Targeting of cytotoxic luteinizing hormone-releasing hormone analogs to breast, ovarian, endometrial, and prostate cancers

Targeted chemotherapy is a modern approach aimed at increasing the efficacy of systemic chemotherapy and reducing its side effects. The peptide receptors expressed primarily on cancerous cells can serve as targets for a selective destruction of malignant tumors. Binding sites for LHRH (now known in genome and microarray databases as GNRH1), were found on 52% of human breast cancers, about 80% of human ovarian and endometrial cancers, and 86% of human prostatic carcinoma specimens. Because LHRH receptors are not expressed on most normal tissues, they represent a specific target for cancer chemotherapy with antineoplastic agents linked to an LHRH vector molecule. To test the efficacy of targeted chemotherapy based on LHRH analogs, we recently developed a cytotoxic analog of LHRH, designated AN-152, which consists of [D-Lys6]LHRH covalently linked to one of the most widely used chemotherapeutic agents, doxorubicin (DOX). In addition, we designed and synthesized a highly active derivative of DOX, 2-pyrrolino-DOX (AN-201), which is 500-1000 times more potent than DOX in vitro. AN-201 is active against tumors resistant to DOX, and noncardiotoxic. As in the case of DOX, AN-201 was coupled to carrier peptide [D-Lys6]LHRH to form a superactive targeted cytotoxic LHRH analog, AN-207. Both AN-152 and AN-207 can effectively inhibit the growth of LHRH receptor-positive human breast, ovarian, endometrial, and prostate cancers xenografted into nude mice. DOX-containing cytotoxic LHRH analog AN-152 is scheduled for clinical phase I/IIa trials in patients with advanced ovarian and breast cancers in 2005.     

An in vivo OctreoScan-negative adrenal pheochromocytoma expresses somatostatin receptors and responds to somatostatin analogs treatment in vitro.

A 52-yr-old woman presented with hypertension, elevated urinary vanillylmandelic acid, metanephrines, normetanephrines, and plasma chromogranin A (CgA), but normal urinary catecholamine levels. Abdominal ultrasonography and subsequent MRI imaging showed a 3 cm nodular lesion of the right adrenal gland also visualized by 123I-meta-iodobenzylguanidine scintigraphy consistent with a pheochromocytoma (PC). Her OctreoScan was negative. The patient underwent right adrenalectomy and histological examination showed a PC. The adrenal medulla tissue was examined for somatostatin (SRIH) receptor subtypes 1 to 5 (SSTR1 to 5) expression by RT-PCR. Cultured tumor cells were treated with either SRIH, Lanreotide (Lan), or an SSTR2 (BIM-23 120) or SSTR5 (BIM-23 206) selective agonist. CgA secretion was measured in the medium by ELISA and catecholamine levels by HPLC after 6h. Cell viability was assessed after 48h. RT-PCR analysis showed that SSTR1, 2, 3 and 4 were expressed. CgA secretion was significantly reduced by SRIH (- 80 %), Lan (- 35 %), and the SSTR2 selective agonist (- 65 %). Norepinephrine secretion was reduced by SRIH (- 66 %), Lan (- 40 %), and BIM-23 120 (- 70 %). Epinephrine and dopamine secretion was also inhibited by treatment with SRIH (- 90 % and - 93 %, respectively) and BIM-23 120 (- 33 % and - 75 %, respectively) but not by Lan. Cell viability was also significantly reduced by SRIH (- 30 %), Lan (- 10 %), and the SSTR2 selective agonist (- 20 %). The SSTR5 selective agonist did not modify either CgA and catecholamine secretion or cell viability. Our data show that SSTRs may be present in a PC although OctreoScan is negative in vivo, and that SRIH and its analogs may reduce both differentiated and proliferative functions in chromaffin cells in vitro. These findings suggest that SRIH analogs with enhanced SSTR2 affinity might be useful in the medical therapy of PC, even when an OctreoScan is negative.     

