The impact of S- and G2-checkpoint response on the fidelity of G1-arrest by cisplatin and its comparison to a non-cross-resistant platinum(IV) analog.

OBJECTIVE: Cisplatin is a DNA-damaging antitumor agent that is highly effective in treating ovarian cancer. It activates the p53/p21 pathway for its cytotoxic mode of action, but it does not induce p21-dependent cell cycle arrest in G1. Therefore, we investigated this paradox, and used the model analog DAP as a positive control for p21-dependent G1-arrest. METHODS: Studies were conducted in p53-proficient ovarian A2780 tumor cells to examine Cdk activity, cell cycle distribution and DNA damage signaling after cisplatin or DAP in combination with the mitotic inhibitor nocodazole. RESULTS: Cisplatin consistently induced transient S-phase arrest by inhibiting Cdk2/cyclin A complex in S-phase at 12 h and then a durable G2/M-arrest by inhibiting Cdc2/cyclin B complex at 12-18 h. These inhibitions were associated with Chk1 and Chk2 activation and resultant increase in inhibitory tyrosine phosphorylation of Cdk2 and Cdc2. Cisplatin also potently inhibited G1-phase Cdk4/cyclin D1 and Cdk2/cyclin E activities at ~18 h. In agreement, exposure of cisplatin-treated A2780, HCT-116(p53-/-) and HCT-116(p21-/-) tumor cells to nocodazole revealed limited G1-arrest that was dependent on p53 and p21. In contrast, the durable G1-arrest by DAP, which failed to activate Chk1 and Chk2, was unaffected by nocodazole. CONCLUSIONS: Cisplatin induced G1-arrest, but at an attenuated level. This was primarily due to orchestration of Cdk inhibition in S-phase first, then in G2, and finally in G1 that effectively blocked cells in G2 and prevented cells from progressing and arresting in G1. These studies demonstrate that cisplatin unequivocally activates G1-checkpoint response, but the fidelity of G1-arrest is compromised by Chk1/2 activation and checkpoint response in S- and G2/M-phase.

Phase II study of a liposome-entrapped cisplatin analog (L-NDDP) administered intrapleurally and pathologic response rates in patients with malignant pleural mesothelioma.

PURPOSE: To determine pathologic response rates to liposome-entrapped cis-bisneodecanoato-trans-R,R-1,2-diaminocyclohexane platinum(II) (L-NDDP) administered intrapleurally in patients with malignant pleural mesothelioma. PATIENTS AND METHODS: Thirty-three patients with malignant pleural mesothelioma and free-flowing pleural effusions received intrapleural L-NDDP once every 3 weeks at a dose of 450 mg/m2. Thoracoscopic evaluation with pleural biopsies was performed before therapy and then after every two cycles. The primary end point was pathologic response as determined by thoracoscopic biopsy. RESULTS: After at least two cycles, post-treatment pleural biopsy analysis was negative in 14 patients for a pathologic response rate of 42% (95% CI, 25% to 61%). Median survival was 11.2 months. There were three treatment-related deaths secondary to peritonitis, cellulitis at the thoracoscopy site, and empyema. Grade 3 nonhematologic toxicities included infection, fever, dyspnea, and anorexia, which occurred in five (15%), one (3%), one (3%), and one (3%) patients, respectively. There were no grade 4 nonhematologic toxicities. Grade 3 or 4 neutropenia, thrombocytopenia, and anemia occurred in five (15%), three (9%), and two (6%) patients, respectively. Two patients with pathologic responses subsequently underwent pleural decortication. Both surgical specimens revealed residual tumor in regions that were not in direct communication with the pleural space. CONCLUSION: Intrapleural L-NDDP therapy in this patient population is feasible with significant but manageable toxicity. Although pathologic responses are highly encouraging, areas of mesothelioma that are not in direct communication with the pleural space will evade drug exposure and limit efficacy in some patients. The optimal role of intrapleural L-NDDP therapy currently remains to be determined.

Induction of p21 by p53 following DNA damage inhibits both Cdk4 and Cdk2 activities.

DNA damage often activates the p53-p21 pathway and causes G(1)-phase arrest in mammalian cells. Although there is ample evidence that p21 induction by p53 leads to Cdk2 inhibition, it is unclear whether this checkpoint event also leads to Cdk4 inhibition. Diaminocyclohexane(trans-diacetato)(dichloro) platinum(IV) (DAP), a platinum-based coordination complex, is a DNA-damaging agent that is effective against a variety of tumor cells resistant to the parental drug cisplatin. Our previous studies established that treatment of human cancer cells with low effective concentrations of DAP specifically activates the G(1)-phase checkpoint and simultaneously inhibit Cdk4 and Cdk2 activities. Here we demonstrate that DAP treatment of human cancer cells activates the p53-p21 pathway without activating other known mechanisms that inhibit Cdk4 and Cdk2 activities. The induced p21 binds to both the Cdk4/cyclin D and Cdk2/cyclin E complexes and inhibits both of their kinase activities. Conversely, inhibition of p21 induction by cycloheximide or by p21 gene deletion prevents DAP-induced inhibition of Cdk4 and Cdk2 activities. Attenuated p53 expression and p21 induction also eliminates DAP-induced G(1)-phase arrest and inhibition of Cdk4 and Cdk2 activities. Together, these findings establish that activation of the p53-p21 pathway is responsible for the DAP-induced G(1)-phase checkpoint response and provide the first solid evidence that p21 induction by p53 during a DNA damage-induced G(1)-phase checkpoint response inhibits both Cdk4 and Cdk2 activities.

