p21 Promotes oncolytic adenoviral activity in ovarian cancer and is a potential biomarker

Cell cycle machinery in oncology: A comprehensive review of therapeutic targets

The cell cycle is tightly regulated to ensure controlled cell proliferation. Dysregulation of the cell cycle machinery is a hallmark of cancer that leads to unchecked growth. This review comprehensively analyzes key molecular regulators of the cell cycle and how they contribute to carcinogenesis when mutated or overexpressed. It focuses on cyclins, cyclin-dependent kinases (CDKs), CDK inhibitors, checkpoint kinases, and mitotic regulators as therapeutic targets. Promising strategies include CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib for breast cancer treatment. Other possible targets include the anaphase-promoting complex/cyclosome (APC/C), Skp2, p21, and aurora kinase inhibitors. However, challenges with resistance have limited clinical successes so far. Future efforts should focus on combinatorial therapies, next-generation inhibitors, and biomarkers for patient selection. Targeting the cell cycle holds promise but further optimization is necessary to fully exploit it as an anti-cancer strategy across diverse malignancies.

Targeting Cell Cycle Facilitates E1A-Independent Adenoviral Replication

DNA replication of E1-deleted first-generation adenoviruses (AdV) in cultured cancer cells has been reported repeatedly and it was suggested that certain cellular proteins could functionally compensate for E1A, leading to the expression of the early region 2 (E2)-encoded proteins and subsequently virus replication. Referring to this, the observation was named E1A-like activity. In this study, we investigated different cell cycle inhibitors with respect to their ability to increase viral DNA replication of dl70-3, an E1-deleted adenovirus. Our analyses of this issue revealed that in particular inhibition of cyclin-dependent kinases 4/6 (CDK4/6i) increased E1-independent adenovirus E2-expression and viral DNA replication. Detailed analysis of the E2-expression in dl70-3 infected cells by RT-qPCR showed that the increase in E2-expression originated from the E2-early promoter. Mutations of the two E2F-binding sites in the E2-early promoter (pE2early-LucM) caused a significant reduction in E2-early promoter activity in trans-activation assays. Accordingly, mutations of the E2F-binding sites in the E2-early promoter in a virus named dl70-3/E2Fm completely abolished CDK4/6i induced viral DNA replication. Thus, our data show that E2F-binding sites in the E2-early promoter are crucial for E1A independent adenoviral DNA replication of E1-deleted vectors in cancer cells. IMPORTANCE E1-deleted AdV vectors are considered replication deficient and are important tools for the study of virus biology, gene therapy, and large-scale vaccine development. However, deletion of the E1 genes does not completely abolish viral DNA replication in cancer cells. Here, we report, that the two E2F-binding sites in the adenoviral E2-early promoter contribute substantially to the so-called E1A-like activity in tumor cells. With this finding, on the one hand, the safety profile of viral vaccine vectors can be increased and, on the other hand, the oncolytic property for cancer therapy might be improved through targeted manipulation of the host cell.

Targeting CA-125 Transcription by Development of a Conditionally Replicative Adenovirus for Ovarian Cancer Treatment

Simple Summary

Ovarian cancer is the fifth most common cause of cancer-related death among women in the US, and new treatments are urgently needed to help those suffering from this deadly disease. A unique feature of ovarian cancer is that a protein called CA-125, encoded by a gene called MUC16, is highly expressed in more than 80% of patients. To date, targeting MUC16/CA-125 for ovarian cancer treatment has not been successful. Here, we describe the development of an artificial virus, called a conditionally replicative oncolytic adenovirus (CRAd), that can only grow in and destroy cancer cells that express CA-125, but not normal cells. We document promising anti-cancer effects of the virus in both human ovarian cancer cells and in animal cancer models. Collectively, our study findings suggest that the development of CRAd targeting MUC16/CA-125 represents a unique and practical approach to ovarian cancer treatment.

