Temsirolimus, an mTOR inhibitor, enhances anti-tumour effects of heat shock protein cancer vaccines.

BACKGROUND: Temsirolimus is a mammalian target of rapamycin (mTOR) inhibitor and rapamycin analogue that is approved for treating advanced renal cell carcinoma (RCC). It is being actively evaluated in clinical trials for melanoma. The mTOR inhibitors are also immunosuppressants and are used clinically to prevent rejection following solid-organ transplant. Novel immunotherapies are being actively developed for immunoresponsive tumours, such as RCC and melanoma. METHODS: Immune-modulating effects of temsirolimus were characterised when used in combination with cancer vaccines targeting RCC (RENCA) and melanoma (B16). Cancer vaccines were recombinant tumour-specific proteins (CA9 or gp100), and recombinant heat shock protein (HSP; hsp110) served as the immune adjuvant. RESULTS: In murine models, temsirolimus enhanced the anti-tumour activity of cancer vaccines used to treat established RENCA and B16 tumours. A tumour prevention model established that the enhanced anti-tumour activity associated with temsirolimus was immune mediated. In mice treated with an HSP-based anti-tumour vaccine, temsirolimus-treated CD8 T cells had greater interferon-γ and cytotoxic T-cell responses when compared with mice treated with vaccine alone. Temsirolimus also enhanced the formation of CD8 memory cells following administration of HSP-based cancer vaccine. CONCLUSION: These results provide a rationale for combining mTOR inhibitor with immunotherapy when treating immunoresponsive tumours.

Engineering secretable forms of chaperones for immune modulation and vaccine development.

Heat shock proteins are present in almost all intracellular compartments and serve by folding newly synthesized proteins, disassembling unstable proteins, and assisting in the transportation of proteins within the cell. Under certain circumstances they are also present on the cell surface, and can be shed or secreted into the extracellular environment. Although they possess many functional roles, their ability to stimulate innate and antigen-specific immunity have made them attractive candidates for vaccine development. Here, we review some of the approaches that have been used to genetically engineer molecular chaperones for their secretion from tumor cells or targeting them to the plasma membrane of such cells in order to promote anti-tumor responses. Treatment of tumor cells engineered to secrete or display chaperones may be of benefit, particularly in the area of cell-based vaccine development.

Molecular chaperones and cancer immunotherapy.

As one of the most abundant and evolutionally conserved intracellular proteins, heat shock proteins, also known as stress proteins or molecular chaperones, perform critical functions in maintaining cell homeostasis under physiological as well as stress conditions. Certain chaperones in extracellular milieu are also capable of modulating innate and adaptive immunity due to their ability to chaperone polypeptides and to interact with the host's immune system, particularly professional antigen-presenting cells. The immunomodulating properties of chaperones have been exploited for cancer immunotherapy. Clinical trials using chaperone-based vaccines to treat various malignancies are ongoing.

Current ideas about applications of heat shock proteins in vaccine design and immunotherapy.

Heat shock proteins (HSPs), as molecular chaperones, perform critical functions in maintaining cell homeostasis. Certain HSPs in extra-cellular milieu are capable of modulating innate and adaptive immunity due to their ability to chaperone polypeptides and to interact with the host's immune system, particularly professional antigen presenting cells (APCs). This review summarizes the immunomodulating functions of HSPs and their potential applications in cancer immunotherapy.

Cancer immunotherapy: stress proteins and hyperthermia.

Heat shock proteins (hsps) can induce anti-cancer immune responses by targeting associated tumour antigens to the immune system. Hsps are not merely carriers of antigen but can also induce maturation of dendritic cells (DCs), resulting in a more efficient antigen presentation. However, improvement of hsp-based vaccines is still desirable if one is to realize their full therapeutic potential. Since the immune system consists of different elements functioning together in a highly integrated way, a combination therapy utilizing important immunomodulators together with hsp-based vaccination may improve therapeutic response. Hyperthermia has been shown to have important stimulatory effects on several cellular and organismal endpoints related to the immune system. This review highlights advantages and disadvantages of various ways of using stress proteins in cancer immunotherapy. It also overviews the interaction of hyperthermia with heat shock protein therapy and the related effects on the host's immune response.

