Combretastatin A-4 Analogue: A Dual-Targeting and Tubulin Inhibitor Containing Antitumor Pt(IV) Moiety with a Unique Mode of Action

Alkaloids from Corydalis saxicola and their antiproliferative activity against cancer cells

Eight undescribed alkaloids named corydalisine D-K (1-7), including one isoquinoline benzopyranone alkaloid (1), one benzocyclopentanone alkaloid (2), four benzofuranone alkaloids (3, 4, and 5a/5b) and two protoberberine alkaloids (6 and 7), along with fourteen known ones, were isolated from the Corydalis saxicola. Their structures, including absolute configurations, were unambiguously identified using spectroscopic techniques, single-crystal X-ray diffraction and electron circular dichroism calculation. Compounds 2, 14 and 21 exhibit antiproliferative activity against five cancer cell lines. The aporphine alkaloid demethylsonodione (compound 14), which exhibited the best activity (IC50 = 3.68 ± 0.25 μM), was subjected to further investigation to determine its mechanism of action against the T24 cell line. The molecular mechanism was related to the arrest of cell cycle S-phase, inhibition of CDK2 expression, accumulation of reactive oxygen species (ROS), induction of cell apoptosis, inhibition of cell migration, and activation of p38 MAPK signaling pathway. The results indicated that 14 could be used as a potential candidate agent for further development of anti-bladder transitional cell carcinoma.

Discovery of the cereblon-recruiting tubulin PROTACs effective in overcoming Taxol resistance in vitro and in vivo

Overexpression of β3-tubulin is a common occurrence in human tumors and is associated with resistance to microtubule-targeting agents. PROTAC strategy has demonstrated significant potential in overcoming drug resistance. Herein, we report the discovery of W13 as the first PROTAC against tubulin, which was created by connecting a CRBN ligand to the widely recognized microtubule-destabilizing agent CA-4. Notably, it retains the inhibitory activity of the parental CA-4 and further exhibits substantial degradation of α/β/β3-tubulin in both A549 and A549/Taxol cell lines. The degradation of tubulin was subsequently verified to be mediated by the ubiquitin-proteasome system. Importantly, tumor xenograft research clearly showed W13's promising antitumor activity against human lung cancer. Taken together, the discovery of W13 demonstrated the practicality and feasibility of PROTAC targeting tubulin, hence establishing a potential therapeutic approach for treating NSCLC caused by the overexpression of β3-tubulin.

Novel Indole-Chalcone Derivative-Ligated Platinum(IV) Prodrugs Attenuate Cisplatin Resistance in Lung Cancer through ROS/ER Stress and Mitochondrial Dysfunction

Developing multifunctional platinum(IV) prodrugs via integrating bioactive pharmacophores into one entity is an attractive strategy to ameliorate the defects of platinum(II) drugs. Herein, a series of indole-chalcone derivative-ligated platinum(IV) complexes were synthesized and evaluated for their anticancer activities. Among them, optimal complex 17a exerted superior activity compared to that of cisplatin (CDDP) against the tested cells but showed lower cytotoxicity toward human normal lung cells. Detailed mechanisms demonstrated that 17a significantly enhanced intracellular accumulation, induced DNA damage, and inhibited migration in A549/CDDP cells. Furthermore, 17a efficiently disturbed the tubulin-microtubule system, initiated reactive oxygen species (ROS)-mediated endoplasmic reticulum stress, and activated a mitochondrion-dependent apoptosis signaling pathway. Besides, 17a was superior to free drugs or their combination in inhibiting cancer growth in A549/CDDP xenografts without inducing obvious side effects. The physical mixture of 16a and CDDP was almost identical to 17a but showed apparent systematic side effects. In summary, our studies may provide an efficient treatment regimen for CDDP resistance.

Recent advances in combretastatin A-4 codrugs for cancer therapy

CA4 is a potent microtubule polymerization inhibitor and vascular disrupting agent. However, the in vivo efficiency of CA4 is limited owing to its poor pharmacokinetics resulting from its high lipophilicity and low water solubility. To improve the water solubility, CA4 phosphate (CA4P) has been developed and shows potent antivascular and antitumor effects. CA4P had been evaluated as a vascular disrupting agent in previousc linical trials. However, it had been discontinued due to the lack of a meaningful improvement in progression-free survival and unfavorable partial response data. Codrug is a drug design approach to chemically bind two or more drugs to improve therapeutic efficiency or decrease adverse effects. This review describes the progress made over the last twenty years in developing CA4-based codrugs to improve the therapeutic profile and achieve targeted delivery to cancer tissues. It also discusses the existing problems and the developmental prospects of CA4 codrugs.

Cisplatin-cyclooxygenase inhibitor conjugates, free and immobilised in mesoporous silica SBA-15, prove highly potent against triple-negative MDA-MB-468 breast cancer cell line

For the development of anticancer drugs with higher activity and reduced toxicity, two approaches were combined: preparation of platinum(IV) complexes exhibiting higher stability compared to their platinum(II) counterparts and loading them into mesoporous silica SBA-15 with the aim to utilise the passive enhanced permeability and retention (EPR) effect of nanoparticles for accumulation in tumour tissues. Three conjugates based on a cisplatin scaffold bearing the anti-inflammatory drugs naproxen, ibuprofen or flurbiprofen in the axial positions (1, 2 and 3, respectively) were synthesised and loaded into SBA-15 to afford the mesoporous silica nanoparticles (MSNs) SBA-15|1, SBA-15|2 and SBA-15|3. Superior antiproliferative activity of both free and immobilised conjugates in a panel of four breast cancer cell lines (MDA-MB-468, HCC1937, MCF-7 and BT-474) with markedly increased cytotoxicity with respect to cisplatin was demonstrated. All compounds exhibit highest activity against the triple-negative cell line MDA-MB-468, with conjugate 1 being the most potent. However, against MCF-7 and BT-474 cell lines, the most notable improvement was found, with IC₅₀ values up to 240-fold lower than cisplatin. Flow cytometry assays clearly show that all compounds induce apoptotic cell death elevating the levels of both early and late apoptotic cells. Furthermore, autophagy as well as formation of reactive oxygen species (ROS) and nitric oxide (NO) were elevated to a similar or greater extent than with cisplatin.

