Faculty Bibliography

Leukaemia is the single most common childhood malignancy. With modern treatment regimens, survival in acute lymphoblastic leukaemia (ALL) approaches 90%. Only about 70% of children with acute myeloid leukaemia (AML) achieve long term survival. Patients who relapse have a dismal prognosis. Novel therapeutic approaches are needed to improve treatment outcomes in newly-diagnosed patients with a poor prognosis and for patients with relapsed/refractory disease that have limited treatment options. One promising approach in treating haematological malignancies has been the use of monoclonal antibodies to target cell surface antigens expressed on malignant cells. Most success with monoclonal antibody therapy in the treatment of haematological malignancies has come in the setting of adult B-cell non-Hodgkin lymphoma with the addition of the anti-CD20 monoclonal antibody rituximab to standard treatment regimens. In order to further advance treatment of haematological malignancies, novel monoclonal antibodies continue to be developed that target a variety of cell surface antigens. Several antibodies continue to be investigated in childhood leukaemias. This review will discuss the development of monoclonal antibodies that target a variety of cell surface antigens for the treatment of childhood ALL and the use of the anti-CD33 antibody gemtuzumab ozogamicin in the treatment of childhood AML.

PURPOSE OF REVIEW: Acute lymphoblastic leukemia (ALL) is the most common and one of the most curable malignancies in children; however, it presents unique challenges in adolescents and young adults (AYAs). The purpose of this review is to discuss factors that contribute to the outcome disparities in AYAs with ALL as well as approaches that can be taken to optimize the care of this patient population. RECENT FINDINGS: AYAs with ALL are unique and have outcomes that have lagged behind those observed in children with ALL. Contributing factors to the challenges faced by this group include distinctive disease biology, different drug pharmacology and toxicity profiles, and complex psychosocial and socioeconomic factors. Several clinical trials conducted worldwide have demonstrated that treatment with pediatric protocols significantly improves outcomes in the AYA population. SUMMARY: Initiatives to improve outcomes for AYAs with ALL include treatment with pediatric regimens tailored to be delivered without excessive toxicity and in centers with the necessary supportive care and medical services to address the specific needs of this population. As more is understood about the unique disease biology of AYA ALL, targeted therapeutic approaches may offer promise for the future.

Whereas the improvement in outcome for children with acute lymphoblastic leukemia has been gratifying, the poor outcome of patients who relapse warrants novel treatment approaches. Previously, we identified a characteristic relapse-specific gene expression and methylation signature associated with chemoresistance using a large cohort of matched-diagnosis relapse samples. We hypothesized that "reversing" such a signature might restore chemosensitivity. In the present study, we demonstrate that the histone deacetylase inhibitor vorinostat not only reprograms the aberrant gene expression profile of relapsed blasts by epigenetic mechanisms, but is also synergistic when applied before chemotherapy in primary patient samples and leukemia cell lines. Furthermore, incorporation of the DNA methyltransferase inhibitor decitabine led to reexpression of genes shown to be preferentially methylated and silenced at relapse. Combination pretreatment with vorinostat and decitabine resulted in even greater cytotoxicity compared with each agent individually with chemotherapy. Our results indicate that acquisition of chemo-resistance at relapse may be driven in part by epigenetic mechanisms. Incorporation of these targeted epigenetic agents to the standard chemotherapy backbone is a promising approach to the treatment of relapsed pediatric acute lymphoblastic leukemia.

Although the cure rate of newly diagnosed acute lymphoblastic leukemia (ALL) has improved over the past four decades, the outcome for patients who relapse remains poor. New therapies are needed for these patients. Our previous global gene expression analysis in a series of paired diagnosis-relapse pediatric patient samples revealed that the antiapoptotic gene survivin was consistently upregulated upon disease relapse. In this study, we demonstrate a link between survivin expression and drug resistance and test the efficacy of a novel antisense agent in promoting apoptosis when combined with chemotherapy. Gene-silencing experiments targeting survivin mRNA using either short-hairpin RNA (shRNA) or a locked antisense oligonucleotide (LNA-ON) specifically reduced gene expression and induced apoptosis in leukemia cell lines. When used in combination with chemotherapy, the survivin shRNA and LNA-ON potentiated the chemotherapeutic antileukemia effect. Moreover, in a mouse primary xenograft model of relapse ALL, the survivin LNA-ON decreased survivin expression in a subset of animals, and produced a statistically significant decrease in tumor progression. Taken together, these findings suggest that targeting endogenous levels of survivin mRNA by LNA-ON methods may augment the response to standard chemotherapy by sensitizing otherwise resistant tumor cells to chemotherapy.

Neuroendocrine tumors of the pancreas are rare in children. They usually occur in the setting of genetic syndromes such as multiple endocrine neoplasia type 1, von Hippel-Lindau disease, and neurofibromatosis 1. These tumors have also been reported in the tuberous sclerosis complex (TSC), but the incidence is low in comparison with other syndromes. Only 9 cases have been described to date, and it is not yet well understood if any connection exists between TSC and pancreatic endocrine tumors. TSC is characterized by mutations in TSC1 and TSC2 genes, which activate the AKT-mTOR oncogenic cascade. Recent molecular studies in pancreatic endocrine tumors showed activation of the same pathway, which points toward a common molecular pathway between these two entities. We present a case of well-differentiated neuroendocrine carcinoma of the pancreas in a child with TSC and discuss the genetic aspects of this disease