Assessment of eligibility criteria in renal cell carcinoma trials evaluating systemic therapy

OBJECTIVES

To characterise the restrictiveness of eligibility criteria in contemporary renal cell carcinoma (RCC) trials, using recommendations from the American Society of Clinical Oncology (ASCO)-Friends of Cancer Research (FCR) initiative.

METHODS

vPhase I-III trials assessing systemic therapies in patients with RCC starting between 30 June 2012 and 30 June 2022 were identified. Eligibility criteria regarding brain metastases, prior or concurrent malignancies, hepatitis B virus (HBV) or hepatitis C virus (HCV) infection, and human immunodeficiency virus (HIV) infection were identified and stratified into three groups: exclusion, conditional inclusion, and not reported. Descriptive statistics were used to determine the frequency of eligibility criteria. Fisher's exact test or chi-square test were used to calculate their associations with certain trial characteristics.

RESULTS

A total of 423 RCC trials were initially identified of which 112 (26.5%) had sufficient accessible information. Exclusion of patients with HIV infection, HBV/HCV infection, brain metastases, and prior or concurrent malignancies were reported in 74.1%, 53.6%, 33.0%, and 8.0% of trials, respectively. In the context of HIV and HBV/HCV infection, patients were largely excluded from trials evaluating immunotherapy (94.4% and 77.8%, respectively). In addition, brain metastases were excluded in trials assessing targeted therapy (36.4%), combined therapy (33.3%), and immunotherapy (22.2%). Exclusion of patients with prior or concurrent malignancies was less frequently reported, accounting for 9.1%, 8.3%, and 5.6% targeted therapy, combined therapy and immunotherapy trials, respectively.

CONCLUSION

A substantial proportion of RCC trials utilise restrictive eligibility criteria, excluding patients with fairly prevalent comorbidities. Implementing the ASCO-FCR recommendations will ensure resulting data are more inclusive and aligned with patient populations in the real-world.

Examining Exclusion Criteria in Advanced Prostate Cancer Clinical Trials: An Assessment of recommendations From the American Society Of Clinical Oncology and Friends of Cancer Research

PURPOSE

Eligibility criteria illustrate the characteristics of the study population and promote the safety of participants. However, overreliance on restrictive eligibility criteria may limit the generalizability of outcomes. As a result, the American Society of Clinical Oncology (ASCO) and Friends of Cancer Research (Friends) issued statements to curtail these challenges. In this study, we aimed to assess restrictiveness in eligibility criteria across advanced prostate cancer clinical trials.

MATERIALS AND METHODS

We identified all phase I, II, and III advanced prostate cancer clinical trials between June 30, 2012, and June 30, 2022, through Clinicaltrials.gov. We evaluated whether a clinical trial excluded, conditionally included, or did not report 4 common criteria: brain metastases, prior or concurrent malignancies, HIV infection, and hepatitis B virus (HBV)/hepatitis C virus (HCV) infection. Performance status (PS) criteria were recorded based on the Eastern Cooperative Oncology Group (ECOG) scale.

RESULTS

Out of 699 clinical trials within our search strategy, 265 (37.9%) trials possessed all the required data and were included in our analysis. The most common excluded condition of our interest was brain metastases (60.8%), followed by HIV positivity (46.4%), HBV/HCV positivity (46.0%), and concurrent malignancies (15.5%). Additionally, 50.9% of clinical trials only included patients with ECOG PS 0 to 1. HIV and HBV/HCV infection were exclusion criteria of 22 (80.8%) and 19 (73.1%) immunotherapy trials, respectively.

CONCLUSION

Patients with brain metastases, prior or concurrent malignancies, HIV infection, HBV/HCV infection, or low-functioning PS were overly restricted from participating in advanced prostate clinical trials. Advocating for broader criteria may ameliorate generalizability.

Evaluation of eligibility criteria in contemporary renal cell carcinoma based on ASCO-FCR recommendations

