Promoters of ASCL1- and NEUROD1-dependent genes are specific targets of lurbinectedin in SCLC cells.

Small-Cell Lung Cancer (SCLC) is an aggressive neuroendocrine malignancy with a poor prognosis. Here, we focus on the neuroendocrine SCLC subtypes, SCLC-A and SCLC-N, whose transcription addiction was driven by ASCL1 and NEUROD1 transcription factors which target E-box motifs to activate up to 40% of total genes, the promoters of which are maintained in a steadily open chromatin environment according to ATAC and H3K27Ac signatures. This leverage is used by the marine agent lurbinectedin, which preferentially targets the CpG islands located downstream of the transcription start site, thus arresting elongating RNAPII and promoting its degradation. This abrogates the expression of ASCL1 and NEUROD1 and of their dependent genes, such as BCL2, INSM1, MYC, and AURKA, which are responsible for relevant SCLC tumorigenic properties such as inhibition of apoptosis and cell survival, as well as for a part of its neuroendocrine features. In summary, we show how the transcription addiction of these cells becomes their Achilles's heel, and how this is effectively exploited by lurbinectedin as a novel SCLC therapeutic endeavor.

Activation of multiple proteolysis systems contributes to acute cadmium cytotoxicity.

Cadmium exhibits both toxic and carcinogenic effects, and its cytotoxicity is linked to various cellular pathways, such as oxidative stress, ubiquitin-proteasome, and p53-mediated response pathways. The molecular mechanism(s) underlying cadmium cytotoxicity appears to be complex, but remains largely unclear. Here, we examined the effects of cadmium on the protein catabolism using two surrogate markers, DNA topoisomerases I and II alpha and its contribution to cytotoxicity. We have found that cadmium exposure induced time- and concentration-dependent decreases in the protein level of surrogate markers and therefore suggest that cadmium may be involved in proteolysis system activation. A pharmacological study further revealed the novel role(s) of these proteolytic activities and reactive oxygen species (ROS) in the cadmium-induced acute toxicity: (i) Proteasome inhibition only partially relieved the cadmium-induced proteolysis of topoisomerases; (ii) Moreover, we report for the first time that the activation of metalloproteases, serine proteases, and cysteine proteases contributes to the acute cadmium cytotoxicity; (iii) Consistent with the notion that both ROS generation and proteolysis system activation contribute to the cadmium-induced proteolysis and cytotoxicity, the scavenger N-acetylcysteine and aforementioned protease inhibition not only reduced the cadmium-induced topoisomerase degradation but also alleviated the cadmium-induced cell killing. Taken together, acute cadmium exposure may activate multiple proteolytic systems and ROS formation, subsequently leading to intracellular damage and cytotoxicity. Thus, our results provide a novel insight into potential action mechanism(s) by which cadmium exerts its cytotoxic effect and suggest potential strategies to prevent cadmium-associated acute toxicity.

Retraction notice to "Design, synthesis, and biological evaluation of heterotetracyclic quinolinone derivatives as anticancer agents targeting topoisomerases" [Eur. J. Med. Chem. 190 (2020) 112074].

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the authors. The authors regret to inform that they would like to withdraw this accepted article, due to serious errors in authorship, affiliations, material sources and supporting grant names/numbers. The authors sincerely apologize for these oversights and miscommunications the study caused.

Selected ellipticine derivatives, known to target topoisomerase II, suppress the alternative lengthening of telomere (ALT) pathway in telomerase-negative cells.

BACKGROUND: DNA topoisomerase and telomerase enzymes are popular targets of several anti-tumor drugs. Smooth proceeding of telomeric recombination requires Topoisomerase II (Top2), which is involved in telomere-telomere recombination through functioning in relaxation of positive supercoils among the cells adopting telomerase-independent Alternative lengthening of telomere (ALT) pathway. Most of the inhibitors reported so far have been designed to targetsolely telomerase-positive cells, which can potentially lead to therapeutic failure because tumor cells treated with telomerase inhibitors can activate the ALT pathway for telomere maintenance. Knowing that ALT cells are more sensitive against a Top2 inhibitor, ICRF-93 agent, compared to telomerase-positive cells, we analyzed two selected ellipticine derivatives that we recently reported as TopII-targeting compounds, to assess their effects on the formation of DNA breaks and suppression of ALT pathway. METHODS: Cell viability, Comet, C-Circle assays, dot blot, immunofluorescence staining, and telomere fluorescence in situ hybridization (FISH) staining were used for determining the effect of the compounds on ALT status of tumor cells. RESULTS AND CONCLUSIONS: Treatment of ALT cells with ellipticine derivatives resulted in the formation of DNA breaks and suppression of ALT-associated phenotypes in vitro. Our results will contribute to the development of therapeutic strategies combining telomerase and ALT pathway inhibitors.

