Dynamics of the Streptomyces chromosome: chance and necessity.

Streptomyces are prolific producers of specialized metabolites with applications in medicine and agriculture. Remarkably, these bacteria possess a large linear chromosome that is genetically compartmentalized: core genes are grouped in the central part, while the ends are populated by poorly conserved genes including antibiotic biosynthetic gene clusters. The genome is highly unstable and exhibits distinct evolutionary rates along the chromosome. Recent chromosome conformation capture (3C) and comparative genomics studies have shed new light on the interplay between genome dynamics in space and time. Here, we review insights that illustrate how the balance between chance (random genome variations) and necessity (structural and functional constraints) may have led to the emergence of spatial structuring of the Streptomyces chromosome.

Correction of non-random mutational biases along a linear bacterial chromosome by the mismatch repair endonuclease NucS.

The linear chromosome of Streptomyces exhibits a highly compartmentalized structure with a conserved central region flanked by variable arms. As double strand break (DSB) repair mechanisms play a crucial role in shaping the genome plasticity of Streptomyces, we investigated the role of EndoMS/NucS, a recently characterized endonuclease involved in a non-canonical mismatch repair (MMR) mechanism in archaea and actinobacteria, that singularly corrects mismatches by creating a DSB. We showed that Streptomyces mutants lacking NucS display a marked colonial phenotype and a drastic increase in spontaneous mutation rate. In vitro biochemical assays revealed that NucS cooperates with the replication clamp to efficiently cleave G/T, G/G and T/T mismatched DNA by producing DSBs. These findings are consistent with the transition-shifted mutational spectrum observed in the mutant strains and reveal that NucS-dependent MMR specific task is to eliminate G/T mismatches generated by the DNA polymerase during replication. Interestingly, our data unveil a crescent-shaped distribution of the transition frequency from the replication origin towards the chromosomal ends, shedding light on a possible link between NucS-mediated DSBs and Streptomyces genome evolution.

Retrospective experience of children with relapsed brain tumors treated with oral combination of axitinib and metronomic etoposide.

Metronomic chemotherapy-based combinations have received interest for relapsed/refractory malignancies. Preclinical and clinical studies showed activity of metronomic etoposide and axitinib. We report our retrospective experience in six children treated with axitinib and metronomic etoposide for refractory/relapsed brain tumors as an "off-label" combination. Three patients with medulloblastoma experienced partial response; one patient with atypical teratoid rhabdoid tumor (ATRT) displays an ongoing stable disease (12 months); two patients with medulloblastoma had progressive disease. Grade 3-4 toxicities were observed in two patients (thrombocytopenia, anemia, diarrhea, fatigue). The axitinib-etoposide combination shows signals of efficacy in heavily pretreated patients with relapsed/refractory brain tumors. These results were based on real-world observation and will need formal evaluation in a phase I/II trial.

Ribosomal RNA operons define a central functional compartment in the Streptomyces chromosome.

Streptomyces are prolific producers of specialized metabolites with applications in medicine and agriculture. These bacteria possess a large linear chromosome genetically compartmentalized: core genes are grouped in the central part, while terminal regions are populated by poorly conserved genes. In exponentially growing cells, chromosome conformation capture unveiled sharp boundaries formed by ribosomal RNA (rrn) operons that segment the chromosome into multiple domains. Here we further explore the link between the genetic distribution of rrn operons and Streptomyces genetic compartmentalization. A large panel of genomes of species representative of the genus diversity revealed that rrn operons and core genes form a central skeleton, the former being identifiable from their core gene environment. We implemented a new nomenclature for Streptomyces genomes and trace their rrn-based evolutionary history. Remarkably, rrn operons are close to pericentric inversions. Moreover, the central compartment delimited by rrn operons has a very dense, nearly invariant core gene content. Finally, this compartment harbors genes with the highest expression levels, regardless of gene persistence and distance to the origin of replication. Our results highlight that rrn operons are structural boundaries of a central functional compartment prone to transcription in Streptomyces.

Bone Morphogenic Proteins in Pediatric Diffuse Midline Gliomas: How to Make New Out of Old?

