CDK4/6 inhibition stabilizes disease in patients with p16-null non-small cell lung cancer and is synergistic with mTOR inhibition

Systematic literature review of real-world evidence for treatments in HR+/HER2- second-line LABC/mBC after first-line treatment with CDK4/6i

BACKGROUND

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are currently recommended by the National Comprehensive Cancer Network (NCCN) guidelines and the European Society for Medical Oncology (ESMO) guidelines as the first-line (1 L) treatment for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative, locally advanced/metastatic breast cancer (HR+/HER2- LABC/mBC). Although there are many treatment options, there is no clear standard of care for patients following 1 L CDK4/6i. Understanding the real-world effectiveness of subsequent therapies may help to identify an unmet need in this patient population. This systematic literature review qualitatively synthesized effectiveness and safety outcomes for treatments received in the real-world setting after 1 L CDK4/6i therapy in patients with HR+/ HER2- LABC/mBC.

METHODS

MEDLINE®, Embase, and Cochrane were searched using the Ovid® platform for real-world evidence studies published between 2015 and 2022. Grey literature was searched to identify relevant conference abstracts published from 2019 to 2022. The review was conducted in accordance with PRISMA guidelines (PROSPERO registration: CRD42023383914). Data were qualitatively synthesized and weighted average median real-world progression-free survival (rwPFS) was calculated for NCCN/ESMO-recommended post-1 L CDK4/6i treatment regimens.

RESULTS

Twenty records (9 full-text articles and 11 conference abstracts) encompassing 18 unique studies met the eligibility criteria and reported outcomes for second-line (2 L) treatments after 1 L CDK4/6i; no studies reported disaggregated outcomes in the third-line setting or beyond. Sixteen studies included NCCN/ESMO guideline-recommended treatments with the majority evaluating endocrine-based therapy; five studies on single-agent ET, six studies on mammalian target of rapamycin inhibitors (mTORi) ± ET, and three studies with a mix of ET and/or mTORi. Chemotherapy outcomes were reported in 11 studies. The most assessed outcome was median rwPFS; the weighted average median rwPFS was calculated as 3.9 months (3.3-6.0 months) for single-agent ET, 3.6 months (2.5-4.9 months) for mTORi ± ET, 3.7 months for a mix of ET and/or mTORi (3.0-4.0 months), and 6.1 months (3.7-9.7 months) for chemotherapy. Very few studies reported other effectiveness outcomes and only two studies reported safety outcomes. Most studies had heterogeneity in patient- and disease-related characteristics.

CONCLUSIONS

The real-world effectiveness of current 2 L treatments post-1 L CDK4/6i are suboptimal, highlighting an unmet need for this patient population.

Bone metastasis in non-small-cell lung cancer: genomic characterization and exploration of potential targets

Background

Bone metastasis (BM) seriously affects the quality of life and reduces the survival time of patients with non-small-cell lung cancer (NSCLC). The genomic characteristics and potential targets of BMs are yet to be fully explored.

Objective

To explore the genetic characteristics and potential targets of BM in NSCLC.

Design

In all, 83 patients with NSCLC were retrospectively selected in this study. Genomic characterization of BMs was explored with the analysis of NGS results from primary tumors and BMs in 6 patients, then combined with NGS results of lung tumors in 16 patients with initial recurrence in bone to analyze mutations potentially associated with BMs, and finally, the correlation was further validated in 61 postoperative patients.

Methods

The next generation sequencing (NGS) was performed to identify genomic differences between pulmonary primary tumors and BM. Fluorescence in situ hybridization and immunohistochemistry were performed in postoperative tumor tissues from patients who had undergone radical surgery to validate the predictive role of molecular targets for BM. The correlation between cyclin-dependent kinase 4 (CDK4) and BM was evaluated by Pearson's chi-square test. The university of alabama at birminghan cancer data analysis portal (UALCAN) was carried out for the detection of CDK4 expression in lung cancer and the relationship between CDK4 and clinicopathological parameters. The relationship between prognosis and CDK4 expression was analyzed by the Kaplan-Meier plotter.

Results

The rate of gene amplification was increased (24% versus 36%) while gene substitution/indel was decreased (64% versus 52%) in BMs. The BM-specific mutations were analyzed in 16 recurrent patients which revealed the highest incidence of CDK4 amplification (18.8%). According to the Kaplan-Meier plotter database, the NSCLC patients with high CDK4 gene expression showed poor overall survival (OS) and recurrence-free survival (RFS) (p < 0.05). The incidence of CDK4 amplification tended to be higher in recurrent patients compared to the patients without BM (18.8% versus 4.7%, p = 0.118).

Conclusion

Compared to the primary tumors of NSCLC, the genome of BMs showed an increased proportion of amplification and a decreased proportion of gene substitution/indel. Furthermore, the CDK4 amplification ratio seemed to be elevated in NSCLC patients with BM which may be associated with poor OS and RFS.

