Elevation of fast but not slow troponin I in the circulation of patients with Becker and Duchenne muscular dystrophy.

INTRODUCTION: One of the hallmarks of injured skeletal muscle is the appearance of elevated skeletal muscle proteins in circulation. Human skeletal muscle generally consists of a mosaic of slow (type I) and fast (type IIa, IIx/d) fibers, defined by their myosin isoform expression. Recently, measurement of circulating fiber-type specific isoforms of troponin I has been used as a biomarker to suggest that muscle injury in healthy volunteers (HV) results in the appearance of muscle proteins from fast but not slow fibers. We sought to understand if this is also the case in severe myopathy patients with Becker and Duchenne muscular dystrophy (BMD, DMD). METHODS: An enzyme-linked immunosorbent assay (ELISA) that selectively measures fast and slow skeletal troponin I (TNNI2 and TNNI1) was used to measure a cross-section of patient plasma samples from HV (N = 50), BMD (N = 49), and DMD (N = 132) patients. Creatine kinase (CK) activity was also measured from the same samples for comparison. RESULTS: TNNI2 was elevated in BMD and DMD and correlated with the injury biomarker, CK. In contrast, TNNI1 levels were indistinguishable from levels in HV. There was an inverse relationship between CK and TNNI2 levels and age, but no relationship for TNNI1. DISCUSSION: We define a surprising discrepancy between TNNI1 and TNNI2 in patient plasma that may have implications for the interpretation of elevated muscle protein levels in dystrophinopathies.

Leveraging Colloidal Aggregation for Drug-Rich Nanoparticle Formulations.

While limited drug loading continues to be problematic for chemotherapeutics formulated in nanoparticles, we found that we could take advantage of colloidal drug aggregation to achieve high loading when combined with polymeric excipients. We demonstrate this approach with two drugs, fulvestrant and pentyl-PABC doxazolidine (PPD; a prodrug of doxazolidine, which is a DNA cross-linking anthracycline), and two polymers, polysorbate 80 (UP80) and poly(d,l-lactide-co-2-methyl-2-carboxytrimethylene carbonate)-graft-poly(ethylene glycol) (PLAC-PEG; a custom-synthesized, self-assembling amphiphilic polymer). In both systems, drug-loaded nanoparticles had diameters < 200 nm and were stable for up to two days in buffered saline solution and for up to 24 h in serum-containing media at 37 °C. While colloidal drug aggregates alone are typically unstable in saline and serum-containing media, we attribute the colloid stability observed herein to the polymeric excipients and consequent decreased protein adsorption. We expect this strategy of polymer-stabilized colloidal drug aggregates to be broadly applicable in delivery formulations.

Large increases in plasma fast skeletal muscle troponin I after whole-body eccentric exercises.

OBJECTIVES: It has been reported that plasma fast skeletal muscle troponin I (fsTnI) but not slow skeletal muscle troponin I (ssTnI) increases after a bout of eccentric exercise of the elbow flexors. The present study compared the first and second bouts of whole-body eccentric exercises for changes in plasma fsTnI and ssTnI concentrations. DESIGN: Observational study in an experimental group. METHODS: Fifteen sedentary men (20-25 y) performed nine eccentric exercises targeting arm, leg and trunk muscles, and repeated them two weeks later. Blood samples were taken before and for five days following each bout, and plasma ssTnI and fsTnl concentrations were measured by enzyme-linked immunosorbent assays. Their changes were compared between bouts and their relationships to plasma CK activity and myoglobin concentrations were analysed. RESULTS: Plasma fsTnI concentration increased after the first bout and peaked at 4 days post-exercise (2152-40,295 ng/mL), but no significant increases were evident after the second bout. Plasma ssTnI concentration did not change significantly from the baseline (<0.08 ng/mL) after either bout. Peak plasma fsTnI concentration was significantly (p < 0.005) correlated with peak plasma CK activity (peak: 23,238-207,304 IU/L, r = 0.727) and myoglobin concentration (1047-3936 µg/L, r = 0.625) after the first bout. CONCLUSIONS: These results suggest that plasma TnI concentrations are more specific biomarker of muscle damage than plasma CK activity and myoglobin concentration. It seems that the whole-body eccentric exercises induced damage preferentially to fast-twitch muscle fibres, and increases in plasma CK activity and myoglobin concentration after eccentric exercise may reflect fast-twitch muscle fibre damage.

