Cell cycle-independent death of prostate adenocarcinoma is induced by the trk tyrosine kinase inhibitor CEP-751 (KT6587).

Advanced prostate cancer remains largely incurable, primarily because the very low growth fraction present in these tumors makes them generally resistant to treatment with standard chemotherapeutic agents that target cell division. Effective therapies should therefore induce death of prostate cancer cells, independent of their growth rate. trkA, the high-affinity tyrosine kinase-linked receptor for nerve growth factor, has been implicated in prostatic cancer growth and may represent a molecular target for therapeutic agents. At low mg/kg doses, the trk tyrosine kinase inhibitor CEP-751 (KT6587) inhibits prostatic cancer growth in nine different animal models independent of the tumor growth rate, androgen sensitivity, metastatic ability, or state of tumor differentiation. CEP-751 is selective for cancerous versus normal prostate cells and affects the growth of only a limited number of nonprostate tumors. Importantly, CEP-751 induces cell death of prostate cancer cells in a cell cycle-independent fashion and, therefore, represents a novel therapeutic approach to the management of both hormone-dependent and hormone-independent prostate cancer.

CEP-751 inhibits TRK receptor tyrosine kinase activity in vitro exhibits anti-tumor activity.

The present report describes the in vitro and in vivo profile of CEP-751, a novel receptor tyrosine kinase inhibitor. CEP-751 at 100 nM inhibits the receptor tyrosine kinase activity of the neurotrophin receptors trkA, trkB and trkC. CEP-751 has no effect on activity of receptors for EGF, IGF-I, insulin or on erbB2; inhibition of receptors for PDGF and bFGF was observed but occurred with lesser potency than inhibition of trk. CEP-751 exhibited anti-tumor efficacy against tumors derived from NIH3T3 cells transfected with trkA. Inhibition of trk phosphorylation could also be measured in these tumors, suggesting that anti-tumor efficacy of CEP-751 is related to inhibition of trk receptor tyrosine kinase activity. CEP-751 was found to be without effect when administered to nude mice bearing SK-OV-3 tumors, which overexpress erbB2 receptors, providing further evidence that inhibition of tumor growth may be related to inhibition of trk receptor tyrosine kinase activity. Our data indicate that CEP-751 is a potent trk inhibitor which possesses anti-tumor activity.

Modulation of cisplatin sensitivity and accumulation by interferon alpha-2A in human squamous carcinoma cell lines.

This study was undertaken to elucidate the mechanism(s) of potentiation of cisplatin (CDDP) cytotoxicity by interferon alpha-2a (IFN alpha-2a) in human squamous carcinoma cell lines SCC-25 and SCC-4. IFN alpha-2a treatment significantly increased the cytotoxicity of CDDP in both cell lines in a dose-dependent manner. In SCC-25 cells, the cytotoxicity of CDDP was increased by about 2- and 4-fold, respectively, by treating the cells with 400 and 800 IU/ml IFN alpha-2a. Sensitivity of SCC-4 cells to CDDP was increased by about 3- and 7-fold, respectively, by 400 and 800 IU/ml IFN alpha-2a treatment. Drug uptake experiments revealed approximately 1.4- to 5-fold higher platinum accumulation in IFN alpha-2a-treated cells as compared to respective controls. Cellular levels of glutathione (GSH) and GSH transferase, which have been suggested to be important determinants of tumor cell sensitivity to CDDP, were not altered by IFN alpha-2a treatment in either of the cell lines. Northern blot analysis showed a moderate increase (about 30-40%) in the level of MT-IIA mRNA by IFN alpha-2a treatment in these cells. Our results suggest that IFN alpha-2a-mediated sensitization of SCC-25 and SCC-4 cell lines to CDDP in vitro may be due to an increase in intracellular platinum accumulation.

Characterization of a human bladder cancer cell line selected for resistance to BMY 25067, a novel analogue of mitomycin C.