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 landscape of response to drug combinations in non-small cell lung cancer

Combination of anti-cancer drugs is broadly seen as way to overcome the often-limited efficacy of single agents. The design and testing of combinations are however very challenging. Here we present a uniquely large dataset screening over 5000 targeted agent combinations across 81 non-small cell lung cancer cell lines. Our analysis reveals a profound heterogeneity of response across the tumor models. Notably, combinations very rarely result in a strong gain in efficacy over the range of response observable with single agents. Importantly, gain of activity over single agents is more often seen when co-targeting functionally proximal genes, offering a strategy for designing more efficient combinations. Because combinatorial effect is strongly context specific, tumor specificity should be achievable. The resource provided, together with an additional validation screen sheds light on major challenges and opportunities in building efficacious combinations against cancer and provides an opportunity for training computational models for synergy prediction.

Sequential Targeting of Retinoblastoma and DNA Synthesis Pathways Is a Therapeutic Strategy for Sarcomas That Can Be Monitored in Real Time

Treatment strategies with a strong scientific rationale based on specific biomarkers are needed to improve outcomes in patients with advanced sarcomas. Suppression of cell-cycle progression through reactivation of the tumor suppressor retinoblastoma (Rb) using CDK4/6 inhibitors is a potential avenue for novel targeted therapies in sarcomas that harbor intact Rb signaling. Here, we evaluated combination treatment strategies (sequential and concomitant) with the CDK4/6 inhibitor abemacicib to identify optimal combination strategies. Expression of Rb was examined in 1,043 sarcoma tumor specimens, and 50% were found to be Rb-positive. Using in vitro and in vivo models, an effective two-step sequential combination strategy was developed. Abemaciclib was used first to prime Rb-positive sarcoma cells to reversibly arrest in G1 phase. Upon drug removal, cells synchronously traversed to S phase, where a second treatment with S-phase targeted agents (gemcitabine or Wee1 kinase inhibitor) mediated a synergistic response by inducing DNA damage. The response to treatment could be noninvasively monitored using real-time positron emission tomography imaging and serum thymidine kinase activity. Collectively, these results show that a novel, sequential treatment strategy with a CDK4/6 inhibitor followed by a DNA-damaging agent was effective, resulting in synergistic tumor cell killing. This approach can be readily translated into a clinical trial with noninvasive functional imaging and serum biomarkers as indicators of response and cell cycling.

SIGNIFICANCE

An innovative sequential therapeutic strategy targeting Rb, followed by treatment with agents that perturb DNA synthesis pathways, results in synergistic killing of Rb-positive sarcomas that can be noninvasively monitored.

Response to Abemaciclib and Immunotherapy Rechallenge with Nivolumab and Ipilimumab in a Heavily Pretreated TMB-H Metastatic Squamous Cell Lung Cancer with CDKN2A Mutation, PIK3CA Amplification and TPS 80%: A Case Report

Inactivation of the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene is considerably more frequent in squamous cell lung cancer (SqCLC) than in other subtypes of lung cancer and may be a promising target for this histology. Here, we present the course of diagnosis and treatment of a patient with advanced SqCLC, harboring not only CDKN2A mutation but also PIK3CA amplification, Tumor Mutational Burden-High (>10 mutations/megabase), and a Tumor Proportion Score of 80%. After disease progression on multiple lines of chemotherapy and immunotherapy, he responded favorably to treatment with the CDK4/6i Abemaciclib and later achieved a durable partial response to immunotherapy rechallenge with a combination of anti-PD-1 and anti-CTLA-4, nivolumab, and ipilimumab.

CDC25C Protein Expression Correlates with Tumor Differentiation and Clinical Outcomes in Lung Adenocarcinoma

Given that, even after multimodal therapy, early-stage lung cancer (LC) often recurs, novel prognostic markers to help guide therapy are highly desired. The mRNA levels of cell division cycle 25C (CDC25C), a phosphatase that regulates G2/M cell cycle transition in malignant cells, correlate with poor clinical outcomes in lung adenocarcinoma (LUAD). However, whether CDC25C protein detected by immunohistochemistry can serve as a prognostic marker in LUAD is yet unknown. We stained an LC tissue array and a cohort of 61 LUAD tissue sections for CDC25C and searched for correlations between CDC25C staining score and the pathological characteristics of the tumors and the patients' clinical outcomes. Clinical data were retrieved from our prospectively maintained departmental database. We found that high expression of CDC25C was predominant among poorly differentiated LUAD (p < 0.001) and in LUAD > 1cm (p < 0.05). Further, high expression of CDC25C was associated with reduced disease-free survival (p = 0.03, median follow-up of 39 months) and with a trend for reduced overall survival (p = 0.08). Therefore, high expression of CDC25C protein in LUAD is associated with aggressive histological features and with poor outcomes. Larger studies are required to further validate CDC25C as a prognostic marker in LUAD.