The role of extracellular vesicles in prostate cancer with clinical applications.

In mammalian cells, extracellular vesicles (EVs) derived from the endosomal system carry many different kinds of bioactive molecule to deliver to recipient cells in a paracrine or endocrine manner. EVs can mediate local and systemic intercellular communications, including reeducating stromal cells, remodeling the architecture of the tumor microenvironment, modulating cancer metabolism and metastases, or even conferring drug resistance. Because the molecular and functional characteristics of prostate cancer (PCa) evolve over time, the bioactive molecule profiles/signatures of tumor-derived EVs (TDEs) reflect the real-time status of cancer cells. TDEs appear to be valuable diagnostic and prognostic biomarkers as well as potential therapeutic vehicles, suggesting their essential role in precision medicine of disease management. We summarized critical aspects of TDEs in PCa and discussed their potential clinical applications.

Design, synthesis, and biological evaluation of heterotetracyclic quinolinone derivatives as anticancer agents targeting topoisomerases.

A series of thiochromeno[2,3-c]quinolin-12-one derivatives with various substitutions were synthesized and evaluated as topoisomerase (Topo) inhibitors. Six (8, 10, 12, 14, 19, and 26) of 23 compounds showed strong inhibitory activities against Topo-mediated DNA relaxation and proliferation of five human cell lines including breast (MDA-MB-231, MDA-MB-468 and MCF7), colorectal (HCT116) and non-small cell lung (H1299) cancers. Among these, compounds 14 and 26 exhibited full inhibitory activities against Topo I at 3 µM and Topo IIα at 1 µM. Cancer cells treated with 26 accumulated DNA damage and were arrested at the G2/M phase. With time, cells proceeded to apoptosis, as revealed by increased amounts of cells with fragmented DNA and cleavage of caspase-8 and -9. In contrast, normal breast epithelial cells showed low sensitivity to 26. Taken together, our study identifies 26 as a potent Topo dual-inhibitor with low toxicity to normal cells, and elucidates that the terminal amino group of N-2-aminoethylamino or N-3-aminopropylamino at the 6th position and 8,10-di-halogen substituents on thiochromeno[2,3-c]quinolin-12-one are critical for the Topo-inhibiting and cancer-killing activities.

The paracrine induction of prostate cancer progression by caveolin-1.

A subpopulation of cancer stem cells (CSCs) plays a critical role of cancer progression, recurrence, and therapeutic resistance. Many studies have indicated that castration-resistant prostate cancer (CRPC) is associated with stem cell phenotypes, which could further promote neuroendocrine transdifferentiation. Although only a small subset of genetically pre-programmed cells in each organ has stem cell capability, CSCs appear to be inducible among a heterogeneous cancer cell population. However, the inductive mechanism(s) leading to the emergence of these CSCs are not fully understood in CRPC. Tumor cells actively produce, release, and utilize exosomes to promote cancer development and metastasis, cancer immune evasion as well as chemotherapeutic resistance; the impact of tumor-derived exosomes (TDE) and its cargo on prostate cancer (PCa) development is still unclear. In this study, we demonstrate that the presence of Cav-1 in TDE acts as a potent driver to induce CSC phenotypes and epithelial-mesenchymal transition in PCa undergoing neuroendocrine differentiation through NFκB signaling pathway. Furthermore, Cav-1 in mCRPC-derived exosomes is capable of inducing radio- and chemo-resistance in recipient cells. Collectively, these data support Cav-1 as a critical driver for mCRPC progression.

Regioselective synthesis and biological evaluation of N-substituted 2-aminoquinazolin-4-ones.

