Abstract 5422: Predictive models of diffusive nanoparticle transport in 3D tumor spheroids

Nanotechnology offers a means to deliver diagnostics and therapeutics, and has emerged as an important tool in cancer translational research. We previously described a computational model that uses nanoparticle (NP)-cell biointerface data to predict diffusive NP transport in 3D tumor spheroids; the model predictions agreed with the experimental results for near-neutral liposomes and negatively-charged polystyrene beads but not for cationic liposomes that contained fusogenic lipid DOPE and underwent significant size change in the presence of tumor cells (Gao et al., AAPS J 15:816, 2013). The present study evaluated if the inferior model performance on cationic liposomes was due to fusogenic lipid, positive surface charge, and/or time-dependent NP size change. We studied eight cationic liposomes containing different levels of cationic lipid DOTAP (10-30 mol%) and fusogenic lipid DOPE (1-20 mol%), with an average initial size of ∼135 nm and 2-fold range in surface charge (+24 to +43 mV). The time-dependent NP size change was monitored by measuring NP size distribution and by live cell confocal microscopy; the results indicate the most substantial change for liposomes containing >10 mol% DOPE. The required NP-cell biointerface parameters (NP association and dissociation with/from cells, NP internalization, maximum NP binding sites) were measured in monolayer cultures. Comparison of model-predicted profiles with experimental results in 3D spheroids showed good agreement (>88% and >95% of predicted data were within 95% and 97.5% confidence intervals of experimental results, respectively; <26% average deviations) for cationic liposomes containing 10-30 mol% DOTAP and low levels DOPE (≤10 mol%), indicating the diffusive transport of these cationic NP in 3D systems could be predicted using the biointerface data. In comparison, inferior predictions were obtained for cationic liposomes with higher DOPE content (up to 88% deviations, average of 41%).In view of the substantial depletion of extracellular concentration and the substantial size increase for selected NP over the 12 hr study (e.g., >8% depletion for 30 mol% DOTAPand 3-times larger size for 20 mol% DOPE), we modified the model to account for these time-dependent changes. The modified model yielded better predictions for liposomes with <10 mol% DOPE, but worse predictions for liposomes containing 20 mol% DOPE (86% average deviations).This finding rules out the time-dependent changes in NP size and concentration, and suggests other DOPE properties not captured by the biointerface parameters, as potential causes of the inferior model performance. In summary, the present study, together with our earlier study, indicates the diffusive transport of NP with different sizes (20-135 nm) and varying surface charges (-49to +43mV) in 3D spheroids, with the exception of liposomes comprising >10 mol% of fusogenic lipid DOPE, can be predicted based on the NP-cell biointerface parameters. RO1EB015253, DHHS.

Citation Format: Mingguang Li, Michael Wientjes, Bertrand Yeung, M. Guillaume Wientjes, Jessie L.S. Au. Predictive models of diffusive nanoparticle transport in 3D tumor spheroids. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5422. doi:10.1158/1538-7445.AM2014-5422

Effect of age on the disposition and tissue clearances of fluorinated pyrimidines in rats

The age dependency of the elimination and tissue clearances of 5-fluorouracil (FU) and its nucleoside analog, 5'-deoxy-5-fluorouridine (dFUR), was investigated in 2 to 12 months old female Fischer rats. In all age groups, the blood clearances of dFUR at infusion rates of 500 and 750 mg kg(-1) day(-1) and of FU at 25 and 35 mg kg(-1) day(-1) were independent of the dose; however, the clearance of FU at a higher infusion rate of 50 mg kg(-1) day(-1) was significantly lower than at 25 mg kg(-1) day(-1). An inverse relationship between animal age and clearance was observed for dFUR at both 500 and 750 mg kg(-1) day(-1) doses, and for FU at the 50 mg kg(-1) day(-1) dose. By contrast, the FU clearance at the 25 and 35 mg kg(-1) day(-1) doses was independent of age. To examine the age effect on the metabolic activities of major eliminating organs, the metabolism of dFUR by liver and small intestine in young and old rats was compared using 13,000 × g supernatant fractions of the tissue homogenates. Data were computer-fitted to the Michaelis-Menten equation. The Km for both tissues of both age groups was approximately 120 µg ml(-1). The intrinsic clearance (Vmax/Km) of dFUR was 5 ml kg(-1) min(-1) in the liver and 8 ml kg(-1) min(-1) in the intestine. The intestinal intrinsic clearance was independent of animal age, but the hepatic intrinsic clearance was significantly decreased in the older rats. The blood concentrations of FU derived as a metabolite from dFUR were also dependent on the animal age; an elevated FU concentration was associated with a lower dFUR metabolic clearance in the old rats. These data indicate that the elimination of FU and dFUR in rats is age-dependent, and that the systemic concentration of FU, a determinant of dFUR selectivity, is elevated in older animals.

Differential time dependency of antiproliferative and apoptotic effects of taxol in human prostate tumors

The pharmacodynamics of taxol in human prostate tumors were studied using histocultures of radical prostatectomy specimens from 34 patients. The results showed that taxol inhibited DNA synthesis and induced apoptosis in all tumors. The taxol-induced DNA inhibition and the apoptotic index increased with drug concentration, but reached a maximal plateau level at a concentration between 120 and 1,200 nM. Increasing the concentration by 10- to 100-fold to 12,000 nM did not significantly increase either effect. To address the existing controversy regarding the effect of treatment duration on cytotoxicity, we evaluated two treatment schedules, (i.e., 24 and 96 hours). Prolonging the treatment time from 24 to 96 hours significantly increased the average maximal inhibition of DNA synthesis (E(max)) from 47% to 70% (p < 0.001) and reduced the incidence of relatively resistant tumors (E(max) < 30%) from 31% to 0% (p = 0.04). By contrast, the prolonged treatment time did not increase the apoptotic effect (p = 0.48). The inter-tumor variation in sensitivity to the antiproliferative effect was substantial; the drug concentration required to produce a 30% DNA inhibition (IC(30)) showed a >300,000- and a 14,000-fold range for the 24 and 96 hour treatments, respectively. In conclusion, data of the present study demonstrate (1) antiproliferative and apoptotic effects of taxol in human prostate tumors, (2) that neither effect was significantly enhanced by increasing the drug concentration above 1,200 nM, and (3) that the antiproliferative effect was affected more significantly by drug exposure time than the apoptotic effect.

Distribution of DT-diaphorase and reduced nicotinamide adenine dinucleotide phosphate: cytochrome p450 oxidoreductase in bladder tissues and tumors

PURPOSE

We previously showed that mitomycin C activity in human bladder tumors is inversely related to tumor stage and muscle invasive tumors are less sensitive than superficial tumors. Because DT-diaphorase and reduced nicotinamide adenine dinucleotide phosphate:cytochrome P450 oxidoreductase (P450R) have a role in mitomycin C bioactivation, we investigated the distribution of these enzymes as a function of depth in the bladder wall and in human bladder tumors located at different parts of the bladder.

MATERIALS AND METHODS

Gene expression of DT-diaphorase and P450R relative to the expression of beta-actin was measured by reverse transcriptase-polymerase chain reaction in 4 dog and 8 human bladder tissue specimens, and in 46 human bladder tumors. DT-diaphorase activity was measured by enzymatic assay in dog and human bladders.

RESULTS

Data showed decreasing expression of DT-diaphorase and P450R from urothelium to muscle layer in the normal bladder wall with higher interindividual variation in humans than in dogs (greater than 40-fold versus approximately 3-fold). The expression of DT-diaphorase and P450R in bladder tumors correlated inversely with tumor stage (p <0.05) and was significantly higher in superficial than in muscle invasive bladder disease. DT-diaphorase and P450R expression in bladder tumors was approximately 6-fold higher than in normal bladder tissue. In normal and tumor tissues DT-diaphorase expression correlated significantly with P450R (r2 = 0.33, p <0.01), while DT-diaphorase expression correlated with its enzyme activity (r2 = 0.84, p <0.01).

CONCLUSIONS

Our results indicate a higher distribution of DT-diaphorase and P450R in superficial bladder tumors and tissues. Preferential enzyme distribution in superficial tumors may be a cause of the higher efficacy of intravesical mitomycin C therapy for superficial versus muscle invasive disease.

Telomere amount and length assay

PURPOSE

Telomeres are specific DNA structure at the ends of chromosomes to protect chromosomes from fusion, recombination, and degradation. Telomere length changes are implicated in cell senescence, aging, tumorigenesis, and DNA repair. The standard method for measuring telomere length is Southern blot analysis. This method has several disadvantages, i.e., loss of DNA during membrane blotting, high background due to nonspecific binding of telomere probe to membrane, and loss of telomeric signal due to extensive washing. These limitations resulted in a low signal-to-noise ratio and, therefore, reduced sensitivity and reproducibility. The multi-step Southern blot is also highly labor-intensive. The present study was to develop a more quantitative assay of telomeric amount and length (TALA).

METHODS

TALA was based on solution hybridization and did not require blotting, prehybridization, and washing. The major steps were (a) DNA preparation and digestion with restriction endonucleases, (b) hybridization between DNA and telomeric probe, (c) agarose gel electrophoresis, and (d) autoradiography and data analysis.

RESULTS

The telomere amount measured by TALA was linearly correlated with the amount of DNA analyzed (r2 = 0.985, P < 0.01). The telomere length measured by TALA also correlated with the telomere length determined by fluorescence in situ hybridization (r2 = 0.99, P < 0.01). Compared to the Southern blot analysis, TALA showed a 4-fold greater sensitivity, 4.6-fold higher signal-to-noise ratio, >2 fold-higher reproducibility, and 4-fold less time requirement.

CONCLUSION

We report here a rapid, sensitive, and quantitative assay for measuring telomere length and amount.

