Erik D. Brady

Targeting of HER2 antigen for the treatment of disseminated peritoneal disease.

The studies reported herein demonstrate the efficacy of α-particle–targeted radiation therapy of peritoneal disease with Herceptin as the targeting vehicle. Using the CHX-A-DTPA linker, Herceptin was radiolabeled with indium-111 and bismuth-213 with high efficiency without compromising immunoreactivity. A pilot radioimmunotherapy study treating mice bearing 5-day LS-174T (i.p.) xenografts, a low but uniform HER2 expressing, human colon carcinoma, with a single dose of 213Bi-CHX-A”-Herceptin, proved disappointing. This defined the effect of tumor burden/size on tumor response to radioimmunotherapy with α-radiation. A more successful experiment with a lower tumor burden (3 days) in mice followed. A specific dose-response (P = 0.009) was observed, and although a maximum-tolerated dose was not determined, a dose of 500 to 750 μCi was selected as the operating dose for future experiments based on changes in animal weight. Median survival was increased from 20.5 days for the mock-treated mice to 43 and 59 days with 500 and 750 μCi, respectively. The therapeutic effectiveness of 213Bi-CHX-A”-Herceptin was also evaluated in a second animal model for peritoneal disease with a human pancreatic carcinoma (Shaw). The results of this study were not as dramatic as with the former model, and higher doses were required to obtain an increase in survival of the mice (P = 0.001).

Potentiation of High-LET Radiation by Gemcitabine: Targeting HER2 with Trastuzumab to Treat Disseminated Peritoneal Disease

Purpose: Recent studies from this laboratory with 212Pb-trastuzumab have shown the feasibility of targeted therapy for the treatment of disseminated peritoneal disease using 212Pb as an in vivo generator of 212Bi. The objective of the studies presented here was improvement of the efficacy of α-particle radioimmunotherapy using a chemotherapeutic agent. Experimental Design: In a series of experiments, a treatment regimen was systematically developed in which athymic mice bearing i.p. LS-174T xenografts were injected i.p. with gemcitabine at 50 mg/kg followed by 212Pb radioimmunotherapy. Results: In a pilot study, tumor-bearing mice were treated with gemcitabine and, 24 to 30 h later, with 5 or 10 μCi 212Pb-trastuzumab. Improvement in median survival was observed at 5 μCi 212Pb-trastuzumab in the absence (31 days) or presence (51 days) of gemcitabine: 45 and 70 days with 10 μCi versus 16 days for untreated mice (P < 0.001). Multiple doses of gemcitabine combined with a single 212Pb radioimmunotherapy (10 μCi) administration was then evaluated. Mice received three doses of gemcitabine: one before 212Pb-trastuzumab and two afterwards. Median survival of mice was 63 versus 54 days for those receiving a single gemcitabine dose before radioimmunotherapy (P < 0.001), specifically attributable to 212Pb-trastuzumab (P = 0.01). Extending these findings, one versus two treatment cycles was compared. A cycle consisted of sequential treatment with gemcitabine, 10 μCi 212Pb radioimmunotherapy, then one or two additional gemcitabine doses. In the first cycle, three doses of gemcitabine resulted in a median survival of 90 versus 21 days for the untreated mice. The greatest benefit was noted after cycle 2 in the mice receiving 10 μCi 212Pb-trastuzumab and two doses of gemcitabine with a median survival of 196.5 days (P = 0.005). Pretreatment of tumor-bearing mice with two doses of gemcitabine before 212Pb radioimmunotherapy was also assessed with gemcitabine injected 72 and 24 h before 212Pb-trastuzumab. The median survival was 56 and 76 days with one and two doses of gemcitabine versus 49 days without gemcitabine. The effect may not be wholly specific to trastuzumab because 212Pb-HuIgG with two doses of gemcitabine resulted in a median survival of 66 days (34 days without gemcitabine). Conclusions: Treatment regimens combining chemotherapeutics with high-LET targeted therapy may have tremendous potential in the management and care of cancer patients.

Multimodality Therapy: Potentiation of High Linear Energy Transfer Radiation with Paclitaxel for the Treatment of Disseminated Peritoneal Disease

