Role of CDK4 and p16INK4A in interleukin-6-mediated growth of multiple myeloma

Combination therapy targeting Erk1/2 and CDK4/6i in relapsed refractory multiple myeloma

Oncogenic activated RAS mutations have been detected in 50% of de novo and 70% of relapsed multiple myeloma (MM) patients. Translocation t(11;14) involving IgH/CCDN1 and overexpression of cyclin-Ds are early events in MM pathogenesis, enhancing uncontrolled MM cell growth. We hypothesized that targeting both RAS/MAPK pathway molecules including Erk1/2 along with cyclin-Ds enhances MM cytotoxicity and minimizes side effects. Recent studies have demonstrated the high potency of Erk1/2 and CDK4/6 inhibitors in metastatic relapsed cancers, and here we tested anti-MM effects of the Erk1/2 + CDK4/6 inhibitor combination. Our studies showed strong synergistic (IC < 0.5) cytotoxicity of Erk1/2i + CDK4/6i in MM-cells. Erk1/2i + CDK4/6i treatment in a dose-dependent manner arrested MM-cells in the G0/G1 phase and activated mitochondrial apoptotic signaling. Our studies showed that Erk1/2i + CDK4/6i treatment-induced inhibition of key target molecules in Erk1/2 and CDK4/6 signaling, such as c-myc, p-RSK, p-S6, p-RB, and E2F1, suggesting on-target activity of these inhibitors. We identified Erk1/2i + CDK4/6i treatment associated five-gene signature which includes SNRPB and SLC25A5; these genes are involved in RNA processing and mitochondrial metabolism, respectively. Overall, our studies provide the preclinical framework for Erk1/2i + CDK4/6i combination clinical trials to target Ras+CDK pathways to improve patient outcome in MM.

MicroRNA-338-3p Inhibits Proliferation and Promotes Apoptosis of Multiple Myeloma Cells Through Targeting Cyclin-Dependent Kinase 4

MicroRNA-338-3p (miR-338-3p) has been reported to be a tumor suppressor in multiple cancer types. However, the biological role of miR-338-3p and its underlying mechanism in multiple myeloma (MM) remain unclear. In the present study, we investigated the biological role and potential of miR-338-3p in MM. We found that miR-338-3p was significantly decreased in newly diagnosed and relapsed MM tissues and cell lines. Overexpression of miR-338-3p in MM cells significantly inhibited proliferation and promoted apoptosis, caspase 3, and caspase 8 activity. Bioinformatics algorithm analysis predicted that cyclin-dependent kinase 4 (CDK4) was a direct target of miR-338-3p, and this was experimentally verified by a dual-luciferase reporter assay. Furthermore, overexpression of miR-338-3p inhibited CDK4 expression on mRNA and protein levels. Of note, the restoration of CDK4 expression markedly abolished the effect of miR-338-3p overexpression on cell proliferation, apoptosis, caspase 3, and caspase 8 activities in MM cells. Taken together, the present study is the first to demonstrate that miR-338-3p functions as a tumor suppressor in MM through inhibiting CDK4. This finding implies that miR-338-3p is a potential therapeutic target for the treatment of MM.

Environmental immune disruptors, inflammation and cancer risk

An emerging area in environmental toxicology is the role that chemicals and chemical mixtures have on the cells of the human immune system. This is an important area of research that has been most widely pursued in relation to autoimmune diseases and allergy/asthma as opposed to cancer causation. This is despite the well-recognized role that innate and adaptive immunity play as essential factors in tumorigenesis. Here, we review the role that the innate immune cells of inflammatory responses play in tumorigenesis. Focus is placed on the molecules and pathways that have been mechanistically linked with tumor-associated inflammation. Within the context of chemically induced disturbances in immune function as co-factors in carcinogenesis, the evidence linking environmental toxicant exposures with perturbation in the balance between pro- and anti-inflammatory responses is reviewed. Reported effects of bisphenol A, atrazine, phthalates and other common toxicants on molecular and cellular targets involved in tumor-associated inflammation (e.g. cyclooxygenase/prostaglandin E2, nuclear factor kappa B, nitric oxide synthesis, cytokines and chemokines) are presented as example chemically mediated target molecule perturbations relevant to cancer. Commentary on areas of additional research including the need for innovation and integration of systems biology approaches to the study of environmental exposures and cancer causation are presented.

Association of CDK4 and CCND1 mRNA overexpression in laryngeal squamous cell carcinomas occurs without CDK4 amplification

CDK4 is involved in the control of G1-S phase transition as a part of the CCND1/CDK4 complexes. CCNDI and CDK4 gene alterations have been implicated in the development of different tumors. CCND1 has been associated with progression in laryngeal carcinomas. CDK4 protein overexpression was described associated to CCND 1 overexpression in these tumors. However, the mechanisms implicated were not known. We analyzed CDK4 gene alterations and mRNA expression in a series of carcinomas of the larynx, and the results were compared to CCND1 expression and clinicopathological characteristics of the patients. CDK4 mRNA was overexpressed in 42 out of 60 tumors (70%) associated with CCND1 mRNA overexpression because 15 out of 16 cases with high CCND1 levels showed simultaneous increased levels of CDK4 mRNA (p = 0.023) and 12 (87%) of the tumors overexpressing both genes were in stage 4. No CDK4 gene amplifications, rearrangements, or mutations were detected in any of the tumors, including 24 overexpressed cases. These findings confirm that CDK4 overexpression is a frequent phenomenon in laryngeal carcinomas, which occurs at the transcriptional level but is related neither to gene amplification nor to gene mutation, and suggest that cooperation with CCND1 may be involved in the progression of laryngeal tumors.

