Causas y factores asociados a las caídas del adulto mayor / Causes and factors associated to falls among the Elder / Causas e fatores associados aquedas no idoso

Objetivo: Determinar la prevalencia, las características, las causas (intrínsecas y extrínsecas) y los factores asociados a las caídas del adulto mayor. Metodología: Estudio transversal y descriptivo con 183 adultos mayores atendidos en un consultorio de geriatría de un hospital público. Para la recolección de los datos fueron utilizados los instrumentos del perfil demográfico, Mini Examen del Estado Mental, Índice de Barthel, Escala de Lawton y Brody, Escala de Depresión Geriátrica; así como el número, las características y causas de las caídas. Para el análisis se utilizó estadística descriptiva y para evaluación del riesgo razón de momios, con significancia < 0.05. Resultados: La prevalencia de caídas fue del 24%. Los lugares más frecuentes de estas fueron en la sala, el dormitorio y la calle. De aquellos que cayeron un 9.1% fueron hospitalizados y el 59.1% sufrieron heridas. Entre las consecuencias de las caídas se identificaron la dificultad para caminar, miedo a sufrir una nueva caída y cambio de domicilio. Los factores asociados con las caídas accidentales fueron tener una edad > 80 años, no estar jubilado y presentar síntomas depresivos. Conclusiones: Las caídas pueden estar asociadas a diferentes factores y el profesional de la salud debe estar capacitado para identificarlos, a fin de crear planes de atención individualizada para evitar eventos adversos.

Objective: To determine the prevalence, characteristics, causes (intrinsic and extrinsic), and factors associated to falls among the elder. Methodology: This is a transversal and descriptive study with 183 elder individuals attending a geriatric unit in a public hospital. Data were collected using a Demographic Profile, the Mini-mental state examination (MMSE), Barthel Scale, Lawton-Brody Instrumental Activities of Daily Living Scale (IADL), and Geriatric Depression Scale (GDS), as well as registers on the number, characteristics and causes of the falls. Descriptive statistics, and risk odds ratios at the level of p < 0.05 were calculated. Results: The prevalence of falls was 24%. The most frequent places of occurrence were the living room, the dorm, and the street. From those who had falls, 9.1% were hospitalized and 59.1% suffered diverse wounds. Among the consequences of falls were: subsequent difficulty to walk; fear to suffering new falls; and changes in the residence location. Among the factors associated to accidental falls were: being 80 years and older; not being work-exempted; and having depressive symptoms. Conclusions: Falls can be associated to diverse factors and thus, health professionals need to be trained to identified them, and provide individualized care plans to prevent possible adverse events.

Objetivo: Determinar a prevalência, as características, causas (intrínsecas e extrínsecas) e os fatores associados aquedas no idoso. Metodologia: Estudo transversal e descritivo com 183 idosos atendidos no ambulatório de geriatria de um hospital público. Para a coleta de dados foram utilizados os instrumentos de perfil demográfico, Mini Exame do Estado Mental, Índice de Barthel, Escala de Lawton e Brody, Escala de Depressão Geriátrica; assim como o número, as características e causas das quedas. Para a análise foi utilizada a estatística descritiva e a razão de prevalência com significância estatística p < 0,05. Resultados: A prevalência de quedas foi de 24%. Os locais mais frequentes destas foram na sala, no dormitório e na rua. Daqueles que caíram, 9,1% foram hospitalizados e 59,1% tiveram ferimentos. Entre as consequências das quedas, foram identificadas a dificuldade para caminhar, medo de sofrer uma nova queda e mudança do domicilio. Os fatores associados as quedas foram ter idade > 80 anos, não ser aposentado e apresentar sintomas depressivos. Conclusão: As quedas podem estar associadas a diferentes fatores e o profissional de saúde deve estar capacitado para identifica-los com a finalidade de criar planos de cuidados individualizados para evitar esses eventos adversos.

Systematic approach for severe respiratory failure due to novel A (H1N1) influenza.