The reaction of methyl anthranilates with N-arylcyanamides in the presence of p-TsOH in t-BuOH under reflux afforded predominantly 3-arylquinazolin-4-ones. In contrast, the reaction of the same reactants with TMSCl in t-BuOH at 60 °C followed by the Dimroth rearrangement in aqueous ethanolic sodium hydroxide gave exclusively the regioisomers, 2-(N-arylamino)quinazolin-4-ones. The regioselective synthesis of N-aryl-substituted 2-aminoquinazolin-4-ones can be further applied to the synthesis of benzimidazo[2,1-b]quinazolin-12-ones.

Inflammatory interferon activates HIF-1α-mediated epithelial-to-mesenchymal transition via PI3K/AKT/mTOR pathway.

BACKGROUND: Tumor microenvironments (TMEs) activate various axes/pathways, predominantly inflammatory and hypoxic responses, impact tumorigenesis, metastasis and therapeutic resistance significantly. Although molecular pathways of individual TME are extensively studied, evidence showing interaction and crosstalk between hypoxia and inflammation remain unclear. Thus, we examined whether interferon (IFN) could modulate both inflammatory and hypoxic responses under normoxia and its relation with cancer development. METHODS: IFN was used to induce inflammation response and HIF-1α expression in various cancer cell lines. Corresponding signaling pathways were then analyzed by a combination of pharmacological inhibitors, immunoblotting, GST-Raf pull-down assays, dominant-negative and short-hairpin RNA-mediated knockdown approaches. Specifically, roles of functional HIF-1α in the IFN-induced epithelial-mesenchymal transition (EMT) and other tumorigenic propensities were examined by knockdown, pharmacological inhibition, luciferase reporter, clonogenic, anchorage-independent growth, wound-healing, vasculogenic mimicry, invasion and sphere-formation assays as well as cellular morphology observation. RESULTS: We showed for the first time that IFN induced functional HIF-1α expression in a time- and dose- dependent manner in various cancer cell lines under both hypoxic and normoxic conditions, and then leading to an activated HIF-1α pathway in an IFN-mediated pro-inflammatory TME. IFN regulates anti-apoptosis activity, cellular metastasis, EMT and vasculogenic mimicry by a novel mechanism through mainly the activation of PI3K/AKT/mTOR axis. Subsequently, pharmacological and genetic modulations of HIF-1α, JAK, PI3K/AKT/mTOR or p38 pathways efficiently abrogate above IFN-induced tumorigenic propensities. Moreover, HIF-1α is required for the IFN-induced invasiveness, tumorigenesis and vasculogenic mimicry. Further supports for the HIF-1α-dependent tumorigenesis were obtained from results of xenograft mouse model and sphere-formation assay. CONCLUSIONS: Our mechanistic study showed an induction of HIF-1α and EMT ability in an IFN-mediated inflammatory TME and thus demonstrating a novel interaction between inflammatory and hypoxic TMEs. Moreover, targeting HIF-1α may be a potential target for inhibiting tumor tumorigenesis and EMT by decreasing cancer cells wound healing and anchorage-independent colony growth. Our results also lead to rationale guidance for developing new therapeutic strategies to prevent relapse via targeting TME-providing IFN signaling and HIF-1α programming.

Producing irreversible topoisomerase II-mediated DNA breaks by site-specific Pt(II)-methionine coordination chemistry.

Human type II topoisomerase (Top2) isoforms, hTop2α and hTop2ß, are targeted by some of the most successful anticancer drugs. These drugs induce Top2-mediated DNA cleavage to trigger cell-death pathways. The potency of these drugs correlates positively with their efficacy in stabilizing the enzyme-mediated DNA breaks. Structural analysis of hTop2α and hTop2ß revealed the presence of methionine residues in the drug-binding pocket, we therefore tested whether a tighter Top2-drug association may be accomplished by introducing a methionine-reactive Pt2+ into a drug to further stabilize the DNA break. Herein, we synthesized an organoplatinum compound, etoplatin-N2ß, by replacing the methionine-juxtaposing group of the drug etoposide with a cis-dichlorodiammineplatinum(II) moiety. Compared to etoposide, etoplatin-N2ß more potently inhibits both human Top2s. While the DNA breaks arrested by etoposide can be rejoined, those captured by etoplatin-N2ß are practically irreversible. Crystallographic analyses of hTop2ß complexed with DNA and etoplatin-N2ß demonstrate coordinate bond formation between Pt2+ and a flanking methionine. Notably, this stable coordinate tether can be loosened by disrupting the structural integrity of drug-binding pocket, suggesting that Pt2+ coordination chemistry may allow for the development of potent inhibitors with protein conformation-dependent reversibility. This approach may be exploited to achieve isoform-specific targeting of human Top2s.