Abstract

CA-125, encoded by the MUC16 gene, is highly expressed in most ovarian cancer cells and thus serves as a tumor marker for monitoring disease progression or treatment response in ovarian cancer patients. However, targeting MUC16/CA-125 for ovarian cancer treatment has not been successful to date. In the current study, we performed multiple steps of high-fidelity PCR and obtained a 5 kb DNA fragment upstream of the human MUC16 gene. Reporter assays indicate that this DNA fragment possesses transactivation activity in CA-125-high cancer cells, but not in CA-125-low cancer cells, indicating that the DNA fragment contains the transactivation region that controls specific expression of the MUC16 gene in ovarian cancer cells. We further refined the promoter and found a 1040 bp fragment with similar transcriptional activity and specificity. We used this refined MUC16 promoter to replace the E1A promoter in the adenovirus type 5 genome DNA, where E1A is an essential gene for adenovirus replication. We then generated a conditionally replicative oncolytic adenovirus (CRAd) that replicates in and lyses CA-125-high cancer cells, but not CA-125-low or -negative cancer cells. In vivo studies showed that intraperitoneal virus injection prolonged the survival of NSG mice inoculated intraperitoneally (ip) with selected ovarian cancer cell lines. Furthermore, the CRAd replicates in and lyses primary ovarian cancer cells, but not normal cells, collected from ovarian cancer patients. Collectively, these data indicate that targeting MUC16 transactivation utilizing CRAd is a feasible approach for ovarian cancer treatment that warrants further investigation.

Multifaceted p21 in carcinogenesis, stemness of tumor and tumor therapy

Cancer cells possess metabolic properties that are different from those of benign cells. p21, encoded by CDKN1A gene, also named p21^Cip1/WAF1, was first identified as a cyclin-dependent kinase regulator that suppresses cell cycle G1/S phase and retinoblastoma protein phosphorylation. CDKN1A (p21) acts as the downstream target gene of TP53 (p53), and its expression is induced by wild-type p53 and it is not associated with mutant p53. p21 has been characterized as a vital regulator that involves multiple cell functions, including G1/S cell cycle progression, cell growth, DNA damage, and cell stemness. In 1994, p21 was found as a tumor suppressor in brain, lung and colon cancer by targeting p53 and was associated with tumorigenesis and metastasis. Notably, p21 plays a significant role in tumor development through p53-dependent and p53-independent pathways. In addition, expression of p21 is closely related to the resting state or terminal differentiation of cells. p21 is also associated with cancer stem cells and acts as a biomarker for such cells. In cancer therapy, given the importance of p21 in regulating the G1/S and G2 check points, it is not surprising that p21 is implicated in response to many cancer treatments and p21 promotes the effect of oncolytic virotherapy.

Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Suppresses Human Adenovirus Gene Expression and Replication

Human adenovirus (HAdV) causes minor illnesses in most patients but can lead to severe disease and death in pediatric, geriatric, and immunocompromised individuals. No approved antiviral therapy currently exists for the treatment of these severe HAdV-induced diseases. In this study, we show that the pan-histone deacetylase (HDAC) inhibitor SAHA reduces HAdV-5 gene expression and DNA replication in tissue culture, ultimately decreasing virus yield from infected cells. Importantly, SAHA also reduced gene expression from more virulent and clinically relevant serotypes, including HAdV-4 and HAdV-7. In addition to SAHA, several other HDAC inhibitors (e.g., trichostatin A, apicidin, and panobinostat) also affected HAdV gene expression. We determined that loss of class I HDAC activity, mainly HDAC2, impairs efficient expression of viral genes, and that E1A physically interacts with HDAC2. Our results suggest that HDAC activity is necessary for HAdV replication, which may represent a novel pharmacological target in HAdV-induced disease.IMPORTANCE Although human adenovirus (HAdV) can cause severe diseases that can be fatal in some populations, there are no effective treatments to combat HAdV infection. In this study, we determined that the pan-histone deacetylase (HDAC) inhibitor SAHA has inhibitory activity against several clinically relevant serotypes of HAdV. This U.S. Food and Drug Administration-approved compound affects various stages of the virus lifecycle and reduces virus yield even at low concentrations. We further report that class I HDAC activity, particularly HDAC2, is required for efficient expression of viral genes during lytic infection. Investigation of the mechanism underlying SAHA-mediated suppression of HAdV gene expression and replication will enhance current knowledge of virus-cell interaction and may aid in the development of more effective antivirals with lower toxicity for the treatment of HAdV infections.

