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Biomedical subjects

C C Benz

Publications and source records attributed to C C Benz.

At least 37 records · Page 2Linked to original sources
PubMed1999

Constitutive expression of Heregulin induces apoptosis in an erbB-2 overexpressing breast cancer cell line SKBr-3.

We have previously reported that Heregulin (HRG)/neu differentiation factor (NDF) induced growth arrest and cellular differentiation in breast cancer cells overexpressing erbB-2 receptor. To elucidate the cellular mechanisms underlying the growth inhibition by HRG, we developed an in vitro model by transfection of HRG cDNA into the erbB-2 overexpressing breast cancer cell line, SKBr-3. We showed that the enforced expression of HRG in SKBr-3 cells induces dramatic morphological changes and pronounced inhibition of anchorage-dependent and -independent growth. Most SKBr-3/HRG-transfected (SK/HRG) cells exhibited about 15-fold increase in size and persisted as multinucleated cells with extended flattened vacuole-filled cytoplasm with reduced cell attachment. The growth suppression of SK/HRG cells was accompanied by a reduction in S phase, the presence of a G2-M cell cycle delay, and an increase in DNA aneuploid components. In addition, DNA fragmentation assays showed that HRG induced apoptosis of SKBr-3 cells. In contrast, while HRG treatment of other erbB-2 overexpressing breast cancer cell lines led to growth arrest and cell detachment, it did not induce apoptotic features. Thus, this study demonstrates that while growth arrest and cell detachment are general effects of HRG towards erbB-2 overexpressing cells, the ability of HRG to induce apoptosis is a phenomenon confined to selective cells including SKBr-3 cells.

Apoptosis↗
PubMed1999

Increased activator protein-1 DNA binding and c-Jun NH2-terminal kinase activity in human breast tumors with acquired tamoxifen resistance.

Human breast tumors that are initially responsive to tamoxifen (TAM) eventually relapse during treatment. Estrogen receptor (ER) expression and function are often preserved in these tumors, and clinical evidence suggests that this relapse may be related to TAM's known agonistic properties. ER can interact with the activator protein-1 (AP-1) transcription factor complex through protein-protein interactions that are independent of ER DNA binding and, in certain ER-positive cells, this may allow TAM to exert an agonist response on AP-1-regulated genes. We, therefore, assessed both AP-1 DNA binding and the known AP-1 activating enzyme, c-Jun NH2-terminal kinase (JNK), in a panel of 30 ER-positive primary human breast tumors with acquired TAM resistance, as compared to a matched panel of 27 untreated control ER-positive breast tumors and a separate control set of 14 primary tumors, which included 7 ER-positive tumors that were growth-arrested by 3 months of preoperative TAM. AP-1 DNA binding activity was measured from cryopreserved tumor extracts using a labeled oligonucleotide probe containing a consensus AP-1 response element by electrophoretic mobility shift assay. JNK was first extracted from the tumor lysates by incubation over a Sepharose-bound c-Jun(1-89) fusion protein, and its activity was then measured by chemiluminescent Western blot by detection of the phosphorylated product using a phospho-Jun(Ser-63)-specific primary antibody. The set of control ER-positive breast tumors growth arrested by TAM showed no significant difference from untreated control tumors in their AP-1 DNA binding and JNK activities. In contrast, there was a significant (P < 0.001) increase in mean AP-1 DNA binding activity for the panel of ER-positive TAM-resistant (TAM-R) tumors as compared to its matched control panel of untreated tumors. Mean JNK activity in the TAM-R tumors was also significantly higher than that found in the untreated tumors (P = 0.038). Overall, there was no significant correlation between JNK activity and AP-1 DNA binding; however, regression analysis showed that, for any given level of JNK activity, the TAM-R tumors possessed a 3.5-fold increase in AP-1 DNA binding activity as compared to the untreated tumors. These findings indicate that, when compared to untreated ER-positive primary breast tumors, TAM-R tumors demonstrate significantly increased levels of AP-1 DNA binding and JNK activity, consistent with experimental models suggesting that TAM-stimulated ER-positive tumor growth may be mediated by enhanced AP-1 transcriptional activity. These observations support the need for further evaluation of these markers in breast tumors as predictors of TAM resistance.

