Norepinephrine-Transporter-Targeted and DNA-Co-Targeted Theranostic Guanidines

Abstract

High risk neuroblastoma often recurs, even with aggressive treatments. Clinical evidence suggests that proliferative activities are predictive of poor outcomes. This report describes syntheses, characterization, and biological properties of theranostic guanidines that target norepinephrine transporter and undergo intracellular processing, and subsequently their catabolites are efficiently incorporated into DNA of proliferating neuroblastoma cells. Radioactive guanidines are synthesized from 5-radioiodo-2′-deoxyuridine, a molecular radiotherapy platform with clinically proven minimal toxicities and DNA-targeting properties. The transport of radioactive guanidines into neuroblastoma cells is active as indicated by the competitive suppression of cellular uptake by meta-iodobenzyl­guanidine. The rate of intracellular processing and DNA uptake is influenced by the agent’s catabolic stability and cell population doubling times. The radiotoxicity is directly proportional to DNA uptake and duration of exposure. Biodistribution of 5-[125I]­iodo-3′-O-(ε-guanidinohexanoyl)-2′-deoxyuridine in a mouse neuroblastoma model shows significant tumor retention of radioactivity. Neuroblastoma xenografts regress in response to the clinically achievable doses of this agent.

Radiolabeled (R)‐(–)‐5‐iodo‐3′‐O‐[2‐(ε‐guanidinohexanoyl)‐2‐phenylacetyl]‐2′‐deoxyuridine: A new theranostic for neuroblastoma

“…In an effort to enhance the biological half‐life of IDG, a potential clinical candidate selected from a large series of 5‐[ 125 I]iodo‐5′‐ O‐ and ‐3′‐ O ‐alkanoylguanidino‐2′‐deoxyuridine derivatives, 14 we decided to increase the stability of its 3′‐ester linkage by producing sterically hindered ( R )‐(–)‐5‐[ 125 I]iodo‐3′‐ O ‐[2‐(ε‐guanidinohexanoyl)‐2‐phenylacetyl]‐2′‐deoxyuridine ( 9 , GPAID). GPAID was prepared by inserting the ( R )‐(–)‐2‐amino‐2‐phenylacetyl segment at the 3′‐ O‐ position of 5‐iodo‐2′‐deoxyuridine (IUdR).…”

“…Previously established protocols were used in these experiment 14,23,24 . Briefly, NB cells plated in TPP T25 flasks (Midwest Scientific, Valley Park, MO) at 5 × 10 5 cells per flask were maintained in culture for 48–72 h, depending on the doubling time of the cell line, until 60%–70% confluent.…”

“…The cellular uptake was calculated in terms of MBq per cell. For subcellular fractionation experiments, NB cells grown as monolayers were treated with GPAID and processed as described previously 14 . In the concentration‐dependent uptake experiments, GPAID in the appropriate medium at several concentrations was added to the cell monolayers.…”

“…Side effects include hematologic toxicities, 8 secondary malignancies, 9–11 damage to ovaries, 12 and thyroid disorders affecting >80% of the long‐term survivors treated with 131 IMIBG 13 . Recently, we reported a series of norepinephrine transporter‐targeted (NET) and DNA cotargeted theranostics developed to ameliorate these deficiencies of MIBG 14 . Employing Auger electron emitters such as 123 I, 124 I, or 125 I yields agents that are virtually harmless when located in the cytoplasm or extracellular spaces but are extraordinarily radiotoxic when either within the structure of DNA or in its immediate vicinity.…”

“…Nearly all of the electron energy associated with the 125 I decay is deposited within a sphere smaller than cell nucleus 15,16 . Our Auger electron‐emitting drugs enter NB cells by the same mechanism as MIBG and are subsequently catabolized to a product that can participate in the DNA synthesis, scheduled or unscheduled 14 . With this dual‐target approach, we expect to deliver therapeutic radiation doses to NB cells while sparing normal tissues.…”