Therapeutic Challenge with a CDK 4/6 Inhibitor Induces an RB-Dependent SMAC-Mediated Apoptotic Response in Non-Small Cell Lung Cancer

Transcriptional regulation and therapeutic potential of cyclin-dependent kinase 9 (CDK9) in sarcoma

Sarcomas include various subtypes comprising two significant groups - soft tissue and bone sarcomas. Although the survival rate for some sarcoma subtypes has improved over time, the current methods of treatment remain efficaciously limited, as recurrent, and metastatic diseases remain a major obstacle. There is a need for better options and therapeutic strategies in treating sarcoma. Cyclin dependent kinase 9 (CDK9) is a transcriptional kinase and has emerged as a promising target for treating various cancers. The aberrant expression and activation of CDK9 have been observed in several sarcoma subtypes, including rhabdomyosarcoma, synovial sarcoma, osteosarcoma, Ewing sarcoma, and chordoma. Enhanced CDK9 expression has also been correlated with poorer prognosis in sarcoma patients. As a master regulator of transcription, CDK9 promotes transcription elongation by phosphorylation and releasing RNA polymerase II (RNAPII) from its promoter proximal pause. Release of RNAPII from this pause induces transcription of critical genes in the tumor cell. Overexpression and activation of CDK9 have been observed to lead to the expression of oncogenes, including MYC and MCL-1, that aid sarcoma development and progression. Inhibition of CDK9 in sarcoma has been proven to reduce these oncogenes' expression and decrease proliferation and growth in different sarcoma cells. Currently, there are several CDK9 inhibitors in preclinical and clinical investigations. This review aims to highlight the recent discovery and results on the transcriptional role and therapeutic potential of CDK9 in sarcoma.

CDK4/6 inhibitors in lung cancer: current practice and future directions

Lung cancer is the leading cause of cancer-related deaths worldwide, and ∼85% of lung cancers are classified as nonsmall cell lung cancer (NSCLC). These malignancies can proliferate indefinitely, in part due to dysregulation of the cell cycle and the resulting abnormal cell growth. The specific activation of cyclin-dependent kinases 4 and 6 (CDK4/6) is closely linked to tumour proliferation. Approximately 80% of human tumours exhibit abnormalities in the cyclin D-CDK4/6-INK4-RB pathway. Specifically, CDK4/6 inhibitors either as monotherapy or combination therapy have been investigated in pre-clinical and clinical studies for the treatment of NSCLC, and promising results have been achieved. This review article focuses on research regarding the use of CDK4/6 inhibitors in NSCLC, including the characteristics and mechanisms of action of approved drugs and progress of pre-clinical and clinical research.

Design and Synthesis of New bis-oxindole and Spiro(triazole-oxindole) as CDK4 Inhibitors with Potent Anti-breast Cancer Activity

BACKGROUND

Since CDKs have been demonstrated to be overexpressed in a wide spectrum of human malignancies, their inhibition has been cited as an effective technique for anticancer drug development.

METHODS

In this context, new bis-oxindole/spiro-triazole-oxindole anti-breast cancer drugs with potential CDK4 inhibitory effects were produced in this work. The novel series of bis-oxindole/spirotriazole- oxindole were synthesized from the reaction of bis-oxindole with the aniline derivatives then followed by 1,3-dipolar cycloaddition of hydrazonoyl chloride.

RESULTS

The structure of these bis-oxindole/spiro-triazole-oxindole series was proven based on their spectral analyses. Most bis-oxindole and bis-spiro-triazole-oxindole compounds effectively inhibited the growth of MCF-7 (IC50 = 2.81-17.61 μM) and MDA-MB-231 (IC50 = 3.23-7.98 μM) breast cancer cell lines with low inhibitory activity against normal WI-38 cells. While the reference doxorubicin showed IC50 values of 7.43 μM against MCF-7 and 5.71 μM against the MDA-MB-231 cell line. Additionally, compounds 3b, 3c, 6b, and 6d revealed significant anti-CDK4 activity (IC50 = 0.157- 0.618 μM) compared to palbociclib (IC50 = 0.071 μM). Subsequent mechanistic investigations demonstrated that 3c was able to trigger tumor cell death through the induction of apoptosis. Moreover, it stimulated cancer cell cycle arrest in the G1 phase. Furthermore, western blotting disclosed that the 3c-induced cell cycle arrest may be mediated through p21 upregulation.

CONCLUSION

According to all of the findings, bis-oxindole 3c shows promise as a cancer treatment targeting CDK4.

The Evolving Pathways of the Efficacy of and Resistance to CDK4/6 Inhibitors in Breast Cancer

The approval of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) has remarkably improved the survival outcomes of patients with advanced hormone receptor-positive (HR+) breast cancer (BC), becoming the new standard of care treatment in these patients. Despite the efficacy of this therapeutic combination, intrinsic and acquired resistance inevitably occurs and represents a major clinical challenge. Several mechanisms associated with resistance to CDK4/6i have been identified, including both cell cycle-related and cell cycle-nonspecific mechanisms. This review discusses new insights underlying the mechanisms of action of CDK4/6i, which are more far-reaching than initially thought, and the currently available evidence of the mechanisms of resistance to CDK4/6i in BC. Finally, it highlights possible treatment strategies to improve CDK4/6i efficacy, summarizing the most relevant clinical data on novel combination therapies involving CDK4/6i.

