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ADCs have emerged as a promising class of therapeutics, combining the targeting specificity of monoclonal antibodies with the cytotoxic potency of small-molecule drugs. Although the majority of approved ADCs are still based on microtubule binder payloads, the recent success of topoisomerase I inhibitors has revitalized interest in the identification of novel agents overcoming present limitations in the field including narrow therapeutic window and chemoresistance. The success of DNA binders as payload for ADCs has been very limited, up to now, due, among other factors, to high hydrophobicity and planar chemical structures resulting in most cases in ADCs with a strong tendency to aggregate, poor plasma stability, and limited therapeutic index. Some of these molecules, however, continue to be of interest due to their favorable properties in terms of cytotoxic potency even in chemoresistant settings, bystander and immunogenic cell death effects, and known combinability with approved drugs. We critically evaluated several clinically tested ADCs containing DNA binders, focusing on payload physicochemical properties, cytotoxic potency, and obtained clinical results. Our analysis suggests that further exploration of certain chemical classes, specifically anthracyclines and duocarmycins, based on the optimization of physicochemical parameters, reduction of cytotoxic potency, and careful design of targeting molecules is warranted. This approach will possibly result in a novel generation of payloads overcoming the limitations of clinically validated ADCs. [ABSTRACT FROM AUTHOR]

Although survival in pediatric acute myeloid leukemia (AML) has increased considerably over the past decades, refractory disease and relapse rates remain high. Refractory and relapsed disease are difficult to treat, with overall survival rates less than 40– 50%. Preventing relapse should, therefore, be one of the highest priorities. Current conventional chemotherapy regimens are hard to intensify due to associated toxic complications, hence more effective therapies that do not increase toxicity are needed. A promising targeted agent is the CD33-directed antibody–drug conjugate gemtuzumab ozogamicin (GO). Because CD33 is highly expressed on leukemic cells in the majority of AML patients, GO can be useful for a broad range of patients. Better relapse-free survival (RFS) after therapy including GO has been reported in several pediatric clinical trials; however, ambiguity about the clinical value of GO in newly diagnosed children remains. Treatment with GO in de novo AML patients aged ≥ 1 month, in combination with standard chemotherapy is approved in the United States, whereas in Europe, GO is only approved for newly diagnosed patients aged ≥ 15 years. In this review, we aimed to clarify the clinical value of GO for treatment of newly diagnosed pediatric AML patients. Based on current literature, GO seems to have additional value, in terms of RFS, and acceptable toxicity when used in addition to chemotherapy during initial treatment. Moreover, in KMT2A-rearranged patients, the clinical value of GO was even more evident. Also, we addressed predictors of response, being CD33 expression and SNPs, PgP-1 and Annexin A5. The near finalized intent-to-file clinical trial in the MyeChild consortium investigates whether fractionated dosing has additional value for pediatric AML, which may pave the way for a broader application of GO in pediatric AML. [ABSTRACT FROM AUTHOR]

Calicheamicin (CLM) is a prominent antitumor agent isolated from Micromonospora echinospora. The large scale production of this antibiotic is limited due to its low yield in fermentation broth. A mutant strain, M. echinospora HF 4-19 was screened by atmospheric pressure plasma jet and its production of CLM was 3.3-fold higher than that of the original strain. Different macroporous adsorption resins were tested to optimize the conditions of mycelia growth and CLM biosynthesis. The weak-polar adsorption resin, H-60, was selected due to better adsorption and desorption capacities. In a 50-L bioreactor containing 3.0% (wt/vol) H-60 resin in fermentation medium, the yield of CLM was 5.6-fold higher than that without the resin. With the improved methods of plasma jet and in situ resin adsorption in fermentation process, the CLM production was significantly increased from 3.1 ± 0.3 to 84.0 ± 2.4 μg/mL. This study established an improved method to produce the CLM, which has the potential to be used for an industrial scale production of CLM. [ABSTRACT FROM AUTHOR]

