Human male germ cell tumors (GCTs) arise from undifferentiated primordial germ cells (PGCs), a stage in which extensive methylation reprogramming occurs. GCTs exhibit pluripotentality and are highly sensitive to cisplatin therapy. The molecular basis of germ cell (GC) transformation, differentiation, and exquisite treatment response is poorly understood.
To assess the role and mechanism of promoter hypermethylation, we analyzed CpG islands of 21 gene promoters by methylation-specific PCR in seminomatous (SGCT) and nonseminomatous (NSGCT) GCTs. We found 60% of the NSGCTs demonstrating methylation in one or more gene promoters whereas SGCTs showed a near-absence of methylation, therefore identifying distinct methylation patterns in the two major histologies of GCT. DNA repair genes MGMT, RASSF1A, and BRCA1, and a transcriptional repressor gene HIC1, were frequently methylated in the NSGCTs. The promoter hypermethylation was associated with gene silencing in most methylated genes, and reactivation of gene expression occured upon treatment with 5-Aza-2' deoxycytidine in GCT cell lines.
Our results, therefore, suggest a potential role for epigenetic modification of critical tumor suppressor genes in pathways relevant to GC transformation, differentiation, and treatment response.
Germ cell tumor; promoter hypermethylation; MGMT; RASSF1A; BRCA1; gene expression
Male germ cell tumors (GCTs) are extremely sensitive to platinum-containing chemotherapy, with only 10% of patients showing therapy resistance. However, the biological basis of the high curability of disseminated GCTs by chemotherapy is still unknown. Recently, we demonstrated that the mammalian serine/arginine-rich protein-specific kinase 1 (SRPK1) is a cisplatin-sensitive gene, inactivation of which leads to cisplatin resistance. Because, in mammalians, the expression of SRPK1 is preferentially high in testicular tissues, cisplatin responsiveness of male GCTs might be associated with SRPK1 levels. In the present study, we monitored SRPK1 protein expression in a unique series of nonseminomatous GCTs by immunohistochemistry. Randomly selected GCTs (n = 70) and tumors from patients responding to standard chemotherapy (n = 20) generally showed strong SRPK1 staining. In contrast, expression in refractory GCTs (n = 20) as well as in GCTs from poor-prognosis patients responding to high-dose chemotherapy only (n = 11) was significantly lower (two-sided Wilcoxon rank sum test: P < .001). In conclusion, our data suggest that SRPK1 expression might be an important prognostic indicator for the chemoresponsiveness of nonseminomatous GCTs.
Chemotherapy resistance; germ cell tumors; chemotherapy sensitivity; protein kinase SRPK1; immunohistochemistry
Cisplatin is among the most widely used cytotoxic anti-cancer agents in solid tumors, however, the development of secondary resistance remains a major obstacle to clinical efficacy. Treatment-related DNA hypermethylation may play a role in creating drug resistant phenotypes by inactivating genes that are required for cytotoxicity. We applied a pharmacologic unmasking approach to detect hypermethylated genes whose inactivation contributes to cisplatin resistance. Utilizing three pairs of isogeneic, cisplatin-sensitive and -resistant cell lines derived from two parental cell lines (KB-3-1 and SCC25), we identified several hundred genes that were down-regulated in each resistant cell line and re-activated by the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-Aza-dC). Among them, 30 genes were common to ≥ 2 cell lines, and/or reported to be down-regulated in previous studies. Bisulfite sequencing confirmed that 14 genes were hypermethylated in resistant cell lines, but not in the sensitive parental cell lines. Six of 14 genes (SAT, C8orf4, LAMB3, TUBB, G0S2, MCAM) were cisplatin-inducible in sensitive, but not in resistant cell lines. siRNA knockdown of two genes, SAT and S100P, increased cell viability with cisplatin treatment in sensitive parental cell lines. S100P knockdown significantly decreased the S-phase fraction (SPF) of parental sensitive cell lines and slowed cell proliferation, which was associated with decreased sensitivity to cisplatin. Based on these findings, we conclude that DNA methylation is a frequent event in cells that are chronically exposed to cisplatin, and that methylation-induced gene silencing may play a role in the development of resistance to cytotoxic chemotherapeutic agents.
