Biomedical subjects

J W Hamilton

Publications and source records attributed to J W Hamilton.

At least 37 records · Page 2Linked to original sources

PubMed1999

Effects of mitomycin C and carboplatin pretreatment on multidrug resistance-associated P-glycoprotein expression and on subsequent suppression of tumor growth by doxorubicin and paclitaxel in human metastatic breast cancer xenografted nude mice.

Overexpression of P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP), and several other proteins has been associated with development of multidrug resistance by cancer cells, which represents a significant obstacle to successful treatment by chemotherapy. We had previously demonstrated that a single noncytotoxic dose of mitomycin C (MMC), carboplatin, or one of several other DNA cross-linking agents suppressed mRNA expression of the mdr1 gene coding for Pgp, leading to a subsequent suppression of Pgp protein levels and a concomitant decrease in drug efflux. Pretreatment with MMC led to a 5- to 10-fold decrease in the ED50 for cell killing by a subsequent agent such as the Pgp substrate, doxorubicin, but did not affect killing by the non-Pgp substrate, cisplatin. In this study, we report that MMC and carboplatin each significantly suppressed Pgp protein levels in human MDA-MB-435 cells xenografted as solid tumors into the lateral mammary fat pads of female nude mice, with a similar time course as had previously been observed in cell culture. Pretreatment of mice with MMC or carboplatin 48-72 h prior to receiving either doxorubicin or paclitaxel caused a significantly greater reduction in tumor growth rate compared to either agent alone or the combination given simultaneously. These data suggest that a combination chemotherapy regimen consisting of a DNA cross-linking agent given to modulate the MDR phenotype, followed by a second cytotoxic agent, may be an effective treatment for human patients with de novo or late stage acquired multidrug-resistant malignancies.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

Selective modulation of collagenase 1 gene expression by the chemotherapeutic agent doxorubicin.

Matrix metalloproteinases (MMPs) play a crucial role in tumor cell invasion and metastasis due to their ability to digest basement membrane and extracellular matrix components, thereby facilitating cell movement through connective tissues. At noncytotoxic concentrations, i.e., concentrations lower than those normally used in cancer chemotherapy, the anthracycline doxorubicin specifically inhibited collagenase 1 (MMP-1) gene expression in the highly invasive and metastatic human melanoma cell line A2058. This inhibition was specific for collagenase 1 because it did not affect the expression of two other MMPs, gelatinase A (MMP-2) and gelatinase B (MMP-9). The reduction in collagenase 1 expression correlated with a decrease in the invasive ability of tumor cells through a collagen type I matrix and was independent of the cytotoxic and antiproliferative effects usually associated with this anticancer drug. The selective modulation of collagenase 1 expression by nontoxic doses of doxorubicin suggests a novel application for this chemotherapeutic agent, perhaps in combination therapy, because it decreases the invasive/metastatic potential of melanoma cells that are otherwise unaffected by this drug.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Detection of mitomycin C-DNA adducts in vivo by 32P-postlabeling: time course for formation and removal of adducts and biochemical modulation.

Mitomycin C (MMC) is a DNA cross-linking agent that has been used in cancer chemotherapy for over 20 years, yet little is known either qualitatively or quantitatively about MMC-induced DNA adduct formation and repair in vivo. As an initial means of investigating this, we used a recently developed 32P-postlabeling assay to examine the formation and loss of MMC-DNA adducts in the tissues of a simple in vivo model test system, the chick embryo, following treatment with a chemotherapeutic dose of MMC. As early as 15 min after MMC treatment, four adducts could be detected in the liver which were tentatively identified as the (CpG) N2G-MMC-N2G interstrand cross-link, the bifunctionally activated MMC-N2G monoadduct, and two isomers (alpha and beta) of the monofunctionally activated MMC-N2G monoadduct. The (GpG) N2G-MMC-N2G intrastrand cross-link appears to be a poor substrate for nuclease P1 and/or T4 kinase and was not evaluable by this assay. Levels of all four detectable adducts increased substantially within the first 2 h after MMC treatment, reached maximal levels by 6 h, and decreased progressively thereafter through 24 h, although low levels of certain adducts persisted beyond 24 h. Lung and kidney had comparable levels of total MMC adducts, which were approximately 60% those of the liver, and there were no significant differences in the proportion of specific adducts among the three tissues. The interstrand cross-link represented approximately 13-14% of the total MMC adducts, which is approximately 5-fold greater than the proportion of CpG sites in the genome. In addition, the interstrand cross-link was selectively decreased after 16 h relative to the three monoadducts, suggesting preferential repair. The effect of modulating different components of the Phase I and Phase II drug metabolism on MMC adduct formation, using either glutethimide, 3,4,3',4'-tetrachlorobiphenyl, dexamethasone, buthionine sulfoximine, ethacrynic acid, or N-acetylcysteine pretreatments, was examined to characterize the possible pathways of MMC metabolism and adduct formation in vivo. Surprisingly, none of these pretreatments had a significant effect on individual or total adducts with the exception of dexamethasone, which caused an almost 2-fold proportional increase in all four adducts in the liver.