Recent Progresses in Conjugation with Bioactive Ligands to Improve the Anticancer Activity of Platinum Compounds

Platinum (Pt) drugs, including cisplatin, are widely used for the treatment of solid tumors. Despite the clinical success, side effects and occurrence of resistance represent major limitations to the use of clinically available Pt drugs. To overcome these problems, a variety of derivatives have been designed and synthetized. Here, we summarize the recent progress in the development of Pt(II) and Pt(IV) complexes with bioactive ligands. The development of Pt(II) and Pt(IV) complexes with targeting molecules, clinically available agents, and other bioactive molecules is an active field of research. Even if none of the reported Pt derivatives has been yet approved for clinical use, many of these compounds exhibit promising anticancer activities with an improved pharmacological profile. Thus, planning hybrid compounds can be considered as a promising approach to improve the available Pt-based anticancer agents and to obtain new molecular tools to deepen the knowledge of cancer progression and drug resistance mechanisms.

Are Pt(IV) Prodrugs That Release Combretastatin A4 True Multi-action Prodrugs?

"Multi-action" Pt(IV) derivatives of cisplatin with combretastatin A4 (CA4) bioactive ligands that are conjugated to Pt(IV) by carbonate are unique because the ligand (IC₅₀ < 10 nM) is dramatically 1000-folds more cytotoxic than cisplatin in vitro. The Pt(IV)-CA4 prodrugs were as cytotoxic as CA4 itself, indicating that the platinum moiety probably plays an insignificant role in triggering cytotoxicity, suggesting that the Pt(IV)-CA4 complexes act as prodrugs for CA4 rather than as true multi-action prodrugs. In vivo tests (Lewis lung carcinoma) show that ctc-[Pt(NH₃)₂(PhB)(CA4)Cl₂] inhibited tumor growth by 93% compared to CA4 (67%), cisplatin (84%), and 1:1:1 cisplatin/CA4/PhB (85%) while displaying <5% body weight loss compared to cisplatin (20%) or CA4 (10%). In this case, and perhaps with other extremely potent bioactive ligands, platinum(IV) acts merely as a self-immolative carrier triggered by reduction in the cancer cell with only a minor contribution to cytotoxicity.

Recent Progress on Tubulin Inhibitors with Dual Targeting Capabilities for Cancer Therapy

Microtubules play a crucial role in multiple cellular functions including mitosis, cell signaling, and organelle trafficking, which makes the microtubule an important target for cancer therapy. Despite the great successes of microtubule-targeting agents in the clinic, the development of drug resistance and dose-limiting toxicity restrict their clinical efficacy. In recent years, multitarget therapy has been considered an effective strategy to achieve higher therapeutic efficacy, in particular dual-target drugs. In terms of the synergetic effect of tubulin and other antitumor agents such as receptor tyrosine kinases inhibitors, histone deacetylases inhibitors, DNA-damaging agents, and topoisomerase inhibitors in combination therapy, designing dual-target tubulin inhibitors is regarded as a promising approach to overcome these limitations and improve therapeutic efficacy. In this Perspective, we discussed rational target combinations, design strategies, structure-activity relationships, and future directions of dual-target tubulin inhibitors.

Hybrid Drugs-A Strategy for Overcoming Anticancer Drug Resistance?

Despite enormous progress in the treatment of many malignancies, the development of cancer resistance is still an important reason for cancer chemotherapy failure. Increasing knowledge of cancers' molecular complexity and mechanisms of their resistance to anticancer drugs, as well as extensive clinical experience, indicate that an effective fight against cancer requires a multidimensional approach. Multi-target chemotherapy may be achieved using drugs combination, co-delivery of medicines, or designing hybrid drugs. Hybrid drugs simultaneously targeting many points of signaling networks and various structures within a cancer cell have been extensively explored in recent years. The single hybrid agent can modulate multiple targets involved in cancer cell proliferation, possesses a simpler pharmacokinetic profile to reduce the possibility of drug interactions occurrence, and facilitates the process of drug development. Moreover, a single medication is expected to enhance patient compliance due to a less complicated treatment regimen, as well as a diminished number of adverse reactions and toxicity in comparison to a combination of drugs. As a consequence, many efforts have been made to design hybrid molecules of different chemical structures and functions as a means to circumvent drug resistance. The enormous number of studies in this field encouraged us to review the available literature and present selected research results highlighting the possible role of hybrid drugs in overcoming cancer drug resistance.

Novel CK2-Specific Pt(II) Compound Reverses Cisplatin-Induced Resistance by Inhibiting Cancer Cell Stemness and Suppressing DNA Damage Repair in Non-small Cell Lung Cancer Treatments

Cancer stem cells (CSCs) have a pivotal impact in drug resistance, tumor metastasis, and progression of various cancer entities, including in non-small cell lung cancer (NSCLC). A CK2 inhibitor HY1 was found to show potent CSC inhibitory effects in A549 cells. By taking advantage of inherent CK2 specificity and CSC inhibition of HY1, a Pt(II) agent (HY1-Pt) was developed by conjugation of HY1 with an active Pt(II) unit to reverse cisplatin-induced resistance in A549/cDDP cell treatment. In vitro biological studies indicated that HY1-Pt can target CK2, suppress DNA damage repair, reinforce cellular accumulation of platinum, and reverse resistance apart from effectively inhibiting CSCs through Wnt/β-catenin signal pathway in A549/cDDP cells. Significantly, HY1-Pt presented an acceptable pharmacokinetic behavior and exhibited higher tumor growth inhibitory efficacy than cisplatin either in A549 or A549/cDDP xenograft models with low toxicity. Overall, HY1-Pt is a promising drug candidate for NSCLC treatment.

