Effect of molecular weight of PGG-paclitaxel conjugates on in vitro and in vivo efficacy.

Polymeric prodrugs are one of the most promising chemotherapeutic agent delivery approaches, displaying unique drug release profiles, serum stability, formulation flexibility, and reduced drug resistance. One of the most important aspects of a polymeric prodrug, albeit a less-extensively studied one, is the polymer's molecular weight, which affects particle formation, drug release and PK/PD profiles, drug stability, and cell uptake; these factors in turn affect the prodrug's maximum tolerated dose and anticancer efficacy. Poly(L-γ-glutamylglutamine) (PGG) is a linear polymer designed to improve the therapeutic index of attached drugs. In this study we selected poly(L-γ-glutamylglutamine)-paclitaxel (PGG­PTX), as a model system for the methodical investigation into the effects of the poly(L-γ-glutamylglutamine) backbone molecular weight on its pharmacological performance. The polymeric prodrug was characterized by NMR, DLS and GPC-MALS, and its anticancer activity in vitro and in vivo was assessed. Herein we present data which provide valuable insight into improving anticancer polymer-based prodrug design and development.

Retinoid-related molecule AGN193198 potently induces G2M arrest and apoptosis in bladder cancer cells.

The novel synthetic retinoid-related molecule 4-[3-(1-heptyl-4,4-dimethyl-2-oxo-1,2,3,4-tetrahydroquinolin-6-yl)-3-oxo-propenyl]benzoic acid (AGN193198) neither binds effectively to retinoic acid receptors (RARs) and retinoid X receptors (RXRs) nor transactivates in RAR- and RXR-mediated reporter assays. Even so, AGN193198 is potent in inducing apoptosis in human prostate and breast carcinoma cells (Keedwell et al., Cancer Res 2004;64:3302-12). Here, we extend these findings to show that AGN193198 potently and rapidly induces apoptosis in bladder carcinoma cell lines. One micromolar of AGN193198 completely abolished the growth of the transitional cell carcinoma lines UM-UC-3 and J82, and the squamous cell carcinoma line SCaBER; the transitional cell papilloma line RT-4 was slightly less sensitive to the growth inhibitory effect of AGN193198. Treated cells accumulated in the G2M phase of the cell cycle. This was accompanied by apoptosis, as revealed by staining cells for exposure of phosphatidylserine at their surface (binding of Annexin V) and FACS analysis of propidium iodide labeled cells. As reported for prostate cancer cells, AGN193198 provoked rapid activation of caspases-3 (by 6 hr), -8 (by 16 hr) and -9 (by 6 hr) in bladder cancer cells. These findings suggest that AGN193198 and related compounds, whose mechanism of action does not appear to involve RARs and RXRs, may be useful in the treatment of bladder cancer.

A retinoid-related molecule that does not bind to classical retinoid receptors potently induces apoptosis in human prostate cancer cells through rapid caspase activation.

Synthetic retinoid-related molecules, such as N-(4-hydroxyphenyl)retinamide (fenretinide) and 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) induce apoptosis in a variety of malignant cells. The mechanism(s) of action of these compounds does not appear to involve retinoic acid receptors (RARs) and retinoid X receptors (RXRs), although some investigators disagree with this view. To clarify whether some retinoid-related molecules can induce apoptosis without involving RARs and/or RXRs, we used 4-[3-(1-heptyl-4,4-dimethyl-2-oxo-1,2,3,4-tetrahydroquinolin-6-yl)-3-oxo-E-propenyl] benzoic acid (AGN193198) that neither binds effectively to RARs and RXRs nor transactivates in RAR- and RXR-mediated reporter assays. AGN193198 potently induced apoptosis in prostate, breast, and gastrointestinal carcinoma cells and in leukemia cells. AGN193198 also abolished growth (by 50% at 130-332 nM) and induced apoptosis in primary cultures established from prostatic carcinoma (13 patients) and gastrointestinal carcinoma (1 patient). Apoptosis was induced rapidly, as indicated by mitochondrial depolarization and DNA fragmentation. Molecular events provoked by AGN193198 included activation of caspase-3, -8, -9, and -10 (by 4-6 h) and the production of BID/p15 (by 6 h). These findings show that caspase-mediated induction of apoptosis by AGN193198 is RAR/RXR-independent and suggest that this compound may be useful in the treatment of prostate cancer.

Consistent helicities from CD and template t/c data for N-templated polyalanines: progress toward resolution of the alanine helicity problem.

The helicity reporting parameters t/c and [theta](222) have been measured at 2, 25, and 60 degrees C in water for the solubilized polyalanine series Ac-Hel-A(n)-(t)LInp(2)K(4)W-NH(2) of length 4 < or = n < or = 14 that bears the helix-initiating and monitoring N-cap Ac-Hel and the spaced solubilizer (t)LInp(2)K(4)W-NH(2) as a C-cap. Correlation of t/c with length shows that the helical propensity for n < or = 6 is ca. 1.0, consistent with our early reports, but that a dramatic increase in temperature dependence and helical propensity occurs for n > or = 8. A model based on hydrogen-bonding cooperativity is proposed to explain this finding, and both t/c and [theta](222) are modeled successfully by length-dependent alanine propensities at 2 degrees C of 1.03 for n = 6, 1.15, for 7 < or = n < or = 9 and 1.26 for n > or = 10. The implications of these results for the energetics of helix formation by alanine-rich peptide sequences are discussed.