Safety, tolerability, pharmacokinetics and pharmacodynamics of the oral cyclin-dependent kinase inhibitor AZD5438 when administered at intermittent and continuous dosing schedules in patients with advanced solid tumours

Repurposing AZD5438 and Dabrafenib for Cisplatin-Induced AKI

SIGNIFICANCE STATEMENT

To combat both untoward effects of nephrotoxicity and ototoxicity in cisplatin-treated patients, two potential therapeutic oral anticancer drugs AZD5438 and dabrafenib, a phase-2 clinical trial protein kinase CDK2 inhibitor and an US Food and Drug Administration-approved drug BRAF inhibitor, respectively, were tested in an established mouse AKI model. Both drugs have previously been shown to protect significantly against cisplatin-induced hearing loss in mice. Each drug ameliorated cisplatin-induced increases in the serum biomarkers BUN, creatinine, and neutrophil gelatinase-associated lipocalin. Drugs also improved renal histopathology and inflammation, mitigated cell death by pyroptosis and necroptosis, and significantly enhanced overall survival of cisplatin-treated mice.

BACKGROUND

Cisplatin is an effective chemotherapy agent for a wide variety of solid tumors, but its use is dose-limited by serious side effects, including AKI and hearing loss. There are no US Food and Drug Administration-approved drugs to treat both side effects. Recently, two anticancer oral drugs, AZD5438 and dabrafenib, were identified as protective against cisplatin-induced hearing loss in mice. We hypothesize that similar cell stress and death pathways are activated in kidney and inner ear cells when exposed to cisplatin and tested whether these drugs alleviate cisplatin-induced AKI.

METHODS

The HK-2 cell line and adult FVB mice were used to measure the protection from cisplatin-induced cell death and AKI by these drugs. Serum markers of kidney injury, BUN, creatinine, and neutrophil gelatinase-associated lipocalin as well as histology of kidneys were analyzed. The levels of markers of kidney cell death, including necroptosis and pyroptosis, pERK, and proliferating cell nuclear antigen, were also examined by Western blotting and immunofluorescence. In addition, CDK2 knockout (KO) mice were used to confirm AZD5438 protective effect is through CDK2 inhibition.

RESULTS

The drugs reduced cisplatin-induced cell death in the HK-2 cell line and attenuated cisplatin-induced AKI in mice. The drugs reduced serum kidney injury markers, inhibited cell death, and reduced the levels of pERK and proliferating cell nuclear antigen, all of which correlated with prolonged animal survival. CDK2 KO mice were resistant to cisplatin-induced AKI, and AZD5438 conferred no additional protection in the KO mice.

CONCLUSIONS

Cisplatin-induced damage to the inner ear and kidneys shares similar cellular beneficial responses to AZD5438 and dabrafenib, highlighting the potential therapeutic use of these agents to treat both cisplatin-mediated kidney damage and hearing loss.

Identification of CDK1, PBK, and CHEK1 as an Oncogenic Signature in Glioblastoma: A Bioinformatics Approach to Repurpose Dapagliflozin as a Therapeutic Agent

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary brain tumor whose median survival is less than 15 months. The current treatment regimen comprising surgical resectioning, chemotherapy with Temozolomide (TMZ), and adjuvant radiotherapy does not achieve total patient cure. Stem cells' presence and GBM tumor heterogeneity increase their resistance to TMZ, hence the poor overall survival of patients. A dysregulated cell cycle in glioblastoma enhances the rapid progression of GBM by evading senescence or apoptosis through an over-expression of cyclin-dependent kinases and other protein kinases that are the cell cycle's main regulatory proteins. Herein, we identified and validated the biomarker and predictive properties of a chemoradio-resistant oncogenic signature in GBM comprising CDK1, PBK, and CHEK1 through our comprehensive in silico analysis. We found that CDK1/PBK/CHEK1 overexpression drives the cell cycle, subsequently promoting GBM tumor progression. In addition, our Kaplan-Meier survival estimates validated the poor patient survival associated with an overexpression of these genes in GBM. We used in silico molecular docking to analyze and validate our objective to repurpose Dapagliflozin against CDK1/PBK/CHEK1. Our results showed that Dapagliflozin forms putative conventional hydrogen bonds with CDK1, PBK, and CHEK1 and arrests the cell cycle with the lowest energies as Abemaciclib.

A novel prognostic signature contributes to precision treatment in colon adenocarcinoma with KRAS mutation

BACKGROUND

Approximately 40% of colon cancer harbor Kirsten rat sarcoma viral oncogene ( KRAS ) mutations, but the prognostic value of KRAS mutations in colon cancer is still controversial.

METHODS

We enrolled 412 colon adenocarcinoma (COAD) patients with KRAS mutations, 644 COAD patients with KRAS wild-type and 357 COAD patients lacking information on KRAS status from five independent cohorts. A random forest model was developed to estimate the KRAS status. The prognostic signature was established using least absolute shrinkage and selection operator-Cox regression and evaluated by Kaplan-Meier survival analysis, multivariate-Cox analysis, receiver operating characteristic curve and nomogram. The expression data of KRAS -mutant COAD cell lines from the Cancer Cell Line Encyclopedia database and the corresponding drug sensitivity data from the Genomics of Drug Sensitivity in Cancer database were used for potential target and agent exploration.

RESULTS

We established a 36-gene prognostic signature classifying the KRAS -mutant COAD as high and low risk. High risk patients had inferior prognoses compared to those with low risk, while the signature failed to distinguish the prognosis of COAD with KRAS wild-type. The risk score was the independent prognostic factor for KRAS -mutant COAD and we further fabricated the nomograms with good predictive efficiency. Moreover, we suggested FMNL1 as a potential drug target and three drugs as potential therapeutic agents for KRAS -mutant COAD with high risk.

CONCLUSION

We established a precise 36-gene prognostic signature with great performance in prognosis prediction of KRAS -mutant COAD providing a new strategy for personalized prognosis management and precision treatment for KRAS -mutant COAD.

