Histamine is an intracellular messenger mediating platelet aggregation.

Inhibition of human platelet aggregation by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE), a novel antagonist of histamine binding, suggested that histamine might serve a critical role in cell function. Phorbol-12-myristate-13-acetate (PMA) or collagen was found to increase platelet histamine content in parallel with promotion of aggregation. Inhibitors of histidine decarboxylase (HDC) suppressed both aggregation and the elevation of histamine content, whereas DPPE inhibited aggregation only. In saponin-permeabilized platelets, added histamine reversed the inhibition by DPPE or HDC inhibitors on aggregation induced by PMA or collagen. The results indicate a role for histamine as an intracellular messenger, which in platelets promotes aggregation.

Increased therapeutic index of antineoplastic drugs in combination with intracellular histamine antagonists.

L-Histidinol, a protein synthesis inhibitor and structural analogue of L-histidine, has been demonstrated in chemotherapy-treated mice to be cytoprotective to normal stem cells but to enhance cytotoxicity to tumor cells. N,N-Diethyl-2-[4-(phenylmethyl) phenoxy]ethanamine.HCl (DPPE) is an antagonist of recently described microsomal and nuclear intracellular histamine receptors implicated in the mediation of proliferation and modulation of prostaglandin synthesis. DPPE is cytotoxic to tumor cells in vitro and cytoprotective to the gut in vivo. Noting the similar pharmacologic profiles for histidinol and DPPE and the structural resemblance between histidinol and histamine, we tested 1) whether binding to intracellular histamine receptors may be important to the action of histidinol, 2) whether there exists a differential effect of DPPE and histidinol on proliferating normal and transformed or malignant cells, and 3) whether DPPE, like histidinol, protects host cells from the effects of chemotherapy while augmenting tumor cell kill in vivo. It was observed that histidinol does compete at intracellular histamine receptors in isolated microsomes and nuclei, but with significantly lower affinity than DPPE. Nevertheless, for each agent, potency at intracellular histamine receptors correlates with potency to inhibit DNA and protein synthesis, without cytotoxicity, in normal mitogen-stimulated murine lymphocytes and to kill transformed mouse lymphocytes or MCF-7 human breast cancer cells. As demonstrated previously for histidinol (1-2 g/kg), DPPE (4 mg/kg) protected murine bone marrow progenitors from doxorubicin or fluorouracil, while doses of 4-50 mg/kg significantly enhanced the antitumor activity of doxorubicin and daunorubicin in murine models of early cancer. One postulate to explain the effects of intracellular histamine receptor ligands is that intracellular histamine mediates DNA and protein synthesis, possibly through a downward modulation of growth-inhibitory prostaglandin levels. Antagonism of the intracellular action of histamine at intracellular histamine receptors by DPPE or histidinol may result in differential perturbations of growth/eicosanoid metabolism in normal and malignant cells, thus forming the basis of a new approach to chemotherapy.

Enhanced cancer growth in mice administered daily human-equivalent doses of some H1-antihistamines: predictive in vitro correlates.

BACKGROUND: Present studies of drug-induced tumor growth promotion have evolved from earlier investigations into the mechanism of action of N,N-diethyl-2-[4-(phenylmethyl)phenoxy[ethanamine.HCl, a tamoxifen derivative which potently inhibits lymphocyte mitogenesis in vitro and stimulates tumor growth in vivo. It is thought that potency to bind to intracellular histamine receptors (HIC), some of which are on cytochromes P450, may correlate with tumor growth-promoting activity. PURPOSE: We assessed the effectiveness of five in vitro assays in predicting in vivo tumor growth stimulation by the H1-antihistamines loratadine, astemizole, cetirizine, hydroxyzine, and doxylamine. METHODS: Potency of each agent was ranked 1-5 in each of the following in vitro assays: 1) inhibition of [3H]histamine binding to microsomal HIC, 2) inhibition of histamine binding to microsomal P450, 3) inhibition of the P450-catalyzed demethylation of aminopyrine, 4) inhibition of lymphocyte mitogenesis, and 5) stimulation of tumor colony formation. An overall rank score was assigned to each drug and correlated with tumor growth stimulation in vivo. Two laboratories conducted in vivo studies in a blinded fashion. Female C57BL and C3H mice were given a subcutaneous injection on day 1 of syngeneic B16F10 melanoma cells (5 x 10(5)) or C-3 fibrosarcoma cells (1 x 10(5)), respectively. Mice were randomly assigned to treatment groups, then received a single, daily intraperitoneal injection of an estimated human-equivalent dose (or range of doses) of antihistamine or vehicle control for 18-21 days before being killed. Tumors were surgically removed and wet weights compared statistically among groups. RESULTS: The cumulative potency of each drug in affecting tumor growth or growth mechanisms in the five in vitro assays ranked as follows: Loratidine and astemizole ranked highest and were equally potent, followed in decreasing order by hydroxyzine, doxylamine, and cetirizine. A significant correlation (r = .97; P < .02) was observed between the rank order of potency of the antihistamines in all five in vitro assays and the rank order to enhance tumor growth in vivo: Loratidine and astemizole significantly (P < .001) promoted the growth of both melanoma and fibrosarcoma, hydroxyzine significantly (P < .001) promoted the growth of melanoma, while doxylamine and cetirizine did not promote the growth of either tumor. CONCLUSION: Data demonstrate that the in vitro assays predicted the propensity of each H1-antihistamine to stimulate cancer growth in vivo. IMPLICATION: These in vitro tests may prove valuable to screen potential tumor growth promoters.

