Structure-activity relationship of alkyl camptothecin esters

The cytotoxicity of camptothecin (CPT) esters 1-6 was measured. Like parental camptothecin, esters 2 and 3, but not 1, 4, 5, and 6, inhibited proliferation of human leukemia cells in culture and induced programmed cell death as assessed by flow cytometry studies. Exhibition of similar levels of antiproliferative activities of CPT 2 and 3 required different incubation time periods in cell cultures, with CPT and 3 requiring the shortest and longest periods, respectively. Both 2 and 3 were inactive against cells resistant to the semisynthetic CPT derivative 9-nitrocamptothecin and unable to stabilize DNA-topoisomerase I (Topo I) "cleavable complexes" in a cell-free system, suggesting that Topo I activity was required but insufficient for the mechanism of action of 2 and 3. Mouse liver homogenate converted esters to parental CPT, but the conversion rates were different with different esters. Of four tested esters in this experiment, ester 2 had the fastest conversion rate. In vivo studies showed that ester 2 had an exceptional lack of toxicity in nude mice, even at enormous doses, and demonstrated extensive activity against human breast and colon tumors grown as xenografts in immunodeficient nude mice, whereas no antitumor activity was observed for the other esters. In conclusion, ester 2 is a prodrug of the antitumor compound CPT, and it can be administered at very high doses in mice with no appearance of toxicity. This study provides a basis for further evaluation of CPT ester 2 as an investigational anticancer agent.

Alternative administration of camptothecin analogues

The binding of camptothecin (CPT) to the DNA-topoisomerase complex is reversible, but it needs to be maintained for maximal inhibitory activity. It is also dependent on the chemical structure of CPT. The lactone form is thought to be necessary for the activity. In human serum, the equilibrium between lactone and carboxylate is in favor of the latter. For these reasons, alternative administration of CPT analogues is being evaluated. The ideal compound would remain in lactone form and would expose the host for long periods of time to its effects. Oral administration of irinotecan (CPT-11) and topotecan (TPT) is discussed by other investigators. We studied oral rubitecan and reported a low lactone to total drug area under the plasma concentration-time curve (AUCP) ratio (14.7%), with low plasma concentration over time despite repeated administrations and the presence of an enterohepatic cycle. Aerosolization of a liposomal formulation of rubitecan is currently under study. Six patients have been treated once a day for 5 days every 3 weeks. The dose was 6.7 micrograms/kg/day. Plasma levels are dose for dose higher than those after oral administration, but the ratio of lactone versus total drug is low. No toxicity was observed. The study will continue with increasing doses and lengths of administration. Intrathecal administration of topotecan has been studied in a phase I trial in children. Doses of 0.4 mg are tolerated without toxicity, and clinical responses have been seen in patients with refractory meningial carcinomatosis. Phase II studies are planned. Intraperitoneal (i.p.) administration of topotecan has been studied in a phase I trial as a 24-hour infusion in 5% dextrose at pH 3.5 every 21 days. Dose-limiting toxicity is 4 mg/m2. Toxic effects are neutropenia, anemia, emesis, fever, and pain. Five of 10 patients with ascites had symptomatic relief. Pharmacokinetic analysis demonstrates a second-order kinetics with elimination half-lives of 0.49 and 2.7 hours. The peritoneal to plasma AUC ratio was 31.2. Intramuscular, transdermal, and subcutaneous administrations have been extensively studied in the mouse.

Altered sensitivities to anticancer and differentiation agents in etoposide-resistant human myeloid leukemia U-937 cells

We previously have exposed U-937 human leukemia cells to stepwise increased concentrations of the anticancer drug etoposide, and this treatment has resulted in stable sublines (termed U-937/RE) exhibiting various extents of resistance to the drug and constitutively expressing c-fms mRNA, a specific marker of monocytic differentiation. In this report, we pursued studies to show that the P-glycoprotein blocker, verapamil, partially restores sensitivity to etoposide in U-937/RE cells. Further, the U-937/RE cells exhibit differential sensitivities to compounds that induce maturation of U-937 cells, as judged by the ability to reduce nitroblue tetrazolium and by morphologic changes, and increased sensitivities to apoptosis induction by the cytokines tumor necrosis factor (TNF) and lymphotoxin (LT) and the anticancer drugs 9-nitrocamptothecin and doxorubicin. In addition, the U-937/RE cells, xenografted in immunodeficient mice, demonstrate decreased or no ability to induce tumors. Taken together, these findings indicate that U-937/RE cells differ from the parental U-937 cells in several functional properties and can serve as models to develop protocols for treatment of human leukemia.

