited by different molecular insults. Senescence results in cell cycle exit and is characterised by multiple phenotypic changes such as the production of a bioactive secretome. Senescent cells accumulate during ageing and are present in cancerous and fibrotic lesions. Drugs that selectively kill senescent cells (senolytics) have shown great promise for the treatment of age-related diseases. Senescence plays paradoxical roles in cancer. Induction of senescence limits cancer progression and contributes to therapy success, but lingering senescent cells fuel progression, recurrence, and metastasis. In this review, we describe the intricate relation between senescence and cancer. Moreover, we enumerate how current anticancer therapies induce senescence in tumour cells and how senolytic agents could be deployed to complement anticancer therapies. "One-two punch" therapies aim to first induce senescence in the tumour followed by senolytic treatment to target newly exposed vulnerabilities in senescent tumour cells. "One-two punch" represents an emerging and promising new strategy in cancer treatment. Future challenges of "one-two punch" approaches include how to best monitor senescence in cancer patients to effectively survey their efficacy.

Indisulam synergizes with palbociclib to induce senescence through inhibition of CDK2 kinase activity

Inducing senescence in cancer cells is emerging as a new therapeutic strategy. In order to find ways to enhance senescence induction by palbociclib, a CDK4/6 inhibitor approved for treatment of metastatic breast cancer, we performed functional genetic screens in palbociclib-resistant cells. Using this approach, we found that loss of CDK2 results in strong senescence induction in palbociclib-treated cells. Treatment with the CDK2 inhibitor indisulam, which phenocopies genetic CDK2 inactivation, led to sustained senescence induction when combined with palbociclib in various cell lines and lung cancer xenografts. Treating cells with indisulam led to downregulation of cyclin H, which prevented CDK2 activation. Combined treatment with palbociclib and indisulam induced a senescence program and sensitized cells to senolytic therapy. Our data indicate that inhibition of CDK2 through indisulam treatment can enhance senescence induction by CDK4/6 inhibition.

Phase I trial of ribociclib with platinum chemotherapy in recurrent ovarian cancer

BACKGROUND

New therapeutic combinations to improve the outcome of ovarian cancer patients are clearly needed. Preclinical studies with ribociclib (LEE-011), a CDK4/6 cell cycle checkpoint inhibitor, demonstrate a synergistic effect with platinum chemotherapy and efficacy as a maintenance therapy after chemotherapy. We tested the safety and initial efficacy of ribociclib in combination with platinum-based chemotherapy in recurrent ovarian cancer.

METHODS

This phase I trial combined weekly carboplatin and paclitaxel chemotherapy with ribociclib followed by ribociclib maintenance in patients with recurrent platinum-sensitive ovarian cancer. Primary objectives were safety and maximum tolerated dose (MTD) of ribociclib when given with platinum and taxane chemotherapy. Secondary endpoints were response rate (RR) and progression-free survival (PFS).

RESULTS

Thirty-five patients were enrolled. Patients had a mean 2.5 prior lines of chemotherapy, and 51% received prior maintenance therapy with Poly (ADP-ribose) polymerase inhibitors (PARPi) and/or Bevacizumab. The MTD was 400mg. The most common AEs included anemia (82.9%), neutropenia (82.9%), fatigue (82.9%), and nausea (77.1%). Overall RR was 79.3% with a stable disease (SD) rate of 18% resulting in a clinical benefit rate of 96.6%. The PFS was 11.4 months. RR and PFS did not differ based on number of lines of prior chemotherapy or prior maintenance therapy.

CONCLUSIONS

This work demonstrates the combination of ribociclib with chemotherapy in ovarian cancer is feasible and safe. With a clinical benefit rate of 97%, this work provides encouraging evidence of clinical efficacy in patients with recurrent platinum-sensitive disease.

TRIAL REGISTRATION

CLINICALTRIALS

gov NCT03056833.

FUNDING

This investigator-initiated trial was supported by Novartis who provided drug and funds for trial execution.

A Platform of Patient-Derived Microtumors Identifies Individual Treatment Responses and Therapeutic Vulnerabilities in Ovarian Cancer

In light of the frequent development of therapeutic resistance in cancer treatment, there is a strong need for personalized model systems representing patient tumor heterogeneity, while enabling parallel drug testing and identification of appropriate treatment responses in individual patients. Using ovarian cancer as a prime example of a heterogeneous tumor disease, we developed a 3D preclinical tumor model comprised of patient-derived microtumors (PDM) and autologous tumor-infiltrating lymphocytes (TILs) to identify individual treatment vulnerabilities and validate chemo-, immuno- and targeted therapy efficacies. Enzymatic digestion of primary ovarian cancer tissue and cultivation in defined serum-free media allowed rapid and efficient recovery of PDM, while preserving histopathological features of corresponding patient tumor tissue. Reverse-phase protein array (RPPA)-analyses of >110 total and phospho-proteins enabled the identification of patient-specific sensitivities to standard, platinum-based therapy and thereby the prediction of potential treatment-responders. Co-cultures of PDM and autologous TILs for individual efficacy testing of immune checkpoint inhibitor treatment demonstrated patient-specific enhancement of cytotoxic TIL activity by this therapeutic approach. Combining protein pathway analysis and drug efficacy testing of PDM enables drug mode-of-action analyses and therapeutic sensitivity prediction within a clinically relevant time frame after surgery. Follow-up studies in larger cohorts are currently under way to further evaluate the applicability of this platform to support clinical decision making.

The Emerging Role of Cyclin-Dependent Kinase Inhibitors in Treating Diet-Induced Obesity: New Opportunities for Breast and Ovarian Cancers?

Overweight and obesity constitute the most impactful lifestyle-dependent risk factors for cancer and have been tightly linked to a higher number of tumor-related deaths nowadays. The excessive accumulation of energy can lead to an imbalance in the level of essential cellular biomolecules that may result in inflammation and cell-cycle dysregulation. Nutritional strategies and phytochemicals are gaining interest in the management of obesity-related cancers, with several ongoing and completed clinical studies that support their effectiveness. At the same time, cyclin-dependent kinases (CDKs) are becoming an important target in breast and ovarian cancer treatment, with various FDA-approved CDK4/6 inhibitors that have recently received more attention for their potential role in diet-induced obesity (DIO). Here we provide an overview of the most recent studies involving nutraceuticals and other dietary strategies affecting cell-cycle pathways, which might impact the management of breast and ovarian cancers, as well as the repurposing of already commercialized chemotherapeutic options to treat DIO.

