Cell proliferation without cyclin E-CDK2

Oncological Properties of Intravenous Leiomyomatosis: Involvement of Mesenchymal Tumor Stem-Like Cells

Uterine leiomyoma, also known as fibroids, is the most common benign neoplasm of the female genital tract. Leiomyoma is the most common uterine tumor. The leiomyoma subtypes account for approximately 10% of leiomyomas. Intravenous leiomyomatosis, a uterine leiomyoma subtype, is an intravascular growth of benign smooth muscle cells, occasionally with pelvic or extrapelvic extension. Uterine leiomyosarcoma, a malignant tumor, tends to metastasize hematogenously, and distant metastasis to the lungs and liver is common. Therefore, the oncological properties of this intravenous leiomyomatosis resemble those of the malignant tumor uterine leiomyosarcoma. Cancer stem cells migrate to distant organs via intravascular infiltration, leading to micrometastases. We examined the oncological properties of intravenous leiomyomatosis using molecular pathological techniques on tissue excised from patients with uterine leiomyoma. CD44-positive mesenchymal tumor stem-like cells were detected in both patients with intravenous leiomyomatosis and uterine leiomyosarcoma. The oncological properties of intravenous leiomyomatosis were found to be similar to those of uterine leiomyosarcoma. However, in intravenous leiomyomatosis, cyclin E and Ki-67-positive cells were rare and no pathological findings suspecting malignancy were observed. It is expected that establishing a treatment method targeting cancer stem cells will lead to the treatment of malignant tumors with a low risk of recurrence and metastasis.

Tethering of Telomeres to the Nuclear Envelope Is Mediated by SUN1-MAJIN and Possibly Promoted by SPDYA-CDK2 During Meiosis

During meiosis, telomeres attach to the nuclear envelope (NE) to promote homologous chromosome moving, pairing, synapsis, and recombination. The telomere-NE attachment is mediated by SUN1, TERB1-TERB2-MAJIN (TTM complex), and TRF1. The interaction of the TTM complex with shelterin is mediated by TERB1 and TRF1, but how SUN1 interacts with the TTM complex is not yet fully understood. In this study, we found that SUN1 not only interacted with TERB1 but also interacted with MAJIN, and the interaction of SUN1 with MAJIN is stronger than TERB1. We also found that SUN1 interacted with SPDYA, an activator of CDK2. The binding sites of MAJIN and SPDYA at SUN1 were mapped, and both MAJIN and SPDYA bound to the N-terminal domain of SUN1 and the two binding sites were close to each other. Furthermore, SPDYA bound to SUN1 via the Ringo domain and recruited CDK2 to SUN1. Then, we found that the interaction of SUN1 with MAJIN was decreased by the CDK2 inhibitors. Taken together, our results provide the possible mechanism of SUN1, MAJIN, and SPDYA-CDK2 in promoting the telomere-NE attachment during meiosis.

The effect of curcumin on the differentiation, apoptosis and cell cycle of neural stem cells is mediated through inhibiting autophagy by the modulation of Atg7 and p62

Curcumin is an orange-yellow colored, lipophilic polyphenol substance derived from the rhizome of Curcuma longa that is widely used in many countries. Curcumin has many reported functions, including antioxidant and anti‑inflammatory effects. Autophagy removes damaged organelles and protein aggregates in the cell. However, whether curcumin mediates its effects on neural stem cell (NSC) differentiation, cell cycle and apoptosis through autophagy is unknown. In the present study, the effects of curcumin and 3‑methyladenine (3MA; an autophagy inhibitor, as a positive control) on the autophagy, differentiation, cell cycle progression and apoptosis of NSCs in different culture states were examined. In order to confirm the role of autophagy in these processes of NSC behavioral change, the protein expression level changes of markers of autophagy, such as autophagy‑related protein 7 (Atg7), light chain (LC)3 and p62, were assessed. When NSCs were in an adherent state, 10 µM curcumin inhibited their differentiation into GFAP+ astrocytes or DCX+ immature neurons, while Atg7 and p62 protein expression were also reduced compared with the untreated control group. When NSCs were in a suspended state, 10 µM curcumin inhibited the cell cycle progression and apoptosis of NSCs as determined by western blotting, which was associated with a decreased autophagic flux and Atg7 expression. In addition, the curcumin‑treated group trended in a similar direction to the 3MA‑treated group. Thus, the data suggest that curcumin can inhibit differentiation, promote cell survival and inhibit cell cycle progression from G1 to S in NSCs, and that these effects are mediated through the regulation of Atg7 and p62.