Aged↗
PubMed1999

Phase II study of weekly intravenous trastuzumab (Herceptin) in patients with HER2/neu-overexpressing metastatic breast cancer.

The HER2/neu proto-oncogene is overexpressed in 25% to 30% of patients with breast cancer. Trastuzumab (Herceptin; Genentech, San Francisco, CA), a recombinant humanized monoclonal antibody with high affinity for the HER2 protein, inhibits the growth of breast cancer cells overexpressing HER2. In this phase II study the efficacy and toxicity of weekly administration of trastuzumab was evaluated in 46 patients with metastatic breast cancer whose tumors overexpressed HER2. A loading dose of 250 mg trastuzumab was administered intravenously, which was followed by 10 weekly doses of 100 mg each. Upon completion of this treatment period, patients with no disease progression could receive a weekly maintenance dose of 100 mg. Patients in this trial had extensive metastatic disease, and most had received prior anticancer therapy. Ninety percent of patients achieved adequate serum levels of trastuzumab. Toxicity was minimal, and no antibodies against trastuzumab could be detected. Objective responses were observed in 5 of the 43 evaluable patients, which included 1 complete remission and 4 partial remissions, for an overall response rate of 11.6%. Responses were seen in mediastinum, lymph nodes, liver, and chest wall lesions. Minor responses (seen in 2 patients) and stable disease (14 patients) lasted for a median of 5.1 months. These results demonstrate that trastuzumab is well tolerated and clinically active in patients with HER2-overexpressing metastatic breast cancers who have received extensive prior therapy. The regression of human cancer through the targeting of putative growth factor receptors such as HER2 warrants further evaluation of trastuzumab in the treatment of breast cancer.

Adult↗
PubMed1998

Oxidant stress impaired DNA-binding of estrogen receptor from human breast cancer.

Full-length (67 kDa) immunoreactive estrogen receptor (ER) extracted from a third of untreated ER-positive primary breast tumors appears unable to bind to its cognate estrogen response element (ERE). We have observed partial reversibility of this ER DNA-binding defect upon treatment of these tumor extracts with excess thiol reducing agent (DTT), suggesting that ER DNA-binding is subject to redox modulation as is reported for other zinc-finger proteins and transcriptional activators. Treatment of recombinant ER DNA-binding domain (ER-DBD) or ER-enriched extracts from CHO(ER) and MCF-7 cells with thiol-reacting oxidants (diamide, iodosobenzoate, H2O2) or alkylator (iodoacetamide) produces a dose-dependent loss in ER DNA-binding capacity. Thiol-specific oxidative loss in ER DNA-binding is fully reversible by DTT reduction, unlike the defect caused by thiol-specific alkylation. Circular dichroism spectrometry shows that both forms of treatment substantially modify ER secondary structure, inducing loss of alpha-helical content within the ER-DBD that is reversible after thiol oxidation but not after thiol alkylation. Oxidant (H2O2, menadione) exposure of cultured CHO(ER) or MCF-7 cells impairs the ability of endogenous ER to bind DNA and transactivate an ER-responsive reporter gene (ERE-tk-CAT), demonstrating that extracellular redox stress can modulate intracellular ER function. Since these thiol-specific oxidant and alkylator treatments have no significant effect on either recombinant ER ligand-binding or intracellular immunoreactive ER content, our findings suggest that DNA-binding and transactivation are the most sensitive intracellular ER functions impaired by oxidant stress in some ER-positive human breast tumors.

Alkylating Agents↗
PubMed1998

Polyamine inhibition of estrogen receptor (ER) DNA-binding and ligand-binding functions.

