The PDGFRβ-AKT pathway contributes to CDDP-acquired resistance in testicular germ cell tumors

Andrographolide sensitizes KRAS-mutant colorectal cancer cells to cetuximab by inhibiting the EGFR/AKT and PDGFRβ/AKT signaling pathways

BACKGROUND

Cetuximab, an inhibitor targeting EGFR, is widely applied in clinical management of colorectal cancer (CRC). Nevertheless, drug resistance induced by KRAS-mutations limits cetuximab's anti-cancer effectiveness. Furthermore, the persistent activation of EGFR-independent AKT is another significant factor in cetuximab resistance. Nevertheless, the mechanism that EGFR-independent AKT drives cetuximab resistance remains unclear. Thus, highlighting the need to optimize therapies to overcome cetuximab resistance and also to explore the underlying mechanism.

PURPOSE

This work aimed to investigate whether and how andrographolide enhance the therapeutic efficacy of cetuximab in KRAS-mutant CRC cells by modulating AKT.

METHODS

The viabilities of CRC cell lines were analyzed by CCK-8. The intracellular proteins phosphorylation levels were investigated by Human Phospho-kinase Antibody Array analysis. Knockdown and transfection of PDGFRβ were used to evaluate the role of andrographolide on PDGFRβ. The western blotting was used to investigate Wnt/β-catenin pathways, PI3K/AKT, and EMT in KRAS-mutant CRC cells. The animal models including subcutaneous tumor and lung metastasis were performed to assess tumor response to therapy in vivo.

RESULTS

Andrographolide was demonstrated to decrease the expression of PI3K and AKT through targeting PDGFRβ and EGFR, and it enhanced cetuximab effect on KRAS-mutant CRC cells by this mechanism. Meanwhile, andrographolide helped cetuximab to inhibit Wnt/β-catenin, CRC cell migration and reduced Vimentin expression, while increasing that of E-cadherin. Lastly, co-treatment with cetuximab and andrographolide reduced the growth of KRAS-mutant tumors and pulmonary metastases in vivo.

CONCLUSIONS

Our findings suggest that andrographolide can overcome the KRAS-mutant CRC cells' resistance to cetuximab through inhibiting the EGFR/PI3K/AKT and PDGFRβ /AKT signaling pathways. This research provided a possible theory that andrographolide sensitizes KRAS-mutant tumor to EGFR TKI.

Ovarian cancer relies on the PDGFRβ-fibronectin axis for tumorsphere formation and metastatic spread

High-grade serous ovarian cancer (HGSOC) is the deadliest gynecological malignancy. The most common form of metastatic spread of HGSOC is transcoelomic dissemination. In this process, detached cells from the primary tumor aggregate as tumorspheres and promote the accumulation of peritoneal ascites. This represents an early event in HGSOC development and is indicative of poor prognosis. In this study, based on tumorspheres isolated from ascitic liquid samples from HGSOC patients, ovarian cancer spheroid 3D cultures, and in vivo models, we describe a key signal for tumorsphere formation in HGSOC. We report that platelet-derived growth factor receptor beta (PDGFRβ) is essential for fibronectin-mediated cell clustering of ovarian cancer cells into tumorspheres. This effect is mediated by the kinase NUAK family SNF1-like kinase 1 (NUAK1) and blocked by PDGFRβ pharmacological or genetic inhibition. In the absence of PDGFRβ, ovarian cancer cells can be provided with fibronectin by cancer-associated fibroblasts to generate chimeric spheroids. This work provides new insights that uncover potential targets to prevent peritoneal dissemination, the main cause of advanced disease in HGSOC patients.

Genome-scale CRISPR screen reveals neddylation to contribute to cisplatin resistance of testicular germ cell tumours

BACKGROUND

Type II testicular germ cell tumours (TGCT) are the most prevalent tumours in young men. Patients suffering from cisplatin-resistant TGCTs are facing very poor prognosis demanding novel therapeutic options. Neddylation is a known posttranslational modification mediating many important biological processes, including tumorigenesis. Overactivation of the neddylation pathway promotes carcinogenesis and tumour progression in various entities by inducing proteasomal degradation of tumour suppressors (e.g., p21, p27).

METHODS

We used a genome-scale CRISPR/Cas9 activation screen to identify cisplatin resistance factors. TGCT cell lines were treated with the neddylation inhibitor (MLN4924)/cisplatin/combination and investigated for changes in viability (XTT assay), apoptosis/cell cycle (flow cytometry) as well as in the transcriptome (3'mRNA sequencing).

RESULTS

NAE1 overexpression was detected in cisplatin-resistant colonies from the CRISPR screen. Inhibition of neddylation using MLN4924 increased cisplatin cytotoxicity in TGCT cell lines and sensitised cisplatin-resistant cells towards cisplatin. Apoptosis, G2/M-phase cell cycle arrest, γH2A.X/P27 accumulation and mesoderm/endoderm differentiation were observed in TGCT cells, while fibroblast cells were unaffected.

CONCLUSIONS

We identified overactivation of neddylation as a factor for cisplatin resistance in TGCTs and highlighted the additive effect of NAE1 inhibition by MLN4924 in combination with cisplatin as a novel treatment option for TGCTs.

Selamectin increases cisplatin sensitivity by inhibiting cisplatin-resistant genes expression and autophagy in uveal melanoma

Cisplatin resistance is the main reason for uveal melanoma (UM) treatment failure. Thus, developing strategy that increasing cisplatin sensitivity is needed. In this study, we performed drug repositioning analysis with the Connectivity Map database using a panel of previously identified cisplatin sensitivity-associated genes and cisplatin resistance-associated genes as the signature and obtained the antiparasitic drug selamectin. We demonstrated that the selamectin and cisplatin combination showed a synergistic effect on inhibiting UM cell growth. Experiments in tumor-bearing nude mice further showed that selamectin and cisplatin have synergistic effects in reducing tumor growth. Previous studies have linked increased autophagy with tumor resistance to chemotherapy. We found that selamectin inhibited the expression of the autophagy-related gene ATG9B, thus reducing autophagy. The cisplatin resistance-associated genes PDGFRB, DUSP1, MAST1 and IL11 were significantly downregulated in UM cells treated with selamectin. In summary, our study shows that selamectin enhanced the sensitivity of UM to cisplatin, through the mechanism of inhibiting cisplatin resistance-associated gene expression and autophagy. These findings may provide a new strategy for the treatment of UM.

Testicular germ cell tumors: Genomic alternations and RAS-dependent signaling

Testicular germ cell tumors (TGCTs) are a common malignancy occurring in young adult men. The various genetic risk factors have been suggested to contribute to TGCT pathogenesis, however, they have a distinct mutational profile with a low rate of somatic point mutations, more frequent chromosomal gains, and aneuploidy. The most frequently mutated oncogenes in human cancers are RAS oncogenes, while their impact on testicular carcinogenesis and refractory disease is still poorly understood. In this mini-review, we summarize current knowledge on genetic alternations of RAS signaling-associated genes (the single nucleotide polymorphisms and point mutations) in this particular cancer type and highlight their link to chemotherapy resistance mechanisms. We also mention the impact of epigenetic changes on TGCT progression. Lastly, we propose a model for RAS-dependent signaling networks, regulation, cross-talks, and outcomes in TGCTs.