cisplatin; drug resistance; S100P; methylation; epigenetics
Cisplatin-based chemotherapy has been commonly used for the treatment of intracranial germ cell tumors (IC-GCTs). However, this treatment exhibits some adverse effects such as renal problems and hearing difficulty. Carboplatin-based chemotherapy was administered to pediatric patients with IC-GCTs from August 2004 at the Samsung Medical Center. In this study, we assessed the responses and adverse effects of carboplatin-based chemotherapy in pediatric IC-GCTs patients according to the risk group, and compared the results with those of the previous cisplatin-based chemotherapy.
We examined 35 patients (27 men and 8 women) diagnosed with IC-GCTs between August 2004 and April 2008 and received risk-adapted carboplatin-based chemotherapy at the Samsung Medical Center. Patients were divided into either low-risk (LR) or high-risk (HR) groups and a retrospective analysis was performed using information from the medical records.
Although hematological complications were common, hearing difficulties or grade 3 or 4 creatinine level elevation were not observed in patients who underwent carboplatin-based chemotherapy. The frequency of febrile neutropenia did not differ between the risk groups. The overall survival was 100% and event-free survival (EFS) was 95.7%. The EFS rate was 100% in the LR group and 90% in the HR group, respectively.
Despite their common occurrence in high-risk patients, no lethal hematological complications were associated with carboplatin-based treatment. The current carboplatin-based chemotherapy protocol is safe and effective for the treatment of pediatric patients with IC-GCTs.
Intracranial germ cell tumor; Carboplatin; Adverse effects
Cisplatin (CDDP) resistance in testicular germ cell tumors (GCTs) is still a clinical challenge, and one associated with poor prognosis. The purpose of this work was to test pazopanib, an anti-tumoral and anti-angiogenic multikinase inhibitor, and its combination with lapatinib (an anti-ErbB inhibitor) in mouse orthotopic models of human testicular GCTs.
We used two different models of human testicular GCTs orthotopically grown in nude mice; a CDDP-sensitive choriocarcinoma (TGT38) and a new orthotopic model generated from a metastatic GCT refractory to first-line CDDP chemotherapy (TGT44). Nude mice implanted with these orthotopic tumors were treated with the inhibitors and the effect on tumoral growth and angiogenesis was evaluated.
TGT44 refractory tumor had an immunohistochemical profile similar to the original metastasis, with characteristics of yolk sac tumor. TGT44 did not respond when treated with cisplatin. In contrast, pazopanib had an anti-angiogenic effect and anti-tumor efficacy in this model. Pazopanib in combination with lapatinib in TGT38, an orthotopic model of choriocarcinoma had an additive effect blocking tumor growth.
We present pazopanib as a possible agent for the alternative treatment of CDDP-sensitive and CDDP-refractory GCT patients, alone or in combination with anti-ErbB therapies.
Pazopanib; Lapatinib; Testicular cancer; Germ-cell tumors; Cisplatin; Refractory
Granulosa cell tumors (GCTs) are relatively rare and are subtypes of the sex-cord stromal neoplasms. Methylation induced silencing in the promoters of genes such as tumor suppressor genes, DNA repair genes and pro-apoptotic genes is recognised as a critical factor in cancer development.
We examined the role of promoter hypermethylation, an epigenetic alteration that is associated with the silencing tumor suppressor genes in human cancer, by studying 5 gene promoters in 25 GCTs cases by methylation specific PCR and RT-PCR. In addition, the compatible tissues (normal tissues distant from lesion) from three non-astrocytoma patients were also included as the control.
Frequencies of methylation in GCTs were 7/25 (28 % for FHIT), 6/25 (24% for FNACF), 3/25 (12% for Cyclin D2), 1/25 (4% for BRCA2) and 14/25 (56%) in RUNX3 genes. Correlation of promoter methylation with clinical characteristics and other genetic changes revealed that overall promoter methylation was higher in more advanced stage of the disease. Promoter methylation was associated with gene silencing in GCT cell lines. Treatment with methylation or histone deacetylation-inhibiting agents resulted in profound reactivation of gene expression.
