In vitro cytotoxicity of 2-chlorodeoxyadenosine and chlorambucil in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is most commonly treated with the alkylating agent chlorambucil (CLB), although the nucleoside analogs, fludarabine (Flu) and 2-chlorodeoxyadenosine (CdA), are also effective in this disease. In this study, we investigated the in vitro cytotoxicity of CdA and CLB in CLL cells from 12 patients in vitro. Treatment with CLB for 6 h, followed by CdA for 18 h, resulted in 2.3- to 7.5-fold synergistic cytotoxicity in leukemic cells from 10 patients and an additive effect in cells from two patients. In general, synergy was greatest in patients who were sensitive to CLB or CdA, and could be enhanced by increasing the concentrations of CLB or CdA. Synergy was only observed if the cells were treated with CLB prior to CdA. Synergy could not be explained by an increase in the incorporation of CdA into DNA, or by the inhibition of repair of CLB-induced DNA crosslinks by CdA. In contrast to CLL cells, treatment of human marrow in vitro with CLB and CdA resulted in a low level of synergy for CFU-GM cells, and additive cell kill in erythroid progenitors. Thus, treatment with CdA and CLB can produce selective synergistic cell kill in CLL cells, and combination therapy may improve the therapeutic index of these agents in chemosensitive patients.

Active transport of glutathione S-conjugate in human colon adenocarcinoma cells

The formation of the glutathione S-conjugate of monochlorobimane (GSH-bimane) in human colon adenocarcinoma cells was identified by HPLC-fluorimetry and its transport from the cells was found to be temperature-sensitive, saturable and ATP-dependent. The apparent K(m) and Vmax values were 2.4 +/- 0.5 nmol GSH-bimane/10(6) cells and 0.5 +/- 0.1 nmol GSH-bimane/min per 10(6) cells, respectively. This active transport of GSH-bimane was inhibited by low micromolar concentrations of classical uncouplers of oxidative phosphorylation, namely carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), carbonylcyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP). The efflux of GSH-bimane was competitively inhibited by chlorambucil (CMB) and 1-chloro-2,4-dinitrobenzene (CDNB), two other substrates of GST. This study demonstrates the presence and kinetic measurements of the glutathione S-conjugate export (GS-X) pump in human colon cancer cells, an export pump whose function has been implicated in the phenomenon of multidrug resistance.

Chlorambucil and bleomycin induce mutations in the specific-locus test in female mice

Specific-locus studies have shown chlorambucil (CHL) and bleomycin (BLE) to be mutagenic in mouse oocytes, almost doubling the number of chemicals previously known to induce mutations in females. The overall CHL-induced mutation rate in oocytes is, however, one order of magnitude below that for male meiotic and postmeiotic stages, and only 1/50 that for early spermatids. For BLE, no specific-locus data for males are available for comparison, but the chemical had earlier been found negative for dominant-lethal induction in males. Both BLE and CHL were significantly mutagenic only in mature and maturing oocytes. In keeping with an earlier report, BLE produced a high incidence of dominant lethals in these stages. CHL failed to induce dominant lethals, indicating that for mature and maturing oocytes, in contrast with results for males, sensitivity to dominant-lethal mutations is not a prerequisite for induction of specific-locus mutations. Exposure of immature oocytes to either BLE or CHL produced neither dominant lethals nor significant induction of specific-locus mutations; however, CHL gave evidence of killing immature oocytes. By contrast, BLE, which has been considered a radiomimetic chemical, does not appear to kill immature oocytes and thus differs markedly from radiation exposures equivalent for dominant-lethal induction. Therefore, the failure to recover specific-locus mutations cannot be ascribed to cell selection resulting from oocyte killing, as has sometimes been done for radiation. Adding results on the nature of the CHL- and BLE-induced mutations to prior information, the estimated minimum proportion of large DNA lesions induced in oocytes by chemicals becomes 35.3%, significantly different from the corresponding figure (approximately 70%) for radiations. For chemical treatments, the oocyte proportion is highly significantly above the 3.6% induced in spermatogonia, but only on the borderline of statistically significant difference from that induced in postspermatogonial stages.

Chlorambucil in chronic lymphocytic leukemia: mechanism of action

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries but the clinical presentation and rate of disease progression are highly variable. When treatment is required the most commonly used therapy is the nitrogen mustard alkylating agent, chlorambucil (CLB), with or without prednisone. Although CLB has been used in the treatment of CLL for forty years the exact mechanism of action of this agent in CLL is still unclear. Studies in proliferating model tumor systems have demonstrated that CLB can bind to a variety of cellular structures such as membranes, RNA, proteins and DNA; however, DNA crosslinking appears to be most important for antitumor activity in these systems. In addition, a number of different mechanisms can contribute to CLB resistance in these tumor models including increased drug metabolism, DNA repair and CLB detoxification resulting from elevated levels of glutathione (GSH) and glutathione S-transferase (GST) activity. However, unlike tumor models in vitro, CLL cells are generally not proliferating and studies in CLL cells have raised questions about the hypothesis that DNA crosslinking is the major mechanism of antitumor action for CLB in this disease. CLB induces apoptosis in CLL cells and this appears to correlate with the clinical effects of this agent. Thus, alkylation of cellular targets other than DNA, which can also induce apoptosis, may contribute to the activity of CLB. Alterations in genes such as p53, mdm-2, bcl-2 and bax which control entry into apoptosis may cause drug resistance. Loss of wild-type p53 by mutation or deletion occurs in 10 to 15% of CLL patients and appears to correlate strongly with poor clinical response to CLB. The induction of apoptosis by CLB is paralleled by an increase in P53 and Mdm-2 but this increase in not observed in patients with p53 mutations indicating that with high drug concentrations CLB can produce cell death through P53 independent pathways. The level of Mdm-2 mRNA in the CLL cells is not a useful predictor of drug sensitivity. In addition, although Bax and Bcl-2 are important regulators of apoptosis and the levels of these proteins are elevated in CLL cells compared with normal B cells, the levels of Bax and Bcl-2, or the Bax:Bcl-2 ratio, are not important determinants of drug sensitivity in this leukemia. Finally, whereas CLB and nucleoside analogs may produce cell death in CLL by a P53 dependent pathway other agents, such as dexamethasone or vincristine, may act through P53-independent pathways.

Failure to induce resistance to cytotoxic drugs in normal lymphocytes

Lymphocytes from patients who had received chemotherapy for lung cancer were examined for evidence of drug resistance using an in vitro assay for sensitivity to the effects of chlorambucil and etoposide. There was no evidence of induced resistance to the effects of chlorambucil or etoposide in the patients' lymphocytes when compared to the sensitivity of the normal control subjects' lymphocytes. In four patients, in whose lymphocytes sensitivity to chlorambucil was measured before and after a course of treatment, there was no significant change in the in vitro drug sensitivity. These findings are in contrast to those made previously using the lymphocytes of patients with chronic lymphocytic leukaemia and indicate that acquired drug resistance is a property of malignant cells and is not inducible in normal lymphocytes.

Inhibition of intracellular pH control and relationship to cytotoxicity of chlorambucil and vinblastine

The uptake and cytotoxicity of weakly acidic or basic chemotherapeutic agents is determined in part by passive diffusion along the pH gradient between the intracellular and extracellular compartments. In vivo it is known that tumour extracellular pH is more acidic than intracellular pH. Using CaNT murine tumour cells in vitro, we found the cytotoxicity of chlorambucil (a weak acid) increased as the extracellular pH of the culture medium (pHmed) was acidified. The cytotoxicity of vinblastine shows a reverse pH relationship with reduced cytotoxicity as pHmed was acidified. Chlorambucil cytotoxicity increased at acidic pHmed because the weak acidic function is ionised to a lesser extent at acidic pH and, therefore, favours drug uptake into the relatively neutral intracellular compartment. Vinblastine cytotoxicity decreased at acidic pHmed because the weak basic function is ionised to a greater extent at acidic pH and therefore does not favour drug uptake into the relatively neutral intracellular compartment. Using a combination of an inhibitor of the cell membrane proton pump, amiloride, and the ionophore, nigericin, the intracellular compartment can be acidified. This results in a time-dependent increase in sensitivity of the cells to low pHmed with significant cytotoxicity after 6 h exposure to pHmed = 6.2 and suggests that there is potential for direct tumour cytotoxicity in vivo if the tumour extracellular pH were equally acidic. An indirect effect of intracellular acidification is to alter the distribution of drugs between the extra- and intracellular compartment by reducing the pH gradient across the cell membrane. In response to intracellular acidification, the cytotoxicity of chlorambucil was reduced and that for vinblastine was increased. Inhibition of cellular pH control may result in direct cytotoxicity by acidification due to inhibition of proton efflux or indirectly by resulting in differential uptake of chemotherapeutic agents with weak acidic or basic functions.