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Background: A consensus statement from the American Society of Clinical Oncology (ASCO) and Friends of Cancer Research (FCR) collaboration highlights the importance of expanding eligibility criteria in cancer trials to more accurately reflect the real-world population (Kim et al., Clin Cancer Res 2021). We sought to characterize use of overly restrictive eligibility criteria in renal cell carcinoma (RCC) trials in the context of ASCO-FCR recommendations. Methods: Studies containing the MeSH terms “(metastatic OR advanced OR stage IV or unresectable) AND (kidney cancer OR renal cell carcinoma OR renal cell cancer)” from June 30, 2012 to June 30, 2022 were identified on the ClinicalTrials.gov platform. Our search query’s inclusion criteria identified international studies examining adult patients aged ≥ 18 in phase I-III trials. Exclusion criteria comprised pan-cancer studies, trials involving localized treatments, radiation therapy, and prognostic tools. Descriptive statistics were used to characterize the frequency of restrictive eligibility criteria across studies, while Fisher’s exact test or chi-square test were utilized to determine the association between treatment type and exclusion criteria. Results: The content of 423 RCC trials were analyzed, of which 112 (26.5%) had adequate data available. 48 (42.9%), 44 (39.3%) and 18 (16.1%) studies examined combination therapy, targeted therapy, and immunotherapy, respectively. The presence of HIV positivity, HBV/HCV positivity, brain metastases, and concurrent malignancies accounted for the most frequently cited exclusionary criteria, seen in 83/112 (74.1%), 60/112 (53.6%), 37/112 (33.0%), and 9/112 (8.0%) studies respectively. Differences in the use of HIV positivity (p<0.001) and HBV/HCV positivity (p<0.001) as eligibility criteria were observed across classes of therapy (see Table). Conclusions: A significant proportion of RCC studies utilize overly restrictive eligibility criteria as highlighted by the ASCO-FCR joint statement. Appropriate broadening of eligibility criteria to incorporate patient populations mirroring a real-world setting will provide more useful data going forward. [Table: see text]

Assessment of eligibility criteria in advanced urothelial cancer (aUC) trials based on ASCO-FCR recommendations

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Background: American Society of Clinical Oncology (ASCO) and the Friends of Cancer Research (FCR) underscored the need to broaden eligibility criteria in cancer trials to increase patient accrual, expand access to investigational treatments, and enhance generalizability of study results (Kim et al., Clin Cancer Res 2021). While eligibility criteria intend to prioritize patient safety and define a specific study population, these criteria are often based on outdated standards and may not be reflective of real-world practice. Our study aimed to characterize the proportion of aUC trial eligibility criteria according to the ASCO-FCR statement. Methods: Protocols indexed on ClinicalTrials.gov with start dates from June 30, 2012 to June 30, 2022 were evaluated. MeSH terms used in our query were “(metastatic OR advanced OR stage IV OR unresectable) AND (bladder cancer OR upper tract urothelial carcinoma OR upper tract urothelial cancer)”. International studies enrolling patients aged 18 and over in phases I-III were included. Studies examining multiple cancer types as well as those involving localized treatments (e.g., surgery or ablation), radiation therapy, and prognostic tools were excluded. Analyses of eligibility criteria focused on those highlighted in the ASCO-FCR statement; descriptive statistics were used to define the frequency of eligibility criteria and chi-square and Fisher’s exact test were used to determine their association with treatment type. Results: Overall, 205 urothelial cancer trials were assessed, with 37 (18.0%) having publicly accessible data. Of these, 13 (35.1%) evaluated combination therapy, 11 (29.7%) evaluated immunotherapy, 8 (21.6%) evaluated targeted therapy, and 5 (13.5%) evaluated chemotherapy. HIV positivity, HBV/HCV positivity, brain metastases, and concurrent malignancies were found to be exclusion criteria in 89.2% (33/37), 56.8% (21/37), 35.1% (13/37), and 5.4% (2/37) of studies, respectively. While brain metastases, concurrent malignancies, and HBV/HCV positivity were found to be independent of the class of therapy, a statistically significant association was observed with HIV positivity. Specifically, trials evaluating combination therapy (100.0%), immunotherapy (100.0%) and targeted therapy (87.5%) more frequently included HIV positivity as an exclusion criterion as compared to chemotherapy trials (40.0%). Conclusions: A modest percentage of a UC studies from the last decade were observed to report overly restrictive eligibility criteria as defined by the ASCO-FCR statement. HIV positivity and HBV/HCV positivity were commonly identified exclusion criteria, despite limited evidence that these criteria significantly impact drug efficacy and tolerability. Reassessing and updating eligibility criteria will ensure that the resulting data is more reflective and inclusive of a real-world population.

