Palbociclib, a selective CDK4/6 inhibitor, enhances the effect of selumetinib in RAS-driven non-small cell lung cancer

Synergistic Efficacy of CDK4/6 Inhibitor Abemaciclib and HDAC Inhibitor Panobinostat in Pancreatic Cancer Cells

The current 5-year survival rate of pancreatic cancer is about 12%, making it one of the deadliest malignancies. The rapid metastasis, acquired drug resistance, and poor patient prognosis necessitate better therapeutic strategies for pancreatic ductal adenocarcinoma (PDAC). Multiple studies show that combining chemotherapeutics for solid tumors has been successful. Targeting two distinct emerging hallmarks, such as non-mutational epigenetic changes by panobinostat (Pan) and delayed cell cycle progression by abemaciclib (Abe), inhibits pancreatic cancer growth. HDAC and CDK4/6 inhibitors are effective but are prone to drug resistance and failure as single agents. Therefore, we hypothesized that combining Abe and Pan could synergistically and lethally affect PDAC survival and proliferation. Multiple cell-based assays, enzymatic activity experiments, and flow cytometry experiments were performed to determine the effects of Abe, Pan, and their combination on PDAC cells and human dermal fibroblasts. Western blotting was used to determine the expression of cell cycle, epigenetic, and apoptosis markers. The Abe-Pan combination exhibited excellent efficacy and produced synergistic effects, altering the expression of cell cycle proteins and epigenetic markers. Pan, alone and in combination with Abe, caused apoptosis in pancreatic cancer cells. Abe-Pan co-treatment showed relative safety in normal human dermal fibroblasts. Our novel combination treatment of Abe and Pan shows synergistic effects on PDAC cells. The combination induces apoptosis, shows relative safety, and merits further investigation due to its therapeutic potential in the treatment of PDAC.

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.

A real-world analysis of trametinib in combination with hydroxychloroquine or CDK4/6 inhibitor as third- or later-line therapy in metastatic pancreatic adenocarcinoma

BACKGROUND

There are no standard third-line treatment options for metastatic pancreatic ductal adenocarcinoma (mPDAC). Trametinib in combination with hydroxychloroquine (HCQ) or CDK4/6 inhibitors for pancreatic adenocarcinoma showed promising efficacy in preclinical studies. However, the regimens have not been well examined in patients with mPDAC.

METHODS

Patients with mPDAC who received the combination of trametinib and HCQ or CDK4/6 inhibitors as third- or later-line therapy were reviewed. The efficacy and prognosis were further analyzed.

RESULTS

A total of 13 mPDAC patients were enrolled, of whom 8 and 5 patients were treated with trametinib plus HCQ or a CDK4/6 inhibitor (palbociclib or abemaciclib), respectively. All enrolled patients had either KRAS G12D or G12V mutations and had received a median of 3 prior lines of therapy (range, 2-6). The median trametinib treatment duration was 1.4 months. Of the 10 patients with measurable disease, only 1 patient achieved stable disease, and the remaining patients had progressive disease. Moreover, in patients treated with trametinib plus HCQ and a CDK4/6 inhibitor, the median progression-free survival was 2.0 and 2.8 months, respectively, and the median overall survival was 4.2 and 4.7 months, respectively. Moreover, 5 (50%) patients experienced grade 3-4 adverse events in 10 patients with available safety data.

CONCLUSIONS

The combination of trametinib and HCQ or CDK4/6 inhibitors may not be an effective later-line treatment for mPDAC, and the current preliminary findings need to be confirmed by other studies with larger sample sizes.

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.

Pan-cancer analysis of UBE2T with a focus on prognostic and immunological roles in lung adenocarcinoma

Background

Ubiquitin-conjugating enzyme E2 T (UBE2T) is a potential oncogene. However, Pan-cancer analyses of the functional, prognostic and predictive implications of this gene are lacking.

Methods

We first analyzed UBE2T across 33 tumor types in The Cancer Genome Atlas (TCGA) project. We investigated the expression level of UBE2T and its effect on prognosis using the TCGA database. The correlation between UBE2T and cell cycle in pan-cancer was investigated using the single-cell sequencing data in Cancer Single-cell State Atlas (CancerSEA) database. The Weighted Gene Co-expression Network analysis (WGCNA), Univariate Cox and Least absolute shrinkage and selection operator (LASSO) Cox regression models, and receiver operating characteristic (ROC) were applied to assess the prognostic impact of UBE2T-related cell cycle genes (UrCCGs). Furthermore, the consensus clustering (CC) method was adopted to divide TCGA-lung adenocarcinoma (LUAD) patients into subgroups based on UrCCGs. Prognosis, molecular characteristics, and the immune panorama of subgroups were analyzed using Single-sample Gene Set Enrichment Analysis (ssGSEA). Results derived from TCGA-LUAD patients were validated in International Cancer Genome Consortium (ICGC)-LUAD data.

