Effect of reactivity on cellular accumulation and cytotoxicity of oxaliplatin analogues

Kinetically Inert Platinum (II) Complexes for Improving Anticancer Therapy: Recent Developments and Road Ahead

The search for better chemotherapeutic drugs to alleviate the deficiencies of existing platinum (Pt) drugs has picked up the pace in the millennium. There has been a disparate effort to design better and safer Pt drugs to deal with the problems of deactivation, Pt resistance and toxic side effects of clinical Pt drugs. In this review, we have discussed the potential of kinetically inert Pt complexes as an emerging class of next-generation Pt drugs. The introduction gives an overview about the development, use, mechanism of action and side effects of clinical Pt drugs as well as the various approaches to improve some of their pharmacological properties. We then describe the impact of kinetic lability on the pharmacology of functional Pt drugs including deactivation, antitumor efficacy, toxicity and resistance. Following a brief overview of numerous pharmacological advantages that a non-functional kinetically inert Pt complex can offer; we discussed structurally different classes of kinetically inert Pt (II) complexes highlighting their unique pharmacological features.

Improving In Vivo Tumor Accumulation and Efficacy of Platinum Antitumor Agents by Electronic Tuning of the Kinetic Lability

The impact of kinetic lability or reactivity on in vitro cytotoxicity, stability in plasma, in vivo tumor and tissue accumulation, and antitumor efficacy of functional platinum(II) (Pt) anticancer agents containing a O˄O β-diketonate leaving ligand remain largely unexplored. To investigate this, we synthesized Pt complexes [(NH3 )2 Pt(L1-H)]NO3 and [(DACH)Pt(L1-H)]NO3 (L1=4,4,4-trifluoro-1-ferrocenylbutane-1,3-dione, DACH=1R,2R-cyclohexane-1,2-diamine) containing an electron deficient [L1-H]- O˄O leaving ligand and [(NH3 )2 Pt(L2-H)]NO3 and [(DACH)Pt(L2-H)]NO3 (L2=1-ferrocenylbutane-1,3-dione) containing an electron-rich [L2-H]- O˄O leaving ligand. While all four complexes have comparable lipophilicity, the presence of the electron-withdrawing CF3 group was found to dramatically enhance the reactivity of these complexes toward nucleophilic biomolecules. In vitro cellular assays revealed that the more reactive complexes have higher cellular uptake and higher anticancer potency as compared to their less reactive analogs. But the scenario is opposite in vivo, where the less reactive complex showed improved tissue and tumor accumulation and better anticancer efficacy in mice bearing ovarian xenograft when compared to its more reactive analog. Finally, in addition to demonstrating the profound but contrasting impact of kinetic lability on in vitro and in vivo antitumor potencies, we also described the impact of kinetic lability on the mechanism of action of this class of promising antitumor agents.

Influence of ring modifications on nucleolar stress caused by oxaliplatin-like compounds

Oxaliplatin, a platinum compound in broad clinical use, can induce cell death through a nucleolar stress pathway rather than the canonical DNA damage response studied for other Pt(II) compounds. Previous work has found that the oxaliplatin 1,2-diaminocyclohexane (DACH) ring but not the oxalate leaving group is important to the ability to induce nucleolar stress. Here we study the influence of DACH ring substituents at the 4-position on the ability of DACH-Pt(II) compounds to cause nucleolar stress. We determine that DACH-Pt(II) compounds with 4-position methyl, ethyl, or propyl substituents induce nucleolar stress, but DACH-Pt(II) compounds with 4-isopropyl substituents do not induce nucleolar stress. This effect is independent of whether the substituent is in the axial or equatorial position relatively to the trans diamines of the ligand. These results suggest that spatially sensitive interactions could be involved in the ability of platinum compounds to cause nucleolar stress.

