Protection against Clostridium difficile infection with broadly neutralizing antitoxin monoclonal antibodies

The spore-forming bacterium Clostridium difficile represents the principal cause of hospital-acquired diarrhea and pseudomembranous colitis worldwide. C. difficile infection (CDI) is mediated by 2 bacterial toxins, A and B; neutralizing these toxins with monoclonal antibodies (mAbs) provides a potential nonantibiotic strategy for combating the rising prevalence, severity, and recurrence of CDI. Novel antitoxin mAbs were generated in mice and were humanized. The humanized antitoxin A mAb PA-50 and antitoxin B mAb PA-41 have picomolar potencies in vitro and bind to novel regions of the respective toxins. In a hamster model for CDI, 95% of animals treated with a combination of humanized PA-50 and PA-41 showed long-term survival relative to 0% survival of animals treated with standard antibiotics or comparator mAbs. These humanized mAbs provide insight into C. difficile intoxication and hold promise as potential nonantibiotic agents for improving clinical management of CDI.

Synergistic co-targeting of prostate-specific membrane antigen and androgen receptor in prostate cancer

BACKGROUND

Antibody-drug conjugates (ADCs) are an emerging class of cancer therapies that have demonstrated favorable activity both as single agents and as components of combination regimens. Phase 2 testing of an ADC targeting prostate-specific membrane antigen (PSMA) in advanced prostate cancer has shown antitumor activity. The present study examined PSMA ADC used in combination with potent antiandrogens (enzalutamide and abiraterone) and other compounds.

METHODS

Antiproliferative activity and expression of PSMA, prostate-specific antigen and androgen receptor were evaluated in the prostate cancer cell lines LNCaP and C4-2. Cells were tested for susceptibility to antiandrogens or other inhibitors, used alone and in combination with PSMA ADC. Potential drug synergy or antagonism was evaluated using the Bliss independence method.

RESULTS

Enzalutamide and abiraterone demonstrated robust, statistically significant synergy when combined with PSMA ADC. Largely additive activity was observed between the antiandrogens and the individual components of the ADC (free drug and unmodified antibody). Rapamycin also synergized with PSMA ADC in certain settings. Synergy was linked in part to upregulation of PSMA expression. In androgen-dependent LNCaP cells, enzalutamide and abiraterone each inhibited proliferation, upregulated PSMA expression, and synergized with PSMA ADC. In androgen-independent C4-2 cells, enzalutamide and abiraterone showed no measurable antiproliferative activity on their own but increased PSMA expression and synergized with PSMA ADC nonetheless. PSMA expression increased progressively over 3 weeks with enzalutamide and returned to baseline levels 1 week after enzalutamide removal.

CONCLUSIONS

The findings support exploration of clinical treatment regimens that combine potent antiandrogens and PSMA-targeted therapies for prostate cancer.

Long-term captopril treatment. Angiotensin II receptors and responses

The purpose of this study was to elucidate the mechanism of the antihypertensive effect of the angiotensin I (Ang I) converting enzyme inhibitor captopril in spontaneously hypertensive rats (SHR). Drinking responses, peripheral vascular reactivity, and angiotensin II (Ang II) receptor binding in both the brain and vascular smooth muscle were examined in control and captopril-treated SHR. Pregnant and nursing dams were treated with oral captopril (100 mg/kg). After weaning, offspring were maintained on captopril (50 mg/kg). The average systolic pressures after 21 weeks of captopril treatment were 122 +/- 3 mm Hg (male) and 118 +/- 4 mm Hg (female) as compared with 169 +/- 4 mm Hg (male) and 162 +/- 2 mm Hg (female) in age-matched controls. Drinking responses to intracerebroventricular (10 ng) and subcutaneous (100 micrograms/kg) administration of Ang I and II were attenuated in captopril-treated SHR in comparison to control SHR. Ang II receptor binding in the hypothalamus, thalamus, and septum of captopril-treated SHR was also significantly reduced. In contrast to a depressed angiotensinergic system in the brain, peripheral vascular reactivity to Ang II, as determined in isolated, artificially perfused kidneys, was elevated. Threshold and ED50 values for Ang II were significantly lower in captopril-treated SHR than in controls. Ang II receptor binding in aortic smooth muscle cells prepared from captopril-treated SHR was also significantly greater than in cells from controls. Thus, lifetime treatment with captopril induced alterations in the renin angiotensin systems in the periphery and brain that were manifested by changes in receptor binding and responsiveness to Ang II.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme activities in endothelial cells and smooth muscle cells from swine aorta