Double-strand DNA break repair: molecular mechanisms and therapeutic targets

Double-strand break (DSB), a significant DNA damage brought on by ionizing radiation, acts as an initiating signal in tumor radiotherapy, causing cancer cells death. The two primary pathways for DNA DSB repair in mammalian cells are nonhomologous end joining (NHEJ) and homologous recombination (HR), which cooperate and compete with one another to achieve effective repair. The DSB repair mechanism depends on numerous regulatory variables. DSB recognition and the recruitment of DNA repair components, for instance, depend on the MRE11-RAD50-NBS1 (MRN) complex and the Ku70/80 heterodimer/DNA-PKcs (DNA-PK) complex, whose control is crucial in determining the DSB repair pathway choice and efficiency of HR and NHEJ. In-depth elucidation on the DSB repair pathway's molecular mechanisms has greatly facilitated for creation of repair proteins or pathways-specific inhibitors to advance precise cancer therapy and boost the effectiveness of cancer radiotherapy. The architectures, roles, molecular processes, and inhibitors of significant target proteins in the DSB repair pathways are reviewed in this article. The strategy and application in cancer therapy are also discussed based on the advancement of inhibitors targeted DSB damage response and repair proteins.

Inhibition of CDK1 Overcomes Oxaliplatin Resistance by Regulating ACSL4-mediated Ferroptosis in Colorectal Cancer

Oxaliplatin is a widely used chemotherapy drug for patients with advanced colorectal cancer (CRC); however, frequent drug resistance limits its therapeutic efficacy in patients. Here, this work identifies cyclin-dependent kinase 1 (CDK1) as a critical contributor to oxaliplatin resistance via in vitro and in vivo CRISPR/Cas9 screening. CDK1 is highly expressed in oxaliplatin-resistant cells and tissues due to the loss of N6-methyladenosine modification. Genetic and pharmacological blockade of CDK1 restore the susceptibility of CRC cells to oxaliplatin in vitro and in cell/patient-derived xenograft models. Mechanistically, CDK1 directly binds to and phosphorylates Acyl-CoA synthetase long-chain family 4 (ACSL4) at S447, followed by recruitment of E3 ubiquitin ligase UBR5 and polyubiquitination of ACSL4 at K388, K498, and K690, which leads to ACSL4 protein degradation. Reduced ACSL4 subsequently blocks the biosynthesis of polyunsaturated fatty acid containing lipids, thereby inhibiting lipid peroxidation and ferroptosis, a unique iron-dependent form of oxidative cell death. Moreover, treatment with a ferroptosis inhibitor nullifies the enhancement of CRC cell sensitivity to oxaliplatin by CDK1 blockade in vitro and in vivo. Collectively, the findings indicate that CDK1 confers oxaliplatin resistance to cells by suppressing ferroptosis. Therefore, administration of a CDK1 inhibitor may be an attractive strategy to treat patients with oxaliplatin-resistant CRC.

AZD5438 a GSK-3a/b and CDK inhibitor is antiapoptotic modulates mitochondrial activity and protects human neurons from mitochondrial toxins

We previously reported that kenpaullone, which inhibits GSK-3a/b and CDKs inhibited CCCP mediated mitochondrial depolarisation and augments the mitochondrial network. To investigate the actions of this class of drug further, we compared the ability of kenpaullone, alsterpaullone, 1-azakenapaullone, AZD5438, AT7519 (CDK and GSK-3a/b inhibitors) and dexpramipexole and olesoxime (mitochondrial permeability transition pore inhibitors) to prevent CCCP mediated mitochondrial depolarisation and found that AZD5438 and AT7519, were the most effective. Furthermore, treatment with AZD5438 alone increased the complexity of the mitochondrial network. We also found that AZD5438 prevented the rotenone induced decrease in PGC-1alpha and TOM20 levels and that it mediated powerful anti-apoptotic effects and promoted glycolytic respiration. Importantly, experiments in human iPSC derived cortical and midbrain neurons showed AZD5438 mediated significant protective effects, preventing the neuronal cell death, and collapse in the neurite and mitochondrial network associated with rotenone treatment. These results suggest drugs that target GSK-3a/b and CDKs should be developed and assessed further as they may have significant therapeutic potential.

CDK inhibitors from past to present: A new wave of cancer therapy

Deregulation of the cell cycle machinery, which has been linked to dysregulation of cyclin-dependent kinases (CDKs), is a defining characteristic of cancer, eventually promoting abnormal proliferation that feeds tumorigenesis and disease development. In this regard, several CDK inhibitors (CDKIs) have been developed during the last few decades (1st, 2nd, and 3rd generation CDKIs) to inhibit cancer cell proliferation. 1st and 2nd generation CDKIs have not received much clinical attention for the treatment of cancer patients because of their limited specificity and high toxicity. However, the recent development of combination strategies allowed us to reduce the toxicity and side effects of these CDKIs, paving the way for their potential application in clinical settings. The 3rd generation CDKIs have yielded the most promising results at the preclinical and clinical levels, propelling them into the advanced stages of clinical trials against multiple malignancies, especially breast cancer, and revolutionizing traditional treatment strategies. In this review, we discuss the most-investigated candidates from the 1st, 2nd, and 3rd generations of CDKIs, their basic mechanisms of action, the reasons for their failure in the past, and their current clinical development for the treatment of different malignancies. Additionally, we briefly highlighted the most recent clinical trial results and advances in the development of 3rd generation FDA-approved selective CDK4/6 inhibitors that combat the most prevalent cancer. Overall, this review will provide a thorough knowledge of CDKIs from the past to the present, allowing researchers to rethink and develop innovative cancer therapeutic regimens.

Cyclin-dependent kinases as potential targets for colorectal cancer: past, present and future

Colorectal cancer (CRC) is a common cancer in the world and its prevalence is increasing in developing countries. Deregulated cell cycle traverse is a hallmark of malignant transformation and is often observed in CRC as a result of imprecise activity of cell cycle regulatory components, viz. cyclins and cyclin-dependent kinases (CDKs). Apart from cell cycle regulation, some CDKs also regulate processes such as transcription and have also been shown to be involved in colorectal carcinogenesis. This article aims to review cyclin-dependent kinases as potential targets for CRC. Furthermore, therapeutic candidates to target CDKs are also discussed.

Lessons Learned from Past Cyclin-Dependent Kinase Drug Discovery Efforts

Inhibition of cyclin-dependent kinases (CDKs) has become an effective therapeutic strategy for treating various diseases, especially cancer. Over almost three decades, although great efforts have been made to discover CDK inhibitors, many of which have entered clinical trials, only four CDK inhibitors have been approved. In the process of CDK inhibitor development, many difficulties and misunderstandings have hampered their discovery and clinical applications, which mainly include inadequate understanding of the biological functions of CDKs, less attention paid to pan- and multi-CDK inhibitors, nonideal isoform selectivity of developed selective CDK inhibitors, overlooking the metabolic stability of early discovered CDK inhibitors, no effective resistance solutions, and a lack of available combination therapy and effective biomarkers for CDK therapies. After reviewing the mechanisms of CDKs and the research progress of CDK inhibitors, this perspective summarizes and discusses these difficulties or lessons, hoping to facilitate the successful discovery of more useful CDK inhibitors.