Nontoxic doses of suramin enhance activity of doxorubicin in prostate tumors

We recently reported that acidic and basic fibroblast growth factors (aFGF and bFGF) confer a broad-spectrum chemoresistance in solid tumors, and that inhibitors of these proteins enhanced the antitumor activity of several anticancer drugs. The present study investigated the effect of FGF inhibitors on doxorubicin activity in human prostate PC3 tumors. In in vitro studies, conditioned medium (CM) obtained from histocultures of rat MAT-LyLu lung metastases and different combinations of recombinant FGF induced a 7- to 15-fold doxorubicin resistance. Suramin had no effect on the doxorubicin activity in the absence of CM or FGF, but reversed the CM- and FGF-induced resistance by > or =90% at concentrations that had no cytotoxicity (i.e., 1-17 microM suramin). In the in vivo study, immunodeficient mice bearing well established, subcutaneous PC3 tumors (approximately 100 mg in size) were treated intravenously with doxorubicin (5 mg/kg) and suramin (10 mg/kg), administered twice weekly for 3 weeks. The suramin dose, selected to yield plasma concentration of below 50 microM, had neither antitumor activity nor toxicity. Doxorubicin alone reduced tumor growth rate by approximately 60%, reduced the density of nonapoptotic tumor cells by approximately 60%, enhanced the apoptotic cell fraction by 4-fold, and reduced the body weight by approximately 15% (p < 0.05 compared with control). Addition of suramin to doxorubicin therapy did not increase weight loss but significantly enhanced the antitumor effect, resulting in complete inhibition of tumor growth, an additional 3-fold reduction in the density of nonapoptotic tumor cells, and an additional 2-fold enhancement of the apoptotic tumor cell fraction (p < 0.05 compared with all other groups). These data indicate significant enhancement of the effectiveness of doxorubicin in prostate tumors by nontoxic and subtherapeutic doses of suramin.

Kinetics of P-glycoprotein-mediated efflux of paclitaxel

Paclitaxel is a substrate of the mdr1 P-glycoprotein (Pgp). The objective of the present study was to determine the kinetics of the Pgp-mediated efflux and its contribution to the overall efflux of paclitaxel at the clinically achievable concentration range of 1 to 1500 nM. Human breast carcinoma BC19 cells that were derived from MCF7 cells by mdr1 transfection and show a >10-fold higher level of the Pgp protein were used to measure the uptake and efflux of [(3)H]paclitaxel. A computational model of intracellular paclitaxel pharmacokinetics was developed to analyze for the Pgp efflux parameters. The results show a saturable Pgp-mediated efflux in BC19 cells; the dissociation constant was 14 nM, and the maximal efflux rate was 2.8 x 10(-4) pmol/h/cell. The contribution of Pgp-mediated efflux to the total efflux decreased with increasing extracellular drug concentrations; the Pgp efflux accounted for 86 and 34% of total efflux at 1 and 1500 nM, respectively. The validity of the model was confirmed by the close agreement between the model-predicted data and the experimentally obtained data (approximately 6% deviation) describing the effect of cell density and intracellular-to-extracellular concentration gradient on the kinetics of drug accumulation and efflux. In conclusion, our results indicate that the Pgp-mediated efflux represents a major efflux mechanism of paclitaxel at the low end of the clinically observed drug concentration range, but accounts for only a minor part of the efflux at higher concentrations in BC19 cells.

Nontoxic doses of suramin enhance activity of paclitaxel against lung metastases

We recently reported that acidic (aFGF) and basic (bFGF) fibroblast growth factors confer a broad spectrum chemoresistance in solid tumors, and that suramin, an inhibitor of multiple growth factors including aFGF and bFGF, enhanced the in vitro antitumor activity of several anticancer drugs including paclitaxel (Song, S., et al., Proc. Natl. Acad. Sci. USA, 97: 8658-8663, 2000). The present study investigated in vitro and in vivo interaction between paclitaxel and suramin, using human PC3-LN cells which, upon i.v. injection into immunodeficient mice, yielded lung metastases in 100% of animals. In in vitro studies, conditioned medium (CM) obtained from histocultures of rat lung metastases induced a 3-fold resistance. The addition of suramin had no effect in the absence of CM but reversed the CM-induced resistance; calculations based on the IC(50) values indicate a complete reversal in the presence of <20 microM suramin. Analysis by the combination index method indicates a synergistic interaction between paclitaxel and suramin. In in vivo studies, animals with well-established lung metastases (at least five nodules of 1 mm in diameter) were treated i.v. with paclitaxel (15 mg/kg) and suramin (10 mg/kg) administered twice weekly for 3 weeks. Single-drug therapy with paclitaxel or suramin did not reduce body weight. Suramin alone had no antitumor activity. Paclitaxel alone reduced the tumor size by approximately 75%, reduced the density of nonapoptotic cells by approximately 70% in residual tumors, and enhanced the fraction of apoptotic cells by approximately 3-fold. The addition of suramin to paclitaxel therapy enhanced the antitumor effect, resulting in an additional 5-fold reduction of tumor size, an additional 9-fold reduction of the density of nonapoptotic cells, and an additional 30% increase in the apoptotic cell fraction. These data indicate significant enhancement of the efficacy of paclitaxel by suramin and support the use of nontoxic doses of suramin with paclitaxel in the treatment of lung cancer.

Determinants of drug delivery and transport to solid tumors

This presentation addresses the barriers and determinants and the importance of drug-induced apoptosis in drug transport and delivery to organs and solid tumors. In particular, we examined the roles of interstitial space, drug removal by capillaries, tissue structure and tissue composition on drug distribution. Drug transport in bladder tissues is described by the distributed model which combined monodimensional Fickian diffusion and first order removal of drug by the perfusing blood. Microscopic evaluation of the spatial drug distribution in bladder, prostate and tongue indicates heterogeneous drug distribution with large and erratic concentration gradient. In general, drug distribution favors interstitial space and vasculature, with little penetration in muscles. Drug penetration into 3-dimensional solid tumors is typically 5- to 10-fold slower than in monolayer cultures. The transport of highly protein-bound drugs such as paclitaxel and doxorubicin in a solid tumor is retarded by a high tumor cell density and enhanced by drug-induced apoptosis. Accordingly, the delivery of a highly protein-bound drug to cells in a solid tumor is affected by its apoptotic effects and is therefore determined by the drug concentration and the treatment duration, i.e. treatment schedule. Under in vitro and in vivo conditions, the delivery of highly protein-bound drugs to tumor can be enhanced by using a pretreatment that induces apoptosis and reduction in cell density, and by using treatment schedules designed to take advantage of these drug-induced changes in tumor tissue composition. In conclusion, in addition to the usual processes involved in drug transport such as distribution through vascular space, transport across microvessel walls, and diffusion through interstitial space in tumor tissue, other factors including tissue structure and composition and alteration by drug-induced apoptosis are important determinants of drug distribution in organs and solid tumors.

Mdr1 transfection causes enhanced apoptosis by paclitaxel: an effect independent of drug efflux function of P-glycoprotein

PURPOSE

We previously reported that in patient tumors the expression of the mdrl p-glycoprotein (Pgp) resulted in a lower paclitaxel-induced inhibition of DNA precursor incorporation, but a higher apoptosis (Clin. Cancer Res. 4:2949-2955, 1998). The present study was to evaluate these findings in an experimental system where the Pgp effect can be studied without confounding factors such as the intra- and inter-tumor heterogeneity associated with patient tumors.

METHODS

To separate the effect of Pgp on intracellular paclitaxel accumulation from its effects on drug sensitivity, we compared the drug activity at various extracellular and intracellular drug concentrations using the human breast MCF7 tumor cells and its mdr1-transfected variant BC19 cells.

RESULTS

Compared to MCF7 cells, BC19 cells showed a 9-fold higher Pgp level and >13-fold higher mdrl expression. Intracellular paclitaxel accumulation was 80-130% lower in BC19 cells when the extracellular concentrations were < or = 100 nM, but the difference was reduced to <15% differences at higher extracellular concentrations of > or = 1,000 nM. For the G2/M block effect MCF7 cells were 43-fold more sensitive than BC19 cells at equal extracellular concentration, and 3.5-fold more sensitive at comparable intracellular concentrations. On the contrary. BC19 cells were more sensitive to the apoptotic effect: BC19 cells showed equal or higher apoptosis compared to MCF7 cells at extracellular concentrations above 100 nM, and a 30-100% higher apoptosis at comparable intracellular concentrations.

CONCLUSIONS

These results confirm our previous observations in patient tumors and indicate that enhanced Pgp expression is associated with enhanced sensitivity to the apoptotic effect of paclitaxel and reduced sensitivity to its G2/M block effect, via yet-unknown mechanisms that are unrelated to the effect of Pgp on intracellular drug accumulation.

Long-term follow-up on an intensified treatment regimen for advanced resectable head and neck squamous cell carcinomas

From February 1993 through July 1994, 37 patients with stage III-IV squamous cell carcinomas of the oral cavity, oropharynx, or hypopharynx (stage II-IV) were registered to a treatment regimen consisting of preoperative continuous infusion cisplatin (80 mg/m2/80 hours) with hyperfractionated external beam radiotherapy (9.1 Gy/7 fractions of 1.3 Gy BID), surgical resection, intraoperative radiotherapy (7.5 Gy), and postoperative radiotherapy (40 Gy) with concurrent cisplatin (100 mg/m2 x 2 courses). The objectives of the regimen were to improve patient compliance while also increasing treatment intensity. The purpose of this article is to report the local, regional (nodal), and distant disease control of these patients after an extended time at risk (median 40 months). Overall compliance (73%), local control at primary site (97%), and regional nodal control (95%) were excellent. The rate of distant metastasis was 19%. Absolute survival at 48 months was 45.9%.

Determinants of paclitaxel uptake, accumulation and retention in solid tumors

This report addresses the determinants of the rate and extent of paclitaxel accumulation in tumors. In a 2-dimensional system such as monolayers where the drug is directly in contact with tumor cells, drug accumulation is determined by the extracellular-to-intracellular concentration gradient, the drug binding to extracellular and intracellular macromolecules, the presence of the mdrl p-glycoprotein (Pgp). and the time-dependent and drug concentration-dependent changes in tubulins and cell density. Intracellular pharmacokinetic models were developed to depict the effects of these parameters. Computer simulation results indicate that at the clinically relevant concentration range of 1 to 1,000 nM, (a) the binding affinity and the number of intracellular saturable drug binding sites are important for drug accumulation at low and high extracellular concentrations, respectively, (b) saturation in the drug binding to the high affinity intracellular binding sites (e.g., tubulin/microtubule) occurs at extracellular drug concentration above 100 nM, (c) treatment with 1,000 nM paclitaxel for >4 hr results in increased levels of tubulin/microtubule and consequently increased intracellular drug accumulation, whereas the continued cell proliferation after treatment with low drug concentrations results in reduced intracellular accumulation, and (d) saturation of Pgp in mdr1-transfected cells occurs at the high end of the clinically relevant concentration range. In a 3-dimensional system such as the solid tumor histocultures, which contain tumor cells as well as stromal cells, the drug accumulation into the inner cell layers is determined by the unique properties of solid tumors, including tumor cell density and spatial arrangement of tumor and stromal tissues. Most interestingly, drug penetration is modulated by the drug-induced apoptosis; the reduced cell density due to apoptosis results in an enhancement of the rate of drug penetration into the inner cell layers of solid tumors. In conclusion, the uptake, accumulation, and retention of paclitaxel in solid tumors are determined by (a) factors that are independent of biological changes in tumor cells induced by paclitaxel, i.e., ratio of extracellular and intracellular concentrations, and drug binding to extracellular and intracellular macromolecules, and (b) factors that are dependent on the time- and drug concentration-dependent biological changes induced by paclitaxel, i.e., induction of apoptosis, enhancement of tubulin/microtubule production, and induction of Pgp expression.