Results

UBE2T is highly expressed and is a prognostic risk factor in most tumors. CancerSEA database analysis revealed that UBE2T was positively associated with the cell cycle in various cancers(r > 0.60, p < 0.001). The risk signature of UrCCGs can reliably predict the prognosis of LUAD (AUC1 year = 0.720, AUC3 year = 0.700, AUC5 year = 0.630). The CC method classified the TCGA-LUAD cohort into 4 UrCCG subtypes (G1–G4). Kaplan–Meier survival analysis demonstrated that G2 and G4 subtypes had worse survival than G3 (Log-rank test PTCGA training set < 0.001, PICGC validation set < 0.001). A comprehensive analysis of immune infiltrates, immune checkpoints, and immunogenic cell death modulators unveiled different immune landscapes for the four subtypes. High immunophenoscore in G3 and G4 tumors suggested that these two subtypes were immunologically “hot,” tending to respond to immunotherapy compared to G2 subtypes (p < 0.001).

Conclusions

UBE2T is a critical oncogene in many cancers. Moreover, UrCCG classified the LUAD cohort into four subgroups with significantly different survival, molecular features, immune infiltrates, and immunotherapy responses. UBE2T may be a therapeutic target and predictor of prognosis and immunotherapy sensitivity.

Sustained Oncogenic Signaling in the Cytostatic State Enables Targeting of Nonproliferating Persistent Cancer Cells

Many advanced therapeutics possess cytostatic properties that suppress cancer cell growth without directly inducing death. Treatment-induced cytostatic cancer cells can persist and constitute a reservoir from which recurrent growth and resistant clones can develop. Current management approaches primarily comprise maintenance and monitoring because strategies for targeting nonproliferating cancer cells have been elusive. Here, we used targeted therapy paradigms and engineered cytostatic states to explore therapeutic opportunities for depleting treatment-mediated cytostatic cancer cells. Sustained oncogenic AKT signaling was common, while nonessential, in treatment-mediated cytostatic cancer cells harboring PI3K-pathway mutations, which are associated with cancer recurrence. Engineering oncogenic signals in quiescent mammary organotypic models showed that sustained, aberrant activation of AKT sensitized cytostatic epithelial cells to proteasome inhibition. Mechanistically, sustained AKT signaling altered cytostatic state homeostasis and promoted an oxidative and proteotoxic environment, which imposed an increased proteasome dependency for maintaining cell viability. Under cytostatic conditions, inhibition of the proteasome selectively induced apoptosis in the population with aberrant AKT activation compared with normal cells. Therapeutically exploiting this AKT-driven proteasome vulnerability was effective in depleting treatment-mediated cytostatic cancer cells independent of breast cancer subtype, epithelial origin, and cytostatic agent. Moreover, transient targeting during cytostatic treatment conditions was sufficient to reduce recurrent tumor growth in spheroid and mouse models. This work identified an AKT-driven proteasome-vulnerability that enables depletion of persistent cytostatic cancer cells harboring PTEN-PI3K pathway mutations, revealing a viable strategy for targeting nonproliferating persistent cancer cell populations before drug resistance emerges.

SIGNIFICANCE

This study finds that sustained oncogenic signaling in therapy-induced cytostatic cancer cells confers targetable vulnerabilities to deplete persistent cancer cell populations and reduce cancer recurrence.

Aloperine: A Potent Modulator of Crucial Biological Mechanisms in Multiple Diseases

Aloperine is an alkaloid found in the seeds and leaves of the medicinal plant Sophora alopecuroides L. It has been used as herbal medicine in China for centuries due to its potent anti-inflammatory, antioxidant, antibacterial, and antiviral properties. Recently, aloperine has been widely investigated for its therapeutic activities. Aloperine is proven to be an effective therapeutic agent against many human pathological conditions, including cancer, viral diseases, and cardiovascular and inflammatory disorders. Aloperine is reported to exert therapeutic effects through triggering various biological processes, including cell cycle arrest, apoptosis, autophagy, suppressing cell migration, and invasion. It has also been found to be associated with the modulation of various signaling pathways in different diseases. In this review, we summarize the most recent knowledge on the modulatory effects of aloperine on various critical biological processes and signaling mechanisms, including the PI3K, Akt, NF-κB, Ras, and Nrf2 pathways. These data demonstrate that aloperine is a promising therapeutic candidate. Being a potent modulator of signaling mechanisms, aloperine can be employed in clinical settings to treat various human disorders in the future.