A tumor mutational burden-derived immune computational framework selects sensitive immunotherapy/chemotherapy for lung adenocarcinoma populations with different prognoses

Background

Lung adenocarcinoma (LUAD) kills millions of people every year. Recently, FDA and researchers proved the significance of high tumor mutational burden (TMB) in treating solid tumors. But no scholar has constructed a TMB-derived computing framework to select sensitive immunotherapy/chemotherapy for the LUAD population with different prognoses.

Methods

The datasets were collected from TCGA, GTEx, and GEO. We constructed the TMB-derived immune lncRNA prognostic index (TILPI) computing framework based on TMB-related genes identified by weighted gene co-expression network analysis (WGCNA), oncogenes, and immune-related genes. Furthermore, we mapped the immune landscape based on eight algorithms. We explored the immunotherapy sensitivity of different prognostic populations based on immunotherapy response, tumor immune dysfunction and exclusion (TIDE), and tumor inflammation signature (TIS) model. Furthermore, the molecular docking models were constructed for sensitive drugs identified by the pRRophetic package, oncopredict package, and connectivity map (CMap).

Results

The TILPI computing framework was based on the expression of TMB-derived immune lncRNA signature (TILncSig), which consisted of AC091057.1, AC112721.1, AC114763.1, AC129492.1, LINC00592, and TARID. TILPI divided all LUAD patients into two populations with different prognoses. The random grouping verification, survival analysis, 3D PCA, and ROC curve (AUC=0.74) firmly proved the reliability of TILPI. TILPI was associated with clinical characteristics, including smoking and pathological stage. Furthermore, we estimated three types of immune cells threatening the survival of patients based on multiple algorithms. They were macrophage M0, T cell CD4 Th2, and T cell CD4 memory activated. Nevertheless, five immune cells, including B cell, endothelial cell, eosinophil, mast cell, and T cell CD4 memory resting, prolonged the survival. In addition, the immunotherapy response and TIDE model proved the sensitivity of the low-TILPI population to immunotherapy. We also identified seven intersected drugs for the LUAD population with poor prognosis, which included docetaxel, gemcitabine, paclitaxel, palbociclib, pyrimethamine, thapsigargin, and vinorelbine. Their molecular docking models and best binding energy were also constructed and calculated.

Conclusions

We divided all LUAD patients into two populations with different prognoses. The good prognosis population was sensitive to immunotherapy, while the people with poor prognosis benefitted from 7 drugs.

Increased mRNA expression of CDKN2A is a transcriptomic marker of clinically aggressive meningiomas

Homozygous deletion of CDKN2A/B was recently incorporated into the World Health Organization classification for grade 3 meningiomas. While this marker is overall rare in meningiomas, its relationship to other CDKN2A alterations on a transcriptomic, epigenomic, and copy number level has not yet been determined. We therefore utilized multidimensional molecular data of 1577 meningioma samples from 6 independent cohorts enriched for clinically aggressive meningiomas to comprehensively interrogate the spectrum of CDKN2A alterations through DNA methylation, copy number variation, transcriptomics, and proteomics using an integrated molecular approach. Homozygous CDKN2A/B deletions were identified in only 7.1% of cases but were associated with significantly poorer outcomes compared to tumors without these deletions. Heterozygous CDKN2A/B deletions were identified in 2.6% of cases and had similarly poor outcomes as those with homozygous deletions. Among tumors with intact CDKN2A/B (without a homozygous or heterozygous deletion), we found a distinct difference in outcome based on mRNA expression of CDKN2A, with meningiomas that had elevated mRNA expression (CDKN2A^high) having a significantly shorter time to recurrence. The expression of CDKN2A was independently prognostic after accounting for copy number loss and consistently increased with WHO grade and more aggressive molecular and methylation groups irrespective of cohort. Despite the discordant and mutually exclusive status of the CDKN2A gene in these groups, both CDKN2A^high meningiomas and meningiomas with CDKN2A deletions were enriched for similar cell cycle pathways but at different checkpoints. High mRNA expression of CDKN2A was also associated with gene hypermethylation, Rb-deficiency, and lack of response to CDK inhibition. p16 immunohistochemistry could not reliably differentiate between meningiomas with and without CDKN2A deletions but appeared to correlate better with mRNA expression. These findings support the role of CDKN2A mRNA expression as a biomarker of clinically aggressive meningiomas with potential therapeutic implications.

