Molecular models of N-benzyladriamycin-14-valerate (AD 198) in complex with the phorbol ester-binding C1b domain of protein kinase C-delta

Pivarubicin Is More Effective Than Doxorubicin Against Triple-Negative Breast Cancer In Vivo

Triple-negative breast cancer (TNBC) is unresponsive to antiestrogen and anti-HER2 therapies, requiring the use of cytotoxic drug combinations of anthracyclines, taxanes, cyclophosphamide, and platinum compounds. Multidrug therapies achieve pathological cure rates of only 20–40%, a consequence of drug resistance and cumulative dose limitations necessitated by the reversible cardiotoxic effects of drug therapy. Safer and more effective treatments for TNBC are required to achieve durable therapeutic responses. This study describes the mechanistic analyses of the novel anthracycline, pivarubicin, and its in vivo efficacy against human primary TNBC. Pivarubicin directly activates PKCd, triggers rapid mitochondrial-dependent apoptosis, and circumvents resistance conferred by overexpression of P-glycoprotein, Bcl-2, Bcl-X_L, and Bcr-Abl. As a consequence, pivarubicin is more cytotoxic than doxorubicin against MDA-MB-231, and SUM159 TNBC cell lines grown in both monolayer culture and tumorspheres. Comparative in vivo efficacy of pivarubicin and doxorubicin was performed in an orthotopic NSG mouse model implanted with MDA-MB-231 human TNBC cells and treated with the maximum tolerated doses (MTDs) of pivarubicin and doxorubicin. Tumor growth was monitored by digital caliper measurements and determination of endpoint tumor weight and volume. Endpoint cardiotoxicity was assessed histologically by identifying microvacuolization in ventricular cardiomyocytes. Primary tumors treated with multiple rounds of doxorubicin at MTD failed to inhibit tumor growth compared with vehicle-treated tumors. However, administration of a single MTD of pivarubicin produced significant inhibition of tumor growth and tumor regression relative to tumor volume prior to initiation of treatment. Histological analysis of hearts excised from drug- and vehicle-treated mice revealed that pivarubicin produced no evidence of myocardial damage at a therapeutic dose. These results support the development of pivarubicin as a safer and more effective replacement for doxorubicin against TNBC as well as other malignancies for which doxorubicin therapy is indicated.

Mutations of p53 decrease sensitivity to the anthracycline treatments in bladder cancer cells

Due to doxorubicin (Dox) cardiotoxicity, the next generation of novel non-cardiotoxic anthracyclines, including AD 312 and AD 198, were synthesized and validated. In this study, we assessed the efficacy and mechanisms of anthracyclines-induced apoptosis and inhibition of cell viability in human bladder cancer cells expressing wild-type (wt) p53 (RT4 and SW780) and mutated (mt) p53 (UM-UC-3, 5637, T-24, J82, and TCCSUP) protein. Anthracyclines inhibited cell viability in tested TCC cells, but were less effective in mt-p53 TCC cells, especially in the drug-resistant J82 and TCCSUP cells. Anthracyclines upregulated the expression of wt p53 protein in RT4 and SW780 cells, but had no effect on expression of mt p53 protein in UM-UC-3, 5637, T-24, J82, and TCCSUP cells. The anthracyclines activated caspase 3/7 and cleavage of PARP in wt-p53 RT4 and SW780 cells, and mt-p53 5637, UM-UC-3, and T-24, but not in mt-p53 J82 and TCCSUP cells. The anthracyclines-induced cleavage of PARP was blocked by p53 siRNA in wt-p53 RT4 cells. Co-treatment of AD 198 with PRIMA-1 significantly inhibited cell viability of mt-p53 J82 cells, but had no effect in wt-p53 RT4 cells. AD 198 blocked c-myc expression in mt-p53 UM-UC-3, 5637, T-24, and J82 cells, however no expression of c-myc was detected in wt-p53 RT4 and SW780 cells. In conclusion, our results demonstrated that the anthracycline-induced resistance in bladder cancer cells positively correlated with TP53 mutations in the tetramerization domain in J82 and TCCSUP cells. Further, AD 312 and AD 198 are promising chemotherapeutic drugs for bladder cancer, especially in combination with PRIMA-1.

N-benzyladriamycin-14-valerate (AD 198) exhibits potent anti-tumor activity on TRAF3-deficient mouse B lymphoma and human multiple myeloma

Background

TRAF3, a new tumor suppressor identified in human non-Hodgkin lymphoma (NHL) and multiple myeloma (MM), induces PKCδ nuclear translocation in B cells. The present study aimed to evaluate the therapeutic potential of two PKCδ activators, N-Benzyladriamycin-14-valerate (AD 198) and ingenol-3-angelate (PEP005), on NHL and MM.