The BMP pathway is one of the major signaling pathways in embryonic development, ontogeny and homeostasis, identified many years ago by pioneers in developmental biology. Evidence of the deregulation of its activity has also emerged in many cancers, with complex and sometimes opposing effects. Recently, its role has been suspected in Diffuse Midline Gliomas (DMG), among which Diffuse Intrinsic Pontine Gliomas (DIPG) are one of the most complex challenges in pediatric oncology. Genomic sequencing has led to understanding part of their molecular etiology, with the identification of histone H3 mutations in a large proportion of patients. The epigenetic remodeling associated with these genetic alterations has also been precisely described, creating a permissive context for oncogenic transcriptional program activation. This review aims to describe the new findings about the involvement of BMP pathway activation in these tumors, placing their appearance in a developmental context. Targeting the oncogenic synergy resulting from this pathway activation in an H3K27M context could offer new therapeutic perspectives based on targeting treatment-resistant cell states.

A new subtype of diffuse midline glioma, H3 K27 and BRAF/FGFR1 co-altered: a clinico-radiological and histomolecular characterisation.

Diffuse midline gliomas (DMG) H3 K27-altered are incurable grade 4 gliomas and represent a major challenge in neuro-oncology. This tumour type is now classified in four subtypes by the 2021 edition of the WHO Classification of the Central Nervous System (CNS) tumours. However, the H3.3-K27M subgroup still appears clinically and molecularly heterogeneous. Recent publications reported that rare patients presenting a co-occurrence of H3.3K27M with BRAF or FGFR1 alterations tended to have a better prognosis. To better study the role of these co-driver alterations, we assembled a large paediatric and adult cohort of 29 tumours H3K27-altered with co-occurring activating mutation in BRAF or FGFR1 as well as 31 previous cases from the literature. We performed a comprehensive histological, radiological, genomic, transcriptomic and DNA methylation analysis. Interestingly, unsupervised t-distributed Stochastic Neighbour Embedding (tSNE) analysis of DNA methylation profiles regrouped BRAFV600E and all but one FGFR1MUT DMG in a unique methylation cluster, distinct from the other DMG subgroups and also from ganglioglioma (GG) or high-grade astrocytoma with piloid features (HGAP). This new DMG subtype harbours atypical radiological and histopathological profiles with calcification and/or a solid tumour component both for BRAFV600E and FGFR1MUT cases. The analyses of a H3.3-K27M BRAFV600E tumour at diagnosis and corresponding in vitro cellular model showed that mutation in H3-3A was the first event in the oncogenesis. Contrary to other DMG, these tumours occur more frequently in the thalamus (70% for BRAFV600E and 58% for FGFR1MUT) and patients have a longer overall survival with a median above three years. In conclusion, DMG, H3 K27 and BRAF/FGFR1 co-altered represent a new subtype of DMG with distinct genotype/phenotype characteristics, which deserve further attention with respect to trial interpretation and patient management.

Health Workers' Perception and Emotions Surrounding Teleconsultation in Pediatric Cancer Care During the COVID-19 Pandemic.

BACKGROUND AND AIMS: During the first lockdown of the coronavirus disease 2019 (COVID-19) pandemic, we developed a teleconsultation model and conducted a survey-based study with the aim to evaluate satisfaction and emotions of health workers (HWs), to assess the feasibility of teleconsultations, and to evaluate technical issues. MATERIALS AND METHODS: This is a prospective monocentric exploratory study based on synchronous, video consultations between HWs and pediatric patients treated for blood or solid malignancies or blood benign diseases. Every HW completed an online survey which covered technical aspects, data concerning satisfaction, quality of the interaction with the patient, and emotions felt after the teleconsultation. A score was calculated for each aspect. RESULTS: Eleven specialists participated in the study, and we selected 84 questionnaires. With a satisfaction rate of 74%, HWs felt mostly calm (80%), relaxed (70%), stress-free (69%), and relieved (65%). We calculated the following median scores: an overall satisfaction score of 6.67 (0 to 10), a global feeling score of 8.79 (3.33 to 10.00), and a quality score of 7.34 (2.50 to 10.00). A strong correlation between the quality of teleconsultation and the satisfaction of the HWs has been highlighted ( r =0.588). CONCLUSION: Our series is an encouragingly positive experience from the perspective of the HWs, their feelings, and perceptions.

Results of the treatment of pineal tumors in children: the Lyon experience.