Disparate impact of butyroyloxymethyl diethylphosphate (AN-7), a histone deacetylase inhibitor, and doxorubicin in mice bearing a mammary tumor

The histone deacetylase inhibitor (HDACI) butyroyloxymethyl diethylphosphate (AN-7) synergizes the cytotoxic effect of doxorubicin (Dox) and anti-HER2 on mammary carcinoma cells while protecting normal cells against their insults. This study investigated the concomitant changes occurring in heart tissue and tumors of mice bearing a subcutaneous 4T1 mammary tumor following treatment with AN-7, Dox, or their combination. Dox or AN-7 alone led to inhibition of both tumor growth and lung metastases, whereas their combination significantly increased their anticancer efficacy and attenuated Dox- toxicity. Molecular analysis revealed that treatment with Dox, AN-7, and to a greater degree, AN-7 together with Dox increased tumor levels of γH2AX, the marker for DNA double-strand breaks and decreased the expression of Rad51, a protein needed for DNA repair. These events culminated in increased apoptosis, manifested by the appearance of cytochrome-c in the cytosol. In the myocardium, Dox-induced cardiomyopathy was associated with an increase in γH2AX expression and a reduction in Rad51 and MRE11 expression and increased apoptosis. The addition of AN-7 to the Dox treatment protected the heart from Dox insults as was manifested by a decrease in γH2AX levels, an increase in Rad51 and MRE11 expression, and a diminution of cytochrome-c release. Tumor fibrosis was high in untreated mice but diminished in Dox- and AN-7-treated mice and was almost abrogated in AN-7+Dox-treated mice. By contrast, in the myocardium, Dox alone induced a dramatic increase in fibrosis, and AN7+Dox attenuated it. The high expression levels of c-Kit, Ki-67, c-Myc, lo-FGF, and VEGF in 4T1 tumors were significantly reduced by Dox or AN-7 and further attenuated by AN-7+Dox. In the myocardium, Dox suppressed these markers, whereas AN-7+Dox restored their expression. In conclusion, the combination of AN-7 and Dox results in two beneficial effects, improved anticancer efficacy and cardioprotection.     

New approaches to treatment of various cancers based on cytotoxic analogs of LHRH,somatostatin and bombesin

The development of targeted cytotoxic analogs of hypothalamic peptides for the therapy of various cancers is reviewed and various oncological studies on experimental tumors are summarized. Novel therapeutic modalities for breast, prostate and ovarian cancer consist of the use of targeted cytotoxic analogs of LH-RH containing doxorubicin (DOX) or 2-pyrrolino-DOX. The same radicals have been incorporated into cytotoxic analogs of somatostatin which can be also targeted to receptors for this peptide in prostatic, mammary, ovarian, renal and lung cancers, brain tumors and their metastases. A targeted cytotoxic analog of bombesin containing 2-pyrrolino-DOX has also been synthesized and successfully tried in experimental models of prostate cancer, small cell lung carcinoma and brain tumors. The development of these new classes of peptide analogs should lead to a more effective treatment for various cancers.     

Oxidative degradation of cardiotoxic anticancer anthracyclines to phthalic acids. Novel function or ferrylmyoglobin

