Phase II study of the cyclin-dependent kinase inhibitor flavopiridol administered to patients with advanced gastric carcinoma

Cyclin-dependent protein kinases and cell cycle regulation in biology and disease

Cyclin Dependent Kinases (CDKs) are closely connected to the regulation of cell cycle progression, having been first identified as the kinases able to drive cell division. In reality, the human genome contains 20 different CDKs, which can be divided in at least three different sub-family with different functions, mechanisms of regulation, expression patterns and subcellular localization. Most of these kinases play fundamental roles the normal physiology of eucaryotic cells; therefore, their deregulation is associated with the onset and/or progression of multiple human disease including but not limited to neoplastic and neurodegenerative conditions. Here, we describe the functions of CDKs, categorized into the three main functional groups in which they are classified, highlighting the most relevant pathways that drive their expression and functions. We then discuss the potential roles and deregulation of CDKs in human pathologies, with a particular focus on cancer, the human disease in which CDKs have been most extensively studied and explored as therapeutic targets. Finally, we discuss how CDKs inhibitors have become standard therapies in selected human cancers and propose novel ways of investigation to export their targeting from cancer to other relevant chronic diseases. We hope that the effort we made in collecting all available information on both the prominent and lesser-known CDK family members will help in identify and develop novel areas of research to improve the lives of patients affected by debilitating chronic diseases.

Therapeutic potential of flavonoids in cancer: ROS-mediated mechanisms

Cancer is a leading cause of morbidity and mortality around the globe. Reactive oxygen species (ROS) play contradicting roles in cancer incidence and progression. Antioxidants have attracted attention as emerging therapeutic agents. Among these are flavonoids, which are natural polyphenols with established anticancer and antioxidant capacities. Increasing evidence shows that flavonoids can inhibit carcinogenesis via suppressing ROS levels. Surprisingly, flavonoids can also trigger excessive oxidative stress, but this can also induce death of malignant cells. In this review, we explore the inherent characteristics that contribute to the antioxidant capacity of flavonoids, and we dissect the scenarios in which they play the contrasting role as pro-oxidants. Furthermore, we elaborate on the pathways that link flavonoid-mediated modulation of ROS to the prevention and treatment of cancer. Special attention is given to the ROS-mediated anticancer functions that (-)-epigallocatechin gallate (EGCG), hesperetin, naringenin, quercetin, luteolin, and apigenin evoke in various cancers. We also delve into the structure-function relations that make flavonoids potent antioxidants. This review provides a detailed perspective that can be utilized in future experiments or trials that aim at utilizing flavonoids or verifying their efficacy for developing new pharmacologic agents. We support the argument that flavonoids are attractive candidates for cancer therapy.

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.

The Role and Clinical Implications of the Retinoblastoma (RB)-E2F Pathway in Gastric Cancer

Gastric cancer is the most common malignant tumor in the digestive tract, with very high morbidity and mortality in developing countries. The pathogenesis of gastric cancer is a complex biological process mediated by abnormal regulation of proto-oncogenes and tumor suppressor genes. Although there have been some in-depth studies on gastric cancer at the molecular level, the specific mechanism has not been fully elucidated. RB family proteins (including RB, p130, and p107) are involved in cell cycle regulation, a process that largely depends on members of the E2F gene family that encode transcriptional activators and repressors. In gastric cancer, inactivation of the RB-E2F pathway serves as a core transcriptional mechanism that drives cell cycle progression, and is regulated by cyclins, cyclin-dependent kinases, cyclin-dependent kinase inhibitors, p53, Helicobacter pylori and some other upstream molecules. The E2F proteins are encoded by eight genes (i.e. E2F1 to E2F8), each of which may play a specific role in gastric cancer. Interestingly, a single E2F such as E2F1 can activate or repress transcription, and enhance or inhibit cell proliferation, depending on the cell environment. Thus, the function of the E2F transcription factor family is very complex and needs further exploration. Importantly, the presence of H. pylori in stomach mucosa may affect the RB and p53 tumor suppressor systems, thereby promoting the occurrence of gastric cancer. This review aims to summarize recent research progress on important roles of the complex RB-E2F signaling network in the development and effective treatment of gastric cancer.

Therapeutic Targeting of the General RNA Polymerase II Transcription Machinery

Inhibitors targeting the general RNA polymerase II (RNAPII) transcription machinery are candidate therapeutics in cancer and other complex diseases. Here, we review the molecular targets and mechanisms of action of these compounds, framing them within the steps of RNAPII transcription. We discuss the effects of transcription inhibitors in vitro and in cellular models (with an emphasis on cancer), as well as their efficacy in preclinical and clinical studies. We also discuss the rationale for inhibiting broadly acting transcriptional regulators or RNAPII itself in complex diseases.

Potent Cytotoxic Natural Flavonoids: The Limits of Perspective

BACKGROUND

Besides the numerous biologic and pharmacologic functions in the human body that act as potent antioxidants, flavonoids (flavones, flavanones, flavonols, flavanols and isoflavones) are noted as cancer preventive or therapeutic agents.

METHODS

This review summarizes the published data using PubMed, Science Direct, and Scopus.

RESULTS

In this context, recognition and introduction of the most active cytotoxic flavonoids as promising agents for cancer therapy gives insight for further evaluations. However, there are some critical points that may affect the entering of flavonoids as active cytotoxic phytochemicals in the clinical phase. Issues such as the abundance of active species in nature, the methods of extraction and purification, solubility, pharmacokinetic profile, presence of the chiral moieties, method of synthesis, and structure modification may limit the entry of a selected compound for use in humans. Although plenty of basic evidence exists for cytotoxic/antitumor activity of the versatility of flavonoids for entry into clinical trials, the above-mentioned concerns must be considered.

CONCLUSION

This review is an effort to introduce cytotoxic natural flavonoids (IC50< 10 µM) that may have the potential to be used against various tumor cells. Also, active constituents, molecular mechanisms, and related clinical trials have been discussed as well as the limitations and challenges of using flavonoids in clinic.

Cisplatin exposure causes c-Myc-dependent resistance to CDK4/6 inhibition in HPV-negative head and neck squamous cell carcinoma

The loss of p16 is a signature event in Human Papilloma Virus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) that leads to increased Cyclin Dependent Kinase 4/6 (CDK) signaling. Palbociclib, a CDK4/6 inhibitor, is active for the treatment of a subset of HNSCC. In this study, we analyzed patient response data from a phase I clinical trial of palbociclib in HNSCC and observed an association between prior cisplatin exposure and CDK inhibitor resistance. We studied the effects of palbociclib on cisplatin-sensitive and -resistant HNSCC cell lines. We found that while palbociclib is highly effective against chemo-naive HNSCC cell lines and tumor xenografts, prior cisplatin exposure induces intrinsic resistance to palbociclib in vivo, a relationship that was not observed in vitro. Mechanistically, in the course of provoking a DNA damage-resistance phenotype, cisplatin exposure upregulates both c-Myc and cyclin E, and combination treatment with palbociclib and the c-Myc bromodomain inhibitor JQ1 exerts a synergistic anti-growth effect in cisplatin-resistant cells. These data show the benefit of exploiting the inherent resistance mechanisms of HNSCC to overcome cisplatin- and palbociclib resistance through the use of c-Myc inhibition.