Overexpressed Cyclin D1 and CDK4 proteins are responsible for the resistance to CDK4/6 inhibitor in breast cancer that can be reversed by PI3K/mTOR inhibitors

CDK4/6 inhibitors are the standard treatment in advanced HR+/HER2- breast cancer patients. Nevertheless, the resistance to CDK4/6 inhibitors is inevitable and the strategies to overcome resistance are of great interest. Here, we show that the palbociclib-resistant breast cancer cells expressed significantly higher levels of Cyclin D1 and CDK4 proteins because of upregulated protein synthesis. Silencing Cyclin D1 or CDK4 led to cell cycle arrest while silencing Cyclin E1 or CDK2 restored the sensitivity to palbociclib. Furthermore, PI3K/mTOR pathway was hyper-activated in palbociclib-resistant cells, leading to more phosphorylated 4E-BP1 and higher levels of Cyclin D1 and CDK4 translation. Targeting PI3K/mTOR pathway with a specific PI3Kα inhibitor (BYL719) or an mTOR inhibitor (everolimus) reduced the protein levels of Cyclin D1 and CDK4, and restored the sensitivity to palbociclib. The tumor samples expressed significantly higher levels of Cyclin D1, CDK4, p-AKT and p-4E-BP1 after progression on palbociclib treatment. In conclusion, our findings suggest that overexpressed Cyclin D1 and CDK4 proteins lead to the resistance to CDK4/6 inhibitor and PI3K/mTOR inhibitors are able to restore the sensitivity to CDK4/6 inhibitors, which provides the biomarker and rationale for the combinational use of CDK4/6 inhibitors and PI3K/mTOR inhibitors after CDK4/6 inhibitor resistance in breast cancer.

Molecular Mechanisms of Anti-Estrogen Therapy Resistance and Novel Targeted Therapies

Breast cancer (BC) is the most commonly diagnosed cancer in women, constituting one-third of all cancers in women, and it is the second leading cause of cancer-related deaths in the United States. Anti-estrogen therapies, such as selective estrogen receptor modulators, significantly improve survival in estrogen receptor-positive (ER+) BC patients, which represents about 70% of cases. However, about 60% of patients inevitably experience intrinsic or acquired resistance to anti-estrogen therapies, representing a major clinical problem that leads to relapse, metastasis, and patient deaths. The resistance mechanisms involve mutations of the direct targets of anti-estrogen therapies, compensatory survival pathways, as well as alterations in the expression of non-coding RNAs (e.g., microRNA) that regulate the activity of survival and signaling pathways. Although cyclin-dependent kinase 4/6 and phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) inhibitors have significantly improved survival, the efficacy of these therapies alone and in combination with anti-estrogen therapy for advanced ER+ BC, are not curative in advanced and metastatic disease. Therefore, understanding the molecular mechanisms causing treatment resistance is critical for developing highly effective therapies and improving patient survival. This review focuses on the key mechanisms that contribute to anti-estrogen therapy resistance and potential new treatment strategies alone and in combination with anti-estrogen drugs to improve the survival of BC patients.

Gilteritinib Enhances Anti-Tumor Efficacy of CDK4/6 Inhibitor, Abemaciclib in Lung Cancer Cells

Abemaciclib is a cyclin-dependent kinases 4/6 (CDK4/6) inhibitor approved for the treatment of metastatic breast cancer. Preclinical studies suggest that abemaciclib has the potential for lung cancer treatment. However, several clinical trials demonstrate that monotherapy with abemaciclib has no obvious superiority than erlotinib to treat lung cancer patients, limiting its therapeutic options for lung cancer treatment. Here, we show that the US Food and Drug Administration (FDA)-approved drug, gilteritinib, enhances the cytotoxicity of abemaciclib through inducing apoptosis and senescence in lung cancer cells. Interestingly, abemaciclib in combination with gilteritinib leads to excessive accumulation of vacuoles in lung cancer cells. Mechanistically, combined abemaciclib and gilteritinib induces complete inactivation of AKT and retinoblastoma (Rb) pathways in lung cancer cells. In addition, RNA-sequencing data demonstrate that combination of abemaciclib and gilteritinib treatment induces G2 phase cell-cycle arrest, inhibits DNA replication, and leads to reduction in homologous recombination associated gene expressions. Of note, abemaciclib-resistant lung cancer cells are more sensitive to gilteritinib treatment. In a mouse xenograft model, combined abemaciclib and gilteritinib is more effective than either drug alone in suppressing tumor growth and appears to be well tolerated. Together, our findings support the combination of abemaciclib with gilteritinib as an effective strategy for the treatment of lung cancer, suggesting further evaluation of their efficacy is needed in a clinical trial.