INTRODUCTION: Pineal tumors are rare and their incidence is of 1% among all pediatric tumors of the central nervous system. Patient survival depends on the histology, the extension of the surgical removal, and the efficacy of the complementary treatment (chemotherapy and cranio-spinal irradiation), as well as the age of the patient. MATERIALS AND METHODS: In this study, we analyzed 151 pediatric patients treated for pineal tumors from 1997 to 2020 in Lyon, France. All patients were recorded in the French Register of Pineal tumors, which has been centralized and maintained in Lyon since 2010. RESULTS: Our analysis shows that benign tumors have an overall positive prognosis with total surgical removal. Concerning pineal parenchymal tumors, pinealoblastomas have a poor prognosis , especially in children less than three years old. A new pathological classification system allows for a better stratification of patient risk within different groups of patients with pineal tumors. It is also important to note that the identification of DICER 1 syndrome in families with pinealoblastomas warrant further medical investigation. Patients with Germ Cell Tumors have more favorable outcomes, with a global survival rate of 87 % and a pure germinoma survival rate of almost 97%. When analyzing the prognosis of pineal gland gliomas, otherwise known as tectal plate gliomas, pilocytic astrocytomas had a promising prognosis. Otherwise, prognosis of other tectal plate gliomas are related to the grade of malignancy and the efficacy of complementary treatment. Lastly, papillary tumors need a complete removal for the best chance of survival, and Atypical teratoid/ rabdoid tumors (AT/TR) still have a bad prognosis, regardless of surgical resection. CONCLUSIONS: Our results show that, with regards to pediatric pineal region tumors, there are still areas in prognostic indicators that need to be improved. Similarly, these pathologies need to be treated via a multidisciplinary approach to improve a patient's survival rate and their quality of life.

The role of irinotecan-bevacizumab as rescue regimen in children with low-grade gliomas: a retrospective nationwide study in 72 patients.

INTRODUCTION: At least half of children with low-grade glioma (LGG) treated with first line chemotherapy experience a relapse/progression and may therefore need a second-line chemotherapy. Irinotecan-bevacizumab has been recommended in this setting in France after encouraging results of pilot studies. We performed a retrospective analysis to define the efficacy, toxicity and predictors for response to the combination on a larger cohort. METHODS: We reviewed the files from children < 19 years of age with progressive or refractory LGG treated between 2009 and 2016 in 7 French centers with this combination. RESULTS: 72 patients (median age 7.8 years [range 1-19]) received a median of 16 courses (range 3-30). The median duration of treatment was 9 months (range 1.4-16.2). 96% of patients experienced at least disease stabilization. The 6-month and 2-year progression-free survivals (PFS) were 91.7% [IC 95% 85.5-98.3] and 38.2% [IC 95% 28.2-51.8] respectively. No progression occurred after treatment in 18 patients with a median follow-up of 35.6 months (range 7.6-75.9 months). Younger patients had a worse PFS (p = 0.005). Prior chemoresistance, NF1 status, duration of treatment, histopathology or radiologic response did not predict response. The most frequent toxicities related to bevacizumab included grades 1-2 proteinuria in 21, epistaxis in 10, fatigue in 12 and hypertension in 8 while gastro-intestinal toxicity was the most frequent side effect related to irinotecan. CONCLUSIONS: Bevacizumab-irinotecan has the potential of disease control clinically and radiographically in children with recurrent LGG whatever their previous characteristics; in many cases however these responses are not sustained, especially in younger children.

Pharmacokinetics of oral vinorelbine in French children with recurrent or progressive primary low-grade glioma.

AIMS: There is a crucial need for pharmacokinetic (PK) data on oral vinorelbine (VNR) in the paediatric population. The aim of this work was to assess the PK profile of orally administered VNR in children with recurrent/progressive primary low-grade glioma (LGG). METHODS: A multicentre, open-label, single-arm intervention phase II study was conducted. Patients, aged between 6 and 18 years, with histologically confirmed recurrent or progressive primary LGG or non-documented typical optic pathway tumours, were included. PK parameters were estimated by non-compartmental analysis using Phoenix WinNonlin® software (version 8.0, Certara, Inc.). The influence of demographic and biological covariates on VNR PK parameters was investigated using a multivariate linear regression analysis. RESULTS: PK analysis included 36 patients with a median age (range) of 11 (6-17) years. Estimates of apparent oral clearance (CL/F), apparent volume of distribution (V/F), half-life (t1/2 ) and their between-subject variability (CV%) at 60 mg m-2 dose level, were 472 L h-1 (51.8%), 7002 L (57.9%) and 10 h (21.0%), respectively. Negligible accumulation of VNR between C1 and C2 was observed. CL/F and V/F were found to increase with body surface area (BSA) (P = .004). Lower area under the concentration-time curve (AUC) levels were observed among children in comparison to adults. CONCLUSION: Higher doses may be necessary for children with LGG. BSA showed a significant impact on VNR systemic exposure. We believe that our findings will serve as a basis for further studies to better characterize the concentration-response relationships of VNR among paediatric patients.