Receptor status and subsequent sensitivity of subclones of MCF-7 human breast cancer cells surviving exposure to diethylstilbestrol.

The estrogen receptor (ER)-positive human breast cancer cell line MCF-7 was incubated continuously in the presence of pharmacological concentrations of diethylstilbestrol (DES) in an attempt to correlate receptor status with DES sensitivity. It was consistently observed that cytotoxicity occurred at DES concentrations greater than 5 X 10(-6)M; however, a small percentage of cells, both from the wild-type MCF-7 line and from subclones derived in soft agar from single MCF-7 cells, survived, with altered morphology, up to 4 months of continuous exposure to DES concentrations ranging from 5 X 10(-6) to 1 X 10(-4)M. Characterization of seven regenerated surviving cell populations suggested that they remained ER positive; no evidence could be found for a block in the pathway of hormonal activation, as determined by progesterone receptor induction, to explain the ability of these cells to survive DES. Three regenerated cell populations were reexposed to DES. Two remained as sensitive to growth inhibition as untreated parent cells from which they were derived; however, one of these, designated MCF-7(35-1), was found to have autonomously high progesterone receptor (463 +/- 94 fmol/mg of cytosol; Kd = 1.8 +/- 0.2 X 10(-9)M) which was not significantly stimulated by the addition of 1 X 10(-8)M 17beta-estradiol for 72 hr. The third population, designated MCF-7(35-3), which survived initial exposure to 5 X 10(-5)M DES for 109 days and which remained ER positive (27 +/- 3 fmol/mg of cytosol; Kd = 0.8 +/- 0.2 X 10(-10)M) and progesterone receptor inducible, demonstrated significantly decreased sensitivity (p = 0.025) on reexposure to DES; conversely, significantly increased sensitivity (p less than 0.03) to the antiestrogen tamoxifen was observed. The mechanisms by which some MCF-7 cells survive prolonged exposure to DES are not certain; the data suggest that there is no clear relationship between ER status and sensitivity to DES and that there is no way of predicting the ultimate status of cells surviving DES treatment.

Peripheral leukocyte migration inhibition reactivity to breast cancer antigens in patients with breast cancer and in normal controls.

The peripheral leukocyte migration inhibition test has been used to assess cellular immunity to soluble antigen extracts of breast cancer in patients and normal controls. In sequential tests over several weeks, 23 of 23 patients with breast cancer in remission reacted intermittently, with 67 of 139 tests (48%) being positive (greater than or equal to 20% migration inhibition). Similarly, 6 of 10 patients in relapse reacted intermittently showing 16 of 61 positive tests (26%) and 126 of 129 normal females reacted intermittently showing 135 of 512 positive tests (26%). The mean percentage of migration inhibition for all tests in patients in remission was 16.4 +/- 1.2% and that for normal controls was 7.2 +/- 0.7%; this difference was highly significant (p less than 0.001). The value for all tests in patients with relapse was 11.8 +/- 1.4%; this was statistically lower than that for patients in remission (p less than 0.05) but statistically higher than that for normal controls (p less than 0.05). A few normal women, some with high risk factors such as a strong family history and/or fibrocystic and proliferative disease, had a mean percentage of migration inhibition value in the range of that for patients with breast cancer. Mean values of sequential tests may be a more meaningful index of cellular immunity against breast cancer antigen in all groups.