Characterization of heat shock protein 110 and glucose-regulated protein 170 as cancer vaccines and the effect of fever-range hyperthermia on vaccine activity.

Several studies have confirmed that certain stress proteins can function as potent vaccines against a specific cancer when purified from the same tumor. Recent studies of two long-recognized but unstudied stress proteins, heat shock protein (hsp) 110 and glucose-regulated protein (grp) 170, have shown them to be efficient peptide chain-binding proteins. The present investigation examines the vaccine potential of hsp110 and grp170. First, it is shown that prior vaccination with hsp110 or grp170 purified from methylcholanthrene-induced fibrosarcoma caused complete regression of the tumor. In a second tumor model, hsp110 or grp170 purified from Colon 26 tumors led to a significant growth inhibition of this tumor. In addition, hsp110 or grp170 immunization significantly extended the life span of Colon 26 tumor-bearing mice when applied after tumor transplantation. A tumor-specific cytotoxic T lymphocyte response developed in the mice immunized with tumor-derived hsp110 or grp170. Furthermore, treatments of the mice with bone marrow-derived dendritic cells pulsed with these two proteins from tumor also elicited a strong antitumor response. Last, we showed that mild, fever-like hyperthermic conditions enhance the vaccine efficiency of hsp110 as well as heat shock cognate 70, but not grp170. These studies indicate that hsp110 and grp170 can be used in hsp-based cancer immunotherapy, that Ag-presenting dendritic cells can be used to mediate this therapeutic approach, and that fever-level hyperthermia can significantly enhance the vaccine efficiency of hsps.

The hsp110 and Grp1 70 stress proteins: newly recognized relatives of the Hsp70s.

Both the Grp170 and Hsp110 families represent relatively conserved and distinct sets of stress proteins, within a more diverse category that also includes the Hsp70s. All of these families are found in a wide variety of organisms from yeasts to humans. Although Hsp110s or Grp170s are not Hsp70s any more than Hsp70s are Hsp110s or Grp170s, it is still reasonable to refer to this combination of related families as the Hsp70 superfamily based on arguments discussed above and since no obvious prokaryotic Hsp110 or Grp170 has yet been identified. These proteins are related to their counterparts in the Hsp70/Grp78 family of eukaryotic stress proteins but are characterized by significantly larger molecular weights. The members of the Grp170 family are characterized by C-terminal ER retention sequences and are ER localized in yeasts and mammals. As a Grp, Grp170 is recognized to be coregulated with other major Grps by a well-known set of stress conditions, sometimes referred to as the unfolded protein response (Kozutsumi et al 1988; Nakaki et al 1989). The Hsp110 family members are localized in the nucleus and cytoplasm and, with other major Hsps, are also coregulated by a specific set of stress conditions, most notably including hyperthermic exposures. Hsp110 is sometimes called Hsp105, although it would be preferable to have a uniform term. The large Hsp70-like proteins are structurally similar to the Hsp70s but differ from them in important ways. In both the Grp170 and Hspl10 families, there is a long loop structure that is interposed between the peptide-binding ,-domain and the alpha-helical lid. In the Hsp110 family and Grp170, there are differing degrees of expansion in the alpha-helical domain and the addition of a C-terminal loop. This gives the appearance of much larger lid domains for Hsp110 and Grp170 compared with Hsp70. Both Hsp110 and Grp170 families have relatively conserved short sequences in the alpha-helical domain in the lid, which are conserved motifs in numerous proteins (we termed these motifs Magic and TedWylee as discussed earlier). The structural differences detailed in this review result in functional differences between the large (Grp170 and Hspl10) members of the Hsp70 superfamily, the most distinctive being an increased ability of these proteins to bind (hold) denatured polypeptides compared with Hsc70, perhaps related to the enlarged C-terminal helical domain. However, there is also a major difference between these large stress proteins; Hsp110 does not bind ATP in vitro, whereas Grp170 binds ATP avidly. The role of the Grp170 and Hsp110 stress proteins in cellular physiology is not well understood. Overexpression of Hsp110 in cultured mammalian cells increases thermal tolerance. Grp170 binds to secreted proteins in the ER and may be cooperatively involved in folding these proteins appropriately. These roles are similar to those of the Hsp70 family members, and, therefore, the question arises as to the differential roles played by the larger members of the superfamily. We have discussed evidence that the large members of the superfamily cooperate with members of the Hsp70 family, and these chaperones probably interact with a large number of chaperones and cochaperones in their functional activities. The fundamental point is that Hsp110 is found in conjunction with Hsp70 in the cytoplasm (and nucleus) and Grp170 is found in conjunction with78 in tha ER in every eucaryotic cell examined from yeast to humans. This would strongly argue that Hsp110 Grp170 exhibit functions in eucaryotes not effectively performed by Hsp70s or Grp78, respectively. Of interest in this respect is the observation that all Hsp110s loss of function or deletion mutants listed in the Drosophila deletion project database are lethal. The important task for the future is to determine the roles these conserved molecular chaperones play in normal and physiologically stressed cells.