Molecular aspects of multiple myeloma

Multiple myeloma is a malignant tumour of plasma cells with a median survival of two to three years. Karyotypic instability is seen at the earliest stage of the disease and increases with disease progression, leading to extreme genetic abnormalities similar to solid tumours. Translocations involving the immunoglobulin heavy chain region on chromosome 14q32 are clearly important in the pathogenesis of most myelomas. This review focuses on the different genetic abnormalities found in myeloma and discusses possible pathogenetic mechanisms and the implications for biologically based treatments.

Multiple myeloma: evolving genetic events and host interactions

Multiple myeloma is a neoplasm of terminally differentiated B cells (plasma cells) in which chromosome translocations frequently place oncogenes under the control of immunoglobulin enhancers. Unlike most haematopoietic cancers, multiple myeloma often has complex chromosomal abnormalities that are reminiscent of epithelial tumours. What causes full-blown myeloma? And can our molecular understanding of this common haematological malignancy be used to develop effective preventive and treatment strategies?

Cyclin D1 and E2F-1 immunoreactivity in bone marrow biopsy specimens of multiple myeloma: relationship to proliferative activity, cytogenetic abnormalities and DNA ploidy

Cyclin D1, encoded by the CCND1 gene, is immunohistochemically detectable in up to one-third of cases of multiple myeloma (MM). To examine the mechanism of cyclin D1 overexpression, we compared cyclin D1 immunoreactivity with the results of conventional cytogenetics to determine if the t(11;14)(q13;q32) or other abnormalities of 11q11-14 explained cyclin D1 overexpression. Karyotypic abnormalities were found in 45 out of 67 (67%) MM cases; the t(11;14) was present in seven cases (10%). Additional 11q11-14 abnormalities were not identified. The t(11;14) correlated with cyclin D1 upregulation in low to intermediately proliferative MM, but was not present in highly proliferative tumours (assessed using bromodeoxyuridine labelling index). Cyclin D1 indirectly activates the transcription factor E2F-1. In the bone marrow biopsy specimens of MM cases, E2F-1 was concurrently expressed with cyclin D1 (P = 0.001), indicating that cyclin D1 is functional. However, as neither E2F-1 nor cyclin D1 expression correlated with proliferative activity, the speculation that t(11;14) upregulates the CCND1 gene to induce higher proliferation and possibly more aggressive disease is not supported. We conclude that in low to intermediately proliferative MM cases, cyclin D1 is probably upregulated by t(11;14), but an alternative mechanism is more probable in highly proliferative MM.

CDK4 expression and activity are required for cytokine responsiveness in T cells

Stimulation of lymphocytes through the Ag receptor can lead to cytokine responsiveness or unresponsiveness. We examined the importance of cyclin-dependent kinase (CDK)4 to establish and maintain IL-2 responsiveness in human T cells. Our results show that a herbimycin A- and staurosporine-sensitive phase of CDK4 expression and activity preceded the acquisition of IL-2-responsiveness in mitogen-stimulated peripheral blood T cells. Intriguingly, CDK4 expression and activity were demonstrable in purified unstimulated peripheral blood T cells from approximately 30% (5/16) of healthy individuals examined for this study. These T cells proliferated in response to IL-2 without additional mitogens, and both the expression and activity of CDK4 and the ability to respond to cytokines were resistant to herbimycin A and staurosporine. The pattern of CDK4 expression and response to IL-2 in this subset of individuals resembled that seen in the human IL-2-dependent Kit-225 T cell line. However, in contrast to normal T cells, Kit-225 cells were rendered unresponsive to IL-2 by stimulation through the Ag receptor. In these cells, PHA, anti-CD3, or PMA induced marked reductions of CDK4 expression and activity that paralleled IL-2 unresponsiveness, and these effects were not reversible by IL-2. Furthermore, IL-2-dependent proliferation could be similarly inhibited in Kit-225 cells by overexpression of the CDK inhibitors p16/Ink4-a or p21/Waf-1a or by overexpression of a kinase-inactive CDK4 mutant. The data indicate that CDK4 expression and activity are necessary to induce and maintain cytokine responsiveness in T cells, suggesting that CDK4 is important to link T cell signaling pathways to the machinery that controls cell cycle progression.

Agonist anti-gp130 transducer monoclonal antibodies are human myeloma cell survival and growth factors

We have previously reported obtaining two monoclonal antibodies (mAb) against the human gp130 interleukin-6 (IL-6) transducer which made possible the dimerization of gp130 and the activation of several IL-6-driven functions when used together. We report here that these mAb induce gp130-mediated signaling in human myeloma cells and support the survival and the long-term growth of five IL-6-dependent human myeloma cell lines. Their agonist activity is not affected by neutralizing antibodies to IL-6 or IL-6R. These mAb induce a transient proliferation of primary myeloma cells from most patients with multiple myeloma. Again, IL-6 inhibitors do not affect this agonist activity. By using highly purified primary myeloma cells, we found that these anti-gp130 mAb supported the long-term survival of primary myeloma cells from five patients with primary plasma cell leukemia but failed to induce their long-term growth. For patients with fulminant disease and secondary extramedullary proliferation, the antibodies supported a long-term survival and growth, and anti-gp130 mAb-dependent cell lines were obtained. For patients with medullary involvement only, a co-stimulatory signal is necessary, together with gp130 activation, to trigger cell survival and cycling. Leukemia (2000) 14, 188-197.