Our results demonstrate the clinical relevance of this series of PDXs as a platform for both basic science studies and therapeutic discovery/drug development. The present report provides the prostate cancer community with a summary of the basic characteristics and a contact information for collaborations using these models.

Background: HSP90 inhibitors increase osteoclast formation and bone loss. Results: Altered Hsf1 activity impacts the ability of stress-inducing compounds to modulate osteoclast formation. Conclusion: Hsf1 plays an important role in stress-associated osteoclast formation, potentially via MITF. Significance: We identified a novel pathway whereby agents inducing stress can enhance osteoclast formation.

Current cancer therapies including cytotoxic chemotherapy, radiation and hyperthermic therapy induce acute proteotoxic stress in tumour cells. A major challenge to cancer therapeutic efficacy is the recurrence of therapyresistant tumours and how to overcome their emergence. The current study examines the concept that tumour cell exposure to acute proteotoxic stress results in the acquisition of a more advanced and aggressive cancer cell phenotype. Specifically, we determined whether heat stress resulted in an epithelial-to-mesenchymal transition (EMT) and/or the enhancement of cell migration, components of an advanced and therapeutically resistant cancer phenotype. We identified that heat stress enhanced cell migration in both the lung A549, and breast MDA-MB-468 human adenocarcinoma cell lines, with A549 cells also undergoing a partial EMT. Moreover, in an in vivo model of thermally ablated liver metastases of the mouse colorectal MoCR cell line, immunohistological analysis of classical EMT markers demonstrated a shift to a more mesenchymal phenotype in the surviving tumour fraction, further demonstrating that thermal stress can induce epithelial plasticity. To identify a mechanism by which thermal stress modulates epithelial plasticity, we examined whether the major transcriptional regulator of the heat shock response, heat shock factor 1 (HSF1), was a required component. Knockdown of HSF1 in the A549 model did not prevent the associated morphological changes or enhanced migratory profile of heat stressed cells. Therefore, this study provides evidence that heat stress significantly impacts upon cancer cell epithelial plasticity and the migratory phenotype independent of HSF1. These findings further our understanding of novel biological downstream effects of heat stress and their potential independence from the classical heat shock pathway.

Heat shock protein 90 (HSP90) regulates multiple signalling pathways critical for tumour growth. As such, HSP90 inhibitors have been shown to act as effective anticancer agents in preclinical studies but, for a number of reasons, the same effect has not been observed in the clinical trials to date. One potential reason for this may be the presence of de novo or acquired resistance within the tumours. To investigate mechanisms of resistance, we generated resistant cell lines through gradual dose escalation of the HSP90 inhibitor 17‐allylamino‐17‐demethoxygeldanamycin (17‐AAG). The resultant resistant cell lines maintained their respective levels of resistance (7–240×) in the absence of 17‐AAG and were also cross‐resistant with other benzoquinone ansamycin HSP90 inhibitors. Expression of members of the histone deacetylase family (HDAC 1, 5, 6) was altered in the resistant cells. To determine whether HDAC activity contributed to resistance, pan‐HDAC inhibitors (TSA and LBH589) and the class II HDAC‐specific inhibitor SNDX275 were found to resensitize resistant cells towards 17‐AAG and 17‐dimethylaminoethylamino‐17‐demethoxygeldanamycin. Most significantly, resistant cells were also identified as cross‐resistant towards structurally distinct HSP90 inhibitors such as radicicol and the second‐generation HSP90 inhibitors CCT018159, VER50589 and AUY922. HDAC inhibition also resensitized resistant cells towards these classes of HSP90 inhibitors. In conclusion, we report that prolonged 17‐AAG treatment results in acquired resistance of cancer cells towards not just 17‐AAG but also to a spectrum of structurally distinct HSP90 inhibitors. This acquired resistance can be inhibited using clinically relevant HDAC inhibitors. This work supports the potential benefit of using HSP90 and HDAC inhibitors in combination within the clinical setting.

HSF1 (heat-shock factor 1) is the master regulator of the heat-shock response; however, it is also activated by cancer-associated stresses and supports cellular transformation and cancer progression. We examined the role of HSF1 in relation to cancer cell clonogenicity, an important attribute of cancer cells. Ectopic expression or HSF1 knockdown demonstrated that HSF1 positively regulated cancer cell clonogenic growth. Furthermore, knockdown of mutant p53 indicated that HSF1 actions were mediated via a mutant p53-dependent mechanism. To examine this relationship more specifically, we ectopically co-expressed mutant p53(R273H) and HSF1 in the human mammary epithelial cell line MCF10A. Surprisingly, within this cellular context, HSF1 inhibited clonogenicity. However, upon specific knockdown of endogenous wild-type p53, leaving mutant p53(R273H) expression intact, HSF1 was observed to greatly enhance clonogenic growth of the cells, indicating that HSF1 suppressed clonogenicity via wild-type p53. To confirm this we ectopically expressed HSF1 in non-transformed and H-Ras(V12)-transformed MCF10A cells. As expected, HSF1 significantly reduced clonogenicity, altering wild-type p53 target gene expression levels consistent with a role of HSF1 increasing wild-type p53 activity. In support of this finding, knockdown of wild-type p53 negated the inhibitory effects of HSF1 expression. We thus show that HSF1 can affect clonogenic growth in a p53 context-dependent manner, and can act via both mutant and wild-type p53 to bring about divergent effects upon clonogenicity. These findings have important implications for our understanding of HSF1's divergent roles in cancer cell growth and survival as well as its disparate effect on mutant and wild-type p53.