CDK4/6 Inhibitors in Combination Therapies: Better in Company Than Alone: A Mini Review

The cyclin D-CDK4/6 complexes play a pivotal role in controlling the cell cycle. Deregulation in cyclin D-CDK4/6 pathway has been described in many types of cancer and it invariably leads to uncontrolled cell proliferation. Many efforts have been made to develop a target therapy able to inhibit CDK4/6 activity. To date, three selective CDK4/6 small inhibitors have been introduced in the clinic for the treatment of hormone positive advanced breast cancer patients, following the impressive results obtained in phase III clinical trials. However, since their approval, clinical evidences have demonstrated that about 30% of breast cancer is intrinsically resistant to CDK4/6 inhibitors and that prolonged treatment eventually leads to acquired resistance in many patients. So, on one hand, clinical and preclinical studies fully support to go beyond breast cancer and expand the use of CDK4/6 inhibitors in other tumor types; on the other hand, the question of primary and secondary resistance has to be taken into account, since it is now very clear that neoplastic cells rapidly develop adaptive strategies under treatment, eventually resulting in disease progression. Resistance mechanisms so far discovered involve both cell-cycle and non-cell-cycle related escape strategies. Full understanding is yet to be achieved but many different pathways that, if targeted, may lead to reversion of the resistant phenotype, have been already elucidated. Here, we aim to summarize the knowledge in this field, focusing on predictive biomarkers, to recognize intrinsically resistant tumors, and therapeutic strategies, to overcome acquired resistance.

Dual Fluorescence Isogenic Synthetic Lethal Kinase Screen and High-Content Secondary Screening for MUC16/CA125 Selective Agents

Significant strides have been made in the development of precision therapeutics for cancer. Aberrantly expressed glycoproteins represent a potential avenue for therapeutic development. The MUC16/CA125 glycoprotein serves as a biomarker of disease and a driver of malignant transformation in epithelial ovarian cancer. Previously, we demonstrated a proof-of-principle approach to selectively targeting MUC16+ cells. In this report, we performed a synthetic lethal kinase screen using a human kinome RNAi library and identified key pathways preferentially targetable in MUC16+ cells using isogenic dual florescence ovarian cancer cell lines. Utilizing a separate approach, we performed high-content small-molecule screening of 6 different libraries of 356,982 compounds for MUC16/CA125 selective agents and identified lead candidates that showed preferential cytotoxicity in MUC16+ cells. Compounds with differential activity were selected and tested in various other ovarian cell lines or isogenic pairs to identify lead compounds for Structural Activity Relationship (SAR) selection. Lead siRNA and small molecule inhibitor candidates preferentially inhibited invasion of MUC16+ cells in vitro and in vivo and we show that this is due to decreased activation of MAP kinase, and non-receptor tyrosine kinases. Taken together, we present a comprehensive screening approach to the development of a novel class of MUC16-selective targeted therapeutics and identify candidates suitable for further clinical development.

The Immunological Role of CDK4/6 and Potential Mechanism Exploration in Ovarian Cancer

Background

Ovarian cancer (OC) is one of the most lethal gynecologic cancers. Growing evidence has proven that CDK4/6 plays a key role in tumor immunity and the prognosis of many cancers. However, the expression and function of CDK4/6 in OC remain unclear. Therefore, we aimed to explore the influence of CDK4/6 in OC, especially on immunity.

Methods

We analyzed CDK4/6 expression and prognosis using The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO) and Genotype Tissue Expression (GTEx) data. Subsequently, we used the cytoHubba plug-in of Cytoscape software and starBase to identify the noncoding RNAs (ncRNAs) regulating CDK4/6. Finally, we verified the effect of CDK4/6 on immunity in OC cell lines and animal models.

Results

CDK4/6 expression was higher in OC tissues than in normal ovarian tissues, and the high expression levels of CDK4/6 contributed to the immunosuppressive state of OC and were thus related to the poor prognosis of OC patients. This was also in general agreement with the results of OC cell line and animal experiments. Mechanistically, the CDK4/6 inhibitor palbociclib increased the secretion of interferon (IFN)-γ and the interferon-stimulated gene (ISG) response, thereby upregulating the expression of antigen-presenting molecules; this effect was partly dependent on the STING pathway and thus activated immunity in OC. Additionally, according to public data, the LRRC75A-AS1-hsa-miR-330-5p axis could inhibit the immune response of OC patients by upregulating CDK4/6, leading to a poor prognosis.

Conclusion

CDK4/6 affects the immune microenvironment of OC and correlates with the prognosis of OC patients.

Synergistic combination of cytotoxic chemotherapy and cyclin-dependent kinase 4/6 inhibitors in biliary tract cancers

BACKGROUND AND AIMS

Biliary tract cancers (BTCs) are uncommon, but highly lethal, gastrointestinal malignancies. Gemcitabine/cisplatin is a standard-of-care systemic therapy, but has a modest impact on survival and harbors toxicities, including myelosuppression, nephropathy, neuropathy, and ototoxicity. Whereas BTCs are characterized by aberrations activating the cyclinD1/cyclin-dependent kinase (CDK)4/6/CDK inhibitor 2a/retinoblastoma pathway, clinical use of CDK4/6 inhibitors as monotherapy is limited by lack of validated biomarkers, diffident preclinical efficacy, and development of acquired drug resistance. Emerging studies have explored therapeutic strategies to enhance the antitumor efficacy of CDK4/6 inhibitors by the combination with chemotherapy regimens, but their mechanism of action remains elusive.

APPROACH AND RESULTS

Here, we report in vitro and in vivo synergy in BTC models, showing enhanced efficacy, reduced toxicity, and better survival with a combination comprising gemcitabine/cisplatin and CDK4/6 inhibitors. Furthermore, we demonstrated that abemaciclib monotherapy had only modest efficacy attributable to autophagy-induced resistance. Notably, triplet therapy was able to potentiate efficacy through elimination of the autophagic flux. Correspondingly, abemaciclib potentiated ribonucleotide reductase catalytic subunit M1 reduction, resulting in sensitization to gemcitabine.

CONCLUSIONS

As such, these data provide robust preclinical mechanistic evidence of synergy between gemcitabine/cisplatin and CDK4/6 inhibitors and delineate a path forward for translation of these findings to preliminary clinical studies in advanced BTC patients.

Ribociclib Induces Broad Chemotherapy Resistance and EGFR Dependency in ESR1 Wildtype and Mutant Breast Cancer

While endocrine therapy is highly effective for the treatment of oestrogen receptor-α (ERα)-positive breast cancer, a significant number of patients will eventually experience disease progression and develop treatment-resistant, metastatic cancer. The majority of resistant tumours remain dependent on ERα-action, with activating ESR1 gene mutations occurring in 15-40% of advanced cancers. Therefore, there is an urgent need to discover novel effective therapies that can eradicate cancer cells with aberrant ERα and to understand the cellular response underlying their action. Here, we evaluate the response of MCF7-derived, CRISPR-Cas9-generated cell lines expressing mutant ERα (Y537S) to a large number of drugs. We report sensitivity to numerous clinically approved inhibitors, including CDK4/6 inhibitor ribociclib, which is a standard-of-care therapy in the treatment of metastatic ERα-positive breast cancer and currently under evaluation in the neoadjuvant setting. Ribociclib treatment induces senescence in both wildtype and mutant ERα breast cancer models and leads to a broad-range drug tolerance. Strikingly, viability of cells undergoing ribociclib-induced cellular senescence is maintained via engagement of EGFR signalling, which may be therapeutically exploited in both wildtype and mutant ERα-positive breast cancer. Our study highlights a wide-spread reduction in sensitivity to anti-cancer drugs accompanied with an acquired vulnerability to EGFR inhibitors following CDK4/6 inhibitor treatment.