These results may have implications in better understanding the underlying epigenetic mechanisms in GCT development, provide prognostic indicators, and identify important gene targets for treatment.
We investigated the epigenetic silencing and genetic changes of the RAS-associated domain family 1A (RASSF1A) gene and the O6-methylguanine-DNA methyltransferase (MGMT) gene in retinoblastoma. We extracted DNA from microdissected tumor and normal retina tissues of the same patient in 68 retinoblastoma cases. Promoter methylation in RASSF1A and MGMT was analyzed by methylation-specific PCR, RASSF1A sequence alterations in all coding exons by direct DNA sequencing, and RASSF1A expression by RT-PCR. Cell cycle staging was analyzed by flow cytometry. We detected RASSF1A promoter hypermethylation in 82% of retinoblastoma, in tumor tissues only but not in adjacent normal retinal tissue cells. There was no expression of RASSF1A transcripts in all hypermethylated samples, but RASSF1A transcripts were restored after 5-aza-2′-deoxycytidine treatment with no changes in cell cycle or apoptosis. No mutation in the RASSF1A sequence was found. MGMT hypermethylation was present in 15% of theretinoblastoma samples, and the absence of MGMT hypermethylation was associated (P = .002) with retinoblastoma at advanced Reese-Ellsworth tumor stage. Our results revealed a high RASSF1A hypermethylation frequency in retinoblastoma. The correlation of MGMT inactivation by promoter hypermethylation with lower-stage diseases indicated that MGMT hypermethylation provides useful prognostic information. Epigenetic mechanism plays an important role in the progression of retinoblastoma.
Retinoblastoma; methylation; RASSF1A; MGMT; RB
Germ cell tumors (GCTs) of the testis are rare, but are the most common cancer in young men. GCTs may consist of one predominant histologic pattern or may represent a mixture of multiple histologic types. For treatment purposes, two broad categories are recognized: 1) pure seminoma and 2) others, which together are termed nonseminomatous GCTs (NSGCTs). In general, seminoma tends to be less aggressive, to be diagnosed at an earlier stage, and to spread predictably along lymphatic channels to the retroperitoneum before spreading hematogenously to the lung or other organs. Compared with NSGCTs, seminoma is exquisitely sensitive to radiation therapy and platinum-based chemotherapy. NSGCTs are usually mixed tumors and teratoma often exists at the sites of metastasis with other GCT elements; cure often requires chemotherapy to kill the chemosensitive-components and surgery to remove the teratomatous components. The main factors contributing to excellent cure rates of GCTs are careful staging at diagnosis; adequate early treatment using chemotherapeutic combinations, with or without radiotherapy and surgery; and very strict follow-up and salvage therapy. We review several clinical studies and summarize the current trends in the management of GCTs.
Neoplasms; Testis; Therapeutics
Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.
Resistance to chemotherapy is a major limitation in the treatment of head and neck squamous cell carcinomas (HNSCCs), accounting for high mortality rates in patients. Here, we investigated the role of replication protein A (RPA) in cisplatin and etoposide resistance.
We used 6 parental HNSCC cell lines. We also generated 1 cisplatin-resistant progeny subline from a parental cisplatin-sensitive cell line, to examine cisplatin resistance and sensitivity with respect to RPA2 hyperphosphorylation and cell-cycle response.
Cisplatin-resistant HNSCC cell levels of hyperphosphorylated RPA2 in response to cisplatin were 80% to 90% greater compared with cisplatin-sensitive cell lines. RPA2 hyperphosphorylation could be induced in the cisplatin-resistant HNSCC subline. The absence of RPA2 hyperphosphorylation correlated with a defect in cell-cycle progression and cell survival.