In populations of cultured arterial endothelial and smooth muscle cells grown under the same conditions, we have measured the total activity per cell of 10 enzymes commonly used as "markers" for subcellular organelles: NADH: ferricyanide reductase, NADH:cytochrome c reductase (rotenone insensitive). NADPH:cytochrome c reductase, alpha-glucosidase, 5'-nucleotidase, alkaline phosphodiesterase I, cytochrome oxidase, monoamine oxidase, cathepsin D, and N-acetyl-beta-glucosaminidase. Significant differences between the cell types were found for 7 of the 10 enzymes tested. The total activity of 5'-nucleotidase in cultured smooth muscle cells was 17 times that of cultured endothelial cells. Comparison of the activities in the two cell types freshly collected and in culture showed that the difference in 5'-nucleotidase in cultured cells is due principally to loss of activity from endothelial cells, suggesting that this activity is regulated differently in the two cell types. In both cell types cathepsin D activity rose during culture.

The capactins, a class of proteins that cap the ends of actin filaments

A number of proteins that bind specifically to the barbed ends of actin filaments in a cytochalasin-like manner have been purified to various degrees from a variety of muscle and non-muscle cells and tissues. Preliminary evidence also indicates that proteins that interact with the pointed ends of filaments are present in skeletal muscle. Because of their ability to cap one or the other end of an actin filament, we have designated this class of proteins as the 'capactins'. On the basis of their effect on actin filament assembly and interaction in vitro, we propose that the capactins play important roles in cellular regulation of actin-based cytoskeletal and contractile functions. Our finding that the disappearance of actin filament bundles in virally transformed fibroblasts can be correlated with an increase in capactin activity in the extracts of these cells is consistent with this hypothesis.

Hypertensive dog plasma inhibits the Na+-K+ pump of cultured vascular smooth muscle

We investigated the effects of plasma from dogs with perinephritic hypertension on the Na+-K+ pump of cultured dog vascular smooth muscle cells. We also measured [3H]ouabain binding by myocardium and vascular tissue. Fresh, unprocessed plasma from healthy dogs during the first 6 weeks of benign one-kidney, one wrapped hypertension and from paired normotensive control dogs was layered over confluent primary cultured puppy aortic smooth muscle cells that had been sodium-loaded with monensin. In 26 paired assays of plasma from four pairs of dogs, cells incubated in the presence of plasma from hypertensive dogs had significantly reduced total (p less than 0.01) and ouabain-sensitive (p less than 0.001) 86Rb+ uptakes, but their intracellular sodium content did not differ from cells incubated in paired normotensive plasma. We no longer detected these uptake differences when passaged cells or cells cocultured with bovine endothelial cells were used for assay or when plasma was treated with protease inhibitors or boiled. However, boiled plasma increased the sodium content of the assay cells, suggesting an ionophorelike effect. Levels of pump inhibitory activity in plasma appeared to remain constant during Weeks 1 to 6 of hypertension. We found no evidence for altered numbers of pump sites in cardiovascular tissues from these hypertensive dogs. These findings support the hypothesis that plasma factors inhibit the membrane Na+-K+ pump in vascular smooth muscle cells in this form of hypertension. These plasma inhibitory factors apparently do not induce pump molecules.