Correction: DNA Topoisomerase II Is Involved in Regulation of Cyst Wall Protein Genes and Differentiation in Giardia lamblia.

[This corrects the article DOI: 10.1371/journal.pntd.0002218.].

Trichodermin induces c-Jun N-terminal kinase-dependent apoptosis caused by mitotic arrest and DNA damage in human p53-mutated pancreatic cancer cells and xenografts.

Pancreatic cancer is an aggressive malignancy, which generally responds poorly to chemotherapy. In this study, trichodermin, an endophytic fungal metabolite from Nalanthamala psidii, was identified as a potent and selective antitumor agent in human pancreatic cancer. Trichodermin exhibited antiproliferative effects against pancreatic cancer cells, especially p53-mutated cells (MIA PaCa-2 and BxPC-3) rather than normal pancreatic epithelial cells. We found that trichodermin induced caspase-dependent and mitochondrial intrinsic apoptosis. Trichodermin also increased apoptosis through mitotic arrest by activating Cdc2/cyclin B1 complex activity. Moreover, trichodermin promoted the activation of c-Jun N-terminal kinase (JNK), and inhibition of JNK by its inhibitor, shRNA, or siRNA significantly reversed trichodermin-mediated caspase-dependent apoptosis. Trichodermin triggered DNA damage stress to activate p53 function for executing apoptosis in p53-mutated cells. Importantly, we demonstrated that trichodermin with efficacy similar to gemcitabine, profoundly suppressed tumor growth through inducing intratumoral DNA damage and JNK activation in orthotopic pancreatic cancer model. Based on these findings, trichodermin is a potential therapeutic agent worthy of further development into a clinical trial candidate for treating cancer, especially the mutant p53 pancreatic cancer.

microRNA-183 Mediates Protective Postconditioning of the Liver by Repressing Apaf-1.

AIMS: Ischemic postconditioning (iPoC) is known to mitigate ischemia-reperfusion (IR) injury of the liver, the mechanisms of which remain to be elucidated. This study explored the role of microRNA-183 (miR-183) in the protective mechanism of iPoC. RESULTS: Microarray analysis showed miR-183 was robustly expressed in rats' livers with iPoC. miR-183 repressed the mRNA expression of Apaf-1, which is an apoptosis promoting factor. Using an oxygen-glucose deprivation (OGD) injury model in Clone 9 cells, hypoxic postconditioning (HPoC) and an miR-183 mimetic significantly decreased cell death after OGD, but miR-183 inhibitors eliminated the protection of HPoC. The increased expression of Apaf-1 and the downstream activation of capsase-3/9 after OGD were mitigated by HPoC or the addition of miR-183 mimetics, whereas miR-183 inhibitor diminished the effect of HPoC on Apaf-1-caspase signaling. In the in vivo experiment, iPoC and agomiR-183 decreased the expression of serum ALT after liver IR in the mice, but antagomiR-183 mitigated the effect of iPoC. The results of hematoxylin and eosin and TUNEL staining were compatible with the biochemical assay. Moreover, iPoC and agomiR-183 decreased the expression of Apaf-1 and 4-HNE after IR injury in mouse livers, whereas the antagomiR-mediated prevention of miR-183 expression led to increased protein expression of Apaf-1 and 4-HNE in the postischemic livers. INNOVATION: Our experiment showed the first time that miR-183 was induced in protective postconditioning and reduced reperfusion injury of the livers via the targeting of apoptotic signaling. CONCLUSION: miR-183 mediated the tolerance induced by iPoC in livers via Apaf-1 repressing. Antioxid. Redox Signal. 26, 583-597.

Rhapontigenin inhibits TGF-ß-mediated epithelial­mesenchymal transition via the PI3K/AKT/mTOR pathway and is not associated with HIF-1α degradation.