Evaluation of eligibility criteria in advanced prostate cancer clinical trials based on ASCO-FCR recommendations

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Background: The American Society of Clinical Oncology (ASCO) and the Friends of Cancer Research (FCR) published a joint statement addressing clinical eligibility for characteristics lacking adequate representation in recent studies (Kim et al., Clin Cancer Res 2021). Herein, we aimed to identify the frequency of other potentially excessive exclusion criteria in the context of metastatic prostate cancer. Methods: The eligibility criteria of advanced prostate cancer studies with start dates between June 30, 2012 and June 30, 2022 were identified through Clinicaltrials.gov. MeSH (Medical Subject Headings) terms in our query were “(metastatic OR advanced OR stage IV OR unresectable) AND (prostate cancer OR prostate adenocarcinoma)”. Our study included trials conducted worldwide and examined patients aged 18 and over in phase I-III trials. To narrow the scope of study, trials including more than one cancer type (basket trials) as well as those focusing on radiation therapy were not included in the study. Descriptive statistics were used to determine the frequency of eligibility criteria while the Fisher’s exact test or chi-square test were performed to demonstrate association between type of treatment and exclusion criteria. Results: 265 of 699 (37.9%) clinical trials within the specified search had sufficiently available data for evaluation. Of these, 136 (51.3%), 51 (19.2%), 26 (9.8%), 20 (7.5%), 19 (7.2%), and 7 (2.6%) of trials investigated treatment with combination therapy, hormone therapy, targeted therapy, immunotherapy, radioligand therapy, and chemotherapy, respectively. The most common ASCO-FCR-cited exclusion criteria in the studies were brain metastases (161/265, 60.8 %), HIV positivity (123/265, 46.4%), HBV/HCV positivity (122/265, 46.0%), and concurrent malignancies (41/265, 16.6%). Statistically significant relationships were identified between type of treatment along with status of brain metastases, HIV, and HBV/HCV (p=0.011, <0.001, and 0.001, respectively. Conclusions: This study represents the first effort to analyze this specific subset of exclusion criteria in relation to type of treatment in advanced prostate cancer. Attention to the ASCO-FCR consensus statement may maximize patient representation in future studies and increase generalizability of data. [Table: see text]

The radiosensitizing effect of the aurora kinase inhibitors, ENMD-2076, on canine mast cell tumours in vitro

ENMD-2076 is an aurora kinase inhibitor that also has multi-target tyrosine kinase inhibitor properties. In this study, the mRNA and the protein expression of aurora-A and aurora-B were evaluated in three canine mast cell tumour cell lines. Dose-dependent cytotoxicity was seen in the cells treated, and it affected the cell cycle with cells in the G2/M phase being selectively killed. The cells were also evaluated for radiosensitivity with/without ENMD-2076, and radiosensitization was seen after 3 Gy and 6 Gy exposures with ENMD-2076 for 48 h. Protein expression of caspase-3 was gradually increased, and the expression intensity was highest at 24 h post irradiation in cells without ENMD-2076 treatment, which indicates that radiation exposure with ENMD-2076-induced cell death faster than radiation treatment alone. Our study results suggest the potential usefulness of treating canine mast cell tumours with aurora kinase inhibitors alone or in conjunction with radiation therapy.

Structure-function studies of the functional and binding epitope of the human 37 kDa laminin receptor precursor protein

Expression of the 37 kDa laminin receptor precursor protein (37LRP) correlates directly with increased invasiveness and the metastatic potential of tumors. The 37LRP matures to a 67 kDa protein which facilitates the binding of cancer cells to basement membranes. The palindrome peptide sequence LMWWML, corresponding to the 173-178-residue stretch of the human 37LRP sequence, has been identified as the laminin-1-binding site. Peptides from 37LRP of species that contain this palindrome-bind laminin-1 with high affinity. Nuclear magnetic resonance (NMR) conformational studies have been undertaken on a synthetic 15-residue peptide (KGAHSVGLMWWMLAR) containing the palindrome to establish the structural basis of this activity. To further correlate the structural data with laminin-1-binding function, analogous structural studies were conducted for a similar peptide (RGKHSIGLIWYLLAR) lacking the palindrome, originating from 37LRP sequence of Saccharomyces cerevisiae and exhibiting low laminin-1-binding affinity. Finally, in vitro cell invasion assays were performed to investigate the possibility that the laminin-1-binding affinity of the peptides influences their inhibitory activity.

Growth factor regulation of secreted matrix metalloproteinase and plasminogen activators in prostate cancer cells, normal prostate fibroblasts and normal osteoblasts

We assessed the relative levels of secreted matrix metalloproteinases (MMPs) and plasminogen activators (PAs) in PC-3 cells, prostate fibroblasts and osteoblasts in the presence and absence of VEGF, TGF beta1 and bFGF. Fibroblasts and osteoblasts secreted more MMPs -1 and -2 than did PC-3 cells, while PC-3 s contributed the majority of PAs. MMP-1 expression was downregulated by transforming growth factor beta-1 (TGF beta1) treatment in prostate fibroblasts and upregulated by basic fibroblast growth factor (bFGF) in both stromal lines. In PC-3 cells, TGF beta1 and bFGF increased urokinase plasminogen activator secretion. TGF beta1 decreased tissue plasminogen activator secretion in all cell lines. Prostate cancer cells associated with fibroblasts or osteoblasts have a variety of MMPs and PAs to facilitate matrix degradation.