The relationship between high-affinity binding of cytochalasin B to 3T3 cells and inhibition of sugar transport and cell motility

Transport and motility inhibitors have been used to classify different types of high-affinity cytochalasin B (CB) binding sites in 3T3 cells. The potency of phloretin and phlorizin as inhibitors of sugar uptake paralleled their effectiveness in displacing high-affinity bound CB from the cells, indicating that the two compounds compete with CB for binding to sites associated with sugar transport proteins. On the other hand, cytochalasins D and E, which did not inhibit sugar uptake, inhibited binding of CB to a portion of the high-affinity sites, most probably those associated with actin-containing cytoskeletal-contractile structures. A small amount of high-affinity CB binding remained in the presence of both phloretin and cytochalasin E, indicating that the cells have a third class of sites which is not related to either sugar transport or cell motility, When isolated membranes were examined, it was found that a fraction of each class of high-affinity CB binding sites were associated with the fraction. In contrast, only sites sensitive to cytochalasin D were recovered in a soluble extract of the cells.

Transformation-dependent increases in endogenous cytochalasin-like activity in chicken embryo fibroblasts infected by Rous sarcoma virus

Transformation of chicken embryo fibroblasts by infection with Rous sarcoma virus has been shown to cause disruption of actin filament organization as seen with fluorescence staining techniques. This study is an attempt to use quantitative biochemical techniques to compare actin-related parameters in normal and transformed cells. Normal cells and cells infected with a temperature-sensitive mutant virus (NY68) and grown at the restrictive temperature of 41.5 degrees C have normal bundles of actin filaments, or F-actin; these cells also have about the same number of high-affinity cytochalasin binding sites at the ends of F-actin (approximately 5 pmol of sites per mg of cellular protein; Kd, 20 nM). In contrast, infected cells grown at the permissive temperature of 37 degrees C have a more diffuse pattern of actin filaments, and the number of cytochalasin binding sites in these transformed cells was below the level of detection. DNase I inhibition assays showed that the percent of unpolymerized actin, or G-actin, in cell extracts was not significantly different between normal and transformed cells (approximately 50%). In assays of cell extracts for endogenous cytochalasin-like activity on actin filaments (i.e., retardation of filament assembly at the fast-growing end, inhibition of cytochalasin binding to actin "nuclei," and decrease of low-shear viscosity of solutions of actin filaments), infected cells at 37 degrees C showed a higher level of activity per mg of protein than did uninfected cells or infected cells at 41.5 degrees C. These results suggest that the increase in endogenous cytochalasin-like activity in transformed cells may relate to the decrease in measurable cytochalasin binding sites and the abnormal distribution of actin filaments previously seen by fluorescence staining techniques.

Antiandrogen modulation of prostate-specific membrane antigen (PSMA): Dynamics and synergy with PSMA-targeted therapy

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Background: Recent approvals of four new prostate cancer (PCa) drugs and a growing number of pipeline agents have created opportunities for designing rational drug combinations. Potent antiandrogens such as enzalutamide and abiraterone affect expression of a host of androgen-regulated molecules, including those that represent targets for therapy. One such target is PSMA, a well-characterized cell-surface antigen abundant on prostate cancer cells. PSMA ADC is a PSMA-targeted antibody-drug conjugate currently in phase II clinical testing, comprised of a fully human IgG1 mAb conjugated to vcMMAE (valine-citrulline monomethylauristatin E). Here we examined the kinetics and reversibility of PSMA induction by potent antiandrogens and their associated effects on the preclinical activity of PSMA ADC. Methods: Androgen-dependent and -independent PCa cell lines with varying basal levels of PSMA expression were cultured for up to one month in the presence of enzalutamide or abiraterone, followed by drug washout. Cells were tested for PSMA expression over time and for susceptibility to cytotoxicity by PSMA ADC. Potential drug synergy or antagonism was evaluated using the combination index method. Results: Enzalutamide (1 mM) increased PSMA expression by approximately 2.5-fold in LNCaP (androgen-dependent) and C4-2 (androgen-independent) cells, with maximal expression observed after approximately 4 weeks’ culture. PSMA expression returned to basal levels within days following removal of enzalutamide from the culture. Enzalutamide and PSMA ADC exhibited synergistic antitumor activity in LNCaP and C4-2 cells (P < 0.05). Similar results were observed for abiraterone in C4-2 cells. Less induction of PSMA expression by antiandrogens and modest effects on cytotoxicity were observed using 22Rv1 cells, an androgen-independent cell line with low basal expression of PSMA. Conclusions: Enzalutamide and abiraterone significantly and reversibly augmented PSMA expression and potentiated the activity of PSMA ADC in PCa cell lines in vitro. The findings support clinical exploration of regimens that combine potent antiandrogens and PSMA-targeted therapies.