Radiotherapy as a tool to elicit clinically actionable signalling pathways in cancer

A variety of targeted anticancer agents have been successfully introduced into clinical practice, largely reflecting their ability to inhibit specific molecular alterations that are required for disease progression. However, not all malignant cells rely on such alterations to survive, proliferate, disseminate and/or evade anticancer immunity, implying that many tumours are intrinsically resistant to targeted therapies. Radiotherapy is well known for its ability to activate cytotoxic signalling pathways that ultimately promote the death of cancer cells, as well as numerous cytoprotective mechanisms that are elicited by cellular damage. Importantly, many cytoprotective mechanisms elicited by radiotherapy can be abrogated by targeted anticancer agents, suggesting that radiotherapy could be harnessed to enhance the clinical efficacy of these drugs. In this Review, we discuss preclinical and clinical data that introduce radiotherapy as a tool to elicit or amplify clinically actionable signalling pathways in patients with cancer.

Transcriptional cyclin-dependent kinases: Potential drug targets in cancer therapy

In the wake of the development of the concept of cell cycle and its limiting points, cyclin-dependent kinases (CDKs) are considered to play a central role in regulating cell cycle progression. Recent studies have strongly demonstrated that CDKs also has multiple functions, especially in response to extracellular and intracellular signals by interfering with transcriptional events. Consequently, how to inhibit their function has been a hot research topic. It is worth noting that the key role of CDKs in regulating transcription has been explored in recent years, but its related pharmacological targets are less developed, and most inhibitors have not entered the clinical stage. Accordingly, this perspective focus on the biological functions of transcription related CDKs and their complexes, some key upstream and downstream signals, and inhibitors for cancer treatment in recent years. In addition, some corresponding combined treatment strategies will provide a more novel perspective for future cancer remedy.

AZD5438-PROTAC: A selective CDK2 degrader that protects against cisplatin- and noise-induced hearing loss

Cyclin-dependent kinase 2 (CDK2) is a potential therapeutic target for the treatment of hearing loss and cancer. Previously, we identified AZD5438 and AT7519-7 as potent inhibitors of CDK2, however, they also targeted additional kinases, leading to unwanted toxicities. Proteolysis Targeting Chimeras (PROTACs) are a new promising class of small molecules that can effectively direct specific proteins to proteasomal degradation. Herein we report the design, synthesis, and characterization of PROTACs of AT7519-7 and AZD5438 and the identification of PROTAC-8, an AZD5438-PROTAC, that exhibits selective, partial CDK2 degradation. Furthermore, PROTAC-8 protects against cisplatin ototoxicity and kainic acid excitotoxicity in zebrafish. Molecular dynamics simulations reveal the structural requirements for CDK2 degradation. Together, PROTAC-8 is among the first-in-class PROTACs with in vivo therapeutic activities and represents a new lead compound that can be further developed for better efficacy and selectivity for CDK2 degradation against hearing loss and cancer.

Cyclin Dependent Kinase-1 (CDK-1) Inhibition as a Novel Therapeutic Strategy against Pancreatic Ductal Adenocarcinoma (PDAC)

The role of CDK1 in PDAC onset and development is two-fold. Firstly, since CDK1 activity regulates the G2/M cell cycle checkpoint, overexpression of CDK1 can lead to progression into mitosis even in cells with DNA damage, a potentially tumorigenic process. Secondly, CDK1 overexpression leads to the stimulation of a range of proteins that induce stem cell properties, which can contribute to the development of cancer stem cells (CSCs). CSCs promote tumor-initiation and metastasis and play a crucial role in the development of PDAC. Targeting CDK1 showed promising results for PDAC treatment in different preclinical models, where CDK1 inhibition induced cell cycle arrest in the G2/M phase and led to induction of apoptosis. Next to this, PDAC CSCs are uniquely sensitive to CDK1 inhibition. In addition, targeting of CDK1 has shown potential for combination therapy with both ionizing radiation treatment and conventional chemotherapy, through sensitizing tumor cells and reducing resistance to these treatments. To conclude, CDK1 inhibition induces G2/M cell cycle arrest, stimulates apoptosis, and specifically targets CSCs, which makes it a promising treatment for PDAC. Screening of patients for CDK1 overexpression and further research into combination treatments is essential for optimizing this novel targeted therapy.

Cyclin-Dependent Kinase 4 and 6 Inhibitors in Cell Cycle Dysregulation for Breast Cancer Treatment

In cell development, the cell cycle is crucial, and the cycle progression’s main controllers are endogenous CDK inhibitors, cyclin-dependent kinases (CDKs), and cyclins. In response to the mitogenic signal, cyclin D is produced and retinoblastoma protein (Rb) is phosphorylated due to activated CDK4/CDK6. This causes various proteins required in the cell cycle progression to be generated. In addition, complexes of CDK1-cyclin A/B, CDK2-cyclin E/A, and CDK4/CDK6-cyclin D are required in each phase of this progression. Cell cycle dysregulation has the ability to lead to cancer. Based on its role in the cell cycle, CDK has become a natural target of anticancer therapy. Therefore, understanding the CDK structures and the complex formed with the drug, helps to foster the development of CDK inhibitors. This development starts from non-selective CDK inhibitors to selective CDK4/CDK6 inhibitors, and these have been applied in clinical cancer treatment. However, these inhibitors currently require further development for various hematologic malignancies and solid tumors, based on the results demonstrated. In drug development, the main strategy is primarily to prevent and asphyxiate drug resistance, thus a determination of specific biomarkers is required to increase the therapy’s effectiveness as well as patient selection suitability in order to avoid therapy failure. This review is expected to serve as a reference for early and advanced-stage researchers in designing new molecules or repurposing existing molecules as CDK4/CDK6 inhibitors to treat breast cancer.

Inhibitors of Cyclin-Dependent Kinases: Types and Their Mechanism of Action

Recent studies on cyclin-dependent kinase (CDK) inhibitors have revealed that small molecule drugs have become very attractive for the treatment of cancer and neurodegenerative disorders. Most CDK inhibitors have been developed to target the ATP binding pocket. However, CDK kinases possess a very similar catalytic domain and three-dimensional structure. These features make it difficult to achieve required selectivity. Therefore, inhibitors which bind outside the ATP binding site present a great interest in the biomedical field, both from the fundamental point of view and for the wide range of their potential applications. This review tries to explain whether the ATP competitive inhibitors are still an option for future research, and highlights alternative approaches to discover more selective and potent small molecule inhibitors.

