Palbociclib: A Novel Cyclin-Dependent Kinase Inhibitor for Hormone Receptor-Positive Advanced Breast Cancer

Baseline and early 18F-FDG PET/CT evaluations as predictors of progression-free survival in metastatic breast cancer patients treated with targeted anti-CDK therapy

BACKGROUND

Exploring the value of baseline and early 18F-FDG PET/CT evaluations in prediction PFS in ER+/HER2- metastatic breast cancer patients treated with a cyclin-dependent kinase inhibitor in combination with an endocrine therapy.

METHODS

Sixty-six consecutive breast cancer patients who underwent a pre-therapeutic 18F-FDG PET/CT and a second PET/CT within the first 6 months of treatment were retrospectively included. Metabolic tumour volume (MTV) and total lesion glycolysis (TLG) and Dmax, which represents tumour dissemination and is defined as the distance between the two most distant lesions, were computed. The variation in these parameters between baseline and early evaluation PET as well as therapeutic evaluation using PERCIST were assessed as prognosticators of PFS at 18 months.

RESULTS

The median follow-up was equal to 22.5 months. Thirty progressions occurred (45.4%). The average time to event was 17.8 ± 10.4 months. At baseline, Dmax was the only predictive metabolic parameter. Patients with a baseline Dmax ≤ 18.10 cm had a significantly better 18 m-PFS survival than the others: 69.2% (7.7%) versus 36.7% (8.8%), p = 0.017. There was no association between PERCIST evaluation and 18 m-PFS status (p = 0.149) and there was no difference in 18 m-PFS status between patients classified as complete, partial metabolic responders or having stable metabolic disease.

CONCLUSION

Disease spread at baseline PET, as assessed by Dmax, is predictive of an event occurring within 18 months. In the absence of early metabolic progression, which occurs in 15% of patients, treatment should be continued regardless of the quality of the initial response to treatment.

The G Protein Estrogen Receptor (GPER) is involved in the resistance to the CDK4/6 inhibitor palbociclib in breast cancer

BACKGROUND

The cyclin D1-cyclin dependent kinases (CDK)4/6 inhibitor palbociclib in combination with endocrine therapy shows remarkable efficacy in the management of estrogen receptor (ER)-positive and HER2-negative advanced breast cancer (BC). Nevertheless, resistance to palbociclib frequently arises, highlighting the need to identify new targets toward more comprehensive therapeutic strategies in BC patients.

METHODS

BC cell lines resistant to palbociclib were generated and used as a model system. Gene silencing techniques and overexpression experiments, real-time PCR, immunoblotting and chromatin immunoprecipitation studies as well as cell viability, colony and 3D spheroid formation assays served to evaluate the involvement of the G protein-coupled estrogen receptor (GPER) in the resistance to palbociclib in BC cells. Molecular docking simulations were also performed to investigate the potential interaction of palbociclib with GPER. Furthermore, BC cells co-cultured with cancer-associated fibroblasts (CAFs) isolated from mammary carcinoma, were used to investigate whether GPER signaling may contribute to functional cell interactions within the tumor microenvironment toward palbociclib resistance. Finally, by bioinformatics analyses and k-means clustering on clinical and expression data of large cohorts of BC patients, the clinical significance of novel mediators of palbociclib resistance was explored.

RESULTS

Dissecting the molecular events that characterize ER-positive BC cells resistant to palbociclib, the down-regulation of ERα along with the up-regulation of GPER were found. To evaluate the molecular events involved in the up-regulation of GPER, we determined that the epidermal growth factor receptor (EGFR) interacts with the promoter region of GPER and stimulates its expression toward BC cells resistance to palbociclib treatment. Adding further cues to these data, we ascertained that palbociclib does induce pro-inflammatory transcriptional events via GPER signaling in CAFs. Of note, by performing co-culture assays we demonstrated that GPER contributes to the reduced sensitivity to palbociclib also facilitating the functional interaction between BC cells and main components of the tumor microenvironment named CAFs.

CONCLUSIONS

Overall, our results provide novel insights on the molecular events through which GPER may contribute to palbociclib resistance in BC cells. Additional investigations are warranted in order to assess whether targeting the GPER-mediated interactions between BC cells and CAFs may be useful in more comprehensive therapeutic approaches of BC resistant to palbociclib.

