Abstract P5-06-01: Talazoparib antitumor effects in BRCA-deficient breast cancer models

Background: BRCA1 and BRCA2 functions are essential for the DNA double-strand break repair process in living cells with DNA damages. Therefore, germline pathogenic mutations in BRCA1/2 increases the risk of developing cancer.1, 2Poly(ADP-ribose) polymerase (PARP) enzymes are proteins responsible for DNA single-strand break repair. Persistent inhibition of PARP-dependent DNA repair in BRCA-deficient breast cancer cells leads to increased DNA damages resulting in cancer cell death. Talazoparib is a novel and potent, orally bioavailable, small molecule PARP inhibitor. Talazoparib's dual mechanism of action inhibits PARP enzyme activity and effectively traps PARP on DNA, preventing DNA repair, resulting in cell death in BRCA1/2-mutated cells.3 In tissue culture studies, talazoparib is more potent at trapping PARP on DNA to induce cancer cell death compared to other PARP inhibitors.4 Previous studies have demonstrated talazoparib inhibited growth in tumors harboring BRCA1/2 gene mutations. In the MX-1 breast cancer model with BRCA1-deficiency, talazoparib inhibited cell growth in vitro and induced regression in solid mouse xenografts.5 Here, we demonstrate antitumor effects of talazoparib monotherapy in a panel of breast cancer cells and patient-derived breast cancer models with pathologic BRCA1/2 mutations.

Method: A panel of human breast cancer cell lines was treated with talazoparib to determine its cytotoxic effects. BRCA1/2 mutations status was correlated to talazoparib cytotoxic effects. At the molecular level, BRCA1/2-mutant and wild type breast cancer cell lines were treated with dose-escalating talazoparib to also assess the relationship between PARP-DNA trapping complex formation and treatment response. Patient-derived breast cancer xenograft models were used to assess talazoparib monotherapy on tumorigenesis. Immunohistochemistry assays were performed to determine Ki-67, gH2AX and caspase 3 marker expression following talazoparib treatment.

Results: Cytotoxicity was observed in 50% (7/14) cell lines at IC50 values that are achieved in the clinic. BRCA1/2 alterations were detected in 21.4% (3/14) of cell lines sensitive to talazoparib treatment. In 14 patient-derived breast cancer xenograft models selected for this study, 57.1% (8/14) responded to talazoparib monotherapy. Of these, 35.7% had mutations in the BRCA1 (28.6%) and BRCA2 (7.1%) genes. Stable disease was observed in 14.2% (2/14). One stable model had BRCA1 mutations. Tumor regression was observed in 42.8% (6/14) of the models treated with talazoparib monotherapy. Importantly, 66.7% (4/6) of patient-derived breast cancer models that regressed on talazoparib monotherapy had mutations in BRCA1/2 genes.

Conclusions: Cytotoxicity was observed with talazoparib monotherapy in breast cancer cell lines and in patient-derived xenograft tumor models harboring BRCA1 or BRCA2 mutations. Our data demonstrate therapeutic potential of talazoparib monotherapy in breast cancer associated with pathologic BRCA1/2 mutations.

1.Couch FJ et al. J Clin Oncol. 2015;33:304-11.

2. Petrucelli N et al. Genet Med. 2010;12:245-59.

3. Wang B et al. J Med Chem. 2016;59:335-57.

4. Murai J et al. Mol Cancer Ther. 2014;13:433-43.

5. Shen Y et al. Clin Cancer Res. 2013;19:5003-15.

Citation Format: Phan VT, Protter AA, Peterson A, Uppal H. Talazoparib antitumor effects in BRCA-deficient breast cancer models [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P5-06-01.

Abstract P2-07-04: A novel diagnostic androgen receptor gene signature links clinical outcomes and preclinical response to enzalutamide, paclitaxel or the combination in triple-negative breast cancer

Background: The androgen receptor (AR) is expressed in ≈70% of all breast cancers (BCs) and may be necessary for proliferation and survival advantage in AR+ tumors. A novel gene signature associated with AR-signaling biology (PREDICT AR) was developed by sequencing triple-negative BC (TNBC) tumors collected in a phase 2 study evaluating enzalutamide (ENZA) monotherapy1; clinical outcomes were superior in patients (pts) with PREDICT AR+ vs PREDICT AR- tumors.1,2 ENZA blocks nuclear localization and suppresses its activity.3 Paclitaxel (PTX) stabilizes microtubules and may also block AR nuclear localization. Thus we hypothesize that response to PTX-based therapy may be additive in PREDICT AR+ vs PREDICT AR- disease. This study sought to identify independent clinical datasets with PREDICT AR+ gene signature to assess outcomes following PTX-based therapy. Preclinically, we investigated the antitumor activity of ENZA, PTX, or ENZA+PTX in AR-driven TNBC models.

Methods: We probed publicly available TNBC clinical databases from Gene Expression Omnibus datasets to assess PREDICT AR status and clinical outcomes. Similarly, we assessed 21 TNBC lines for PREDICT AR status. BT549, MDA-MB-436, and MDA-MB-453 were treated with ENZA, PTX, or ENZA+PTX to determine activity. Cell signaling and pathway activation were assessed by western blot. ENZA and PTX activity was assessed in PREDICT AR+ xenograft models. Tumor RNA sequencing and immunohistochemistry were used to identify gene signatures, potentially predictive biomarkers, and potential synergistic effects of ENZA+PTX.