Heat shock proteins and cancer immunotherapy.

Vaccination with heat shock proteins from tumor have been shown to elicit an anti-tumor response. Current studies indicate that the immunogenicity of HSPs is derived from the antigenic peptides which they associate with. Mechanisms by which the HSP-peptide complexes induce an immune response and the possible role of HSPs in antigen presentation is discussed in this article. The use of HSP-peptide complexes can be used as tumor vaccines for cancer immunotherapy is reviewed.

The distribution and localization of hsp110 in brain.

Hsp110 is one of the few, major heat shock proteins of mammalian cells and was one of the earliest heat shock proteins described. However, it has only recently been cloned and studied at the molecular level. It has been noted that of all tissues examined, brain expresses the highest level of hsp110, with expression levels in unstressed brain being similar to the levels seen in heat shocked cells. The present report describes a combined Northern and Western blot analysis of hsp110 expression in various regions of mouse and human brain. These observations are further expanded by an immunohistochemical characterization of hsp110 cellular localization in mouse brain. It is seen that although hsp110 is an abundant protein in most regions of the brain, its expression is heterogeneous, with little being detectable in the cerebellum. Within the cerebral hemispheres, hsp110 is present in neurons in all regions including the cerebral cortex, the hippocampus, the thalamus and the hypothalamus. In contrast, in the cerebellum, the Purkinje cells are the major hsp110 containing cells while the more abundant granule cells show little if any hsp110 labeling. Since hsp110 has been shown to protect cells and proteins from thermal damage, this differential pattern of expression may have ramifications in the pathophysiology of brain, specifically involving cerebellar sequelae.

Mammalian Hsp70 and Hsp110 proteins bind to RNA motifs involved in mRNA stability.

In this study, in vitro RNA binding by members of the mammalian 70-kDa heat shock protein (Hsp) family was examined. We show that Hsp/Hsc70 and Hsp110 proteins preferentially bound AU-rich RNA in vitro. Inhibition of RNA binding by ATP suggested the involvement of the N-terminal ATP-binding domain. By using deletion mutants of Hsp110 protein, a diverged Hsp70 family member, RNA binding was localized to the N-terminal ATP-binding domain of the molecule. The C-terminal peptide-binding domain did not bind RNA, but its engagement by a peptide substrate abrogated RNA binding by the N terminus of the protein. Interestingly, removal of the C-terminal alpha-helical structure or the alpha-loop domain unique to Hsp110 immediately downstream of the peptide-binding domain, but not both, resulted in considerably increased RNA binding as compared with the wild type protein. Finally, a 70-kDa activity was immunoprecipitated from RNA-protein complexes formed in vitro between cytoplasmic proteins of human lymphocytes and AU-rich RNA. These findings support the idea that certain heat shock proteins may act as RNA-binding entities in vivo to guide the appropriate folding of RNA substrates for subsequent regulatory processes such as mRNA degradation and/or translation.

