VHL and renal cell carcinoma: The three modified PEI-derived biomaterials, including PCFC-g-PEI, FA-PEAs and HPEI, had an increased transfection efficiency in vitro and obviously lower toxicities compared with their precursor PEI with 25-kD or 2-kD molecule weight, and the gene therapy effects on RCC model mice were obvious by using FA-PEAs:pVHL complexes to treat tumor.