Identification of human intestinal carboxylesterase as the primary enzyme for activation of a doxazolidine carbamate prodrug.

Doxazolidine (Doxaz), a formaldehyde-doxorubicin (Dox) conjugate, exhibits markedly increased tumor toxicity with respect to Dox without a concurrent increase in toxicity to cardiomyocytes. Pentyl PABC-Doxaz (PPD) is a Doxaz carbamate prodrug that is hydrolyzed by carboxylesterases. Here, we identify human intestinal carboxylesterase (hiCE) as the agent of activation for PPD. Upon prodrug treatment, cells that express higher levels of hiCE responded with lower IC50 values for growth inhibition. Exposing MCF-7 human breast cancer cells, which respond poorly and express little hiCE, to PPD together with hiCE resulted in a dramatic decrease in the IC50, a decrease that was absent when human carboxylesterase 1 was added to prodrug treatment. Finally, U373MG glioblastoma cells overexpressing hiCE displayed approximately 100-fold reduction in the IC50 for PPD compared to cells lacking the carboxylesterase. Overall, our studies indicate that PPD is selectively hydrolyzed to the active metabolite by hiCE.

Anthracycline-formaldehyde conjugates and their targeted prodrugs.

The sequence of research leading to a proposal for anthracycline cross-linking of DNA is presented.The clinical anthracycline antitumor drugs are anthraquinones, and as such are redox active. Their redoxchemistry leads to induction of oxidative stress and drug metabolites. An intermediate in reductive glycosidiccleavage is a quinone methide, once proposed as an alkylating agent of DNA. Subsequent research nowimplicates formaldehyde as a mediator of anthracycline-DNA cross-linking. The cross-link at 5'-GC-3'sites consists of a covalent linkage from the amino group of the anthracycline to the 2-amino groupof the G-base through a methylene from formaldehyde, hydrogen bonding from the 9-OH to the G-base onthe opposing strand, and hydrophobic interactions through intercalation of the anthraquinone. The combinationof these interactions has been described as a virtual cross-linkof DNA. The origin of the formaldehyde in vivo remains a mystery. In vitro, doxorubicin reacts withformaldehyde to give firstly a monomeric oxazolidine, doxazolidine, and secondly a dimeric oxazolidine,doxoform. Doxorubicin reacts with formaldehyde in the presence of salicylamide to give the N-Mannich baseconjugate, doxsaliform. Doxsaliform is several fold more active in tumor cell growth inhibition than doxorubicin,but doxazolidine and doxoform are orders of magnitude more active than doxorubicin. Exploratory researchon the potential for doxsaliform and doxazolidine as targeted cytotoxins is presented. A promisinglead design is pentyl PABC-Doxaz, targeted to a carboxylesterase enzyme overexpressed in liver cancercells and/or colon cancer cells.

Design, synthesis, and preliminary evaluation of doxazolidine carbamates as prodrugs activated by carboxylesterases.

The synthesis and tumor cell growth inhibition by doxazolidine carbamate prodrugs are reported. The carbamates were designed for selective hydrolysis by one or more human carboxylesterases to release doxazolidine (Doxaz), the formaldehyde-oxazolidine of doxorubicin that cross-links DNA to trigger cell death. Simple butyl and pentyl, but not ethyl, carbamate prodrugs inhibited the growth of cancer cells that overexpress carboxylesterase CES1 (hCE1) and CES2 (hiCE). Relative CES1 and CES2 expression levels were determined by reverse transcription of the respective mRNAs, followed by polymerase chain reaction amplification. More complex structures with a p-aminobenzyl alcohol (PABA) self-eliminating spacer showed better growth inhibition (IC50=50 nM for Hep G2 liver cancer cells) while exhibiting reduced toxicity toward rat cardiomyocytes, relative to the parent drug doxorubicin. Pentyl 4-(N-doxazolidinylcarbonyloxymethyl)phenylcarbamate, the lead compound for further investigation, appears to be activated in Hep G2 cells that express both CES1 and CES2.

Correlation of in Situ Oxazolidine Formation with Highly Synergistic Cytotoxicity and DNA Cross-Linking in Cancer Cells from Combinations of Doxorubicin and Formaldehyde.