Loss of RPA2 hyperphosphorylation occurs in HNSCC cells and may be a marker of cellular sensitivities to cisplatin and etoposide in HNSCC.
replication protein A (RPA); phosphorylation; cisplatin; etoposide; cell cycle
Testicular germ cell tumour (TGCT) is the most common malignancy in young males. Although most TGCTs are sensitive to cisplatin-based chemotherapy, significant numbers of TGCT patients still relapse and die each year because of the development of resistance to cisplatin. Previously, we first reported that a key regulator of the mitotic checkpoint, mitotic arrest deficient-2 (MAD2), was a mediator of cisplatin sensitivity in human cancer cells. In this study, we investigated whether MAD2 played a role in cellular sensitivity to cisplatin in TGCT cells and the underlying molecular mechanisms responsible. Using 10 TGCT cell lines, we found that increased MAD2 expression was correlated with cellular sensitivity to cisplatin, which was associated with activation of the MEK pathway. Treatment of cells expressing high levels of MAD2 with an MEK inhibitor, U0126, led to cellular protection against cisplatin-induced apoptosis. Inactivation of MAD2 by transfecting a dominant-negative construct in TGCT cells with high levels of MAD2 resulted in the suppression of MEK pathway and resistance to cisplatin-induced cell death. These results support previous suggestion on the involvement of mitotic checkpoint in DNA damage response in human cancer cells and demonstrate a possible molecular mechanism responsible for the MAD2-mediated sensitivity to cisplatin in TGCT cells. Our results also suggest that downregulation of MAD2 may be an indicator for identification of TGCT cancer cells that are potentially resistant to cisplatin-based therapy.
MAD2; MEK; cisplatin; TGCT
While allelic losses and mutations of tumor suppressor genes implicated in the etiology of astrocytoma have been widely assessed, the role of epigenetics is still a matter of study. We analyzed the frequency of promoter hypermethylation by methylation-specific PCR (MSP) in five tumor suppressor genes (PTEN, MGMT, RASSF1A, p14ARF, and p16INK4A), in astrocytoma samples and cell lines. RASSF1A was the most frequently hypermethylated gene in all grades of astrocytoma samples, in cell lines, and in adult secondary GBM. It was followed by MGMT. PTEN showed a slight methylation signal in only one GBM and one pilocytic astrocytoma, and in two cell lines; while p14ARF and p16INK4A did not show any evidence of methylation in primary tumors or cell lines. In pediatric GBM, RASSF1A was again the most frequently altered gene, followed by MGMT; PTEN, p14 and p16 showed no alterations. Lack or reduced expression of RASSF1A in cell lines was correlated with the presence of methylation. RASSF1A promoter hypermethylation might be used as a diagnostic marker for secondary GBM and pediatric GBM. Promoter hypermethylation might not be an important inactivation mechanism in other genes like PTEN, p14ARF and p16INK4A, in which other alterations (mutations, homozygous deletions) are prevalent.
Extragonadal localization of germ cell tumors (GCTs) is rare; to the best of our knowledge, a location in the soft tissue of the arm has never been previously reported in the literature.
We report the case of a 37-year-old man who presented with a primary malignant mixed non-seminomatous GCT (teratocarcinoma variety) in the right arm, treated by a combination of cisplatin-based chemotherapy and surgery. After 18 months of close follow-up, no locoregional recurrence or distant metastases have been detected.
A combination of chemotherapy and surgery is the most appropriate treatment strategy for extragonadal GCTs, to ensure both local and systemic control.
Chemotherapy; Embryonic carcinoma; Extragonadal; Mixed germ cell tumors; Surgery; Teratoma
Giant cell tumor (GCT) is usually a benign but locally aggressive primary bone neoplasm in which monocytic macrophage/osteoclast precursor cells and multinucleated osteoclast-like giant cells infiltrate the tumor. The etiology of GCT is unknown, however the tumor cells of GCT have been reported to produce chemoattractants that can attract osteoclasts and osteoclast precursors. Rarely, GCT can originate at extraosseous sites. More rarely, GCT may exhibit a much more aggressive phenotype. The role of chemotherapy in metastatic GCT is not well defined.