Abstract Introduction Inotuzumab ozogamicin (InO) is an antibody-drug conjugate composed of a recombinant, humanized immunoglobulin type G, subtype 4 (IgG4) antibody covalently bound to a semisynthetic derivative of calicheamicin via an acid-labile linker. It was developed for the treatment of relapsed or refractory non-Hodgkin lymphoma (NHL) and acute lymphoblastic leukemia (ALL). Based on the perceived relatively low immunogenicity risk for this product, a standard approach to immunogenicity testing was utilized during the clinical studies. This manuscript describes the analytical aspects of antibody measurement and highlights the immunogenicity data from clinical studies in patients with hematologic malignancies. Methods Anti-drug antibodies (ADAs) were determined using an enzyme-linked immunosorbent assay for patients with NHL and a bridging electrochemiluminescence assay for patients with ALL. ALL patients who tested positive for ADA were also tested for neutralizing antibodies (pivotal studies only) using a cell-based assay. Results Immunogenicity assays were validated per current industry practice and regulatory guidelines. Positive ADAs were observed in 7 of 164 (4%) patients with ALL during the pivotal trial. Neutralizing antibodies were not detected in any patients with positive ADAs. No ADAs were detected during the phase I/II ALL study. In NHL studies, antibodies to InO were observed in 27 of 630 (4%) patients. InO clearance was similar between ADA-positive and ADA-negative ALL patients. Conclusion Standard immunogenicity strategy provided data to evaluate impact on InO efficacy, pharmacokinetics, or other clinical parameters in patients. The incidence of ADA to InO is low and is not clinically meaningful.

Cytotoxic small‐molecule drugs have a major influence on the fate of antibody–drug conjugates (ADCs). An ideal cytotoxic agent should be highly potent, remain stable while linked to ADCs, kill the targeted tumor cell upon internalization and release from the ADCs, and maintain its activity in multidrug‐resistant tumor cells. Lessons learned from successful and failed experiences in ADC development resulted in remarkable progress in the discovery and development of novel highly potent small molecules. A better understanding of such small‐molecule drugs is important for development of effective ADCs. The present review discusses requirements making a payload appropriate for antitumor ADCs and focuses on the main characteristics of commonly‐used cytotoxic payloads that showed acceptable results in clinical trials. In addition, the present study represents emerging trends and recent advances of payloads used in ADCs currently under clinical trials. [ABSTRACT FROM AUTHOR]

PF‐06647263, a novel antibody–drug conjugate consisting of an anti‐EFNA4 antibody linked to a calicheamicin payload, has shown potent antitumor activity in human xenograft tumor models, including triple‐negative breast cancer (TNBC). In the dose‐escalation part 1 of this multicenter, open‐label, phase I study (NCT02078752), successive cohorts of patients (n, 48) with advanced solid tumors and no available standard therapy received PF‐06647263 every 3 weeks (Q3W) or every week (QW), following a modified toxicity probability interval (mTPI) method (initial dosing: 0.015 mg/kg Q3W). Primary objective in part 1 was to estimate the maximum tolerated dose (MTD) and select the recommended phase 2 dose (RP2D). In part 2 (dose‐expansion cohort), 12 patients with pretreated, metastatic TNBC received PF‐06647263 at the RP2D to further evaluate tumor response and overall safety. PF‐06647263 QW administration (n, 23) was better tolerated than the Q3W regimen (n, 25) with only 1 DLT reported (thrombocytopenia). The most common AEs with the QW regimen (fatigue, nausea, vomiting, mucosal inflammation, thrombocytopenia, and diarrhea) were mostly mild to moderate in severity. The MTD was not estimated. PF‐06647263 exposures increased in a dose‐related manner across the doses evaluated. The RP2D was determined to be 0.015 mg/kg QW. Six (10%) patients achieved a confirmed partial response and 22 (36.7%) patients had stable disease. No correlations were observed between tumor responses and EFNA4 expression levels. Study findings showed manageable safety and favorable PK for PF‐06647263 administered QW at the RP2D, with preliminary evidence of limited antitumor activity in patients with TNBC and ovarian cancer. What's new? The ephrin‐A4 (EFNA4) ligand is aberrantly expressed in solid tumors and aggressive tumor‐initiating cells, making it a promising target for novel anticancer therapies. Of particular interest is the anti‐EFNA4 antibody‐drug conjugate, PF‐06647263, which previously was shown to induce DNA damage and cell death in EFNA4‐expressing xenograft models of breast and ovarian cancer. Here, PF‐06647263 was evaluated for the first time in human patients with advanced malignancies. PF‐06647263 was relatively safe for patients and had a favorable pharmacokinetic profile. While partial responses and stable disease were observed, patients with advanced triple‐negative breast cancer and ovarian cancer showed limited benefit. [ABSTRACT FROM AUTHOR]