Expression of DT-diaphorase and cytochrome P450 reductase correlates with mitomycin C activity in human bladder tumors

Mitomycin C (MMC) is activated by DT-diaphorase (DTD) and cytochrome P450 reductase (P450R). In cancer cell lines, MMC cytotoxicity is correlated with DTD and P450R expression levels. The present study investigated the relationship between enzyme expression/activity and MMC cytotoxicity in patient bladder tumors. DTD and P450R expression was detected by competitive reverse transcription-PCR and their activity was measured by bioreductive assays. The expression of DTD and P450R in patient tumors (n = 29), as ratios to beta-actin levels, varied from 0 to 90% and 0 to 29%, respectively. The DTD expression was significantly correlated with P450R expression (r(2), 0.32; P < 0.01), whereas the average DTD level was 2-fold higher than that of P450R (P < 0.01). Among the 29 tumors, 21 provided sufficient materials to evaluate tumor sensitivity to MMC. The concentration of MMC required to produce 50% inhibition (IC(50)) of DNA precursor incorporation for a 2-h treatment ranged from 0.17 to 18.1 microg/ml, indicating a 110-fold intertumor variation, with the high-grade and more invasive tumors being less chemosensitive compared with the low-grade and less invasive tumors. Tumor sensitivity to MMC, as indicated by the inverse of IC(50) values, was positively correlated with the expression of DTD (r(2), 0.28; P < 0.05) and P450R (r(2), 0.26; P < 0.05). Multivariate analysis indicates DTD expression and P450R expression as better determinants of MMC activity compared with other pathobiological factors (e.g., tumor grade, stage, and labeling index) that have been shown to significantly correlate with MMC activity. Eleven tumors were studied for the relationship between gene expression level and enzyme activity of DTD and P450R. The DTD activity was significantly correlated with the gene expression level (r(2), 0.84; P < 0.001). For P450R, there is a trend of a correlation between enzyme activity and its mRNA level, but the correlation was not statistically significant (r(2), 0.28; P = 0.09). These data indicate that the sensitivity of patient bladder tumors to MMC is correlated with the expression of DTD and P450R in tumors and suggest that the lower expression of these enzymes in the high-grade and more invasive tumors is a cause of the lower efficacy of intravesical MMC in these tumors.

Methods to improve efficacy of intravesical mitomycin C: results of a randomized phase III trial

BACKGROUND

Intravesical chemotherapy (i.e., placement of the drug directly in the bladder) with mitomycin C is beneficial for patients with superficial bladder cancer who are at high risk of recurrence, but standard therapy is empirically based and patient response rates have been variable, in part because of inadequate drug delivery. We carried out a prospective, two-arm, randomized, multi-institutional phase III trial to test whether enhancing the drug's concentration in urine would improve its efficacy.

METHODS

Patients with histologically proven transitional cell carcinoma and at high risk for recurrence were eligible for the trial. Patients in the optimized-treatment arm (n = 119) received a 40-mg dose of mitomycin C, pharmacokinetic manipulations to increase drug concentration by decreasing urine volume, and urine alkalinization to stabilize the drug. Patients in the standard-treatment arm (n = 111) received a 20-mg dose without pharmacokinetic manipulations or urine alkalinization. Both treatments were given weekly for 6 weeks. Primary endpoints were recurrence and time to recurrence. Treatment outcome was examined by use of Kaplan-Meier analysis with log-rank tests. Statistical tests were two-sided.

RESULTS

Patients in the two arms did not differ in demographics or history of intravesical therapy. Dysuria occurred more frequently in the optimized arm but did not lead to more frequent treatment termination. In an intent-to-treat analysis, patients in the optimized arm showed a longer median time to recurrence (29.1 months; 95% confidence interval [CI] = 14.0 to 44.2 months) and a greater recurrence-free fraction (41.0%; 95% CI = 30.9% to 51.1%) at 5 years than patients in the standard arm (11.8 months; 95% CI = 7.2 to 16.4 months) and 24.6% (95% CI = 14.9% to 34.3%) (P =.005, log-rank test for time to recurrence). Improvements were found in all risk groups defined by tumor stage, grade, focality, and recurrence.

CONCLUSIONS

This study identified a pharmacologically optimized intravesical mitomycin C treatment with statistically significantly enhanced efficacy.

A quantitative assay of telomerase activity

PURPOSE

Telomerase is a ribonucleoprotein that extends telomeres at the ends of chromosome. Increased telomerase activity is associated with cellular immortality. The currently available assay for telomerase, i.e., telomeric repeat amplification protocol (TRAP), consists of 2 steps: (a) telomerase-mediated extension of an oligonucleotide primer by the enzyme-containing extracts of cells and tissues, and (b) amplification of the telomerase-extended primer products by polymerase chain reaction (PCR) and detection of the PCR products. It is generally accepted that the current TRAP assay lacks quantitative precision. The present study was to develop a quantitative telomerase assay with greater precision and sensitivity.

METHODS

This new method used the primer extension method as in TRAP, plus the following modifications: (a) used a lysis buffer that yielded complete lysis of nuclei; (b) removal of PCR inhibitors by phenol/chloroform extraction after primer extension; and (c) used primers for the internal standard that were designed to reduce their competition with the telomerase products for PCR.

RESULTS

The modified method showed a good correlation (r2 = 0.99, P < 0.001) between telomerase amount (expressed as total protein in cell lysate) and its activity (expressed as telomerase products). Compared to the conventional TRAP, the new method (a) was more sensitive (average of 5.5-fold in cultured cancer cells and >5.9-fold in patient tumors), (b) had a lower inter- and intra-day variability (>3fold), and (c) showed a 2 to 4-fold broader range of linearity in the standard curve. The higher assay sensitivity further enabled the use of a nonradioactive method, i.e., ethidium bromide staining of DNA, to detect the TRAP products, as opposed to the use of radioactive nucleotide and the more labor-intensive autoradiography mandated by the conventional TRAP.

CONCLUSION

We report here a quantitative assay for telomerase activity in cultured human cancer cells and patient tumors.

Enhancement of paclitaxel delivery to solid tumors by apoptosis-inducing pretreatment: effect of treatment schedule

The limited penetration of paclitaxel into solid tumors may limit its therapeutic efficacy. We recently showed a correlation between an increase in interstitial space and an enhancement of drug delivery in solid tumors. The present study evaluated whether this observation can be used to develop a treatment strategy, where an apoptosis-inducing pretreatment with paclitaxel is used to enhance its own delivery to solid tumors. In histocultures of human pharynx FaDu xenograft tumors, pretreatment with 1 microM nonradiolabeled paclitaxel, which resulted in approximately 25% apoptosis and a 25% reduction in cell density, enhanced the penetration rate of [(3)H]paclitaxel. Likewise, dividing a total drug exposure to two treatments, separated by an interval to allow apoptosis to occur, resulted in higher drug penetration rate and accumulation compared with giving the same drug exposure continuously. Similar results were obtained in rats bearing subcutaneously implanted prostate MAT-LyLu tumors; fractionation of the dose, to include 1) a pretreatment that yielded sufficient and clinically relevant plasma concentration to induce apoptosis and 2) a second dose given at an interval selected to allow apoptosis and reduction in tumor cell density to occur, resulted in higher tumor concentration compared with other treatments using the same total dose but either did not include an apoptosis-inducing pretreatment or did not allow for apoptosis to occur. We conclude that the pharmacological effect of paclitaxel affects its own delivery to solid tumors and that modifications of the paclitaxel treatment schedule can enhance drug delivery in solid tumors.

A pharmacodynamic analysis method to determine the relative importance of drug concentration and treatment time on effect

PURPOSES

The pharmacodynamics of most drugs follow the empirical relationship, C(n) x T = h, where C is drug concentration, T is exposure time and h is drug exposure constant. The value of n indicates the relative importance of C and T in determining the effect. An n value greater than 1.0 indicates that for two infusions that produce the same C x T, a short infusion that delivers high concentrations over a short duration will produce a greater C(n) x T and therefore a greater effect, compared to a long infusion that delivers lower concentrations. The reverse is true for an n value less than 1.0 and would support the use of a slow infusion. Hence, it is important to determine the n values and whether the n value significantly differs from 1.0. This report describes a three-step method for this purpose.

METHODS

First, we obtained experimental data on the relationship between drug concentration, treatment time and effect, and analyzed the data with a three-dimensional surface response method to obtain the pharmacodynamic model parameters and the magnitude of data variability. The experiments used mitomycin C and two human cancer cell lines, i.e. bladder RT4 and pharynx FaDu cells. The n values obtained from four experiments ranged from 1.04 to 1.16 for FaDu cells and from 1.14 to 1.46 for RT4 cells. The variability in the effect data decreased from 11.9% at 0% effect to 6.14% at 100% effect. Second, these results were used with Monte Carlo simulations to generate 100 concentration-time-effect data sets, which contained randomly and normally distributed data variability comparable to the experimentally observed variability, for each experimentally determined n value. This is analogous to performing 100 experiments under the same experimental conditions. Third, we analyzed the simulated data sets to obtain 100 estimated n values. The frequency with which these estimated n values fell above or below 1.0 indicated the probability that the experimentally determined n value used in the Monte Carlo simulations was truly different from 1.0. We defined this frequency for individual experiments as F(one), and calculated the overall probability for multiple experiments (F(multiple)). A probability of greater than 97.5% (i.e. P < 0.05 for a two-tailed test) was considered statistically significant.

RESULTS

Analysis of the mitomycin C pharmacodynamic data yielded F(one) and F(multiple) of 99% to 100% for FaDu and RT4 cells, indicating that the n values for these cells were significantly higher than 1.0. A comparison of the statistical significance of the n value analyzed by the three-step pharmacodynamic analysis method, a conventional statistical method such as the Student's t-test and nonlinear regression analysis, indicated two advantages for the pharmacodynamic method: fewer experiments were required (theoretically only one experiment with three replicates would be sufficient) and a higher statistical significance of the n value was obtained.

