Aminopeptidase N (CD13): Expression, Prognostic Impact, and Use as Therapeutic Target for Tissue Factor Induced Tumor Vascular Infarction in Soft Tissue Sarcoma

Genetic heterogeneity of liver cancer stem cells

Cancer cell heterogeneity is a serious problem in the control of tumor progression because it can cause chemoresistance and metastasis. Heterogeneity can be generated by various mechanisms, including genetic evolution of cancer cells, cancer stem cells (CSCs), and niche heterogeneity. Because the genetic heterogeneity of CSCs has been poorly characterized, the genetic mutation status of CSCs was examined using Exome-Seq and RNA-Seq data of liver cancer. Here we show that different surface markers for liver cancer stem cells (LCSCs) showed a unique propensity for genetic mutations. Cluster of differentiation 133 (CD133)-positive cells showed frequent mutations in the IRF2, BAP1, and ERBB3 genes. However, leucine-rich repeat-containing G protein-coupled receptor 5-positive cells showed frequent mutations in the CTNNB1, RELN, and ROBO1 genes. In addition, some genetic mutations were frequently observed irrespective of the surface markers for LCSCs. BAP1 mutations was frequently observed in CD133-, CD24-, CD13-, CD90-, epithelial cell adhesion molecule-, or keratin 19-positive LCSCs. ASXL2, ERBB3, IRF2, TLX3, CPS1, and NFATC2 mutations were observed in more than three types of LCSCs, suggesting that common mechanisms for the development of these LCSCs. The present study provides genetic heterogeneity depending on the surface markers for LCSCs. The genetic heterogeneity of LCSCs should be considered in the development of LCSC-targeting therapeutics.

Therapeutic Performance Evaluation of 213Bi-Labelled Aminopeptidase N (APN/CD13)-Affine NGR-Motif ([213Bi]Bi-DOTAGA-cKNGRE) in Experimental Tumour Model: A Treasured Tailor for Oncology

Since NGR-tripeptides (asparagine-glycine-arginine) selectively target neoangiogenesis-associated Aminopeptidase N (APN/CD13) on cancer cells, we aimed to evaluate the in vivo tumour targeting capability of radiolabelled, NGR-containing, ANP/CD13-selective [²¹³Bi]Bi-DOTAGA-cKNGRE in CD13pos. HT1080 fibrosarcoma-bearing severe combined immunodeficient CB17 mice. 10 ± 1 days after cancer cell inoculation, positron emission tomography (PET) was performed applying [⁶⁸Ga]Ga-DOTAGA-cKNGRE for tumour verification. On the 7th, 8th, 10th and 12th days the treated group of tumourous mice were intraperitoneally administered with 4.68 ± 0.10 MBq [²¹³Bi]Bi-DOTAGA-cKNGRE, while the untreated tumour-bearing animals received 150 μL saline solution. In addition to body weight (BW) and tumour volume measurements, ex vivo biodistribution studies were conducted 30 and 90 min postinjection (pi.). The following quantitative standardised uptake values (SUV) confirmed the detectability of the HT1080 tumours: SUV_mean and SUV_max: 0.37 ± 0.09 and 0.86 ± 0.14, respectively. Although no significant difference (p ≤ 0.05) was encountered between the BW of the treated and untreated mice, their tumour volumes measured on the 9th, 10th and 12th days differed significantly (p ≤ 0.01). Relatively higher [²¹³Bi]Bi-DOTAGA-cKNGRE accumulation of the HT1080 neoplasms (%ID/g: 0.80 ± 0.16) compared with the other organs at 90 min time point yields better tumour-to-background ratios. Therefore, the therapeutic application of APN/CD13-affine [²¹³Bi]Bi-DOTAGA- cKNGRE seems to be promising in receptor-positive fibrosarcoma treatment.