Background and Objective: Gemtuzumab ozogamicin is an antibody-drug conjugate composed of the anti-CD33 monoclonal antibody hP67.6 covalently linked to N-acetyl-gamma-calicheamicin dimethylhydrazide, a potent cytotoxic antibiotic. The aim of this study was to characterize the population pharmacokinetics of gemtuzumab ozogamicin, represented by total hP67.6 antibody and unconjugated calicheamicin, in adult patients with acute myeloid leukemia to support drug dosing strategies and explore intrinsic and extrinsic factors that may influence exposure. Pharmacokinetic data from seven previous phase I and II studies in adult patients with relapsed, refractory, or de novo acute myeloid leukemia were integrated and analyzed using nonlinear mixed-effects modeling.Methods: The pharmacokinetics of total hP67.6 antibody was described in 407 patients (5643 concentrations) who received gemtuzumab ozogamicin doses ranging from 0.25 to 9 mg/m2 using a two-compartment model with linear and time-dependent clearance components. The pharmacokinetics of unconjugated calicheamicin was characterized in 338 patients (4281 concentrations) using a two-compartment model with an input rate of formation dependent on the amount of hP67.6 eliminated. No statistically significant baseline covariates (sex, albumin, bone marrow, and peripheral blast percentage) demonstrated a clinically meaningful impact.Results and Conclusion: Total hP67.6 antibody disposition did not appear altered in patients with mild or moderate renal disease or hepatic impairment. Gemtuzumab ozogamicin was approved for the treatment of acute myeloid leukemia by the US Food and Drug Administration in September 2017. The model-based simulations described here provided a pharmacokinetic rationale for the approved dosing regimen of 3 mg/m2 on days 1, 4, and 7, and served as the basis for all exposure-response modeling included in the recent Biologics License Application submission. Clinical trials identifiers: 0903A1-101-US; 0903A1-103-JA; 0903B1-201-US/CA (NCT00003131); 0903B1-202-EU; 0903B1-203-US/EU (NCT00003673); 0903B1-205-US/EU/AU (NCT00037596); and 0903B1-206-US/EU/AU (NCT00037583). [ABSTRACT FROM AUTHOR]

Inotuzumab ozogamicin (IO) is an anti-CD22 calicheamicin immunoconjugate that has been recently approved for the treatment of relapsed or refractory B-Acute Lymphoblastic Leukemia (r/r B-ALL). We employed both immortalized and primary cells derived from CD22-positive lymphoproliferative disorders to investigate the signaling pathways contributing to IO sensitivity or resistance. We found that the drug reduced the proliferation rate of CD22-positive cell lines expressing wild-type p53, but was remarkably less effective on cells exhibiting mutant p53. In addition, CD22-positive cells surviving IO were mostly blocked in the G2/M phase of the cell cycle because of Chk1 activation that, in the presence of a wild-type p53 background, led to p21 induction. When we combined IO with the Chk1 inhibitor UCN-01, we successfully abrogated IO-induced G2/M arrest regardless of the underlying p53 status, indicating that the DNA damage response triggered by IO is also modulated by p53-independent mechanisms. To establish a predictive value for p53 in determining IO responsiveness, we expressed mutant p53 in cell lines displaying the wild-type gene and observed an increase in IO IC50 values. Likewise, overexpression of an inducible wild-type p53 in cells natively presenting a mutant protein decreased their IC50 for IO. These results were also confirmed in primary CD22-positive cells derived from B-ALL patients at diagnosis and from patients with r/r B-ALL. Furthermore, co-treatment with IO and UCN-01 significantly increased cell death in primary cells expressing mutant p53. In summary, our findings suggest that p53 status may represent a biomarker predictive of IO efficacy in patients diagnosed with CD22-positive malignancies. [ABSTRACT FROM AUTHOR]

Background and Objective: To date, the population pharmacokinetics (popPK) of gemtuzumab ozogamicin (GO), a CD33-directed antibody-drug conjugate consisting of hP67.6 antibody linked to N-acetyl gamma calicheamicin used in the treatment of acute myeloid leukemia (AML), has not been characterized in pediatric patients. This report describes the popPK of GO following intravenous administration in 29 pediatric patients aged ≤ 17 years with relapsed or refractory AML who were enrolled in the 0903A1-102-US phase I/II study.Methods: The pharmacokinetics (PK) of GO, as represented by total hP67.6 antibody, were described by a two-compartment model with two clearance components: a linear clearance (CL1) and time-dependent clearance that includes a decay coefficient. The PK of unconjugated calicheamicin (UC; payload) were described by a two-compartment model with CL1 and an input rate of formation based on antibody rate of elimination. Allometric scaling was included in both models, with baseline body weight as a fixed effect on CL1 and central volume.Results and Conclusions: PK parameters for hP67.6 and UC were not significantly affected by any of the available demographic factors and safety laboratory values tested as covariates (except baseline body weight). Simulations to compare GO dosing regimens (6, 7.5, and 9 mg/m2 on days 1 and 15 versus, 3 mg/m2 fractionated dosing on days 1, 4, and 7) were performed, showing that total antibody and UC trough concentrations were maintained at higher concentrations during treatment following the more frequent dosing than following the original regimen.Study Identifier: 0903A1-102-US. [ABSTRACT FROM AUTHOR]

