br Conflict of Interest br Transparency Document

Conflict of Interest
Transparency Document
Introduction Mitoxantrone (MXT) is an androstenedione chemotherapeutic agent that is used to treat acute nonlymphocytic leukemia, acute lymphoblastic leukemia, prostate cancer, metastatic breast cancer, and non-Hodgkin’s lymphoma [13], [14]. It is also approved by the Food and Drug Administration (FDA) for progressive/relapsing (also called worsening relapsing-remitting) and secondary progressive multiple sclerosis (MS) [7], [47]. Its chemical structure is similar to that of doxorubicin, a widely used anthracycline chemotherapeutic agent. MXT causes apoptosis in proliferating and non-proliferating cells by inhibiting DNA replication, DNA-dependent RNA synthesis and DNA repair by topoisomerase II [13]. The drug also has numerous effects on immune function, resulting in decreased lymphocyte proliferation, decreased cytokine release, suppression of T-cell and B-cell function, including antibody production [9], [13]. However, the therapeutic efficacy of MXT is limited by its irreversible cumulative dose-related cardiotoxicity [33], [60] and its potential to cause secondary leukemias [5], [13]. Pituitary adenylate cyclase-activating polypeptide (PACAP) was first isolated from the hypothalamus during a search for novel hypophysiotropic factors [48], but it rapidly became clear that it is a multifunctional peptide with potent anti-inflammatory and potent cytoprotective properties [69]. PACAP is a member of the secretin/growth hormone-releasing hormone/vasoactive intestinal peptide (VIP) family. It exists as two α-amidated peptides with 38 (PACAP38) or 27 (PACAP27) amino acids, and PACAP27 has 68% sequence identity with VIP. PACAP binds to three subtypes of Class II (secretin-type) G protein-coupled receptors that are called the PAC1, VPAC1 and VPAC2 receptors [23]. PACAP binds not only to the PAC1 receptor with high affinity, but it also binds to the VPAC1 (VIP1) and VPAC2 (VIP2) receptors with affinities comparable to or greater than VIP. On the other hand, VIP binds to the PAC1 receptor with an affinity 100–1000 times lower than PACAP [24]. PACAP is most abundant in the brain, but there are high levels in other organs, including the thymus, spleen, lymph nodes, and duodenal mucosa [69]. The cytoprotective effects of PACAP have been most extensively studied in the Bay 11-7085 and kidney [40], [69], [72]. PACAP has both direct and indirect cytoprotective effects in the brain and kidney [32], [72]. The direct protective effects of PACAP in the brain and kidney are mediated mainly via the cyclic AMP/protein kinase A signal transduction pathway, while the indirect protective effects of PACAP are mediated by multiple signal transduction pathways [32], [69], [72]. PACAP protects the brain, kidney and liver against ischemia/reperfusion injury [28], [31], [59], [68] and protects the brain and kidney from injury caused by a wide range of therapeutic agents [2], [32], [40], [41], [69]. Despite extensive library screens by major pharmaceutical companies over several decades, small molecule orthosteric agonists have not been found for the cognate receptors for any member of the secretin/growth hormone-releasing hormone/VIP family [24], [27]. PACAP/VIP receptors are found in the myocardium: the PAC1 receptor is the predominant receptor in cardiac myocytes and the VPAC2 receptor is the predominant receptor in cardiac fibroblasts [63]. The VPAC2 receptor is also the predominant PACAP/VIP receptor in vascular smooth muscle cells [63], [69]. PACAP has positive inotropic and chronotropic effects on the heart [61] and increases blood flow to most major organs [69]. PACAP has only a slight transient effect on systemic blood pressure [4], [39]. PACAP directly protects cardiomyocytes in vitro against oxidative stress and doxorubicin [18], [19], [56], [57]. In addition, the cardiotoxicity elicited by doxorubicin is exacerbated in PACAP-deficient mice and significantly reduced in PACAP-deficient mice by treatment with PACAP38 [49]. Mori and colleagues [49] did not determine whether PACAP can protect wild-type mice against doxorubicin. Whether PACAP can protect against MXT-induced cardiotoxicity has not been determined in vitro or in vivo. Therefore, the purpose of this study was to test the hypothesis that PACAP can block MXT-induced cardiotoxicity in mice. We show for the first time that PACAP significantly attenuates MXT-induced left ventricular dysfunction and remodeling in wild-type mice in vivo. However, the clinical utility of these observations would be limited if PACAP also blocked the therapeutic actions of MXT. Therefore, we also demonstrated that PACAP does not protect cultured human leukemia cells against MXT-induced cell death. PACAP has already been shown by several laboratories to be efficacious in preclinical in vivo models for MS [15], [20], [30], [66], [67].