This study describes characteristics of a human bladder cancer cell line, SCaBER/R, selected for resistance to a mitomycin C (MMC) analogue BMY 25067. The SCaBER/R cell line was isolated by repeated 24 h exposures of the parental cells to 0.09 microM BMY 25067 (IC90, 24 h drug exposure) over a period of about 180 days. Approximately 2.2-fold higher concentration of BMY 25067 was required to kill 50% of the SCaBER/R cell line compared with parental cells (p < 0.001). The IC20 and IC90 values for BMY 25067 were also significantly higher in the SCaBER/R cell line than in SCaBER. Unlike most MMC resistant cell lines, the SCaBER/R cell line displayed a marked cross-resistance to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and lacked cross-resistance to cisplatin, doxorubicin or VP-16. The SCaBER/R cell line also displayed a marked cross-resistance to the parent drug (MMC) and BMY 25282, another analogue of MMC. NADPH cytochrome P450 reductase activity, an enzyme implicated in bio-reductive activation of MMC, did not differ significantly in these cells. DT-diaphorase activity, another MMC activation enzyme, was significantly lower in the SCaBER/R cell line when compared to the SCaBER cells. These results suggest that relatively lower sensitivity of SCaBER/R cell line to MMC and BMY 25067 may result from impaired drug activation. Cellular levels of glutathione (GSH) and GSH-transferase (GST), which have been suggested to affect the cytotoxicity of MMC, were comparable in SCaBER and SCaBER/R cell lines. BMY 25067 induced DNA interstrand cross-links (DNA-ISC) could not be detected in either of the cell lines even at drug concentrations which produced a significant cell kill. These findings suggest that (a) cellular resistance to BMY 25067 in the SCaBER/R cell line may be due to impaired drug activation, and (b) the nature of the cytotoxic produced by BMY 25067 may be different from that of MMC.

Mechanism of cross-resistance to cisplatin in a mitomycin C-resistant human bladder cancer cell line.

This study was undertaken to elucidate the mechanism(s) of cross-resistance to cisplatin (CDDP) in a mitomycin C (MMC)-resistant human bladder cancer cell line, J82/MMC. The J82/MMC cell line displayed 2- to 3-fold cross-resistance to CDDP and carboplatin when compared to the parental J82/WT cells. Drug uptake studies revealed that cross-resistance to CDDP in the J82/MMC cell line was independent of reduced platinum accumulation. The J82/MMC cell line exhibited approximately a 1.5-fold resistance to cadmium chloride, an indicator for increased metallothionein (MT) content, when compared to the J82/WT cells. Northern blot analysis showed a 2.7-fold higher level of MT-IIA mRNA in the J82/MMC cell line compared with J82/WT. We have reported previously that, whereas glutathione (GSH) level is comparable in these cells, GSH transferase (GST) activity is significantly higher in the J82/MMC cell line compared with J82/WT. Results of the present study showed that the elevated GST activity in the J82/MMC cell line was due to an over-expression of pi-type GST protein. Although buthionine-S,R-sulfoximine (BSO)-induced GSH depletion significantly enhanced CDDP cytotoxicity in both cell lines, the magnitude of potentiation was markedly higher in J82/MMC cells (about 2.1-fold) relative to J82/WT (about 1.6-fold). Our results suggest that cross-resistance to CDDP in the J82/MMC cell line may be due to alterations in cellular thiols.

Activity of melphalan in combination with the glutathione transferase inhibitor sulfasalazine.

Glutathione (GSH) transferases (GST), a family of detoxification enzyme proteins, are suggested to play an important role in tumor cell resistance to melphalan. The GST-activity inhibitor ethacrynic acid has been shown to increase the antitumor activity of melphalan in vitro as well as in vivo. In this study we determined the activity and toxicity of melphalan in combination with another GST-activity inhibitor, sulfasalazine, an agent used to treat ulcerative colitis. We entered 37 previously treated patients with advanced cancer of different histologies on sulfasalazine given at the individually calculated maximum tolerated dose (MTD) and melphalan given at doses beginning at 20 mg/m2. The main toxicity arising from this combination was nausea and vomiting, whereas increased myelosuppression was not observed. A partial response was seen in 2/4 of the ovarian cancer patients only. Plasma sulfasalazine levels varied between 2.5 and 47.1 micrograms/ml. Although reductions in GSH/GST levels were observed in peripheral mononuclear cells of certain patients following sulfasalazine treatment, there was no correlation between the extent of reduction and the plasma sulfasalazine level. A larger patient population must be studied to determine the usefulness of this combination.

