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PubMed1986

Folate requirements of methotrexate-resistant human acute lymphoblastic leukemia cell lines.

We studied the folate requirements of a human acute lymphoblastic leukemia cell line, MOLT-3, and methotrexate (MTX)-resistant sublines established in vitro. The requirement of pteroylglutamate (PGA) for optimal cell growth was different for each cell line. With increasing MTX resistance, there was progressive increase in PGA requirements, moving the PGA concentration-cell growth curve (dose-response curve) 1 log order of magnitude to the right. The increases in the requirement of 5-methyltetrahydrofolate (5-methyl-THF) by the resistant sublines were more pronounced than PGA requirement, moving the dose-response curve nearly 3 log orders in magnitude to the right. The concentrations in vitro of 5-methyl-THF required for optimal growth of the MTX-resistant sublines far exceeded the normal serum 5-methyl-THF concentrations known in humans. These observations show that MTX-resistant cell established in vitro in culture media containing PGA instead of 5-methyl-THF, a physiological folate, cannot be expected to grow in vivo. The collateral sensitivity of transport-impaired MTX-resistant sublines to 2,4-diamino-5-methyl-6-[(3',4',5'- trimethoxyanilino) methyl] quinazoline (trimetrexate, TMQ) was negated in the absence of PGA. With the addition of 5-methyl-THF, the parent cells became more resistant than the transport-impaired sublines to TMQ These data indicate that the collateral sensitivity of MTX resistant cells to the substituted 2,4-diaminoquinazoline is due to functional folate deficiency by virtue of the impaired transport of folate.

Biological Transport↗
PubMed1982

Isolation of fluoropyrimidine-resistant murine leukemic cell lines by one-step mutation and selection.

The effectiveness of the clinically useful fluoropyrimidines in the treatment of human cancer is often limited by the development of resistance to the drugs by the tumor. In order to systematically study the mechanisms of resistance to 5-fluorouracil and its nucleoside derivatives, several cell lines resistant to these drugs have been derived from murine leukemia cells by a one-step mutation and selection procedure. Logarithmically growing suspension cultures of L1210 and P388 cells were treated with ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine, or ICR-191 at concentrations which result in 20 to 30% cell survival. After a 10-day expression time, mutagenized cells were plated into soft-agarose medium that contained 10(-5) M 5-fluorouracil, 10(-5) M 5-fluoro-2'-deoxyuridine, or 10(-6) M 5-fluorouridine. Twenty stable clones were isolated and found to be 5- to 28-fold resistant to growth inhibition by 5-fluorouracil, 4,000- to 25,000-fold resistant to 5-fluoro-2'-deoxyuridine, or 8- to 220-fold resistant to 5-fluorouridine. The clones retain their drug-resistant phenotype after repeated passaging in the absence of selection. Since the biochemical changes responsible for resistance to one drug can render the cells collaterally sensitive to other drugs, the growth-inhibitory effects of antimetabolites that inhibit other steps in pyrimidine metabolism were examined in the wild-type cells and in the fluoropyrimidine-resistant sublines. Although cross-resistance to 5-azacytidine was found in L1210 cells selected for resistance to 5-fluorouridine, none of the cell lines tested demonstrated collateral sensitivity to methotrexate, 1-beta-D-arabinofuranosylcytosine, 5-azacytidine, or N-(phosphonacetyl)-L-aspartate.

Animals↗
PubMed1996

2-deoxy-D-glucose toxicity and transport in human multidrug-resistant KB carcinoma cell lines.

