PubMed Health⌕ Search

Biomedical subjects

A M Senderowicz

Publications and source records attributed to A M Senderowicz.

At least 37 records · Page 2Linked to original sources
PubMed1999

Down-regulation of cyclin D1 by transcriptional repression in MCF-7 human breast carcinoma cells induced by flavopiridol.

Flavopiridol is a novel flavonoid that induces cell cycle arrest at different stages of the cell cycle because of the inhibition of cyclin-dependent kinases (cdks). In previous studies from our laboratory, (B. A. Carlson et al., Cancer Res., 56: 2973-2978, 1996), we observed that exposure of the MCF-7 breast carcinoma cell line to flavopiridol resulted in G1-S arrest, which was associated with the loss of cdk4 and cdk2 activity by 24 h of exposure. Along with this inhibition, flavopiridol decreased total cyclin-D protein levels in this cell line. In this work, we demonstrate that using isoform-specific antibodies, flavopiridol induces an early (by 6 h) decrease in cyclin D1 protein levels. This decline is followed by a decline in cyclin D3 with no effect on cyclin D2 or cyclin E levels by 10 h. Furthermore, at early time points (up to 8 h), the activity of cdk4 and the expression of endogenous phosphorylated retinoblastoma species from intact cells exposed to flavopiridol are unchanged. Thus, the decline in cdk4 activity and the induction of retinoblastoma hypophosphorylation follows cyclin D1 decline. Turnover studies demonstrate that the half-life of cyclin D1 (approximately 30 min) is not shortened in flavopiridol-exposed cells, and that the turnover of cdk4-bound cyclin D1 is unaltered. However, steady-state levels of cyclin D1 mRNA display a significant decrease by 4 h of flavopiridol treatment, with total disappearance by 8 h. This mRNA decline is not abrogated by the presence of cycloheximide. Furthermore, we have found that flavopiridol specifically represses the activity of the full-length cyclin D1 promoter linked to a luciferase reporter gene. In summary, we have found that the flavopiridol-induced decline in cyclin D1 is an early event, specific and, at least in part, due to the transcriptional repression of the cyclin D1 promoter. These results extend our understanding of flavopiridol's action to include regulation of cyclin D1 transcription.

Antineoplastic Agents↗
PubMed1999

Identification of cytosolic aldehyde dehydrogenase 1 from non-small cell lung carcinomas as a flavopiridol-binding protein.

The synthetic flavone flavopiridol can be cytostatic or cytotoxic to mammalian cells, depending on the concentration of the drug and the duration of exposure. It has been shown to inhibit the cyclin-dependent kinase (CDK) family of cell cycle regulatory enzymes. However, the existence of additional potential targets for drug action remains a matter of interest to define. To identify cellular targets, flavopiridol was immobilized. CDKs, particularly CDK 4, bound weakly to immobilized flavopiridol when ATP was absent but not in its presence. Two proteins with molecular weights of 40 kDa and 120 kDa had high affinities to the immobilized flavopiridol independent of the presence of ATP. They were present in all cell lines analyzed: cervical (HeLa), prostate and non-small cell lung carcinoma (NSCLC) cell lines. A 60-kDa protein, which was present only in NSCLC cells and bound similarly well to immobilized flavopiridol, was identified as cytosolic aldehyde dehydrogenase class 1 (ALDH-1). The level of this protein correlated with the resistance of NSCLC cell lines to cytotoxicity caused by 500 nM flavopiridol but not higher flavopiridol concentrations. Despite binding to ALDH-1, there was no inhibition of dehydrogenase activity by flavopiridol concentrations as high as 20 microM and flavopiridol was not metabolized by ALDH-1. The results suggest that high cellular levels of ALDH-1 may reduce cytotoxicity of flavopiridol and contribute to relative resistance to the drug. This is the first report that flavopiridol binds to proteins other than CDKs.

Aldehyde Dehydrogenase↗
PubMed1999

Discovery and initial characterization of the paullones, a novel class of small-molecule inhibitors of cyclin-dependent kinases.