In September 2017, the US FDA announced re-approval of gemtuzumab ozogamicin (GO), a CD33-targeting immunoconjugate, for treatment of newly diagnosed and relapsed/refractory acute myeloid leukemia (AML). This is a very significant step toward defining new treatment regimens in AML, as the treatment has essentially stayed unchanged with the '7 + 3 induction regimen' (7 days cytarabine and 3 days of anthracycline) since 1973. GO is the first antibody-drug conjugate to receive FDA approval for treating cancer. This review article discusses the challenges faced and lessons learned during the journey of GO for AML treatment. Selected trials that have made significant contribution in our understanding of the most efficacious and safe use of GO for treating AML patients as well as factors influencing GO response are highlighted in this article. [ABSTRACT FROM AUTHOR]

Antibody–drug conjugates (ADCs) are an emerging class of anticancer therapeutics, delivering highly cytotoxic molecules directly to cancer cells. ADCs are composed of an antibody, a small molecule drug, and a linker attaching one to another. Antibodies are directed to a large variety of antigens overexpressed on tumor cells, tumor vasculature, or tumor-supporting stroma. After internalization, the ADC is transferred to lysosomes where the cytotoxic component is released, finally killing the target cell. All ADCs are administered via intravenous injection. Once in the circulation, linker stability in plasma is of high importance. In vivo studies in animals address the release of payload over time and typically measure total antibody, conjugated ADC, and free drug. ADC development is driven by ICH (International Council for Harmonisation) guidelines S6(R1) and S9. Dose-limiting toxicities of current ADCs are mainly associated with the payload and correlate well between clinical trials and nonclinical studies in rodents and nonrodents. This mini review is intended to provide general information about ADCs in oncology and shall assist the toxicologic pathologist in correctly interpreting morphological findings acquired in toxicity studies with this entity. [ABSTRACT FROM AUTHOR]

Introduction: Gemtuzumab ozogamicin (GO) is an antibody-drug conjugate consisting of a monoclonal antibody targeting CD33 linked to a cytotoxic derivative of calicheamicin. Despite the known clinical efficacy in relapsed/refractory acute myeloid leukemia (AML), GO was withdrawn from the market in 2010 due to increased early deaths witnessed in newly diagnosed AML patients receiving GO + intensive chemotherapy. In 2017, new data on the clinical efficacy and safety of GO administered on a fractionated-dosing schedule led to re-approval for newly diagnosed and relapsed/refractory AML. Areas covered: Addition of fractionated GO to chemotherapy significantly improved event-free survival of newly diagnosed AML patients with favorable and intermediate cytogenetic-risk disease. GO monotherapy also prolonged survival in newly diagnosed unfit patients and relapse-free survival in relapsed/refractory AML. This new dosing schedule was associated with decreased incidence of hepatotoxicity, veno-occlusive disease, and early mortality. Expert commentary: GO represents the first drug-antibody conjugate approved (twice) in the United States for AML. Its re-emergence adds a valuable agent back into the armamentarium for AML. The approval of GO as well as three other agents for AML in 2017 highlights the need for rapid cytogenetic and molecular characterization of AML and incorporation into new treatment algorithms. [ABSTRACT FROM AUTHOR]

