A systematic review on understanding the mechanistic pathways and clinical aspects of natural CDK inhibitors on cancer progression.: Unlocking cellular and biochemical mechanisms.

Cell division, differentiation, and controlled cell death are all regulated by phosphorylation, a key biological function. This mechanism is controlled by a variety of enzymes, with cyclin-dependent kinases (CDKs) being particularly important in phosphorylating proteins at serine and threonine sites. CDKs, which contain 20 unique components, serve an important role in regulating vital physiological functions such as cell cycle progression and gene transcription. Methodologically, an extensive literature search was performed using reputable databases such as PubMed, Google Scholar, Scopus, and Web of Science. Keywords encompassed "cyclin kinase," "cyclin dependent kinase inhibitors," "CDK inhibitors," "natural products," and "cancer therapy." The inclusion criteria, focused on relevance, publication date, and language, ensured a thorough representation of the most recent research in the field, encompassing articles published from January 2015 to September 2023. Categorization of CDKs into those regulating transcription and those orchestrating cell cycle phases provides a comprehensive understanding of their diverse functions. Ongoing clinical trials featuring CDK inhibitors, notably CDK7 and CDK4/6 inhibitors, illuminate their promising potential in various cancer treatments. This review undertakes a thorough investigation of CDK inhibitors derived from natural (marine, terrestrial, and peptide) sources. The aim of this study is to provide a comprehensive comprehension of the chemical classifications, origins, target CDKs, associated cancer types, and therapeutic applications.

The association between HER2-low status and survival in patients with metastatic breast cancer treated with Cyclin-dependent kinases 4 and 6 inhibitors: a systematic review and meta-analysis.

PURPOSE: The cyclin-dependent kinase (CDK) 4/6 inhibitors significantly altered the treatment landscape of hormone-positive (HR+), HER2- metastatic breast cancer (MBC). However, biomarkers predicting long-term benefit and early progression are yet to be defined. Several studies suggested the possibility of diminished efficacy in patients with HER2-low disease. Therefore, we conducted a systematic review and meta-analysis to evaluate the association between low-level HER2 expression and efficacy outcomes (PFS, OS, ORR) with CDK 4/6 inhibitors. METHODS: The Pubmed, Web of Science, and Scopus databases were used to systematically filter the published studies from inception to 08 August 2023 for this systemic review. Studies including MBC patients treated with CDK 4/6 inhibitors and reported survival outcomes according to HER2 expression were included. We performed the meta-analyses with the generic inverse-variance method with a fixed-effects model and used HRs with 95% two-sided CIs as the principal summary measure. RESULTS: Nine studies encompassing 2705 patients were included in the analyses. In the pooled analysis of nine studies, the risk of progression and/or death was higher in patients with HER2-low tumors compared to HER2-zero (HR: 1.22, 95% CI 1.10-1.35, p < 0.001). In the pooled analysis of five studies, although the median follow-up was short, the risk of death was higher in the HER2-low group compared to the HER2-zero group (HR: 1.22, 95% CI 1.04-1.44, p = 0.010). CONCLUSION: The available evidence demonstrates a significantly higher risk of progression or death with CDK 4/6 inhibitors in HER2-low tumors. Further research is needed to improve outcomes in patients with HR+-HER2-low tumors.

Targeting cyclin-dependent kinases in rheumatoid arthritis and psoriasis - a review of current evidence.

INTRODUCTION: Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with synovial proliferation and bone erosion, which leads to the structural and functional impairment of the joints. Immune cells, together with synoviocytes, induce a pro-inflammatory environment and novel treatment agents target inflammatory cytokines. Psoriasis is a chronic immune-mediated skin disease, and several cytokines are considered as typical mediators in the progression of the disease, including IL-23, IL-22, and IL-17, among others. AREA COVERED: In this review, we try to evaluate whether cyclin-dependent kinases (CDK), enzymes that regulate cell cycle and transcription of various genes, could become novel therapeutic targets in RA and psoriasis. We present the main results of in vitro and in vivo studies, as well as scarce clinical reports. EXPERT OPINION: CDK inhibitors seem promising for treating RA and psoriasis because of their multidirectional effects. CDK inhibitors may affect not only the process of osteoclastogenesis, thereby reducing joint destruction in RA, but also the process of apoptosis of neutrophils and macrophages responsible for the development of inflammation in both RA and psoriasis. However, assessing the efficacy of these drugs in clinical practice requires multi-center, long-term clinical trials evaluating the effectiveness and safety of CDK-blocking therapy in RA and psoriasis.