Dietary 4-HPR suppresses the development of bone metastasis in vivo in a mouse model of prostate cancer progression

The effects of the synthetic retinoid N-(4-hydroxyphenyl) retinamide (4-HPR) on prostate cancer metastasis in vivo were evaluated in the mouse prostate reconstitution (MPR) model. MPRs were produced by infection of either heterozygous (+/-) or nullizygous (-/-) p53-mutant fetal prostatic epithelial cells with the recombinant retrovirus Zipras/myc 9. Previous studies have documented that loss of p53 function potentiates metastasis in this model system. MPRs were grafted into homozygous (+/+) p53 male mice, fed a 4-HPR containing diet or a control diet and maintained until the status of tumor progression dictated sacrifice. Under these experimental conditions, treatment with 4-HPR did not have a significant effect on primary tumor wet weight for either p53 +/- or p53 -/- MPRs. For, p53 +/- MPRs the animals fed the 4-HPR diet had a slight improvement in survival and a significant reduction in the number of mesenteric metastases (P = 0.0477, t-test). Notably, in p53 +/- MPRs the incidence of metastasis to lumbar spine and sternum was 92% in the control animals compared to 54% in the 4-HPR treated animals (P = 0.035, chi2-test). In p53 -/- MPRs there was a trend toward a reduction in the number of soft tissue metastases to lung and liver in the 4-HPR group relative to the control diet group and a statistically significant reduction in the incidence of metastasis to bone was demonstrated in that 50% of control animals versus 30% of 4-HPR treated p53 -/- animals harbored bone metastases (P = 0 < 0.05, chi2-test). Cell lines were established from portions of the primary tumor and from selected metastatic deposits in each experimental group. Clonal analysis, by retroviral integration pattern, indicated increased clonal diversity in both the primary tumors and metastasis-derived cell lines from 4-HPR treated animals relative to the control animals. In vitro treatment with 4-HPR did not reveal discriminating differences between cell lines derived from primary tumors and bone metastases or control and treatment groups in regard to growth arrest or apoptotic responses. Overall these studies indicate limited anti-tumor and anti-metastatic activity in this highly aggressive in vivo mouse model of prostate cancer, yet 4-HPR treatment significantly suppressed the development of bone metastases in p53 +/- and p53 -/- MPRs revealing a novel and potentially clinically useful activity of this retinoid.

Inhibition of murine prostate tumor growth and activation of immunoregulatory cells with recombinant canarypox viruses

BACKGROUND

Immunization with modified tumor cells carrying recombinant immunomodulatory genes is being explored as cancer immunotherapy. In this study, we examine whether canarypox ALVAC viruses carrying immunostimulatory cytokine genes (granulocyte-macrophage colony-stimulating factor, interleukin 2, interleukin 12, and tumor necrosis factor-alpha) can induce antitumor immunity (to rechallenge) in the RM-1 model of a highly aggressive, weakly immunogenic murine prostate cancer.

METHODS

For antitumor activity studies, RM-1 murine prostate cancer cells were infected with the parental ALVAC virus or one or two recombinant ALVAC-cytokine viruses and then injected into male C57BL/6 mice. For rechallenge studies, other mice were first given an injection subcutaneously with irradiated (nonproliferating) recombinant ALVAC-infected RM-1 cells and then (10 days later) with untreated RM-1 cells. For the determination of which immune cells were required for antitumor activity, mice were immunodepleted of CD4, CD8, or natural killer (NK) NK1.1 cells with the corresponding monoclonal antibodies and were then given an injection of ALVAC-cytokine-infected RM-1 cells. For all experiments, tumor outgrowth and animal survival were monitored.

RESULTS

After subcutaneous injection into mice, RM-1 cells infected with one (except ALVAC-interleukin 2) or two ALVAC-cytokine recombinants had statistically significantly greater antitumor activity than RM-1 cells infected with parental ALVAC (P<.001 for all; two-sided test). The antitumor activity of RM-1 cells infected with any two ALVAC-cytokine recombinants was greater than, but not statistically significantly different from, that of RM-1 cells infected with any one ALVAC-cytokine recombinant. NK1.1 cells were necessary for antitumor activity, but tumor-specific CD4(+) regulatory T cells were also induced that inhibited CD8(+) RM-1-specific cytotoxic T cells, resulting in the lack of immunity to a rechallenge by RM-1 cells.

