Telomerase enzyme inhibition (TEI) and cytolytic therapy in the management of androgen independent osseous metastatic prostate cancer.

BACKGROUND: Recurrent prostate cancer can be osseous, androgen independent and lethal. The purpose is to discern the efficacy of synthetic small molecule telomerase enzyme inhibitors (TEI) alone or in combination with other cytotoxic therapies in controlling metastatic osseous prostate cancer. METHODS: C4-2B was pre-treated with a match or mismatch TEI for 6 weeks and then inoculated into nude mice subcutaneously or intraosseously. In a separate experiment, untreated C4-2B was injected into femur of nude mice. The mice were divided into seven systemic "combination" treatment groups of control, Ad-BSP-E1a virus, docetaxel, mismatch and match TEI. Serum PSA was followed longitudinally. Histology analyses and histomorphometry were performed. Repeated measure analysis was applied for statistical analysis and Bonferroni method was used in multiple comparisons. RESULTS: In the pre-treated study, the PSA of match treated cells in subcutaneous or intraosseous model was significantly lower than mismatch TEI or PBS treated group (P < 0.05). Histology revealed increased fibrosis, apoptosis and decreased PSA staining in the match TEI treated subcutaneous xenografts. In the combination treatment study, the PSA was significantly lower in single/double treatment and triple treatment than control (P < 0.05). Histology revealed that triple therapy mice had normal femur architecture. Histomorphometrics revealed that the area of femur tumor and woven bone was significantly positively correlated (P = 0.007). CONCLUSIONS: Multiple lines of data point toward the efficacy of systemically administered telomerase inhibitors. Combining cytotoxic regimens with telomerase inhibitors could be beneficial in controlling prostate cancer. Clinical trials are warranted to explore the efficacy of TEI in prostate cancer.

Small molecule, oligonucleotide-based telomerase template inhibition in combination with cytolytic therapy in an in vitro androgen-independent prostate cancer model.

PURPOSE: Determine the efficacy and timing of small molecule oligonucleotide-based inhibitors to the enzyme telomerase in an in vitro model of androgen-independent, osseous prostate cancer. MATERIALS AND METHODS: Telomerase was inhibited in prostate cancer cell lines C4-2/C4-2B and in controls by using small molecule antisense oligonucleotide-based inhibitors alone or in various combinations of small-dose Taxotere (sanofi-aventis, Bridgewater, NJ) and/or conditionally replication competent adenovirus (AD-BSP-E1a). After transfection and proliferation, telomerase telomeric repeat amplification protocol and telomere restriction fragment assays were performed, with specific times for evaluating telomere length. Specimens were stained for analysis with hematoxylin and eosin (H&E), terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL), and prostate-specific antigen (PSA). RESULTS: C4-2/C4-2B cell lines had the shortest initial mean telomere length (approximately 2.5 kilobase [kb]) compared to PC-3 (approximately 5.5 kb). Dose-dependent inhibition of telomerase activity was seen using match oligonucleotide-based inhibitors to telomerase (50% inhibitory concentration 3-5 nm), whereas mismatch compound showed no telomerase inhibition. Significant growth delay and apoptosis in cell lines occurred after > 50 days of treatment. Cells treated with combination "triple therapy" (i.e., telomerase inhibitors, adenovirus, and Taxotere) had the highest amount of apoptosis. Compared to controls, all combination treatment groups had statistically significant reductions in prostate-specific antigen in the conditioned media. CONCLUSIONS: Combining cytotoxic regimens with small molecule inhibitors to telomerase with oligonucleotide-based agents could be beneficial in controlling osseous hormone refractory prostate cancer, as evidenced by these in vitro, preclinical investigations. Telomerase inhibition needs to move into in vivo models and human studies.