CONCLUSIONS

In summary, the three-step pharmacodynamic study design and analysis method can be used to define the relative importance of drug concentration and treatment time on drug effect.

Fibroblast growth factors: an epigenetic mechanism of broad spectrum resistance to anticancer drugs

Based on the observation that removal of tumors from metastatic organs reversed their chemoresistance, we hypothesized that chemoresistance is induced by extracellular factors in tumor-bearing organs. By comparing chemosensitivity and proteins in different tumors (primary vs. metastases) and different culture systems (tumor fragment histocultures vs. monolayer cultures derived from the same tumor), we found elevated levels of acidic (aFGF) and basic (bFGF) fibroblast growth factors in the conditioned medium (CM) of solid and metastatic tumors. These CM induced broad spectrum resistance to drugs with diverse structures and action mechanisms (paclitaxel, doxorubicin, 5-fluorouracil). Inhibition of bFGF by mAb and its removal by immunoprecipitation resulted in complete reversal of the CM-induced chemoresistance, whereas inhibition/removal of aFGF resulted in partial reversal. Using CM that had been depleted of aFGF and/or bFGF and subsequently reconstituted with respective human recombinant proteins, we found that bFGF but not aFGF induced chemoresistance whereas aFGF amplified the bFGF effect. aFGF and bFGF fully accounted for the CM effect, indicating these proteins as the underlying mechanism of the chemoresistance. The FGF-induced resistance was not due to reduced intracellular drug accumulation or altered cell proliferation. We further showed that an inhibitor of aFGF/bFGF (suramin) enhanced the in vitro and in vivo activity of chemotherapy, resulting in shrinkage and eradication of well established human lung metastases in mice without enhancing toxicity. These results indicate elevated levels of extracellular aFGF/bFGF as an epigenetic mechanism by which cancer cells elude cytotoxic insult by chemotherapy, and provide a basis for designing new treatment strategies.

Computational model of intracellular pharmacokinetics of paclitaxel

The intracellular pharmacokinetics of paclitaxel is closely related to its pharmacodynamics. Although drug transport across the cell membrane and extracellular and intracellular drug binding have been shown to affect intracellular drug accumulation, their quantitative relationship is unknown. This study was designed to establish a mathematical model for computing the intracellular paclitaxel pharmacokinetics. As a starting point, the model assumes drug transport into and out of cells via passive diffusion. Experimental data on the intracellular pharmacokinetics of [(3)H]paclitaxel were obtained using monolayer cultures of human breast MCF7 tumor cells, which have negligible expression of the mdr1 P-glycoprotein. The results indicate that, in addition to drug binding and microtubule concentration, changes in cell number due to cell growth and drug effects also affected intracellular drug accumulation. A kinetic model was developed to describe several concomitant processes: 1) saturable drug binding to extracellular proteins, 2) saturable and nonsaturable drug binding to intracellular components, 3) time- and concentration-dependent drug depletion from culture medium, 4) cell density-dependent drug accumulation, and 5) time- and drug concentration-dependent enhancement of tubulin concentration. The model was validated by the close prediction (<7% deviation) of the effects of extracellular-to-intracellular concentration gradient and cell density on the kinetics of drug accumulation and efflux. This model was used to predict the effects of changing several parameters (number and binding affinity of intracellular binding sites, free fraction, and concentration of drug in extracellular fluid) on intracellular drug accumulation. In conclusion, the computational model of intracellular paclitaxel pharmacokinetics provides the means to predict drug concentration in cells.

Intensification regimen 2 for advanced head and neck squamous cell carcinomas

OBJECTIVE

To determine the feasibility, toxicity, and compliance of an intense treatment regimen for patients with advanced, previously untreated, resectable head and neck squamous cell carcinomas.

DESIGN

Prospective, nonrandomized, controlled (phase 1 or 2) clinical trial; median time at risk, 25 months (range, 7 days to 36 months).

SETTING

Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, The Ohio State University, Columbus.

PATIENTS

Forty-three patients (median age, 59 years; range, 32-76 years) with resectable, previously untreated stage III or IV squamous cell carcinomas of the oral cavity, oropharynx, or hypopharynx or stage II squamous cell carcinomas of the hypopharynx (referred sample of patients).

INTERVENTIONS

Days 1 to 4, perioperative, slightly accelerated, hyperfractionated radiotherapy (9.1 Gy) to off cord fields; days 1 to 3, cisplatin, 30 mg/m2 per day; day 4, surgical resection and intraoperative radiotherapy boost (7.5 Gy); days 45 to 52, postoperative radiotherapy (40 Gy to the primary site and upper neck and 45 Gy to the supraclavicular areas); days 24, 45, and 66, paclitaxel, 135 mg/m2 per 24 hours, with routine granulocyte colony-stimulating factor support; and days 25 and 46, cisplatin, 100 mg/m2.

MAIN OUTCOME MEASURES

Toxicity, compliance, local control, and distant metastatic rates.

RESULTS

Patient compliance was 91% (39 of 43 patients), but protocol compliance was only 58% (25 of 43 patients), reflecting increased toxicity of the systemic regimen (2 [5%] of the 43 patients experienced grade 5 hematologic toxicity due to the regimen; 16 [37%], grade 4; and 10 [23%], grade 3). Local-regional control was 92% (23 of 25 patients), and the distant metastatic rate was 8% (2 of 25) in patients completing treatment per protocol. One patient had surgical salvage of a second primary tumor.

CONCLUSIONS

Local control and patient compliance were encouraging, but systemic toxicity was unacceptable. Thus, the paclitaxel was changed to a weekly regimen.

Cremophor reduces paclitaxel penetration into bladder wall during intravesical treatment

PURPOSE

We have previously shown that paclitaxel, when dissolved in water and instilled into the bladder, readily penetrates the urothelium. The FDA-approved formulation uses Cremophor and ethanol to dissolve paclitaxel. In the present study, the effects of this solvent system on the urine, bladder tissue, and plasma pharmacokinetics of intravesical paclitaxel were evaluated.

METHODS

Plasma, urine, and tissue pharmacokinetics were determined in five dogs treated for 120 min with paclitaxel (500 microg per 20 ml of 0.22% w/v Cremophor and 0.21% v/v ethanol) by intravesical instillation. Equilibrium dialysis was used to determine the free fraction of paclitaxel and the presence of Cremophor micelles was verified using a fluorescent probe method.

RESULTS

The average bladder tissue concentration was > 1600-fold higher than the plasma concentration. Comparison of the results for paclitaxel dissolved in Cremophor/ethanol with our previous results of paclitaxel dissolved in water (500 microg per 20 ml) indicates that Cremophor/ethanol decreased the paclitaxel partition across the urothelium and reduced the average bladder tissue concentration by 75%, but did not alter the rate of paclitaxel penetration across the bladder wall, the urine pharmacokinetics or the plasma pharmacokinetics of paclitaxel. For Cremophor, the urine concentrations during the 120-min treatment ranged from 0.12% to 0.22%, and the concentration in bladder tissue from 0.00004% to 0.0009%. The threshold Cremophor concentration for micelle formation was 0.008%. We found that ethanol at concentrations up to 1% and Cremophor at concentrations below 0.01% did not alter the free fraction of paclitaxel, whereas Cremophor at higher concentrations, i.e. 0.065% and 0.25%, significantly reduced the free fraction by two- to six-fold, respectively. These results indicate that during intravesical instillation of the FDA-approved paclitaxel formulation, the concentration of Cremophor in urine was sufficient to form micelles, resulting in sequestration of paclitaxel into micelles, reduction in the free fraction of paclitaxel and consequently a reduction in paclitaxel penetration across the urothelium. In contrast, the Cremophor concentrations in bladder tissue were inadequate to form micelles and thus did not alter the drug penetration through the bladder tissue.

CONCLUSIONS

We conclude that intravesical paclitaxel treatment using the FDA-approved formulation provides a significant bladder tissue targeting advantage, although the advantage is lower than when paclitaxel is dissolved in water.

Regional heterogeneity and pharmacodynamics in human solid tumor histoculture

PURPOSE

Human solid tumor histocultures represent a clinically relevant experimental system for pharmacodynamic study. The evaluation of the drug-induced antiproliferative effect in histocultures is usually performed by manual microscopic scoring of individual cells. This procedure, because of its labor intensive nature, is performed on a single microscopic field, i.e. the field with the highest proliferative activity. Because regional heterogeneity in a solid tumor may result in different drug sensitivities in different parts of a tumor, there is the question as to whether the pharmacodynamic data determined in the most proliferative field is representative of those in the whole tumor. This question was addressed in the present study.

METHODS

A recently developed automated image analysis method was used to measure the labeling index of tumor cells. The drug-induced inhibition of DNA precursor incorporation into nuclei of cells in the region with the highest proliferative activity was compared to the inhibition in cells in the entire histoculture. This study was performed in human bladder tumor histocultures treated with several drugs (doxorubicin, mitomycin C, paclitaxel and 5-fluorouridine). A total of 724 pairs of data obtained from untreated and drug-treated histocultures (each data point representing the average of 1 to 6 tumor histocultures) were analyzed.

RESULTS

The absolute value of the labeling index in the most proliferative region (LI(one)) was significantly higher than the absolute value of the labeling index in the whole tumor (LI(all)), in both untreated and drug treated samples (mean difference of 18%, range 1-27%). However, when the absolute LI values in drug-treated samples were normalized to the values in untreated controls and expressed as a percentage of control, and used to construct the concentration-response curves, the two curves obtained using LI(one) and LI(all) yielded comparable pharmacodynamic parameters, i.e. curve shape parameters and drug concentrations that produce 30, 50, and 70% inhibition.

CONCLUSION

These results indicate comparable pharmacodynamics in the most proliferative region and the whole tumor, and confirm the validity of using the most proliferative field for evaluating chemosensitivity in solid tumor histocultures.

Kinetics of hallmark biochemical changes in paclitaxel-induced apoptosis

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.