Human Radiosensitivity and Radiosusceptibility: What Are the Differences?

The individual response to ionizing radiation (IR) raises a number of medical, scientific, and societal issues. While the term "radiosensitivity" was used by the pioneers at the beginning of the 20st century to describe only the radiation-induced adverse tissue reactions related to cell death, a confusion emerged in the literature from the 1930s, as "radiosensitivity" was indifferently used to describe the toxic, cancerous, or aging effect of IR. In parallel, the predisposition to radiation-induced adverse tissue reactions (radiosensitivity), notably observed after radiotherapy appears to be caused by different mechanisms than those linked to predisposition to radiation-induced cancer (radiosusceptibility). This review aims to document these differences in order to better estimate the different radiation-induced risks. It reveals that there are very few syndromes associated with the loss of biological functions involved directly in DNA damage recognition and repair as their role is absolutely necessary for cell viability. By contrast, some cytoplasmic proteins whose functions are independent of genome surveillance may also act as phosphorylation substrates of the ATM protein to regulate the molecular response to IR. The role of the ATM protein may help classify the genetic syndromes associated with radiosensitivity and/or radiosusceptibility.

Bacterial NHEJ: a never ending story.

Double-strand breaks (DSBs) are the most detrimental DNA damage encountered by bacterial cells. DBSs can be repaired by homologous recombination thanks to the availability of an intact DNA template or by Non-Homologous End Joining (NHEJ) when no intact template is available. Bacterial NHEJ is performed by sets of proteins of growing complexity from Bacillus subtilis and Mycobacterium tuberculosis to Streptomyces and Sinorhizobium meliloti. Here, we discuss the contribution of these models to the understanding of the bacterial NHEJ repair mechanism as well as the involvement of NHEJ partners in other DNA repair pathways. The importance of NHEJ and of its complexity is discussed in the perspective of regulation through the biological cycle of the bacteria and in response to environmental stimuli. Finally, we consider the role of NHEJ in genome evolution, notably in horizontal gene transfer.

Phase II study of temozolomide and topotecan (TOTEM) in children with relapsed or refractory extracranial and central nervous system tumors including medulloblastoma with post hoc Bayesian analysis: A European ITCC study.

AIM: To assess objective response after two cycles of temozolomide and topotecan (TOTEM) in children with refractory or relapsed miscellaneous extracranial solid and central nervous system (CNS) tumors, including medulloblastoma and primitive neuroectodermal tumors (PNET). PROCEDURE: Multicenter, nonrandomized, phase 2 basket trial including children with solid tumors, completed by a one-stage design confirmatory cohort for medulloblastoma, and an exploratory cohort for PNET. Main eligibility criteria were refractory/relapsed measurable disease and no more than two prior treatment lines. Temozolomide was administered orally at 150 mg/m2 /day followed by topotecan at 0.75 mg/m2 /day intravenously for five consecutive days every 28 days. Tumor response was assessed every two cycles according to WHO criteria and reviewed independently. RESULTS: Thirty-two patients were enrolled and treated in the miscellaneous solid tumor and 33 in the CNS strata; 20 patients with medulloblastoma and six with PNET were included in the expansion cohorts. The median age at inclusion was 10.0 years (range, 0.9-20.9). In the basket cohorts, confirmed complete and partial responses were observed in one glioma, four medulloblastoma, and one PNET, leading to the extension. The overall objective response rate (ORR) in medulloblastoma was 28% (95% CI, 12.7-47.2) with 1/29 complete and 7/29 partial responses, those for PNET 10% (95% CI, 0.3-44.5). Post hoc Bayesian analysis estimates that the true ORR in medulloblastoma is probably between 20% and 30% and below 20% in PNET. The most common treatment-related toxicities of the combination therapy were hematologic. CONCLUSIONS: Temozolomide-topotecan results in significant ORR in children with recurrent and refractory medulloblastoma with a favorable toxicity profile.

Exploring heterogeneity of adrenal cortical tumors in children: The French pediatric rare tumor group (Fracture) experience.