Current research and management of undifferentiated pleomorphic sarcoma/myofibrosarcoma

Undifferentiated pleomorphic sarcoma (UPS), once termed as malignant fibrous histiocytoma, has always been diagnosed exclusively in clinical practice because it lacks any defined resemblance to normal mesenchymal tissue. Although myxofibrosarcoma (MFS) has been separated from UPS due to its fibroblastic differentiation with myxoid stroma, UPS and MFS are still identified as a sarcoma group in terms of molecular landscapes. In this review article, we will describe the associated genes and signaling pathways involved in the process of sarcoma genesis and make a summary of conventional management, targeted therapy, immunotherapy, and some novel potential treatments of UPS/MFS. With the progressive advancements in medical technology and a better understanding about the pathogenic mechanism of UPS/MFS in the coming decades, new lights will be shed on the successful management of UPS/MFS.

Quantum Dot-Based Screening Identifies F3 Peptide and Reveals Cell Surface Nucleolin as a Therapeutic Target for Rhabdomyosarcoma

Active drug delivery by tumor-targeting peptides is a promising approach to improve existing therapies for rhabdomyosarcoma (RMS), by increasing the therapeutic effect and decreasing the systemic toxicity, e.g., by drug-loaded peptide-targeted nanoparticles. Here, we tested 20 different tumor-targeting peptides for their ability to bind to two RMS cell lines, Rh30 and RD, using quantum dots Streptavidin and biotin-peptides conjugates as a model for nanoparticles. Four peptides revealed a very strong binding to RMS cells: NCAM-1-targeting NTP peptide, nucleolin-targeting F3 peptide, and two Furin-targeting peptides, TmR and shTmR. F3 peptide showed the strongest binding to all RMS cell lines tested, low binding to normal control myoblasts and fibroblasts, and efficient internalization into RMS cells demonstrated by the cytoplasmic delivery of the Saporin toxin. The expression of the nucleophosphoprotein nucleolin, the target of F3, on the surface of RMS cell lines was validated by competition with the natural ligand lactoferrin, by colocalization with the nucleolin-binding aptamer AS1411, and by the marked sensitivity of RMS cell lines to the growth inhibitory nucleolin-binding N6L pseudopeptide. Taken together, our results indicate that nucleolin-targeting by F3 peptide represents a potential therapeutic approach for RMS.

Biomaterials-Mediated Tumor Infarction Therapy

Agents for tumor vascular infarction are recently developed therapeutic agents for the vascular destruction of tumors. They can suppress the progression of the tumor by preventing the flow of nutrition and oxygen to its tissues. Agents of tumor vascular infarction can be divided into three categories according to the differences in their pathways of action: those that use the thrombin-activating pathway, fibrin-activating pathway, and platelet-activating pathway. However, poor targeting ability, low permeation, and potential side-effects restrict the development of the corresponding drugs. Biomaterials can subtly avoid these drawbacks to suppress the tumor. In this article, the authors summarize currently used biomaterials for tumor infarction therapy with the goal of identifying its mechanism, and discuss outstanding deficiencies in methods of this kind.

Peptide-Based Drug Delivery Systems

Peptide-based drug delivery systems have many advantages when compared to synthetic systems in that they have better biocompatibility, biochemical and biophysical properties, lack of toxicity, controlled molecular weight via solid phase synthesis and purification. Lysosomes, solid lipid nanoparticles, dendrimers, polymeric micelles can be applied by intravenous administration, however they are of artificial nature and thus may induce side effects and possess lack of ability to penetrate the blood-brain barrier. An analysis of nontoxic drug delivery systems and an establishment of prospective trends in the development of drug delivery systems was needed. This review paper summarizes data, mainly from the past 5 years, devoted to the use of peptide-based carriers for delivery of various toxic drugs, mostly anticancer or drugs with limiting bioavailability. Peptide-based drug delivery platforms are utilized as peptide–drug conjugates, injectable biodegradable particles and depots for delivering small molecule pharmaceutical substances (500 Da) and therapeutic proteins. Controlled drug delivery systems that can effectively deliver anticancer and peptide-based drugs leading to accelerated recovery without significant side effects are discussed. Moreover, cell penetrating peptides and their molecular mechanisms as targeting peptides, as well as stimuli responsive (enzyme-responsive and pH-responsive) peptides and peptide-based self-assembly scaffolds are also reviewed.