Overcoming Chemotherapy Resistance in Germ Cell Tumors

Testicular germ cell tumors (GCTs) are highly curable malignancies. Excellent survival rates in patients with metastatic disease can be attributed to the exceptional sensitivity of GCTs to cisplatin-based chemotherapy. This hypersensitivity is probably related to alterations in the DNA repair of cisplatin-induced DNA damage, and an excessive apoptotic response. However, chemotherapy fails due to the development of cisplatin resistance in a proportion of patients. The molecular basis of this resistance appears to be multifactorial. Tracking the mechanisms of cisplatin resistance in GCTs, multiple molecules have been identified as potential therapeutic targets. A variety of therapeutic agents have been evaluated in preclinical and clinical studies. These include different chemotherapeutics, targeted therapies, such as tyrosine kinase inhibitors, mTOR inhibitors, PARP inhibitors, CDK inhibitors, and anti-CD30 therapy, as well as immune-checkpoint inhibitors, epigenetic therapy, and others. These therapeutics have been used as single agents or in combination with cisplatin. Some of them have shown promising in vitro activity in overcoming cisplatin resistance, but have not been effective in clinical trials in refractory GCT patients. This review provides a summary of current knowledge about the molecular mechanisms of cisplatin sensitivity and resistance in GCTs and outlines possible therapeutic approaches that seek to overcome this chemoresistance.

Downregulation of inhibitor of apoptosis protein induces apoptosis and suppresses stemness maintenance in testicular teratoma

Inhibitors of apoptosis (IAPs) are a family of cell death inhibitors found in viruses and metazoans that physically interact with a variety of pro-apoptotic proteins and inhibit apoptosis induced by diverse stimuli. Melanoma IAP (ML-IAP) is a potent anti-apoptotic protein that is strongly upregulated in melanoma and confers protection against a variety of pro-apoptotic stimuli. In the present study, it was revealed that ML-IAP was expressed at high levels in testicular teratoma. Deletion and mutational analysis demonstrated that ML-IAP silencing significantly decreased P19 cell proliferation while inducing cell cycle arrest and apoptosis. ML-IAP knockdown significantly induced caspase-3/8/9-mediated apoptosis in P19 cells. In addition, metabolism and stemness maintenance in P19 cells were suppressed by ML-IAP knockdown. These results indicated that ML-IAP silencing is a powerful inducer of apoptosis mediated by cell death receptors and may function as a direct activator of downstream effector caspases.

MicroRNAs as Therapeutic Targets for Anticancer Drugs in Lung Cancer Therapy

MicroRNAs (miRNAs) are short, non-coding RNA molecules that regulate gene expression by translational repression or deregulation of messenger RNAs. Accumulating evidence suggests that miRNAs play various roles in the development and progression of lung cancers. Although their precise roles in targeted cancer therapy are currently unclear, miRNAs have been shown to affect the sensitivity of tumors to anticancer drugs. A large number of recent studies have demonstrated that some anticancer drugs exerted antitumor activities by affecting the expression of miRNAs and their targeted genes. These studies have elucidated the specific biological mechanism of drugs in tumor suppression, which provides a new idea or basis for their clinical application. In this review, we summarized the therapeutic mechanisms of drugs in lung cancer therapy through their effects on miRNAs and their targeted genes, which highlights the roles of miRNAs as targets in lung cancer therapy.

Testicular Germ Cell Tumors Acquire Cisplatin Resistance by Rebalancing the Usage of DNA Repair Pathways

Simple Summary

Germ cell tumors are a model of curable solid tumors due to their unique sensitivity to cisplatin-based chemotherapy. Patients are typically young adults, and despite high cure rate, about 20% of them do not achieve remission or relapse, and 50% of them succumb to the disease. The mechanisms behind their resistance to therapy are largely unknown. By using Testicular Germ Cell Tumor (TGCT) cell lines as a model, we investigated the mechanism of acquired resistance to cisplatin. We demonstrated that resistance occurred by a fine modulation of the DNA repair pathway choice. Namely, in resistant cells, repair of double-strand breaks by non-homologous end joining was dampened by the reduced expression of TP53-binding protein 1 (53BP1) and DNA-dependent protein kinase (DNA-PKcs). However, cisplatin-induced damage was repaired efficiently by homologous recombination. Additionally, we demonstrate that pharmacological inhibition of poly (ADP-ribose) polymerase (PARP) combined with cisplatin had an additive/synergistic effect on cisplatin-resistant cells, which represents the proof of concept for introducing PARP inhibitors in salvage therapy.

Abstract

Despite germ cell tumors (GCTs) responding to cisplatin-based chemotherapy at a high rate, a subset of patients does not respond to treatment and have significantly worse prognosis. The biological mechanisms underlying the resistance remain unknown. In this study, by using two TGCT cell lines that have acquired cisplatin resistance after chronic exposure to the drug, we identified some key proteins and mechanisms of acquired resistance. We show that cisplatin-resistant cell lines had a non-homologous end-joining (NHEJ)-less phenotype. This correlated with a reduced basal expression of TP53-binding protein 1 (53BP1) and DNA-dependent protein kinase (DNA-PKcs) proteins and reduced formation of 53BP1 foci after cisplatin treatment. Consistent with these observations, modulation of 53BP1 protein expression altered the cell line’s resistance to cisplatin, and inhibition of DNA-PKcs activity antagonized cisplatin cytotoxicity. Dampening of NHEJ was accompanied by a functional increase in the repair of DNA double-strand breaks (DSBs) by the homologous recombination repair pathway. As a result, cisplatin-resistant cells were more resistant to PARP inhibitor (PARPi) monotherapy. Moreover, when PARPi was given in combination with cisplatin, it exerted an additive/synergistic effect, and reduced the cisplatin dose for cytotoxicity. These results suggest that treatment of cisplatin-refractory patients may benefit from low-dose cisplatin therapy combined with PARPi.

The PI3K/AKT Pathway Is Activated by HGF in NT2D1 Non-Seminoma Cells and Has a Role in the Modulation of Their Malignant Behavior

Overactivation of the c-MET/HGF system is a feature of many cancers. We previously reported that type II testicular germ cell tumor (TGCT) cells express the c-MET receptor, forming non-seminomatous lesions that are more positive compared with seminomatous ones. Notably, we also demonstrated that NT2D1 non-seminomatous cells (derived from an embryonal carcinoma lesion) increase their proliferation, migration, and invasion in response to HGF. Herein, we report that HGF immunoreactivity is more evident in the microenvironment of embryonal carcinoma biopsies with respect to seminomatous ones, indicating a tumor-dependent modulation of the testicular niche. PI3K/AKT is one of the signaling pathways triggered by HGF through the c-MET activation cascade. Herein, we demonstrated that phospho-AKT increases in NT2D1 cells after HGF stimulation. Moreover, we found that this pathway is involved in HGF-dependent NT2D1 cell proliferation, migration, and invasion, since the co-administration of the PI3K inhibitor LY294002 together with HGF abrogates these responses. Notably, the inhibition of endogenous PI3K affects collective cell migration but does not influence proliferation or chemotactic activity. Surprisingly, LY294002 administered without the co-administration of HGF increases cell invasion at levels comparable to the HGF-administered samples. This paradoxical result highlights the role of the testicular microenvironment in the modulation of cellular responses and stimulates the study of the testicular secretome in cancer lesions.

Establishment and characterisation of testicular cancer patient-derived xenograft models for preclinical evaluation of novel therapeutic strategies

Testicular cancer (TC) is the most common solid tumour in young men. While cisplatin-based chemotherapy is highly effective in TC patients, chemoresistance still accounts for 10% of disease-related deaths. Pre-clinical models that faithfully reflect patient tumours are needed to assist in target discovery and drug development. Tumour pieces from eight TC patients were subcutaneously implanted in NOD scid gamma (NSG) mice. Three patient-derived xenograft (PDX) models of TC, including one chemoresistant model, were established containing yolk sac tumour and teratoma components. PDX models and corresponding patient tumours were characterised by H&E, Ki-67 and cyclophilin A immunohistochemistry, showing retention of histological subtypes over several passages. Whole-exome sequencing, copy number variation analysis and RNA-sequencing was performed on these TP53 wild type PDX tumours to assess the effects of passaging, showing high concordance of molecular features between passages. Cisplatin sensitivity of PDX models corresponded with patients' response to cisplatin-based chemotherapy. MDM2 and mTORC1/2 targeted drugs showed efficacy in the cisplatin sensitive PDX models. In conclusion, we describe three PDX models faithfully reflecting chemosensitivity of TC patients. These models can be used for mechanistic studies and pre-clinical validation of novel therapeutic strategies in testicular cancer.