RecA-catalyzed, sequence-specific alkylation of DNA by cross-linking oligonucleotides. Effects of length and nonhomologous base substitutions

Oligodeoxyribonucleotides (ODNs) bearing the reactive nitrogen mustard chlorambucil have been used as sequence-directed affinity labeling reagents to investigate the length and homology requirements for RecA-catalyzed alkylation of double-stranded DNA. The cross-linkage reaction, which takes place at the N-7 position of a targeted complementary strand guanine following strand exchange, was highly sequence specific with both a 272 bp DNA fragment and a linearized plasmid. Alkylation required the ODN to be at least 26 nucleotides long and to possess homology to the target in the vicinity of the modification site. The extent of alkylation was improved by using longer ODNs, with a 50-mer giving over 50% reaction. Mismatches inhibited alkylation when they perturbed the structure of the strand exchange product near the targeted guanine. Longer heterology also inhibited alkylation when it prevented strand exchange. Our inability to detect cross-linkage in stable synaptic complexes unable to undergo complete strand exchange is best explained by a model for homologous alignment in which the presynaptic filament approaches from the minor groove of the duplex. Since the N-7 position of guanine is in the major groove, it is inaccessible to the tethered chlorambucil group of the ODN during the search for homology. The reaction specificity of chlorambucil-bearing ODNs suggests that they may have general use as recombinase-mediated DNA targeting agents.

Retrovirus-mediated gene transfer of rat glutathione S-transferase Yc confers in vitro resistance to alkylating agents in human leukemia cells and in clonogenic mouse hematopoietic progenitor cells

Recently, we have reported that N2Yc, a Moloney-based retrovirus vector expressing the Yc isoform of rat glutathione S-transferase (GST-Yc), conferred resistance to alkylating agents in mouse NIH-3T3 fibroblasts. In this report, we address the feasibility of using rat GST-Yc somatic gene transfer to confer chemoprotection to the hematopoietic system. Human chronic myelogenous leukemia K-562 cells were efficiently transduced with the N2Yc retrovirus vector and showed a significant increase in the 50% inhibitory concentration of chlorambucil (3.2- to 3.3-fold), mechlorethamine (4.7- to 5.3-fold), and melphalan (2.1- to 2.2-fold). In addition, primary murine clonogenic hematopoietic progenitor cells transduced with the N2Yc vector were significantly more resistant to alkylating agents in vitro than cells transduced with the antisense N2revYc vector. The survival of Yc-transduced hematopoietic colonies at 400 nM mechlorethamine and 4 mu M chlorambucil was 39.4% and 42.6%, respectively, compared to 27.2% and 30.4% for N2revYc-transduced cells. Future experiments will determine the level of chemoprotection achievable in vivo, following transplantation of N2Yc-transduced hematopoietic cells in mice.

Excision of DNA adducts of nitrogen mustards by bacterial and mammalian 3-methyladenine-DNA glycosylases

Nitrogen mustards are among the DNA alkylating agents most widely used in chemotherapy. The homogeneous Escherichia coli AlkA protein (3-methyladenine-DNA glycosylase II) is shown to excise damaged guanine and adenine bases from DNA modified by mechlorethamine, uracil mustard, phenylalanine mustard and chlorambucil, and less efficiently acridine mustard adducts. Homogeneous recombinant human and rat 3-methyladenine-DNA glycosylases excise adducts formed by nitrogen mustards less efficiently than the AlkA protein. In addition to the in vitro excision of adducts, the AlkA protein eliminates cytotoxic mechlorethamine adducts from DNA in vivo.

Novel ex vivo analysis of nonclassical, pleiotropic drug resistance and collateral sensitivity induced by therapy provides a rationale for treatment strategies in chronic lymphocytic leukemia

Extensive research into mechanisms of cytotoxic drug resistance and subsequent clinical trials of drug resistance modifiers have produced few encouraging results. In this report, we analyze 4,400+ ex vivo Differential Staining Cytotoxicity (DiSC) assay drug response results from patients with chronic lymphocytic leukemia (CLL) to investigate the development of drug resistance during treatment. Patients were untreated (n = 216) or previously treated with various cytotoxic agents (n = 188). Data was processed to identify ex vivo resistance (or sensitivity) induced by treating patients with prednisolone, chlorambucil, cyclophosphamide, anthracycline, or fludarabine. Induced resistance was apparently not associated with any one known mechanism. Treatment with chlorambucil induced a 10-fold sensitivity to steroids; cyclophosphamide induced greater resistance to anthracyclines than alkylating agents; anthracyclines induced greatest resistance to chlorambucil, cisplatin, carboplatin, and cladribine. Patients previously treated with at least two regimens were only 2.16-fold more resistant to CLL drugs than untreated patients, but had significantly reduced survival (median survival, 7.9 months compared with 61.1 months for untreated patients). These results suggest that chlorambucil and/or an antimetabolite should be administered before cyclophosphamide or anthracyclines to delay the onset of extensive pleiotropic drug resistance. Because individual differences in drug sensitivity are considerable, specific guidance could be obtained from ex vivo assay results. Furthermore, as a model for investigating drug resistance mechanisms, fresh CLL lymphocytes represent a useful alternative to drug-resistant cell lines.

The sensitivity of chronic lymphocytic leukaemia lymphocytes to irradiation in vitro

The inhibition of [3H]-thymidine incorporation into the DNA of mitogen-stimulated chronic lymphocytic leukaemia lymphocytes by chlorambucil or gamma-irradiation in vitro was measured in a series of patients, some of whom were untreated, some treated and some who were showing resistance to first-line or second-line treatment. There was evidence of resistance to irradiation developing in parallel with that to chlorambucil. The resistance to chlorambucil in chronic lymphocytic leukaemia (CLL) is not necessarily due to altered drug transport or metabolism but to a more fundamental process affecting DNA damage.

Enhancing and suppressive effects of immunosuppressants cyclosporin A, FK506, and KM2210 on the colony formation of murine bone marrow cells

Immunosuppressants cyclosporin A (CsA), FK506, and KM2210 modulated colony formations of murine hematopoietic progenitor cells. In a 4-h treatment with CsA, 10 micrograms/ml increased the formation of colony-forming units of mixed lineages (CFU-Mix) but decreased the formation of highly proliferative potential colony-forming units (CFU-HPP); 1 microgram/ml of CsA increased the formations of CFU-HPP, CFU-Mix, and colony-forming units of granulocytes/macrophages (CFU-GM); 0.1 microgram of CsA increased the formation of CFU-Mix and burst-forming units of erythroid lineage (BFU-E). Lower doses of CsA appeared to induce an increase in various colony formations. FK506 increased CFU-HPP and CFU-Mix formations at lower doses. Another immunosuppressant, KM2210, increased CFU-HPP and CFU-GM formations but decreased CFU-Mix and BFU-E formations. In a 24-h treatment, 10 micrograms/ml and 1 microgram/ml of CsA inhibited all the colony formations, but 0.1 microgram/ml of CsA increased CFU-Mix, CFU-GM, and BFU-E formations. Similarly, 100 ng/ml and 10 ng/ml of FK506 decreased all the colony formations but 1 ng/ml of FK506 increased CFU-HPP and CFU-GM formations. KM2210 inhibited all the colony formations. These findings showed that lower doses of CsA and FK506 appeared to increase the colony formations, although higher doses of these drugs decreased the colony formations, similar to the findings in a 4-h treatment. On the other hand, KM2210 showed opposing effects on colony formation with 4-h and 24-h treatments.