We show that the pseudoperoxidase activity of ferrylmyoglobin (MbIV) promotes oxidative degradation of doxorubicin (DOX), an anticancer anthracycline known to induce severe cardiotoxicity. MbIV, formed in vitro by reacting horse heart MbIII with H2O2, caused disappearance of the spectrum of DOX at 477 nm and appearance of UV-absorbing chromophores that indicated opening and degradation of its tetracyclic ring. Electron spray ionization mass spectrometry analyses of DOX/MbIV ultrafiltrates showed that DOX degradation resulted in formation of 3-methoxyphthalic acid, the product of oxidative modifications of its methoxy-substituted ring D. Other methoxy-substituted anthracyclines similarly released 3-methoxyphthalic acid after oxidation by MbIV, whereas demethoxy analogs released simple phthalic acid. Kinetic and stoichiometric analyses of reactions between DOX and MbIII/H2O2 or hemin/H2O2 showed that the porphyrin radical of MbIV-compound I and the iron-oxo moiety of MbIV-compound II were sequentially involved in oxidizing DOX; however, oxidation by compound I formed more 3-methoxyphthalic acid than oxidation by compound II. Sizeable amounts of 3-methoxyphthalic acid were formed in the heart of mice treated with DOX, in human myocardial biopsies exposed to DOX in vitro, and in human cardiac cytosol that oxidized DOX after activation of its endogenous myoglobin by H2O2. Importantly, H9c2 cardiomyocytes were damaged by low concentrations of DOX but could tolerate concentrations of 3-methoxyphthalic acid higher than those measured in murine or human myocardium. These results unravel a novel function for MbIV in the oxidative degradation of anthracyclines to phthalic acids and suggest that this may serve a salvage pathway against cardiotoxicity.     

Mu-opiate binding and morphine antagonism by octapeptide analogs of somatostatin

A series of cyclic conformationally restrained octapeptide analogs of somatostatin were examined for their ability to inhibit the binding of tritiated mu, kappa, and delta opiate receptor ligands. Several of these substances were found to have high affinity for mu opiate receptors while having very low affinity for both kappa and delta receptors. Previous suggestions that somatostatin analogs exhibit opiate antagonist activity led to a study of the ability of the two most potent compounds to inhibit morphine analgesia in rats after intracerebroventricular injection. One of the compounds significantly antagonized morphine analgesia although the other displayed severe toxicity. These two compounds differed in that the very toxic compound had previously been found to possess significant somatostatin activity. It thus appears that the structural requirements for toxicity and somatostatin activity can be differentiated from those for opiate activity.     

Somatostatin, but not somatostatin receptor subtypes 2 and 5 selective agonists, inhibits calcitonin secretion and gene expression in the human medullary thyroid carcinoma cell line, TT.

Somatostatin (SRIH) analogs are commonly used to treat symptoms in medullary thyroid carcinoma (MTC), that expresses SRIH receptors (SSTR1 to SSTR5), as does the human MTC cell line TT. The aim of this work was to evaluate whether SRIH, SSTR2 and SSTR5-selective agonists influence calcitonin (CT) secretion and gene expression in the TT cell line. CT secretion was evaluated by chemiluminescence, and gene expression was analyzed by Northern blot. TT cell line proliferation was also assessed by [(3)H] thymidine ([(3)H]thy) incorporation and viable cell number count. SRIH significantly (p < 0.05) reduced [(3)H]thy incorporation (approx. 50 %), viable cell number (approx. 20 %), CT secretion (-30 %) and CT gene expression (approx. 2-fold). Exposure to the SSTR2-selective agonist, BIM-23 120, and to the SSTR5-selective agonist, BIM-23 206, did not modify CT secretion and mRNA levels in TT cells. Thus, SRIH inhibits DNA synthesis, cell proliferation, CT secretion and CT gene expression in the TT cell line, while SSTR2 and 5 selective agonists, although influencing DNA synthesis and cell proliferation, do not modify CT gene expression, suggesting that SRIH may influence gene expression acting through SSTRs other than subtypes 2 and 5. Furthermore, these findings may explain the erratic response of MTC patients in terms of CT plasma levels to treatment with SRIH analogs, like octreotide and lanreotide, which interact mainly with SSTR2 and 5.     

