The potential role of PD0332991 (Palbociclib) in the treatment of multiple myeloma

The CDK4/6 Inhibitor Palbociclib Induces Cell Senescence of High-grade Serous Ovarian Cancer Through Acetylation of p53

Cell senescence is an anti-cancer strategy following DNA repair and apoptosis, which is associated with the initiation, progression, and treatment of ovarian cancer. The CDK4/6 inhibitor alters cell cycle and induces cell senescence dependent on retinoblastoma (RB) family proteins. Objective Herein, we aimed to explore the effects of Palbociclib (a CDK4/6 inhibitor) on cellular senescence of high-grade serous ovarian cancer (HGSOC). Cell viability and cell cycle were evaluated by cell counting kit-8 and flow cytometry. Cell senescence was analyzed using the SA-β-gal staining assay. The senescence-associated secretory phenotype was assessed using quantitative PCR (qPCR). Senescence-related markers were tested using western blot. The role of Palbociclib in vivo was clarified using xenograft tumor. Acetylation of p53 was evaluated by qPCR and western blot. The results showed that Palbociclib inhibited cell viability, blocked cell cycle at G0/G1 phase, and induced cell senescence. A rescue study indicated that knockdown of p53 reversed the effects on cell cycle and senescence induced by Palbociclib. Moreover, we found that Palbociclib promotes P300-mediated p53 acetylation, thus increasing p53 stability and transcription activity. Moreover, Palbociclib suppressed tumor growth in vivo with increased p53 and acetylated p53 levels. In conclusion, Palbociclib induced cell senescence of HGSOC through P300-mediated p53 acetylation, suggesting that Palbociclib may have the effect of treating HGSOC.

Immunophenotypic expression profile of multiple myeloma cases at a tertiary hospital in Nairobi Kenya

Introduction

Multiple myeloma (MM) is a plasma cell neoplasm that constitutes 10-15% of all hematopoietic neoplasms. Kenya is placed among the top five African countries for MM incidence and MM-related mortality. Prior studies have suggested that the aberrant expression of Cyclin D1, CD56, CD117 and Ki-67 on neoplastic plasma cells is useful in disease prognostication. The prevalence and significance of expression of these markers in a cohort of MM cases in Kenya has not been studied previously.

Methods

A retrospective cross-sectional study was carried out at the Aga Khan University Hospital, Nairobi. The study population included 83 MM cases with available trephine blocks archived between 1st of January 2009 and 31st of March 2020. Immunohistochemical expression of Cyclin D1, CD56, CD117, and Ki-67 was analyzed and scored. The biomarkers were described using frequencies based on the positive and negative results. Fisher's exact test was used to determine the association between the immunophenotypic markers and categorical variables.

Results

Of the 83 selected cases, expression of Cyclin D1, CD56, CD117 and Ki-67 was identified in 28.9, 34.9, 7.2, and 50.6%, respectively. Cyclin D1 positivity was significantly associated with hypercalcemia. Absence of CD117 expression was noted to be associated with adverse risk parameters including an IgA isotype or light chain disease, International Staging System (ISS) stage III disease, abnormal baseline serum free light chains (sFLC) and a high plasma cell burden.

Conclusion

Cyclin D1 expression was congruent with previously reported studies. The frequency of CD56 and CD117 expression was lower than previously reported. This may be due to differences in disease biology between the study populations. Approximately half of cases were Ki-67 positive. Our data showed limited associations between the expression of studied markers and clinicopathologic variables. However, this could be attributed to the small study sample size. We would recommend further characterization of the disease in a larger prospective study with the inclusion of survival outcomes and cytogenetic studies.

EmCyclinD-EmCDK4/6 complex is involved in the host EGF-mediated proliferation of Echinococcus multilocularis germinative cells via the EGFR-ERK pathway

The larval stage of the tapeworm Echinococcus multilocularis causes alveolar echinococcosis (AE), one of the most lethal helminthic infections in humans. The tumor-like growth and development of the metacestode larvae within host organs are driven by a population of somatic stem cells, the germinative cells, which represent the only proliferative cells in the parasite. Host-derived factors have been shown to promote germinative cell proliferation. Since cells sense the external signal mainly in G1 phase of the cell cycle, host factors are expected to exert impacts on the machinery regulating G1/S phase of the germinative cells, which still remains largely unknown in E. multilocularis. In this study, we described the characterization of two key members of the G1/S phase cell-cycle regulation, EmCyclinD and EmCDK4/6. Our data show that EmCyclinD and EmCDK4/6 display significant sequence similarity to their respective mammalian homologs, and that EmCyclinD interacts with EmCDK4/6, forming a kinase-active complex to activate its substrate Rb1. EmCyclinD was actively expressed in the germinative cells. Addition of human EGF caused an elevated expression of EmCyclinD while inhibition of the EGFR-ERK signaling pathway in the parasite reduced the expression of EmCyclinD and downstream transcriptional factors. Treatment with Palbociclib, a specific CDK4/6 inhibitor, downregulated the expression of cell cycle-related factors and impeded germinative cell proliferation and vesicle formation from protoscoleces. Our data demonstrated that the EmCyclinD-EmCDK4/6 complex participates in the cell cycle regulation of germinative cells which is mediated by host EGF via the EGFR-ERK-EmCyclinD pathway in E. multilocularis.