Cell cycle, cytoskeleton dynamics and beyond: the many functions of cyclins and CDK inhibitors

While targeting experiments carried out on the genes encoding many cell cycle regulators have challenged our views of cell cycle control, they also suggest that redundancy might not be the only explanation for the observed perplexing phenotypes. Indeed, several observations hint at functions of cyclins and CDK inhibitors that cannot be accounted for by their sole role as kinase regulators. They are found involved in many cellular transactions, depending or not on CDKs that are not directly linked to cell cycle control, but participating to general mechanisms such as transcription, DNA repair or cytoskeleton dynamics. In this review we discuss the roles that these alternative functions might have in cancer cell proliferation and migration that sometime even challenge their definition as proliferation markers.

Recent advances in the identification of Tat-mediated transactivation inhibitors: progressing toward a functional cure of HIV

The current anti-HIV combination therapy does not eradicate the virus that persists mainly in quiescent infected CD4(+) T cells as a latent integrated provirus that resumes after therapy interruption. The Tat-mediated transactivation (TMT) is a critical step in the HIV replication cycle that could give the opportunity to reduce the size of latent reservoirs. More than two decades of research led to the identification of various TMT inhibitors. While none of them met the criteria to reach the market, the search for a suitable TMT inhibitor is still actively pursued. Really promising compounds, including one in a Phase III clinical trial, have been recently identified, thus warranting an update.

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.

Dual targeting of CDK and tropomyosin receptor kinase families by the oral inhibitor PHA-848125, an agent with broad-spectrum antitumor efficacy

Altered expression and activity of cyclin-dependent kinase (CDK) and tropomyosin receptor kinase (TRK) families are observed in a wide variety of tumors. In those malignancies with aberrant CDK activation, the retinoblastoma protein (pRb) pathway is deregulated, leading to uncontrolled cell proliferation. Constitutive activation of TRKs is instead linked to cancer cell survival and dissemination. Here, we show that the novel small-molecule PHA-848125, a potent dual inhibitor of CDKs and TRKs, possesses significant antitumor activity. The compound inhibits cell proliferation of a wide panel of tumoral cell lines with submicromolar IC(50). PHA-848125-treated cells show cell cycle arrest in G(1) and reduced DNA synthesis, accompanied by inhibition of pRb phosphorylation and modulation of other CDK-dependent markers. The compound additionally inhibits phosphorylation of TRKA and its substrates in cells, which functionally express this receptor. Following oral administration, PHA-848125 has significant antitumor activity in various human xenografts and carcinogen-induced tumors as well as in disseminated primary leukemia models, with plasma concentrations in rodents in the same range as those found active in inhibiting cancer cell proliferation. Mechanism of action was also confirmed in vivo as assessed in tumor biopsies from treated mice. These results show that the dual CDK-TRK inhibitor PHA-848125 has the potential for being a novel and efficacious targeted drug for cancer treatment.

Thymoquinone hydrazone derivatives cause cell cycle arrest in p53-competent colorectal cancer cells

Thymoquinone (TQ), the major compound of black seed oil, has been shown to induce pro-apoptotic signaling pathways in various human cancer models. Although TQ is commonly used in traditional medicine, its use in humans is limited due to its chemical properties and poor membrane penetration capacity. We therefore attached saturated and unsaturated fatty acid residues to TQ and evaluated the effect on cell proliferation, apoptosis and underlying signaling pathways in HCT116 and HCT116(p53-/-) colon cancer and HepG2 hepatoma cells in vitro. Treatment with thymoquinone-4-α-linolenoylhydrazone (TQ-H-10) or thymoquinone-4-palmitoylhydrazone (TQ-H-11) induced a cytostatic effect, particularly in p53-competent HCT116 cells, mediated by an up-regulation of p21(cip1/waf1) and a down-regulation of cyclin E, and associated with an S/G(2) arrest of the cell cycle. Cells lacking p53 (HCT116(p53-/-)) or HepG2 liver cancer cells showed only a minor response to TQ-H-10. These findings demonstrate that derivatives of TQ inhibit cell proliferation dependent on p53 status by activating the cell cycle inhibitor p21(cip1/waf1) at lower concentrations than unmodified TQ. Structural modifications can therefore contribute to the further clinical development of TQ.