In vivo and in vitro studies of immunotherapy of nasopharyngeal carcinoma with transfer factor.

Epstein-Barr virus, the apparent cause of infectious mononucleosis, may also be an etiological agent in nasopharyngeal carcinoma and Burkitt's lymphoma. Lymphocytes from normal individuals with anti-Epstein-Barr virus antibody activity may be sensitized to Epstein-Barr virus and contain transfer factor with the potential to program and/or recruit other lymphocytes to react against the virus and/or viral antigens. A patient with nasopharyngeal carcinoma refractory to conventional therapy was treated with transfer factor obtained from normal, young adults with previous history of infectious mononucleosis. Following immunotherapy, apparent slowing of tumor growth was observed, which was associated with intense lymphocytic infiltration of the tumor and reconstitution of delayed cutaneous hypersensitivity reactions to microbial recall antigens. A double-blind randomized clinical trial has been initiated to determine whether transfer factor immunotherapy is a useful adjunct to radiotherapy in the primary treatment of patients with nasopharyngeal carcinoma. If successful, a similar trial might be considered for African patients with Burkitt's lymphoma.

Histamine and growth: interaction of antiestrogen binding site ligands with a novel histamine site that may be associated with calcium channels.

N,N-Diethyl-2-[(4-phenylmethyl)-phenoxy]ethanamine hydrochloride (DPPE) is a novel paradiphenylmethane derivative with antiproliferative and antiestrogenic properties. Like tamoxifen (TAM), DPPE binds to the microsomal antiestrogen binding site with high affinity (Kd approximately 50 nM), but, conversely, not to estrogen receptor or calmodulin. We now demonstrate that DPPE competes for [3H]histamine binding in rat cerebral cortex with an affinity (Ki = 4.5 +/- 2.6 X 10(-6) M) significantly greater than that of the H1 antagonist pyrilamine (Ki = 7.2 +/- 2.2 X 10(-5) M), despite the previous demonstration that pyrilamine is up to 1000 times more potent than DPPE in antagonizing histamine-induced contraction in canine tracheal smooth muscle. DPPE demonstrates antiproliferative activity against MCF-7 cells at concentrations between 1 X 10(-7) and 1 X 10(-5) M; the IC50 value of DPPE for growth inhibition at 7 days in this assay is 5 X 10(-6) M, a value equivalent to its Ki value for histamine binding. DPPE also competes for [3H]verapamil binding in membranes from whole rat brain with an affinity equal to that for verapamil (Kd = 4.0 +/- 1.8 X 10(-7) M); however, verapamil competes for [3H]DPPE binding in brain membranes and rat liver microsomes with an affinity markedly lower (Ki approximately 1 X 10(-4) M) than that of DPPE, suggesting allosteric interactions between the verapamil and DPPE sites. Unlike DPPE, verapamil is not antiproliferative in vitro against MCF-7 cells at concentrations up 1 X 10(-5) M, but, like DPPE, is cytotoxic at concentrations of 1 X 10(-4) M. In immature oophorectomized rats, verapamil or DPPE alone is antiuterotropic; however, verapamil shows no antagonism of exogenous estradiol on uterine growth, as opposed to DPPE which is a partial antagonist. Thus, the antiproliferative and antiestrogenic properties of DPPE either are not associated with calcium channel antagonism, or result from a qualitatively different effect on channels than verapamil. The in vitro antiproliferative effect of DPPE (7.5 X 10(-6) M) on MCF-7 cells at 72 h is significantly reversed by 10 mM L-histidine (70.2 +/- 12.6% reversal) and L-methionine (92.4 +/- 11.1% reversal), but not by L-ornithine, L-arginine, L-phenylalanine, or exogenous histamine. At lower concentrations of TAM (0.75 X 10(-6) M), where growth inhibition is estrogen-reversible, L-ornithine, but not L-histidine or L-methionine, causes significant reversal of growth inhibition (66.8 +/- 13.3%; p less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Correlation of the antiproliferative action of diphenylmethane-derivative antiestrogen binding site ligands with antagonism of histamine binding but not of protein kinase C-mediated phosphorylation.