Pt(IV) Prodrugs with NSAIDs as Axial Ligands

A chemo-anti-inflammatory strategy is of interest for the treatment of aggressive cancers. The platinum (IV) prodrug with non-steroidal anti-inflammatory drugs (NSAIDs) as axial ligands is designed to efficiently enter tumor cells due to high lipophilicity and release the cytotoxic metabolite and NSAID intracellularly, thereby reducing side effects and increasing the therapeutic efficacy of platinum chemotherapy. Over the last 7 years, a number of publications have been devoted to the design of such Pt(IV) prodrugs in combination with anti-inflammatory chemotherapy, with high therapeutic efficacy in vitro and In vivo. In this review, we summarize the studies devoted to the development of Pt(IV) prodrugs with NSAIDs as axial ligands, the study of the mechanism of their cytotoxic action and anti-inflammatory activity, the structure-activity ratio, and therapeutic efficacy.

Disruption of the Microtubule Network and Inhibition of VEGFR2 Phosphorylation by Cytotoxic N,O-Coordinated Pt(II) and Ru(II) Complexes of Trimethoxy Aniline-Based Schiff Bases

Platinum-based complexes are one of the most successful chemotherapeutic agents having a significant ground in cancer chemotherapy despite their side effects. During the past few decades, Ru(II) complexes have been emerging as efficient alternatives owing to their promising activities against platinum-resistant cancer. The pathway of action, lipophilicity, and cytotoxicity of a Pt or Ru complex may be tuned by varying the attached ligands, the coordination mode, and the leaving group. In this work, we report a family of Pt(II) and Ru(II) complexes (1-5) of three N,O and N,N donor-based trimethoxyanilines containing Schiff bases with the general formula [Pt^II(L)(DMSO)Cl], [Ru^II(L)(p-cymene)Cl], [Ru^II(L)(p-cymene)Cl]⁺, and [Pt^II(L)Cl₂]. All of the complexes are characterized by different analytical techniques. ¹H NMR and electrospray ionization mass spectrometry (ESI-MS) data suggest that the N,O-coordinated Pt(II) complexes undergo slower aquation compared to the Ru(II) analogues. The change of the coordination mode to N,N causes the Ru complexes to be more inert to aquation. The N,O-coordinating complexes show superiority over N,N-coordinating complexes by displaying excellent in vitro antiproliferative activity against different aggressive cancer cells, viz., triple-negative human metastatic breast adenocarcinoma MDA-MB-231, human pancreatic carcinoma MIA PaCa-2, and hepatocellular carcinoma Hep G2. In vitro cytotoxicity studies suggest that Pt(II) complexes are more effective than their corresponding Ru(II) analogues, and the most cytotoxic complex 3 is 10-15 times more toxic than the clinical drugs cisplatin and oxaliplatin against MDA-MB-231 cells. Cellular studies show that all of the N,O-coordinated complexes (1-3) initiate disruption of the microtubule network in MDA-MB-231 cells in a dose-dependent manner within 6 h of incubation and finally lead to the arrest of the cell cycle in the G2/M phase and render apoptotic cell death. The disruption of the microtubule network affects the agility of the cytoskeleton rendering inhibition of tyrosine phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2), a key step in angiogenesis. Complexes 1 and 2 inhibit VEGFR2 phosphorylation in a dose-dependent fashion. Among the Pt(II) and Ru(II) complexes, the former displays higher cytotoxicity, a stronger effect on the cytoskeleton, better VEGFR2 inhibition, and strong interaction with the model nucleobase 9-ethylguanine (9-EtG).

Novel diaryl-2H-azirines: Antitumor hybrids for dual-targeting tubulin and DNA

Multiple-target drugs may achieve better therapeutic effect via different pathways than single-target ones, especially for complex diseases. Tubulin and DNA are well-characterized molecular targets for anti-cancer drug development. A novel class of diaryl substituted 2H-azirines were designed based on combination of pharmacophores from Combretastatin A-4 (CA-4) and aziridine-type alkylating agents, which are known tubulin polymerization inhibitor and DNA damaging agents, respectively. The antitumor activities of these compounds were evaluated in vitro and 6h showed the most potent activities against four cancer cell lines with IC₅₀ values ranging from 0.16 to 1.40 μM. Further mechanistic studies revealed that 6h worked as a bifunctional agent targeting both tubulin and DNA. In the nude mice xenograft model, 6h significantly inhibited the tumor growth with low toxicity, demonstrating the promising potential for further developing novel cancer therapy with a unique mechanism.

Tubulin Inhibitors Binding to Colchicine-Site: A Review from 2015 to 2019

Due to the three domains of the colchicine-site which is conducive to the combination with small molecule compounds, colchicine-site on the tubulin has become a common target for antitumor drug development, and accordingly, a large number of tubulin inhibitors binding to the colchicine-site have been reported and evaluated over the past years. In this study, tubulin inhibitors targeting the colchicine-site and their application as antitumor agents were reviewed based on the literature from 2015 to 2019. Tubulin inhibitors were classified into ten categories according to the structural features, including colchicine derivatives, CA-4 analogs, chalcone analogs, coumarin analogs, indole hybrids, quinoline and quinazoline analogs, lignan and podophyllotoxin derivatives, phenothiazine analogs, N-heterocycle hybrids and others. Most of them displayed potent antitumor activity, including antiproliferative effects against Multi-Drug-Resistant (MDR) cell lines and antivascular properties, both in vitro and in vivo. In this review, the design, synthesis and the analysis of the structure-activity relationship of tubulin inhibitors targeting the colchicine-site were described in detail. In addition, multi-target inhibitors, anti-MDR compounds, and inhibitors bearing antitumor activity in vivo are further listed in tables to present a clear picture of potent tubulin inhibitors, which could be beneficial for medicinal chemistry researchers.

On the hydrolytic stability of unsymmetric platinum(iv) anticancer prodrugs containing axial halogens

The hydrolytic stability of Pt(iv) complexes is determined by all the six ligands that coordinate to the Pt(iv) center. By appropriately choosing all the ligands during the design of Pt(iv) prodrugs, the stability of Pt(iv) prodrugs can be improved.