Patient-tailored design for selective co-inhibition of leukemic cell subpopulations

The extensive drug resistance requires rational approaches to design personalized combinatorial treatments that exploit patient-specific therapeutic vulnerabilities to selectively target disease-driving cell subpopulations. To solve the combinatorial explosion challenge, we implemented an effective machine learning approach that prioritizes patient-customized drug combinations with a desired synergy-efficacy-toxicity balance by combining single-cell RNA sequencing with ex vivo single-agent testing in scarce patient-derived primary cells. When applied to two diagnostic and two refractory acute myeloid leukemia (AML) patient cases, each with a different genetic background, we accurately predicted patient-specific combinations that not only resulted in synergistic cancer cell co-inhibition but also were capable of targeting specific AML cell subpopulations that emerge in differing stages of disease pathogenesis or treatment regimens. Our functional precision oncology approach provides an unbiased means for systematic identification of personalized combinatorial regimens that selectively co-inhibit leukemic cells while avoiding inhibition of nonmalignant cells, thereby increasing their likelihood for clinical translation.

Selective inhibition of CDK4/6: A safe and effective strategy for developing anticancer drugs

The sustained cell proliferation resulting from dysregulation of the cell cycle and activation of cyclin-dependent kinases (CDKs) is a hallmark of cancer. The inhibition of CDKs is a highly promising and attractive strategy for the development of anticancer drugs. In particular, third-generation CDK inhibitors can selectively inhibit CDK4/6 and regulate the cell cycle by suppressing the G1 to S phase transition, exhibiting a perfect balance between anticancer efficacy and general toxicity. To date, three selective CDK4/6 inhibitors have received approval from the U.S. Food and Drug Administration (FDA), and 15 CDK4/6 inhibitors are in clinical trials for the treatment of cancers. In this perspective, we discuss the crucial roles of CDK4/6 in regulating the cell cycle and cancer cells, analyze the rationale for selectively inhibiting CDK4/6 for cancer treatment, review the latest advances in highly selective CDK4/6 inhibitors with different chemical scaffolds, explain the mechanisms associated with CDK4/6 inhibitor resistance and describe solutions to overcome this issue, and briefly introduce proteolysis targeting chimera (PROTAC), a new and revolutionary technique used to degrade CDK4/6.

A Precision Medicine Drug Discovery Pipeline Identifies Combined CDK2 and 9 Inhibition as a Novel Therapeutic Strategy in Colorectal Cancer

Colorectal cancer is the third most common cancer in the United States and responsible for over 50,000 deaths each year. Therapeutic options for advanced colorectal cancer are limited, and there remains an unmet clinical need to identify new treatments for this deadly disease. To address this need, we developed a precision medicine pipeline that integrates high-throughput chemical screens with matched patient-derived cell lines and patient-derived xenografts (PDX) to identify new treatments for colorectal cancer. High-throughput screens of 2,100 compounds were performed across six low-passage, patient-derived colorectal cancer cell lines. These screens identified the CDK inhibitor drug class among the most effective cytotoxic compounds across six colorectal cancer lines. Among this class, combined targeting of CDK1, 2, and 9 was the most effective, with IC₅₀s ranging from 110 nmol/L to 1.2 μmol/L. Knockdown of CDK9 in the presence of a CDK2 inhibitor (CVT-313) showed that CDK9 knockdown acted synergistically with CDK2 inhibition. Mechanistically, dual CDK2/9 inhibition induced significant G₂-M arrest and anaphase catastrophe. Combined CDK2/9 inhibition in vivo synergistically reduced PDX tumor growth. Our precision medicine pipeline provides a robust screening and validation platform to identify promising new cancer therapies. Application of this platform to colorectal cancer pinpointed CDK2/9 dual inhibition as a novel combinatorial therapy to treat colorectal cancer.

CDK9 as an Appealing Target for Therapeutic Interventions

Cyclin Dependent Kinase 9 (CDK9) as a serine/threonine kinase belongs to a great number of CDKs. CDK9 is the main core of PTEF-b complex and phosphorylates RNA polymerase (RNAP) II besides other transcription factors which regulate gene transcription elongation in numerous physiological processes. Multi-functional nature of CDK9 in diverse cellular pathways proposes that it is as an appealing target. In this review, we summarized the recent findings on the molecular interaction of CDK9 with critical participant molecules to modulate their activity in various diseases. Furthermore, the presented review provides a rationale supporting the use of CDK9 as a therapeutic target in clinical developments for crucial diseases; particularly cancers will be reviewed.

Radiosensitizing Effect of Novel Phenylpyrimidine Derivatives on Human Lung Cancer Cells via Cell Cycle Perturbation

Radiotherapy is one of the most common treatments for cancer, but radioresistance and injury to normal tissue are considered major obstacles to successful radiotherapy. Thus, there is an urgent need to develop radiosensitizers to improve the therapeutic outcomes of radiotherapy in cancer patients. Our previous efforts to identify novel radiosensitizers, using high-throughput screening targeting p53 and Nrf2 revealed a promising N-phenylpyrimidin-2-amine (PPA) lead compound. In the present study, 17 derivatives of this lead compound were examined, and it was found that 4-(4-fluorophenyl)-N-(4-nitrophenyl)-6-phenylpyrimidin-2-amine (PPA5), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)-3-methoxy-N-methyl -benzamide (PPA13), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA14), 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA15), and 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)-N-methylbenzamide (PPA17) inhibited cell viability by more than 50%, with a marked increase in the proportion of cells arrested at the G₂/M phase of cell cycle. Among these compounds, PPA15 markedly increased the sub-G₁ cell population and increased the levels of cyclin B1 and the phosphorylation levels of cyclin-dependent kinase (CDK) 1. Combined treatment with radiation and PPA14 or PPA15 significantly decreased clonogenic survival. An in vitro kinase assay revealed that PPA15 inhibited multiple CDKs involved in cell cycle regulation. Compared with drug or radiation treatment alone, combined treatment with PPA15 and radiation resulted in the suppression of A549 tumor growth in mice by 59.5% and 52.7%, respectively. Treatment with PPA15 alone directly inhibited tumor growth by 25.7%. These findings suggest that the novel pan CDK inhibitor, PPA15, may be a promising treatment to improve the effectiveness of radiotherapy for the treatment of cancer. SIGNIFICANCE STATEMENT: Several inhibitors of CDK have been successfully evaluated in combination with other chemotherapeutics in clinical trials, but negative side effects have partially restricted their clinical use. In this study, we identified a novel pan-CDK inhibitor to increase radiosensitivity, and we hope this work will encourage the development of promising small-molecule radiosensitizers.