Acetylcysteine↗

PubMed1998

Role of chest CT scanning in the management of patients presenting with head and neck cancer.

BACKGROUND: The detection of synchronous tumors, whether they be second primaries or distant metastases, in patients with head and neck carcinoma drastically affects prognosis and may alter management. Computerized tomographic (CT) scanning of the chest is an effective screening investigation in this group of patients, both in the detection of synchronous second primary tumors, the incidence of which in this study is 15%, and for accurate staging of metastatic pulmonary disease. The incidence of synchronous tumors in patients who are initially seen with head and neck squamous cell carcinoma (HNSCC) has been reported in large retrospective studies as being between 1% and 3%. These may be either second primary tumors or metastases, and the lung is the commonest site for both. METHODS: Eighty-one head and neck cancer patients (67 primary and 14 secondary referrals) treated at the Royal Liverpool University Hospital between 1994 and 1996 underwent CT scanning of the chest with ultrasound of the liver as part of their routine staging. The results were compared with standard chest x-rays also performed in each patient. RESULTS: Fourteen patients had pulmonary tumors detected on the chest CT scan. In 67 patients, the scan was negative. Patients with negative scans tended not to have neck node metastases (64%), whereas patients with positive scans were much more likely to have neck node metastases with negative necks present in only 36% of patients. Where multivariate analysis was carried out, there was a correlation between neck node metastases and positive CT scans of the chest (estimate = 0.5755, standard error = 0.3066, chi2(1) = 6.73, p .047). The sensitivity of chest x-ray compared with CT scan was only 21 % and the specificity 99%. The positive predictive value of a chest x-ray was 75% and the negative predictive value 86%. Intra-abdominal lesions were detected in two patients, one in the liver and one in the adrenal gland. In the latter patient, this was an isolated lesion, but in the former, the chest scan was also positive. In the 67 patients, who were initially seen at the Royal Liverpool Hospital (primary referrals), the incidence of synchronous tumors was 15%. CONCLUSIONS: Synchronous tumors, whether they be second primary tumors or distant metastases, are more common in patients initially seen with head and neck cancer than is realized, their incidence being significantly higher in those patients with cervical metastases. Computerized tomographic scanning of the chest is a more effective screening investigation than chest x-ray in this group of patients and is now used routinely in our department prior to undertaking major head and neck surgery.

Adult↗

PubMed1998

Developmentally specific effects of the DNA cross-linking agent mitomycin C on phosphoenolpyruvate carboxykinase gene expression in vivo: correlation with changes in chromatin structure within the promoter region of the gene.

Previous studies in our laboratory have demonstrated that genotoxic chemical carcinogens have strong preferential effects on expression of certain inducible genes at nonovertly toxic doses in vivo. The effects of the DNA cross-linking agent and chemotherapy drug, mitomycin C (MMC), on expression of the developmental and hormone-regulated gene, phosphoenolpyruvate carboxykinase (PEPCK), were examined in chick embryo liver in vivo as a function of development and were compared with changes in the chromatin structure of the PEPCK gene promoter. The liver PEPCK gene was fully hormone inducible as early as 8 days of embryonic development but was refractory to MMC until after day 10. This onset of responsiveness to MMC was correlated with qualitative changes in the pattern of DNase I hypersensitive sites (DHS) within the PEPCK promoter. There was also a gradual decrease and then a complete loss of both hormone inducibility and MMC responsiveness between 14 and 17 days of development that was correlated with a quantitative change in the overall DNase sensitivity of the liver PEPCK gene promoter over this period. These results suggest that carcinogen sensitivity of the PEPCK gene is related to its ability to respond to its normal induction signals and that chromatin structure may play a central role in these effects.