INTRODUCTION: Pediatric adrenal cortical tumors are characterized by a wide spectrum of behavior. Questions remain regarding intermediate disease stages with isolated tumor rupture or relapse. OBJECTIVES: To describe clinical characteristics, treatment strategy, and outcome of patients depending on disease stage, tumor rupture, or in case of a refractory tumor, to discuss optimal management. MATERIAL AND METHODS: Pediatric patients with histological material reviewed and treated between 2000 and 2018 in 23 French oncology centers were included. RESULTS: Among 95 cases, 59% of patients had stage I tumors (n = 55), 16% had stage II tumors (n = 16), 19% had stage III tumors (n = 17), and 5% had stage IV tumors (n = 5) (missing data: 2). Overall, 27% of patients (n = 25) had an unfavorable histology. Initial tumor resection was performed for 90% of patients (n = 86). Systemic therapies included mitotane in 20 cases and chemotherapy in 13 cases. Among 17 stage III patients, 12 had microscopic residual tumor due to an initial biopsy (n = 5), intraoperative rupture (n = 8), or surgical resection with microscopic residue or tumor spillage surgery (n = 1) (two patients with two modalities). After a median follow-up of 96 months (25-119), four early progressions and two relapses occurred. A total of seven patients died, including five of disease. Stage III diseases due to microscopic residual disease correlated with a worse prognosis: 5-year progression-free survival 44% (95% CI, 22-87%) versus 82% (95% CI, 73-91%) for the whole cohort (P < .0001). Among the 14 patients with refractory disease, only 3 were alive and free of disease after multimodal second-line therapy. CONCLUSIONS: Stage III diseases due to a microscopic residual tumor have a dismal prognosis, arguing for the systematic use of adjuvant therapy. Patients with a relapsed disease should be included in experimental studies.

Revisiting the role of the pathological grading in pediatric adrenal cortical tumors: results from a national cohort study with pathological review.

The prognosis of malignant pediatric adrenocortical tumors is closely related to disease stage, which is used to guide perioperative treatment recommendations. However, current scoring systems are inadequate to distinguish between benign and malignant adrenocortical tumors. Robust microscopic prognostic features that could help determine perioperative therapy are also lacking. The aim of this national study was to review the prognostic value of the Wieneke scoring criteria and Ki67 labeling index in unselected pediatric adrenocortical tumors. Using strict definitions previously defined by expert pathologists, a Wieneke score was re-attributed to each tumor after an independent and centralized review. In addition, Ki67 proliferation index was performed and reviewed for each case. A total of 95 cases were selected; all were treated between 2000 and 2018 and had histopathologic material and sufficient outcome-related information available. Localized disease was found in 88% of patients. Among those with advanced disease, 6% had tumor extension into adjacent organs and 5% had metastases at diagnosis. Median follow-up was 5 years and 3 months. The 5-year PFS was 82%, 95% CI [73%-91%]. Tumor stage significantly correlated with PFS (p < 0.0001). Tumor weight up to 200 g, extra-adrenal extension and initial non-complete surgical resection were statistically associated with worse outcomes. No recurrences nor metastases occurred when the Ki67 index was < 15%. Up to two of the following five factors including tumor necrosis, adrenal capsular invasion, venous invasion, mitotic count > 15/20 high-power fields, and Ki67 index > 15%, significantly correlated with worse outcomes. We propose a pathological scoring system incorporating the Ki67 index as part of a two-step approach after disease staging to guide adjuvant treatment in pediatric adrenocortical tumors, especially after incomplete resection. These results should be validated in an independent cohort.

Family history of cancer and the risk of childhood brain tumors: a pooled analysis of the ESCALE and ESTELLE studies (SFCE).

PURPOSE: Although some specific genetic syndromes such as neurofibromatosis (NF) have been identified as risk factor of childhood brain tumors (CBT), the potential role of inherited susceptibility in CBT has yet to be elucidated. METHODS: To further investigate this, we conducted a pooled analysis of two nationwide case-control studies ESCALE and ESTELLE. The mothers of 509 CBT cases and 3,102 controls aged under 15 years who resided in France at diagnosis/interview, frequency-matched by age and gender, responded to a telephone interview conducted by trained interviewers. Pooled odds ratio (OR) and 95% confidence intervals (95% CI) were estimated using unconditional logistic regression. RESULTS: CBT was significantly associated with the family history of cancer in relatives (OR 1.2, 95% CI 1.0-1.5). The OR was slightly higher for maternal relatives than for paternal relatives, and when at least two relatives had a history of cancer. CBT was significantly associated with a family history of brain tumor (OR 2.1, 95% CI 1.3-3.7). This association seemed stronger for first-degree relatives (mother, father, and siblings), for whom, by contrast, no association was seen for cancers other than CBT. No specificity by CBT subtypes or by age of the children were found for any of these findings. CONCLUSION: Our findings support the hypothesis of a familial susceptibility of CBT, not due to being a known NF carrier.