Cell cycle machinery in oncology: A comprehensive review of therapeutic targets

The cell cycle is tightly regulated to ensure controlled cell proliferation. Dysregulation of the cell cycle machinery is a hallmark of cancer that leads to unchecked growth. This review comprehensively analyzes key molecular regulators of the cell cycle and how they contribute to carcinogenesis when mutated or overexpressed. It focuses on cyclins, cyclin-dependent kinases (CDKs), CDK inhibitors, checkpoint kinases, and mitotic regulators as therapeutic targets. Promising strategies include CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib for breast cancer treatment. Other possible targets include the anaphase-promoting complex/cyclosome (APC/C), Skp2, p21, and aurora kinase inhibitors. However, challenges with resistance have limited clinical successes so far. Future efforts should focus on combinatorial therapies, next-generation inhibitors, and biomarkers for patient selection. Targeting the cell cycle holds promise but further optimization is necessary to fully exploit it as an anti-cancer strategy across diverse malignancies.

Catalysts of Healing: A Symphony of Synthesis and Clinical Artistry in Small-Molecule Agents for Breast Cancer Alleviation

Breast cancer, characterized by its molecular intricacy, has witnessed a surge in targeted therapeutics owing to the rise of small-molecule drugs. These entities, derived from cutting-edge synthetic routes, often encompassing multistage reactions and chiral synthesis, target a spectrum of oncogenic pathways. Their mechanisms of action range from modulating hormone receptor signaling and inhibiting kinase activity, to impeding DNA damage repair mechanisms. Clinical applications of these drugs have resulted in enhanced patient survival rates, reduction in disease recurrence, and improved overall therapeutic indices. Notably, certain molecules have showcased efficacy in drug-resistant breast cancer phenotypes, highlighting their potential in addressing treatment challenges. The evolution and approval of small-molecule drugs have ushered in a new era for breast cancer therapeutics. Their tailored synthetic pathways and defined mechanisms of action have augmented the precision and efficacy of treatment regimens, paving the way for improved patient outcomes in the face of this pervasive malignancy. The present review embarks on a detailed exploration of small-molecule drugs that have secured regulatory approval for breast cancer treatment, emphasizing their clinical applications, synthetic pathways, and distinct mechanisms of action.

Palbociclib-Induced Cellular Senescence Is Modulated by the mTOR Complex 1 and Autophagy

Despite not dividing, senescent cells acquire the ability to synthesize and secrete a plethora of bioactive molecules, a feature known as the senescence-associated secretory phenotype (SASP). In addition, senescent cells often upregulate autophagy, a catalytic process that improves cell viability in stress-challenged cells. Notably, this "senescence-related autophagy" can provide free amino acids for the activation of mTORC1 and the synthesis of SASP components. However, little is known about the functional status of mTORC1 in models of senescence induced by CDK4/6 inhibitors (e.g., Palbociclib), or the effects that the inhibition of mTORC1 or the combined inhibition of mTORC1 and autophagy have on senescence and the SASP. Herein, we examined the effects of mTORC1 inhibition, with or without concomitant autophagy inhibition, on Palbociclib-driven senescent AGS and MCF-7 cells. We also assessed the pro-tumorigenic effects of conditioned media from Palbociclib-driven senescent cells with the inhibition of mTORC1, or with the combined inhibition of mTORC1 and autophagy. We found that Palbociclib-driven senescent cells display a partially reduced activity of mTORC1 accompanied by increased levels of autophagy. Interestingly, further mTORC1 inhibition exacerbated the senescent phenotype, a phenomenon that was reversed upon autophagy inhibition. Finally, the SASP varied upon inhibiting mTORC1, or upon the combined inhibition of mTORC1 and autophagy, generating diverse responses in cell proliferation, invasion, and migration of non-senescent tumorigenic cells. Overall, variations in the SASP of Palbociclib-driven senescent cells with the concomitant inhibition of mTORC1 seem to depend on autophagy.