Expression of prostate-specific membrane antigen (PSMA) on circulating tumor cells (CTCs) in castration-resistant prostate cancer

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Background: Prostate-specific membrane antigen (PSMA) is expressed ubiquitously in prostate adenocarcinoma, and the intensity of expression increases with disease aggressiveness. Exploiting PSMA for therapy could potentially be aided by a minimally invasive means for measuring PSMA on tumor cells. Here we describe the development and characteristics of a novel assay for quantitating PSMA on canonical and non-canonical circulating tumor cells (CTCs). Methods: The PSMA CTC test was developed using LNCaP (high PSMA), 22Rv1 (low PSMA) and PC3 (no PSMA) cells spiked into normal blood. Nucleated blood cells were plated onto glass slides and subjected to immunofluorescent staining followed by CTC identification using the Pyxis Scanning Platform at Epic Sciences. The four-color assay evaluated PSMA expression on individual CTCs, identified as cells which are cytokeratin+, CD45-, and with an intact DAPI nucleus. Multiple antibody clones and assay conditions were evaluated, and the final PSMA CTC test has high specificity and sensitivity. Acceptance criteria included signal intensities in LNCaP versus PC3, subcellular localization of PSMA, and potential interference by a PSMA-targeted therapy. Clinical feasibility of the optimized assay was assessed on samples from CRPC patients. Results: The average PSMA signal intensity for LNCaP was 20-fold higher than that for PC3 and 10-fold higher than the minimum cutoff. PSMA displayed a predominantly membrane-localized pattern of staining that was distinct from cytokeratin. Assay performance was unaffected by the presence of PSMA ADC, a PSMA-targeted antibody-drug conjugate that is in phase II clinical testing. In feasibility tests on patient samples, the assay demonstrated utility in detecting and quantitating PSMA on individual and clustered CTCs as well as on apoptotic, cytokeratin-negative, and small cytokeratin-positive CTC candidates. Conclusions: PSMA expression was successfully detected and quantitated on diverse types of circulating cells present in the blood of patients with CRPC. Assay performance was unaffected by the presence of a PSMA-targeted therapeutic agent. PSMA CTC data are being collected in the ongoing phase II study of PSMA ADC for comparison with treatment outcomes.

Aortic hypertrophy and "waterlogging" in the development of coarctation hypertension

To study the mechanisms and roles of vascular structural changes during the development of hypertension, we coarcted or sham-coarcted the abdominal aorta of rats. At intervals of 3 to 56 days later, we obtained standardized segments of thoracic and abdominal aortas for measurement of dry weight, water content, and amino acid content. Carotid arterial pressure was elevated by day 5 in coarcted rats and remained elevated. Femoral and tail arterial pressures remained normal. Cardiac ventricular weight and dry weight of the thoracic aorta, normalized for body weight, rose rapidly over 3-10 days in coarcted rats, remaining constant at 50-60% above levels in sham-coarcted rats thereafter. In contrast, water content of thoracic aorta in coarcted rats peaked at 123% of control values on day 7 (p less than 0.001), falling rapidly thereafter to levels about half of peak. Increments in dry weight and water content of the normotensive abdominal aortic segments were of far lesser magnitude and occurred 1 to 2 weeks later, probably reflecting the effects of initial hypotension of the hindquarters. Percent hydroxyproline of intima-media segments of the thoracic aorta remained normal during the 8-week period, indicating that increases in aortic dry weight did not represent disproportional fibrosis and thus are attributable to muscular hypertrophy. These results provide support for the hypothesis that arterial wall "waterlogging" is primarily an early manifestation of the hypertensive process. The greatest magnitude of waterlogging coincides with the rapid early increase in aortic dry weight, representing hypertrophy, which suggests common mechanisms, such as activation of Na+-H+ antiport.