Flavopiridol as cyclin dependent kinase (CDK) inhibitor: a review

Flavopiridol (alvocidib) is a synthetic flavonoid based on the extract from an Indian plant developed for potential treatment of cancer whose first clinical trials were initiated in 1994 as a frontline combination therapy for leukaemia.

Phase II trial of veliparib in patients with previously treated BRCA-mutated pancreas ductal adenocarcinoma

PURPOSE

BRCA-associated cancers have increased sensitivity to poly(ADP-ribose) polymerase inhibitors (PARPis). This single arm, non-randomised, multicentre phase II trial evaluated the response rate of veliparib in patients with previously treated BRCA1/2- or PALB2-mutant pancreatic adenocarcinoma (PDAC).

METHODS

Patients with stage III/IV PDAC and known germline BRCA1/2 or PALB2 mutation, 1-2 lines of treatment, Eastern Cooperative Oncology Group 0-2, were enrolled. Veliparib was dosed at a volume of 300 mg twice-daily (N = 3), then 400 mg twice-daily (N = 15) days 1-28. The primary end-point was to determine the response rate of veliparib; secondary end-points included progression-free survival (PFS), duration of response, overall survival (OS) and safety.

RESULTS

Sixteen patients were enrolled; male N = 8 (50%). Median age was 52 years (range 43-77). Five (31%) had a BRCA1 and 11 (69%) had a BRCA2 mutation. Fourteen (88%) patients had received prior platinum-based therapy. No confirmed partial responses (PRs) were seen: one (6%) unconfirmed PR was observed at 4 months with disease progression (PD) at 6 months; four (25%) had stable disease (SD), whereas 11 (69%) had PD as best response including one with clinical PD. Median PFS was 1.7 months (95% confidence interval [CI] 1.57-1.83) and median OS was 3.1 months (95% CI 1.9-4.1). Six (38%) patients had grade III toxicity, including fatigue (N = 3), haematology (N = 2) and nausea (N = 1).

CONCLUSIONS

Veliparib was well tolerated, but no confirmed response was observed although four (25%) patients remained on study with SD for ≥ 4 months. Additional strategies in this population are needed, and ongoing trials are evaluating PARPis combined with chemotherapy (NCT01585805) and as a maintenance strategy (NCT02184195).

Inhibitors of cyclin-dependent kinases as cancer therapeutics

Over the past two decades there has been a great deal of interest in the development of inhibitors of the cyclin-dependent kinases (CDKs). This attention initially stemmed from observations that different CDK isoforms have key roles in cancer cell proliferation through loss of regulation of the cell cycle, a hallmark feature of cancer. CDKs have now been shown to regulate other processes, particularly various aspects of transcription. The early non-selective CDK inhibitors exhibited considerable toxicity and proved to be insufficiently active in most cancers. The lack of patient selection biomarkers and an absence of understanding of the inhibitory profile required for efficacy hampered the development of these inhibitors. However, the advent of potent isoform-selective inhibitors with accompanying biomarkers has re-ignited interest. Palbociclib, a selective CDK4/6 inhibitor, is now approved for the treatment of ER+/HER2- advanced breast cancer. Current developments in the field include the identification of potent and selective inhibitors of the transcriptional CDKs; these include tool compounds that have allowed exploration of individual CDKs as cancer targets and the determination of their potential therapeutic windows. Biomarkers that allow the selection of patients likely to respond are now being discovered. Drug resistance has emerged as a major hurdle in the clinic for most protein kinase inhibitors and resistance mechanism are beginning to be identified for CDK inhibitors. This suggests that the selective inhibitors may be best used combined with standard of care or other molecularly targeted agents now in development rather than in isolation as monotherapies.

Karenitecin (bnp1350) and flavopridol as radiosensitizers in malignant glioma

The poor prognosis of malignant glioma patients highlights the need to develop low toxicity, tumor specific agents with the ability to synergize with proven efficacious treatment modalities, e.g., ionizing irradiation. This paper investigates the potential of BNP1350 (karenitecin), a topoisomerase I-targeting anticancer agent, and flavopridol a cyclin-dependent kinase inhibitor as radiosensitizers at clinically relevant doses in glioblastoma cell lines. A clonogenic survival and apoptosis assays were performed to test the effect of karenitecin (0.1 nM to 10 nM), flavopridol, (50 nM to 500 nM), radiation (1 Gy to 5.5 Gy) and a combination of radiation and karenitecin or radiation and flavopridol on the glioma cell lines T986 and M059K. Cells were stained for cyclins B and D using antibodies followed by flow cytometry. Propidium Iodide staining was used to reveal the various phases of the cell cycle; cyclin staining in the G0/G1 and G2/M phase of the cell cycle was estimated as the Mean Fluorescence Intensity (MFI) after subtracting the MFI recorded by the isotype controls. Results demonstrated that in irradiated cells, pretreatment with karenitecin induced apoptosis, a transient arrest in the G2/M phase of the cell cycle and increased the expression of cyclin B1. Flavopridol treatment also induced apoptosis and a transient block in the G2/M phase of the cell cycle. The combined effects of karenitecin and flavopridol displayed synergistic effects. The unique radiosensitizing activity of orally administrable karenitecin and flavopridol is consistent with continued investigation of these compounds preclinically, as well as in the clinical setting.

Targeting CDK9: a promising therapeutic opportunity in prostate cancer

Cyclin-dependent kinase 9 (CDK9) is a key transcriptional regulator and a lucrative target for cancer treatment. Targeting CDK9 can effectively confine the hyperactivity of androgen receptor and the constitutive expression of anti-apoptotic proteins; both being main causes of prostate cancer (PCa) development and progression. In castrate-resistant PCa, traditional therapies that only target androgen receptor (AR) have become obsolete due to reprograming in AR activity to make the cells independent of androgen. CDK9 inhibitors may provide a new and better therapeutic opportunity over traditional treatment options by targeting both androgen receptor activity and anti-apoptotic proteins, improving the chances of positive outcomes, especially in patients with the advanced disease. This review focuses on biological functions of CDK9, its involvement with AR and the potential for therapeutic opportunities in PCa treatment.

Flavonoids, Flavonoid Subclasses, and Esophageal Cancer Risk: A Meta-Analysis of Epidemiologic Studies

Flavonoids have been suggested to play a chemopreventive role in carcinogenesis. However, the epidemiologic studies assessing dietary intake of flavonoids and esophageal cancer risk have yielded inconsistent results. This study was designed to examine the association between flavonoids, each flavonoid subclass, and the risk of esophageal cancer with a meta-analysis approach. We searched for all relevant studies with a prospective cohort or case-control study design published from January 1990 to April 2016, using PUBMED, EMBASE, and Web of Science. Pooled odds ratios (ORs) were calculated using fixed or random-effect models. In total, seven articles including 2629 cases and 481,193 non-cases were selected for the meta-analysis. Comparing the highest-intake patients with the lowest-intake patients for total flavonoids and for each flavonoid subclass, we found that anthocyanidins (OR = 0.60, 95% CI: 0.49-0.74), flavanones (OR = 0.65, 95% CI: 0.49-0.86), and flavones (OR = 0.78, 95% CI 0.64-0.95) were inversely associated with the risk of esophageal cancer. However, total flavonoids showed marginal association with esophageal cancer risk (OR = 0.78, 95% CI: 0.59-1.04). In conclusion, our study suggested that dietary intake of total flavonoids, anthocyanidins, flavanones, and flavones might reduce the risk of esophageal cancer.