We report a case of an aggressive GCT of the uterus with rapidly growing lung metastases, and its response to chemotherapy with pegylated-liposomal doxorubicin, ifosfamide, and bevacizumab, along with a review of the literature.
Aggressive metastasizing GCT may arise in the uterus, and may respond to combination chemotherapy.
Tumors frequently develop resistance to cisplatin, a platinum drug used as a cornerstone of present day chemotherapy regimens, significantly decreasing its usefulness in the clinic. Although it is known that cisplatin-resistant (CP-r) cancer cells commonly grow more slowly and exhibit reduced uptake of various compounds including nutrients, the effect of tumor metabolism on cisplatin resistance is unclear. It was found that in CP-r cells, uptake of 2-deoxyglucose was reduced due to dysfunction and altered morphology of mitochondria compared to cisplatin-sensitive (CP-s) parental cancer cells. The CP-r cells overexpressed SIRT1, a histone deacetylase that plays a central role in DNA damage response and transcriptional silencing. Incubation of drug-sensitive cells in low glucose medium induced the expression of SIRT1 and increased cellular resistance to cisplatin. Reduced SIRT1 expression by a SIRT1 SMART siRNA duplex sensitized the >20-fold resistant CP-r cells to cisplatin treatment 1.5- to 2-fold, and SIRT1 overexpression by SIRT1 cDNA transfection increased cisplatin resistance in CP-s cells by 2- to 3-fold. Our findings therefore suggest that reduced glucose use and altered mitochondrial metabolism mediated by SIRT1 is one of several alterations that contribute to cellular resistance to cisplatin.
While platinum-based chemotherapeutic agents are widely used to treat various solid tumors, the acquired platinum resistance is a major impediment in their successful treatment. Since enhanced DNA repair capacity is a major factor in conferring cisplatin resistance, targeting of DNA repair pathways is an effective stratagem for overcoming cisplatin resistance. This study was designed to delineate the role of nucleotide excision repair (NER), the principal mechanism for the removal of cisplatin-induced DNA intrastrand crosslinks, in cisplatin resistance and reveal the impact of DNA repair interference on cisplatin sensitivity in human ovarian cancer cells.
We assessed the inherent NER efficiency of multiple matched pairs of cisplatin-sensitive and -resistant ovarian cancer cell lines and their expression of NER-related factors at mRNA and protein levels. Our results showed that only the cisplatin-resistant ovarian cancer cell line PEO4 possessed an increased NER capacity compared to its inherently NER-inefficient parental line PEO1. Several other cisplatin-resistant cell lines, including CP70, CDDP and 2008C13, exhibited a normal and parental cell-comparable NER capacity for removing cisplatin-induced DNA intrastrand cross-links (Pt-GG). Concomitant gene expression analysis revealed discordance in mRNA and protein levels of NER factors in various ovarian cancer cell lines and NER proteins level were unrelated to the cisplatin sensitivity of these cell lines. Although knockdown of NER factors was able to compromise the NER efficiency, it only caused a minimal effect on cisplatin sensitivity. On the contrary, downregulation of BRCA2, a critical protein for homologous recombination repair (HRR), significantly enhanced the efficacy of cisplatin in killing ovarian cancer cell line PEO4.
Our studies indicate that the level of NER factors in ovarian cancer cell lines is neither a determinant of their NER capacity nor of the sensitivity to cisplatin, and suggest that manipulation of the HRR but not the NER factor expression provides an effective strategy for sensitizing cisplatin-resistant tumors to platinating agents.
