In melanoma, therapies with inhibitors to oncogenic BRAFV600E are highly effective but responses are often short-lived due to the emergence of drug-resistant tumor subpopulations. We describe here a mechanism of acquired drug resistance through the tumor microenvironment, which is mediated by human tumor-associated B cells. Human melanoma cells constitutively produce the growth factor FGF-2, which activates tumor-infiltrating B cells to produce the growth factor IGF-1. B-cell-derived IGF-1 is critical for resistance of melanomas to BRAF and MEK inhibitors due to emergence of heterogeneous subpopulations and activation of FGFR-3. Consistently, resistance of melanomas to BRAF and/or MEK inhibitors is associated with increased CD20 and IGF-1 transcript levels in tumors and IGF-1 expression in tumor-associated B cells. Furthermore, first clinical data from a pilot trial in therapy-resistant metastatic melanoma patients show anti-tumor activity through B-cell depletion by anti-CD20 antibody. Our findings establish a mechanism of acquired therapy resistance through tumor-associated B cells with important clinical implications.

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Melanoma is a heterogeneous tumor with different subpopulations showing different proliferation rates. Slow-cycling cells were previously identified in melanoma, but not fully biologically characterized. Using the label-retention method, we identified a subpopulation of slow-cycling cells, defined as label-retaining cells (LRC), with strong invasive properties. We demonstrate through live imaging that LRC are leaving the primary tumor mass at a very early stage and disseminate to peripheral organs. Through global proteome analyses, we identified the secreted protein SerpinE2/protease nexin-1 as causative for the highly invasive potential of LRC in melanomas.

The performance of two proteomic sample preparation methods, "pseudoshotgun" (PSG) and filter-aided sample preparation (FASP) were compared in terms of the number of identified proteins, representation of cellular component GO (gene ontology) categories in the obtained list of proteins, and the efficiency of both methods in the proteomic analysis of a very low number of cells. Both methods were combined to obtain a proteomic profile of a short-term culture (passage 3) of melanoma cells, established in our laboratory from a human metastatic melanoma lesion. The data revealed that with FASP, usually more proteins are identified than with PSG when analyzing a higher number of cells (≥ 5000/injection), whereas PSG is favorable when analyzing only a very small amount of cells (250-500/injection). PSG and FASP, however, are complementary techniques, as combining both methods further increases the number of identified proteins. Moreover, we show that it is feasible to identify a substantial number of proteins from only 250 cells/injection that is equivalent to 60 ng of protein.

Complexes consisting of cyclin-dependent kinases (CDKs) and their regulatory subunits (the cyclins) control the progression of normal mammalian cells through the cell cycle. However, during malignant transformation this regulatory apparatus malfunctions, allowing cells to undergo unchecked proliferation. In many cases, the high mitotic potential of malignant cells is due to the constitutive activation of CDK-cyclin complexes, facilitated by the inactivation of cellular CDK inhibitors, such as p16(INK4A) or p27(Kip1), and the loss of functional tumor suppressors, such as the p53 and pRb proteins. It has recently been suggested that pharmacological intervention based on remedying the deficiency or loss of activity of these negative regulators of the cell cycle could be a very effective therapeutic option in the treatment of cancer. Multiple CDK inhibitors have been synthesized over the last two decades, spanning at least five classes of compounds. While these inhibitors can be classified on the basis of their chemical structure, it may be more interesting to categorize them according to their pharmacological nature, as broad-spectrum unspecific, pan-specific, or very selective antagonists. This review offers a critical assessment of the advantages and disadvantages of both pan-specific and highly selective CDK inhibitors in therapy.

Abstract:Estrogens play an important role in the growth and terminal differentiation of the mammary gland. Prolonged exposure to estrogens seems to predispose women to breast cancer. It recently became evident that not only the intrinsic hormonal status but also external factors such as the occurrence of pharmaceuticals and chemicals with hormone activity in the environment may put women at greater risk of developing breast cancer. We focused on the interference of endocrine disruptors in breast cancer therapy. We observed that phenol red added to the culture medium strongly promoted the cell proliferation and cell cycle progression of human cells expressing the estrogen receptor, and affected their susceptibility to chemotherapy.

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Exposure of asynchronously growing human HeLa cervical carcinoma cells to roscovitine (ROSC), a selective cyclin-dependent kinases (CDKs) inhibitor, arrests their progression at the transition between G(2)/M and/or induces apoptosis. The outcome depends on the ROSC concentration. At higher dose ROSC represses HPV-encoded E7 oncoprotein and initiates caspase-dependent apoptosis. Inhibition of the site-specific phosphorylation of survivin and Bad, occurring at high-dose ROSC treatment, precedes the onset of apoptosis and seems to be a prerequisite for cell death. Considering the fact that in HeLa cells the G(1)/S restriction checkpoint is abolished by E7, we addressed the question whether the inhibition of CDKs by pharmacological inhibitors in synchronized cells would be able to block the cell-cycle in G(1) phase. For this purpose, we attempted to synchronize cells by serum withdrawal or by blocking of the mitotic apparatus using nocodazole. Unlike human MCF-7 cells, HeLa cells do not undergo G(1) block after serum starvation, but respond with a slight increase of the ratio of G(1) population. Exposure of G(1)-enriched HeLa cells to ROSC after re-feeding does not block their cell-cycle progression at G(1)-phase, but increases the ratio of S- and G(2)-phase, thereby mimicking the effect on asynchronously growing cells. A quite different impact is observed after treatment of HeLa cells released from mitotic block. ROSC prevents their cell cycle progression and cells transiently accumulate in G(1)-phase. These results show that inhibition of CDKs by ROSC in cells lacking the G(1)/S restriction checkpoint has different outcomes depending on the cell-cycle status prior to the onset of treatment.