Conformational analyses of sandostatin analogs containing stereochemical changes in positions 6 or 8

We report the conformational analysis by 1H nmr in DMSO and computer simulations involving distance geometry and molecular dynamics simulations of analogs of the cyclic octapeptide D-Phe1-c[Cys2-Phe3-D-Trp4-Lys5-Thr6-Cys 7]-Thr8-ol (sandostatin, octreotide). The analogs D-Phe1-c[Cys2-Phe3-D-Trp4-Lys5-Xaa6-Cys 7]-Xbb8-NH2 (Xaa = allo-Thr, D-allo-Thr, D-beta-Hyv, beta-Hyv, D-Thr, and Xbb = Thr or Xaa = Thr and Xbb = allo-Thr, D-allo-Thr, beta-Hyv, D-Thr) contain stereochemical changes in the Thr residues in positions 6 and 8, which allow us to investigate the influence of the stereochemistry within these residues on conformation and binding affinity. The molecular dynamics simulations provide insight into the conformational flexibility of these analogs. The compounds with (S)-configuration at the C(alpha) of residue 6 adopt beta-sheet structures containing a type II' beta-turn with D-Trp in the i+1 position, and these conformations are "folded" about residues 6 and 3. The structures are very similar to those observed for sandostatin, and the disulfide bridge results in a close proximity of the H(alpha) protons of residues 7 and 2, which confirms earlier observations that a disulfide bridge is a good mimic for a cis peptide bond. The compounds with (R)-configuration at the C(alpha) of residue 6 adopt considerably different backbone conformations. The structures observed for these analogs contain either a beta-turn about residue Lys and Xaa6 or a gamma-turn about the Xaa6 residue. These compounds do not exhibit significant binding to the somatostatin receptors, while the compounds with (S) configuration in position 6 bind potently to the sst2, 3, and 5 receptors. The nmr spectra of analogs with (R) or (S) configuration at the C(alpha) of residue 8 are strikingly similar to each other. We have demonstrated that the chemical shifts of protons of residues 3, 4, 5, and 6, which are part of the type II' beta-turn, and especially the effect on the Lys gamma-protons are considerably different in active molecules as compared to inactive analogs. Since the presence of a type II' beta-turn is crucial for the binding to the receptors, the chemical shifts, the amide temperature coefficients of the Thr residue and the medium strength NOE between LysNH and ThrNH can be extremely useful as an initial screening tool to separate the active molecules from inactive analogs.     

Inhibition of human non-small cell lung cancers with a targeted cytotoxic somatostatin analog, AN-162

Human non-small cell lung cancers (NSCLCs) express receptors for somatostatin. The cytotoxic analog of somatostatin AN-162 (AEZS-124), consisting of doxorubicin linked to a somatostatin analog RC-121 binds to receptors for somatostatin and is targeted to tumors expressing these receptors. The aim of this study was to investigate the effect of targeted cytotoxic somatostatin analog AN-162 on a panel of human NSCLC cell lines (A549, H460, H838, H1299) in vitro (at 0.5–100 μM concentrations) and in vivo on H460 and H1299 NSCLCs xenografted into nude mice (at the dose of 2.5 μmol/kg, i.v., once a week). The expression of mRNA for somatostatin receptor subtypes was investigated by RT-PCR in cell lines and tumor tissues. Somatostatin receptor proteins were also characterized by ligand competition assay and Western blotting. AN-162 significantly decreased cell proliferation in vitro and tumor growth (p < 0.05 vs. all groups) of H460 and H1299 NSCLCs in vivo. Based on real-time PCR array data, AN-162 induced several apoptosis-related genes in vivo in both models. Our results suggest that cytotoxic somatostatin analog AN-162 (AEZS-124) should be considered for the further development of a therapy of patients with NSCLC.     

In-vitro investigation of oxazol and urea analogues of morphinan at opioid receptors

A series of 2-amino-oxazole (7 and 8) analogs and 2-one-oxazole analogs (9 and 10) were synthesized from cyclorphan (1) or butorphan (2) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors and compared with their 2-aminothiozole analogs 5 and 6. Ligands 7-10 showed decreased affinities at kappa and mu receptors. Urea analogs (11-14) were also prepared from 2-aminocyclorphan (3) or 2-aminobutorphan (4) and evaluated in-vitro by their binding affinity at mu, delta, and kappa opioid receptors. The urea derived opioids retained their affinities at mu receptors while showing increased affinities at delta receptors and decreased affinities at kappa receptors. Functional activities of these compounds were measured in the [35S]GTPgammaS binding assay, illustrating that all of these ligands were kappa agonists. At the mu receptor, compounds 11 and 12 were mu agonist/antagonists.     