Model platinum nucleobase and nucleoside complexes and antitumor activity: X-ray crystal structure of [PtIV(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-ethylguanine)Cl]NO3.H2O.

A series of platinum(II) and (IV) monoadducts of the type [Pt(II)(DACH)LCl]NO3 and [Pt(IV)(DACH)trans-(X)2LCl]NO3 (where DACH=trans-1R,2R-diaminocyclohexane, L=adenine, guanine, hypoxanthine, cytosine, adenosine, guanosine, inosine, cytidine, 9-ethylguanine (9-EtGua), or 1-methylcytosine and X=hydroxo or acetato ligand) have been synthesized and characterized by elemental analysis and by 1H and 195Pt nuclear magnetic resonance (NMR) spectroscopy. The crystal structure of the model nucleobase complex [Pt(IV)(trans-1R,2R-diaminocyclohexane)trans-(acetate)2(9-EtGua)Cl]NO3.H2O was determined using a single crystal X-ray diffraction method. The compound crystallized in the monoclinic space group P2(1), with a=10.446(2) A, b=22.906(5) A, c=10.978(2) A, Z=4, and R=0.0718, based upon the total of 11,724 collected reflections. In this complex, platinum had a slightly distorted octahedron geometry owing to the presence of a geometrically strained five-member ring. The two adjacent corners of the platinum plane were occupied by the two amino nitrogen of DACH, whereas, the other two equatorial positions occupied by chloride ion and 9-ethylguanine. The remaining two axial positions were occupied by the oxygen atoms of acetato ligands. The DACH ring was in a chair configuration. An intricate network of intermolecular hydrogen bonds held the crystal lattice together. Some of these synthesized models of DACH-Pt-DNA adducts have good in vitro cytotoxic activity against the cisplatin-sensitive human cancer ovarian A2780 cell line (IC50=1-8 microM). Interestingly, a substituted nucleobase (9-ethylguanine) adduct was over 6-fold more potent than regular adducts. The cross-resistance factor against the 44-fold cisplatin-resistant 2780CP/clone 16 cells was about 3-9; thus, the cytotoxicity of adducts was indicative of low potency, but the resistance factors were also substantially low. These results suggest that DNA adducts of DACH-Pt are cytotoxic with low cross-resistance.

Increased sensitivity of a metastatic model of prostate cancer to a novel tetravalent platinum analog.

BACKGROUND: DACH-Ac-Pt [(1R,2R-diaminocyclohexane)-(trans-diacetato)-(dichloro)-platinum(IV)] is a novel cisplatin (CDDP) analog, and we have evaluated its potential activity in human prostate cancers. METHODS: Cytotoxic, biochemical pharmacologic, cell cycle, and Western blot evaluations were conducted with platinum agents to assess the role of p53 genotype and androgen-dependence status on cellular response. RESULTS: CDDP and DACH-Ac-Pt were equiactive against mutant p53 and androgen-independent DU-145 or PC-3 tumor cells. In wild-type p53 cells, CDDP was threefold more potent against androgen-dependent LNCaP than isogenic androgen-independent LNCaP-LN3 cells. However, the analog was equipotent in these two wild-type p53 tumor models. The greater potency of DACH-Ac-Pt than CDDP in wild-type p53 cells was not due to increased cellular drug uptake or increased adduct levels, but correlated with a lower tolerance to DNA damage. The analog also activated the p53-p21(WAF1/CIP1) signal transduction pathway more efficiently in LNCaP and LNCaP-LN3 cells, and this induced G(1)-phase cell-cycle arrest. CDDP, in contrast, activated this pathway efficiently in LNCaP cells only. In addition, and compared to CDDP, DACH-Ac-Pt was more effective in inducing Bax and increasing the Bax/Bcl-2 ratios in both the tumor models. CONCLUSIONS: DACH-Ac-Pt is highly effective against wild-type p53 LNCaP and its LN3 variant, and this activity is androgen-independent. The differential induction of p21(WAF1/CIP1) and increase in Bax/Bcl-2 ratios with CDDP and DACH-Ac-Pt in LNCaP-LN3 cells appear to be linked to the relative activity of the two agents against this model.

cis-1,4-diaminocyclohexane-Pt(II) and -(IV) adducts with DNA bases and nucleosides.

