Dc. Asman et al., GENE THERAPEUTIC APPROACH TO PRIMARY AND METASTATIC BRAIN-TUMORS .1. CD44 VARIANT PRE-RNA ALTERNATIVE SPLICING AS A CEPT CONTROL ELEMENT, Journal of neuro-oncology, 26(3), 1995, pp. 243-250
Our laboratory and others have shown alternative splicing of up to ten
exons at a discrete extracellular site to be primarily responsible fo
r the generation of CD44 variant (CD44v) isoforms. Based on clear diff
erences in the expression of these CD44v isoforms between normal and m
alignant tissues, we believe that elucidation of the mechanisms underl
ying the regulation of CD44 alternative splicing may provide a new gen
e therapeutic targeting approach based on CD44 pre-mRNA processing in
vivo. This strategy incorporates utilization of CD44 alternative splic
ing control elements into a chimeric enzyme/prodrug therapy (CEPT), a
novel modification of the virus-directed enzyme/prodrug therapy (VDEPT
) approach for the treatment of brain metastases from tumors of system
ic origin. As initial steps towards the development of a gene therapeu
tic approach based on targeting tumor cell expression of specific CD44
v alternatively spliced isoforms, we have: (1) developed a novel in vi
vo assay system that allows the rapid analyses of potentially therapeu
tic CD44 alternative splicing minigene constructs; and (2) cloned the
E. coli cytosine deaminase (CD) gene and fused its enzymatically activ
e domain to alternatively spliced CD44 exons (CD44/CD). Deamination of
cytosine by this CD44/CD chimeric fusion protein is demonstrated in E
. coil cell lysates to be equal to that of wild type cytosine deaminas
e.