The anti-tumor efficacy of CDK4/6 inhibition is enhanced by the combination with PI3K/AKT/mTOR inhibitors through impairment of glucose metabolism in TNBC cells

Immunomodulatory effects of antiangiogenic tyrosine kinase inhibitors in renal cell carcinoma models: Impact on following anti-PD-1 treatments

The approval of immune checkpoint inhibitors (ICIs) has revolutionized the management of metastatic renal cell carcinoma (RCC), introducing several ICI-based combinations as the new standard of care for affected patients. Nonetheless, monotherapy with antiangiogenic tyrosine kinase inhibitors (TKIs), such as pazopanib or sunitinib, still represents a first-line treatment option for selected patients belonging to the favorable risk group according to the International mRCC Database Consortium (IMDC) model. After TKI monotherapy, the main second-line option is represented by ICI monotherapy with the anti-Programmed Death Receptor 1(PD-1) nivolumab. To date, the expected clinical outcomes are similar with pazopanib or sunitinib and there is no clear indication for selecting one TKI over the other. Moreover, their impact on subsequent ICI treatment outcomes is not well defined, yet. Based on these premises, we investigated the immunomodulatory activity of these drugs in vitro and in vivo.Both TKIs induced Programmed Cell Death Ligand-1 (PD-L1) expression and soluble PD-L1 release in RCC cells, and hampered T cell activation, reducing cytokine production and the proportion of activated T cells. Nevertheless, in a syngeneic co-culture system with peripheral blood mononuclear cells (PBMCs) and tumor cells, incubation with anti-PD-1 antibody following TKIs treatment significantly restored T cell function, potentiating the cytotoxic effects against tumor cells. Pazopanib and sunitinib followed by anti-PD-1 antibody produced a comparable inhibition of tumor growth in a RCC syngeneic mouse model. Our findings suggest that pazopanib and sunitinib, showing similar immunomodulatory effects, may have a comparable impact on the subsequent effectiveness of PD-1/PD-L1 blockade.

High-throughput Screening for Cushing Disease: Therapeutic Potential of Thiostrepton via Cell Cycle Regulation

Cushing disease is a life-threatening disorder caused by autonomous secretion of ACTH from pituitary neuroendocrine tumors (PitNETs). Few drugs are indicated for inoperative Cushing disease, in particular that due to aggressive PitNETs. To explore agents that regulate ACTH-secreting PitNETs, we conducted high-throughput screening (HTS) using AtT-20, a murine pituitary tumor cell line characterized by ACTH secretion. For the HTS, we constructed a live cell-based ACTH reporter assay for high-throughput evaluation of ACTH changes. This assay was based on HEK293T cells overexpressing components of the ACTH receptor and a fluorescent cAMP biosensor, with high-throughput acquisition of fluorescence images. We treated AtT-20 cells with compounds and assessed ACTH concentrations in the conditioned media using the reporter assay. Of 2480 screened bioactive compounds, over 50% inhibition of ACTH secreted from AtT-20 cells was seen with 84 compounds at 10 μM and 20 compounds at 1 μM. Among these hit compounds, we focused on thiostrepton (TS) and determined its antitumor effects in both in vitro and in vivo xenograft models of Cushing disease. Transcriptome and flow cytometry analyses revealed that TS administration induced AtT-20 cell cycle arrest at the G2/M phase, which was mediated by FOXM1-independent mechanisms including downregulation of cyclins. Simultaneous TS administration with a cyclin-dependent kinase 4/6 inhibitor that affected the cell cycle at the G0/1 phase showed cooperative antitumor effects. Thus, TS is a promising therapeutic agent for Cushing disease. Our list of hit compounds and new mechanistic insights into TS effects serve as a valuable foundation for future research.

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Small molecule agents for triple negative breast cancer: Current status and future prospects

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with poor prognosis. The number of cases increased by 2.26 million in 2020, making it the most commonly diagnosed cancer type in the world. TNBCs lack hormone receptor (HR) and human epidermal growth factor 2 (HER2), which limits treatment options. Currently, paclitaxel-based drugs combined with other chemotherapeutics remain the main treatment for TNBC. There is currently no consensus on the best therapeutic regimen for TNBC. However, there have been successful clinical trials exploring large-molecule monoclonal antibodies, small-molecule targeted drugs, and novel antibody-drug conjugate (ADC). Although monoclonal antibodies have produced clinical success, their large molecular weight can limit therapeutic benefits. It is worth noting that in the past 30 years, the FDA has approved small molecule drugs for HER2-positive breast cancers. The lack of effective targets and the occurrence of drug resistance pose significant challenges in the treatment of TNBC. To improve the prognosis of TNBC, it is crucial to search for effective targets and to overcome drug resistance. This review examines the clinical efficacy, adverse effects, resistance mechanisms, and potential solutions of targeted small molecule drugs in both monotherapies and combination therapies. New therapeutic targets, including nuclear export protein 1 (XPO1) and hedgehog (Hh), are emerging as potential options for researchers and become integrated into clinical trials for TNBC. Additionally, there is growing interest in the potential of targeted protein degradation chimeras (PROTACs), degraders of rogue proteins, as a future therapy direction. This review provides potentially valuable insights with clinical implications.

Beyond cell cycle regulation: The pleiotropic function of CDK4 in cancer

CDK4, along with its regulatory subunit, cyclin D, drives the transition from G1 to S phase, during which DNA replication and metabolic activation occur. In this canonical pathway, CDK4 is essentially a transcriptional regulator that acts through phosphorylation of retinoblastoma protein (RB) and subsequent activation of the transcription factor E2F, ultimately triggering the expression of genes involved in DNA synthesis and cell cycle progression to S phase. In this review, we focus on the newly reported functions of CDK4, which go beyond direct regulation of the cell cycle. In particular, we describe the extranuclear roles of CDK4, including its roles in the regulation of metabolism, cell fate, cell dynamics and the tumor microenvironment. We describe direct phosphorylation targets of CDK4 and decipher how CDK4 influences these physiological processes in the context of cancer.

Preclinical evaluation of the CDK4/6 inhibitor palbociclib in combination with a PI3K or MEK inhibitor in colorectal cancer

BACKGROUND

Studies have demonstrated the efficacy of Palbociclib (CDK 4/6 inhibitor), Gedatolisib (PI3K/mTOR dual inhibitor) and PD0325901 (MEK1/2 inhibitor) in colorectal cancer (CRC), however single agent therapeutics are often limited by the development of resistance.

METHODS

We compared the anti-proliferative effects of the combination of Gedatolisib and Palbociclib and Gedatolisib and PD0325901 in five CRC cell lines with varying mutational background and tested their combinations on total and phosphoprotein levels of signaling pathway proteins.

RESULTS

The combination of Palbociclib and Gedatolisib was superior to the combination of Palbociclib and PD0325901. The combination of Palbociclib and Gedatolisib had synergistic anti-proliferative effects in all cell lines tested [CI range: 0.11-0.69] and resulted in the suppression of S6rp (S240/244), without AKT reactivation. The combination of Palbociclib and Gedatolisib increased BAX and Bcl-2 levels in PIK3CA mutated cell lines. The combination of Palbociclib and Gedatolisib caused MAPK/ERK reactivation, as seen by an increase in expression of total EGFR, regardless of the mutational status of the cells.

CONCLUSION

This study shows that the combination of Palbociclib and Gedatolisib has synergistic anti-proliferative effects in both wild-type and mutated CRC cell lines. Separately, the phosphorylation of S6rp may be a promising biomarker of responsiveness to this combination.