Mechanisms of Hydroxyurea-Induced Cellular Senescence: An Oxidative Stress Connection?

Hydroxyurea (HU) is a water-soluble antiproliferative agent used for decades in neoplastic and nonneoplastic conditions. HU is considered an essential medicine because of its cytoreduction functions. HU is an antimetabolite that inhibits ribonucleotide reductase, which causes a depletion of the deoxyribonucleotide pool and dramatically reduces cell proliferation. The proliferation arrest, depending on drug concentration and exposure, may promote a cellular senescence phenotype associated with cancer cell therapy resistance and inflammation, influencing neighboring cell functions, immunosuppression, and potential cancer relapse. HU can induce cellular senescence in both healthy and transformed cells in vitro, in part, because of increased reactive oxygen species (ROS). Here, we analyze the main molecular mechanisms involved in cytotoxic/genotoxic HU function, the potential to increase intracellular ROS levels, and the principal features of cellular senescence induction. Understanding the mechanisms involved in HU's ability to induce cellular senescence may help to improve current chemotherapy strategies and control undesirable treatment effects in cancer patients and other diseases.

The life cycle of polyploid giant cancer cells and dormancy in cancer: Opportunities for novel therapeutic interventions

Recent data suggest that most genotoxic agents in cancer therapy can lead to shock of genome and increase in cell size, which leads whole genome duplication or multiplication, formation of polyploid giant cancer cells, activation of an early embryonic program, and dedifferentiation of somatic cells. This process is achieved via the giant cell life cycle, a recently proposed mechanism for malignant transformation of somatic cells. Increase in both cell size and ploidy allows cells to completely or partially restructures the genome and develop into a blastocyst-like structure, similar to that observed in blastomere-stage embryogenesis. Although blastocyst-like structures with reprogrammed genome can generate resistant or metastatic daughter cells or benign cells of different lineages, they also acquired ability to undergo embryonic diapause, a reversible state of suspended embryonic development in which cells enter dormancy for survival in response to environmental stress. Therapeutic agents can activate this evolutionarily conserved developmental program, and when cells awaken from embryonic diapause, this leads to recurrence or metastasis. Understanding of the key mechanisms that regulate the different stages of the giant cell life cycle offers new opportunities for therapeutic intervention.

The cyclin-dependent kinase inhibitor AT7519 augments cisplatin's efficacy in ovarian cancer via multiple oncogenic signaling pathways

Although cisplatin is the most active drug for the treatment of ovarian cancer, majority of patients develop resistance and ultimately relapse. Enhancing the efficacy of cisplatin could represent a promising strategy to improve the clinical outcome of patients with ovarian cancer. AT7519 is a multitargeted cyclin-dependent kinase (CDK) inhibitor and displays potent anticancer activities. In this work, we show that the combination of AT7519 with cisplatin is much more superior to cisplatin alone in inhibiting ovarian cancer. AT7519 at nanomolar concentrations inhibits proliferation and migration and induces apoptosis of multiple ovarian cancer cell lines. In contrast, AT7519 at the same concentrations either does not affect survival or is significantly less effective in inhibiting proliferation and migration in normal ovarian cells and fibroblast cells. AT7519 significantly augments the inhibitory effects of cisplatin in ovarian cancer cells in a dose-dependent manner. Mechanistic studies suggest that AT7519 (i) inhibits proliferation via decreasing activities of CDK1 and 2, and via inhibiting RNA transcription; (ii) inhibits migration via suppressing epithelial-mesenchymal transition (EMT); and (iii) induces apoptosis via decreasing Mcl-1 and increasing Bim in ovarian cancer cells. Using a human ovarian cancer xenograft mouse model, we confirm the in vivo efficacy of AT7519 alone, and the synergistic effects of AT7519 and cisplatin in combination, at doses that cause minimal toxicity in mice. Our findings provide systematic preclinical evidence to support the initialization of clinical trials of the AT7519 and cisplatin combination for the treatment of ovarian cancer.

Histone Deacetylase Inhibitor-Induced CDKN2B and CDKN2D Contribute to G2/M Cell Cycle Arrest Incurred by Oxidative Stress in Hepatocellular Carcinoma Cells via Forkhead Box M1 Suppression

Forkhead box protein M1 (FOXM1) is a pivotal regulator of G2/M cell cycle progression in many types of cancer. Previously, our study demonstrated that histone deacetylase inhibition (HDACi) sensitizes hepatocellular carcinoma cells (HCC) to oxidative stress through FOXM1 suppression. However, the mechanism underlying its suppression by HDACi still requires elucidation. We hypothesized that HDACi induce genes responsible for destabilizing and inactivating FOXM1. The transcriptome in the HepG2 was revealed by massive analysis of cDNA end (MACE). Expression of mRNA and proteins were analyzed by quantitative real-time PCR (qPCR) and western blot, respectively. Cell cycle was analyzed by fluorescence-activated cell sorting (FACS). Oxidative stress and HDACi suppressed CDK4/6 levels while enhancing CDK inhibitor 2B and 2D (CDKN2B and CDKN2D) expressions in HCC. Palbociclib, a specific inhibitor of CDK4/6, induced G2/M cell cycle arrest in HCC by down-regulating phosphorylation level of FOXM1, and its downstream target genes such as aurora kinase A (AURKA) and polo-like kinase 1 (PLK1). HDACi treatment increased the ubiquitination level of FOXM1 by suppressing ubiquitin-specific peptidase 21 (USP21), which deubiquitinates FOXM1. Inhibiting FOXM1 degradation with MG132 treatment affected neither palbociclib-induced G2/M cell cycle arrest nor expression of its target genes. Double knockdown of CDKN2B and CDKN2D reduced the oxidative stress and HDACi-induced G/2M cell cycle arrest. In conclusion, oxidative stress and HDACi synergistically cause G2/M cell cycle arrest via CDKN2 induction, which sequentially inhibits CDK4/6, FOXM1, and its downstream target genes AURKA, PLK1, and CCNB1 phosphorylation in HCC.