The nonestrogen receptor-mediated antiproliferative action of antiestrogen binding site (AEBS) ligands, including triphenylethylene antiestrogens and phenothiazines, has been linked to their ability to inhibit protein kinase C (PKC). Recent studies indicate that some diphenylmethane derivatives inhibit growth, are potent AEBS ligands, and antagonize histamine binding at an AEBS-related histamine site different from H1 and H2. Three novel diphenylmethane derivatives, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine.HCI (DPPE), 4-decanoyl-DPPE (dec-DPPE), and 4-benzylphenyl decanoate (BPD) were studied in an attempt to determine whether PKC or histamine interactions best correlate with their antiproliferative effects. Platelet aggregation and the phosphorylation of a platelet Mr 47,000 protein (p47) induced by phorbol-12-myristate-13-acetate (PMA) represent two processes mediated by PKC. DPPE inhibits PMA-induced aggregation [50% inhibitory concentration (IC50) = 31.2 +/- 2.4 (SEM) x 10(-6) M] but does not significantly inhibit either PMA-induced phosphorylation of Mr 47,000 protein (IC50 greater than 500 x 10(-6) M), or binding of [3H]phorbol dibutyrate to platelets. dec-DPPE is a more potent inhibitor of PMA-induced platelet aggregation (IC50 = 18.8 +/- 0.7 x 10(-6) M), a weak inhibitor of Mr 47,000 phosphorylation (IC50 = 80-200 x 10(-6) M), but is without effect on [3H]phorbol dibutyrate binding. BPD, which lacks the alkylaminoethoxy side chain necessary for binding to the AEBS/DPPE site, is devoid of anti-PMA effects. These results are compared to the inhibition of [3H]histamine binding in rat cortex membranes (Ki value for DPPE = 0.83 +/- 0.62 x 10(-6) M; Ki value for dec-DPPE = 6.6 +/- 3.5 x 10(-6) M; BPD is inactive) and growth inhibition of MCF-7 cells (IC50 value for DPPE = 4.5 x 10(-6) M; IC50 value for dec-DPPE = 1.5 x 10(-5) M; BPD is ineffective at all concentrations tested). Thus, while dec-DPPE is a more potent inhibitor of PKC-mediated phosphorylation, DPPE is a more potent inhibitor of histamine binding and is correspondingly more antiproliferative than dec-DPPE. The results support a relationship between antagonism of histamine binding and growth inhibition but argue against an association between the antiproliferative effects of DPPE and dec-DPPE and inhibition of PKC. The findings for DPPE suggest that platelet response to PMA, antagonized by diphenylmethane-type AEBS-ligands, may be mediated, at least in part, by mechanisms other than activation of protein kinase C-dependent phosphorylation.

Stimulation of malignant growth in rodents by antidepressant drugs at clinically relevant doses.

Tricyclic antidepressants, such as amitriptyline (Elavil), and the nontricyclic agent, fluoxetine (Prozac), bind to growth-regulatory intracellular histamine receptors, associated with anti-estrogen binding sites in microsomes and nuclei. The prototype anti-estrogen binding site/intracellular histamine receptor ligand, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl, inhibits normal cell proliferation in vitro but stimulates tumor growth in vivo. Because of their structural similarity to N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl, we carried out studies to determine whether amitriptyline and fluoxetine stimulate tumor growth and/or development in rodents at concentrations relevant to the treatment of human depression (equivalent human dose range, approximately 100-150 mg/day for amitriptyline and approximately 20-80 mg/day for fluoxetine). All experiments were performed blinded. In studies of growth stimulation of transplantable syngeneic tumors, groups of mice were inoculated s.c. with C-3 fibrosarcoma cells or given i.v. or s.c. injections of B16f10 melanoma cells, followed 24 h later by daily i.p. injections of saline, amitriptyline, or fluoxetine. Tumor latency (fibrosarcoma), aggregate tumor weight (s.c. injected melanoma), or time to death from pulmonary metastasis (i.v. injected melanoma) was determined; drug-induced stimulation of DNA synthesis in C-3 fibrosarcoma cells in vitro was correlated with tumor growth acceleration in vivo. In a mammary carcinogenesis model, the effects of chronic saline, amitriptyline, or fluoxetine administration on the rate and frequency of development of mammary tumors in rats fed dimethylbenzanthracene (DMBA) were compared. Eight of 20 amitriptyline- or fluoxetine-treated mice developed fibrosarcoma tumors by day 5, as compared to none of 20 saline controls (P less than 0.002). Similarly, 20 of 21 DMBA-treated rats receiving the antidepressant drugs developed 33 mammary tumors by week 15 as compared to 5 tumors in 4 of 7 DMBA-treated rats receiving saline (P less than 0.001). For both models, tumor latency decreased 30-40% and, in the DMBA model, tumor frequency increased greater than 2-fold in the antidepressant-treated rats as compared to controls. Stimulation of fibrosarcoma growth in vivo correlated with a corresponding bell-shaped drug-induced increase in DNA synthesis in vitro. While the median time to death from pulmonary metastases did not differ among groups given i.v. injections of melanoma cells, a significant (P less than 0.01) stimulation of growth of s.c. injected melanoma was observed in mice receiving the antidepressants.(ABSTRACT TRUNCATED AT 400 WORDS)

