Structure -activity relationships of PDE5 inhibitors.

cGMP has a short-term effect on smooth muscle tone and a longer-term effect on responses to chronic drug treatment or proliferative signals. cGMP-Phosphodiesterase type 5 (PDE5) hydrolizes cGMP, and the result is smooth muscle contraction. PDE5 is a relatively novel therapeutic target of various diseases, such as erectile dysfunction and pulmonary hypertension. The most intensively examined and marketed PDE5 inhibitor was sildenafil (Viagra) but recently vardenafil (Levitra) and tadalafil (Cialis) were launched with beneficial ADME parameters and PDE5 selectivity. The increasing interest in PDE5 inhibition made it reasonable to collect the available inhibitory data from the scientific literature and set up a structure-activity relationship study. Chemical structures of 438 compounds and their cGMP-PDE5 inhibitory data (IC50) were collected from recently published articles. In this paper physiology, regulation and inhibition of PDE5 (and briefly other PDE-s) are discussed and inhibitors are tabulated by the core structures. Finally, a general QSAR model built from these data is presented. All data used in the QSAR study were summarized in a Supplement (for description please see the online version of the article).

Antitumor activity of the somatostatin structural derivative (TT-232), against mouse and human melanoma tumor models.

BACKGROUND: The somatostatin structural deivative, TT-232, has a special 5'-residue ring structure (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH2) and very different characteristics from the known growth hormone (GH) active somatostatin analogs. TT-232 inhibited tyrosine kinase activity of tumor cell lines and this inhibition correlated well with the inhibition of cell proliferation of a large number of cancer cell lines in vitro and reduces the size of different tumors in animal models in vivo. The antitumor efficacy of TT-232 has been found to be associated with the induction of apoptosis in tumor cells, resulting in highly selective elimination of tumor tissue. TT-232 was found to be devoid of GH release inhibitory activity but to possess strong antitumor effects. It binds with a high affinity to SSTR1 and SSTR4. This compound was also found to inhibit inflammation in a number of experimental models. MATERIALS AND METHODS: The study compared the antitumor effect of TT-232 in various long-term administration routes: an intermittent (injection) versus continuous (infusion) treatment via subcutaneously inserted 2002 type Alzet osmotic minipumps in two different tumor models (B-16 rodent melanoma and HT-18 human lymphoid melanoma). Treatment with TT-232 started after disease development. The antitumor efficacy of TT-232 was evaluated on the basis of tumor growth inhibition and survival time. RESULTS: In the case of B-16 rodent melanoma, the TT-232 treatments resulted in 35%-39% (injection) and 47%-63% (infusion) tumor growth inhibition, and the infusion treatment an approximately 61% increase in survival time. The tumor growth inhibitory effect of TT-232 on HT-18 lymphoid melanoma tumor proved to be significant, resulting in 41%-63% (injection) and 69%-79% (infusion) decreases in tumor volume and in a 25%-30% increase in survival time (infusion treatments). CONCLUSION: The results indicate that TT-232 could be a potentially useful therapeutic agent if these data are translated into clinical practice.

Evaluation of the antitumor efficacy of the somatostatin structural derivative TT-232 on different tumor models.

The antitumor effects of the somatostatin structural derivative TT-232 in different rodent and xenograft tumor models are summarized in this report. TT-232 had previously been shown to inhibit the proliferation of a large number of cancer cell lines in vitro and reduce the size of different tumors in animal models in vivo. The effects of TT-232 by different routes of administration and treatment schedules were studied in various types of rodent and human xenograft tumor models. In the rodent tumor models S-180 sarcoma and P-388 lymphoid leukemia tumor the infusion treatment resulted in 76%-100% tumor growth inhibition and in 20%-60% of the mice being long-term and tumor-free survivors. In the aggressive C-26 colon carcinoma and MXT breast carcinoma, the TT-232 treatments resulted in 71%-75% tumor growth inhibition and an approximately 50% increased survival time. The tumor growth inhibitory effect of TT-232 on human tumor xenografts proved to be significant, resulting in 30%-80% decrease in tumor volume and in 20%-40% tumor-free animals. This antitumor efficacy of TT-232 was seen in almost all the tumors investigated. In our study, the route of infusion was shown to increase drug efficacy relative to conventional delivery methods. Our results suggested that TT-232 is an effective and promising antitumor agent.

A comparison of the tumor growth inhibitory effect of intermittent and continuous administration of the somatostatin structural derivative TT-232 in various human tumor models.

