Structure-activity relationships of antineoplastic agents in multidrug resistance.

Clinical resistance to many antineoplastic agents is a major cause of treatment failure. The well-documented phenomenon addressed as multidrug resistance (MDR) allows cells to withstand exposure to lethal doses of drugs with dissimilar chemical structures, modes of action, and physicochemical properties. In one of the earliest studies on MDR, Biedler and Riehm in an attempt to explain the cross-resistance profile of actinomycin D resistant Chinese hamster cells suggested that molecular weight was an important determinant. Our statistical analysis of their data validates their claim and indeed strongly demonstrates that cross resistance is enhanced by the increased size and hydrophobicity of the antitumor agent. Our preliminary studies with methotrexate-resistant L1210 cells indicates that cross resistance is increased in the case of moderate-sized, hydrophilic drugs. These two studies and others suggest that current chemotherapy regimens may be improved by treating resistant cells with antineoplastic agents displaying physicochemical characteristics opposite to that of the original inducing agent.

Comparison of triazines as inhibitors of L1210 dihydrofolate reductase and of L1210 cells sensitive and resistant to methotrexate.

The inhibition of dihydrofolate reductase from L1210 leukemia cells as well as the inhibition of intact L1210 cells, both sensitive and resistant, to methotrexate by over 100, 4,6-diamino-2,2-dihydro-2,2-dimethyl-1-(X-phenyl)-s-triazines was studied. Quantitative structure-activity relationships were derived for the three systems. These equations, based on a set of congeners having a range in lipophilicity of about 700,000,000 on the octanol-water scale, delineate the inhibitory potency of the triazines in relation to their hydrophobicity. The data demonstrate that there is a close parallel between the way isolated dihydrofolate reductase and methotrexate sensitive cells respond to the triazines. However, the resistant L1210 cells behave in an entirely different manner, which suggests that the passive diffusion of triazines into the cells dominates the structure-activity relationship. The optimum lipophilicity (pi 0) of triazine substituents for purified L1210 dihydrofolate reductase is 1.76 to 2.11; for sensitive cells, it is 1.45 to 1.83, and for resistant cells, it is approximately 6.

Recent studies on the anticancer activities of mistletoe (Viscum album) and its alkaloids.

Detailed methods for in vitro/in vivo evaluation of anticancer drugs, with special reference to mistletoe extracts, have been reviewed. Mistletoe extracts have been shown to possess significant antitumor activity, in vivo, against murine tumors, Lewis lung carcinoma, colon adenocarcinoma 38 and C3H mammary adenocarcinoma 16/C. Methods for the extraction of biologically active alkaloids from mistletoe and their anticancer activities are presented. The possible origin of alkaloids in mistletoe plants, and their contributions towards a mechanism of anticancer activities of mistletoe extracts, are proposed.

Comparative structure-activity relationships of antifolate triazines inhibiting murine tumor cells sensitive and resistant to methotrexate.

The inhibitory effect of 108 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(substituted-phenyl)-s-triazines on murine L5178Y tumor cells, resistant and sensitive to methotrexate (MTX), has been studied. From the pI50 values, quantitative structure-activity relationships have been formulated which show that the lipophilic triazines are much more inhibitory against resistant cells than methotrexate or hydrophilic triazines. The results are compared with the behavior of other antifolate drugs that have been used in chemotherapy, as well as with eight antitumor drugs that are not antifolates. The acquired resistance of these cells toward hydrophilic antifolates may be attributed to the combined effect of an impaired active-transport system, a change in the conformation of dihydrofolate reductase in the resistant cells, and an amplified production of dihydrofolate reductase in the resistant cells.

Novel N-hydroxyguanidine derivatives as anticancer and antiviral agents.