Desensitization of 5HT2 receptors by protein kinase C activation in distal pulmonary vascular smooth muscle cells in culture.

OBJECTIVE: Although acute and chronic roles of microvascular smooth muscle cells as effectors of pulmonary vascular resistance and remodeling are well appreciated, relatively little is known regarding the direct effects of neurohumoral agents on these cells. We recently reported that microvascular smooth muscle cells isolated from distal rat lung (RPC) express mRNA and binding sites for 5HT2 receptors. The objective of the current study was to determine if protein kinase C (PKC) affected 5HT-induced changes in intracellular calcium and phosphoinositide metabolism in RPC. METHODS: 5HT-induced changes in intracellular calcium ([Ca2+]i) in single RPC were determined microspectrofluorometrically using the calcium-sensitive dye, Fura-2. RESULTS: Phorbol 12-myristate 13-acetate (PMA: 100 nM) caused a rapid desensitization of 5HT-induced increases in [Ca2+]i. Staurosporine, a putative PKC inhibitor, abolished the PMA-induced desensitization. Downregulation of PKC with prolonged (24 hr) PMA exposure also abolished subsequent PMA-induced desensitization of 5HT response. Neither short- nor long-term exposure of RPC to PMA affected binding of [125I]LSD. Activation of PKC by PMA was associated, however, with complete inhibition of 5HT-induced increases in intracellular inositol monophosphate. CONCLUSIONS: These data are consistent with PKC causing desensitization of 5HT2 receptors by affecting elements of signal transduction and uncoupling receptor-G protein complex from phospholipase C in RPC.

Metastasis of B16F10 mouse melanoma inhibited by lovastatin, an inhibitor of cholesterol biosynthesis.

Lovastatin (LST) is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme that regulates the biosynthesis of cholesterol. This drug is used clinically to treat patients with hypercholesterolemia. Numerous studies have also suggested an important, if not essential, role of the cholesterol biosynthetic pathway to cell growth and proliferation. In fact, recent studies demonstrating the inhibitory effects of LST on various tumor cells have drawn much attention. We now describe a novel action of LST that inhibited experimental lung metastasis of the highly metastatic B16F10 mouse melanoma in nude mice. Further, when used in in vitro studies, LST pretreatment of B16F10 cells resulted in inhibition of attachment, motility, and invasion, which are key steps in the dynamic sequence of events that comprise the metastatic cascade. Our studies also suggested that the antimetastatic effect of LST on B16F10 cells is probably not mediated by a growth inhibitory action. We submit that these observations identify an antimetastatic agent with potentially useful clinical application.

Neutralization of bleomycin hydrolase by an epitope-specific antibody.

Bleomycin hydrolase (BH) is a cysteine proteinase that terminates the pharmacological action of bleomycin (BLM). Amino acid sequence data obtained from a tryptic digest fragment of purified rabbit lung BH were used to synthesize a 14-amino acid peptide (LAVLEQEPIVLPAK; BHP14), which was conjugated to horseshoe crab hemocyanin and used to produce rabbit antiserum that was immunoreactive to both BHP14 and rabbit BH. Anti-BHP14 binding to BHP14 could be competitively blocked by the presence of either BHP14 or BH. Anti-BHP14 recognized both purified rabbit liver BH and postmicrosomal fraction from rabbit liver on Western blot, as a single band of M(r) approximately 48,000. Anti-BHP14 inhibited, in a concentration-dependent manner, BH activity in rabbit liver cytosolic fractions, as measured by deamido-BLM A2 formation. Thus, we have generated an epitope-specific neutralizing antibody to rabbit BH, which can block the metabolism of BLM by homogenates from rabbit tissue. These results suggest that the LAVLEQEPIVLPA epitope of rabbit BH is involved in the metabolism of BLM or is topologically near the active site. Furthermore, a BLM-resistant squamous carcinoma (C-10E) exhibited slightly more immunoreactivity, by enzyme-linked immunosorbent assay, to anti-BHP14 than did the parental A-253 cells, and a partially revertant (C-10E ND) cell line had intermediate anti-BHP14 binding. BH activity in these cell lines was in the same rank order as antibody binding, but differences in immunoreactivity were less than differences in enzymatic activity. Our epitope-specific neutralizing antibody should be useful in the further characterization of BH.