MiRNA signatures in nasopharyngeal carcinoma: molecular mechanisms and therapeutic perspectives

Nasopharyngeal carcinoma (NPC) is a prevalent cancerous tumor that affects the head and neck region. Recent studies have provided compelling evidence indicating the significant involvement of microRNAs (miRNAs) in the development and progression of NPC. This review aims to present a comprehensive summary of the current knowledge regarding miRNA signatures in NPC, encompassing their expression patterns, molecular mechanisms, and potential therapeutic implications. Initially, the article outlines the aberrant expression of miRNAs in NPC and elucidates their roles in tumor initiation, invasion, and metastasis. Subsequently, the underlying molecular mechanisms of miRNA-mediated regulation of NPC-associated signaling pathways are discussed. Additionally, the review highlights the potential clinical applications of miRNAs as diagnostic and prognostic biomarkers, as well as their therapeutic potential in NPC treatment. In conclusion, this review underscores the critical involvement of miRNAs in NPC pathogenesis and underscores their promise as novel therapeutic targets for combating this devastating disease.

Recent advances in targeted strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC), a highly aggressive subtype of breast cancer, negatively expresses estrogen receptor, progesterone receptor, and the human epidermal growth factor receptor 2 (HER2). Although chemotherapy is the main form of treatment for patients with TNBC, the effectiveness of chemotherapy for TNBC is still limited. The search for more effective therapies is urgent. Multiple targeted therapeutic strategies have emerged according to the specific molecules and signaling pathways expressed in TNBC. These include PI3K/AKT/mTOR inhibitors, epidermal growth factor receptor inhibitors, Notch inhibitors, poly ADP-ribose polymerase inhibitors, and antibody-drug conjugates. Moreover, immune checkpoint inhibitors, for example, pembrolizumab, atezolizumab, and durvalumab, are widely explored in the clinic. We summarize recent advances in targeted therapy and immunotherapy in TNBC, with the aim of serving as a reference for the development of individualized treatment of patients with TNBC in the future.

Novel cancer treatment paradigm targeting hypoxia-induced factor in conjunction with current therapies to overcome resistance

Chemotherapy, radiotherapy, targeted therapy, and immunotherapy are established cancer treatment modalities that are widely used due to their demonstrated efficacy against tumors and favorable safety profiles or tolerability. Nevertheless, treatment resistance continues to be one of the most pressing unsolved conundrums in cancer treatment. Hypoxia-inducible factors (HIFs) are a family of transcription factors that regulate cellular responses to hypoxia by activating genes involved in various adaptations, including erythropoiesis, glucose metabolism, angiogenesis, cell proliferation, and apoptosis. Despite this critical function, overexpression of HIFs has been observed in numerous cancers, leading to resistance to therapy and disease progression. In recent years, much effort has been poured into developing innovative cancer treatments that target the HIF pathway. Combining HIF inhibitors with current cancer therapies to increase anti-tumor activity and diminish treatment resistance is one strategy for combating therapeutic resistance. This review focuses on how HIF inhibitors could be applied in conjunction with current cancer treatments, including those now being evaluated in clinical trials, to usher in a new era of cancer therapy.

Out of the cycle: Impact of cell cycle aberrations on cancer metabolism and metastasis

The use of cell cycle inhibitors has necessitated a better understanding of the cell cycle in tumor biology to optimize the therapeutic approach. Cell cycle aberrations are common in cancers, and it is increasingly acknowledged that these aberrations exert oncogenic effects beyond the cell cycle. Multiple facets such as cancer metabolism, immunity and metastasis are also affected, all of which are beyond the effect of cell proliferation alone. This review comprehensively summarized the important recent findings and advances in these interrelated processes. In cancer metabolism, cell cycle regulators can modulate various pathways in aerobic glycolysis, glucose uptake and gluconeogenesis, mainly through transcriptional regulation and kinase activities. Amino acid metabolism is also regulated through cell cycle progression. On cancer metastasis, metabolic plasticity, immune evasion, tumor microenvironment adaptation and metastatic site colonization are intricately related to the cell cycle, with distinct regulatory mechanisms at each step of invasion and dissemination. Throughout the synthesis of current understanding, knowledge gaps and limitations in the literature are also highlighted, as are new therapeutic approaches such as combinational therapy and challenges in tackling emerging targeted therapy resistance. A greater understanding of how the cell cycle modulates diverse aspects of cancer biology can hopefully shed light on identifying new molecular targets by harnessing the vast potential of the cell cycle.

Investigation of the Therapeutic Effects of Palbociclib Conjugated Magnetic Nanoparticles on Different Types of Breast Cancer Cell Lines

Introduction

Drug targeting and controlled drug release systems in cancer treatment have many advantages over conventional chemotherapy in terms of limiting systemic toxicity, side effects, and overcoming drug resistance.

Methods and Results

In this paper, fabricating nanoscale delivery system composed of magnetic nanoparticles (MNPs) covered with poly-amidoamine (PAMAM) dendrimers and using its advantages were fully used to help the chemotherapeutic drug, Palbociclib, effectively reach tumors, specifically and stay stable in the circulation longer. In order to determine whether conjugate selectivity can be increased for the specific drug type, we have reported different strategies for loading and conjugation of Palbociclib to different generations of magnetic PAMAM dendrimers. The best method leading to the highest amount of Palbociclib conjugation was chosen, and the characterization of the Palbociclib conjugated dendrimeric magnetic nanoparticles (PAL-DcMNPs) were performed. In vitro pharmacological activity of the conjugation was demonstrated by measuring the cell viability and lactate dehydrogenase (LHD) release. Obtained results indicated that PAL-DcMNPs treatment of the breast cancer cell lines, leads to an increase in cell toxicity compared to free Palbociclib. The observed effects were more evident for MCF-7 cells than for MDA-MB231 and SKBR3 cells, considering that viability decreased to 30% at 2.5 µM treatment of PAL-DcMNPs at MCF-7 cells. Finally, in Palbociclib and PAL-DcMNPs treated breast cancer cells, the expression levels of some pro-apoptotic and drug resistance related genes were performed by RT-PCR analysis.

Conclusion

Our knowledge indicates that the proposed approach is novel, and it can provide new insight into the development of Palbociclib targeting delivery system for cancer treatment.

Prognostic Relevance and In Vitro Targeting of Concomitant PTEN and p16 Deficiency in Chordomas

Chordomas are rare bone tumors arising along the spine. Due to high resistance towards chemotherapy, surgical resection—often followed by radiation therapy—is currently the gold standard of treatment. So far, targeted systemic therapies have not been approved. The most frequent molecular alterations include the loss of PTEN and CDKN2A (encoding p16), being associated with poor prognoses in chordoma patients. Specific inhibitors of the PI3K/AKT/mTOR pathway as well as CDK4/6 have shown antitumor activity in preclinical studies and have recently been under investigation in phase II clinical trials; however, the clinical impacts and therapeutic consequences of concomitant PTEN and p16 deficiency have not yet been investigated in chordomas. In a cohort of 43 chordoma patients, 16% of the cases were immunohistochemically negative for both markers. The simultaneous loss of PTEN and p16 was associated with a higher KI-67 index, a tendency to metastasize, and significantly shorter overall survival. Additionally, 30% of chordoma cell lines (n = 19) were PTEN-/p16-negative. Treating these chordoma cells with palbociclib (CDK4/6 inhibitor), rapamycin (mTOR inhibitor) or the pan-PI3K inhibitor buparlisib significantly reduced cell viability. Synergistic effects were observed when combining palbociclib with rapamycin. In conclusion, we show that patients with PTEN-/p16-negative chordomas have poor prognoses and provide strong preclinical evidence that these patients might benefit from a Palbociclib/rapamycin combination treatment.

Recent Advances in Targeted Nanocarriers for the Management of Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a life-threatening form of breast cancer which has been found to account for 15% of all the subtypes of breast cancer. Currently available treatments are significantly less effective in TNBC management because of several factors such as poor bioavailability, low specificity, multidrug resistance, poor cellular uptake, and unwanted side effects being the major ones. As a rapidly growing field, nano-therapeutics offers promising alternatives for breast cancer treatment. This platform provides a suitable pathway for crossing biological barriers and allowing sustained systemic circulation time and an improved pharmacokinetic profile of the drug. Apart from this, it also provides an optimized target-specific drug delivery system and improves drug accumulation in tumor cells. This review provides insights into the molecular mechanisms associated with the pathogenesis of TNBC, along with summarizing the conventional therapy and recent advances of different nano-carriers for the management of TNBC.