Methods

In vitro anti-tumor activities of AD 198 and PEP005 were determined using TRAF3^-/- mouse B lymphoma and human patient-derived MM cell lines as model systems. In vivo therapeutic effects of AD 198 were assessed using NOD SCID mice transplanted with TRAF3^-/- mouse B lymphoma cells. Biochemical studies were performed to investigate signaling mechanisms induced by AD 198 or PEP005, including subcellular translocation of PKCδ.

Results

We found that AD 198 exhibited potent in vitro and in vivo anti-tumor activity on TRAF3^-/- tumor B cells, while PEP005 displayed contradictory anti- or pro-tumor activities on different cell lines. Detailed mechanistic investigation revealed that AD 198 did not affect PKCδ nuclear translocation, but strikingly suppressed c-Myc expression and inhibited the phosphorylation of ERK, p38 and JNK in TRAF3^-/- tumor B cells. In contrast, PEP005 activated multiple signaling pathways in these cells, including PKCδ, PKCα, PKCϵ, NF-κB1, ERK, JNK, and Akt. Additionally, AD198 also potently inhibited the proliferation/survival and suppressed c-Myc expression in TRAF3-sufficient mouse and human B lymphoma cell lines. Furthermore, we found that reconstitution of c-Myc expression conferred partial resistance to the anti-proliferative/apoptosis-inducing effects of AD198 in human MM cells.

Conclusions

AD 198 and PEP005 have differential effects on malignant B cells through distinct biochemical mechanisms. Our findings uncovered a novel, PKCδ-independent mechanism of the anti-tumor effects of AD 198, and suggest that AD 198 has therapeutic potential for the treatment of NHL and MM involving TRAF3 inactivation or c-Myc up-regulation.

Protection from doxorubicin-induced cardiomyopathy using the modified anthracycline N-benzyladriamycin-14-valerate (AD 198)

The anthracycline doxorubicin (Dox) is an effective antitumor agent. However, its use is limited because of its toxicity in the heart. N-Benzyladriamycin-14-valerate (AD 198) is a modified anthracycline with antitumor efficacy similar to that of Dox, but with significantly less cardiotoxicity and potentially cardioprotective elements. In the present study, we investigated the possibility of in vivo protective effects of low-dose AD 198 against Dox-induced cardiomyopathy. To do this, rats were divided into four groups: vehicle, Dox (20 mg/kg; single injection day 1), AD 198 (0.3 mg/kg per injection; injections on days 1, 2, and 3), or a combination treatment of Dox + AD 198. Seventy-two hours after beginning treatment, hearts from the Dox group had decreased phosphorylation of AMP kinase and troponin I and reduced poly(ADP-ribose) polymerase, β-tubulin, and serum albumin expression. Dox also increased the phosphorylation of phospholamban and expression of inducible nitric-oxide synthase in hearts. Each of these Dox-induced molecular changes was attenuated in the Dox + AD 198 group. In addition, excised hearts from rats treated with Dox had a 25% decrease in left ventricular developed pressure (LVDP) and a higher than normal increase in LVDP when perfused with a high extracellular Ca(2+) solution. The Dox-induced decrease in baseline LVDP and hyper-responsiveness to [Ca(2+)] was not observed in hearts from the Dox + AD 198 group. Thus Dox, with well established and efficient antitumor protocols, in combination with low levels of AD 198, to counter anthracycline cardiotoxicity, may be a promising next step in chemotherapy.

Topical application of valrubicin has a beneficial effect on developing skin tumors

Valrubicin is a second generation anthracycline characterized by an excellent safety profile presenting no skin toxicity or necrosis upon contact. In its current liquid formulation (Valstar; Indevus Pharmaceuticals, Lexington, MA), it is approved solely for the treatment of bladder cancer. Recently, valrubicin was incorporated in a cream formulation rendering this drug available for topical application. The cytostatic property of valrubicin can, thus, be employed for treating hyperproliferative skin diseases as was recently described for psoriasis. In the present study, the effect of topical application of valrubicin was investigated in skin tumor development; we hypothesized that valrubicin may be employed in treating actinic keratosis, a hyperproliferative skin condition that may transform into malignancy. A two-stage chemical mouse skin carcinogenesis model that represents the multistage etiology of human skin cancer-from developing papillomas to squamous cell carcinoma (SCC) was used. Moreover, two human skin SCC cell lines: DJM-1 and HSC-1 were cultured, to further investigate the effect of valrubicin in vitro. Cell viability was assessed by adenosine triphosphate presence, proliferation as proliferative cell nuclear antigen expression and apoptosis as cytokeratin 18 cleavage, caspase activation, poly-adenosine diphosphate-ribose-polymerase cleavage and bax and bcl-2 regulation. Valrubicin significantly inhibited tumor formation in the mouse skin carcinogenesis model and significantly decreased cell viability of the cultured human skin SCC cells. In both mouse skin and SCC cells, proliferation was significantly decreased. Apoptosis was significantly increased in SCC cells but unchanged in the treated mouse skin at study completion. This study demonstrated that topical application of valrubicin has a beneficial effect in treating developing skin tumors.