Combining a CDK4/6 Inhibitor With Pemetrexed Inhibits Cell Proliferation and Metastasis in Human Lung Adenocarcinoma

Background

Recent clinical trials of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in human lung adenocarcinoma (LUAD) have not achieved satisfactory results. The disappointing results of single-drug treatments have prompted studies about synergistic therapies of CDK4/6i with other drugs. We aimed to test the anti-tumor effect of ribociclib (a CDK4/6i) combined with pemetrexed on LUAD and the potential mechanisms.

Methods

Cell lines were exposed to ribociclib and pemetrexed at different doses. Antitumor effects were measured using growth inhibition. Cell cycle distribution and apoptosis were evaluated using flow cytometry. Cell migration and invasion were measured using wound healing and transwell invasion assays, respectively. The expression levels of proteins were analyzed using western blotting. Mice xenograft models were used for validation in vivo.

Results

Synergism was associated with a combination of cell cycle effects from both agents. Cell cycle analysis revealed that pemetrexed blocked cells in the S phase, whereas ribociclib arrested cells in the G1 phase. Concomitant treatment with pemetrexed and ribociclib resulted in a significantly stronger antitumor ability than treatment alone. We also found that ribociclib strongly enhanced the pro-apoptotic activity of pemetrexed via the caspase/bcl-2 signaling pathway. In addition, we report for the first time that combination treatment with ribociclib and pemetrexed significantly inhibits the migration and invasion of LUAD cells.

Conclusions

Combining ribociclib and pemetrexed showed a powerful ability to inhibit cancer proliferation, invasion, and metastasis, and it holds potential as a novel effective combinative therapy for patients with LUAD.

Design and Synthesis of a Novel 4-aryl-N-(2-alkoxythieno [2,3-b]pyrazine-3-yl)-4-arylpiperazine-1-carboxamide DGG200064 Showed Therapeutic Effect on Colon Cancer through G2/M Arrest

Cancer cells are characterized by an abnormal cell cycle. Therefore, the cell cycle has been a potential target for cancer therapeutic agents. We developed a new lead compound, DGG200064 (7c) with a 2-alkoxythieno [2,3-b]pyrazine-3-yl)-4-arylpiperazine-1-carboxamide core skeleton. To evaluate its properties, compound DGG200064 was tested in vivo through a xenograft mouse model of colorectal cancer using HCT116 cells. The in vivo results showed high cell growth inhibition efficacy. Our results confirmed that the newly synthesized DGG200064 inhibits the growth of colorectal cancer cells by inducing G2/M arrest. Unlike the known cell cycle inhibitors, DGG200064 (GI₅₀ = 12 nM in an HCT116 cell-based assay) induced G2/M arrest by selectively inhibiting the interaction of FBXW7 and c-Jun proteins. Additionally, the physicochemical properties of the lead compounds were analyzed. Based on the results of the study, we suggested further development of DGG200064 as a novel oral anti-colorectal cancer drug.

Therapeutic potential of CDK4/6 inhibitors in renal cell carcinoma

The treatment of advanced and metastatic kidney cancer has entered a golden era with the addition of more therapeutic options, improved survival and new targeted therapies. Tyrosine kinase inhibitors, mammalian target of rapamycin (mTOR) inhibitors and immune checkpoint blockade have all been shown to be promising strategies in the treatment of renal cell carcinoma (RCC). However, little is known about the best therapeutic approach for individual patients with RCC and how to combat therapeutic resistance. Cancers, including RCC, rely on sustained replicative potential. The cyclin-dependent kinases CDK4 and CDK6 are involved in cell-cycle regulation with additional roles in metabolism, immunogenicity and antitumour immune response. Inhibitors of CDK4 and CDK6 are now commonly used as approved and investigative treatments in breast cancer, as well as several other tumours. Furthermore, CDK4/6 inhibitors have been shown to work synergistically with other kinase inhibitors, including mTOR inhibitors, as well as with immune checkpoint inhibitors in preclinical cancer models. The effect of CDK4/6 inhibitors in kidney cancer is relatively understudied compared with other cancers, but the preclinical studies available are promising. Collectively, growing evidence suggests that targeting CDK4 and CDK6 in kidney cancer, alone and in combination with current therapeutics including mTOR and immune checkpoint inhibitors, might have therapeutic benefit and should be further explored.

p27kip1 expression and phosphorylation dictate Palbociclib sensitivity in KRAS-mutated colorectal cancer

