Preliminary results of concurrent radiotherapy and chemotherapy with cis-platinum, vincristine, and bleomycin in bulky, advanced cervical carcinoma: A pilot study

Twenty-four patients with bulky (greater than 4 cm), advanced (stages IIB-IVA) carcinoma of the uterine cervix were prospectively treated with a concurrent combination of radiotherapy (RT) and chemotherapy (CT). RT consisted of 4400 cGy (22 fractions) to the whole pelvis and a 1400-cGy boost to the parametrium. This was followed by two to three intracavitary brachytherapy courses. CT consisted of one to four course (median, three) of cisplatin (50 mg/m2) on Day 1, vincristine (1 mg/m2) on Day 2, and bleomycin (25 mg/m2) on Days 2-4. CT was started on the first day of external radiation and the scheduled course interval was 21 days. Among the 20 evaluable patients who completed at least one course of chemotherapy and a full course of radiation, 13 (65%) achieved complete response and 5 (25%) had partial response. Fatal complication occurred in 1 patient with stationary disease who died of septic shock due to ruptured pyometra. The other patient with primary stage IVA disease had progressive disease with ascites appearance after two courses of CT and later expired. Transient drug fever occurred in 19 (40.4%) of the 47 bleomycin-containing CT cycles. Grade 2 or 3 hematological toxicities occurred in 16 (30.2%) of a total of 53 CT cycles. Treatment delays of 1 to 7 days occurred in 15 (28.3%) CT cycles. Except for the case of septic shock, all of the other toxicities were generally tolerable and reversible. From this preliminary result we concluded that this particular combination of RT and CT in bulky, advanced cervical carcinoma is effective in enhancing local pelvic tumor control and well tolerated if strict selection of accrued patients is applied. Further investigation to assess its impact on long-term survival is in progress.

Rice cystatin: bacterial expression, purification, cysteine proteinase inhibitory activity, and insect growth suppressing activity of a truncated form of the protein

A cDNA clone that encodes oryzacystatin, a cysteine protease inhibitor from rice, was isolated and expressed in Escherichia coli BL-21 (DE3) using an expression plasmid under the control of a T7 RNA polymerase promoter. The construct pT7OC 9b encoded a fusion protein containing 11 amino acid residues of the NH2 terminus of the bacterial protein phi 10 and 79 residues of oryzacystatin lacking 23 NH2-terminal residues of the wild-type protein. Recombinant oryzacystatin (ROC) constituted approximately 10% of the total bacterial protein mass and was purified in a single step by anion-exchange chromatography. The inhibitory activity of ROC toward papain (Ki = 3 x 10(-8) M) was comparable with that of the naturally occurring protein isolated from rice. Caseinolytic activity in midgut homogenates from seven species of stored product insects was inhibited from 18 to 85% by ROC, whereas the same activity was inhibited from 14 to 69% by the serine proteinase inhibitor phenylmethylsulfonyl fluoride. Midguts of stored product insects apparently contain both cysteine proteinases and serine proteinases, but the relative amounts vary with the species. When fed to the red flour beetle, Tribolium castaneum, 10 wt% ROC in the diet suppressed growth approximately 35% relative to that of the control group of insects.

Metabolism of 4'-azidothymidine. A compound with potent and selective activity against the human immunodeficiency virus