Molecular targeted therapy for the treatment of gastric cancer

Despite the global decline in the incidence and mortality of gastric cancer, it remains one of the most common malignant tumors of the digestive system. Although surgical resection is the preferred treatment for gastric cancer, chemotherapy is the preferred treatment for recurrent and advanced gastric cancer patients who are not candidates for reoperation. The short overall survival and lack of a standard chemotherapy regimen make it important to identify novel treatment modalities for gastric cancer. Within the field of tumor biology, molecular targeted therapy has attracted substantial attention to improve the specificity of anti-cancer efficacy and significantly reduce non-selective resistance and toxicity. Multiple clinical studies have confirmed that molecular targeted therapy acts on various mechanisms of gastric cancer, such as the regulation of epidermal growth factor, angiogenesis, immuno-checkpoint blockade, the cell cycle, cell apoptosis, key enzymes, c-Met, mTOR signaling and insulin-like growth factor receptors, to exert a stronger anti-tumor effect. An in-depth understanding of the mechanisms that underlie molecular targeted therapies will provide new insights into gastric cancer treatment.

Dietary intake of flavonoids and oesophageal and gastric cancer: incidence and survival in the United States of America (USA)

BACKGROUND

Flavonoids, polyphenolic compounds concentrated in fruits and vegetables, have experimentally demonstrated chemopreventive effects against oesophageal and gastric cancer. Few epidemiologic studies have examined flavonoid intake and incidence of these cancers, and none have considered survival.

METHODS

In this USA multicentre population-based study, case participants (diagnosed during 1993-1995 with oesophageal adenocarcinoma (OEA, n=274), gastric cardia adenocarcinoma (GCA, n=248), oesophageal squamous cell carcinoma (OES, n=191), and other gastric adenocarcinoma (OGA, n=341)) and frequency-matched controls (n=662) were interviewed. Food frequency questionnaire responses were linked with USDA Flavonoid Databases and available literature for six flavonoid classes and lignans. Case participants were followed until 2000 for vital status. Multivariable-adjusted odds ratios (ORs) and hazard ratios (HRs) (95% confidence intervals (CIs)) were estimated, comparing highest with lowest intake quartiles, using polytomous logistic and proportional hazards regressions, respectively.

RESULTS

Little or no consistent association was found for total flavonoid intake (main population sources: black tea, orange/grapefruit juice, and wine) and incidence or survival for any tumour type. Intake of anthocyanidins, common in wine and fruit juice, was associated with a 57% reduction in the risk of incident OEA (OR=0.43, 95% CI=0.29-0.66) and OES (OR=0.43, 95% CI=0.26-0.70). The ORs for isoflavones, for which coffee was the main source, were increased for all tumours, except OES. Anthocyanidins were associated with decreased risk of mortality for GCA (HR=0.63, 95% CI=0.42-0.95) and modestly for OEA (HR=0.87, 95% CI=0.60-1.26), but CIs were wide.

CONCLUSIONS

Our findings, if confirmed, suggest that increased dietary anthocyanidin intake may reduce incidence and improve survival for these cancers.

Clinical potential of novel therapeutic targets in breast cancer: CDK4/6, Src, JAK/STAT, PARP, HDAC, and PI3K/AKT/mTOR pathways

Breast cancers expressing estrogen receptor α, progesterone receptor, or the human epidermal growth factor receptor 2 (HER2) proto-oncogene account for approximately 90% of cases, and treatment with antiestrogens and HER2-targeted agents has resulted in drastically improved survival in many of these patients. However, de novo or acquired resistance to antiestrogen and HER2-targeted therapies is common, and many tumors will recur or progress despite these treatments. Additionally, the remaining 10% of breast tumors are negative for estrogen receptor α, progesterone receptor, and HER2 (“triple-negative”), and a clinically proven tumor-specific drug target for this group has not yet been identified. Therefore, the identification of new therapeutic targets in breast cancer is of vital clinical importance. Preclinical studies elucidating the mechanisms driving resistance to standard therapies have identified promising targets including cyclin-dependent kinase 4/6, phosphoinositide 3-kinase, poly adenosine diphosphate–ribose polymerase, Src, and histone deacetylase. Herein, we discuss the clinical potential and status of new therapeutic targets in breast cancer.

Recent advances and future trends in the targeted therapy of metastatic gastric cancer

The better understanding of the molecular mechanisms behind gastric cancer has led to the development of new therapeutic strategies that are likely to improve patient outcomes in the near future. Recently, targeting the HER2 and the VEGF pathways with trastuzumab and ramucirumab, respectively, have been found to improve survival, while directed therapies against a number of other pathways are under clinical evaluation. These include the hepatocyte growth factor and its receptor c-MET, the insulin-like growth factor 1, the fibroblast growth factor, the mammalian target of rapamycin (mTOR), the epidermal growth factor receptor, and other pathways, as well as relevant immunotherapeutic strategies. This article reviews recent advances and future trends of these concepts for gastric cancer and adenocarcinoma of the gastroesophageal junction.

Venous thromboembolism in patients receiving perioperative chemotherapy for esophagogastric cancer

The association between venous thromboembolism and chemotherapy for esophagogastric cancer is well known in patients treated with palliative intent. Whether this risk extends to the neoadjuvant and perioperative setting is unclear. A retrospective interrogation of databases of patients receiving perioperative chemotherapy for potentially curative intent at the Leicester (2006-2011) and Nottingham (2004-2011) esophagogastric cancer centers was performed. Thromboembolic events were diagnosed in 48 of 384 patients (12.5%), 21 (5.5%) at presentation, 12 (3%) during neoadjuvant chemotherapy, and 15 (3.9%) in the postoperative period. There were no deaths from thromboembolic disease. By site these comprised catheter-related axillary vein thrombosis in 7 patients, deep venous thrombosis in 12 patients, and pulmonary embolism in 29 patients. Twenty-five of the 29 pulmonary emboli were incidental findings on staging computed tomography imaging. Combination chemotherapy with epirubicin, cisplatin, and capecitabine appeared to carry the greatest risk for the development of thromboembolism. Seven of the 12 patients (58%) who developed thromboembolism during neoadjuvant chemotherapy did not proceed to surgery because of deterioration in performance status. Preoperative thromboembolic disease resulted in a significant increase in the interval between chemotherapy and surgery, but did not influence either length of hospital stay or survival. Venous thromboembolism will develop in 12.5% of patients treated with potentially curative intent. This adverse event can occur at any time during the patient journey. In contrast to the commonly held view, this did not translate into a poorer prognosis.