Loss of parkin reduces lung tumor development by blocking p21 degradation

Several epidemiological studies have demonstrated the reciprocal relationship between the development of cancer and Parkinson’s disease (PD). However, the possible mechanisms underlying this relationship remain unclear. To identify this relationship, we first compared lung tumor growth in parkin knockout (KO) mice and wild-type (WT) mice. Parkin KO mice showed decreased lung tumor growth and increased expression of p21, a cell cycle arrester, as compared with WT mice. We also found that parkin interacts with p21, resulting in its degradation; however, parkin KO, knockdown, as well as mutation (R275W or G430D) reduced the degradation of p21. We investigated whether parkin KO increases the association of p21 with proliferating cell nuclear antigen (PCNA) or CDK2 by reducing p21 degradation, and, thus, arresting the cell cycle. The interaction between p21 and PCNA or CDK2 was also enhanced by parkin knockdown, and this increased interaction induced sub G0/G1 arrest, leading to cell death. Therefore, our data indicate that parkin KO reduces the development of lung tumors via cell cycle arrest by blocking the degradation of p21. These findings suggest that PD could be associated with lower lung cancer incidence.

A p53-independent apoptotic mechanism of adenoviral mutant E1A was involved in its selective antitumor activity for human cancer

The conserved regions (CR) of adenoviral E1A had been shown to be necessary for disruption of pRb-E2F transcription factor complexes and induction of the S phase. Here we constructed a mutant adenoviral E1A with Rb-binding ability absent (E1A 30-60aa and 120-127aa deletion, mE1A) and investigated its antitumor capacities in vitro and in vivo. The mE1A suppressed the viability of tumor cells as efficiently as the wild type E1A, and there was no cytotoxic effect on normal cells. Although the mE1A arrested tumor cell cycle with the same manner as E1A, the former played a different role on cell cycle regulation compared with E1A in normal cells, which might contribute to its selective antitumor activity. E1A and mE1A had accumulated inactive p53, decreased the expression of mdm2, Cdkn1a (also named p21), increased p21's nuclear distribution and induced tumor cell apoptosis in a p53-indenpent manner. Further, E1A or mE1A significantly suppressed tumor growth in subcutaneous hepatocellular carcinoma xenograft models. Especially, tumor-bearing mice treated with mE1A had higher survival rate than those treated with E1A. Our data demonstrated that mutant adenoviral E1A significantly induced tumor cell apoptosis in a p53-indenpednt manner and had selective tumor suppressing ability. The observations of adenoviral E1A mutant had provided a novel mechanism for E1A's complex activities during infection.