It is shown that a series of colchicine-selected multidrug-resistant (MDR) human KB carcinoma cell lines displayed increasing 2-deoxy-D-glucose collateral sensitivity, which correlated with increasing multidrug resistance. The relative resistance of MDR cell lines to 2-deoxy-D-glucose was reduced to 0.73 (KB-8-5), 0.3 (KB-8-5-11) and 0.2 (KB-C1) when compared with parental KB-3-1 (1.0). 2-Deoxy-D-glucose accumulation was found to be reduced in the MDR cell lines in a manner that correlated with 2-deoxy-D-glucose collateral sensitivity. At 30 min 2-deoxy-D-glucose accumulation was reduced to 0.61 (KB-8-5), 0.41 (KB-8-5-11) and 0.22 (KB-C1) relative to KB-3-1 uptake (1.0). The efflux of 2-deoxy-D-glucose was not significantly different between resistant and sensitive cell lines. Analysis of 2-deoxy-D-glucose uptake kinetics, by initial rate measurements, showed alterations in K(t) and J(max) for MDR when compared with KB-3-l cells. The levels of GLUT-1 facilitative transporter were found to be reduced significantly in the MDR cell lines in total cell homogenate and plasma membrane fractions by using Western blot analysis. Changes in the plasma membrane level of GLUT-1 correlated with 2-deoxy-D-glucose toxicity and uptake for MDR cell lines, where relative GLUT-i levels were reduced to 0.71 (KB-8-5), 0.43 (KB-8-5-1 1) and 0.27 (KB-Cl) relative to KB-31(1.0). It is concluded that the response of human KB MDR cells to 2-deoxy-D-glucose involved alterations in the level and activity of the facilitative glucose transporter, GLUT-1, in a manner that is associated with the degree of multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Characterization of a hydroxyurea-resistant human KB cell line with supersensitivity to 6-thioguanine.

Hydroxyurea (HU) is currently used in the clinic for the treatment of chronic myelogenous leukemia, head and neck carcinoma, and sarcoma. One of its drawbacks, however, is the development of HU resistance. To study this problem, we developed a HU-resistant human KB cell line which exhibits a 15-fold resistance to HU. The characterization of this HU-resistant phenotype revealed a gene amplification of the M2 subunit of ribonucleotide reductase (RR), increased levels of M2 mRNA and protein, and a 3-fold increase of RR activity. This HU-resistant cell line also expressed a "collateral sensitivity" to 6-thioguanine (6-TG), with a 10-fold decrease in the dose inhibiting cell growth by 50% as compared to the KB parental line. The mechanism responsible for this supersensitivity to 6-TG is believed to be related to an increasingly efficient conversion of 6-TG to its triphosphate form, which is subsequently incorporated into DNA. After passage of the resistant cells in the absence of HU, the cell line reverts. The revertant cells lose their resistance to HU and concomitantly their sensitivity to 6-TG. This phenomenon is due to the return of RR to levels comparable to that of the KB parental cell line. These observations and their relevance to cancer chemotherapy will be discussed in this paper. Our results suggest that a clinical protocol could be designed which would allow for a lower dose of 6-TG to be used by taking advantage of the increased RR activity in HU-refractory cancer patients. Two drugs which display collateral sensitivity are known as a "Ying-Yang" pair. Alternate treatment with two different Ying-Yang pairs is the rationale for the "Ying-Yang Ping-Pong" theory in cancer treatment. This rationale allows for effective cancer chemotherapy with reduced toxicity.

Animals↗
PubMed1997

Cross-resistance to antifolates in multidrug resistant cell lines with P-glycoprotein or multidrug resistance protein expression.