Promising novel therapies for relapsed and refractory testicular germ cell tumors

INTRODUCTION

Germ cell tumors (GCTs) are the most common solid malignancies in young men. The overall cure rate of GCT patients in metastatic stage is excellent, however; patients with relapsed or refractory disease have poor prognosis. Attempts to treat refractory disease with novel effective treatment to improve prognosis have been historically dismal and the ability to predict prognosis and treatment response in GCTs did not sufficiently improve in the last three decades.

AREAS COVERED

We performed a comprehensive literature search of PubMed/MEDLINE to identify original and review articles (years 1964-2020) reporting on current improvement salvage treatment in GCTs and novel treatment options including molecularly targeted therapy and epigenetic approach. Review articles were further searched for additional original articles.

EXPERT OPINION

Despite multimodal treatment approaches the treatment of relapsed or platinum-refractory GCTs remains a challenge. High-dose chemotherapy (HDCT) regimens with autologous stem-cell transplant (ASCT) from peripheral blood showed promising results in larger retrospective studies. Promising results from in vitro studies raised high expectations in molecular targets. So far, the lacking efficacy in small and unselected trials do not shed a light on targeted therapy. Currently, wide inclusion of patients into clinical trials is highly advised.

Carcinoma-Associated Mesenchymal Stem Cells Promote Chemoresistance in Ovarian Cancer Stem Cells via PDGF Signaling

Within the ovarian cancer tumor microenvironment, cancer stem-like cells (CSC) interact with carcinoma associated mesenchymal stem/stromal cells (CA-MSC) through multiple secreted cytokines and growth factors. These paracrine interactions have been revealed to cause enrichment of CSC and their chemoprotection; however, it is still not known if platelet-derived growth factor (PDGF) signaling is involved in facilitating these responses. In order to probe this undiscovered bidirectional communication, we created a model of ovarian malignant ascites in the three-dimensional (3D) hanging drop heterospheroid array, with CSC and CA-MSC. We hypothesized that PDGF secretion by CA-MSC increases self-renewal, migration, epithelial to mesenchymal transition (EMT) and chemoresistance in ovarian CSC. Our results indicate that PDGF signaling in the CSC-MSC heterospheroids significantly increased stemness, metastatic potential and chemoresistance of CSC. Knockdown of PDGFB in MSC resulted in abrogation of these phenotypes in the heterospheroids. Our studies also reveal a cross-talk between PDGF and Hedgehog signaling in ovarian cancer. Overall, our data suggest that when the stromal signaling via PDGF to ovarian CSC is blocked in addition to chemotherapy pressure, the tumor cells are significantly more sensitive to chemotherapy. Our results emphasize the importance of disrupting the signals from the microenvironment to the tumor cells, in order to improve response rates. These findings may lead to the development of combination therapies targeting stromal signaling (such as PDGF and Hedgehog) that can abrogate the tumorigenic, metastatic and platinum resistant phenotypes of ovarian CSC through additional investigations.

Investigation of EGFR/pi3k/Akt signaling pathway in seminomas

Activation of the receptor for epidermal growth factor (EGFR) in some testicular tumors activates several signaling pathways. Some components of these pathways are phosphorylated or mutated in testicular germ tumors (TCGT), including EGFR, Kirstein ras oncogen (KRAS) and cell surface protein of the germ cell (KIT). The latter two activate RAF ⁄MEK⁄ERK and PI3 K⁄AKT, and interconnect with the EGFR/pI3 k/Akt pathway. We investigated the expression of EGFR/pI3 k/Akt pathway proteins in seminomas and in their precursor lesion, germinal cell neoplasia in situ (GCNIS) and related genetic mutations. We used immunohistochemistry for pEGFR, pI3 k and pAkt expression with a scoring system for 46 seminoma surgical specimens: 36 classical and 10 GCNIS. In 17 samples, the mutations of EGFR (exons 19 - 21), KIT (exons 11, 17) and KRAS (exons 2, 3) were investigated using qPCR and sequencing. Of the 36 seminomas studied, 22 (61%) expressed pEGFR. Ten samples exhibited high scores for pEGFR, pI3 k and pAkt. In 5 of 17 cases (33%) some mutation was exhibited in the exons studied: 21 of EGFR (2), 17 of EGFR (1), 3 of KRAS (1) and 11 of KIT (1). Six cases exhibited nuclear translocation of EGFR; of these, four exhibited mutations of EGFR, KRAS and KIT. Eight of ten of the GCNIS expressed a high pEGFR score (80%). In 2 of 6 cases (33%), mutation was detected in exon 21 of EGFR and one smear showed EGFR translocation to the nucleus. The translocation represents a subpopulation with worse prognosis for TCGT. The EGFR/pI3 k/Akt signaling pathway is linked to TDRG1, which regulates chemosensitivity to cisplatin; this is a mechanism of resistance to treatment. TDRG1 and the EGFR/pI3 k/pAkt pathway could be therapeutic targets for seminomas resistant to cisplatin.

Cisplatin Resistance in Testicular Germ Cell Tumors: Current Challenges from Various Perspectives

Testicular germ cell tumors share a marked sensitivity to cisplatin, contributing to their overall good prognosis. However, a subset of patients develop resistance to platinum-based treatments, by still-elusive mechanisms, experiencing poor quality of life due to multiple (often ineffective) interventions and, eventually, dying from disease. Currently, there is a lack of defined treatment opportunities for these patients that tackle the mechanism(s) underlying the emergence of resistance. Herein, we aim to provide a multifaceted overview of cisplatin resistance in testicular germ cell tumors, from the clinical perspective, to the pathobiology (including mechanisms contributing to induction of the resistant phenotype), to experimental models available for studying this occurrence. We provide a systematic summary of pre-target, on-target, post-target, and off-target mechanisms putatively involved in cisplatin resistance, providing data from preclinical studies and from those attempting validation in clinical samples, including those exploring specific alterations as therapeutic targets, some of them included in ongoing clinical trials. We briefly discuss the specificities of resistance related to teratoma (differentiated) phenotype, including the phenomena of growing teratoma syndrome and development of somatic-type malignancy. Cisplatin resistance is most likely multifactorial, and a combination of therapeutic strategies will most likely produce the best clinical benefit.

Testicular cancer: Determinants of cisplatin sensitivity and novel therapeutic opportunities

Testicular cancer (TC) is the most common solid tumor among men aged between 15 and 40 years. TCs are highly aneuploid and the 12p isochromosome is the most frequent chromosomal abnormality. The mutation rate is of TC is low, with recurrent mutations in KIT and KRAS observed only at low frequency in seminomas. Overall cure rates are high, even in a metastatic setting, resulting from excellent cisplatin sensitivity of TCs. Factors contributing to the observed cisplatin sensitivity include defective DNA damage repair and a hypersensitive apoptotic response to DNA damage. Nonetheless, around 10-20% of TC patients with metastatic disease cannot be cured by cisplatin-based chemotherapy. Resistance mechanisms include downregulation of OCT4 and failure to induce PUMA and NOXA, elevated levels of MDM2, and hyperactivity of the PI3K/AKT/mTOR pathway. Several pre-clinical approaches have proven successful in overcoming cisplatin resistance, including specific targeting of PARP, MDM2 or AKT/mTOR combined with cisplatin. Finally, patient-derived xenograft models hold potential for mechanistic studies and pre-clinical validation of novel therapeutic strategies in TC. While clinical trials investigating targeted drugs have been disappointing, pre-clinical successes with chemotherapy and targeted drug combinations fuel the need for further investigation in clinical setting.