The tumor growth inhibitory efficacy of the somatostatin structural derivative TT-232 was studied using different routes of administration and treatment schedules in various human tumor models. TT-232, containing a five-residue ring structure, has a strong antitumor activity both in vitro and in vivo. The antineoplastic activity of TT-232 has been found to be associated with the induction of programmed cell death in tumor cells, resulting in highly-selective elimination of the neoplastic tissue. The study compared the antitumor efficacy of TT-232 in various long-term administration routes; the intermittent (injection) versus continuous (infusion) treatment via subcutaneously-inserted Alzet osmotic minipumps in different human tumor models: T-47/D human breast carcinoma and A-431 human epidermoid carcinoma. Treatment with TT-232 started after disease development. The antitumor activity of TT-232 was evaluated on the basis of the tumor growth inhibition. In the case of T-47/D human breast carcinoma, the intermittent treatment resulted in 23%-26% and the infusion treatment resulted in 48%-53% tumor growth inhibition. The tumor growth inhibitory effect of TT-232 on A-431 human epidermoid carcinoma tumor resulted in 35%-43% (intermittent treatment) and 70%-74% (continuous treatment) decreases in tumor volume. This antitumor efficacy of TT-232 was observed in the two human tumors investigated. In this study, the route of infusion was shown to increase drug efficacy relative to conventional delivery methods. The results suggest that TT-232 is an effective and promising antitumor agent.

Growth inhibitory effect of the somatostatin structural derivative (TT-232) on leukemia models.

TT-232 is a structural derivative of the natural signal inhibitory peptide somatostatin, with selective antiproliferative and anti-inflammatory properties. TT-232 activates SSTR receptors (primarily the SSTR-1), which leads to irreversible cell cycle arrest, followed by secondary induction of apoptosis. TT-232 has passed phase I clinical trials without toxicity and significant side-effects. We examined the antiproliferative effect in vitro and the antitumor effect in vivo of TT-232 on leukemia cell lines. During in vivo experiments, we evaluated the therapeutic efficacy of TT-232 in various long-term administration routes; traditional injection versus infusion treatment via an inserted Alzet minipump on P-388 mice and HL-60 human leukemia models. Treatment with TT-232 started after development of the disease. In vitro, TT-232 inhibited the proliferation of P-388 mice lymphoid cells and HL-60 human promyelocytic leukemia cells in the range of 46%-97% with 24-hour treatment and 82%-100% with 48-hour treatment. Cells were treated with 30 microg/ml and 60 microg/ml dose of TT-232. With the same in vivo models, the best results were achieved when TT-232 was applied by infusion treatments. The infusion treatment with TT-232 produced 50%-80% inhibition of growth and resulted in 20%-40% long-term and leukemia-free survivors. TT-232 showed dose-, time- and administration mode-dependent antileukemia activity in vitro and in vivo, both on rodent and human models. Our results suggest that TT-232 is a promising new antileukemia agent.

Characterization of lipophilicity and antiproliferative activity of E-2-arylmethylene-1-tetralones and their heteroanalogues.

A molecular library based on E-2-arylmethylene-1-tetralone has been designed and synthesized. A reversed phase high performance liquid chromatographic (RP-HPLC) method has been developed and applied to separate them and to characterize their lipophilicity. The chromatographic method applied here was suitable to separate the structural (ortho and para) isomers of compounds and was sensitive enough to differentiate their lipophilicities. The measured (k') and computer calculated (CLOGP) lipophilicity values has been compared. Good linear correlation has been found in the case of these structurally related molecules. In vitro biological assay has been performed with Methylene blue dying to investigate the antiproliferative potency of the compounds synthesized in this work. The measured (k') and calculated (CLOGP) lipophilicities of the compounds were compared with the antiproliferative activities and an optimum value of lipophilicity has been found for these compounds.

Comparison of measured and calculated lipophilicity of substituted aurones and related compounds.

A molecule library containing 55 aurone- and thioaurone-type structures has been designed and synthesised. Reversed phase high performance liquid chromatographic (RP-HPLC) method has been developed to separate these compounds and to characterise their lipophilicity by experimental method (k'). The experimental lipophilicity data have been compared with the computer calculated lipophilicity parameters (CLOGPs) of the same molecules. In general, good correlations between the measured and calculated lipophilicities have been found with the exception of structure isomers and compounds capable for hydrogen bonding. The chromatographic method was suitable to separate the structure (ortho and para) isomers of aurone and thioaurones and was sensitive enough to differentiate their lipophilicities. Our findings suggest the usefulness of the chromatographic method in fast characterisation of the lipophilicity of structurally closely related molecules.

Determination of the basicity of Mannich ketones by capillary electrophoresis.

