Lipid Metabolism and KSHV-associated Lymphoma Pathogenesis

DESCRIPTION (provided by applicant): The Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of cancers arising preferentially within immune compromised hosts, including patients infected with HIV. One of these cancers, a clonal B-cell malignancy known as primary effusion lymphoma (PEL), is associated with significant mortality, and there are currently no effective therapies for reducing the progression of PEL or prolonging survival. Pathogenesis of PEL involves KSHV gene expression and activation of specific signal transduction pathways which induce proliferation and prolong survival of tumor cells. Therefore, the development of novel compounds targeting these pathways specifically activated by KSHV may result in more effective and safe treatment options for PEL. Bioactive sphingolipids play an important role in many physiologic processes, but aberrant sphingolipid metabolism related to the action of sphingosine kinase (SK) and the generation of sphingosine-1-phosphate (S1P) also contribute to cancer progression. We have generated an active compound, ABC294640, that specifically targets multiple SK isoforms and effectively impairs S1P- mediated signal transduction while inducing tumor cell death in vitro and in vivo. With the knowledge that ABC294640 inhibits signal transduction relevant to PEL pathogenesis, we performed preliminary studies to determine whether ABC294640 inhibits PEL cell growth. Our in vitro studies revealed that ABC294640 selectively inhibits KSHV-infected lymphoma cell growth but not the growth of KSHV-negative lymphoma cells. These data compliment our additional data wherein ABC294640 induces apoptosis in KSHV-infected primary cells but not uninfected cells. Moreover, ABC294640 induced a dose-dependent increase in ceramides-lipid moieties known to induce apoptosis in other cancer cell lines. ABC294640 also upregulated proapoptotic JNK activation while reducing constitutive NF-kB activation in PEL cells, two events previously implicated in the initiation of cancer cell apoptosis. Finally, ABC294640 induced lytic KSHV gene expression in PEL cells-a process known to cause cell death. Therefore, we hypothesize that ABC294640 induces apoptosis and cell death preferentially in PEL cells through the accumulation of ceramides and/or the induction of lytic KSHV gene expression and downstream proapoptotic signaling, and that ABC294640 reduces progression of PEL in vivo. To evaluate the feasibility of reducing PEL formation in vivo with the systemic administration of ABC294640 and to better understand how ABC294640 selectively targets KSHV-infected cells, we propose three aims: 1) to synthesize sufficient amounts of ABC294640 for in vivo studies; 2) to evaluate the ability of ABC294640 to inhibit PEL formation in immune deficient mice; and 3) to determine mechanisms for ABC294640 reduction of KSHV-infected cell growth and survival. Through the completion of these studies, we hope to move toward the performance of clinical trials to evaluate the efficacy and safety of ABC294640 administration in HIV-infected patients with PEL. Our additional mechanistic studies should also provide inroads for future studies to address the role of ABC294640 in selectively targeting virus-infected cells. PUBLIC HEALTH RELEVANCE: Tumors etiologically linked to the Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8), including primary effusion lymphoma (PEL), are among those HIV-associated illnesses which portend a poor prognosis for HIV-infected patients. Current PEL therapies are not efficacious and incur significant toxicity. Therefore, preclinical testing of promising compounds in animal models which inhibit PEL cell growth and which selectively target KSHV-infected cells would provide a basis for testing these compounds in future clinic trials for PEL.