Emerging drug profile: cyclin-dependent kinase inhibitors

Abstract As the rational application of targeted therapies in cancer supplants traditional cytotoxic chemotherapy, there is an ever-greater need for a thorough understanding of the complex machinery of the cell and an application of this knowledge to the development of novel therapeutics and combinations of agents. Here, we review the current state of knowledge of the class of targeted agents known as cyclin-dependent kinase (CDK) inhibitors, with a focus on chronic lymphocytic leukemia (CLL). Flavopiridol (alvocidib) is the best studied of the CDK inhibitors, producing a dramatic cytotoxic effect in vitro and in vivo, with the principal limiting factor of acute tumor lysis. Unfortunately, flavopiridol has a narrow therapeutic window and is relatively non-selective with several off-target (i.e. non-CDK) effects, which prompted development of the second-generation CDK inhibitor dinaciclib. Dinaciclib appears to be both more potent and selective than flavopiridol, with at least an order of magnitude greater therapeutic index, and is currently in phase III clinical trials. In additional to flavopiridol and dinaciclib, we also review the current status of other members of this class, and provide commentary as to the future direction of combination therapy including CDK inhibitors.

Targeting cell cycle kinases and kinesins in anticancer drug development

The cell cycle is regulated by kinases such as the cyclin-dependent kinases (CDKs) and non-CDKs, which include Aurora and polo-like kinases, as well as checkpoint proteins. Mitotic kinesins are involved in the establishment of the mitotic spindle formation and function, and also play a role in cell cycle control. The disruption of the cell cycle is a hallmark of malignancy. Genetic or epigenetic events result in the upregulation of these kinases and mitotic kinesins in a myriad of tumour types, suggesting that their inhibition could result in preferential targeting of malignant cells. Such findings make the development of these inhibitors a rational and attractive new area for cancer therapeutics. Although challenges of potency and non-specificity have hampered their progress through the clinic, several novel compounds are presently in various phases of clinical trial evaluation.

A pharmacokinetic/pharmacodynamic model of tumor lysis syndrome in chronic lymphocytic leukemia patients treated with flavopiridol

PURPOSE

Flavopiridol, the first clinically evaluated cyclin-dependent kinase inhibitor, shows activity in patients with refractory chronic lymphocytic leukemia, but prevalent and unpredictable tumor lysis syndrome (TLS) presents a major barrier to its broad clinical use. The purpose of this study was to investigate the relationships between pretreatment risk factors, drug pharmacokinetics, and TLS.

EXPERIMENTAL DESIGN

A population pharmacokinetic/pharmacodynamic model linking drug exposure and TLS was developed. Plasma data of flavopiridol and its glucuronide metabolite (flavo-G) were obtained from 111 patients treated in early-phase trials with frequent sampling following initial and/or escalated doses. TLS grading was modeled with logistic regression as a pharmacodynamic endpoint. Demographics, baseline disease status, and blood chemistry variables were evaluated as covariates.

RESULTS

Gender was the most significant pharmacokinetic covariate, with females displaying higher flavo-G exposure than males. Glucuronide metabolite exposure was predictive of TLS occurrence, and bulky lymphadenopathy was identified as a significant covariate on TLS probability. The estimated probability of TLS occurrence in patients with baseline bulky lymphadenopathy less than 10 cm or 10 cm or more during the first 2 treatments was 0.111 (SE% 13.0%) and 0.265 (SE% 17.9%), respectively, when flavo-G area under the plasma concentration versus time curve was at its median value in whole-patient group.

CONCLUSIONS

This is the first population pharmacokinetic/pharmacodynamic model of TLS. Further work is needed to explore potential mechanisms and to determine whether the associations between TLS, gender, and glucuronide metabolites are relevant in patients with chronic lymphocytic leukemia treated with other cyclin-dependent kinase inhibitors.

Phase I trial of the combination of flavopiridol and imatinib mesylate in patients with Bcr-Abl+ hematological malignancies

PURPOSE

Imatinib is an inhibitor of the Bcr-Abl tyrosine kinase; however, resistance is common. Flavopiridol, a cyclin-dependent kinase (CDK) inhibitor, down-regulates short-lived anti-apoptotic proteins via inhibition of transcription. In preclinical studies, flavopiridol synergizes with imatinib to induce apoptosis. We investigated this novel combination regimen in patients with Bcr-Abl(+) malignancies.

METHODS

In a phase I dose-escalation study, imatinib was administered orally daily, and flavopiridol by 1 h intravenous infusion weekly for 3 weeks every 4 weeks. Adults with chronic myelogenous leukemia or Philadelphia chromosome-positive acute leukemia were eligible. Patients were divided into two strata based on peripheral blood and bone marrow blast counts. The primary objective was to identify the recommended phase II doses for the combination. Correlative pharmacokinetic and pharmacodynamic studies were also performed.

RESULTS

A total of 21 patients received study treatment. Four dose levels were evaluated before the study was closed following the approval of the second-generation Bcr-Abl tyrosine kinase inhibitors (TKIs). Five patients responded, including four sustained responses. Four patients had stable disease. All but one responder, and all patients with stable disease had previously been treated with imatinib. One patient had a complete response sustained for 30 months. Changes in expression of phospho-Bcr/Abl, -Stat5, and Mcl-1 were monitored. No major pharmacokinetic interaction was observed.

CONCLUSIONS

This is the first study to evaluate the combination of a CDK inhibitor and a TKI in humans. The combination of flavopiridol and imatinib is tolerable and produces encouraging responses, including in some patients with imatinib-resistant disease.

Cyclin dependent kinases in cancer: potential for therapeutic intervention

Cell cycle progression through each phase is regulated by heterodimers formed by cyclin-dependent kinases (CDKs) and their regulatory partner proteins, the cyclins. Together they coordinate the cellular events through cell cycle. De-regulation of cell-cycle control due to aberrant CDK activity is a common feature of most cancer types. Intensive research on small molecules that target cell cycle regulatory proteins has led to the identification of many candidate inhibitors that are able to arrest proliferation and induce apoptosis in neoplastic cells as a promising strategy to treat cancer. Interestingly, cyclin-dependent kinases (CDKs) have also been proposed as therapeutic targets for Multiple Myeloma (MM). Overexpression and aberrant expression of the cyclins, specifically the D cyclins is seen in the majority of MM underscoring the value of exploring CDK inhibition in MM which currently remains an incurable neoplastic plasma-cell disorder. It is characterized by clonal proliferation of malignant plasma cells in the bone marrow microenviroment and associated organ dysfunction. Recent preclinical and early clinical data explore several CDK inhibitors in the context of MM. This review will provide an overview of the main classes of CDK inhibitors with a focus on their mechanism of action and discuss clinical and pharmacological implications of CDK inhibitors as possible therapeutic approaches for the treatment of cancer with specific consideration to MM.

Phase I and II clinical trials for gastric cancer

Gastric cancer remains a global public health problem with considerable heterogeneity in pathogenesis and clinical presentation across geographic regions. Improved understanding of the molecular biology of this disease has opened avenues for targeted intervention. An individualized treatment approach is required for optimal management of this cancer. Overcoming resistance to therapy requires combining targeted agents with the traditional options of chemotherapy/radiation therapy, and also targeting more than 1 pathway of carcinogenesis at a time. Encouraging molecular hypothesis and biomarker-driven trials will lead to improved patient outcomes and may eventually enable the therapeutic nihilism associated with gastric cancer to be overcome.