Fluorescent probes for visualizing ROS-associated proteins in disease

Abnormal expression of proteins, including catalytic and expression dysfunction, is directly related to the development of various diseases in living organisms. Reactive oxygen species (ROS) could regulate protein expression by redox modification or cellular signal pathway and thus influence the development of disease. Determining the expression level and activity of these ROS-associated proteins is of considerable importance in early-stage disease diagnosis and the identification of new drug targets. Fluorescence imaging technology has emerged as a powerful tool for specific in situ imaging of target proteins by virtue of its non-invasiveness, high sensitivity and good spatiotemporal resolution. In this review, we summarize advances made in the past decade for the design of fluorescent probes that have contributed to tracking ROS-associated proteins in disease. We envision that this review will attract significant attention from a wide range of researchers in their utilization of fluorescent probes for in situ investigation of pathological processes synergistically regulated by both ROS and proteins.

The Evolution of Safe and Effective Coaguligands for Vascular Targeting and Precision Thrombosis of Solid Tumors and Vascular Malformations

In cardiovascular and cerebrovascular biology, control of thrombosis and the coagulation cascade in ischemic stroke, myocardial infarction, and other coagulopathies is the focus of significant research around the world. Ischemic stroke remains one of the largest causes of death and disability in developed countries. Preventing thrombosis and protecting vessel patency is the primary goal. However, utilization of the body’s natural coagulation cascades as an approach for targeted destruction of abnormal, disease-associated vessels and tissues has been increasing over the last 30 years. This vascular targeting approach, often termed “vascular infarction”, describes the deliberate, targeted delivery of a thrombogenic effector to diseased blood vessels with the aim to induce localized activation of the coagulation cascade and stable thrombus formation, leading to vessel occlusion and ablation. As systemic delivery of pro-thrombotic agents may cause consternation amongst traditional stroke researchers, proponents of the approach must suitably establish both efficacy and safety to take this field forward. In this review, we describe the evolution of this field and, with a focus on thrombogenic effectors, summarize the current literature with respect to emerging trends in “coaguligand” development, in targeted tumor vessel destruction, and in expansion of the approach to the treatment of brain vascular malformations.

Targeting Tissue Factor to Tumor Vasculature to Induce Tumor Infarction

Simple Summary

Among multiple other functional roles of tissue factor (TF) and other coagulation proteins in the development and targeting of malignant disease, some scientific groups are attempting to modify TF and target the molecule or truncated forms of the molecule to tumor vasculature to selectively induce local blood vessel thromboembolic occlusion resulting in tumor infarction. This review briefly describes the characteristics and development of some of these proteins and structures, including tTF-NGR, which as the first drug candidate from this class has entered clinical trials in cancer patients.

Abstract

Besides its central functional role in coagulation, TF has been described as being operational in the development of malignancies and is currently being studied as a possible therapeutic tool against cancer. One of the avenues being explored is retargeting TF or its truncated extracellular part (tTF) to the tumor vasculature to induce tumor vessel occlusion and tumor infarction. To this end, multiple structures on tumor vascular wall cells have been studied at which tTF has been aimed via antibodies, derivatives, or as bifunctional fusion protein through targeting peptides. Among these targets were vascular adhesion molecules, oncofetal variants of fibronectin, prostate-specific membrane antigens, vascular endothelial growth factor receptors and co-receptors, integrins, fibroblast activation proteins, NG2 proteoglycan, microthrombus-associated fibrin-fibronectin, and aminopeptidase N. Targeting was also attempted toward cellular membranes within an acidic milieu or toward necrotic tumor areas. tTF-NGR, targeting tTF primarily at aminopeptidase N on angiogenic endothelial cells, was the first drug candidate from this emerging class of coaguligands translated to clinical studies in cancer patients. Upon completion of a phase I study, tTF-NGR entered randomized studies in oncology to test the therapeutic impact of this novel therapeutic modality.