Platinum(IV)-Estramustine Multiaction Prodrugs Are Effective Antiproliferative Agents against Prostate Cancer Cells

Herein, we describe the synthesis, characterization, and biological properties of Pt(IV) derivatives of cisplatin with estramustine at the first axial position, which is known to disrupt the microtubule assembly and act as an androgen antagonist, and varying the second axial position using an innocent ligand (acetate or hydroxyl) to prepare dual-action and triple-action prodrugs with known inhibitors of histone deacetylase, cyclooxygenase, and pyruvate dehydrogenase kinase. We demonstrate superior antiproliferative activity at submicromolar concentrations of the prodrugs against a panel of cancer cell lines, particularly against prostate cancer cell lines. The results obtained in this study exemplify the complex mode of action of "multiaction" Pt(IV) prodrugs. Interestingly, changing the second axial ligand in the Pt-estramustine complex has a significant effect on the mode of action, suggesting that all three components of the Pt(IV) prodrugs (platinum moiety and axial ligands) contribute to the killing of cells and not just one dominant component.

More Than Resveratrol: New Insights into Stilbene-Based Compounds

The concept of a scaffold concerns many aspects at different steps on the drug development path. In medicinal chemistry, the choice of relevant "drug-likeness" scaffold is a starting point for the design of the structure dedicated to specific molecular targets. For many years, the chemical uniqueness of the stilbene structure has inspired scientists from different fields such as chemistry, biology, pharmacy, and medicine. In this review, we present the outstanding potential of the stilbene-based derivatives. Naturally occurring stilbenes, together with powerful synthetic chemistry possibilities, may offer an excellent approach for discovering new structures and identifying their therapeutic targets. With the development of scientific tools, sophisticated equipment, and a better understanding of the disease pathogenesis at the molecular level, the stilbene scaffold has moved innovation in science. This paper mainly focuses on the stilbene-based compounds beyond resveratrol, which are particularly attractive due to their biological activity. Given the "fresh outlook" about different stilbene-based compounds starting from stilbenoids with particular regard to isorhapontigenin and methoxy- and hydroxyl- analogues, the update about the combretastatins, and the very often overlooked and underestimated benzanilide analogues, we present a new story about this remarkable structure.

More Than Resveratrol: New Insights into Stilbene-Based Compounds

The concept of a scaffold concerns many aspects at different steps on the drug development path. In medicinal chemistry, the choice of relevant "drug-likeness" scaffold is a starting point for the design of the structure dedicated to specific molecular targets. For many years, the chemical uniqueness of the stilbene structure has inspired scientists from different fields such as chemistry, biology, pharmacy, and medicine. In this review, we present the outstanding potential of the stilbene-based derivatives. Naturally occurring stilbenes, together with powerful synthetic chemistry possibilities, may offer an excellent approach for discovering new structures and identifying their therapeutic targets. With the development of scientific tools, sophisticated equipment, and a better understanding of the disease pathogenesis at the molecular level, the stilbene scaffold has moved innovation in science. This paper mainly focuses on the stilbene-based compounds beyond resveratrol, which are particularly attractive due to their biological activity. Given the "fresh outlook" about different stilbene-based compounds starting from stilbenoids with particular regard to isorhapontigenin and methoxy- and hydroxyl- analogues, the update about the combretastatins, and the very often overlooked and underestimated benzanilide analogues, we present a new story about this remarkable structure.

Hybrid micelles based on Pt (IV) polymeric prodrug and TPGS for the enhanced cytotoxicity in drug-resistant lung cancer cells

Multidrug resistance (MDR) is a primary cause of failure in oncotherapy and interest is growing in the design of multi-stimuli responsive nano-carriers to synergistically deliver chemotherapeutic agents and P-gp inhibitors to reverse MDR. The hybrid micelles based on a Platinum (IV)-coordinate polymeric prodrugs and TPGS were developed to improve chemotherapy and reduce side effects. The pH/redox dual-sensitive polymers were synthesized by condensation polymerization using ortho ester monomer and diamminedichlorodisuccinatoplatinum (DSP). The hybrid micelles possessed uniform size (38 nm) and displayed good stability in various physiological conditions. In contrast, in vitro drug release profiles indicated that these micelles could be completely depolymerized under acidic and reducing environment, thereby more than 80 % cisplatin were released within 12 h at pH 5.0 plus 10 mM DTT. More importantly, a large amount of TPGS released simultaneously could effectively inhibit the function of drug efflux pumps, which significantly enhanced the cytotoxicity of cisplatin against A549/DDP cells. The growth inhibition rate of micelles on A549/DDP multicellular spheroids was 79.5 %, while that of free cisplatin was only 6.8 %. Therefore, these hybrid micelles are promising in overcoming tumor MDR and worth doing further research in vivo and extend to other therapeutic agents.

Recent advances in platinum-based chemotherapeutics that exhibit inhibitory and targeted mechanisms of action

Current platinum-based drugs used in chemotherapy, like cisplatin and its derivatives, are greatly limited due to side-effects and drug resistance. This has inspired the search for novel platinum-based drugs that deviate from the conventional mechanism of action seen with current chemotherapeutics. This review highlights recent advances in platinum(II) and platinum(IV)-based complexes that have been developed within the past six years. The platinum compounds explored within this review are those that display a more targeted approach by incorporating ligands that act on selected cellular targets within cancer cells. This includes mitochondria, overexpressed receptors or proteins and enzymes that contribute to cancer cell proliferation. These types of platinum compounds have shown significant improvements in anticancer activity and as such, this review highlights the importance of pursuing these new designed platinum drugs for cancer therapy, with the potential of undergoing clinical trials.

