Yuebo Gan

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.

Telomere Amount and Length Assay

AbstractPurpose. 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.

Cytostatic and apoptotic effects of paclitaxel in human ovarian tumors.

AbstractPurpose. 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 ∼30%) and induced apoptosis in about 90% of tumors (maximum apoptotic index of ∼15%). In responsive tumors, maximum cytostatic and apoptotic effects were achieved at ≤1 μM with no further enhancement by increasing the drug concentration to 10 μM. 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 μM may not improve treatment outcome.

Synergy Between 3′Azido-3′deoxythymidine and Paclitaxel in Human Pharynx FaDu Cells

AbstractPurpose. We recently demonstrated simultaneous targeting of telomere and telomerase as a novel cancer therapeutic approach, and that telomerase inhibitors such as 3′azido-3′deoxythymidine (AZT) significantly enhanced the antitumor activity of paclitaxel, which causes telomere erosion, in telomerase-positive human pharynx FaDu tumors in vitro and in vivo (1). The present study evaluated the synergy between AZT and paclitaxel to identify optimal combinations for future clinical evaluation. Methods. FaDu cells were incubated with or without AZT for 24 h and then treated with AZT with or without paclitaxel for an additional 48 h. Under these conditions, single agent paclitaxel produced a 60% maximum reduction of cell number (IC50 was 7.3 nM), and single agent AZT produced a 97% reduction (IC50 was 5.6 μM). Synergy was evaluated using fixed-concentration and fixed-ratio methods, and data were analyzed by the combination index method. Results. The results indicate a concentration-dependent synergy between the two drugs; the synergy was higher for combinations containing greater paclitaxel-to-AZT concentration ratios and increased with the level of drug effect. For example, in combinations containing 1 μM AZT, synergy was 1.3-fold at the 20% effect level and 3.1-fold at the 60% effect level. Because the major antitumor activity, determined by comparing the posttreatment cell number to the pretreatment cell number, was antiproliferation at the 20% effect level and cell kill at the 60% effect level, our results suggest that AZT mainly enhances the cell kill effect of paclitaxel. Conclusion. In summary, the present study demonstrates a synergistic interaction between paclitaxel and AZT and supports a combination using a low and nontoxic AZT dose in combination with a therapeutically active dose of paclitaxel.

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 (∼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 μM ) compared to the maximum cytostatic effect (1 μM ). Neither of these effects was enhanced by increasing the drug concentration to 10 μM. 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 μM suggests further increasing the dose to elevate plasma concentration beyond 1 μM may not improve treatment outcome.

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.

Antiproliferative and Cytotoxic Effects of Geldanamycin, Cytochalasin E, Suramin and Thiacetazone in Human Prostate Xenograft Tumor Histocultures

AbstractPurpose. 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 ≥ 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.

Intraprostatic Chemotherapy: Distribution and Transport Mechanisms

Purpose: The present study evaluated the tissue distribution and targeting advantage of intraprostatic chemotherapy. Experimental Design: We studied the delivery and spatial distribution of a fluorescent drug, doxorubicin, in the prostate of beagle dogs, after intraprostatic or i.v. administration. Drug concentrations were measured using high-performance liquid chromatography and confocal fluorescence microscopy. Results: I.v. and intraprostatic injections yielded qualitatively and quantitatively different doxorubicin distribution in the prostate. A relatively homogeneous distribution was found after i.v. administration, whereas intraprostatic injection yielded a highly heterogeneous distribution with >10-fold higher concentrations localized in a cone-shaped glandular lobule bound by fibromuscular stroma, compared with other parts of the prostate. Compared with i.v. injection, intraprostatic injection yielded, on average, ∼100-fold higher tissue-to-plasma concentration ratio, ranging from 963-fold near the injection site to 19-fold in the contralateral half of the prostate. The drug distribution within the prostate further suggests an important role for acinar flow in intraprostatic drug transport. Conclusions: Intraprostatic administration represents a viable option to deliver high drug concentrations within the prostate. The results further suggest the fibromuscular stroma separating the prostatic lobules as a major barrier to drug transport and convective flow as an important drug transport mechanism in the prostate.

Biodegradable intraprostatic doxorubicin implants

Systemic chemotherapy is not effective in the treatment of prostate-confined cancer. We developed biodegradable, doxorubicin-loaded cylinders for intraprostatic implantation and evaluated the feasibility of using regional intraprostatic drug therapy to treat prostate-confined cancer. Cylinders were prepared using poly(lactide-co-glycolide) (PLG) or PLG copolymers. The in vitro and in vivo drug release, intraprostatic pharmacokinetics, and histopathology in dogs implanted with the cylinders were studied. The doxorubicin-loaded cylinders made of PLG polymers of 7.9 to 54 kDa molecular weight (MW) had a diameter of ∼800 μm, drug loading of 10% to 30% (wt/wt), and even distribution of crystalline drug throughout the matrix. Burst release varied from 3% to 73%, and 7-day cumulative release from 4% to 90%. Decreasing polymer MW and increasing drug loading were associated with higher initial burst release and overall release rates. The in vivo drug release from cylinders (33-kDa PLG, 30% drug loading) in dog prostates was rapid (∼80% in 48 hours). Spatial drug distribution, visualized using confocal fluorescence microscopy, showed high concentrations confined to the lobule containing the implant (referred to as the implanted lobule), with steep concentration gradients over the septa separating the lobules. Concentrations in the implanted lobule were about 8 times higher than concentrations delivered by an intravenous injection. The implants caused necrotic cell death in the implanted lobule, without damage to prostatic nerve bundles or the urethra. These results indicate the feasibility of using biodegradable PLG cylinders as intraprostatic implants to selectively deliver high drug concentrations to prostate tissue.

Telomere maintenance in telomerase-positive human ovarian SKOV-3 cells cannot be retarded by complete inhibition of telomerase.

The two known mechanisms for telomere maintenance in eukaryocytes are telomerase in telomerase‐positive cells and alternative lengthening of telomeres (ALT) in telomerase‐negative cells. We report here that telomere maintenance in the telomerase‐positive human ovarian SKOV‐3 cells was not affected by inhibition of telomerase. For comparison, the effect of telomerase inhibitors on telomere maintenance in another telomerase‐positive cell line (i.e. human pharynx FaDu cells) and the telomerase‐negative human osteosarcoma Saos‐2 cells was examined. Telomerase activity was measured using a modified telomeric repeat amplification protocol and telomere length was measured using a solution hybridization‐based method and fluorescence in situ hybridization. A reverse transcriptase inhibitor (3′‐azido‐deoxythymidine or AZT) and an antisense against a component of human telomerase RNA (antisense hTR) were used to inhibit telomerase. FaDu and SKOV‐3 cells showed comparable baseline telomerase activity. Telomerase activity in both cells was inhibited about equally by AZT (maximal inhibition of ∼80%) and by expression of antisense hTR (complete inhibition in SKOV‐3 cells and maximal inhibition of ∼80% in FaDu cells). However, treatment with telomerase inhibitors resulted in ∼50% telomere shortening in FaDu cells but had no effect on SKOV‐3 nor Saos‐2 cells. SKOV‐3 cells did not show the characteristic features of ALT (i.e. heterogeneous telomere length and promyelocytic leukemia bodies), whereas these ALT features were observed in Saos‐2 cells. Collectively, these results suggest the existence of a telomerase‐independent mechanism of telomere maintenance in the telomerase‐positive SKOV‐3 cells.