Polyamines are known to inhibit sequence specific DNA-binding activity of several zinc-finger transcription factors, including estrogen receptor (ER) binding to its cognate estrogen response element (ERE). The mechanism accounting for this disruption of protein-DNA interaction is unknown, although polyamine induction of DNA conformational changes has been suggested. To determine if polyamines can directly impair ER action, we compared the effects of putrescine (Putr), spermidine (Spd), and spermine (Spm) on ER DNA-binding (ER-ERE complex formation), ER ligand-binding (estradiol), ER structure (circular dichroism and sucrose gradient sedimentation), and the capacity of ER to transactivate an ERE-tk-CAT reporter in transient transfection assays. Polyamine concentrations causing 50% inhibition of ER-ERE formation (IC50 values) were found to be 1 mM for Putr, 4 mM for Spd, and 3 mM for Spm. This loss of ER DNA-binding was associated with a direct and irreversible effect on the ER DNA-binding domain (ER-DBD). Additionally, polyamines were observed to inhibit ER ligand-binding with IC50 values of 10 mM for Putr, 2 mM for Spd, and < 0.1 mM for Spm; and this correlated with a measureable change in higher-order ER structure (5S to 3.5S sedimentation) and inhibition of intracellular ER transactivation. These findings suggest that in ER-positive human breast tumors with increased polyamine (especially Spm) content, ER structure and function may be directly altered by tight-ion polyamine complexing that results in loss of ER-mediated gene regulation.

Breast↗
PubMed1998

The epithelium-specific ets transcription factor ESX is associated with mammary gland development and involution.

To study mammary gland expression of the epithelium-restricted Ets factor, ESX, mouse cDNA and genomic sequences were cloned and a approximately 350 bp proximal promoter region with >80% mouse-human homology was identified that mediates ESX induction by serum, heregulin (HRG), or epidermal growth factor (EGF). ESX mRNA expression progressively increases during embryonic mouse development from day 7 and is detectable in virgin mammary glands; it shows little if any change during pregnancy, then declines to barely detectable levels after 3 days of lactation. Similarly, cultured HC11 cells from midpregnant mouse mammary epithelium show an increase in ESX expression upon reaching lactogenic competency (in the presence of EGF or HRG), with a decline to barely detectable levels upon exposure to lactogenic hormones that induce milk protein (beta-casein) expression. In contrast, involuting mouse and rat mammary glands show maximal ESX expression. High ESX levels are also seen in the involuting ventral prostate gland of rats. These findings, including the persistence of up-regulated ESX in fully regressed mammary glands, suggest that ESX expression can be induced by soluble growth factors and is maximally up-regulated in those partially committed epithelial cells destined to survive both the apoptotic and remodeling phases of glandular involution.

Amino Acid Sequence↗
PubMed1997

Anti-HER2 immunoliposomes for targeted therapy of human tumors.

Anti-HER2 immunoliposomes (ILs) have been constructed by conjugation of Fab' fragments of recombinant humanized monoclonal antibody rhuMAbHER2 to small sterically stabilized unilamellar liposomes, to create a targeted drug delivery vehicle for the treatment of HER2 (c-erbB-2, neu)-overexpressing cancers. Parameters affecting in vitro binding and internalization of ILs include liposome composition, Fab' linkage site and Fab' density. Anti-HER2 ILs have been constructed to optimize intracellular drug delivery. Doxorubicin (dox)-loaded ILs are highly stable and exhibit prolonged circulation in rats. In nude mice bearing HER2-overexpressing tumor xenografts, anti-HER2 ILs administered i.v. resulted in efficient tumor localization, with penetration of the ILs throughout the tumor mass and accumulation within tumor cells. In contrast, non-targeted liposomes resulted in extracellular tumor accumulation only. In multiple HER2-overexpressing human breast tumor xenograft models, treatment with dox-loaded anti-HER2 ILs produces significantly increased antitumor cytotoxicity as compared to free dox or dox-loaded non-targeted liposomes and significantly less systemic toxicity than free dox. To explore further the intracellular delivery advantages of ILs, anti-HER2 ILs bearing cationic lipids are being developed for nucleic acid delivery. These cationic immunoliposomes mediate efficient and specific transfection of target cells with reporter genes, as well as intracellular delivery of labeled oligonucleotides. Thus, anti-HER2 ILs represent an efficient and feasible strategy to achieve targeted intracellular delivery of therapeutic agents.