Modulation of purine analogs- and chlorambucil-induced cytotoxicity by alpha-interferon and interleukin-2 in chronic lymphocytic leukemia

The decrease in cell viability observed in vitro from the effect of chlorambucil (CLB), fludarabine (FAMP) and 2-chlorodeoxy-adenosine (CDA) on peripheral lymphocytes from 49 untreated CLL patients was investigated by the MTT colorimetric assay. The effects of recombinant-interleukin (r-IL)-2 and alpha-interferon (alpha-IFN) on drug-induced cell death were evaluated. r-IL-2 significantly increased in vitro resistance to CLB, while purine analog cytotoxicity was slightly reduced by the cytokine. The potential in vivo significance of r-IL-2, acting as a survival signal on CLB-induced cell death, is supported by the correlation between the lowest IL-2 serum levels, the highest in vitro sensitivity to CLB and a major clinical response after CLB treatment in six out of eight CLL patients. Using 25 samples, alpha-IFN enabled CLL cells to increase resistance to CLB, CDA and FAMP in 14, eight and seven samples, respectively; conversely, alpha-IFN showed a synergism with both CLB and FAMP in six samples and with CDA in four. These results correlate with immunoenzymatic assay data showing that alpha-IFN either up- or down-regulates tumor necrosis factor and IL-1 levels in supernatants of some CLL samples. Apparently, alpha-IFN plays a dual role in regulating drug-induced cell death, while IL-2 seems to solely favor cell survival in CLL.

Growth inhibitory effect of estrogen conjugated drugs against primary cultured breast cancer cells

An in vitro assay method for predicting the hormonal response of primary cultured cells was used in 38 women with breast carcinoma. The response to 17 beta-estradiol (E2) was compared with other hormone treatments, such as tamoxifen (TAM), estracyt (EC) and bestrabucil (BB). The response to the E2-conjugated drugs (EC and BB) and TAM showed a good correlation with the response to E2 (p < 0.01). Coincidental rates of EC and BB response (stimulatory, insensitive, and inhibitory) with E2 response were 47% (16/34) and 53% (16/30) of cases, respectively. Cells showing an inhibitory response to E2 were also inhibited by EC and BB in 60% (6/10) and 100% (8/8) of cases, respectively. In premenopausal women, 28% (5/18) and 43% (6/14) of cases were inhibited by EC and BB, respectively, whereas in postmenopausal women 44% (7/16) and 56% (9/16) of cases showed inhibition with EC and BB, respectively. The inhibitory response to the E2-conjugated drugs was not significantly different between pre- and post-menopausal women. Cells resistant to inhibition by TAM were inhibited by EC and BB, respectively, in 17% (4/24) and 30% (6/20) of cases. These results indicate that E2-conjugated drugs may inhibit the growth of breast cancer cells and that their inhibitory actions might be different from those of TAM.

Synthesis, DNA binding, and sequence specificity of DNA alkylation by some novel cyclic peptide-chlorambucil conjugates

In an effort to investigate the potential of cyclic peptides as carriers for cytotoxic agents, we synthesized four cyclic peptide-chlorambucil conjugates: cyclo[Lys(CHB)-Lys(CHB)-Gaba-] (peptide Y), cyclo[Lys(CHB)-Gly-Lys(CHB)-Gaba-] (peptide A), cyclo[Lys(CHB)-beta-Ala-Lys(CHB)-Gaba-] (peptide B) and cyclo[Lys(CHB)-Gaba-Lys(CHB)-Gaba-] (peptide C). The cyclic peptides were synthesized by coupling protected amino acid residues in solution and the subsequent cyclization was performed by the pentafluorophenyl ester method as described previously (Sheh et al., 1990, 1993a,b). After deblocking the lysyl-carbobenzyloxy protecting group (Z), the conjugation was achieved by reaction with the pentafluorophenyl ester of chlorambucil (CHB). These cyclic peptides differ from one another in ring size and are disubstituted with CHB via the epsilon-amino group of the lysyl residue. The various conjugates were designed to study the effect of ring size on the mode of DNA binding and alkylation. A DNA-binding assay using lambda-DNA with ethidium bromide showed that whereas peptide Y and CHB have no observable binding affinity, the apparent binding constants for peptide A, peptide B and peptide C on lambda-DNA were determined to be 2.36 x 10(5), 1.27 x 10(5) and 3.50 x 10(5), respectively. Thus, it is suggested that cyclic peptides bearing aliphatic side chains attached to a ring larger in size than 14 members would be more favourable as regards augmenting the binding affinity. DNase I footprinting showed that no footprinting patterns were observed for the 253-mer fragment and 117-mer fragment with peptide A, but two new bands corresponding to G69 and G80 were observed for the 117-mer fragment. DNA alkylation studies using a piperidine cleavage assay on the 117-mer DNA fragment showed that the sequence selectivity, judged by reaction intensity observed with peptide A, peptide B and peptide C, was similar to that seen with CHB alone. The selectivity of alkylation for both CHB and its peptide derivatives appears to be: 3'-Pur-G-Pyr-5' > 3'-Pyr-G-Pyr-5' > 3'-Pyr-G-Pur-5' = 3'Pur-G-Pur-5'. However, there are apparent differences in the intensity of alkylation by peptides A, B, C and CHB at certain guanine residues.

Potentiation of chlorambucil toxicity in B-CLL lymphocytes using the DNA synthesis inhibitors aphidicolin and 1-beta-D-arabinofuranosylcytosine

Previous studies in our laboratory have identified enhanced cross-link repair as a primary mechanism of resistance to nitrogen mustards in B-cell chronic lymphocytic leukemia (B-CLL). To evaluate the therapeutic potential for modulation of DNA repair by aphidicolin and 1-beta-D-arabinofuranosylcytosine (ara-C), we examined the interaction between these two agents and chlorambucil in lymphocytes from untreated and treated-resistant B-CLL patients. We found that both aphidicolin and ara-C displayed synergy with chlorambucil over a range of inhibitor concentrations. This synergy was not restricted to the resistant samples. Our results indicate that these combinations can enhance the potency of chlorambucil in a clinically relevant model and should be considered for further preclinical and, eventually, clinical trials.

The effect of chlorambucil on the biosynthesis of the HMG and histone H1 chromosomal proteins of HEp-2 cells

The effect of chlorambucil, a bisalkylating agent, on the biosynthesis of the 5% PCA extractable protein fraction of the cancer cell line, HEp-2, has been analyzed. It was found that the synthesis of all the high mobility group proteins as well as that of the H1 and H1o histone proteins are inhibited by this agent. HMG 14 and the H1, H1o proteins are inhibited to the same extent as that reported for the core histones of the same cell line [7], while slightly higher levels of inhibition were found for the HMG 1, 2 and 17 proteins. The proteins, P1 and HMG I exhibited the highest level of inhibition of the entire fraction. These findings extend previous findings regarding the histone proteins and may be correlated to a dysfunction in the normal process of chromatin condensation and a potential cytotoxic effect of this agent during the G2 phase.