N-Benzyladriamycin-14-valerate (AD 198): a non-cardiotoxic anthracycline that is cardioprotective through PKC-epsilon activation

N-Benzyladriamycin-14-valerate (AD 198) is one of several novel anthracycline protein kinase C (PKC)-activating agents developed in our laboratories that demonstrates cytotoxic superiority over doxorubicin (Adriamycin; DOX) through its circumvention of multiple mechanisms of drug resistance. This characteristic is attributed at least partly to the principal cellular action of AD 198: PKC activation through binding to the C1b (diacylglycerol binding) regulatory domain. A significant dose-limiting effect of DOX is chronic, dose-dependent, and often irreversible cardiotoxicity ascribed to the generation of reactive oxygen species (ROS) from the semiquinone ring structure of DOX. Despite the incorporation of the same ring structure in AD 198, we hypothesized that AD 198 might also be cardioprotective through its ability to activate PKC-epsilon, a key component of protective ischemic preconditioning in cardiomyocytes. Chronic administration of fractional LD(50) doses of DOX and AD 198 to mice results in histological evidence of dose-dependent ventricular damage by DOX but is largely absent from AD 198-treated mice. The absence of significant cardiotoxicity with AD 198 occurs despite the equal ability of DOX and AD 198 to generate ROS in primary mouse cardiomyocytes. Excised rodent hearts perfused with AD 198 prior to hypoxia induced by vascular occlusion are protected from functional impairment to an extent comparable to preconditioning ischemia. AD 198-mediated cardioprotection correlates with increased PKC-epsilon activation and is inhibited in hearts from PKC-epsilon knockout mice. These results suggest that, despite ROS production, the net cardiac effect of AD 198 is protection through activation of PKC-epsilon.

N-benzyladriamycin-14-valerate (AD 198) activates protein kinase C-?? holoenzyme to trigger mitochondrial depolarization and cytochrome c release independently of permeability transition pore opening and Ca2+ influx

Unlike nuclear-targeted anthracyclines, the extranuclear-targeted doxorubicin congener, N-benzyladriamycin-14-valerate (AD 198), does not interfere with normal topoisomerase II activity, but binds to the C1b regulatory domain of conventional and novel isoforms of protein kinase C (PKC). The resulting interaction leads to enzyme activation and rapid apoptosis in a variety of mammalian cell lines through a pathway involving mitochondrial events such as membrane depolarization (Deltapsim) and cytochrome c release. Unlike other triggers of apoptosis, AD 198-mediated apoptosis is unimpeded by the expression of Bcl-2 and Bcl-XL. We have further examined AD 198-induced apoptosis in 32D.3 mouse myeloid cells to determine how the anti-apoptotic effects of Bcl-2 are circumvented. The PKC-delta inhibitor, rottlerin, and transfection with a transdominant-negative PKC-delta expression vector both inhibit AD 198 cytotoxicity through inhibition of Deltapsim and cytochrome c release. While the pan-caspase inhibitor Z-VAD-FMK blocks AD 198-induced PKC-delta cleavage, however, it does not inhibit Deltapsim and cytochrome c release, indicating that AD 198 induces PKC-delta holoenzyme activation to achieve apoptotic mitochondrial effects. AD 198-mediated Deltapsim and cytochrome c release are also unaffected by cellular treatment with either the mitochondrial permeability transition pore complex (PTPC) inhibitor cyclosporin A or the Ca chelators EGTA and BAPTA-AM. These results suggest that AD 198 activates PKC-delta holoenzyme, resulting in Deltapsim and cytochrome c release through a mechanism that is independent of both PTPC activation and Ca flux across the mitochondria. PTPC-independent mitochondrial activation by AD 198 is consistent with the inability of Bcl-2 and Bcl-XL expression to block AD 198-induced apoptosis.