Inhibition of CDK4/6 as Therapeutic Approach for Ovarian Cancer Patients: Current Evidences and Future Perspectives

Simple Summary

Altered regulation of the cell cycle is a hallmark of cancer. The recent clinical success of the inhibitors of CDK4 and CDK6 has convincingly demonstrated that targeting cell cycle components may represent an effective anti-cancer strategy, at least in some cancer types. However, possible applications of CDK4/6 inhibitors in patients with ovarian cancer is still under evaluation. Here, we describe the possible biological role of CDK4 and CDK6 complexes in ovarian cancer and provide the rationale for the use of CDK4/6 inhibitors in this pathology, alone or in combination with other drugs. This review, coupling basic, preclinical and clinical research studies, could be of great translational value for investigators attempting to design new clinical trials for the better management of ovarian cancer patients.

Abstract

Alterations in components of the cell-cycle machinery are present in essentially all tumor types. In particular, molecular alterations resulting in dysregulation of the G1 to S phase transition have been observed in almost all human tumors, including ovarian cancer. These alterations have been identified as potential therapeutic targets in several cancer types, thereby stimulating the development of small molecule inhibitors of the cyclin dependent kinases. Among these, CDK4 and CDK6 inhibitors confirmed in clinical trials that CDKs might indeed represent valid therapeutic targets in, at least some, types of cancer. CDK4 and CDK6 inhibitors are now used in clinic for the treatment of patients with estrogen receptor positive metastatic breast cancer and their clinical use is being tested in many other cancer types, alone or in combination with other agents. Here, we review the role of CDK4 and CDK6 complexes in ovarian cancer and propose the possible use of their inhibitors in the treatment of ovarian cancer patients with different types and stages of disease.

Genetic alterations and their therapeutic implications in epithelial ovarian cancer

BACKGROUND

Genetic alterations for epithelial ovarian cancer are insufficiently characterized. Previous studies are limited regarding included histologies, gene numbers, copy number variant (CNV) detection, and interpretation of pathway alteration patterns of individual patients.

METHODS

We sequenced 410 genes to analyze mutations and CNV of 82 ovarian carcinomas, including high-grade serous (n = 37), endometrioid (n = 22) and clear cell (n = 23) histologies. Eligibility for targeted therapy was determined for each patient by a pathway-based approach. The analysis covered DNA repair, receptor tyrosine kinase, PI3K/AKT/MTOR, RAS/MAPK, cell cycle, and hedgehog pathways, and included 14 drug targets.

RESULTS

Postulated PARP, MTOR, and CDK4/6 inhibition sensitivity were most common. BRCA1/2 alterations, PTEN loss, and gain of PIK3CA and CCND1 were characteristic for high-grade serous carcinomas. Mutations of ARID1A, PIK3CA, and KRAS, and ERBB2 gain were enriched in the other histologies. PTEN mutations and high tumor mutational burden were characteristic for endometrioid carcinomas. Drug target downstream alterations impaired actionability in all histologies, and many alterations would not have been discovered by key gene mutational analysis. Individual patients often had more than one actionable drug target.

CONCLUSIONS

Genetic alterations in ovarian carcinomas are complex and differ among histologies. Our results aid the personalization of therapy and biomarker analysis for clinical studies, and indicate a high potential for combinations of targeted therapies.

Autophagy and senescence in cancer therapy

Tumor cells can undergo diverse responses to cancer therapy. While apoptosis represents the most desirable outcome, tumor cells can alternatively undergo autophagy and senescence. Both autophagy and senescence have the potential to make complex contributions to tumor cell survival via both cell autonomous and cell non-autonomous pathways. The induction of autophagy and senescence in tumor cells, preclinically and clinically, either individually or concomitantly, has generated interest in the utilization of autophagy modulating and senolytic therapies to target autophagy and senescence, respectively. This chapter summarizes the current evidence for the promotion of autophagy and senescence as fundamental responses to cancer therapy and discusses the complexity of their functional contributions to cell survival and disease outcomes. We also highlight current modalities designed to exploit autophagy and senescence in efforts to improve the efficacy of cancer therapy.

Cisplatin Cytotoxicity in Human Testicular Germ Cell Tumor Cell Lines Is Enhanced by the CDK4/6 Inhibitor Palbociclib

BACKGROUND

Cisplatin-based chemotherapy is the mainstay of pharmacological treatment of testicular germ cell tumors (TGCTs) that, together with early diagnosis, surgery, and/or radiotherapy, has dramatically improved the prognosis. However, under the pressure of such pharmacological therapy (both classical cytotoxic drugs and targeted therapy), cancer cells may develop resistance. Thus, combination therapy that may include cytotoxic drugs and targeted therapy could offer an advantage to curing cancers. Here, we investigated the in vitro and in vivo antitumor activity of cisplatin, as a single-agent or in combination with palbociclib.

PATIENTS AND METHODS

The cell viability of Ntera-2/cl.D1 (NT2/D1) and 833K after exposure to palbociclib and/or cisplatin was evaluated by MTT dye reduction assay and by ATPLite Luminescence Assay. Gene and protein expression was evaluated by quantitative reverse transcription polymerase chain reaction and by western blot. Flow cytometric cell-cycle analysis was performed, as well. The in vivo experiments were conducted on NT2/D1 xenografts in AB zebrafish embryos exposed to the drugs.

RESULTS

Palbociclib and cisplatin decreased TGCT cell viability both in vitro and in vivo. This effect was additive when cells were exposed to the drug combination. In the NT2/D1 cell lines, the drug combination also exerted a positive effect with regard to delaying cell recovery after the toxic insult. In the combination experiments, cisplatin-induced cell accumulation in G2/M was predominant compared with the palbociclib effect.

CONCLUSIONS

These results could provide the rationale for developing further studies to improve the pharmacological treatment of TGCTs, but they must be demonstrated in a dedicated clinical trial.

Aldehyde dehydrogenase inhibitors promote DNA damage in ovarian cancer and synergize with ATM/ATR inhibitors

Rationale: Aldehyde dehydrogenase (ALDH) enzymes are often upregulated in cancer cells and associated with therapeutic resistance. ALDH enzymes protect cells by metabolizing toxic aldehydes which can induce DNA double stand breaks (DSB). We recently identified a novel ALDH1A family inhibitor (ALDHi), 673A. We hypothesized that 673A, via inhibition of ALDH1A family members, could induce intracellular accumulation of genotoxic aldehydes to cause DSB and that ALDHi could synergize with inhibitors of the ATM and ATR, proteins which direct DSB repair.

Methods: We used immunofluorescence to directly assess levels of the aldehyde 4-hydroxynonenal and comet assays to evaluate DSB. Western blot was used to evaluate activation of the DNA damage response pathways. Cell counts were performed in the presence of 673A and additional aldehydes or aldehyde scavengers. ALDH inhibition results were confirmed using ALDH1A3 CRISPR knockout. Synergy between 673A and ATM or ATR inhibitors was evaluated using the Chou-Talalay method and confirmed in vivo using cell line xenograft tumor studies.