RIPK3 promotes adenovirus type 5 activity

Oncolytic adenoviral mutants infect human malignant cells and replicate selectively within them. This induces direct cytotoxicity that can also trigger profound innate and adaptive immune responses. However, the mechanism by which adenoviruses produce cell death remains uncertain. We previously suggested that type 5 adenoviruses, including the E1A CR2 deletion mutant dl922-947, might induce a novel form of programmed death resembling necroptosis. Here we have investigated the roles of core necrosis proteins RIPK1, RIPK3 and MLKL in the cytotoxicity of dl922-947 and other adenovirus serotypes. By electron microscopy, we show that dl922-947 induces similar necrotic morphology as TSZ treatment (TNF-α, Smac mimetic, zVAD.fmk). However, dl922-947-mediated death is independent of TNF-α signalling, does not require RIPK1 and does not rely upon the presence of MLKL. However, inhibition of caspases, specifically caspase-8, induces necroptosis that is RIPK3 dependent and significantly enhances dl922-947 cytotoxicity. Moreover, using CRISPR/Cas9 gene editing, we demonstrate that the increase in cytotoxicity seen upon caspase inhibition is also MLKL dependent. Even in the absence of caspase inhibition, RIPK3 expression promotes dl922-947 and wild-type adenovirus type 5 efficacy both in vitro and in vivo. Together, these results suggest that adenovirus induces a form of programmed necrosis that differs from classical TSZ necroptosis.

Cytotoxicity of replication-competent adenoviruses powered by an exogenous regulatory region is not linearly correlated with the viral infectivity/gene expression or with the E1A-activating ability but is associated with the p53 genotypes

Background

Replication-competent adenoviruses (Ad) produced cytotoxic effects on infected tumors and have been examined for the clinical applicability. A biomarkers to predict the cytotoxicity is valuable in a clinical setting.

Methods

We constructed type 5 Ad (Ad5) of which the expression of E1A gene was activated by a 5′ regulatory sequences of survivin, midkine or cyclooxygenase-2, which were highly expressed in human tumors. We also produced the same replication-competent Ad of which the fiber-knob region was replaced by that of Ad35 (AdF35). The cytotoxicity was examined by a colorimetric assay with human tumor cell lines, 4 kinds of pancreatic, 9 esophageal carcinoma and 5 mesothelioma. Ad infectivity and Ad-mediated gene expression were examined with replication-incompetent Ad5 and AdF35 which expressed the green fluorescence protein gene. Expression of cellular receptors for Ad5 and AdF35 was also examined with flow cytometry. A transcriptional activity of the regulatory sequences was investigated with a luciferase assay in the tumor cells. We then investigated a possible correlation between Ad-mediated cytotoxicity and the infectivity/gene expression, the transcriptional activity or the p53 genotype.

Results

We found that the cytotoxicity was greater with AdF35 than with Ad5 vectors, but was not correlated with the Ad infectivity/gene expression irrespective of the fiber-knob region or the E1A-activating transcriptional activity. In contrast, replication-competent Ad produced greater cytotoxicity in p53 mutated than in wild-type esophageal carcinoma cells, suggesting a possible association between the cytotoxicity and the p53 genotype.

Conclusions

Sensitivity to Ad-mediated cytotoxic activity was linked with the p53 genotype but was not lineally correlated with the infectivity/gene expression or the E1A expression.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3621-x) contains supplementary material, which is available to authorized users.

RAD51 and BRCA2 Enhance Oncolytic Adenovirus Type 5 Activity in Ovarian Cancer

Homologous recombination (HR) function is critically important in high-grade serous ovarian cancer (HGSOC). HGSOC with intact HR has a worse prognosis and is less likely to respond to platinum chemotherapy and PARP inhibitors. Oncolytic adenovirus, a novel therapy for human malignancies, stimulates a potent DNA damage response that influences overall antitumor activity. Here, the importance of HR was investigated by determining the efficacy of adenovirus type 5 (Ad5) vectors in ovarian cancer. Using matched BRCA2-mutant and wild-type HGSOC cells, it was demonstrated that intact HR function promotes viral DNA replication and augments overall efficacy, without influencing viral DNA processing. These data were confirmed in a wider panel of HR competent and defective ovarian cancer lines. Mechanistically, both BRCA2 and RAD51 localize to viral replication centers within the infected cell nucleus and that RAD51 localization occurs independently of BRCA2. In addition, a direct interaction was identified between RAD51 and adenovirus E2 DNA binding protein. Finally, using functional assays of HR competence, despite inducing degradation of MRE11, Ad5 infection does not alter cellular ability to repair DNA double-strand break damage via HR. These data reveal that Ad5 redistributes critical HR components to viral replication centers and enhances cytotoxicity.