DISCUSSION

Canarypox viruses can transfer immunostimulatory cytokine genes into RM-1 prostate cancer cells. When such cells were injected into mice, the cytokines induced an antitumor response against this highly aggressive, weakly immunogenic tumor. This response, however, did not protect the mouse against a rechallenge with RM-1 cells because suppressor CD4(+) T cells were induced that inhibited tumor-specific CD8(+) cytotoxic T cells.

Novel regulation of type IV collagenase (matrix metalloproteinase-9 and -2) activities by transforming growth factor-beta1 in human prostate cancer cell lines

The type IV collagenases/gelatinases matrix metalloproteinase-2 (MMP-2) and MMP-9 play a variety of important roles in both physiological and pathological processes and are regulated by various growth factors, including transforming growth factor-beta1 (TGF-beta1), in several cell types. Previous studies have suggested that cellular control of one or both collagenases can occur through direct transcriptional mechanisms and/or after secretion through proenzyme processing and interactions with metalloproteinase inhibitors. Using human prostate cancer cell lines, we have found that TGF-beta1 induces the MMP-9 proenzyme; however, this induction does not result from direct effects on gene transcription but, instead, through a protein synthesis-requiring process leading to increased MMP-9 mRNA stability. In addition, we have examined levels of TGF-beta1 regulation of MMP-2 in one prostate cancer cell line and found that TGF-beta1 induces higher secreted levels of this collagenase through increased stability of the secreted 72-kDa proenzyme. These results identify two novel nontranscriptional pathways for the cellular regulation of MMP-9 and MMP-2 collagenase gene expression and activities.

Neuropeptides induce Mr 92,000 type IV collagenase (matrix metalloprotease-9) activity in human prostate cancer cell lines

The type IV collagenases matrix metalloprotease (MMP)-2 and MMP-9 are linked with a wide array of biological activities, including tumor invasion, metastasis, and angiogenesis. Here, we report that neuropeptide hormones, which are present in prostatic adenocarcinomas, can stimulate secreted activity of MMP-9 in human prostate cancer cell lines. Northern blotting analyses demonstrated that neuropeptide stimulation lead to elevated mRNA levels of MMP-9 but not MMP-2. Further assays of MMP-9 promoter activation and a nuclear run-off indicated that neuropeptide induction of MMP-9 expression occurs at the level of transcription. These data indicate that neuropeptides can regulate MMP activity, which, in turn, could facilitate prostate cancer progression.

Requirement for matrix metalloproteinase-9 (gelatinase B) expression in metastasis by murine prostate carcinoma

Although a number of effective therapies are available for localized prostate cancer, metastatic prostate cancer is difficult to treat and impossible to cure. Identification of the gene products that enable a prostatic carcinoma cell to metastasize should facilitate an understanding of the processes leading to metastasis. To characterize the contribution of matrix metalloproteinase-9 (MMP-9, gelatinase B or the 92-kd type IV gelatinase/collagenase) to the development of metastasis in prostate cancer, we reduced MMP-9 expression in metastatic murine prostatic carcinoma cells using a ribozyme. The ribozyme transfected cells had lower basal levels of MMP-9 as well as decreased levels after stimulation by transforming growth factor-beta or phorbol 12-myristate 13-acetate when compared with the parental cells or with control transfectants. The cells with down-regulated MMP-9 were unable to form lung colonies in the experimental metastasis assay, whereas the controls and parental cells readily formed metastases. All cell types readily formed tumors after injection and down-regulation of MMP-9 did not adversely affect the rate of tumor growth. Thus, MMP-9 expression is required for hematogenous metastasis in a murine prostate model system raising the possibility that it may play an equivalent role in human prostate cancer.

Transforming growth factor beta1 stimulates contrasting responses in metastatic versus primary mouse prostate cancer-derived cell lines in vitro

Tumor progression to the stage of metastasis may result in part from the selection of certain primary tumor cell clones which are phenotypically competent for survival, invasion, and growth at secondary sites. Selection for traits such as loss of growth inhibitory responses, acquisition of increased adhesiveness, increased local immunosuppression, and enhanced motility and collagenase activities likely contribute to cancer progression and may be regulated through the action of growth factors. The transforming growth factors (TGF-beta) family of growth factors has often been associated with these traits and tumor progression; therefore, elimination or subversion of TGF-beta-responsive pathways should be considered as a mechanistic framework for metastatic events. In this report, we have compared growth and extracellular matrix responses to TGF-beta in six metastatic and six primary tumor-derived cell lines in a mouse model of prostate cancer. We have found that tumor cell lines derived from focal pulmonary metastasis secreted relatively greater quantities of total TGF-betas, lost most or all TGF-beta1 growth inhibition, but responded to TGF-beta1 through induction of the type IV collagenase matrix metalloproteinase-9, whereas cell lines derived from tumors which proliferated at the primary site retained the growth inhibition but lacked collagenase activity. Synthesis of another extracellular matrix protein, plasminogen activator inhibitor 1, was stimulated by TGF-beta1 in both primary as well as metastatic tumors. These results suggest that acquisition of differential responses to the TGF-beta family could result in phenotypic traits which facilitate tumor metastasis from certain primary site clones.