Anthracyclines are a class of antitumor compounds that are successful and widely used but suffer from cardiotoxicity and acquired tumor resistance. Formaldehyde interacts with anthracyclines to enhance antitumor efficacy, bypass resistance mechanisms, improve the therapeutic profile, and change the mechanism of action from a topoisomerase II poison to a DNA cross-linker. Contrary to current dogma, we show that both efficient DNA cross-linking and potent synergy in combination with formaldehyde correlate with the anthracycline's ability to form cyclic formaldehyde conjugates as oxazolidine moieties and that the cyclic conjugates are better cross-linking agents and cytotoxins than acyclic conjugates. We also provide evidence that suggests that the oxazolidine forms in situ, since cotreatment with doxorubicin and formaldehyde is highly cytotoxic to dox-resistant tumor cell lines, and that this benefit is absent in combinations of formaldehyde and epirubicin, which cannot form stable oxazolidines. These results have potential clinical implications in the active field of anthracycline prodrug design and development.

Doxazolidine, a proposed active metabolite of doxorubicin that cross-links DNA.

A crystal structure establishes doxoform as a dimeric formaldehyde conjugate of the oxazolidine of doxorubicin. Doxoform is a prodrug of doxazolidine, a monomeric doxorubicin formaldehyde-oxazolidine. Both doxoform and doxazolidine inhibit the growth of cancer cells at 1-4 orders of magnitude lower concentration than doxorubicin. They also inhibit the growth of cancer cells better than doxsaliform, a prodrug for an acyclic doxorubicin-formaldehyde conjugate. Doxoform rapidly hydrolyzes to doxazolidine, which then hydrolyzes to doxorubicin with a half-life of 3 min in human serum at 37 degrees C. Both doxoform and doxazolidine are taken up by multidrug-resistant MCF-7/Adr cells 3- to 4-fold better than doxorubicin. A molecular model suggests that doxazolidine can cross-link DNA by direct reaction with a G-base in a tautomeric form with synchronous ring opening of the oxazolidine. These results point to doxoform being a prodrug for doxazolidine that is the reactive species that directly cross-links DNA.

Synthesis and biological characterization of protease-activated prodrugs of doxazolidine.

Doxazolidine (doxaz) is a new anthracycline anticancer agent. While structurally similar to doxorubicin (dox), doxaz acts via a distinct mechanism to selectively enhance anticancer activity over cardiotoxicity, the most significant clinical impediment to successful anthracycline treatment. Here, we describe the synthesis and characterization of a prodrug platform designed for doxaz release mediated by secreted proteolytic activity, a common association with invasiveness and poor prognosis in cancer patients. GaFK-Doxaz is hydrolyzable by the proteases plasmin and cathepsin B, both strongly linked with cancer progression, as well as trypsin. We demonstrate that activation of GaFK-Doxaz releases highly potent doxaz that powerfully inhibits the growth of a wide variety of cancer cells (average IC(50) of 8 nM). GaFK-Doxaz is stable in human plasma and is poorly membrane permeable, thereby limiting activation to locally secreted proteolytic activity and reducing the likelihood of severe side effects.

Preclinical efficacy of a carboxylesterase 2-activated prodrug of doxazolidine.

Doxazolidine (Doxaz) is a functionally distinct formaldehyde conjugate of doxorubicin (Dox) that induces cancer cell death in Dox-sensitive and resistant cells. Pentyl PABC-Doxaz (PPD) is a prodrug of Doxaz that is activated by carboxylesterase 2 (CES2), which is expressed by liver, non-small-cell lung, colon, pancreatic, renal, and thyroid cancer cells. Here, we demonstrate that in two murine models, PPD was effective at slowing tumor growth and demonstrated markedly reduced cardiotoxic and nephrotoxic effects, as well as better tolerance, relative to Dox. Hepatotoxicity, consistent with liver expression of the murine CES2 homologue, was induced by PPD. Unlike irinotecan, a clinical CES2-activated prodrug, PPD produced no visible gastrointestinal damage. Finally, we demonstrate that cellular response to PPD may be predicted with good accuracy using CES2 expression and Doxaz sensitivity, suggesting that these metrics may be useful as clinical biomarkers for sensitivity of a specific tumor to PPD treatment.