New frontiers in the treatment of multiple myeloma

Oscillating expression of interleukin-16 in multiple myeloma is associated with proliferation, clonogenic growth, and PI3K/NFKB/MAPK activation

Multiple myeloma (MM) is an incurable hematologic malignancy emerging from a plasma cell clone located in the bone marrow and is characterized by a high rate of fatal relapses after initially effective treatment. We have previously identified Interleukin-16 (IL-16) as an important factor promoting the proliferation of MM cells. We demonstrate here an upregulated, periodic expression, and secretion of IL-16 by MM cells leading to high extracellular IL-16 levels. The level of IL-16 released from a given MM cell line correlated with its proliferative activity. Establishing an inducible knockdown system and performing gene expression arrays we observed an association between IL-16 expression and activation of PI3, NFκB and MAP kinase pathways and, specifically, genes involved in tumor cell proliferation. Functional assays showed that IL-16 knockdown reduced the proliferative activity with a significant delay in cell cycle progression to G2 phase of conventional MM cells and completely suppressed the growth of clonogenic MM cells, which are suspected to be responsible for the high relapse rates in MM. Overall, our results demonstrate that tumor-regenerating MM cells may be particularly susceptible to IL-16 neutralization, suggesting an important role of anti-IL-16 therapies in the treatment of MM, particularly in combination with existing strategies targeting the bulk of myeloma cells.

BRCA1 mutation site may be linked with nuclear DNA ploidy in BRCA1-mutated ovarian carcinomas

AIMS

BRCA1 has a role in maintaining normal nuclear DNA content during cell division and its inactivation may result in DNA aneuploidy and cancer progression. BRCA1-linked breast cancers are more aneuploid and have a worse prognosis, but this has not been elucidated in ovarian cancers. This study explores the potential difference in ploidy status between BRCA1-mutated and sporadic ovarian carcinomas. It also explores the potential association between BRCA1 mutation site and DNA ploidy status.

METHODS

This study compared DNA ploidy status of tumor blocks from 23 BRCA1-mutated ovarian carcinomas with that of 23 sporadic ovarian carcinomas matched for histologic subtype, patient age, stage and grade. DNA content of the nuclei was measured by Feulgen-Schiff staining followed by image cytometry and compared.

RESULTS

BRCA1-linked tumors with a stop codon closer to the N-terminal (between 1 and 500 aa; 6/6, 100%) had a significantly higher frequency of nondiploidy compared with those with stop codon above 500 aa (7/12, 58%) (P = 0.033). A diploid peak was detected in 28% of BRCA1-mutated ovarian cancers and in 33% of sporadic ovarian cancers.

CONCLUSIONS

The present study concluded that ovarian tumors with mutations closer to the N-terminal of BRCA1 may have a higher risk of DNA aneuploidy. There is no significant difference between BRCA1-mutated and sporadic ovarian carcinomas with respect to the DNA content.

Naltrindole inhibits human multiple myeloma cell proliferation in vitro and in a murine xenograft model in vivo

It has been demonstrated previously that immune cell activation and proliferation were sensitive to the effects of naltrindole, a nonpeptidic δ-opioid receptor-selective antagonist; therefore, we hypothesized that human multiple myeloma (MM) would be a valuable model for studying potential antineoplastic properties of naltrindole. [(3)H]naltrindole exhibited saturable, low-affinity binding to intact human MM cells; however, the pharmacological profile of the binding site differed considerably from the properties of δ-, κ-, and μ-opioid receptors, and opioid receptor mRNA was not detected in MM cells by reverse transcriptase-polymerase chain reaction. Naltrindole inhibited the proliferation of cultured human U266 MM cells in a time- and dose-dependent manner with an EC(50) of 16 μM. The naltrindole-induced inhibition of U266 cell proliferation was not blocked by a 10-fold molar excess of naltrexone, a nonselective opioid antagonist. Additive inhibition of MM cell proliferation was observed when using a combination of naltrindole with the histone deacetylase inhibitor sodium valproate, the proteasome inhibitor bortezomib, the glucocorticoid receptor agonist dexamethasone, and the HMG CoA reductase inhibitor simvastatin. Treatment of U266 cells with naltrindole significantly decreased the level of the active, phosphorylated form of the kinases, extracellular signal-regulated kinase and Akt, which may be related to its antiproliferative activity. The antiproliferative activity of naltrindole toward MM cells was maintained in cocultures of MM and bone marrow-derived stromal cells, mimicking the bone marrow microenvironment. In vivo, naltrindole significantly decreased tumor cell volumes in human MM cell xenografts in severe combined immunodeficient mice. We hypothesize that naltrindole inhibits the proliferation of MM cells through a nonopioid receptor-dependent mechanism.