Targeting drug delivery system for platinum(Ⅳ)-Based antitumor complexes

Classical platinum(II) anticancer agents are widely-used chemotherapeutic drugs in the clinic against a range of cancers. However, severe systemic toxicity and drug resistance have become the main obstacles which limit their application and effectiveness. Because divalent cisplatin analogues are easily destroyed in vivo, their bioavailability is low and no selective to tumor tissues. The platinum(IV) prodrugs are attractive compounds for cancer treatment because they have great advantages, e.g., higher stability in biological media, aqueous solubility and no cross-resistance with cisplatin, which may become the next generation of platinum anticancer drugs. In addition, platinum(IV) drugs could be taken orally, which could be more acceptable to cancer patients, breaking the current situation that platinum(II) drugs can only be given by injection. The coupling of platinum(IV) complexes with tumor targeting groups avoids the disadvantages such as instability in blood, irreversible binding to plasma proteins, rapid renal clearance, and non-specific distribution in normal tissues. Because of the above advantages, the combination of platinum complexes and tumor targeting groups has become the hottest field in the research and development of new platinum drugs. These approaches can be roughly categorized into two groups: active and passive targeted strategies. This review concentrates on various targeting and delivery strategies for platinum(IV) complexes to improve the efficacy and reduce the side effects of platinum-based anticancer drugs. We have made a summary of the related articles on platinum(IV) targeted delivery in recent years. We believe the results of the studies described in this review will provide new ideas and strategies for the development of platinum drugs.

Dual-functional conjugates improving cancer immunochemotherapy by inhibiting tubulin polymerization and indoleamine-2,3-dioxygenase

A series of novel conjugates comprising tublin and IDO inhibitors were designed, synthesized and evaluated for their antiproliferative activity. Among them, HI5, composed of combretastatin A-4 (CA-4) and (D)-1-methyltryptophan (D-MT) by a linker, exhibited the most potent antitumor activity, in particular with higher IC₅₀ value (0.07 μM) than CA-4 (0.21 μM) against HeLa cancer cell line. Mechanism studies indicated that HI5 can inhibit tubulin polymerization and cell migration, cause G2/M phase arrest, concurrent induce apoptosis via the mitochondrial dependent apoptosis pathway and cause reactive oxidative stress generation in HeLa cells. Furthermore, HI5 can inhibit IDO expression and decrease kynurenine production, leading to stimulating T cells activation and proliferation to enhance antitumor immunity in vitro. Interestingly, HI5 can effectively limit the tumor growth in the HeLa xenograft mice models without causing significant loss of body weight. Consequently, such a conjugation can be a potent and safe immunochemotherapeutic method for improving cancer therapy.

Expanding the Arsenal of PtIV Anticancer Agents: Multi-action PtIV Anticancer Agents with Bioactive Ligands Possessing a Hydroxy Functional Group

Most multi-action Pt^IV prodrugs have bioactive ligands containing carboxylates. This is probably due to the ease of carboxylating the OH axial ligands and because following reduction, the active drug is released. A major challenge is to expand the arsenal of bioactive ligands to include those without carboxylates. We describe a general approach for synthesis of Pt^IV prodrugs that release drugs with OH groups. We linked the OH groups of gemcitabine (Gem), paclitaxel (Tax), and estramustine (EM) to the Pt^IV derivative of cisplatin by a carbonate bridge. Following reduction, the axial ligands lost CO₂ , rapidly generating the active drugs. In contrast, succinate-linked drugs did not readily release the free drugs. The carbonate-bridged ctc-[Pt(NH₃ )₂ (PhB)(Gem-Carb)Cl₂ ] was significantly more cytotoxic than the succinate-bridged ctc-[Pt(NH₃ )₂ (PhB)(Gem-Suc)Cl₂ ], and more potent and less toxic than gemcitabine, cisplatin, and co-administration of cisplatin and gemcitabine.

Synthesis, structures and cytotoxic effects in vitro of cis- and trans-[PtIVCl4(NHC)2] complexes and their PtII precursors

Four new bis(N,N-dialkylbenzimidazol-2-ylidene)dichlorido platinum(ii) complexes 2 featuring N-alkyl substituents of increasing size (a: Me, b: Et, c: n-butyl, d: n-octyl) were synthesised and oxidised with PhICl₂ to give the corresponding [Pt^IVCl₄(N,N-dialkylbenzimidazol-2-ylidene)₂] complexes 4 as potential anticancer prodrugs. The known bis(N,N-dibenzylimidazol-2-ylidene)dichlorido platinum(ii) complex 1 was likewise oxidised to [Pt^IVCl₄(N,N-dibenzylimidazol-2-ylidene)₂] 3. In contrast, oxidation of complexes 1 and 2 with H₂O₂ or hypochlorites, or exchange of chlorido for hydroxo ligands in tetrachlorido complexes 4 failed to give isolable complexes of type [Pt^IVCl_4-n(OH)_n(NHC)₂]. In MTT assays the [Pt^IICl₂(NHC)₂]/[Pt^IVCl₄(NHC)₂] complex couples 1/3, 2c/4c, and trans-2c/trans-4c, bearing either N-benzyl or N-butyl substituents, each showed similar single-digit micromolar IC₅₀ values against at least three out of five human cancer cell lines, presumably due to an intracellular reduction of the Pt^IV complexes to their active Pt^II congeners. Unlike cisplatin, whose anticancer effect requires functional p53, each of them was active both in wildtype and in p53-negative HCT116 colon carcinoma cells. In ethidium bromide saturation assays with isolated DNA, cis-(bis-NHC)Pt^II complexes such as 1 caused morphological DNA changes more pronounced than those initiated by cisplatin, while the corresponding cis-(bis-NHC)Pt^IV complexes such as 3 interacted with DNA in a less structure-modifying way.

Improving the anticancer activity of platinum(iv) prodrugs using a dual-targeting strategy with a dichloroacetate axial ligand

Four novel platinum(iv) complexes, characteristic of DCA/TFA and with chloride ions as axial ligands, were designed and synthesized. This type of platinum(iv) complexes 1a–2b exhibited significant cytotoxic activity, and the cytotoxicity of 1b was the greatest among these four complexes, which was 20.61 fold and 7.65 fold higher than that of cisplatin against HepG-2 and NCI-H460 cancer cells, respectively. The result from the apoptosis assay of 1b was consistent with the result from the cytotoxicity assay. In addition, complexes 1a and 1b induced cell cycle arrest at the S phase on HepG-2 cells. Taken together, our data showed that Pt(iv) complex 1b released the corresponding Pt(ii) complex and DCA, and induced apoptosis as well as disruption of the mitochondrial membrane potential, establishing Pt(iv) complex 1b as a potential dual-targeting anticancer agent.