Breast cancers with high proliferation and low ER-related signalling have poor prognosis and unique molecular features with implications for therapy.

BACKGROUND: Luminal breast cancers with high proliferation (MKShi) and low ER-related signalling (ERSlo) have a poor prognosis. We investigated treatment responses and molecular features of MKShi/ERSlo tumours to inform potential therapies. METHODS: Gene expression data from patients who received neoadjuvant chemotherapy (NAC) without (MDACC, N = 199) or with pembrolizumab (I-SPY2, N = 40), or endocrine therapy (NET) without (POETIC, N = 172) or with palbociclib (NeoPalAna, N = 32) were analyzed to assess treatment response by MKS/ERS-subgroups. TCGA was used to assess the mutational landscape and biomarkers associated with palbociclib-resistance (Cyclin-E, RBsig, IRPR) and immunotherapy-response (TMB, TILs, T-cell inflamed) by MKS/ERS-subgroups. RESULTS: Compared to MKShi/ERShi tumours, MKShi/ERSlo tumours had higher pathological response rates to NAC (22% vs 8%, p = 0.06) but a higher recurrence risk (4-year metastasis-free survival 70% vs 94%, p = 0.01). MKShi/ERSlo tumours frequently harboured TP53 (34%) and PIK3CA (33%) mutations, and showed high expression of Cyclin-E, RBsig and IRPR, high TMB and elevated TIL and T-cell inflamed metagene expression. MKShi/ERSlo tumours retained high proliferation after NET with or without palbociclib but had higher pathological complete response rates when pembrolizumab was added to NAC (42% vs 21%, p = 0.07). CONCLUSIONS: MKShi/ERSlo tumours have dismal outcomes and are enriched in chemotherapy-sensitive but ET- and palbociclib-resistant tumours. Biomarker analysis and clinical data suggest a potential role for immunotherapy in this group.

Essential oil of lemon myrtle (Backhousia citriodora) induces S-phase cell cycle arrest and apoptosis in HepG2 cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Lemon myrtle (Backhousia citriodora F.Muell.) leaves, whether fresh or dried, are used traditionally in folk medicine to treat wounds, cancers, skin infections, and other infectious conditions. However, the targets and mechanisms related to anti-cancer effect of lemon myrtle are unavailable. In our study, we found that the essential oil of lemon myrtle (LMEO) showed anti-cancer activity in vitro, and we initially explored its mechanism of action. MATERIALS AND METHODS: We analyzed the chemical compositions of LMEO by GC-MS. We tested the cytotoxicity of LMEO on various cancer cell lines using the MTT assay. Network pharmacology was used also to analyze the targets of LMEO. Moreover, the mechanisms of LMEO were investigated through scratch assay, flow cytometry analysis, and western blot in the HepG2 liver cancer cell line. RESULTS: LMEO showed cytotoxicity on various cancer cell lines with values of IC50 40.90 ± 2.23 (liver cancer HepG2 cell line), 58.60 ± 6.76 (human neuroblastoma SH-SY5Y cell line), 68.91 ± 4.62 (human colon cancer HT-29 cell line) and 57.57 ± 7.61 µg/mL (human non-small cell lung cancer A549 cell line), respectively. The major cytotoxic chemical constituent in LMEO was identified as citrals, which accounted for 74.9% of the content. Network pharmacological analysis suggested that apurinic/apyrimidinic endodeoxyribonuclease 1 (APEX1), androgen receptor (AR), cyclin-dependent kinases 1 (CDK1), nuclear factor erythroid 2-related factor 2 (Nrf-2), fatty acid synthase (FASN), epithelial growth factor receptor (EGFR), estrogen receptor 1 (ERα) and cyclin-dependent kinases 4 (CDK4) are potential cytotoxic targets of LMEO. These targets are closely related to cell migration, cycle and apoptosis. Notley, the p53 protein had the highest confidence to co-associate with the eight common targets, which was further confirmed by scratch assay, flow cytometry analysis, and western blot in the HepG2 liver cancer cell line. LMEO significantly inhibited the migration of HepG2 cells in time-dependent and dose-dependent manner. Moreover, LMEO caused a S-phase blocking on HepG2 cells and promoted apoptosis in the meanwhile. Western blot results indicated that p53 protein, Cyclin A2 and Bax proteins were up-regulated, while Cyclin E1 and Bcl-2 proteins were down-regulated. CONCLUSION: LMEO showed cytotoxicity in various cancer cell lines in vitro. Pharmacological networks showed LMEO to have multi-component and multi-targeting effects that are related to inhibit migration of HepG2 cells, and affect cell cycle S-phase arrest and apoptosis through modulation of p53 protein.