4'-Azidothymidine (ADRT) is a novel nucleoside analog, that selectively inhibits human immunodeficiency virus replication in human lymphocytes. Unlike the dideoxyribonucleoside analogs and 3'-azido-2',3'-dideoxythymidine (AZT), ADRT retains the 3'-hydroxy group. The pathways of ADRT metabolism were elucidated by determining: (i) the kinetics of the interactions of ADRT and its metabolites with enzymes of thymidine metabolic pathways, (ii) the pool sizes of phosphorylated metabolites, and (iii) the nature of ADRT incorporation into human DNA. ADRT is not a substrate for thymidine phosphorylase, but is metabolized by kinases. Thymidine kinase phosphorylates ADRT to ADRT monophosphate (ADRT-MP). For this enzyme, ADRT has a Ki value of 5.2 microM, in comparison to a Km value of 0.7 microM for thymidine. The Km value of ADRT toward thymidine kinase is 8.3 microM and the rate of ADRT phosphorylation is 1.4% that of thymidine phosphorylation. ADRT-MP has a low affinity toward thymidylate kinase (a Ki value of 28.9 microM versus a Km value of 0.56 microM for thymidylate), and toward thymidylate synthase (a Ki value of 180 microM versus a Km value of 8 microM for deoxyuridylate). The results suggest that ADRT can be activated effectively by cellular kinases without significant interference of normal thymidine metabolism. In cultured human lymphocytes (A3.01, H9, and U937 cells), ADRT was phosphorylated efficiently to ADRT 5'-triphosphate (ADRT-TP), which is the major metabolite of ADRT. The intracellular concentrations of ADRT-TP ranged from 1 to 3.3 microM after 24 h of incubation with 2 microM of ADRT and the half-life of ADRT-TP varied from 3 to 6 h. Although ADRT-TP is a poor competitive inhibitor against dTTP toward DNA polymerases alpha and beta with Ki values of 62.5 and 150 microM, respectively. ADRT-MP was found to be internally incorporated into cellular DNA. The extent of ADRT-MP substitution for dTMP in DNA was 1 in 6979 for A3.01 cells incubated with 2.9 microM ADRT for 24 h. Internal incorporation of ADRT-MP contrasts with the mechanism of other 2',3'-dideoxynucleoside analogs (i.e. AZT, ddC, ddI, d4T...), which are DNA chain terminators. This finding indicates that a 3'-deoxy structure in a nucleoside analog is not a prerequisite for anti-human immunodeficiency virus activity.

Prognostic assessment of tumor regression after external irradiation for cervical cancer

From February 1980 to December 1986, 428 cases of cervical cancer in Stage I through IVA were given curative radiation therapy at Chang Gung Memorial Hospital, Taipei. All of them received external irradiation and intracavitary brachytherapy. The degree of tumor regression was assessed immediately before the first intracavitary brachytherapy treatment. Patients were classified at this time as having (a) no gross residual tumor, or (b) gross residual tumor. Factors found to be associated with tumor regression by logistic regression analysis were stage, age and hemoglobin level. Patients with advanced cancer (Stage III, IVA), young age (less than 40 years), and low hemoglobin level (less than 10 g/dl) had a low incidence of no gross residual tumor. Five-year survival rate was 77% in patients with no gross residual tumor and 31% in patients with gross residual tumor (p less than 0.001). This significant difference held true even when one compared these two groups stage for stage; the difference was 77% versus 41% (p less than 0.001) in Stage II and 72% versus 28% (p less than 0.001) in Stage III. The local relapse rate was 59% in the gross residual tumor groups, significantly greater (p less than 0.001) than the 12% found in the no gross residual tumor group. It was concluded that patients whose tumors did not regress after external pelvic irradiation tended to recur after intracavitary brachytherapy, most often locally. This would justify a more aggressive treatment to improve local tumor control in this subset of high risk patients.

A theoretical model for understanding dentists' behavior in treating patients with AIDS

This paper attempts to expand on a model from the theory of reasoned action to help us identify and better understand the reasons dentists do or do not treat dental patients with, or at risk for, AIDS. We propose in the model that the dentist's actual behavior in treating dental patients with, or at risk for, AIDS, in his or her practice is a function of both his or her intention to treat such patients and his or her nonvolitional factors relevant to the behavior. The dentist's intention to treat patients with AIDS or HIV infection, or those belonging to high risk groups, is influenced by two belief components: (1) attitudinal variables, which are the dentist's beliefs about the consequences of treating such patients and the value that these consequences have for him or her; and (2) normative variables, which indicate the dentist's perceptions of how his or her reference groups view the treatment of such patients in his or her practice and his or her motivation to comply with those views. Finally, both the two belief components and the nonvolitional factors are affected by the personal characteristics and the environmental variables.

Choroideremia: a study of two families

Choroideremia is a bilateral and progressive chorioretinal degenerative disease of X-linked inheritance. In Taiwan, the disease has rarely been reported. We recently found 8 male patients and 5 female carriers in two Chinese families with choroideremia and studied the clinical, psychophysical and electrophysiological properties of the disease. All patients revealed characteristic fundus and fluorescein angiographic changes in retinal pigment epithelium, and choroidal atrophy of variable extent. The severity of the functional impairments paralleled the fundus changes and the patients' age. However dark adaptation and the visual field were affected earlier than visual acuity and color sensation. In addition, rod cell impairment was found to be more severe than cone cell impairment in the electroretinographic studies. On the other hand, all carriers revealed similar diffuse punctate pigmentary changes and only mild abnormalities in dark adaptation. These findings may suggest that in choroideremia patients the photoreceptor cells are very sensitive to the influence of the choroidal atrophy, and that rod cells may be even more vulnerable than cone cells.