Resistance to some (lipophilic) antifolates has been associated with P-glycoprotein (P-gp)-mediated multidrug resistance (MDR). A possible relationship with non-P-gp MDR has not been established. We studied resistance to antifolates in SW-1573 human lung carcinoma cells, a P-gp overexpressing variant SW-1573/2R160 and a multidrug resistance protein (MRP) overexpressing variant SW-1573/2R120. In this study, thymidylate synthase (TS) inhibitors with different properties concerning the efficiency of membrane transport and the efficiency of polyglutamylation were tested for cross-resistance in SW-1573/2R120 and SW-1573/2R160 cells. Growth inhibition patterns in this cell line panel were measured by the Sulforhodamine B (SRB) assay. Resistance factors for TS inhibitors were: 2.4 and 0.4 for 5-fluorouracil (5FU), 18.8 and 8.8 for ZD1694, 17 and 0.7 for AG337, and 40 and 8.3 for BW1843U89 in SW-1573/2R160 and SW-1573/2R120, respectively. This study showed changes in the TS enzyme kinetics during the induction of doxorubicin resistance in both SW-1573 variants, resulting in 2-fold lower Km values for 2'-deoxyuridine-5'-monophosphate (dUMP) in both resistant variants compared to the parental cell line. TS activity, TS protein induction and TS mRNA expression all had 2-fold increased in the SW-1573/2R120 compared to the SW-1573/2R160. 3H-MTX influx was 2-fold lower in SW-1573/2R160 cells compared to SW-1573/2R120 and SW-1573 cells. In the SW-1573/2R160 cell line, an aberrant intracellular trafficking towards the target TS was observed, compared to SW-1573/2R120 and SW-1573 cells as measured by the TS in situ assay. The rate of TS inhibition by the TS inhibitors used in this study was similar in all cell lines. In conclusion, collateral sensitivity to 5FU and the lipophilic AG337 and cross-resistance to other antifolates were observed in non-P-gp MDR SW-1573/2R120 cells, as well as resistance to all antifolates in P-gp SW-1573/2R160 cells. The mechanism of resistance in SW-1573/2R160 cells possibly involves reduced influx and changes in intracellular trafficking routes. For the SW-1573/2R120 cell line, several changes related to the TS enzyme possibly play a role in the observed cross-resistance and collateral sensitivity pattern.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1986

Selection of nitrogen mustard resistance in a rat tumor cell line results in loss of guanine-O6-alkyl transferase activity.

Cell killing, DNA-interstrand crosslinks, and DNA-protein crosslinks were assayed in nitrogen mustard-resistant Walker 256 carcinoma (WR) cells and the parent cell line (WS) after treatment with 5-[3-(2-chloroethyl)-1-triazenyl]imidazo-4-carboxamide (MCTIC). The WR cells, which also express collateral sensitivity to chloroethylnitrosoureas, were approximately twice as sensitive to the cytotoxic effects of MCTIC as were WS cells. Following treatment with 100 microM MCTIC, there was a rapid accumulation of both DNA-interstrand and DNA-protein crosslinks in the WR cell line, which reached a maximum at 6 and 12 hr, respectively. There was considerably less crosslinking in the WS cells and both cell lines were proficient in repairing most of the crosslinks by 24 hr. Measurement of guanine-O6-alkyl transferase activity showed the enzyme to be present in WS but not in WR cells. These data indicate that the collateral sensitivity of nitrogen mustard-resistant WR cells to chloroethylating drugs is in part due to the loss of guanine-O6-alkyl transferase activity which is present in the parent line.

Animals↗
PubMed1994

Elevated DNA polymerase alpha, DNA polymerase beta, and DNA topoisomerase II in a melphalan-resistant rhabdomyosarcoma xenograft that is cross-resistant to nitrosoureas and topotecan.

Previous investigations have revealed that the human TE-671 MR human rhabdomyosarcoma xenograft selected in vivo for melphalan resistance (M. C. Rosenberg, et al., Cancer Res., 49: 6917-6922, 1989) is cross-resistant to a wide variety of alkylating agents and to bleomycin, but is collaterally sensitive to etoposide. Although glutathione levels were noted to be elevated in TE-671 MR compared to the melphalan-sensitive parental TE-671 xenograft, treatment with buthionine sulfoximine to deplete glutathione levels did not fully restore melphalan sensitivity in the TE-671 MR xenograft. The present studies were undertaken to search for additional mechanisms of resistance in the TE-671 MR xenograft. Drug sensitivity testing performed at the dose of agents that was lethal to 10% of the animals revealed that the TE-671 MR xenograft maintained resistance to the bifunctional cross-linking agent 1,3-bis(2-chloroethyl)-1-nitrosourea and was cross-resistant to the topoisomerase I poison topotecan. Treatment with buthionine sulfoximine did not sensitize the TE-671 MR xenograft to 1,3-bis(2-chloroethyl)-1-nitrosourea. Further, even though O6-alkylguanine-DNA alkyltransferase levels were high in both the TE-671 and TE-671 MR xenografts, depletion of O6-alkylguanine-DNA alkyltransferase activity by treatment with O6-benzylguanine substantially sensitized the TE-671 xenografts but not the TE-671 MR xenografts, suggesting an additional mechanism of resistance. Measurement of additional enzyme activities that might be involved in DNA repair revealed significant elevations in DNA polymerase alpha (46 +/- 8 (SD) units/mg protein in TE-671, 69 +/- 6 units/mg protein in TE-671 MR, P < 0.05) and DNA polymerase beta (0.43 +/- 0.01 units/mg protein in TE-671, 0.78 +/- 0.12 units/mg protein in TE-671 MR, P < 0.05) but not DNA polymerase delta or total DNA ligase. Examination of topoisomerases by activity assays and Western blotting revealed a 2-fold increase in topoisomerase II and a 2-fold decrease in topoisomerase I in the TE-671 MR xenograft compared to the parental xenograft, apparently explaining the collateral sensitivity to etoposide and cross-resistance to topotecan. These results suggest that TE-671 MR xenografts contain multiple changes in activities of DNA repair-related proteins and other nuclear proteins that could contribute to alkylating agent resistance.