A single nucleotide mutation drastically increases the expression of tumor-homing NGR-TNFα in the E. coli M15-pQE30 system by improving gene transcription

Due to their potent immune stimulation, tumor necrosis factor alpha (TNFα) variants with tumor-homing activity are attractive as novel antitumor drugs. The promising antitumor effect of NGR-TNFα in clinical trials triggered extensive interest in developing novel tumor-homing TNFα variants in recent years. Owing to its promising antitumor effect, NGR-TNFα is usually used as a control for newly developed tumor-homing TNFα variants. In our previous works, we produced a pericyte-targeting Z-TNFα at high levels using the Escherichia coli (E. coli) M15-pQE30 system. To further compare Z-TNFα and NGR-TNFα, we attempted to express NGR-TNFα using the same system. Surprisingly, native NGR-TNFα was expressed at a low (~ 0.2 mg/L) level in E. coli M15 containing the pQE30 plasmid. However, a single nucleotide mutation of C to G, resulting in a substitution of leucine (L) with valine (V) at the start of TNFα, increased the expression of NGR-TNFα by ~ 100 times through improving transcription. In addition, the amino acid substitution showed a little impact on the receptor binding, in vitro cytotoxicity, and in vivo antitumor effect of NGR-TNFα. As fusing NGR to the N-terminus of TNFα with a valine substitution did not reduce the protein yield, the TNFα gene with a C > G mutation might be used to prepare novel tumor-homing TNFα when the native TNFα-based variant is expressed at an extremely low level in E. coli. Notably, in addition to the mutated valine, the impact of N-terminal additional amino acids provided by pQE30 vector on the function of TNFα variant must be carefully evaluated. KEY POINTS : • A single nucleotide mutation increased the expression of NGR-TNFα by two orders. • Nucleotide mutation-induced amino acid substitution did not reduce NGR-TNFα activity.

CD13 promotes hepatocellular carcinogenesis and sorafenib resistance by activating HDAC5-LSD1-NF-κB oncogenic signaling

RATIONALE

CD13 is a new marker for liver cancer stem cells (CSCs) that contributes to sorafenib resistance in hepatocellular carcinoma (HCC). However, the underlying mechanism of CD13 in HCC sorafenib resistance remains enigmatic.

METHODS

The expression of CD13 in HCC cell lines and tissues was assayed by RT-PCR, western-blot, and immunohistochemistry staining. Athymic BALB/c nu/nu mice model was used to study the in vivo functions of CD13. Clinical significance of CD13 was evaluated by Kaplan-Meier methods. Cellular proliferation rate was evaluated by cell counting kit-8 cell proliferation assay and colony formation assay. Tunel assay was used to detect cell death ratio. Transwell assay was used to evaluate the motility of cells. Immunoprecipitation (IP), liquid chromatography-mass spectrometry (LC-MS)/MS, and co-IP were applied to investigate potential protein interactions of CD13.

RESULTS

In this research, we found that CD13 expression was higher in metastatic HCC samples, and its overexpression was predicted worse prognosis for patients after surgical resection. Functionally, CD13 promoted HCC proliferation, invasion, cell cycle progression as well as sorafenib resistance. Mechanistically, CD13 interacted with histone deacetylase5 (HDAC5) to promote its protein stability, thus resulting in HDAC5-mediated lysine-specific demethylase 1 (LSD1) deacetylation and protein stabilization. Consequently, LSD1 decreased the NF-κB catalytic unit p65 methylation that led to p65 protein stability. A CD13 inhibitor ubenimex in combination with sorafenib, suppressed the tumor growth and attenuated the resistance of HCC cells toward sorafenib in patient-derived xenograft models.