N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine in combination with cyclophosphamide: an active, low-toxicity regimen for metastatic hormonally unresponsive prostate cancer.

PURPOSE: The intracellular histamine antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine. HCl (DPPE), potentiates chemotherapy cytotoxicity to malignant cells but protects normal tissue, including bone marrow, gut, and hair. We assessed the response to and clinical toxicity of DPPE/cyclophosphamide therapy in 20 patients with advanced hormonally unresponsive prostate cancer, 19 of whom were symptomatic. PATIENTS AND METHODS: Subjects received a maximally tolerated dose of DPPE (6 mg/kg) intravenously (IV) over 80 minutes. Cyclophosphamide (600 to 800 mg/m2; maximum dose, 1,500 mg) was administered over the last 20 minutes of DPPE infusion. Treatments (usually outpatient) were given once weekly for 4 weeks, followed by a 1-week delay, and then 2 of every 3 weeks as long as the patient was deemed to benefit. RESULTS: Five of seven patients (71%) with measurable soft tissue disease had a partial remission (PR). Three of 16 (19%) with assessable bone disease responded (one complete remission [CR] and two PRs). Nine of 18 (50%) with an elevated serum level of prostate-specific antigen (PSA) had more than a 50% (mean +/- SD, 78% +/- 14%) decrease. Eleven of 13 (85%) with bone pain had partial or complete resolution of this symptom; the PSA level and bone scan improved in six and two of these subjects, respectively. Acute treatment toxicity consisted of nausea/vomiting (six of 20) and ataxia (20 of 20), which correlated with peak serum levels of DPPE. Delayed effects (24 to 48 hours) consisted mainly of tiredness and mild nausea; one patient developed hemorrhagic cystitis. Bone marrow and hair follicle toxicity was negligible in 14 and 15 patients, respectively. CONCLUSION: DPPE/cyclophosphamide appears to be an active regimen for metastatic prostate cancer, with the added benefit of relatively low toxicity.

Results of a clinical trial in humans with refractory cancer of the intracellular histamine antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl, in combination with various single antineoplastic agents.

PURPOSE: We assessed N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE) potentiation of chemotherapy in vitro and performed a pharmacokinetic study and phase I/II trial of DPPE, combined with various single agents, in patients with advanced refractory cancer. PATIENTS AND METHODS: In vitro chemopotentiation by DPPE was assessed in drug-sensitive and -resistant (multidrug resistant-positive [MDR+]) human tumor cells using a colony survival assay. The effect of DPPE and verapamil on the intracellular concentration of daunorubicin in MDR+ cells was compared. For the clinical study, subjects with progressive malignancy received a weekly infusion of a maximally tolerated dose of DPPE (240 mg/m2) over 80 or 440 minutes, in conjunction with a single chemotherapy drug to which, in most cases, the patient's tumor was previously resistant. Concentrations of DPPE in blood and urine were determined by high-performance liquid chromatography (HPLC). RESULTS: In vitro, micromolar concentrations of DPPE potentiated (fivefold to 10-fold) chemotherapy cytotoxicity to both drug-sensitive and -resistant cells, but did not inhibit the p-glycoprotein pump; in vivo, serum levels of DPPE were 3 to 5 mumol/L at the end of 80 minutes and 1 to 2 mumol/L after 440 minutes of infusion. Of 48 patients monitored for a minimum of four DPPE/chemotherapy treatment cycles, 16 (33%) progressed, 12 (25%) stabilized, 12 (25%) improved, and eight (17%) responded (one complete and seven partial remissions). Four of 11 subjects who did not respond to the 80-minute infusion regimen improved with the 440-minute infusion; one had a partial remission of melanoma. In more than 600 patient-treatments, bone marrow toxicity was negligible (mean absolute neutrophil count [ANC] > 2.0 x 10(9)/L). Acute CNS symptoms associated with DPPE infusions were of relatively short duration (1 to 4 hours); delayed toxicity attributable to DPPE consisted of mild nausea and/or fatigue (1 to 2 days). CONCLUSION: Although preliminary, the results suggest that more structured trials should be performed to determine whether DPPE may increase the therapeutic index of certain chemotherapy drugs.