Hydroxyguanidine contains both features of guanidine and hydroxyurea and has antiviral and anticancer activities both in vitro and in vivo. In order to enhance the antiviral and anticancer activity of this compound, a new series of hydroxyguanidine derivatives with the following structures were synthesized: R = NNHC(= NH)NHOH, where R = aromatic or heterocyclic aldehyde. This series of compounds was prepared in order to alter the lipophilic/hydrophilic balance, as well as the electronic and steric properties of hydroxyguanidine. The anticancer activities of the compounds were tested against cultured L1210 cells. The ID50 values of the above compounds are in the range of 7.80-126 microM. They are about 10-fold more active than hydroxyurea and hydroxyguanidine. The antiviral activities were also tested by assaying the inhibition of transformation of chicken embryo fibroblasts infected with Rous sarcoma virus. The ID50 values of these new compounds are in the range of 2.76-195.2 microM. The most active ones are about 100-fold more active than hydroxyguanidine. At the ID50, no apparent toxicity to the cells was noticed.

synthesis and antitumor activity of 2-deoxyribofuranosides of 3-deazaguanine.

Synthesis of 2-deoxyribofuranosides of 3-deazaguanine (IX-XII) has been achieved by a base-catalyzed ring closure of appropriate 2-deoxyribofuranosides of methyl 5(4)-(cyanomethyl)imidazole-4(5)-carboxalate (IV-VII). The separation of isomers and anomers were accomplished by column chromatography and HPLC. The site of glycosidic linkage and the anomeric configurations were established on the basis of C-13 and proton magnetic resonance spectroscopy, as well as UV absorption characteristics. Preliminary results of the antitumor activity of these derivatives, in vitro and in vivo, are described.

3-deazaguanine, a candidate drug for the chemotherapy of breast carcinomas?

3-Deazaguanine (3-DG) is a new purine antagonist that is active against slow- and rapid-growing solid experimental tumors, especially those that are models for human breast carcinomas. These tumors include mammary adenocarcinomas 13762, R3230AC, and C3H/16C. 3-DG also showed positive activity against leukemias L1210 and L1210/araC, adenocarcinoma 755, and EMT-6 mammary adenocarcinoma. On the basis of its activity against these tumors, 3-DG is to undergo clinical trials.

Inhibition by 5-(substituted-benzyl)-2,4-diaminopyrimidines of murine tumor (L5178Y) cell cultures sensitive to and resistant to methotrexate. Further evidence for the sensitivity of resistant cells to hydrophobic drugs.

Forty-three 5-(substituted-benzyl)-2,4-diaminopyrimidines have been studied as inhibitors of murine tumor cell cultures (L5178Y). Two types of cells were used--one resistant to methotrexate and one sensitive to methotrexate. The formulation of quantitative structure--activity relationships showed that the methotrexate-resistant cells are more sensitive to the more hydrophobic congeners. pi 0 for the sensitive cells is about 1.4, while pi 0 for the methotrexate-resistant cells is above 3. These results are similar to those found for 2,4-diaminotriazines (Selassie, C.D.; Guo, Z. R.; Hansch, C.; Khwaja, T. A.; Pentecost, S. J. Med. Chem. 1982, 25, 157).

Comparison of quantitative structure-activity relationships of the inhibition of leukemia cells in culture with the inhibition of dihydrofolate reductase from leukemia cells and other cell types.

A set of 2,4-diamino-5-(3-X-phenyl)-s-triazines was used to inhibit the growth of tumor cells (L5178 leukemia) in culture. The molar concentration (C) of triazine causing 50% reduction in the rate of cell growth was used to develop a quantitative structure-activity relationship: log 1/C = 1.32 pi - 1.70 log (beta.10 pi + 1) + 0.44I + 8.10, where pi is the hydrophobic constant for X, beta is a disposable parameter, and I is an indicator variable for congeners containing a -CH2Z-C6H4-Y moiety (Z = O or NH). This equation is compared with similar equations derived for the inhibition of dihydrofolate reductase from leukemia cells and bovine liver.

A comparison of the inhibition of growth of methotrexate-resistant and -sensitive leukemia cells in culture by triazines. Evidence for a new mechanism of cell resistance to methotrexate.