The Renaissance of KRAS Targeting in Advanced Non-Small-Cell Lung Cancer: New Opportunities Following Old Failures

Non-small cell lung cancer (NSCLC) represents the perfect paradigm of ‘precision medicine’ due to its complex intratumoral heterogeneity. It is truly characterized by a range of molecular alterations that can deeply influence the natural history of this disease. Several molecular alterations have been found over time, paving the road to biomarker-driven therapy and radically changing the prognosis of ‘oncogene addicted’ NSCLC patients. Kirsten rat sarcoma (KRAS) mutations are present in up to 30% of NSCLC (especially in adenocarcinoma histotype) and have been identified decades ago. Since its discovery, its molecular characteristics and its marked affinity to a specific substrate have led to define KRAS as an undruggable alteration. Despite that, many attempts have been made to develop drugs capable of targeting KRAS signaling but, until a few years ago, these efforts have been unsuccessful. Comprehensive genomic profiling and wide-spectrum analysis of genetic alterations have only recently allowed to identify different types of KRAS mutations. This tricky step has finally opened new frontiers in the treatment approach of KRAS-mutant patients and might hopefully increase their prognosis and quality of life. In this review, we aim to highlight the most interesting aspects of (epi)genetic KRAS features, hoping to light the way to the state of art of targeting KRAS in NSCLC.

AZD5153 reverses palbociclib resistance in ovarian cancer by inhibiting cell cycle-related proteins and the MAPK/PI3K-AKT pathway

The CDK4/6 inhibitor, palbociclib has recently entered clinic-trial stage for breast cancer treatment. However, translating its efficacy to other solid tumors has been challenging, especially for aggressive solid tumors. We found that the effect of palbociclib as a single agent was limited due to primary and acquired resistance in multiple ovarian cancer (OC) models. Among these, patient-derived organoid and xenograft models are two most representative models of drug responsiveness in patients with OC. In preclinical models, this study demonstrated that activated MAPK/PI3K-AKT pathway and cell cycle-related proteins induced the resistance to palbociclib, which was overcome by the addition of the bromodomain protein 4 (BRD4) inhibitor AZD5153. Moreover, this study revealed that AZD5153 and palbociclib had a synergistic lethal effect on inducing the cell cycle arrest and increasing apoptosis, even in RB-deficient cell lines. Based on these results, it is anticipated that this class of drugs, including AZD5153, which inhibit the cell cycle-related protein and MAPK/PI3K-AKT pathway, will exhibit synergistic effects with palbociclib in OC.

Human Protein Complex-Based Drug Signatures for Personalized Cancer Medicine

Disease signature-based drug repositioning approaches typically first identify a disease signature from gene expression profiles of disease samples to represent a particular disease. Then such a disease signature is connected with the drug-induced gene expression profiles to find potential drugs for the particular disease. In order to obtain reliable disease signatures, the size of disease samples should be large enough, which is not always a single case in practice, especially for personalized medicine. On the other hand, the sample sizes of drug-induced gene expression profiles are generally large. In this study, we propose a new drug repositioning approach (HDgS), in which the drug signature is first identified from drug-induced gene expression profiles, and then connected to the gene expression profiles of disease samples to find the potential drugs for patients. In order to take the dependencies among genes into account, the human protein complexes (HPC) are used to define the drug signature. The proposed HDgS is applied to the drug-induced gene expression profiles in LINCS and several types of cancer samples. The results indicate that the HPC-based drug signature can effectively find drug candidates for patients and that the proposed HDgS can be applied for personalized medicine with even one patient sample.

Cyclin-dependent kinases-based synthetic lethality: Evidence, concept, and strategy

Synthetic lethality is a proven effective antitumor strategy that has attracted great attention. Large-scale screening has revealed many synthetic lethal genetic phenotypes, and relevant small-molecule drugs have also been implemented in clinical practice. Increasing evidence suggests that CDKs, constituting a kinase family predominantly involved in cell cycle control, are synthetic lethal factors when combined with certain oncogenes, such as MYC, TP53, and RAS, which facilitate numerous antitumor treatment options based on CDK-related synthetic lethality. In this review, we focus on the synthetic lethal phenotype and mechanism related to CDKs and summarize the preclinical and clinical discoveries of CDK inhibitors to explore the prospect of CDK inhibitors as antitumor compounds for strategic synthesis lethality in the future.

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.