Abstract 798: Androgen receptor, PI3K/mTOR and PSMA: Exploring and exploiting the interplay between therapeutic targets in prostate cancer

Introduction: Androgen receptor (AR), the PI3K/mTOR signaling pathway and prostate-specific membrane antigen (PSMA) represent significant potential targets for prostate cancer therapy. The present study examined the cross-regulation and co-targeting of these molecular pathways.

Methods: Cytotoxicity and the kinetics of antigen expression were evaluated in prostate cancer cell lines (LNCaP and C4-2) that vary according to androgen dependence. Expression of PSMA, prostate-specific antigen (PSA), and AR was evaluated in cells cultured in rapamycin and AR inhibitors. Cells were tested for susceptibility to PI3K/mTOR inhibitors used alone and in combination with PSMA ADC, a fully human PSMA monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE). Potential drug synergy or antagonism was evaluated using the Bliss independence method.

Results: In androgen-dependent LNCaP cells, rapamycin exerted antiproliferative effects that were accompanied by an increase in AR expression and signaling in the absence of any significant effect on PSMA expression. In androgen-independent C4-2 cells, rapamycin increased AR expression/signaling and PSMA expression in the absence of any significant anti-proliferative effect. AR inhibitors synergized with PSMA ADC in LNCaP and C4-2 cells, but PI3K/mTOR pathway inhibitors synergized with PSMA ADC in C4-2 cells only. More modest synergy was observed by combining non-targeted microtubule inhibitors with inhibitors of AR or mTOR. Compared with rapamycin, GDC0941 (PI3K inhibitor) and MK-2206 (Akt inhibitor), both upstream of mTOR, synergized less strongly with PSMA ADC in C4-2 cells.

Conclusions: In this study, AR and PI3K/mTOR pathways exhibited cross-regulation impacting PSMA expression. PSMA ADC synergized with AR and mTOR inhibitors via a multimodal mechanism involving increased PSMA expression and disruption of microtubule function. The findings support clinical exploration of regimens combining PSMA-targeted therapies with inhibitors of the AR and/or PI3K/mTOR signaling pathways.

Citation Format: Jose D. Murga, Wells W. Magargal, Sameer M. Moorji, Vincent A. DiPippo, William C. Olson. Androgen receptor, PI3K/mTOR and PSMA: Exploring and exploiting the interplay between therapeutic targets in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 798. doi:10.1158/1538-7445.AM2014-798

Abstract 3668: Single-dose activity of PSMA ADC against prostate cancer xenograft and explant tumors

Introduction: Prostate-specific membrane antigen (PSMA) is an attractive target for antibody-targeted therapy of prostate cancer due to its abundant and selective expression on the surface of prostate cancer cells. We have generated a novel antibody-drug conjugate (ADC) by linking a fully human PSMA monoclonal antibody to monomethylauristatin-E (MMAE), a potent tubulin inhibitor. Here, we describe the use of PSMA ADC to treat SCID mice bearing LNCaP xenografts or LuCaP explants derived from surgical resections of prostate cancer patients.