Energy metabolism pathways in breast cancer progression: The reprogramming, crosstalk, and potential therapeutic targets

Breast cancer (BC) is a malignant tumor that seriously endangers health in women. BC, like other cancers, is accompanied by metabolic reprogramming. Among energy metabolism-related pathways, BC exhibits enhanced glycolysis, tricarboxylic acid (TCA) cycle, pentose phosphate pathway (PPP), glutamate metabolism, and fatty acid metabolism activities. These pathways facilitate the proliferation, growth and migration of BC cells. The progression of BC is closely related to the alterations in the activity or expression level of several metabolic enzymes, which are regulated by the intrinsic factors such as the key signaling and transcription factors. The metabolic reprogramming in the progression of BC is attributed to the aberrant expression of the signaling and transcription factors associated with the energy metabolism pathways. Understanding the metabolic mechanisms underlying the development of BC will provide a druggable potential for BC treatment and drug discovery.

CDK4/6 Inhibition Enhances the Efficacy of Standard Chemotherapy Treatment in Malignant Pleural Mesothelioma Cells

BACKGROUND

The loss of the CDKN2A/ARF (cyclin-dependent kinase inhibitor 2A/alternative reading frame) gene is the most common alteration in malignant pleural mesothelioma (MPM), with an incidence of about 70%, thus representing a novel target for mesothelioma treatment. In the present study, we evaluated the antitumor potential of combining the standard chemotherapy regimen used for unresectable MPM with the CDK4/6 (cyclin-dependent kinase 4 or 6) inhibitor abemaciclib.

METHODS

Cell viability, cell death, senescence, and autophagy induction were evaluated in two MPM cell lines and in a primary MPM cell culture.

RESULTS

The simultaneous treatment of abemaciclib with cisplatin and pemetrexed showed a greater antiproliferative effect than chemotherapy alone, both in MPM cell lines and in primary cells. This combined treatment induced cellular senescence or autophagic cell death, depending on the cell type. More in detail, the induction of cellular senescence was related to the increased expression of p21, whereas autophagy induction was due to the impairment of the AKT/mTOR signaling. Notably, the effect of the combination was irreversible and no resumption in tumor cell proliferation was observed after drug withdrawal.

CONCLUSION

Our results demonstrated the therapeutic potential of CDK4/6 inhibitors in combination with chemotherapy for the treatment of MPM and are consistent with the recent positive results in the MiST2 arm in abemaciclib-treated patients.

Current Molecular Combination Therapies Used for the Treatment of Breast Cancer

Breast cancer is the second leading cause of death for women worldwide. While monotherapy (single agent) treatments have been used for many years, they are not always effective, and many patients relapse after initial treatment. Moreover, in some patients the response to therapy becomes weaker, or resistance to monotherapy develops over time. This is especially problematic for metastatic breast cancer or triple-negative breast cancer. Recently, combination therapies (in which two or more drugs are used to target two or more pathways) have emerged as promising new treatment options. Combination therapies are often more effective than monotherapies and demonstrate lower levels of toxicity during long-term treatment. In this review, we provide a comprehensive overview of current combination therapies, including molecular-targeted therapy, hormone therapy, immunotherapy, and chemotherapy. We also describe the molecular basis of breast cancer and the various treatment options for different breast cancer subtypes. While combination therapies are promising, we also discuss some of the challenges. Despite these challenges, the use of innovative combination therapy holds great promise compared with traditional monotherapies. In addition, the use of multidisciplinary technologies (such as nanotechnology and computer technology) has the potential to optimize combination therapies even further.

miR-199a-3p increases the anti-tumor activity of palbociclib in liver cancer models

Palbociclib is in early-stage clinical testing in advanced hepatocellular carcinoma (HCC). Here, we investigated whether the anti-tumor activity of palbociclib, which prevents the CDK4/6-mediated phosphorylation of RB1 but simultaneously activates AKT signaling, could be improved by its combination with a PI3K/AKT/mTOR inhibitor in liver cancer models. The selective pan-AKT inhibitor, MK-2206, or the microRNA-199a-3p were tested in combination with palbociclib in HCC cell lines and in the TG221 HCC transgenic mouse model. The combination palbociclib/MK-2206 was highly effective, but too toxic to be tolerated by mice. Conversely, the combination miR-199a-3p mimics/palbociclib not only induced a complete or partial regression of tumor lesions, but was also well tolerated. After 3 weeks of treatment, the combination produced a significant reduction in number and size of tumor nodules in comparison with palbociclib or miR-199a-3p mimics used as single agents. Moreover, we also reported the efficacy of this combination against sorafenib-resistant cells in vitro and in vivo. At the molecular level, the combination caused the simultaneous decrease of the phosphorylation of both RB1 and of AKT. Our findings provide pre-clinical evidence for the efficacy of the combination miR-199a-3p/palbociclib as anti-HCC treatment or as a new approach to overcome sorafenib resistance.

CDK4/6 inhibitors versus PI3K/AKT/mTOR inhibitors in women with hormone receptor-positive, HER2-negative metastatic breast cancer: An updated systematic review and network meta-analysis of 28 randomized controlled trials

Background

Updated evidence was required to compare the efficacy and safety of cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) inhibitors for patients with hormone receptor-positive and HER2-negative metastatic breast cancer.

Methods

A systematic review and network meta-analysis was conducted utilizing data from randomized controlled trials (RCTs) that contained interventions of CDK4/6 inhibitors or PI3K/AKT/mTOR inhibitors. Progression-free survival (PFS), overall survival (OS), and treatment-related adverse events (TRAEs) were primary outcomes of interest. Pooled hazard ratios (HRs) and odds ratios (ORs) with 95% credible intervals (CrIs) were used to assess the survival outcomes and safety profiles, respectively.

Results

A total of 28 RCTs with 12,129 participants were included. Pooled analysis showed that CDK4/6 inhibitors significantly prolonged PFS than PI3K/AKT/mTOR inhibitors (HR, 0.81; 95% CrI, 0.69–0.94), whereas no significant differences were detected regarding OS. After balancing the treatment lines and metastatic sites, the superiority of CDK4/6 inhibitors only appeared in the visceral and non-visceral subgroups. Among CDK4/6 inhibitors, abemaciclib was significantly better than others in ≥3 grade neutropenia (OR, 0.04; 95% CrI, 0.01–0.15). The incidence of stomatitis and digestive disorders was different among diverse kinds of PI3K/AKT/mTOR inhibitors. Discrepancies appeared regarding TRAEs of hepatotoxicity, diarrhea, and hyperglycemia among different interventions.

Conclusions

CDK4/6 inhibitors showed better efficacy in PFS, but the benefits disappeared when taking treatment line into consideration. Specific and discrepant safety profiles were found in two categories of agents.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO, identifier CRD42022321172.

Review: Precise sarcoma patient-derived orthotopic xenograft (PDOX) mouse models enable identification of novel effective combination therapies with the cyclin-dependent kinase inhibitor palbociclib: A strategy for clinical application

Introduction

Sarcomas are rare heterogeneous malignant tumors that originate and develop in soft tissue or bone. Effective treatment for sarcomas is still limited to traditional chemotherapy and surgery that are often ineffective for recurrent disease. Cyclin-dependent kinases (CDKs) promote abnormal cell cycling and cell division in many cancers including sarcomas. Therefore, our hypothesis was that CDK inhibitors may be useful candidates for sarcoma treatment. Patient-derived orthotopic xenograft (PDOX) mouse models mimic the clinical disease for all major cancer types and have identified effective treatments that hold much clinical promise. The present report reviews sarcoma PDOX models that we have established for their potential to discover effective combination treatments based on CDK inhibitors for recalcitrant sarcoma.

Methods

We have previously reported six sarcoma PDOX studies evaluating the CDK inhibitor palbociclib on sarcoma, including osteosarcoma, Ewing sarcoma, de-differentiated liposarcoma, and peritoneal metastatic leiomyosarcoma.