Targeting CDK4 overcomes EMT-mediated tumor heterogeneity and therapeutic resistance in KRAS mutant lung cancer

Lack of sustained response to therapeutic agents in patients with KRAS-mutant lung cancer poses a major challenge and arises partly due to intratumor heterogeneity that defines phenotypically distinct tumor subpopulations. To attain better therapeutic outcomes, it is important to understand the differential therapeutic sensitivities of tumor cell subsets. Epithelial-mesenchymal transition is a biological phenomenon that can alter the state of cells along a phenotypic spectrum and cause transcriptional rewiring to produce distinct tumor cell subpopulations. We utilized functional shRNA screens, in in vitro and in vivo models, to identify and validate an increased dependence of mesenchymal tumor cells on cyclin-dependent kinase 4 (CDK4) for survival, as well as a mechanism of resistance to MEK inhibitors. High zinc finger E-box binding homeobox 1 levels in mesenchymal tumor cells repressed p21, leading to perturbed CDK4 pathway activity. Increased dependence on CDK4 rendered mesenchymal cancer cells particularly vulnerable to selective CDK4 inhibitors. Coadministration of CDK4 and MEK inhibitors in heterogeneous tumors effectively targeted different tumor subpopulations, subverting the resistance to either single-agent treatment.

NRAS mutant melanoma: Towards better therapies

Genetic alterations affecting RAS proteins are commonly found in human cancers. Roughly a fourth of melanoma patients carry activating NRAS mutations, rendering this malignancy particularly challenging to treat. Although the development of targeted as well as immunotherapies led to a substantial improvement in the overall survival of non-NRAS^mut melanoma patients (e.g. BRAF^mut), patients with NRAS^mut melanomas have an overall poorer prognosis due to the high aggressiveness of RAS^mut tumors, lack of efficient targeted therapies or rapidly emerging resistance to existing treatments. Understanding how NRAS-driven melanomas develop therapy resistance by maintaining cell cycle progression and survival is crucial to develop more effective and specific treatments for this group of melanoma patients. In this review, we provide an updated summary of currently available therapeutic options for NRAS^mut melanoma patients with a focus on combined inhibition of MAPK signaling and CDK4/6-driven cell cycle progression and mechanisms of the inevitably developing resistance to these treatments. We conclude with an outlook on the most promising novel therapeutic approaches for melanoma patients with constitutively active NRAS. STATEMENT OF SIGNIFICANCE: An estimated 75000 patients are affected by NRAS^mut melanoma each year and these patients still have a shorter progression-free survival than BRAF^mut melanomas. Both intrinsic and acquired resistance occur in NRAS-driven melanomas once treated with single or combined targeted therapies involving MAPK and CDK4/6 inhibitors and/or checkpoint inhibiting immunotherapy. Oncolytic viruses, mRNA-based vaccinations, as well as targeted triple-agent therapy are promising alternatives, which could soon contribute to improved progression-free survival of the NRAS^mut melanoma patient group.

Palbociclib induces DNA damage and inhibits DNA repair to induce cellular senescence and apoptosis in oral squamous cell carcinoma

BACKGROUND/PURPOSE

Palbociclib is an FDA-approved cyclin-dependent kinase (CDK) 4/6 inhibitor that has been clinically proven to be effective in breast cancer. However, its use in oral cancer is not well researched. In this study, we investigated the inhibitory activity of palbociclib against oral squamous cell carcinoma (OSCC) cells and explored the mechanism of inhibition.

METHODS

The effects of palbociclib on the cytotoxicity of OSCC cells were determined by MTT and colony formation assays. β-Galactosidase staining and cell-cycle analysis were used to determine palbociclib-induced cellular senescence and apoptosis of OSCC cells. Wound healing and transwell assays were performed to assess the effects of palbociclib treatment on migration and invasion ability of OSCC cells. Whole transcriptome sequencing was conducted to show the relationship between DNA damage repair of OSCC cells and palbociclib treatment. Palbociclib-induced DNA damage and repair capacity of OSCC cells were confirmed by comet assay and immunofluorescence confocal microscopy. Western blotting was used to verify the palbociclib-mediated changes in the CDK/pRB/c-Myc/CDC25A pathway. Finally, in vitro findings were tested in a mouse xenograft model.

RESULTS

Our results showed that palbociclib can significantly inhibit the growth, migration, and invasive ability of OSCC cells and can accelerate cellular senescence and apoptosis. We found that palbociclib induced DNA damage and p21 expression through the p53-independent pathway, thereby downregulating c-Myc and CDC25A expression to inhibit cell cycle progression. In addition, palbociclib downregulated RAD51 expression to inhibit DNA damage repair ability of OSCC cell.

CONCLUSION

Palbociclib was found to have anti-oral squamous cell carcinoma activity and to simultaneously induce DNA damage and inhibit its repair, and to accelerated cellular senescence and apoptosis.

CDK4/6 and MAPK-Crosstalk as Opportunity for Cancer Treatment

Despite the development of targeted therapies and novel inhibitors, cancer remains an undefeated disease. Resistance mechanisms arise quickly and alternative treatment options are urgently required, which may be partially met by drug combinations. Protein kinases as signaling switchboards are frequently deregulated in cancer and signify vulnerable nodes and potential therapeutic targets. We here focus on the cell cycle kinase CDK6 and on the MAPK pathway and on their interplay. We also provide an overview on clinical studies examining the effects of combinational treatments currently explored for several cancer types.