Salutary clinical response of prostate cancer to antiandrogen withdrawal: assessment of flutamide in an in vitro paradigm predictive of tumor growth enhancement.

Salutary clinical responses to withdrawal of flutamide have been widely reported, indicating the potential of this arylalkylamine antiandrogen to stimulate the growth of prostate cancer. Flutamide is known to inhibit cytochrome P450-mediated testosterone synthesis and metabolism. Our laboratory has shown that arylalkylamine potencies in three in vitro assays of P450 binding or function correspond to a propensity of the drugs to enhance tumor growth in vivo. Accordingly, we measured inhibition by flutamide of (a) histamine binding to cytochrome P450 in rat liver microsomes, as determined spectrally, (b) P450-mediated demethylation of aminopyrine, and (c) DNA synthesis in mouse spleen cells stimulated by concanavalin A, and we compared its potencies in these assays with those of other arylalkylamine pharmaceuticals. Flutamide inhibited histamine binding to P450 (Ki = 31 +/- 7 microM), aminopyrine demethylation (Ki = 39 +/- 2 microM), and mitogenesis (IC50 = 12 +/- 1 microM). In overall potency, it ranked with a group of eight drugs, including the antiestrogen tamoxifen, all linked with enhanced tumor growth. In the context of clinical observations that some patients with prostate cancer benefit from flutamide withdrawal, our findings underline concerns that many arylalkylamine drugs have the potential to stimulate the growth or development of malignancies, including prostate cancer. Tumor growth enhancement by flutamide and other arylalkylamines may result from drug perturbation and/or induction of histamine-binding P450 enzymes involved in the synthesis of steroid and eicosanoid mediators that regulate gene function and cell growth.

Biochemical and ultrastructural studies suggest that the effects of thapsigargin on human platelets are mediated by changes in intracellular calcium but not by intracellular histamine.

The involvement of intracellular histamine in thapsigargin (Tg)-induced platelet aggregation was studied. Platelet aggregation induced by 0.25 and 0.5 microM Tg was not accompanied by a rise in intracellular histamine but a significant (p < 0.01) increase in the level of intracellular histamine was observed at 1 microM Tg. Preincubation of platelets with inhibitors of histamine metabolizing enzymes had little effect on intracellular histamine levels in platelets stimulated by 0.5 microM Tg. In addition, the inhibitors of histidine decarboxylase (HDC), alpha-methyl histidine (alpha-MH) and alpha-fluoromethyl histidine (alpha-FMH) failed to inhibit Tg-induced aggregation. The intracellular histamine receptor antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine. HCl (DPPE), inhibited Tg-induced aggregation but with IC50 values dependent on the concentration of agonist used. The inhibitory effects of DPPE on Tg-induced aggregation were not reversed by the addition of histamine to saponin-permeabilized platelets suggesting non-histamine mediated effects of DPPE on Tg-induced aggregation. Tg stimulated an increase in the cytosolic free calcium concentration which was unaffected by DPPE indicating that the effects of DPPE are also not due to the inhibition of mobilization of cytosolic calcium. The ultrastructural studies suggest that the major Tg-induced changes (pseudopod formation and granule centralization) are consistent with a primary role for Tg to mobilize calcium; DPPE had very little effect on these ultrastructural changes. The results indicate that the effects of Tg on human platelets are mediated by an increase in cytosolic calcium but not by intracellular histamine.

H3 receptor antagonist, thioperamide, inhibits adrenal steroidogenesis and histamine binding to adrenocortical microsomes and binds to cytochrome P450.