CONCLUSIONS

CD13 promotes HCC progression and induces sorafenib resistance, mainly via interacting with HDAC5 to prevent the degradation of p65 and activate NF-kB signaling pathway. CD13 is a prognostic indicator for HCC patients underwent curative resection as well as a predictor of response to treatment with sorafenib. Our study establishes the new therapeutic potential of targeting CD13-HDAC5-LSD1-NF-κB in HCC.

Animal Safety, Toxicology, and Pharmacokinetic Studies According to the ICH S9 Guideline for a Novel Fusion Protein tTF-NGR Targeting Procoagulatory Activity into Tumor Vasculature: Are Results Predictive for Humans?

Simple Summary

Non-clinical safety, toxicology, and pharmacokinetic studies according to ICH guidelines with a new fusion protein tTF-NGR consisting of human truncated tissue factor (TF) and a small targeting peptide are reported. Results are compared with those of a phase I clinical dose escalation trial with tTF-NGR in cancer patients. Most of the non-clinical results were not predictive for human tolerability. Thus, animal sparing alternative pathways for translation of such a bio-pharmaceutical compound from preclinical studies on efficacy and mode of action into the clinic are discussed.

Abstract

Background: CD-13 targeted tissue factor tTF-NGR is a fusion protein selectively inducing occlusion of tumor vasculature with resulting tumor infarction. Mechanistic and pharmacodynamic studies have shown broad anti-tumor therapeutic effects in xenograft models. Methods: After successful Good Manufacturing Practice (GMP) production and before translation into clinical phase I, ICH S9 (S6) guideline-conforming animal safety, toxicology, and pharmacokinetic (PK) studies were requested by the federal drug authority in accordance with European and US regulations. Results: These studies were performed in mice, rats, guinea pigs, and beagle dogs. Results of the recently completed clinical phase I trial in end-stage cancer patients showed only limited predictive value of these non-clinical studies for patient tolerability and safety in phase I. Conclusions: Although this experience cannot be generalized, alternative pathways with seamless clinical phase 0 microdosing—phase I dose escalation studies are endorsed for anticancer drug development and translation into the clinic.

In vivo assessment of aminopeptidase N (APN/CD13) specificity of different 68Ga-labelled NGR derivatives using PET/MRI imaging

Aminopeptidase N (APN/CD13) plays an important role in neoangiogenic process in malignancies. Our previous studies have already shown that ⁶⁸Ga-labelled NOTA conjugated asparagine-glycine-arginine peptide (c[KNGRE]-NH₂) specifically bind to APN/CD13 expressing tumors. The aim of this study was to evaluate and compare the APN/CD13 specificity of newly synthesized ⁶⁸Ga-labelled NGR derivatives in vivo by PET/MRI imaging using hepatocellular carcinoma (He/De) and mesoblastic nephroma (Ne/De) tumor models. PET/MRI and ex vivo biodistribution studies were performed 11 ± 1 days after subcutaneous injection of tumor cells and 90 min after intravenous injection of ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR) (MG1) or ⁶⁸Ga-NODAGA-c(NGR) (MG2). The APN/CD13 selectivity was confirmed by blocking experiments and the APN/CD13 expression was verified by immunohistochemistry. ⁶⁸Ga-labelled c(NGR) derivatives were produced with high specific activity and radiochemical purity. In control animals, low radiotracer accumulation was found in abdominal and thoracic organs. Using tumor-bearing animals we found that the ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), and ⁶⁸Ga-NODAGA-c(NGR) (MG1) derivatives showed higher uptake in He/De and Ne/De tumors, than that of the accumulation of ⁶⁸Ga-NODAGA-c(NGR) (MG2). APN/CD13 is a very promising target in PET imaging, however, the selection of the appropriate ⁶⁸Ga-labelled NGR-based radiopharmaceutical is critical for the precise detection of tumor neo-angiogenesis and for monitoring the efficacy of anticancer therapy.