Dual mTORC1/2 Inhibition Sensitizes Testicular Cancer Models to Cisplatin Treatment

Testicular cancer is the most common cancer type among young men. Despite highly effective cisplatin-based chemotherapy, around 20% of patients with metastatic disease will still die from the disease. The aim of this study was to explore the use of kinase inhibitors to sensitize testicular cancer cells to cisplatin treatment. Activation of kinases, including receptor tyrosine kinases and downstream substrates, was studied in five cisplatin-sensitive or -resistant testicular cancer cell lines using phospho-kinase arrays and Western blotting. The phospho-kinase array showed AKT and S6 to be among the top phosphorylated proteins in testicular cancer cells, which are part of the PI3K/AKT/mTORC pathway. Inhibitors of most active kinases in the PI3K/AKT/mTORC pathway were tested using apoptosis assays and survival assays. Two mTORC1/2 inhibitors, AZD8055 and MLN0128, strongly enhanced cisplatin-induced apoptosis in all tested testicular cancer cell lines. Inhibition of mTORC1/2 blocked phosphorylation of the mTORC downstream proteins S6 and 4E-BP1. Combined treatment with AZD8055 and cisplatin led to reduced clonogenic survival of testicular cancer cells. Two testicular cancer patient-derived xenografts (PDX), either from a chemosensitive or -resistant patient, were treated with cisplatin in the absence or presence of kinase inhibitor. Combined AZD8055 and cisplatin treatment resulted in effective mTORC1/2 inhibition, increased caspase-3 activity, and enhanced tumor growth inhibition. In conclusion, we identified mTORC1/2 inhibition as an effective strategy to sensitize testicular cancer cell lines and PDX models to cisplatin treatment. Our results warrant further investigation of this combination therapy in the treatment of patients with testicular cancer with high-risk relapsed or refractory disease.

Therapeutic Challenges for Cisplatin-Resistant Ovarian Germ Cell Tumors

The majority of patients with advanced ovarian germ cell cancer are treated by cisplatin-based chemotherapy. Despite adequate first-line treatment, nearly one third of patients relapse and almost half develop cisplatin-resistant disease, which is often fatal. The treatment of cisplatin-resistant disease is challenging and prognosis remains poor. There are limited data on the efficacy of specific chemotherapeutic regimens, high-dose chemotherapy with autologous progenitor cell support and targeted therapies. The inclusion of patients in clinical trials is strongly recommended, especially in clinical trials on the most frequent male germ cell tumors, to offer wider therapeutic opportunities. Here, we provide an overview of current and potential new treatment options including combination chemotherapy, high-dose chemotherapy and molecular targeted therapies, for patients with cisplatin-resistant ovarian germ cell tumors.

Mechanisms of cisplatin sensitivity and resistance in testicular germ cell tumors

Testicular germ cell tumors (TGCTs) are a cancer pharmacology success story with a majority of patients cured even in the highly advanced and metastatic setting. Successful treatment of TGCTs is primarily due to the exquisite responsiveness of this solid tumor to cisplatin-based therapy. However, a significant percentage of patients are, or become, refractory to cisplatin and die from progressive disease. Mechanisms for both clinical hypersensitivity and resistance have largely remained a mystery despite the promise of applying lessons to the majority of solid tumors that are not curable in the metastatic setting. Recently, this promise has been heightened by the realization that distinct (and perhaps pharmacologically replicable) epigenetic states, rather than fixed genetic alterations, may play dominant roles in not only TGCT etiology and progression but also their curability with conventional chemotherapies. In this review, it discusses potential mechanisms of TGCT cisplatin sensitivity and resistance to conventional chemotherapeutics.

Testis developmental related gene 1 regulates the chemosensitivity of seminoma TCam-2 cells to cisplatin via autophagy

We previously identified testis developmental related gene 1 (TDRG1), a gene implicated in proliferation of TCam-2 seminoma cells. Recent evidence has revealed that autophagy influences the chemosensitivity of cancer cells to chemotherapy. However, whether TDRG1 protein regulates autophagy in seminoma cells and influences their sensitivity to cis-dichlorodiammine platinum (CDDP) remains unknown. In this study, we used TCam-2 cells and male athymic BALB/c nude mice with xenografts of TCam-2 cells to investigate autophagy, cell viability, apoptosis and the p110β/Rab5/Vps34 (PI3-kinase Class III) pathway under the conditions of TDRG1 overexpression or knockdown and with or without CDDP treatment. We found that TDRG1 upregulation promoted autophagy in both TCam-2 cells and seminoma xenografts via p110β/Rab5/Vps34 activation. Inhibition of autophagy reduced cell viability and promoted apoptosis during CDDP treatment of TCam-2 cells. Similarly, TDRG1 knockdown inhibited autophagy, reduced cell viability and promoted apoptosis during CDDP treatment of TCam-2 cells. TDRG1 knockdown inhibited tumour growth and promoted apoptosis in TCam-2 cell xenografts, whereas TDRG1 overexpression had the opposite effect. According to these results, we propose that high expression of TDRG1 promotes autophagy through the p110β/Rab5/Vps34 pathway in TCam-2 cells. TDRG1 overexpression promotes autophagy and leads to CDDP resistance, whereas TDRG1 knockdown inhibits autophagy and promotes chemosensitivity to CDDP both in vivo and in vitro. This study has uncovered a novel role of TDRG1 in reducing chemoresistance during CDDP treatment and provides potential therapeutic strategies for the treatment of human seminoma.

Targeting platelet-derived growth factor receptor β inhibits the proliferation and motility of human pterygial fibroblasts

Background: Pterygium, a common eye disease with high postoperative recurrence, lacks effective therapeutic strategies. Therefore, it's urgent to identify specific targets to develop rationally targeted molecular drugs for the pterygial therapy. Methods: The cell proliferation and motility were studied in both the primary human pterygial fibroblasts (hPFs) and an ex vivo pterygium model. hPFs transfected with the pCMV3-PDGFRB plasmid, PDGFRB siRNA and CRISPR/Cas9 system were used to determine the role of PDGFR-β in pterygial fibroblasts functions. Western blotting, immunohistochemistry and immunofluorescence were performed to evaluate the expression of the key proteins. Results: PDGFR-β expression in the pterygial stroma and primary hPFs was significantly higher than that in the conjunctiva and human conjunctival fibroblasts. PDGF-BB promoted the proliferation, migration and invasion of hPFs, which can be significantly suppressed by sunitinib via inhibition of the PDGFR-β/extracellular signal-regulated kinase (ERK) pathway. In the ex vivo model, the knockout of PDGFRB and sunitinib treatment blocked the proliferation and motility of fibroblasts in the pterygial stroma via the suppression of PDGFR-β/ERK pathway. Conclusion: This study demonstrates that PDGFR-β may be a potential therapeutic target for pterygium, and inhibition of PDGFR-β by sunitinib is a promising and effective approach for pterygium treatment.

IGF signalling in germ cells and testicular germ cell tumours: roles and therapeutic approaches

The insulin-like growth factor (IGF) axis plays key roles in normal tissue growth and development as well as in the progression of several tumour types and their subsequent growth and progression to a metastatic phenotype. This review explores the role of IGF system in normal germ cell development and function in addition to examining the evidence for deregulation of IGF signalling in cancer, with particular relevance to evidence supporting a role in testicular germ cell tumours (TGCTs). Despite the clear preclinical rationale for targeting the IGF axis in cancer, there has been a lack of progress in identifying which patients may benefit from such therapy. Future employment of agents targeting the IGF pathway is expected to concentrate on their use in combination with other treatments to prevent resistance and exploit their potential as chemo- and radiosensitizers.