Determinants of paclitaxel penetration and accumulation in human solid tumor

The present study examined the determinants of the penetration and accumulation of [(3)H]paclitaxel (12-12,000 nM) in three-dimensional histocultures of patient tumors and of a human xenograft tumor in mice. The results showed 1) significant and saturable drug accumulation in tumors, 2) extensive drug retention in tumors, and 3) a slower penetration but a more extensive accumulation in the xenograft tumor compared with patient tumors. Drug penetration was not rate-limited by drug diffusion from medium through the matrix supporting the histocultures. The difference in the expression of the mdr1 P-glycoprotein did not fully account for the difference in the drug accumulation in xenograft and patient tumors. Autoradiography and imaging were used to evaluate the spatial relationship between tumor architecture, tumor cell distribution, and drug distribution as a function of time and initial drug concentration in culture medium. The tumor cell density and the kinetics of drug-induced apoptosis were also evaluated. The results indicate that a high tumor cell density is a barrier to paclitaxel penetration and that the apoptotic effect of paclitaxel enhances its penetration in solid tumor. These factors are responsible for the time- and concentration-dependent drug penetration rate, with drug penetration confined to the periphery until apoptosis and reduction of epithelial cell density occurred at 24 h, after which time paclitaxel penetrated the inner parts of the tumor.

Relationship between paclitaxel activity and pathobiology of human solid tumors

We previously reported the pharmacodynamics of antiproliferative and apoptotic effects of paclitaxel in histocultures of bladder, breast, head and neck, ovarian, and prostate tumors obtained from patients. This study examined the relationship between paclitaxel pharmacodynamics and tumor pathobiological parameters [i.e., stage, grade, proliferation status, expression of P-glycoprotein (Pgp), p53, and Bcl-2]. Pgp, p53, and Bcl-2 proteins were detected by immunohistochemical methods. The drug sensitivity rank order of the five tumor types is as follows: prostate > or = head and neck = bladder > breast > ovarian for the antiproliferative effect and breast = ovarian = head and neck > prostate = bladder for the apoptotic effect. When the pathobiological parameters were considered as single parameters, the antiproliferative effect was inversely correlated with tumor stage, grade, labeling index (LI), and expression of Pgp, p53, and Bcl-2 (P < 0.05 in all cases). The apoptotic effect was positively correlated with Pgp expression, LI, and tumor grade (P < 0.01) but was not related to tumor stage and expression of p53 and Bcl-2 (P > 0.2). Results of multivariate analysis indicated that the maximum antiproliferative effect was best predicted by the combination of tumor stage and expression of Pgp and p53 (inverse correlation) and that the maximum apoptotic effect was best predicted by the combination of tumor LI and Pgp expression (positive correlation). In summary, these results indicate that the two major effects of paclitaxel in human solid tumors, i.e., antiproliferation and apoptosis, correlate with different tumor properties. The second finding that drug-induced apoptosis was equal or higher in tumors that expressed Pgp, p53, and Bcl-2 compared to tumors that did not express these proteins supports the use of paclitaxel in treating Pgp-, p53- and Bcl-2-positive tumors.

Antiproliferative and cytotoxic effects of geldanamycin, cytochalasin E, suramin and thiacetazone in human prostate xenograft tumor histocultures

PURPOSE

We have shown that the three human prostate xenograft tumors, i.e. the androgen-dependent CWR22 tumor, and the androgen-resistant CWR22R and CWR91 tumors, are comparable to patient tumors in their expression of prostate specific antigen, multidrug resistance p-glycoprotein, p53 and Bcl-2 and in their sensitivity to doxorubicin and paclitaxel. The present study used histocultures of these xenograft tumors to evaluate the antiproliferative and cytotoxic effects of several drugs (geldanamycin, cytochalasin E and thiacetazone), which have diverse action mechanisms and have shown activity against primary cultures of human prostate cancer cells. Suramin, a clinically active compound was included for comparison. Methods. The antiproliferative effect of 96 h drug treatment was measured by inhibition of DNA precursor incorporation, and the cytotoxic or cell kill effect was measured by in situ DNA end labeling of apoptotic and necrotic cells and by reduction of live cell density.

RESULTS

The rank order of molar potency was geldanamycin > cytochalasin E > suramin > or = thiacetazone. Thiacetazone produced antiproliferation only in CWR22 tumor and had no cytotoxicity, whereas the other three drugs produced both antiproliferation and cytotoxicity in all three tumors. Geldanamycin, but not cytochalasin E and suramin, showed greater antiproliferation and cytotoxicity in tumor cells compared to normal stromal cells. The two androgen-resistant tumors were 4 to >40-fold less sensitive than the androgen-dependent tumor to drug-induced antiproliferation but were about equally or 4 to >20-fold more sensitive to drug-induced cytotoxicity. The ratios of drug concentrations that produced 50% antiproliferation to the concentrations that produced 50% cytotoxicity ranged from <0.04 to 0.3 in CWR22 tumor, but ranged from 0.3 to 2.7 in CWR22R and CWR91 tumors, indicating a shift from antiproliferation as the predominant drug effect in the androgen-dependent tumor to cytotoxicity in the androgen-resistant tumors.

CONCLUSIONS

Our results indicate (a) differential drug effects in human prostate xenograft tumors with antiproliferation and cytotoxicity as the predominant drug effect in the androgen-dependent and androgen-resistant tumors, respectively, (b) that progression of tumors from androgen-dependent state to androgen-resistant state appears to be associated with a lower sensitivity to drug-induced antiproliferation and an equal or greater sensitivity to drug-induced cytotoxicity, and (c) that geldanamycin but not thiacetazone warrants further development.

Proliferation indices as molecular pharmacodynamic endpoints in evaluation of anticancer drug effect in human solid tumors

PURPOSE

The present study compared proliferative indices, i.e. incorporation of DNA precursor (i.e. thymidine or TdR, and bromodeoxyuridine or BrdU) and expression of proliferating cell nuclear antigen (PCNA), as molecular pharmacodynamic endpoints in evaluation of anticancer drug effect in human solid tumors.

METHODS

Tumor specimens obtained from patients were grown as histocultures. After treatment with doxorubicin, mitomycin C, and/or paclitaxel, cells labeled by [3H]TdR were identified using autoradiography, and cells labeled by BrdU and PCNA were identified using immunohistochemical techniques. Drug effect was measured as reduction of DNA precursor-labeled cells or PCNA-expressing cells.

RESULTS

The results indicate that (a) the two DNA precursors, TdR and BrdU, labeled the same cells and resulted in identical pharmacodynamics, (b) the pharmacodynamics established using inhibition of DNA precursor incorporation were qualitatively and quantitatively different from the pharmacodynamics established using inhibition of PCNA expression, (c) the inhibition of PCNA expression was erratic in some tumors, and (d) the differences in pharmacodynamics established using the two end points are drug-specific, with greater differences for paclitaxel than for mitomycin C.

CONCLUSIONS

The erratic results measured by the PCNA labeling method suggest that this method may be less reliable than the conventional DNA precursor labeling method. The finding of identical pharmacodynamics of doxorubicin and paclitaxel established using BrdU and [3H]TdR indicates that the two precursors are interchangeable. Because the methodology for detecting BrdU incorporation requires less time and does not require the use of radioactivity, we conclude that inhibition of BrdU incorporation represents a useful endpoint for evaluating the antiproliferative activity of anticancer drugs in human solid tumors.

Cytostatic and apoptotic effects of paclitaxel in human breast tumors

PURPOSE

We have previously reported incomplete cytotoxic responses of other human solid tumors (bladder, head and neck, ovarian and prostate) to paclitaxel. This finding is qualitatively different from the nearly complete response observed in monolayer cultures of human cancer cell lines. The present study examined the pharmacodynamics of paclitaxel in human breast tumors.

METHODS

Three-dimensional histocultures of patient tumors were used. The cytostatic effect was evaluated by measurement of the inhibition of 48-h cumulative bromodeoxyuridine (BrdUrd) incorporation. The apoptotic effect was evaluated in terms of morphological changes and by in situ DNA end labeling.

RESULTS

Paclitaxel produced partial cytostasis (approximately 30% maximum) and induced apoptosis (maximum apoptotic index of 3.3% to 29%) in all 15 tumors. More than 95% of apoptotic cells were BrdUrd labeled, but not all BrdUrd-labeled cells were apoptotic. The maximal apoptotic indices in the tumors were significantly correlated with the BrdUrd labeling index of untreated controls (r2 = 0.63, P < 0.01). The maximum apoptotic effect was observed at a tenfold lower drug concentration (0.1 microM) compared to the maximum cytostatic effect (1 microM). Neither of these effects was enhanced by increasing the drug concentration to 10 microM.

CONCLUSIONS

The pharmacodynamics of paclitaxel in human breast tumors are comparable to those found in other human solid tumors. The labeling of apoptotic cells by BrdUrd and the correlation between the proliferation index and apoptosis suggest that drug-induced apoptosis is linked to cell proliferation and is completed after DNA synthesis. The finding that maximal cytostatic and apoptotic effects of paclitaxel were achieved at or below the clinically achievable concentration of 1 microM suggests further increasing the dose to elevate plasma concentration beyond 1 microM may not improve treatment outcome.

Androgen-dependent and -independent human prostate xenograft tumors as models for drug activity evaluation

The present study evaluated three human prostate xenograft tumors (CWR22, CWR22R, and CWR91) as models for drug activity evaluation. The chemosensitivity and the expression of several proteins (i.e., p-glycoprotein or Pgp, prostate specific antigen or PSA, p53, and Bcl-2) in xenograft tumors were compared with those in patient tumors obtained through radical prostatectomy (n = 26). CWR22 is androgen-dependent, CWR22R is the androgen-independent subline of CWR22, and CWR91 is a separately derived androgen-independent tumor. The results of immunohistochemical and/or Western blot analysis indicate that the expression of PSA, Pgp, p53, and Bcl-2 in the three CWR xenograft tumors are representative of their expression in 100, 85, 90, and 60%, respectively, of patient tumors. The responses of histocultures of xenograft tumors to doxorubicin and paclitaxel, including inhibition of DNA precursor incorporation and cell death induction, were qualitatively similar to the responses of patient tumors. For example, in all three xenograft and patient tumors, doxorubicin produced complete antiproliferation and cytotoxicity (ie., cell kill) whereas paclitaxel produced incomplete effects. A comparison of the concentration-effect relationships in xenograft and patient tumors (population median values) indicates that the chemosensitivity observed in patient tumors is represented by the chemosensitivity of one or more of the three xenograft tumors, as follows: (a) the three xenograft tumors and patient tumors responded equally to doxorubicin-induced antiproliferation; (b) CWR22R, CWR91 and patient tumors responded equally to doxorubicin-induced cytotoxicity, whereas CWR22 was 2-3-fold less sensitive; (c) CWR22 and CWR22R tumors were less sensitive to paclitaxel-induced antiproliferation compared with patient tumors, whereas CWR91 was several-fold more sensitive; and (d) CWR22, CWR22R and patient tumors responded equally to paclitaxel-induced cytotoxicity, whereas CWR91 was 2-3-fold more sensitive. The results of this study indicate that the three xenograft tumors, which show chemosensitivity comparable with the results of > or =50% patient tumors and encompass the majority of the heterogeneous patient prostate tumors in the expression of Pgp, PSA, p53 and Bcl-2 proteins, are useful models for drug activity evaluation.