Cyclin-dependent kinase inhibitors AZD5438 and R547 show potential for enhancing efficacy of daunorubicin-based anticancer therapy: Interaction with carbonyl-reducing enzymes and ABC transporters

Daunorubicin (DAUN) has served as an anticancer drug in chemotherapy regimens for decades and is still irreplaceable in treatment of acute leukemias. The therapeutic outcome of DAUN-based therapy is compromised by its cardiotoxicity and emergence of drug resistance. This phenomenon is often caused by pharmacokinetic mechanisms such as efflux of DAUN from cancer cells through ATP-binding cassette (ABC) transporters and its conversion to less cytostatic but more cardiotoxic daunorubicinol (DAUN-OL) by carbonyl reducing enzymes (CREs). Here we aimed to investigate, whether two cyclin-dependent kinase inhibitors, AZD5438 and R547, can interact with these pharmacokinetic mechanisms and reverse DAUN resistance. Using accumulation assays, we revealed AZD5438 as potent inhibitor of ABCC1 showing also weaker inhibitory effect to ABCB1 and ABCG2. Combination index analysis, however, shown that inhibition of ABCC1 does not significantly contribute to synergism between AZD5438 and DAUN in MDCKII-ABCC1 cells, suggesting predominant role of other mechanism. Using pure recombinant enzymes, we found both tested drugs to inhibit CREs with aldo-keto reductase 1C3 (AKR1C3). This interaction was further confirmed in transfected HCT-116 cells. Moreover, these cells were sensitized to DAUN by both compounds as Chou-Talalay combination index analysis showed synergism in AKR1C3 transfected HCT-116, but not in empty vector transfected control cell line. In conclusion, we propose AZD5438 and R547 as modulators of DAUN resistance that can prevent AKR1C3-mediated DAUN biotransformation to DAUN-OL. This interaction could be beneficially exploited to prevent failure of DAUN-based therapy as well as the undesirable cardiotoxic effect of DAUN-OL.

Development of Second-Generation CDK2 Inhibitors for the Prevention of Cisplatin-Induced Hearing Loss

There are currently no FDA-approved therapies to prevent the hearing loss associated with the usage of cisplatin in chemotherapeutic regimens. We recently demonstrated that the pharmacologic inhibition with kenpaullone or genetic deletion of CDK2 preserved hearing function in animal models treated with cisplatin, which suggests that CDK2 is a promising therapeutic target to prevent cisplatin-induced ototoxicity. In this study, we identified two lead compounds, AT7519 and AZD5438, from a focused library screen of 187 CDK2 inhibitors, performed in an immortalized cell line derived from neonatal mouse cochleae treated with cisplatin. Moreover, we screened 36 analogues of AT7519 and identified analogue 7, which exhibited an improved therapeutic index. When delivered locally, analogue 7 and AZD5438 both provided significant protection against cisplatin-induced ototoxicity in mice. Thus, we have identified two additional compounds that prevent cisplatin-induced ototoxicity in vivo and provided further evidence that CDK2 is a druggable target for treating cisplatin-induced ototoxicity.

CDK1 inhibition sensitizes normal cells to DNA damage in a cell cycle dependent manner

Cyclin-dependent kinase 1 (CDK1) orchestrates the transition from the G2 phase into mitosis and as cancer cells often display enhanced CDK1 activity, it has been proposed as a tumor specific anti-cancer target. Here we show that the effects of CDK1 inhibition are not restricted to tumor cells but can also reduce viability in non-cancer cells and sensitize them to radiation in a cell cycle dependent manner. Radiosensitization by the specific CDK1 inhibitor, RO-3306, was determined by colony formation assays in three tumor lines (HeLa, T24, SQ20B) and three non-cancer lines (HFL1, MRC-5, RPE). Initial results showed that CDK1 inhibition radiosensitized tumor cells, but did not sensitize normal fibroblasts and epithelial cells in colony formation assays despite effective inhibition of CDK1 signaling. Further investigation showed that normal cells were less sensitive to CDK1 inhibition because they remained predominantly in G1 for a prolonged period when plated in colony formation assays. In contrast, inhibiting CDK1 a day after plating, when the cells were going through G2/M phase, reduced their clonogenic survival both with and without radiation. Our finding that inhibition of CDK1 can damage normal cells in a cell cycle dependent manner indicates that targeting CDK1 in cancer patients may lead to toxicity in normal proliferating cells. Furthermore, our finding that cell cycle progression becomes easily stalled in non-cancer cells under normal culture conditions has general implications for testing anti-cancer agents in these cells.

Mitochondrial dysfunction RAD51, and Ku80 proteolysis promote apoptotic effects of Dinaciclib in Bcl-xL silenced cells

In the present study, we investigated the effect of CDK inhibitors (ribociclib, palbociclib, seliciclib, AZD5438, and dinaciclib) on malignant human glioma cells for cell viability, apoptosis, oxidative stress, and mitochondrial function using various assays. None of the CDK inhibitors induced cell death at a clinically relevant concentration. However, low nanomolar concentrations of dinaciclib showed higher cytotoxic activity against Bcl-xL silenced cells in a time- and concentration-dependent manner. This effect was not seen with other CDK inhibitors. The apoptosis-inducing capability of dinaciclib in Bcl-xL silenced cells was evidenced by cell shrinkage, mitochondrial dysfunction, DNA damage, and increased phosphatidylserine externalization. Dinaciclib was found to disrupt mitochondrial membrane potential, resulting in the release of cytochrome c, AIF, and smac/DIABLO into the cytoplasm. This was accompanied by the downregulation of cyclin-D1, D3, and total Rb. Dinaciclib caused cell cycle arrest in a time- and concentration-dependent manner and with accumulation of cells in the sub-G1 phase. Our results also revealed that dinaciclib, but not ribociclib or palbociclib or seliciclib or AZD5438 induced intrinsic apoptosis via upregulation of the levels of pro-apoptotic proteins (Bax and Bak), resulting in the activation of caspases and cleavage of PARP. We also found an additional mechanism for the dinaciclib-induced augmentation of apoptosis due to abrogation RAD51-cyclin D1 interaction, specifically proteolysis of the DNA repair proteins RAD51 and Ku80. Our results suggest that successfully interfering with Bcl-xL function may restore sensitivity to dinaciclib and could hold the promise for an effective combination therapeutic strategy.