Background: Inotuzumab ozogamicin (InO), an anti-CD22 antibody-calicheamicin conjugate, demonstrated superior clinical activity versus standard-of-care (SOC) chemotherapies for relapsed/refractory B-cell acute lymphoblastic leukemia in the phase 3 randomized controlled INO-VATE trial. The authors assessed patient-reported outcomes (PROs) from that study.Methods: Patients were randomized to receive either InO (1.8 mg/m2 per cycle for ≤6 cycles) or SOC (fludarabine/cytarabine [ara-C]/granulocyte colony-stimulating factor, or ara-C plus mitoxantrone, or high-dose ara-C for ≤4 cycles) and completed the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire and the EuroQoL 5 Dimensions Questionnaires at baseline, on day 1 of each cycle, and at the end of treatment. Treatment differences in PROs were assessed using longitudinal mixed-effects models with random intercepts and slopes.Results: Questionnaire completion rates in the InO (n = 164) and SOC (n = 162) arms were 85% and 65%, respectively. Baseline scores were similar between arms. Patients who received InO reported better quality of life (QoL), functioning, and symptom scores (except for constipation and emotional functioning). Least-squares mean (95% confidence interval [CI]) differences in physical, role, and social functioning and in appetite loss were significant (6.9 [95% CI, 1.4-12.3], 11.4 [95% CI, 3.2-19.5], 8.4 [95% CI, 0.7-16.1], and -8.7 [95% CI, -16.0 to -1.4], respectively; all P < .05) and had exceeded the minimally important difference of 5. Mean treatment differences in favor of InO on the EuroQoL visual analog scale and the global health status/QoL, dyspnea, and fatigue scales reached or approached the minimally important difference of 5, although without statistical significance. No dimensions were significantly worse with InO versus SOC.Conclusions: The current PRO data support the favorable benefit/risk ratio of InO for the treatment of relapsed/refractory acute lymphoblastic leukemia, with superior clinical efficacy and better QoL. Cancer 2018;124:2151-60. © 2018 American Cancer Society. [ABSTRACT FROM AUTHOR]

Calicheamicin, γ 1 I , is a remarkable DNA binding-cleaving, enediyne-containing, natural product that exhibits potent antitumor activity. In this study, we used electronic circular dichroism spectroscopy to monitor potential drug-induced DNA conformational changes and DNA induced conformational changes in the calicheamicin aglycone. Three DNA dodecamer sequences were examined: one containing a primary TCCT binding/cleavage site and two dodecamers containing less prominent CTCT and TCTC sites. The binding was monitored by taking advantage of the drug’s unique negative exciton couplet (−313 nm/+275 nm) in phosphate buffer/ethanol 10%. Specifically the CD analysis focused at the longest wavelength region around 313 nm where there is no interference by the positive CD contributions of the DNA. Upon binding at a DNA/drug ratio of 1/1.2 and 1/2.7 a slight red shift from 313 nm to 319 nm was observed. At a ratio of 1/1.2, the CE intensity remained practically unchanged from that of free drug, which indicates no conformational changes in the bound aglycone itself. A larger amount of drug, at a molar ratio of DNA/drug of 1/2.7 but especially at 1/6 and up to 1/10, however, caused a surprisingly distinct decrease in the intensity at this negative CD band and a further small red-shift to 322 nm, evidence for non-specific binding. [ABSTRACT FROM AUTHOR]

Attaching a cytotoxic "payload" to an antibody to form an antibody-drug conjugate (ADC) provides a mechanism for selective delivery of the cytotoxic agent to cancer cells via the specific binding of the antibody to cancer-selective cell surface molecules. The first ADC to receive marketing authorization was gemtuzumab ozogamicin, which comprises an anti-CD33 antibody conjugated to a highly potent DNA-targeting antibiotic, calicheamicin, approved in 2000 for treating acute myeloid leukemia. It was withdrawn from the US market in 2010 following an unsuccessful confirmatory trial. The development of two classes of highly potent microtubule-disrupting agents, maytansinoids and auristatins, as payloads for ADCs resulted in approval of brentuximab vedotin in 2011 for treating Hodgkin lymphoma and anaplastic large cell lymphoma, and approval of ado-trastuzumab emtansine in 2013 for treating HER2-positive breast cancer. Their success stimulated much research into the ADC approach, with >60 ADCs currently in clinical evaluation, mostly targeting solid tumors. Five ADCs have advanced into pivotal clinical trials for treating various solid tumors-platinum-resistant ovarian cancer, mesothelioma, triple-negative breast cancer, glioblastoma, and small cell lung cancer. The level of target expression is a key parameter in predicting the likelihood of patient benefit for all these ADCs, as well as for the approved compound, ado-trastuzumab emtansine. The development of a patient selection strategy linked to target expression on the tumor is thus critically important for identifying the population appropriate for receiving treatment. [ABSTRACT FROM AUTHOR]