Synthesis, metal ion binding, and biological evaluation of new anticancer 2-(2'-hydroxyphenyl)benzoxazole analogs of UK-1

UK-1 is a bis(benzoxazole) natural product displaying activity against a wide range of human cancer cell lines. A simplified analog of UK-1, 4-carbomethoxy-2-(2'-hydroxyphenyl)benzoxazole, was previously found to be almost as active as UK-1 against cancer cell lines, and similar to the natural product, formed complexes with a variety of metal ions such as Mg2+ and Zn2+. A series of 4-substituted-2-(2'-hydroxyphenyl)benzoxazole analogs of this 'minimal pharmacophore' of UK-1 were prepared. The anti-cancer activity of these analogs was examined in breast and lung cancer cell lines. Spectrophotometric titrations in methanol were carried out in order to assess the ability of UK-1 and these analogs to coordinate with Mg2+ and Cu2+ ions. Although none of the new analogs were more cytotoxic than 4-carbomethoxy-2-(2'-hydroxyphenyl)benzoxazole, some analogs were identified that display similar cytotoxicity to this simplified UK-1 analog with improved water solubility. UK-1 and all of these new analogs bind Cu2+ ions better than Mg2+ ions, and the nature of the 4-substituent is important for the Mg2+ ion binding ability of these 2-(2'-hydroxyphenyl)benzoxazoles. Previous studies of a limited number of UK-1 analogs demonstrated a correlation between Mg2+ ion binding ability and cytotoxicity; however, within this series of 4-substituted-2-(2'-hydroxyphenyl)benzoxazoles the variations in cytotoxicity do not correlate with either Mg2+ or Cu2+ ion binding ability. These results, together with recent ESI-MS studies of Cu2+-mediated DNA binding by UK-1 and analogs, indicate that UK-1 and analogs may exert their cytotoxic effects by interaction with Cu2+ or other transition metal ions, rather than Mg2+, and that metal ion-mediated DNA binding, rather than metal ion binding affinity, is important for the cytotoxic effect of these compounds. The potential role of Cu2+ ions in the cytotoxic action of UK-1 is further supported by the observation that UK-1 in the presence of Cu2+ displays enhanced cytotoxicity to MCF-7 and A549 cells when compared to UK-1 alone.     

CNS and antimalarial activity of synthetic meridianin and psammopemmin analogs

The marine invertebrate-derived meridianin A, the originally proposed structure for psammopemmin A, and several related 3-pyrimidylindole analogs were synthesized and subsequently investigated for central nervous system, antimalarial, and cytotoxic activity. A Suzuki coupling of an indoleborate ester to the pyrimidine electrophile was utilized to form the natural product and derivatives thereof. The 3-pyrimidineindoles were found to prevent radioligand binding to several CNS receptors and transporters, most notably, serotonin receptors (<0.2 μM K(i) for 5HT(2B)). Two compounds also inhibited the human malaria parasite Plasmodium falciparum (IC(50) <50 μM). Only the natural product was cytotoxic toward A549 cells (IC(50)=15 μM).     

Resistance to somatostatin (SRIH) analog therapy in acromegaly. Re-evaluation of the correlation between the SRIH receptor status of the pituitary tumor and the in vivo inhibition of GH secretion in response to SRIH analog.