Targeted inhibition of glutamine metabolism enhances the antitumor effect of selumetinib in KRAS-mutant NSCLC

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The glutamine utilization of KRAS-mutant NSCLC is higher than that of KRAS wild-type.

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Targeted GLS1 and MEK inhibition enhance antitumor activity in vitro and in vivo.

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The therapeutic response can be well identified by ¹⁸F-FDG PET imaging.

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Dual inhibition of GLS1 and MEK induce redox and energetic stress.

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Dual inhibition of GLS1 and MEK suppress the phosphorylation of AKT.

Regulated by the tumor microenvironment, the metabolic network of the tumor is reprogrammed, driven by oncogenes and tumor suppressor genes. The metabolic phenotype of tumors of different driven-genes and different tissue types is extremely heterogeneous. KRAS-mutant non-small cell lung cancer (NSCLC) has glutamine dependence. In this study, we demonstrated that glutamine utilization of KRAS-mutant NSCLC was higher than that of KRAS wild-type. CB839, an efficient glutaminase inhibitor, synergized with the MEK inhibitor selumetinib to enhance antitumor activity in KRAS-mutant NSCLC cells and xenografts, and the therapeutic response could be well identified by ¹⁸F-FDG PET imaging. Combination therapy induced redox stress, manifesting as a decrease in mitochondrial membrane potential and an increase in ROS levels, and energetic stress manifesting as suppression of glycolysis and glutamine degradation. The phosphorylation of AKT was also suppressed. These effects combined to induce autophagy and thereby caused cancer cell death. Our results suggest that dual inhibition of the MEK-ERK pathway and glutamine metabolism activated by KRAS mutation may be an effective treatment strategy for KRAS-driven NSCLC.

Targeted drug therapy in non-small cell lung cancer: Clinical significance and possible solutions-Part I

INTRODUCTION

Non-small cell lung cancer (NSCLC) comprises of 84% of all lung cancer cases. The treatment options for NSCLC at advanced stages are chemotherapy and radiotherapy. Chemotherapy involves conventional nonspecific chemotherapeutics, and targeted-protein/receptor-specific small molecule inhibitors. Biologically targeted therapies such as an antibody-based immunotherapy have been approved in combination with conventional therapeutics. Approved targeted chemotherapy is directed against the kinase domains of mutated cellular receptors such as epidermal growth factor receptor (EGFR), anaplastic lymphoma kinases (ALK), neurotrophic receptor kinases (NTRK) and against downstream signaling molecules such as BRAF (v-raf murine sarcoma viral oncogene homolog B1). Approved biologically targeted therapy involves the use of anti-angiogenesis antibodies and antibodies against immune checkpoints.

AREAS COVERED

The rationale for the employment of targeted therapeutics and the resistance that may develop to therapy are discussed. Novel targeted therapeutics in clinical trials are also included.

EXPERT OPINION

Molecular and histological profiling of a given tumor specimen to determine the aberrant onco-driver is a must before deciding a targeted therapeutic regimen for the patient. Periodic monitoring of the patients response to a given therapeutic regimen is also mandatory so that any semblance of resistance to therapy can be deciphered and the regimen may be accordingly altered.

Enhanced antitumor effect of alectinib in combination with cyclin-dependent kinase 4/6 inhibitor against RET-fusion-positive non-small cell lung cancer cells

Rearranged during transfection (RET) fusion-positive non-small cell lung cancer (NSCLC) accounts for 1% of lung adenocarcinoma. Although small molecule agents with RET kinase inhibitory activity such as alectinib, vandetanib, and cabozantinib have been clinically evaluated in RET-fusion-positive NSCLC, an effective monotherapy regimen has not been established. We explored agents to use in combination with alectinib to enhance the antitumor effect of alectinib against RET-fusion cells. Cell proliferation under co-treatment with alectinib plus each of six chemotherapeutic agents or six molecularly targeted agents was evaluated in vitro. The combination effect was analyzed by IC₅₀ isobologram and combination index using LC-2/ad and Ba/F3-KIF5B-RET cells. The in vivo combination effect was investigated in a Ba/F3-KIF5B-RET xenograft model. The phosphorylation levels of proteins regulating proliferation were measured by immunoblotting. Palbociclib, a CDK4/6 inhibitor, showed the greatest synergy against LC-2/ad cells in the isobologram analysis and combination index. This synergistic effect was also observed against Ba/F3-KIF5B-RET cells. Another CDK4/6 inhibitor, abemaciclib, also showed a synergistic effect. In vivo, the combination of alectinib plus palbociclib showed a more enhanced antitumor effect than each single agent in a mouse xenograft model with transplanted Ba/F3-KIF5B-RET cells. This combination suppressed the phosphorylation of S6 and Rb more intensely than did either single agent in both LC-2/ad and Ba/F3-KIF5B-RET cell lines, both in vitro and in vivo. Combination therapy with alectinib plus the CDK4/6 inhibitor enhanced the antitumor effect against RET-fusion-positive cells in vitro and in vivo.