Animals↗

PubMed1998

Developmental regulation of the 3-methylcholanthrene- and dioxin-inducible CYP1A5 gene in chick embryo liver in vivo.

The cDNA sequences for two dioxin-inducible cytochrome P450s in chicken, CYP1A4 and CYP1A5, have recently been reported which correspond to two dioxin-inducible forms of P450 previously designated as TCDDAHH and TCDDAA, respectively. The developmental expression of CYP1A4-associated aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity and its association with expression of the Ah receptor had previously been characterized in chick embryo liver. The purpose of this study was to examine the developmental regulation of the second dioxin-inducible P450 gene, CYP1A5, in chick embryo liver. A partial gene sequence for CYP1A5 indicated that the intron/exon organization of this gene was identical to that of the CYP1A1 and CYP1A2 mammalian genes and was present in a single copy in the genome. CYP1A5 mRNA was expressed basally in chick embryo liver and was highly inducible by the Ah receptor ligands, 3-methylcholanthrene, beta-naphthoflavone, and 3,4,3', 4'-tetrachlorobiphenyl (TCB), but not by the phenobarbital analog, glutethimide. CYP1A5 mRNA levels were increased 40- to 50-fold within 5 h after a single TCB treatment, corresponding to a 30- to 40-fold increase in the transcription rate of the CYP1A5 gene at this time point. In contrast to a previous report that CYP1A5 mRNA expression was inducible by estradiol, we observed no effects of estradiol or dexamethasone on CYP1A5 mRNA expression, either alone or in combination with TCB. Basal and TCB-inducible CYP1A5 mRNA expression was maximal in liver at 8 days of development and remained high throughout the remainder of embryonic development. Thus, CYP1A5 appears to be regulated in a very similar manner to CYP1A4 in chick embryo liver.

Animals↗

PubMed1998

Mucosal melanoma of the head and neck.

Two hundred and fifty-nine patients with mucosal melanoma of the head and neck were reviewed. The data of these patients were obtained from the records of the Department of Head and Neck Oncology at the University of Liverpool and from the Merseyside and Cheshire Cancer Registry. Survival curves were constructed using the life table method and differences were investigated by the Log Rank Test. Prognostic factors were further analysed by Cox's proportional hazards model. Melanomas of the nasal cavities and sinuses accounted for 69%; 22% occurred in the oral cavity and 9% in the pharynx, larynx and upper oesophagus. In 49% treatment was by wide local resection and in 8% by irradiation. Thirty-six per cent had combined modalities of treatment. Primary site recurrence occurred in 52% and 36% developed nodal recurrence. The tumour specific survival at 5 years was 45% at 10 years 28%, at 20 years 17% and closely resembled the observed survival. Young male patients tended to have a favourable prognosis as did those treated surgically. Radiotherapy on its own was ineffective. Amelanotic melanoma had a particularly poor survival. Whereas site had no effect on survival. The study confirms the poor prognosis of mucosal melanoma of the head and neck. Young patients should be offered radical surgical treatment combined with radical radiotherapy if feasible as this offers the best chance of cure.

Adult↗

PubMed1998

Molecular basis for effects of carcinogenic heavy metals on inducible gene expression.

Certain forms of the heavy metals arsenic and chromium are considered human carcinogens, although they are believed to act through very different mechanisms. Chromium(VI) is believed to act as a classic and mutagenic agent, and DNA/chromatin appears to be the principal target for its effects. In contrast, arsenic(III) is considered nongenotoxic, but is able to target specific cellular proteins, principally through sulfhydryl interactions. We had previously shown that various genotoxic chemical carcinogens, including chromium (VI), preferentially altered expression of several inducible genes but had little or no effect on constitutive gene expression. We were therefore interested in whether these carcinogenic heavy metals might target specific but distinct sites within cells, leading to alterations in gene expression that might contribute to the carcinogenic process. Arsenic(III) and chromium(VI) each significantly altered both basal and hormone-inducible expression of a model inducible gene, phosphoenolpyruvate carboxykinase (PEPCK), at nonovertly toxic doses in the chick embryo in vivo and rat hepatoma H411E cells in culture. We have recently developed two parallel cell culture approaches for examining the molecular basis for these effects. First, we are examining the effects of heavy metals on expression and activation of specific transcription factors known to be involved in regulation of susceptible inducible genes, and have recently observed significant but different effects of arsenic(III) and chromium(VI) on nuclear transcription factor binding. Second, we have developed cell lines with stably integrated PEPCK promoter-luciferase reporter gene constructs to examine effects of heavy metals on promoter function, and have also recently seen profound effects induced by both chromium(VI) and arsenic(III) in this system. These model systems should enable us to be able to identify the critical cis (DNA) and trans (protein) cellular targets of heavy metal exposure leading to alterations in expression of specific susceptible genes. It is anticipated that such information will provide valuable insight into the mechanistic basis for these effects as well as provide sensitive molecular biomarkers for evaluating human exposure.