The epithelial-mesenchymal transition (EMT) is a pivotal event in cancer cell invasion and metastasis. Emerging evidence suggests that rhapontigenin (Rha) may impede the progression of cancer by disrupting angiogenesis and the EMT. However, the underlying mechanism of Rha has not yet been clarified. In this study, we used transforming growth factor ß (TGF-ß) to trigger EMT in diverse types of cancer cells and revealed that Rha inhibited TGF-ß-induced EMT and derived­cell invasiveness. The effects of TGF-ß were blocked by Rha via interference with the PI3K/AKT/mTOR/GSK3ß/ß­catenin signaling pathway. Furthermore, Rha also inhibited TGF-ß­induced expression of transcription regulators Snail and hypoxia-inducible factor 1α (HIF-1α) by causing their degradation by the 26S proteasome. Surprisingly, although HIF-1α was degraded with Snail as a result of Rha exposure, HIF-1α was not a key factor involved in TGF-ß-mediated EMT induced by Rha. Knocking-down Snail expression, but not HIF-1α expression, by RNA interference dramatically reversed TGF-ß-mediated EMT. Moreover, Rha abolished TGF-ß-triggered cell invasiveness. Our results demonstrate that Rha inhibits TGF-ß-induced EMT in cancer cells by suppressing the activity of the PI3K/AKT/mTOR pathway. Therefore, Rha may represent a new route for therapeutic intervention in cancer patients and merits future studies to assess its potential.

Evaluation of an Epitypified Ophiocordyceps formosana (Cordyceps s.l.) for Its Pharmacological Potential.

The substantial merit of Cordyceps s.l. spp. in terms of medicinal benefits is largely appreciated. Nevertheless, only few studies have characterized and examined the clinical complications of the use of health tonics containing these species. Here, we epitypified C. formosana isolates that were collected and characterized as Ophiocordyceps formosana based on morphological characteristics, molecular phylogenetic analyses, and metabolite profiling. Thus, we renamed and transferred C. formosana to the new protologue Ophiocordyceps formosana (Kobayasi & Shimizu) Wang, Tsai, Tzean & Shen comb. nov. Additionally, the pharmacological potential of O. formosana was evaluated based on the hot-water extract from its mycelium. The relative amounts of the known bioactive ingredients that are unique to Cordyceps s.l. species in O. formosana were found to be similar to the amounts in O. sinensis and C. militaris, indicating the potential applicability of O. formosana for pharmacological uses. Additionally, we found that O. formosana exhibited antioxidation activities in vitro and in vivo that were similar to those of O. sinensis and C. militaris. Furthermore, O. formosana also displayed conspicuously effective antitumor activity compared with the tested Cordyceps s.l. species. Intrinsically, O. formosana exhibited less toxicity than the other Cordyceps species. Together, our data suggest that the metabolites of O. formosana may play active roles in complementary medicine.

Involvement of p38 MAPK in the Anticancer Activity of Cultivated Cordyceps militaris.

Cordyceps militaris is a traditional Chinese medicine frequently used for tonic and therapeutic purposes. Reports from our laboratory and others have demonstrated that extracts of the cultivated fruiting bodies of C. militaris (CM) exhibit a potent cytotoxic effect against many cancer cell lines, especially human leukemia cells. Here, we further investigated the underlying mechanism through which CM is cytotoxic to cancer cells. The CM-mediated induction of PARP cleavage and its related DNA damage signal (γH2AX) was diminished by caspase inhibitor I. In contrast, a ROS scavenger failed to prevent CM-mediated leukemia cell death. Moreover, two signaling molecules, AKT and p38 MAPK, were activated during the course of apoptosis induction. Employing MTT analysis, we found that a p38 MAPK inhibitor but not an AKT inhibitor could rescue cells from CM-mediated cell death, as well as inhibit the cleavage of PARP, formation of apoptotic bodies and up-regulation of the γH2AX signal. These results suggest that CM-mediated leukemia cell death occurs through the activation of the p38 MAPK pathway, indicating its potential therapeutic effects against human leukemia.

Topoisomerase II inhibition suppresses the proliferation of telomerase-negative cancers.