Use of high-density vitreous substitutes in the removal of posteriorly dislocated lenses or intraocular lenses

We successfully used high-density vitreous substitutes to remove four dislocated crystalline lenses and three dislocated intraocular lenses (IOLs) from the vitreous cavity. Fluorosilicone oil (300 cs) was used to remove the four lenses and one of the IOLs. Perfluorophenanthrene (Vitreon) was used to remove the other two dislocated IOLs. The dislocated lenses or IOLs were floated by the high-density vitreous substitutes and removed safely without damaging the retina; there were no intraoperative complications. Postoperative residual fluorosilicone oil droplets were found in one case.

Multiple forms of dynamin are encoded by shibire, a Drosophila gene involved in endocytosis

Dynamin was discovered in bovine brain tissue as a nucleotide-sensitive microtubule-binding protein of relative molecular mass 100,000. It was found to cross-link microtubules into highly ordered bundles, and appeared to have a role in intermicrotubule sliding in vitro. Cloning and sequencing of rat brain dynamin complementary DNA identified an N-terminal region of about 300 amino acids which contained the three consensus elements characteristic of GTP-binding proteins. Extensive homology was found between this domain and the mammalian Mx proteins which are involved in interferon-induced viral resistance, and with the product of the VPS1 locus in Saccharomyces cerevisiae, which has been implicated both in membrane protein sorting, and in meiotic spindle pole separation. Dynamin-containing microtubule bundles were not observed in an immunofluorescence study of cultured mammalian cells, but a role for a GTP-requiring protein in intermicrotubule sliding during mitosis in plants has been reported. We report here that Drosophila melanogaster contains multiple tissue-specific and developmentally-regulated forms of dynamin, which are products of the shibire locus previously implicated in endocytic protein sorting.

Ocular fundus examination in premature infants

In order to better acknowledge the ocular fundus picture in premature infants and to determine the incidence and clinical course of retinopathy of prematurity (ROP), from October 1987 to April 1989, 187 cases with a gestational age of less than 38 weeks or a birth weight of less than 2,500 g were enrolled for examination and follow-up study with indirect ophthalmoscope. One hundred and fifty cases (80.21%) were free from ROP bilaterally. Thirty-seven cases (19.79%) had ROP. Except for one case that showed unilateral regressed ROP, all were bilaterally affected. The mean birth weight and gestational age in the nonROP group were 1,824 +/- 426 g and 33.6 +/- 2.9 weeks, respectively, and in the ROP group were 1,395 +/- 490 g and 30.7 +/- 3.9 weeks, respectively. The difference for both factors between the two groups were statistically significant (p less than 0.05). Several specific fundus features were noticed in a high percentage of the nonROP group, these included a small cup to disc (C/D) ratio, pigmented ring around the disc, hypopigmented fundus and a greenish-gray color in the peripheral vascularized retina. In addition, 8.2% of this group had persistent primary vitreous remnant, and 5.6% had retinal hemorrhage. The macular development was subdivided into three stages. In both the ROP and nonROP groups, the difference of gestational age at each advancing stage was statistically significant by the Student t-test. No delay in macular development was noticed in the ROP group.(ABSTRACT TRUNCATED AT 250 WORDS)

High-dose-rate afterloading technique in the radiation treatment of uterine cervical cancer: 399 cases and 9 years experience in Taiwan

Carcinoma of the uterine cervix has been the leading malignant neoplasm treated in our department. A comparative study was carried out using conventional low dose rate (LDR) with 137Cs sources (less than or equal to 100 cGy/hr) versus high dose rate (HDR) with 60Co sources (greater than 100 cGy/min) in the intracavitary (IC) application following external pelvic irradiation. A total of 399 patients were treated with external RT plus HDR radiation treatment alone from February 1980 through December 1985. Stage IIb and IIIb comprised 79.4% of cases (317 cases). The rate of initial complete response of the tumor, local control, and survival rate seemingly were better in the HDR group, but there was no significant difference statistically. The actuarial survival rates in all cases/definitive RT cases are 85%/85% for Stage 0-IIa, 53%/70% for IIb, 43%/49% for IIIa, 43%/53% for IIIb, 42%/47% for IVa, respectively. Complications were similar and the rectal complications were slightly higher in HDR group. The combination of pelvic irradiation with HDR intracavitary irradiation was more convenient for patients and also for personnel. The HDR technique may be a good substitution for IC treatment.