Inhibition of human immunodeficiency virus type 1 transcription by N-aminoimidazole derivatives

This study describes the mechanism of antiviral action of the N-aminoimidazole derivatives which exclusively inhibit retroviruses such as HIV-1, HIV-2, SIV and MSV. These antiretroviral compounds, with lead prototype NR-818, were found to inhibit HIV-1 replication at the transcriptional level. Analysis of each individual step of viral transcription, including transcriptional activation mediated by NF-kappaB, the chromatin remodeling process at the viral promoter and viral mRNA transcription mediated by RNAPII, showed that NR-818 was able to prolong the binding of NF-kappaB to its consensus sequence. The compound also increased the acetylation of histones H3 and H4 within the nucleosome nuc-1 at the transcription initiation site and inhibited the recruitment of viral Tat and the phosphorylation of the RNA polymerase II C-terminal domain (RNAPII CTD) at the viral promoter upon stimulation of latently HIV-1-infected cell lines. As a result, viral mRNA expression and subsequent viral p24 production in stimulated latently HIV-1-infected cell lines was suppressed by NR-818. These data suggest that the N-aminoimidazole derivatives effectively inhibit the reactivation of HIV-1 and may contribute to the control of the latent HIV-1 reservoir.

Discovery of a potent CDK2 inhibitor with a novel binding mode, using virtual screening and initial, structure-guided lead scoping

Virtual screening against a pCDK2/cyclin A crystal structure led to the identification of a potent and novel CDK2 inhibitor, which exhibited an unusual mode of interaction with the kinase binding motif. With the aid of X-ray crystallography and modelling, a medicinal chemistry strategy was implemented to probe the interactions seen in the crystal structure and to establish SAR. A fragment-based approach was also considered but a different, more conventional, binding mode was observed. Compound selectivity against GSK-3beta was improved using a rational design strategy, with crystallographic verification of the CDK2 binding mode.

Developmental expression of Cyclin H and Cdk7 in zebrafish: the essential role of Cyclin H during early embryo development

Cyclin-dependent kinase 7 (Cdk7) is the catalytic subunit of the metazoan Cdk-activating kinase (CAK). Activation of Cdk7 requires its association with a regulatory subunit, Cyclin H. Although the Cdk7/Cyclin H complex has been implicated in the regulation of RNA polymerase in several species, the precise function of their orthologs in zebrafish has not been fully elucidated. In this study, we isolated from zebrafish blastula embryos two cDNAs encoding the orthologs of human Cyclin H and Cdk7, and examined the role of Cdk7/Cyclin H in zebrafish embryogenesis. Sequence analysis showed that the zebrafish Cyclin H and Cdk7 cDNAs encode proteins with 65% and 86% identity to the respective human orthologs. RT-PCR and whole-mount in situ hybridization analyses of their expression in unfertilized eggs, embryos and organs of adult fish suggested that Cyclin H and Cdk7 messages are maternally loaded. Our data also showed that their transcripts were detected throughout development. Distribution of Cyclin H transcripts was found to be ubiquitous during early stages of development and become restricted to the anterior neural tube, brain, eyes, procreate tissues, liver and heart by 5 days post-fertilization. Expression of a dominant-negative form of Cyclin H delayed the onset of zygotic transcription in the early embryo, resulting in apoptosis at 5 hours post-fertilization and leading to sever defects in tissues normally exhibiting high levels of Cyclin H expression. These results implicate Cyclin H in the regulation of the transcriptional machinery during midblastula transition and suggest that it is an essential gene in early zebrafish larval development.

Triazolo[1,5-a]pyrimidines as novel CDK2 inhibitors: Protein structure-guided design and SAR

Crystallographic and modelling data, in conjunction with a medicinal chemistry template-hopping approach, led to the identification of a series of novel and potent inhibitors of human cyclin-dependent kinase 2 (CDK2), with selectivity over glycogen synthase kinase-3beta (GSK-3beta). One example had a CDK2 IC(50) of 120 nM and showed selectivity over GSK-3beta of 167-fold.

3-Amino-1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles: A new class of CDK2 inhibitors

We have recently reported about a new class of Aurora-A inhibitors based on a bicyclic tetrahydropyrrolo[3,4-c]pyrazole scaffold. Here we describe the synthesis and early expansion of CDK2/cyclin A-E inhibitors belonging to the same chemical class. Synthesis of the compounds was accomplished using a solution-phase protocol amenable to rapid parallel expansion. Compounds with nanomolar activity in the biochemical assay and able to efficiently inhibit CDK2-mediated tumor cell proliferation have been obtained.