Analysis of the National Cancer Institute Human Tumor Cell Line Anti-Cancer Drug Screen data using the COMPARE algorithm to detect similarities in the pattern of compound action to flavopiridol, a known inhibitor of cyclin-dependent kinases (CDKs), has suggested several possible novel CDK inhibitors. 9-Bromo-7,12-dihydro-indolo[3,2-d][1]benzazepin-6(5H)-one, NSC-664704 (kenpaullone), is reported here to be a potent inhibitor of CDK1/cyclin B (IC50, 0.4 microM). This compound also inhibited CDK2/cyclin A (IC50, 0.68 microM), CDK2/cyclin E (IC50, 7.5 microM), and CDK5/p25 (IC50, 0.85 microM) but had much less effect on other kinases; only c-src (IC50, 15 microM), casein kinase 2 (IC50, 20 microM), erk 1 (IC50, 20 microM), and erk 2 (IC50, 9 microM) were inhibited with IC50s less than 35 microM. Kenpaullone acts by competitive inhibition of ATP binding. Molecular modeling indicates that kenpaullone can bind in the ATP binding site of CDK2 with residue contacts similar to those observed in the crystal structures of other CDK2-bound inhibitors. Analogues of kenpaullone, in particular 10-bromopaullone (NSC-672234), also inhibited various protein kinases including CDKs. Cells exposed to kenpaullone and 10-bromopaullone display delayed cell cycle progression. Kenpaullone represents a novel chemotype for compounds that preferentially inhibit CDKs.

Algorithms↗
PubMed1999

Flavopiridol: the first cyclin-dependent kinase inhibitor in human clinical trials.

The discovery and cloning of the cyclin-dependent kinases (cdks), main regulators of cell cycle progression, allowed several investigators to design novel modulators of cdk activity. Flavopiridol (HMR 1275, L86-8275), a flavonoid derived from an indigenous plant from India, demonstrated potent and specific in vitro inhibition of all cdks tested (cdks 1, 2, 4 and 7) with clear block in cell cycle progression at the G1/S and G2/M boundaries. Moreover, preclinical studies demonstrated the capacity of flavopiridol to induce programmed cell death, promote differentiation, inhibit angiogenic processes and modulate transcriptional events. The relationship between the latter effects and cdk inhibition is still unclear. Initial testing in early clinical human trials with infusional flavopiridol showed activity in some patients with non-Hodgkin's lymphoma, renal, prostate, colon and gastric carcinomas. Main side effects were secretory diarrhea and a pro-inflammatory syndrome associated with hypotension. Biologically active plasma concentrations of flavopiridol (approximately 300-500 nM) are easily achievable in patients receiving infusional flavopiridol. Phase 2 trials with infusional flavopiridol in several tumor types, other schedules and combination with standard chemotherapies are being assessed. In conclusion, flavopiridol is the first cdk inhibitor to be tested in clinical trials. Although important questions remain to be answered, this positive experience will stimulate the development of novel cdk modulators for cancer therapy.

Antineoplastic Agents↗
PubMed1999

A phase II trial of gallium nitrate in patients with androgen-metastatic prostate cancer.

INTRODUCTION: Due to in vitro data suggesting antitumor activity with gallium nitrate, we sought to evaluate the safety and activity in patients with androgen-independent prostate cancer. METHOD: Patients were eligible for this study if they had an ECOG performance status of < or = 2, stage D2 metastatic prostate cancer that was progressing following combined androgen ablation (medical or surgical castration plus antiandrogen) and had failed antiandrogen withdrawal. Therapy consisted of gallium nitrate (200 mg/m(2)/day) as a continuous infusion for 7 days, administered every 21 days, with hydration (100 ml/m(2)/h). Individuals that had previously received suramin were treated at a dose of 150 mg/m(2)/day of gallium nitrate. RESULTS: Eight patients were enrolled: 4 patients at the 200 mg/m(2)/day dose level and 4 patients at the lower dosage (150 mg/m(2)/day). One of 8 patients had a >75% decline in prostate-specific antigen (PSA), 3 patients had stable PSA values for 17, 18 and 22 weeks, and 4 patients had progression by PSA (>50% increase over baseline). Anemia requiring transfusion occurred in 5 of 8 patients (63%). Two patients (25%) developed grade 4 toxicity: 1 patient developed complete blindness with partial reversal over 12 months, and another patient had pulmonary infiltrates, hypoxemia, and fever. Serious adverse events were not correlated to prior suramin exposure, or gallium plasma concentrations (total or free), but appeared to be related to cumulative cycles of gallium nitrate. Remaining adverse events were grade 1 or 2. No patients developed renal or neurological toxicity. CONCLUSION: This trial was prematurely terminated because repeated administration of gallium nitrate was poorly tolerated in an elderly population with androgen-independent prostate cancer. Gallium had modest clinical activity in this disease.