Applications and mechanisms of the cyclin-dependent kinase 4/6 inhibitor, PD-0332991, in solid tumors

Abnormal CDK4/6-Rb-E2F signal transduction is a common finding in tumors and is a driving factor for the excessive proliferation of various tumor cells. PD-0332991, a highly specific, small molecule inhibitor for CDK4 and 6, has been shown to inhibit tumor growth by abrogating the phosphorylating capacity of CDK4/6 and suppressing Rb phosphorylation. It has been promoted for the treatment of breast cancer and potentially for other tumor types such as liver cancers, lung cancers and sarcomas. Due to the risk of monotherapy resistance, PD-0332991 is commonly used in combination with other drugs. Such combination treatments have proved able to inhibit tumor proliferation more effectively, induce stronger senescence and apoptosis, and enhance the efficiency of immunotherapy. Therefore, tumor cells with senescence induced by PD-0332991 are now used as ideal screening tools of cytolytic drugs with more efficient and thorough anti-tumor properties. With more extensive understandings about the branching points between senescence and apoptosis, it is possible to refine the dosage of PD-0332991. Better characterization of resistant cells, of inhibitors and of adverse effects such as leukopenia are needed to overcome obstacles in the use of PD-0332991. In this review of PD-0332991 research, we hope to provide guidance of transitions from laboratory findings to clinical applications of PD-0332991 and to facilitate PD-0332991-based multi-inhibitor combination therapies for various tumors.

Palbociclib Induces the Apoptosis of Lung Squamous Cell Carcinoma Cells via RB-Independent STAT3 Phosphorylation

Lung squamous cell carcinoma (LUSC) treatment response is poor and treatment alternatives are limited. Palbociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor, has recently been approved for hormone receptor-positive breast cancer patients and applied in multiple preclinical models, but its use for LUSC therapy remains elusive. Here, we investigated whether palbociclib induced cell apoptosis and dissected the underlying mechanism in LUSC. We found that palbociclib induced LUSC cell apoptosis through inhibition of Src tyrosine kinase/signal transducers and activators of transcription 3 (STAT3). Interestingly, palbociclib reduced STAT3 signaling in LUSC cells interfered by retinoblastoma tumor-suppressor gene (RB), suggesting that pro-apoptosis effect of palbociclib was independent of classic CDK4/6-RB signaling. Furthermore, palbociclib could suppress IL-1β and IL-6 expression, and therefore blocked Src/STAT3 signaling, which were rescued by either recombinant human IL-1β or IL-6. Moreover, Myc mediated the sensitivity of LUSC cells to palbociclib. Our discoveries demonstrated that palbociclib induces apoptosis of LUSC cells through the Src/STAT3 axis in an RB-independent manner, and provided a reliable experimental basis of clinical studies in LUSC patients.

Exploring the Expression of Survivin on Neoadjuvant Chemotherapy in Invasive Breast Carcinoma

Background:   Biomarkers are required to monitor the response to neoadjuvant chemotherapy (NC) in patients with invasive breast cancer (IBC). The purpose of this study is to determine the function of Survivin in the administration of NC, both taxane- and non-taxane-based, to patients with IBC. Methods: Thirty-one samples were categorized according to the NC's administrative status (before or after) and the type of NC used (taxane- or non-taxane-based). Age, tumor grade, receptor status (ER, PR, HER2, Ki-67), and survivin expression were evaluated. Survivin expressions were evaluated by IHC staining and categorized according median H-score cut-offs, while other data were collected from archives. Data was gathered and analyzed using generalized linear model.  Results:  Survivin expression decreased following NC administration, although not significantly (p=0.285). The taxane group had lower survivin expression. Statistically, this was not significant (p=0.329). The non-taxane group had the same outcome (p=0.792). The decline in survivin expression was greater in the taxane group than in the non-taxane group, although it was not statistically significant (p=0.369). Conclusion: Although the changes in survivin expression were not statistically significant, when clinical and laboratory data are analyzed, survivin expression has the potential to be a predictive biomarker of NC response as well as clinical outcome in IBC.

Targeting CDK4 and CDK6 in cancer

Cyclin-dependent kinase 4 (CDK4) and CDK6 are critical mediators of cellular transition into S phase and are important for the initiation, growth and survival of many cancer types. Pharmacological inhibitors of CDK4/6 have rapidly become a new standard of care for patients with advanced hormone receptor-positive breast cancer. As expected, CDK4/6 inhibitors arrest sensitive tumour cells in the G1 phase of the cell cycle. However, the effects of CDK4/6 inhibition are far more wide-reaching. New insights into their mechanisms of action have triggered identification of new therapeutic opportunities, including the development of novel combination regimens, expanded application to a broader range of cancers and use as supportive care to ameliorate the toxic effects of other therapies. Exploring these new opportunities in the clinic is an urgent priority, which in many cases has not been adequately addressed. Here, we provide a framework for conceptualizing the activity of CDK4/6 inhibitors in cancer and explain how this framework might shape the future clinical development of these agents. We also discuss the biological underpinnings of CDK4/6 inhibitor resistance, an increasingly common challenge in clinical oncology.