Testicular germ cell tumor: a comprehensive review

Testicular tumors are the most common tumors in adolescent and young men and germ cell tumors (TGCTs) account for most of all testicular cancers. Increasing incidence of TGCTs among males provides strong motivation to understand its biological and genetic basis. Gains of chromosome arm 12p and aneuploidy are nearly universal in TGCTs, but TGCTs have low point mutation rate. It is thought that TGCTs develop from premalignant intratubular germ cell neoplasia that is believed to arise from the failure of normal maturation of gonocytes during fetal or postnatal development. Progression toward invasive TGCTs (seminoma and nonseminoma) then occurs after puberty. Both inherited genetic factors and environmental risk factors emerge as important contributors to TGCT susceptibility. Genome-wide association studies have so far identified more than 30 risk loci for TGCTs, suggesting that a polygenic model fits better with the genetic landscape of the disease. Despite high cure rates because of its particular sensitivity to platinum-based chemotherapy, exploration of mechanisms underlying the occurrence, progression, metastasis, recurrence, chemotherapeutic resistance, early diagnosis and optional clinical therapeutics without long-term side effects are urgently needed to reduce the cancer burden in this underserved age group. Herein, we present an up-to-date review on clinical challenges, origin and progression, risk factors, TGCT mouse models, serum diagnostic markers, resistance mechanisms, miRNA regulation, and database resources of TGCTs. We appeal that more attention should be paid to the basic research and clinical diagnosis and treatment of TGCTs.

Synthesis of a novel platinum(II) complex with 6,7-dichloro-5,8-quinolinedione and the study of its antitumor mechanism in testicular seminoma

A new platinum(II) complex, [Pt(ClClQ)(DMSO)Cl] (1), utilizing 6,7-dichloro-5,8-quinolinedione (ClClQ) as a ligand, has been synthesized and fully characterized. Single-crystal X-ray diffraction and other spectroscopic and analytical methods revealed that the coordination geometry of Pt(II) in complex 1 can also be described as a four-coordinated square planar geometry. The aim of the study was to explore the in vitro anticancer properties of complex 1. Our studies showed that complex 1 can regulate the viability of testicular seminoma cells in vitro, including cell proliferation and apoptosis. We further observed negative regulation by complex 1 of the expression levels of the key elements in the phosphoinositide-3 kinase (PI3K)/protein kinase B (Akt)/glycogen synthase kinase-3β (GSK3β) pathway, including phosphorylated phosphoinositide-3 kinase (p-PI3K), phosphorylated protein kinase B(p-Akt) and phosphorylated glycogen synthase kinase-3β (p-GSK3β). Moreover, the negative effect of complex 1 was reversed by LiCl, a GSK3β-specific inhibitor of the PI3K signaling pathway. Meanwhile, the levels of Bcl2 associated death promoter (Bad), cytochrome c, active-caspase-3 and active-caspase-9 increased significantly. In conclusion, we observed that complex 1 can regulate the viability of testicular seminoma cells through the PI3K/Akt/GSK3β signaling pathway and the mitochondria-mediated apoptotic pathway in vitro, and thus, complex 1 may have potential for use as a drug in the treatment of testicular germ cell tumors.

Epigenetic treatment combinations to effectively target cisplatin-resistant germ cell tumors: past, present, and future considerations

BACKGROUND

Type II germ cell tumors represent the most common solid malignancy in men aged 15-45 years. Despite high cure rates of >90% over all stages, 10-15% of advanced patients develop treatment resistance and potentially succumb to their disease. Treatment of refractory germ cell tumors remains unsatisfactory, and new approaches are needed to further improve outcomes.

OBJECTIVES

With this narrative review, we highlight epigenetic mechanisms related to resistance to standard systemic treatment, which may act as promising targets for novel combined epigenetic treatment approaches.

MATERIALS AND METHODS

A comprehensive literature search of PubMed and MEDLINE was conducted to identify original and review articles on resistance mechanisms and/or epigenetic treatment of germ cell tumors in vitro and in vivo. Review articles were hand-searched to identify additional articles.

RESULTS

Distinct epigenetic phenomena have been linked to chemotherapy resistance in germ cell tumors, among which DNA hypermethylation, histone acetylation, and bromodomain proteins appear as promising targets for therapeutic exploitation. Inhibitors of key regulators, for example DNA methyltransferases (e.g. decitabine, guadecitabine), histone deacetylases (e.g. romidepsin), and bromodomain proteins (e.g. JQ1) decreased cell viability, triggered apoptosis, and growth arrest. Additionally, these epigenetic drugs induced differentiation and led to loss of pluripotency and re-sensitization towards cisplatin in cell lines and animal models.

DISCUSSION

Epigenetic treatments hold promise to (i) reduce the treatment burden of and (ii) overcome resistance to standard cisplatin-based chemotherapy. Combined approaches may enhance activity, while the ideal target and treatment combination of epigenetic drugs, either with another epigenetic agent or conventional cytotoxic agents need to be defined.

CONCLUSION

Epigenetic (combination) treatment for germ cell tumors should be further explored in pre-clinical and clinical research for its potential to further improve germ cell tumor treatment.

Current pharmacotherapy for testicular germ cell cancer

INTRODUCTION

With the implementation of platinum-based chemotherapy, germ cell tumors (GCTs) became a model for a curable solid tumor, with survival rates of 95% in all patients with >80% survival in metastatic stages.

AREAS COVERED

Herein, the authors review the current standards of adjuvant chemotherapy for stage I GCTs as well as first-line and salvage treatments for metastatic disease. Novel approaches for refractory disease are also reviewed.

EXPERT OPINION

Active surveillance should be considered for all stage I patients and is the preferred approach for stage I seminoma. In stage I non-seminomas with vascular invasion, one cycle of bleomycin, etoposide, and cisplatin (BEP) substantially reduces the relapse risk. For most advanced GCTs, BEP remains the first-line standard of care. For poor prognosis disease treatment, stratification according to tumor marker decline is recommended. The role of primary high-dose chemotherapy (HDCT) for selected very high-risk patients remains to be prospectively evaluated. Salvage HDCT at relapse seems superior to conventional chemotherapy, retrospectively. The treatment of multiply relapsed disease remains challenging. The gemcitabine/oxaliplatin/paclitaxel (GOP) protocol is considered the standard for refractory disease. However, overall, outcomes are poor and new treatment approaches are urgently needed with targeted therapies so far failing to yield relevant clinical activity.

Molecular Mechanisms of Cisplatin Chemoresistance and Its Circumventing in Testicular Germ Cell Tumors

PURPOSE OF REVIEW

Testicular germ cell tumors (TGCTs) represent the most common solid tumors affecting young men. Majority of TGCTs respond well to cisplatin-based chemotherapy. However, patients with refractory disease have limited treatment modalities associated with poor prognosis. Here, we discuss the main molecular mechanisms associated with acquired cisplatin resistance in TGCTs and how their understanding might help in the development of new approaches to tackle this clinically relevant problem. We also discuss recent data on the strategies of circumventing the cisplatin resistance from different tumor types potentially efficient also in TGCTs.

RECENT FINDINGS

Recent data regarding deregulation of various signaling pathways as well as genetic and epigenetic mechanisms in cisplatin-resistant TGCTs have contributed to understanding of the mechanisms related to the resistance to cisplatin-based chemotherapy in these tumors. Understanding of these mechanisms enabled explaining why majority but not all TGCTs patients are curable with cisplatin-based chemotherapy. Moreover, it could lead to the development of more effective treatment of refractory TGCTs and potentially other solid tumors resistant to platinum-based chemotherapy. This review provides additional insights into mechanisms associated with cisplatin resistance in TGCTs, which is a complex phenomenon, and there is a need for novel modalities to overcome it.

[Identification of diagnostic tumour markers and therapeutic targets in testicular tumours]

Today, tumour classification has been expanded due to immunohistochemical and molecular-pathological analyses due to corresponding patterns/profiles of protein and gene expression. The latter analyses often include growth factors and their ligands, intracellular signalling pathways, DNA-binding proteins, and oncogenes and suppressor genes, thus functionally including primarily the regulation of growth including angiogenesis and apoptosis as well as the induction of metastases to adhesion and migration disorders. Based on observations that testicular tumours often show microcalcifications, possibly due to impaired calcium metabolism, we focused on calcium-dependent transmembrane proteins, particularly cadherins, in the search for new tumour markers and therapeutic targets. N‑cadherin is expressed differently in the various subtypes of germ cell tumours and is useful in N‑cadherin-positive germ cell tumours as a novel therapeutic targeting structure, particularly in cisplatin resistance, due to functional analysis. In the tumours of the sex cord stroma beta-catenin and the transcription factor SOX-9 give a clear classification of these tumours. Thus, morphological investigations prove to be pilot experiments to purposefully narrow the spectrum of functionally important proteins and thus to establish promising new differential diagnostic markers or target structures.

