Membrane-localized activation of glucuronide prodrugs by beta-glucuronidase enzymes.

Gene-mediated enzyme prodrug therapy (GDEPT) seeks to increase the therapeutic index of anti-neoplastic agents by promoting selective activation of relatively nontoxic drug derivatives at sites of specific enzyme expression. Glucuronide prodrugs are attractive for GDEPT due to their low toxicity, bystander effect in the interstitial tumor space and the large range of possible glucuronide drug targets. In this study, we expressed human, murine and Esherichia coli beta-glucuronidase on tumor cells and examined their in vitro and in vivo efficacy for the activation of glucuronide prodrugs of 9-aminocamptothecin and p-hydroxy aniline mustard. We show that (1) fusion of beta-glucuronidase to the Ig-like C(2)-type and Ig-hinge-like domains of the B7-1 antigen followed by the B7-1 transmembrane domain anchored high levels of active murine and human beta-glucuronidase on cells, (2) strong bystander killing of tumor cells was achieved in vitro by murine beta-glucuronidase activation of prodrug, (3) potent in vivo anti-tumor activity was achieved by prodrug treatment of tumors that expressed murine beta-glucuronidase and (4) the p-hydroxy aniline prodrug was more effective in vivo than the 9-aminocamptothecin prodrug. Our results demonstrate that surface expression of murine beta-glucuronidase for activation of a glucuronide prodrug of p-hydroxy aniline mustard may be useful for more selective therapy of cancer.

Design and synthesis of water-soluble glucuronide derivatives of camptothecin for cancer prodrug monotherapy and antibody-directed enzyme prodrug therapy (ADEPT).

Glucuronide prodrugs of 9-aminocamptothecin were synthesized. Prodrug 4, in which 9-aminocamptothecin was connected to glucuronic acid by an aromatic spacer via a carbamate linkage, was stable in both aqueous solution and human plasma. Prodrug 4 and its potassium salt 12 were 20-80-fold less toxic than 9-aminocamptothecin to human tumor cell lines. The simultaneous addition of beta-glucuronidase and 4 or 12 to tumor cells resulted in a cytotoxic effect equal to that of 9-aminocamptothecin alone. Prodrugs 4 and 12 were over 80 and 4000 times more soluble than 9-aminocamptothecin in aqueous solutions at pH 4.0, respectively. Compounds 4 and 12 may be useful for prodrug monotherapy of tumors that accumulate extracellular lysosomal beta-glucuronidase as well as for antibody-directed enzyme prodrug therapy (ADEPT) of cancer.

Synthesis and cytotoxic evaluation of substituted sulfonyl-N-hydroxyguanidine derivatives as potential antitumor agents.

A series of sulfonyl-N-hydroxyguanidine derivatives was designed and synthesized for cytotoxic evaluation as potential anticancer agents on the basis of the lead compound LY-181984. Replacement of the ureido moiety of the lead compound with hydroxyguanidine provided a stable cytotoxic agent. The conformation of sulfonyl-N-hydroxyguanidine derivatives, such as N-(4-chlorophenyl)-N'-[(benzo[2,1,3]thiadiazol-4-yl)sulfonyl]-N"- hydroxyguanidine (4g), investigated utilizing HMBC NMR, theoretical calculations, and X-ray crystallography, indicated stacking of the two aromatic rings. The derivatives were evaluated for in vitro cytoxicity against five human tumor cell lines, including HepG2, TSGH 8302, COLO 205, KB, and MOLT-4. The cytotoxic activities of the derived compounds against the human tumor cell lines were equal to or greater than that of the lead compound. N-(4-Chlorophenyl)-N'-[[3,5-dichloro-4-(4-nitrophenoxy)phenyl]sulfonyl]- N"- hydroxyguanidine (4n) and N-(4-chlorophenyl)-N'-[[3,5-dichloro-4-(2-chloro-4-nitrophenoxy)phenyl] sulfonyl]-N"-hydroxyguanidine (4o) exhibited the greatest growth inhibition of solid tumor cell lines. Compound 4o was found to possess antitumor activity against murine K1735/M2 melanoma xenografts.

Constituents and cytotoxic principles of Nothapodytes foetida.

A new naturally occurring alkaloid, acetylcamptothecin, together with 17 known compounds, (+)-1-hydroxypinoresinol, omega-hydroxypropioguaiacone, p-hydroxybenzaldehyde, scopoletin, uracil, thymine, sitosterol, sitosteryl-beta-D-glucoside, 3 beta-hydroxy-stigmast-5-en-7-one, stigmast-5-en-3 beta,7 alpha-diol, 6 beta-hydroxystigmast-4-en-3-one, sitost-4-en-3-one, linoleic acid, trigonelline, camptothecin, 9-O-methoxycamptothecin and pumiloside were isolated and characterized from the stem of Nothapodytes foetida. Among them, scopoletin, camptothecin, 9-O-methoxycamptothecin and O-acetylcamptothecin showed significant cytotoxic activity.

Enhancement of CPT-11 antitumor activity by adenovirus-mediated expression of ß-glucuronidase in tumors.