Cell cycle involvement in cancer therapy; WEE1 kinase, a potential target as therapeutic strategy

Mitosis is the process of cell division and is regulated by checkpoints in the cell cycle. G1-S, S, and G2-M are the three main checkpoints that prevent initiation of the next phase of the cell cycle phase until previous phase has completed. DNA damage leads to activation of the G2-M checkpoint, which can trigger a downstream DNA damage response (DDR) pathway to induce cell cycle arrest while the damage is repaired. If the DNA damage cannot be repaired, the replication stress response (RSR) pathway finally leads to cell death by apoptosis, in this case called mitotic catastrophe. Many cancer treatments (chemotherapy and radiotherapy) cause DNA damages based on SSBs (single strand breaks) or DSBs (double strand breaks), which cause cell death through mitotic catastrophe. However, damaged cells can activate WEE1 kinase (as a part of the DDR and RSR pathways), which prevents apoptosis and cell death by inducing cell cycle arrest at G2 phase. Therefore, inhibition of WEE1 kinase could sensitize cancer cells to chemotherapeutic drugs. This review focuses on the role of WEE1 kinase (as a biological macromolecule which has a molecular mass of 96 kDa) in the cell cycle, and its interactions with other regulatory pathways. In addition, we discuss the potential of WEE1 inhibition as a new therapeutic approach in the treatment of various cancers, such as melanoma, breast cancer, pancreatic cancer, cervical cancer, etc.

Mechanisms and Implications of CDK4/6 Inhibitors for the Treatment of NSCLC

Cyclin-dependent kinases (CDKs) are key regulators of cell cycle progression in malignant tumor cells and play an important role through complex molecular interactions. Dysregulation of CDK dependent pathways is often found in non-small cell lung cancer, which indicates its vulnerability and can be used in clinical benefit. CDK4/6 inhibitors can prevent tumor cells from entering the G approved 1 and S phases, which have been studied in a series of explorations and brought great clinical effect to patients and encouragement to both physicians and researchers, thereby showing potential as a new therapeutic agent. A series of preclinical and clinical studies have been carried out on CDK4/6 inhibitors in NSCLC, and have been achieved some results, which may become a new potential treatment in the future. This review focuses on the research progress on CDK4/6 inhibitors in NSCLC, particularly the mechanisms of action, drugs, clinical research progress, and future application.

Retinoblastoma: from discovery to clinical management

The retinoblastoma gene (RB1) was the first tumour suppressor cloned; the role of its protein product (RB) as the principal driver of the G1 checkpoint in cell cycle control has been extensively studied. However, many other RB functions are continuously reported. Its role in senescence, DNA repair and apoptosis, among others, is indications of the significance of RB in a vast network of cellular interactions, explaining why RB loss or its malfunction is one of the leading causes of a large number of paediatric and adult cancers. RB was first reported in retinoblastoma, a common intraocular malignancy in the paediatric population worldwide. Currently, its diagnosis is clinical, and in nondeveloped countries, where the incidence is higher, it is performed in advanced stages of the disease, compromising the integrity of the eye and the patient's life. Even though new treatments are being continuously developed, enucleation is still a major choice due to the late disease stage diagnosis and treatments costs. Research into biomarkers is our best option to improve the chances of good results in the treatment and hopes of patients' good quality of life. Here, we recapitulated the history of the disease and the first treatments to put the advances in its clinical management into perspective. We also review the different functions of the protein and the progress in the search for biomarkers. It is clear that there is still a long way to go, but we should offer these children and their families a better way to deal with the disease with the community's effort.

Bioinformatics analysis and experimental validation of TTK as a biomarker for prognosis in non-small cell lung cancer

Background: Despite the prominent development of medical technology in recent years, the prognosis of non-small cell lung cancer (NSCLC) is still not optimistic. It is crucial to identify more reliable diagnostic biomarkers for the early diagnosis and personalized therapy of NSCLC and clarify the molecular mechanisms underlying NSCLC progression.

Methods: In the present study, bioinformatics analysis was performed on three datasets obtained from the Gene Expression Omnibus to identify the NSCLC-associated differentially expressed genes (DEGs). Immunohistochemistry-based tissue microarray of human NSCLC was used to experimental validating the potential targets obtained from bioinformatics analysis.

Results: By using protein–protein interaction (PPI) network analysis, Kaplan–Meier plotter, and Gene Expression Profiling Interactive Analysis, we selected 40 core DEGs for further study. Then, a re-analysis of 40 selected genes via Kyoto Encyclopedia of Genes and Genomes pathway enrichment showed that nine key genes involved in the cell cycle and p53 signaling pathway participated in the development of NSCLC. Then, we checked the protein level of nine key genes by semi-quantitative of IHC and checked the distribution at a single-cell level. Finally, we validated dual-specificity protein kinase TTK as a biomarker for prognosis in a tissue microarray. High TTK expression associated with a higher histological stage, advanced TNM stage, high frequency of positive lymph nodes, and worse 5-year overall survival.

Conclusions: We found nine key genes were enriched in the cell cycle and p53 signaling pathway. TTK could be considered as a potential therapeutic target and for the prognosis biomarker of NSCLC. These findings will provide new insights for the development of individualized therapeutic targets for NSCLC.