AIM: In April 2009, a novel influenza A (H1N1) virus appeared in Mexico. It rapidly acquired the characteristics of a pandemic disease. Our objective is to present a case series of mechanically ventilated patients with severe influenza, treated with a systematic approach. METHODS: Prospective, observational, single-center study in a University Hospital. A (H1N1) virus was confirmed by rRT-PCR. In this report, we only considered patients that required mechanical ventilation (MV). All patients received antibiotics, steroids and oseltamivir from the time of admission. The main strategies incorporated in the systematic approach were a lung-protective strategy, PEEP adjusted for each patient, protocol-guided sedoanalgesia, restrictive fluid management, weaning protocol, and prolonged prone ventilation and extracorporeal membrane oxygenation (ECMO) as rescue therapies. RESULTS: We studied 19 patients: age 41 ± 13 years old, APACHE II 16 ± 7 and SOFA 8 ± 4. All patients presented PaO2/FiO2 ≤ 200 before connection to MV. Their worst values within the first 24 hours for oxygenation index, PaO2/FiO2, and PaCO2 on MV were 21.8 ± 13, 98 ± 39, and 48 ± 16 mmHg, respectively. Sixteen patients achieved ARDS; three exhibited acute lung injury criteria. Ten required a prone position, and two required ECMO (one patient required both therapies). Time on MV was 16 ± 13 days. Length of stay in the ICU and in hospital was 18 ± 12 and 28 ± 17 days, respectively. Mortality was 21%. CONCLUSION: Severe hypoxemia and a high rate of rescue therapies were observed among our patients. Nevertheless, mortality was lower than previously reported in comparable populations, which may be related to the management by a critical care team and the use of a systematic approach for ventilatory and non-ventilatory therapeutic strategies.

Efectos de la ventilación en posición prono extendida en SDRA secundario a influenza A(H1N1) / Impact of extended prone position ventilation in patients with severe ARDS secondary to influenza A(H1N1)

Introducción: Durante la pandemia por influenza A(H1N1), Chile alcanzó una de las tasas de casos más alta del mundo. Nuestro hospital recibió numerosos afectados el 2009 y 2010. Evaluamos el impacto de ventilación en posición prono (VPP) extendida, en las variables respiratorias de pacientes con SDRA grave secundario a influenza, y comparamos estos resultados con los obtenidos en otras series de VPP. Métodos: Estudio prospectivo, intervencional en UCI. Los pacientes recibieron oseltamivir y antibióticos y fueron manejados según protocolos (ventilatorio y no ventilatorio). Aquellos con criterios de SDRA grave fueron pronados hasta un índice de oxigenación <10. Se registraron parámetros de intercambio gaseoso, ventilatorios y desenlaces clínicos. Resultados: 12 pacientes con SDRA grave (edad 46+/-12 años, 7 hombres, APACHE II 17+/-6, SOFA 9+/-3) requirieron VPP, que se instauró a las 14(7-39) horas de ventilación mecánica (VM) y se mantuvo por 72(54-96) horas. Ningún paciente experimentó complicaciones mayores. La PaO2:FiO2 mejoró de 82(63-101) mmHg a 145(138-223) mmHg, (p<0.001). El tiempo en VM fue 20+/-13 días y en UCI 22+/-13 días. La mortalidad hospitalaria fue 25 por ciento y no cambió en el seguimiento de más de 8 meses. Este comportamiento con VPP fue similar al observado en otras series de SDRA grave. Conclusión: Los resultados obtenidos sugieren que la VPP resultó segura y se asoció a mejoría del intercambio gaseoso en pacientes con SDRA por influenza A(H1N1). Aunque el número reducido de pacientes no permite sacar mayores conclusiones, la VPP extendida podría ser de utilidad en los casos más graves causados por esta nueva influenza.

Introduction: During pandemic for influenza A(H1N1), Chile achieved one of the highest rates of infection worldwide. On 2009 and 2010, our hospital received a large number of infected patients. We evaluated the impact of extended prone position ventilation (PPV) on respiratory variables from severe ARDS patients secondary to this influenza. We also compared these results with those obtained with PPV in other series. Methods: Prospective, interventional study, performed in a mixed-ICU. Patients received oseltamivir and antibiotics, and were treated according to protocols (ventilatory and non-ventilatory). Severe ARDS patients were proned until oxygenation index was < 10. Oxygen exchange, ventilatory parameters and clinical outcomes were registered. Results: 12 severe ARDS patients (46+/-12 y.o., 7 men, APACHE II 17+/-6, SOFA 9+/-3) required PPV, which was started 14(7-39) hours after mechanical ventilation (MV) initiation, and it was maintained for 72(54-96) straight hours. No major complication was described. Three patients needed two periods of PPV. PaO2:FiO2 improved significantly with PPV from 82(63-101) mmHg to 145(138-223) mmHg, (p<0.001). Time on MV was 20+/-13 days, and LOS in UCI was 22+/-13 days. Hospital mortality was25 percent and remained unchanged for at least 8 month of follow-up. PPV had the same effect than in other severe ARDS series. Conclusion: Our results suggest PPV is safe and it was associated with improvement in oxygen exchange in ARDS secondary to A(H1N1) influenza. Although the small number of patients does not allow drawing any major conclusion, we believe PPV can be useful to treat severe ARDS cases due to influenza infection.