Where We Stand With Precision Therapeutics in Myeloma: Prosperity, Promises, and Pipedreams

Multiple myeloma remains an incurable disease despite numerous novel agents being approved in the last decade. Furthermore, disease behavior and susceptibility to current treatments often vary drastically from patient to patient. To date there are no approved therapies in myeloma that are targeted to specific patient populations based on genomic or immunologic findings. Precision medicine, using biomarkers descriptive of a specific tumor’s biology and predictive of response to appropriate agents, may continue to push the field forward by expanding our treatment arsenal while refining our ability to expose patients to only those treatments likely to be efficacious. Extensive research efforts have been carried out in this endeavor including the use of agents targeting Bcl2 and the RAS/MAPK and PI3K/AKT/mTOR pathways. Thus far, clinical trials have yielded occasional successes intermixed with disappointments, reflecting significant hurdles which still remain including the complex crosstalk between oncogenic pathways and the nonlinear genetic development of myeloma, prone to cultivating sub-clones with distinctive mutations. In this review, we explore the landscape of precision therapeutics in multiple myeloma and underscore the degree to which research efforts have produced tangible clinical results.

Cyclin-Dependent Kinase Inhibitors in Hematological Malignancies-Current Understanding, (Pre-)Clinical Application and Promising Approaches

Simple Summary

Cyclin-dependent kinases are involved in the regulation of cancer-initiating processes like cell cycle progression, transcription, and DNA repair. In hematological neoplasms, these enzymes are often overexpressed, resulting in increased cell proliferation and cancer progression. Early (pre-)clinical data using cyclin-dependent kinase inhibitors are promising but identifying the right drug for each subgroup and patient is challenging. Certain chromosomal abnormalities and signaling molecule activities are considered as potential biomarkers. We therefore summarized relevant studies investigating cyclin-dependent kinase inhibitors in hematological malignancies and further discuss molecular mechanisms of resistance and other open questions.

Abstract

Genetically altered stem or progenitor cells feature gross chromosomal abnormalities, inducing modified ability of self-renewal and abnormal hematopoiesis. Cyclin-dependent kinases (CDK) regulate cell cycle progression, transcription, DNA repair and are aberrantly expressed in hematopoietic malignancies. Incorporation of CDK inhibitors (CDKIs) into the existing therapeutic regimens therefore constitutes a promising strategy. However, the complex molecular heterogeneity and different clinical presentation is challenging for selecting the right target and defining the ideal combination to mediate long-term disease control. Preclinical and early clinical data suggest that specific CDKIs have activity in selected patients, dependent on the existing rearrangements and mutations, potentially acting as biomarkers. Indeed, CDK6, expressed in hematopoietic cells, is a direct target of MLL fusion proteins often observed in acute leukemia and thus contributes to leukemogenesis. The high frequency of aberrancies in the retinoblastoma pathway additionally warrants application of CDKIs in hematopoietic neoplasms. In this review, we describe the preclinical and clinical advances recently made in the use of CDKIs. These include the FDA-approved CDK4/6 inhibitors, traditional and novel pan-CDKIs, as well as dual kinase inhibitors. We additionally provide an overview on molecular mechanisms of response vs. resistance and discuss open questions.

Cereblon modulator CC-885 induces CRBN-dependent ubiquitination and degradation of CDK4 in multiple myeloma

Molecular glue degraders that hijack cellular E3 ubiquitin ligases to target disease-driven proteins for proteosome-dependent degradation are emerging as a promising treatment. Immunomodulatory drugs are classical molecular glue that bind to cereblon (CRBN) to repurpose the function of the CRL4(CRBN) E3 ubiquitin ligase and developed to treat various hematological malignancies. Recently, a novel cereblon modulator CC-885 was developed to elicit broad antitumor activity. Although the degradation of GSPT1 is essential for the broad in vitro antitumor activity of CC-885, it is unclear whether other neosubstrates also contribute to the pharmacological effects of CC-885, especially in multiple myeloma (MM). Here, we show that CC-885 treatment caused growth retardant of MM cells via impairment of cell cycle progression and cell death both in vitro and in vivo. Mechanically, CC-885 selectively induced the ubiquitination and degradation of CDK4 in MM cells in a CRBN-dependent manner. CC-885-mediated CDK4 destruction decreased the phosphorylation of the tumor suppressor retinoblastoma (RB) and prevented the expression of E2F downstream genes. Importantly, genetic ablation or pharmacological inhibition of CDK4 enhances CC-885-induced cytotoxicity in MM cells, suggesting CDK4 destruction contributed to the cytotoxicity of CC-885 in MM cells.