Inhibitors of cyclin-dependent kinase modulators for cancer therapy

Most human malignancies have an aberration in the Rb pathway due to 'cdk hyperactivation'. Several small-molecule cdk modulators are being discovered and tested in the clinic. The first ATP-competitive cdk inhibitors tested in clinical trials, flavopiridol and UCN-01, have shown promising results with evidence of antitumor activity and plasma concentrations sufficient to inhibit cdk-related functions. The best schedule to be administered, combination with standard chemotherapeutic agents, best tumor types to be targeted, and demonstration of cdk modulation from tumor samples from patients in these trials are important issues that need to be answered to advance these agents to the clinical arena.

Inhibition of HIV-1 virus replication using small soluble Tat peptides

Although the introduction of highly active antiretroviral therapy (HAART) has led to a significant reduction in AIDS-related morbidity and mortality, unfortunately, many patients discontinue their initial HAART regimen, resulting in development of viral resistance. During HIV infection, the viral activator Tat is needed for viral progeny formation, and the basic and core domains of Tat are the most conserved parts of the protein. Here, we show that a Tat 41/44 peptide from the core domain can inhibit HIV-1 gene expression and replication. The peptides are not toxic to cells and target the Cdk2/Cyclin E complex, inhibiting the phosphorylation of serine 5 of RNAPII. Using the Cdk2 X-ray crystallography structure, we found that the low-energy wild-type peptides could bind to the ATP binding pocket, whereas the mutant peptide bound to the Cdk2 interface. Finally, we show that these peptides do not allow loading of the catalytic domain of the cdk/cyclin complex onto the HIV-1 promoter in vivo.

Structure-guided design of pyrazolo[1,5-a]pyrimidines as inhibitors of human cyclin-dependent kinase 2

The protein structure guided design of a series of pyrazolo[1,5-a]pyrimidines with high potency for human cyclin-dependent kinase 2 (CDK2) is described. Some examples were shown to inhibit the growth of human colon tumour cells, were equipotent for CDK1 and were selective against GSK-3beta and other kinases.

Antiviral Activity of CYC202 in HIV-1-infected Cells

There are currently 40 million individuals in the world infected with human immunodeficiency virus (HIV). The introduction of highly active antiretroviral therapy (HAART) has led to a significant reduction in AIDS-related morbidity and mortality. Unfortunately, up to 25% of patients discontinue their initial HAART regimen. Current HIV-1 inhibitors target the fusion of the virus to the cell and two viral proteins, reverse transcriptase and protease. Here, we examined whether other targets, such as an activated transcription factor, could be targeted to block HIV-1 replication. We specifically asked whether we could target a cellular kinase needed for HIV-1 transcription using CYC202 (R-roscovitine), a pharmacological cyclin-dependent kinase inhibitor. We targeted the cdk2-cyclin E complex in HIV-1-infected cells because both cdk2 and cyclin E are nonessential during mammalian development and are likely replaced by other kinases. We found that CYC202 effectively inhibits wild type and resistant HIV-1 mutants in T-cells, monocytes, and peripheral blood mononuclear cells at a low IC(50) and sensitizes these cells to enhanced apoptosis resulting in a dramatic drop in viral titers. Interestingly, the effect of CYC202 is independent of cell cycle stage and more specific for the cdk2-cyclin E complex. Finally, we show that cdk2-cyclin E is loaded onto the HIV-1 genome in vivo and that CYC202 is able to inhibit the uploading of this cdk-cyclin complex onto HIV-1 DNA. Therefore, targeting cellular enzymes necessary for HIV-1 transcription, which are not needed for cell survival, is a compelling strategy to inhibit wild type and mutant HIV-1 strains.

p42, a novel cyclin-dependent kinase-activating kinase in mammalian cells

The cyclin-dependent kinase (CDK)-activating kinase (CAK) phosphorylates a conserved threonine residue on CDKs and activates them. Two known classes of CAKs are represented by monomeric Cak1p in budding yeast Saccharomyces cerevisiae and by heterotrimeric CDK7-cyclin H-Mat1 in human and other metazoa. We report here the identification of p42, a novel CAK activity in human cells. p42 has sequence homology to both Cak1p and CDK7 groups of CAKs. p42 is essential for the phosphorylation of Thr-160 and activation of CDK2. A dominant-negative p42 mutant, T161A, and posttranscriptional gene silencing of p42 with RNA(i)-impaired Thr-160 phosphorylation and activity of CDK2. Purified p42 phosphorylated glutathione S-transferase-CDK2 at Thr-160 within the T-loop and activated its histone H1 kinase activity. Finally, p42 is indispensable for cell growth. Cells lacking p42 were incapable of growing and forming colonies whereas cells with a reduced level of p42 grew at significantly slower rates than control cells. Our findings suggest that p42 represents a novel CAK activity in mammalian cells.