Pharmacodynamics of immediate and delayed effects of paclitaxel: role of slow apoptosis and intracellular drug retention

The kinetics of the time-dependent antitumor effects of paclitaxel are not fully understood; some literature reports indicate a higher activity by prolonging treatment durations, whereas other reports indicate no enhancement under in vitro conditions. The present study was designed to address this controversy and to determine the mechanism of the higher cytotoxicity associated with longer treatment durations. Six human epithelial cancer cell lines (bladder RT4, breast MCF7, pharynx FaDu, ovarian SKOV3, and prostate PC3 and DU145) were used. To determine whether the higher activity observed for the longer treatment durations is due to a delayed exhibition of drug effects and/or a reflection of cumulative effects that required a continuous drug exposure, cells were treated with paclitaxel for 3-96 h and then either: (a) immediately processed for drug effect measurement; or (b) washed, incubated in drug-free medium, and processed for drug effect measurement at 96 h. The overall drug effect (i.e., combination of cytostatic and apoptotic effects) was determined by the sulforhodamine B assay, which measures the cellular protein. In addition, to determine whether apoptosis occurs with a time delay, apoptosis was measured in cells that were collected immediately after drug treatment for various durations or in cells that were treated with drugs for 3 h but collected at later time points. Apoptosis was determined using agarose gel electrophoresis and by measuring the cytoplasmic DNA-histone complex using ELISA. The contribution of the intracellularly retained drug to the delayed drug effect was studied by characterizing the kinetics of cellular drug uptake and efflux and by examining the effect of removal of the intracellularly retained drug. All six cell lines showed similar results, as follows: (a) paclitaxel produced cytotoxicity that was exhibited immediately after treatment (immediate effect) and after treatment was terminated (delayed effect); (b) the immediate and delayed effects showed different pharmacodynamics. The immediate effect increased with treatment duration and drug concentration. For the delayed effect, all treatments produced the same maximum effect at 96 h, although treatments for < or = 12 h showed higher IC50s than longer treatments, whereas treatments for > or = 24 h showed indistinguishable IC50s; (c) treatment for as brief as 3 h was sufficient to induce apoptosis, which occurred with a lag time of about 24 h, although longer treatments produced a greater extent of apoptosis; (d) The intracellular and extracellular concentrations reached an equilibrium at approximately 5 h, which rules out slow and/or insufficient uptake as the cause of the lower effects at shorter treatment times (i.e., < 24 h); (e) upon removal of drug-containing medium, the amount of drug retained intracellularly was about 10% of the applied dose and was reduced to approximately 0.5% after three successive washes, separated by 3-h equilibration periods; and (f) the delayed effect of the 3-h treatment was largely due to the drug retained intracellularly, whereas the delayed effect of the 24 h treatment was independent of the drug retained intracellularly. In conclusion, in human epithelial cancer cells, paclitaxel-induced cytotoxicity occurred after termination of drug treatment, which was partly due to the slow manifestation of apoptosis and partly due to the significant amount of drug retained intracellularly. Based on these findings and recognizing that some previous studies measured the immediate effect whereas the other studies measured the delayed effect, we propose that the conflicting data in the literature regarding the effect of treatment duration on paclitaxel activity under in vitro conditions are in part due to the different pharmacodynamics of the immediate and delayed drug effects. Furthermore, differences in the delayed effects for treatments of < 24 h and the minimal differences for treatments of > or = 24 h indicate that th

Pharmacodynamics of doxorubicin in human prostate tumors

The pharmacodynamics of doxorubicin in human prostate tumors were studied using histocultures of radical prostatectomy specimens. Drug treatment lasted 96 h. The antiproliferative effect was measured by the inhibition of DNA precursor ([3H]thymidine) incorporation, and the cytotoxic effect was measured by monitoring cells with fragmented DNA, as indicated by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay. The average [3H]thymidine labeling index in 17 tumors was 39% (range, 20-56%). The antiproliferative and cytotoxic effects were concentration dependent and reached 100% at 6 and 17 microM doxorubicin. The cytotoxic concentrations were significantly higher than the antiproliferative concentrations, indicating that prostate tumors were more sensitive to the antiproliferative effect than they were to the cytotoxic effect of doxorubicin. The antiproliferative effect was inversely correlated with patient's age (P < 0.02) and weakly correlated with LI and Gleason grade (P = 0.07 and 0.06, respectively), but it was not correlated with clinical stage, prostate-specific antigen secretion, or race of patients (P > 0.12). In contrast, the cytotoxic effect was positively correlated with Gleason grade (P < 0.05) and weakly correlated with stage (P < 0.08), but it was not correlated with the other parameters (P > 0.18). The opposite correlations between the two effects with tumor grade suggest that the two effects are not coupled. A comparison of the drug concentrations required to produce 50% antiproliferative (0.06 microM) and cytotoxic (2 microM) effects and the literature data on plasma drug concentrations derived from systemic treatment suggest that there are minimal drug effects at the clinically achievable drug concentrations and that regional delivery of doxorubicin to the prostate may be necessary to provide adequate concentrations to produce antiproliferative and cytotoxic effects.

Pharmacologic effects of paclitaxel in human bladder tumors

PURPOSE

The goal of this study was to determine whether paclitaxel, when given by a 2-h treatment, produces significant cytotoxic effects in human bladder transitional cell carcinoma and hence qualifies as a candidate drug for intravesical treatment.

METHODS

Histocultures of surgical specimens from patients (n = 16) were used.

RESULTS

Paclitaxel produced partial inhibition of DNA precursor incorporation in about 70% of tumors and induced apoptosis in about 90% of tumors, while these effects were minimal or not detectable in the remaining tumors. In the responsive tumors, the average maximal inhibition of DNA synthesis was 60% and the average maximal apoptotic index was 15%. Resistance to antiproliferative and apoptotic effects was not always found in the same individual tumors, and no relationship was found between the magnitude of antiproliferative and apoptotic effects in individual tumors. The maximal apoptotic index correlated with the LI for the untreated control (r2 = 0.42, P < 0.01). More than 95% of apoptotic cells were labeled by DNA precursor, whereas not all labeled cells were apoptotic. The pharmacologic effects of paclitaxel in bladder tumors were qualitatively equivalent to those previously found in human head and neck tumors and in human prostate tumors after treatment for longer periods of 24 to 96 h.

CONCLUSIONS

These results indicate that a 2-h paclitaxel treatment was sufficient to produce antiproliferation and apoptosis in 70-90% of human bladder tumors, and the apoptotic effect appeared to be linked to proliferation and occurred after DNA synthesis.

Cytostatic and apoptotic effects of paclitaxel in human ovarian tumors

PURPOSE

The present study evaluated the cytostatic and apoptotic effects of a 24-hr paclitaxel treatment in ovarian tumors.

METHODS

Three-dimensional histocultures of surgical specimens from patients (n = 17) were used. The cytostatic effect was measured by inhibition of 96-hr cumulative DNA precursor incorporation and induction of apoptosis was determined by morphological changes.

RESULTS

Paclitaxel produced partial inhibition of DNA precursor incorporation in about 40% of tumors (maximum inhibition of approximately 30%) and induced apoptosis in about 90% of tumors (maximum apoptotic index of approximately 15%). In responsive tumors, maximum cytostatic and apoptotic effects were achieved at < or = 1 microM with no further enhancement by increasing the drug concentration to 10 microM. In individual tumors, the apoptotic effect inversely correlated with cytostatic effect (r2 = 0.27, p = 0.031), and the maximal apoptotic index correlated with the LI for the untreated controls (r2 = 0.38, p < 0.01). More than 95% of apoptotic cells after paclitaxel treatment were labeled with DNA precursor. The incomplete cytostatic and apoptotic effects of paclitaxel and the link between DNA synthesis and apoptosis in ovarian tumors are similar to our previous findings in other human solid tumors.

CONCLUSIONS

These findings suggest that (a) apoptosis is the major paclitaxel effect in advanced ovarian tumors, (b) tumor sensitivity to drug-induced cytostatic effect is opposite to sensitivity to apoptotic effect, (c) paclitaxel-induced apoptosis increases with increased cell proliferation and is completed after DNA synthesis, and (d) further increasing the dose to elevate plasma concentration beyond 1 microM may not improve treatment outcome.

Bladder tissue uptake of mitomycin C during intravesical therapy is linear with drug concentration in urine

The design of an ongoing Phase III study of intravesical mitomycin C therapy to treat bladder cancer is partly based on the assumption that drug penetration into bladder tissue is linearly related to drug concentration. The present study was designed to (a) test this assumption and (b) to compare drug concentrations in tumor and adjacent normal tissues in human bladders. We previously reported the uptake kinetics of a 20-mg dose in dog and human bladders (M. G. Wientjes et al., Cancer Res., 51: 4347-4354, 1991, and Cancer Res., 53: 3314-3320, 1993). The present study used a 40 mg/20 ml dose. Serial blood and urine samples were taken from dogs during the 120-min instillation. Bladder tissues were harvested from dogs and patients at the end of instillation. A comparison of the results of the present and previous studies indicates identical tissue penetration kinetic parameters in dogs for the two doses, i.e., a approximately 30-fold concentration drop across the urothelium and a half-width of approximately 500 microns. In addition, the average tissue concentration in dog and human bladders attained with the 40-mg dose (8.77 micrograms/g in dogs and 7.55 micrograms/g in humans) was about twice that achieved with the 20-mg dose (4.33 micrograms/g in dogs and 3.91 micrograms/g in humans). In dogs, the plasma concentration of MMC reached a steady state within 10 min; the mean maximal plasma concentration was 8.5 ng/ml. This plasma concentration is indistinguishable from the concentration derived from the 20-mg dose and indicates a minimal systemic exposure even at the higher dose. The average MMC concentration in tumor-bearing tissues was about 40% higher than the concentration in adjacent normal tissues (P = 0.01). In conclusion, the linear relationship between drug uptake in bladder tissues and drug concentration in urine supports the assumption used in the design of the ongoing Phase III clinical trial.