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.

Comprehensive molecular profiling of extrahepatic cholangiocarcinoma in Chinese population and potential targets for clinical practice

Background

Cholangiocarcinoma (CCA) is a diverse group of malignancies arising from the intra- or extrahepatic biliary epithelium and characterized by its late diagnosis and fatal outcome. Extrahepatic cholangiocarcinoma (ECC) accounts for 90% of CCA. However, little is known about the comprehensive genomic alterations of ECC in Chinese population for providing clinical managements especially targeted therapy.

Methods

Comprehensive genomic profiling (CGP) was performed with next generation sequencing panel on paraffin-embedded tumor from a cohort of 80 Chinese ECC patients.

Results

The most frequently altered genes were TP53 (68%), KRAS (46%), SMAD4 (22%), ARID1A (20%) and CDKN2A (19%). Mutual exclusivity was observed between multiple genes including ARID1A:TP53, KRAS:LRP1B and NF2:TP53. Genetic alterations with potential therapeutic implications were identified in 43% of patients. The top three actionable alterations include CDKN2A (n=11), BRAF (n=5) and ERBB2 (n=4). Potentially actionable alterations were mainly enriched in the G1-S transition, homologous recombination repair, MAPK/ERK pathway.

Conclusions

This is the largest data set of ECC cases providing a comprehensive view on genetic alterations in Chinese population which differs significantly from a US cohort, and indicates the potential clinical implications for targeted therapies.

Combination therapy with BYL719 and LEE011 is synergistic and causes a greater suppression of p-S6 in triple negative breast cancer

A third of patients with triple negative breast cancer (TNBC) have relapsed disease within 2-5 years from initial diagnosis, leaving an unmet need for therapeutic targets. TNBC frequently harbors alterations of the PI3K/AKT/mTOR pathway, but single agent PI3K/AKT/mTOR inhibitors have not shown marked efficacy. In this study, we investigated a strategy to improve efficacy of PI3K-α inhibitor BYL719 (alpelisib) in TNBC. While BYL719 is effective at inhibiting cell proliferation in T47D, a triple positive cell line, it had limited activity in TNBC. This may be partially due to persistent phosphorylation of RB, and incomplete inhibition of p-S6 in TNBC, since the inhibitory effect of BYL719 on p-RB and p-S6 was significantly reduced in TNBC compared to T47D cells. Addition of the CDK4/6 inhibitor LEE011 to BYL719 caused a simultaneous reduction of p-RB and p-S6, and a more complete inhibition of p-S6, leading to decreased expression of the pro-survival protein MCL-1, an induction of apoptosis, and an enhanced reduction of tumor growth in a PDX model of TNBC. These findings suggest that inhibition of p-RB and p-S6 is important for an effective response to the treatment of TNBC, and provides a strong rationale for clinical development of combination therapy with BYL719 and LEE011 for treatment of metastatic TNBC with intact RB.Presentation: This study was presented in part as an abstract at the 2016 San Antonio Breast Cancer Symposium (P3-03-15) and the 2018 Cancer Research and Targeted Therapy in London.

RB constrains lineage fidelity and multiple stages of tumour progression and metastasis

Mutations in the Retinoblastoma (RB) tumour suppressor pathway are a hallmark of cancer and a prevalent feature of lung adenocarcinoma^1,2,3. Despite being the first tumour suppressor to be identified, the molecular and cellular basis underlying selection for persistent RB loss in cancer remains unclear^4–6. Methods that reactivate the RB pathway using inhibitors of cyclin-dependent kinases CDK4 and CDK6 are effective in some cancer types and currently under evaluation in lung adenocarcinoma^7–9. Whether RB pathway reactivation will have therapeutic effects and if targeting CDK4/6 is sufficient to reactivate RB pathway activity in lung cancer is unknown. Here, we model RB loss during lung adenocarcinoma progression and pathway reactivation in established oncogenic KRAS-driven tumours in the mouse. We show that RB loss enables cancer cells to bypass two distinct barriers during tumour progression. First, RB loss abrogates the requirement for MAPK signal amplification during malignant progression. We identify CDK2-dependent phosphorylation of RB as an effector of MAPK signalling and critical mediator of resistance to CDK4/6 inhibition. Second, RB inactivation deregulates expression of cell state-determining factors, facilitates lineage infidelity, and accelerates the acquisition of metastatic competency. In contrast, reactivation of RB reprograms advanced tumours toward a less metastatic cell state, but is nevertheless unable to halt cancer cell proliferation and tumour growth due to adaptive rewiring of MAPK pathway signalling, which restores a CDK-dependent suppression of RB. Our study demonstrates the power of reversible gene perturbation approaches to identify molecular mechanisms of tumour progression, causal relationships between genes and the tumour suppressive programs they control, and critical determinants of successful therapy.