Forty-five 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(3-X-phenyl)-s-triazine inhibitors of dihydrofolate reductase (DHFR) and methotrexate (MTX) were tested on L5178Y/R murine tumor cell culture. The concentration of inhibitor causing a 50% decrease in growth rate was determined, and from these results a quantitative structure-activity relationship (QSAR) was developed. This QSAR is compared with QSAR for the same inhibitors acting on isolated DHFR and on L5178Y cell culture sensitive to MTX. The results show that very potent triazine inhibitors of resistant tumor cell growth can easily be made by making the triazines strongly hydrophobic. The optimum pi value for inhibition of MTX-sensitive cell culture is 0.8, while pi 0 for the resistant cell culture is about 6.0. The QSAR for MTX-sensitive and -resistant tumor cell culture inhibition is compared with the corresponding QSAR for Lactobacillus casei cells. Both the mammalian and bacterial cells appear to protect themselves from the highly hydrophilic MTX by erecting lipophilic barriers.

Isolation of biologically active alkaloids from Korean mistletoe Viscum album, coloratum.

Anticancer activity of certain highly cytotoxic alkaloids present in Korean mistletoe has been demonstrated in experimental animals. Unlike European mistletoe, no cytotoxic proteins were found in the Korean mistletoe.

8-Phosphorus substituted isosteres of purine and deazapurines.

Synthesis of 8-phosphorus substituted isosteres of purine [pyrimidino (4,5-d)-1,3,2-diazaphosphole], 1-deazapurine [pyridino (2,3-d)-1,3,2-diazaphosphole] and 3-deazapurine [pyridino (4,5-d)-1,3,2-diazaphosphole] has been achieved by the reaction of equimolar amounts of triphenylphosphite and 4,5-diaminopyrimidine, 2,3-diaminopyridine and 3,4-diaminopyridine, respectively. These compounds hydrolyzed (cleavage of the phosphorus-nitrogen bounds) in aqueous solutions to provide the corresponding diaminopyrimidine or diaminopyridines. These three new basic ring systems constitute the first reported synthesis of purines in which ring carbon atom is substituted with a phosphorus atom. 8-Phosphorus substituted purine at a concentration of 4 X 10(-4)M caused a 50% inhibition in the growth of leukemia L1210 cells in culture. The biochemical rationale for the synthesis of these compounds is discussed.

Synthesis and antitumor and antiviral activities of 1-beta-D-arabinofuranosyl-2-amino-1,4(2H)-iminopyrimidine and its derivatives.

1-beta-D-Arabinofuranosyl-2-amino-1,4(2H)-imino-5-fluoropyrimidine (10), 1-beta-D-arabinofuranosyl-2-amino-1,4(2H)-imino-5-fluoropyrimidine 3'-phosphate (9), and 1-beta-D-arabinofuranosyl-2-amino-1,4(2H)-imino-5-chloropyrimidine (11) have been synthesized from 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorocytosine (5), 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-fluorocytosine 3'-phosphate (4), and 2,2'-anhydro-1-beta-D-arabinofuranosyl-5-chlorocytosine (6), respectively. 2,2'-Anhydro-1-beta-D-arabinofuranosylcytosine 3'-phosphate (7), 1-beta-D-arabinofuranosyl-2-amino-1,4-(2H)-iminopyrimidine (13), 1-beta-D-arabinofuranosyl-2-amino-1,3(2H)-iminopyrimidine 3'-phosphate (12), and compounds 4, 5, and 9 showed significant in vitro activity against a number of DNA viruses. Compounds 7 and 12 were also effective in vivo against type 1 herpes simplex virus. Compounds 7, 12, and 13 were extremely effective in the treatment of mice bearing leukemia L1210.

Synthesis and antiviral acticity of some phosphates of the broad-spectrum antiviral nucleoside, 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin).