Gynecologic malignancies in older women.

The aging of the population is a social phenomenon that will present a challenge to clinical practice in the 21st century. Women constitute a majority of the elderly population as they outlive males by 5 to 7 years. Ovarian, endometrial, and vulvar cancers are diseases seen more commonly in postmenopausal and elderly women. Cervical cancer continues to be a significant problem in the elderly and is usually detected at a later stage in that population than in younger patients. Accordingly, primary care clinicians ought to possess a thorough knowledge of gynecologic malignancies and should refer women who present with these disorders to a gynecologic oncologist. Ovarian cancer patients treated by a gynecologic oncologist are more likely to undergo proper surgical staging, leading to optimal debulking surgery and improved survival. Age, by itself, should not alter the diagnostic and therapeutic approach to gynecologic malignancy. Elderly patients can safely undergo radical pelvic surgery. Multiagent chemotherapy is also possible in the elderly without excess morbidity, and without compromise of response rates. Radiation therapy for cervical cancer appears to be as effective and is generally well tolerated. The Papanicolaou (Pap) test continues to be the primary screening tool for cervical cancer. Although transvaginal ultrasound seems to be useful in detecting early-stage ovarian cancer, its cost effectiveness for screening the general population remains to be demonstrated. The main considerations in the treatment of ovarian, endometrial, cervical, and vulvar cancer are discussed.

Activation of the Fas pathway independently of Fas ligand during apoptosis induced by camptothecin in p53 mutant human colon carcinoma cells.

The present study explored the role of the cell surface receptor Fas (CD95/APO-1) in apoptosis induced by camptothecin (CPT) in the HT29 colon carcinoma cell line. CPT-induced apoptosis was associated with high molecular weight DNA fragmentation as measured by filter elution. This fragmentation was inhibited by the caspase inhibitor, z-VAD-fmk and by cycloheximide, which also prevented proteolytic activation of caspase-3 and poly(ADP-ribose)polymerase cleavage. Under such conditions, Fas, Fas ligand, Bax, and p21 expression were increased and Fas recruited the FADD adaptor. Fas expression increase was blocked by cycloheximide but not by z-VAD-fmk, consistent with caspase activation downstream from Fas. Treatment of HT29 cells with FasL or with the CH-11 agonistic anti-Fas antibody potentiated the apoptotic response of cells treated with CPT. The anti-Fas blocking antibody ZB4 and the Fas-ligand inhibitor failed to protect HT29 cells from CPT-induced apoptosis. Such a protection was obtained by transient expression of constructs encoding a dominant-negative mutant of FADD, FADD in an antisense orientation and E8 or MC159 viral proteins that inhibit Fas-induced apoptosis at the level of FADD and procaspase-8, respectively. Together, these data show that topoisomerase I-mediated DNA damage-induced apoptosis involves activation of the Fas pathway without detectable Fas-ligand requirement in CPT-treated cells.

Initiation of DNA fragmentation during apoptosis induces phosphorylation of H2AX histone at serine 139.

Histone H2AX is a ubiquitous member of the H2A histone family that differs from the other H2A histones by the presence of an evolutionarily conserved C-terminal motif, -KKATQASQEY. The serine residue in this motif becomes rapidly phosphorylated in cells and animals when DNA double-stranded breaks are introduced into their chromatin by various physical and chemical means. In the present communication we show that this phosphorylated form of H2AX, referred to as gamma-H2AX, appears during apoptosis concurrently with the initial appearance of high molecular weight DNA fragments. gamma-H2AX forms before the appearance of internucleosomal DNA fragments and the externalization of phosphatidylserine to the outer membrane leaflet. gamma-H2AX formation is inhibited by N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone and the inhibitor of caspase-activated DNase, and it is induced when DNase I and restriction enzymes are introduced into cells, suggesting that any apoptotic endonuclease is sufficient to induce gamma-H2AX formation. These results indicate that gamma-H2AX formation is an early chromatin modification following initiation of DNA fragmentation during apoptosis.

