Partial characterization of human leukemia U-937 cell sublines resistant to 9-nitrocamptothecin

9-Nitrocamptothecin liposome aerosol treatment of human cancer subcutaneous xenografts and pulmonary cancer metastases in mice

The purpose of this study was to test the anticancer properties of the water-insoluble derivative of camptothecin, 9-nitrocamptothecin (9NC), administered in a liposome formulation (L-9NC) in aerosol to mice with subcutaneous xenografts of three human cancers and in mice with murine melanoma and human osteosarcoma pulmonary metastases. The drug was formulated with dilauroylphosphatidylcholine and nebulized in particle sizes of 1.2-1.6 microns mass median aerodynamic diameter and a geometric standard deviation of 2.0. The aerosol was generated with the nebulizer flowing at 10 l/min and delivered to mice in sealed plastic cages or in a nose-only exposure chamber. Aerosol was administered for 15 min to 2 hr daily, delivering deposited doses in the respiratory tract of 8.1-306.7 micrograms of 9NC/kg. With subcutaneous tumors, growth was greatly inhibited or tumors were undetectable after several weeks of treatment. We also showed that oral dosage with L-9NC had no detectable effect on cancer growth, and thus the benefit from aerosol treatment was due to pulmonary deposition and not the larger fraction of drug deposited in the nose of mice during aerosol treatment which is promptly swallowed. Intramuscular L-9NC in slightly larger doses than given in the aerosol had detectable anticancer activity, but it was significantly less than in mice receiving the drug by aerosol. With metastatic pulmonary cancers, treated animals showed highly significantly less cancer growth than control animals. L-9NC aerosol showed a major therapeutic benefit in the treatment of subcutaneous human cancer xenografts in nude mice, suggesting that cancers at systemic sites might be responsive to this treatment. In addition, the strong anticancer effect of L-9NC aerosol on pulmonary metastases offers a therapeutic approach for treatment of pulmonary cancers. Thus, L-9NC aerosol may have applicability in the treatment of cancers throughout the body.

Susceptibility to apoptosis is restored in human leukemia HCW-2 cells following induction and stabilization of the apoptotic effector Bak

We demonstrate that treatment of HCW-2 cells, an apoptotic resistant variant of the human HL-60 promyelocytic leukemia cell line with phorbol-12-myristate acetate (PMA), induced differentiation along the monocytic lineage. During this process there was a dramatic increase in the mitochondrial levels of the apoptosis effector, Bak, due to the stabilization of bak mRNA, which was correlated with the sensitization of HCW-2 cells to respond to the apoptotic effect of staurosporine (STS). Treatment of PMA-differentiated, but not undifferentiated, HCW-2 cells induced processing of Bid, substantial efflux of cytochrome c from mitochondria to the cytosol, activation of caspase-3 and apoptosis. The biological significance of the increased mitochondrial Bak in differentiated HCW-2 cells was supported by the finding that transient transfection of a bak cDNA into HCW-2 cells conferred sensitivity to STS-triggered apoptosis, as determined by pro-caspase-3 processing, cytochrome c efflux and DNA fragmentation. Our results suggest that the induction of Bak, upon monocytic differentiation, may be a critical event that regulates the apoptotic sensitivity of differentiated HCW-2 cells. Oncogene (2000) 19, 4108 - 4116

SUMO-1 conjugation to topoisomerase I: A possible repair response to topoisomerase-mediated DNA damage

Ubiquitin/26S proteasome-dependent degradation of topoisomerase I (TOP1) has been suggested to be a unique repair response to TOP1-mediated DNA damage. In the current study, we show that treatment of mammalian cells or yeast cells expressing human DNA TOP1 with camptothecin (CPT) induces covalent modification of the TOP1 by SUMO-1/Smt3p, a ubiquitin-like protein. This conclusion is based on the following observations: (i) Mammalian DNA TOP1 conjugates induced by CPT were cross-reactive with SUMO-1/Smt3p-specific antibodies both in yeast expressing human DNA TOP1 as well as mammalian cells. (ii) The formation of TOP1 conjugates was shown to be dependent on UBC9, the E2 enzyme for SUMO-1/Smt3p. (iii) TOP1 physically interacts with UBC9. (iv) Ubc9 mutant yeast cells expressing human DNA TOP1 was hypersensitive to CPT, suggesting that UBC9/SUMO-1 may be involved in the repair of TOP1-mediated DNA damage.

