Translation of the preclinical observations of rhTRAIL or agonistic anti-TRAIL receptor monoclonal antibodies into the clinical realm has begun in recent years. A phase Ia trial of rhTRAIL consisting of a dose escalation to 15 mg/kg for patients with advanced solid tumors or non-Hodgkin's lymphoma has yielded encouraging results with no attributable toxicities (Herbst et al., 2006
). Of the 32 patients evaluated, 17 (53%) had stable disease, 13 (41%) had progression and one patient with chondrosarcoma had a confirmed partial response. Preliminary results of a phase Ib trial of rhTRAIL in combination with rituximab in patients who have progressed after treatment for low-grade non-Hodgkin lymphoma have recently been reported (Yee et al., 2007
). There were no dose-limiting toxicities or serious adverse events at doses of 4 and 8 mg/kg, and of the 5 patients assessed, 2 had stable disease, 1 had a partial response, and 2 had a complete response.
Clinical trials of agonistic anti-TRAIL receptor-1 and TRAIL receptor-2 monoclonal antibodies are also underway. In a phase I study of the TRAIL-R1 agonist mapatumumab, 49 patients with advanced solid malignancies safely received doses of up to 10 mg/kg every 14 days (Tolcher et al., 2007
). The mean half-life of the antibody was 18 days. Nineteen patients had stable disease, with 2 instances lasting 9 months, but 2 patients did have elevated liver function tests probably related to mapatumumab administration. A phase Ib study of mapatumumab given to patients with advances malignancies in combination with paclitaxel and carboplatin achieved a partial response in 4/28 patients (Chow et al., 2006
). In another phase Ib study of mapatumumab with gemcitabine and cisplatin given to patients with advanced solid malignancies, doses as high as 30 mg/kg every 3 weeks were safe with 9/45 patients achieving a partial response and 13/45 patients experiencing stable disease after 6 cycles (Oldenhuis et al., 2008
). A phase II trial of mapatumumab as a single agent was carried out in 32 previously treated patients with advanced non-small cell lung cancer. At a dose of 10 mg/kg given every 21 days, the antibody was well-tolerated and 9/32 patients had stable disease; however, none of the patients showed a response based on the Response Evaluation Criteria in Solid Tumors (RECIST) criteria (Greco et al., 2008
A phase I trial of lextumumab, a TRAIL receptor-2 agonistic antibody, in patients with advanced solid malignancies has been carried out with a dose of 10 mg/kg given every 21 days identified at the maximum tolerated dose (Plummer et al., 2007
). The half-life of this antibody was 16 days, and 12 out of 37 patients had stable disease lasting a median of 4.5 months. Lexatumumab has also been evaluated in combination with gemcitabine, premetrexed, doxorubicin and FOLFIRI (leucovorin, fluorouracil and irinotecan) in a phase 1b study (Sikic et al., 2007
). In this combination study, lexatumumab was well tolerated at 10 mg/kg with 3/41 patients experiencing a confirmed partial response.
Apomab is another agonistic antibody that interacts with an epitope on TRAIL receptor-2 that partially overlaps with both regions of the TRAIL binding site, and is capable of inducing TRAIL receptor-2 clustering and apoptosis (Adams et al., 2008
). Apomab has undergone a phase I trial in patients with advanced, treatment-refractory solid tumors (Camidge et al., 2007
). Doses up to 20 mg/kg given every 14 days were well tolerated. This antibody's half-life was 15-20 days, and no human anti-human antibodies were detected. There were no objective responses observed, but 1 patient with appendiceal cancer had stable disease and 1 patient with colorectal cancer had symptomatic improvement and shrinkage of target lesions.
We recently completed a Phase I clinical trial with Ad5-TRAIL in men with locally-confined prostate cancer, with the primary objectives of determining the toxicity profile and maximal tolerated dose. The ability of the vector to induce tumor cell death was also evaluated. Patients with histologically confirmed adenocarcinoma of the prostate [clinical stage T1c, T2a, T2b (as per American Joint Committee on Cancer 2002, 6th edition) all of whom were clinically N0, M0] and scheduled to undergo radical prostatectomy within 10 days following study entry were eligible for the study. As part of their staging evaluation, patients with a serum PSA >10ng/ml or tumors of Gleason grade >7 on biopsy also underwent a bone scan to rule out metastatic disease. All patients also underwent a staging endorectal MRI of the prostate prior to enrollment. Additional study inclusion criteria included the patients having no prior malignancies within the past 5 years with the exception of curatively treated basal cell or squamous cell carcinoma of the skin, an Eastern Cooperative Oncology Group performance status of 0 or 1, and no parenteral antibiotics < 7 days prior to study entry. Radiologic studies to document measurable or evaluable disease were done within 4 weeks prior to study entry. Each patient provided a signed informed consent form. Exclusion from the study occurred if there was a prior history of transurethral resection of the prostate, transurethral needle ablation of the prostate or microwave therapy to the prostate; a prior history of external beam radiation to the prostate or interstitial seed implantation (brachytherapy) to the prostate; a prior history of androgen ablation therapy for prostate cancer; a prior history of abdominoperineal resection or other procedure precluding patient from undergoing a transrectal ultrasound; a documented history of allergy to Gelfoam; or the presence of active infection.