1-beta-D-Ribofuranosyl-1,2,4-triazole-3-carboxamide 5'-phosphate (2) was prepared and converted into the following derivatives: the 5'-phosphoramidate 3, the 5'-diphosphate 4, the 5'-triphosphate 5, and the cyclic 3',5'-phosphate 6. The cyclic 2',3'-phosphate 7 was prepared from the parent nucleoside, 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (1), and was opened to the 2'(3')-phosphate 8. These compounds were found to exhibit significant antiviral activity against several viruses in cell culture. Ribavirin 5'-phosphate (2) was shown to be effective when tested against lethal infections in mice caused by influenza A2, influenza B, and murine hepatitis viruses.

Adjuvant postoperative chemotherapy with 5-fluorouracil and methotrexate: effect of schedule of administration on metastasis of 13762 mammary adenocarcinoma.

Metastasizing mammary adenocarcinoma 13762 in female Fischer rats has been used as a model for studying postoperative adjuvant chemotherapy, using methotrexate (Mtx) and 5-fluouracil (5FU) either singly or in combinations. All animals that received postoperative adjuvant chemotherapy of 5FU alone, 5FU and Mtx simultaneously, or Mtx followed by 5FU had significant improvement of survivals. Methotrexate alone was ineffective in treating the visceral metastasis. The addition of Mtx at the time of 5FU administration actually decreased the therapeutic effectiveness of 5FU given by itself. Fluorouracil alone improved survival of rats with small or large tumors, whereas Mtx followed by 5FU was better than 5FU alone in rats with smaller tumors. Among all rats treated with chemotherapy, those rats that got Mtx followed by 5FU had the lowest amount of lung metastasis, and concomitant administration of nonspecific BCG immunotherapy delayed death from visceral metastasis only for rats receiving drugs according to this schedule.

A new hamster fibrosarcoma model for in vitro/in vivo evaluation of cancer chemotherapeutic agents.

A hamster fetal cell clone has been developed for in vitro chemotherapeutic studies as well as in an in vivo fibrosarcoma model system. Highly reproducible quantitative in vitro chemotherapeutic data can be obtained with this cell line within 5 days, and as few as 10(2) cells produce rapidly growing fibrosarcomas when injected subcutaneously into adult hamsters. We found using these cells in vitro that 1-beta-D-arabinofuranosylcytosine (ara-C) can antagonize the effect of 5-azacytidine (aza-C) if given simultaneously or if aza-C treatment is preceded by a 2-hr exposure to ara-c. Using the same cell line as in vivo model for chemotherapy it was also shown that ara-C and cyclocytidine significantly inhibited tumor growth. This hamster cell line may be quite useful as an in vitro/in vivo model system for the study of cancer chemotherapeutic agents.

2' Derivatives of guanosine and inosine cyclic 3',5'-phosphates. Synthesis, enzymic activity, and the effect of 8-substituents.