Alkyl esters of camptothecin and 9-nitrocamptothecin: synthesis, in vitro pharmacokinetics, toxicity, and antitumor activity

Eleven camptothecin esters, 6a-e and 7a-f, were prepared by straightforward acylation of camptothecins with the corresponding acylating reagents such as organic anhydrides and carboxylic acid chlorides. The in vitro pharmacokinetic determination of lactone levels of esters 6a and 7b showed that the biological life span of their lactone forms in human and mouse plasma significantly increased when compared with their mother compounds, camptothecin (3) and 9-nitrocamptothecin (4). The differences of lactone levels between human plasma and mouse plasma for 6a and 7b were much smaller than what was observed for their mother compounds. The in vivo antitumor activity and toxicity studies demonstrated that some of these esters were very active against human tumor xenografts in nude mice and had an exceptional lack of toxicity in nude mice, even at enormous doses.

Establishment of human prostate tumor xenografts in nude mice and response to 9-nitrocamptothecin in vivo and in vitro does not correlate with the expression of various apoptosis-regulating proteins

Flow cytometry and microscopy analyses have demonstrated that 9-nitrocamptothecin (9NC) induces apoptosis in prostate carcinoma LNCaP, DU-145 and PC-3 cells grown in culture or as xenografts. 9NC induces apoptosis regardless of the ability of the cells to induce tumors following xenografting into nude mice. Detection of apoptosis by flow cytometry was preceded or accompanied by increased cell size, loss of nuclear structure and vacuolization, as the tumor regressed, but no visible chromatin fragmentation. This is the first demonstration that 9NC is curative for human prostate carcinoma xenografts in the nude mouse model in the absence of detectable drug-induced toxicity during and after tumor regression. These findings indicate that 9NC may develop into a chemotherapeutic drug for the effective treatment of prostate cancer patients. Further, there was no apparent correlation of the steady-state level of the apoptosis-regulating proteins, Bcl-2, Bcl-XL, Bax and Ich-1, with tumorigenicity of the prostate cells xenografted in nude mice, aggressiveness of tumors grown in nude mice, and induction of apoptosis by 9NC. However, the TIAR protein was present at markedly high levels in all prostate carcinoma cell lines and this may correlate with their susceptibility to 9NC-induced apoptosis.

Monocytic differentiation and synthesis of proteins associated with apoptosis in human leukemia U-937 cells acquiring resistance to vincristine

Human leukemia U-937/WT cells were exposed to stepwise increased concentrations of Vincristine so that Vincristine-resistant cell sublines (termed U-937/RV) were developed. Established U-937/RV cell sublines have continuously propagated over a year, both in absence and presence of VCR, and have demonstrated similar features. In contrast to U-937/WT cells, U-937/RV cells have longer doubling time, and are more differentiated as determined by appearance of distinct morphological features and synthesis of mRNA that codes for the monocyte colony-stimulating factor-1 receptor (c-fms). Both apoptosis-suppressing Bcl-2 and Bcl-XL proteins were undectable in U-937/WT cells, whereas Bcl-2 was nearly detectable and Bcl-XL readily detectable in U-937/RV cells. The apoptosis-promoting Bax protein was also absent in U-937/WT cells and readily detected in U-937/RV cells. Vincristine-resistant cells with different levels of resistance synthesize similar levels of c-fms mRNA and Bax protein. Finally, unlike U-937/WT cells, U-937/RV cells have no ability to induce tumors when xenografted in immunodeficient mice. The findings collectively suggest that development of resistance to Vincristine in U-937/WT cells may correlate with cell differentiation and synthesis of proteins that regulate apoptosis.

Development of human leukemia U-937 cell sublines resistant to doxorubicin: induction of differentiation and altered sensitivities to topoisomerase-directed drugs

Cell sublines resistant to doxorubicin (DOX) were developed from the human leukemia cell line, U-937/WT, exposed to stepwise DOX increases. In contrast to U-937/WT cells, the DOX-resistant U-937/RD cells have longer doubling time; are more differentiated along the monocytic lineage as determined by the presence of morphological features and mRNA coding for the monocyte colony-stimulating factor-1 receptor; synthesize the apoptosis-associated Bax protein; are less sensitive to apoptosis-inducing topoisomerase II-directed drugs, apparently because of increased synthesis of P-glycoprotein; and are practically non-tumorigenic when xenografted in nude mice. However, U-937/WT and U-937/RD cells exhibit similar sensitivity to the apoptosis-inducing drug 9-nitrocamptothecin. These findings suggest that several mechanisms are involved in the development of DOX-resistance in U-937 cells, and further, 9-nitrocamptothecin can overcome resistance to DOX. These findings may have clinical implications.