In vivo circumvention of human colon carcinoma resistance to bleomycin.

Metabolic inactivation of bleomycin (BLM) by cysteine proteinase-like enzymes is thought to be a major mechanism of BLM tumor resistance. We now report that the human colon carcinoma COLO-205 is highly resistant to BLM and that E-64, a cysteine proteinase inhibitor, sensitizes COLO-205 to BLM. Treatment of COLO-205-bearing nude mice with either E-64 (40 mg/kg) or BLM (10 mg/kg) alone did not inhibit COLO-205 growth. However, pretreatment with E-64 prior to BLM prevented these xenografts from growing. Analysis by high performance liquid chromatography of in vivo BLM metabolism following [3H]BLM A2 treatment of COLO-205-bearing nude mice showed a different metabolic profile among the various organs and the tumor. Whereas [3H]BLM A2 was the only major radioactive peak detected in sera and tumors, several metabolites, including deamido-BLM A2, were found in kidney, liver, and lung as early as 15 min. Pretreatment of mice with E-64 inhibited tumor, kidney, and lung BLM A2 metabolism. Furthermore, pretreatment with E-64 increased BLM A2 accumulation in tumors (6.1-fold), kidney (4.0-fold), lung (2.8-fold), liver (1.8-fold), and serum (1.7-fold). E-64 pretreatment did not enhance the major toxicity of BLM, pulmonary fibrosis, as determined by both lung hydroxyproline levels and histopathology. Thus, the cysteine proteinase inhibitor E-64 affects the metabolic fate and the levels of accumulation of BLM in vivo. These results demonstrate that resistance of human COLO-205 tumors to BLM can be circumvented by E-64 without enhancement of the major side effect of BLM, suggesting a possible clinical use of this combination therapy.

Synthesis and evaluation of fluoromycin: a novel fluorescence-labeled derivative of talisomycin S10b.

We have synthesized fluoromycin (FLM), a novel fluorescein-labeled derivative of talisomycin S10b (TLM S10b), and used it to evaluate cellular drug accumulation and distribution in bleomycin (BLM)-sensitive and -resistant cell lines. The fluorescence intensity of FLM was 300- to 400-fold greater than that of BLM A2, TLM S10b, or the lipophilic BLM analogue, liblomycin. FLM possessed an antiproliferative potency similar to liblomycin in BLM-sensitive human A-253 squamous carcinoma cells but was less potent than BLM A2 or TLM S10b. C-10E cells, a clone of A-253 cells with 40- to 50-fold resistance to BLM A2 and TLM S10b, were 50-fold resistant to FLM. A partially revertant cell population (C-10E ND) regained sensitivity to BLM A2, TLM S10b, and FLM. FLM like BLM cleaved pGEM-3Z plasmid DNA in vitro in a concentration-dependent manner. Flow cytometric analysis of FLM content in C-10E and C-10E ND cell lines showed 4-fold and 2-fold lower fluorescence intensity, respectively, compared with A-253 cells. Similar results were seen by fluorescence spectrophotometry with cell extracts. Fluorescence microscopy indicated heterogeneous distribution among A-253 cells with at least 50% of the cells exhibiting marked nuclear fluorescence localization. In contrast, C-10E cells displayed lower cellular fluorescence and predominantly cytoplasmic localization. C-10E ND cells exhibited a mixed population of nuclear and cytoplasmic vesicular localization with fluorescence levels that were intermediate between A-253 and C-10E cells. Thus, BLM-resistant cells have reduced levels of FLM and appear to have a lower nuclear:cytoplasmic ratio of FLM. FLM may be useful in studying the intracellular fate of BLM-like drugs as well as providing a tool to detect and isolate BLM-resistant cells.

In vivo sensitization of human lung carcinoma to bleomycin by the cysteine proteinase inhibitor E-64.