Promoting heart health for Southeast Asians: a database for planning interventions

This paper is a report of baseline data that the authors collected on the prevalence of hypertension in a sample of 397 Southeast Asian immigrants residing in central Ohio and the implications of those data for the design of ethnically approved and scientifically valid interventions. The context for collection of these data over a 9-month period in 1989 is described. Baseline demographic characteristics including distributions by ethnicity, sex, age, and length of stay in the United States, as well as family heart health history, hypertension level, and heart health awareness of these subjects are presented. For example, 85 percent of the immigrants did not know what could be done to prevent heart disease. Implications for the design of ethnically approved and scientifically valid prevention strategies are discussed. Based on these data, the authors realized that multiple health education strategies tailored to what they were learning about Southeast Asians would be needed. Through Southeast Asian leaders, they were led to using wall calendars, with words specific to each Southeast Asian language, that had a monthly heart health slogan as one avenue to reach Southeast Asians. Another strategy was to develop videotapes featuring cultural content but including heart health "commercials." The authors concluded that, although scientific validity of risk reduction interventions are important, customizing these strategies to ethnically specific modes of interaction are equally important.

Prognostic factors of nasopharyngeal carcinoma: a multivariate analysis

Between 1979 and 1985, 561 patients with nasopharyngeal carcinoma were reviewed to determine prognostic factors that may influence survival. Sex (p = 0.294) and histopathology (p = 0.677) had no correlation to the actuarial survival, whereas the site of cervical metastasis (p = 0.001) and the radiation doses to the nasopharynx and regional lymph nodes (p = 0.03) were both significant when one used univariate analyses. Cox's multivariate regression model revealed that the presence rather than the site of distant metastases was the single most important independent factor influencing the treatment outcome (p less than 0.0001). The addition of chemotherapy, on the other hand, did not show a survival benefit even when one took available confounding factors into account. There are, however, survival advantages associated with: (a) young age (less than or equal to 40 years), (b) asymptomatic status, (c) Stage I or II lesions, and (d) biopsy via nasopharynx instead of neck nodes. These favorable prognostic factors may be used for therapeutic guidance and end-result reporting.

A comparison of diabetic control status between urban and rural diabetic patients in Taiwan

Between 1985 and 1987, in two urban and five rural areas in Taiwan, a total of 16,636 subjects aged 40 or over were screened for diabetes mellitus according to the WHO criteria. Four hundred and fifty-two previously diagnosed patients and 274 newly diagnosed patients were found. All were non-insulin-dependent diabetics. The blood glucose control status was compared between the urban and rural previously diagnosed diabetics. Those living in the rural areas were found to have better control with a higher percentage under regular treatment. Stepwise multiple regression failed to discover a significant correlation between control status and any of the following factors: sex, age, body mass index (BMI), diabetic duration, treatment regularity, exercise, occupation, education, family income and the presence of hypertension or large vessel diseases. About 30% of the patients in rural areas and 40% in urban areas were poorly controlled. This indicates that our diabetic control program should be strengthened.

[Behcet's disease with ocular involvement in Taiwan: a joint survey of six major ophthalmological departments]

A total of 103 cases with ocular involvement of Behcet's disease, seen over a period of 19 years (1970 to 1988), were collected from the ophthalmological departments of 6 major medical centers in Taiwan. The yearly number of patients who first visited these hospitals from 1979 through 1983 was about 5 cases and about 14 cases from 1984 to 1988. The domiciles of the patients were most commonly (51.5%) in Northern Taiwan. All 103 patients were Chinese, of which 78 (75.7%) were men and 25 (24.3%) were women; the male to female ratio was 3.1. Extraocular symptoms of Behçet's disease, major or minor, and their frequencies among these patients included; oral ulcers, 97.1%, skin lesions, 74.8%; genital ulcers, 61.2%; arthritis, 47.6%; gastrointestinal lesions, 14.6%; epididymitis, 5.8%; central nervous system lesions, 2.9%; vascular lesions, 1.9%; pulmonary lesions, 2.9% and urinary lesions, 4.9%. Fifty-one (49.5%) patients were of the complete type and 52 (50.5%) of the incomplete type. The peak distribution of ages at the onset of the ocular lesions, was from 20 to 40 years. As for visual prognosis, 37.9% of the 198 diseases eyes had a visual acuity of 0.5 or better, 9.1% between 0.5 and 0.1, 25.3% between 0.1 and 0.01 and 27.8% were 0.01 or worse. In 24 (12.1%) eyes, the vision was completely lost. In HLA studies, a significantly increased incidence of HLA-A26 (p less than 0.01) and HLA-B51 (p less than 0.001) was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Microalbuminuria and diabetic complications in Chinese non-insulin-dependent diabetic patients: a prospective study