Upregulated OCT3 has the potential to improve the survival of colorectal cancer patients treated with (m)FOLFOX6 adjuvant chemotherapy

PURPOSE

To investigate the influence of organic cation transporter 3 (OCT3) expression on the effect of the combination regimen of 5-fluorouracil, folinic acid and oxaliplatin ((m)FOLFOX6) in colorectal cancer (CRC) patients.

METHODS

This is a retrospective study conducted at a single centre (Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, China). Patients with stage IIb-IV resectable CRC who were being postoperatively treated with (m)FOLFOX6 as a first-line adjuvant chemotherapy regimen for at least 5 cycles and had resected primary tumour samples available were eligible for the study. Patients who preoperatively received chemotherapy and/or radiotherapy or were treated with targeted drugs or other anticancer drugs were excluded from the study. Immunohistochemical staining and digital image analysis were used to assess OCT3 expression in tumour samples. According to OCT3 expression level, the receiver operating characteristic curve (ROC curve) was used to divide the patients into two groups. Cox proportional risk regression was performed with the forward LR (forward stepwise regression based on maximum likelihood estimation) method using SPSS17.0 software. The primary endpoint was the 2-year progression-free survival.

RESULTS

In total, 57 patients were included between 2014 and 2016 according to the inclusion and exclusion criteria (22 had low OCT3 expression, and 35 had high OCT3 expression). The mean age was 55.7 (30-74) years, and 37 of the total patients were male. According to TNM stage, 5 patients had stage IV disease, 44 patients had stage III disease, and 8 patients had stage II disease. Through Cox regression analysis, we found that among patients receiving the (m)FOLFOX6 regimen, those with higher OCT3 expression had a higher two-year progression-free survival rate than those with lower OCT3 expression (P = 0.038). The hazard ratio of patients with high OCT3 expression compared with patients with low OCT3 expression was 0.247. Besides, it was found that the age of patients was negatively correlated with expression level of OCT3, which can explain why patients over 70 years do not benefit from oxaliplatin-containing chemotherapy.

CONCLUSIONS

High OCT3 expression in CRC tissues may be a protective factor for CRC patients treated with (m)FOLFOX6.

Relevance of copper transporter 1 and organic cation transporters 1-3 for oxaliplatin uptake and drug resistance in colorectal cancer cells

Oxaliplatin is a routinely used drug in the treatment of colorectal cancer. However, development of resistance is a major hurdle of the chemotherapy success. Defects in cellular accumulation represent a frequently reported feature of cells with acquired resistance to platinum drugs. Nevertheless, the mechanisms of oxaliplatin uptake and their role in oxaliplatin resistance remain poorly elucidated. The aim of this study was to investigate the relevance of copper transporter 1 (CTR1) and organic cation transporters 1-3 (OCT1-3) for oxaliplatin uptake and resistance to the drug in sensitive and oxaliplatin-resistant ileocecal colorectal adenocarcinoma cells. Co-incubation with copper(ii) sulfate, a CTR1 substrate, significantly decreased oxaliplatin accumulation but not cytotoxicity in both cell lines. Pre- as well as co-incubation with the OCT1 inhibitor atropine led to a significant reduction in oxaliplatin accumulation in sensitive but not in resistant cells. However, oxaliplatin cytotoxicity was also decreased in the presence of atropine in both cell lines. Cimetidine, an inhibitor of OCT2, induced a significant reduction in the cellular accumulation and potency of oxaliplatin in sensitive and resistant cells. An inhibitor of OCT3, decynium-22, had no influence on oxaliplatin accumulation and cytotoxicity in either cell line. No differences in the transporter expressions were observed between the cell lines, drug-treated or not, either at the mRNA or protein levels. A fluorescent oxaliplatin derivative CFDA-oxPt co-localized with CTR1, OCT1 and OCT2 in sensitive cells, but only with CTR1 and OCT2 in the resistant cell line. Our results suggest that oxaliplatin is transported into the cell by CTR1 in both cell lines. However, contribution of CTR1-mediated uptake to resistance seems unlikely. Uptake of oxaliplatin via OCT1 appears to take place in the sensitive but not in the resistant cell line underscoring the transporter relevance for oxaliplatin resistance. OCT2 is likely to be involved in the uptake of oxaliplatin to a similar extent in both cell lines suggesting no major contribution of this transporter to resistance. In contrast, OCT3 appears to be irrelevant for oxaliplatin transport into the cell and resistance.

