Niche-Based Screening in Multiple Myeloma Identifies a Kinesin-5 Inhibitor with Improved Selectivity over Hematopoietic Progenitors

SummaryNovel therapeutic approaches are urgently required for multiple myeloma (MM). We used a phenotypic screening approach using co-cultures of MM cells with bone marrow stromal cells to identify compounds that overcome stromal resistance. One such compound, BRD9876, displayed selectivity over normal hematopoietic progenitors and was discovered to be an unusual ATP non-competitive kinesin-5 (Eg5) inhibitor. A novel mutation caused resistance, suggesting a binding site distinct from known Eg5 inhibitors, and BRD9876 inhibited only microtubule-bound Eg5. Eg5 phosphorylation, which increases microtubule binding, uniquely enhanced BRD9876 activity. MM cells have greater phosphorylated Eg5 than hematopoietic cells, consistent with increased vulnerability specifically to BRD9876’s mode of action. Thus, differences in Eg5-microtubule binding between malignant and normal blood cells may be exploited to treat multiple myeloma. Additional steps are required for further therapeutic development, but our results indicate that unbiased chemical biology approaches can identify therapeutic strategies unanticipated by prior knowledge of protein targets

GBP1 overexpression is associated with a paclitaxel resistance phenotype

In the search for novel genes involved in the paclitaxel resistance phenotype, prior studies of gene expression in paclitaxel-resistant cell lines and their paired drug-sensitive parental lines using high-density Affymetrix GeneChip arrays identified guanylate-binding protein 1 (GBP1) gene as an overexpressed transcript. The GBP1 gene encodes a large GTPase that is induced by interferon gamma (IFN-gamma) in a variety of eukaryotic cells. In this report we characterize GBP1 and demonstrate that GBP1 expression is consistently upregulated in 7 of 8 paclitaxel or doxorubicin-resistant human cancer cell lines as compared to its expression in the relevant drug-sensitive parental lines. Analysis of GBP1 expression using the Cancer Profiling Array showed that GBP1 is ubiquitously expressed with no significant difference in expression levels between normal and tumor tissue. Parallel analysis of the Cancer Cell Line Profiling Array determined that GBP1 expression in a majority of cell lines derived from human tumors of different tissue origin was induced to variable levels following exposure to multiple stress agents including paclitaxel and doxorubicin. Importantly, stable expression of a GBP1 transgene in the paclitaxel-sensitive ovarian cancer cell line OVCAR8 was sufficient to confer moderate paclitaxel resistance. Our data suggest that increased expression of the GBP1 gene may play an important role in the development of multi-drug resistance (MDR)

PHD3 Loss in Cancer Enables Metabolic Reliance on Fatty Acid Oxidation via Deactivation of ACC2

While much research has examined the use of glucose and glutamine by tumor cells, many cancers instead prefer to metabolize fats. Despite the pervasiveness of this phenotype, knowledge of pathways that drive fatty acid oxidation (FAO) in cancer is limited. Prolyl hydroxylase domain proteins hydroxylate substrate proline residues and have been linked to fuel switching. Here, we reveal that PHD3 rapidly triggers repression of FAO in response to nutrient abundance via hydroxylation of acetyl-coA carboxylase 2 (ACC2). We find that PHD3 expression is strongly decreased in subsets of cancer including acute myeloid leukemia (AML) and is linked to a reliance on fat catabolism regardless of external nutrient cues. Overexpressing PHD3 limits FAO via regulation of ACC2 and consequently impedes leukemia cell proliferation. Thus, loss of PHD3 enables greater utilization of fatty acids but may also serve as a metabolic and therapeutic liability by indicating cancer cell susceptibility to FAO inhibition