In colorectal cancer, mutation of KRAS (RAS^MUT) reduces therapeutic options, negatively affecting prognosis of the patients. In this setting, administration of CDK4/6-inhibitors, alone or in combination with other drugs, is being tested as promising therapeutic strategy. Identifying sensitive patients and overcoming intrinsic and acquired resistance to CDK4/6 inhibition represent still open challenges, to obtain better clinical responses. Here, we investigated the role of the CDK inhibitor p27^kip1 in the response to the selective CDK4/6-inhibitor Palbociclib, in colorectal cancer. Our results show that p27^kip1 expression inversely correlated with Palbociclib response, both in vitro and in vivo. Generating a model of Palbociclib-resistant RAS^MUT colorectal cancer cells, we observed an increased expression of p27^kip1, cyclin D, CDK4 and CDK6, coupled with an increased association between p27^kip1 and CDK4. Furthermore, Palbociclib-resistant cells showed increased Src-mediated phosphorylation of p27^kip1 on tyrosine residues and low doses of Src inhibitors re-sensitized resistant cells to Palbociclib. Since p27^kip1 showed variable expression in RAS^MUT colorectal cancer samples, our study supports the possibility that p27^kip1 could serve as biomarker to stratify patients who might benefit from CDK4/6 inhibition, alone or in combination with Src inhibitors.

The Role of Inherited Pathogenic CDKN2A Variants in Susceptibility to Pancreatic Cancer

ABSTRACT

CDKN2A is cell cycle negative regulator, and the role of CDKN2A in the development of pancreatic ductal adenocarcinoma, which continues to be a lethal cancer, is well-established. Somatic loss of CDKN2A is considered one of the major drivers of pancreatic tumorigenesis. CDKN2A gene is one of the pancreatic cancer susceptibility gene; in addition to melanoma, pathogenic germline CDKN2A variants have been identified in up to 3.3% patients with pancreatic ductal adenocarcinoma depending on family history of disease. Carriers of a known pathogenic germline CDKN2A variant have up to a 12.3-fold increased risk of developing pancreatic cancer. Recently, several studies have demonstrated the benefit of clinical surveillance in patients with pathogenic germline CDKN2A variants. Therefore, identification of patients with a pathogenic germline CDKN2A variant is important for screening of at-risk relatives for pancreatic cancer. It has the potential to lead to the detection of early, potentially curable pancreatic cancer and precursor neoplasms, and reduce mortality. Furthermore, patients with a germline pathogenic CDKN2A variant and somatic loss of CDKN2A may benefit in the future from treatment with targeted therapies, such as a CDK4/6 inhibitor.

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.

CDK4/6 inhibition synergizes with inhibition of P21-Activated Kinases (PAKs) in lung cancer cell lines

Theoretically, small molecule CDK4/6 inhibitors (CDK4/6is) represent a logical therapeutic option in non-small cell lung cancers since most of these malignancies have wildtype RB, the key target of CDKs and master regulator of the cell cycle. Unfortunately, CDK4/6is are found to have limited clinical activity as single agents in non-small cell lung cancer. To address this problem and to identify effective CDK4/6i combinations, we screened a library of targeted agents for efficacy in four non-small cell lung cancer lines treated with CDK4/6 inhibitors Palbociclib or Abemaciclib. The pan-PAK (p21-activated kinase) inhibitor PF03758309 emerged as a promising candidate with viability ratios indicating synergy in all 4 cell lines and for both CDK4/6is. It is noteworthy that the PAKs are downstream effectors of small GTPases Rac1 and Cdc42 and are overexpressed in a wide variety of cancers. Individually the compounds primarily induced cell cycle arrest; however, the synergistic combination induced apoptosis, accounting for the synergy. Surprisingly, while the pan-PAK inhibitor PF03758309 synergizes with CDK4/6is, no synergy occurs with group I PAK inhibitors FRAX486 or FRAX597. Cell lines treated only with Ribociclib, FRAX486 or FRAX597 underwent G1/G0 arrest, whereas combination treatment with these compounds predominantly resulted in autophagy. Combining high concentrations of FRAX486, which weakly inhibits PAK4, and Ribociclib, mimics the autophagy and apoptotic effect of PF03758309 combined with Ribociclib. FRAX597, a PAKi that does not inhibit PAK4 did not reduce autophagy in combination with Ribociclib. Our results suggest that a unique combination of PAKs plays a crucial role in the synergy of PAK inhibitors with CDK4/6i. Targeting this unique PAK combination, could greatly improve the efficacy of CDK4/6i and broaden the spectrum of cancer treatment.

ERK Inhibitor LY3214996-Based Treatment Strategies for RAS-Driven Lung Cancer

RAS gene mutations are the most frequent oncogenic event in lung cancer. They activate multiple RAS-centric signaling networks among them the MAPK, PI3K, and RB pathways. Within the MAPK pathway, ERK1/2 proteins exert a bottleneck function for transmitting mitogenic signals and activating cytoplasmic and nuclear targets. In view of disappointing antitumor activity and toxicity of continuously applied MEK inhibitors in patients with KRAS-mutant lung cancer, research has recently focused on ERK1/2 proteins as therapeutic targets and on ERK inhibitors for their ability to prevent bypass and feedback pathway activation. Here, we show that intermittent application of the novel and selective ATP-competitive ERK1/2 inhibitor LY3214996 exerts single-agent activity in patient-derived xenograft (PDX) models of RAS-mutant lung cancer. Combination treatments were well tolerated and resulted in synergistic (ERKi plus PI3K/mTORi LY3023414) and additive (ERKi plus CDK4/6i abemaciclib) tumor growth inhibition in PDX models. Future clinical trials are required to investigate if intermittent ERK inhibitor-based treatment schedules can overcome toxicities observed with continuous MEK inhibition and-equally important-to identify biomarkers for patient stratification.