Combination of miR‑143 and miR‑506 reduces lung and pancreatic cancer cell growth through the downregulation of cyclin‑dependent kinases

Lung cancer (LC) and pancreatic cancer (PC) are the first and fourth leading causes of cancer‑related deaths in the US. Deregulated cell cycle progression is the cornerstone for rapid cell proliferation, tumor development, and progression. Here, we provide evidence that a novel combinatorial miR treatment inhibits cell cycle progression at two phase transitions, through their activity on the CDK4 and CDK1 genes. Following transfection with miR‑143 and miR‑506, we analyzed the differential gene expression of CDK4 and CDK1, using qPCR or western blot analysis, and evaluated cell cycle inhibition, apoptosis and cytotoxicity. The combinatorial miR‑143/506 treatment downregulated CDK4 and CDK1 levels, and induced apoptosis in LC cells, while sparing normal lung fibroblasts. Moreover, the combinatorial miR treatment demonstrated a comparable activity to clinically tested cell cycle inhibitors in inhibiting cell cycle progression, by presenting substantial inhibition at the G1/S and G2/M cell cycle transitions. More importantly, the miR‑143/506 treatment presented a broader application, effectively downregulating CDK1 and CDK4 levels, and reducing cell growth in PC cells. These findings suggest that the miR‑143/506 combination acts as a promising approach to inhibit cell cycle progression for cancer treatment with minimal toxicity to normal cells.

Inhibition of Cyclin-dependent Kinase (CDK) Decreased Survival of NB4 Leukemic Cells: Proposing a p53-Independent Sensitivity of Leukemic Cells to Multi-CDKs Inhibitor AT7519

An unbounded number of events exist beneath the intricacy of each particular hematologic malignancy, prompting the tumor cells into an unrestrained proliferation and invasion. Aberrant expression of cyclin-dependent kinases (CDKs) is one of these events which disrupts the regulation of cell cycle and subsequently, results in cancer progression. In this study, we surveyed the repressive impact of multi-CDK inhibitor AT7519 on a panel of leukemia-derived cell lines. Our data underlined that AT7519 abated the survival of all tested cells; however, in an overview, the response rate of leukemic cells to the inhibitor was varied irrespective of p53 status. Notably, the less sensitivity of leukemia cells to AT7519 was found to be mediated partly by the compensatory activation of c-Myc oncogene which was confirmed by the induction of a superior cytotoxicity upon its suppression in less sensitive cell. The blockage of cell cycle, as announced by induction of sub-G1 arrest as well as reduced S phase, resulted in a significant decrease in survival of acute promyelocytic leukemia (APL)-derived NB4 cells, as the most sensitive cell line, either as monotherapy or in combination with arsenic trioxide. Anti-leukemic effects of the inhibitor were further verified by apoptosis analysis, where we discovered that AT7519 induced apoptosis via alteration of pro- and anti-apoptotic genes in NB4. All in all, this study proposed that AT7519 is a rewarding agent opposed to APL; however, additional examinations should be performed to determine the advantages of this inhibitor in clinical setting.

Design, synthesis and biological assessment of novel CDK4 inhibitor with potent anticancer activity

Efforts toward finding potent CDK4 inhibitor for cancer therapy, a series of fluorine substituted pyrrolo[2,3-d]pyrimidine derivatives were designed, synthesized, and evaluated. Among them, the optimal lead compound 18i was discovered with potent activity against CDK4 at the nanomolar level (IC₅₀ = 2.5 nM) and exquisite selectivity which demonstrated only modest activity against 3 out of the 394 protein kinases. 18i exhibited a much greater in vitro antiproliferative activity against several human cancer cell lines than that of the approved drug ribociclib. Further mechanism studies revealed that 18i effectively stimulated cancer cell cycle arrest in G₁ phase and induced tumor cell apoptosis. In the comparison of in vivo therapeutic effects in xenograft mouse models of breast cancer, oral administration of 18i showed a significantly better degree of inhibitory effect to ribociclib without obvious toxicity. All of the results indicated that 18i could be a promising CDK4 inhibitor for treating malignancies.

Palbociclib negatively regulates fatty acid synthesis due to upregulation of AMPKα and miR-33a levels to increase apoptosis in Panc-1 and MiaPaCa-2 cells

Fatty acids (FAs) synthesis mechanism has various regulators such as fatty acid synthase (FASN), AMP-regulated protein kinase (AMPK), or mammalian target of rapamycin (mTOR), which are aberrantly dysregulated in various pancreatic cancer cells. In this study, we aim to understand the regulatory role of palbociclib, a CDK4/6 inhibitor, on the cellular energy metabolism through regulation of AMPK/mTOR signaling by modulation of intracellular miR-33a levels in Panc-1 and MiaPaCa-2 cells. Palbociclib downregulated FAs metabolism more effectively in MiaPaCa-2 cells than Panc-1 cells. Moreover, palbociclib treatment increased the levels of miR-33a in each cell line albeit a higher increase was evident in MiaPaCa-2 cells. Stress-mediated activation of mTOR signaling axis was found associated with palbociclib-mediated AMPKα activation and miR33a upregulation. These findings provided that a deeper understanding about possible interactions of cell cycle activity and reduction of FAs synthesis may facilitate the enhancement of cell death mechanisms in pancreatic cancer cells.