Application of automatic thresholding in image analysis scoring of cells in human solid tumors labeled for proliferation markers

We previously reported an image analysis program that uses four investigator-defined parameters including two thresholds, i.e., gray-level threshold (GLT) and hue threshold (HT), to determine the number of cells (TC) and the proliferating cell nuclear antigen (PCNA) or bromodeoxyuridine (BrdUrd) labeling indices (LI) in human solid tumors. The present study investigated if the accuracy and reproducibility of image analysis results can be improved by using computer-defined GLT and HT. Three investigators evaluated 142 images on 3 days, using visual analysis and four image analysis routines, which used different combinations of computer- and investigator-selected GLT and HT. The data show that image analysis using computer-selected GLT and HT yielded (i) LI of PCNA and BrdUrd that were indistinguishable from visual analysis, (ii) equal (BrdUrd LI) or better (TC and PCNA LI) inter-day reproducibility relative to visual analysis results, and (iii) results that were equally (TC) or more accurate (LI of PCNA and BrdUrd) with higher inter-day reproducibility (TC and LI of PCNA and BrdUrd) than image analysis obtained using investigator-defined thresholds. We conclude that the use of computer-defined GLT and HT improved the accuracy and reproducibility of image analysis results.

Bladder tissue pharmacokinetics and antitumor effect of intravesical 5-fluorouridine

The present study evaluates whether intravesical 5-fluorouridine (FUR), a potent fluorinated pyrimidine, is effective against bladder cancer. The tissue and plasma pharmacokinetics of i.v. and intravesical FUR were studied in dogs to determine the tissue targeting advantage by the intravesical route. The i.v. study used a bolus FUR dose of 4 mg/kg, which is tolerated in humans. The disposition of FUR was biphasic, with a peak concentration of 8.8 microgram/ml and a clearance of 127 ml/min/kg. 5-Fluorouracil was the major circulating metabolite, reaching a peak concentration of 3.2 microgram/ml. In the intravesical study, FUR (approximately 2 mg/kg in 20 ml of water) was instilled in the dog bladder. At the end of the 2-h treatment, FUR concentration in urine decreased by about 40%, due mainly to dilution by residual and newly produced urine. The concentration at the interface between urothelium and lamina propria was 14 microgram/g, or approximately 2% of the urine concentration, and declined logarithmically to 2 microgram/g in the deep muscles. The concentrations of FUR and 5-fluorouracil in plasma were below the assay detection limit of 20 ng/ml, or > 200-fold lower than the concentration after the i.v. dose (adjusted to the difference in the i.v. and intravesical dose). These data indicate a > 200-fold advantage in the reduction of systemic exposure by the intravesical route. To determine whether the achievable tissue concentrations of FUR produced significant antitumor activity, we studied the effect of FUR against human bladder tumors maintained as 3-dimensional histocultures. The FUR concentrations (IC50s) required to produce 50% inhibition of DNA precursor ([3H]thymidine or bromodeoxyuridine) incorporation in human superficial bladder tumors (i.e., Ta and T1 tumors, n = 4) and muscle-invading tumors (i.e., T3 and T4 tumors, n = 4) were 9 and 22 microgram/ml, respectively. In conclusion, intravesical FUR therapy delivers effective drug concentration to superficial bladder tissues without resulting in appreciable systemic blood concentration. We propose that intravesical FUR represents a potentially effective treatment against superficial bladder cancer.

Isocratic high-performance liquid chromatographic determination of thiacetazone by direct injection of plasma into an internal surface reversed-phase column

This report describes the determination of thiacetazone in human and rat plasma by direct-injection high-performance liquid chromatography (HPLC). Plasma filtrate (50 microliters) was injected directly into the internal surface reversed-phase (ISRP) mixed-functional phenyl column (Capcell Pak, 50 x 4.6 mm, 5 microns) and eluted with an aqueous mobile phase containing 7.5% acetonitrile at a flow-rate of 1 ml/min. With UV detection at 322 nm, thiacetazone eluted at 11.0 min whereas endogenous interferences eluted before 5 min. The lower detection limit for a 50-microliter sample at a signal-to-noise ratio of 5 was 63 ng/ml, which was several hundred fold lower than its cytotoxic concentrations determined from in vitro cell line studies. At a concentration range of 0.17 to 2.7 micrograms/ml, the recovery of thiacetazone was 98.0 +/- 4.4% (mean +/- S.D.). The intra- and inter-day coefficients of variation were 3.0 +/- 1.4% and 4.2 +/- 2.1%, respectively. This method was successfully applied to study the pharmacokinetics of thiacetazone in rats. The direct injection method is simple, requires small sample volume and does not require sample extraction, internal standard, or gradient elution.

Physiologically based pharmacokinetic models of 2',3'-dideoxyinosine

PURPOSE

The goal of this study was to develop physiologically based pharmacokinetic (PBPK) models for 2',3'-dideoxyinosine (ddI) in rats when the drug was administered alone (ddI model) and with pentamidine (ddI + pentamidine model), and to use these models to evaluate the effect of our previously reported pentamidine-ddI interaction on tissue ddI exposure in humans.

METHODS

The PBPK models consisted of pharmacologically relevant tissues (blood, brain, gut, spleen, pancreas, liver, kidney, lymph nodes, muscle) and used the assumptions of perfusion-rate limited tissue distribution and linear tissue binding of ddI. The required physiologic model parameters were obtained from the literature, whereas the pharmacokinetic parameters and the tissue-to-plasma partition coefficients were calculated using plasma and tissue data.

RESULTS

The ddI model in rats yielded model-predicted concentration-time profiles that were in close agreement with the experimentally determined profiles after an intravenous ddI dose (5% deviation in plasma and 20% deviation in tissues). The ddI + pentamidine model incorporated the pentamidine-induced increases of ddI partition in pancreas and muscle. The two PBPK models were scaled-up to humans using human physiologic and pharmacokinetic parameters. A comparison of the model-predicted plasma concentration-time profiles with the observed profiles in AIDS patients who often received ddI with pentamidine showed that the ddI model underestimated the terminal half-life (t1/2, beta) by 39% whereas the ddI + pentamidine model yielded identical t1/2, beta and area-under-the-curve as the observed values (< 1% deviation). Simulations of ddI concentration-time profiles in human tissues using the two models showed that pancreas and lymph nodes received about 2- to 30-fold higher ddI concentration than spleen and brain, and that coadministration of pentamidine increased the AUC of ddI in the pancreas by 20%.

CONCLUSIONS

Data of the present study indicate that the plasma ddI concentration-time profile in patients were better described by the ddI + pentamidine model than by the ddI model, suggesting that the pentamidine-induced changes in tissue distribution of ddI observed in rats may also occur in humans.

Comparative scoring by visual and image analysis of cells in human solid tumors labeled for proliferation markers

This study determined the validity of an image analysis program developed to score individual cells in human solid tumors labeled by proliferating cell nuclear antigen (PCNA) or bromodeoxyuridine (BrdUrd). The program used nuclear size, grey level, and perimeter convexity to identify cells, and evaluated labeling by the fraction of nuclear area displaying positive immunostaining (MPB). Total cell number (TC) and BrdUrd or PCNA labeling index (LI) were evaluated in 142 images using visual (TCvisual, LIvisual) and image analysis (TC(IA), LI(IA)). Without the perimeter convexity criterion, image analysis resulted in a) TC(IA) equal to TCvisual in spite of the presence of various non-cellular objects and b) significant correlations between LI(IA) and LIvisual for PCNA and BrdUrd, although for these markers the LI(IA) were 4 and 6% lower than their respective LIvisual. Both visual and image analyses yielded significant inter-investigator variation among three investigators (coefficient of variation between 8.2 and 47.5%) and significant intra-investigator, inter-day variation (coefficients of variation between 3.8 and 51.8%). We conclude that image analysis using size, grey level and MPB is a valid alternative to visual scoring of PCNA and BrdUrd LI in individual cells.

Intensified regimen for advanced head and neck squamous cell carcinomas

OBJECTIVE

To devise an intensified treatment regimen for patients with advanced, resectable head and neck squamous cell carcinomas.

DESIGN

Phase I/II clinical trial consisting of perioperative cisplatin chemoradiotherapy, surgical resection, intraoperative radiotherapy, and postoperative cisplatin chemoradiotherapy.

SETTING

The Ohio State University Comprehensive Cancer Center, Columbus.

PATIENTS

Thirty-seven patients (median age, 63 years) with advanced oral cavity, oropharyngeal, or hypopharyngeal carcinomas.

RESULTS

The range of time at risk was 1 to 30 months (median, 21 months). Thirty of the 37 registered patients were analyzable; 11 have died (5 with distant metastases; 1 of lung carcinoma; and 5 were cancer-free); 2 experienced second primary tumors in the oral cavity (out of or adjacent to the previous radiotherapy portals). Treatment compliance was excellent (92%), morbidity was low, and excellent locoregional control was achieved.

CONCLUSIONS

The initial results are encouraging; the future strategy will intensify the systemic component of therapy based on results from concurrent laboratory studies.

Bladder tissue pharmacokinetics of intravesical taxol

Our previous studies have suggested that the ineffectiveness of intravesical mitomycin C or doxorubicin therapy against muscle-invading bladder cancer is in part because of the inability of these drugs to penetrate the urothelium (the urothelial drug concentration is < 5% of the concentration in urine). The goal of the present study was to identify agents that are efficiently absorbed across the urothelium. To evaluate the potential use of taxol in intravesical therapy for bladder cancer, we examined the bladder tissue and systemic plasma pharmacokinetics of intravesical taxol in dogs. Animals (approximately 8 kg body weight) were given an instillation of taxol at 500 micrograms in 20 ml water. At 120 min postinstillation, the bladder was emptied and excised, and about 85% of the dose was recovered in the urine. The taxol concentration in the urothelium was about 50% of the concentration in the urine, the concentrations then declined logarithmically in the underlying capillary-perfused tissues. The average tissue concentration (-2 micrograms/g) was two to three times the reported plasma concentration of 0.75 microgram/ml in patients following intravenous infusion of the > 100-fold higher dose of 250 mg/m2. The steady-state plasma concentration was < 0.02% of the average tissue concentration, and was < 0.05% of the maximally tolerated plasma concentration in patients. The octanol:water partitioning coefficients of taxol, doxorubicin, and mitomycin were > 99, 0.52, and 0.41, which parallels the rank order of the partitioning across urothelium, i.e. taxol (approximately 50%) > > doxorubicin approximately mitomycin C (-3%). In summary, the partitioning of taxol across the urothelium was more favorable than the partitioning of mitomycin C and doxorubicin, and the systemic concentration of taxol resulting from intravesical treatment was insignificant in spite of the extensive absorption into the bladder. We conclude that intravesical delivery of taxol provides a significant bladder tissue targeting advantage, and that taxol represents a viable candidate drug for intravesical bladder cancer therapy.