IMPLICATIONS

Oncolytic adenoviral therapy may be most clinically relevant in tumors with intact HR function.

Paclitaxel resistance increases oncolytic adenovirus efficacy via upregulated CAR expression and dysfunctional cell cycle control

Resistance to paclitaxel chemotherapy frequently develops in ovarian cancer. Oncolytic adenoviruses are a novel therapy for human malignancies that are being evaluated in early phase trials. However, there are no reliable predictive biomarkers for oncolytic adenovirus activity in ovarian cancer. We investigated the link between paclitaxel resistance and oncolytic adenovirus activity using established ovarian cancer cell line models, xenografts with de novo paclitaxel resistance and tumour samples from two separate trials. The activity of multiple Ad5 vectors, including dl922-947 (E1A CR2-deleted), dl1520 (E1B-55K deleted) and Ad5 WT, was significantly increased in paclitaxel resistant ovarian cancer in vitro and in vivo. This was associated with greater infectivity resulting from increased expression of the primary receptor for Ad5, CAR (coxsackie adenovirus receptor). This, in turn, resulted from increased CAR transcription secondary to histone modification in resistant cells. There was increased CAR expression in intraperitoneal tumours with de novo paclitaxel resistance and in tumours from patients with clinical resistance to paclitaxel. Increased CAR expression did not cause paclitaxel resistance, but did increase inflammatory cytokine expression. Finally, we identified dysregulated cell cycle control as a second mechanism of increased adenovirus efficacy in paclitaxel-resistant ovarian cancer. Ad11 and Ad35, both group B adenoviruses that utilise non-CAR receptors to infect cells, are also significantly more effective in paclitaxel-resistant ovarian cell models. Inhibition of CDK4/6 using PD-0332991 was able both to reverse paclitaxel resistance and reduce adenovirus efficacy. Thus, paclitaxel resistance increases oncolytic adenovirus efficacy via at least two separate mechanisms - if validated further, this information could have future clinical utility to aid patient selection for clinical trials.

Ovarian cancer cells, not normal cells, are damaged by Mirk/Dyrk1B kinase inhibition

Prior studies had shown that the Mirk/dyrk1B gene is amplified/upregulated in about 75% of ovarian cancers, that protein levels of this kinase are elevated in quiescent G0 cells and that Mirk maintains tumor cells in quiescence by initiating rapid degradation of cyclin D isoforms and by phosphorylation of a member of the DREAM complex. Depletion of Mirk/dyrk1B led to increased cyclin D levels, an elevated reactive oxygen species (ROS) content and loss of viability. However, many normal cells in vivo are quiescent, and therefore, targeting a kinase found in quiescent cells might be problematic. In our study, Mirk kinase activity was found to be higher in ovarian cancer cells than in normal cells. Pharmacological inhibition of Mirk/dyrk1B kinase increased cyclin D levels both in quiescent normal diploid cells and in quiescent CDKN2A-negative ovarian cancer cells, but led to more active CDK4/cyclin D complexes in quiescent ovarian cancer cells, allowing them to escape G0/G1 quiescence, enter cycle with high ROS levels and undergo apoptosis. The ROS scavenger N-acetyl cysteine reduced both the amount of cleaved poly(ADP-ribose) polymerase (PARP) and the extent of cancer cell loss. In contrast, normal cells were spared because of their expression of cyclin directed kinase (CDK) inhibitors that blocked unregulated cycling. Quiescent early passage normal ovarian epithelial cells and two strains of quiescent normal diploid fibroblasts remained viable after the inhibition of Mirk/dyrk1B kinase, and the few cells that left G0/G1 quiescence were accumulated in G2+M. Thus, inhibition of Mirk kinase targeted quiescent ovarian cancer cells.