DNA protein cross-links produced by NSC 652287, a novel thiophene derivative active against human renal cancer cells.

2, 5-bis(5-Hydroxymethyl-2-thienyl)furan (NSC 652287), is a representative of a series of thiophene derivatives that exhibit potent and selective antitumor activity against several tumor cell lines in the National Cancer Institute Anticancer Drug Screen. NSC 652287 has noticeable activity for the renal cell lines and produces cures in certain corresponding xenografts. The cellular mechanisms of action of NSC 652287 were therefore investigated in this study in greater detail. The most sensitive renal carcinoma cell line, A498, exhibited cell cycle arrest in G(0)-G(1) and G(2)-M at 10 nM NSC 652287, with increased p53 and p21(WAF1) protein. At higher concentrations, NSC 652287 still induced p53 elevation but with p21(WAF1) reduction and massive apoptosis. These results collectively suggested that NSC 652287 induced DNA damage. Using alkaline elution techniques, we found that NSC 652287 induced both DNA-protein and DNA-DNA cross-links with no detectable DNA single-strand breaks. These DNA-protein cross-links (DPC) persisted for at least 12 h after drug removal and their frequency was correlated with cytotoxicity in the renal cell lines studied. The most sensitive cells (A498) produced the highest DPC followed by the cell line with intermediate sensitivity (TK-10). DPC were minimal in the two resistant cell lines, ACHN and UO-31. Nonetheless, a similar degree of DPC occurred at doses imparting equitoxic effects. These results indicate that DNA is a primary target for the novel and potent anticancer thiophene derivative, NSC 652287. NSC 652287 did not cross-link purified DNA or mammalian topoisomerase I suggesting the importance of active metabolite(s) for the cross-linking activity.

Apoptotic response to camptothecin and 7-hydroxystaurosporine (UCN-01) in the 8 human breast cancer cell lines of the NCI Anticancer Drug Screen: multifactorial relationships with topoisomerase I, protein kinase C, Bcl-2, p53, MDM-2 and caspase pathways.

Derivatives of camptothecins, topoisomerase I inhibitors and 7-hydroxystaurosporine (UCN-01), a protein kinase C (PKC) inhibitor and cell cycle checkpoint abrogator, are promising anticancer drugs. We characterized the apoptotic response to camptothecin and UCN-01 for the 8 human breast carcinoma cell lines (MCF-7, MCF-7/ADR, T47D, HS578T, BT549, MDA-N, MDA MB231, MDA435) from the National Cancer Institute (NCI) Anticancer Drug Screen. MCF-7 and T47D cells exhibited marked resistance to apoptosis, whereas MCF-7/ADR (NCI/ADR-RES) and HS578T cells exhibited the most pronounced apoptotic response. Apoptotic response was not correlated with growth inhibition measured by sulforhodamine B (SRB) assay, indicating that apoptosis is not the only mechanism of drug-induced cell death. Measurements of topoisomerase I levels and cleavage complexes and of PKC isoforms demonstrated that primary target inhibition was not correlated with apoptotic response. Several key apoptotic pathways were evaluated. Only MCF-7 cells had wild-type p53, indicating that p53 is not required for drug-induced apoptosis. MCF-7 cells also showed the highest MDM-2 expression (along with T47D cells, which were also resistant to apoptosis). Bcl-2, Mcl-1 and caspases 2 and 3 protein levels varied widely, whereas Bax expression was comparable among cell lines. Interestingly, Bcl-2, Mcl-1 and Bcl-X(L) cumulative expressions were inversely correlated with apoptotic response. Our results provide a comparative molecular characterization for the breast cancer cell lines of the NCI Anticancer Drug Screen and demonstrate the diversity of cellular responses to drugs (apoptosis vs. cell cycle arrest) and the importance of multifactorial analyses for modulating/predicting the apoptotic response to chemotherapy.

Role of oxygen radicals generated by NADPH oxidase in apoptosis induced in human leukemia cells.