We recently demonstrated that the cysteine proteinase inhibitor, E-64, sensitizes human Burkitt's lymphoma (Daudi) to the antitumor action of bleomycin (BLM) by blocking its metabolism. We now report that E-64 sensitizes the BLM resistant human lung carcinoma A-549 by a mechanism unrelated to the inhibition of BLM metabolism. Treatment of A-549 tumor-bearing nude mice with either BLM (10 mg/kg) or E-64 (40 mg/kg) every other day for 10 days did not inhibit tumor growth. However, a 30 min pretreatment with E-64 prior to BLM caused complete and sustained inhibition of tumor growth. In contrast to our results with Burkitt's lymphoma, E-64 did not inhibit BLM metabolism but rather enhanced the tumor accumulation of BLM; within 10 min of BLM administration, tumors from E-64 pretreated mice showed a 6-fold higher accumulation of BLM A2 compared to non-pretreated xenografts. Furthermore, the level of tumor-associated BLM A2 remained 2-fold higher in E-64 pretreated mice 20 and 30 min after BLM administration. In E-64 pretreated mice, the plasma level of BLM was increased by 2-fold. These results demonstrate that the cysteine proteinase inhibitor, E-64, sensitized human lung carcinoma A-549 to BLM and, contrary to the expected mechanism, this effect of E-64 was not related to the inhibition of BLM metabolism.

Polycyclic aromatic hydrocarbons in traditional medicinal preparations.

Ayurvedic medicinal preparations, commonly known as bhasmas, were analysed for the determination of polycyclic aromatic hydrocarbons (PAH). All the preparations contained PAH. The level of total PAH varied widely (2.32-9.55 ppm) among the preparations tested. Similarly, the benzo(a)pyrene level also varied the highest concentration being 9.7 ppm.

Cysteine proteinase inhibitors and bleomycin-sensitive and -resistant cells.

We have isolated a new human head and neck carcinoma cell line (C-10E) that is highly resistant to BLM (40-fold) when compared to the parental (A-253) cell line. Consonant with BLM resistance in the C-10E cell line, we found that this cell line accumulated 2- to 3-fold less BLM A2 than A-253 cells. Kinetic analyses of BLM A2 association revealed a decreased Vmax for C-10E cells with little change in Ka. Furthermore, the BLM-resistant cell line (C-10E) metabolized BLM A2 to a greater extent than its sensitive counterpart (A-253). Thus, compared to A-253 cells, the C-10E cells exhibited both decreased cellular association and increased metabolism of BLM. Synergistic cytotoxicity was seen when BLM was combined with either E-64 or leupeptin, cysteine proteinase inhibitors known to block BLM metabolism in vitro. E-64 inhibited the metabolism of BLM A2 in both C-10E and A-253 cells, and cellular accumulation of radiolabeled BLM A2 was increased by leupeptin or E-64 in only A-253 cells. These results suggest that both inhibition of drug metabolism and increased drug accumulation contribute to this synergism.

Lovastatin, a cholesterol biosynthesis inhibitor, inhibits the growth of human H-ras oncogene transformed cells in nude mice.

Post-translational modification of oncogenic p21ras proteins with farnesyl, a lipid intermediate in cholesterol biosynthesis, is required for p21ras membrane association and for the ability of p21ras to transform cultured cells. We have tested the ability of lovastatin, a specific inhibitor of cholesterol biosynthesis, to inhibit the growth of ras oncogene-transformed cells in vivo. Balb/c mouse 3T3 cells, transfected with H-ras oncogene from human EJ bladder carcinoma, were highly tumorigenic in nude mice. Immunoprecipitation studies with transformed EJ cells showed that lovastatin (1-100 microM) inhibited p21ras membrane association in a concentration-dependent manner and that a 10 microM concentration reduced the amount of p21ras bound to the membrane by 50%. Lovastatin also inhibited EJ cell growth in a concentration range that closely paralleled that required for inhibition of p21ras membrane association. Treatment of nude mice bearing subcutaneous (s.c.) EJ tumors with lovastatin (50 mg/kg) significantly inhibited the abilities of these tumors to grow as early as four days and, by day 12, the lovastatin treated group of animals had tumors with an average size that was 3-fold smaller than those in the saline treated group. Western blotting studies showed that lovastatin (50 mg/kg) was also able to inhibit p21ras membrane association in EJ tumors implanted s.c. in nude mice. These results demonstrate that lovastatin, an inhibitor of cholesterol biosynthesis, inhibited in vivo tumor growth of H-ras oncogene transformed cells. The results also suggest that inhibition of p21ras membrane association, an essential step in ras oncogene neoplastic transformation, is one mechanism by which lovastatin may express its antitumor activity.