Results: The prevalence of PREDICT AR+ tumors in one cohort of 182 pts with primary TNBC4 was 51%. Distant relapse-free survival following PTX-based adjuvant/neoadjuvant therapy was not statistically different between pts with PREDICT AR+ vs PREDICT AR- TNBC (p=0.605). Pathologic complete response rates were 12.5% for PREDICT AR+ vs 21.0% for PREDICT AR- TNBC. Additional sets of pts with primary TNBC are being evaluated. Preclinically, we observed a dose-dependent inhibition of cell viability with either ENZA or PTX in AR+ TNBC cell lines and additive effects from ENZA+PTX. In PREDICT AR+ xenograft models, ENZA or PTX treatment resulted in a dose-dependent antitumor response. Combination studies are underway. Tumor RNA sequencing are being evaluated for gene signature of synergistic antitumor response to ENZA+PTX.

Conclusion: Analyzing publicly available clinical datasets, we found that PREDICT AR+ status was not associated with differential outcomes following PTX-based therapy in primary TNBC, suggesting there is potential to provide additive benefits in PTX-based therapy with ENZA. In preclinical studies, we observed additive effects when combining ENZA+PTX in PREDICT AR+ TNBC lines compared with single agent treatments. Taken together, these data suggest ENZA combined with PTX might provide additive benefits in a clinical setting for pts with PREDICT AR+ TNBC.

References

1. Traina TA et al. J Clin Oncol 2015:33(suppl):abstr 1003.

2. Parker J et al. J Clin Oncol 2015;33(suppl):abstr 1083.

3. Tran C et al. Science 2009;324:787-90.

4. Hatzis C et al. JAMA 2011;305:1873-81.

Citation Format: Phan VT, Protter AA, Peterson AC, Parker JS, Yoon K, Tudor IC, Paton V, Noonberg S, Uppal H. A novel diagnostic androgen receptor gene signature links clinical outcomes and preclinical response to enzalutamide, paclitaxel or the combination in triple-negative breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-07-04.

Inhibition of p38alpha MAPK enhances proteasome inhibitor-induced apoptosis of myeloma cells by modulating Hsp27, Bcl-X(L), Mcl-1 and p53 levels in vitro and inhibits tumor growth in vivo

Inhibition of p38 kinase blocks the production of tumor-promoting factors in the multiple myeloma (MM) bone marrow microenvironment. Proteasome inhibitors MG132 and bortezomib have been shown to have direct cytotoxic effects on MM cells. We show that a selective inhibitor of p38alpha, SCIO-469, enhances the ability of MG132 and bortezomib to induce the apoptosis of MM cells. Previously, we showed that p38 inhibition with SCIO-469 enhances MM cytotoxicity of bortezomib by inhibiting the transient expression and phosphorylation of Hsp27, a downstream target of p38. Here we show that continued treatment of MM cells with bortezomib leads to a SCIO-469-enhanced downregulation of Hsp27 and to increased MM apoptosis. Furthermore, we show that p38 inhibition enhances the bortezomib-induced MM apoptosis by upregulation of p53 and downregulation of Bcl-X(L) and Mcl-1. In a mouse xenograft plasmacytoma model of MM, we found that inhibiting p38 augments the effects of bortezomib in decreasing MM tumor growth in vivo. Thus, in addition to its role in suppressing an activated MM microenvironment, co-treatment with a p38 inhibitor, such as SCIO-469, may enhance the cytotoxicity of bortezomib by modulating pro-apoptotic and anti-apoptotic factors in MM cells, suggesting great potential for co-therapy.

Inhibition of p38 Mitogen-Activated Protein Kinase Protects Human Islets From Cryoinjury and Improves the Yield, Viability, and Quality of Frozen-Thawed Islets

The development of an optimal islet cryopreservation method will permit transplantation of islets from multiple donors in a single procedure and contribute to alleviation of the islet shortage. In this study, we have improved human islet cryopreservation methods under serum-free conditions using an intracellular-based islet cryopreservation solution (ICS), especially supplemented with a p38 pathway inhibitor (p38IH) to suppress p38 mitogen-activated protein kinase (MAPK) activation. Three different solutions were compared for freezing and thawing of human islets (1) conventional RPMI1640 medium, (2) ICS, and (3) ICS supplemented with a p38IH, SD-282 (ICS-p38IH). Islet cryopreservation with ICS-p38IH significantly improved islet recovery, viability, and quality after thawing of cryopreserved islets. This improvement may allow the use of cryopreserved islets in clinical islet transplantation.

Peripheral and central p38 MAPK mediates capsaicin-induced hyperalgesia

The stress-activated mitogen-activated protein kinase (MAPK) p38 is emerging as an important mediator of pain. The present study examined the possible involvement of peripheral and spinal p38 MAPK in capsaicin-induced thermal hyperalgesia. Topical capsaicin produced phosphorylation of p38 MAPK in the skin from the affected hindpaw as well as the corresponding lumbar spinal cord in a time dependent manner. Topical capsaicin produced robust C-fiber mediated thermal hyperalgesia that was inhibited by systemic, local peripheral, or central intrathecal pre-treatment with the p38 MAPK inhibitor, SD-282. Intraperitoneal SD-282 (10-60 mg/kg) significantly and dose-dependently attenuated capsaicin-induced C-fiber mediated thermal hyperalgesia. Similarly, 0.1-5mg/kg subcutaneous SD-282 in the hindpaw dose-dependently attenuated capsaicin-induced thermal hyperalgesia. Intrathecal administration of 1microg SD-282 was also anti-hyperalgesic in this model. Functionally, SD-282 decreased capsaicin-induced release of calcitonin gene related peptide in an in vitro skin release assay, consistent with a role for p38 MAPK in peripheral nerve function. These results suggest that p38 MAPK plays a role in the development of hyperalgesic states, exerting effects both centrally in the spinal cord and peripherally in sensory C fibers.