Urinary albumin excretion rate (AER) was monitored for periods of up to 3 years and 8 months with an ELISA method in 63 non-insulin-dependent diabetic Chinese subjects and was compared with 50 normal subjects. AER was 3.15 +/- 0.25 micrograms/min (M +/- SE) with a range of 0.27-8.40 micrograms/min for the normal subjects and 7.11 +/- 0.50 (2.11-19.45) micrograms/min for the diabetic subjects. The latter had significantly higher AER (P less than 0.0005). Age, sex, duration of diabetes, HbA1c and BMI did not correlate with AER in the diabetics. The presence of hypertension was found to be accompanied by an accelerated elevation of AER (5.96 +/- 1.58 vs 10.16 +/- 2.17 micrograms/min, at the beginning and at the end of the observation, respectively). Once hypertension became evident, control of blood pressure to a level comparable to that of the non-hypertensive group was not sufficient to halt the deterioration of urinary albumin excretion.

A comparison of newly and previously diagnosed diabetics in Taiwan

Between 1985 and 1986, during a population survey of diabetes in 1 urban and 5 rural areas of Taiwan, a total of 11,478 adults aged 40 or older were screened. Capillary whole blood glucose was determined with a glucometer (Ames Co.) The diabetic criteria followed the WHO designations. From this survey, a comparison of 225 newly diagnosed and 383 previously diagnosed diabetics was conducted. Multiple regression analysis revealed a highly significant correlation for all diabetics with regard to age, body mass index, family history and hypertension, but no specific correlation to habitat. Mean fasting glucose levels in previously and newly diagnosed diabetics were 172 and 158 (males 158 vs 147 and females 184 vs 165) mg/dl, respectively, which suggest that treatment is apparently inadequate in this population. The prevalent rate (%) of retinopathy for previously and newly diagnosed diabetics was 45.2 and 28.3 (males 42.8 vs 33.3 and females 47.5 vs 24.8), respectively. The prevalence is as common as those reported in western countries. In conclusion, previously diagnosed diabetics had higher fasting glucose concentrations and prevalent rates of retinopathy than newly diagnosed diabetics, and these findings were particularly prominent in females.

Conjunctival concretions. Polarized microscopic, histopathologic, and ultrastructural studies

To elucidate the pathophysiologic features of conjunctival concretions, we performed polarized microscopic examinations, immunocytochemical studies, histochemical stains, and electron microscopic studies of concretions obtained from five patients with chronic conjunctivitis. Electron-dense secretory granules, ranging from 0.2 to 0.5 micron in diameter and stained positively for periodic acid-Schiff and mucicarmine, were found in the superficial lining epithelial cells of the pseudogland of Henle. In view of the granular and membranous figures reflecting degenerating epithelial cells and secretory granules in the concretions, we argue that the concretions, are mostly composed of the mucinous secretion of the transformed conjunctival glands admixed with the degenerative products of the epithelial cells.

Synthetic HIV-2 protease cleaves the GAG precursor of HIV-1 with the same specificity as HIV-1 protease

A 99-amino acid protein having the deduced sequence of the protease from human immunodeficiency virus type 2 (HIV-2) was synthesized by the solid phase method and tested for specificity. The folded peptide catalyzes specific processing of a recombinant 43-kDa GAG precursor protein (F-16) of HIV-1. Although the protease of HIV-2 shares only 48% amino acid identity with that of HIV-1, the HIV-2 enzyme exhibits the same specificity toward the HIV-1 GAG precursor. Fragments of 34, 32, 24, 10, and 9 kDa were generated from F-16 GAG incubated with the protease. N-terminal amino acid sequence analysis of proteolytic fragments indicate that cleavage sites recognized by HIV-2 protease are identical to those of HIV-1 protease. The verified cleavage sites in F-16 GAG appear to be processed independently, as indicated by the formation of the intermediate fragments P32 and P34 in nearly equal ratios. The site nearest the amino terminus is quite conserved between the two viral GAG proteins (...VSQNY-PIVQN...in HIV-1,...KGGNY-PVQHV...in HIV-2). In contrast, the putative second site (...IPFAA-AQQKG...) of HIV-2 GAG shares minimal sequence identity with site 2 of HIV-1 GAG (...SATIM-MQRGN...). These sequence variations in the substrates suggest higher order structural features that may influence recognition by the proteases. Pepstatin A inhibits HIV-2 protease, whereas 1,10-phenanthroline and phenylmethylsulfonylfluoride do not; these results are in agreement with the finding that proteases of HIV and other retroviruses are aspartyl proteases.