P53 pathway is a major determinant in the radiosensitizing effect of Palbociclib: Implication in cancer therapy

Targeting cell cycle has become one of the major challenges in cancer therapy, being Palbociclib, a CDK4/6 inhibitor, an excellent example. Recently, it has been reported that Palbociclib could be a novel radiosensitizer agent. In an attempt to clarify the molecular basis of this effect we have used cell lines from colorectal (HT29, HCT116) lung (A549, H1299) and breast cancer (MCF-7). Our results indicate that the presence of a p53 wild type is strictly required for Palbociclib to exert its radiosensitizing effect, independently of the inhibitory effect exerted on CDK4/6. In fact, abrogation of p53 in cells with functional p53 blocks the radiosensitizing effect of Palbociclib. Moreover, no radiosensitizing effect is observed in cells with non-functional p53, but restoration of p53 function promotes radiosensitivity associated to Palbociclib. Furthermore, the presence of Palbociclib blocks the transcriptional activity of p53 in an ATM-dependent-fashion after ionizing radiation exposure, as the blockage of p21/WAF1 expression demonstrates. These observations are a proof of concept for a more selective therapy, based on the combination of CDK4/6 inhibition and radiotherapy, which would only benefit to those patients with a functional p53 pathway.

CDK4/6 inhibitor palbociclib enhances the effect of pyrotinib in HER2-positive breast cancer

Human epidermal growth factor receptor 2 (HER2) is amplified in about 20% breast cancers. Treat of HER2 positive breast cancers has been greatly promoted in last few years, but the accompany HER2 blockade has hindered the therapeutic effect. Pyrotinib is a pan-HER kinase inhibitor that suppresses signaling through the RAS/RAF/MEK/MAPK and PI3K/AKT pathways. Palbociclib is a CDK4/6 inhibitor that inhibits cell cycle progression and cancer cell proliferation in ER+ breast cancers. We hypothesized that the combination of pan-HER kinase inhibitors and CDK4/6 inhibitors would show synergistic antitumor activity in vivo in vitro. Our data show that a combination of palbociclib and pyrotinib was highly synergistic in inhibiting cancer proliferation and colony formation. The combined treatment also induced significant decreases in pAKT and pHER3 activation, induced G0-G1 cell cycle arrest, and increased rates of apoptosis. In the xenograft model, the combination treatment demonstrated greater antitumor activity than either agent alone, with no apparent increase in toxicity. Our results offer a preclinical rationale clinical investigation of the effectiveness of a combination treatment of palbociclib with pyrotinib for breast cancer treatment.

CDK4/6 Inhibition in Cancer: Beyond Cell Cycle Arrest

Pharmacologic inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) have recently entered the therapeutic armamentarium of clinical oncologists, and show promising activity in patients with breast and other cancers. Although their chief mechanism of action is inhibition of retinoblastoma (RB) protein phosphorylation and thus the induction of cell cycle arrest, CDK4/6 inhibitors alter cancer cell biology in other ways that can also be leveraged for therapeutic benefit. These include modulation of mitogenic kinase signaling, induction of a senescence-like phenotype, and enhancement of cancer cell immunogenicity. We describe here the less-appreciated effects of CDK4/6 inhibitors on cancer cells, and suggest ways by which they might be exploited to enhance the benefits of these agents for cancer patients.

Ras proteins as therapeutic targets

Oncogenic mutations in RAS genes underlie the pathogenesis of many human tumours, and there has been intense effort for over 30 years to develop effective and tolerated targeted therapeutics for patients with Ras-driven cancers. This review summarises the progress made in Ras drug discovery, highlighting some of the recent developments in directly targeting Ras through advances in small molecule drug design and novel therapeutic strategies.