We have used a human leukemia cell line that, after homologous recombination knockout of the gp91-phox subunit of the phagocyte respiratory-burst oxidase cytochrome b-558, mimics chronic granulomatous disease (X-CGD) to study the role of oxygen radicals in apoptosis. Camptothecin (CPT), a topoisomerase I inhibitor, induced significantly more apoptosis in PLB-985 cells than in X-CGD cells. Sensitivity to CPT was enhanced after neutrophilic differentiation, but was lost after monocytic differentiation. No difference between the two cell lines was observed after treatment with other apoptosis inducers, including etoposide, ultraviolet radiation, ionizing radiation, hydrogen peroxide, or 7-hydroxystaurosporine. After granulocytic differentiation of both cell lines, CPT still induced apoptosis, suggesting independence from replication in fully differentiated and growth-arrested cells. Pyrrolidine dithiocarbamate (an antioxidant inhibitor of NF-kappaB) and catalase partially inhibited CPT-induced DNA fragmentation in granulocytic-differentiated PLB-985 cells, but had no effect in X-CGD cells. Flow cytometry analysis revealed that reactive oxygen intermediates were generated in CPT-treated PLB-985 cells. These data indicate that oxygen radicals generated by NADPH oxidase may contribute directly or indirectly to CPT-induced apoptosis in human leukemia and in neutrophilic-differentiated cells.

Early induction of apoptosis in hematopoietic cell lines after exposure to flavopiridol.

Flavopiridol (NSC 649890; Behringwerke L86-8275, Marburg, Germany), is a potent inhibitor of cyclin dependent kinases (CDKs) 1, 2, and 4. It has potent antiproliferative effects in vitro and is active in tumor models in vivo. While surveying the effect of flavopiridol on cell cycle progression in different cell types, we discovered that hematopoietic cell lines, including SUDHL4, SUDHL6 (B-cell lines), Jurkat, and MOLT4 (T-cell lines), and HL60 (myeloid), displayed notable sensitivity to flavopiridol-induced apoptosis. For example, after 100 nmol/L for 12 hours, SUDHL4 cells displayed a similar degree of DNA fragmentation to that shown by the apoptosis-resistant PC3 prostate carcinoma cells only after 3,000 nmol/L for 48 hours. After exposure to 1,000 nmol/L flavopiridol for 12 hours, typical apoptotic morphology was observed in SUDHL4 cells, but not in PC3 prostate carcinoma cells despite comparable potency (SUDHL4: 120 nmol/L; PC3: 203 nmol/L) in causing growth inhibition by 50% (IC50). Flavopiridol did not induce topoisomerase I or II cleavable complex activity. A relation of p53, bcl2, or bax protein levels to apoptosis in SUDHL4 was not appreciated. While flavopiridol caused cell cycle arrest with decline in CDK1 activity in PC3 cells, apoptosis of SUDHL4 cells occurred without evidence of cell cycle arrest. These results suggest that antiproliferative activity of flavopiridol (manifest by cell cycle arrest) may be separated in different cell types from a capacity to induce apoptosis. Cells from hematopoietic neoplasms appear in this limited sample to be very susceptible to flavopiridol-induced apoptosis and therefore clinical trials in hematopoietic neoplasms should be of high priority.

Novel 7-alkyl methylenedioxy-camptothecin derivatives exhibit increased cytotoxicity and induce persistent cleavable complexes both with purified mammalian topoisomerase I and in human colon carcinoma SW620 cells.

An alkylating camptothecin (CPT) derivative, 7-chloromethyl-10,11-methylenedioxy-camptothecin (7-CM-MDO-CPT) was recently shown to produce irreversible topoisomerase I (top1) cleavage complexes by binding to the +1 base of the scissile strand of a top1 cleavage site. We demonstrate that 7-CM-EDO-CPT (7-chloromethyl-10,11-ethylenedioxy-camptothecin) also induces irreversible top1-DNA complexes. 7-CM-MDO-CPT, 7-CM-EDO-CPT, and the nonalkylating derivative 7-ethyl-10,11-methylenedioxy-camptothecin (7-E-MDO-CPT) also induced reversible top1 cleavable complexes, which were markedly more stable to salt-induced reversal than those induced by 7-ethyl-10-hyroxy-CPT, the active metabolite of CPT-11. This greater stability of the top1 cleavable complexes was contributed by the 7-alkyl and the 10,11-methylene- (or ethylene-) dioxy substitutions. Studies in SW620 cells showed that 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT are more potent inducers of cleavable complexes and more cytotoxic than CPT. The reversal of the cleavable complexes induced by 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT was markedly slower after drug removal than that for CPT, which is consistent with the data with purified top1. By contrast to CPT, 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT were cytotoxic irrespective of the presence of 10 microM aphidicolin. These results suggest that 7-E-MDO-CPT, 7-CM-MDO-CPT, and 7-CM-EDO-CPT are more potent top1 poisons than CPT and produce long lasting top1 cleavable complexes and greater cytotoxicity than CPT in cells.