Differential expression of cardiac ANP and BNP in a rabbit model of progressive left ventricular dysfunction

OBJECTIVE

Activation of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) is considered a hallmark of myocardial remodeling. To determine magnitude and relative proportion of activation during the progression to heart failure, we assessed ANP and BNP gene expression in atrial and left ventricular (LV) tissue in a newly developed model of progressive rapid ventricular pacing-induced heart failure in rabbits.

METHODS

Six animals underwent progressive pacing with incremental rates (330 beats per min (bpm) to 380 bpm over 30 days), resulting in congestive heart failure (CHF). Five animals underwent pacing at 330 bpm for 10 days only (early LV dysfunction, ELVD) and five additional animals served as control group (CTRL).

RESULTS

ELVD was characterized by decreased mean arterial pressure (P=0.05 vs. CTRL) as well as significantly impaired LV function (LV fractional shortening (FS) P<0.01 vs. CTRL) and dilatation (P<0.01 vs. CTRL). CHF was characterized by further decreased mean arterial pressure (P<0.01 vs. ELVD), further impaired LV function (FS P<0.03 vs. ELVD) and dilatation (P<0.01 vs. CTRL). In control animals, significant ANP expression was observed only in atrial tissue (P<0.02 vs. BNP) while BNP expression was ubiquitous but marginal (LV P<0.05 vs. ANP). In ELVD, activation of ANP (atria and LV P<0.05 vs. CTRL) and BNP (atria P<0.05 vs. CTRL, LV n.s.) was observed. In CHF, LV-BNP increased further markedly (P<0.01 vs. CTRL, P<0.05 vs. ELVD) while atrial ANP and BNP expression as well as LV ANP expression remained unchanged (all P=n.s. vs. ELVD).

CONCLUSION

The current studies demonstrate differential activation of atrial and LV ANP and BNP under normal conditions and during the progression to heart failure and provide a molecular basis for the superiority of BNP as marker of LV dysfunction and CHF.

Altered patterns of gene expression in response to myocardial infarction

The use of cDNA microarrays has made it possible to simultaneously analyze gene expression for thousands of genes. Microarray technology was used to evaluate the expression of >4000 genes in a rat model of myocardial infarction. More than 200 genes were identified that showed differential expression in response to myocardial infarction. Gene expression changes were monitored from 2 to 16 weeks after infarction in 2 regions of the heart, the left ventricle free wall and interventricular septum. A novel clustering program was used to identify patterns of expression within this large set of data. Unique patterns were revealed within the transcriptional responses that illuminate changes in biological processes associated with myocardial infarction.

Clearance of human brain natriuretic peptide in rabbits; effect of the kidney, the natriuretic peptide clearance receptor, and peptidase activity

Although the synthetic version of the cardiac peptide human brain natriuretic peptide (hBNP) has demonstrated beneficial cardiovascular effects in clinical studies, little is known about mechanisms governing its elimination from the blood. This study measured the role of the kidney, the natriuretic peptide clearance (NP-C) receptor, and peptidase digestion on the elimination of synthetic hBNP from the plasma compartment of rabbits. The estimated plasma steady state resulting from a continuous i.v. infusion was achieved within 50 min and was related in a linear manner with the infusion rate of the drug. Complete restriction of kidney blood flow by bilateral suture-ligation of the renal arteries compared with sham-treated animals reduced the clearance of hBNP by approximately half (24 +/- 9 ml/min versus 47 +/- 14 ml/min, respectively, p <. 007). Pharmacological blockade of the NP-C receptor with a clearance receptor-specific analog of atrial natriuretic peptide increased in a statistically significant and dose-related manner the plasma steady-state level of hBNP during continuous i.v. infusion of hBNP (maximum effect of 1.9 +/- 0.3-fold, p <.01). The peptidase inhibitor phosphoramidon increased in a dose-related manner the plasma steady-state level of hBNP 1.7 +/- 0.4-fold during continuous i.v. infusion of hBNP in rabbits. These data suggest that the kidney, the NP-C receptor, and peptidases are all important in the elimination of hBNP from the plasma compartment.

Coronary vasodilator effects of BNP: mechanisms of action in coronary conductance and resistance arteries

Brain natriuretic peptide (BNP), a hormone secreted predominantly in ventricular myocytes, may influence coronary vascular tone. We studied the coronary vasodilatory response to BNP under physiological conditions and after preconstriction with endothelin-1 (ET-1) in anesthetized pigs. Average peak-flow velocity (APV) was measured using intracoronary Doppler, and cross-sectional area (CSA) was measured using intravascular ultrasound. Coronary blood flow (CBF) was calculated. Intracoronary BNP induced dose-dependent increases in CSA, APV, and CBF similar in magnitude to those induced by nitroglycerin (NTG). The magnitude of BNP-induced vasodilation was accentuated after preconstriction with ET-1. Pretreatment with either the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester or the cyclooxygenase inhibitor indomethacin attenuated the coronary vasodilator effect of BNP in resistance arteries without influencing epicardial vasodilation. Pretreatment with the ATP-sensitive potassium-channel blocker glibenclamide enhanced epicardial vasodilation in response to BNP. We conclude that BNP exerts coronary vasodilator effects, predominantly in epicardial conductance vessels. An accentuated vasodilatory response to BNP occurs in ET-1-preconstricted arteries. BNP-induced vasodilation in coronary resistance arteries may be partially mediated via nitric oxide and/or prostaglandin release.