Radiotherapy of thyroid cancer with I-131 is abrogated by inherent loss of radioiodine uptake due to loss of sodium iodide symporter (NIS) expression in poorly differentiated tumor cells. It is also known that ionizing radiation per se down-regulates NIS (the stunning effect), but the mechanism is unknown. Here we investigated whether loss of NIS-mediated iodide transport may be elicited by DNA damage. Calicheamicin, a fungal toxin that specifically cleaves double-stranded DNA, induced a full scale DNA damage response mediated by the ataxia-telangiectasia mutated (ATM) kinase in quiescent normal thyrocytes. At sublethal concentrations (<1 nM) calicheamicin blocked NIS mRNA expression and transepithelial iodide transport as stimulated by thyrotropin; loss of function occurred at a much faster rate than after I-131 irradiation. KU-55933, a selective ATM kinase inhibitor, partly rescued NIS expression and iodide transport in DNA-damaged cells. Prolonged ATM inhibition in healthy cells also repressed NIS-mediated iodide transport. ATM-dependent loss of iodide transport was counteracted by IGF-1. Together, these findings indicate that NIS, the major iodide transporter of the thyroid gland, is susceptible to DNA damage involving ATM-mediated mechanisms. This uncovers novel means of poor radioiodine uptake in thyroid cells subjected to extrinsic or intrinsic genotoxic stress. [ABSTRACT FROM AUTHOR]

CalE6 from Micromonospora echinospora is a (pyridoxal 5' phosphate) PLP-dependent methionine ?-lyase involved in the biosynthesis of calicheamicins. We report the crystal structure of a CalE6 2-(N-morpholino)ethanesulfonic acid complex showing ligand-induced rotation of Tyr100, which stacks with PLP, resembling the corresponding tyrosine rotation of true catalytic intermediates of CalE6 homologs. Elastic network modeling and crystallographic ensemble refinement reveal mobility of the N-terminal loop, which involves both tetrameric assembly and PLP binding. Modeling and comparative structuralanalysis of PLP-dependent enzymes involved in Cys/Met metabolism shine light on the functional implications of the intrinsic dynamic properties of CalE6 in catalysis and holoenzyme maturation. [ABSTRACT FROM AUTHOR]

The article discusses the Acute Leukemia French Association (ALFA)-0701 study which analyzes the positive impact of the level of blast CD33 expression to gemtuzumab ozogamicin (GO) in patients with acute myeloid leukemia. The in vitro result which shows the clear relationship between CD33 expression and GO efficacy and the evaluation of CD33 expression as a continuous covariable and highest response rates were reported for patients with CD33 expression in phase 2 study are mentioned.

Whilst most adult patients with acute lymphoblastic leukaemia will go into remission with standard induction chemotherapy, many will relapse. Response rates to standard salvage chemotherapy regimens are low and the outlook on relapse is very poor and associated with significant morbidity and mortality hence the need for newer targeted approaches. Inotuzumab ozogamicin (previously known as CMC-544) is an antibody-drug conjugate and consists of a monoclonal anti-CD22 antibody bound to calicheamicin. The target, CD22, is widely expressed on acute lymphoblastic leukaemia cells making it a potential therapeutic target. The calicheamicin is delivered intracellularly and causes leukaemia cell apoptosis. Overall response rates of 57% were observed in a Phase II study and the final results of a Phase III randomised controlled trial comparing this drug to the investigator choice ‘standard of care’ chemotherapy are eagerly awaited. Whilst initial results are promising, there have been concerns regarding liver toxicity and the incidence of veno-occlusive disease of the liver especially in patients who have previously received or go on to allogeneic stem cell transplant. [ABSTRACT FROM PUBLISHER]

Structure analysis and ensemble refinement of the apo-structure of thymidine diphosphate (TDP)-rhamnose 3'-O-methyltransferase reveal a gate for substrate entry and product release. TDP-rhamnose 3'-O-methyltransferase (CalS11) catalyses a 3'-O-methylation of TDP-rhamnose, an intermediate in the biosynthesis of enediyne antitumor antibiotic calicheamicin. CalS11 operates at the sugar nucleotide stage prior to glycosylation step. Here, we present the crystal structure of the apo form of CalS 11 at 1.89 Å resolution. We propose that the L2 loop functions as a gate facilitating and/or providing specificity for substrate entry or promoting product release. Ensemble refinement analysis slightly improves the crystallographic refinement statistics and furthermore provides a compelling way to visualize the dynamic model of loop L2, supporting the understanding of its proposed role in catalysis. [ABSTRACT FROM AUTHOR]