Complex 1b could release complex B and DCA, playing a dual-targeting anti-tumor effect against cancer cells, targeting nuclear DNA and mitochondria, respectively.

Synthesis, Structure, Stability, and Inhibition of Tubulin Polymerization by RuII-p-Cymene Complexes of Trimethoxyaniline-Based Schiff Bases

Four trimethoxy- and dimethoxyphenylamine-based Schiff base (L1-L4)-bearing Ru^II-p-cymene complexes (1-4) of the chemical formula [Ru^II(η⁶-p-cymene)(L)(Cl)] were synthesized, isolated in pure form, and structurally characterized using single-crystal X-ray diffraction and other analytical techniques. The complexes showed excellent in vitro antiproliferative activity against various forms of cancer that are difficult to cure, viz., triple negative human metastatic breast carcinoma MDA-MB-231, human pancreatic carcinoma MIA PaCa-2, and hepatocellular carcinoma Hep G2. The ¹H nuclear magnetic resonance data in the presence of 10% dimethylformamide-d₇ or dimethyl sulfoxide-d₆ in phosphate buffer (pD 7.4, containing 4 mM NaCl) showed that the complexes immediately generate the aquated species that is stable for at least 24 h. Electrospray ionization mass spectrometry data showed that they do not bind with guanine nitrogen even in the presence of 5 molar equivalents of 9-EtG, during a period of 24 h. The best complex in the series, 1, exhibits an IC₅₀ of approximately 10-15 μM in the panel of tested cancer cell lines. The complexes do not enhance the production of reactive oxygen species in the cells. Docking studies with a tubulin crystal structure (Protein Data Bank entry 1SAO ) revealed that 1 and 3 as well as L1 and L3 have a high affinity for the interface of the α and β tubulin dimer in the colchicine binding site. The immunofluorescence studies showed that 1 and 3 strongly inhibited microtubule network formation in MDA-MB-231 cells after treatment with an IC₂₀ or IC₅₀ dose for 12 h. The cell cycle analysis upon treatment with 1 showed that the complexes inhibit the mitotic phase because the arrest was observed in the G2/M phase. In summary, 1 and 3 are Ru^II half-sandwich complexes that are capable of disrupting a microtubule network in a dose-dependent manner. They depolarize the mitochondria, arrest the cell cycle in the G2/M phase, and kill the cells by an apoptotic pathway.

Cisplatin and beyond: molecular mechanisms of action and drug resistance development in cancer chemotherapy

Background

Platinum-based anticancer drugs are widely used in the chemotherapy of human neoplasms. The major obstacle for the clinical use of this class of drugs is the development of resistance and toxicity. It is therefore very important to understand the chemical properties, transport and metabolic pathways and mechanism of actions of these compounds. There is a large body of evidence that therapeutic and toxic effects of platinum drugs on cells are not only a consequence of covalent adducts formation between platinum complexes and DNA but also with RNA and many proteins. These processes determine molecular mechanisms that underlie resistance to platinum drugs as well as their toxicity. Increased expression levels of various transporters and increased repair of platinum-DNA adducts are both considered as the most significant processes in the development of drug resistance. Functional genomics has an increasing role in predicting patients’ responses to platinum drugs. Genetic polymorphisms affecting these processes may play an important role and constitute the basis for individualized approach to cancer therapy. Similar processes may also influence therapeutic potential of nonplatinum metal compounds with anticancer activity.

Conclusions

Cisplatin is the most frequently used platinum based chemotherapeutic agent that is clinically proven to combat different types of cancers and sarcomas.

Hybrid cis-stilbene Molecules: Novel Anticancer Agents

The growing interest in anticancer hybrids in the last few years has resulted in a great number of reports on hybrid design, synthesis and bioevaluation. Many novel multi-target-directed drug candidates were synthesized, and their biological activities were evaluated. For the design of anticancer hybrid compounds, the molecules of stilbenes, aromatic quinones, and heterocycles (benzimidazole, imidazole, pyrimidine, pyridine, pyrazole, quinoline, quinazoline) were applied. A distinct group of hybrids comprises the molecules built with natural compounds: Resveratrol, curcumin, coumarin, and oleanolic acid. In this review, we present the studies on bioactive hybrid molecules of a well-known tubulin polymerization inhibitor, combretastatin A-4 and its analogs with other pharmacologically active entities. The mechanism of anticancer activity of selected hybrids is discussed considering the structure-activity relationship.

Multifunctional platinum(IV) complexes as immunostimulatory agents to promote cancer immunochemotherapy by inhibiting tryptophan-2,3-dioxygenase

Increasing evidences suggested that cisplatin can be involved in a tumor-specific immune response as an immunomodulator to improve antitumor immunity, but the designation and development are limited. Here, we report a series of novel Pt(IV) complexes derived from the conjugation of platinum(II) anticancer agents with an immune checkpoint TDO inhibitor. These complexes not only showed significant cytotoxic effects on the tested cancer cell lines, but also could enhance antitumor immune response. Particularly, complex T2, the mono-conjuagte of oxoplatin and (E)-4-oxo-4-(3-(2-(pyridin-3-yl)vinyl)-1H-indol-1-yl)butanoic acid, displayed 35-fold more potency than cisplatin against TDO-overexpressed HepG-2 cancer cells. Further study indicated that T2 could inhibit TDO via releasing a derivative of a TDO inhibitor and block kynurenine production, resulting in T-cell activation and proliferation in vitro. In vivo tests proved that T2 as a potent immunomodulator could highly promote the antitumor activity of cisplatin and effectively suppress the expression of TDO. This immunochemotherapeutic strategy can be promisingly applied to treat with TDO-overexpressed cancers.