Adenocarcinoma↗
PubMed1999

Induction of differentiation accompanies inhibition of Cdk2 in a non-small cell lung cancer cell line.

Induction of differentiation in a variety of model systems is accompanied by cell cycle exit and inhibition of Cdk2 kinase activity. We asked whether inhibition of Cdk2 activity is sufficient to allow differentiation to occur in a non-small cell lung cancer cell line. Treatment of NCI-H358 with flavopiridol, an inhibitor of multiple Cdk's, resulted in growth arrest and induction of mucinous differentiation. The onset of differentiation coincided temporally with loss of Cdk2 kinase activity. Western analysis revealed that flavopiridol treatment resulted in depletion of both cyclin E and D1, suggesting that loss of the regulatory subunits is at least partially responsible for the loss of Cdk kinase activity. Similarly, roscovitine, an inhibitor of Cdk's 1, 2, and 5, but not Cdk4, also induced differentiation in NCI-H358, although the resulting pattern of expression of cell cycle regulatory genes differed from the pattern obtained with flavopiridol. Furthermore, stable expression of an antisense Cdk2 construct in NCI-H358 also resulted in the appearance of a marker of mucinous differentiation. These results show that the inhibition of activity of cyclin dependent kinases, particularly Cdk2, by multiple different mechanisms is accompanied by differentiation. Thus, induction of differentiation is one potential mechanism of action for agents that down-regulate Cdk activity.

CDC2-CDC28 Kinases↗
PubMed1998

UCN-01 abrogates G2 arrest through a Cdc2-dependent pathway that is associated with inactivation of the Wee1Hu kinase and activation of the Cdc25C phosphatase.

We have previously demonstrated that UCN-01, a potent protein kinase inhibitor currently in phase I clinical trials for cancer treatment, abrogates G2 arrest following DNA damage. Here we used murine FT210 cells, which contain temperature-sensitive Cdc2 mutations, to determine if UCN-01 abrogates G2 arrest through a Cdc2-dependent pathway. We report that UCN-01 cannot induce mitosis in DNA-damaged FT210 cells at the non-permissive temperature for Cdc2 function. Failure to abrogate G2 arrest was not due to UCN-01-inactivation at the elevated temperature because parental FM3A cells, which have wild-type Cdc2, were sensitive to UCN-01-induced G2 checkpoint abrogation. Having established that UCN-01 acted through Cdc2, we next assessed UCN-01's effect on the Cdc2-inhibitory kinase, Wee1Hu, and the Cdc2-activating phosphatase, Cdc25C. We found that Wee1Hu was indeed inactivated in UCN-01-treated cells, possibly just prior to Cdc2 activation and entry of DNA-damaged cells into mitosis. This inhibition appeared, however, to be a consequence of a further upstream action since in vitro studies revealed purified Wee1Hu was relatively resistant to UCN-01-inhibition. Consistent with such an upstream action, UCN-01 also promoted the hyperphosphorylation (activation) of Cdc25C in DNA-damaged cells. Our results suggest that UCN-01 abrogates G2 checkpoint function through inhibition of a kinase residing upstream of Cdc2, Wee1Hu, and Cdc25C, and that changes observed in these mitotic regulators are downstream consequences of UCN-01's actions.

Alkaloids↗
PubMed1998

Flavopiridol, a novel cyclin-dependent kinase inhibitor, suppresses the growth of head and neck squamous cell carcinomas by inducing apoptosis.