Cyclins and cyclin-dependent kinases: from biology to tumorigenesis and therapeutic opportunities.

The discussion on cell proliferation cannot be continued without taking a look at the cell cycle regulatory machinery. Cyclin-dependent kinases (CDKs), cyclins, and CDK inhibitors (CKIs) are valuable members of this system and their equilibrium guarantees the proper progression of the cell cycle. As expected, any dysregulation in the expression or function of these components can provide a platform for excessive cell proliferation leading to tumorigenesis. The high frequency of CDK abnormalities in human cancers, together with their druggable structure has raised the possibility that perhaps designing a series of inhibitors targeting CDKs might be advantageous for restricting the survival of tumor cells; however, their application has faced a serious concern, since these groups of serine-threonine kinases possess non-canonical functions as well. In the present review, we aimed to take a look at the biology of CDKs and then magnify their contribution to tumorigenesis. Then, by arguing the bright and dark aspects of CDK inhibition in the treatment of human cancers, we intend to reach a consensus on the application of these inhibitors in clinical settings.

Breast Cancer in Geriatric Patients: Current Landscape and Future Prospects.

Breast cancer is the most common cancer diagnosed among women worldwide and more than half are diagnosed above the age of 60 years. Life expectancy is increasing and the number of breast cancer cases diagnosed among older women are expected to increase. Undertreatment, mostly due to unjustifiable fears of advanced-age and associated comorbidities, is commonly practiced in this group of patients who are under-represented in clinical trials and their management is not properly addressed in clinical practice guidelines. With modern surgery and anesthesia, breast surgeries are considered safe and is usually associated with very low complication rates, regardless of extent of surgery. However, oncoplastic surgery and management of the axilla can be tailored based on patients'- and disease-related factors. Most of chemotherapeutic agents, along with targeted therapy and anti-Human epidermal growth factor receptor-2 (HER2) drugs can be safely given for older patients, however, dose adjustment and close monitoring of potential adverse events might be needed. The recently introduced cyclin-D kinase (CDK) 4/6-inhibitors in combination with aromatase inhibitors (AI) or fulvestrant, which changed the landscape of breast cancer therapy, are both safe and effective in older patients and had substituted more aggressive and potentially toxic interventions. Despite its proven efficacy, adjusting or even omitting adjuvant radiation therapy, at least in low-risk older patients, is safe and frequently practiced. In this paper, we review existing data related to breast cancer management among older patients across the continuum; from resection of the primary tumor through adjuvant chemotherapy, radiation and endocrine therapy up to the management of recurrent and advanced-stage disease.

A patent and literature review of CDK12 inhibitors.

INTRODUCTION: Cyclin-dependent kinase 12 (CDK12) belongs to the CDK family of serine/threonine protein kinases and is associated with cyclin K to exert its biological functions, including regulating gene transcription, mRNA processing, and translation. Increasing evidences demonstrate the importance of CDK12 in various human cancers, illustrating its potential as both biomarker and therapeutic target. In addition, CDK12 is also a promising target for the treatment of myotonic dystrophy type 1. Efforts have been taken to discover small molecule inhibitors to validate this important therapeutic target. AREAS COVERED: This review covers the patented CDK12 inhibitors from 2016 to present, as well as these from peer-reviewed literature. It provides the reader an update of the discovery strategies, chemical structures, and molecular profiling of all available CDK12 inhibitors. EXPERT OPINION: CDK12 inhibitors with various mechanism of actions have been discovered, and it is a great set of tools to evaluate the therapeutic potential of CDK12 in different disease models. CDK12 inhibitors have shown promising results in myotonic dystrophy type 1 mouse model and several preclinical cancer models either as single agent or combination with other anti-cancer agents. Its therapeutic value awaits more rigorous preclinical testing and further clinical investigation.