A study on platinum(iv) species containing an estrogen receptor modulator to reverse tamoxifen resistance of breast cancer

Several dual-action Tam-Pt(iv) complexes derived from tamoxifen (Tam) and platinum(ii) drugs were designed and synthesized for targeting estrogen receptors (ERs) and DNA. These novel compounds not only exhibited potent cytotoxicity against breast cancer cells, but also reversed the tamoxifen resistance of TamR-MCF-7 cancer cells. Computational docking assays together with cellular uptake data demonstrated that the ER ligand portion of these conjugates plays a targeting role in ER-positive tumor cells and promotes the uptake of platinum via an estrogen receptor-mediated pathway. A study on the preliminary mechanism of the typical conjugate, complex 1, revealed that the Tam-Pt(iv) complex induced apoptosis via the mitochondrial-dependent apoptosis pathway mediated through the activation of caspase 3 and PARP proteins. These results suggested that the conjugation of estrogen receptor modulators with the platinum moiety could facilitate a selective enrichment of platinum in estrogen-positive tumors and possibly broaden the scope of ER ligand clinical use to resistant breast tumors.

Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

While medicinal inorganic chemistry has been practised for over 5000 years, it was not until the late 1800s when Alfred Werner published his ground-breaking research on coordination chemistry that we began to truly understand the nature of the coordination bond and the structures and stereochemistries of metal complexes. We can now readily manipulate and fine-tune their properties. This had led to a multitude of complexes with wide-ranging biomedical applications. This review will focus on the use and potential of metal complexes as important therapeutic agents for the treatment of cancer. With major advances in technologies and a deeper understanding of the human genome, we are now in a strong position to more fully understand carcinogenesis at a molecular level. We can now also rationally design and develop drug molecules that can either selectively enhance or disrupt key biological processes and, in doing so, optimize their therapeutic potential. This has heralded a new era in drug design in which we are moving from a single- toward a multitargeted approach. This approach lies at the very heart of medicinal inorganic chemistry. In this review, we have endeavored to showcase how a "multitargeted" approach to drug design has led to new families of metallodrugs which may not only reduce systemic toxicities associated with modern day chemotherapeutics but also address resistance issues that are plaguing many chemotherapeutic regimens. We have focused our attention on metallodrugs incorporating platinum and ruthenium ions given that complexes containing these metal ions are already in clinical use or have advanced to clinical trials as anticancer agents. The "multitargeted" complexes described herein not only target DNA but also contain either vectors to enable them to target cancer cells selectively and/or moieties that target enzymes, peptides, and intracellular proteins. Multitargeted complexes which have been designed to target the mitochondria or complexes inspired by natural product activity are also described. A summary of advances in this field over the past decade or so will be provided.

Promoting antitumor efficacy by suppressing hypoxia via nano self-assembly of two irinotecan-based dual drug conjugates having a HIF-1α inhibitor

Conjugated a hydrophobic HIF-1α inhibitor (YC-1) with a hydrophilic anticancer drug, irinotecan (Ir), into one molecular entity, provided a new insight into the design of smart nanodrug delivery systems to hypoxic tumor tissue.

1-Arylsulfonyl indoline-benzamides as a new antitubulin agents, with inhibition of histone deacetylase

We report structure-activity relationships of 1-arylsulfonyl indoline based benzamides. The benzamide (9) exhibits striking tubulin inhibition with an IC₅₀ value of 1.1 μM, better than that of combretastain A-4 (3), and substantial antiproliferative activity against a variety of cancer cells, including MDR-positive cell lines with an IC₅₀ value of 49 nM (KB), 79 nM (A549), 63 nM (MKN45), 64 nM (KB-VIN10), 43 nM (KB-S15), and 46 nM (KB-7D). Dual inhibitory potential of compound 9 was found as it demonstrated significant inhibitory potential against HDAC1, 2 and 6 in comparison to MS-275 (6). Some key interactions of 9 with the amino acid residues of the active site of tubulin and with amino acid residues of HDAC 1 isoform have been figured out by molecular modeling. Compound 9 also demonstrated significant in vivo efficacy in the human non-small cell lung cancer A549 xenograft model as well as B-cell lymphoma BJAB xenograft tumor model.

Current Developments in Pt(IV) Prodrugs Conjugated with Bioactive Ligands

To overcome the side effects of and resistance to cisplatin, a variety of Pt(IV) prodrugs were designed and synthesized via different modifications including combination with lipid chains to increase hydrophobicity, conjugation with short peptide chains or nanoparticles to improve drug delivery, or addition of bioactive ligands to the axial positions of Pt(IV) complexes to exert dual-function effects. This review summarizes the recent progress in the development of Pt(IV) prodrugs conjugated with bioactive-targeting ligands, including histone deacetylase inhibitors, p53 agonists, alkylating agents, and nonsteroidal anti-inflammatory agents. Although Pt(IV) complexes that conjugated with bioactive ligands show satisfactory anticancer effects, none has been approved for clinical use. Therefore, we hope that this review will contribute to further study and development of Pt(IV) complexes conjugated with bioactive and other ligands.

Pt(IV) prodrugs containing microtubule inhibitors displayed potent antitumor activity and ability to overcome cisplatin resistance

It is well-known that cisplatin exhibited a broad spectrum of anticancer activities against many solid tumors, but its severe toxicity and drug resistance have largely limited wider clinical applications. Various strategies have been tried to discover new Pt (II) drugs with at least equal activity as well as low toxicity compared to cisplatin, but the inherent problem remains unsolved. Here we report that Pt (IV) complexes comprising a CA-4 analogue, as dual-targeting Pt (IV) prodrug, were synthesized and evaluated for anti-proliferative activity using MTT assay. Among them, complex 19 displayed most potent activity against the tested cancer cell lines, and simultaneously exhibited better cell selectivity between cancer cells and normal cells than that of cisplatin. Mechanism studies revealed that complex 19 effectively induced cell cycle arrest at the G2/M phase and dramatically disrupted the microtubule organization. Moreover, complex 19 significantly induced cell apoptosis and decreased MMP. Importantly, complex 19 significantly inhibited tumor growth in SK-OV-3 xenograft model in vivo without apparent toxicity.