Telomere maintenance is required for chromosome stability, and telomeres are typically elongated by telomerase following DNA replication. In both tumor and yeast cells that lack telomerase, telomeres are maintained via an alternative recombination mechanism. Previous studies have indicated that yeast Sgs1 and Top3 may work together to remove highly negative supercoils that are generated from recombination. However, the mechanism by which cells eradicate highly positive supercoils during recombination remains unclear. In the present study, we demonstrate that TOP2 is involved in telomere-telomere recombination. Disturbance of telomeric structure by RIF1 or RIF2 deletion alleviates the requirement for TOP2 in telomere-telomere recombination. In human telomerase-negative alternative lengthening of telomere (ALT) cells, TOP2α or TOP2ß knockdown decreases ALT-associated PML bodies, increases telomere dysfunction-induced foci and triggers telomere shortening. Similar results were observed when ALT cells were treated with ICRF-193, a TOP2 inhibitor. Importantly, ICRF-193 treatment blocks ALT-associated phenotypes in vitro, causes telomere shortening, and inhibits ALT cell proliferation in mice. Taken together, these findings imply that TOP2 is involved in the ALT pathway, perhaps by resolving the highly positive supercoil structure at the front of the helicase. Inhibition of topoisomerase II may be a promising therapeutic approach that can be used to prevent cell proliferation in ALT-type cancer cells.

Synergistic property of cordycepin in cultivated Cordyceps militaris-mediated apoptosis in human leukemia cells.

Cordyceps militaris is a well-known Chinese traditional medicinal mushroom frequently used for tonics and recently of a potential interest for cancer intervention. Here, we explored the cancer cell killing activity of the hot water extracts of C. militaris cultured mycelia (CM(MY)) and cultivated fruiting bodies (CM(FB)). We found that CM(FB) exhibited a greater cytotoxic effect against various cancer cells over CM(MY). Apoptotic phenotypes including apoptotic body formation, DNA laddering, caspase 3 activation and cleavage of PARP proteins were induced by CM(FB) treatment but only slightly induced by same concentration of CM(MY) treatment in human HL-60 leukemia cells. Cordycepin in CM(FB) (10.47 mg/g) is significantly higher (∼ 15.2 times) than that of CM(MY) (0.69 mg/g). Using isobolographic analysis, the synergy of cytotoxicity was observed across different combined concentrations of CM(MY) and cordycepin. By complementing cordycepin into CM(MY) to the level comparable with CM(FB), we observed that CM(MY) (500 µg/ml) with cordycepin (4.8 µg/ml) induced apoptosis to a level similar to that induced by CM(FB) (500 µg/ml). Together, our results suggest that cordycepin possesses a synergistic cytotoxic effect with Cordyceps militaris-mediated apoptosis in human leukemia cells and therefore explaining a better anti-proliferating activity of CM(FB) over CM(MY).

DNA topoisomerase III alpha regulates p53-mediated tumor suppression.

PURPOSE: Human DNA topoisomerase III alpha (hTOP3α) is involved in DNA repair surveillance and cell-cycle checkpoints possibly through formatting complex with tumor suppressors. However, its role in cancer development remained unsolved. EXPERIMENTAL DESIGN: Coimmunoprecipitation, sucrose gradient, chromatin immunoprecipitation (ChIP), real time PCR, and immunoblotting analyses were performed to determine interactions of hTOP3α with p53. Paired cell lines with different hTOP3α levels were generated via ectopic expression and short hairpin RNA (shRNA)-mediated knockdown approaches. Cellular tumorigenic properties were analyzed using cell counting, colony formation, senescence, soft agar assays, and mouse xenograft models. RESULTS: The hTOP3α isozyme binds to p53 and cofractionizes with p53 in gradients differing from fractions containing hTOP3α and BLM. Knockdown of hTOP3α expression (sh-hTOP3α) caused a higher anchorage-independent growth of nontumorigenic RHEK-1 cells. Similarly, sh-hTOP3α and ectopic expression of hTOP3α in cancer cell lines caused increased and reduced tumorigenic abilities, respectively. Genetic and mutation experiments revealed that functional hTOP3α, p53, and p21 are required for this tumor-suppressive activity. Mechanism-wise, ChIP data revealed that hTOP3α binds to the p53 and p21 promoters and positively regulates their expression. Two proteins affect promoter recruitments of each other and collaborate in p21 expression. Moreover, sh-hTOP3α and sh-p53 in AGS cells caused a similar reduction in senescence and hTOP3α mRNA levels were lower in gastric and renal tumor samples. CONCLUSION: We concluded that hTOP3α interacts with p53, regulates p53 and p21 expression, and contributes to the p53-mediated tumor suppression.