SFCE METRO-01 four-drug metronomic regimen phase II trial for pediatric extracranial tumor.

OBJECTIVE: To investigate the antitumor activity of a four-drug metronomic chemotherapy (MC) regimen in relapsed/progressing pediatric extracranial solid tumors (EST). The primary objective was clinical benefit (complete response /partial response/stable disease [SD]) after two cycles of therapy (four months). METHODS: Patients aged ≥4 to 25 years with progressing EST and adequate organ function were eligible. Treatment consisted of an eight-week cycle of oral celecoxib b.i.d., weekly vinblastine, and oral cyclophosphamide for three weeks alternating with oral methotrexate for three weeks, with a two-week rest. The Kepner-Chang two-stage model was used with 10 patients in the first stage. If primary objective was reached in two or more patients, eight additional patients were included according to four groups: neuroblastoma (NBL), soft-tissue sarcoma (STS), bone sarcoma (BS), and miscellaneous (Misc.). RESULTS: Forty-four patients were evaluable. The NBL cohort could be expanded to 18 patients: 4 of 18 patients stabilized with MC treatment for 6 (n = 1) and 12 (n = 3) months. In STS, two of seven patients (metastatic hemangioendothelioma and angiosarcoma) had SD for > 2 cycles. One of nine Misc. (metastatic myoepithelial carcinoma) had SD for one year. All patients with BS had progressive disease. One-year progression-free survival of the whole cohort was 6.8% and one-year overall survival was 55.3%. Grade 3 toxicity occurred in 18 patients and grade 4 in 15 patients. The most frequent toxicity was hematologic, predominantly neutropenia. CONCLUSIONS: This MC has no activity in BS and limited though interesting activity in NBL with some patients being stable for > 1 year. It is not possible to conclude activity in STS and Misc.

Maternal residential pesticide use during pregnancy and risk of malignant childhood brain tumors: A pooled analysis of the ESCALE and ESTELLE studies (SFCE).

Some previous epidemiological studies have suggested that pesticide exposure during pregnancy may have a possible role in the development of childhood brain tumors (CBT). We pooled data from two French national population-based, case-control studies to investigate the association between maternal residential use of pesticides during pregnancy and the risk of CBT. The mothers of 437 CBT cases and 3,102 controls aged under 15 years who resided in France at diagnosis/interview, frequency-matched by age and gender, answered a structured telephone interview conducted by trained interviewers. Unconditional logistic regression was used to estimate pooled odds ratio (OR) and 95% confidence intervals (95% CI). CBT was significantly associated with the maternal home use of pesticides during pregnancy (OR 1.4, 95% CI 1.2-1.8) and, more specifically, with insecticide (OR 1.4, 1.2-1.8). We could not draw any conclusions about herbicides and/or fungicides because few women used them during pregnancy and most of these mothers also used insecticides. Although potential recall bias cannot be excluded, our findings of this pooled analysis support the hypothesis that residential maternal use of pesticides during pregnancy and particularly insecticides may increase the risk of CBT. Future investigations to verify these findings and to explore for CBT subtypes and dose-response are necessary to have a better understanding of the possible role of pesticides in etiology of CBT.

Enzymatically Activated Glyco-Prodrugs of Doxorubicin Synthesized by a Catalysis-Free Diels-Alder Reaction.

The severe side effects associated with the use of anthracycline anticancer agents continues to limit their use. Herein we describe the synthesis and preliminary biological evaluation of three enzymatically activatable doxorubicin-oligosaccharide prodrugs. The synthetic protocol allows late stage variation of the carbohydrate and is compatible with the use of disaccharides such as lactose as well as more complex oligosaccharides such as xyloglucan oligomers. The enzymatic release of doxorubicin from the prodrugs by both protease (plasmin) and human carboxylesterases (hCE1 and 2) was demonstrated in vitro and the cytotoxic effect of the prodrugs was assayed on MCF-7 breast cancer cells.