A series of representative derivatives of guanosine cyclic 3',5'-phosphate (cGMP) and inosine cyclic 3',5'-phosphate (cIMP) which contained modifications in either the 2' position or the 8 and 2' positions were synthesized. Three types of derivatives were investigated: (1) derivatives in which the 2' position has been altered to produce a 2'-deoxynucleoside cyclic 3',5'-phosphate or a 9-beta-D-arabinofuranosylpurine cyclic 3',5'-phosphate; (2) 2'-omicron-acyl derivatives; and (3) doubly modified derivatives containing a 2' modification [as in (1) and (2)] and an 8-substitution. 2'-Deoxyinosine cyclic 3',5'-phosphate and 9-beta-D-arabinofuranosylhypoxanthine cyclic 3',5'-phosphate were obtained by HNO2 deamination of 2'-deoxyadenosine cyclic 3',5'-phosphate and 9-beta-D-arabinofuranosyladenine cyclic 3',5'-phosphate (ara-cAMP), respectively. Treatment of 8-bromo-2'-omicron-(p-toluenesulfonyl) adenosine cyclic 3',5'-phosphate with NaSH yielded the intermediate 8,2'-anhydro-9-beta-D-arabinofuranosyl-8-mercaptoadenine cyclic 3',5-phosphate, which was converted directly to 2'-deoxyadenosine cyclic 3',5'-phosphate (dcAMP) by treatment with Raney nickel. 8-Bromo-2'-omicron-(p-toluenesulfonyl) guanosine cyclic 3',5'-phosphate was converted to 8,2'-anhydro-9-beta-D-arabinofuranosyl-8-mercaptoguanine cyclic 3',5'-phosphate, and the latter was desulfurized with Raney nickel to give 2-deoxyguanosine cyclic 3',5'-phosphate. Ara-cAMP, 9-beta-D-arabinofuranosylguanine cyclic 3',5'-phosphate, and 9-beta-D-arabinofuranosyl-8-mercaptoguanine cyclic 3',5'-phosphate have been previously reported (Mian et al. (1974), J. Med. Chem. 17, 259). 8-Bromo-2'-omicron-acetylinosine cyclic 3',5'-phosphate and 8-[(p-chlorophenyl)thio]-2'-omicron-acetylinosine cyclic 3',5'-phosphate were produced by acylation of 8-bromoinosine cyclic 3',5'-phosphate and 8-[(p-chlorophenyl)thio]inosine cyclic 3',5'-phosphate, respectively; while 8-bromo-2'-omicron-butyrylguanosine cyclic 3',5'-phosphate was synthesized by bromination of 2'-omicron-butyrylguanosine cyclic 3',5'-phosphate.

8-Substituted derivatives of adenosine 3',5'-cyclic phosphate require an unsubstituted 2'-hydroxyl group in the ribo configuration for biological activity.

Derivatives of adenosine 3',5'-cyclic phosphate (cAMP) with modifications in both the 2' and the 8 positions were synthesized and their enzymic activities as activators of cAMP-dependent protein kinase and as substrates for and inhibitors of cAMP phosphodiesterases were determined. Three types of derivatives were investigated: 8-substituted derivatives of O2'-Bt-cAMP, 8-substituted derivatives of 9-beta-D-arabinofuranosyladenine 3',5'-cyclic phosphate (ara-cAMP), and 8-substituted derivatives of 8,2'-anhydro-9-beta-D-arabinofuranosyladenine 3,'5'-cyclic phosphate (8,2'-anhydro-cAMP). The 8-substituted O2'-Bt-cAMP derivatives were synthesized by acylation of the preformed 8-substituted cAMP (8-HS-cAMP, 8-MeS-cAMP, and 8-PhCH2S-cAMP). 8-Br-O2'-tosyl-cAMP was sued as an intermediate for the preparation of 8,2'-anhydro-cAMP derivatives (8-HO-, 8-SH-, 8-H2N-, and 8-H3 CHN derivatives of 8,2'-anhydro-cAMP). 8-Substituted ara-cAMP derivatives were obtained by ring opening of 8-HO-8,2'-anhydro-cAMP with H+/H2O, NH3/MeOH, or MeONa/MeOH (to yield the 8-HO-, 8-H2N-, and 8-MeO-ara-cAMP derivatives). All of these doubly modified derivatives of cAMP are less than one-hundredth as active as cAMP at activating protein kinase and did not serve as substrates for the phosphodiesterase. These data show that the general inactivity of 2' derivatives of cAMP with kinase was not overcome by addition of an 8-substituent, even though many 8-substituted derivatives of cAMP activate the kinase more efficiently than does cAMP itself. In addition they show that while 2'-modification were tolerated by the phosphodiesterase, addition of an 8-substituent countermanded the allowable 2'-modification. The 8-substituted derivates of 02'-Bt-cAMP were found in general to be slightly better inhibitors of phosphodiesterase than the parent compounds containing no o2'-Bt substitution. As a group, the 8-substituted ara-cAMP derivatives were poorer inhibitors of phosphodiesterase than 8-substituted cAMP derivatives while the 8,2'-anhydro-cAMP derivatives were much poorer inhibitors than the 8-substituted ara-cAMP derivatives.