Targeted therapies for gastric cancer: current status

Gastric cancer represents one of the most common cancers internationally. Unfortunately the majority of patients still present at an advanced stage, and despite advances in diagnostic and treatment strategies, outcomes still remain poor with high mortality rates despite a decline in incidence. Whilst the utility of classical chemotherapy agents has been explored thoroughly (and continues to be investigated, alone or in various combinations), advances have been slow and the efficacy of these agents has reached a plateau. As such, the focus of recent study has shifted toward developing a greater understanding of the molecular biology of carcinogenesis and the cancer cell phenotype, and, in turn, the development of rationally designed drugs that target molecular aberrancies in signal transduction pathways specific to gastric cancer. These targets include circulating growth and angiogenic factors, cell surface receptors, and other molecules that comprise downstream intracellular signalling pathways, including receptor tyrosine kinases. Therapeutic advances in this area significantly lag behind other solid organ malignancies such as breast and colorectal cancer. This article reviews the role of targeted therapies in gastric cancer, including rationale and mechanism of action, current and emerging data, as single-agent therapy or in combination regimens. A recently published randomized phaseIII trial supporting the use of trastuzumab, an anti-human epidermal growth factor receptor 2 (HER2)/neu monoclonal antibody, in a selected population of patients is discussed. Therapies that have been evaluated in phase II trials are also reviewed, as well as promising new therapies currently being investigated in preclinical or phase I studies. There is optimism that targeted therapies, whether as single-agent therapy or in combination with traditional therapies, including chemotherapy, radiotherapy and surgery, may yet have an impact on improvement of the overall prognosis of gastric cancer.

Discovery of new anticancer agents from higher plants

Small organic molecules derived from higher plants have been one of the mainstays of cancer chemotherapy for approximately the past half a century. In the present review, selected single chemical entity natural products of plant origin and their semi-synthetic derivatives currently in clinical trials are featured as examples of new cancer chemotherapeutic drug candidates. Several more recently isolated compounds obtained from plants showing promising in vivo biological activity are also discussed in terms of their potential as anticancer agents, with many of these obtained from species that grow in tropical regions. Since extracts of only a relatively small proportion of the ca. 300,000 higher plants on earth have been screened biologically to date, bioactive compounds from plants should play an important role in future anticancer drug discovery efforts.

CDK INHIBITORY NUCLEOSIDE ANALOGS PREVENT TRANSCRIPTION FROM VIRAL GENOMES

Targeting viral proteins has lead to many successful antivirals. Yet, such antivirals rapidly select for resistance, tend to be active against only a few related viruses, and require previous characterization of the target proteins. Alternatively, antivirals may be targeted to cellular proteins. Replication of many viruses requires cellular CDKs and pharmacological CDK inhibitors (PCIs), such as the purine-based roscovitine (Rosco), are proving safe in clinical trials against cancer. Rosco inhibits replication of wild-type or (multi-)drug resistant HIV, HCMV, EBV, VZV, and HSV-1 and 2. However, the antiviral mechanisms of purine PCIs remain unknown. Our objective is to characterize these mechanisms using HSV as a model We have shown that Rosco prevents initiation of transcription from viral, but not cellular, genomes. This inhibition is promoter independent, but genome dependent, and requires no viral proteins. This is a novel antiviral mechanism and a previously unknown activity for purine PCIs.

First-time-in-human study of GSK923295, a novel antimitotic inhibitor of centromere-associated protein E (CENP-E), in patients with refractory cancer

PURPOSE

GSK923295 is an inhibitor of CENP-E, a key cellular protein important in the alignment of chromosomes during mitosis. This was a Phase I, open-label, first-time-in-human, dose-escalation study, to determine the maximum-tolerated dose (MTD), safety, and pharmacokinetics of GSK923295.

PATIENTS AND METHODS

Adult patients with previously treated solid tumors were enrolled in successive cohorts at GSK923295 doses ranging from 10 to 250 mg/m(2). GSK923295 was administered by a 1-h intravenous infusion, once weekly for three consecutive weeks, with treatment cycles repeated every 4 weeks.

RESULTS

A total of 39 patients were enrolled. The MTD for GSK923295 was determined to be 190 mg/m(2). Observed dose-limiting toxicities (all grade 3) were as follows: fatigue (n = 2, 5%), increased AST (n = 1, 2.5%), hypokalemia (n = 1, 2.5%), and hypoxia (n = 1, 2.5%). Across all doses, fatigue was the most commonly reported drug-related adverse event (n = 13; 33%). Gastrointestinal toxicities of diarrhea (n = 12, 31%), nausea (n = 8, 21%), and vomiting (n = 7, 18%) were generally mild. Frequency of neutropenia was low (13%). There were two reports of neuropathy and no reports of mucositis or alopecia. GSK923295 exhibited dose-proportional pharmacokinetics from 10 to 250 mg/m(2) and did not accumulate upon weekly administration. The mean terminal elimination half-life of GSK923295 was 9-11 h. One patient with urothelial carcinoma experienced a durable partial response at the 250 mg/m(2) dose level.

CONCLUSIONS

The novel CENP-E inhibitor, GSK923295, had dose-proportional pharmacokinetics and a low number of grade 3 or 4 adverse events. The observed incidence of myelosuppression and neuropathy was low. Further investigations may provide a more complete understanding of the potential for GSK923295 as an antiproliferative agent.

The CDK inhibitors in cancer research and therapy

Chemical compounds that interfere with an enzymatic function of kinases are useful for gaining insight into the complicated biochemical processes in mammalian cells. Cyclin-dependent kinases (CDK) play an essential role in the control of the cell cycle and/or proliferation. These kinases as well as their regulators are frequently deregulated in different human tumors. Aberrations in CDK activity have also been observed in viral infections, Alzheimer's, Parkinson's diseases, ischemia and some proliferative disorders. This led to an intensive search for small-molecule CDK inhibitors not only for research purposes, but also for therapeutic applications. Here, we discuss seventeen CDK inhibitors and their use in cancer research or therapy. This review should help researchers to decide which inhibitor is best suited for the specific purpose of their research. For this purpose, the targets, commercial availability and IC(50) values are provided for each inhibitor. The review will also provide an overview of the clinical studies performed with some of these inhibitors.

A Phase II Study of Flavopiridol in Patients With Previously Untreated Advanced Soft Tissue Sarcoma

Purpose. Flavopiridol is a potent cyclin-dependent kinase (CDK) inhibitor that has preclinical activity in many tumours. This synthetic flavonoid was tested in a phase II nonrandomized, nonblinded multicentre clinical trial to determine its activity and toxicity in patients with previously untreated metastatic or locally advanced soft tissue sarcoma. Methods. A total of 18 patients with histologically confirmed nonoperable soft tissue was treated with flavopiridol administered at a dose of 50 mg/m² IV over 1 hour daily ×3 days every 3 weeks. Results. Eighteen patients were accrued to the study over a period of 6 months. No objective responses were noted in the seventeen evaluable patients. Eight patients (47%) exhibited stable disease after 2 cycles (median duration of 4.3 months (range 1.4–6.9 months). Kaplan-Meier estimates for 3- and 6-month progression-free survivial rates were 44 percent and 22 percent, respectively. The only grade 3 toxicities were diarrhea (N = 2), nausea (N = 2), gastritis (N = 1), and fatigue (N = 1). Ninety-four percent of patients received ≥ 90% of the planned dose intensity, during 55 treatment cycles. Conclusions. Flavopiridol was well tolerated at the dose and schedule used in this study, however, no objective treatment responses were seen and thus our results do not support further exploration of flavopiridol as a monotherapy at this dose and schedule in soft tissue sarcomas.