Differentiation of human malignant melanoma cells that escape apoptosis after treatment with 9-nitrocamptothecin in vitro

After in-vitro exposure to 0.05 micromol/L 9-nitrocamptothecin (9NC) for periods of time longer than 5 days, 65% to 80% of the human malignant melanoma SB1B cells die by apoptosis, whereas the remaining cells are arrested at the G2-phase of the cell cycle. Upon discontinuation of exposure to 9NC the G2-arrested cells resume cell cycling or remain arrested depending on the duration of 9NC exposure. In contrast to cycling malignant cells, the cells irreversibly arrested at G2 exhibit features of normal-like cells, the melanocytes, as assessed by the appearance of dendrite-like structures; loss of proliferative activity; synthesis of the characteristic pigment, melanin; and, particularly, loss of tumorigenic ability after xenografting in immunodeficient mice. Further, the expression of the cyclin-dependent kinase inhibitor p16 is upregulated in the 9NC-treated, G2-arrested, but downregulated in density G1-arrested cells, whereas the reverse is observed in the expression of another cyclin-dependent kinase inhibitor, p21. These results suggest that malignant melanoma SB1B cells that escape 9NC-induced death by apoptosis undergo differentiation toward nonmalignant, normal-like cells.

9-nitrocamptothecin selectively inhibits human immunodeficiency virus type 1 replication in freshly infected parental but not 9-nitrocamptothecin-resistant U937 monocytoid cells

We have previously reported that 9-nitrocamptothecin (9NC) inhibited human immunodeficiency type 1 (HIV-1) replication in latently HIV-1-infected T lymphocytic ACH-2 cells stimulated with the cytokine tumor necrosis factor alpha (TNF-alpha) (Moulton et al., AIDS Res Hum Retroviruses 1998;14:39). 9NC induced an accelerated apoptosis in HIV-1-infected, but not uninfected, lymphocytic cells. The present study demonstrates that 9NC selectively inhibits release of HIV-1 from freshly infected monocytoid U937 cells in a dose-response manner. Significant inhibition was achieved with concentrations of 9NC that were not toxic. In contrast, HIV-1 replication in 9NC-resistant monocytoid cells, derived from U937, was not inhibited by similar doses of 9NC. Importantly, sensitivity of HIV-1 replication to 9NC correlated with the effect of 9NC on topoisomerase I (topo I) activity. In a 9NC-sensitive subline, 9NC induced posttranslational activation of the nuclear transcription factor kappaB (NF-kappaB) after the drug treatment. This activation was neither related to selective 9NC suppression of HIV-1 replication, nor was it sufficient for the 9NC-induced toxicity in the drug-sensitive monocytoid cells. Taken together, the selective inhibition of HIV-1 replication in both lymphoid and monocytoid cells lends further credence to the potential development of 9NC as an alternative drug for treating HIV-1 infection.

Induction of apoptosis in malignant and camptothecin-resistant human cells

Flow cytometry studies demonstrate that androgen-independent human prostate carcinoma DU-145 cells are arrested at the G1-phase of the cell cycle in the presence of suramin, but they die by apoptosis in the presence of 9-nitrocamptothecin (9NC). The addition of cytostatic concentrations of suramin increases the apoptotic action of 9NC on DU-145 cells, and induces apoptosis in 9NC-resistant DU-145/RC cells that were derived from the parental DU-145 cells by continuous exposure to progressively increased concentrations of 9NC. In addition, the topoisomerase II-directed drug etoposide exerts more extensive apoptotic action on DU-145/RC than DU-145 cells. Increased resistance of DU-145 cells to 9 NC and collaterally increased sensitivity to etoposide and suramin appear to correlate with alterations in the structure rather than synthesis of topoisomerases and possibly with specific cellular proteins that regulate apoptosis. The results suggest that etoposide and suramin may be successful alternative treatments for 9NC-resistant androgen-independent prostate cancer.

The water-insoluble camptothecin analogues: promising drugs for the effective treatment of haematological malignancies

After failing to exhibit benefits in clinical studies with cancer patients in the early 1970s, camptothecin (CPT) and its water-insoluble analogues are re-emerging as promising drugs with multiple actions in the treatment of human haematological malignancies. CPT analogues interfere with the mechanism of action of the nuclear enzyme topoisomerase I, while the cells progress through the S-phase of the cell cycle and this results in cell death by apoptosis. Modulations of topoisomerase I phosphorylation may indirectly modulate the cytotoxic activity of CPT analogues. In vitro, CPT analogues have exhibited increased or unaltered killing activity against leukaemia cells resistant to epipodophyllotoxins, anthracyclines, anthracenediones, and Vinca alkaloids, while development of resistance to CPT analogues renders leukaemia and lymphoma cells more sensitive to topoisomerase II-directed drugs, inducers of cell differentiation, and immunotoxins. Oral administration of the CPT analogues has circumvented the inconvenience of solubility of these drugs. Metabolic conversion of the CPT analogue 9-nitro-CPT to equally or more potent 9-amino-CPT practically makes unnecessary treatment of the patient with 9-amino-CPT, which, in addition, is costlier to prepare than 9-nitro-CPT. Considering the therapeutic, economic and handling viewpoints, the overall conclusion is that the water-insoluble CPT analogues are very promising antileukaemia/antilymphoma agents that warrant further preclinical and clinical studies.