polyamines having the formula : or a salt thereof with a pharmaceutically acceptable acid wherein : r 1 - r 6 may be the same or different and are alkyl , aryl , aryl alkyl , cycloalkyl , optionally having an alkyl chain interrupted by at least one etheric oxygen atom , or hydrogen ; n 1 , n 2 , n 3 and n 4 are nitrogen atoms capable of protonation at physiological ph &# 39 ; s ; a and b may be the same or different and are integers from 1 to 4 ; a , b and c may be the same or different and are bridging groups which effectively maintain the distance between the nitrogen atoms such that the polyamines : are capable of uptake by a target cell upon administration thereof to a human or non - human animal ; and upon uptake by the target cell , competitively bind via an electrostatic interaction between the positively charged nitrogen atoms to substantially the same biological counter - anions as the intracellular natural polyamines in the target cell ; the polyamines , upon binding to the biological counter - anion in the cell , function in a manner biologically different than the intracellular polyamines , the polyamines not occurring in nature ; as well as pharmaceutical compositions embodying the polyamines and methods of treating patients requiring anti - neoplastic therapy .