Failure of translation of human adenovirus mRNA in murine cancer cells can be partially overcome by L4-100K expression in vitro and in vivo

Adaptive immune responses may be vital in the overall efficacy of oncolytic viruses in human malignancies. However, immune responses to oncolytic adenoviruses are poorly understood because these viruses lack activity in murine cells, which precludes evaluation in immunocompetent murine cancer models. We have evaluated human adenovirus activity in murine cells. We show that a panel of murine carcinoma cells, including CMT64, MOVCAR7, and MOSEC/ID8, can readily be infected with human adenovirus. These cells also support viral gene transcription, messenger RNA (mRNA) processing, and genome replication. However, there is a profound failure of adenovirus protein synthesis, especially late structural proteins, both in vitro and in vivo, with reduced loading of late mRNA onto ribosomes. Our data also show that in trans expression of the nonstructural late protein L4-100K increases both the amount of viral mRNA on ribosomes and the synthesis of late proteins, accompanied by reduced phosphorylation of eIF2α and improved anticancer efficacy. These results suggest that murine models that support human adenovirus replication could be generated, thus allowing evaluation of human adenoviruses in immunocompetent mice.

Sequential genetic change at the TP53 and chemokine receptor CXCR4 locus during transformation of human ovarian surface epithelium

Early genetic events in the development of high-grade serous ovarian cancer, HGSOC, may define the molecular basis of the profound structural and numerical instability of chromosomes in this disease. To discover candidate genetic changes we sequentially passaged cells from a karyotypically normal hTERT immortalised human ovarian surface epithelial line (IOSE25) resulting in the spontaneous formation of colonies in soft agar. Cell lines (TOSE 1 and 4) established from these colonies had an abnormal karyotype and altered morphology but were not tumorigenic in immunodeficient mice.

TOSE cells showed loss of heterozygosity at TP53, increased nuclear p53 immunoreactivity and altered expression profile of p53 target genes. The parental IOSE25 cells contained a missense, heterozygous R175H mutation in TP53 whereas TOSE cells had loss of heterozygosity at the TP53 locus with a new R273H mutation at the previous wild-type TP53 allele.

Cytogenetic and array CGH analysis of TOSE cells also revealed a focal genomic amplification of CXCR4, a chemokine receptor commonly expressed by HGSOC cells. TOSE cells had increased functional CXCR4 protein and its abrogation reduced epidermal growth factor receptor, EGFR, expression, as well as colony size and number. The CXCR4 ligand, CXCL12, was epigenetically silenced in TOSE cells and its forced expression increased TOSE colony size. TOSE cells had other cytogenetic changes typical of those seen in HGSOC ovarian cancer cell lines and biopsies. In addition, enrichment of CXCR4 pathway in expression profiles from HGSOC correlated with enrichment of a mutated TP53 gene expression signature and of EGFR pathway genes.

Our data suggest that mutations in TP53 and amplification of the CXCR4 gene locus may be early events in the development of HGSOC, and associated with chromosomal instability.

Genomic DNA damage and ATR-Chk1 signaling determine oncolytic adenoviral efficacy in human ovarian cancer cells