Alkyl and Aryl Transferases↗
PubMed1988

Intracellular doxorubicin concentrations and drug-induced DNA damage in a human colon adenocarcinoma cell line and in a drug-resistant subline.

The mechanisms of resistance to doxorubicin (DX) were investigated using a human colon adenocarcinoma cell line (LoVo) and a subline approximately 30 times less sensitive to doxorubicin. LoVo and LoVo/DX were similar in terms of DNA and protein content, cell volume, duration of S phase and the generation time, and proportion of cycling cells. LoVo/DX showed cross-resistance to other anthracyclines, to vinca alkaloids, epipodophyllotoxin derivatives, 4'-(9-acridinylamino-methanesulfon-m-aniside) and actinomycin D. LoVo/DX was equally sensitive to melphalan and showed collateral sensitivity to cis-platinum and 1-beta-D-arabinofuranosylcytosine. On exposing LoVo and LoVo/DX to 1.25 and 40 micrograms/ml DX respectively, for 4 hr, similar DX intracellular concentrations were reached in the two cell lines. In these treatment conditions protein associated DNA-single strand breaks or DNA-double strand breaks, assessed by alkaline elution methods were only slightly less in LoVo/DX than in LoVo cells. In LoVo/DX cells, however, DNA breaks disappeared very quickly after drug removal whereas they persisted longer in LoVo cells. This persistance is probably related to the much slower DX efflux from LoVo than LoVo/DX. When verapamil was combined with DX it inhibited the rapid DX efflux from LoVo/DX and reversed the resistance in this cell line, but it had no significant activity on LoVo cells. Verapamil also increased DX-induced DNA-single strand breaks and DNA-double strand breaks in LoVo/DX cells, but not in LoVo cells.

Adenocarcinoma↗
PubMed1986

Characterization of a new drug-resistant human myeloma cell line that expresses P-glycoprotein.

Multiple myeloma is a disease with a high initial chemotherapeutic response but virtually no cures due to emergence of drug resistance. A doxorubicin-resistant human myeloma cell line (8226/Dox) has been selected from the myeloma cell line RPMI8226 by continuously exposing cells to gradually increasing doses of doxorubicin. The resistant phenotype has been retained for over 2 months despite growth in drug-free medium. The resistant subline was cross-resistant to mitoxantrone, acronycine, etoposide, and vincristine. The 8226/Dox cell line remained sensitive to melphalan but acquired collateral sensitivity to dexamethasone. Intracellular doxorubicin accumulation, as measured by [14C]doxorubicin and high-performance liquid chromatography, was decreased by 54% at 1 h for 8226/Dox compared to the sensitive line. Efflux of doxorubicin was significantly greater in the resistant subline as compared to the sensitive parent cell line. Membrane analysis using immunoblotting techniques detected increased expression of the integral membrane protein P-glycoprotein (Mr 170,000) in the resistant subline. Cytogenetic analysis of 8226/Dox revealed a 7q-anomaly not seen in the parent cell line. No double minutes or homogeneously staining regions were observed. The drug sensitivity/resistance pattern of the resistant cell line correlates well with clinical observations indicating the potential of this cell line as a model for resistance in multiple myeloma.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1984

Cytochemical characterization of Yoshida sarcoma cells resistant to dibromodulcitol.