Results

Palbociclib monotherapy significantly inhibited, but not regressed, the PDOX growth of osteosarcoma, Ewing sarcoma, de-differentiated liposarcoma, and peritoneal metastatic leiomyosarcoma. A combination of palbociclib and a mammalian target of rapamycin (mTOR) inhibitor, everolimus, significantly inhibited, but did not regress, the PDOX growth of osteosarcoma. Combinations of palbociclib with a multikinase inhibitor, sorafenib, and palbociclib combined with recombinant methioninase were effective and regressed the osteosarcoma and de-differentiated liposarcoma PDOX models, respectively.

Conclusions

Novel effective drug combinations using the CDK inhibitor palbociclib were identified in PDOX models of the major types of sarcomas. Methionine restriction effected by methioninase increased the efficacy of palbociclib. Combination therapy with palbociclib is a promising future strategy for improved sarcoma therapy in the clinic.

DTSyn: a dual-transformer-based neural network to predict synergistic drug combinations

Drug combination therapies are superior to monotherapy for cancer treatment in many ways. Identifying novel drug combinations by screening is challenging for the wet-lab experiments due to the time-consuming process of the enormous search space of possible drug pairs. Thus, computational methods have been developed to predict drug pairs with potential synergistic functions. Notwithstanding the success of current models, understanding the mechanism of drug synergy from a chemical-gene-tissue interaction perspective lacks study, hindering current algorithms from drug mechanism study. Here, we proposed a deep neural network model termed DTSyn (Dual Transformer encoder model for drug pair Synergy prediction) based on a multi-head attention mechanism to identify novel drug combinations. We designed a fine-granularity transformer encoder to capture chemical substructure-gene and gene-gene associations and a coarse-granularity transformer encoder to extract chemical-chemical and chemical-cell line interactions. DTSyn achieved the highest receiver operating characteristic area under the curve of 0.73, 0.78. 0.82 and 0.81 on four different cross-validation tasks, outperforming all competing methods. Further, DTSyn achieved the best True Positive Rate (TPR) over five independent data sets. The ablation study showed that both transformer encoder blocks contributed to the performance of DTSyn. In addition, DTSyn can extract interactions among chemicals and cell lines, representing the potential mechanisms of drug action. By leveraging the attention mechanism and pretrained gene embeddings, DTSyn shows improved interpretability ability. Thus, we envision our model as a valuable tool to prioritize synergistic drug pairs with chemical and cell line gene expression profile.

CDK4/6 inhibitors improve the anti-tumor efficacy of lenvatinib in hepatocarcinoma cells

Hepatocellular carcinoma (HCC) is the most frequent primary liver cancer with a poor prognosis and limited treatment options. Considering that alterations of the CDK4/6-cyclin D-Rb pathway occur frequently in HCC, we tested the efficacy of two CDK4/6 inhibitors, abemaciclib and ribociclib, in combination with lenvatinib, a multi-kinase inhibitor approved as first-line therapy for advanced HCC, in a panel of HCC Rb-expressing cell lines. The simultaneous drug combinations showed a superior anti-proliferative activity as compared with single agents or sequential schedules of treatment, either in short or in long-term experiments. In addition, the simultaneous combination of abemaciclib with lenvatinib reduced 3D cell growth, and impaired colony formation and cell migration. Mechanistically, these growth-inhibitory effects were associated with a stronger down-regulation of c-myc protein expression. Depending on the HCC cell model, reduced activation of MAPK, mTORC1/p70S6K or src/FAK signaling was also observed. Abemaciclib combined with lenvatinib arrested the cells in the G1 cell cycle phase, induced p21 accumulation, and promoted a stronger increase of cellular senescence, associated with elevation of β-galactosidase activity and accumulation of ROS, as compared with single treatments. After drug withdrawal, the capacity of forming colonies was significantly impaired, suggesting that the anti-tumor efficacy of abemaciclib and lenvatinib combination was persistent.

Our pre-clinical results demonstrate the effectiveness of the simultaneous combination of CDK4/6 inhibitors with lenvatinib in HCC cell models, suggesting that this combination may be worthy of further investigation as a therapeutic approach for the treatment of advanced HCC.

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.

AKT1 Is Required for a Complete Palbociclib-Induced Senescence Phenotype in BRAF-V600E-Driven Human Melanoma

Cellular senescence is a carefully regulated process of proliferative arrest accompanied by functional and morphologic changes. Senescence allows damaged cells to avoid neoplastic proliferation; however, the induction of the senescence-associated secretory phenotype (SASP) can promote tumor growth. The complexity of senescence may limit the efficacy of anti-neoplastic agents, such as CDK4/6 inhibitors (Cdk4/6i), that induce a senescence-like state in tumor cells. The AKT kinase family, which contains three isoforms that play both unique and redundant roles in cancer progression, is commonly hyperactive in many cancers including melanoma and has been implicated in the regulation of senescence. To interrogate the role of AKT isoforms in Cdk4/6i-induced cellular senescence, we generated isoform-specific AKT knockout human melanoma cell lines. We found that the CDK4/6i Palbociclib induced a form of senescence in these cells that was dependent on AKT1. We then evaluated the activity of the cGAS-STING pathway, recently implicated in cellular senescence, finding that cGAS-STING function was dependent on AKT1, and pharmacologic inhibition of cGAS had little effect on senescence. However, we found SASP factors to require NF-κB function, in part dependent on a stimulatory phosphorylation of IKKα by AKT1. In summary, we provide the first evidence of a novel, isoform-specific role for AKT1 in therapy-induced senescence in human melanoma cells acting through NF-κB but independent of cGAS.

The Renaissance of Cyclin Dependent Kinase Inhibitors

Cyclin-dependent kinases (CDK) regulate cell cycle progression. During tumor development, altered expression and availability of CDKs strongly contribute to impaired cell proliferation, a hallmark of cancer. In recent years, targeted inhibition of CDKs has shown considerable therapeutic benefit in a variety of tumor entities. Their success is reflected in clinical approvals of specific CDK4/6 inhibitors for breast cancer. This review provides a detailed insight into the molecular mechanisms of CDKs as well as a general overview of CDK inhibition. It also summarizes the latest research approaches and current advances in the treatment of head and neck cancer with CDK inhibitors. Instead of monotherapies, combination therapies with CDK inhibitors may especially provide promising results in tumor therapy. Indeed, recent studies have shown a synergistic effect of CDK inhibition together with chemo- and radio- and immunotherapy in cancer treatment to overcome tumor evasion, which may lead to a renaissance of CDK inhibitors.

miR-130b suppresses the invasion and migration of prostate cancer via inhibiting DLL1 and regulating the PI3K/Akt pathways

Prostate cancer occurs in the prostatic epithelium and poses a threat to the health of middle-aged and older males. The objective of the present study was to explore the roles of microRNA (miRNA/miR)-130b in prostate cancer and potential molecular mechanisms in order to control the migration and invasion of prostate cancer. For this purpose, reverse transcription-PCR was performed to evaluate the mRNA levels of DLL1, phosphoinositide-3 kinase (PI3K), protein kinase B (Akt) and matrix metalloproteinase (MMP)9, and western blot analysis was carried out to detect the protein expression levels of DLL1, phosphorylated (p)-PI3K, p-Akt and MMP9. A Transwell assay was conducted to examine the invasion rate of prostate cancer cells. Furthermore, a scratch wound assay was performed to examine the migration rate of prostate cancer cells. A luciferase assay was performed to examine the interaction between miRNA and its target mRNA. The results revealed that miR-130b had abnormal (low) expression in tumor tissues compared with that in the adjacent normal tissue. An miR-130b mimic suppressed the expression of DLL1. The expression of p-PI3K, p-Akt and MMP9 in prostate cancer cells transfected with the miR-130b mimic was decreased in comparison to the negative control and control groups. Furthermore, migration and invasion were significantly suppressed in the miR-130b mimic group. In conclusion, a novel pathway interlinking miR-130b and MMP9, p-Akt and p-PI3K, which regulates the migration and invasion of prostate cancer cells, was identified. These findings provide an intriguing biomarker and treatment strategy for patients with prostate cancer.