Widespread deregulation of phosphorylation-based signaling pathways in multiple myeloma cells: opportunities for therapeutic intervention

Multiple myeloma (MM) is a neoplasm of plasma cell origin that is largely confined to the bone marrow (BM). Chromosomal translocations and other genetic events are known to contribute to deregulation of signaling pathways that lead to transformation of plasma cells and progression to malignancy. However, the tumor stroma may also provide trophic support and enhance resistance to therapy. Phosphorylation of proteins on tyrosine, serine and threonine residues plays a pivotal role in cell growth and survival. Therefore, knowing the status of phosphorylation-based signaling pathways in cells may provide key insights into how cell growth and survival is promoted in tumor cells. To provide a more comprehensive molecular analysis of signaling disruptions in MM, we conducted a kinome profile comparison of normal plasma cells and MM plasma cells as well as their surrounding cells from normal BM and diseased BM. Integrated pathway analysis of the profiles obtained reveals deregulation of multiple signaling pathways in MM cells but also in surrounding bone marrow blood cells compared to their normal counterparts. The deregulated kinase activities identified herein, which include the mTOR (mammalian target of rapamycin)/p70S6K and ERK1/2 (extracellular signal-regulated kinases 1 and 2) pathways, are potential novel molecular targets in this lethal disease.

Molecular enzymology of 5-aminolevulinate synthase, the gatekeeper of heme biosynthesis

Pyridoxal-5'-phosphate (PLP) is an obligatory cofactor for the homodimeric mitochondrial enzyme 5-aminolevulinate synthase (ALAS), which controls metabolic flux into the porphyrin biosynthetic pathway in animals, fungi, and the α-subclass of proteobacteria. Recent work has provided an explanation for how this enzyme can utilize PLP to catalyze the mechanistically unusual cleavage of not one but two substrate amino acid α-carbon bonds, without violating the theory of stereoelectronic control of PLP reaction-type specificity. Ironically, the complex chemistry is kinetically insignificant, and it is the movement of an active site loop that defines k(cat) and ultimately, the rate of porphyrin biosynthesis. The kinetic behavior of the enzyme is consistent with an equilibrium ordered induced-fit mechanism wherein glycine must bind first and a portion of the intrinsic binding energy with succinyl-Coenzyme A is then utilized to perturb the enzyme conformational equilibrium towards a closed state wherein catalysis occurs. Return to the open conformation, coincident with ALA dissociation, is the slowest step of the reaction cycle. A diverse variety of loop mutations have been associated with hyperactivity, suggesting the enzyme has evolved to be purposefully slow, perhaps as a means to allow for rapid up-regulation of activity in response to an as yet undiscovered allosteric type effector. Recently it was discovered that human erythroid ALAS mutations can be associated with two very different diseases. Mutations that down-regulate activity can lead to X-linked sideroblastic anemia, which is characterized by abnormally high iron levels in mitochondria, while mutations that up-regulate activity are associated with X-linked dominant protoporphyria, which in contrast is phenotypically identified by abnormally high porphyrin levels. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.

Multiple myeloma: biology, standard therapy, and transplant therapy

The understanding of the pathogenesis of multiple myeloma has undergone a major transformation over the past eight years. New insights into the microenvironment of the plasma cell as well as elucidation of signaling pathways that prevent plasma cell apoptosis are leading to rapid new drug development. The introduction of novel agents has led to a significant increase in survival. Combinations of novel agents are expected to provide higher complete response rate with anticipated prolongation of relapse free and overall survival. Autologous and allogeneic stem cell transplantation remains an integral part of therapy further improving the outcomes following induction with novel agents.

Drug resistance in cancer - searching for mechanisms, markers and therapeutic agents

Treatment resistance, whether inherent or acquired, is a major problem reducing the activity of conventional and newer, molecularly targeted, cancer drugs. A more complex picture of the causes and contributions of specific forms of resistance is now emerging through application of pharmacological, proteomic and gene expression technologies and we have entered an exciting time where new molecular research tools are being applied not only to characterise the causes of such resistance, but to identify rational new treatments and treatment combinations that are being rapidly translated to clinical evaluations with increasing success. This review outlines many of the contributing causes of resistance to established cytotoxics and to the new breed of molecularly targeted agents, both monoclonal antibodies and small molecules, and the research methods being used to wage war on resistant cancer.