Differential effects of the immunosuppressants cyclosporin A, FK506 and KM2210 on cytokine gene expression

Cyclosporin A (CsA) inhibited interleukin 2 (IL-2), IL-3, interferon gamma (IFN gamma), GM-CSF and tumor necrosis factor alpha (TNF alpha) mRNA expression in spleen cells stimulated with concavalin A (Con A) when determined by the semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. FK506 which has a similar immunosuppressive mechanism to that of CsA also showed the same inhibitory effects except for decreased IL-5 and IL-6 mRNA expression. In contrast, both CsA and FK506 enhanced transforming growth factor beta (TGF beta) and IL-1 beta mRNA expression. Another immunosuppressant KM2210 did not show any inhibitory effects on cytokine gene expression but rather enhanced IL-10, IL-6, TGF beta and IL-1 mRNA expression, thus suggesting that KM2210 has a completely different immunosuppressive mechanism from that of CsA and FK506. Anti-TFG beta 1 antibody abrogated the suppression by KM2210 of BALB/c anti-3H/He mixed lymphocyte reaction (MLR) whereas this antibody did not abrogate the suppression by CsA and FK506 of BALB/c anti-C3H/He MLR. These results indicate that TGF beta is one of the major cytokines in KM2210 immunosuppression, in addition to IL-10, but not in immunosuppression by CsA and FK506.

Nitrogen mustard drug resistant B-cell chronic lymphocytic leukemia as an in vivo model for crosslinking agent resistance

Acquired resistance is a limiting factor in chemotherapy. We have employed nitrogen mustard resistant B-cell chronic lymphocytic leukemia (B-CLL) as a clinically relevant model to study this phenomenon. Resistance in B-CLL is associated with enhanced repair of nitrogen mustard crosslinks. In order to identify the repair pathway responsible for nitrogen mustard resistance, lymphocytes were screened for cross-resistance to a variety of DNA damaging agents. The MTT assay was used to measure the resistance of B-CLL lymphocytes to various DNA damaging agents, including nitrogen mustards, UV light, methyl methanesulfonate, and mitomycin C. We have shown that B lymphocytes from patients with nitrogen mustard resistant chronic lymphocytic leukemia reflect their clinical status. This assay allows us to classify lymphocytes as nitrogen mustard sensitive or resistant, based on in vitro observations. The resistant population was 5.6 and 4.1 fold more resistant to the nitrogen mustard analogs, chlorambucil and melphalan, respectively. Resistant lymphocytes displayed no increased resistance to either methyl methanesulfonate or UV light, indicating that neither classical base nor nucleotide excision repair is rate-limiting in resistance. Resistant lymphocytes were 6.0 and 2.2 fold more resistant to mitomycin C and cis-diamminedichloroplatinum (II), respectively, suggesting enhanced crosslink repair. Neither glutathione nor glutathione S-transferase levels correlated with resistance. The development of nitrogen mustard drug resistance in B-CLL appears to be associated with cross-resistance to other bifunctional alkylating agents which produce interstrand crosslinks. Our results indicate that resistance to nitrogen mustards in chronic lymphocytic leukemia is associated with enhanced repair of DNA crosslinks which may involve a recombination dependent system. This model should prove very useful in the elucidation of the molecular mechanisms of crosslink repair.

Glutathione-S-transferase activity and multidrug resistance phenotype in chronic lymphocytic leukemia: do they have any clinical relevance?

BACKGROUND

Lymphocytes from patients affected by B-cell chronic lymphocytic leukemia (B-CLL) have frequently been shown to be positive for the multidrug resistance (MDR) phenotype. However, this phenotype does not seem to be responsible for the resistance to alkylating agents usually employed in the management of CLL.

METHODS

Lymphocytes from 42 patients were evaluated by flow cytometry for P-170 expression and by spectrophotometry for glutathione-S-transferase (GST) activity.

RESULTS

Our findings show that GST is not related to any clinical parameter but is increased in treated patients. Conversely, 85% of patients were positive for P-170 and this was related to the percentage of CD5/CD19-positive lymphocytes. CD5/CD19-negative patients were also negative for P-170. MDR was not related to any clinical parameter evaluated nor to GST activity in lymphocytes.

CONCLUSIONS

MDR is constitutively expressed in B-cell chronic lymphocytic leukemia and seems to be related to a CD5/CD19 B-CLL phenotype. The increase of GST activity in treated patients is statistically significant (p < 0.005).

Protection of chymotrypsin from inactivation by a N-mustard analog

Chymotrypsin activity is rapidly inactivated by the N-mustard anti-tumor drug, chlorambucil. Since mustards react with thiols, amines, carboxyls, imidazoles, and sulfide sites on proteins, N-acetylcysteine, 2 proprietary protein hydrolyzates, beta-mercaptoethanol, ethanolamine, and sodium lactate were tested for their capacity to protect chymotrypsin from inactivation by the mustard. In each instance, protection was afforded to chymotrypsin. In as much as N-acetylcysteine protected chymotrypsin from inactivation by chlorambucil, it is suggested that this thiol compound may serve as a detoxication agent and may not require prior transformation into glutathione by cells in order to reduce mustard levels within the cells, as suggested by Smith and Gross (Proceedings of the NATO Panel VIII meeting, Grenoble, France, 1991.) It is further suggested that amino acids present as biosynthetic and degradative components of cells may detoxify mustards.

Methylprednisolone in advanced chronic lymphocytic leukaemia: rationale for, and effectiveness of treatment suggested by DiSC assay

The effect of methylprednisolone on fresh cells from patients with chronic lymphocytic leukaemia (CLL) has been studied using the differential staining cytotoxicity (DiSC) assay resulting in LC90s of < or = 0.2 to 2,000 micrograms/ml. Cells from previously treated patients were, on average, significantly more sensitive to methylprednisolone than those from untreated patients (mean LC90 = 5.7 micrograms/ml, n = 61 vs 31.0 micrograms/ml, n = 17, respectively; p < 0.05). Twelve patients with advanced disease were given high-dose methylprednisolone (1 g/m2/day i.v. x 5 days). In 7 cases, > or = 3 courses were given; 3 patients did not respond (2 achieved palliation) and 4 (57%) achieved a good partial response. These latter 4 patients were all clinically resistant to chlorambucil and anthracyclines and 2 were resistant to fludarabine. In 5 cases, 1 or 2 courses were given but no patients responded. The 8 nonresponders survived a median of 3.5 months whilst the responders have survived a median of 28.5+ months (3 of 4 still alive). This work suggests a rationale for why CLL patients resistant to standard chemotherapy may benefit from high-dose methylprednisolone therapy. Due to cost and toxicity associated with therapy, the decision to treat would be best made on the basis of a DiSC assay result. This pilot study requires confirmation with a well-designed controlled clinical trial.

No evidence of effect on male mice germ cells after acute treatment with thiram

Thiram is a dithiocarbamate compound widely used for industrial processes and agriculture. Animal studies reveal that this compound may affect the male reproductive system. Aim of this study was to test, using sensitive testicular parameters, whether thiram directly affects germinal cells. For this purpose, B6C3F1 mice were intraperitoneally injected with thiram in oil (single dose: 75 mg/kg; repeated five daily doses: 25 mg/kg). Although both treatments were toxic, none of the parameters examined, i.e., testis weight, spermatid head number, specific enzyme levels at different times after treatment (14, 28, 35, 56 days) showed significant variations from the controls. On the contrary, in the positive controls (treated with chlorambucil), a marked reduction of sperm head number as well as a decrease of lactate dehydrogenasex and sorbitol dehydrogenase activity levels were evidenced at day 28, with a tendency to recover at day 35. Under these conditions thiram did not cause cytotoxicity on differentiating spermatogonia and on late spermatocyte stages of mice gonads.

DNA damage and mutagenesis induced by nitrogen mustards

The nitrogen mustards are bifunctional alkylating agents which, although used extensively in cancer chemotherapy, are themselves highly carcinogenic. All nitrogen mustards induce monofunctional guanine-N7 adducts, as well as interstrand N7-N7 crosslinks involving the two guanines in GNC.GNC (5'-->3'/5'-->3') sequences. In addition, the aromatic mustards melphalan and chlorambucil also induce substantial alkylation at adenine N3, while cyclophosphamide forms phosphotriesters with relatively high frequency. Nitrogen mustards are genotoxic in virtually every assay, and produce a wide array of mutations, including base substitutions at both G.C and A.T base pairs, intragenic as well as multilocus deletions, and chromosomal rearrangements. Mutational spectra generated by these agents in various model systems vary widely, and no single lesion has been implicated as being primarily responsible for mustard-induced mutagenesis. On the contrary, adducts of both adenine and guanine, and monofunctional as well as bifunctional adducts, appear to be involved. Further, it is still not known which types of mutation are responsible for mustard-induced cancers, since no genes have yet been identified which are consistently altered in these malignancies.