Capillary electrophoretic (CE) method to characterise Mannich ketones (MKs) containing morpholine moiety was developed. Basicity (pKa,exp) of the MKs was characterised by measured data derived from the electrophoretic mobility values obtained in the CE separation. The MKs were found to be weaker bases than the parent morpholine molecule itself and the experimentally determined basicity values proved to be dependent on the chemical structure of the MKs. Since the basicity of the MKs has an influence on their reactivity and biological activity it seems to be useful to determine experimentally the pKa,exp values of the newly synthesised compounds to support rational drug design or screening of the molecule libraries.

The antitumor activity of the somatostatin structural derivative (TT-232) on different human tumor xenografts.

A somatostatin structural derivative (TT-232) has been developed in our laboratory with strong antiproliferative effect but no GH- release inhibitory activity. TT-232 inhibited tyrosine kinase activity of tumor cells lines and this inhibition correlated well with the inhibition of cell proliferation. The antineoplastic activity of TT-232 has been found to be associated with induction of programmed cell death (apoptosis) in tumor cell, resulting in highly selective elimination of neoplastic tissue. The aim of this study was the therapeutic efficacy of TT-232 on different human models: PC-3 prostate carcinoma, MDA-MB-231 (ER-) and MCF-7 (ER+) breast carcinoma, HT-29 colon carcinoma, HT-18 melanoma, HL-60 promyelocytic leukemia. We studied the therapeutic efficacy of the novel somatostatin analog, it for 30 days with intermittent injection once daily and for 14 days with s.c. infusion using the Alzet osmotic minipump (model 2002). The antitumor activity of TT-232 was evaluated on the basis of survival time and tumor growth inhibition. The tumor growth inhibitory effect of TT-232 on human tumor xenografts proved to be significant, resulting in 30%-80% decrease in tumor volume and in 20-60% tumor free animals. This antitumor efficacy of the novel somatostatin analog was observable in almost all tumors investigated. These data suggest that the novel somatostatin analog (TT-232) is an effective and promising antitumor agent.

TT-232: a somatostatin structural derivative as a potent antitumor drug candidate.

TT-232 (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH2) has been developed as an antitumor somatostatin analog. TT-232 has no growth hormone release inhibitory effect and does not inhibit the secretion of gastric acid. This analog induces apoptosis in and exerts pronounced antiproliferative effects on various human tumors (colon, pancreas, lymphoma, leukemia, melanoma, hepatoma) cell lines. The growth of human xenografts (prostate, breast carcinoma, lymphoma, melanoma) and animal tumors (colon-26, P-388, S-180, B16, MXT) was inhibited by TT-232 (dose range: 30-750 microg/kg/day) in 54-98% of cases. Continuous long-term infusion proved to be the most effective way of administration. TT-232 combined with decarbazine or etoposide treatment enhanced the antitumor activity of these drugs on human melanoma and lymphoma xenografts, respectively. Regarding the mode of action, TT-232 activates cell cycle inhibitors via SSTR receptors, inhibits tyrosine kinases through interfering with the proliferative signaling cascades, and interacts with an intracellular receptor and an enzyme involved in glycolysis causing translocation of this enzyme to the nucleus, thus inducing apoptosis. TT-232 may be a promising candidate in the therapy of human malignancies.

Reliability of logP predictions based on calculated molecular descriptors: a critical review.

Correct QSAR analysis requires reliable measured or calculated logP values, being logP the most frequently utilized and most important physico-chemical parameter in such studies. Since the publication of theoretical fundamentals of logP prediction, many commercial software solutions are available. These programs are all based on experimental data of huge databases therefore the predicted logP values are mostly acceptable - especially for known structures and their derivatives. In this study we critically reviewed the published methods and compared the predictive power of commercial softwares (CLOGP, KOWWIN, SciLogP/ULTRA) to each other and to our recently developed automatic QS(P)AR program. We have selected a very diverse set of 625 known drugs (98%) and drug-like molecules with experimentally validated logP values. We have collected 78 reported "outliers" as well, which could not be predicted by the "traditional" methods. We used these data in the model building and validation. Finally, we used an external validation set of compounds missing from public databases. We emphasized the importance of data quality, descriptor calculation and selection, and presented a general, reliable descriptor selection and validation technique for such kind of studies. Our method is based on the strictest mathematical and statistical rules, fully automatic and after the initial settings there is no option for user intervention. Three approaches were applied: multiple linear regression, partial least squares analysis and artificial neural network. LogP predictions with a multiple linear regression model showed acceptable accuracy for new compounds therefore it can be used for "in-silico-screening" and/or planning virtual/combinatorial libraries.