The Role of Thrombomodulin in Estrogen-Receptor-Positive Breast Cancer Progression, Metastasis, and Curcumin Sensitivity

Estrogen and estrogen receptors (ER) play a key role in breast cancer progression, which can be treated with endocrine therapy. Nevertheless, resistance to endocrine therapies is developed over time. The tumor expression of thrombomodulin (TM) is correlated with favorable prognosis in several types of cancer. However, this correlation has not yet been confirmed in ER-positive (ER⁺) breast cancer. This study aims to evaluate the role of TM in ER⁺ breast cancer. Firstly, we found that lower TM expression correlates to poor overall survival (OS) and relapse-free survival (RFS) rates in ER⁺ breast cancer patients through Kaplan-Meier survival analysis (p < 0.05). Silencing TM in MCF7 cells (TM-KD) increased cell proliferation, migration, and invasion ability. Additionally, TM-KD MCF7 cells showed higher sensitivity (IC₅₀ 15 μM) to the anti-cancer agent curcumin than the scrambled control cells. Conversely, overexpression of TM (TM-over) in T47D cells leads to decreased cell proliferation, migration, and invasion ability. Furthermore, TM-over T47D cells showed more resistance (IC₅₀ > 40 μM) to the curcumin treatment. The PI staining, DAPI, and tunnel assay also confirmed that the curcumin-induced apoptosis in TM-KD MCF7 cells was higher (90.34%) than in the scrambled control cells (48.54%). Finally, the expressions of drug-resistant genes (ABCC1, LRP1, MRP5, and MDR1) were determined by qPCR. We found that the relative mRNA expression levels of ABCC1, LRP1, and MDR1 genes after curcumin treatment were higher in scrambled control cells than in TM-KD cells. In conclusion, our results demonstrated that TM plays a suppressive role in the progression and metastasis of ER⁺ breast cancer, and it regulates curcumin sensitivity by interfering with ABCC1, LRP1, and MDR1 gene expression.

Novel markers in breast pathology

Breast pathology is an ever-expanding database of information which includes markers, or biomarkers, that detect or help treat the disease as prognostic or predictive information. This review focuses on these aspects of biomarkers which are grounded in immunohistochemistry, liquid biopsies and next-generation sequencing.

Development of a SPE-LC-MS Method for the Quantitation of Palbociclib and Abemaciclib in Human Plasma

Palbociclib and abemaciclib are two cyclin-dependent kinases 4 and 6 used for breast cancer treatment. Levels of these medicines present a significant interindividual variability, so monitoring those concentrations might be necessary in therapy. Most of the methods presented so far in the literature use simple protein precipitation of plasma proteins as sample preparation method followed by direct injection of the supernatant into the LC instrument, preceded or not by a simple filtration step. Within that approach, the probability of injecting proteins in the chromatographic system is increased. With the purpose of obtaining a cleaner extract of the drugs, we developed and validated a simple and accurate LC-MS method for determining palbociclib and abemaciclib in human plasma. Solid phase extraction (SPE) using Oasis PRiME HLB^® cartridges was used for plasma sample preparation. The method provided clean extracts with a recovery extraction higher than 85% for both compounds. Separation was achieved by high-performance liquid chromatography (HPLC), using a C18 (4.6 × 50 mm) column, with a gradient elution of ammonium acetate/acetic acid-acetonitrile as the mobile phase. Detection was performed by mass spectrometry (MS) in single ion recording (SIR) mode. Intra-day and inter-day precision data for both analytes were 3.8-7.2% and 3.6-7.4%, respectively. Calibration curves were both linear between 2 and 400 ng/mL with a correlation coefficient higher than 0.998. The LC-MS method can be used to quantify the drugs in human plasma in routine analysis. The method proved to be useful in determining real plasma levels in patients involved in cancer therapy. Drug concentrations were determined in a 10 min run-time, including re-equilibration of the column.

The Role of CDK Pathway Dysregulation and Its Therapeutic Potential in Soft Tissue Sarcoma

Soft tissue sarcomas (STSs) are tumors that are challenging to treat due to their pathologic and molecular heterogeneity and their tumor biology that is not yet fully understood. Recent research indicates that dysregulation of cyclin-dependent kinase (CDK) signaling pathways can be a strong driver of sarcogenesis. CDKs are enzyme forms that play a crucial role in cell-cycle control and transcription. They belong to the protein kinases group and to the serine/threonine kinases subgroup. Recently identified CDK/cyclin complexes and established CDK/cyclin complexes that regulate the cell cycle are involved in the regulation of gene expression through phosphorylation of critical components of transcription and pre-mRNA processing mechanisms. The current and continually growing body of data shows that CDKs play a decisive role in tumor development and are involved in the proliferation and growth of sarcoma cells. Since the abnormal expression or activation of large numbers of CDKs is considered to be characteristic of cancer development and progression, dysregulation of the CDK signaling pathways occurs in many subtypes of STSs. This review discusses how reversal and regulation can be achieved with new therapeutics and summarizes the current evidence from studies regarding CDK modulation for STS treatment.