A series of new platinum(II) and platinum(IV) adducts of type [P(II)(cis-1,4-DACH)LCl]NO(3,) where cis-1,4-DACH=cis-1,4-diaminocyclohexane, and L=9-ethylguanine, 1-methylcytosine, adenine, adenosine, cytosine, cytidine, guanine, and [Pt(IV)(cis-1,4-DACH)Ltrans-(X)(2)Cl]NO(3), (where Y=hydroxo or acetato), were synthesized and characterized by elemental analysis, infrared spectroscopy, and 1H and 195Pt nuclear magnetic resonance spectroscopy.

Status of p53 phosphorylation and function in sensitive and resistant human cancer models exposed to platinum-based DNA damaging agents.

PURPOSE: Resistance to chemotherapeutic drugs is a hallmark of many human cancers, which can occur independent of p53 gene status; however, the presence of wild-type p53 in chemorefractory tumors confers greater resistance to cisplatin, but such tumors do not display complete cross-resistance to the platinum analog (1R,2R-diaminocyclohexane)(trans-diacetato)(dichloro)platinumIV (DACH-Ac-Pt). In this article we examine DNA damage-induced phosphorylation of p53 and downstream p53-dependent transactivation events in cisplatin-sensitive and cisplatin-resistant human cancer cell lines possessing wild-type p53. METHODS: Western-blot analysis was utilized to study the effect of cisplatin and the analog on p53 phosphorylation and p53-dependent target genes. RESULTS: In response to CDDP and DACH-Ac-Pt, both CDDP-sensitive and CDDP-resistant models demonstrated time- and dose-dependent inductions of total p53 protein and an increase in Ser-15 phosphorylation, which was more pronounced with CDDP. Although phosphorylation of p53 at Ser-392 was also observed in CDDP-treated sensitive and resistant cells, it was weak or absent in response to DACH-Ac-Pt. Lack of Ser-392 phosphorylation by DACH-Ac-Pt, however, did not affect the induction of p21(WAF1/CIP1) or Mdm2. Similarly, inductions of p21(WAF1/CIP1) and Mdm2 were observed in sensitive cells exposed to cisplatin. In marked contrast, cisplatin-mediated induction of p21(WAF1/CIP1) was minimal or absent in resistant cells, but that of Mdm2 was unaffected. Wortmannin, a PI3-kinase (PI3-K) inhibitor, caused a dose-dependent inhibition of total p53 accumulation, Ser-15 phosphorylation and p21(WAF1/CIP1) transactivation in response to both CDDP and DACH-Ac-Pt, indicating that members of the PI3-K family are involved in phosphorylation of p53 and that transactivation of p21(WAF1/CIP1) is p53 dependent. CONCLUSION: These studies demonstrate that cisplatin and DACH-Ac-Pt differentially phosphorylate p53 through independent DNA damage-induced pathways, and that the kinase-mediated phosphorylation of p53 at Ser-15 or Ser-392 is unaltered in resistance. Moreover, the phosphorylation status of Ser-392 on its own does not appear to correlate with p21(WAF1/CIP1) or Mdm2 induction in these studies; however, a lack of increase in p21(WAF1/CIP1) by cisplatin, but not DACH-Ac-Pt, provides a correlation with resistance and its circumvention, and implicates the role for cyclin-dependent kinase inhibitor in the differential cytotoxic effects of the two platinum agents against resistant cells.

Preparation, characterization, and antitumor activity of new cisplatin analogues with 1-methyl-4-(methylamino)piperidine: crystal structure of [PtII(1-methyl-4-(methylamino) piperidine)(oxalate)].

A series of new platinum(II) complexes of the type [Pt(II)(mmap)X] (where mmap, 1-methyl-4-(methylamino)piperidine and X, 1,1-cyclobutanedicarboxylato (CBDCA), oxalato, malonato, methylmalonato, dimethylmalonato, ethylmalonato, diethylmalonato or 2,3-naphthalene dicarboxylato (NDCA)) have been synthesized and characterized by elemental analysis, infrared (IR), and 13C and 195Pt nuclear magnetic resonance (NMR) spectroscopy. The crystal structure of the analogue [Pt(II)(mmap)(oxalate)] was determined using the single crystal X-ray diffraction method. Based upon a total of 4964 collected reflections, we determined that the compound crystallizes in the monoclinic space group P2(1)/c (with a=11.890(2) A, b=9.6695(19) A, c=9.875(2) A, beta=102.03(3) degrees, Z=4, and R=0.0428). In this complex, platinum has a slightly distorted square planar geometry with the two adjacent corners being occupied by two nitrogen atoms of the mmap ligand, whereas the remaining cis positions are occupied by two oxygen atoms of the oxalate molecule. The mmap ligand is in a boat conformation and forms six-membered chelating rings as well as the oxalate molecule forms five-membered chelating rings with platinum. The complexes were evaluated for their cytotoxic potential against the sensitive A2780 tumor model and cisplatin-resistant clone derived in vitro from potential cells.