Two Yoshida ascites sarcoma cell populations, one of them originally sensitive and another rendered resistant to the alkylating agent dibromodulcitol (DBD), were compared for doubling time, labeling index, survival time, morphological features, cellular DNA content and modal DNA value. Cross-resistance studies were carried out on bilaterally growing solid tumours derived from the sensitive and resistant Yoshida cell populations. Glycogen-containing granules appeared in the cytoplasm of the DBD-resistant sarcoma cells; these were not present in the sensitive tumour. The growth parameters of the sensitive tumour were throughout the 10-day observation period characteristic of rapidly proliferating tumours, whereas those of the DBD-resistant tumour was characteristic of slowly proliferating systems. As compared to the mean DNA values for normal somatic cells (lymphocytes), those found for both tumours indicated that the cells were hyperdiploid aneuploid. The DNA stem line in the resistant tumour proved to be significantly smaller than that in the sensitive tumour. These results indicate that a reduction of malignancy in the Yoshida tumour is associated with a developed resistance to dibromodulcitol. The resistant tumour showing cross-resistance to dianhydrogalactitol, diacetyl-dianhydrogalactitol and to nitrogen mustard retained full sensitivity to cyclophosphamide and adriablastin (Adriamycin), and proved to be collaterally sensitive to vincristin.

Animals↗
PubMed1994

Synthesis and biological activity of N omega-hemiphthaloyl-alpha,omega- diaminoalkanoic acid analogues of aminopterin and 3',5-dichloroaminopterin.

Analogues of N alpha-(4-amino-4-deoxypteroyl)-N delta-(hemiphthaloyl)-L-ornithine (PT523) with 3',5'-dichloro substitution in the p-aminobenzoyl moiety or with one less or one more CH2 group in the amino acid moiety were synthesized and tested as inhibitors of dihydrofolate reductase (DHFR) activity and cell growth. Replacement of L-ornithine in PT523 by L-2,4-diaminobutanoic acid or L-lysine did not decrease binding to human recombinant DHFR but resulted in some loss of activity against SCC25 human and SCC VII murine squamous cell carcinoma and against MCF-7 human breast carcinoma in culture. PT523 was several times more potent than methotrexate (MTX), aminopterin (AMT), or trimetrexate (TMQ). 3',5'-Dichloro substitution did not decrease either DHFR binding or cytotoxicity. A new synthetic route to PT523 from 2,4-diamino-6-(hydroxymethyl)pteridine and methyl N alpha-(4-aminobenzoyl)-N delta-phthaloyl-L-ornithinate was investigated but was not found superior to previously described methods. In comparative experiments on the ability of PT523 and MTX to competitively inhibit the influx of (6R)-5,10-dideazatetra-hydrofolate (DDATHF, lometrexol), used here as a surrogate for MTX and reduced folates, the Ki of PT523 was lower than that of MTX in both wild-type CCRF-CEM human leukemic lymphoblasts and the transport- and polyglutamylation-defective subline CEM/MTX. The CCRF-CEM cells were 10-fold more sensitive to PT523 than to MTX, whereas the CEM/MTX cells were 240-fold more sensitive. However, in contrast to other MTX-resistant cells where collateral sensitivity to PT523 has been seen. CEM/MTX cells still showed substantial cross resistance to PT523 which may reflect an unusual heightened ability to utilize exogenous folic acid. The good correlation observed with both cell lines between the cytotoxicity of PT523 and MTX and the ability to inhibit DDATHF influx supported the view that PT523 and MTX share, at least in part, a common protein carrier for membrane transport.