Systemic Administration of a Brain Permeable Cdk5 Inhibitor Alters Neurobehavior

Cyclin-dependent kinase 5 (Cdk5) is a crucial regulator of neuronal signal transduction. Cdk5 activity is implicated in various neuropsychiatric and neurodegenerative conditions such as stress, anxiety, depression, addiction, Alzheimer's disease, and Parkinson's disease. While constitutive Cdk5 knockout is perinatally lethal, conditional knockout mice display resilience to stress-induction, enhanced cognition, neuroprotection from stroke and head trauma, and ameliorated neurodegeneration. Thus, Cdk5 represents a prime target for treatment in a spectrum of neurological and neuropsychiatric conditions. While intracranial infusions or treatment of acutely dissected brain tissue with compounds that inhibit Cdk5 have allowed the study of kinase function and corroborated conditional knockout findings, potent brain-penetrant systemically deliverable Cdk5 inhibitors are extremely limited, and no Cdk5 inhibitor has been approved to treat any neuropsychiatric or degenerative diseases to date. Here, we screened aminopyrazole-based analogs as potential Cdk5 inhibitors and identified a novel analog, 25-106, as a uniquely brain-penetrant anti-Cdk5 drug. We characterize the pharmacokinetic and dynamic responses of 25-106 in mice and functionally validate the effects of Cdk5 inhibition on open field and tail-suspension behaviors. Altogether, 25-106 represents a promising preclinical Cdk5 inhibitor that can be systemically administered with significant potential as a neurological/neuropsychiatric therapeutic.

Pharmacokinetic/Pharmacodynamic Model of Neutropenia in Real-Life Palbociclib-Treated Patients

Palbociclib is an oral CDK4/6 inhibitor indicated in HR+/HER2- advanced or metastatic breast cancer in combination with hormonotherapy. Its main toxicity is neutropenia. The aim of our study was to describe the kinetics of circulating neutrophils from real-life palbociclib-treated patients. A population pharmacokinetic (popPK) model was first constructed to describe palbociclib pharmacokinetic (PK). Individual PK parameters obtained were then used in the pharmacokinetic/pharmacodynamic (PK/PD) model to depict the relation between palbociclib concentrations and absolute neutrophil counts (ANC). The models were built with a population of 143 patients. Palbociclib samples were routinely collected during therapeutic drug monitoring, whereas ANC were retrospectively retrieved from the patient files. The optimal popPK model was a mono-compartmental model with a first-order absorption constant of 0.187 h^-1 and an apparent clearance Cl/F of 57.09 L (32.8% of inter individuality variability (IIV)). The apparent volume of distribution (1580 L) and the lag-time (T_lag: 0.658 h) were fixed to values from the literature. An increase in creatinine clearance and a decrease in alkaline phosphatase led to an increase in palbociclib Cl/F. To describe ANC kinetics during treatment, Friberg's PK/PD model, with linear drug effect, was used. Parameters estimated were Base (2.92 G/L; 29.6% IIV), Slope (0.0011 L/µg; 28.8% IIV), Mean Transit Time (MTT; 5.29 days; 17.9% IIV) and γ (0.102). The only significant covariate was age on the initial ANC (Base), with lower ANC in younger patients. PK/PD model-based simulations show that the higher the estimated C_ressSS (trough concentration at steady state), the higher the risk of developing neutropenia. In order to present a risk lower than 20% to developing a grade 4 neutropenia, the patient should show an estimated C_ressSS lower than 100 µg/L.

Oral self-management of palbociclib (Ibrance®) using mobile technology protocol

AIM

This study will test the feasibility and effectiveness of mobile technology intervention on the patients' self-management of oral anticancer medication. Secondary objectives include acceptability, the usefulness of text messages, and satisfaction by participants and nurses.

METHODS

This prospective two-arm study will recruit patients (N = 220) with metastatic breast cancer and initiating treatment with palbociclib (Ibrance ®). Allowing for attrition, patients will be randomized into the control (N = 100) or intervention (N = 100) group. Unidirectional text message reminders will be sent during the treatment cycle through a secure web application using the patient's smartphone. Self-reported survey responses will be collected at three time points; at consent, end of treatment cycles, and the follow-up clinic visit and include a demographic questionnaire, the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire, Post study questionnaire and the R-15 Patient Satisfaction Questionnaire. Nurses providing care for study patients will complete the Adaptation of Stamps Nurse Workload questionnaire. Data will be analysed an intent-to-treat analysis comparing the two arms. Study approval was obtained in December 2019 and funded in January 2020.

