Combination treatment of prostate cancer with FGF receptor and AKT kinase inhibitors

Abstract

Activation of the PI3K/AKT pathway occurs in the vast majority of advanced prostate cancers (PCas). Activation of fibroblast growth factor receptor (FGFR) signaling occurs in a wide variety of malignancies, including PCa. RNA-Seq of castration resistant PCa revealed expression of multiple FGFR signaling components compatible with FGFR signaling in all cases, with multiple FGF ligands expressed in 90% of cases. Immunohistochemistry confirmed FGFR signaling in the majority of xenografts and advanced PCas. AZD5363, an AKT kinase inhibitor and AZD4547, a FGFR kinase inhibitor are under active clinical development. We therefore sought to determine if these two drugs have additive effects in PCa models. The effect of both agents, singly and in combination was evaluated in a variety of PCa cell lines in vitro and in vivo. All cell lines tested responded to both drugs with decreased invasion, soft agar colony formation and growth in vivo, with additive effects seen with combination treatment. Activation of the FGFR, AKT, ERK and STAT3 pathways was examined in treated cells. AZD5363 inhibited AKT signaling and increased FGFR1 signaling, which partially compensated for decreased AKT kinase activity. While AZD4547 could effectively block the ERK pathway, combination treatment was needed to completely block STAT3 activation. Thus combination treatment with AKT and FGFR kinase inhibitors have additive effects on malignant phenotypes in vitro and in vivo by inhibiting multiple signaling pathways and mitigating the compensatory upregulation of FGFR signaling induced by AKT kinase inhibition. Our studies suggest that co-targeting these pathways may be efficacious in advanced PCa.

Fibroblast growth factor receptor signaling plays a key role in transformation induced by the TMPRSS2/ERG fusion gene and decreased PTEN

“…Examination of the smaller number of metastatic cases with mRNA revealed a similar pattern. As seen in Figure 7B , 16 of 19 metastatic cases had upregulation of one or more FGF ligands, with up to 13 ligands increased in some cases, similar to our previously reported finding in the metastatic cancers analyzed at Fred Hutchison Cancer Center [ 26 ]. PTEN loss was much more common in the metastatic cases, as is well known [ 34 ].…”

“…Previous studies by our group and others [ 21 , 22 , 25 – 27 , 29 , 31 ] individual ligands and receptors have shown multiple ligands and receptors are increased in PCa. Our recent collaborative bioinformatic study of metastatic prostate cancers based on RNA sequencing showed a pattern like our current study; almost ubiquitous but highly variable expression of FGF ligands and receptors in these cancers [ 26 ]. Given that PTEN is lost or AKT is activated by alternative mechanisms in the vast majority of advanced PCas [ 34 ], our current studies provide a reasonable explanation for these observations.…”

“…There is little literature on the expression of FGF5 in PCa [ 44 ]. However, data from our current study our prior in silico analysis [ 26 ] indicates that it is expressed commonly in both primary and metastatic PCa. It may represent an alternative pathway to activate FGF signaling in those PCas without PTEN loss and/or AKT activation, although at least in some contexts (such as 22RV1 cells), it can be induced by decreased PTEN activity.…”

“…Examination of the genes that were uniquely altered at the chosen thresholds in PTEN KD/TE showed that both FGF3 and FGFR4 were upregulated in these cells. Given that there is a large body of evidence that FGFs and their receptors are upregulated in PCa and that FGFR signaling is a potential drug target [ 26 ], we chose to examine the role of FGFs and FGFRs in the phenotypes observed in the TE, PTEN KD and PTEN KD/TE cell lines. FGF2, FGF3, FGF5, FGFR1, FGFR2 and FGFR4 were all upregulated at least 1.4-fold in one or more cell lines, with lower levels of increase observed as well (Figure 5A ).…”

“…Each experiment was repeated 3 times. For drug treatment AZD4547 or AZD5363 was added in media in the bottom wells with the final concentration of 300 nM for both drugs as described previously [ 26 ].…”