18F-FDG PET/CT Metabolic Response With Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer Treated With Cyclin-Dependent 4/6 Kinase Inhibitors.

ABSTRACT: Dysregulation of the cyclin D-CDK4/6-INK4-RB pathway, which leads to uncontrolled cell proliferation, is frequently observed in breast cancer. Recently, 3 CDK4/6 inhibitors have been FDA approved as first-line treatment for patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. Despite promising clinical results, the metabolic response to treatment with these new drugs has not been elaborately demonstrated yet. Herein, we presented a patient with hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer who demonstrated a complete metabolic response on 18F-FDG PET/CT to treatment with a CDK4/6 inhibitor (ribociclib).

Estudio de una cohorte de pacientes tratados con tigeciclina por infección intraabdominal tras cirugía abdominal compleja: epidemiologia y factores pronósticos / Epidemiology and risk factors of patients with intra-abdominal postsurgical infection treated with tigecycline: a cohort study

Objetivos. Estudiar la epidemiología de la infección intraabddominal postquirúrgica, la efectividad de tigeciclina y los factores asociadas a la mortalidad. Paciente y métodos. Estudio prospectivo de los pacientes con infección intraabdominal postquirúrgica con documentación microbiológica y tratados con tigeciclina. Resultados. Se estudiaron 103 pacientes, de los que sólo fueron evaluados 61 que cumplían todos los criterios de selección y que recibieron tratamiento con tigeciclina sola o en combinación. La edad media de los pacientes fue de 67 años con predominio de hombres (72%), el índice de Charlson ≥ 3 estaba presente en el 65,5% de los casos, siendo la diabetes y la neoplasia de colon las enfermedades más frecuentes. La cirugía neoplásica fue la más realizada (n=44, 72%), constatando en 43 (69%) casos el uso previo de antibióticos. El índice de Pitt ≥3 fue del 69%, aislándose como microorganismos más frecuentes Escherichia coli (38%), Enterococcus spp. (34%) con predominio de Enterococcus faecium, y Klebsiella pneumoniae más Enterobacter cloacae en 28%. Todos los pacientes recibieron tigeciclina, sola en 17 (28%) casos o en combinación 44 (72%), fundamentalmente con meropenem 25 (57%) o amikacina 19 (43%). De los 61 pacientes, 11 (18%) fallecieron, habiendo precisado todos ellos cirugía neoplásica ampliada y con aislamientos de enterobacterias productoras de betalactamasas de espectro extendido. En el análisis univariado se identificaron como factores pronósticos asociados significativamente con mayor mortalidad el índice de Charlson >3, pH venoso <7,30 y leucocitosis >20.000 cells/mm3. Conclusiones. Dado que se trata de una cohorte de pacientes tratados con tigeciclina, el aislamiento de E. faecium era muy frecuente. Tigeciclina, en monoterapia o en combinación, se asoció a una tasa de curación del 82%, constituyendo probablemente, una alternativa de gran interés en el tratamiento empírico de estas infecciones graves (AU)