Methods: PSMA expression in LNCaP and LuCaP tumor cells was evaluated by flow cytometry. Activity of PSMA ADC, assessed by decrease in tumor volume, was evaluated in LNCaP xenograft and LuCaP explant models. SCID mice were implanted subcutaneously with cultured LNCaP tumor cells or disaggregated human LuCaP 70 or LuCaP 77 prostate tumor tissue obtained from tumor-bearing mice. When average tumor size reached ∼300mm3, animals were randomized into groups of 9-10 mice and each animal was treated with a single intravenous dose of vehicle control, a control ADC of irrelevant specificity, or PSMA ADC. Treatment effects were assessed by measuring tumor volume and overall survival for up to 41 days post-treatment.

Results: Surface expression of PSMA was assessed by flow cytometry, with a rank order of expression as follows: LNCaP &gt; LuCaP 70, LuCaP 77, LuCaP 105 &gt; LuCaP 96.1 &gt; LuCaP 35V, LuCaP 141. Single-dose PSMA ADC demonstrated significant activity against LNCaP xenografts at a dose of 5 mg/kg (p&lt;0.0001 relative to either vehicle or control ADC) and against LuCaP 77 explants at a dose of 10 mg/kg (p=0.0003 relative to either vehicle or control ADC). A trend toward delayed tumor growth was observed in the LuCaP 70 tumor model.

Conclusion: Single-dose PSMA ADC showed activity against LNCaP xenografts and LuCaP explants derived from surgical resections of prostate cancer patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3668. doi:10.1158/1538-7445.AM2011-3668

Distribution of membrane marker enzymes in cultured arterial endothelial and smooth muscle cells. The subcellular location of oleoyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase

The subcellular distribution of oleoyl-CoA:1-acyl-sn-glycero-3-phosphocholine acyltransferase (E.C.2.3.1.23) in cultured swine aorta endothelial cells and smooth muscle cells was investigated. Isolated membrane pellets were centrifuged through linear sucrose gradients, and the distributions of the activities of seven membrane-bound enzymes were measured. The distribution of acyltrasferase activity was similar to that of the endoplasmic reticulum enzymes. Gradient fractions which contained intact mitochondria had very low activities of acyltransferase. Experiments using mixed fractions and measurements made under conditions which inhibit phospholipase A2 showed that no acyltransferase activity from this location was masked by competing activities. When membranes were treated with digitonin, plasma membranes specifically increased in density, facilitating their separation from endoplasmic reticulum membranes. The plasma membranes were free of acyltransferase activity. We conclude that in cultured swine arterial smooth muscle and endothelial cells, acyltransferase is located primarily in the endoplasmic reticulum.

Effect of hypertensive rat plasma on ion transport of cultured vascular smooth muscle

We layered fresh, unprocessed plasma from healthy rats with early (less than or equal to 7 days) or benign, chronic (greater than 3 wk) one-kidney, one-clip hypertension and from paired one-kidney normotensive control rats over confluent primary-cultured rat aortic smooth muscle cells. Plasma from all rats increased cellular ouabain-sensitive 86Rb+ uptake and sodium content and decreased ouabain-insensitive 86Rb+ uptake compared with uptakes and content in the presence of balanced salt solution (P less than 0.01). Cells incubated in the presence of plasma from rats with early (P less than 0.02) or chronic hypertension (P less than 0.01) had significantly reduced ouabain-sensitive 86Rb+ uptake when compared with cells incubated in normotensive plasma, but their intracellular Na+ contents were not lower. We no longer detected this uptake difference when chronic hypertensives drank 0.9% NaCl instead of water. Plasma from hypertensive rats also altered ouabain-insensitive 86Rb+ uptake by the cultured cells. These findings of this new, reproducible, and specific assay system support the hypothesis that plasma factors inhibit the membrane sodium-potassium pump in vascular smooth muscle cells in this form of hypertension. The abnormality occurs in both early and chronic stages, but may not be related to sodium intake. The data also provide evidence for plasma factors in hypertension altering membrane K+ permeability.