The Combination of the CDK4/6 Inhibitor, Palbociclib, With the Vitamin D3 Analog, Inecalcitol, Has Potent In Vitro and In Vivo Anticancer Effects in Hormone-Sensitive Breast Cancer, But Has a More Limited Effect in Triple-Negative Breast Cancer

Active vitamin D₃, 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], and its synthetically derived analogs possess potent anticancer properties. In breast cancer (BC) cells, 1,25(OH)₂D₃ blocks cell proliferation and induces apoptosis through different cell-type specific mechanisms. In this study, we evaluated if the combination of the potent vitamin D₃ analog, inecalcitol, with a selective CDK4/6 inhibitor, palbociclib, enhanced the antiproliferative effects of both single compounds in hormone-sensitive (ER⁺) BC, for which palbociclib treatment is already approved, but also in triple-negative BC (TNBC). Inecalcitol and palbociclib combination treatment decreased cell proliferation in both ER⁺ (T47D-MCF7) and TNBC (BT20-HCC1143-Hs578T) cells, with a more pronounced antiproliferative effect in the former. In ER⁺ BC cells, the combination therapy downregulated cell cycle regulatory proteins (p)-Rb and (p)-CDK2 and blocked G1-S phase transition of the cell cycle. Combination treatment upregulated p-mTOR and p-4E-BP1 protein expression in MCF7 cells, whereas it suppressed expression of these proteins in BT20 cells. Cell survival was decreased after inecalcitol treatment either alone or combined in MCF7 cells. Interestingly, the combination therapy upregulated mitochondrial ROS and mitotracker staining in both cell lines. Furthermore, in vivo validation in a MCF7 cell line-derived xenograft mouse model decreased tumor growth and cell cycle progression after combination therapy, but not in a TNBC BT20 cell line-derived xenograft model. In conclusion, we show that addition of a potent vitamin D₃ analog to selective CDK4/6 inhibitor treatment results in increased antiproliferative effects in ER⁺ BC both in vitro and in vivo.

CDK4/6 inhibitors: A potential therapeutic approach for triple negative breast cancer

Triple negative breast cancer (TNBC) cells lack expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER-2). Thus, TNBC does not respond to hormone-based therapy. TNBC is also an aggressive subtype associated with poorer prognoses compared to other breast cancers. Conventional chemotherapeutics are used to manage TNBC although systemic relapse is common with limited benefits being reported as well as adverse events being documented. Here, we discuss current therapies for TNBC in the neo- and adjuvant settings, as well as recent advancements in the targeting of PD-L1-positive tumors and inclusion of PARP inhibitors for TNBC patients with BRCA mutations. The recent development of cyclin-dependent kinase (CDK) 4/6 inhibitors in ER-positive breast cancers has demonstrated significant improvements in progression free survival in patients. Here, we review preclinical data of CDK 4/6 inhibitors and describe current clinical trials assessing these in TNBC disease.

Chemoresistance in breast cancer: PI3K/Akt pathway inhibitors vs the current chemotherapy

Breast cancer is the most prevalent type of cancer among women. Several types of drugs, targeting the specific proteins expressed on the breast cancer cell surface (such as receptor tyrosine kinases and immune checkpoint regulators) and proteins involved in cell cycle and motility (including cyclin-dependent kinases, DNA stabilisers, and cytoskeleton modulators) are approved for different subtypes of breast cancer. However, breast cancer also has a poor response to conventional chemotherapy due to intrinsic and acquired resistance, and an Akt fingerprint is detectable in most drug-resistant cases. Overactivation of Akt and its upstream and downstream regulators in resistant breast cancer cells is considered a major potential target for novel anti-cancer therapies, suggesting that Akt signalling acts as a cellular mechanism against chemotherapy. The present review has shown that sustained activation of Akt results in resistance to different types of chemotherapy. Akt signalling plays a cellular defence role against chemotherapy and (1) enhances multi-drug resistance, (2) increases reactive oxygen species at breast tumor microenvironment, (3) enhances anaerobic metabolism, (4) inhibits the tricarboxylic cycle, (5) promotes PD-L1 upregulation, (6) inhibits apoptosis, (7) increases glucose uptake, and more importantly (8) recruits and interconnects the plasma membrane, nucleus, endoplasmic reticulum, and mitochondria to hijack breast cancer cells and rescue these cells from chemotherapy. Therefore, Akt signalling is considered a cellular defence mechanism employed against chemotherapeutic effects. In addition, interfering roles of PI3K/Akt signalling on the current cytotoxic and molecularly targeted therapy as well as immunotherapy of breast cancer are discussed with a clinical approach. Although, alpelisib, a PIK3CA inhibitor, is the only PI3K/Akt pathway inhibitor approved for breast cancer, we also highlight well-evaluated inhibitors of PI3K/Akt signalling based on different subtypes of breast cancer, which are under clinical trials whether as monotherapy or in combination with other types of chemotherapy.

Treatment of Retinoblastoma 1-Intact Hepatocellular Carcinoma With Cyclin-Dependent Kinase 4/6 Inhibitor Combination Therapy

BACKGROUND AND AIMS

Synthetic cyclin-dependent kinase (CDK) 4/6 inhibitors exert antitumor effects by forcing RB1 in unphosphorylated status, causing not only cell cycle arrest but also cellular senescence, apoptosis, and increased immunogenicity. These agents currently have an indication in advanced breast cancers and are in clinical trials for many other solid tumors. HCC is one of promising targets of CDK4/6 inhibitors. RB family dysfunction is often associated with the initiation of HCC; however, this is revivable, as RB family members are not frequently mutated or deleted in this malignancy.

APPROACH AND RESULTS

Loss of all Rb family members in transformation related protein 53 (Trp53)^-/- mouse liver resulted in liver tumor reminiscent of human HCC, and re-expression of RB1 sensitized these tumors to a CDK4/6 inhibitor, palbociclib. Introduction of an unphosphorylatable form of RB1 (RB7LP) into multiple liver tumor cell lines induced effects similar to palbociclib. By screening for compounds that enhance the efficacy of RB7LP, we identified an I kappa B kinase (IKK)β inhibitor Bay 11-7082. Consistently, RB7LP expression and treatment with palbociclib enhanced IKKα/β phosphorylation and NF-κB activation. Combination therapy using palbociclib with Bay 11-7082 was significantly more effective in hepatoblastoma and HCC treatment than single administration. Moreover, blockade of IKK-NF-κB or AKT pathway enhanced effects of palbociclib on RB1-intact KRAS Kirsten rat sarcoma viral oncogene homolog mutated lung and colon cancers.

CONCLUSIONS

In conclusion, CDK4/6 inhibitors have a potential to treat a wide variety of RB1-intact cancers including HCC when combined with an appropriate kinase inhibitor.

mTOR Activity and Autophagy in Senescent Cells, a Complex Partnership

Cellular senescence is a form of proliferative arrest triggered in response to a wide variety of stimuli and characterized by unique changes in cell morphology and function. Although unable to divide, senescent cells remain metabolically active and acquire the ability to produce and secrete bioactive molecules, some of which have recognized pro-inflammatory and/or pro-tumorigenic actions. As expected, this “senescence-associated secretory phenotype (SASP)” accounts for most of the non-cell-autonomous effects of senescent cells, which can be beneficial or detrimental for tissue homeostasis, depending on the context. It is now evident that many features linked to cellular senescence, including the SASP, reflect complex changes in the activities of mTOR and other metabolic pathways. Indeed, the available evidence indicates that mTOR-dependent signaling is required for the maintenance or implementation of different aspects of cellular senescence. Thus, depending on the cell type and biological context, inhibiting mTOR in cells undergoing senescence can reverse senescence, induce quiescence or cell death, or exacerbate some features of senescent cells while inhibiting others. Interestingly, autophagy—a highly regulated catabolic process—is also commonly upregulated in senescent cells. As mTOR activation leads to repression of autophagy in non-senescent cells (mTOR as an upstream regulator of autophagy), the upregulation of autophagy observed in senescent cells must take place in an mTOR-independent manner. Notably, there is evidence that autophagy provides free amino acids that feed the mTOR complex 1 (mTORC1), which in turn is required to initiate the synthesis of SASP components. Therefore, mTOR activation can follow the induction of autophagy in senescent cells (mTOR as a downstream effector of autophagy). These functional connections suggest the existence of autophagy regulatory pathways in senescent cells that differ from those activated in non-senescence contexts. We envision that untangling these functional connections will be key for the generation of combinatorial anti-cancer therapies involving pro-senescence drugs, mTOR inhibitors, and/or autophagy inhibitors.