Sensitivity of camptothecin-resistant human leukemia cells and tumors to anticancer drugs with diverse mechanisms of action

Human leukemia U-937 cell clones resistant to 9-nitrocamptothecin (9NC) appear after exposure to increase 9NC-concentrations. Drug resistance is irreversible, regardless of whether the 9NC-resistant (U-937/CR150) cells grow in media with or without 9NC. U-937/CR150 cells are more sensitive than wild type U-937 (U-937/wt) cells to topoisomerase II-directed drugs, amsacrine, daunorubicin, and etoposide. The mitotic inhibitor, vincristine, induces hyperdiploidy in U-937/wt, but not in U-937/CR150 cells, whereas the antimetabolites, cytarabine and methotrexate, and the nitrosourea, carmustine, elicit similar responses in both U-937/wt and U-937/CR150 cells. U-937/CR150-generated tumors in nude mice are sensitive to etoposide. The clinical implications of increased sensitivity of 9NC-resistant tumors to some anticancer drugs are discussed.

Therapeutic efficacy of camptothecin derivatives against human malignant melanoma xenografts

Camptothecin (CPT) and some of its derivatives are currently used in several clinical studies with patients bearing leukaemias, lymphomas, and malignancies of various solid tissues. Therefore, it is important to establish parameters and conditions that will allow the drugs to exhibit maximal anti-cancer effectiveness with minimal toxic effects. We tested several water-insoluble CPT derivatives for their ability to inhibit growth of human melanoma tumours xenografted in nude mice. We found that anti-tumour effectiveness and drug-induced toxicity depended on (a) the CPT derivative; (b) the drug dose administered; (c) the mode of administration; and (d) the scheduling of drug administration. For all practical purposes, oral administration of the CPT derivative, 9-nitrocamptothecin, has produced the best overall results.

Identification of a mutant human topoisomerase I with intact catalytic activity and resistance to 9-nitro-camptothecin

Human U-937 myeloid leukemia cells were selected for resistance to increasing concentrations of the camptothecin derivative, 9-nitro-20(S)camptothecin (9-NC). The isolated single cell clone, designated U-937/CR, was approximately 20-fold resistant to 9-NC. Analysis of topoisomerase I (topo I) gene expression in U-937/CR cells demonstrated similar mRNA levels as compared with U-937 cells. Immunoblotting with an anti-topo I serum revealed reactive proteins at 100, 75, and 67 kDa which were expressed at the same level in the parental and 9-NC-resistant clones. These cell lines also demonstrated similar levels of topo I catalytic activity as determined by assaying nuclear extracts for relaxation of supercoiled plasmid DNA. In contrast, catalytic assays performed in the presence of 9-NC demonstrated that topo I activity from U-937/CR cells was approximately 10-fold more resistant than that from U-937 cells. Nucleotide sequencing of topo I cDNAs revealed the substitution of phenylalanine (TTC) at residue 361 in U-937 cells with serine (TCC) in the 9-NC-resistant clone. Expression and partial purification of the mutant topo I protein in Escherichia coli demonstrated resistance of this enzyme to 9-NC in catalytic assays. Taken together, these findings identify a novel mutation in topo I which confers resistance to 9-NC and support the involvement of this region in the interaction between topo I and 9-NC.

An osteosarcoma cell line with hypodiploid chromosome number and complex structural anomalies

Giemsa-banding analysis performed on a newly established metastatic osteosarcoma cell line (SP-388) that was passaged through the nude mouse revealed a hypodiploid stemline number of 39 chromosomes. This cell line showed both numerical and structural abnormalities, including the abnormally banded region in certain marker chromosomes. Chromosomes 3, 15, 17 and the X were the most frequently absent elements of this tumor. Segments of chromosomes 3, 15 and X could not be identified even in rearranged chromosomes (Ml to M15). We suggest that more cases of osteosarcoma should be studied so that specific primary and secondary chromosomal anomalies can be identified in human osteosarcoma.