Therapeutic approaches for refractory germ cell cancer

INTRODUCTION

Most germ cell cancer patients with metastatic disease are cured by cisplatin-based combination chemotherapy. 30% of metastatic patients will develop relapse or progress despite adequate first-line treatment and will require salvage therapy, with about 10% of metastasized patients ultimately developing platinum-resistant and fatal disease. Areas covered: Based on a comprehensive literature search of MEDLINE, EMBASE and conference proceedings of ESMO, ASCO and EAU meetings, this review provides an overview on current and potential future treatment options for platinum-refractory germ cell cancer patients including cytostatics and molecularly targeted therapies. Expert commentary: Treatment of platinum-refractory disease remains challenging and long-term survival is rarely achieved despite multimodal treatment approaches. Targeted treatment approaches do not yet play a role in the treatment of platinum-refractory disease due to lacking efficacy in small, unselected clinical trials. Inclusion of patients into clinical trials is strongly recommended.

Key Players of Cisplatin Resistance: Towards a Systems Pharmacology Approach

The major obstacle in the clinical use of the antitumor drug cisplatin is inherent and acquired resistance. Typically, cisplatin resistance is not restricted to a single mechanism demanding for a systems pharmacology approach to understand a whole cell's reaction to the drug. In this study, the cellular transcriptome of untreated and cisplatin-treated A549 non-small cell lung cancer cells and their cisplatin-resistant sub-line A549^rCDDP²⁰⁰⁰ was screened with a whole genome array for relevant gene candidates. By combining statistical methods with available gene annotations and without a previously defined hypothesis HRas, MAPK14 (p38), CCL2, DOK1 and PTK2B were identified as genes possibly relevant for cisplatin resistance. These and related genes were further validated on transcriptome (qRT-PCR) and proteome (Western blot) level to select candidates contributing to resistance. HRas, p38, CCL2, DOK1, PTK2B and JNK3 were integrated into a model of resistance-associated signalling alterations describing differential gene and protein expression between cisplatin-sensitive and -resistant cells in reaction to cisplatin exposure.

EGF Receptor and mTORC1 Are Novel Therapeutic Targets in Nonseminomatous Germ Cell Tumors

Germ cell tumors (GCT) are malignant tumors that arise from pluripotent embryonic germ cells and occur in children and young adults. GCTs are treated with cisplatin-based regimens which, while overall effective, fail to cure all patients and cause significant adverse late effects. The seminoma and nonseminoma forms of GCT exhibit distinct differentiation states, clinical behavior, and response to treatment; however, the molecular mechanisms of GCT differentiation are not fully understood. We tested whether the activity of the mTORC1 and MAPK pathways were differentially active in the two classes of GCT. Here we show that nonseminomatous germ cell tumors (NSGCT, including embryonal carcinoma, yolk sac tumor, and choriocarcinoma) from both children and adults display activation of the mTORC1 pathway, while seminomas do not. In seminomas, high levels of REDD1 may negatively regulate mTORC1 activity. In NSGCTs, on the other hand, EGF and FGF2 ligands can stimulate mTORC1 and MAPK signaling, and members of the EGF and FGF receptor families are more highly expressed. Finally, proliferation of NSGCT cells in vitro and in vivo is significantly inhibited by combined treatment with the clinically available agents erlotinib and rapamycin, which target EGFR and mTORC1 signaling, respectively. These results provide an understanding of the signaling network that drives GCT growth and a rationale for therapeutic targeting of GCTs with agents that antagonize the EGFR and mTORC1 pathways. Mol Cancer Ther; 17(5); 1079-89. ©2018 AACR.

IGF1R signalling in testicular germ cell tumour cells impacts on cell survival and acquired cisplatin resistance

Testicular germ cell tumours (TGCTs) are the most frequent malignancy and cause of death from solid tumours in the 20‐ to 40‐year age group. Although most cases show sensitivity to cis‐platinum‐based chemotherapy, this is associated with long‐term toxicities and chemo‐resistance. Roles for receptor tyrosine kinases other than KIT are largely unknown in TGCT. We therefore conducted a phosphoproteomic screen and identified the insulin growth factor receptor‐1 (IGF1R) as both highly expressed and activated in TGCT cell lines representing the nonseminomatous subtype. IGF1R was also frequently expressed in tumour samples from patients with nonseminomas. Functional analysis of cell line models showed that long‐term shRNA‐mediated IGF1R silencing leads to apoptosis and complete ablation of nonseminoma cells with active IGF1R signalling. Cell lines with high levels of IGF1R activity also showed reduced AKT signalling in response to decreased IGF1R expression as well as sensitivity to the small‐molecule IGF1R inhibitor NVP‐AEW541. These results were in contrast to those in the seminoma cell line TCAM2 that lacked IGF1R signalling via AKT and was one of the two cell lines least sensitive to the IGF1R inhibitor. The dependence on IGF1R activity in the majority of nonseminomas parallels the known role of IGF signalling in the proliferation, migration, and survival of primordial germ cells, the putative cell of origin for TGCT. Upregulation of IGF1R expression and signalling was also found to contribute to acquired cisplatin resistance in an in vitro nonseminoma model, providing a rationale for targeting IGF1R in cisplatin‐resistant disease. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

A Role for CXCR4 in Peritoneal and Hematogenous Ovarian Cancer Dissemination

Epithelial ovarian cancer is characterized by a low recovery rate because the disease is typically diagnosed at an advanced stage, by which time most patients (80%) already exhibit disseminated neoplasia. The cytokine receptor CXCR4 has been implicated in the development of metastasis in various tumor types. Using a patient-derived tissue macroarray and mRNA expression analysis, we observed high CXCR4 levels in high-grade serous epithelial ovarian carcinomas, the most metastatic tumor, compared with those in endometrioid carcinomas. CXCR4 inhibition by treatment with the CXCR4 antagonist AMD3100 or by expression of shRNA anti-CXCR4 similarly inhibited angiogenesis in several models of ovarian carcinomas orthotopically grown in nude mice, but the effect on tumor growth was correlated with the levels of CXCR4 expression. Moreover, CXCR4 inhibition completely blocked dissemination and metastasis. This effect was associated with reduced levels of active Src, active ERKs, the inhibition of EMT transition, and block of hematogenous ovarian cancer dissemination decreasing circulating human tumoral cells (CTC). In tumors, CXCR4-expressing cells also had more mesenchymal characteristics. In conclusion, our results indicate that CXCR4 expression confers a proinvasive phenotype to ovarian carcinoma cells. Thus, anti-CXCR4 therapy is a possible agent for a complementary treatment of advanced disseminated epithelial high-grade serous ovarian cancer patients. Mol Cancer Ther; 17(2); 532-43. ©2017 AACR.

Exploring the molecular aspects associated with testicular germ cell tumors: a review

Testicular germ cell tumors (TGCTs) represent the most common solid tumors affecting young men. They constitute a distinct entity because of their embryonic origin and their unique biological behavior. Recent preclinical data regarding biological signaling machinery as well as genetic and epigenetic mechanisms associated with molecular patterns of tumors have contribute to explain the pathogenesis and the differentiation of TGCTs and to understand the mechanisms responsible for the development of resistance to treatment. In this review, we discuss the main genetic and epigenetic events associated with TGCTs development in order to better define their role in the pathogenesis of these tumors and in cisplatin-acquired resistance.