Aminopterin↗
PubMed2001

Activity of a trinuclear platinum complex in human ovarian cancer cell lines sensitive and resistant to cisplatin: cytotoxicity and induction and gene-specific repair of DNA lesions.

A collateral sensitivity or a very modest cross-resistance to BBR 3464 was found in 2 ovarian cancer cell lines with experimentally induced resistance to cisplatin. Loss of mismatch repair proteins (hMLH1, hPMS2) or overexpression of nucleotide excision repair proteins (ERCC1) was not detrimental for the cellular sensitivity to BBR 3464. Moreover, interesting differences in the kinetics of formation and removal of DNA lesions at the single-gene (N- ras) level were observed between BBR 3464 and CDDP.

Adaptor Proteins, Signal Transducing↗
PubMed1989

Activity of the pyrazoloacridines against multidrug-resistant tumor cells.

A series of 2-aminoalkyl-5-nitropyrazolo [3,4,5-kl]acridines (pyrazoloacridines) were tested in vitro against a panel of multidrug-resistant cell lines comprising Adriamycin-resistant P388 leukemia, B16 melanoma, and mammary adenocarcinoma 16c. This new class of anticancer agents, particularly the 9-substituted methoxy derivatives, exhibited significant activity against all of the lines tested. The degree of cross-resistance to these compounds ranged from zero to 8-fold in the 138-fold Adriamycin-resistant P388/ADR line and was greatly diminished in the B16/ADR and 16c/ADR lines. Selected pyrazoloacridines were subsequently tested in vivo against B16 and B16/ADR cells established as solid tumors from the tissue culture line and shown to retain a significant degree of Adriamycin resistance. Whereas the B16/ADR line exhibited 2 logs less net tumor-cell kill than the B16 parent in response to Adriamycin treatment, the resistant tumor was completely sensitive to the pyrazoloacridines tested and proved in some experiments to be collaterally sensitive. The favorable activity of the pyrazoloacridines against these Adriamycin-resistant tumor lines points to the potential efficacy of these compounds against multidrug-resistant tumors encountered clinically.

Acridines↗
PubMed2000

Selection of human leukemic CEM cells for resistance to the DNA topoisomerase II catalytic inhibitor ICRF-187 results in increased levels of topoisomerase IIalpha and altered G(2)/M checkpoint and apoptotic responses.

ICRF-187 is a bisdioxopiperazine anticancer drug that inhibits the catalytic activity of DNA topoisomerase (topo) II without stabilizing DNA-topoII cleavable complexes. To better understand the mechanisms of action of and resistance to topoII catalytic inhibitors, human leukemic CEM cells were selected for resistance to ICRF-187. The clones CEM/ICRF-8 and CEM/ICRF-18 are approximately 40- and 69-fold resistant to ICRF-187, and 12- and 67-fold cross-resistant to ICRF-193, respectively, but are sensitive to other topoII catalytic inhibitors (merbarone and aclarubicin), as well as collaterally sensitive to the DNA-topoII complex-stabilizing drug etoposide (VP-16). Both the number of VP-16- induced DNA-topoII complexes formed and the amount of in vitro topoII catalytic activity are enhanced in the drug-resistant cells. The ICRF-187-resistant clones contain approximately 5-fold increase in topoIIalpha protein levels and approximately 2.2-fold increase in topoIIalpha mRNA levels. Furthermore, CEM/ICRF-8 expresses approximately 3.5-fold increase in topoIIalpha promoter activity, suggesting that up-regulation of topoIIalpha in this clone occurs at the transcriptional level. Treatment of the drug-resistant or -sensitive cells with equitoxic doses of merbarone or teniposide results in a G(2)/M arrest. In marked contrast, when treated with equitoxic ICRF-187 doses, the drug-resistant clones exhibit either a transient arrest or completely lack the G(2)/M checkpoint compared with the drug-sensitive cells. This aberrant cell cycle profile is associated with a 48-h delay in drug-induced apoptotic cell death, as revealed by fluorescent-end labeling of DNA and poly (ADP-ribose) polymerase cleavage. In summary, resistance to ICRF-187 in CEM cells is associated with increased levels of catalytically active topoIIalpha and altered G(2)/M checkpoint and apoptotic responses.

