A texaphyrin-oxaliplatin conjugate that overcomes both pharmacologic and molecular mechanisms of cisplatin resistance in cancer cells

Abstract

A texaphyrin-oxaliplatin conjugate, oxaliTEX, was designed to test the concept that a platinum analog can overcome defects in drug accumulation and p53-dependent DNA damage response in a tumor model expressing multifactorial mechanisms of cisplatin resistance. Cytotoxic studies resulted in a resistance factor of only 1.2, which essentially indicated complete reversal of resistance in 2780CP cells expressing a factor of 22 with cisplatin. Unlike cisplatin, oxaliTEX accumulated and formed DNA adducts, stabilized and activated p53 at similar levels in both sensitive and resistant cells, and induced apoptosis in both models. The ability and importance of a designer drug, such as oxaliTEX, to overcome cisplatin resistance by targeting two dominant resistance mechanisms is discussed.

Fig. 1

Various Pt(II) complexes, motexafin gadolinium (1, MGd), and texaphyrin–platinum conjugates 2 (cisTex), and 3 (oxaliTEX).

Fig. 2

Cytotoxicity profiles of (A) cisTEX (2) and (B) oxaliTEX (3) with cisplatin sensitive A2780 and cisplatin resistant 2780CP. The complex was made up as a stock solution (for which the Pt concentration was confirmed by FAAS) and serially diluted before adding to cells, which were then incubated for 5 days at 37 °C in 5% CO₂. Error bars represent the standard deviation.

Fig. 3

Platination of FBS proteins with various platinum agents. Half-lives were determined by fitting the data to an exponential decay curve between 0 and 13 h during which time the logarithmic decay phase was linear.

Fig. 4

Cellular uptake of platinum drugs. Levels of intracellular platinum in A2780 and 2780CP were determined by FAAS after a 4-hour incubation with 200 μM of the respective complex (concentrations confirmed by FAAS). p < 0.05 by Student’s t-test for platinum uptake of cisplatin and oxaliplatin in 2780CP vs. A2780.

Fig. 5

Cellular platination of DNA by oxaliTEX (3), cisplatin, and oxaliplatin. DNA adducts were determined by FAAS after a 4-hour incubation with 200 μM of the respective complex (concentrations confirmed by FAAS). p < 0.05 by Student’s t-test for Pt–DNA lesions by oxaliTEX, cisplatin, and oxaliplatin in 2780CP vs. A2780.

Fig. 6

DNA Damage tolerance of oxaliTEX, oxaliplatin, and cisplatin. These calculated values were determined from the ratio of DNA–Pt adducts/([complex] × IC₅₀), with the primary data obtained from three separate experiments.

Fig. 7

Percent positive Annexin V-FITC signal of (A) A2780 and (B) 2780CP cells after exposure to oxaliTEX (3), oxaliplatin, and MGd (1).

Fig. 8

Induction of total and Ser-15 phosphorylated p53 protein following incubation of (A) A2780 and (B) 2780CP human ovarian cancer cells with conjugate 3 and oxaliplatin. Quantification of fold increase in total p53 protein in (C) A2780 and (D) 2780CP.

Fig. 9

Transactivation of p21 protein resulting from incubation of (A) A2780 and (B) 2780CP human ovarian cancer cells with oxaliplatin and oxaliTEX. Fold p21 protein increase in (C) A2780 and (D) 2780CP.