Interrogating open issues in cancer precision medicine with patient-derived xenografts

Patient-derived xenografts (PDXs) have emerged as an important platform to elucidate new treatments and biomarkers in oncology. PDX models are used to address clinically relevant questions, including the contribution of tumour heterogeneity to therapeutic responsiveness, the patterns of cancer evolutionary dynamics during tumour progression and under drug pressure, and the mechanisms of resistance to treatment. The ability of PDX models to predict clinical outcomes is being improved through mouse humanization strategies and the implementation of co-clinical trials, within which patients and PDXs reciprocally inform therapeutic decisions. This Opinion article discusses aspects of PDX modelling that are relevant to these questions and highlights the merits of shared PDX resources to advance cancer medicine from the perspective of EurOPDX, an international initiative devoted to PDX-based research.

The Role of PDGFR-β Activation in Acquired Resistance to IGF-1R Blockade in Preclinical Models of Rhabdomyosarcoma

To determine what alternative pathways may act as mechanisms of bypass resistance to type 1 insulin-like growth factor receptor (IGF-1R) blockade in rhabdomyosarcoma (RMS), we compared expression of receptor tyrosine kinase activity in a number of IGF-1R antibody-resistant and -sensitive RMS cell lines. We found that platelet-derived growth factor receptor β (PDGFR-β) activity was upregulated in three xenograft-derived IGF-1R antibody-resistant cell lines that arose from a highly sensitive fusion-positive RMS cell line (Rh41). Furthermore, we identified four additional fusion-negative RMS cell lines that similarly upregulated PDGFR-β activity when selected for IGF-1R antibody resistance in vitro. In the seven cell lines described, we observed enhanced growth inhibition when cells were treated with dual IGF-1R and PDGFR-β inhibition in vitro. In vivo studies have confirmed the enhanced effect of targeting IGF-1R and PDGFR-β in several mouse xenograft models of fusion-negative RMS. These findings suggest that PDGFR-β acts as a bypass resistance pathway to IGF-1R inhibition in a subset of RMS. Therapy co-targeting these receptors may be a promising new strategy in RMS care.

Patient-derived xenografts for childhood solid tumors: a valuable tool to test new drugs and personalize treatments

The use of preclinical models is essential in translational cancer research and especially important in pediatric cancer given the low incidence of each particular type of cancer. Cell line cultures have led to significant advances in cancer biology. However, cell lines have adapted to growth in artificial culture conditions, thereby undergoing genetic and phenotypic changes which may hinder the translational application. Tumor grafts developed in mice from patient tumor tissues, generally known as patient-derived xenografts (PDXs), are interesting alternative approaches to reproducing the biology of the original tumor. This review is focused on highlighting the interest of PDX models in pediatric cancer research and supporting strategies of personalized medicine. This review provides: (1) a description of the background of PDX in cancer, (2) the particular case of PDX in pediatric cancer, (3) how PDX can improve personalized medicine strategies, (4) new methods to increase engraftment, and, finally, (5) concluding remarks.

Platinum-refractory germ cell tumors: an update on current treatment options and developments

PURPOSE

In general, 50 % up to 80 % of metastasized germ cell tumor patients can be cured by platinum-based chemotherapy. However, 3-5 % of patients will still die of platinum-refractory disease and new systemic treatment options are needed to improve treatment success in this difficult setting. This review aims to give an overview on treatment options and current developments in the field of platinum-refractory male germ cell tumors.

METHODS

A comprehensive literature search was conducted searching PubMed, Medline, Cochrane and Embase to identify clinical trials regarding the treatment of platinum-refractory disease. ASCO, EAU and ESMO conference proceedings were searched to identify unpublished results of relevant trials. Comprehensive review papers were hand searched for additional references. Clinicaltrials.gov was checked for ongoing clinical trials in the field of platinum-refractory germ cell tumors.

RESULTS

Outcome of platinum-refractory disease remains poor. Single-agents with reasonable activity are gemcitabine, oxaliplatin and paclitaxel, but complete remissions resulting in long-term survival could not be achieved. The triple-combination of gemcitabine, oxaliplatin and paclitaxel followed by resection of residual masses provides the best outcomes with objective responses in 51 % of patients and long-term survival in approximately 10-15 %. To date, no molecularly targeted agent has shown reasonable activity.

CONCLUSIONS

Treatment options for platinum-refractory disease are limited, but a small subset of patients may achieve long-term disease-free survival by multimodal treatment. The potential of novel targeted agents, i.e. by immune-checkpoint-inhibition remains to be defined.

C-Jun N-terminal kinase signalling pathway in response to cisplatin

Cisplatin (cis diamminedichloroplatinum II, cDDP) is one of the most effective cancer chemotherapeutic agents and is used in the treatment of many types of human malignancies. However, inherent tumour resistance is a major barrier to effective cisplatin therapy. So far, the mechanism of cDDP resistance has not been well defined. In general, cisplatin is considered to be a cytotoxic drug, for damaging DNA and inhibiting DNA synthesis, resulting in apoptosis via the mitochondrial death pathway or plasma membrane disruption. cDDP-induced DNA damage triggers signalling pathways that will eventually decide between cell life and death. As a member of the mitogen-activated protein kinases family, c-Jun N-terminal kinase (JNK) is a signalling pathway in response to extracellular stimuli, especially drug treatment, to modify the activity of numerous proteins locating in the mitochondria or the nucleus. Recent studies suggest that JNK signalling pathway plays a major role in deciding the fate of the cell and inducing resistance to cDDP-induced apoptosis in human tumours. c-Jun N-terminal kinase regulates several important cellular functions including cell proliferation, differentiation, survival and apoptosis while activating and inhibiting substrates for phosphorylation transcription factors (c-Jun, ATF2: Activating transcription factor 2, p53 and so on), which subsequently induce pro-apoptosis and pro-survival factors expression. Therefore, it is suggested that JNK signal pathway is a double-edged sword in cDDP treatment, simultaneously being a significant pro-apoptosis factor but also being associated with increased resistance to cisplatin-based chemotherapy. This review focuses on current knowledge concerning the role of JNK in cell response to cDDP, as well as their role in cisplatin resistance.

Investigational targeted therapies for the treatment of testicular germ cell tumors

INTRODUCTION

Germ cell tumors (GCTs) are the most common malignancy among men aged between 15 to 45. Despite high cure rates of >90% over all GCTs, 3 to 5% of patients will still die of platinum-refractory disease. New systemic treatment options are needed to improve treatment success in this challenging setting.

AREAS COVERED

To review targeted treatment options and preclinical developments in platinum-refractory GCTs, a comprehensive literature search of PubMed, Medline and scientific meeting abstracts on published clinical trials and reports on molecularly targeted approaches was conducted. Outcomes of platinum-refractory disease and of patients failing high-dose chemotherapy remain poor. Currently, no molecularly targeted treatment has shown clinically meaningful activity in unselected patient populations in clinical trials, but individual patients may achieve short-lived objective responses by treatment with sunitinib, brentuximab vedotin or imatinib. Targeted trials based on molecular selection of patients have not yet been performed.

EXPERT OPINION

The limited activity of targeted agents in refractory GCT is disappointing. Assessment of druggable biomarkers and marker-stratified treatment may help individual patients, but is largely lacking. The low incidence and high curability of GCTs make the design of larger clinical trials difficult. The potential of novel agents, i.e. immune-checkpoint inhibitors, remains to be elucidated.

