Tumor invasion, metastasis, and resistance to chemotherapeutic drugs o
r radiation are major obstacles for the successful treatment of cancer
. To overcome some of these limitations, therapeutic strategies that i
ncrease the specificity and efficacy and reduce the toxicity of the an
ti-cancer drugs or toxins are being explored. Cancer cells overexpress
specific protein antigens and carbohydrate structures that may functi
on as cell surface receptors. These cancer cell specific markers can b
e exploited while designing new cancer therapies. Monoclonal antibodie
s that have been humanized to reduce immunogenicity and targeted to sp
ecific antigens on cancer cells, enzyme-monoclonal antibody/prodrug co
njugates that will selectively kill the cells following drug activatio
n, and recombinant toxins are some of the novel classes of agents in d
evelopment. Another novel approach being investigated to treat cancers
is the use of inactive pore-forming toxins with built-in biological '
'triggers'' that will activate the toxin, following a biological stimu
lus. These pore-forming cytolytic toxins can be rendered active by tum
or-specific proteases, that are often overexpressed in cancer cells, t
hereby targeting the toxic effects. Such pore-forming or membrane-acti
ng toxins may serve as novel cytolytic agents against solid tumors, wh
ich, to date, have proved to be more resistant to conventional toxins.
(C) 1998 Elsevier Science Inc.