Cerebrospinal fluid homovanillic acid is reduced in untreated Huntington's disease.

We measured homovanillic acid (HVA), 5-hydroxy indole acetic acid (5-HIAA), and tryptophan (TP) in cerebrospinal fluid (CSF) of 20 neuroleptic-free patients with Huntington's disease (HD), and compared mean values with those from four control groups including 15 normal individuals, 38 patients with dystonia, 23 untreated patients with Parkinson's disease, and 61 patients with other neurological diseases (ONDs). The mean levels of HVA in the CSF of patients with HD were reduced compared with those from normal controls (p < 0.001), dystonic patients (p < 0.005), individuals with ONDs (p < 0.0001), and even from untreated parkinsonian patients (p < 0.05). 5-HIAA and TP levels in the CSF of patients with HD were not significantly different from those in the CSF of control patients. Our data suggest a reduced dopamine neurotransmission in HD and may account for the bradykinesia observed in our patients.

The effects of cisapride on plasma L-dopa levels and clinical response in Parkinson's disease.

Cisapride (CIS) is a prokinetic agent that increases gastrointestinal motility in normal individuals and improves constipation in Parkinson's disease (PD). We studied the effects of CIS on the clinical response and the peripheral pharmacokinetics of orally administered L-dopa given to patients with PD. Twenty patients with idiopathic PD and chronic constipation, whose response to L-dopa was suboptimal or characterized by fluctuations, agreed to participate in an open study that lasted for 2 weeks. Fourteen patients completed the study (mean age 65 +/- 9.3 years, mean duration of treatment 5.7 +/- 4.2 years, mean L-dopa daily doses 658.9 +/- 269.9 mg); six patients were excluded due to lack of compliance or changes in medication during the study. The end points of the study included the mean levels of L-dopa, the height of the peak of L-dopa in plasma, mean plasma levels of 3-OM-dopa, and the speed and quality of gait and visuomanual coordination before and during treatment with CIS. CIS increased peak plasma levels of L-dopa by 37% and the mean plasma levels of L-dopa by 13% with respect to those obtained with the same dose of L-dopa before the addition of CIS. Therefore, CIS appears to increase early absorption of L-dopa through acceleration of gastric emptying. CIS also increased plasma 3-OM-dopa levels, improved visuomanual coordination, and reduced gait disability. CIS improves gastrointestinal function and response to L-dopa in patients with PD and could be a helpful add-on medication in these patients.

S-phase population analysis does not correlate with the cytotoxicity of camptothecin and 10,11-methylenedioxycamptothecin in human colon carcinoma HT-29 cells.

Previous studies in rapidly proliferating rodent cells have suggested that the lethal effect of the DNA topoisomerase I inhibitor, camptothecin (CPT) is dependent upon the active participation of DNA replication (Holm et al. Cancer Res. 49:6365-6368; 1989). The purpose of the current study was to determine if this relationship applies to more slowly growing human cells. In our present study, we employed the human colon carcinoma cell line, HT-29 (45 hr doubling time). Flow cytometric determination of S-phase cells either by S-phase fit model or rectangle fit model analysis predicted that 21% of exponentially growing HT-29 cells were undergoing DNA replication. These findings were confirmed by immunofluorescence microscopy of bromodeoxyuridine labeled cells. Based on these findings, we would have expected only 20-30% of the cells to be susceptible to brief treatment (30 min) with CPT. Instead, 90-95% of HT-29 cells were killed. This apparent disparity was not due to prolonged cellular retention of drug after treatment because protein-linked DNA strand breaks reversed within 15 min of drug removal. Moreover, the DNA replication inhibitor, aphidicolin, fully protected HT-29 cells against CPT-induced killing but did not affect the production of CPT-induced protein-linked DNA strand breaks. Similar results were also obtained using the CPT-analog, 10,11-methylenedioxy-camptothecin, which was 5- to 10-fold more potent than camptothecin (O'Connor et al. Cancer Commun. 2:395-400; 1990).(ABSTRACT TRUNCATED AT 250 WORDS)