[Resistance associated with the glutathione system]

Several mechanisms of resistance (of bacteria to antibiotics, of plants to herbicides, of insects to insecticides, of cancer cells to cytotoxic agents...) have now been described. The most studied one is the glycoprotein coded by the mdr1 gene, which is involved in the efflux of numerous compounds of natural origin (anthracyclines, podophyllotoxins...) thus decreasing the intracellular concentration of such drugs. Nevertheless, many chemotherapeutic protocols include alkylating agents, such as cyclophosphamide and cisplatin, which are electrophilic species prone to react readily with the tripeptide glutathione, most often through glutathione-S-transferases. Therefore, it appears of major importance to evaluate the role of glutathione and that of the polymorphism of the glutathione-S-transferases, as prognostic factors in the response to chemotherapy.

Apoptosis or necrosis: intracellular levels of glutathione influence mode of cell death

The effect of lowering intracellular glutathione (GSH) concentrations on the toxicity of alkylating agents, and RNA synthesis inhibitor and topoisomerase 1 and 2 inhibitors to a number of human leukaemic cell lines were evaluated. By using the GSH synthesis inhibitor DL-buthionine-(S,R)-sulfoximine (BSO), GSH levels were artificially reduced. Cells with low GSH concentrations were exposed to a number of cytotoxic agents and the resultant mode of cell death was analysed using morphological and biochemical criteria. It was found that untreated cells exposed to the above drugs underwent apoptosis to varying extents. However, the toxicity of alkylating agents was dramatically increased to all cell lines on lowering GSH levels, with the mode of cell death switching from apoptosis to necrosis. The reduction of GSH levels had no effect on the toxicity of actinomycin-D, camptothecin or etoposide, nor did it affect the mode of cell death induced by these agents. These observations suggest that modulation of GSH levels effect the toxicity of alkylating agents and that GSH influences the mode of cell death induced by alkylating agents.

Retrovirus-mediated gene transfer of rat glutathione S-transferase Yc confers alkylating drug resistance in NIH 3T3 mouse fibroblasts

A major limitation to successful cancer treatment is the existence of drug resistance. While several mechanisms of drug resistance have now been well characterized, mechanisms of resistance to alkylating drugs have remained less well defined. Several experimental models of alkylator resistance have implicated isoforms of glutathione S-transferase (GST) but transfection experiments using cloned isoforms of GST have yielded conflicting results. While there are several plausible explanations for these apparently contradictory findings, the issue that clonal variability might potentially confound the results of conventional transfection experiments has been raised. To address this issue properly, we have studied rat GST-Yc expression and drug sensitivity to alkylating drugs in populations of mouse NIH 3T3 fibroblasts following either transfection or transduction with an N2-based retrovirus vector. In comparison with cells treated with an antisense vector, Yc-transfected and Yc-transduced populations of NIH 3T3 cells expressed increased levels of GST-Yc mRNA (Northern blot), increased levels of immunodetectable GST-Yc (Western blot), and, respectively, 1.4- and 1.9-fold increases in total GST activity and 6.1- and 8.3-fold increases in glutathione peroxidase activity (associated with the Yc subunit). Yc-transfected and Yc-transduced cell populations were, respectively, 5.8- (P < 0.001) and 2.4-fold (P < 0.05) resistant to chlorambucil and 10.8- (P < 0.01) and 5.4-fold (P < 0.001) resistant to mechlorethamine. The range of resistance of clonal isolates from either population was 1.8-6.0-fold for chlorambucil and 4.6-6.1-fold for mechlorethamine (P < 0.05). In contrast, these cells showed unaltered sensitivity to the antimetabolite methotrexate, a nonalkylating drug. These results clearly demonstrate that the rat GTS-Yc is able to confer alkylating drug resistance in mouse fibroblasts. The ability to confer alkylating drug resistance following retrovirus-mediated gene transfer also raises the possibility of using GST-Yc somatic gene transfer to confer protection to the hematopoietic system in a gene therapy strategy applicable to cancer.

Chlorambucil induced apoptosis in chronic lymphocytic leukemia (CLL) and its relationship to clinical efficacy

Chlorambucil induced apoptosis was measured in CLL cells treated with clinically achievable drug doses in vitro. While spontaneous apoptosis occurred in CLL cells incubated in vitro in the absence of drug, the level of apoptosis, as measured by the extent of DNA fragmentation, was greater in cells treated with chlorambucil. In addition, macrophages were shown to engulf drug treated CLL cells in vitro. To determine if chlorambucil can also induce apoptosis in vivo, CLL cells were isolated from patients before treatment and at intervals after clinical therapy with chlorambucil (0.9 mg/kg given over 3 days). Apoptosis was measured in these cells immediately after isolation and following incubation in vitro for 72 hr. No apoptotic changes were detected in cells immediately after isolation either before or after clinical treatment. In contrast, apoptosis was observed in cells that were incubated ex vivo for 72 hr, and the level of apoptosis was greater in cells that were isolated after chlorambucil treatment compared with cells obtained prior to therapy. The increased apoptosis observed in CLL cells ex vivo after therapy was related to the fall in the patient's lymphocyte count. In general, a large increase in apoptosis ex vivo after treatment was followed by a significant decrease in the patient's lymphocyte count. Thus, chlorambucil may produce its antitumor effect in CLL by inducing apoptosis-associated membrane changes that result in rapid clearance of the apoptotic cells by the immune system.

Glutathione-S-transferase P-form dependent chlorambucil resistance in Yoshida rat ascites hepatoma cell lines

Yoshida rat ascites hepatoma (AH) has several cell lines with a characteristic sensitivity to antitumor drugs. AH66 cells overexpressed 160-170 kDa P-glycoprotein (P-gp) in the membrane and glutathione-S-transferase placental form (GST-P) in the cytosol. AH44 cells did not express P-gp but contained GST-P isozyme, while normal rat liver had GST-(1,2) and-(3,4) classes. AH44 and AH66 cells were more resistant to chlorambucil (CLB) than AH66F cells, which are a variant cell line derived from AH66 cells and lacked both proteins. CLB-resistant AH44 and AH66 cells contained a high amount of glutathione (GSH) and higher GST activity than AH66F cells. Ethacrynic acid, a GST-P inhibitor, and buthionine sulfoximine, a GSH biosynthesis inhibitor, significantly decreased the CBL resistance of AH44 and AH66 cells without influencing the sensitivity of AH66F cells. The CLB resistance of these cell lines were hardly influenced by verapamil, a calcium channel blocker with P-gp antagonistic action, which significantly decreased the vinblastine resistance of AH66 cells. This study indicates that AH66 cells showed multiple drug resistance dependent on P-gp and GST-P isozyme and that the AH44 cell line was CLB resistant through the GSH/GST-P detoxification system. These hepatomas are useful for investigation of the drug resistance of hepatic carcinomas and development of counteracting drugs.

MDR1 gene expression in chronic lymphocytic leukemia

In order to assess the clinical role of the MDR1 gene in chronic lymphocytic leukemia (CLL), we determined its expression in the leukemic cells of 39 patients with CLL and compared this with other clinical and laboratory parameters. MDR1 RNA expression was detected in 29 patients. MDR1 RNA transcripts were independent of age, treatment status of the patients and the clinical stage of CLL, but correlated with the white blood cell count and MDR2 RNA transcripts. Expression of the tumor suppressor gene p53 was found in 30 out of 37 patients and was associated with MDR1 RNA expression (P < 0.001). Immunocytochemistry using the monoclonal antibody C219 was performed in 38 patients, and in 28 cases, more than 5% of the leukemic cells were found to express cell surface P-glycoprotein. P-glycoprotein expression correlated with the expression of MDR1 RNA (P = 0.048).