Antibodies, Monoclonal↗
PubMed1997

HER2/Neu and the Ets transcription activator PEA3 are coordinately upregulated in human breast cancer.

HER2/Neu is overexpressed in 25-30% of all human breast cancers as a result of both gene amplification and enhanced transcription. Transcriptional upregulation of HER2/neu leads to a 6-8-fold increased abundance of its mRNA per gene copy and likely results from the elevated activity of transcription factors acting on the HER2/neu promoter. Here we report that transcripts of PEA3, an ETS transcription factor implicated in oncogenesis, were increased in 93% of HER2/Neu-overexpressing human breast tumor samples. Analyses to uncover the molecular basis for elevated PEA3 transcripts in HER2/Neu-positive breast tumors revealed that the HER2/Neu receptor tyrosine kinase initiated an intracellular signaling cascade resulting in increased PEA3 transcriptional activity; transcriptionally-activated PEA3 stimulated HER2/neu and PEA3 gene transcription by binding to sites in the promoters of these genes. PEA3 also activates transcription of genes encoding matrix-degrading proteinases, enzymes required for tumor cell migration and invasion. These findings implicate PEA3 in the initiation and progression of HER2/Neu positive breast cancer, and suggest that PEA3 and signaling proteins affecting its regulation are appropriate therapeutic targets.

Animals↗
PubMed1997

Comparison of estrogen receptor DNA binding in untreated and acquired antiestrogen-resistant human breast tumors.

Preliminary studies have suggested that measuring the ability of immunoreactive 67-kDa estrogen receptor (ER) to bind DNA and form in vitro complexes with its cognate estrogen response element (ERE) might serve to identify breast tumors most likely to respond to antiestrogens like tamoxifen. Data from two different surveys of untreated primary breast tumors confirmed that only 67% (74 of 111) of ER-positive tumors express a receptor capable of forming ER-ERE complexes by gel-shift assay, with tumors of lower ER content having significantly reduced ER DNA-binding frequency (56%) relative to those of higher ER content (82%; P = 0.007). In contrast to these untreated tumors, a panel of 41 receptor-positive breast tumors excised after acquiring clinical resistance to tamoxifen during either primary (n = 26) or adjuvant therapy (n = 15) showed a significantly greater ER DNA-binding frequency, with nearly 90% capable of forming ER-ERE complexes (P < 0.02). To assess experimentally whether ER DNA-binding function is altered during the development of antiestrogen resistance, nude mouse MCF-7 tumor xenografts were analyzed before and after the acquisition of in vivo resistance to either tamoxifen or a pure steroidal antiestrogen, ICI 182,780. Tamoxifen-resistant MCF-7 tumors retained full expression of 67-kDa DNA-binding ER, and despite a markedly reduced ER content in the ICI 182,780-treated tumors, the expressed ER in these antiestrogen-resistant tumors exhibited full ability to form ER-ERE complexes. These findings indicate that breast tumors with acquired antiestrogen resistance continue to express ER of normal size and DNA-binding ability and suggest that the failure of antiestrogens to arrest tumor growth during emergence of clinical resistance results from an altered gene-regulatory mechanism(s) other than ER-ERE complex formation.

Animals↗
PubMed1997

ESX: a structurally unique Ets overexpressed early during human breast tumorigenesis.