Purpose: Studies herein explore paclitaxel enhancement of the therapeutic efficacy of α-particle-targeted radiation therapy. Experimental Design: Athymic mice bearing 3 day i.p. LS-174T xenografts were treated with 300 or 600 μg paclitaxel at 24 h before, concurrently, or 24 h after [213Bi] or [212Pb]trastuzumab. Results: Paclitaxel (300 or 600 μg) followed 24 h later with [213Bi]trastuzumab (500 μCi) provided no therapeutic enhancement. Paclitaxel (300 μg) administered concurrently with [213Bi]trastuzumab or [213Bi]HuIgG resulted in median survival of 93 and 37 days, respectively; no difference was observed with 600 μg paclitaxel. Mice receiving just [213Bi]trastuzumab or [213Bi]HuIgG or left untreated had a median survival of 31, 21, and 15 days, respectively, 23 days for just either paclitaxel dose alone. Paclitaxel (300 or 600 μg) given 24 h after [213Bi]trastuzumab increased median survival to 100 and 135 days, respectively. The greatest improvement in median survival (198 days) was obtained with two weekly doses of paclitaxel (600 μg) followed by [213Bi]trastuzumab. Studies were also conducted investigating paclitaxel administered 24 h before, concurrently, or 24 h after [212Pb]trastuzumab (10 μCi). The 300 μg paclitaxel 24 h before radioimmunotherapy (RIT) failed to provide benefit, whereas 600 μg extended the median survival from 44 to 171 days. Conclusions: These results suggest that regimens combining chemotherapeutics and high linear energy transfer (LET) RIT may have tremendous potential in the management and treatment of cancer patients. Dose dependency and administration order appear to be critical factors requiring careful investigation.

Improved Efficacy of α-Particle–Targeted Radiation Therapy: Dual Targeting of Human Epidermal Growth Factor Receptor–2 and Tumor-Associated Glycoprotein 72*

Human epidermal growth factor receptor–2 (HER‐2) and tumor‐associated glycoprotein 72 (TAG‐72) have proven to be excellent molecular targets for cancer imaging and therapy. Trastuzumab, which binds to HER‐2, is effective in the treatment of disseminated intraperitoneal disease when labeled with 213Bi or 212Pb. 213Bi‐humanized CC49 monoclonal antibody (HuCC49ΔCH2), which binds to TAG‐72, inhibits the growth of subcutaneous xenografts. A next logical step to improve therapeutic benefit would be to target tumors with both molecules simultaneously.

Novel bimodal bifunctional ligands for radioimmunotherapy and targeted MRI.

The structurally novel bifunctional ligands C-NETA and C-NE3TA, each possessing both acyclic and macrocyclic moieties, were prepared and evaluated as potential chelates for radioimmunotherapy (RIT) and targeted magnetic resonance imaging (MRI). Heptadentate C-NE3TA was fortuitously discovered during the preparation of C-NETA. An optimized synthetic method to C-NETA and C-NE3TA including purification of the polar and tailing reaction intermediates, tert-butyl C-NETA (2) and tert-butyl C-NE3TA (3) using semiprep HPLC was developed. The new Gd(III) complexes of C-NETA and C-NE3TA were prepared as contrast enhancement agents for use in targeted MRI. The T 1 relaxivity data indicate that Gd(C-NETA) and Gd(C-NE3TA) possess higher relaxivity than Gd(C-DOTA), a bifunctional version of a commercially available MRI contrast agent; Gd(DOTA). C-NETA and C-NE3TA were radiolabeled with (177)Lu, (90)Y, (203)Pb, (205/6)Bi, and (153)Gd; and in vitro stability of the radiolabeled corresponding complexes was assessed in human serum. The in vitro studies indicate that the evaluated radiolabeled complexes were stable in serum for 11 days with the exception being the (203)Pb complexes of C-NETA and C-NE3TA, which dissociated in serum. C-NETA and C-NE3TA radiolabeled (177)Lu, (90)Y, or (153)Gd complexes were further evaluated for in vivo stability in athymic mice and possess excellent or acceptable in vivo biodistribution profile. (205/6)Bi- C-NE3TA exhibited extremely rapid blood clearance and low radioactivity level at the normal organs, while (205/6)Bi- C-NETA displayed low radioactivity level in the blood and all of the organs except for the kidney where relatively high renal uptake of radioactivity is observed. C-NETA and C-NE3TA were further modified for conjugation to the monoclonal antibody Trastuzumab.

Monoclonal Antibody Targeted Radiation Cancer Therapy

Rituximab (Rituxan), a monoclonal antibody (mAb) against CD-20, and trastuzumab (Herceptin), a mAb against HER2, have shown efficacy in clinical trials and have gained approval for therapeutic use from the Food and Drug Administration (FDA). Mylotarg, an anti-CD33 mAb conjugated with the exceedingly cytotoxic antibiotic calicheamicin, has also proven effective for treating patients with acute myeloid leukemia (AML) and it has also received FDA approval. A major area of development in mAb therapeutics involves the use of radionuclides to augment the inherent mAb activity and to exploit specific targeting properties. Zevalin, an anti-CD20 mAb armed with 90Y, and Bexxar, an anti-CD20 mAb armed with 131I, are two radionuclide-bearing mAbs that have recently been approved by the FDA. This chapter presents the background and strategies pertaining to radiolabeled monoclonal antibody therapy.