The development of a long-acting somatostatin (SRIH) analog (octreotide, Sandoz) has been a major breakthrough in the treatment of acromegaly. However, in 20-30% of the patients, growth hormone (GH) plasma levels remain elevated (> 10 micrograms/l) despite treatment with octreotide. This raised the concept of resistance to SRIH analog therapy in acromegaly. Indeed, in vivo response to SRIH analogs varies greatly among acromegalic patients. According to the reviews in the literature and our own autoradiographic data, no direct correlation can be established between the GH response to octreotide and the number or affinity of the SRIH receptors located on the tumor. In our series a greater density of SRIH receptors is present on tumors from patients very sensitive to the SRIH agonist. A subset of patients resistant to octreotide could result from a very low density of SRIH receptor although this type of GH-secreting tumor constitutes certainly a rare case. A subset of GH-secreting pituitary tumors can be characterized by a mutation on the alpha subunit of the guanine nucleotide-dependent protein coupled to the stimulation of adenylate cyclase (G alpha s). This mutation results in a high basal adenylate cyclase activity and a low GHRH-stimulated activity. However, when the adenomas are separated according to their basal adenylate cyclase activity, SRIH is able to decrease cAMP levels in both types of tumor. In addition, in our series no direct correlation is observed between the SRIH inhibition of adenylate cyclase and the amount of SRIH-binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine and non-endocrine activities of growth hormone secretagogues in humans

Growth hormone (GH) secretagogues (GHS) are synthetic peptidyl and non-peptidyl molecules which possess strong, dose-dependent and reproducible GH releasing effects as well as significant prolactin (PRL) and adrenocorticotropic hormone (ACTH) releasing effects. The neuroendocrine activities of GHS are mediated by specific receptors mainly present at the pituitary and hypothalamic level but also elsewhere in the central nervous system. GHS release GH via actions at the pituitary and (mainly) the hypothalamic level, probably acting on GH releasing hormone (GHRH) secreting neurons and/or as functional somatostatin antagonists. GHS release more GH than GHRH and the coadministration of these peptides has a synergistic effect but these effects need the integrity of the hypothalamo-pituitary unit. The GH releasing effect of GHS is generally gender-independent and undergoes marked age-related variations reflecting age-related changes in the neural control of anterior pituitary function. The PRL releasing activity of GHS probably comes from direct pituitary action, which indeed is slight and independent of both age and gender. The acute stimulatory effect of GHS on ACTH/cortisol secretion is similar to that of corticotropin releasing hormone (CRH) and arginine vasopressin (AVP). In physiological conditions, the ACTH releasing activity of GHS is mediated by central mechanisms, at least partially, independent of both CRH and AVP but probably involving GABAergic mechanisms. The ACTH releasing activity of GHS is gender-independent and undergoes peculiar age-related variations showing a trend towards increase in ageing. GHS possess specific receptors also at the peripheral levels in endocrine and non-endocrine human tissues. Cardiac receptors are specific for peptidyl GHS and probably mediate GH-independent cardiotropic activities both in animals and in humans.     

Bioisosteric phentolamine analogs as potent alpha-adrenergic antagonists

The synthesis and biological evaluation of a new series of bioisosteric phentolamine analogs are described. Replacement of the carbon next to the imidazoline ring of phentolamine with a nitrogen atom provides compounds (2, 3) that are about 1.6 times and 4.1 times more potent functionally than phentolamine on rat alpha1-adrenergic receptors, respectively. In receptor binding assays, the affinities of phentolamine and its bioisosteric analogs were determined on the human embryonic kidney (HEK) and Chinese Hamster ovary (CHO) cell lines expressing the human alpha1- and alpha2-AR subtypes, respectively. Analogs 2 and 3, both, displayed higher binding affinities at the alpha2- versus the alpha1-ARs, affinities being the least at the alpha1B-AR. Binding affinities of the methoxy ether analog 2 were greater than those of the phenolic analog 3 at all six alpha-AR subtypes. One of the nitrogen atoms in the imidazoline ring of phentolamine was replaced with an oxygen atom to give compounds 4 and 5, resulting in a 2-substituted oxazoline ring. The low functional antagonist activity on rat aorta, and binding potencies of these two compounds on human alpha1A- and alpha2A-AR subtypes indicate that a basic functional group is important for optimum binding to the alpha1- and alpha2A-adrenergic receptors.     