The >30 known members of the Ets multigene family of transcriptional regulators are increasingly being recognized for their involvement in early embryonic development and late tissue maturation, directing stage-specific and tissue-restricted programs of target gene expression. Identifiable primarily by their 85 amino acid ETS DNA-binding domain and dispersed across all metazoan lineages into distinct subfamilies, Ets genes also produce malignancies in humans and other vertebrates when overexpressed or rearranged into chimeras retaining the ETS domain, suggesting that their oncogenic potential is determined by the program of target genes they regulate. Searching for Ets factors that regulate expression of the HER2/neu (c-erbB2) oncogene in human breast cancer, we identified a new epithelium-restricted Ets encoding an ETS domain homologous to the Drosophila E74/human Elf-1 subfamily, an amino-terminal region (A-region or Pointed domain) homologous to the distantly related Ets-1 subfamily, and a serine-rich box homologous to the transactivating domain of the lymphocyte-restricted High Mobility Group (HMG) protein, SOX4. Recombinant protein encoded by ESX (for epithelial-restricted with serine box) exhibits Ets-like DNA binding specificity in electrophoretic mobility shift assays and, in transient transfection assays, transactivates Ets-responsive promoter elements including that found in the HER2/neu oncogene. ESX is located at chromosome 1q32 in a region known to be amplified in 50% of early breast cancers, is heregulin-inducible and overexpressed in HER2/neu activated breast cancer cells. Tissue hybridization suggests that ESX becomes overexpressed at an early stage of human breast cancer development known as ductal carcinoma in situ (DCIS).

Amino Acid Sequence↗
PubMed1997

Sterically stabilized anti-HER2 immunoliposomes: design and targeting to human breast cancer cells in vitro.

Liposomes (70-100 nm) of 1-palmitoyl-2-oleoylphosphatidylcholine, cholesterol, and poly(ethylene glycol) (PEG)-modified phosphatidylethanolamine (PEG-DSPE) were conjugated to Fab' fragments of a humanized recombinant MAb against the extracellular domain of HER2/neu to create sterically stabilized immunoliposomes (anti-HER2 SL) as a drug carrier targeting HER2-overexpressing cancers. Conjugation employed maleimide-terminated membrane-anchored spacers of two kinds: a short spacer, providing attachment of Fab' close to the liposome bilayer, or a long spacer, with Fab' attachment at the distal terminus of the PEG chain. Confocal microscopy and spectrofluorometry of HER2-overexpressing breast cancer cells incubated with fluorescently labeled anti-HER2 SL prepared with either spacer showed binding of liposomes (8000-23000 vesicles/cell) followed by endocytosis (rate constant ke = 0.012-0.033 min-1) via the coated-pit pathway, evidenced by intracellular acidification and colocalization with transferrin. Uptake of anti-HER2 immunoliposomes by breast cancer cells with low HER2 expression, or after preincubation of cells with free anti-HER2 Fab', was less than 0.2% and 4.3%, respectively, of the uptake by HER2-overexpressing cells. Increasing PEG-DSPE content (up to 5.7 mol %) in anti-HER2-SL prepared with the short spacer decreased liposome-cell binding affinity 60-100-fold, while ke decreased only 2-fold; however, when Fab' fragments were conjugated via a PEG spacer, both binding affinity and ke were unaffected by PEG-DSPE content. Cell binding and internalization of anti-HER2 immunoliposomes increased at higher surface density of conjugated Fab' fragments, reaching plateaus at approximately 40 Fab'/liposome for binding and approximately 10-15 Fab'/liposome for internalization. Uptake of anti-HER2 immunoliposomes correlated with the cell surface density of HER2 and significantly (p < 0.005) correlated with the antiproliferative effect of the targeting antibody but not with the total level of cellular HER2 expression. The results obtained were used to optimize in vivo preclinical studies of anti-HER2 SL loaded with antineoplastic drugs.