Flavopiridol (HMR 1275) has been identified recently as a novel antineoplastic agent in the primary screen conducted by the Developmental Therapeutics Program, National Cancer Institute. Flavopiridol inhibits most cyclin-dependent kinases (cdks) and displays unique anticancer properties. Here, we investigated whether this compound was effective against head and neck squamous cell carcinomas (HNSCC). Exposure of HNSCC cells to flavopiridol diminished cdc2 and cdk2 activity and potently inhibited cell proliferation (IC50 43-83 nM), which was concomitant with the appearance of cells with a sub-G1 DNA content. Moreover, DNA fragmentation and TUNEL (terminal deoxynucleotidyl transferase-mediated nick end labeling) reaction confirmed that flavopiridol induces apoptosis in all cell lines, even on certain HNSCC cells that are insensitive to apoptosis to DNA-damaging agents (gamma-irradiation and bleomycin). A tumorigenic HNSCC cell line was used to assess the effect of flavopiridol in vivo. Treatment (5 mg/kg per day, intraperitoneally) for 5 d led to the appearance of apoptotic cells in the tumor xenografts and caused a 60-70% reduction in tumor size, which was sustained over a period of 10 wk. Flavopiridol treatment also resulted in a remarkable reduction of cyclin D1 expression in HNSCC cells and tumor xenografts. Our data indicate that flavopiridol exerts antitumor activity in HNSCC, and thus it can be considered a suitable candidate drug for testing in the treatment of refractory carcinomas of the head and neck.

Animals↗
PubMed1998

Unpredicted clinical pharmacology of UCN-01 caused by specific binding to human alpha1-acid glycoprotein.

The pharmacokinetics of UCN-01 after administration as a 72- or 3-h infusion to cancer patients in initial Phase I trials displayed distinctive features that could not have been predicted from preclinical data. The distribution volumes (0.0796-0.158 liters/kg) and the systemic clearance (0.0407-0.252 ml/h/kg) were extremely low, in contrast to large distribution volume and rapid systemic clearance in experimental animals. The elimination half-lives (253-1660 h) were unusually long. In vitro protein binding experiments demonstrated that UCN-01 was strongly bound to human alpha1-acid glycoprotein. The results suggest that unusual pharmacokinetics of UCN-01 in humans could be due, at least in part, to its specifically high binding to alpha1-acid glycoprotein.

Alkaloids↗
PubMed1998

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.

Apoptosis↗
PubMed1998

Clinical pharmacology of UCN-01: initial observations and comparison to preclinical models.

UCN-01 (7-hydroxystaurosporine; NSC 638850) is a protein kinase antagonist selected for clinical trial based in part on evidence of efficacy in a preclinical renal carcinoma xenograft model. Schedule studies and in vitro studies suggested that a 72-h continuous infusion would be appropriate. In rats and dogs, maximum tolerated doses produced peak plasma concentrations of approximately 0.2-0.3 microM. However, concentrations 10-fold greater are well tolerated in humans, and the compound has a markedly prolonged T1/2. Specific binding to human alpha1-acidic glycoprotein has been demonstrated. These findings reinforce the need to consider actual clinical pharmacology data in "real time" with phase I studies.

Adult↗
PubMed1998

Metabolism of the anticancer drug flavopiridol, a new inhibitor of cyclin dependent kinases, in rat liver.

Flavopiridol (FLAP) is a promising novel chemotherapeutic agent currently undergoing clinical phase I trials. To examine hepatic metabolism and biliary disposition of FLAP we applied the isolated perfused rat liver system. Besides FLAP two metabolites were detected by high performance liquid chromatography in bile and perfusate. Twenty-five min after FLAP (30 microM) addition to the perfusion medium, biliary secretion of metabolite 1 and 2 reached a maximum of 1.04 +/- 0.52 and 11.34 +/- 4.72 nmol/g.liver.min, respectively. Biliary excretion of parent FLAP, however, continuously increased for 60 min up to 406 +/- 134 pmol/g liver.min. In the perfusate, metabolite 1 was below detection limit and release of metabolite 2 was low (2.8 +/- 0.7 pmol/g liver.min after 60 min). Enzymatic hydrolysis with beta-glucuronidase, mass spectroscopy and electron absorption spectroscopy revealed that both metabolites are monoglucuronides with the glucuronide in position 5 and 7 of the flavonoid core, respectively. The amount of FLAP, metabolite 1 and metabolite 2 excreted into bile during the 60 min of perfusion was 1.94 +/- 0.91, 5.15 +/- 1.95 and 57.29 +/- 23.60% of FLAP cleared from the perfusate during 60 min, respectively. In contrast to the structurally similar flavonoids genistein and daidzein, no inhibition of UDP-glucuronyltransferase with methylumbelliferone as a substrate was observed indicating that different UDP-glucuronyltransferase isoforms are involved in FLAP metabolism. In conclusion, we find that glucuronidation is the major mechanism of hepatic FLAP biotransformation. Metabolites are mainly excreted into bile but also released into systemic circulation. The pharmacological and toxicological effects of these metabolites remain to be elucidated.