Platinum-based chemotherapies such as cisplatin are used as first-line treatment for many cancers. Although there is often a high initial responsiveness, the majority of patients eventually relapse with platinum-resistant disease. For example, a subset of testicular cancer patients still die even though testicular cancer is considered a paradigm of cisplatin-sensitive solid tumors, but the mechanisms of chemoresistance remain elusive. Here, we have shown that one key determinant of cisplatin-resistance in testicular embryonal carcinoma (EC) is high cytoplasmic expression of the cyclin-dependent kinase (CDK) inhibitor p21. The EC component of the majority of refractory testicular cancer patients exhibited high cytoplasmic p21 expression, which protected EC cell lines against cisplatin-induced apoptosis via CDK2 inhibition. Localization of p21 in the cytoplasm was critical for cisplatin resistance, since relocalization of p21 to the nucleus by Akt inhibition sensitized EC cell lines to cisplatin. We also demonstrated in EC cell lines and human tumor tissue that high cytoplasmic p21 expression and cisplatin resistance of EC were inversely associated with the expression of Oct4 and miR-106b seed family members. Thus, targeting cytoplasmic p21, including by modulation of the Oct4/miR-106b/p21 pathway, may offer new strategies for the treatment of chemoresistant testicular and other types of cancer.
Recognition of the therapeutic role of retroperitoneal lymph node dissection (RPLND) in the setting of testicular germ cell tumors (GCTs) is of utmost importance. Although the histologic findings of RPLND provide diagnostic and prognostic information, the adequacy of initial RPLND is an independent predictor of clinical outcome. Despite the advent of effective cisplatin-based chemotherapy for testicular GCTs, patients who have undergone suboptimal surgery at the time of initial RPLND are compromised. Despite the initial enthusiasm surrounding anatomic mapping studies, the use of modified RPLND templates has the potential to leave a significant number of patients with unresected retroperitoneal disease. Teratomatous elements are particularly common. Patients with retroperitoneal relapse following initial RPLND should be treated with reoperative RPLND and chemotherapy and can expect long term survival rates nearing 70% when treated in tertiary centers by experienced surgeons.
Recurrence; relapse; reoperative; retroperitoneal lymph node dissection; testicular cancer
We previously reported a dose-finding and phase II trial of the TI-CE regimen (paclitaxel [T] plus ifosfamide [I] followed by high-dose carboplatin [C] plus etoposide [E] with stem-cell support) in germ cell tumor (GCT) patients predicted to have a poor prognosis with conventional-dose salvage therapy. We now report the efficacy of TI-CE with prognostic factors for disease-free survival (DFS) and overall survival (OS) in our full data set of 107 patients.
Patients and Methods
Eligible patients had advanced GCTs with progressive disease following chemotherapy and unfavorable prognostic features (extragonadal primary site, incomplete response [IR] to first-line therapy, or relapse/IR to ifosfamide-cisplatin–based conventional-dose salvage). Univariate and multivariate analyses (MVAs) of prognostic factors were performed. The predictive ability of the Einhorn and Beyer prognostic models was assessed.
Most patients were platinum refractory and had an IR to first-line chemotherapy. There were 54 (5%) complete and eight (8%) partial responses with negative markers; 5-year DFS was 47% and OS was 52% (median follow-up, 61 months). No relapses occurred after 2 years. Five (24%) of 21 primary mediastinal nonseminomatous GCTs are continuously disease free. On MVA, primary mediastinal site (P < .001), two or more lines of prior therapy (P < .001), baseline human chorionic gonadotropin ≥ 1,000 U/L (P = .01), and lung metastases (P = .02) significantly predicted adverse DFS. Poor-risk patients did worse than good- or intermediate-risk patients according to both Beyer (P < .002) and Einhorn (P < .05) models.
TI-CE is effective salvage therapy for GCT patients with poor prognostic features. Mediastinal primary site and two or more lines of prior therapy were most predictive of adverse DFS. Beyer and Einhorn models can assist in predicting outcome.