Prostate cancer gene therapy: herpes simplex virus thymidine kinase gene transduction followed by ganciclovir in mouse and human prostate cancer models

Prostate cancer is the most common internal malignancy in men in the United States. Most cancers are diagnosed when they are locally advanced or metastatic and there is no effective treatment. In this study we evaluated the effectiveness of cytotoxic gene therapy in human PC-3 and DU145 prostate cancer cell lines and in a rodent cell line, RM-1, derived from the mouse prostate reconstitution model system. The cell lines were efficiently transduced in vitro by a replicative-defective recombinant adenovirus (ADV) carrying the herpes simplex virus thymidine kinase gene (HSV-tk). A virus titer-dependent sensitivity to ganciclovir (GCV) was observed. To determine a target therapeutic viral dose in vivo, subcutaneous tumors were generated by injection of RM-1 cells in syngeneic male hosts and injected with escalating doses of HSV-tk virus (5 x 10(7) to 1 x 10(9) pfu). The mice received GCV twice daily for 6 days and were sacrificed when tumor volumes exceeded 2.5 cm3 or when they appeared to be in distress. Because the two highest doses were equally as effective, further controlled studies were performed with the lower dose of 5 x 10(8) pfu with ADV/RSV-tk or a control virus containing the beta-galactosidase gene (ADV/RSV-beta-Gal) and treated with GCV or saline (PBS). The mean tumor volume in the treated animals was 16% that of control animals at 13 days. Histologically, treated tumors demonstrated necrosis and had a significantly higher apoptotic index. Survival data indicated that the treatment animals lived 7 days (21 in total) longer than the control animals, with 1 treatment animal being totally free of tumor. These results demonstrate that HSV-tk + GCV cytotoxic gene therapy can inhibit the growth of mouse and human prostate cancer cells in vitro and interrupt tumor growth of an aggressive mouse prostate cancer cell line in vivo.

In vivo gene therapy with p53 or p21 adenovirus for prostate cancer

We introduced the gene for wild-type human p53 or p21, a critical downstream mediator of p53-induced growth suppression, into a p53-deficient mouse prostate cancer cell line using a recombinant adenoviral vector (Ad5CMV-p53 or Ad5CMV-p21). Elevated levels of endogenous mouse p21 mRNA provided evidence for the functional activity of virally transduced p53. Functional activity of viral-transduced p21 was demonstrated through immunoprecipitation of cellular protein extracts, which showed that the viral-transduced p21 associates with cyclin-dependent kinase 2 and was sufficient to down-regulate the activity of the cyclin-dependent kinase by approximately 65%. In vitro growth assays revealed significantly higher growth suppression after Ad5CMV-p21 infection compared to Ad5CMV-p53. In vivo studies in syngeneic male mice with established s.c. prostate tumors demonstrated that the rate of growth and final tumor volume were reduced to a much greater extent in mice that received intratumor injection of Ad5CMV-p21 compared to Ad5CMV-p53. In addition, the survival of host animals bearing tumors that were infected with Ad5CMV-p21, but not Ad5CMV-p53, was significantly extended. These data suggest that Ad5CMV-p21 may be effective as a therapeutic agent for prostate cancer.

Progression to androgen insensitivity in a novel in vitro mouse model for prostate cancer

We have shown previously that the ras and myc oncogenes can induce poorly differentiated mouse prostate carcinomas in vivo with high frequency (greater than 90%) using inbred C57BL/6 mice in the mouse prostate reconstitution model system. To study the androgen sensitivity of these carcinomas, we have developed an in vitro model system which includes a cell line from normal urogenital sinus epithelium (CUGE) and cell lines from three ras + myc transformed mouse prostate carcinomas (RM-9, RM-1, and RM-2). CUGE cells, as well as all prostate carcinoma cell lines, were positive for cytokeratin 18 mRNA and immunoreactive to cytokeratin-specific antiserum. Two out of three of the early passage carcinoma cell lines were clonal with respect to Zipras/myc 9 retrovirus integration as determined by Southern blot analysis. Whereas significant mitogenic effects of testosterone (10 nM) were not seen in CUGE cells grown in serum-free medium, under similar conditions approx. 2-fold increases in cell number were seen in all low passage prostate carcinoma cell lines. Also, in the presence of growth inhibitory levels of suramin (50 micrograms/ml), testosterone was capable of significant growth stimulation in the carcinoma cell lines. With further propagation from low passage [20-25 population doublings (PD)] to high passage (75-100 PD), all carcinoma cell lines demonstrated increased and similar growth rate in the presence and absence of testosterone. These cell lines maintained stable androgen receptor numbers and binding kinetics during the transition from testosterone-responsive growth to reduced responsivity over multiple passages in culture (> 150 PD). Overall, our studies indicate that the capacity to bind testosterone is stably maintained through the transition of the androgen-sensitive to insensitive phenotype and raise the possibility that androgen sensitivity can persist throughout progression but is masked by the acquisition of autocrine pathways.