Mechanisms of resistance to cyclin-dependent kinase 4/6 inhibitors

Cyclin-dependent kinase (CDK) 4/6 inhibitors have emerged in the treatment of metastatic hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer. However, most patients will eventually present disease progression, highlighting the inevitable resistance of cancer cells to CDK4/6 inhibition. Several studies have suggested that resistance mechanisms involve aberrations of the molecules that regulate the cell cycle, and the re-wiring of the cell to escape CDK4/6 dependence and turn to alternative pathways. Loss of retinoblastoma function, overexpression of CDK 6, upregulation of cyclin E, overexpression of CDK 7, and dysregulation of several signaling pathways, notably the PI3/AKT/mTOR pathway, have been implicated in the development of resistance to CDK4/6 inhibitors. Overlap with endocrine resistance mechanisms might be possible. Combinational therapeutic strategies should be explored in order to prevent resistance and optimize the management of patients after progression under CDK 4/6 inhibition.

Palbociclib in Patients With Non–Small-Cell Lung Cancer With CDKN2A Alterations: Results From the Targeted Agent and Profiling Utilization Registry Study

PURPOSE

The Targeted Agent and Profiling Utilization Registry (TAPUR) Study is a phase II pragmatic basket trial evaluating antitumor activity of commercially available targeted agents in patients with advanced cancer with genomic alterations known to be drug targets. Results in a cohort of patients with non–small-cell lung cancer (NSCLC) with CDKN2A alterations treated with palbociclib are reported.

METHODS

Eligible patients were ≥ 18 years old with advanced NSCLC, no remaining standard treatment options, measurable disease, Eastern Cooperative Oncology Group performance status of 0 to 2, and adequate organ function. Patients with NSCLC with CDKN2A alterations and no Rb mutations received palbociclib 125 mg orally once daily for 21 days, followed by 7 days off. Simon’s two-stage design was used with a primary study end point of objective response or stable disease (SD) of at least 16 weeks in duration. Secondary end points are progression-free survival (PFS), overall survival (OS), and safety.

RESULTS

Twenty-nine patients were enrolled from January 2017 to June 2018; two patients were not evaluable for response but were included in safety analyses. One patient with partial response and six patients with SD were observed, for a disease control rate of 31% (90% CI, 19% to 40%). Median PFS was 8.1 weeks (95% CI, 7.1 to 16.0 weeks), and median OS was 21.6 weeks (95% CI, 14.1 to 41.1 weeks). Eleven patients had at least 1 grade 3 or 4 adverse event (AE) or serious AE (SAE) possibly related to palbociclib (most common, cytopenias). Other AEs or SAEs possibly related to the treatment included anorexia, fatigue, febrile neutropenia, hypophosphatemia, sepsis, and vomiting.

CONCLUSION

Palbociclib monotherapy demonstrated evidence of modest antitumor activity in heavily pretreated patients with NSCLC with CDKN2A alterations. Additional investigation is necessary to confirm efficacy and utility of palbociclib in this population.

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.

CDK4/6 inhibitor palbociclib overcomes acquired resistance to third-generation EGFR inhibitor osimertinib in non-small cell lung cancer (NSCLC)

Background

The third‐generation EGFR‐TKI, represented by osimertinib, has been widely used in clinical practice; however, resistance eventually emerges. At present, it remains unclear whether an abnormal cell cycle is involved in acquired resistance, and whether the combination of palbociclib (CDK4/6 inhibitor) and osimertinib can overcome the third‐generation TKI resistance.

Methods

We established osimertinib‐resistant cells (H1975 OR) derived from EGFR‐mutant NSCLC cells H1975. Drug effects on cells were assessed with Cell Counting Kit‐8 (CCK8). Protein alterations were detected with western blot analysis. RT‐PCR was used to evaluate the differences of gene mRNA. Cell cycle distribution of H1975 S and H1975 OR cells was compared using flow cytometry.

Results

Compared with H1975, the sensitivity of H1975OR to the CDK4/6 inhibitor was increased and the proportion of cells in G1 phase was decreased. The mRNA level of CDK4, CDK 6 and the protein level of CDK4, pRB were increased in H1975OR. In the H1975OR cells, palbociclib significantly increased the proportion of G1 phase cells. The combination of osimertinib and palbociclib synergistically decreased the survival of H1975OR by cell cycle arrest. Combined treatment was found to inhibit the initial phosphorylation of RB by inhibiting the function of CDK4/6, significantly reducing the level of p‐RB, and blocking cell proliferation.