Metabolic inactivation: a mechanism of human tumor resistance to bleomycin.

The mechanism of human tumor resistance to the antineoplastic drug bleomycin (BLM) is not known. We now provide evidence implicating metabolic inactivation in the resistance of human Burkitt's (Daudi) lymphoma to BLM. Daudi lymphoma and human head and neck squamous cell carcinoma (A-253) cells grown (s.c.) in nude mice were found to be resistant and sensitive to BLM treatment, respectively. Within 1 h of s.c. injection of [3H]BLM A2, Daudi xenografts accumulated less BLM and metabolized this drug to a much greater extent than did A-253 xenografts. The BLM-resistant Daudi xenografts metabolized BLM A2 to at least 6 metabolites and only a small proportion of the drug remained as unmetabolized BLM A2. In the BLM-sensitive A-253 xenografts, however, BLM A2 remained the major component. Incubation of BLM A2 with Daudi cytosolic fractions resulted in a complex mixture of metabolites similar to that formed by Daudi xenografts in nude mice. This BLM metabolite mixture was biologically inactive in plasmid DNA degradation assays. Treatment of mice bearing Daudi xenografts with an inhibitor of BLM hydrolase, L-trans-epoxysuccinyl-leucylamido-(4-guanidino)butane (E-64), prior to [3H]BLM A2 treatment did not affect the amount of BLM accumulated but inhibited BLM A2 metabolism in the xenografts. Furthermore, although E-64 alone did not inhibit the growth of Daudi xenografts, it potentiated the antitumor activity of BLM. These results indicate that Daudi tumors resist BLM by metabolically inactivating it and that inhibition of BLM metabolism in vivo enhances the antitumor activity of BLM and hence overcomes resistance.

Bleomycin hydrolase: molecular cloning, sequencing, and biochemical studies reveal membership in the cysteine proteinase family.

Bleomycin (BLM) hydrolase catalyzes the inactivation of the antitumor drug BLM and is believed to protect normal and malignant cells from BLM toxicity. The normal physiological function of BLM hydrolase is not known. We now provide evidence for its membership in the cysteine proteinase family. BLM hydrolase was purified to homogeneity from rabbit lungs, and a partial amino acid sequence was determined from a tryptic digest peptide. On the basis of this sequence a 36-mer oligonucleotide was synthesized. The 36-mer oligonucleotide probe hybridized to a single mRNA species of 2.5 kb from several species and was used to isolate an 832-bp cDNA insert from a lambda gt11 rabbit liver cDNA library. This insert encoded the tryptic digest peptide previously identified in rabbit lung BLM hydrolase by amino acid sequencing. Analysis of the predicted amino acid sequence coded by the 832-bp BLM hydrolase cDNA fragment indicated no significant homology with any currently known proteins except for a 15 amino acid portion, which displayed remarkable homology with the active site of cysteine proteinases. Within this active-site region, 10 of the amino acid residues of papain and 9 of aleurain, cathepsin H, and cathepsin L were identical with those of rabbit liver BLM hydrolase. The catalytic cysteine of thiol proteinases was also conserved in BLM hydrolase, and cysteine proteinase specific inhibitors, such as E-64, were found to be potent inhibitors of BLM hydrolase activity. Furthermore, bleomycin hydrolase exhibited cathepsin H like enzymatic activity. Bleomycin hydrolase had, however, no significant cathepsin B or L activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Histological and pharmacological changes in vas deferens of rats exposed to hexachlorocyclohexane.

The effect of hexachlorocyclohexane (HCH) treatment in male albino rats at dosages of 3 and 6 mg/kg body weight by force-feeding were studied over a period of 180 days. Histological observations revealed graded degeneration in the muscular layer of vas deferens. Moreover, the accumulation of HCH residue in serum and vas deferens is highly significant in the experimental group. The contractility of muscles showed marked inhibition by in vitro study.