Pharmacokinetics and biological actions of subcutaneously administered human brain natriuretic peptide

Human brain natriuretic peptide (hBNP) has demonstrated favorable hemodynamic effects in patients with congestive heart failure; however, the peptidic nature of this compound has focused clinical testing on protocols involving intravenous delivery. We have studied subcutaneous delivery as an alternative method of administering hBNP. Administration of 30 microgram/kg hBNP by either subcutaneous or intravenous delivery protocols resulted in significant hBNP-immunoreactive material in the plasma with area under the plasma concentration-time curve values of 310 +/- 20 nmolxmins/liter and 187 +/- 47 nmolxmins/liter, respectively. Plasma cyclic GMP, a surrogate marker of activation of the biological receptor for hBNP, was elevated for a longer period of time following subcutaneous delivery compared with intravenous delivery. Subcutaneous delivery of 30 microg/kg hBNP resulted in natriuresis, diuresis and reduced systolic blood pressure in anesthetized normotensive rabbits, effects similar in magnitude yet prolonged in duration compared with those elicited by the same dose of hBNP delivered intravenously. Systolic blood pressure following hBNP treatment remained below base-line values for 50 and 150 min following intravenous and subcutaneous delivery protocols, respectively. These results suggests that subcutaneous delivery of hBNP may be a viable therapeutic alternative to intravenous modes of delivery.

Clearance receptors and endopeptidase: equal role in natriuretic peptide metabolism in heart failure

The effects of separate and combined endopeptidase inhibition (by SCH-32615) and natriuretic peptide receptor C blockade [by C-ANP-(4-23)] on the clearance and bioactivity of atrial (ANP) and brain (BNP) natriuretic peptides was investigated in eight sheep with heart failure. SCH-32615 and C-ANP-(4-23) administered separately induced significant and proportionate dose-dependent rises in plasma ANP, BNP, and guanosine 3',5'-cyclic monophosphate (cGMP) levels. Associated with these changes were reductions in arterial pressure, left atrial pressure, and peripheral resistance and increases in cardiac output, urine volume, sodium excretion, and creatinine clearance. SCH-32615 induced greater diuresis and natriuresis than C-ANP-(4-23). Combined administration of SCH-32615 and C-ANP-(4-23) induced greater than additive rises in plasma ANP, BNP, and cGMP concentrations, with enhanced hemodynamic effects, diuresis, and natriuresis and reduced plasma aldosterone levels. In conclusion, we find that the enzymatic and receptor clearance pathways contribute equally to the metabolism of endogenous ANP and BNP in sheep with heart failure. Combined inhibition of both degradative pathways was associated with enhanced hormonal, hemodynamic, and renal effects and may have greater potential therapeutic value than either agent separately.

Human brain natriuretic peptide reduces blood pressure in normotensive and acute norepinephrine-induced hypertensive rabbits

Human brain natriuretic peptide (hBNP) is a cardiac-derived peptide hormone with potent hemodynamic and renal effects in dogs, monkeys, and humans, but not in rats. At present there is no small animal model to study the actions of hBNP. These studies describe the effects of hBNP in New Zealand White rabbits in normotensive and acute norepinephrine-induced hypertensive states. Intravenous administration of hBNP (1, 3, 10, and 30 microg/kg) to anesthetized rabbits resulted in a dose-dependent diuresis and natriuresis and a decrease in systolic blood pressure. Bolus administration of hBNP resulted in a time- and dose-dependent accumulation of plasma cyclic GMP, consistent with activation of a particulate guanylyl cyclase receptor. The hemodynamic actions of hBNP suggest clinical utility for the management of acute hypertension associated with numerous surgical procedures, a condition linked to catecholamine activation. In rabbits with norepinephrine-induced acute hypertension, bolus and continuous infusion of hBNP markedly reduced blood pressure. These studies demonstrate that the rabbit is a useful species to study the hemodynamic and renal effects of hBNP and that this peptide may have therapeutic utility for the acute reduction of hypertension associated with catecholamine activation.

A bradykinin antagonist inhibits both bradykinin- and the allergen-induced airway response in primates

Bradykinin is a mediator of bronchoconstriction and may play a role in the development of the asthmatic response after antigen challenge. Our objective was to study the effectiveness of NPC 17731 as a specific bradykinin beta 2-receptor antagonist and as an antagonist of the allergen-induced early phase of asthma. A primate model was used for all studies. Intracutaneous end-point titrations were performed with bradykinin. A shift of the bradykinin end-point titer was seen when NPC 17731 was injected by the intradermal route prior to performing the end-point titration. Using an aerosolized bradykinin or Ascaris suum antigen airway threshold challenge system, inhibition of the bradykinin or Ascaris airway response was evaluated after pretreatment with aerosolized NPC 17731. NPC 17731 proved to be a safe, effective specific bradykinin receptor antagonist in both cutaneous and airway challenges. NPC 17731 was able to inhibit the antigen-induced airway response in the primate. Bradykinin may play a larger role in mediating the early phase of the antigen-induced asthmatic response than previously was appreciated.