Conclusions

An osimertinib acquired resistance cell line (H1975 OR) was successfully established. The expression of cell cycle related genes was altered in H1975OR. The expression of CDK4 and the phosphorylation of Rb, the downstream molecule of CDK4/6, was increased in H1975OR cells. The combination of CDK4/6 inhibitor palbociclib and osimertinib could overcome the acquired resistance of osimertinib.

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.

CDK4/6 inhibition suppresses tumour growth and enhances the effect of temozolomide in glioma cells

In adults, glioma is the most commonly occurring and invasive brain tumour. For malignant gliomas, the current advanced chemotherapy includes TMZ (temozolomide). However, a sizeable number of gliomas are unyielding to TMZ, hence, giving rise to an urgent need for more efficient treatment choices. Here, we report that cyclin-dependent kinases 4 (CDK4) is expressed at significantly high levels in glioma cell lines and tissues. CDK4 overexpression enhances colony formation and proliferation of glioma cells and extends resistance to inhibition of TMZ-mediated cell proliferation and induction of apoptosis. However, CDK4 knockdown impedes colony formation and cell proliferation, and enhances sensitivity of glioma cells to TMZ. The selective inhibition of CDK4/6 impedes glioma cell proliferation and induces apoptotic induction. The selective inhibitors of CDK4/6 may enhance glioma cell sensitivity to TMZ. We further showed the possible role of RB phosphorylation mediated by CDK4 for its oncogenic function in glioma. The growth of glioma xenografts was inhibited in vivo, through combination treatment, and corresponded to enhanced p-RB levels, reduced staining of Ki-67 and enhanced activation of caspase 3. Therefore, CDK4 inhibition may be a favourable strategy for glioma treatment and overcomes TMZ resistance.

The Role of Cavin3 in the Progression of Lung Cancer and Its Mechanism

OBJECTIVE

The purpose of this study was to describe the role of Cavin3 in the progression of lung cancer and its underlying mechanism.

METHODS

Totally, 200 cases of lung cancer tissues and corresponding paracancer tissues were collected. Cavin3 expression in samples was determined by qRT-PCR, and the correlation with lung cancer stages as well as prognosis was statistically analyzed combined with matched clinical information. To investigate the mechanism of Cavin3 in lung cancer progression, firstly, Cavin3 was detected in lung cancer cell lines A549, PC9, and H520. Then, cells with stable Cavin3 overexpression and Cavin3 knockout were established to determine the effect of Cavin3 overexpression on the mammalian target of rapamycin (mTOR) signaling pathway. Subsequently, cells were harvested for cell proliferation, migration, and invasion assays in vitro, as well as nude mouse transplantation tumor experiment in vivo.

RESULTS

Cavin3 was seen to be highly expressed in cancer tissues. Statistical analysis with matched clinical data showed that Cavin3 as a prognostic indicator of lung cancer had important clinical value. In addition, it could be found that high expression of Cavin3 was able to promote cell proliferation, migration, and invasion and also potentiate tumor formation in vivo.

CONCLUSION

Cavin3 was highly expressed in lung cancer, and it was capable to promote cell proliferation, invasion, and migration.

[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.

Cyclin-dependent kinase inhibitors for the treatment of lung cancer

INTRODUCTION

Cyclin-dependent kinases (CDKs) are critical regulators of cell cycle progression in both normal and malignant cells, functioning through complex molecular interactions. Deregulation of CDK-dependent pathways is commonly found in both non-small cell and small cell lung cancer, and these derangements suggest vulnerabilities that can be exploited for clinical benefit.

AREAS COVERED

In this review, the authors present an overview of the biology of CDKs in normal and malignant cells, with a focus on lung cancer, followed by an assessment of preclinical work that has demonstrated the vital role of CDKs in lung cancer development and progression, and the activity of CDK inhibitors in a variety of lung cancer models. Finally, the experience with clinical trials of CDK inhibitors in lung cancer is discussed along with the current status of these agents in cancer therapy.

EXPERT OPINION

Despite strong biological rationale and promising preclinical studies, the results of clinical trials of CDK inhibitors in lung cancer have thus far been disappointing. Further clinical development of CDK inhibitors in lung cancer will depend on the identification of predictive biomarkers and the design of combination regimens that take advantage of the unique molecular alterations that drive lung cancer growth and survival.