The chaperoning activity of hsp110. Identification of functional domains by use of targeted deletions.

hsp110 is one of major heat shock proteins of eukaryotic cells and is a diverged relative of the hsp70 family. It has been previously shown that hsp110 maintains heat-denatured luciferase in a soluble, folding competent state and also confers cellular heat resistance in vivo. In the present study the functional domains of hsp110 that are responsible for its chaperoning activity are identified by targeted deletion mutagenesis using the DnaK structure as the model. The chaperoning activity of mutants is assessed based on their ability to solubilize heat-denatured luciferase as well as to refold luciferase in the presence of rabbit reticulocyte lysate. It is shown that these functions require only an internal region of hsp110 that includes the predicted peptide binding domain and two immediately adjacent C-terminal domains. It is also shown that although hsp110 binds ATP, binding can be blocked by its C-terminal region.

Tumor cell apoptosis, lymphocyte recruitment and tumor vascular changes are induced by low temperature, long duration (fever-like) whole body hyperthermia.

A single treatment of low-temperature, long-duration, whole-body hyperthermia of either severe combined immunodeficient (SCID) mice bearing human breast tumor xenografts or Balb/c mice bearing syngeneic tumors for 6-8 hr can cause a temporary reduction of tumor volume and/or a growth delay. In both animal model systems, this inhibition is correlated with the appearance of large numbers of apoptotic tumor cells. Because this type of mild heat exposure, comparable to a common fever, is not itself directly cytotoxic, other explanations for the observed tumor cell death were considered. Our data support the hypothesis that this hyperthermia protocol stimulates some component(s) of the immune response, which results in increased antitumor activity. In support of this hypothesis, increased numbers of lymphocyte-like cells, macrophages, and granulocytes are observed in the tumor vasculature and in the tumor stroma immediately following this mild hyperthermia exposure. In Balb/c mice, an infiltrate persists in the tumor for at least 2 weeks. Using the SCID mouse/human tumor system, we found that both host natural killer (NK) cells and injected human NK cells were increased at the site of tumor following hyperthermia treatment. Experiments using anti-asialo-GM1 antibodies indicate that the tumor cell apoptosis seen in the SCID mouse appears to be due largely to the activity of NK cells, although additional roles for other immunoeffector cells and cytokines appear likely in the immunologically complete Balb/c model. Another interrelated hypothesis is that immunoeffector cells may have greater access to the interior of the tumor because we have observed that this treatment causes an obvious expansion in the diameter of blood vessels within the tumor and an increase in nucleated blood cells within the vessels, which persists as long as 2 weeks after treatment. Further study of the mechanisms by which mild hyperthermia exerts antitumor activity could result in this treatment protocol being used as an effective, nontoxic adjuvant to immunotherapy and/or other cancer therapies.

Fever-range hyperthermia enhances L-selectin-dependent adhesion of lymphocytes to vascular endothelium.

The L-selectin leukocyte adhesion molecule plays an important role in controlling leukocyte extravasation in peripheral lymph nodes and at sites of tissue injury or infection. Although febrile responses during infection and inflammation are associated with enhanced immune activity, the contribution of fever-range temperatures to controlling lymphocyte recruitment to tissues has not been previously examined. In this report we provide evidence that direct exposure of lymphocytes to fever-range temperatures (38-41 degrees C) in vitro for 9 to 24 h resulted in a >100% increase in L-selectin-dependent adhesion of these cells to lymph node high endothelial venules (HEV). Moreover, culture of lymphocytes under hyperthermia conditions markedly enhanced the ability of these cells to traffic in an L-selectin-dependent manner to peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. In contrast, febrile temperatures did not increase LFA-1 function as assessed by measuring lymphocyte adhesion to ICAM-1-3T3 transfectants. Fever-range hyperthermia further did not increase L-selectin surface density on lymphocytes or L-selectin-dependent recognition of soluble carbohydrate substrates; however, a marked increase in ultrastructural immunogold-labeling of L-selectin was observed in response to thermal stimuli. These results suggest that elevated temperatures enhance L-selectin adhesion and/or avidity through the regulation of L-selectin conformation or organization in the plasma membrane. Finally, the observed thermal effects on L-selectin adhesion were attributed to soluble factors in the conditioned medium of heat-treated cells. Taken together, these data provide new insight into the potential physiologic role of the febrile response in enhancing lymphocyte recruitment to tissues through the regulation of L-selectin adhesion.

Distribution of HSP70, protein kinase C, and spectrin is altered in lymphocytes during a fever-like hyperthermia exposure.