Animals↗
PubMed1998

Phase I trial of continuous infusion flavopiridol, a novel cyclin-dependent kinase inhibitor, in patients with refractory neoplasms.

PURPOSE: We conducted a phase I trial of the cyclin-dependent kinase inhibitor, flavopiridol (National Service Center [NSC] 649890), to determine the maximum-tolerated dose (MTD), toxicity profile, and pharmacology of flavopiridol given as a 72-hour infusion every 2 weeks. PATIENTS AND METHODS: Seventy-six patients with refractory malignancies with prior disease progression were treated with flavopiridol, with first-cycle pharmacokinetic sampling. RESULTS: Forty-nine patients defined our first MTD, 50 mg/m2/d x 3 with dose-limiting toxicity (DLT) of secretory diarrhea at 62.5 mg/kg/d x 3. Subsequent patients received antidiarrheal prophylaxis (ADP) to define a second MTD, 78 mg/m2/d x 3 with DLT of hypotension at 98 mg/m2/d x 3. Other toxicities included a proinflammatory syndrome with alterations in acute-phase reactants, particularly at doses >50 mg/ m2/d x 3, which in some patients prevented chronic therapy every 2 weeks. In some patients, ADP was not successful, requiring dose-deescalation. Although approximately 70% of patients displayed predictable flavopiridol pharmacology, we observed unexpected interpatient variability and postinfusion peaks in approximately 30% of cases. At the two MTDs, we achieved a mean plasma flavopiridol concentration of 271 nM (50 mg/m2/d x 3) and 344 nM (78 mg/m2/d x 3), respectively. One partial response in a patient with renal cancer and minor responses (n=3) in patients with non-Hodgkin's lymphoma, colon, and renal cancer occurred. CONCLUSION: The MTD of infusional flavopiridol is 50 mg/m2/d x 3 with dose-limiting secretory diarrhea at 62.5 mg/m2/d x 3. With ADP, 78 mg/m2/d x 3 was the MTD, with dose-limiting hypotension at 98 mg/m2/d x 3. Based on chronic tolerability, 50 mg/m2/d x 3 is the recommended phase II dose without ADP. Antitumor effect was observed in certain patients with renal, prostate, and colon cancer, and non-Hodgkin's lymphoma. Concentrations of flavopiridol (200 to 400 nM) needed for cyclin-dependent kinase inhibition in preclinical models were achieved safely.

Adult↗
PubMed1997

An intra-abdominal small round cell neoplasm with features of primitive neuroectodermal and desmoplastic round cell tumor and a EWS/FLI-1 fusion transcript.

We report an intra-abdominal round cell tumor in a young man which exhibited the light and electron microscopic appearance of a peripheral primitive neuroectodermal tumor (PNET), in addition to the clinical and topographic characteristics, desmoplasia and a complex immunophenotypic profile of the intra-abdominal desmoplastic round cell tumor (DSRCT). Reverse transcription polymerase chain reaction revealed a EWS/FLI-1 fusion transcript as in PNET/Ewing's sarcoma, instead of the EWS/WT1 transcript of DSRCT. The tumor was also strongly positive for the mic2 protein. This is a unique case of a hybrid tumor arising in the peritoneal cavity of a young male. The existence of such a hybrid tumor in this location suggests that DSRCT and PNET may be related and possibly share a common histogenesis.

Abdominal Neoplasms↗
PubMed1997

Phase II trial of suramin, leuprolide, and flutamide in previously untreated metastatic prostate cancer.