Neurotensin is an autocrine trophic factor stimulated by androgen withdrawal in human prostate cancer

After therapeutic hormone deprivation, prostate cancer cells often develop androgen-insensitive growth through mechanisms thus far undefined. Neuropeptides have been previously implicated as growth factors in some prostate cancers. Here, we demonstrate that androgen-sensitive LNCaP human prostate cancer cells produce and secrete neurotensin following androgen withdrawal. We show that while LNCaP cells express the neurotensin receptor, only androgen-deprived cells exhibit a growth response to exogenous neurotensin. We further demonstrate that androgen-stimulated cells may be refractory to exogenous neurotensin due to androgen induction of a metalloprotease active toward neurotensin. Thus, prostate cancer cells deprived of androgen develop an alternative autocrine growth mechanism involving neurotensin.

Epidermal growth factor receptor-dependent stimulation of amphiregulin expression in androgen-stimulated human prostate cancer cells

Amphiregulin is a heparin-binding epidermal growth factor (EGF)-related peptide that binds to the EGF receptor (EGF-R) with high affinity. In this study, we report a role for amphiregulin in androgen-stimulated regulation of prostate cancer cell growth. Androgen is known to enhance EGF-R expression in the androgen-sensitive LNCaP human prostate carcinoma cell line, and it has been suggested that androgenic stimuli may regulate proliferation, in part, through autocrine mechanisms involving the EGF-R. In this study, we demonstrate that LNCaP cells express amphiregulin mRNA and peptide and that this expression is elevated by androgenic stimulation. We also show that ligand-dependent EGF-R stimulation induces amphiregulin expression and that androgenic effects on amphiregulin synthesis are mediated through this EGF-R pathway. Parallel studies using the estrogen-responsive breast carcinoma cell line, MCF-7, suggest that regulation of amphiregulin by estrogen may also be mediated via an EGF-R pathway. In addition, heparin treatment of LNCaP cells inhibits androgen-stimulated cell growth further suggesting that amphiregulin can mediate androgen-stimulated LNCaP proliferation. Together, these results implicate an androgen-regulated autocrine loop composed of amphiregulin and its receptor in prostate cancer cell growth and suggest that the mechanism of steroid hormone regulation of amphiregulin synthesis may occur through androgen upregulation of the EGF-R and subsequent receptor-dependent pathways.

Preferential inhibition of the platelet-derived growth factor receptor tyrosine kinase by staurosporine

Ligand stimulation of the platelet-derived growth factor receptor (PDGF-R) results in rapid activation of the receptor tyrosine kinase, stimulation of phosphoinositide hydrolysis, an increase in intracellular free Ca2+ concentration ([Ca2+]i), and, ultimately, cellular proliferation. In a previous study, we demonstrated that staurosporine, a known inhibitor of protein kinase C, blocked PDGF-induced [Ca2+]i increases in Swiss mouse 3T3 fibroblasts by a mechanism that appeared unrelated to inhibition of protein kinase activity (Olsen, R., Melder, D., Seewald, M., Abraham, R., and Powis, G. (1990) Biochem. Pharmacol. 39, 968-972). In the present study, we report that staurosporine inhibits ligand-dependent PDGF-R tyrosine kinase activation in cell-free receptor preparations and in intact Swiss 3T3 cells. At the same concentrations (10(-8)-10(-6) M), staurosporine suppressed both the tyrosine phosphorylation of phospholipase C activity and the hydrolysis of phosphoinositides induced by PDGF stimulation of intact cells. In contrast, guanine nucleotide-binding protein-dependent phospholipase C activation induced by bradykinin or fluoroaluminate anion was relatively insensitive to staurosporine. A preferential inhibitory effect of staurosporine on signal generation by the PDGF-R was indicated by findings that epidermal growth factor receptor (EGF-R) tyrosine kinase activity and EGF-dependent phospholipase C in A-431 carcinoma cells were approximately 100-fold less sensitive to this drug. These data indicate that submicromolar concentrations of staurosporine inhibit PDGF-dependent phosphoinositide hydrolysis and Ca2+ mobilization through a proximal inhibitory effect on ligand-induced activation of the PDGF-R tyrosine kinase.