Delayed administration of basic fibroblast growth factor (bFGF) attenuates cognitive dysfunction following parasagittal fluid percussion brain injury in the rat

The present study evaluates the therapeutic effects of delayed administration of bFGF on cognitive dysfunction and histopathological damage following lateral fluid-percussion (FP) brain injury. Male Sprague-Dawley rats were trained to learn a visuospatial task in a Morris Water Maze (MWM) paradigm and then were anesthetized and subjected to either FP brain injury of moderate severity (2.5-2.8 atm, n = 32) or surgery without brain injury (n = 10). Twenty-four hours postinjury, an infusion cannula connected to a mini-osmotic pump was implanted into the area of maximal cortical injury to continuously infuse either bFGF (2.0 g) or vehicle for 7 days. Treatment with bFGF significantly attenuated posttraumatic memory dysfunction in the MWM at 8 days postinjury when compared to vehicle treatment (p < 0.05). The cortical lesion and significant cell loss in the ipsilateral CA3 region of the hippocampus, produced by FP injury, was not affected by bFGF treatment. However, immunohistochemical evaluation of glial fibrillary acidic protein revealed a trend toward increased astrocytosis in the injured cortex of bFGF-treated animals compared to vehicle-treated animals (p < 0.1). These results indicate that bFGF may be efficacious in attenuating cognitive dysfunction associated with traumatic brain injury.

Relaxant effect of human brain natriuretic peptide on human artery and vein tissue

Brain natriuretic peptide (BNP) is a cardiac-derived peptide hormone with cardiovascular and renal actions that is structurally and functionally related to atrial natriuretic peptide (ANP). Previous studies using rat vascular tissue have demonstrated a direct vasorelaxant effect of BNP. However, species-specific potency issues have precluded an accurate measurement of the effect of human BNP. This report demonstrates the vasorelaxant effects of human BNP on human vascular tissue prepared from internal mammary artery and saphenous vein samples. The vasorelaxant effect of human BNP is compared to the other members of the natriuretic peptide family, human ANP and C-type natriuretic peptide (CNP). With regard to potency and magnitude of effect, human BNP and human ANP were similar in relaxing arterial tissue preconstricted with endothelin-1 (BNP ED50 = 1.9 nmol/L and ANP ED50 = 1.8 nmol/L) or phenylephrine (BNP ED50 = 10 nmol/L and ANP ED50 = 19 nmol/L), while CNP was significantly less effective. All three natriuretic peptides exhibited weak venodilating action. These data demonstrate that human BNP is a potent inhibitor of the vasoconstrictive actions of endothelin-1 and the alpha-adrenergic agonist phenylephrine on isolated human artery tissue preparations.

Identification of proteins associated with apolipoprotein A-I-containing lipoproteins purified by selected-affinity immunosorption

The isolation of apolipoprotein A-I-containing lipoproteins [Lp(A-I)] by selected-affinity immunosorption minimizes the loss of associated proteins that occurs during the isolation of high-density lipoproteins (HDL) by sequential ultracentrifugation. We have used two-dimensional gel electrophoretic analysis to separate the proteins associated with Lp(A-I). Using a combination of amino acid sequencing of transblotted proteins and Western blotting with specific antisera, we have identified a number of associated proteins. The positions of the apolipoproteins (apo) A-I, A-II, A-IV, C-III, D, and E were located on the gels. Lecithin-cholesterol acyltransferase and cholesteryl ester transfer protein were identified in association with Lp(A-I) to a greater extent than found associated with HDL after centrifugation. In addition to those proteins previously identified in association with HDL, we detected a number of plasma proteins associated with Lp(A-I), namely, fibrinogen, haptoglobin, proline-rich protein (C4b-binding protein), and apolipoprotein J (SP40,40 sulfated glycoprotein). The co-isolation of these proteins with Lp(A-I) does not appear to be an artifact in that they have very low affinity for a sham column containing covalently bound preimmune goat IgG in place of the anti-apoA-I IgG. These findings suggest that in addition to apolipoproteins that exist largely in association with lipoproteins there is another class of proteins which exist in lipoprotein-associated form and in the dispersed state. Detection and identification of these lipoprotein-associated proteins may aid in the mechanistic determination of a number of observed functions attributed to HDL.

CD36 is a receptor for oxidized low density lipoprotein

The oxidation of low density lipoprotein (LDL) in the arterial wall is thought to contribute to human atherosclerotic lesion formation, in part by the high affinity uptake of oxidized LDL (OxLDL) by macrophages, resulting in foam cell formation. We have utilized cloning by expression to identify CD36 as a macrophage receptor for OxLDL. Transfection of a CD36 clone into 293 cells results in the specific and high affinity binding of OxLDL, followed by its internalization and degradation. An anti-CD36 antibody blocks 50% of the binding of OxLDL to platelets and to human macrophage-like THP cells. Furthermore, like mouse macrophages, 293 cells expressing CD36 recognize LDL which has been oxidized only 4 h, whereas more extensive oxidation of the LDL is required for recognition by the other known OxLDL receptors, the acetylated LDL (AcLDL) receptor and Fc gamma RII-B2. CD36 may play a role in scavenging LDL modified by oxidation and may mediate effects of OxLDL on monocytes and platelets in atherosclerotic lesions.