Aloperine inhibits proliferation, migration and invasion and induces apoptosis by blocking the Ras signaling pathway in human breast cancer cells

Aloperine (Alo), as a quinolizidine alkaloid extracted from S. alopecuroide, has the positive activities of anti-inflammatory, anti-allergenic, antitumor and anti-viral. However, the role and mechanism of Alo in breast cancer have not been studied yet. In the present study, Alo markedly inhibited the proliferation and suppressed the colony formation ability of the breast cancer cell lines MCF-7 and MDA-MB-231 in a dose-dependent manner by Cell Counting kit-8 and colony formation assays, respectively. In addition, the results of confocal microscopy analysis and flow cytometry detection revealed that Alo induced the apoptosis of MCF-7 and MDA-MB-231 cells, and western blotting indicated that Alo upregulated the protein levels of Bax, caspase-3 and caspase-9, and downregulated the expression of Bcl-2. Furthermore, the results of wound healing, Transwell migration and invasion assays demonstrated that Alo inhibited the migration and invasion of MCF-7 and MDA-MB-231 cells, and reduced the protein levels of matrix metalloproteinase (MMP)-2 and MMP-9. Alo also downregulated the protein expressions of Ras, phosphorylated (p)-Raf proto-oncogene, serine/threonine kinase 1 and p-extracellular signal-regulated kinase 1/2. Furthermore, ISIS 2503, a Ras inhibitor, inhibited colony formation, induced apoptosis, and suppressed the migration and invasion of MCF-7 and MDA-MB-231 cells. These effects were more marked in the presence of ISIS 2503 and Alo, when compared with those of either agent alone. In conclusion, the present study reported a novel use of Alo in inhibiting the proliferation, migration and invasion, and inducing the apoptosis of human breast cancer cells by blocking the Ras signaling pathway.

Naringin promotes cellular chemokine synthesis and potentiates mesenchymal stromal cell migration via the Ras signaling pathway

Directional migration of mesenchymal stem cells (MSCs) is known to serve roles in bone fracture healing. Naringin is a traditional medicine used in China to treat bone injury and has been confirmed to act as a chemoattractant to MSCs. In the present study, the secretion of chemokines and stimulation of relevant signaling pathways by naringin were detected to determine the molecular mechanism of naringin-induced MSC migration. In these experiments, Quantibody^® arrays were used to detect chemokines secreted by MSCs with or without the addition of naringin. The results revealed differential naringin-induced chemokine secretion of C-X-C motif chemokine (CXCL)5, CXCL6 and C-C motif chemokine 20. Furthermore, the Ras signaling pathway was markedly activated in the naringin-treated groups, suggesting that naringin may enhance the migrational ability of MSCs via Ras activation. Furthermore, naringin was able to promote the secretion of various chemokines derived from MSCs, which would, in turn, increase the mobility of MSCs. The aim of the present study was to provide novel candidate agents for clinical orthopedics and theoretical basis for the future improvement of adjunctive medication for bone fracture healing.

Management of KRAS-Mutant Non-Small Cell Lung Cancer in the Era of Precision Medicine

OPINION STATEMENT

The discovery of genomic alterations that drive the development and progression of non-small cell lung cancer (NSCLC) has transformed how we treat metastatic disease. However, the promise of precision medicine remains elusive for the most commonly mutated oncogene in NSCLC, KRAS. This is perhaps due to the substantial heterogeneity within the broader genomic context of KRAS-mutant NSCLC. At this time, approaches for treating metastatic KRAS-mutant NSCLC mirror those for treating NSCLC that lacks a known driver mutation, including standard chemotherapeutic and immunotherapeutic approaches. Ongoing research aims to define further subgroups of KRAS-mutant NSCLC based on mutation subtype and co-occurring mutations. These efforts offer the potential to optimize standard-of-care regimens within these emerging subgroups and harness innovative strategies to realize precision medicine in this setting.

Expression and therapeutic implications of cyclin-dependent kinase 4 (CDK4) in osteosarcoma

Overexpression and/or hyperactivation of cyclin-dependent kinase 4 (CDK4) has been found in many types of human cancers, and a CDK4 specific inhibitor, palbociclib, has been recently approved by the FDA for the treatment of breast cancer. However, the expression and the therapeutic potential of CDK4 in osteosarcoma remain unclear. In the present study, CDK4 was found to be highly expressed in human osteosarcoma tissues and cell lines as compared with normal human osteoblasts. Elevated CDK4 expression correlated with metastasis potential and poor prognosis in osteosarcoma patients as determined by immunohistochemical analysis in a human osteosarcoma tissue microarray (TMA). CDK4 inhibition by either palbociclib or specific small interference RNA (siRNA) exhibited dose-dependent inhibition of osteosarcoma cell proliferation and growth, accompanied by suppression of the CDK4/6-cyclinD-Rb signaling pathway. Flow cytometry analysis showed that CDK4 knockdown arrested osteosarcoma cells in the G1 phase of the cell cycle and induced cell apoptosis. Furthermore, inhibition of CDK4 significantly decreased osteosarcoma cell migration in vitro determined by the wound healing assay. These data highlight that CDK4 may be a potential promising therapeutic target in the treatment of human osteosarcoma.