Animals↗

PubMed1998

Binding of nuclear proteins associated with mammalian DNA repair to the mitomycin C-DNA interstrand crosslink.

Mitomycin C (MMC) is a DNA crosslinking agent that is used in cancer chemotherapy. Unlike the DNA crosslinks formed by cisplatin or psoralen, which significantly distort the DNA helix, the MMC crosslink does not significantly disturb the B-DNA helical structure. Nonetheless, MMC interstrand crosslinks and total MMC adducts are rapidly removed in vivo. We investigated whether mammalian nuclear proteins can recognize and bind to a model 23 bp DNA duplex containing a single MMC lesion. Electrophoretic mobility shift assays identified two complexes in nuclear extracts from rodent cell lines and three complexes in human cell lines, containing proteins that appeared to specifically recognize the MMC interstrand crosslink. Nuclear extracts from normal and excision repair-defective mutant Chinese hamster ovary (CHO) cell lines, from human Xeroderma Pigmentosum (XP) complementation group A and E cell lines, and a Fanconi's Anemia cell line were also examined. The UV-20 CHO line, defective in ERCC-1, was missing one of the two rodent complexes. Two of the three human complexes were also absent in the XPA human cell line and the intensity of the third complex was significantly diminished. Based on these results, a model for MMC crosslink recognition is proposed in which ERCC-1 and XPA each participate in formation of one or more multimeric complexes on the crosslinked DNA and XPA also aids in the formation, but is not a component of a higher molecularweight multimeric complex that may contain ERCC-1.

Animals↗

PubMed1997

Adenoid cystic carcinoma of the head and neck.

Adenoid cystic carcinoma has a long natural history but frequently proves fatal. The present study describes 108 patients with an adenoid cystic carcinoma of the head and neck seen over a 30-year period. Analysis of the data utilized both univariate and multivariate methods. Forty per cent of patients had tumours arising from the oral cavity and half of these were in the hard palate; 29% occurred in the major salivary glands; 41% of tumours were locally advanced at presentation and 11% had lymph node metastases at this time. The histological pattern was solid in 25%, cribriform in 40% and tubular in 20%. In addition, 15% of patients had a polymorphous low-grade adenocarcinoma and these were analysed separately. Primary site recurrence was more common in the presence of locally advanced tumours at presentation (T3-4) (P = 0.0093). Only six patients had surgery with adjuvant radiotherapy. Six patients had no curative treatment, 21 had primary radiotherapy, 39 had local excision and 42 radical excision. The actuarial primary site recurrence rate was 100% at 30 years. The neck node recurrence rate was 23% at 15 years. Tumour specific survival was 40% at 20 years. Solid histology had a worse prognosis than other histological types (P = 0.0429) but those patients with polymorphous low-grade adenocarcinomas fared very well. Patients with tumours of the hard palate fared better than those patients with tumours at other sites (P = 0.0301). Early disease at the primary site (T1-2) was a good prognostic sign (P = 0.0013). Patients with neck node metastases at presentation tended to do badly (P = 0.009).

Carcinoma, Adenoid Cystic↗

PubMed1997

The magnitude of random errors in acoustic rhinometry and re-interpretation of the acoustic profile.