A macrophage Fc receptor for IgG is also a receptor for oxidized low density lipoprotein

The internalization of oxidized low density lipoprotein (OxLDL) by macrophages is hypothesized to contribute to foam cell formation and eventually to atherosclerotic lesion formation. OxLDL is a ligand for the acetylated low density lipoprotein (AcLDL) receptor, however, our data show that this receptor accounts for less than half of OxLDL uptake by mouse macrophages, suggesting additional receptors for OxLDL. We have developed a novel expression cloning strategy in order to isolate clones encoding OxLDL receptors. In addition to the AcLDL receptor, we isolated a molecular clone for a structurally unrelated receptor capable of mediating the high affinity uptake of OxLDL following transfection into cells. This receptor has been identified as the mouse Fc gamma RII-B2, a member of a family of receptors known to mediate immune complex uptake through recognition of the Fc region of IgG. The uptake of OxLDL by cells transfected with the Fc gamma RII-B2 clone is not blocked by AcLDL but is blocked by the anti-Fc gamma RII monoclonal antibody, 2.4G2.

C-type natriuretic peptide inhibits growth factor-dependent DNA synthesis in smooth muscle cells

We have examined the ability of C-type natriuretic peptide (CNP) to interact with guanylate cyclase-coupled natriuretic peptide receptors by measuring its ability to stimulate intracellular guanosine 3',5'-cyclic monophosphate (cGMP) accumulation in cultured bovine aortic endothelial (BAE) and bovine aortic smooth muscle (BASM) cells. Our experiments indicate that CNP is unable to stimulate the production of cGMP in BAE cells, whereas both atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) markedly elevate cGMP levels in these cells (ANP = BNP >> CNP). In contrast, CNP is the most effective of the three peptides with respect to the stimulation of cGMP levels in BASM cells, fetal human vascular smooth muscle cells, and rat A10 cells (CNP >> ANP > BNP), with the maximal level of stimulation being approximately 5- to 10-fold over that observed for ANP. We have also shown that CNP is able to inhibit serum- and growth factor-induced DNA synthesis in BASM cells. Low concentrations of CNP (20 x 10(-9) M) inhibit up to 80% of the [3H]-thymidine incorporation induced by basic fibroblast growth factor, platelet derived growth factor, epidermal growth factor (EGF), and heparin binding EGF-like growth factor. These data indicate that, although CNP has been detected only in the central nervous system and not in the circulation, it may possess multiple effects on vascular tissue.

Carboxyl terminal analysis of human B-48 protein confirms the novel mechanism proposed for chain termination

In this study we have confirmed the presence of a single base difference between intestinal mRNA coding for B-48 and hepatic mRNA coding for B-100, which results in the substitution of a stop codon (UAA) for a glutamine codon (CAA) at a point corresponding to amino acid residue 2153 in the B-100 sequence. Based on this finding, B-48 is predicted to terminate at residue 2152 with the sequence ... Met Ile. To confirm this finding at the protein level, B-48 and B-100 were each digested with cyanogen bromide and the digestion products were analysed for the presence of isoleucine. Isoleucine was found only in cyanogen bromide digests of B-48 confirming that only B-48 terminates with the predicted amino acid sequence ... Met Ile.

Apolipoprotein B: structure, biosynthesis and role in the lipoprotein assembly process

The complete amino acid sequence of the liver-synthesized apolipoprotein B (apoB) species, apoB 100, has been derived from cloned cDNA. The protein consists of 4536 amino acids (+ a 27 amino acid signal sequence). Cysteine is clustered in the N-terminal 1/10 of the protein, suggesting the presence of a stabilized tertiary structure in this part of the molecule. Three types of structure are suggested to be of importance for the binding of the protein to lipids; (i) hydrophobic sequences with a high probability for beta-sheet structure, (ii) strict amphipathic beta-sheets, and (iii) amphipathic alfa-helices. An apoB 100 molecule is completed within 10-14 min and secreted after approximately 30 min, 1/3 of which is due to the transfer through the endoplasmic reticulum (ER), while 2/3 is spent in the Golgi apparatus. ApoB 100 is co-translationally N-glycosylated and 25% of the oligosaccharide chains is processed in the Golgi compartment. Other posttranslational modifications that have been discussed include covalent acylation and phosphorylation. It has also been suggested that the lipid moiety of the apoB 100 lipoproteins are modified during the passage through the Golgi apparatus. The site of lipoprotein assembly is suggested to be separated from the site of apoB 100 synthesis, and apoB 100 appears to be co-translationally bound to the ER membrane and from this transferred to the ER lumen. Based on these observations a model for the assembly of apoB 100 lipoproteins is discussed in this paper. The intestinal derived apoB species, apoB 48, has a molecular mass of 210 kDa and appears to correspond to the N-terminal 48% of apoB 100. The mechanism by which apoB 48 is formed is still not known. Available data indicate that the protein is formed within the intestinal cells, these data also argue against the possibility that apoB 48 is formed by posttranslational proteolysis of apoB 100. The formation of a separate apoB 48 mRNA by alternative splicing has been suggested, based on the observation of a 7 kb mRNA which corresponds to the 5' portion of the apoB 100 mRNA. However, the most abundant apoB mRNA species found in the intestine have a size that corresponds to that of the apoB 100 mRNA, furthermore the observation that apoB 48 appears to terminate in a 7.5 kb exon that appears to lack alternative splice sites, does not favour the possibility of alternative splicing.