Evaluating the impact of P.L. 99-252 on decreasing smokeless tobacco use

Literally, Public Law 99-252 (otherwise known as the Comprehensive Smokeless Tobacco Health Education Act of 1986) includes provisions that are informational in nature. Implicitly, however, this law is considered part of the federal effort in disease prevention and health promotion. This paper reviews the societal and legislative context of that act and presents a plan to evaluate the impact of this law on decreasing smokeless tobacco use. The uniqueness of this plan is its incorporation of nine disciplinary perspectives in the derivation of indicators to measure process, impact, and outcome measures for decreasing smokeless tobacco use. A basic prevention strategy is suggested by this interdisciplinary approach. In addition, specific lessons could be applied from the history of successes in public health to decreasing smokeless tobacco use.

Gene rearrangement of cutaneous T-cell lymphoma

Gene Rearrangement is considered to be a helpful tool for diagnosis of cutaneous T-cell lymphoma. In this study five patients with clinical diagnosis of cutaneous T-cell lymphoma were reviewed for their clinical presentation, skin biopsies and surface marker phenotypes. Southern blot analysis of DNA extracted from their skins revealed that rearrangement of T-cell receptor beta chain (TCRB) genes happened in three patients but rearrangement of immunoglobulin heavy chain genes was absent. TCRB rearrangement could also detect lymphoma involvement of lymph nodes, peripheral blood and bone marrow in our patients. In these conditions, systemic therapy is suggested.

An epilogue to evaluating the impact of P.L. 99-252 on decreasing smokeless tobacco use

In a previous paper, "Evaluating the Impact of P.L. 99-252 on Decreasing Smokeless Tobacco Use," the context of this law and the theoretical framework for an evaluation plan for measuring its impact were described. In this paper, the methodology and selected findings from this project as well as their implications are discussed. This discussion includes the identification of the six indicators considered to be the most relevant, valid, reliable, accessible, and practical for measuring the impact of this law on decreasing smokeless tobacco use, as well as a report on the feasibility analysis of three of these indicators. Pilot data on two indicators--pounds of smokeless tobacco sold and incidence rates of tobacco-induced leukoplakia--are presented and analyzed.

Identification of the carboxyl-terminal amino acids important for the ADP-ribosylation activity of Pseudomonas exotoxin A

The ADP-ribosylation domain of Pseudomonas exotoxin A (PE) has been identified to reside in structural domain III (residues 405-613) and a portion of domain Ib (residues 385-404) of the molecule (Hwang, J., FitzGerald, D. J., Adhya, S., and Pastan, I. (1987) Cell 48, 129-136). To further determine the carboxyl end region essential for ADP-ribosylation activity, we constructed sequential deletions at the carboxyl-terminal of PE. Our results show that a clone with a deletion of the carboxyl-terminal amino acid residues from Arg-609 to Lys-613 and replaced with Arg-Asn retained wild-type PE ADP-ribosylation activity. Deletion of the terminal amino acid residues from Ala-596 to Lys-613 and replaced with Val-Ile-Asn reduced ADP-ribosylation activity by 75%, while deletions of 36 or more amino acids from the carboxyl terminus completely lose their ADP-ribosylation activity. These modified PEs were also examined for their ability to block PE cytotoxicity. Our results shown that modified PEs which lost their ADP-ribosylation activity correspondingly lost their cytotoxicity. Furthermore, extracts containing PE fragments without ADP-ribosylation activity were able to block the cytotoxic activity of intact PE. Our results thus indicate that carboxyl-terminal amino acids in the Ser-595 region are crucial for ADP-ribosylation activity and, consequently, cytotoxicity of PE. The modified PEs which have lost their ADP-ribosylation activity may also be a route to new PE vaccines.