1. Thioperamide (TP), an imidazole and a highly potent, specific antagonist of the histamine H3 receptor, inhibited the secretion of cortisol from bovine isolated adrenocortical cells (IC50 0.20 microM) and in the rat (5 mg kg-1) prevented both basal and stress-induced secretion of corticosterone. 2. In adrenocortical microsomes, low affinity binding of [3H]-histamine (KD 27.7 microM) was potently inhibited by TP (Ki 0.33 microM). 3. In adrenocortical microsomal membranes, both histamine and TP yielded type II difference absorption spectra, characteristic of the interaction between imidazole and cytochrome P450 enzymes. Dissociation constants for binding to P450, calculated from spectral data, were 15.9 microM and 1.5 mM for histamine, and 0.3 microM and 3.7 microM for TP. 4. In view of previously reported evidence for an intracellular mediator role of histamine in platelets, the present findings suggest a physiological role for histamine in the modulation of adrenal P450 monooxygenases that generate adrenocortical steroids. 5. The results suggest that direct adrenocortical inhibition by thioperamide at a non-H3 intracellular site must be taken into account in studies designed to elucidate functional roles of H3 receptors.

The antiproliferative properties of tamoxifen and phenothiazines may be mediated by a unique histamine receptor (?H3) distinct from the calmodulin-binding site.

N,N-diethyl-2-[(4-phenylmethyl)-phenoxy]-ethanamine HCl (DPPE), a novel histamine antagonist (?H3), which selectively binds with high affinity to the antiestrogen-binding site (AEBS/?H3), inhibits the activity of calmodulin-dependent myosin light chain kinase (MLCK) only at concentrations greater than 1 mM, as opposed to tamoxifen (TAM), which has an IC50 = 4 microM in the same assay. This suggests that the antiestrogen-binding site is distinct from the site on calmodulin which binds TAM and phenothiazines. However, at an in vitro concentration of 1 X 10(-6) M, the antiproliferative effects of DPPE and several phenothiazines, which also compete for binding to AEBS/?H3, are about equal; this suggests that affinity for AEBS/?H3 rather than that for the calmodulin-binding site may correlate with clinically relevant antigrowth effects of these compounds.

N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine (DPPE) a chemopotentiating and cytoprotective agent in clinical trials: interaction with histamine at cytochrome P450 3A4 and other isozymes that metabolize antineoplastic drugs.

PURPOSE: N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine HCl (DPPE), an intracellular histamine (HA) antagonist with chemopotentiating and cytoprotective properties, is currently in phase 2 and 3 clinical trials in breast and prostate cancer. DPPE modulates growth at in vitro concentrations that antagonize HA binding to cytochromes P450 in rat liver microsomes. HA inhibits P450 metabolism of some drugs. Recent in vitro studies in human colon cancer cells have linked DPPE enhancement of paclitaxel, doxorubicin and vinblastine cytotoxicity to inhibition of the P-glycoprotein (P-gp) pump. Many substrates of P-gp are also substrates of CYP3A4, a P450 isozyme that metabolizes a variety of antineoplastic agents and is highly expressed in some malignant tissues. Therefore, we assessed whether (a) DPPE and HA interact at CYP3A4 and other P450 human isozymes, and (b) DPPE inhibits the catalytic activity of CYP3A4. METHODS: Using spectral analysis, we measured DPPE and HA binding to insect microsomes that express human P450 isozymes 1A1, 2B6, 2D6 or 3A4. Employing thin-layer chromatography, we assessed the metabolism of DPPE by each isozyme and DPPE inhibition of testosterone metabolism by CYP3A4 and by rat liver microsomes. RESULTS: (1) DPPE evoked "type I" (substrate site binding) absorbance-difference spectra with CYP2D6 (K(S) = 4.1 +/- 0.4 microM), CYP3A4 (K(S) = 31 +/- 15 microM) and CYP1A1 (K(S) = 40 +/- 9 microM), but not with CYP2B6. (2) In correspondence with the binding studies, DPPE was metabolized by CYP2D6, CYP3A4 and CYP1A1; no metabolism occurred with CYP2B6. (3) HA evoked "type II" (heme iron binding) absorbance-difference spectra with all four isozymes, with K(S) values in the range 80-600 microM. DPPE inhibited HA (600 microM) binding to CYP2D6 (IC50 = 4 microM, 95% CI= 1.8-8.9 microM) and CYP1A1 (IC50 = 135 microM: 95% CI = 100-177 microM), but stimulated HA (500 and 1000 microM) binding to CYP3A4 (EC50 = 155 microM, 95% CI = 104-231 microM). DPPE did not affect HA binding to CYP2B6. (4) DPPE inhibited the metabolism of testosterone by CYP3A4. The concentration/effect curve was biphasic: DPPE inhibited metabolism by 30% at the first site (IC50 = 3 microM, 95% CI = 0.5-25.5 microM), and an additional 70% inhibition occurred at the second site (IC50 = 350 microM, 95% CI = 215-570 microM). A similar result was observed with rat liver microsomes. CONCLUSION: DPPE is a substrate for CYP3A4, CYP2D6 and CYP1A1, but not CYP2B6. DPPE inhibits testosterone metabolism by interacting at two sites on CYP3A4, the first correlating with its K(S) value to bind the substrate site and the second, with its EC50 value to enhance HA binding to the heme iron. We postulate that (1) the inhibitory effect of DPPE on CYP3A4 activity is mediated directly at the substrate site and indirectly by its enhancement of the binding of HA to the heme moiety; (2) in tumor cells that express high constitutive levels of CYP3A4, potentiation of chemotherapy cytotoxicity by DPPE results, in part, from inhibition of CYP3A4-mediated metabolism and P-gp-mediated efflux of antineoplastic drugs; (3) in normal cells that express low constitutive levels of the isozyme, cytoprotection by DPPE results, in part, from induction of CYP3A4 and P-gp, resulting in an increase both in metabolism and efflux of antineoplastic drugs.

