Preclinical evaluation of investigational radiopharmaceutical RISAD-P intended for use as a diagnostic and molecular radiotherapy agent for prostate cancer.

BACKGROUND: The androgen receptor (AR) plays a dominant role in the pathogenesis of prostate cancer. 5-Radioiodo-3'-O-(17ß-succinyl-5α-androstan-3-one)-2'-deoxyuridin-5'-yl phosphate (RISAD-P) is an AR-targeting reagent developed for noninvasive assessment of AR and proliferative status of the AR-expressing tumors, and for molecular radiotherapy with Auger electron-emitting radionuclides. In this study, the preclinical toxicity and targeting potential of RISAD-P was evaluated. METHODS: Effects of nonradioactive ISAD-P and RISAD-P labeled with (123) I, (124) I, and (125) I were evaluated in male mice. Expanded-acute single dose toxicity studies, hematologic toxicity, liver and kidney function, pharmacokinetics, biodistribution, and imaging studies were conducted. Imaging and pilot therapy studies were conducted in transgenic mice. RESULTS: RISAD-P is not toxic at doses projected for clinical use. Its tissue distribution compares favorably with the distribution reported for (18) F-dihydrotestosterone derivatives. RISAD-P has excellent prostate cancer targeting properties. One hour after (125) IRISAD-P administration, nearly 10% of the injected dose is associated with prostate tumor. The tumor clearance is biphasic and plateaus between 24 and 48 hr post-injection. The estimated radiation doses calculated for 1 g tumor using the MIRD convention are well within the therapeutic range with values of 170, 250, 1,240 Gy × MBq(-1) × g(-1) for (125) I-, (123) I-, and (124) I-labeled RISAD-P, respectively. The transient uptake of radioactivity is observed in the genitourinary tract and stomach. Without the potassium iodide blockade, thyroid uptake is also observed. CONCLUSIONS: Biodistribution, toxicity, and radiation dosimetry studies suggest that RISAD-P holds characteristics of a promising candidate for imaging of AR expression and tumor proliferation, as well as molecular radiotherapy for metastatic or locally, regionally advanced prostate cancer.

Phase II trial of 131-Iodine tositumomab with high-dose chemotherapy and autologous stem cell transplantation for relapsed diffuse large B cell lymphoma.

The purpose of this study was to evaluate the standard outpatient dose of 131-Iodine tositumomab (75 cGy) combined with high-dose carmustine, etoposide, cytarabine, and melphalan (BEAM) followed by autologous stem cell rescue for the treatment of chemotherapy-sensitive relapsed or refractory, or high-risk first complete remission (CR) patients with diffuse large B cell non-Hodgkin's lymphoma (DLBCL). Forty patients with chemotherapy-sensitive persistent or relapsed or high/intermediate or high international prognostic index DLCBL were treated in a phase II trial combining 75 cGy 131-Iodine tositumomab with high-dose BEAM followed by autologous stem cell transplantation. The CR rate after transplantation was 78%, and the overall response rate was 80%. Short-term and long-term toxicities were similar to historical control patients treated with BEAM alone. With a median follow-up of 6 years (range, 3-10 years), the 5-year overall survival (OS) was 72% (95% confidence interval [CI], 55%-83%), and the 5-year progression-free survival (PFS) rate was 70% (95% CI, 53%-82%). The PFS and OS were encouraging in this group of chemotherapy-sensitive persistent, relapsed, or high-risk patients with DLBCL. A follow-up phase III trial with 131-Iodine tositumomab/BEAM vs rituximab/BEAM was planned based on this information.

Phase I trial of iodine-131 tositumomab with high-dose chemotherapy and autologous stem-cell transplantation for relapsed non-Hodgkin's lymphoma.

PURPOSE: To determine the maximum outpatient dose of iodine-131 tositumomab (up to 0.75 Gy) combined with high-dose carmustine, etoposide, cytarabine, and melphalan (BEAM) followed by autologous stem-cell transplantation (ASCT) for the treatment of chemotherapy-resistant relapsed or refractory B-cell non-Hodgkin's lymphoma (NHL). PATIENTS AND METHODS: Twenty-three patients with chemotherapy-refractory or multiply-relapsed B-cell NHL were treated in a phase I trial combining iodine-131 tositumomab (ranging from 0.30 to 0.75 Gy total-body dose [TBD]) with high-dose BEAM followed by ASCT. RESULTS: The complete response rate after transplantation was 57%, and the overall response rate was 65%. Short-term and long-term toxicities were similar to historical control patients treated with BEAM alone. With a median follow-up of 38 months (range, 27 to 60 months), the overall survival (OS) rate was 55%, and the event-free survival (EFS) rate was 39%. CONCLUSION: There were no significant added toxicities apparent with the addition of iodine-131 tositumomab up to a dose of 0.75 Gy TBD to high-dose BEAM chemotherapy followed by ASCT. The EFS and OS were encouraging in this group of chemotherapy-resistant or refractory B-cell NHL patients. A follow-up phase II trial with iodine-131 tositumomab at the dose of 0.75 Gy TBD with BEAM is currently ongoing.

Radiolabeled constructs for evaluation of the asialoglycoprotein receptor status and hepatic functional reserves.

Transplantation of isolated hepatocytes may eventually replace a whole liver transplantation for the treatment of selected liver metabolic disorders and acute hepatic failure. To understand the behavior of transplanted hepatocytes, methods for longitudinal assessment of functional activity and survival of hepatocyte transplants must be developed. Targeting of asialoglycoprotein receptor (ASGPr) with various radiolabeled or Gd-labeled constructs of asialofetuin (AF) is expected to allow noninvasive and quantitative assessments of the ASGPr status in functioning hepatocytes before and after the transplant. Six new constructs of (125)I-, (99m)Tc-, (153)Gd-, and (111)In-radiolabeled AF with distinct stabilities and clearance rates were prepared and evaluated in vitro in mice, rat, porcine, and human hepatocytes, and in vivo in mice and rats. The blood and organ clearance rates, as well as liver and spleen uptake, were measured. Even extensive chemical modifications of AF with poly-l-lysine and various chelating agents do not appear to diminish AF's binding to ASGPr. Binding to isolated hepatocytes and the in vivo liver uptake studies indicate unimpaired functional activity of AF as evidenced by the rapid (<10 min) and nearly complete hepatic extraction of AF constructs from the systemic circulation. The catabolic processing and elimination of AF constructs from liver depend on the chemical modification used in the preparation of a given reagent. Radioiodinated AF has by far the shortest postabsorption (5.1 min +/- 0.05 min) and elimination half-lives (2.8 +/- 0.06 h) in liver. In comparison, the AF construct prepared by conjugation of DTPA- and 2-iminothiolane-substituted p-Lys with N-sulfosuccinimidyl 4-(p-maleimidophenyl)butyrate (SMPB)-modified AF (AF-SMPB-Traut-p-Lys-((111)In-DTPA)(20)(-)(30)) has a hepatic postabsorption time of 9.1 +/- 0.1 min and an elimination half-life of 44.3 +/- 3.08 h, whereas [(99m)Tc]technetium-labeled AF appears to be permanently retained in liver. These differences in rates of liver uptake and clearance of catabolized radiolabeled AF can be used to determine functional activity of liver and transplanted hepatocytes.