Many B and T lymphocytes display a significant heterogeneity with respect to the subcellular distribution of the cytoskeletal protein spectrin and protein kinase C (PKC), both of which often can be found in a large cytoplasmic aggregate in these cell types. In addition to spectrin and PKC, we recently have reported that HSP70 is also a component of this lymphocyte aggregate. Moreover, these three proteins can undergo dynamic and reversible changes in their localization causing "assembly" of the aggregate in response to various conditions associated with lymphocyte activation, indicating that this naturally occurring aggregate structure is sensitive to activation status. We show here that the same changes in HSP70/spectrin/PKC localization induced by PKC activation also can be caused, in vitro and in vivo, by a mild hyperthermia exposure, as occurs during a natural fever (39.5-40 degrees C, 2-12 hr). This mild heat exposure also triggers the activation of PKC, a major heat shock response, and lymphocyte proliferation. The increase in PKC activity, HSP70-spectrin-PKC aggregate formation, and heat shock protein expression resulting from exposure to fever-like hyperthermia are all inhibited by calphostin C, a specific inhibitor of PKC. These data demonstrate that changes observed during lymphocyte activation could be induced by a mild hyperthermia exposure occurring during a normal febrile episode.

Hsp110 protects heat-denatured proteins and confers cellular thermoresistance.

The 110-kDa heat shock protein (hsp110) has long been recognized as one of the primary heat shock proteins in mammalian cells. It belongs to a recently described protein family that is a significantly diverged subgroup of the hsp70 family and has been found in organisms as diverse as yeast and mammals. We describe here the first analysis of the ability of hsp110 to protect cellular and molecular targets from heat damage. It was observed that the overexpression in vivo of hsp110 conferred substantial heat resistance to both Rat-1 and HeLa cells. In vitro heat denaturation and refolding assays demonstrate that hsp110 is highly efficient in selectively recognizing denatured proteins and maintaining them in a soluble, folding-competent state and is significantly more efficient in performing this function than is hsc70. hsp110-bound proteins can then be refolded by the addition of rabbit reticulocyte lysate or hsc70 and Hdj-1, whereas Hdj-1 does not itself function as a co-chaperone in folding with hsp110. hsp110 is one of the principal molecular chaperones of mammalian cells and represents a newly identified component of the primary protection/repair pathway for denatured proteins and thermotolerance expression in vivo.

Identification of a major subfamily of large hsp70-like proteins through the cloning of the mammalian 110-kDa heat shock protein.

A major mammalian heat shock protein of 110 kDa (hsp110) has long been observed, but has not been cloned. We have cloned the hamster cDNA for hsp110 and show that it hybridizes on a Northern blot to a 3.5-kilobase heat-inducible message in hamster and mouse. The hsp110 sequence was found to share an approximately 30-33% amino acid identity with members of the hsp70 family, most of which occurs in the conserved ATP-binding domain of these molecules. In addition, five sequences were found to be highly similar to hsp110. These are the sea urchin egg receptor for sperm (Foltz, K.R., Partin, J. S., and Lennarz, W.J. (1993) Science 259, 1421-1425) and additional sequences from human and Caenorhaditis elegans and two from yeast. The carboxyl-terminal two-thirds of hsp110 and these five related proteins contain a pattern of highly conserved regions of sequence unique to this group. A probe containing these conserved sequences was found to strongly cross-react on a Southern blot with genomic sequences from yeast to man. A Western blot analysis of several murine tissues indicates that hsp110 is constitutively expressed in all mouse tissues and is highly expressed in brain. Therefore, hsp110 belongs to a new category of large and structurally unique stress proteins that are the most distantly related known members of the hsp70 family.

The 170-kDa glucose-regulated stress protein is an endoplasmic reticulum protein that binds immunoglobulin.

