The subject invention concerns N-thiolated .beta.-lactam compounds of formula A, ##STR00001## wherein R.sub.1 is a hydrocarbon group having 1-8 carbon atoms; R.sub.3 is an organothio group; and R.sub.4 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, heterocycloalkyl, cycloalkenyl, or heterocycloalkenyl, and analogs and pharmaceutically acceptable salts, esters and amides thereof. The subject invention also concerns methods for inducing tumor cell death or inhibiting tumor cell proliferation, and methods for inducing DNA damage, inhibiting DNA replication, activating p38 MAP kinase, or activating caspase cascade activation, or releasing cytochrome C from mitochondria into the cytoplasm in a tumor cell. Methods for treating cancer using N-thiolated .beta.-lactam compounds, as well as pharmaceutical compositions comprising the same are further disclosed.