Oncolytic adenoviruses replicate selectively within and lyse malignant cells. As such, they are being developed as anticancer therapeutics. However, the sensitivity of ovarian cancers to adenovirus cytotoxicity varies greatly, even in cells of similar infectivity. Using both the adenovirus E1A-CR2 deletion mutant dl922-947 and WT adenovirus serotype 5 in a panel of human ovarian cancer cell lines that cover a 3-log range of sensitivity, we observed profound overreplication of genomic DNA only in highly sensitive cell lines. This was associated with the presence of extensive genomic DNA damage. Inhibition of ataxia telangiectasia and Rad3-related checkpoint kinase 1 (ATR-Chk1), but not ataxia telangiectasia mutated (ATM), promoted genomic DNA damage and overreplication in resistant and partially sensitive cells. This was accompanied by increased adenovirus cytotoxicity both in vitro and in vivo in tumor-bearing mice. We also demonstrated that Cdc25A was upregulated in highly sensitive ovarian cancer cell lines after adenovirus infection and was stabilized after loss of Chk1 activity. Knockdown of Cdc25A inhibited virus-induced DNA damage in highly sensitive cells and blocked the effects of Chk1 inhibition in resistant cells. Finally, inhibition of Chk1 decreased homologous recombination repair of virus-induced genomic DNA double-strand breaks. Thus, virus-induced host cell DNA damage signaling and repair are key determinants of oncolytic adenoviral activity, and promoting unscheduled DNA synthesis and/or impeding homologous recombination repair could potentiate the effects of oncolytic adenoviruses in the treatment of ovarian cancer.

Examination of the optimal condition on the in vitro sensitivity to telomelysin in head and neck cancer cell lines

OBJECTIVE

Telomelysin (OBP-301) is a telomerase-specific replication-competent adenovirus with a human telomerase reverse transcriptase (hTERT) promoter. Telomelysin has a strong antitumor effect on a variety of cancers, including head and neck squamous cell carcinoma (HNSCC), and combining telomelysin treatment with paclitaxel or cisplatin enhances the antitumor effect on HNSCC. In the present study, we investigated the relationship between the antitumor activity of telomelysin and tumor cell doubling time(DT), S-phase fraction, and E1A expression. We also investigated whether the antitumor effects of OBP-301-resistant tumor cells are enhanced by cisplatin, paclitaxel, or streptolysin O.

METHODS

The tumor cell DT of 17 human HNSCC cell lines was examined. Antitumor activities of telomelysin (OBP-301) for each HNSCC cell line were examined by MTT assay. Cell cycle analysis was conducted by flowcytometry. E1A gene expressions after infection with telomelysin, hTERT, CAR (Cocksackie Adenovirus Receptor), and c-Myc were examined by quantitative PCR, and E1A expressions were examined again after pretreatment with cisplatin, paclitaxel, or streptolysin O. Correlations were analyzed by Spearman's correlation coefficient.

RESULTS

There was a significant relationship between telomelysin sensitivity and DT, S-phase fraction and early E1A expression, and pretreatment with cisplatin, paclitaxel, and streptolysin O increased infectivity of telomelysin-resistant HNSCC cell lines.

CONCLUSION

These findings are useful for advancing clinical trials, and suggest that adjuvant telomelysin treatment would be effective even in telomelysin-resistant HNSCC cell lines.

Low-dose paclitaxel synergizes with oncolytic adenoviruses via mitotic slippage and apoptosis in ovarian cancer

The microtubule-stabilizing drug paclitaxel has activity in relapsed ovarian cancer. dl922-947, an oncolytic adenovirus with a 24-bp deletion in E1A CR2, replicates selectively within and lyses cells with a dysregulated Rb pathway and has efficacy in ovarian cancer. In the aggressive A2780CP xenograft, combination treatment with weekly dl922-947 and paclitaxel has significantly greater efficacy than either treatment alone and can produce complete tumor eradication in some animals. We investigated the mechanisms of paclitaxel's synergy with dl922-947 in ovarian cancer. The host-cell microtubule network is grossly rearranged and stabilized following adenovirus infection, but paclitaxel does not increase this significantly. Paclitaxel does not synergize by increasing infectivity, viral protein expression or virus release. However, destabilizing the microtubule network with nocodazole reduces viral exit, revealing a novel microtubule-dependent pathway for non-lytic adenoviral exit. dl922-947 can override multiple cell cycle checkpoints but induces cell death by a non-apoptotic mechanism. In combination, dl922-947 and low-dose paclitaxel induces aberrant, multipolar mitoses, mitotic slippage and multinucleation, triggering an apoptotic cell death.