Dual blockade of EGFR and CDK4/6 delays head and neck squamous cell carcinoma progression by inducing metabolic rewiring

Despite preclinical success, monotherapies targeting EGFR or cyclin D1-CDK4/6 in Head and Neck squamous cell carcinoma (HNSCC) have shown a limited clinical outcome. Here, we aimed to determine the combined effect of palbociclib (CDK4/6) and afatinib (panEGFR) inhibitors as an effective strategy to target HNSCC. Using TCGA-HNSCC co-expression analysis, we found that patients with high EGFR and cyclin D1 expression showed enrichment of gene clusters associated with cell-growth, glycolysis, and epithelial to mesenchymal transition processes. Phosphorylated S6 (p-S6), a downstream effector of EGFR and cyclin D1-CDK4/6 signalling, showed a progressive increase from normal oral tissues to leukoplakia and frank malignancy, and associated with poor outcome of the patients. This increased p-S6 expression was drastically reduced after combination treatment with afatinib and palbociclib in the cell lines and mouse models, suggesting its utiliy as a prognostic marker in HNSCC. Combination treatment also reduced the cell growth and induced cell senescence via increasing reactive oxygen species with concurrent ablation of glycolytic and tricarboxylic acid cycle intermediates. Finally, our findings in sub-cutaneous and genetically engineered mouse model (K14-CreERtam;LSL-KrasG12D/+;Trp53R172H/+) studies showed a significant reduction in the tumor growth and delayed tumor progression after combination treatment. This study collectively demonstrates that dual targeting may be a critical therapeutic strategy in blocking tumor progression via inducing metabolic alteration and warrants clinical evaluation.

Potential Prospect of CDK4/6 Inhibitors in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive, difficult-to-treat subtype of cancer with a poor prognosis; there is an urgent need for effective, targeted molecular therapies. The cyclin D/cyclin-dependent kinase (CDK)4/6–retinoblastoma protein (Rb) pathway plays a critical role in regulating cell cycle checkpoints, a process which is often disrupted in cancer cells. Selective CDK4/6 inhibitors can prevent retinoblastoma protein phosphorylation by invoking cell cycle arrest in the first growth phase (G1), and may therefore represent an effective treatment option. In this article, we review the molecular mechanisms and therapeutic efficacy of CDK4/6 inhibitors in combination with other targeted therapies for the treatment of triple-negative breast cancer. Three selective CDK4/6 inhibitors have so far received the approval of the Food and Drug Administration (FDA) for patients with estrogen receptor (ER)+/human epidermal growth factor receptor 2 (HER2) breast cancer. Trilaciclib, a small molecule short-acting inhibitor of CDK4/6, has also been approved recently for people with small cell lung cancer, and is also expected to be clinically effective against breast cancer. Although the efficacy of CDK4/6 inhibitors in patients with triple-negative breast cancer remains uncertain, their use in conjunction with other targeted therapies may improve outcomes and is therefore currently being explored. Identifying biomarkers for response or resistance to CDK4/6 inhibitor treatment may optimize the personalization of treatment strategies for this disease. Ongoing and future clinical trials and biomarker studies will shed further light on these topics, and help to realize the full potential of CDK4/6 inhibitor treatment in triple-negative breast cancer.

Quantifying cell cycle-dependent drug sensitivities in cancer using a high throughput synchronisation and screening approach

BACKGROUND

Chemotherapy and targeted agent anti-cancer efficacy is largely dependent on the proliferative state of tumours, as exemplified by agents that target DNA synthesis/replication or mitosis. As a result, cell cycle specificities of a number of cancer drugs are well known. However, they are yet to be described in a quantifiable manner.

METHODS

A scalable cell synchronisation protocol used to screen a library of 235 anti-cancer compounds exposed over six hours in G1 or S/G2 accumulated AsPC-1 cells to generate a cell cycle specificity (CCS) score.

FINDINGS

The synchronisation method was associated with reduced method-related cytotoxicity compared to nocodazole, delivering sufficient cell cycle purity and cell numbers to run high-throughput drug library screens. Compounds were identified with G1 and S/G2-associated specificities that, overall, functionally matched with a compound's target/mechanism of action. This annotation was used to describe a synergistic schedule using the CDK4/6 inhibitor, palbociclib, prior to gemcitabine/AZD6738 as well as describe the correlation between the CCS score and published synergistic/antagonistic drug schedules.

INTERPRETATION

This is the first highly quantitative description of cell cycle-dependent drug sensitivities that utilised a tractable and tolerated method with potential uses outside the present study. Drug treatments such as those shown to be G1 or S/G2 associated may benefit from scheduling considerations such as after CDK4/6 inhibitors and being first in drug sequences respectively.

FUNDING

Cancer Research UK (CRUK) Institute core grants C14303/A17197 and C9545/A29580. The Li Ka Shing Centre where this work was performed was generously funded by CK Hutchison Holdings Limited, the University of Cambridge, CRUK, The Atlantic Philanthropies and others.

Metabolic modulation by CDK4/6 inhibitor promotes chemokine-mediated recruitment of T cells into mammary tumors

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) delay progression of metastatic breast cancer. However, complete responses are uncommon and tumors eventually relapse. Here, we show that CDK4/6i can enhance efficacy of T cell-based therapies, such as adoptive T cell transfer or T cell-activating antibodies anti-OX40/anti-4-1BB, in murine breast cancer models. This effect is driven by the induction of chemokines CCL5, CXCL9, and CXCL10 in CDK4/6i-treated tumor cells facilitating recruitment of activated CD8+ T cells, but not Tregs, into the tumor. Mechanistically, chemokine induction is associated with metabolic stress that CDK4/6i treatment induces in breast cancer cells. Despite the cell cycle arrest, CDK4/6i-treated cells retain high metabolic activity driven by deregulated PI3K/mTOR pathway. This causes cell hypertrophy and increases mitochondrial content/activity associated with oxidative stress and inflammatory stress response. Our findings uncover a link between tumor metabolic vulnerabilities and anti-tumor immunity and support further development of CDK4/6i and immunotherapy combinations.

AMPK Is the Crucial Target for the CDK4/6 Inhibitors Mediated Therapeutic Responses in PANC-1 and MIA PaCa-2 Pancreatic Cancer Cell Lines

The survival rate of pancreatic ductal adenocarcinoma (PDAC) patients is short, and PDAC is a cancer type that ranks fourth in the statistics regarding death due to cancer. Mutation in the KRAS gene, which plays a role in pancreatic cancer development, activates the PI3K/AKT/mTOR signaling pathway. The activity of the AMPK as a cellular energy sensor is one of the fundamental mechanisms that can induce effective therapeutic responses against CDK4/6 inhibitors via adjusting the cellular and tumor microenvironment stress management. The phosphorylation of AMPKα at the different phosphorylation residues such as Thr172 and Ser 377 causes metabolic differentiation in the cells following CDK4/6 inhibitor treatment in accordance with an increased cell cycle arrest and senescence under the control of different cellular players. In this study, we examined the competencies of the CDK4/6 inhibitors LY2835219 and PD-0332991 on the mechanism of cell survival and death based on AMPK signaling. Both CDK4/6 inhibitors LY2835219 and PD-0332991 modulated different molecular players on the PI3K/AKT/mTOR and AMPK signaling axis in different ways to reduce cell survival in a cell type dependent manner. These drugs are potential inducers of apoptosis and senescence that can alter the therapeutic efficacy cells.