By measuring the effect of incomplete acoustic seal and increasing nosepiece insertion depth on the derived nasal acoustic profile, this study quantifies the random errors that may arise in the course of the clinical practice of acoustic rhinometry using the insert nosepiece. The relative movement of the nose and nosepiece also enables us to separate the contribution of each to the acoustic curve. Sixteen volunteers were tested using a commercial rhinometer. As a consequence of this study we are able to formulate the following conclusions: (1) The first minimum of the nasal acoustic profile is due to the end of the nosepiece, but may be further diminished by the position of the nosepiece tip on or within the nose. (2) The second minimum is due to the nasal valve, to which the head of the inferior turbinate contributes. (3) Acoustic rhinometry is extremely sensitive to acoustic leaks and results obtained without a fluid acoustic sealant cannot be considered valid. (4) The errors associated with the nosepiece insertion technique are very small unless the nosepiece is forced into the nasal vestibule.

Acoustics↗

PubMed1997

Subtotal petrosectomy in the treatment of cerebrospinal fluid fistulae of the lateral skull base.

Cerebrospinal fluid (CSF) fistulae almost invariably lead to meningitis, even in the absence of other clinically obvious sequelae of the fistula such as a CSF fluid leak. The only effective means of reducing the risk of meningitis is surgical closure of the fistula. If surgery is to be recommended to patients with CSF fistulae even if they are currently asymptomatic, the morbidity of the procedure must be a principal determinant of the chosen technique. Recovery after the extracranial approach to a CSF fistula is much more rapid than after an intracranial procedure. The extracranial route is also free of the long-term risk of epilepsy which accompanies a craniotomy. The principal disadvantage of the lateral extracranial approach, failure of treatment, has been largely eliminated following studies into the obliteration of simple bony cavities using free adipose grafts. This paper describes our use of the extracranial approach to closure of CSF fistulae of the lateral skull base.

Adult↗

PubMed1997

Suppression of P-glycoprotein expression and multidrug resistance by DNA cross-linking agents.

Overexpression of the trans-membrane drug efflux pump P-glycoprotein is one of the major mechanisms by which cancer cells develop multidrug resistance. We demonstrated previously that noncytotoxic doses of various genotoxic chemicals, particularly DNA cross-linking agents, preferentially altered expression of inducible genes. These effects occurred principally at the transcriptional level and were closely correlated temporally with DNA damage. Because the mdr1 gene coding for P-glycoprotein has been reported to be highly inducible, we were interested in the effects of genotoxic cancer chemotherapy agents on its expression. We report that the DNA cross-linking agent mitomycin C significantly suppressed mRNA and protein expression of P-glycoprotein and decreased the rate of drug efflux. Mitomycin C pretreatment also significantly increased the sensitivity of cancer cells to subsequent killing by the P-glycoprotein substrate doxorubicin, decreasing the ED50 by 5- to 10-fold. Suppression of P-glycoprotein expression was also observed with subtoxic doses of the DNA cross-linking agents cisplatin, BMS181174, and chromium(VI). These effects occurred in both human and rodent cell lines; in cell lines derived from colon, breast, leukemia, neuroblastoma, and hepatoma tumors; and under both monolayer and "spheroid" culture conditions. These results suggest the basis for novel clinical cancer chemotherapy regimens aimed at drug-resistant tumors, in which a sub-chemotherapeutic dose of a DNA cross-linking agent is used to modulate the multidrug resistance phenotype prior to treatment with a second cytotoxic agent.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

The diving reflex in non-eosinophilic non-allergic rhinitis.

The usual nasal response to head submersion in aquatic mammals is an increase in resistance to airflow, the so-called diving reflex. Although less well developed in humans, it is nevertheless present. It is likely to occur due to a relative increase of parasympathetic over sympathetic control of the nasal vasculature. Non-eosinophilic non-allergic rhinitis is thought to be due to a similar imbalance and we have attempted to establish whether the diving reflex is abnormal in this condition. Sixteen normal subjects and 18 subjects with non-eosinophilic non-allergic rhinitis (NENAR) underwent simulated diving using the "cold face test'. Expiratory total nasal airway resistance (ETR) was measured before and after the test by means of active anterior rhinomanometry. There was no significant increase in ETR in the normal group but a significant increase in ETR in the NENAR group (pre-test median ETR-0.464 kPa.s.l(-1). post-test median ETR 0.667 kPa.s.l(-1), (Wilcoxon's signed rank test P < 0.05). The change in median ETR in the NENAR group was also significantly higher than the median change in ETR in the normal group (Mann-Whitney, extract probability P = 0.04). We conclude the nasal airway response to simulated diving in NENAR is abnormal.