Anoxia, glucose starvation, calcium ionophore A23187, EDTA, glucosamine, and several other conditions that adversely affect the function of the endoplasmic reticulum (ER) induce the synthesis of the glucose-regulated class of stress proteins (GRPs). The primary GRPs induced by these stresses migrate at 78 and 94 kDa (GRP78 and GRP94). In addition, another protein of approximately 150-170 kDa (GRP170) has been previously observed and is coordinately induced with GRP78 and GRP94. To characterize this novel stress protein, we have prepared an antisera against purified GRP170. Immunofluorescence, Endoglycosidase H sensitivity, and protease resistance of this protein in microsomes indicates that GRP170 is an ER lumenal glycoprotein retained in a pre-Golgi compartment. Immunoprecipitation of GRP170 with our antibody coprecipitates the GRP78 (also referred to as the B cell immunoglobulin-binding protein) and GRP94 members of this stress protein family in Chinese hamster ovary cells under stress conditions. ATP depletion, by immunoprecipitation in the presence of apyrase, does not affect the interaction between GRP78 and GRP170 but results in the coprecipitation of an unidentified 60-kDa protein. In addition, GRP170 is found to be coprecipitated with immunoglobulin (Ig) in four different B cell hybridomas expressing surface IgM, cytoplasmic Ig light chain only, cytoplasmic Ig heavy chain only, or an antigen specific secreted IgG. In addition, in IgM surface expressing WEHI-231 B cells, anti-IgM coprecipitates GRP78, GRP94, as well as GRP170; antibodies against GRP170 and GRP94 reciprocally coprecipitate GRP94/GRP170 as well as GRP78. Results suggest that this 170-kDa GRP is a retained ER lumenal glycoprotein that is constitutively present and that may play a role in immunoglobulin folding and assembly in conjunction or consecutively with GRP78 and GRP94.

Induction of glucose regulated proteins during growth of a murine tumor.

Chronic anoxia, glucose starvation, low pH, and numerous other conditions induce the glucose-regulated system of stress proteins (GRPs), whose principal members are observed at 78, 94, and 170 kDa. These stresses may be expected to occur during growth in untreated tumors. To examine the possibility that GRPs are correspondingly induced, we have examined the protein profiles of small (< 0.1 g), intermediate (0.2-0.8 g), and large (> 1.8 g) radiation-induced fibrosarcoma (RIF) tumors grown on C3H mice. One and two-dimensional gel electrophoresis indicate that the principal GRPs at 78 and 94 are coordinately and substantially increased in large tumor masses, relative to the small, and may be partially increased in the intermediate tumors. Necrotic material removed from large tumors exhibited an identical pattern of GRP induction with no visible indication of protein degradation and also contained a significant fraction of viable cells. Western blot analysis using rabbit antisera raised against the 78 and 170 kDa GRPs also demonstrated the enhanced accumulation of these proteins in the large tumors. The antibody against the 170 kDa GRP was also capable of detecting the induction of this stress protein in large tumors by indirect immunofluorescence analysis. Northern blot studies using a probe for the GRP 78 gene also showed an increase in GRP 78 message in large tumors as well as in RIF cells exposed to anoxic stress in vitro. Two-dimensional gel electrophoresis indicated that the major heat shock proteins at 70 and 90 kDa were not increased in the larger tumors, and the amount of the 90 kDa species was reduced. Finally, the quantity of vimentin and its degradation products is significantly diminished in large tumors and in anoxic cells. This study demonstrates that RIF tumor cells undergo a glucose regulated stress response in situ during tumor growth.

Induction of heat-shock proteins by glutamine. The 'feeding effect'.

Subconfluent, log-phase Chinese hamster ovary cells induced the major heat-shock proteins (hsp) when cells were refed, 40 hours after seeding. This method of inducing heat-shock proteins was also obtained by refeeding with fresh serum-free media, but not with media with a long shelf life or with media prepared without glutamine. It was observed that addition of glutamine alone to cultures at 40 hours post-seeding induced heat-shock proteins. Addition of ammonium chloride, however, had no discernible effect on heat-shock protein synthesis. Northern blot analysis indicated that this phenomenon reflected an increase in the levels of message for the constitutive/inducible member of the hsp 70 family, but not the non-constitutive member. To determine the effect of this induction on heat sensitivity, unfed and 'heat-shock-induced' refed cultures were heated at 45 degrees C. No significant difference in cell survival was observed. Therefore glutamine is the necessary ingredient required for the induction of heat-shock proteins and this method of inducing heat-shock proteins does not alter heat sensitivity.