DISCUSSION

Smartphones are globally available and have text messaging capability which is increasingly being used as an intervention in healthcare studies. This study will test a low-cost, nurse-led intervention that enhances the patient's experience with oral anti-cancer medications, improves access to care, reduces costs, and improves the satisfaction of nurses caring for oncology patients.

IMPACT

Despite the ease of administering oral anti-cancer medications, oncology patients maynot take them as prescribed and consequently, these factors affect patient outcomes and disease control. Given the importance of taking oral anti-cancer medications and the difficulties patients experience in achieving it, the effective use of mobile technology interventions can actively engage patients in their care and improve medication self-management of anticancer treatment regimens.

An available strategy based on accurate mass by ultra high performance liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry technology to characterization of metabolic profile of palbociclib in rat urine, feces and bile

Palbociclib (named PD 0332991) is a novel highly selective cyclin-dependent kinase 4 and 6 (CDK 4/6) inhibitor, which has been approved by the Food and Drug Administration (FDA) for the treatment of hormone-receptor-positive advanced breast cancer. This present study developed a comprehensive strategy to investigate the metabolic profile of palbociclib in rat urine, feces and bile samples based on an ultra high performance liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry (UHPLC-FT-ICR MS). A total of 29 metabolites, including 18 phase I metabolites and 11 phase II metabolites, were detected and identified. The metabolic pathways included hydroxylation, oxidation, dehydrogenation, N-dealkylation, carbonylation, oxidative deamination, acetylation, glucuronidation, sulphate conjugation as well as the crossover of multiple metabolic pathways in vivo, and 16 of these metabolites were proposed for the first time. This study showed an insight into the metabolism of palbociclib in vivo, which may provide relevant chemical information for subsequent studies in the future.

Response evaluation with 18F-FDG PET/CT in metastatic breast cancer patients treated with Palbociclib: first experience in clinical practice

OBJECTIVE

Palbociclib is a cyclin-dependent kinase 4/6 inhibitor recently approved for treatment in advanced or metastatic breast cancer (BC) patients. The use of ¹⁸F-FDG PET/CT for chemo/endocrine therapy response assessment in BC patients is well reported in the literature, but no studies have evaluated its role for assessing Palbociclib efficacy in clinical practice. Our study aimed to evaluate the potential role of ¹⁸F-FDG PET/CT in this setting.

METHODS

In 12 metastatic BC patients (mean age = 62 ± 10 years) treated with Palbociclib plus endocrine therapy and who underwent a baseline and post-therapy ¹⁸F-FDG PET/CT, we retrospectively compared the Metabolic Response Evaluation (MRE, based on PET/CT) to the Standard Response Evaluation (SRE, based on clinico-laboratory and morphological data); we also assessed the influence of additional PET/CT information on the patients' management.

RESULTS

Compared to SRE, MRE increased the proportion of patients classified with progressive disease from 25 to 50% and differed from SRE in 8/12 patients: 3/8 shifted from stable disease or undetermined response to metabolic progression (more unfavorable category), 4/8 from stable disease to partial or complete metabolic response, and 1/8 from partial response to complete metabolic response (more favorable category). Additional PET/CT information led to a change in patients' management in 3/12 (25%) patients.

CONCLUSION

In BC patients treated with Palbociclib, additional ¹⁸F-FDG PET/CT information seems clinically useful, with respect to personalized management, to early intercept patients who should discontinue Palbociclib because of progressive disease and to select patients requiring a strict monitoring of additional metabolic findings. Further studies are needed to confirm these preliminary results.

A paradigm shift for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer: a review of CDK inhibitors

In the last 3 years, a novel class of targeted therapy has been approved for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer. There are currently three approved agents, which are oral cyclin-dependent kinase 4/6 (CDK4/6) inhibitors. All of the approved drugs exhibit progression-free survival benefit when compared to standard of care and generally have less adverse events compared to traditional chemotherapeutic options. The treatment of HR+/HER2- advanced breast cancer is a continuously evolving landscape, and the addition of CDK4/6 inhibitors is the newest mechanism for treatment. In this review, we summarize all available data, highlight the unanswered questions, and discuss pharmacological differences between each CDK4/6 inhibitor.