Classical UDP-glucose 6-dehydrogenases (UGDHs; EC 1.1.1.22) catalyze the conversion of UDP-α-D-glucose (UDP-Glc) to the key metabolic precursor UDP-α-D-glucuronic acid (UDP-GlcA) and display specificity for UDP-Glc. The fundamental biochemical and structural study of the UGDH homolog CalS8 encoded by the calicheamicin biosynthetic gene is reported and represents one of the first studies of a UGDH homolog involved in secondary metabolism. The corresponding biochemical characterization of CalS8 reveals CalS8 as one of the first characterized base-permissive UGDH homologs with a >15-fold preference for TDP-Glc over UDP-Glc. The corresponding structure elucidations of apo-CalS8 and the CalS8'substrate'cofactor ternary complex (at 2.47 and 1.95 Å resolution, respectively) highlight a notably high degree of conservation between CalS8 and classical UGDHs where structural divergence within the intersubunit loop structure likely contributes to the CalS8 base permissivity. As such, this study begins to provide a putative blueprint for base specificity among sugar nucleotide-dependent dehydrogenases and, in conjunction with prior studies on the base specificity of the calicheamicin aminopentosyltransferase CalG4, provides growing support for the calicheamicin aminopentose pathway as a TDP-sugar-dependent process. [ABSTRACT FROM AUTHOR]

Objective This study aims to examine the potential of radiomimetic compounds as antimicrobial therapeutics, as the recent advances in radiomimetic targeting as well as rapid increase of multidrug resistant bacteria make these compounds attractive for future development. Methods Representative radiomimetics from each of the three major categories was examined; C-1027 and neocarzinostatin from the protein-chromophore enediyne family; Calicheamicin from the non-protein chromophore enediyne family and Bleomycin and Tallysomycin S10b from the glycopeptide family. The activity of these compounds was examined against 12 distinct bacteria species. Inhibition was determined using disc diffusion assays and a subsequent examination of minimum inhibitory concentration of a representative organism. The onset of action of the compounds was also determined by incubating the organisms with drug in liquid media, before plating, and then determining if growth occurred. Results We found that the radiomimetic glycopeptides were more active against Gram-negative species, while the enediynes were more effective against Gram-positive species. The radiomimetics also maintained their rapid onset of action, working as quickly as 5 min. Conclusions Radiomimetic compounds have activity against a wide variety of microorganisms and would support the development of radiomimetic-antibody conjugates as potential antibiotics as an option against severe bacterial infections. [ABSTRACT FROM AUTHOR]

Calicheamicin is a DNA-damaging agent that, following intracellular activation, binds to DNA in the minor groove and introduces double-strand DNA breaks, leading to G2/M arrest and subsequent cell death. Importantly, the mechanism of action of calicheamicin is fundamentally different from the tubulin-binding class of cytotoxics targeting the mitotic spindle, which represent the most common class of payloads for antibody–drug conjugates (ADCs) currently undergoing clinical development. Spindle poisons that target tubulin, including auristatins and maytansines, are most effective against rapidly proliferating cells. In contrast, calicheamicin induces DNA double-strand breaks and apoptosis independent of cell cycle progression. Such properties may be advantageous when targeting malignant cells that are not markedly different in their proliferation status compared to normal cells. Here we review calicheamicin conjugates, with a particular focus on the preclinical- and clinical development of inotuzumab ozogamicin, targeting the CD22 antigen expressed on a large variety of hematologic malignancies. In pre-clinical experiments, inotuzumab ozogamicin potently induced tumor regressions in models of non-Hodgkin's lymphoma (NHL), either alone or in combination with the anti-CD20 antibody Rituximab. Promising anti-tumor responses were observed in early stage clinical trials, where inotuzumab ozogamicin was administered either as single agent or in combination with Rituximab. Consistent with the cell cycle independent mechanism of action of the calicheamicin payload, high rates of complete responses were observed in less aggressive forms of lymphomas, including follicular lymphoma (FL) and relapsed, diffuse large B-cell lymphoma (DLBCL). Inotuzumab ozogamicin is currently being tested in phase III clinical trials in acute lymphocytic leukemia (ALL). Particular focus is dedicated to reviewing the pre-clinical and clinical data generated with this compound in NHL and to outline future focus areas for pre-clinical- and clinical research of inotuzumab ozogamicin, and the calicheamicin class of antibody–drug conjugates more generally. [ABSTRACT FROM AUTHOR]

This study evaluated the safety and efficacy of inotuzumab ozogamicin (INO), a targeted humanized anti-CD22 antibody conjugated to calicheamicin, plus rituximab (R-INO) every 3 weeks, up to six cycles, followed by high dose therapy and autologous stem cell transplant (HDT-aSCT) in patients with high-risk relapsed/refractory diffuse large B-cell lymphoma (DLBCL). The primary endpoint was overall response (OR) rate after three cycles of R-INO. Sixty-three patients were enrolled. Common grade 3/4 adverse events during R-INO treatment were thrombocytopenia, lymphopenia and neutropenia. OR rate after three cycles of R-INO was 28.6% (95% confidence interval: 17.9–41.4). Eighteen patients underwent HDT-aSCT; 2-year progression-free survival (PFS) for these patients was 61.1%. Serious infections and hepatic toxicity following aSCT occurred in 33% and 22%, respectively. One- and 2-year PFS rates for all enrolled patients were 28.9% and 25.3%, respectively (median, 3.0 months). R-INO had lower than expected activity as a salvage regimen for transplant eligible patients with DLBCL. [ABSTRACT FROM AUTHOR]

