Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - TiDrugArchitectures (Highly Competent and Safe Titanium(IV) Therapeutic Frameworks that are Cancer Targeted based on Complex 1, 2, and 3D Chemical Architectures)

Teaser

Cancer diseases of more than 100 different kinds represent a major cause of human deaths worldwide, with more than 10 million new cases diagnosed each year. Since the historical mentions of cancer conditions back in 500 BC, significant progress was achieved in recent years...

Summary

Cancer diseases of more than 100 different kinds represent a major cause of human deaths worldwide, with more than 10 million new cases diagnosed each year. Since the historical mentions of cancer conditions back in 500 BC, significant progress was achieved in recent years with better understanding of malignancy and novel therapeutic methodologies, such as immunotherapy and precision (personalized) medicine. Nevertheless, such approaches are applicable only for specific cases and are very limited to particular cancer types and populations. The vast majority of cancer cases thus still relies on chemotherapy for attempted treatment, and will surely continue to do so for many years to come. As the main limitation of classical chemotherapy is the severe side effects accompanying drug efficacy, developing highly potent chemotherapy of reduced/negligible side effects, effective toward a wide range of cancer types, is of incredible merit.
Cisplatin as a pioneering metal-based anticancer drug represents a landmark in cancer chemotherapy. It is a highly effective drug used in the clinic toward certain types of cancers, including testicular, ovarian, lung, and more. Nevertheless, cisplatin, along with its Pt-based derivatives, suffer from two main limitations: development of resistance in some cancer types, and most severely – acute side effects in the treated patients, imposing irreversible critical damages to vital organs. These features damage the patient\'s quality of life during treatment and risk the patient’s health after treatment termination – thus limiting the tolerated dose and by that – the drug efficacy and chances for cure.
The titanium(IV) metal is known to be a biologically friendly metal. The compound titanium dioxide is widely used in food products, cosmetics, and drugs. It is completely safe, with no side effects or any dietary restrictions. The titanium metal of different forms is used in medicine for transplants and various devices.
In the quest toward alternative anti-cancer metallodrugs, titanium(IV) complexes were previously investigated, and demonstrated high antitumor efficacy with no reports on titanium resistance in treated cells/tumours to date. Importantly, in accordance with the biocompatibility of the titanium metal, markedly reduced toxicity was detected in mice treated with the titanium(IV) compounds, where the minor toxicity was mostly reversible. These features reflect the high advantage in the use of titanium(IV) in anticancer chemotherapy.
The past titanium(IV) complexes did not proceed beyond phase II clinical trials due to their limiting feature – hydrolytic instability. This feature also hampered mechanistic investigations of the past compounds. Nevertheless, the hydrolysis to form the final safe product titanium dioxide, which can leave the human body without harm, is a big advantage for the use of titanium(IV) complexes as drugs. Thus, to utilize the titanium(IV) potential, more stable titanium(IV) complexes were needed.
We have introduced advanced titanium(IV) anticancer complexes that are based on strongly binding ligands, decelerating hydrolysis. Through the current ERC-CoG, we synthesize various derivatives and analyze their anticancer and hydrolytic reactivities. Our objectives include: (a) synthesizing optimal derivatives with high activity and slow hydrolysis, and establish the role of symmetry and geometry; (b) determining the mechanism of operation of these drugs and cellular pathways affected by the treatment; and (c) developing particular drug delivery systems based on tailored architectures for selective transport to cancer tissue. These studies should substantially promote the development of safe and effective anticancer chemotherapy.

Work performed

We have developed several compounds with different structural motifs, all include a hexadentate ligand system with no labile groups altogether, providing complexes that are stable for weeks in water solutions. These complexes are also stable under various biological conditions and a wide pH range. A lead complex of this family (phenolaTi) has shown high activity toward several cell lines, including cells resistant to known drugs (cisplatin-resistant and multi-drug-resistant). PhenolaTi also demonstrated activity in mice and importantly, no toxicity was observed for phenolaTi, unlike the major toxicity observed for the control drug cisplatin currently employed in the clinic. PhenolaTi is also active in combinations with Pt based drugs, both in cell cultures and on animals. Preliminary mechanistic studies have shown that the complex induces ordered cell death. Studies with fluorescent complexes have also shed light on the bio-distribution of the Ti-based complexes in the cells.

Final results

In depth mechanistic investigations were conducted based on gene expression analyses, identifying the genes for which the expression changed significantly upon treatment with phenolaTi. Unique alterations of cellular pathways were detected, evincing that the mechanism of phenolaTi is different than that of cisplatin or other known anticancer metallodrugs. Additional insights are expected when comparing the results obtained on the tested cells with those obtained on cells resistant the phenolaTi. Thus far, no reports on Ti resistance exist. We have started with direct attempts to obtain cells resistant to phenolaTi by gradual exposure to the drug. We have not obtained resistance thus far. If indeed resistance cannot be achieved – this would have incredible medicinal implications.
Detection of Ti-based compounds is possible through detection of fluorinated ligands. Therefore, fluorinated derivatives were synthesized and quantitation analysis of different cellular organelles is underway. Additionally, we employ fluorescent derivatives for cell imaging, which, as mentioned above, provided vital insights on the cellular and sub-cellular accumulation of the Ti compounds. Additional studies with stable derivatives are underway.
Drug delivery studies are also underway. Preliminary indications were obtained for the development of a suitable ligand scaffold for binding cell penetrating peptides or other active species. Synthetic attempts toward construction of the spherical entities have begun recently, and are still underway. Optimization studies are required, to be followed by conjugation and analyses of reactivity.
To conclude, much progress was done with the promising family of Ti-based complexes, with the lead complex phenolaTi showing incredible combination of activity and cancer selectivity, with admirable hydrolytic stability, and with very first clear indications on its mechanistic pathway. Toward the end of the project we anticipate to both establish the mechanism of action of phenolaTi, as well as develop costume drug delivery systems for more selective transport of phenolaTi to cancer cells. A particularly safe and widely effective anticancer chemotherapy should result.