Activity of nintedanib in germ cell tumors

Germ cell tumors (GCTs) are the most frequent malignancy in male patients between 15 and 45 years of age. Cisplatin-based chemotherapy shows excellent cure rates, but patients with cisplatin-resistant GCTs have a poor prognosis. Nintedanib (BIBF 1120, Vargatef) inhibits the receptor classes vascular endothelial growth factor receptor, platelet derived growth factor receptor, and fibroblast growth factor receptor, and has shown activity against many tumors, as well as in idiopathic lung fibrosis and bleomycin-induced lung injury. Here, we investigated the antineoplastic and antiangiogenic properties of nintedanib in cisplatin-resistant and cisplatin-sensitive GCT cells, both alone and in combination with classical cytotoxic agents such as cisplatin, etoposide, and bleomycin. The half-maximal inhibitory concentration (IC50) of nintedanib was 4.5 ± 0.43 μmol/l, 3.1 ± 0.45 μmol/l, and 3.6 ± 0.33 μmol/l in cisplatin-sensitive NTERA2, 2102Ep, and NCCIT cells, whereas the IC50 doses of the cisplatin-resistant counterparts were 6.6 ± 0.37 μmol/l (NTERA2-R), 4.5 ± 0.83 μmol/l (2102Ep-R), and 6.1 ± 0.41 μmol/l (NCCIT-R), respectively. Single treatment with nintedanib induced apoptosis and resulted in a sustained reduction in the capacity of colony formation in both cisplatin-sensitive and cisplatin-resistant GCT cells. Cell cycle analysis showed that nintedanib induced a strong G0/G1-phase arrest in all investigated cell lines. Combination treatment with cisplatin did not result in additive, synergistic, or antagonistic effects. The in-vivo activity was studied using the chorioallantoic membrane assay and indicated the antiangiogenic potency of nintedanib with markedly reduced microvessel density. Topical treatment of inoculated tumor plaques resulted in a significant reduction of the tumor size. This indicates that nintedanib might be a promising substance in the treatment of GCT.

TDRG1 regulates chemosensitivity of seminoma TCam-2 cells to cisplatin via PI3K/Akt/mTOR signaling pathway and mitochondria-mediated apoptotic pathway

We previously identified TDRG1 (testis developmental related gene 1), a novel gene with exclusive expression in testis, promoted the proliferation and progression of cultured human seminoma cells through PI3K/Akt/mTOR signaling. As increasing evidence reveal that aberrant activation of this signaling is involved in cisplatin resistance. Then, in this study, we further explored whether TDRG1 regulated the chemosensitivity of seminoma TCam-2 cells to cisplatin. Our researches showed TDRG1 could regulate the viability of TCam-2 cells following cisplatin treatment in vitro through control of both cell apoptosis and cell cycle. Mechanistically, we observed TDRG1 positively regulated the expression levels of the key elements in PI3K/Akt/mTOR pathway including p-PI3K, p-Akt and p-mTOR and also affected the translocation of nuclear p-Akt in TCam-2 cells during cisplatin treatment. Meanwhile, the levels of Bad, cytochrome c, caspase-9 ratio (activated/total), caspase-3 ratio (activated/total) and cleaved-PARP were negatively modulated by TDRG1, which meant the involvement of mitochondria-mediated apoptotic pathway. Furthermore, we found the effect of TDRG1 knockdown or TDRG1 overexpression could be reversed by IGF-1, a PI3K signaling activator, or LY294002, a inhibitor of this pathway, respectively. Similar effects of TDRG1 on cisplatin chemosensitivity and associated molecular mechanism were also confirmed in vivo by employing xenograft assays. In addition, the positive correlation between TDRG1 and p-PI3K, or p-Akt, was found in tumor tissues from seminoma patients. In conclusion, we uncover that TDRG1 regulates chemosensitivity of TCam-2 cells to cisplatin through PI3K/Akt/mTOR signaling and mitochondria-mediated apoptotic pathway both in vitro and in vivo.

Update in germ cell tumours

PURPOSE OF REVIEW

The purpose of this study is to update the reader on advances in postpubertal male germ cell tumours (GCTs) over the last 18 months.

RECENT FINDINGS

Single nucleotide polymorphisms, including in four sex-determination genes, have been identified as additional genetic susceptibility loci to testicular GCT development. New insights into cisplatin resistance implicate the PDGFR-PIK3CA-AKT and RAS pathways. Circulating tumour cells and circulating microRNAs are potential new biomarkers. In clinical stage I (CS-I) GCT, two large studies have confirmed the excellent outcomes achieved with surveillance, which is now the management option of choice for CS I-A nonseminoma and all CS-I seminomas; CS I-B nonseminoma remains controversial. First-line trials of dose-dense multidrug regimens reported promising results but have not yet supplanted BEPx4. Survivorship issues, including secondary malignancies from chemotherapy, remain important in this disease and are a continuing focus of ongoing research.

SUMMARY

Important research questions remain across all aspects of GCT. The next decade is likely to produce many new and exciting discoveries that will benefit GCT patients.

Molecular biology of testicular germ cell tumors

Testicular germ cell tumors (TGCTs) are the most common solid tumors in young adult men. They constitute a unique pathology because of their embryonic and germ origin and their special behavior. Genetic predisposition, environmental factors involved in their development and genetic aberrations have been under study in many works throughout the last years trying to explain the susceptibility and the transformation mechanism of TGCTs. Despite the high rate of cure in this type of tumors because its particular sensitivity to cisplatin, there are tumors resistant to chemotherapy for which it is needed to find new therapies. In the present work, it has been carried out a literature review on the most important molecular aspects involved in the onset and development of such tumors, as well as a review of the major developments regarding prognostic factors, new prognostic biomarkers and the possibility of new targeted therapies.

Platelet-derived growth factor (PDGF) signalling in cancer: rapidly emerging signalling landscape

Platelet-derived growth factor (PDGF)-mediated signalling has emerged as one of the most extensively and deeply studied biological mechanism reported to be involved in regulation of growth and survival of different cell types. However, overwhelmingly increasing scientific evidence is also emphasizing on dysregulation of spatio-temporally controlled PDGF-induced signalling as a basis for cancer development. We partition this multi-component review into recently developing understanding of dysregulation PDGF signalling in different cancers, how PDGF receptors are quantitatively controlled by microRNAs. Moreover, we also summarize most recent advancements in therapeutic targeting of PDGFR as evidenced by preclinical studies. Better understanding of the PDGF-induced intracellular signalling in different cancers will be helpful in catalysing the transition from a segmented view of cancer biology to a conceptual continuum.

Cisplatin resistance in germ cell tumours: models and mechanisms

Recent years have led to a better understanding of the mechanisms underlying cisplatin response and resistance in germ cell tumours (GCT), and several promising targets have been identified. Two main mechanisms of the responsiveness to DNA damaging agents have been postulated. Firstly, GCT readily activate a DNA damage response, but show deficits in several damage repair pathways. In particular, they have been found to have defects in interstrand crosslink repair and in homologous recombination (HR). Secondly, GCT, especially embryonal carcinoma (EC) cells, show a hypersensitive apoptotic response to DNA damage, which activates p53, and leads to up-regulation of the pro-apoptotic factors Noxa, Puma and Fas in non-resistant EC. These cells fail to activate p21 which induces a G1/S arrest, but accumulate in G2/M phase. In the absence of functional p53, family members like p73 and GTAp63 might be important in initiating this response. Mechanisms involved in cisplatin resistance are as follows: down-regulation of Oct4 (e.g. as a result of hypoxia, treatment with retinoic acid or exposure to cisplatin) and failure to induce Puma and Noxa; changes in the expression levels of micro-RNAs such as miR-17/-106b, miR-302a, or miR-371 to -373; elevated levels of MDM2 and cytoplasmic translocation of p21 by phosphorylation; and activation of the PDGFRβ/PI3K/pAKT pathway. Several approaches to overcome resistance have been successfully examined in vitro and in vivo, including PARP inhibitors, especially in cells showing deficient HR-repair; stabilization of p53 using nutlin-3; inhibition of several components of the PI3K/pAKT pathway using small molecules; and DNA demethylation by 5-azacytidine or 5-aza-deoxy-cytidine, among others. Many of these substances deserve further exploration, alone or in combination with DNA damaging agents, and the most promising approaches should be taken forward to clinical testing. Targeted therapy based on mechanistic insights holds the promise to turn cisplatin-resistant GCT into a curable disease.