Murine and human hematopoietic colony formation: a possible regulatory role for intracellular histamine.

Increasing number of data suggests that locally produced histamine is involved in regulation of hematopoiesis. In this study the granulocyte/macrophage (CFU-GM) colony formation by normal murine or human bone marrow cells, leukaemic colony formation (CFU-L) by a murine leukemia cell line (WEHI 3B), and colony formation by bone marrow cells from patients with chronic myeloid leukemia (CML) have been examined. We detected mRNA and protein expression of histidine decarboxylase (HDC), the only enzyme responsible for histamine synthesis both in normal bone marrow progenitor cells and in leukaemic progenitors. The significance of in situ generated histamine was shown on colony formation by inhibitory action of alphaFMH (blocking HDC activity, i.e. de novo histamine formation) and by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]-ethanamine-HCl (DPPE) disturbing the interference of histamine with intracellular binding sites. These data provide further confirmation of the role of histamine in development and colony formation of bone marrow derived cells.

Phase II trial of tesmilifene plus mitoxantrone and prednisone for hormone refractory prostate cancer: high subjective and objective response in patients with symptomatic metastases.

PURPOSE: Symptomatic, hormone refractory prostate cancer (HRCAP) is a major cause of morbidity with a median survival of less than 12 months and a 2-year survival of only up to 10% in most series. Mitoxantrone has been approved by the Food and Drug Administration for HRCAP. Preliminary data suggest that DPPE (N,N-diethyl-2-[4-(phenylmethyl) phenoxy]-ethanamine) or tesmilifene modulates cytotoxics to enhance the anticancer effect. In this phase II trial we assessed whether there is sufficient evidence of enhanced efficacy of DPPE and mitoxantrone to lead to a phase III clinical trial. MATERIALS AND METHODS: A total of 29 patients with a median age of 73 years, of whom 10% were older than 80 years, with progressive HRCAP received 5.3 mg/kg DPPE intravenously every 3 weeks, 12 mg/m mitoxantrone intravenously every weeks and 5 mg prednisone orally twice daily. All patients had pain at presentation, while 97% had bone metastases, 10% had liver metastases and 17% had lung metastases. Median prostate specific antigen (PSA) was 210 ng/ml (IQR 77 to 430). RESULTS: Of the patients 75% had some pain improvement, 66% had decreased analgesia, 59% had a PSA decrease of 50% or greater and 45% had a PSA decrease of 75% or greater. Actual (not actuarial) 2-year survival was 21%. CONCLUSIONS: Despite major limitations of historical comparison the PSA decrease and decreased symptoms with DPPE-mitoxantrone-prednisone compare favorably to those of mitoxantrone-prednisone and docetaxel-estramustine in the literature. The 2-year survival rate of 21% mandates further assessment. This will be tested in a phase III Southwest Oncology Group trial.