Results: The ALDHi 673A cellular accumulation of toxic aldehydes which induce DNA double strand breaks. This is exacerbated by addition of exogenous aldehydes such as vitamin-A (retinaldehyde) and ameliorated by aldehyde scavengers such as metformin and hydralazine. Importantly, ALDH1A3 knockout cells demonstrated increased sensitivity to ATM/ATR inhibitors. And, ALDHi synergized with inhibitors of ATM and ATR, master regulators of the DSB DNA damage response, both in vitro and in vivo. This synergy was evident in homologous recombination (HR) proficient cell lines.

Conclusions: ALDHi can be used to induce DNA DSB in cancer cells and synergize with inhibitors the ATM/ATR pathway. Our data suggest a novel therapeutic approach to target HR proficient ovarian cancer cells.

A broad analysis in clinical and in vitro models on regulator of G-protein signalling 10 regulation that is associated with ovarian cancer progression and chemoresistance

Ovarian cancer is one of the deadliest types of gynaecological cancers and more than half of the patients die within 5 years after diagnosis. Recurrence in advanced staged patients after chemotherapy is associated with increased chemoresistance, which results in poor prognosis. Regulator of G-protein signalling 10 (RGS10) negatively regulates cell proliferation, migration and survival by attenuating G-protein coupled-receptors mediated signalling pathways. Recent studies have shown that loss of RGS10 expression is significantly associated with proliferation and cisplatin resistance in ovarian cancer cells. SIGNIFICANCE OF THE STUDY: In this study, we analysed differential RGS10 expression levels using public microarray datasets from clinical and in vitro ovarian cancer samples. We validated that cancer progression and chemotherapy exposure change RGS10 expression. We enriched our study to evaluate the relationship between chemoresistance and differential RGS10 expression against ovarian cancer potential chemotherapeutic agent, palbociclib. Results showed that palbociclib treatment reduced cell viability, despite significantly decreased RGS10 expression in chemoresistant cells. Overall, the results confirmed that cancer progression and chemoresistance are significantly associated with the down-regulation of RGS10 while some chemotherapeutics seem to be beneficial in decreasing chemoresistance in ovarian cancer.

Novel sequential treatment with palbociclib enhances the effect of cisplatin in RB-proficient triple-negative breast cancer

Background

Triple-negative breast cancer (TNBC) is a highly aggressive malignancy that lacks sensitivity to chemotherapy, endocrine therapy or targeted therapy. CDK4/6 inhibitors, combined with endocrine therapy, have been shown to be effective in postmenopausal women with HR-positive, HER2-negative advanced or metastatic breast cancer. Therefore, we investigated whether the CDK4/6 inhibitor palbociclib (PD) could enhance the effects of cisplatin (CDDP) on TNBC.

Methods

The effects of different drug regimens consisting of PD and CDDP on MDA-MB-231 and RB-knockdown MDA-MB-231 (sh-MDA-MB-231) cells were assessed in vitro and in vivo. MDA-MB-468 and RB-overexpressing MDA-MB-468 cells were used to assess the effect of the PD-CDDP regimens in vitro. Immunoblotting illustrated the role of the cyclin D1/RB/E2F axis signalling pathway.

Results

PD induced G1 phase cell cycle arrest in the MDA-MB-231 cell line. However, synchronous treatment with PD and CDDP for 24 h, treatment with PD for 24 h followed by CDDP and treatment with CDDP for 24 h followed by PD had no influence on MDA-MB-231 cell apoptosis. We further investigated the effect of PD or CDDP withdrawal on the effects of sequential treatment and found that PD treatment for 48 h followed by withdrawal for 48 h and subsequent CDDP treatment (PD-CDDP) significantly increased apoptosis and inhibited the cell viability and colony formation of MDA-MB-231 cells, while with other regimens, PD and CDDP had an additive or antagonistic response. The preferential use of PD increased DNA damage induced by CDDP, as measured through γH2AX immunofluorescence. These findings were not observed in sh-MDA-MB-231 cells, and experiments to assess cell function in MDA-MB-468 and RB-overexpressing MDA-MB-468 cells yielded similar results, which indicated that PD enhanced the sensitivity of TNBC cells to CDDP in an RB-dependent manner. In vivo, compared with single drug treatment, combination treatment inhibited tumour growth and Ki-67 expression in MDA-MB-231 xenograft models. Western blot analysis revealed that PD enhanced sensitivity to CDDP through the CDK4/6-cyclin D1-RB-E2F pathway.

Conclusions

Pre-treatment with PD synchronized the tumour cell cycle through the CDK4/6-cyclin D1-RB-E2F pathway, which increased the antitumour effect of CDDP. Thus, PD-CDDP might be an effective treatment for RB-proficient TNBC patients.

CDK4/6 inhibition promotes immune infiltration in ovarian cancer and synergizes with PD-1 blockade in a B cell-dependent manner

Great progress has been made in the field of tumor immunotherapy in the past decade. However, the therapeutic effects of immune checkpoint blockade (ICB) against ovarian cancer are still limited. Recently, an inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6i) has been reported to enhance antitumor immunity in preclinical models. The combined use of CDK4/6i and ICB may be beneficial, but the effects of CDK4/6is on the tumor immune microenvironment and whether they can synergize with ICB in treating ovarian cancer remain unknown.

Methods: In this study, we first assessed the antitumor efficacy of abemaciclib, an FDA-approved CDK4/6i, in a syngeneic murine ovarian cancer model. Then, immunohistochemistry, immunofluorescence and flow cytometry were performed to evaluate the number, proportion, and activity of tumor-infiltrating lymphocytes. Cytokine and chemokine production was detected both in vivo and in vitro by PCR array analysis and cytokine antibody arrays. The treatment efficacy of combined abemaciclib and anti-PD-1 therapy was evaluated in vivo, and CD8+ and CD4+ T cell activities were analyzed using flow cytometry. Lastly, the requirement for both CD8+ T cells and B cells in combination treatment was evaluated in vivo, and potential cellular mechanisms were further analyzed by flow cytometry.

Results: We observed that abemaciclib monotherapy could enhance immune infiltration, especially CD8+ T cell and B cell infiltration, in the ID8 murine ovarian cancer model. Immunophenotyping analysis showed that abemaciclib induced a proinflammatory immune response in the tumor microenvironment. PCR array analysis suggested the presence of a Th1-polarized cytokine profile in abemaciclib-treated ID8 tumors. In vitro studies showed that abemaciclib-treated ID8 cells secreted more CXCL10 and CXCL13, thus recruiting more lymphocytes than control groups. Combination treatment achieved better tumor control than monotherapy, and the activities of CD8+ and CD4+ T cells were further enhanced when compared with monotherapy. The synergistic antitumor effects of combined abemaciclib and anti-PD-1 therapy depended on both CD8+ T cells and B cells.

Conclusion: These findings suggest that combined treatment with CDK4/6i and anti-PD-1 antibody could improve the efficacy of anti-PD-1 therapy and hold great promise for the treatment of poorly immune-infiltrated ovarian cancer.