Slow channel calcium activators, a new group of pharmacological agents

Specific calcium channels in myocardium and vascular smooth muscle and pharmacologic agents which possess the ability to block them have been the subject of intense research over the past several years. Many studies have utilized dihydropyridine derivatives (e.g. nifedipine, nitrendipine, nisoldipine) which have been shown to be efficacious inhibitors of calcium influx through voltage sensitive slow channels. Administration of these agents results in vascular smooth muscle relaxation and negative inotropic effects. Recently, novel dihydropyridines such as Bay k 8644, CGP 28 392 and YC-170, with actions diametrically opposed to those of compounds typified by nifedipine have been synthesized. These agents demonstrate vaso-constrictor and positive inotropic effects - actions which might be expected of compounds capable of stimulating the transmembrane influx of calcium into vascular smooth muscle and myocardium. Actions of Bay k 8644 and CGP 28 392 studied in vitro and in vivo have also shown that pharmacological blockade of beta or alpha adrenergic receptors does not influence the direct effects of these agents. Future analogs, with similar but more selective actions on myocardial calcium channels, may prove useful in the management of pathologic states characterized by insufficient contractile function of the heart.     

Synthesis and binding potencies of cyclic hexapeptide analogs of somatostatin incorporating acidic and basic peptoid residues.

The synthesis, binding affinity, and structure-activity relationships of compounds related to the cyclic hexapeptide, c[Pro6-Phe7-D-Trp8-Lys9-Thr10-Phe11], L-363,301 (the numbering in the sequence refers to the position of the residue in native somatostatin) is reported. The Pro residue in this compound is replaced with the peptoid residues Nasp [N-(2-carboxyethyl) glycine], Ndab [N-(2-aminoethyl) glycine] and Nlys [N-(4-aminobutyl) glycine]. This series of compounds enables us to draw conclusions about the influence of positively or negatively charged residues in the bridging region on the binding affinity towards the isolated human somatostatin receptors. A loss of binding to the recombinant human somatostatin (hsst) receptors in the Nasp analog compared with L-363,301 and compared with the Ndab and Nlys analogs clearly demonstrates that the presence of an acidic residue in the bridging region is unfavorable for binding to the hsst receptors. Comparison between the Ndab analog and the Nlys analog suggests that the presence of a basic residue in the bridging region might be advantageous for binding to the hsst5 receptor provided that the residue bearing the basic group extends far enough to allow for interaction with the receptor, while the length of the basic peptoid residue does not influence binding to the hsst2 receptor. These results are useful for the design of hsst5 selective somatostatin analogs.     

Evaluation of anticancer effects of newly synthesized dihydropyridine derivatives in comparison to verapamil and doxorubicin on T47D parental and resistant cell lines in vitro