PURPOSE: To assess the efficacy and toxicity of suramin, hydrocortisone, leuprolide, and flutamide in previously untreated metastatic prostate cancer. PATIENTS AND METHODS: Patients with stage D2 and poor-prognosis stage D1 prostate cancer were given suramin on a pharmacokinetically derived dosing schedule to maintain suramin concentrations between 175 and 300 micrograms/mL. Additionally, all patients received flutamide 250 mg orally three times daily, initiated on day 1 and continued until disease progression; depot leuprolide 7.5 mg intramuscularly begun on day 5 and repeated every 4 weeks indefinitely; and replacement doses of hydrocortisone. RESULTS: Fifty patients were entered onto the study: 48 with stage D2 and two with stage D1 disease. The median age was 59 years (range, 42 to 79) and 31 patients had a Karnofsky performance status (KPS) of 100%. Forty-five patients had bone metastases and 25 had measurable soft tissue disease. Forty-one (82%) had severe disease. The overall response rate in 49 assessable patients was three complete responses (CRs) and 30 partial responses (PRs) for an overall response rate of 67%. Eighteen patients have died. The median survival time has not been reached, with a median potential follow-up duration of 44 months. Grade 3 to 4 toxicity was seen in 38% of patients and was predominantly hematologic and reversible. CONCLUSION: The high response rate and prolonged survival in a poor-prognosis group of patients with metastatic prostate cancer warrant a phase III randomized comparison of this regimen versus hormonal therapy alone. Toxicity was moderate and reversible.

Adult↗
PubMed1995

Jasplakinolide's inhibition of the growth of prostate carcinoma cells in vitro with disruption of the actin cytoskeleton.

BACKGROUND: Jasplakinolide, a cyclodepsipeptide produced by an Indo-Pacific sponge, Jaspis johnstoni, has been reported to inhibit the growth of breast cancer cells. PURPOSE: The effects of jasplakinolide on the proliferation of three human immortalized prostate carcinoma cell lines (PC-3, LNCaP, and TSU-Pr1) were studied. The growth-inhibitory effect of jasplakinolide on the PC-3 cell line was studied in detail to elucidate its mechanism of action. METHODS: Cell counts were used to study growth inhibition. A protein-based microplate assay was used to assess the time of exposure needed to cause persistent growth inhibition and to study the effects of jasplakinolide analogues. Metabolic changes were assessed by following the incorporation of radiolabeled precursors. The effects of jasplakinolide on the cytoskeleton were studied by fluorescent microscopy, using rhodamine phalloidin (RP) and antibodies to cytoskeletal components. Changes in RP binding were quantified by extracting bound fluorescent material from fixed cells and measuring the amount of fluorescence in a spectrofluorometer. RESULTS: The growth of PC-3, LNCaP, and TSU-Pr1 cells was potently inhibited by exposure to jasplakinolide for 48 hours; doses of jasplakinolide that led to 50% growth inhibition were 65 nM for PC-3 cells, 41 nM for LNCaP cells, and 170 nM for TSU-Pr1 cells. In PC-3 cells, exposure to 160 nM for 48 hours led to total growth inhibition, which persisted for several days even after drug removal. Several jasplakinolide analogues also inhibited the growth of PC-3 cells, although analogues in which the rigidity of the macrolide ring was altered were ineffective. No early changes in the synthesis of DNA, RNA, or protein or in intracellular adenosine triphosphate levels were seen in the PC-3 cells after exposure to jasplakinolide. Growth inhibition by jasplakinolide was accompanied by striking morphologic changes. Exposure for several doublings led to multinucleated cells. Further investigation of these changes in the PC-3 cells revealed a dramatic and early disruption of the actin cytoskeleton and a statistically significant decrease in RP binding. The doses of jasplakinolide, the time of exposure, and the pattern of growth inhibition by structural analogues corresponded with the changes seen in actin distribution. CONCLUSIONS: Jasplakinolide represents a novel marine natural product with potent in vitro antiproliferative activity against human prostate carcinoma cell lines, and it appears to target the actin cytoskeleton. IMPLICATIONS: Jasplakinolide is a potential candidate for further preclinical development and a lead structure for a novel class of therapeutic agents that can disrupt the actin cytoskeleton in mammalian cells.

Actins↗