Chemotherapy and CDK4/6 Inhibitors: Unexpected Bedfellows

Cyclin-dependent kinases 4 and 6 (CDK4/6) have emerged as important therapeutic targets. Pharmacologic inhibitors of these kinases function to inhibit cell-cycle progression and exert other important effects on the tumor and host environment. Because of their impact on the cell cycle, CDK4/6 inhibitors (CDK4/6i) have been hypothesized to antagonize the antitumor effects of cytotoxic chemotherapy in tumors that are CDK4/6 dependent. However, there are multiple preclinical studies that illustrate potent cooperation between CDK4/6i and chemotherapy. Furthermore, the combination of CDK4/6i and chemotherapy is being tested in clinical trials to both enhance antitumor efficacy and limit toxicity. Exploitation of the noncanonical effects of CDK4/6i could also provide an impetus for future studies in combination with chemotherapy. Thus, while seemingly mutually exclusive mechanisms are at play, the combination of CDK4/6 inhibition and chemotherapy could exemplify rational medicine.

The E2F Pathway Score as a Predictive Biomarker of Response to Neoadjuvant Therapy in ER+/HER2- Breast Cancer

E2F transcription factors play critical roles in the cell cycle. Therefore, their activity is expected to reflect tumor aggressiveness and responsiveness to therapy. We scored 3905 tumors of nine breast cancer cohorts for this activity based on their gene expression for the Hallmark E2F targets gene set. As expected, tumors with a high score had an increased expression of cell proliferation-related genes. A high score was significantly associated with shorter patient survival, greater MKI67 expression, histological grade, stage, and genomic aberrations. Furthermore, metastatic tumors had higher E2F scores than the primary tumors from which they arose. Although tumors with a high score had greater infiltration by both pro- and anti-cancerous immune cells, they had an increased expression of immune checkpoint genes. Estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative cancer with a high E2F score achieved a significantly higher pathological complete response (pCR) rate to neoadjuvant chemotherapy. The E2F score was significantly associated with the expression of cyclin-dependent kinase (CDK)-related genes and strongly correlated with sensitivity to CDK inhibition in cell lines. In conclusion, the E2F score is a marker of breast cancer aggressiveness and predicts the responsiveness of ER-positive/HER2-negative patients to neoadjuvant chemotherapy and possibly to CDK and immune checkpoint inhibitors.

A systematic literature review assessing if genetic biomarkers are predictors for platinum-based chemotherapy response in ovarian cancer patients

BACKGROUND

Ovarian cancer is the deadliest of gynecologic malignancies with the 5-year overall survival rate remaining at approximately 30%, a rate that has not improved over the last three decades. Standard of care for epithelial ovarian cancer patients consists of a platinum compound with a taxane given intravenously following debulking surgery; however, 80% of cases relapse within 2 years of diagnosis. This review sought to identify key underlying biomarkers related to platinum resistance in ovarian cancer to establish possible prognostic biomarkers of chemoresponse.

METHODS

A systematic literature review was conducted across three databases PubMed, EMBASE and SCOPUS to summarise the evidence for prognostic biomarkers in platinum-resistant ovarian cancer patients.

RESULTS

Forty-eight human studies were used in the review encompassing 6719 participants in retrospective and prospective study designs. A total of 68 biomarkers were reported that were significantly correlated with chemoresponse and/or survival reporting a p value less than or equal to 0.05.

CONCLUSION

This review accentuates the pleiotropic phenotypic complexities related to the response to platinum therapy in ovarian cancer. A one-size-fits-all approach may be ineffective in a large portion of patients, emphasising the need for a whole system-based approach and personalised treatment strategies. Identifying key biomarkers to aid clinical decision-making is the first essential step in developing and appropriating therapies for at-risk patients, reducing toxicity and improving quality of life.

NFATC4 promotes quiescence and chemotherapy resistance in ovarian cancer

Development of chemotherapy resistance is a major problem in ovarian cancer. One understudied mechanism of chemoresistance is the induction of quiescence, a reversible nonproliferative state. Unfortunately, little is known about regulators of quiescence. Here, we identify the master transcription factor nuclear factor of activated T cells cytoplasmic 4 (NFATC4) as a regulator of quiescence in ovarian cancer. NFATC4 is enriched in ovarian cancer stem-like cells and correlates with decreased proliferation and poor prognosis. Treatment of cancer cells with cisplatin resulted in NFATC4 nuclear translocation and activation of the NFATC4 pathway, while inhibition of the pathway increased chemotherapy response. Induction of NFATC4 activity resulted in a marked decrease in proliferation, G0 cell cycle arrest, and chemotherapy resistance, both in vitro and in vivo. Finally, NFATC4 drove a quiescent phenotype in part via downregulation of MYC. Together, these data identify NFATC4 as a driver of quiescence and a potential new target to combat chemoresistance in ovarian cancer.

Therapy-Induced Senescence: An "Old" Friend Becomes the Enemy

For the past two decades, cellular senescence has been recognized as a central component of the tumor cell response to chemotherapy and radiation. Traditionally, this form of senescence, termed Therapy-Induced Senescence (TIS), was linked to extensive nuclear damage precipitated by classical genotoxic chemotherapy. However, a number of other forms of therapy have also been shown to induce senescence in tumor cells independently of direct genomic damage. This review attempts to provide a comprehensive summary of both conventional and targeted anticancer therapeutics that have been shown to induce senescence in vitro and in vivo. Still, the utility of promoting senescence as a therapeutic endpoint remains under debate. Since senescence represents a durable form of growth arrest, it might be argued that senescence is a desirable outcome of cancer therapy. However, accumulating evidence suggesting that cells have the capacity to escape from TIS would support an alternative conclusion, that senescence provides an avenue whereby tumor cells can evade the potentially lethal action of anticancer drugs, allowing the cells to enter a temporary state of dormancy that eventually facilitates disease recurrence, often in a more aggressive state. Furthermore, TIS is now strongly connected to tumor cell remodeling, potentially to tumor dormancy, acquiring more ominous malignant phenotypes and accounts for several untoward adverse effects of cancer therapy. Here, we argue that senescence represents a barrier to effective anticancer treatment, and discuss the emerging efforts to identify and exploit agents with senolytic properties as a strategy for elimination of the persistent residual surviving tumor cell population, with the goal of mitigating the tumor-promoting influence of the senescent cells and to thereby reduce the likelihood of cancer relapse.