First-In-Class CD13-Targeted Tissue Factor tTF-NGR in Patients with Recurrent or Refractory Malignant Tumors: Results of a Phase I Dose-Escalation Study

Background: Aminopeptidase N (CD13) is present on tumor vasculature cells and some tumor cells. Truncated tissue factor (tTF) with a C-terminal NGR-peptide (tTF-NGR) binds to CD13 and causes tumor vascular thrombosis with infarction. Methods: We treated 17 patients with advanced cancer beyond standard therapies in a phase I study with tTF-NGR (1-h infusion, central venous access, 5 consecutive days, and rest periods of 2 weeks). The study allowed intraindividual dose escalations between cycles and established Maximum Tolerated Dose (MTD) and Dose-Limiting Toxicity (DLT) by verification cohorts. Results: MTD was 3 mg/m² tTF-NGR/day × 5, q day 22. DLT was an isolated and reversible elevation of high sensitivity (hs) Troponin T hs without clinical sequelae. Three thromboembolic events (grade 2), tTF-NGR-related besides other relevant risk factors, were reversible upon anticoagulation. Imaging by contrast-enhanced ultrasound (CEUS) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) showed major tumor-specific reduction of blood flow in all measurable lesions as proof of principle for the mode of action of tTF-NGR. There were no responses as defined by Response Evaluation Criteria in Solid Tumors (RECIST), although some lesions showed intratumoral hemorrhage and necrosis after tTF-NGR application. Pharmacokinetic analysis showed a t_{1/2(terminal)} of 8 to 9 h without accumulation in daily administrations. Conclusion: tTF-NGR is safely applicable with this regimen. Imaging showed selective reduction of tumor blood flow and intratumoral hemorrhage and necrosis.

Co-Administration of Vadimezan and Recombinant Coagulase-NGR Inhibits Growth of Melanoma Tumor in Mice

Purpose: Tumor vascular targeting appeared as an appealing approach to fight cancer, though, the results from the clinical trials and drugs in the market were proved otherwise. The promise of anti-angiogenic therapy as the leading tumor vascular targeting strategy was negatively affected with the discovery that tumor vascularization can occur non-angiogenic mechanisms such as co-option. An additional strategy is induction of tumor vascular infarction and ischemia. Methods: Such that we used truncated coagulase (tCoa) coupled to tumor endothelial targeting moieties to produce tCoa-NGR fusion proteins. We showed that tCoa-NGR can bypass coagulation cascade to induce selective vascular thrombosis and infarction of mild and highly proliferative solid tumors in mice. Moreover, combination therapy can be used to improve the potential of cancer vascular targeting modalities. Herein, we report combination of tCoa-NGR with vascular disrupting agent (VDA), vadimezan. Results: Our results show that synergistic work of these two agents can significantly suppress growth of B16-F10 melanoma tumors in C57/BL6 mice. Conclusion: For the first time, we used the simultaneous benefits of two strategies for inducing thrombosis and destruction of tumor vasculature as spatial co-operation. The tCoa-NGR induce thrombosis which reduces blood flow in the peripheral tumor region. And combined with the action of DMXAA, which target inner tumor mass, growth and proliferation of melanoma tumors can be significantly suppressed.

CD13 as a new tumor target for antibody-drug conjugates: validation with the conjugate MI130110

Background

In the search for novel antibody-drug conjugates (ADCs) with therapeutic potential, it is imperative to identify novel targets to direct the antibody moiety. CD13 seems an attractive ADC target as it shows a differential pattern of expression in a variety of tumors and cell lines and it is internalized upon engagement with a suitable monoclonal antibody. PM050489 is a marine cytotoxic compound tightly binding tubulin and impairing microtubule dynamics which is currently undergoing clinical trials for solid tumors.

Methods

Anti-CD13 monoclonal antibody (mAb) TEA1/8 has been used to prepare a novel ADC, MI130110, by conjugation to the marine compound PM050489. In vitro and in vivo experiments have been carried out to demonstrate the activity and specificity of MI130110.