Inhibition of growth factor-dependent inositol phosphate Ca2+ signaling by antitumor ether lipid analogues

Cytotoxic ether lipid analogues have been studied for their ability to inhibit growth factor-dependent [Ca2+]i signaling in Swiss 3T3 fibroblasts. 1-Octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) inhibited 45Ca2+ uptake and inositol(1,4,5)trisphosphate-induced 45Ca2+ release in saponin permeabilized cells with concentration producing 50% inhibition values of 55 and 360 microM, respectively. When cells were exposed to ET-18-OCH3 for 18 h before permeabilization there was selective inhibition of inositol(1,4,5)trisphosphate-induced 45Ca2+ release with a concentration producing 50% inhibition value of 20 microM, but no effect on 45Ca2+ uptake, or on 45Ca2+ release by arachidonic acid. The concentration of ET-18-OCH3 with continuous exposure to inhibit cell growth 50% was 19 microM. The ether lipid analogues 1-hexadecylthio-2-ethyl-rac-glycero-3- phosphocholine and 1-S-octadecyl-2-O-methylthiopropyl-3-N,N-dimethyl-gamma-hydroxy pro pyl ammonium iodide had effects similar to those of ET-18-OCH3 but the noncytotoxic analogue 1-alkyl-2-hydroxy-sn-glycero-3- phosphocholine was without effect. Exposure of cells to 10 microM ET-18-OCH3 produced 81% inhibition of platelet-derived growth factor-stimulated inositol phosphate formation and 66% inhibition of fluoroaluminate anion-stimulated inositol phosphate formation. Addition of ET-18-OCH3 to cells in medium with 10% fetal calf serum gave a transient increase in [Ca2+]i without causing an increase in resting [Ca2+]i, while the addition of ET-18-OCH3 to cells in medium without serum gave a sustained increase in resting [Ca2+]i. Cells exposed to 5 microM ET-18-OCH3 for 18 h showed no increase in resting [Ca2+]i but there was 95% inhibition of the [Ca2+]i response to platelet-derived growth factor, 63% inhibition of the response to bradykinin, and 55% inhibition of the response to vasopressin. The block by ether lipid analogues of inositol phosphate-mediated [Ca2+]i signaling suggests a mechanism for preventing the action of growth factors that could contribute to the inhibition of cell proliferation by the agents.

Platelet-derived growth factor stimulates non-mitochondrial Ca2+ uptake and inhibits mitogen-induced Ca2+ signaling in Swiss 3T3 fibroblasts

Changes in intracellular free Ca2+ concentration [( Ca2+]i) were used to study the interaction between mitogens in Swiss 3T3 fibroblasts. Platelet-derived growth factor (PDGF) produced an increase in [Ca2+]i and markedly decreased the increases in [Ca2+]i caused by subsequent addition of bradykinin and vasopressin. If the order of the additions was reversed the [Ca2+]i response to PDGF was not inhibited by bradykinin or vasopressin. Inhibition of protein kinase C by staurosporine or chronic treatment of the cells with phorbol 12-myristate 13-acetate prevented the inhibitory effect of PDGF on the [Ca2+]i response to vasopressin but not bradykinin. PDGF did not decrease the receptor binding of bradykinin and produced only a small decrease in the receptor binding of vasopressin. PDGF decreased the rise in [Ca2+]i caused by the Ca2+ ionophores 4-bromo-A23187 and ionomycin and by a membrane perturbing ether lipid, 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine, both in the presence and absence of external Ca2+. There was no change in cell 45Ca2+ influx caused by PDGF, vasopressin, or bradykinin. 45Ca2+ efflux from cells exposed to PDGF and vasopressin mirrored the changes in [Ca2+]i caused by the agents, that is, PDGF added after vasopressin produced a further increase in 45Ca2+ efflux but vasopressin did not increase 45Ca2+ efflux after PDGF. PDGF but not vasopressin caused an increase in the uptake of 45Ca2+ into an inositol 1,4,5-trisphosphate-insensitive non-mitochondrial store in permeabilized cells. The results suggest that the decreased [Ca2+]i response to mitogens after PDGF represents an action of PDGF at a point beyond the release of intracellular Ca2+ and the influx of external Ca2+, caused by an increase in the rate of removal of cytoplasmic free Ca2+. This increased removal of cytoplasmic Ca2+ by PDGF is not due to the increased export of Ca2+ from the cell but results from increased Ca2+ uptake into non-mitochondrial stores.