CDK4/6 Inhibitors Impair Recovery from Cytotoxic Chemotherapy in Pancreatic Adenocarcinoma

Inhibition of the cell-cycle kinases CDK4 and CDK6 is now part of the standard treatment in advanced breast cancer. CDK4/6 inhibitors, however, are not expected to cooperate with DNA-damaging or antimitotic chemotherapies as the former prevent cell-cycle entry, thus interfering with S-phase- or mitosis-targeting agents. Here, we report that sequential administration of CDK4/6 inhibitors after taxanes cooperates to prevent cellular proliferation in pancreatic ductal adenocarcinoma (PDAC) cells, patient-derived xenografts, and genetically engineered mice with Kras G12V and Cdkn2a-null mutations frequently observed in PDAC. This effect correlates with the repressive activity of CDK4/6 inhibitors on homologous recombination proteins required for the recovery from chromosomal damage. CDK4/6 inhibitors also prevent recovery from multiple DNA-damaging agents, suggesting broad applicability for their sequential administration after available chemotherapeutic agents.

Ribociclib (LEE011) suppresses cell proliferation and induces apoptosis of MDA-MB-231 by inhibiting CDK4/6-cyclin D-Rb-E2F pathway

Triple-negative breast cancer (TNBC) stands for a refractory subtype, which predicts poor prognosis and has no effective therapies yet for improving it. Given the restrictions of traditional treatments, novel therapeutic strategies need excavating to alleviate the intrinsic or acquired resistance. Ribociclib, a selective CDK4/6 inhibitor, has successfully prevented cancers from deteriorating by intervening the CDK4/6-cyclin D-Rb-E2F pathway, especially for estrogen receptor-positive (ER +) breast cancer. However, there still remains limited accessibility referring to TNBC. Performing experiments on MDA-MB-231 cells, we found that LEE011 could suppress cell proliferation, and this suppression tended to be dose-dependently. Western blotting analysis presented significant decrease with the expression of CDK4/6 after LEE011 treated, and other proteins associated with this axis such as cyclin D1, p-Rb, Rb, E2F1 showed aberrant changes. Moreover, LEE011 induced G₀-G₁ phase cell cycle arrest, promoted cell apoptosis, and reduced cell migration in vitro. In addition, tumor growth was remarkably impeded without obvious side-effects in MDA-MB-231 xenograft models. Our research has identified that LEE011 was not completely invalid for MDA-MB-231. Considering its pivotal status in TNBC, the CDK4/6-cyclin D-Rb-E2F pathway informed us the possibility and practicality of Ribociclib (LEE011) as pharmacological intervention, but challenges warrant further validation in prospective studies.

The "life code": A theory that unifies the human life cycle and the origin of human tumors

Tumors arise from the transformation of normal stem cells or mature somatic cells. Intriguingly, two types of tumors have been observed by pathologists for centuries: well-differentiated tumors and undifferentiated tumors. Well-differentiated tumors are architecturally similar to the tissues from which they originate, whereas undifferentiated tumors exhibit high nuclear atypia and do not resemble their tissue of origin. The relationship between these two tumor types and the human life cycle has not been clear. Here I propose a unifying theory that explains the processes of transformation of both tumor types with our life cycle. Human life starts with fertilization of an egg by a sperm to form a zygote. The zygote undergoes successive rounds of cleavage division to form blastomeres within the zona pellucida, with progressive decreases in cell size, and the cleaved blastomeres then compact to form a 32-cell or a "64n" morula [n = 1 full set of chromosomes]. Thus early embryogenesis can be interpreted as a progressive increase in ploidy, and if the zona pellucida is considered a cell membrane and cleavage is interpreted as endomitosis, then the 32-cell morula can be considered a multinucleated giant cell (or 64n syncytium). The decrease in cell size is accompanied by an increase in the nuclear-to-cytoplasmic (N/C) ratio, which then selectively activates a combined set of embryonic transcription factors that dedifferentiate the parental genome to a zygotic genome. This process is associated with a morphologic transition from a morula to a blastocyst and formation of an inner cell mass that gives rise to a new embryonic life. If the subsequent differentiation proceeds to complete maturation, then a normal life results. However, if differentiation is blocked at any point along the continuum of primordial germ cell to embryonic maturation to fetal organ maturation, a well-differentiated tumor will develop. Depending on the level of developmental hierarchy at which the stem cell differentiation is blocked, the resulting tumor can range from highly malignant to benign. Undifferentiated tumors are derived from mature somatic cells through dedifferentiation via a recently described reprogramming mechanism named the giant cell life cycle or the giant cell cycle. This mechanism can initiate "somatic embryogenesis" via an increase in ploidy ranging from 4n to 64n or more, similar to that in normal embryogenesis. This dedifferentiation mechanism is initiated through an endocycle and is followed by endomitosis, which leads to the formation of mononucleated or multinucleated polyploid giant cancer cells (PGCCs), that is, cancer stem-like cells that mimic the blastomere-stage embryo. The giant cell life cycle leads to progressive increases in the N/C ratio and awakens the suppressed embryonic reprogram, resulting in mature somatic transformation into undifferentiated tumors. Thus, the increase in ploidy explains not only normal embryogenesis for well-differentiated tumors but also "somatic embryogenesis" for undifferentiated tumors. I refer to this ploidy increase as the 'life code". The concept of the "life code" may provide a simple theoretical framework to guide our immense efforts to understand cancer and fight this disease.

A multi-center phase II trial evaluating the efficacy of palbociclib in combination with carboplatin for the treatment of unresectable recurrent or metastatic head and neck squamous cell carcinoma

Background Palbociclib is a selective inhibitor of CDK4/6 approved in metastatic breast cancer as well as evidence of activity in malignancies with CDK4-amplifications. Extensive preclinical evidence has demonstrated synergy of CDK4/6 inhibitors with platinum chemotherapy suggesting a potential role for clinical synthetic lethality. Given the sensitivity to platinum therapy as well as the landscape of genomic alterations, concurrent treatment with platinum chemotherapy and palbociclib is of significant interest as a novel treatment approach. Patients and Methods Patients with unresectable, recurrent, or metastatic head and neck cancer (R/M HNC) were enrolled. Eligible patients were required to have no previous treatment with cytotoxic chemotherapy in the recurrent/metastatic setting. This was a multicenter phase II trial in which patients were administered carboplatin in addition to concurrent palbociclib. The primary endpoint of this trial was 12-week disease control rate (DCR). Results Twenty-one patients were enrolled and 18 were evaluable for response. Grade 3/4 treatment related toxicities were seen in 79% of patients of which the most common were related to myelosuppression. 12-week DCR was 33% (5 patients with stable disease, 1 with a partial response). Median progression free survival was 2.9 months (range: 1.2-13.3) and overall survival was 4.6 months (range: 1.4-14.8). Conclusion The combination of carboplatin and palbociclib is associated with significant treatment related toxicity and insufficient anti-tumor activity.