Different pH dependency of mitomycin C activity in monolayer and three-dimensional cultures

PURPOSE

Previous studies by other investigators have shown an enhancement of mitomycin C (MMC) activity at acidic extracellular pH (pHe) in monolayer cultures of human cells. The goal of the present study was to determine if the efficacy of intravesical MMC therapy in patients treated for superficial bladder cancer can be enhanced by using acidified dosing solutions. We evaluated (a) the effect of pHe on MMC activity in patient bladder tumors in vitro, and (b) the pH dependency of MMC activity in 2-dimensional monolayer and 3-dimensional multilayer cultures of human bladder RT4 tumor cells.

METHODS

Patient bladder tumors were maintained as 3-dimensional histocultures. RT4 cells were harvested and maintained as monolayer cultures or as 3-dimensional cell pellets on a collagen gel matrix. The cell pellets were 300-450 cell layers and 4,000-5,000 microns in diameter. Tumors or cells were incubated for 2 hr with MMC-containing media at pHe of 5, 6, and 7.4. The drug effect was measured by the inhibition of DNA precursor (thymidine) incorporation. The stability of MMC as a function of pHe was determined. About 24% of MMC was degraded following 2 hr exposure at pHe 5 and < or = 2% at pHe 6 and 7.4.

RESULTS

The drug concentrations required to inhibit thymidine incorporation by 50% (IC50) were corrected for the degraded MMC at acidic pHe. The results showed no pH-dependent MMC activity in human patient bladder tumors nor in RT4 multilayer cultures; the IC50 values were about 10 micrograms/ml at all three pHe. In contrast, the monolayer RT4 cultures showed a pH-dependent MMC cytotoxicity; the IC50 were 0.1, 0.8 and 1.2 micrograms/ ml at pHe 5, 6 and 7.4, respectively (p < 0.05). Pre-incubation of multilayered RT4 cultures in acidic pH medium for 8 hr enhanced the MMC activity; the IC50 was reduced by about 5 fold at pHe about 3 fold at pHe 6. Similar pH-dependent MMC activity was found when multilayers were pre-treated for 1 hr with 0.5 microgram/ml nigericin, a proton ionophore known to cause the intracellular pH (pHi) to equilibrate with pHe.

CONCLUSIONS

These data suggest that the difference in the pH dependency of MMC activity in the monolayer and multilayer systems was due to the different experimental conditions. The time lag for pHi to equilibrate with pHe in the multilayer systems and the instability of MMC at low pHe imply that the efficacy of intravesical MMC therapy is unlikely to be enhanced by using acidic dosing solution.

Differential effect of taxol in rat primary and metastatic prostate tumors: site-dependent pharmacodynamics

PURPOSE

This study compared the sensitivity of rat prostate MAT-LyLu primary and lymph node metastatic tumors to taxol.

METHODS

Tumors were established by subcutaneous implantation of tumor cells in a hind leg (primary site) of male Copenhagen rats. Lymph node metastases were used for serial transplantation. Eleven pairs of primary and metastatic tumors between the sixth and twentieth generations were harvested and maintained as 3-dimensional histocultures. The effects of taxol (24 hr treatment at 1 nM to 10 microM) were measured by the appearance of apoptotic cells, and by the inhibition of DNA precursor (thymidine) incorporation. To determine the basis of differential sensitivity of primary and metastatic tumors to the DNA inhibition, we examined the expression of multidrug resistance pglycoprotein (Pgp) and the accumulation of 3H-taxol after 24 hr exposure and the retention after a 48 hr washout period.

RESULTS

The fraction of apoptotic cells increased linearly with the logarithm of taxol concentration to a maximal value of 25%; the concentration-response curves for primary and metastatic tumors were superimposable. Taxol produced a sigmoidal, concentration-dependent inhibition of thymidine incorporation; the maximal inhibition of approximately 40% was reached at 0.1 and 1 microM for primary and metastatic tumors, respectively. Within the primary or metastatic subgroups, the IC30 (drug concentration that produced a 30% inhibition of DNA synthesis) among consecutive generations varied by < 5 fold, but the primary tumor consistently showed a lower IC30 than the daughter or the parent metastatic tumor (mean, 20-fold; median, 15-fold; range, 6- to 56-fold). The finding that the lower drug sensitivity in metastatic tumors was not exhibited in its daughter primary tumor but was regained in its daughter metastatic tumors suggests that the chemoresistant phenotype is maintained only in lymph nodes and not in the primary site. There were no differences in the Pgp status (neither tumor expressed Pgp), accumulation and retention of taxol in primary and metastatic tumors.

CONCLUSIONS

Taxol induced apoptosis and inhibited DNA synthesis in the rat MAT-LyLu primary and lymph node metastatic tumors. The apoptotic effect was not different among the two tumors, whereas the primary tumor was more sensitive to the inhibition of DNA synthesis. The differential sensitivity of the two tumors to the DNA effect is not associated with a difference in Pgp expression, drug accumulation nor drug retention, and appears to be associated with changes that are linked to lymph node metastasis.

Pharmacodynamics of doxorubicin in human bladder tumors

Intravesical doxorubicin treatment delivers high drug concentrations to the bladder wall, yet the treatment produces only a variable and incomplete response in superficial bladder cancer and insignificant activity in muscle-invading disease. This study evaluated the pharmacological basis for the clinical observations and potential prognostic indicators of tumor sensitivity to doxorubicin. The pharmacodynamics of doxorubicin were studied using histocultures of surgical specimens of seven superficial (Ta and T1) and nine invasive (T2-T4) tumors. After a 2-h exposure, drug treatment caused a concentration-dependent inhibition of proliferation, as measured by bromodeoxyuridine incorporation into DNA. Extensive cell death was observed at high concentrations (>10 micrometer) in sensitive tumors. The IC50 values ranged from 0.14 to 5.2 micrometer for superficial tumors and from 1.4 to >100 micrometer for invasive tumors. A comparison of the IC50 and IC90 values with the drug concentrations previously determined in human bladder walls showed that IC50 was achieved in all Ta tumors, 67-100% of T1 tumors, and one of the nine invasive tumors, whereas IC90 was achieved in all Ta tumors but none of the other tumors. To determine the biological basis of variable doxorubicin sensitivity among different tumors, we examined the relationship of chemosensitivity with tumor pathology and with expression of multidrug resistance p-glycoprotein (Pgp) and p53 protein. The invasive, high-grade, highly proliferative, p53- and Pgp-positive tumors were more resistant than the superficial, lower-grade, p53- and Pgp-negative tumors. All tumors were negative for bcl-2. The rank order of these factors was p53 expression > tumor stage > grade > bromodeoxyuridine labeling index > Pgp. Statistical analysis using the Akaike Information Criterion indicates that the two-parameter combination of p53 expression with stage further improved the predictive value. The present study shows that: (a) there was a >700-fold difference in doxorubicin sensitivity among superficial and invasive tumors; (b) the variable and incomplete response of superficial bladder cancer to intravesical doxorubicin therapy is likely due to the 35-fold variability in tumor chemosensitivity and, to a lesser degree, the 4-fold variability in tissue pharmacokinetics; (c) the lack of response of invasive cancer to intravesical doxorubicin therapy is likely the result of the inadequate drug concentrations presented to the deep muscle layers and the low chemosensitivity of the more aggressive tumors; and (d) the combination of p53 expression and high stage was the most significant predictor of doxorubicin sensitivity, whereas Pgp expression was the least important.

Pharmacodynamics of taxol in human head and neck tumors

The pharmacodynamics of taxol in human head and neck squamous cell carcinoma were studied using histocultures of surgical specimens from patients (n = 22). Tumors were treated with taxol for 24 h. The inhibition of DNA synthesis was determined by 48 h cumulative bromodexyuridine (BrdUrd) incorporation. The induction of apoptosis was measured by morphological changes, in situ DNA end labeling, post-exonuclease III BrdUrd labeling, and DNA fragmentation. Inhibition of the BrdUrd labeling index (LI) by taxol was incomplete, with 11 tumors showing maximal inhibition (Emax) of 30-50% and the remaining 11 tumors showing and Emax of 50-80%. For both groups, the inhibition approached maximum values at 1 microM taxol concentration; an additional 10-fold increase in drug concentrations did not significantly enhance the inhibition. The taxol concentrations required for a 30% inhibition (IC30) were 4.2 and 0.3 microM for the first and second groups, respectively. The IC30 correlated with the Emax (r2 = 0.39; P < 0.001). Taxol induced apoptosis in all tumors, 11 tumors showed a maximal fraction of apoptotic tumor cells between 3 and 10% and 11 tumors between 13 and 28%, whereas untreated controls showed a maximal apoptotic index of < 1%. For individual tumors, the maximal apoptotic index occurred between 0.1 and 3 microM, and correlated with the BrdUrd LI for the untreated control (r2 = 0.37; P < 0.01). It is interesting that > 95% of apoptotic cells were BrdUrd labeled, whereas not all BrdUrd-labeled cells were apoptotic. To investigate the basis of the variable tumor response to taxol, we determined the expression of multidrug resistance P-glycoprotein (Pgp), p53, and bcl-2 proteins, using immunohistochemical staining and Western blot analysis. Eleven (50%), 10 (45%), and 7 (32%) tumors expressed Pgp, p53, and bcl-2, respectively. Patients with Pgp-positive tumors showed a higher number of affected lymph nodes than those with Pgp-negative tumors (P < 0.05). Compared with moderately and well differentiated tumors, the poorly differentiated tumors expressed p53 and Pgp more frequently and showed a lower maximum inhibition of DNA synthesis and a higher apoptotic fraction after taxol treatment (P < 0.05 in both cases). Pgp expression correlated differently with taxol-induced inhibition of DNA synthesis than with apoptosis; Pgp-positive tumors showed a significantly higher Emax (63%) and IC30 (4.2 microM) but also a higher apoptotic index (17%) than Pgp-negative tumors (Emax 36%; IC30, 0.3 microM; and apoptotic index; 6%; P < 0.05 for all cases). p53 and bcl-2 expression did not correlated with taxol-induced inhibition of DNA synthesis or apoptosis. The data indicate that taxol acts through apoptosis and inhibition of proliferation in human head and neck cancer. Pgp overexpression appears to protect cells from the antiproliferative effect of taxol but correlated with a higher apoptosis.