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.

Recent progress of cyclin-dependent kinase inhibitors as potential anticancer agents

Deregulation of the cell cycle is a common feature in human cancer. The inhibition of cyclin-dependent kinases (CDKs), which play a crucial role in control of the cell cycle, has always been one of the most promising areas in cancer chemotherapy. This review first summarizes the biology of CDKs and then focuses on the recent advances in both broad-range and selective CDK inhibitors during the last 5 years. The design rationale, structural optimization and structure–activity relationships analysis of these small molecules have been discussed in detail and the key interactions with the amino-acid residues of the most important compounds are highlighted. Future perspectives for CDKs inhibitors will be defined in the development of highly selective CDK inhibitors, an accurate knowledge of gene control mechanism and further predictive biomarker research.

Pharmacological cyclin dependent kinase inhibitors: Implications for colorectal cancer

Colorectal cancer accounts for a significant proportion of cancer deaths worldwide. The need to develop more chemotherapeutic agents to combat this disease is critical. Cyclin dependent kinases (CDKs), along with its binding partner cyclins, serve to control the growth of cells through the cell cycle. A new class of drugs, termed CDK inhibitors, has been studied in preclinical and now clinical trials. These inhibitors are believed to act as an anti-cancer drug by blocking CDKs to block the uncontrolled cellular proliferation that is hallmark of cancers like colorectal cancer. CDK article provides overview of the emerging drug class of CDK inhibitors and provides a list of ones that are currently in clinical trials.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

Adapalene inhibits the activity of cyclin-dependent kinase 2 in colorectal carcinoma

Cyclin-dependent kinase 2 (CDK2) has been reported to be overexpressed in human colorectal cancer; it is responsible for the G1‑to‑S‑phase transition in the cell cycle and its deregulation is a hallmark of cancer. The present study was the first to use idock, a free and open‑source protein‑ligand docking software developed by our group, to identify potential CDK2 inhibitors from 4,311 US Food and Drug Administration‑approved small molecular drugs with a re‑purposing strategy. Among the top compounds identified by idock score, nine were selected for further study. Among them, adapalene (ADA; CD271,6‑[3‑(1‑adamantyl)‑4‑methoxyphenyl]‑2‑naphtoic acid) exhibited the highest anti‑proliferative effects in LOVO and DLD1 human colon cancer cell lines. Consistent with the expected properties of CDK2 inhibitors, the present study demonstrated that ADA significantly increased the G1‑phase population and decreased the expression of CDK2, cyclin E and retinoblastoma protein (Rb), as well as the phosphorylation of CDK2 (on Thr‑160) and Rb (on Ser‑795). Furthermore, the anti‑cancer effects of ADA were examined in vivo on xenograft tumors derived from DLD1 human colorectal cancer cells subcutaneously inoculated in BALB/C nude mice. ADA (20 mg/kg orally) exhibited marked anti‑tumor activity, comparable to that of oxaliplatin (40 mg/kg), and dose‑dependently inhibited tumor growth (P<0.05), while combined administration of ADA and oxaliplatin produced the highest therapeutic effect. To the best of our knowledge, the present study was the first to indicate that ADA inhibits CDK2 and is a potential candidate drug for the treatment of human colorectal cancer.

The history and future of targeting cyclin-dependent kinases in cancer therapy

Cancer represents a pathological manifestation of uncontrolled cell division; therefore, it has long been anticipated that our understanding of the basic principles of cell cycle control would result in effective cancer therapies. In particular, cyclin-dependent kinases (CDKs) that promote transition through the cell cycle were expected to be key therapeutic targets because many tumorigenic events ultimately drive proliferation by impinging on CDK4 or CDK6 complexes in the G1 phase of the cell cycle. Moreover, perturbations in chromosomal stability and aspects of S phase and G2/M control mediated by CDK2 and CDK1 are pivotal tumorigenic events. Translating this knowledge into successful clinical development of CDK inhibitors has historically been challenging, and numerous CDK inhibitors have demonstrated disappointing results in clinical trials. Here, we review the biology of CDKs, the rationale for therapeutically targeting discrete kinase complexes and historical clinical results of CDK inhibitors. We also discuss how CDK inhibitors with high selectivity (particularly for both CDK4 and CDK6), in combination with patient stratification, have resulted in more substantial clinical activity.

Amygdalin blocks bladder cancer cell growth in vitro by diminishing cyclin A and cdk2

Amygdalin, a natural compound, has been used by many cancer patients as an alternative approach to treat their illness. However, whether or not this substance truly exerts an anti-tumor effect has never been settled. An in vitro study was initiated to investigate the influence of amygdalin (1.25–10 mg/ml) on the growth of a panel of bladder cancer cell lines (UMUC-3, RT112 and TCCSUP). Tumor growth, proliferation, clonal growth and cell cycle progression were investigated. The cell cycle regulating proteins cdk1, cdk2, cdk4, cyclin A, cyclin B, cyclin D1, p19, p27 as well as the mammalian target of rapamycin (mTOR) related signals phosphoAkt, phosphoRaptor and phosphoRictor were examined. Amygdalin dose-dependently reduced growth and proliferation in all three bladder cancer cell lines, reflected in a significant delay in cell cycle progression and G0/G1 arrest. Molecular evaluation revealed diminished phosphoAkt, phosphoRictor and loss of Cdk and cyclin components. Since the most outstanding effects of amygdalin were observed on the cdk2-cyclin A axis, siRNA knock down studies were carried out, revealing a positive correlation between cdk2/cyclin A expression level and tumor growth. Amygdalin, therefore, may block tumor growth by down-modulating cdk2 and cyclin A. In vivo investigation must follow to assess amygdalin's practical value as an anti-tumor drug.

Dinaciclib for the treatment of breast cancer

INTRODUCTION

Cyclin-dependent kinases (CDK) represent attractive targets in oncology due to their key role in controlling gene transcription and cell cycle progression. Dinaciclib (MK-7965, formerly SCH727965) is a relatively novel CDK 1/2/5/9 inhibitor that has shown promising results in preclinical studies and an acceptable safety profile in Phase I clinical trials. It is currently under clinical evaluation for the treatment of hematological and solid malignancies, including breast cancer.

AREAS COVERED

This review summarizes the current understanding of CDK's role in physiology and cancer, and the therapeutic value of blocking their pathways in breast cancer. Particularly, the article reviews the preclinical and clinical data for dinaciclib in its use for the treatment of breast cancer.