A unique CDK4/6 inhibitor: Current and future therapeutic strategies of abemaciclib

Cell cycle dysregulation, characterised by aberrant activation of cyclin dependent kinases (CDKs), is a hallmark of cancer. After years of research on the first and second generations of less selective CDK inhibitors with unfavourable clinical activity and toxicity profiles, CDK4/6 inhibitors become the first and only class of highly specific CDK inhibitors being approved for cancer treatment to date. CDK4/6 inhibitors have transformed the treatment paradigm of estrogen receptor-positive (ER+) breast cancer, dramatically improving the survival outcomes of these patients when incorporated with conventional endocrine therapies in both the first and later-line settings. Currently, the efficacies of CDK4/6 inhibitors in other breast cancer subtypes and cancers are being actively explored. All three CDK4/6 inhibitors have demonstrated very similar clinical efficacies. However, being the least similar structurally, abemaciclib is the only CDK4/6 inhibitor with single agent activity in refractory metastatic ER + breast cancer, the ability to cross the blood brain barrier efficiently, and a distinct toxicity profile of lower myelosuppression such that it can be dosed continuously. Here, we further discuss the distinguishing features of abemaciclib as compared to the other two CDK4/6 inhibitors, palbociclib and ribociclib. Besides being the most potent inhibitor of CDK4/6, abemaciclib exhibits a wider selectivity towards other CDKs and kinases, and functions through additional mechanisms of action besides inducing G1 cell cycle arrest, in a dose dependent manner. Hence, abemaciclib has the potential to act independently of the CDK4/6-cyclin D-RB pathway, resulting in crucial implications on the possibly expanded clinical indications and predictive biomarkers of abemaciclib, in contrast to the other CDK4/6 inhibitors. The current status of preclinical evidence and clinical studies of abemaciclib as a single agent and in combination treatment in breast and other cancers, together with its potential predictive biomarkers, is also summarised in this review.

lncRNA HNF1A-AS1 modulates non-small cell lung cancer progression by targeting miR-149-5p/Cdk6

Growing evidence have shown the important regulation of lncRNAs (long noncoding RNAs) in non-small cell lung cancer (NSCLC). lncRNA hepatocyte nuclear factor 1 homeobox A (HNF1A)-antisense RNA 1 (AS1), an "oncogene", was reported to regulate human tumors progression. However, the molecular mechanism of HNF1A-AS1 involved in the development of NSCLC is still under investigation. In the current study, we found that HNF1A-AS1 was relatively upregulated in both NSCLC patient tissues and cell lines. Functional studies established that overexpression of HNF1A-AS1 promoted cell proliferation, cell cycle, invasion, and migration of NSCLC cells in vitro. The promotion abilities of HNF1A-AS1 on NSCLC cell progression were suppressed via knockdown of HNF1A-AS1. miR-149-5p was then proved to be a novel target of HNF1A-AS1, whose expression was negatively correlated with HNF1A-AS1 in NSCLC patient tissues and cell lines. HNF1A-AS1 increased the expression of cyclin-dependent kinase 6 (Cdk6) via sponging with miR-149-5p. Gain- and loss-of-functional studies indicated that HNF1A-AS1 promoted NSCLC progression partially through inhibition of miR-363-3p and induction of Cdk6. Subcutaneous xenotransplanted tumor model confirmed that interference of HNF1A-AS1 suppressed the tumorigenic ability of NSCLC via upregulation of miR-149-5p and downregulation of Cdk6 in vivo. In conclusion, our findings clarified the biologic significance of the HNF1A-AS1/miR-149-5p/Cdk6 axis in NSCLC progression and provided novel evidence that HNF1A-AS1 may be a new potential therapeutic target for the treatment of NSCLC.

Deubiquitinase DUB3 Regulates Cell Cycle Progression via Stabilizing Cyclin A for Proliferation of Non-Small Cell Lung Cancer Cells

The deubiquitinase DUB3 is frequently overexpressed in non-small cell lung cancer (NSCLC) and contributes to its malignant phenotype. However, the underlying molecular mechanism of DUB3 in NSCLC is largely unknown. In this study, we report that DUB3 regulates cell cycle progression by deubiquitinating cyclin A that links to proliferation of NSCLC cells. We found that knockdown of DUB3 decreases cyclin A levels, whereas overexpression of DUB3 strongly increases cyclin A levels. Mechanistically, DUB3 interacts with cyclin A, which removes the polyubiquitin chains conjugated onto cyclin A and stabilizes the cyclin A protein. Furthermore, we demonstrate that DUB3 regulates cell cycle progression by stabilizing cyclin A, because ablation of DUB3 arrests cell cycle from G0/G1 to S phase and the resulting effect can be rescued by introducing cyclin A into NSCLC cells. Functionally, we found that the effect of DUB3 on cyclin A mediates proliferation of NSCLC cells. Moreover, a significant correlation between DUB3 abundance and cyclin A expression levels were also found in NSCLC samples. Taken together, these results reveal that DUB3 functions as a novel cyclin A regulator through maintaining cyclin A stability, and that the DUB3-cyclin A signaling axis plays a critical role in cell cycle progression for proliferation of NSCLC.