Flavopiridol causes cell cycle inhibition and demonstrates anti-cancer activity in anaplastic thyroid cancer models

Anaplastic thyroid cancer (ATC) is a rare, but nearly uniformly fatal disease that is typically resistant to chemotherapy and radiation. Alternative strategies to target this cancer at a molecular level are necessary in order to improve dismal outcomes for ATC patients. We examined the effects of flavopiridol, a CDK inhibitor, in a panel of ATC cell lines. When cell lines were treated over a ten-point concentration range, CAL62, KMH2 and BHT-101 cell lines had a sub micromolar half-maximal inhibitory concentration, while no effect was seen in the non-cancerous cell line IMR-90. Flavopiridol treatment resulted in decreased levels of the cell cycle proteins CDK9 and MCL1, and induced cell cycle arrest. Flavopiridol also decreased the in vitro ability of ATC cells to form colonies and impeded migration using a transwell migration assay. In vivo, flavopiridol decreased tumor weight and tumor volume over time in a patient-derived xenograft model of ATC. Given the observed in vitro and in vivo activity, flavopiridol warrants further investigation for treatment of ATC.

Future perspectives and challenges with CDK4/6 inhibitors in hormone receptor-positive metastatic breast cancer

There are three US FDA-approved CDK4/6 inhibitors: palbociclib, ribociclib and abemaciclib for patients with HR-positive, HER2-negative (HR+/HER2-) metastatic breast cancer (MBC). They are all equally effective, so the question becomes how to choose among these agents and how to sequence them. Other areas with active investigation include identifying predictive biomarkers for the selection of patients whom may benefit more from CDK4/6 inhibitors, deciding whether to continue CDK4/6 inhibitors after disease progression on CDK4/6 inhibitors, creating novel treatment combinations and expanding use beyond HR+/HER2- MBC. Here, we review the current use of and potential next directions for CDK4/6 inhibitors in the treatment of patients with HR+/HER2- MBC.

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.

Palbociclib treatment alters nucleotide biosynthesis and glutamine dependency in A549 cells

BACKGROUND

Aberrant activity of cell cycle proteins is one of the key somatic events in non-small cell lung cancer (NSCLC) pathogenesis. In most NSCLC cases, the retinoblastoma protein tumor suppressor (RB) becomes inactivated via constitutive phosphorylation by cyclin dependent kinase (CDK) 4/6, leading to uncontrolled cell proliferation. Palbociclib, a small molecule inhibitor of CDK4/6, has shown anti-tumor activity in vitro and in vivo, with recent studies demonstrating a functional role for palbociclib in reprogramming cellular metabolism. While palbociclib has shown efficacy in preclinical models of NSCLC, the metabolic consequences of CDK4/6 inhibition in this context are largely unknown.

METHODS

In our study, we used a combination of stable isotope resolved metabolomics using [U-13C]-glucose and multiple in vitro metabolic assays, to interrogate the metabolic perturbations induced by palbociclib in A549 lung adenocarcinoma cells. Specifically, we assessed changes in glycolytic activity, the pentose phosphate pathway (PPP), and glutamine utilization. We performed these studies following palbociclib treatment with simultaneous silencing of RB1 to define the pRB-dependent changes in metabolism.

RESULTS

Our studies revealed palbociclib does not affect glycolytic activity in A549 cells but decreases glucose metabolism through the PPP. This is in part via reducing activity of glucose 6-phosphate dehydrogenase, the rate limiting enzyme in the PPP. Additionally, palbociclib enhances glutaminolysis to maintain mitochondrial respiration and sensitizes A549 cells to the glutaminase inhibitor, CB-839. Notably, the effects of palbociclib on both the PPP and glutamine utilization occur in an RB-dependent manner.

CONCLUSIONS

Together, our data define the metabolic impact of palbociclib treatment in A549 cells and may support the targeting CDK4/6 inhibition in combination with glutaminase inhibitors in NSCLC patients with RB-proficient tumors.

[Research Progress of CDK4/6 Inhibitors in Non-small Cell Lung Cancer]

Lung cancer is the leading cause of cancer-related death worldwide. Non-small cell lung cancer (NSCLC) accounts for 80%-85% of lung cancer. Malignant tumors can proliferate indefinitely, and cell cycle regulation is abnormal which is one of the characteristics of malignant tumor. Cyclin D-dependent kinase (CDK) 4/6 inhibitor can prevent tumor cells from entering S phase through G₁ phase and inhibit tumor proliferation. The CDK4/6 inhibitor has achieved good effect in hormone receptor positive breast cancer, and CDK4/6 inhibitor combined with endocrine therapy has become a standard treatment for this kind of patients. Cell cycle regulation is usually abnormal in NSCLC, which incidence is about 22%-45%. CDK4/6 inhibitors have also carried out a series of research and achieved some results, which may become a new treatment in the future. This review focuses on the research progress of CDK4/6 inhibitors in NSCLC, including the mechanism and the approved drugs, clinical research progress in NSCLC, biomarkers for efficacy prediction and current limitations.