Objectives. To study a cohort of patients with intra-abdominal postsurgical infection treated with tigecycline to analyze its effectiveness and mortality related factors. Patients and methods. Prospective study of patients with intra-abdominal postsurgical infection with microbiological isolation and treated with tigecycline. Results. Out of 103 patients only 61 full fit inclusion criteria. Mean age was 67 year-old and 72% were male. Charlson score was ≥ 3 in 65.5%, being diabetes and colon cancer the most prevalent diseases. Cancer surgery was the most frequent procedure (n=44, 72%) and previous antibiotic administration was present in 43 cases (69%). Pitt score was ≥ 3 in 69% and most prevalent bacteria were Escherichia coli (38 %), Enterococcus spp. (34%; mainly Enterococcus faecium) and Klebsiella pneumoniae together with Enterobacter cloacae (28%). Tigecycline was prescribed alone (17; 28%) or in combination with other antibiotics (44; 72%), mainly meropenem (25; 57%) or amikacin (19, 43%). 11 patients died (18%), all of which suffered extended cancer surgery and isolation of extended-spectrum betalactamase producing Enterobacteriaceae. Factors statistically associated to death in univariate analysis were Charlson score 3, pH <7.3 and leucocyte count >20.000 cells/mm3. Conclusions. As being a cohort of patients treated with tigecycline, E. faecium isolation was very frequent. Non-fatal evolution was achieved in 82% cases, being tigecycline a potentially good option in the empiric treatment of very severe infections (AU)

RNAi-mediated downregulation of cyclin Y to attenuate human breast cancer cell growth.

Cyclin Y (CCNY) is a newly identified PFTK1 interacting protein and has been found to be associated with the proliferation and tumorigenesis of human non-small cell lung cancer. In the present study, we analyzed the expression levels of CCNY in 65 cases of breast cancer (BC) tissues and in four BC cell lines, BT-474, MDA-MB-231, T-47D and MCF-7. Lentivirus-mediated short hairpin RNA (shRNA) was employed to knock down CCNY expression in MCF-7 and MDA-MB-231 cells. The effects of CCNY depletion on cell growth were examined by MTT, colony formation and flow cytometry assays. The results showed that immunohistochemical expression of CCNY in tumor tissues is stronger than that in normal tissues. CCNY was also expressed in all four BC cells. The knockdown of CCNY resulted in a significant reduction in cell proliferation and colony formation ability. Cell cycle analysis showed that CCNY knockdown arrested MDA-MB­231 cells in the G0/G1 phase. Furthermore, depletion of CCNY inhibited BC cell growth via the activation of Bad and GSK3ß, as well as cleavages of PARP and caspase-3 in a p53-dependent manner. Therefore, we believe that CCNY has biological effect in BC development, and its inhibition via an RNA interference lentiviral system may provide a therapeutic option for BC.

Cell cycle activation contributes to increased neuronal activity in the posterior thalamic nucleus and associated chronic hyperesthesia after rat spinal cord contusion.

Spinal cord injury (SCI) causes not only sensorimotor and cognitive deficits, but frequently also severe chronic pain that is difficult to treat (SCI pain). We previously showed that hyperesthesia, as well as spontaneous pain induced by electrolytic lesions in the rat spinothalamic tract, is associated with increased spontaneous and sensory-evoked activity in the posterior thalamic nucleus (PO). We have also demonstrated that rodent impact SCI increases cell cycle activation (CCA) in the injury region and that post-traumatic treatment with cyclin dependent kinase inhibitors reduces lesion volume and motor dysfunction. Here we examined whether CCA contributes to neuronal hyperexcitability of PO and hyperpathia after rat contusion SCI, as well as to microglial and astroglial activation (gliopathy) that has been implicated in delayed SCI pain. Trauma caused enhanced pain sensitivity, which developed weeks after injury and was correlated with increased PO neuronal activity. Increased CCA was found at the thoracic spinal lesion site, the lumbar dorsal horn, and the PO. Increased microglial activation and cysteine-cysteine chemokine ligand 21 expression was also observed in the PO after SCI. In vitro, neurons co-cultured with activated microglia showed up-regulation of cyclin D1 and cysteine-cysteine chemokine ligand 21 expression. In vivo, post-injury treatment with a selective cyclin dependent kinase inhibitor (CR8) significantly reduced cell cycle protein induction, microglial activation, and neuronal activity in the PO nucleus, as well as limiting chronic SCI-induced hyperpathia. These results suggest a mechanistic role for CCA in the development of SCI pain, through effects mediated in part by the PO nucleus. Moreover, cell cycle modulation may provide an effective therapeutic strategy to improve reduce both hyperpathia and motor dysfunction after SCI.

Disseminated cutaneous lymphoid hyperplasia of 12 years' duration triggered by vaccination.