Antibodies, Monoclonal↗
PubMed1996

Evidence of post-transcriptional regulation of U6 small nuclear RNA.

Mechanisms regulating the intracellular level of endogenous U6 small nuclear RNA were studied by transient transfection of ectopic U6 gene constructs into immortalized normal and malignant human cell lines. Transfection and expression of a modified U6 gene containing native promoter, capping, and termination sequences but lacking all highly conserved internal spliceosome sequences produced dose-dependent effects on endogenous U6 gene expression. At low transfection doses, no significant changes in endogenous U6 RNA levels or half-life were noted. However, as the dose of the transfected gene and its expression increased, native U6 RNA levels dramatically decreased in association with an apparent decrease in U6 RNA half-life. Down-regulation of native U6 RNA levels was transient, with recovery noted within 48-96 h in conjunction with declining expression of the ectopic gene. These modulatory effects appeared specific to endogenous U6 transcripts, because no changes were noted in 7sk, U1, U3, or 5S RNA levels or half-lives. Transfection with an unmodified U6 gene did not alter total U6 transcript levels but did produce a similar dose-dependent decrease in U6 RNA half-life. These studies suggest a hitherto unrecognized U6-specific intracellular regulatory mechanism, through which over-accumulation of U6 small nuclear RNA is prevented.

Cell Line↗
PubMed1996

Phase II study of weekly intravenous recombinant humanized anti-p185HER2 monoclonal antibody in patients with HER2/neu-overexpressing metastatic breast cancer.

PURPOSE: Breast cancer frequently overexpresses the product of the HER2 proto-oncogene, a 185-kd growth factor receptor (p185HER2). The recombinant humanized monoclonal antibody (rhuMAb) HER2 has high affinity for p185HER2 and inhibits the growth of breast cancer cells that overexpress HER2. We evaluated the efficacy and toxicity of weekly intravenous administration of rhuMAb HER2 in patients with HER2-overexpressing metastatic breast cancer. PATIENTS AND METHODS: We treated 46 patients with metastatic breast carcinomas that overexpressed HER2. Patients received a loading dose of 250 mg of intravenous rhuMAb HER2, then 10 weekly doses of 100 mg each. Patients with no disease progression at the completion of this treatment period were offered a maintenance phase of 100 mg/wk. RESULTS: Study patients had extensive metastatic disease, and most had received extensive prior anticancer therapy. Adequate pharmacokinetic levels of rhuMAb HER2 were obtained in 90% of the patients. Toxicity was minimal and no antibodies against rhuMAb HER2 were detected in any patients. Objective responses were seen in five of 43 assessable patients, and included one complete remission and four partial remissions (overall response rate, 11.6%; 95% confidence interval, 4.36 to 25.9). Responses were observed in liver, mediastinum, lymph nodes, and chest wall lesions. Minor responses, seen in two patients, and stable disease, which occurred in 14 patients, lasted for a median of 5.1 months. CONCLUSION: rhuMAb HER2 is well tolerated and clinically active in patients with HER2-overexpressing metastatic breast cancers that had received extensive prior therapy. This is evidence that targeting growth factor receptors can cause regression of human cancer and justifies further evaluation of this agent.

Adult↗
PubMed1995

ERBB-2 (HER2/neu) gene copy number, p185HER-2 overexpression, and intratumor heterogeneity in human breast cancer.