Hypermethylated in cancer 1(HIC1) was identified as a strong suppressor gene in chromosome region 17p13.3 telomeric to TP53. This gene encodes a transcriptional repressor and is ubiquitously expressed in normal tissues but downexpressed in different tumor tissues where it is hypermethylated. The hypermethylation of this chromosomal region leads to epigenetic inactivation of HIC1, which would prompt cancer cells to alter survival and signaling pathways or specific transcription factors during the period of tumorigenesis. In vitro, HIC1 function is mainly a sequence-specific transcriptional repressor interacting with a still growing range of histone deacetylase(HDAC)-dependent and HDAC-independent corepressor complexes. Furthermore, a role for HIC1 in tumor development is firmly supported by Hic1 deficient mouse model and two double heterozygote models cooperate with p53 and Ptch1. Notably, our findings suggest that potential factors derived from tumor microenviroment may play a role in modulating HIC1 expression in tumor cells by epigenetic modification, which is responsible for tumor progression. In this review, we will describe genomic and proteinic structure of HIC1, and summary the potential role of HIC1 in human various solid tumors and leukemia, and explore the influence of tumor microenviroment on inducing HIC1 expression in tumor cells.
HIC1; Epigenetic modification; Tumor microenviroment; Tumor progression
Testicular Germ Cell Tumors (TGCT) and patient-derived cell lines are extremely sensitive to cisplatin and other interstrand cross-link (ICL) inducing agents. Nevertheless, a subset of TGCTs are either innately resistant or acquire resistance to cisplatin during treatment. Understanding the mechanisms underlying TGCT sensitivity/resistance to cisplatin as well as the identification of novel strategies to target cisplatin-resistant TGCTs have major clinical implications. Herein, we have examined the proficiency of five embryonal carcinoma (EC) cell lines to repair cisplatin-induced ICLs. Using γH2AX staining as a marker of double strand break formation, we found that EC cell lines were either incapable of or had a reduced ability to repair ICL-induced damage. The defect correlated with reduced Homologous Recombination (HR) repair, as demonstrated by the reduction of RAD51 foci formation and by direct evaluation of HR efficiency using a GFP-reporter substrate. HR-defective tumors cells are known to be sensitive to the treatment with poly(ADP-ribose) polymerase (PARP) inhibitor. In line with this observation, we found that EC cell lines were also sensitive to PARP inhibitor monotherapy. The magnitude of sensitivity correlated with HR-repair reduced proficiency and with the expression levels and activity of PARP1 protein. In addition, we found that PARP inhibition strongly enhanced the response of the most resistant EC cells to cisplatin, by reducing their ability to overcome the damage. These results point to a reduced proficiency of HR repair as a source of sensitivity of ECs to ICL-inducing agents and PARP inhibitor monotherapy, and suggest that pharmacological inhibition of PARP can be exploited to target the stem cell component of the TGCTs (namely ECs) and to enhance the sensitivity of cisplatin-resistant TGCTs to standard treatments.
Cisplatin and its analogues are the most commonly used agents in the treatment of head and neck squamous cell carcinoma (HNSCC). In this study, we investigated a possible role of epidermal growth factor receptor (EGFR), phosphorylation and degradation in cisplatin-induced cytotoxicity. Cisplatin treatment led to an increase in initial EGFR phosphorylation at the Y1045, the binding site of ubiquitin ligase, Casitas B-lineage lymphoma (c-Cbl), followed by ubiquitination in the relatively cisplatin-sensitive cell lines. However, cisplatin-resistant cell lines underwent minimal EGFR phosphorylation at the Y1045 site and minimal ubiquitination. We found that EGFR degradation in response to cisplatin was highly correlated with cytotoxicity in seven head and neck cancer cell lines. Pretreatment with epidermal growth factor (EGF), enhanced cisplatin-induced EGFR degradation and cytotoxicity, whereas erlotinib pretreatment blocked EGFR phosphorylation, degradation, and cisplatin-induced cytotoxicity. Expression of a mutant Y1045F EGFR, which is relatively resistant to c-Cbl mediated degradation, in Chinese hamster ovary cells and the UMSCC11B human head and neck cancer cell line protected EGFR from cisplatin-induced degradation and enhanced cell survival compared to WT-EGFR. Transfection of WT-c-Cbl enhanced EGFR degradation and cisplatin-induced cytotoxicity compared to control vector. These results demonstrate that cisplatin-induced EGFR phosphorylation and subsequent ubiquitination and degradation is an important determinant of cisplatin sensitivity. Our findings suggest that treatment with an EGFR inhibitor before cisplatin would be antagonistic, as EGFR inhibition would protect EGFR from cisplatin-mediated phosphorylation and subsequent ubiquitination and degradation, which may explain the negative results of several recent clinical trials. Furthermore, they suggest that EGFR degradation is worth exploring as an early biomarker of response and as a target to improve outcome.