Small-Molecule Drug Discovery in Triple Negative Breast Cancer: Current Situation and Future Directions

Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, but an effective targeted therapy has not been well-established so far. Considering the lack of effective targets, where do we go next in the current TNBC drug development? A promising intervention for TNBC might lie in de novo small-molecule drugs that precisely target different molecular characteristics of TNBC. However, an ideal single-target drug discovery still faces a huge challenge. Alternatively, other new emerging strategies, such as dual-target drug, drug repurposing, and combination strategies, may provide new insight into the improvement of TNBC therapeutics. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in TNBC therapy, including single-target drugs, dual-target drugs, as well as drug repurposing and combination strategies that will together shed new light on the future directions targeting TNBC vulnerabilities with small-molecule drugs for future therapeutic purposes.

Jasmonates induce Arabidopsis bioactivities selectively inhibiting the growth of breast cancer cells through CDC6 and mTOR

Phytochemicals are used often in vitro and in vivo in cancer research. The plant hormones jasmonates (JAs) control the synthesis of specialized metabolites through complex regulatory networks. JAs possess selective cytotoxicity in mixed populations of cancer and normal cells. Here, direct incubation of leaf explants from the non-medicinal plant Arabidopsis thaliana with human breast cancer cells, selectively suppresses cancer cell growth. High-throughput LC-MS identified Arabidopsis metabolites. Protein and transcript levels of cell cycle regulators were examined in breast cancer cells. A synergistic effect by methyljasmonate (MeJA) and by compounds upregulated in the metabolome of MeJA-treated Arabidopsis leaves, on the breast cancer cell cycle, is associated with Cell Division Cycle 6 (CDC6), Cyclin-dependent kinase 2 (CDK2), Cyclins D1 and D3, indicating that key cell cycle components mediate cell viability reduction. Bioactives such as indoles, quinolines and cis-(+)-12-oxophytodienoic acid, in synergy, could act as anticancer compounds. Our work suggests a universal role for MeJA-treatment of Arabidopsis in altering the DNA replication regulator CDC6, supporting conservation, across kingdoms, of cell cycle regulation, through the crosstalk between the mechanistic target of rapamycin, mTOR and JAs. This study has important implications for the identification of metabolites with anti-cancer bioactivities in plants with no known medicinal pedigree and it will have applications in developing disease treatments.

CDK4/6 Inhibition Reprograms Mitochondrial Metabolism in BRAFV600 Melanoma via a p53 Dependent Pathway

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors are being tested in numerous clinical trials and are currently employed successfully in the clinic for the treatment of breast cancers. Understanding their mechanism of action and interaction with other therapies is vital in their clinical development. CDK4/6 regulate the cell cycle via phosphorylation and inhibition of the tumour suppressor RB, and in addition can phosphorylate many cellular proteins and modulate numerous cellular functions including cell metabolism. Metabolic reprogramming is observed in melanoma following standard-of-care BRAF/MEK inhibition and is involved in both therapeutic response and resistance. In preclinical models, CDK4/6 inhibitors overcome BRAF/MEK inhibitor resistance, leading to sustained tumour regression; however, the metabolic response to this combination has not been explored. Here, we investigate how CDK4/6 inhibition reprograms metabolism and if this alters metabolic reprogramming observed upon BRAF/MEK inhibition. Although CDK4/6 inhibition has no substantial effect on the metabolic phenotype following BRAF/MEK targeted therapy in melanoma, CDK4/6 inhibition alone significantly enhances mitochondrial metabolism. The increase in mitochondrial metabolism in melanoma cells following CDK4/6 inhibition is fuelled in part by both glutamine metabolism and fatty acid oxidation pathways and is partially dependent on p53. Collectively, our findings identify new p53-dependent metabolic vulnerabilities that may be targeted to improve response to CDK4/6 inhibitors.

How selective are clinical CDK4/6 inhibitors?

Pharmacological inhibition of cyclin-dependent kinase 4/6 (CDK4/6) has emerged as an efficient approach for treating breast cancer, and its clinical potential is expanding to other cancers. CDK4/6 inhibitors were originally believed to act by arresting proliferation in the G1 phase, but it is gradually becoming clear that the cellular response to these compounds is far more complex than this. Multiple context-dependent mechanisms of action are emerging, involving modulation of quiescence, senescence, autophagy, cellular metabolism, and enhanced tumor cell immunogenicity. These mechanisms may be driven by interactions with unexpected targets. We review cellular responses to the Food and Drug Administration-approved CDK4/6 inhibitors palbociclib, ribociclib, and abemaciclib, and summarize available knowledge of other drugs undergoing clinical trials, including data on their off-target landscapes. We emphasize the importance of comprehensively characterizing drugs' selectivity profiles to maximize their clinical efficacy and safety and to facilitate their repurposing to treat additional diseases based on their target spectrum.

Power of two: combination of therapeutic approaches involving glucose transporter (GLUT) inhibitors to combat cancer

Cancer research of the Warburg effect, a hallmark metabolic alteration in tumors, focused attention on glucose metabolism whose targeting uncovered several agents with promising anticancer effects at the preclinical level. These agents' monotherapy points to their potential as adjuvant combination therapy to existing standard chemotherapy in human trials. Accordingly, several studies on combining glucose transporter (GLUT) inhibitors with chemotherapeutic agents, such as doxorubicin, paclitaxel, and cytarabine, showed synergistic or additive anticancer effects, reduced chemo-, radio-, and immuno-resistance, and reduced toxicity due to lowering the therapeutic doses required for desired chemotherapeutic effects, as compared with monotherapy. The combinations have been specifically effective in treating cancer glycolytic phenotypes, such as pancreatic and breast cancers. Even combining GLUT inhibitors with other glycolytic inhibitors and energy restriction mimetics seems worthwhile. Though combination clinical trials are in the early phase, initial results are intriguing. The various types of GLUTs, their role in cancer progression, GLUT inhibitors, and their anticancer mechanism of action have been reviewed several times. However, utilizing GLUT inhibitors as combination therapeutics has received little attention. We consider GLUT inhibitors agents that directly affect glucose transporters by binding to them or indirectly alter glucose transport by changing the transporters' expression level. This review mainly focuses on summarizing the effects of various combinations of GLUT inhibitors with other anticancer agents and providing a perspective on the current status.

Molecular Mechanisms of the Action of Myricetin in Cancer

Natural compounds, such as paclitaxel and camptothecin, have great effects on the treatment of tumors. Such natural chemicals often achieve anti-tumor effects through a variety of mechanisms. Therefore, it is of great significance to conduct further studies on the anticancer mechanism of natural anticancer agents to lay a solid foundation for the development of new drugs. Myricetin, originally isolated from Myrica nagi, is a natural pigment of flavonoids that can inhibit the growth of cancer cells (such as liver cancer, rectal cancer, skin cancer and lung cancer, etc.). It can regulate many intracellular activities (such as anti-inflammatory and blood lipids regulation) and can even be bacteriostatic. The purpose of this paper is to outline the molecular pathways of the anticancer effects of myricetin, including the effect on cancer cell death, proliferation, angiogenesis, metastasis and cell signaling pathway.