Camptothecin and its derivatives induce expression of the c-jun protooncogene in human myeloid leukemia cells

We have recently demonstrated that certain camptothecin derivatives are effective agents in the treatment of human tumor xenografts in nude mice. While camptothecin and its derivatives are recognized as inhibitors of topoisomerase I, little is known about the effects of these agents on specific gene expression, particularly genes involved in growth control. The c-jun early response gene codes for a leucine zipper transcription factor. The present studies demonstrate that 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin inhibit the growth of human U-937 myeloid leukemia cells and induce expression of the c-jun gene. c-jun transcripts were increased at 3 h and reached a maximum at 6 h of drug exposure. We also demonstrate that the induction of c-jun gene expression by these agents occurs at the transcriptional level. H7, a nonselective inhibitor of protein kinase C, completely blocked c-jun expression in 20(S)-camptothecin-treated cells, while another protein kinase inhibitor, HA1004, had no detectable effect. Similar findings were obtained for other leucine zipper encoding genes, including jun-B. These results suggest that 20(S)-camptothecin, 9-amino-20(S)-camptothecin, and 9-nitro-20(S)-camptothecin activate a cellular response involving the induction of early response genes. Finally, we demonstrate that induction of c-jun expression occurs in association with internucleosomal DNA fragmentation, a characteristic of programmed cell death.

Effect of sequential application of hyperthermia and chemotherapy on the survival of a thermoresistant human melanoma cell line

The human melanoma cell line M14 has been proven in previous experiments to be much less sensitive to the action of heat (42 degrees C, 60 min) than other melanoma lines. In the present study, we have investigated the possibility of increasing the effect of heat by means of drug treatment. Thermochemotherapy was applied to exponentially growing cells according to different schedulings, and was analyzed in its efficacy by measuring the impairment of the cellular colony-forming ability. Findings of the present study point out that: (a) appropriate sequencing between hyperthermia and cis-diamminedichloroplatinum II(DDP), melphalan (L-Pam), 1,2,4-dichlorobenzyl-1H-indazol-3-carboxylic acid (LNA) or 5-3,3-dimethyl-1-triazeno-imidazole-4-carboxamide (DTIC) strongly influences the cytotoxic effect of the two agents; and (b) the optimal combination appears to be the simultaneous application of heat and drugs. However, as far as thermochemotherapy with DDP is concerned, a synergistic effect may also be achieved when hyperthermia precedes DDP.

Establishment and characterization of cell lines from human small cell and large cell carcinomas of the lung

Five new small cell carcinomas (SCC) cell lines and a large cell carcinoma (LCC) cell line were established from human lung cancers. The SCC cell lines had, as a group, common phenotypic properties which distinguished them from non-SCC cell lines. However, the studies also revealed a considerable biological heterogeneity among the individual SCC cell lines. Thus, the SCC cell lines had a typical growth pattern with cell clusters in suspension or partly adherent to the bottom. All the lines examined grew in agarose with variable cloning efficiencies, and all but one line formed tumors subcutaneously in nude mice. The ultrastructure of the SCC cell lines was characteristic with dense core granules at a variable frequency. Neuron-specific enolase was detectable in all SCC cell lines, usually in large amounts, and an inconstant production of a spectrum of polypeptide hormones was found, typical of SCC. The LCC cells proliferated in monolayers, formed colonies in agarose and grew in nude mice. Ultrastructurally, the LCC cell line differed from the SCC cell lines in having intra- and intercellular lumina and tonofilaments. The capacity of the LCC and a previously established squamous cell carcinoma cell line (U-1752) to produce neuron-specific enolase and polypeptide hormones was characteristically much lower than that of the SCC cell lines. We conclude from this study that SCC cell lines, although individually distinct from one another, are quite homogeneous as a group in expressing a set of basic common neuro-endocrine markers. However, these studies also suggest some biological relationship between SCC, LCC and SQC by virtue of their expression of some common neuro-endocrine markers, in support of the concept of a common histogenetic origin of human lung cancers.

A 3q+ marker chromosome in EBV-carrying nasopharyngeal carcinomas

The malignant epithelial cells of two anaplastic EBV-carrying nasopharyngeal carcinomas (NPC) were investigated cytogenetically by Giemsa banding technique. Both tumors had a similar 3q+ marker chromosome with an involvement of band q25, either a duplication of the region q25-q27, or insertion of an unidentified segment at band q25.