We hypothesized that the intraprostatic delivery of Ad5-TRAIL could have two modes of action: direct infection of tumor cells resulting in tumor cell death and infection of normal prostate cells that are turned into “by-stander tumor killers.” Still, adequate distribution of the vector throughout the prostate needed to be addressed to increase the efficacy of the Ad5-TRAIL therapy. Numerous substances have been used as carriers to enhance and sustain the delivery of soluble products to cancerous and normal tissues (Lee et al., 1997
; Machan et al., 1997
). One such agent is Gelfoam (Pfizer, Kalamazoo, MI), a collagen-based matrix that enhances the distribution and expression of virally-delivered genes when injected intratumorally (Siemens et al., 2000a
; Siemens et al., 2000b
). Gelfoam is able to absorb and hold within its interstices ~45 times its weight of blood and other fluids (Chemistry, 1947
), and the absorptive capacity of Gelfoam is a function of its physical size, increasing with increasing gelatin volume (Goodman and Gliman, 1980
). Gelfoam has been used for the delivery of soluble proteins and drugs, including antibiotics, and growth factors (Lee et al., 1997
; Park and Kim, 1997
; Stepnick et al., 1995
). Studies have evaluated the potential of Gelfoam to enhance intratumoral gene transfer and antitumor activity. Initial investigation showed Gelfoam enhanced canarypox (ALVAC) virus-mediated gene transfer () when compared with ALVAC injection in buffered saline (fluid phase). Subsequent studies were performed to compare adenoviral-mediated gene transfer to ALVAC with and without Gelfoam. As observed for ALVAC, Gelfoam also enhanced gene transfer with adenovirus suggesting the general applicability of the enhancement mechanisms (). In addition, adenoviral transgene expression was significantly higher that ALVAC transgene expression. To further examine the Gelfoam-mediated enhancement of gene delivery, adenoviral transgene distribution in benign dog prostate was evaluated. Injection of Ad5-βgal in phosphate buffered saline produced minimal β-gal expression, but Ad5-β-gal co-injected with Gelfoam resulted in an extensive expansion of β-gal expression (). These data show that Gelfoam effectively enhances the distribution of virally transferred gene expression among prostate cells near the injection site, and suggest utility in gene therapy studies involving intraprostatic injections.
Figure 3 Effect of Gelfoam on viral distribution and transgene expression. (A) ALVAC-β-gal was injected into RM-1 tumors (400-600 mm3), which were removed 4 h later, fixed and stained for β-gal activity. (B) ALVAC-luc and Ad5-luc (107 pfu) were (more ...)
The vector was administered intraprostatically in a collagen (Gelfoam, 30 mg/ml) matrix to 12 patients using the following dose escalation: 1.3×108 pfu (4.2×109 particles); 4.2×108 pfu (1.3×1010 particles); 1.3×109 pfu (4.2×1010 particles); 4.2×109 pfu (1.3×1011 particles). For use in the delivery of Ad5-TRAIL, Gelfoam powder was mixed with sterile saline containing the appropriate dose of Ad5-TRAIL. The Gelfoam concentration was based on the fluid retention capacity, and not viral particle counts. Each group received 4 injections of Ad5-TRAIL in Gelfoam divided equally into both lobes of the prostate, further divided into 2 injection points in each lobe. The total volume injected was 2.5 ml. No adverse reactions were observed in any of the patients treated, and all patients tolerated the injection. Further, there were no complications with the surgical removal of the prostate after Ad5-TRAIL injection. A comparison of several surgical parameters compared to non-injected patients undergoing radical prostatectomy is shown in .
Surgical comparison between prostate cancer patients receiving intraprostatic injections of Ad5-TRAIL and uninjected prostate cancer patients with similar disease stage.
Intraprostatic injection performed on the first 3 subjects also revealed the Ad5-TRAIL/Gelfoam mixture to be echogenic, allowing us to confirm its presence in the prostatic parenchyma (). The clinical trial protocol specified that 3 subjects be enrolled at each of 4 dose levels with a 4 week break between dose levels to allow observation for side effects at each level. The Gelfoam was also detected by histological assessment in the injected prostate after prostatectomy (). Inflammatory cells were evident in the areas where Gelfoam was present, as well as TUNEL-positive staining () – indicating DNA fragmentation indicative of apoptotic death.
Histological assessment of human prostate after Ad5-TRAIL/Gelfoam injection. (A) H&E staining of area where Gelfoam (amorphous purple component) was evident. (B) TUNEL staining of serial section.