Structural comparison of human apolipoproteins B-48 and B-100

In this study we have investigated the structural relationship between human apolipoproteins B-48 and B-100 by comparing protein structure and by comparing nucleotide sequence from intestinal and hepatic cDNA clones. Sequences from intestinal and hepatic cDNA were identical over the entire distance analyzed (7194 bases), which is more than required to code for B-48. The amino-terminal amino acid sequences from intact B-48 and B-100 proteins were also identical over the entire distance analyzed (16 residues). Additional protein homology was evaluated by the combined techniques of peptide mapping and immunoblotting. Purified B-48 and B-100 were each digested with three different endoproteases, and the resulting peptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Peptide bands were then detected by silver stain and by Western blotting with antisera against specific regions of B-48 and B-100. The resulting patterns suggest that B-48 is extensively homologous with the amino-terminal portion of B-100. We have identified only four peptides from B-48 (at least one in each digest) that are absent from the parallel digests of B-100. These peptides appear to arise from the ultimate carboxyl terminus of B-48 and appear to be totally homologous with a region located near the center of B-100. Our observations suggest that mature, circulating B-48 is homologous over its entire length (estimated to be between 2130 and 2144 amino acid residues) with the amino-terminal portion of B-100 and contains no sequence from the carboxyl end of B-100.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and characterization of human apolipoprotein A-I in Chinese hamster ovary cells

We produced human apolipoprotein A-I (apoA-I) in Chinese hamster ovary (CHO) cells. The CHO cells were transfected with an expression plasmid which placed the human apoA-I gene under the direction of the human metallothionein II gene promoter. Isolation of a clonal cell line resulted in high level expression of apoA-I. Greater than 30% of total protein secreted by these CHO cells was apoA-I, which enabled us to purify apoA-I with a single step purification scheme. As a result, large quantities of apoA-I can be produced and isolated without having to rely on plasma sources. Structural characterization of the recombinant apoA-I showed it to be identical to authentic apoA-I from human serum high density lipoprotein. Furthermore, we demonstrated approximately equal to 90% of the apoA-I secreted by CHO cells is processed, mature protein. A portion of the secreted recombinant apoA-I was associated with lipid and floated at a density approximately equal to 1.10 g/ml. Additional analysis identified the presence of five isoforms of apoA-I in the CHO cell conditioned medium. Processing and post-translational modification of the recombinant apoA-I occurred in the CHO cell cultures in the absence of serum components. We conclude that the human apoA-I produced by CHO cells is identical to circulating, mature apoA-I in humans and that recombinant mammalian expression offers an opportunity to investigate apoA-I processing.

Mapping of human apolipoprotein B antigenic determinants

A minimum of 16 epitopes which provide a group of topographical markers to study the conformation of apolipoprotein (apo) B have been mapped in relation to elements of the sequence of apo B-100. Six of these epitopes are identified by monoclonal antibodies (Mabs) directed against low density lipoprotein (LDL) apo B, while at least 10 others react with Mabs obtained by immunization with delipidated and solubilized apo B. Five epitopes which are also expressed on apo B-48 have been assigned to the thrombolytic fragment T4 on the N-terminal side of apo B-100. None of these five epitopes requires the presence of lipids for its expression, suggesting that the conformation of the T4 region of apo B is more dependent on peptide-chain interactions than on peptide-lipid interactions. Four distinct epitopes have been assigned to the median thrombolytic fragment T3 of apo B-100, all of which require the presence of lipids for their expression; those epitopes closer to the C-terminus of T3 require specific interaction with cholesteryl esters. The same lipid dependence also characterizes a cluster of epitopes mapped to the N-terminal region of fragment T2. The epitopes that are close to the T2/T3 cleavage site and depend on the presence of cholesteryl esters for their expression are also those that react with the Mabs that inhibit the binding of LDL to its receptor. Therefore this region, which in addition contains two sequences with structural homology to the apo E receptor binding domain, probably constitutes a physiologically important receptor binding site for apo B. Finally, four other distinct epitopes which do not require the presence of lipids for their expression have been mapped on T2. In conclusion, the present report presents evidence that the immunochemical analogy of apo B-48 and apo B-100 is on the N-terminal half of apo B-100, whereas the apo B receptor binding domain is localized on the C-terminal half of apo B-100 close to the T2/T3 cleavage site.

RFLPs for the human apolipoprotein B gene: HincII and PvuII

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Analysis of cDNA clones encoding the entire B-26 region of human apolipoprotein B

We report the characterization of intestine and liver cDNA clones for human apolipoprotein B (apoB) that map to the 5' end of the mRNA. The protein sequence encoded by the 5011 nucleotides derived from sequence analysis of these clones includes 1643 amino acid residues of the mature protein of Mr 184,000. The amino acid sequence at the amino terminus of B-74 peptide was determined and mapped to residue 1298. The size (Mr 145,700) and amino acid composition of the B-26 region encoded by these clones (including amino acid residues 1-1297) closely match the values obtained from the B-26 peptide. The amino acid sequence of peptide B-100 at the junction of peptides B-26 and B-74 (Phe-Lys decreases- Ser) shows structural homology to the site on human kininogen (Phe-Arg decreases- Ser) that is cleaved by the protease plasma kallikrein. The encoded protein contains five potential N-glycosylation sites and several regions in which the hydroxyamino acids, serine and threonine, are present in high abundance. The protein sequence presented in this report represents approximately 30% of the total B-100 protein and will aid in the characterization of additional cDNA clones.