A Randomized Phase I Study of Abemaciclib in Chinese Patients with Advanced and/or Metastatic Cancers

Background

Abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, is approved in combination with endocrine therapy or as monotherapy for hormone receptor-positive and human epidermal growth factor receptor-2-negative (HR+/HER2−) advanced breast cancer outside of China.

Objective

To evaluate the safety, tolerability, and pharmacokinetic (PK) profile of abemaciclib in Chinese patients with advanced and/or metastatic cancers.

Patients and methods

A multicenter, open-label, phase I trial of abemaciclib in Chinese patients with advanced and/or metastatic cancers was conducted. Patients were randomized (1:1) to oral abemaciclib 150 or 200 mg every 12 h on a 28-day cycle. Safety analyses (primary outcome) included all patients receiving at least one dose of abemaciclib. PK and antitumor activity were also assessed.

Results

Of the 26 patients randomized, 25 received abemaciclib 150 mg (n = 12) or 200 mg (n = 13). All 25 patients reported ≥ 1 treatment-emergent adverse event (TEAE). The majority of TEAEs were Common Terminology Criteria for Adverse Events (CTCAE) Grade 1 or 2 in severity. The most frequent TEAEs of Grade ≥ 3 were neutropenia (32%) and thrombocytopenia (24%). Four patients (16%) discontinued treatment due to AEs. Abemaciclib exhibited slow absorption and clearance at single dose, with maximum concentrations achieved after around 6 h and an elimination half-life of approximately 24 h. No complete response was observed, two patients (8%) achieved partial response, with one confirmed responder, and the disease control rate was 68% (n = 17).

Conclusions

Abemaciclib was well tolerated and the safety and PK profiles in Chinese patients were comparable to those previously reported in non-Chinese populations. Preliminary antitumor activity was observed.

ClinicalTrials.gov identifier

NCT02919696.

The homeobox transcription factor MEIS2 is a regulator of cancer cell survival and IMiDs activity in Multiple Myeloma: modulation by Bromodomain and Extra-Terminal (BET) protein inhibitors

The transcription factor Myeloid Ecotropic Insertion Site 2 (MEIS2) has been identified as a cellular substrate of the E3-ubiquitin ligase complex CRL4-cereblon (^CRL4CRBN) in crystal structure and by biochemical screen. Emerging evidence suggests that IMiDs can block MEIS2 from binding to CRBN facilitating the subsequent activation of a ^CRL4CRBN^IMiD-E3-ubiquitin ligase activity and proteasome-mediated degradation of critical substrates regulators of Multiple Myeloma (MM) cell survival and proliferation. Bromodomain and Extra-Terminal (BET) family of proteins are important epigenetic regulators involved in promoting gene expression of several oncogenes, and many studies have revealed important anticancer activities mediated by BET inhibitors (BETi) in hematologic malignancies including MM. Here, we investigated MEIS2 in MM, the role of this protein as a modulator of IMiDs activity and the ability of BETi to inhibit its expression. Our observations indicate that inhibition of MEIS2 in MM cells by RNA interference correlates with reduced growth, induction of apoptosis and enhanced efficacy of different anti-MM drugs. In addition, MEIS2 regulates the expression of Cyclin E/CCNE1 in MM and induction of apoptosis after treatment with the CDK inhibitor Seliciclib/Roscovitine. Interestingly, modulation of MEIS2 can regulate the expression of NKG2D and DNAM-1 NK cell-activating ligands and, importantly, the activity of IMiDs in MM cells. Finally, BETi have the ability to inhibit the expression of MEIS2 in MM, underscoring a novel anticancer activity mediated by these drugs. Our study provides evidence on the role of MEIS2 in MM cell survival and suggests therapeutic strategies targeting of MEIS2 to enhance IMiDs anti-myeloma activity.

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

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

Oral ulcers in patients treated with palbociclib: a case report

Introduction: Palbociclib is an approved drug in the treatment of women with advanced or metastatic estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative, breast cancer. The purpose of this article is to present the first case ever described of oral ulcers caused by palbociclib. Observation: A case of drug-induced oral ulcers is reported. The patient was treated with a combination of palbociclib and Fulvestrant for a breast cancer relapse with pulmonary involvement. These ulcers were localized on the ventral face of the tongue and on the gum. A therapeutic combination of infrared laser biostimulation and a topical application of Dermoval® and Dynexan® were carried out. Palbociclib was concurrently discontinued. The lesions healed in about 15 days. Comments: Palbociclib is an inhibitor of cyclin-dependent kinases 4 and 6 (CDK 4/6). Thereby, it blocks many signaling pathways responsible for cell proliferation. This property weakens the oral mucosa and could be the cause of the observed ulcers. These latter having been particularly debilitating for the patient. Conclusion: Palbociclib-related oral aphthous ulcers are similar to those reported with other targeted therapies. The combination of infrared laser biostimulation and local corticosteroid therapy did not prevent the discontinuation of the cancer treatment.