Vaccine-induced cutaneous lymphoid hyperplasia (CLH) is rare. Its natural evolution is not well known, nor is its treatment. We report a case of B-cell CLH with secondary dissemination that occurred following vaccination. The symptoms lasted 12 years and were efficiently treated by thalidomide. A 17-year-old girl presented CLH which had begun at the age of 8 at the site of hepatitis B vaccination. The lesions progressively enlarged and disseminated far from the injection sites. There was no spontaneous remission. Cyclins and hydroxychloroquine were inefficient. Thalidomide treatment finally led to complete remission. Aluminium hydroxide is used as adjuvant in the majority of vaccinations. In this case, occurrence of lesions far from the injection site of the vaccine suggested that it was not the only cause and that CLH may occur in other localizations after a vaccination. Furthermore, the diagnosis of CLH should not be excluded in front of such a prolonged course, and we underline the potential efficacy of thalidomide.

Cytoplasmic p21(Cip1/WAF1) enhances axonal regeneration and functional recovery after spinal cord injury in rats.

p21(Cip1/WAF1), known as a cell-cycle inhibitory protein, facilitates neurite outgrowth from neurons when present in the cytoplasm. The molecular mechanism of this action is that p21(Cip1/WAF1) forms a complex with Rho-kinase and inhibits its activity. As myelin-derived inhibitors of axonal outgrowth act on neurons by activating Rho, that is responsible for the lack of spontaneous regeneration of the injured central nervous system (CNS), Rho-kinase may be a good molecular target against injuries in the CNS. In this study, we delivered TAT-fusion protein of cytoplasmic p21(Cip1/WAF1) locally after dorsal hemisection of the thoracic spinal cord in rats. The treatment significantly stimulated axonal regeneration and recovery of hindlimb function, and inhibited the cavity formation in the spinal cord after the injury. Cytoplasmic p21(Cip1/WAF1) may provide a potential therapeutic agent that produces functional regeneration following CNS injuries.

Cell-cycle targeted therapies.

Eukaryotic organisms depend on an intricate and evolutionary conserved cell cycle to control cell division. The cell cycle is regulated by a number of important protein families which are common targets for mutational inactivation or overexpression in human tumours. The cyclin D and E families and their cyclin-dependent kinase partners initiate the phosphorylation of the retinoblastoma tumour suppressor protein and subsequent transition through the cell cycle. Cyclin/cdk activity and therefore control of cell division is restrained by two families of cyclin dependent kinase inhibitors. A greater understanding of the cell cycle has led to the development of a number of compounds with the potential to restore control of cell division in human cancers. This review will introduce the protein families that regulate the cell cycle, their aberrations in malignant progression and pharmacological strategies targeting this important process.

[Experimental gene therapy using p21/WAF1 gene in esophageal squamous cell carcinoma--adenovirus infection and gene gun technology].

p21/WAF1 (p21) inhibits the activity of the cyclin/cdk complex and controls the G1 to S cell phase transition. In the present study, we used a recombinant adenoviral approach and gene gun technology to introduce p21 into esophageal cancer cells in order to assess the effect of p21 on cell growth. Infection with the p21 adenovirus (AdV) using gene gun technology resulted in inhibition of TE9 and KE3 cell growth. The levels of involucrin, which is a marker of squamous epithelium differentiation, markedly increased at 48 h and 72 h after p21 AdV infection in TE9 cells. These results indicate that p21 plays an important role in esophageal cancer cell proliferation. Overexpression of the p21 gene can inhibit cell growth and induce differentiation in esophageal cancer cells. p21 gene therapy may prove beneficial in the treatment of esophageal cancer.

Comparisons of tumor suppressor p53, p21, and p16 gene therapy effects on glioblastoma tumorigenicity in situ.