Results

CD13 is readily internalized upon TEA1/8 mAb binding, and the conjugation with PM050489 did not have any effect on the binding or the internalization of the antibody. MI130110 showed remarkable activity and selectivity in vitro on CD13-expressing tumor cells causing the same effects than those described for PM050489, including cell cycle arrest at G2, mitosis with disarrayed and often multipolar spindles consistent with an arrest at metaphase, and induction of cell death. In contrast, none of these toxic effects were observed in CD13-null cell lines incubated with MI130110. Furthermore, in vivo studies showed that MI130110 exhibited excellent antitumor activity in a CD13-positive fibrosarcoma xenograft murine model, with total remissions in a significant number of the treated animals. Mitotic catastrophes, typical of the payload mechanism of action, were also observed in the tumor cells isolated from mice treated with MI130110. In contrast, MI130110 failed to show any activity in a xenograft mouse model of myeloma cells not expressing CD13, thereby corroborating the selectivity of the ADC to its target and its stability in circulation.

Conclusion

Our results show that MI130110 ADC combines the antitumor potential of the PM050489 payload with the selectivity of the TEA1/8 monoclonal anti-CD13 antibody and confirm the correct intracellular processing of the ADC. These results demonstrate the suitability of CD13 as a novel ADC target and the effectiveness of MI130110 as a promising antitumor therapeutic agent.

Future Options of Molecular-Targeted Therapy in Small Cell Lung Cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. With a focus on histology, there are two major subtypes: Non-small cell lung cancer (NSCLC) (the more frequent subtype), and small cell lung cancer (SCLC) (the more aggressive one). Even though SCLC, in general, is a chemosensitive malignancy, relapses following induction therapy are frequent. The standard of care treatment of SCLC consists of platinum-based chemotherapy in combination with etoposide that is subsequently enhanced by PD-L1-inhibiting atezolizumab in the extensive-stage disease, as the addition of immune-checkpoint inhibition yielded improved overall survival. Although there are promising molecular pathways with potential therapeutic impacts, targeted therapies are still not an integral part of routine treatment. Against this background, we evaluated current literature for potential new molecular candidates such as surface markers (e.g., DLL3, TROP-2 or CD56), apoptotic factors (e.g., BCL-2, BET), genetic alterations (e.g., CREBBP, NOTCH or PTEN) or vascular markers (e.g., VEGF, FGFR1 or CD13). Apart from these factors, the application of so-called 'poly-(ADP)-ribose polymerases' (PARP) inhibitors can influence tumor repair mechanisms and thus offer new perspectives for future treatment. Another promising therapeutic concept is the inhibition of 'enhancer of zeste homolog 2' (EZH2) in the loss of function of tumor suppressors or amplification of (proto-) oncogenes. Considering the poor prognosis of SCLC patients, new molecular pathways require further investigation to augment our therapeutic armamentarium in the future.

Chemically synthesized LYRM03 could inhibit the metastasis of human breast cancer MDA-MB-231 cells in vitro and in vivo

Aminopeptidase N (APN) belongs to the aminopeptidase family, which is widely distributed throughout the animal and plant kingdoms. APN is thought to be a very important target for cancer therapy as it is linked to cancer progression and metastasis. However, bestatin (Ubenimex) is the only approved drug that targets various aminopeptidases for the treatment of acute myelocytic leukemia and lymphedema. A compound 3-amino-2-hydroxy-4-phenylbutanoylvalylisoleucine (also known as LYRM03), isolated from a Streptomyces strain HCCB10043, exhibited more potent inhibitory activity than bestatin. In this work, we applied a chemical synthesis strategy to generate LYRM03 to overcome the low yields typically achieved from fermentation. Finally, we explored a suite of experiments to determine the bioactivity of LYRM03 and revealed that the metastasis of MDA-MB-231 cells was significantly restrained with LYRM03 treatment or injection both in vitro and in vivo. Because of its anti-metastasis capacity, further structure modifications of LYRM03 will be of interest for its use alone or in combination as a therapy in cancer.