EXPERT OPINION

A better understanding of the molecular mechanisms underlying cell cycle dysregulation in cancer is needed in order to develop novel CDK inhibitors. Additionally, further efforts are needed to identify potential biomarkers of dinaciclib efficacy, which could allow a better selection of patients enrolled in clinical trials. Moreover, combination therapies with dinaciclib or other CDK and chemotherapy, endocrine therapy or targeted therapies might be further evaluated in breast cancer patients.

A first-in-human, phase 1, dose-escalation study of dinaciclib, a novel cyclin-dependent kinase inhibitor, administered weekly in subjects with advanced malignancies

Background

Dinaciclib, a small-molecule, cyclin-dependent kinase inhibitor, inhibits cell cycle progression and proliferation in various tumor cell lines in vitro. We conducted an open-label, dose-escalation study to determine the safety, tolerability, and bioactivity of dinaciclib in adults with advanced malignancies.

Methods

Dinaciclib was administered starting at a dose of 0.33 mg/m², as a 2-hour intravenous infusion once weekly for 3 weeks (on days 1, 8, and 15 of a 28-day cycle), to determine the maximum administered dose (MAD), dose-limiting toxicities (DLTs), recommended phase 2 dose (RP2D), and safety and tolerability. Pharmacodynamics of dinaciclib were assessed using an ex vivo phytohemagglutinin lymphocyte stimulation assay and immunohistochemistry staining for retinoblastoma protein phosphorylation in skin biopsies. Evidence of antitumor activity was assessed by sequential computed tomography imaging after every 2 treatment cycles.

Results

Forty-eight subjects with solid tumors were treated. The MAD was found to be 14 mg/m² and the RP2D was determined to be 12 mg/m²; DLTs at the MAD included orthostatic hypotension and elevated uric acid. Forty-seven (98%) subjects reported adverse events (AEs) across all dose levels; the most common AEs were nausea, anemia, decreased appetite, and fatigue. Dinaciclib administered at the RP2D significantly inhibited lymphocyte proliferation, demonstrating a pharmacodynamic effect. Ten subjects treated at a variety of doses achieved prolonged stable disease for at least 4 treatment cycles.

Conclusions

Dinaciclib administered every week for 3 weeks (on days 1, 8, and 15 of a 28-day cycle) was generally safe and well tolerated. Initial bioactivity and observed disease stabilization support further evaluation of dinaciclib as a treatment option for patients with advanced solid malignancies.

Trial registration

ClinicalTrials.gov # NCT00871663

Targeting cell cycle regulation in cancer therapy

Cell proliferation is an essential mechanism for growth, development and regeneration of eukaryotic organisms; however, it is also the cause of one of the most devastating diseases of our era: cancer. Given the relevance of the processes in which cell proliferation is involved, its regulation is of paramount importance for multicellular organisms. Cell division is orchestrated by a complex network of interactions between proteins, metabolism and microenvironment including several signaling pathways and mechanisms of control aiming to enable cell proliferation only in response to specific stimuli and under adequate conditions. Three main players have been identified in the coordinated variation of the many molecules that play a role in cell cycle: i) The cell cycle protein machinery including cyclin-dependent kinases (CDK)-cyclin complexes and related kinases, ii) The metabolic enzymes and related metabolites and iii) The reactive-oxygen species (ROS) and cellular redox status. The role of these key players and the interaction between oscillatory and non-oscillatory species have proved essential for driving the cell cycle. Moreover, cancer development has been associated to defects in all of them. Here, we provide an overview on the role of CDK-cyclin complexes, metabolic adaptations and oxidative stress in regulating progression through each cell cycle phase and transitions between them. Thus, new approaches for the design of innovative cancer therapies targeting crosstalk between cell cycle simultaneous events are proposed.

AZD5438, an inhibitor of Cdk1, 2, and 9, enhances the radiosensitivity of non-small cell lung carcinoma cells

PURPOSE

Radiation therapy (RT) is one of the primary modalities for treatment of non-small cell lung cancer (NSCLC). However, due to the intrinsic radiation resistance of these tumors, many patients experience RT failure, which leads to considerable tumor progression including regional lymph node and distant metastasis. This preclinical study evaluated the efficacy of a new-generation cyclin-dependent kinase (Cdk) inhibitor, AZD5438, as a radiosensitizer in several NSCLC models that are specifically resistant to conventional fractionated RT.

METHODS AND MATERIALS

The combined effect of ionizing radiation and AZD5438, a highly specific inhibitor of Cdk1, 2, and 9, was determined in vitro by surviving fraction, cell cycle distribution, apoptosis, DNA double-strand break (DSB) repair, and homologous recombination (HR) assays in 3 NSCLC cell lines (A549, H1299, and H460). For in vivo studies, human xenograft animal models in athymic nude mice were used.

RESULTS

Treatment of NSCLC cells with AZD5438 significantly augmented cellular radiosensitivity (dose enhancement ratio rangeing from 1.4 to 1.75). The degree of radiosensitization by AZD5438 was greater in radioresistant cell lines (A549 and H1299). Radiosensitivity was enhanced specifically through inhibition of Cdk1, prolonged G(2)-M arrest, inhibition of HR, delayed DNA DSB repair, and increased apoptosis. Combined treatment with AZD5438 and irradiation also enhanced tumor growth delay, with an enhancement factor ranging from 1.2-1.7.

CONCLUSIONS

This study supports the evaluation of newer generation Cdk inhibitors, such as AZD5438, as potent radiosensitizers in NSCLC models, especially in tumors that demonstrate variable intrinsic radiation responses.

Phase I study of the safety, tolerability and pharmacokinetics of PHA-848125AC, a dual tropomyosin receptor kinase A and cyclin-dependent kinase inhibitor, in patients with advanced solid malignancies

PURPOSE

This phase I trial assessed the safety, maximally tolerated dose (MTD) and pharmacokinetics of TRKA/CDK inhibitor PHA-848125AC in adult patients with advanced/metastatic solid tumors.

PATIENTS AND METHODS

Patients with relapsed or refractory solid tumors, for which no standard therapy existed, were eligible. PHA-848125AC was administered orally in two schedules: daily for 7 consecutive days in 2-week cycles (i.e. 7 days on/7 days off q2wks; S1) or daily for 4 consecutive days a week for 3 weeks in 4-week cycles (i.e. 4 days on/3 days off x 3wks q4wks; S2).