Synthesis of aminopyrazole analogs and their evaluation as CDK inhibitors for cancer therapy

We synthesized a library of aminopyrazole analogs to systematically explore the hydrophobic pocket adjacent to the hinge region and the solvent exposed region of cyclin dependent kinases. Structure-activity relationship studies identified an optimal substitution for the hydrophobic pocket and analog 24 as a potent and selective CDK2/5 inhibitor.

A metabolite of nobiletin, 4'-demethylnobiletin and atorvastatin synergistically inhibits human colon cancer cell growth by inducing G0/G1 cell cycle arrest and apoptosis

Combining different chemopreventive agents is a promising strategy to reduce cancer incidence and mortality due to potential synergistic interactions between these agents. Previously, we demonstrated that oral administration of nobiletin (NBT, a citrus flavonoid) at 0.05% (w/w, in diet) together with atorvastatin (ATST, a lipid-lowering drug) at 0.02% (w/w, in diet) produced much stronger inhibition against colon carcinogenesis in rats in comparison with that produced by NBT (at 0.1% w/w in diet) or ATST (at 0.04% w/w in diet) alone at higher doses. To further elucidate the mechanism of this promising synergy between NBT and ATST, herein, we measured the levels of NBT, its major metabolites and ATST in the colonic tissue of rats fed NBT (0.05% w/w, in diet) + ATST (0.02% w/w, in diet), and determined the mode of interaction between the major NBT metabolite and ATST in inhibiting colon cancer cell growth. HPLC-MS analysis showed that 4'-demethylnobiletin (4DN) is the most abundant metabolite of NBT with a level about 5-fold as high as that of NBT in the colonic tissue, which indicated the potential significance of 4DN in mediating the biological effects of NBT in the colon. We found that co-treatments of 4DN/ATST at 2 : 1 concentration ratio produced much stronger growth inhibitory effects on human colon cancer HT-29 cells than 4DN or ATST alone, and isobologram analysis confirmed that this enhanced inhibitory effect by the 4DN/ATST combination was highly synergistic. The co-treatment of 4DN/ATST led to G0/G1 cell cycle arrest and induced extensive apoptosis in HT-29 cells. Furthermore, the 4DN/ATST co-treatment profoundly modulated key signaling proteins related to the regulation of the cell cycle and apoptosis. Our results demonstrated a strong synergy produced by the 4DN/ATST co-treatment in inhibiting colon cancer cell growth, which provided a novel mechanism by which NBT/ATST in combination synergistically inhibit colon carcinogenesis.

In vitro and in vivo metabolic investigation of the Palbociclib by UHPLC-Q-TOF/MS/MS and in silico toxicity studies of its metabolites

Palbociclib (PAB) is a CDK4/6 inhibitor and U. S Food and Drug Administration (FDA) granted regular approval for the treatment of hormone receptor (HR) positive, metastatic breast cancer in combination with an aromatase inhibitor in postmenopausal women. Metabolite identification is a crucial aspect during drug discovery and development as the drug metabolites may be pharmacologically active or possess toxicological activity. As there are no reports on the metabolism studies of the PAB, the present study focused on investigation of the in vitro and in vivo metabolic fate of the drug. The in vitro metabolism studies were carried out by using microsomes (HLM and RLM) and S9 fractions (Human and rat). The in vivo metabolism of the drug was studied by administration of the PAB orally to the Sprague-Dawley rats followed by analysis of urine, faeces and plasma samples. The sample preparation includes simple protein precipitation (PP) followed by solid phase extraction (SPE). The extracted samples were analyzed by ultrahigh-performance liquid chromatography-quadruple time-of-flight tandem mass spectrometry (UHPLC/Q-TOF/MS/MS). A total of 14 metabolites were detected in in vivo matrices. The PAB was metabolized via hydroxylation, oxidation, sulphation, N-dealkylation, acetylation and carbonylation pathways. A few of the metabolites were also detected in in vitro samples. Metabolite identification and characterization were performed by using UHPLC/Q-TOF/MS/MS in combination with HRMS data. To identify the toxicity potential of these metabolites, in silico toxicity assessment was carried out using TOPKAT and DEREK softwares.