CPT-11 is a clinically important prodrug that requires conversion into the active metabolite SN-38, a potent topoisomerase I poison, for antitumor activity. However, SN-38 is rapidly metabolized to the inactive SN-38 glucuronide (SN-38G) in the liver, which reduces the amount of SN-38 available for killing cancer cells. Here, we investigated if local expression of ß-glucuronidase (ßG) on cancer cells to catalytically convert SN38G to SN38 could enhance the antitumor activity of CPT-11. ßG was tethered on the plasma membrane of three different human cancer cell lines: human colon carcinoma (LS174T), lung adenocarcinoma (CL1-5) and bladder carcinoma (EJ). Surface ß-glucuronidase-expressing cells were 20 to 80-fold more sensitive to SN-38G than the parental cells. Intravenous CPT-11 produced significantly greater suppression of CL1-5 and LS174 T tumors that expressed ßG as compared with unmodified tumors. Furthermore, an adenoviral vector expressing membrane-tethered ßG (Ad.ßG) increased the sensitivity of cancer cells to SN-38G even at multiplicity of infections as low as 0.16, indicating bystander killing of non-transduced cancer cells. Importantly, intratumoral injection of Ad.ßG significantly enhanced the in vivo antitumor activity of CPT-11 as compared with treatment with CPT-11 or Ad vectors alone. This study shows that Ad.ßG has potential to boost the therapeutic index of CPT-11.

Constituents of the roots and stems of Aristolochia mollissima.

Five new sesquiterpenes, mandolins R (1), S (2), U (3), W (4), and X (5), together with 39 known compounds, were isolated from the dried roots and stems of Aristolochia mollissima. Their structures were determined by spectroscopic methods.

Constituents from the stem and root of Aristolochia kaempferi.

Three new phenanthrene derivatives, aristoliukine-C, aristofolin-E and aristolochic acid-Ia methyl ester, and one new sesquiterpene, madolin-P, together with 58 known compounds were isolated from the stem and root of Aristolochia kaempferi. The structures of these compounds were determined by spectral analysis. The cytotoxicity and antiplatelet activity of the isolated compounds are also discussed.

The constituents of the root and stem of Aristolochia heterophylla Hemsl.

Seven new compounds, sodium aristolochate-VII (1), aristolactam-CIV (2), madolin-I (3), -J (4), -K (5), -L (6) and -M (7) together with 71 known compounds were isolated and characterized from the fresh root and stem of Aristolochia heterophylla Hemsl. Their structures were determined by spectral methods. Compound 8 was revised as aromadendrane-4beta, 10beta-diol by spectral data and single-crystal X-ray analysis.

The constituents of the root and stem of Aristolochia cucurbitifolia Hayata and their biological activity.

Four new compounds, three phenanthrene derivatives, aristolochic acid-III methyl ester (1), cepharanone C (2), and sodium 7-hydroxyl-8-methoxyaristolate (3), and the benzoate derivative, sodium 3,4-dimethoxybenzoate (4), together with 53 known compounds were isolated and characterized from the fresh root and stem of Aristolochia cucurbitifolia. Their structures were elucidated by spectral analyses and chemical transformations. The cytotoxicity and antiplatelet activity of the isolated compounds are also discussed.

Sesquiterpene esters of aristolochic acid from the root and stem of Aristolochia heterophylla.

Three novel sesquiterpene esters of aristolochic acid, aristoloterpenate-II (2), -III (3), and-IV (4), together with known aristoloterpenate-I (1), were isolated and characterized from the root and stem of Aristolochia heterophylla. Their structures were elucidated by spectroscopic methods. The absolute configuration of these compounds at C-4' was determined as R by circular dichroic studies. These compounds showed cytotoxicity against hepatoma G2, 2, 2, 15 cells.

Anti-tumour activity and toxicity of the new prodrug 9-aminocamptothecin glucuronide (9ACG) in mice.

Cancer chemotherapy is limited by the modest therapeutic index of most antineoplastic drugs. Some glucuronide prodrugs may display selective anti-tumour activity against tumours that accumulate beta-glucuronidase. We examined the toxicity and anti-tumour activity of 9-aminocamptothecin glucuronide, a new glucuronide prodrug of 9-aminocamptothecin, to evaluate its potential clinical utility. 9-aminocamptothecin glucuronide was 25-60 times less toxic than 9-aminocamptothecin to five human cancer cell lines. Beta-glucuronidase activated 9-aminocamptothecin glucuronide to produce similar cell killing as 9-aminocamptothecin or topotecan. The in vivo toxicity of 9-aminocamptothecin glucuronide in BALB/c mice was dose-, route-, sex- and age-dependent. 9-aminocamptothecin glucuronide was significantly less toxic to female than to male mice but the difference decreased with age. 9-aminocamptothecin glucuronide and 9-aminocamptothecin produced similar inhibition (approximately 80%) of LS174T human colorectal carcinoma tumours. 9-aminocamptothecin glucuronide cured a high percentage of CL1-5 human lung cancer xenografts with efficacy that was similar to or greater than 9-aminocamptothecin, irinotecan and topotecan. The potent anti-tumour activity of 9-aminocamptothecin glucuronide suggests that this prodrug should be further evaluated for cancer treatment.

Naphthoquinone esters from the root of Rhinacanthus nasutus.

Reinvestigation of the root of Rhinacanthus nasutus afforded, in addition to rhinacanthin-A to -D reported previously, two new dimethyldihydropyranonaphthoquinone esters (5, 6) and eight new 2-hydroxy-1,4-naphthoquinone esters (7-14) were isolated. The stereochemistry of rhinacanthin-A was determined as the R configuration. Compounds rhinacanthin-G to -N, belong to a class of 2-hydroxy-3-(3-hydroxy-2,2-dimethylpropyl)-1,4-naphthoquinone esters, and so far have been isolated only in this plant. Their biosynthesis is also discussed.