Novel prodrugs which are activated to cytotoxic alkylating agents by carboxypeptidase G2

Abstract

The synthesis of three novel prodrugs, 4-[bis[2-(mesyloxy)ethyl]amino]benzoyl-L-glutamic acid (7), 4-[(2-chloroethyl)[2-(mesyloxy)ethyl]amino]benzoyl-L-glutamic acid (8), and 4-[bis(2-chloroethyl)amino]benzoyl-L-glutamic acid (9), for use as anticancer agents, is described here. Each is a bifunctional alkylating agent in which the activating effect of the ionized carboxyl function is masked through an amide bond to the glutamic acid residue. These relatively inactive prodrugs are designed to be activated to their corresponding nitrogen alkylating agents (10, 11, and 12, respectively) at a tumor site by prior administration of a monoclonal antibody conjugated to the bacterial enzyme carboxypeptidase G2 (CPG2). The viability of two different tumor cell lines was monitored with each prodrug in the presence of CPG2. All three compounds showed substantial prodrug activity--with conversion to the corresponding active drug leading to greatly increased cytotoxicity.

Disposition of the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid and its active parent drug in mice

“…It was shown previously that the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid had very little cytotoxicity against the human JAR choriocarcinoma and LS174T colonic cell lines in culture (Springer et al, 1990). On the other hand the activated prodrug was over 100 times more cytotoxic to JAR cells.…”

“…It is a mustard glutamate prodrug (Figure 1) which has been designed and shown to be activated by CPG2 to form the active drug benzoic acid mustard (Bagshawe et al, 1988;Springer et al, 1990).…”

Novel Gene Therapeutic Approaches to Brain Cancer

“…When combined with the prodrug 4-benzoyl-Lglutamic acid (CMDA), a DNA-crosslinking mustard drug is released (165). Unlike HSV1-TK and CD, catalysis of the prodrug with CPG2 does not require further enzymatic processing to become the final toxic compound.…”

Professor Tom Connors and the development of novel cancer therapies by the Phase I/II Clinical Trials Committee of Cancer Research UK

“…The ADEPT approach was initiated using alkylating agentderived prodrugs (Bagshawe et al, 1988Mann et al, 1990;Springer et al, 1990) and carboxypeptidase G2 (CPG2) as the activating enzyme (Melton et al, 1990). The rationale for the use of alkylating agents as drugs in this approach was that:…”

“…An advantage of this system was that the prodrug uptake into cells (ie penetration across cell membranes) could be minimised due to the two acidic functional groups of the glutamate in contrast to that of the active drug, which is more lipophilic. This was the rationale for the synthesis of a series of L-glutamyl amides of nitrogen mustards derived from 4-aminobenzoic acid, notably the CMDA prodrug (XIII) (Mann et al, 1990;Springer et al, 1990), and after cleavage of the amide bond by CPG2 the resulting drugs become more reactive. Further studies of this ADEPT system demonstrated its ability to achieve both the ablation of chemo-resistant CC3 choriocarcinoma human tumour xenografts in nude mice and growth delays of OvCa-433 ovarian human tumour xenografts .…”