Targeting the hypoxia pathway in malignant plasma cells by using 17-allylamino-17-demethoxygeldanamycin

Abstract

Multiple myeloma (MM) is characterized as a clonal expansion of malignant plasma cells in the bone marrow, which is often associated with pancytopenia and osteolytic bone disease. Interestingly, myeloma-infiltrated bone marrow is considered to be hypoxic, providing selection pressure for a developing tumour. Since HSP90 was shown to participate in stabilization of the subunit of the key transcription factor HIF-1, which controls the hypoxic response, the aim of this study was to investigate the influence of a HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG), on MM cells cultured under low oxygenation conditions. We confirmed that 17-AAG inhibits hypoxic induction of the HIF-1 target genes in malignant plasma cells and demonstrate the concentration range of severe hypoxia-specific cytotoxicity. Next, we selected the malignant plasma cells under severe hypoxia/re-oxygenation culture conditions in the presence or absence of 17-AAG and subsequently, the cells which survived were further expanded and analyzed. Interestingly, we have noticed significant changes in the survival and the response to anti-MM drugs between the parental cell lines and those selected in cyclic severe hypoxia in the presence and absence of 17-AAG. Importantly, we also observed that the lack of oxygen itself, irrespectively of HIF-1 inhibition, is the main/pivotal factor driving the selection process in the experiments presented here.

Overexpression of HIF-1α contributes to melphalan resistance in multiple myeloma cells by activation of ERK1/2, Akt, and NF-κB

“…It was reported that myeloma patients with t(4;14) translocations, a poorer clinical outcome, showed significantly higher expression of HIF-1α, and that high expression of HIF-1α and EP300 are correlated with poor prognosis [11,52]. In addition, hypoxia conditions enhanced tumor initiation and induced resistance to bortezomib and carfilzomib in MM cells [53,54]. It was also reported that downregulation of HIF-1α expression enhanced sensitivity to bortezomib and lenelidomide [55,56].…”

Analysis of Malignant Melanoma Cell Lines Exposed to Hypoxia Reveals the Importance of PFKFB4 Overexpression for Disease Progression

“…Both cell lines were obtained from ESTDAB Melanoma Cell Bank (Tubingen, Germany) and were grown according to their recommendation. Reduced oxygen culture conditions (1% O 2 hypoxia) were obtained, as described previously (32).…”

Influence of metformin on HIF-1 pathway in multiple myeloma

“…To further determine if the reduction of HIF-1α subunit accumulation attenuates HIF-1 transcriptional activity, RT-PCR assay was performed. The genes selected for that analysis were proven previously as the targets of HIF-1 transcription factor and their induction, as a consequence of HIF-1 nuclear accumulation, has been reported in malignant plasma cells [ 5 , 8 ]. In accordance with the protein data, in both tested cell lines, cultured in hypoxic conditions, the induction of target genes was observed, while in the presence of metformin (5 mM) the expression level of analyzed genes was comparable with the control cells (1B, upper panel).…”

“…Moreover, oxygen deficiency was described as a factor stimulating migration and homing of malignant plasma cells to the new BM niches [4], promoting osteolytic bone destruction and significantly contributing to MM-induced angiogenesis [5][6][7]. In consequence, several studies have reported the inhibition of HIF-1, critical regulator of cellular responses to low oxygen levels, as the strategy to target hypoxia-induced alterations in malignant plasma cells [7][8][9]. Nevertheless, despite promising rationale, none of HIF-1 inhibitors has so far been approved for treating cancer patients, due to the limited therapeutic efficacy as well as toxic side effects [10].…”