Breakthroughs in modern cancer therapy and elusive cardiotoxicity: Critical research-practice gaps, challenges, and insights

To date, five cancer treatment modalities have been defined. The three traditional modalities of cancer treatment are surgery, radiotherapy, and conventional chemotherapy, and the two modern modalities include molecularly targeted therapy (the fourth modality) and immunotherapy (the fifth modality). The cardiotoxicity associated with conventional chemotherapy and radiotherapy is well known. Similar adverse cardiac events are resurging with the fourth modality. Aside from the conventional and newer targeted agents, even the most newly developed, immune-based therapeutic modalities of anticancer treatment (the fifth modality), e.g., immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cell therapy, have unfortunately led to potentially lethal cardiotoxicity in patients. Cardiac complications represent unresolved and potentially life-threatening conditions in cancer survivors, while effective clinical management remains quite challenging. As a consequence, morbidity and mortality related to cardiac complications now threaten to offset some favorable benefits of modern cancer treatments in cancer-related survival, regardless of the oncologic prognosis. This review focuses on identifying critical research-practice gaps, addressing real-world challenges and pinpointing real-time insights in general terms under the context of clinical cardiotoxicity induced by the fourth and fifth modalities of cancer treatment. The information ranges from basic science to clinical management in the field of cardio-oncology and crosses the interface between oncology and onco-pharmacology. The complexity of the ongoing clinical problem is addressed at different levels. A better understanding of these research-practice gaps may advance research initiatives on the development of mechanism-based diagnoses and treatments for the effective clinical management of cardiotoxicity.

CDK4/6 inhibitors in HER2-positive breast cancer

Notwithstanding the continuous progress made in cancer treatment in the last 20 years, and the availability of new targeted therapies, metastatic Breast Cancer (BC) is still incurable. Targeting the cell cycle machinery has emerged as an attractive strategy to tackle cancer progression, showing very promising results in the preclinical and clinical settings. The first selective inhibitors of CDK4/6 received breakthrough status and FDA approval in combination with letrozole (February 2015) and fulvestrant (February 2016) as first-line therapy in ER-positive advanced and metastatic BC. Considering the success of this family of compounds in hormone-positive BC, new possible applications are being investigated in other molecular subtypes. This review summarizes the latest findings on the use of CDK4/6 inhibitors in HER2 positive BC.

Expression of the lncRNA Maternally Expressed Gene 3 (MEG3) Contributes to the Control of Lung Cancer Cell Proliferation by the Rb Pathway

Maternally expressed gene 3 (MEG3, mouse homolog Gtl2) encodes a long noncoding RNA (lncRNA) that is expressed in many normal tissues, but is suppressed in various cancer cell lines and tumors, suggesting it plays a functional role as a tumor suppressor. Hypermethylation has been shown to contribute to this loss of expression. We now demonstrate that MEG3 expression is regulated by the retinoblastoma protein (Rb) pathway and correlates with a change in cell proliferation. Microarray analysis of mouse embryonic fibroblasts (MEFs) isolated from mice with genetic deletion of all three Rb family members (TKO) revealed a significant silencing of Gtl2/MEG3 expression compared to WT MEFs, and re-expression of Gtl2/MEG3 caused decrease in cell proliferation and increased apoptosis. MEG3 levels also were suppressed in A549 lung cancer cells compared with normal human bronchial epithelial (NHBE) cells, and, similar to the TKO cells, re-constitution of MEG3 led to a decrease in cell proliferation and elevated apoptosis. Activation of pRb by treatment of A549 and SK-MES-1 cells with palbociclib, a CDK4/6 inhibitor, increased the expression of MEG3 in a dose-dependent manner, while knockdown of pRb/p107 attenuated this effect. In addition, expression of phosphorylation-deficient mutant of pRb increased MEG3 levels in both lung cancer cell types. Treatment of these cells with palbociclib also decreased the expression of pRb-regulated DNA methyltransferase 1 (DNMT1), while conversely, knockdown of DNMT1 resulted in increased expression of MEG3. As gene methylation has been suggested for MEG3 regulation, we found that palbociclib resulted in decreased methylation of the MEG3 locus similar to that observed with 5-aza-deoxycytidine. Anti-sense oligonucleotide silencing of drug-induced MEG3 expression in A549 and SK-MES-1 cells partially rescued the palbociclib-mediated decrease in cell proliferation, while analysis of the TCGA database revealed decreased MEG3 expression in human lung tumors harboring a disrupted RB pathway. Together, these data suggest that disruption of the pRb-DNMT1 pathway leads to a decrease in MEG3 expression, thereby contributing to the pro-proliferative state of certain cancer cells.