A dose-finding, pharmacokinetic and pharmacodynamic study of a novel schedule of flavopiridol in patients with advanced solid tumors

PURPOSE

Based on the promising activity and tolerability of flavopiridol administered with a pharmacokinetically-derived dosing schedule in chronic lymphocytic leukemia (CLL), we conducted a phase I study using this schedule in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Flavopiridol was given IV as a 30-min loading dose followed by a 4-hr infusion weekly for 4 weeks repeated every 6 weeks. Dose-escalation was in cohorts of three patients using the standard 3+3 phase I study design. Blood samples were obtained for pharmacokinetic and pharmacodynamic studies.

RESULTS

Thirty-four eligible patients with advanced solid tumors received a total of 208 doses (median 7, range 1-24). Total doses ranged from 40 to 105 mg/m(2). The primary dose limiting toxicity was cytokine release syndrome (CKRS). No antitumor responses were observed. The mean peak plasma concentration across all doses was 1.65 ± 0.86 μM. Area under the concentration-versus-time curve ([Formula: see text]) ranged from 4.31 to 32.2 μM[Symbol: see text]hr with an overall mean of 13.6 ± 7.0 μM[Symbol: see text]hr. Plasma flavopiridol concentrations and AUC increased proportionally with dose. There was no correlation between cytokine levels and clinical outcomes.

CONCLUSIONS

The maximum-tolerated dose of flavopiridol is 20 mg/m(2) bolus followed by 20 mg/m(2) infusion over 4 h given weekly for 4 weeks on a 6-week cycle in patients with advanced solid tumors. Flavopiridol PK was notably different, and there was a higher frequency of CKRS, despite prophylactic steroids, seen in this patient group compared to previous studies with CLL using a similar dosing schedule.

A phase I study of flavopiridol in combination with gemcitabine and irinotecan in patients with metastatic cancer

BACKGROUND

Flavopiridol (HMR 1275) is a synthetic flavone with antineoplastic properties through inhibition of cyclin-dependent kinase inhibitor. Flavopiridol synergizes in a sequence-dependent fashion with chemotherapy. Major adverse events of flavopiridol in single agent phase I studies are secretory diarrhea, neutropenia, thrombosis, and fatigue.

PATIENTS AND METHODS

Patients with advanced solid tumors were treated with gemcitabine 800 mg/m and irinotecan 80 mg/m on day 1, followed by flavopiridol, starting dose of 30 mg/m on day 2 with increment of 15 mg/m per dose level, repeated on days 8 and 9 for the first 6 patients (3-week cycle), and then repeated on days 15 and 16 for the remainder patients (4-week cycle). The protocol had to be amended for inability to redose after 1 week.

RESULTS

Fourteen women and 7 men with advanced solid tumors were enrolled. The median age was 51 years and the median number of prior chemotherapies was 3 (0-9). Neutropenic sepsis (1 patient), grade 3 diarrhea (1 patient), and neutropenia (2 patients) preventing retreatment on day 8 were observed among the 6 subjects treated on the first schedule. The recommended phase II dose of flavopiridol was 45 mg/m in combination with irinotecan and gemcitabine every 2 weeks. Dose-limiting toxicities were electrolyte imbalance with fatigue (1 patient), and renal failure and dyspnea with hypoxia (1 patient each), seen at 45 and 60 mg/m doses, respectively. The most common side effects were fatigue (81%), nausea (71%), diarrhea (67%), transient myelosuppression (43%), and vomiting (24%).

CONCLUSIONS

The every 2 week dosing is well tolerated with a phase II recommended dose of 45 mg/m of flavopiridol in combination with irinotecan (80 mg/m) and gemcitabine (800 mg/m).

Phase I clinical and pharmacokinetic study of a novel schedule of flavopiridol in relapsed or refractory acute leukemias

BACKGROUND

A pharmacokinetically derived schedule of flavopiridol administered as a 30 min intravenous bolus followed by 4-hour continuous intravenous infusion (IVB/CIVI) is active in fludarabine-refractory chronic lymphocytic leukemia, but no studies examining the feasibility and maximum tolerated dose of this schedule have been reported in acute leukemia.

DESIGN AND METHODS

We conducted a phase I dose escalation trial of single-agent flavopiridol in adults with relapsed/refractory acute leukemias, utilizing a modification of the intravenous bolus/continuous intravenous infusion approach, intensifying treatment for administration on days 1, 2, and 3 of 21-day cycles.

RESULTS

Twenty-four adults with relapsed/refractory acute myeloid leukemia (n=19) or acute lymphoblastic leukemia (n=5) were enrolled. The median age was 62 years (range, 23-78). The maximum tolerated dose of flavopiridol was 40 mg/m(2) intravenous bolus plus 60 mg/m(2) continuous intravenous infusion (40/60). The dose limiting toxicity was secretory diarrhea. Life-threatening hyperacute tumor lysis syndrome requiring hemodialysis on day 1 was observed in one patient. Pharmacokinetics were dose-dependent with increased clearance observed at the two highest dose levels. Diarrhea occurrence and severity significantly correlated with flavopiridol concentrations at the end of the 4-hour infusion, volume of distribution, and elimination half-life. Modest anti-leukemic activity was observed, with most patients experiencing dramatic but transient reduction/clearance of circulating blasts lasting for 10-14 days. One refractory acute myeloid leukemia patient had short-lived complete remission with incomplete count recovery.

CONCLUSIONS

Flavopiridol as a single agent given by intravenous bolus/continuous intravenous infusion causes marked, immediate cytoreduction in relapsed/refractory acute leukemias, but objective clinical responses were uncommon. With this schedule, the dose is limited by secretory diarrhea.

Sequential treatment with flavopiridol synergistically enhances pyrrolo-1,5-benzoxazepine-induced apoptosis in human chronic myeloid leukaemia cells including those resistant to imatinib treatment

The Bcr-Abl kinase inhibitor, imatinib mesylate, is the front line treatment for chronic myeloid leukaemia (CML), but the emergence of imatinib resistance has led to the search for alternative drug treatments and the examination of combination therapies to overcome imatinib resistance. The pro-apoptotic PBOX compounds are a recently developed novel series of microtubule targeting agents (MTAs) that depolymerise tubulin. Recent data demonstrating enhanced MTA-induced tumour cell apoptosis upon combination with the cyclin dependent kinase (CDK)-1 inhibitor flavopiridol prompted us to examine whether this compound could similarly enhance the effect of the PBOX compounds. We thus characterised the apoptotic and cell cycle events associated with combination therapy of the PBOX compounds and flavopiridol and results showed a sequence dependent, synergistic enhancement of apoptosis in CML cells including those expressing the imatinib-resistant T315I mutant. Flavopiridol reduced the number of polyploid cells formed in response to PBOX treatment but only to a small extent, suggesting that inhibition of endoreplication was unlikely to play a major role in the mechanism by which flavopiridol synergistically enhanced PBOX-induced apoptosis. The addition of flavopiridol following PBOX-6 treatment did however result in an accelerated exit from the G2/M transition accompanied by an enhanced downregulation and deactivation of the CDK1/cyclin B1 complex and an enhanced degradation of the inhibitor of apoptosis protein (IAP) survivin. In conclusion, results from this study highlight the potential of these novel series of PBOX compounds, alone or in sequential combination with flavopiridol, as an effective therapy against CML.