Germ cell tumors (GCTs) affect infants, children, and adults and are the most common cancer type in young men. Progress in understanding the molecular basis of GCTs has been hampered by a lack of suitable animal models. Here we report the identification of a zebrafish model of highly penetrant, heritable testicular GCT isolated as part of a forward genetic screen for cancer susceptibility genes. The mutant line develops spontaneous testicular tumors at a median age of 7 months, and pedigree analysis indicates dominant inheritance of the GCT susceptibility trait. The zebrafish model exhibits disruption of testicular tissue architecture and the accumulation of primitive, spermatogonial-like cells with loss of spermatocytic differentiation. Radiation treatment leads to apoptosis of the tumor cells and tumor regression. The GCT-susceptible line can serve as a model for understanding the mechanisms regulating germ cells in normal development and disease and as a platform investigating new therapeutic approaches for GCTs.
Ovarian cancer is the leading cause of death among gynecological cancers. Cisplatin is one of the most effective anticancer drugs used in the treatment of ovarian cancer. Development of resistance to cisplatin limits its therapeutic use. Most of the anticancer drugs, including cisplatin, are believed to kill cancer cells by inducing apoptosis and a defect in apoptotic signaling can contribute to drug resistance. The tumor suppressor protein p53 plays a critical role in DNA damage-induced apoptosis. During a yeast-based drug screening, NSC109268 was identified to enhance cellular sensitivity to cisplatin. The objective of the present study is to determine if p53 is responsible for cisplatin sensitization by NSC109268.
NSC109268 enhanced sensitivity of ovarian cancer 2008 cells and its cisplatin resistant counterpart 2008/C13* cells which express wild-type p53. The potentiation of cisplatin sensitivity by NSC109268 was greater in 2008/C13* cells compared to 2008 cells. Cisplatin caused a concentration-dependent increase in p53 in 2008 and 2008/C13* cells, and the induction of p53 correlated with cisplatin-induced apoptosis as determined by the cleavage of PARP. NSC109268 alone had no effect on p53 but it enhanced p53 level in response to cisplatin. Knockdown of p53 by siRNA, however, did not attenuate cell death in response to cisplatin or combination of NSC109268 and cisplatin.
These results demonstrate that NSC109268 enhances sensitivity of ovarian cancer 2008 cells to cisplatin independent of p53.
To determine the impact of treatment protocols on the outcome of central nervous system germ cell tumors (CNS-GCTs), we reviewed the medical records of 53 patients who received front-line chemotherapy from September 1997 to September 2006. Pure germinoma, normal alpha-fetoprotein level and beta-human chorionic gonadotropin level <50 mIU/mL were regarded as low-risk features and the others as high-risk. Patients from different time periods were divided into 3 groups according to the chemotherapy protocols. Group 1 (n=19) received 4 cycles of chemotherapy comprising cisplatin, etoposide and bleomycin. Group 2 (n=16) and group 3 (n=18) received 4 cycles of chemotherapy with cisplatin, etoposide, cyclophosphamide and vincristine in the former and with carboplatin, etoposide, cyclophosphamide and bleomycin in the latter. In group 2 and group 3, high-risk patients received double doses of cisplatin, carboplatin and cyclophosphamide. Radiotherapy was given after chemotherapy according to the clinical requirements. The event-free survivals of groups 1, 2, and 3 were 67.0%, 93.8%, and 100%, respectively (group 1 vs. 2, P=0.06; group 2 vs. 3, P=0.29; group 1 vs. 3, P=0.02). Our data suggest that risk-adapted intensive chemotherapy may improve the outcome of patients with malignant CNS-GCTs.
Neoplasms, Germ Cell and Embryonal; Central Nervous System; Drug Therapy; Survival