Synthesis, Structure, and Cytotoxicity of Oxaliplatin-Based Platinum(IV) Anticancer Prodrugs Bearing One Axial Fluoride

Fluorine plays more and more important roles in drug design and development. In recent years, fluorine-containing organic drugs have already been applied in a broad range of therapeutic areas. Herein, we report our attempt to introduce an axial fluorine ligand to Pt(IV) complexes by oxidizing oxaliplatin with electrophilic fluorinating reagents in different protic solvents. The crystal structure of one representative complex is presented. The fluorinated Pt(IV) complexes are further expanded by functionalization with different anhydrides, and their analogues bearing one different axial ligand (OAc or OH group) are also synthesized. Further investigations show that the axial fluorine atom has dramatic effects on the chemical properties of these prodrugs. These new fluorinated Pt(IV) complexes are proved to be stable in physiological conditions. For most of the fluorinated Pt(IV) complexes, a higher reduction potential indicates its greater tendency to be reduced by ascorbate. Introducing an axial fluorine ligand in Pt(IV) complexes does not lead to the increase of their lipophilicity. Moreover, these new fluorinated Pt(IV) complexes show better cytotoxicity than nonfluorinated analogues which may derive from their higher cellular accumulation in cancer cells. Therefore, the good stability and high cytotoxicity of these fluorinated Pt(IV) prodrugs indicate their great potential as a building block for further functionalization.

Dual-targeting antitumor hybrids derived from Pt(IV) species and millepachine analogues

Many strategies have been developed to circumvent the shortcomings of Pt(II)-based chemotherapy, but the inherent problems still have not been effectively resolved. Here we report a new series of dual-targeting Pt(IV) prodrugs, conjugates of millepachine analogues with the related Pt(IV) complexes derived from cisplatin or oxaliplatin, respectively, which can inhibit tubulin polymerization and induce DNA damage. Among them, compound 19 possessed excellent antitumor activities against the tested human cancer cell lines, and arrested the cell cycle at the G2/M phases and ultimately induced cell apoptosis. Interestingly, its low cytotoxicity toward two human normal cells and sensitivity toward two cisplatin-resistant cells revealed the possibility for cancer therapy. More importantly, 19 displayed excellent antitumor efficacy in the SK-OV-3 xenograft model better than cisplatin and the corresponding millepachine analogue. Our research provided an efficient strategy for multi-targeting antitumor drug development.

Pt(IV) complexes conjugating with chalcone analogue as inhibitors of microtubule polymerization exhibited selective inhibition in human cancer cells

Six novel of Pt(IV) complexes comprising chalcone analogues were synthesized and evaluated for anti-proliferative activity using MTT assay. In vitro evaluation revealed that all Pt(IV) complexes showed better and more potent activity against three human cancer cells including CDDP resistant cells than that of their corresponding mother Pt(II) species. Among them, two representative complexes, 14 and 17, exhibited better cell selectivity between cancer cells and normal cells than CDDP. Molecular docking study indicated that complexes 14 and 17 could bind to the colchicine site of tubulin. Moreover, complexes 14 and 17 also remarkably displayed inhibition of cell migration against HUVEC cells in vitro. Molecular mechanism studies suggested that 14 and 17 induced production of reactive oxygen species (ROS), cell cycle arrest at the G2/M phase, and mitochondria-mediated apoptosis by regulating the expression of Bcl-2 family members.

Bright Side of Lignin Depolymerization: Toward New Platform Chemicals

Lignin, a major component of lignocellulose, is the largest source of aromatic building blocks on the planet and harbors great potential to serve as starting material for the production of biobased products. Despite the initial challenges associated with the robust and irregular structure of lignin, the valorization of this intriguing aromatic biopolymer has come a long way: recently, many creative strategies emerged that deliver defined products via catalytic or biocatalytic depolymerization in good yields. The purpose of this review is to provide insight into these novel approaches and the potential application of such emerging new structures for the synthesis of biobased polymers or pharmacologically active molecules. Existing strategies for functionalization or defunctionalization of lignin-based compounds are also summarized. Following the whole value chain from raw lignocellulose through depolymerization to application whenever possible, specific lignin-based compounds emerge that could be in the future considered as potential lignin-derived platform chemicals.

Dual or multi-targeting inhibitors: The next generation anticancer agents

Dual-targeting/Multi-targeting of oncoproteins by a single drug molecule represents an efficient, logical and alternative approach to drug combinations. An increasing interest in this approach is indicated by a steady upsurge in the number of articles on targeting dual/multi proteins published in the last 5 years. Combining different inhibitors that destiny specific single target is the standard treatment for cancer. A new generation of dual or multi-targeting drugs is emerging, where a single chemical entity can act on multiple molecular targets. Dual/Multi-targeting agents are beneficial for solving limited efficiencies, poor safety and resistant profiles of an individual target. Designing dual/multi-target inhibitors with predefined biological profiles present a challenge. The latest advances in bioinformatic tools and the availability of detailed structural information of target proteins have shown a way of discovering multi-targeting molecules. This neoteric artifice that amalgamates the molecular docking of small molecules with protein-based common pharmacophore to design multi-targeting inhibitors is gaining great importance in anticancer drug discovery. Current review focus on the discoveries of dual targeting agents in cancer therapy using rational, computational, proteomic, bioinformatics and polypharmacological approach that enables the discovery and rational design of effective and safe multi-target anticancer agents.

Platinum(IV) prodrugs multiply targeting genomic DNA, histone deacetylases and PARP-1

Several Pt(IV) prodrugs containing SAA, a histone deacetylases inhibitor, were designed and prepared for multiply targeting genomic DNA, histone deacetylases and PARP-1. The resulting Pt(IV) prodrug had significantly strong antiproliferative activity against the tested cancer cell lines, especially SAA1, derived from the conjugation of cisplatin and SAA, had potent ability to overcome cisplatin resistance. Under the combined action of DNA platination and inhibition of HDACs and PARP-1 activity, the cytotoxic activity of SAA1 was 174-fold higher than cisplatin against cisplatin-resistant SGC7901/CDDP cancer cells. The mechanism of action of SAA1 was preliminarily investigated, in which cellular uptake, cell apoptosis and cell cycle arrest as well as western blot analysis were made by treating SAA1 with SGC7901/CDDP cells. Besides, HDACs inhibition activity and PARP-1 enzyme inhibition of SAA1 were also studied.