Cyclin-dependent kinase inhibitor SU9516 enhances sensitivity to methotrexate in human T-cell leukemia Jurkat cells

Methotrexate (MTX) has been used to treat various hematological malignancies. Since MTX prevents tumor cells from proliferating by inhibiting dihydrofolate reductase (DHFR), DHFR expression is a key determinant of resistance to MTX in malignant hematological tumor cells. The antiproliferative effect of MTX was significantly enhanced by the knockdown of DHFR expression by siRNA in Jurkat cells. Therefore, a novel strategy down-regulating DHFR expression seems promising for enhancing sensitivity to MTX. We found that SU9516, a cyclin-dependent kinase inhibitor, reduced the expression of both DHFR mRNA and protein. Moreover, we found that DHFR promoter activity was attenuated by SU9516 dependent on the E2F site. Finally, pretreatment with SU9516 significantly enhanced sensitivity to MTX in a colony formation assay. We conclude that a combination of cyclin-dependent kinase inhibitors and MTX may be useful for overcoming resistance to MTX.

Flavopiridol in chronic lymphocytic leukemia: a concise review

Patients with chronic lymphocytic leukemia (CLL) with high-risk cytogenetic features such as del(17p13) have limited treatment options and decreased overall survival. Dysfunction of p53 leads to resistance to fludarabine-based therapies. Cyclin-dependent kinase inhibitors (CDKi) are a novel class of agents that induce apoptosis in CLL cells independent of p53 mutational status. The synthetic flavone flavopiridol demonstrated promising in vitro activity in CLL. In initial phase I studies using a continuous infusion dosing schedule in a variety of malignancies, no clinical activity was observed. Detailed pharmacokinetic modeling led to the development of a novel dosing schedule designed to achieve target drug concentrations in vivo. In phase I testing, this dosing schedule resulted in acute tumor lysis syndrome (TLS) as the dose-limiting toxicity. With the implementation of a standardized protocol to prevent severe TLS, flavopiridol was administered safely, and responses were observed in heavily pretreated, fludarabine-refractory patients, cytogenetically high-risk patients, and patients with bulky lymphadenopathy. In a pharmacokinetic analysis, flavopiridol area under the plasma concentration-time curve (AUC) correlated with clinical response and cytokine release syndrome. Phase II studies are under way with encouraging preliminary results. Flavopiridol is currently under active investigation in combination with other agents and as a means to eradicate minimal residual disease in patients following cytoreductive chemotherapy. Several other investigational CDKi in preclinical and early clinical development are briefly discussed in this review.

Regulation of HIV-1 transcription in cells of the monocyte-macrophage lineage

Human immunodeficiency virus type 1 (HIV-1) has been shown to replicate productively in cells of the monocyte-macrophage lineage, although replication occurs to a lesser extent than in infected T cells. As cells of the monocyte-macrophage lineage become differentiated and activated and subsequently travel to a variety of end organs, they become a source of infectious virus and secreted viral proteins and cellular products that likely initiate pathological consequences in a number of organ systems. During this process, alterations in a number of signaling pathways, including the level and functional properties of many cellular transcription factors, alter the course of HIV-1 long terminal repeat (LTR)-directed gene expression. This process ultimately results in events that contribute to the pathogenesis of HIV-1 infection. First, increased transcription leads to the upregulation of infectious virus production, and the increased production of viral proteins (gp120, Tat, Nef, and Vpr), which have additional activities as extracellular proteins. Increased viral production and the presence of toxic proteins lead to enhanced deregulation of cellular functions increasing the production of toxic cellular proteins and metabolites and the resulting organ-specific pathologic consequences such as neuroAIDS. This article reviews the structural and functional features of the cis-acting elements upstream and downstream of the transcriptional start site in the retroviral LTR. It also includes a discussion of the regulation of the retroviral LTR in the monocyte-macrophage lineage during virus infection of the bone marrow, the peripheral blood, the lymphoid tissues, and end organs such as the brain. The impact of genetic variation on LTR-directed transcription during the course of retrovirus disease is also reviewed.

A combination of cisplatin-eluting gelatin microspheres and flavopiridol enhances anti-tumour effects in a rabbit VX2 liver tumour model

The aim of this study was to investigate whether the combination of cisplatin-eluting gelatin microspheres (GMSs) and flavopiridol enhances anti-tumour effects in a rabbit VX2 liver tumour model. Tumour-bearing rabbits (n = 21) were divided into five groups and infused from the proper hepatic artery. Group 1 (n = 5) received cisplatin-eluting GMSs (1 mg kg(-1)) and flavopiridol (3 mg kg(-1)), group 2 (n = 5) cisplatin-eluting GMSs alone (1 mg kg(-1)), Group 3 (n = 5) flavopiridol (3 mg kg(-1)), Group 4 (n = 3) GMSs alone (1 mg kg(-1)), and Group 5 (n = 3) was the control group receiving physiological saline (1 ml kg(-1)). On days 0 and 7 after procedures the liver tumour volume was measured using a horizontal open MRI system and the relative tumour volume growth rates for 7 days after treatment were calculated. On T(1) weighted images, the tumours were visualised as circular, low-intensity areas just below the liver surface. After treatment, the signals remained similar. The relative tumour volume growth rate for 7 days after treatment was 54.2+/-22.4% in Group 1, 134.1+/-40.1% in Group 2,166.7+/-48.1% in Group 3, 341.8+/-8.6% in Group 4 and 583.1+/-46.9% in Group 5; the growth rate was significantly lower in Group 1 than the other groups (p<0.05). We concluded that in our rabbit model of liver tumours the combination of cisplatin-eluting GMSs and flavopiridol was effective.

Phase II study of flavopiridol in relapsed chronic lymphocytic leukemia demonstrating high response rates in genetically high-risk disease

PURPOSE

Patients with chronic lymphocytic leukemia (CLL) with high-risk genomic features achieve poor outcomes with traditional therapies. A phase I study of a pharmacokinetically derived schedule of flavopiridol suggested promising activity in CLL, irrespective of high-risk features. Given the relevance of these findings to treating genetically high-risk CLL, a prospective confirmatory study was initiated.

PATIENTS AND METHODS

Patients with relapsed CLL were treated with single-agent flavopiridol, with subsequent addition of dexamethasone to suppress cytokine release syndrome (CRS). High-risk genomic features were prospectively assessed for response to therapy.

RESULTS

Sixty-four patients were enrolled. Median age was 60 years, median number of prior therapies was four, and all patients had received prior purine analog therapy. If patients tolerated treatment during week 1, dose escalation occurred during week 2. Dose escalation did not occur in four patients, as a result of severe tumor lysis syndrome; three of these patients required hemodialysis. Thirty-four patients (53%) achieved response, including 30 partial responses (PRs; 47%), three nodular PRs (5%), and one complete response (1.6%). A majority of high-risk patients responded; 12 (57%) of 21 patients with del(17p13.1) and 14 (50%) of 28 patients with del(11q22.3) responded irrespective of lymph node size. Median progression-free survival among responders was 10 to 12 months across all cytogenetic risk groups. Reducing the number of weekly treatments per cycle from four to three and adding prophylactic dexamethasone, which abrogated interleukin-6 release and CRS (P < or = .01), resulted in improved tolerability and treatment delivery.