Failure of current anticancer drugs mandates screening for new compounds of synthetic or biological origin to be used in cancer therapy. Multidrug resistance (MDR) is one of the main obstacles in the chemotherapy of cancer. Efflux of cytotoxic agents mediated by P-glycoprotein (P-gp or MDR1) is believed to be an important mechanism of multidrug resistance. Therefore, we decided to investigate the antiproliferative effects of seven newly synthesized 1,4-dihydropyridine (DHP) derivatives in comparison to verapamil (VP) and doxorubicin (DOX) on human breast cancer T47D cells and its MDR1 overexpressed and moderately resistant cells (RS cells) using MTT cytotoxicity assay. We also examined the effects of these compounds on cytotoxicity of DOX in these two cell types. The cytotoxicity assays using MTT showed that most of the tested new DHP derivatives and VP at 10 μM concentration had varying levels of toxicity on both T47D and RS cells. The toxicity was mostly in the range of 10–25%. However, the cytotoxicity of these DHP derivatives, similar to VP, was significantly less than DOX when comparing IC₅₀ values. Furthermore, these compounds in general had relatively more cytotoxicity on T47D vs RS cells at 10-μM concentration. Among new DHPs, compounds 7a (3,5-dibenzoyl-4-(2-methylthiazol-4-yl)-1,4-dihydro-2,6-dimethylpyridine) and 7d (3,5-diacetyl-4-[2-(2-chlorophenyl)thiazol-4-yl)]-1,4-dihydro-2,6-dimethylpyridine) showed noticeable potentiation of DOX cytotoxicity (reduction of DOX IC₅₀) compared to DOX alone in both cells, particularly in RS cells. This effect was similar to that of VP, a known prototype of MDR1 reversal agent. In other words, compounds 7a and 7d resensitized RS cells to DOX or reversed their resistance. Results indicate that compound 7d exerts highest effect on RS cells. Therefore, these two newly synthesized DHP derivatives, compounds 7a and 7d, are promising as potential new MDR1 reversal agents and should be further studied on other highly resistant cells due to MDR1 overexpression and with further molecular investigation.     

Estrogen-like properties of brominated analogs of bisphenol A in the MCF-7 human breast cancer cell line

Tetrabromobisphenol A (TeBBPA) is a four-meta-brominated variant of bisphenol A (BPA) and is one of the most commonly used brominated flame retardants worldwide. We compared the estrogenic potency of TeBBPA, BPA and the brominated analogs mono- (MBBPA), di- (DBBPA), and tribromobisphenol A (TrBBPA) in the estrogen-dependent human breast cancer cell line MCF-7. All of the compounds competed with 17β-estradiol for binding to the estrogen receptor, although the affinity of the test chemicals to the estrogen receptor was much lower than that of 17β-estradiol. TrBBPA and TeBBPA showed a considerably lower access to the estrogen receptors within intact MCF-7 cells incubated in 100% serum compared to incubation in serum-free medium, indicating a strong binding to serum proteins. BPA, MBBPA, and DBBPA showed only a slightly reduced access to the receptors. All of the test compounds induced proliferation in MCF-7 cells, the potential decreasing with increasing number of bromo-substitutions. TeBBPA did not induce maximal cell growth, indicating cytotoxic effects at high concentrations. BPA and the brominated analogs, except TeBBPA, induced progesterone receptor and pS2 to the same extent as 17β-estradiol, although at much higher concentrations. Our studies demonstrate that compared to 17β-estradiol, BPA and the brominated analogs have much lower estrogenic potencies for all of the endpoints tested, TeBBPA being the least estrogenic compound. This revised version was published online in July 2006 with corrections to the Cover Date.     

alpha-adrenergic receptor in rat heart. Effects of thyroidectomy.

The effects of thyroid status on alpha-adrenergic receptors in the rat myocardium were investigated. The potent antagonist [3H]dihydroergokryptine was used to identify alpha-adrenergic receptors in rat heart particulate and sarcolemmal fractions. Administration of triiodothyronine to thyroidectomized rats decreased specific binding to alpha-adrenergic receptors in heart particulate and sarcolemmal fractions by 41% and 45%, respectively. Scatchard analysis revealed that the cardiac sarcolemmal fraction from thyroidectomized rats contained 29.3 fmol/mg of protein, as compared with 17.0 fmol/mg of protein found in the heart preparation of thyroidectomized rats treated with triiodothyronine. The equilibrium dissociation constants for the interaction of receptors with dihydroergokryptine were similar (about 1.5 nM) in the heart sarcolemmal fractions derived from these two groups of rats. The results of this study demonstrate that thyroid hormone can regulate the number of cardiac alpha-adrenergic receptors. In addition, there appears to be a reciprocal relationship between alpha-adrenergic and beta-adrenergic receptors in the rat myocardium.