Pvu II RFLP in the 5' of the human apolipoprotein B gene

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Isolation of a cDNA clone encoding the amino-terminal region of human apolipoprotein B

A partial cDNA clone for the B-26 region of apolipoprotein B was isolated from an adult human liver DNA library by screening with an oligonucleotide probe derived from amino-terminal protein sequence obtained from purified B-26 peptide. Antisera against a synthetic 17-residue peptide whose amino acid sequence was encoded by the clone cross-reacts with apolipoproteins B-26, B-100, and B-48, but not with B-74. The nucleotide sequence immediately upstream from the amino terminus of B-26 codes for an apparent signal sequence, implying that the B-26 moiety is in an amino-terminal locus in the B-100 protein. That this sequence represents a 5' end region is further supported by primer extension analysis using a fragment of the cDNA clone and by S1 nuclease protection experiments using the corresponding region in a genomic clone.

Isolation and sequence analysis of the human apolipoprotein CIII gene and the intergenic region between the apo AI and apo CIII genes

We have isolated and characterized the gene for human apolipoprotein CIII, a major component of the triglyceride-rich lipoproteins. Determination of the complete DNA sequence of this gene revealed that the coding sequence is interrupted by three introns, which occur in the 5' noncoding region, in the region encoding the signal sequence and in the region coding for the mature plasma protein, respectively. We present an analysis of the structure of the apo CIII gene and compare it to the gene for apolipoprotein AI. In addition, we present the DNA sequence of the intergenic region lying between the apo AI and the apo CIII genes.

Independent developmental programs for two estrogen-regulated genes

Measurement of hepatic apolipoprotein II and vitellogenin II messenger RNA during chicken embryogenesis showed that these genes acquire estrogen responsiveness at different stages of development. Sensitive solution hybridization assays with excess complementary DNA showed that apolipoprotein II transcripts were induced to 500 molecules per cell at day 9, whereas induction of vitellogenin II messenger RNA was not found until day 11. Thus, two estrogen regulated genes of common function and coordinately regulated in the adult may be on independent developmental programs.

Isolation and DNA sequence of full-length cDNA and of the entire gene for human apolipoprotein AI--discovery of a new genetic polymorphism in the apo AI gene

We have isolated full-length cDNA clones for apolipoprotein AI from a human fetal liver cDNA library made in the vector lambda gt10. One such clone, pBL13AI, was 965 nucleotides long and contained the entire preproapolipoprotein AI sequence, in addition to 86 nucleotides of 5' untranslated region and 75 nucleotides of the 3' untranslated region. The complete structure of this clone is presented. Furthermore, we have obtained a 20-kb genomic fragment from a human genomic library, encompassing the entire apo AI gene. Sequence analysis of the gene shows that the coding region is interrupted by three introns of 197, 187, and 588 bp, respectively. Digestion of the DNA of various individuals with the endonuclease Msp I revealed a new restriction site polymorphism in the apo AI gene.

Isolation and characterization of a cDNA clone specific for avian vitellogenin II

A clone for vitellogenin, a major avian, estrogen responsive egg yolk protein, was isolated from the cDNA library of estrogen-induced rooster liver. Two forms of plasma vitellogenin, vitellogenin I (VTG I) and vitellogenin II (VTG II), distinguishable on the basis of their unique partial proteolysis maps, have been characterized and their corresponding hepatic precursor forms identified. We have used this criterion to specifically characterize which vitellogenin protein had been cloned. Partial proteolysis maps of BTG I and VTG II standards, synthesized in vivo, were compared to maps of protein synthesized in vitro using RNA hybrid-selected by the vitellogenin plasmid. Eight major digest fragments were found common to the in vitro synthesized vitellogenin and the VTG II standard while no fragments were observed to correspond to the VTG I map. A restriction map of the VTG II cDNA clone permits comparison to previously described cDNA and genomic vitellogenin clones.

Biosynthesis of apolipoprotein B in rooster kidney, intestine, and liver

After in vitro incubation with radiolabeled amino acids, extracts of various chicken tissues were screened for newly synthesized proteins reactive with antibody to plasma apolipoprotein B (apo B). An immunologically related protein was found in kidney as well as liver and intestine. This kidney protein showed the same mobility upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis as plasma apo B or pulse-labeled apo B made by liver or intestine. Partial proteolysis mapping with porcine elastase or V8 protease revealed nearly identical partial cleavage maps of pulse-labeled apo B from kidney, intestine, and liver. These data show that the kidney is a site of apo B synthesis and suggest that the kidney may be a significant source of plasma lipoproteins. Apo B synthesis was also detected in the distal small intestine and colon as well as in the proximal small intestine. The relative rate of apo B synthesis was 5% of total protein synthesis in the duodenum and decreased progressively to about 1% of protein synthesis in the colon. The synthesis of apo B in the distal small intestine and colon may indicate a similar capacity for dietary fat absorption via lipoprotein particles in all intestinal regions. The large intestine may be an additional source of plasma lipoproteins.