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1.  Time-and concentration-dependent penetration of doxorubicin in prostate tumors 
AAPS PharmSci  2001;3(2):69-77.
The penetration of paclitaxel into multilayered solid tumors is time- and concentration-dependent, a result of the drug-induced apoptosis and changes in tissue composition. This study evaluates whether this tissue penetration property applies to other highly protein-bound drugs capable of inducing apoptosis. The penetration of doxorubicin was studied in histocultures of prostate xenograft tumors and tumor specimens obtained from patients who underwent radical prostatectomy. The kinetics of drug uptake and efflux in whole tumor histocultures were studied by analyzing the average tumor drug concentration using high-pressure liquid chromatography. Spatial drug distribution in tumors and the drug concentration gradient across the tumors were studied using fluorescence microscopy. The results indicate that drug penetration was limited to the periphery for 12 hours in patient tumors and to 24 hours in the more densely packed xenograft tumors. Subsequently, the rate of drug penetration to the deeper tumor tissue increased abruptly in tumors treated with higher drug concentrations capable of inducing apoptosis (i.e., >5 μm), but not in tumors treated with lower concentrations. These findings indicate a time- and concentration-dependent penetration of doxorubicin in solid tumors, similar to that of paclitaxel. We conclude that doxorubicin penetration in solid tumors is time- and concentration-dependent and is enhanced by drug-induced cell death.
doi:10.1208/ps030215
PMCID: PMC2779556  PMID: 11741266
Doxorubicin; Delivery; Apoptosis; Solid Tumor
2.  Kinetics of hallmark biochemical changes in paclitaxel-induced apoptosis 
AAPS PharmSci  1999;1(3):7-14.
Apoptosis is associated with cascades of biochemical changes, including caspase activation, cleavage of poly-ADP-ribose polymerase (PARP), and fragmentation of genomic DNA. Knowledge of the kinetics of these changes in drug-induced apoptosis is important for designing pharmacodynamic studies. We have shown that the slow manifestation of apoptosis contributes to the delayed pharmacological effects of paclitaxel (Cancer Res. 58:2141–2148, 1998). The present study examined the timing of the biochemical changes in paclitaxel-induced apoptosis in human prostate PC3 cancer cells. After treatment with 20 nM paclitaxel, the fraction of cells that detached from the culture flask increased with time to reach 68% at the end of the 96-hour experiment. In contrast, the control samples showed <1% detachment. The attached and detached paclitaxel-treated cells showed different biochemical properties. The detached cells exhibited the full spectrum of apoptotic changes, whereas the attached cells only showed activation of caspase-3-like proteases but not PARP cleavage, DNA fragmentation, nor release of DNA fragments to the cytoplasm. Activation of caspases in the attached cells was several-fold lower and occurred at a later time (ie, 24 vs 12 hours) compared to the detached cells. In the detached cells, caspase activation was first detected at 12 hours and peaked at 36 hours, whereas PARP cleavage was first detected at 24 hours and was completed prior to 72 hours. In contrast, the extent of internucleosomal DNA fragmentation and the release of DNA-histone complex to the cytoplasm (both were first detected at 24 hours) were cumulative over time up to the last time point of 96 hours. In summary, in paclitaxel-induced apoptosis, caspase activation was followed with a 12-hour lag time by PARP cleavage, internucleosomal DNA fragmentation, and release of DNA-histone complex to the cytoplasm. There was no detectable lag time between PARP cleavage and DNA fragmentation. The observation that only the detached cells but not the attached cells showed the full spectrum of apoptotic changes suggests that detachment is either a part of the initiation execution phases of apoptosis and or is required for their completion.
doi:10.1208/ps010308
PMCID: PMC2761122  PMID: 11741204
paclitaxel; apoptosis; anoikis; caspase activation; PARP cleavage; DNA fragmentation

Results 1-2 (2)