Novel CDKs inhibitors for the treatment of solid tumour by simultaneously regulating the cell cycle and transcription control

A novel series of cyclin-dependent kinases (CDKs) inhibitors, which play critical roles in the cell cycle control and regulation of cell transcription, were synthesised. A systematic study of enzymatic and cellular assays led to the identification of compound X22 with a nanomolar potency against CDK4 and CDK9 and potent antiproliferative activities against a panel of tumour cell lines. X22 could induce cell cycle arrest and cell apoptosis in cancer cell lines. X22 dose-dependently inhibits signalling pathways downstream of CDKs in cancer cells. In vivo antitumor activity assays, oral administration of X22 led to significant tumour regression in mouse model without obvious toxicity. Superior anti-cancer efficacy in vitro and in vivo of X22 demonstrated combined depletion of cell cycle and transcriptional CDK all contributed to antitumor activity. Taken together, concomitant inhibition of cell cycle and transcriptional CDK activities provided valuable guide for further structural optimisation.

CDK4/6 Inhibitor Palbociclib Amplifies the Radiosensitivity to Nasopharyngeal Carcinoma Cells via Mediating Apoptosis and Suppressing DNA Damage Repair

Background

Radiotherapy is the primary approach for nasopharyngeal carcinoma (NPC). Although high survival rates can be obtained with radiation for early stage lesions, distant metastasis and local recurrence frequently occur. In this study, we pioneeringly investigated the antitumor activity and underlying mechanism of cyclin-dependent kinase 4/6 inhibitor (palbociclib) combined with radiation on NPC cells.

Methods

Evaluation of radiation enhancement with palbociclib was based on results from CCK8 and clonogenicity assays for cell proliferation, flow cytometry for apoptosis, ROS level and cell cycle and immunocytochemistry for DNA double-strand break repair.

Results

Palbociclib inhibited cellular growth of RB-proficient CNE-1 and CNE-2 via reducing RB phosphorylation and arresting cell cycle. Combination regimens of palbociclib plus radiation were significantly superior to palbociclib or radiation only through inhibiting cellular growth and inducing apoptosis. Moreover, the antitumor activity of both concurrent palbociclib plus radiation and radiation followed by palbociclib consistently preceded that of palbociclib followed by radiation. Meanwhile, the two preferable combination regimens possessed higher proportion of G2/M phase cells, evidently inhibited DNA double-strand break repair and eventually triggered tumor cell apoptosis.

Conclusion

Our study demonstrated that palbociclib could provoke a strong antitumor activity as a potential adjuvant to radiation therapy for NPC harboring RB expression.

The Kinome of Human Alveolar Type II and Basal Cells, and Its Reprogramming in Lung Cancer

The discovery of mutant tyrosine kinases as oncogenic drivers of lung adenocarcinomas has changed the basic understanding of lung cancer development and therapy. Yet, expressed kinases (kinome) in lung cancer progenitor cells, as well as whether kinase expression and the overall kinome changes or is reprogrammed upon transformation, is incompletely understood. We hypothesized that the kinome differs between lung cancer progenitor cells, alveolar type II cells (ATII), and basal cells (BC) and that their respective kinomes undergo distinct lineage-specific reprogramming to adenocarcinomas and squamous cell carcinomas upon transformation. We performed RNA sequencing on freshly isolated human ATII, BC, and lung cancer cell lines to define the kinome in nontransformed cells and transformed cells. Our studies identified a unique kinome for ATII and BC and changes in their kinome upon transformation to their respective carcinomas.

The Proliferative and Apoptotic Landscape of Basal-like Breast Cancer

Basal-like breast cancer (BLBC) is an aggressive molecular subtype that represents up to 15% of breast cancers. It occurs in younger patients, and typically shows rapid development of locoregional and distant metastasis, resulting in a relatively high mortality rate. Its defining features are that it is positive for basal cytokeratins and, epidermal growth factor receptor and/or c-Kit. Problematically, it is typically negative for the estrogen receptor and human epidermal growth factor receptor 2 (HER2), which means that it is unsuitable for either hormone therapy or targeted HER2 therapy. As a result, there are few therapeutic options for BLBC, and a major priority is to define molecular subgroups of BLBC that could be targeted therapeutically. In this review, we focus on the highly proliferative and anti-apoptotic phenotype of BLBC with the goal of defining potential therapeutic avenues, which could take advantage of these aspects of tumor development.

Cyclin-dependent kinase 9 (CDK9) is a novel prognostic marker and therapeutic target in osteosarcoma

Background

Cyclin-dependent protein kinase 9 (CDK9) has been shown to play an important role in the pathogenesis of malignant tumors. However, the expression and function of CDK9 remain unknown in osteosarcomas. The purpose of this study is to assess the expression, function and clinical prognostic relationship of CDK9 in osteosarcomas.

Methods

A tissue microarray of 70 patient specimens was analyzed by immunohistochemistry to measure CDK9 expression, which was further investigated for correlation with patient clinical characteristics. CDK9 expression in osteosarcoma cell lines and patient tissues was also evaluated by Western blotting. CDK9-specific siRNA and the CDK9 inhibitor were applied to determine the effect of CDK9 inhibition on osteosarcoma cell proliferation and anti-apoptotic activity. The clonogenicity and migration activity were also examined using clonogenic and wound healing assays. A 3D cell culture model was performed to mimic the in vivo osteosarcoma environment to further validate the effect of CDK9 inhibition on osteosarcoma cells.