Inhibitory effects of bestrabucil, a conjugate of chlorambucil and estradiol, on the production of androgen-induced growth factor(s) by Shionogi carcinoma 115 cells

It is known that diffusible trophic factors play an important role in both the normal and cancerous growth regulatory processes of hormone-responsive cells such as are found in the prostate and mammary glands. Consequently, it is important to identify whether the production of such growth factors is affected by administration of therapeutic agents. We examined the effect of bestrabucil, a benzoate of an estradiol-chlorambucil conjugate, on the production of growth factor(s) by Shionogi carcinoma 115 (SC-115) cells, an androgen-responsive cultured cancer cell line. We then investigated whether the inhibitory effect found was specific to bestrabucil, or if it was also produced by a mixture of the 2 compounds, estradiol and chlorambucil. Bioassay employing BALB/3T3 cells demonstrated the presence of two kinds of growth factor in the conditioned medium obtained by culturing SC-115 cells in medium containing 10(-8) M testosterone; these factors could be separated by heparin-sepharose column chromatography using 0.5 M NaCl and 1.1 M NaCl. When the SC-115 cells were cultured in medium containing bestrabucil, at a concentration of 10(-5) M, no growth factor activity was detected in the fraction eluted from the heparin-sepharose column by 1.1 M NaCl. At bestrabucil concentrations of 10(-5)-10(-7) M, concentration-dependent inhibition of growth factor production by SC-115 cells could be demonstrated by 3H-thymidine uptake assay. However, this inhibitory effect could not be demonstrated using only a mixture of estradiol and chlorambucil.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased levels of alpha-class and pi-class glutathione S-transferases in cell lines resistant to 1-chloro-2,4-dinitrobenzene

Glutathione S-transferase (GST) enzymes are often over-expressed in tumor cells made resistant to cytotoxic drugs but it is unclear whether GST over-expression is directly linked to the resistance mechanism. We have made a human lung tumor cell line resistant to 1-chloro-2,4-dinitrobenzene (CDNB) in order to establish whether selection for resistance with a model GST substrate results in selection of a cell line with higher GST levels. The resistant line (CDNBr), although only twofold more resistant to this compound, exhibited a marked (15-fold) increase in GST activity compared to the wild-type cell line (28 +/- 10 versus 357 +/- 30 nmol CDNB conjugated.min-1 x mg-1 protein, respectively). Resistance to CDNB was associated with a marked increase in the level of both alpha-class and pi-class GST. Resolution of the GST by reverse-phase HPLC demonstrated that the increase in the expression of the alpha-class enzymes was due to elevated levels of both the B1 and B2 subunits. The increased levels of alpha-class and pi-class GST in the CDNBr cells was not due to either gene amplification or increased mRNA levels and appears to involve either altered mRNA utilization or protein stabilization. In addition to being resistant to CDNB, the CDNBr cell line also showed a 2.5-fold resistance to cumene hydroperoxide but was not cross-resistant to the anticancer drug chlorambucil. To demonstrate that the increased GST level was part of the resistance mechanism the alpha-class GST B1 cDNA under control of the beta-actin promoter was stably expressed in the breast tumor cell line MCF-7. The cell lines generated were twofold more resistant to CDNB relative to the parental line.

Treatment of antigen-induced arthritis in rabbits by the intra-articular injection of methylprednisolone, 90Y or chlorambucil

Rabbits with a bilateral antigen-induced arthritis were injected intra-articularly (i.a.) in one joint with methylprednisolone (1 mg), 90Y (18.5 MBq) or chlorambucil (1 mg) as a single dose. The severity of arthritis was determined by measuring joint swelling and skin surface temperature, macroscopic and histological changes in the joint being assessed 8 weeks after induction of arthritis when the rabbits were killed. Methylprednisolone injected at the time of antigen challenge or 3 weeks later caused a reduction in joint swelling and temperature (P < 0.05) for 1 to 6 weeks after injection. 90Y had an initial proinflammatory effect lasting several days, but later caused a modest reduction in joint swelling for up to 4 weeks (P < 0.05). Eight weeks after induction of arthritis, neither methylprednisolone nor 90Y-treated joints showed any significant reduction in erosion or histopathology compared with control arthritic joints. Chlorambucil injected 1 week after antigen challenge caused a rapid reduction in joint swelling which was maintained for the duration of the study. Joint surface temperature was reduced to a lesser extent. Eight weeks after induction of arthritis, chlorambucil-treated joints showed a decrease (P < 0.05) in all of the parameters of disease pathology assessed. Treatment with chlorambucil intra-articularly was clearly more effective than with methylprednisolone or 90Y at the doses employed and deserves further study as a potential treatment for chronic synovitis.

Clastogenicity of chlorambucil to the mouse bone marrow: consideration in relation to its genetic specificity of action in some assays

The human carcinogen and mouse germ cell mutagen chlorambucil is reported here to give a strong positive response in the mouse bone marrow micronucleus assay (4 mg/kg; single intraperitoneal injection). An increased incidence of micronucleated bone marrow white cells was also observed. It is concluded that chlorambucil is a broad spectrum mutagen that possesses subtle and specific mutagenic activities in some assay systems.

In vitro chemosensitivity of chronic lymphocytic leukemia B-cells to multidrug regimen (CEOP) compounds using the MTT colorimetric assay

BACKGROUND

Anthracycline-containing regimens have given controversial clinical results in CLL. Therefore, we explored the in vitro behavior of CLL B-cells after exposure to the compounds included in the most frequently used combination therapy regimen (CEOP).

METHODS

A 4-day MTT colorimetric assay was used in vitro to test the effect of CEOP regimen drugs, either alone or in combination, on CLL B-cells. All drugs but mafosfamide, tested in place of cyclophosphamide, were used at concentrations corresponding to the in vivo dosage employed in the CEOP regimen. Chlorambucil was also studied since it represents the standard treatment for this disease.

RESULTS

Epirubicin, prednisone and vincristine displayed a cytotoxic effect in 15, 13 and 4 out of 30 samples, respectively. Combinations of the same drugs showed a synergistic effect in 6 out of 13 assays. A cytotoxic effect of chlorambucil was detected in 2 out of 5 responders to the combination of CEOP regimen drugs, and in 3 out of 7 non responders. Mafosfamide induced a reduction in cell survival in 60-80% of the samples, depending on its concentration.

CONCLUSIONS

The MTT assay is suitable for evaluating the in vitro chemosensitivity of CLL B-cells to multidrug regimen compounds. In the present study 40% of samples were resistant to CEOP regimen components in vitro. The possible role of MTT in predicting the clinical response to the CEOP regimen should still be established by prospective in vitro and in vivo studies.

Development of lipophilic anticancer agents for the treatment of brain tumors by the esterification of water-soluble chlorambucil

The lipophilic derivatives of the anticancer alkylating agent chlorambucil, chlorambucil-methyl, -isopropyl and -tertiary butyl esters, were synthesized and administered i.v. to anesthetized rats. Plasma and brain concentrations of these agents and of their active metabolites, chlorambucil and phenylacetic mustard, then were determined by high-performance liquid chromatography between 5 and 60 min. Whereas large amounts of chlorambucil-tertiary butyl ester entered and were maintained in brain, lower amounts of chlorambucil-isopropyl ester and no chlorambucil-methyl ester were found in brain. The comparative brain/plasma concentration-time integral ratios of the total active agents generated from chlorambucil-tertiary butyl, -isopropyl and -methyl esters were 0.85, 0.12 and 0.06, respectively, compared to a ratio of 0.02 for chlorambucil. In vitro alkylating activity of each ester was compared to that of equimolar chlorambucil, by reaction with 4-(p-nitrobenzyl)pyridine. Each ester possessed high intrinsic alkylating activity, equal to 38.4, 57.0 and 69.9% of chlorambucil activity, for the -tertiary butyl, -isopropyl and -methyl esters, respectively. Therefore each is an active antineoplastic agent irrespective of whether or not chlorambucil is regenerated. The rates of ester hydrolysis of these derivatives to chlorambucil were measured in fresh rat blood and in liver and brain homogenates at 37 degrees C. Chlorambucil-methyl and -isopropyl esters were hydrolysed quickly within 30 s in blood and liver, whereas chlorambucil-tertiary butyl ester was more stable with half-lives of approximately 7 h and 2 h, respectively. All proved to be relatively stable in brain homogenate. Steric hindrance around the ester linkage of chlorambucil-tertiary butyl ester reduces its affinity to and rate of hydrolysis by plasma and liver esterases, and allows it to accumulate within the brain. Chlorambucil-tertiary butyl ester maintains high levels in brain despite rapidly declining plasma concentrations and, due to these favorable pharmacokinetics and to its intrinsic anticancer activity, it possess promising characteristics for the treatment of malignant brain tumors.