The emerging roles and therapeutic potential of cyclin-dependent kinase 11 (CDK11) in human cancer

Overexpression and/or hyperactivation of cyclin-dependent kinases (CDKs) are common features of most cancer types. CDKs have been shown to play important roles in tumor cell proliferation and growth by controlling cell cycle, transcription, and RNA splicing. CDK4/6 inhibitor palbociclib has been recently approved by the FDA for the treatment of breast cancer. CDK11 is a serine/threonine protein kinase in the CDK family and recent studies have shown that CDK11 also plays critical roles in cancer cell growth and proliferation. A variety of genetic and epigenetic events may cause universal overexpression of CDK11 in human cancers. Inhibition of CDK11 has been shown to lead to cancer cell death and apoptosis. Significant evidence has suggested that CDK11 may be a novel and promising therapeutic target for the treatment of cancers. This review will focus on the emerging roles of CDK11 in human cancers, and provide a proof-of-principle for continued efforts toward targeting CDK11 for effective cancer treatment.

Profile of palbociclib in the treatment of metastatic breast cancer

Breast cancer is the most common cancer diagnosed in women. Each year, thousands die either because of disease progression or failure of treatment. Breast cancer is classified into different subtypes based on the molecular expression of estrogen receptor (ER), progesterone receptor, and/or human epidermal growth factor receptor 2 (HER2). These receptors represent important therapeutic targets either through monoclonal antibodies or through small-molecule inhibitors directed toward them. However, up to 40% of patients develop either a primary or a secondary resistance to the current treatments. Therefore, there is an urgent need for investigating new targets in order to overcome the resistance and/or enhance the current therapies. Cell cycle is altered in many human cancers, especially in breast cancer. Cyclin-dependent kinases (CDKs), especially CDK4 and CDK6, play a pivotal role in cell cycle progression that makes them potential targets for new promising therapies. CDK inhibition has shown strong antitumor activities, ranging from cytostatic antiproliferative effects to synergistic effects in combination with other antitumor drugs. In order to overcome the drawbacks of the first-generation CDK inhibitors, recently, new CDK inhibitors have emerged that are more selective to CDK4 and CDK6 such as palbociclib, which is the most advanced CDK4/6 inhibitor in trials. In preclinical studies, palbociclib has shown a very promising antitumor activity, especially against ERα+ breast cancer subtype. Palbociclib has gained world attention, and US the Food and Drug Administration has accelerated its approval for first-line treatment in combination with letrozole for the first-line systematic treatment of postmenopausal women with ERα+/HER2− locally advanced or metastatic breast cancer. In this review, we discuss the potential role of CDK inhibition in breast cancer treatment, and focus on palbociclib progress from preclinical studies to clinical trials with mentioning the most recent ongoing as well as planned Phase II and Phase III trials of palbociclib in advanced breast cancer.

G0S2 Suppresses Oncogenic Transformation by Repressing a MYC-Regulated Transcriptional Program

Methylation-mediated silencing of G0-G1 switch gene 2 (G0S2) has been detected in a variety of solid tumors, whereas G0S2 induction is associated with remissions in patients with acute promyelocytic leukemia, implying that G0S2 may possess tumor suppressor activity. In this study, we clearly demonstrate that G0S2 opposes oncogene-induced transformation using G0s2-null immortalized mouse embryonic fibroblasts (MEF). G0s2-null MEFs were readily transformed with HRAS or EGFR treatment compared with wild-type MEFs. Importantly, restoration of G0S2 reversed HRAS-driven transformation. G0S2 is known to regulate fat metabolism by attenuating adipose triglyceride lipase (ATGL), but repression of oncogene-induced transformation by G0S2 was independent of ATGL inhibition. Gene expression analysis revealed an upregulation of gene signatures associated with transformation, proliferation, and MYC targets in G0s2-null MEFs. RNAi-mediated ablation and pharmacologic inhibition of MYC abrogated oncogene-induced transformation of G0s2-null MEFs. Furthermore, we found that G0S2 was highly expressed in normal breast tissues compared with malignant tissue. Intriguingly, high levels of G0S2 were also associated with a decrease in breast cancer recurrence rates, especially in estrogen receptor-positive subtypes, and overexpression of G0S2 repressed the proliferation of breast cancer cells in vitro. Taken together, these findings indicate that G0S2 functions as a tumor suppressor in part by opposing MYC activity, prompting further investigation of the mechanisms by which G0S2 silencing mediates MYC-induced oncogenesis in other malignancies.