Chemotherapy impacts on the cellular response to CDK4/6 inhibition: distinct mechanisms of interaction and efficacy in models of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a therapy recalcitrant disease characterized by the aberrations in multiple genes that drive pathogenesis and limit therapeutic response. While CDK4/6 represents a downstream target of both KRAS mutation and loss of the CDKN2A tumor suppressor in PDAC, clinical and preclinical studies indicate that pharmacological CDK4/6 inhibitors are only modestly effective. Since chemotherapy represents the established backbone of PDAC treatment we evaluated the interaction of CDK4/6 inhibitors with gemcitabine and taxanes that are employed in the treatment of PDAC. Herein, we demonstrate that the difference in mechanisms of actions of chemotherapeutic agents elicit distinct effects on the cellular response to CDK4/6 inhibition. Gemcitabine largely ablates the function of CDK4/6 inhibition in S-phase arrested cells when administered contemporaneously; although, when cells recover from S-phase block they exhibit sensitivity to CDK4/6 inhibition. In contrast, pharmacological inhibition of CDK4/6 yields a cooperative cytostatic effect in combination with docetaxel and prevents adaptation and cell cycle re-entry, which is a common basis for resistance to such agents. Importantly, using organoid and PDX models we could confirm the cooperative effects between chemotherapy and CDK4/6 inhibition. These data indicate that the combination of cytotoxic and cytostatic agents could represent an important modality in those tumor types that are relatively resistant to CDK4/6 inhibitors.

Combining CDK4/6 inhibitors ribociclib and palbociclib with cytotoxic agents does not enhance cytotoxicity

Cyclin-dependent kinases 4 and 6 (CDK4/6) play critical roles in the G₁ to S checkpoint of the cell cycle and have been shown to be overactive in several human cancers. Small-molecule inhibitors of CDK4/6 have demonstrated significant efficacy against many solid tumors. Since CDK4/6 inhibition is thought to induce cell cycle arrest at the G1/S checkpoint, much interest has been focused on combining CDK4/6 inhibitors with cytotoxic agents active against the S or M phase of the cell cycle to enhance therapeutic efficacy. However, it remains unclear how best to combine these two classes of drugs to avoid their potentially antagonistic effects. Here, we test various combinations of highly selective and potent CDK4/6 inhibitors with commonly used cytotoxic drugs in several cancer cell lines derived from lung, breast and brain cancers, for their cell-killing effects as compared to monotherapy. All combinations, either concurrent or sequential, failed to enhance cell-killing effects. Importantly, in certain schedules, especially pre-treatment with a CDK4/6 inhibitor, combining these drugs resulted in reduced cytotoxicity of cytotoxic agents. These findings urge cautions when combining these two classes of agents in clinical settings.

Evolving trends in pancreatic cancer therapeutic development

Despite advances in translational research, the overall 5-year survival for pancreatic cancer remains dismal and with rising incidence pancreatic cancer is predicted to be the second leading cause of cancer death for many developed countries. Surgical intervention followed by cytotoxic chemotherapy are currently the best options for treatment, but disease recurrence is very common. Efforts to develop new therapeutic agents and delivery systems are necessary to achieve better clinical efficacy with less toxicity. Promising prospects are arising with new preclinical and clinical therapeutic strategies using small molecule targeted therapies, RNAi, stromal therapies, and immunotherapies. With a better understanding of the biology to aid target selection and discovery of biomarkers to aid precision medicine, better opportunities will evolve to shape the therapeutic landscape, enhance patient quality of life and increase overall survival.

Targeting NF-κB-mediated inflammatory pathways in cisplatin-resistant NSCLC

OBJECTIVES

The majority of patients with non-small cell lung cancer (NSCLC) present with advanced stage disease, at which time chemotherapy is usually the most common treatment option. While somewhat effective, patients treated with platinum-based regimens will eventually develop resistance, with others presenting with intrinsic resistance. Multiple pathways have been implicated in chemo-resistance, however the critical underlying mechanisms have yet to be elucidated. The aim of this project was to determine the role of inflammatory mediators in cisplatin-resistance in NSCLC.

MATERIALS AND METHODS

Inflammatory mediator, NF-κB, and its associated pathways were investigated in an isogenic model of cisplatin-resistant NSCLC using age-matched parental (PT) and corresponding cisplatin-resistant (CisR) sublines. Pathways were assessed using mass spectrometry, western blot analysis and qRT-PCR. The cisplatin sensitizing potential of an NF-κB small molecule inhibitor, DHMEQ, was also assessed by means of viability assays and western blot analysis.

RESULTS

Proteomic analysis identified dysregulated NF-κB responsive targets in CisR cells when compared to PT cells, with increased NF-κB expression identified in four out of the five NSCLC sub-types examined (CisR versus PT). DHMEQ treatment resulted in reduced NF-κB expression in the presence of cisplatin, and re-sensitized CisR cells to the cytotoxic effects of the drug.

CONCLUSION

This study identified NF-ĸB as a potential therapeutic target in cisplatin-resistant NSCLC. Furthermore, inhibition of NF-ĸB using DHMEQ re-sensitized chemo-resistant cells to cisplatin treatment.

Ribociclib, a selective cyclin D kinase 4/6 inhibitor, inhibits proliferation and induces apoptosis of human cervical cancer in vitro and in vivo

Cervical cancer remains one of the main factors leading to tumor-related death worldwide. Many strategies of cancer treatment such as chemotherapy are developed and used nowadays. However, for the cancer chemotherapy resistance, reduction of the limitation of cancer chemotherapy efficacy is one of the aims of several oncology teams. Moreover, the cyclin-dependent kinase 4/6-cyclin D-retinoblastoma protein-E2F pathway is an important mechanism for cell cycle control and its dysregulation is one of the key factors for cancers development including cervical cancer. Ribociclib is one of the selective CDK4/6 inhibitors and is a new therapeutic approach showing promise as a good strategy of therapy in many human cancers. However, there are not the studies regarding the investigation of effects of Ribociclib in cervical cancer yet. In the present study, by western blotting and immunofluorescence assay, we found respectively that CDK4, CDK6 and cyclin D1 are highly expressed and are mostly localized in the nucleus with some localized in the cytoplasm of cervical cancer cell lines. Moreover, Ribociclib induced cell cycle arrest in G0-G1 phase and cell apoptosis, and inhibited C33A cell proliferation in dose - dependent manner following by decreased expression of certain related genes such as CDK4, CDK6, E2F1, P-Rb, and increased Bax expression. In C33A xenografts, Ribociclib inhibited tumor growth associated with decreased expressions of CDK4, CDK6, cyclin D1, Rb and Ki-67, and also significantly increased tumor cell apoptosis. However, we didn't find side effect of Ribociclib concerning heart, liver and kidney perturbation and any Ribociclib anti-tumor effects on HeLa in vitro and in vivo which may be due to Hela cell infection by HPV. Based on our findings, the Rb-E2F pathway can be considered as an important factor in human cervical cancer pathogenesis and as a mechanism of Ribociclib, a potential strategy of treatment for the improvement of new therapeutic measures for the treatment of HPV-negative cervical cancer which application for HPV-positive cervical cancer is desired in further study.