Antigens, Neoplasm↗
PubMedDate not supplied

The synergism of 6-mercaptopurine plus cytosine arabinoside followed by PEG-asparaginase in human leukemia cell lines (CCRF/CEM/0 and (CCRF/CEM/ara-C/7A) is due to increased cellular apoptosis.

BACKGROUND: The only effective drug against ALL that inhibits protein synthesis is Asparaginase (ASNase). The drug depletes asparagine (Asn) in serum and cells and since the leukemic T-cells (thymic origin cells) lack asparagine synthetase, the amino acid starvation leads to apoptosis. When PEG-ASNase is combined with antimetabolite drugs such as ara-C, or combinations of 6-MP followed by ara-C, it augments the cytotoxic effect synergistically against human T-leukemia cells. MATERIALS AND METHODS: Synergism studies with two- or three-drug combination regimens in the human leukemia cell lines, CEM/0 and CEM/ara-C/7A have been investigated along with its effect in inducing apoptosis. RESULTS: The IC50 (approximately Dm) values of ara-C were 0.032 microM and 0.11 microM, and that of PEG-ASNase were 0.002 IU/ml and 1.52 IU/ml against CEM/0 and CEM/ara-C/7A cells, respectively. Thus, CEM/ara-C/7A cell line that is partially resistant to ara-C exhibited 681-fold cross-resistant to PEG-ASNase as compared to CEM/0. The concurrent drug exposure of ara-C and PEG-ASNase for 48 hours resulted in IC50 values of 0.56 nM for ara-C and 0.56 mIU/ml for PEG-ASNase respectively, in CEM/0 cells which represents a 57.4-fold synergism compared to ara-C alone. In the CEM/ara-C/7A cell line, the co-incubation with these two drugs resulted in IC50 value of 0.015 microM for ara-C and 0.015 IU/ml for PEG-ASNase respectively, or a 7.25-fold synergism as compared to ara-C and 101.1-fold synergism in comparison with PEG-ASNase alone. Pre-clinical studies involving three-drug combination consisting of 6-MP, ara-C and PEG-ASNase in a sequence-specific manner showed a 15.6-fold synergism against CEM/0 cell line over the two-drug combination of 6-MP followed by ara-C or approximately 160-fold syneryism over ara-C alone. CONCLUSION: The two-drug combination of ara-C and PEG-ASNase or the three-drug combination of 6-MP, ara-C and PEG-ASNase in the ara-C sensitive and resistant cell line showed significant drug synergism and CEM/ara-C/7A cells exhibited collateral sensitivity to PEG-ASNase. The three-drug combination also induced dose-dependent apoptotic DNA fragmentation which was higher than the two-drug combination of 6-MP and ara-C. We also conclude that the sequence specific use of PEG-ASNase in combination with the nucleoside analog drugs may benefit leukemia patients in early relapse.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

The effect of vinca alkaloids in enhancing the sensitivity of a methotrexate-resistant (L1210/R7A) line, studied by flow cytometric and chromosome number analysis.

Two L1210 murine lymphoma cell lines sensitive and resistant to methotrexate (L1210 and L1210/ R7A , respectively) and previously shown to exhibit collateral sensitivity to the vinca alkaloids have been studied by flow cytofluorimetric techniques following propidium iodide staining of the DNA. Following treatment with a range of concentrations of vincristine, both cell lines showed a build-up of fluorescence in the 4n position. However, the methotrexate-resistant cell line exhibited this effect at lower doses of vincristine. On an equimolar basis, the vinca alkaloids ranked for intensity of this effect in the order vinblastine greater than vindesine greater than vincristine. DNA fluorescent histograms following various times of continuous exposure to vincristine showed an accumulation of material at the 8n position, which was shown by chromosome analysis to be due to polyploidy. It was concluded that methotrexate-resistant cells (L1210/ R7A ) experience difficulty in traversing mitosis and this difficulty is enhanced by the vinca alkaloids.

Animals↗