Amplification of the ERBB-2 (HER-2/neu) gene is accompanied by overexpression of its cell surface receptor product, p185HER-2. Heterogeneity has been observed for both the gene copy number and the level of overexpression of its protein product. To better understand their relationship, correlation between the level of cellular expression of p185HER-2 and ERBB-2 gene amplification was studied in four human breast cancer cell lines (BT-474, SK-BR-3, MDA-453, and MCF-7) and in a primary human breast tumor sample. The relative expression of p185HER-2 was measured by immunofluorescence by using flow and/or image cytometry while correlated DNA analysis was performed on the same cells by fluorescence in situ hybridization to determine ERBB-2 gene and chromosome 17 copy numbers. Marked heterogeneity was observed in both protein expression and ERBB-2 copy number. Despite this heterogeneity, and in accordance with previous studies, the average levels of p185HER-2 expression correlated well with average ERBB-2 gene copy numbers in the four lines examined (r = 0.99). When the relationship between copy number and protein expression was studied on a cell-by-cell basis, p185HER-2 expression correlated with both the absolute number of ERBB-2 gene copies/cell (r = 0.59-0.63) and chromosome 17 copy number (r = 0.45-0.61). It is of interest that there was weak or no correlation between p185HER-2 protein expression and the ERBB-2 copy number:chromosome 17 copy number ratio (r = 0.0-0.25). In more than one-half of cells expressing a high level of p185HER-2, the chromosome 17 copy number was high (two or three times the average copy number), whereas < 2% of an unselected population had a high chromosome 17 copy number. Bromodeoxyuridine incorporation indicated that the S-phase-labeling index was homogeneous across various p185HER-2-expressing subpopulations in the SK-BR-3 cell line. Analysis of the primary breast tumor sample showed results similar to the cell lines, supporting the strong possibility of a mechanistic link among p185HER-2 overexpression, ERBB-2 amplification, and high chromosome 17 copy number.

Breast Neoplasms↗
PubMed1995

Gene diagnostics provide new insights into breast cancer prognosis and therapy.

Breast cancer is the most frequent cancer of women in developed countries. It is not surprising, therefore, that major research efforts have been made to improve early detection and treatment strategies directed at this malignancy. In this keynote article, we outline future perspectives on breast cancer genetics, risk factors and prognostic factors, focusing on novel developments relating to the estrogen receptor and the family of ErbB growth factor receptors.

Base Sequence↗
PubMed1995

Developing gossypol derivatives with enhanced antitumor activity.

Preclinical and clinical studies have pointed to the antitumor potential of the naturally occurring polyphenolic binaphthyl dialdehyde, gossypol, as well as its purified (-,+) enantiomers. To explore further the antitumor properties of this multifunctional agent, we synthesized several reactive derivatives including the (-,+) enantiomers of gossypolone and four different gossypol Schiff's bases (AR1, AR2, AR3, AR4). The biological activities of these new agents were screened by measuring their in vitro antiproliferative activity against malignant (MCF-7, MCF-7/adr) or immortalized (HBL-100) human breast epithelial cell lines. Racemic gossypolone showed relatively uniform antiproliferative activity against all of the breast epithelial cell lines with 3- to 5-fold less activity than (--)-gossypol against MCF-7 and MCF-7/adr cells. Of interest, the relative antitumor potency of purified gossypolone enantiomers was reverse that of gossypol enantiomers, since (+)-gossypolone showed up to 3-fold greater inhibition of MCF-7 culture growth than (--)-gossypolone. Of the Schiff's base derivatives only AR3 with its isopropyl amine substituent demonstrated cytotoxic activity comparable to that of (--)-gossypol; derivatives with ethyl, propyl, or butyl amine substituents (AR1, AR2, AR4) had little growth inhibitory activity at culture concentrations up to 25 microM. AR3 activity was greatest against HBL-100 and MCF-7 cells [MCF-7 IC50 values: AR3 = 0.9 microM, (--)-gossypol = 2.3 microM]; unlike (--)-gossypol, however, AR3 showed substantially reduced activity against the multidrug-resistant subline, MCF-7/adr. These structure-activity comparisons suggest that isolation of (-,+)-enantiomers of AR3 and additional chemical modifications including the synthesis of an isopropyl amine Schiff's base of gossypolone will likely yield a newer generation of gossypol analogues with enhanced anticancer potential.

Antineoplastic Agents, Phytogenic↗