Background: Calicheamicins (CAL) are enedyine natural products with potent antibiotic and cytotoxic activity, used in anticancer therapy. The O-methyltransferase CalO6 is proposed to catalyze methylation of the hydroxyl moiety at the C2 position of the orsellinic acid group of CAL. Results: Crystals of CalO6 diffracted non-isotropically, with the usable data extending to 3.4 Å. While no single method of crystal structure determination yielded a structure of CalO6, we were able to determine its structure by using molecular replacement-guided single wavelength anomalous dispersion by using diffraction data from native crystals of CalO6 and a highly non-isomorphous mercury derivative. The structure of CalO6 reveals the methyltransferase fold and dimeric organization characteristic of small molecule O-methyltransferases involved in secondary metabolism in bacteria and plants. Uncommonly, CalO6 was crystallized in the absence of S-adenosylmethionine (SAM; the methyl donor) or S-adenosylhomocysteine (SAH; its product). Conclusions: Likely as a consequence of the dynamic nature of CalO6 in the absence of its cofactor, the central region of CalO6, which forms a helical lid-like structure near the active site in CalO6 and similar enzymes, is not observed in the electron density. We propose that this region controls the entry of SAM into and the exit of SAH from the active site of CalO6 and shapes the active site for substrate binding and catalysis. [ABSTRACT FROM AUTHOR]

Conventional chemotherapy is ineffective in the majority of patients with acute myeloid leukaemia (AML), and monoclonal antibodies recognising CD33 expressed on myeloid progenitors (e.g. gemtuzumab ozogamicin (GO)) have been reported to improve outcome in patients with AML. Reports of excess toxicity have resulted in GO's licence being withdrawn. As a result, the role of these agents remains unclear. A systematic review and meta-analysis included studies of patients with AML who had entered a randomised control trial (RCT), where one arm included anti-CD33 antibody therapy. Fixed effect meta-analysis was used, involving calculation of observed minus expected number of events, and variance for each endpoint in each trial, with the overall treatment effect expressed as Peto's odds ratio with 95 % confidence interval. Meta-analysis of 11 RCTs with 13 randomisations involving GO was undertaken. Although GO increased induction deaths ( p = 0.02), it led to a reduction in resistant disease ( p = 0.0009); hence, there was no improvement in complete remission. Whilst GO improved relapse-free survival (hazard ratio (HR) = 0.90, 95 % confidence interval (CI) = 0.84-0.98, p = 0.01), there was no overall benefit of GO in overall survival (OS) (HR = 0.96, 95 % CI = 0.90-1.02, p = 0.2). GO improved OS in patients with favourable cytogenetics, with no evidence of benefit in patients with intermediate or adverse cytogenetics (test for heterogeneity between subtotals p = 0.01). GO has a potent clinically detectable anti-leukaemic effect. Further trials to investigate its optimum delivery and identification of patient populations who may benefit are needed. [ABSTRACT FROM AUTHOR]

A simple method forthe study of sugar-nucleotide-dependent multienzymecascades is highlighted where the use of selectively 13C-labeled sugar nucleotides and inverse 13C detectionNMR offers fast, direct detection and quantification of reactantsand products and circumvents the need for chromatographic separation.The utility of the method has been demonstrated by characterizingfour previously uncharacterized sugar nucleotide biosynthetic enzymesinvolved in calicheamicin biosynthesis. [ABSTRACT FROM AUTHOR]

Monoclonal antibodies are likely to make a considerable contribution in the treatment of acute lymphoblastic leukemia (ALL). High expression of CD22 antigen is found on the surface of leukemia cells in ALL. Inotuzumab ozogamicin, a CD22 monoclonal antibody conjugated to calicheamicin, which has shown efficacy in patients with lymphomas, has also shown encouraging activity in relapsed or refractory ALL with a high morphologic and molecular response rate. This article summarizes the current approaches to treating ALL with inotuzumab ozogamicin, based on available data from the literature. [ABSTRACT FROM AUTHOR]