Abemaciclib: a CDK4/6 inhibitor for the treatment of HR+/HER2- advanced breast cancer

Although early breast cancer (BC) is highly curable, advanced or metastatic disease poses numerous challenges in terms of medical management and treatment decisions and is associated with significantly worse prognosis. Among the new targeted agents, anticancer drugs exploiting the cell-cycle machinery have shown great potential in preclinical studies. CDK4/6 inhibitors target the cyclin D/CDK/retinoblastoma signaling pathway, inducing cell-cycle arrest, reduced cell viability and tumor shrinking. As the cyclin D/CDK complex is activated downstream of estrogen signaling, the combination of CDK4/6 inhibitors with standard endocrine therapies represents a rational approach to elicit synergic antitumor activity in hormone receptor-positive BC. The results of clinical trials have indeed confirmed the superiority of the combination of CDK4/6 inhibitors plus endocrine therapies over endocrine therapy alone. Currently approved are three compounds that exhibit similar structural characteristics as well as biological and clinical activities. Abemaciclib is the latest CDK4/6 inhibitor approved by the US Food and Drug Administration (FDA) in view of the results of the MONARCH 1 and 2 trials. Further trials are ongoing as other important questions await response. In this review, we focus on abemaciclib to examine preclinical and clinical results, describing current therapeutic indications, open questions and ongoing clinical trials.

Kinase inhibitors as potential agents in the treatment of multiple myeloma

Recent years have witnessed a dramatic increase in the number of therapeutic options available for the treatment of multiple myeloma (MM) - from immunomodulating agents to proteasome inhibitors to histone deacetylase (HDAC) inhibitors and, most recently, monoclonal antibodies. Used in conjunction with autologous hematopoietic stem cell transplantation, these modalities have nearly doubled the disease's five-year survival rate over the last three decades to about 50%. In spite of these advances, MM still is considered incurable as resistance and relapse are common. While small molecule protein kinase inhibitors have made inroads in the therapy of a number of cancers, to date their application to MM has been less than successful. Focusing on MM, this review examines the roles played by a number of kinases in driving the malignant state and the rationale for target development in the design of a number of kinase inhibitors that have demonstrated anti-myeloma activity in both in vitro and in vivo xenograph models, as well as those that have entered clinical trials. Among the targets and their inhibitors examined are receptor and non-receptor tyrosine kinases, cell cycle control kinases, the PI3K/AKT/mTOR pathway kinases, protein kinase C, mitogen-activated protein kinase, glycogen synthase kinase, casein kinase, integrin-linked kinase, sphingosine kinase, and kinases involved in the unfolded protein response.

Emerging therapies for breast cancer

HER2 and CDK4/6 are undoubted two most important biological targets for breast cancer. Anti-HER2 treatments enhance objective response and progression-free survival/disease-free survival as well as overall survival. Three CDK4/6 inhibitors consistently improve objective response and progression-free survival; however, overall survival data are waited. Optimization of chemotherapy and endocrine strategies remains an unmet need. Check point inhibitor-based immunotherapy combined with chemotherapy is a promising field, especially for triple-negative breast cancer.

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.

RB1 dual role in proliferation and apoptosis: cell fate control and implications for cancer therapy

Inactivation of the retinoblastoma (RB1) tumor suppressor is one of the most frequent and early recognized molecular hallmarks of cancer. RB1, although mainly studied for its role in the regulation of cell cycle, emerged as a key regulator of many biological processes. Among these, RB1 has been implicated in the regulation of apoptosis, the alteration of which underlies both cancer development and resistance to therapy. RB1 role in apoptosis, however, is still controversial because, depending on the context, the apoptotic cues, and its own status, RB1 can act either by inhibiting or promoting apoptosis. Moreover, the mechanisms whereby RB1 controls both proliferation and apoptosis in a coordinated manner are only now beginning to be unraveled. Here, by reviewing the main studies assessing the effect of RB1 status and modulation on these processes, we provide an overview of the possible underlying molecular mechanisms whereby RB1, and its family members, dictate cell fate in various contexts. We also describe the current antitumoral strategies aimed at the use of RB1 as predictive, prognostic and therapeutic target in cancer. A thorough understanding of RB1 function in controlling cell fate determination is crucial for a successful translation of RB1 status assessment in the clinical setting.

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.