The mutation and/or deletion of tumor suppressor genes have been postulated to play a major role in the genesis and the progression of gliomas. In this study, the functional expression and efficacy in tumor suppression of 3 tumor suppressor genes (p53, p21, and p16) were tested and compared in a rat GBM cell line (RT-2) after retrovirus mediated gene delivery in vitro and in vivo. Significant reductions in tumor cell growth rate were found in p16 and p21 infected cells (60 +/- 12% vs 66 +/- 15%) compared to p53 (35 +/- 9%). In vitro colony formation assay also showed significant reductions after p16 and p21 gene delivery (98 +/- 5% vs 91 +/- 10%) compared to p53 (50 +/- 18%). In addition, the tumor suppression efficacy were investigated and compared in vivo. Retroviral mediated p16 and p21 gene deliveries in glioblastomas resulted in more than 90% reductions in tumor growth (92 +/- 26% vs 90 +/- 22%) compared to p53 (62 +/- 18%). Tumor suppressor gene insertions in situ further prolonged animal survival. Overall p16 and p21 genes showed more powerful tumor suppressor effects than p53. The results were not surprising, as p16 and p21 are more downstream in the cell cycle regulatory pathway compared to p53. Moreover, the mechanism involved in each of their suppressor effects is different. This study demonstrates the feasibility of using tumor suppressor genes in regulating the growth of glioma in vitro and in situ.

Long term inhibition of neointima formation in balloon-injured rat arteries by intraluminal instillation of a matrix-targeted retroviral vector bearing a cytocidal mutant cyclin G1 construct.

Restenosis from neointimal proliferation is a frequent complication of intracoronary stenting and catheter-based revascularization procedures. Currently, there is no known therapeutic strategy that has been sufficiently effective to warrant its widespread use. In the present study, the anti-proliferative properties of a matrix (collagen)-targeted retroviral vector bearing a mutant cyclin G1 (DNT 41-249) construct was evaluated in vitro and in vivo. In controlled one-month efficacy studies, the intraluminal instillation of the mutant cyclin G1 vector significantly inhibited neointima lesion formation in balloon-injured rat arteries without neointimal growth, associated necrosis or intense inflammatory reaction. Taken together, these data extend the potential utility of the matrix-targeted mutant cyclin G1 retroviral vector for management of vascular restenosis.

Perspectives for cancer therapies with cdk2 inhibitors.

Modern anticancer strategies are designed against specific molecular targets with the goal of sparing normal, non-neoplastic tissues. Choosing specific molecular targets, however, is problematic. Cdk2 (Cyclin dependent kinase 2, cell division kinase 2, p33) is an important candidate target for therapeutic intervention. Phosphorylation of retinoblastoma protein (pRb) by Cdk2 is the penultimate step in the transition from G1 to S phase. Inhibition of this step could potentially result in inhibition of proliferation, cytostasis and possibly apoptosis in human tumors. Cdk2 also plays a critical role in the transition through S phase and the S to G2 transition as well. Inhibitors of the cyclin dependent kinases, such as flavopiridol and UCN-01, are currently in clinical trials. While demonstrating clinical activity, neither acts specifically against Cdk2. Other more specific Cdk2 inhibitors are currently in preclinical development. Further studies to explore the therapeutic worth of such agents are warranted.

Adenoviral transfer of cyclin-dependent kinase inhibitor genes suppresses collagen-induced arthritis in mice.

In rheumatoid synovial tissues, synovial fibroblasts are activated by proinflammatory cytokines and proliferate to develop hyperplastic pannus tissues, which irreversibly damage the affected joints. We recently reported that the cyclin-dependent kinase inhibitors p16(INK4a) and p21(Cip1) are not expressed in vivo in rheumatoid synovial fibroblasts, but are readily inducible in vitro. This observation was followed by the successful treatment of rat adjuvant arthritis by local p16(INK4a) gene transfer, showing that the inhibition of the cell cycle of the synovial cells ameliorates the arthritis. In this study, we show that another animal model of rheumatoid arthritis, murine collagen-induced arthritis, can be effectively treated by local gene transfer of p21(Cip1) as well as that of p16(INK4a). The anti-arthritic effects were observed even when the treatment was conducted after the arthritis had developed. Furthermore, the effects included suppression of the expression of proinflammatory cytokines such as IL-1ss, IL-6, and TNF-alpha. Our results demonstrate that the ectopic expression of cyclin-dependent kinase inhibitors not only prevents synovial overgrowth but also ameliorates the proinflammatory milieu in the affected joints. The induction of p21(Cip1) in rheumatoid synovial tissues by pharmacological agents may also be an effective strategy to treat rheumatoid arthritis.