RESULTS

Thirty-seven patients were treated in this study, 22 in S1 and 15 in S2. The recommended phase II dose (RP2D) was 150 mg/day for either schedule. The dose-limiting toxicities (DLTs) in S1 included ataxia (Grade 2-4) and tremors (Grade 2-3). In S2, DLTs included tremors (Grade 2-3), elevated lipase (Grade 3), increased creatinine (Grade 2), and nausea and vomiting (Grade 3). These events were all reversible. In S2, out of 14 patients evaluable for efficacy, 2 patients with thymic carcinoma, showed partial response and stable disease was observed in 3 patients. Stable disease was observed in 6 out 14 patients evaluable for efficacy on S1. Drug pharmacokinetics demonstrated a half-life of approximately 33 h, and dose-proportionality with accumulation by a factor of 3 after repeated administrations.

CONCLUSION

The RP2D of PHA-848125AC was 150 mg/day on both schedules. Based on the responses noted in thymic carcinoma, a phase II study for patients with that disease is currently enrolling.

Cyclin-dependent kinases (cdks) and the DNA damage response: rationale for cdk inhibitor-chemotherapy combinations as an anticancer strategy for solid tumors

IMPORTANCE OF THE FIELD

The eukaryotic cell division cycle is a tightly regulated series of events coordinated by the periodic activation of multiple cyclin-dependent kinases (cdks). Small-molecule cdk-inhibitory compounds have demonstrated preclinical synergism with DNA-damaging agents in solid tumor models. An improved understanding of how cdks regulate the DNA damage response now provides an opportunity for optimization of combinations of cdk inhibitors and DNA damaging chemotherapy agents that can be translated to clinical settings.

AREAS COVERED IN THIS REVIEW

Here, we discuss novel work uncovering multiple roles for cdks in the DNA-damage-response network. First, they activate DNA damage checkpoint and repair pathways. Later their activity is turned off, resulting in cell cycle arrest, allowing time for DNA repair to occur. Recent clinical data on cdk inhibitor-DNA-damaging agent combinations are also discussed.

WHAT THE READER WILL GAIN

Readers will learn about novel areas of cdk biology, the complexity of DNA damage signaling networks and clinical implications.

TAKE HOME MESSAGE

New data demonstrate that cdks are 'master' regulators of DNA damage checkpoint and repair pathways. Cdk inhibition may therefore provide a means of potentiating the clinical activity of DNA-damaging chemotherapeutic agents for the treatment of cancer.

Phase I evaluation of seliciclib (R-roscovitine), a novel oral cyclin-dependent kinase inhibitor, in patients with advanced malignancies

AIM

Phase I study of seliciclib (CYC202, R-roscovitine), an inhibitor of cyclin-dependent kinases 2, 7 and 9, causing cell cycle changes and apoptosis in cancer cells.

PATIENTS AND METHODS

This phase I trial aimed at defining the toxicity profile, the maximum tolerated dose (MTD), the recommended phase II dose (RD) and the main pharmacokinetic and pharmacodynamic parameters of oral seliciclib. Three schedules were evaluated: seliciclib given twice daily for 5 consecutive days every 3 weeks (schedule A), for 10 consecutive days followed by 2 weeks off (schedule B) and for 3d every 2 weeks (schedule C).

RESULTS

Fifty-six patients received a total of 218 cycles of seliciclib. Dose-Limiting Toxicities (DLT) consisting of nausea, vomiting, asthenia and hypokalaemia occurred at 1600 mg bid for schedule A and in schedule C, DLT of hypokalaemia and asthenia occurred at 1800 mg bid. The evaluation of longer treatment duration in schedule B was discontinued because of unacceptable toxicity at lower doses. Other adverse events included transient serum creatinine increases and liver dysfunctions. Pharmacokinetic data showed that exposure to seliciclib and its carboxylate metabolite increased with increasing dose. Soluble cytokeratin 18 fragments allowed monitoring of seliciclib-induced cell death in the blood of patients treated with seliciclib at doses above 800 mg/d. One partial response in a patient with hepatocellular carcinoma and sustained tumour stabilisations were observed.

CONCLUSIONS

The MTD and RD for seliciclib are 1250 mg bid for 5d every 3 weeks and 1600 mg bid for 3d every 2 weeks, respectively.

A molecular risk score based on 4 functional pathways for advanced classical Hodgkin lymphoma

Despite improvement in the treatment of advanced classical Hodgkin lymphoma, approximately 30% of patients relapse or die as result of the disease. Current predictive systems, determined by clinical and analytical parameters, fail to identify these high-risk patients accurately. We took a multistep approach to design a quantitative reverse-transcription polymerase chain reaction assay to be applied to routine formalin-fixed paraffin-embedded samples, integrating genes expressed by the tumor cells and their microenvironment. The significance of 30 genes chosen on the basis of previously published data was evaluated in 282 samples (divided into estimation and validation sets) to build a molecular risk score to predict failure. Adequate reverse-transcription polymerase chain reaction profiles were obtained from 262 of 282 cases (92.9%). Best predictor genes were integrated into an 11-gene model, including 4 functional pathways (cell cycle, apoptosis, macrophage activation, and interferon regulatory factor 4) able to identify low- and high-risk patients with different rates of 5-year failure-free survival: 74% versus 44.1% in the estimation set (P < .001) and 67.5% versus 45.0% in the validation set (P = .022). This model can be combined with stage IV into a final predictive model able to identify a group of patients with very bad outcome (5-year failure-free survival probability, 25.2%).

Transcriptional analysis of an E2F gene signature as a biomarker of activity of the cyclin-dependent kinase inhibitor PHA-793887 in tumor and skin biopsies from a phase I clinical study

A transcriptional signature of the pan-cyclin-dependent kinase (Cdk) inhibitor PHA-793887 was evaluated as a potential pharmacodynamic and/or response biomarker in tumor and skin biopsies from patients treated in a phase I clinical study. We first analyzed the expression of a number of known E2F-dependent genes that were predicted to be modulated after Cdk2 and Cdk4 inhibition in xenograft tumor and skin samples of mice treated with the compound. This panel of 58 selected genes was then analyzed in biopsies from seven patients treated with PHA-793887 in a phase I dose escalation clinical trial in solid tumors. Quantitative real-time PCR or microarray analyses were done in paired skin and tumor biopsies obtained at baseline and at cycle 1. Analysis by quantitative real-time PCR of the signature in skin biopsies of patients treated at three different doses showed significant transcriptional downregulation with a dose-response correlation. These data show that PHA-793887 modulates genes involved in cell cycle regulation and proliferation in a clinical setting. The observed changes are consistent with its mechanism of action and correlate with target modulation in skin and with clinical benefit in tumors.