Simultaneous Combination of the CDK4/6 Inhibitor Palbociclib With Regorafenib Induces Enhanced Anti-tumor Effects in Hepatocarcinoma Cell Lines

Advanced hepatocarcinoma (HCC) is an aggressive malignancy with poor prognosis and limited treatment options. Alterations of the cyclin D-CDK4/6-Rb pathway occur frequently in HCC, providing the rationale for its targeting at least in a molecular subset of HCC. In a panel of HCC cell lines, we investigated whether the CDK4/6 inhibitor palbociclib might improve the efficacy of regorafenib, a powerful multi-kinase inhibitor approved as second-line treatment for advanced HCC after sorafenib failure and currently under clinical investigation as first-line therapy in combination with immunotherapy. In Rb-proficient cells, the simultaneous drug combination, but not the sequential schedules, inhibited cell proliferation, either in short or in long-term experiments, and induced cell death more strongly than individual treatments. Moreover, the combination significantly reduced spheroid cell growth and inhibited cell migration/invasion. The superior efficacy of palbociclib plus regorafenib emerged also under hypoxia and was associated with a significant down-regulation of CDK4/6-Rb-myc and mTORC1/p70S6K signaling. Moreover, regorafenib suppressed palbociclib-induced expression of cyclin D1 contributing to the cytotoxic effects of the combination. Besides these inhibitory effects on cell viability/proliferation, palbociclib and regorafenib reduced glucose uptake, although this effect was dependent on the cell model and on the oxygen availability (normoxia or hypoxia). Palbociclib and regorafenib combination impaired glucose uptake and utilization, down-regulating basal and hypoxia-induced expression of HIF-1α, HIF-2α, GLUT-1, and MCT4 proteins as well as the activity/expression of glycolytic enzymes (HK2, PFKP, aldolase A, PKM2). In addition, regorafenib alone reduced mitochondrial respiration. The combined treatment impaired glucose metabolism and respiration without enhancing the effects of the single agents. Our findings provide pre-clinical evidence for the effectiveness of palbociclib and regorafenib combination in HCC cell models.

Hypomorphic mTOR Downregulates CDK6 and Delays Thymic Pre-T LBL Tumorigenesis

PI3K/AKT/mTOR pathway hyperactivation is frequent in T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LBL). To model inhibition of mTOR, pre-T-cell lymphoblastic leukemia/lymphoma (pre-T LBL) tumor development was monitored in mice with T lymphocyte-specific, constitutively active AKT (Lck-MyrAkt2) that were either crossed to mTOR knockdown (KD) mice or treated with the mTOR inhibitor everolimus. Lck-MyrAkt2;mTOR KD mice lived significantly longer than Lck-MyrAkt2;mTOR wild-type (WT) mice, although both groups ultimately developed thymic pre-T LBL. An increase in survival was also observed when Lck-MyrAkt2;mTOR WT mice were treated for 8 weeks with everolimus. The transcriptional profiles of WT and KD thymic lymphomas were compared, and Ingenuity Pathway Upstream Regulator Analysis of differentially expressed genes in tumors from mTOR WT versus KD mice identified let-7 and miR-21 as potential regulatory genes. mTOR KD mice had higher levels of let-7a and miR-21 than mTOR WT mice, and rapamycin induced their expression in mTOR WT cells. CDK6 was one of the most downregulated targets of both let-7 and miR21 in mTOR KD tumors. CDK6 overexpression and decreased expression of let-7 in mTOR KD cells rescued a G₁ arrest phenotype. Combined mTOR (rapamycin) and CDK4/6 (palbociclib) inhibition decreased tumor size and proliferation in tumor flank transplants, increased survival in an intravenous transplant model of disseminated leukemia compared with single agent treatment, and cooperatively decreased cell viability in human T-ALL/LBL cell lines. Thus, mTOR KD mice provide a model to explore drug combinations synergizing with mTOR inhibitors and can be used to identify downstream targets of inhibition.

Dual Inhibition of CDK4/6 and PI3K/AKT/mTOR Signaling Impairs Energy Metabolism in MPM Cancer Cells

Background: Malignant pleural mesothelioma (MPM) is an aggressive malignancy associated to asbestos exposure. One of the most frequent genetic alteration in MPM patients is CDKN2A/ARF loss, leading to aberrant activation of the Rb pathway. In MPM cells, we previously demonstrated the therapeutic efficacy of targeting this signaling with the CDK4/6 inhibitor palbociclib in combination with PI3K/mTOR inhibitors. Here, we investigated whether such combination may have an impact on cell energy metabolism. Methods: The study was performed in MPM cells of different histotypes; metabolic analyses were conducted by measuring GLUT-1 expression and glucose uptake/consumption, and by SeaHorse technologies. Results: MPM cell models differed for their ability to adapt to metabolic stress conditions, such as glucose starvation and hypoxia. Independently of these differences, combined treatments with palbociclib and PI3K/mTOR inhibitors inhibited cell proliferation more efficaciously than single agents. The drugs alone reduced glucose uptake/consumption as well as glycolysis, and their combination further enhanced these effects under both normoxic and hypoxic conditions. Moreover, the drug combinations significantly impaired mitochondrial respiration as compared with individual treatments. These metabolic effects were mediated by the concomitant inhibition of Rb/E2F/c-myc and PI3K/AKT/mTOR signaling. Conclusions: Dual blockade of glycolysis and respiration contributes to the anti-tumor efficacy of palbociclib-PI3K/mTOR inhibitors combination.

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.

Retinoblastoma protein expression and its predictors in triple-negative breast cancer

Retinoblastoma protein (Rb) is a product of the RB tumor suppressor gene. Its expression is highly prevalent in luminal breast cancers and is critical to the success of cyclin-dependent kinase (CDK) 4/6 inhibitor therapy. Expression of Rb in triple-negative breast cancer (TNBC), tumors generally associated with basal biology, is not well known. However, heterogeneity among TNBC and presence of subtypes with luminal features are well described. The purpose of this study was to determine prevalence and predictors of Rb protein expression in BRCA1-associated and sporadic TNBCs. We studied 180 TNBC patients (70 BRCA1-associated and 110 sporadic). The clinical and pathologic features of these cases were previously assessed and reported. For this study, immunohistochemical stains for Rb were performed on tissue microarray sections. Details of treatment and outcome were abstracted from medical records. Fifty-one percent of TNBC were Rb positive (≥10% nuclei staining), and 85% of these cases had ≥50% nuclei staining. Rb expression was significantly associated with sporadic TNBC (71.4% vs 49.4%; p < 0.001), androgen receptor (AR) expression (16.5% vs 3.4%; p = 0.007), histologic grade 1 or 2 (9.9% vs 2.2%; p = 0.04), and first recurrence in bone (8.8% vs 1.1%; p = 0.03). Expression of p53 was not associated with Rb expression. Expression of Rb in TNBC was significantly associated with sporadic TNBC, AR expression, lower histologic grade, and metastasis to bone. These observations characterize a TNBC subtype with features suggestive of luminal-like biology and the potential to benefit from CDK 4/6 inhibition.

The application and prospect of CDK4/6 inhibitors in malignant solid tumors

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, which block the transition from the G1 to S phase of the cell cycle by interfering with Rb phosphorylation and E2F release, have shown potent antitumor activity and manageable toxicity in HR+/HER2− breast cancer patients. Some clinical trials involving CDK4/6 inhibitors in other tumors have achieved preliminary impressive efficacy. Whether CDK4/6 inhibitors possess great potential as broad-spectrum antitumor drugs and how to maximize their clinical benefits remain uncertain. TCGA database analysis showed that CDK4/6 genes and related genes are widely expressed among various tumors, and high or moderate expression of CDK4/6 genes commonly indicates poor survival. CDK4/6 gene expression is significantly higher in COAD, ESCA, STAD, LIHC, and HNSC, suggesting that CDK4/6 inhibitors could be more efficacious in those tumors. Moreover, network analysis with the STRING database demonstrated that CDK4/6-related proteins were co-expressed or co-occurred with the classical tumor signaling pathways, such as the cell cycle pathway, RAS pathway, PI3K pathway, Myc pathway, and p53 pathway. The extensive antitumor effects of CDK4/6 inhibitors may be achieved by synergizing or antagonizing with other signaling molecule inhibitors, and combination therapy might be the most effective treatment strategy. This article analyzed the feasibility of expanding the application of CDK4/6 inhibitors at the genetic level and further summarized the associated clinical/preclinical studies to collect supportive evidence. This is the first study that presents a theoretical foundation for CDK4/6 inhibitor precision therapy via combined analysis of comprehensive gene information and clinical research results.