Airway Resistance↗

PubMed1996

The effect of intranasal fluticasone propionate on the diving reflex in patients with non-eosinophilic non-allergic rhinitis.

The usual nasal response to head submersion in aquatic mammals is an increase in resistance to airflow, the so-called "diving reflex". Although less well-developed in humans, it is nevertheless present. It is likely to occur due to a relative increase of parasympathetic over sympathetic control of the nasal vasculature. Non-eosinophilic non-allergic rhinitis is thought to be due to a similar imbalance and we have attempted to establish whether the diving reflex is abnormal in this condition and whether intranasal fluticasone propionate for 6 weeks has any effect in modifying the nasal response.

Administration, Intranasal↗

PubMed1996

Free revascularized jejunal loop repair following total pharyngolaryngectomy for carcinoma of the hypopharynx: report of 90 patients.

Ninety patients with carcinoma of the hypopharynx underwent pharyngolaryngectomy and reconstruction with a jejunal free autograft. Fifty-five patients had primary surgery and 35 salvage surgery for recurrence after radiotherapy. Following primary surgery 28 patients had postoperative radiotherapy and 27 did not. Complications occurred in 51 per cent of patients, the most common being necrosis of the jejunal graft (19 per cent); 12 per cent developed significant stenosis and 4 per cent died in the perioperative period. Eleven per cent of patients developed a fistula. The total number of complications diminished as the experience of the unit increased. Median follow-up was 4.9 years. Of patients treated with primary surgery, 48 per cent developed primary site recurrence (at 3 years) and 53 per cent neck node recurrence (at 5 years). The tumour-specific 5-year survival rate for all patients was 42 per cent. Following primary surgery 28 per cent survived for 5 years and after salvage surgery the rate was 59 per cent. Positive resection margins and extensive neck disease adversely affected survival (P = 0.02 and P = 0.001 respectively). The free revascularized jejunal graft is a safe and predictable method of repair following total pharyngolaryngectomy.

Adult↗

PubMed1995

Preferential effects of the chemotherapeutic DNA crosslinking agent mitomycin C on inducible gene expression in vivo.

The immediate effects of a single dose of the chemotherapeutic DNA crosslinking agent, mitomycin C (MMC), on the expression of several constitutive and drug-inducible genes were examined in a simple in vivo system, the 14 day chick embryo. We observed no effect of MMC on the steady-state mRNA expression of the constitutively expressed beta-actin, transferrin, or albumin genes. In contrast, MMC treatment significantly altered both the basal and drug-inducible mRNA expression of two glutethimide-inducible genes, 5-aminolevulinic acid (ALA) synthase and cytochrome P450 CYP2H1. The basal expression of these genes was transiently but significantly increased over a 24 hr period following a single dose of MMC. Conversely, MMC significantly suppressed the glutethimide-inducible expression of these genes when administered 1 to 24 hr prior to the inducing drug. The effects of MMC on both basal and drug-inducible ALA synthase and CYP2H1 mRNA expression were principally a result of changes in the transcription rates of these genes. In contrast, MMC treatment had little or no effect on glutethimide-induced expression of ALA synthase or CYP2H1 when administered 1 hr after the inducing drug, suggesting that a very early event in the induction process represents the target for these MMC effects. Covalent binding studies demonstrated that the effects of MMC on gene expression were closely correlated temporally with formation of [3H]-porfiromycin-DNA adducts. These results support the hypothesis that genotoxic chemicals specifically target their effects to inducible genes in vivo.

5-Aminolevulinate Synthetase↗

PubMed1995

Peter Shaffer's Amadeus as a further expression of twinship conflict.

In Peter Shaffer's Amadeus, which has much of a thematic and symbolic nature in common with its forerunners, Equus and The Royal Hunt of the Sun, stemming genetically from the unique sibling rivalry of twinship, there is more pronounced emphasis on the influence of envy and vengeance on human behavior than in the other two plays. It is postulated that the success of Equus and its implications pertinent to the competitive aspect of the relationship with his twin brother stirred appreciable intrapsychic turmoil in Shaffer and was a decisive motivating factor in his writing of Amadeus.

Humans↗