N-Benzyladriamycin-14-Valerate (AD198) Induces Apoptosis through Protein Kinase C-δ–Induced Phosphorylation of Phospholipid Scramblase 3

Phospholipid scramblase 3 (PLS3) is an enzyme that plays a critical role in mitochondrial morphology, functions, and apoptotic response. During apoptosis, activated protein kinase C-delta (PKC-delta) translocates to mitochondria and phosphorylates PLS3. Here, we utilize an extranuclear-targeted anthracycline N-benzyladriamycin-14-valerate (AD198), a PKC-delta activator, to investigate the mechanism of PLS3 phosphorylation by PKC-delta. Overexpression of PLS3 enhanced, whereas down-regulation of PLS3 by small interfering RNA decreased, the sensitivity of AD198-induced apoptosis. Overexpression of PKC-delta, but not the kinase-defective PKC-delta, and AD198 treatment enhanced threonine phosphorylation of PLS3. The phosphorylated threonine was mapped to Thr21 of PLS3. Mutation of Thr21 to alanine did not affect mitochondrial localization of PLS3 but abolished threonine phosphorylation by PKC-delta in vitro and AD198-induced PLS3 phosphorylation in vivo. Expression of PLS3(T21A) in cells could not enhance AD198-induced apoptosis compared with expression of the wild-type PLS3. Using benzyloxycarbonyl-Val-Ala-Asp-(OMe) fluoromethyl ketone and cyclosporine A, we also showed that AD198-induced PLS3 phosphorylation occurs upstream of caspase activation and independent of mitochondrial permeability transition. These studies establish that AD198-activated PKC-delta induces phosphorylation of mitochondrial PLS3 at Thr21 and that PLS3 is a critical downstream effector of PKC-delta in AD198-induced apoptosis.

Molecular Interaction Model for the C1B Domain of Protein Kinase C-γ in the Complex with Its Activator Phorbol-12-myristate-13-acetate in Water Solution and Lipid Bilayer

Detailed molecular models of the free C1B domain of protein kinase C-gamma (PKC-gamma) and the C1B domain with its activator phorbol-12-myristate-13-acetate (PMA) in water solution and in the presence of dipalmitoylphosphatidylcholine (DPPC) bilayer are presented. Molecular dynamics of the free C1B domain reveals hydrogen bonds, which are critical for the forming of the diacylglycerols/phorbol esters binding site, and indicates the important role of Gln27 for the geometry of this site. According to the model, PMA interacts with the C1B domain by hydrophobic interactions with Pro11 and Tyr22 and by three persistent hydrogen bonds between the C3 carbonyl group of PMA and Gly23 and between the C20 hydroxyl group of PMA and the Leu21 and Thr12 residues of the C1B domain. The C9 hydroxyl group of PMA does not interact with the C1B domain, but it is involved in the interaction with the DPPC bilayer. Two preferential orientations of the C1B-PMA complex toward the DPPC bilayer resulted from our molecular modeling study.

Circumvention of nuclear factor kappaB-induced chemoresistance by cytoplasmic-targeted anthracyclines

Nuclear factor kappaB (NF-kappaB) has been implicated in inducible chemoresistance against anthracyclines. In an effort to improve the cytotoxicity of anthracyclines while reducing their cardiotoxic effects, we have developed a novel class of extranuclear-localizing 14-O-acylanthracyclines that bind to the phorbol ester/diacylglycerol-binding C1b domain of conventional and novel protein kinase C (PKC) isoforms, thereby promoting an apoptotic response. Because PKCs have been shown to be involved in NF-kappaB activation, in this report, we determined the mechanism of NF-kappaB activation by N-benzyladriamycin-14-valerate (AD 198) and N-benzyladriamycin-14-pivalate (AD 445), two novel 14-O-acylanthracylines. We show that the induction of NF-kappaB activity in response to drug treatment relies on the activation of PKC-delta and NF-kappaB-activating kinase (NAK), independent of ataxia telengectasia mutated and p53 activities. In turn, NAK activates the IKK complex through phosphorylation of the IKK-2 subunit. We find that neither NF-kappaB activation nor ectopic expression of Bcl-X(L) confers protection from AD 198-induced cell killing. Overall, our data indicate that activation of novel PKC isoforms by cytoplasmic-targeted 14-O-acylanthracyclines promotes an apoptotic response independent of DNA damage, which is unimpeded by inducible activation of NF-kappaB.

Anthracycline drug targeting: cytoplasmic versus nuclear--a fork in the road

The anthracycline antibiotics doxorubicin (Adriamycin; DOX) and daunorubicin (DNR) continue to be essential components of first-line chemotherapy in the treatment of a variety of solid and hematopoietic tumors. The overall efficacies of DOX and DNR are, however, impeded by serious dose-limiting toxicities, including cardiotoxicity, and the selection of multiple mechanisms of cellular drug resistance. These limitations have necessitated the development of newer anthracyclines whose structural and functional modifications circumvent these impediments. In this review, we will present recent strategies in anthracycline design and assess their potential therapeutic merits. Current anthracycline design has diverged to target either cytoplasmic or nuclear sites. Nuclear targets have been broadened to include not only topoisomerase II (topo II) inhibition through ternary complex stabilization and catalytic inhibition, but also topoisomerase I (topo I) inhibition and transcriptional inhibition. In contrast, cytoplasmic targeting focuses on anthracycline binding to protein kinase C (PKC) regulatory domain with consequent modulation of activity.