CONCLUSION

Flavopiridol achieves significant clinical activity in patients with relapsed CLL, including those with high-risk genomic features and bulky lymphadenopathy. Subsequent clinical trials should use the amended treatment schedule developed herein and prophylactic corticosteroids.

A novel class of cyclin-dependent kinase inhibitors identified by molecular docking act through a unique mechanism

The cyclin-dependent kinase (Cdk) family is emerging as an important therapeutic target in the treatment of cancer. Cdks 1, 2, 4, and 6 are the key members that regulate the cell cycle, as opposed to Cdks that control processes such as transcription (Cdk7 and Cdk9). For this reason, Cdks 1, 2, 4, and 6 have been the subject of extensive cell cycle-related research, and consequently many inhibitors have been developed to target these proteins. However, the compounds that comprise the current list of Cdk inhibitors are largely ATP-competitive. Here we report the identification of a novel structural site on Cdk2, which is well conserved between the cell cycle Cdks. Small molecules identified by a high throughput in silico screen of this pocket exhibit cytostatic effects and act by reducing the apparent protein levels of cell cycle Cdks. Drug-induced cell cycle arrest is associated with decreased Rb phosphorylation and decreased expression of E2F-dependent genes. Multiple lines of evidence indicate that the primary mechanism of action of these compounds is the direct induction of Cdk1, Cdk2, and Cdk4 protein aggregation.

Gastric cancer in the era of molecularly targeted agents: current drug development strategies

Gastric cancer is the second most common cause of cancer death worldwide with approximately one million cases diagnosed annually. Despite considerable improvements in surgical techniques, innovations in clinical diagnostics and the development of new chemotherapy regimens, the clinical outcome for patients with advanced gastric cancer and cancer of the GEJ is generally poor with 5-year survival rates ranging between 5 and 15%. The understanding of cancer relevant events has resulted in new therapeutic strategies, particularly in developing of new molecular targeted agents. These agents have the ability to target a variety of cancer relevant receptors and downstream pathways including the epidermal growth factor receptor (EGFR), the vascular endothelial growth factor receptor (VEGFR), the insulin-like growth factor receptor (IGFR), the c-Met pathway, cell-cycle pathways, and down-stream signalling pathways such as the Akt-PI3k-mTOR pathway. In the era of new molecularly targeted agents this review focuses on recent developments of targeting relevant pathways involved in gastric cancer and cancer of the GEJ.

Cyclin-dependent kinase inhibitors as potential targeted anticancer agents

Cyclin-dependent kinases (CDKs) are core components of the cell cycle machinery that govern the transition between phases during cell cycle progression. Genes involved in cell cycle are frequently mutated in human cancer and deregulated CDK activity represents a hallmark of malignancy. This knowledge provides a rationale for regarding CDKs and their associated molecules as potential targets for new drug development in anticancer research. The present article will review the most relevant CDK inhibitors with emphasis on the newer molecules in clinical development and the biological rationale of this therapeutic approach.

Clinical response and pharmacokinetics from a phase 1 study of an active dosing schedule of flavopiridol in relapsed chronic lymphocytic leukemia

We previously reported interim results of a phase 1 trial in patients with chronic lymphocytic leukemia (CLL) whereby flavopiridol was administered intravenously as a 30-minute bolus followed by 4-hour infusion. We now report full pharmacokinetic (PK) data, correlations of PK with clinical outcomes, and final response and progression-free survival (PFS). Twenty-one (40%) of 52 patients with relapsed CLL achieved a partial response (PR) with a median PFS of 12 months. Responders included 17 (40%) of 43 fludarabine refractory patients, 7 (39%) of 18 patients with del(17p13), and 14 (74%) of 19 patients with del(11q22). Six responders received repeat therapy at relapse, and 5 responded again with a second median PFS of 10 months. Noncompartmental analysis and nonlinear mixed effects modeling was used to estimate PK parameters and evaluate covariates. Two-compartment population parameter estimates were 31.4 L/h, 65.8 L, 8.49 L/h, and 157 L for CL, V1, Q, and V2, respectively. Flavopiridol area under the plasma concentration-time curve (AUC) correlated with clinical response and cytokine release syndrome, and glucuronide metabolite AUC correlated with tumor lysis syndrome. These composite results confirm high activity of this pharmacokinetically derived schedule in relapsed, genetically high-risk CLL. Furthermore, PK describes some, but not all, variability in response and toxicity.

Development and validation of a sensitive liquid chromatography/mass spectrometry method for quantitation of flavopiridol in plasma enables accurate estimation of pharmacokinetic parameters with a clinically active dosing schedule

A high-performance liquid chromatographic assay with tandem mass spectrometric detection was developed and validated for quantitation of the broad spectrum kinase inhibitor, flavopiridol, in human plasma. Sample preparation conditions included liquid-liquid extraction in acetonitrile (ACN), drying, and reconstitution in 20/80 water/ACN. Flavopiridol and the internal standard (IS), genistein, were separated by reversed phase chromatography using a C-18 column and a gradient of water with 25 mM ammonium formate and ACN. Electrospray ionization and detection of flavopiridol and genistein were accomplished with single reaction monitoring of m/z 402.09>341.02 and 271.09>152.90, respectively in positive-ion mode [M+H](+) on a triple quadrupole mass spectrometer. Recovery was greater than 90% throughout the linear range of 3-1000 nM. Replicate sample analysis indicated within- and between-run accuracy and precision to be less than 13% throughout the linear range. This method has the lowest lower limit of quantitation (LLOQ) reported to date for flavopiridol, and it allows for more accurate determination of terminal phase concentrations and improved pharmacokinetic parameter estimation in patients receiving an active dosing schedule of flavopiridol.

Flavopiridol displays preclinical activity in acute lymphoblastic leukemia

BACKGROUND

New agents are needed for treatment of children with relapsed acute lymphoblastic leukemia (ALL). Based on altered expression of cell cycle regulatory proteins, including frequent p16 (INK4A) and p15 (INK4B) deletions, flavopiridol (FP; Alvocidib) is an attractive agent for relapsed ALL.

PROCEDURE

We evaluated the efficacy of FP in ALL cell lines using cell proliferation assays, determined the effects of FP treatment on cell growth and viability in cell lines and patient samples, examined cell cycle kinetics, and evaluated the effect of FP on endogenous cyclin-dependent kinase (CDK) activity, Mcl-1 expression, and RNA polymerase II expression and phosphorylation.

RESULTS

ALL cell lines are sensitive to FP. At lower concentrations, FP induces transient G(1)-S cell cycle arrest and modest levels of apoptosis in cell lines. In contrast, a sustained G(1)-S and G(2)-M arrest and substantial apoptosis are observed following exposure to higher FP concentrations. After treatment with FP, ALL cell lines have decreased expression of retinoblastoma protein phosphorylated at serines 795 and 807/811, indicating reduced CDK activity. We also show that ALL cell lines are sensitive to clinically achievable concentrations of FP in medium supplemented with human serum and that FP reduces the expression of Mcl-1 and phosphorylated forms of the C-terminal domain of RNA polymerase II. FP also increases cell death by approximately twofold over baseline in primary ALL blasts.

CONCLUSIONS

These data provide a biological rationale for testing FP in relapsed ALL.