Time course of glutathione S-transferase elevation in Walker mammary carcinoma cells following chlorambucil exposure

Resistance of Walker 256 rat mammary carcinoma cells to chlorambucil has been shown to be accompanied by a specific increase in the A2-2 subunit of glutathione S-transferase (GST) (Buller et al., Mol Pharmacol 31: 575-578, 1987). Analysis of the time course of GST activity following chlorambucil exposure revealed a 7.5- and 3-fold elevation on day 7 post-treatment in Walker-sensitive (WS) and Walker-resistant (WR) cells, respectively. Flow activated cell sorting (FACS) analyses using antibodies specific for rat liver cytosolic GST supported these results and demonstrated the heterogeneous response of WS cells to chlorambucil exposure. The range of GST levels in drug-treated cells was very broad as compared to that of untreated cells. Transcripts for each class of GST (alpha, mu and pi) were quantified for days 1-9 post-treatment from densitometric scans of RNA slot blots. Elevations in GST alpha RNA preceded increases in GST activity (day 7) in both WS and WR cells. Because fluctuations in GSTA1-1 transcripts were not observed, it was concluded that the increased expression of the alpha class must be attributed to increases in GSTA2-2 transcripts. Amplification of the GST genes in drug-treated cells was not present. These results support the role of GSTA2-2 in the detoxification of chlorambucil. The time course of the cellular response to chlorambucil suggests that the elevation of GSTA2-2 transcripts following alkylating agent exposure may represent only one component of a series of events which collectively confer protection and lead to the establishment of drug resistance.

Human glucocorticoid receptor gene deletion following exposure to cancer chemotherapeutic drugs and chemical mutagens

The sensitivity of the human glucocorticoid receptor (hGR) gene to mutagenesis by the cancer chemotherapeutic drugs adriamycin, bleomycin, and chlorambucil was evaluated using glucocorticoid-sensitive (dexs) subclones of the human leukemic cell line CEM-C7. Treatment of cells with either bleomycin or chlorambucil increased the frequency of glucocorticoid-resistant (dexr) clones 3.3- and 10-fold, respectively. Measurement of steroid-binding activity in intact dexr cells demonstrated that the predominant phenotype of drug-induced dexr clones was receptorless (r-). dexs CEM cells express only one functional hGR allele and, in addition, are heterozygous for a BclI restriction fragment length polymorphism in the hGR gene (L. A. Palmer and J. M. Harmon, Cancer Res., 51:5224-5231, 1991). To determine the basis of the r- phenotype, BclI digests of genomic DNA isolated from r+ and r- cell lines were examined for the presence of the polymorphic 2.4- and 4.4-kilobase digestion products. A deletion of all or part of the hGR gene was demonstrated by the absence of the 4.4-kilobase fragment in one of two bleomycin-induced dexr clones, as well as the ICR191-induced dexr cell line ICR27TK.3. Cytogenetic analysis of ICR27TK.3 showed that the distal portion of the long arm of one chromosome 5 had been replaced with a portion of chromosome 15. Thus, in at least two dexr cell lines, deletions and/or chromosome breaks in the hGR locus appear to account for the r- phenotype.

Glutathione depletion in chronic lymphocytic leukemia B lymphocytes

Glutathione (GSH) content may be the major determinant of a cell's sensitivity to cytotoxic alkylating agents. In the present study, the GSH concentration was determined in lymphocytes isolated from the blood of normal subjects and patients with chronic lymphocytic leukemia (CLL). Comparable levels were found in both types of cells. Incubation for 20 hours led to a decrease in GSH to 51% of baseline values in CLL B cells. Under the same conditions, normal B- or T-lymphocyte GSH content remained constant. GSH depletion was shown to be a characteristic of the B-CLL B lymphocyte. It was not found in the T cells of patients with B-CLL or in cells from patients with T-CLL. Chlorambucil (CLB) contributes to the decrease in GSH in B-CLL lymphocytes; after incubation with the drug, lower levels of GSH were found than in the normal B or T lymphocytes, B-CLL T cells, or T-CLL (CD4 or CD8) cells. GSH depletion of CLL B lymphocytes may be related to the greater therapeutic efficacy of CLB in B-CLL than in T-CLL.

Very late return of spermatogenesis after chlorambucil therapy: case reports

Two men were treated for a nephrotic syndrome with high-dose chlorambucil therapy; 6.5 and 14 years later, respectively, both were azoospermic with high plasmatic FSH values. Both patients showed active spermatogenesis, 15 and 19 years after the end of the treatment. This suggests that a return of spermatogenesis can occur even after very high cumulative doses of chlorambucil (between 3,000 and 6,500 mg) and after a very long time.

The alloantigen-specific immunosuppressive activity of estradiol-chlorambucil conjugate (KM2210) and its beneficial effect on allogeneic bone marrow transplantation in mice

KM2210, a conjugate of estradiol and chlorambucil (CBL), which was originally developed as an anti-breast cancer agent, inhibits proliferative response of human mononuclear cells to alloantigens in mixed lymphocyte culture in a dose-dependent manner, but has no effect on their response to phytohemagglutinin. Neither estradiol benzoate nor CBL alone showed these unique actions. The suppressive effect of KM2210 on MLC was abrogated by adding of anti-transforming growth factor-beta (TGF-beta) antibody to the culture, but was not affected by the addition of interleukin-2, suggesting that KM2210, unlike CBL, displays its actions via TGF-beta. In experimental allogeneic bone marrow transplantation using mice, daily oral administration of KM2210 (2 mg/kg/day) for 30 days posttransplant significantly inhibited the alloantigen-specific immune reactions. Furthermore, the survival rate of the KM2210-treated mice was significantly higher than that of the cyclosporine-treated (2 mg/kg/day, p.o.) mice, and no adverse effect of KM2210 on hematopoietic recovery was found. These results strongly suggest possible clinical benefits of KM2210 as a new immunosuppressive agent for the prevention and treatment of graft-versus-host disease and other allospecific immune reactions.

Preferential induction of AT-TA transversion, but not deletions, by chlorambucil at the hisG428 site of Salmonella typhimurium TA102

The chemotherapeutic agent chlorambucil effectively induces deletion mutations in mouse germ cells. The possibility that this chemical also effectively induces deletion mutations in bacterial DNA was examined using Ames Salmonella tester strains. Chlorambucil was mutagenic only to strains TA102 (hisG428, rfa/pKM101) and YG2975 (hisG46, rfa/pKM101) when S9 mix was absent. Since strain TA102 can detect short deletions, the mutational changes of TA102 induced by this agent without S9 mix were directly determined by the DNA sequencing technique. It turned out that chlorambucil did not induce deletion mutations but preferentially induced AT-TA transversions at the hisG428 site of plasmid pAQ1 of strain TA102. These results caution that the positive results induced by chlorambucil in mutagenicity tests do not necessarily mean the occurrence of deletions.