Establishment and characterization of a human EBV-negative B cell line (MN 60)

A permanent cell line, MN 60, was established from the peripheral blood of a patient with an acute lymphoblastic leukemia (ALL) classified morphologically as being of the L3 type. Cell growth started rapidly in vitro and no feeder cells were needed. Cells of the MN-60 line were identical to the original leukemic cells with respect to surface immunoglobulin (Ig) expression and karyotype, including the presence of four marker chromosomes [1q+, 6q-, t(8;14)]. Continuous proliferation was maintained in stationary suspension culture with a doubling time of 25 h. The cells were tumorigenic in athymic nude mice and had the capacity to form colonies in semi-solid medium in vitro. Monoclonal surface Ig (mu lambda) was demonstrated whereas no cytoplasmic immunoglobulin could be demonstrated. The MN-60 cells were Epstein-Barr virus (EBV) negative as evidenced by EBNA tests and by nucleic acid hybridization studies. The cells expressed HLA-A-C, HLA-DR. beta 2-Microglobulin and cALL, but not Fc gamma. C3, sheep and mouse red blood cell receptors. No reactivity was found with anti-glycophorin A or the anti-BL 38.13 monoclonal antibody. Cell growth was retarded in the G0/G1 phase of the cell cycle after incubation with leukocyte interferon, hydrocortisone, phorbol myristate acetate and dimethyl sulphoxide.

Growth of diploid, Epstein-Barr virus-carrying human lymphoblastoid cell lines heterotransplanted into nude mice under immunologically privileged conditions

Human Epstein-Barr virus-carrying lymphoid cell lines which have been classified on the basis of studies on clonality and morphological, chromosomal and functional parameters as lymphoblastoid cell lines (LCL) of presumed non-neoplastic origin were inoculated intracerebrally into nude mice. All eighteen of them grew, killing the host mice within 7 to 25 days, except for 2 which grew more slowly. At autopsy, the brain of the nudes was found to be invaded by infiltrating lymphomas. Sixteen of these lymphomas, when recultured in vitro, gave rise to cell lines with growth properties and morphology indistinguishable from those of the inoculated LCL. Chromosomal examinations showed that 3/7 cell lines injected, which grew as lymphomas in the brain, were still normal diploid on reexplantation whereas the remaining four had become aneuploid. Four lines derived from intracerebral lymphomas (2 diploid, 1 aneuploid and 1 untested) were inoculated subcutaneously into adult nude mice. None of them grew. When the corresponding four original LCL lines were inoculated subcutaneously into newborn nude mice, they grew rapidly, but failed to do so in newborn normal mice or intracerebrally in adult normal mice. One such line, U-1450, was treated with anti-lymphocyte serum (ALS). Small nodules developed at the site of inoculation. From one nodule a cell line was cultured, 1450 ALSAD. It was morphologically indistinguishable from the line of origin. The lines obtained from nude mice inoculated with polyclonal LCL seem to have a restricted clonal representation, but were not monoclonal, as evidenced by analyses of their pattern of immunoglobulin synthesis.

An EBV-genome-negative cell line established from an American Burkitt lymphoma; receptor characteristics. EBV infectibility and permanent conversion into EBV-positive sublines by in vitro infection

An in vitro line was derived from an American Burkitt lymphoma, designated Ra No. 1, which produced malignant tumors when inoculated into thymus-deficient nude mice. The cells have B-lymphocyte characteristics, with surface-associated mu and kappa chains and Epstein-Barr virus (EBV) receptors, and can be readily infected with EBV in vitro. B95-8 virus induced EBV-determined nuclear antigen (EBNA) but not early antigen (EA) in Ra No. 1 cells, whereas P3HR-1 virus induced both EBNA and EA, but the EA level was much lower than in the prototype Raji strain, EBNA and EA levels were comparable in Ra No. 1 and in the previously established, EBV-infection-sensitive BJA-B lymphoma. The two lines differed, however, because BJA-B could be converted into a permanent EBV-carrying line by the B95-8 but not by the P3HR-1 virus strain, whereas Ra No. 1 could be converted by the P3HR-1 virus. This demonstrates that different B-lymphocyte-derived lymphoma lines can vary with regard to the restrictive control they can exert on the same virus strain. Furthermore, virus strains vary in their sensitivity to the restrictions of the same host cell. Permanent EBV conversion of the Ra No. 1 cell did not appear to change the cellular controls, as judged by the unchanged sensitivity of the cell to viral antigen (EA, viral capsid antigen) induction by P3HR-1 virus superinfection.