Transporter-Mediated Interaction Between Platinum Drugs and Sorafenib at the Cellular Level

Combining the multikinase inhibitor sorafenib with the platinum-based chemotherapy of solid tumors was expected to improve treatment outcome. However, in many clinical trials, no benefit from sorafenib addition to the platinum-containing regimen could be demonstrated. Moreover, in some studies, decreased survival of ovarian cancer patients as well as non-small cell lung cancer patients with squamous cell histology was observed. The aim of this study was to investigate the cellular mechanisms of the pharmacological interaction between platinum drugs and sorafenib in different cancer cell lines. The interaction was characterized by combination index analysis, platinum accumulation and DNA platination were determined using flameless atomic absorption spectrometry, and protein expression was assessed with Western blot. In the sensitive A2780 ovarian carcinoma and H520 squamous cell lung carcinoma cell lines, sorafenib induced downregulation of Na⁺,K⁺-ATPase. In A2780 cells, the kinase inhibitor also decreased the expression of copper transporter 1 (CTR1). As a result, sorafenib treatment led to a diminished cellular accumulation of cisplatin and carboplatin and to a decrease in DNA platination in these cell lines. This was not the case in the cisplatin-resistant A2780cis ovarian carcinoma and H522 lung adenocarcinoma cell lines featuring lower basal expression of the above-mentioned transporters. In all cell lines studied, an antagonistic interaction between platinum drugs and sorafenib was found. Our results suggest that sorafenib impairs cisplatin and carboplatin uptake through downregulation of CTR1 and/or Na⁺,K⁺-ATPase resulting in reduction of DNA platination. This effect is not observed in cancer cells with defects in platinum accumulation.

A Lipophilic Pt(IV) Oxaliplatin Derivative Enhances Antitumor Activity

Side effects and acquired resistance by cancer cells limit the use of platinum anticancer drugs. Modification of oxaliplatin (OXA) into a lipophilic Pt(IV) complex [Pt(DACH)(OAc)(OPal)(ox)] (1), containing both lipophilic and hydrophilic axial ligands, was applied to improve performance and facilitate incorporation into polymeric nanoparticles. Complex 1 exhibited unique potency against a panel of cancer cells, including cisplatin-resistant tumor cells. [Pt(DACH)(OAc)(OPal)(ox)] incorporated nanoparticles (2) presented a mean diameter of 146 nm with encapsulation yields above 95% as determined by HPLC. Complexes 1 and 2 showed enhanced in vitro cellular Pt accumulation, DNA platination, and antiproliferative effect compared to OXA. Results of an orthotopic intraperitoneal model of metastatic ovarian cancer (SKOV-3) and a xenograft subcutaneous model of colon (HCT-116) tumor in SCID-bg mice showed that the activity of 1 and 2 significantly decreased tumor growth rates compared to control and OXA treatment groups. Consequently, these findings warrant further development toward clinical translation.

A Potent Glucose-Platinum Conjugate Exploits Glucose Transporters and Preferentially Accumulates in Cancer Cells

Three rationally designed glucose-platinum conjugates (Glc-Pts) were synthesized and their biological activities evaluated. The Glc-Pts, 1-3, exhibit high levels of cytotoxicity toward a panel of cancer cells. The subcellular target and cellular uptake mechanism of the Glc-Pts were elucidated. For uptake into cells, Glc-Pt 1 exploits both glucose and organic cation transporters, both widely overexpressed in cancer. Compound 1 preferentially accumulates in and annihilates cancer, compared to normal epithelial, cells in vitro.