Cytogenetic and molecular characterization of the mutagenicity of chlorambucil in V79 cells

Chlorambucil (CBC) is used as a chemotherapeutic agent and immunosuppressant. Recently, it could be shown that CBC is considerably more effective than radiation or any chemical investigated to date in inducing high yields of germ-line mutations that appear to be multilocus deletions or other structural changes. We therefore reinvestigated the in vitro genotoxic effects of CBC in V79 cells and characterized induced sister-chromatid exchanges (SCEs), chromosome aberrations and gene mutations by means of cytogenetic and molecular methods. CBC effectively induced chromosome aberrations and SCEs in a dose-dependent manner. The chromosome aberrations found after a 14-h treatment were mainly chromatid-type aberrations. 3-Aminobenzamide (3AB) did not influence the incidence of CBC-induced SCEs and chromosome aberrations. Combined treatment with CBC and caffeine (CAF) strongly increased the frequency of aberrations, but had no effect on the yield of SCEs. CAF at lower concentrations enhanced the production of chromatid breaks and exchange figures while higher concentrations (10(-3) M) caused multiple breaks and pulverised mitoses. Mutations at the hprt locus were induced in a narrow range of CBC concentrations (10(-5) M-2 x 10(-5) M) and the mutagenic effect was accompanied by strong cytotoxicity. The CBC-induced gene mutation frequency was not increased after CAF treatment. The molecular analysis of CBC-induced mutations by Southern hybridization and PCR demonstrated that CBC predominantly produced small alterations but not deletions or gross structural alterations in the hprt gene of V79 cells. For the first time, these results reveal striking differences in the mutagenic action of an alkylating agent in cultivated cells compared to germ-line cells at the molecular level.

Targeting of tumor cells and DNA by a chlorambucil-spermidine conjugate

Many tumor cells, including murine ADJ/PC6 plasmacytoma cells, possess an active energy dependent polyamine uptake system which selectively accumulates endogenous polyamines and structurally related compounds. We have attempted to target the cytotoxic drug chlorambucil to a tumor possessing this uptake system by conjugating it to the polyamine spermidine. Furthermore, since polyamines have a high affinity for DNA, the attachment of spermidine to chlorambucil should also facilitate its targeting to DNA. This was supported by the observation that the chlorambucil-spermidine conjugate was approximately 10,000-fold more active than chlorambucil at forming interstrand crosslinks with naked DNA. In vitro cytotoxicity and in vivo antitumor studies were carried out using the ADJ/PC6 plasmacytoma. In vitro, using [3H]thymidine incorporation to assess cell viability following a 1-h exposure to control and polyamine depleted ADJ/PC6 cells, chlorambucil-spermidine was 35- and 225-fold, respectively, more toxic than chlorambucil. The increased toxicity of the conjugate compared to chlorambucil was possibly due to enhanced DNA binding and/or facilitated uptake via the polyamine uptake system. The enhanced toxicity of the conjugate but not chlorambucil by prior polyamine depletion with difluoromethylornithine, together with the observation that the conjugate but not chlorambucil competitively inhibited spermidine uptake into tumor cells, supported the suggestion that the conjugate utilized the polyamine uptake system. In vivo following a single i.p. dose, the conjugate was 4-fold more potent than chlorambucil in its ability to inhibit ADJ/PC6 tumor growth in BALB/c mice. However, the therapeutic index was not increased. Our results support the hypothesis that polyamines linked to cytotoxics facilitate their entry into tumor cells possessing a polyamine uptake system and increase their selectivity to DNA. This may have therapeutic application in the delivery of cytotoxic agents linked to polyamines to certain tumors.

The cytotoxicity, DNA crosslinking ability and DNA sequence selectivity of the aniline mustards melphalan, chlorambucil and 4-[bis(2-chloroethyl)amino] benzoic acid

Three aniline derivatives melphalan (L-PAM), chlorambucil (CHL) and 4-[bis(2-chloroethyl)amino] benzoic acid (BAM) have been compared on the basis of their in vitro cytotoxicities, DNA interstrand crosslinking ability and DNA sequence selectivity. Cytotoxicity was assessed in the human colonic adenocarcinoma LS174T and leukaemic K562 cell lines using the sulpho-rhodamine B and tetrazolium dye reduction assays. The order of cytotoxicities was L-PAM greater than CHL greater than BAM in both cell lines with K562 being less sensitive than LS174T. This was different from the order CHL greater than L-PAM greater than BAM which would be predicted from simple chemical reactivity or rate of hydrolysis, parameters which have been used previously as indicators of biological potency for aromatic nitrogen mustards. DNA interstrand crosslinking in cells as determined by alkaline elution showed a correlation with IC50 values. The ranking order of activity was further predicted by the ability of the agents to produce interstrand crosslinks in isolated DNA. The extent of guanine N-7 alkylation, assessed using a modified DNA sequencing technique, mirrored cytotoxicity and crosslinking ability, but at equivalent levels of alkylation there was no significant difference in DNA sequence selectivity. These data demonstrates that simple chemical reactivity or hydrolysis rate is not a good indicator of DNA reactivity or cytotoxicity for a number of aniline mustards, whereas DNA interstrand crosslinking ability either measured directly in cells or in isolated DNA, gives a good indication of biological activity.

Role of glutathione and glutathione S-transferase in chlorambucil resistance

A chlorambucil (CLB)-resistant cell line, N50-4, was developed from the established mouse fibroblast cell line NIH 3T3, by multistep drug selection. The mutant cells exhibited greater than 10-fold resistance to CLB. Alterations in GSH and glutathione S-transferase (GST) were found in CLB-resistant variants. A 7-10-fold increase in cellular GSH content and a 3-fold increase in GST activity were detected in N50-4 cells, compared with parental cells, as determined by enzymatic assays. An increase in steady state levels of the GST-alpha isozyme mRNA was found in the CLB-resistant cells, as analyzed by Northern blotting. No GST gene amplification or rearrangement was shown by Southern blot analysis. To test the relative roles of GSH and GST in CLB resistance, a number of GSH- and GST-blocking agents were used. The CLB toxicity was significantly enhanced in N50-4 cells by administration of either the GSH-depleting agent buthionine sulfoximine or the GST inhibitors ethacrynic acid or indomethacin. The resistance to CLB cytotoxicity in N50-4 cells, however, was still significantly higher than that of parental cells. The resistance of N50-4 cells to CLB was almost completely abolished by combination pretreatment yielding both GSH depletion and GST inhibition. The results indicate that both increased cellular GSH content and increased GST activity play major roles in CLB resistance in N50-4 mutant cells.

Growth-inhibitory action of an estrogen-chlorambucil conjugate (KM2210) in human breast cancer cell line MCF-7: its relation to reduction of estrogen receptor and transforming growth factor-alpha secretion

We investigated the effects of a benzoate of an estradiol-chlorambucil conjugate (KM2210) and chlorambucil on growth, estrogen receptor, and secretion of transforming growth factor (TGF)-alpha in the hormone-dependent human breast cancer cell line MCF-7. In the presence of 10(-10)-10(-6) M KM2210, the estrogen-induced growth of MCF-7 was completely inhibited. Inhibited growth of MCF-7 treated with 10(-8) or 10(-6) M KM2210 for 4 days was not rescued by removal of the drug and the addition of estradiol. By treatment of MCF-7 with KM2210 for 4 days, estrogen receptor-binding sites were decreased at 10(-8) M and were not detected at 10(-6) M but were unaltered by 10(-8) M chlorambucil. Moreover, estrogen receptor immunoreactivity and the level of estrogen receptor mRNA were decreased through treatment with 10(-6) M KM2210 for 4 days. These suppressions occurred prior to the onset of inhibitory action on MCF-7 growth. Secretion of TGF-alpha from MCF-7 was decreased by 4 days of treatment with 10(-8) and 10(-6) M KM2210 but not with chlorambucil. The addition of exogenous TGF-alpha generally restored the growth of MCF-7 treated with 10(-8) M KM2210. We concluded that KM2210 has irreversible or at least long-standing inhibitory effect on estrogen-dependent growth of MCF-7. It is conceivable that the decrease of estrogen receptor renders the cell unable to respond to estrogen with increased TGF-alpha secretion and succeeding cell growth.