Lack of multicellular drug resistance observed in human ovarian and prostate carcinoma treated with the proteasome inhibitor PS-341

A Frankel, S Man, P Elliott, J Adams, R S Kerbel
Clinical Cancer Research 2000, 6 (9): 3719-28
Almost all known conventional cytotoxic anticancer drugs are less effective in killing tumor cells grown as multicellular spheroids than in killing tumor cells grown as monolayer cell cultures. This "multicellular resistance" reflects the relative intrinsic drug-resistant phenotype of most solid tumors growing in vivo and is due to factors such as limited drug penetration or reduced fractions of proliferating cells. Proteasome inhibitors such as PS-341, a dipeptide boronic acid analogue, represent an interesting new class of potential anticancer drugs, which are entering early-phase clinical trials. PS-341 has been found to have good broad-spectrum cytotoxic activity in the 60-monolayer cell line National Cancer Institute screen. However, because its relative potency has not been tested in spheroid systems, we analyzed the activity of PS-341 in a spheroid/solid tumor context using four different human ovarian carcinoma cell lines and three prostate carcinoma cell lines, respectively. We found, with one exception, that PS-341 showed equal or greater activity in spheroids than in the respective monolayer cell cultures, even in a prostate cancer spheroid model with a very low growth fraction. PS-341 induced apoptotic cell death in carcinoma cells in both culture systems. We also noted a decrease in XIAP protein, a member of the inhibitor of apoptosis (IAP) family of apoptosis inhibitors, and phosphorylation of Bcl-XL in PS-341-treated ovarian carcinoma cells. Furthermore, DNA fragmentation, a hallmark of apoptosis (in this case, induced by PS-341), was completely inhibited by the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD). Taken together, the results indicate that unlike most other known anticancer cytotoxic drugs, PS-341 appears to be as effective in killing tumor cells grown in the form of multicell spheroids as in killing tumor cells grown in monolayer cell culture. Hence, this compound has the potential to circumvent multicellular drug resistance and, as such, may show promising activity against solid tumors with low growth fractions in vivo, which are frequently intrinsically resistant to conventional cytotoxic anticancer drugs.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Trending Papers

Remove bar
Read by QxMD icon Read

Save your favorite articles in one place with a free QxMD account.


Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"