Findings

We demonstrated that higher CDK9-expression is associated with significantly shortened patient survival by immunohistochemistry. Expression of CDK9 is inversely correlated to the percent of tumor necrosis post-neoadjuvant chemotherapy, which is the most important predictive factor of disease outcome for osteosarcoma patients. Knockdown of CDK9 with siRNA and inhibition of CDK9 activity with inhibitor decreased cell proliferation and induced apoptosis in osteosarcoma.

Interpretation

High expression of CDK9 is an independent predictor of poor prognosis in osteosarcoma patients. Our results suggest that CDK9 is a novel prognostic marker and a promising therapeutic target for osteosarcomas.

Flavopiridol's effects on metastasis in KRAS mutant lung adenocarcinoma cells

BACKGROUND

There is still no clinically approved agent for mutant KRAS, which is the most common alteration in non-small-cell lung cancer (NSCLC). Flavopiridol is a semisynthetic flavonoid that inhibits cell growth through cyclin-dependent kinases in G1/S or G2/M of the cell cycle and induces apoptosis. In this study, we evaluated its effect on cellular apoptosis, survival, and metastasis mechanisms on KRAS mutant A549, Calu-1, and H2009 cell lines.

METHODS

The cytotoxic effects of flavopiridol on NSCLC cells were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability test. The cells were treated with 200 and 400 nM flavopiridol, and, then, apoptosis, survival, and metastasis-related protein expressions were determined by Western blot analysis. The antimetastatic effects of flavopiridol were assessed by wound healing and Galectin-3 activity assay.

RESULTS

Flavopiridol drastically affected toxicity in all KRAS mutant NSCLC cells at nanomolar concentrations. Also, it could efficiently inhibit wound healing and Galectin-3 activity in all the cells tested. However, the metastasis-related protein expressions did not reflect these obvious effects on blotting. p-Erk was activated as a cellular survival mechanism to escape apoptosis in all the cells tested.

CONCLUSION

Although there are many mechanisms that still need to be elucidated, flavopiridol can be used as a metastasis inhibitor and an apoptosis inducer in KRAS mutant NSCLC.

XPO1 inhibition by selinexor induces potent cytotoxicity against high grade bladder malignancies

Treatment options for high grade urothelial cancers are limited and have remained largely unchanged for several decades. Selinexor (KPT-330), a first in class small molecule that inhibits the nuclear export protein XPO1, has shown efficacy as a single agent treatment for numerous different malignancies, but its efficacy in limiting bladder malignancies has not been tested. In this study we assessed selinexor-dependent cytotoxicity in several bladder tumor cells and report that selinexor effectively reduced XPO1 expression and limited cell viability in a dose dependent manner. The decrease in cell viability was due to an induction of apoptosis and cell cycle arrest. These results were recapitulated in in vivo studies where selinexor decreased tumor growth. Tumors treated with selinexor expressed lower levels of XPO1, cyclin A, cyclin B, and CDK2 and increased levels of RB and CDK inhibitor p27, a result that is consistent with growth arrest. Cells expressing wildtype RB, a potent tumor suppressor that promotes growth arrest and apoptosis, were most susceptible to selinexor. Cell fractionation and immunofluorescence studies showed that selinexor treatment increased nuclear RB levels and mechanistic studies revealed that RB ablation curtailed the response to the drug. Conversely, limiting CDK4/6 dependent RB phosphorylation by palbociclib was additive with selinexor in reducing bladder tumor cell viability, confirming that RB activity has a role in the response to XPO1 inhibition. These results provide a rationale for XPO1 inhibition as a novel strategy for the treatment of bladder malignancies.

Palbociclib resistance confers dependence on an FGFR-MAP kinase-mTOR-driven pathway in KRAS-mutant non-small cell lung cancer

CDK4 is emerging as a target in KRAS-mutant non-small cell lung cancer (NSCLC). We demonstrate that KRAS-mutant NSCLC cell lines are initially sensitive to the CDK4/6 inhibitor palbociclib, but readily acquire resistance associated with increased expression of CDK6, D-type cyclins and cyclin E. Resistant cells also demonstrated increased ERK1/2 activity and sensitivity to MEK and ERK inhibitors. Moreover, MEK inhibition reduced the expression and activity of cell cycle proteins mediating palbociclib resistance. In resistant cells, ERK activated mTOR, driven in part by upstream FGFR1 signaling resulting from the extracellular secretion of FGF ligands. A genetically-engineered mouse model of KRAS-mutant NSCLC initially sensitive to palbociclib similarly developed acquired resistance with increased expression of cell cycle mediators, ERK1/2 and FGFR1. In this model, resistance was delayed with combined palbociclib and MEK inhibitor treatment. These findings implicate an FGFR1–MAP kinase–mTOR pathway resulting in increased expression of D-cyclins and CDK6 that confers palbociclib resistance and indicate that CDK4/6 inhibition acts to promote MAP kinase dependence.