immunoglobulins directed against cell membrane constituents. 

 The inhibitors used are generally non-specific in their 

 mode of action and without some means for increasing the 

 selectivity of uptake they are unable to inhibit a specific 

 subpopulation of cells within a larger population. Without 

 selectivity, they are of limited use for differentially 

 inhibiting the growth of transformed cells, the primary 

 goal of drug targeting research. Various low molecular 

 weight inhibitors have been coupled to protein carriers. 

 Most of these inhibitors have as the basis for their toxi- 

 city interaction with nucleic acid structure or synthetic 

 processes. 5-Flurodeoxuridine (FUDR) and albumin were 

 coupled (Barbanti-Brodano and Fiume, 1974), producing con- 

 jugates that inhibited transformed 3T3 fibroblasts in vitro 

 almost as well as free FUDR but did not inhibit non-dividing 

 macrophages. High molecular weight conjugates of methotrexate 

 and albumin were effective in prolonging the half life of 

 the drug i_n vivo but displayed no selectivity in uptake by 

 cells (Chu and Whiteley, 1977). Triaziquone conjugated to 

 y-globulin or albumin was toxic to polyoma transformed baby 

 hamster kidney (BHK) cells. Inhibition of pinocytosis did 

 not affect the toxicity of the conjugates, suggesting mem- 

 brane mediated uptake of the drug. However, normal BHK 

 cells were 3-fold more susceptible to the conjugates than 

 the transformed cell (Linford and Froese, 1978). Addition- 

 ally, no actual binding of the conjugate was detectable by 

 fluorescein labeling which would imply a distinct lack of 



