Pleiotropic focused anticancer approach of dihydropyridines, dihydropyrimidines and heteroaromatic compounds

Complex, focused anticancer therapy approach has been developed in the Latvian Institute of Organic Synthesis by making use of privileged partially hydrogenated nitrogen-containing heterocycles, namely dihydropyridines, dihydropyrimidines, their oxidized heteroaromatic derivatives. Topics of research include:
1. Conventional approach by chemotherapy and synergism of anticancer drugs [1];
2. Inhibition of multidrug resistance by inhibition of drug efflux pumps [2];
3. Mitigation of cancer risk factors – e.g., hepatitis B virus chemotherapy for prevention of chronic liver diseases, because chronic hepatitis, in up to 40% of cases, progresses to cyrrhosis and further to hepatocellular carcinoma [3];
4. Improvement of efficacy of cancer radiotherapy by use of radioprotectors to prevent damage of normal tissues. So, radioprotector diethone (dietone) for skin protection was discovered, elaborated, and developed as ointment. Compounds for protection of eyes, mucous tissues, salivary glands etc have been synthesized. Toxicity of dietone and novel radioprotectors is very low;
5.Amphiphilic compounds have been synthesized, nanoparticles for anticancer drug and gene delivery have been created, pleiotropic properties have been checked, inclusion of magnetic particles for targeted transport performed [4].

Acknowledgements
The research was partially supported by the Latvian State Program Biomedicine.

References
1.Bisenieks E., Duburs G. et al., Pharmaceutical combination of 5-fluorouracil and derivatives of 1,4-dihydropyridine. US 8492413B2, 2013.
2.Krauze A., Grinberga S. et al., Thieno[2,3-b]pyridines – a new class of multidrug resistance (MDR) modulators. Bioorg.Med.Chem. 2014, 22 (21), 5860-5870.
3.Sipola A., Dubova U., et al., Synthesis and evaluation of 1,4-dihydropyrimidine derivatives – hepatitis B virus capsid self-assembly inhibitors. EFMC International Symposium on Medicinal Chemistry. Ljubljana, Slovenia, 2018, P176.
4.Pajuste K. et al., Gene delivery agents possessing antiradical activity: Self-assembling cationic amphiphilic 1,4-dihydropyridine derivatives. New J.Chem. 2013, 37 (10), 3062-3075.

Membrane forming lipid type compounds (amphiphilic, comprising heterocycles or conjugated systems as linkers, self-assembling, capable to form nanoparticles) GPCRs -incorporated into membrane matrix; synthesis of GPCR regulators Partially hydrogenated nitrogen heterocycles, condensed and heteroaromatic derivatives: dihydropyridines, dihydropyridones, dihydropyrimidines, hexahydroquinolines, polynuclear heterocycles, 5-and 7member analogues; Redoxproceses; antioxidants, radioprotectors. Chemoenzymatic enantioselective transformations. Synthesis of anticancer and antiviral agents Regulators of transmembrane transport functions: •selective inhibitors or activators of Ca 2+ transport; •regulators of drug efflux (inhibition of multiresistance) •Nanoparticles for transport of nucleic acids, drugs, proteins Anticancer chemotherapy agent 5-fluorouracil (5-FU) is widely used in chemotherapeutic praxis as an antimetabolic anticancer agent for the treatment and palliative management of various forms of cancer including colorectal, pancreatic, breast and stomach cancer. 5-FU is associated with side effects such as mucositis, dermatitis, cardial toxicity, etc.. As an alternative strategy, 5-FU can be combined with synergists, which may enhance the efficacy of chemotherapy with reduced toxicity to normal cells [1].Synergists could be used also regarding other chemotherapy agents [2].
4-Alkyl-2,6-dimethyl-1,4-dihydropyridine-3,5-bis-carbonyloxyacetic acid disodium salts increase antitumor activity of 5-fluorouracil (in vitro)the most active compounds are 4-methyl-and 4-ethylderivatives. Their 4-dezalkyl analogue(carbatone) possesses antimetastatic activity, and also some potentiating effect on the activity of various antitumor agents, it was used to decrease the cyclophosphane toxicity in mice; it also potentiates the cytostatic activity of cyclophosphane, 5fluorouracil and arabinosyl cytosine against leukemia P 388, murine sarcoma 37 and Walker's carcinosarcoma. Carbatone exhibited no antitumor activity. 4-Alkylcarbatone analogues possess superior potentiation activity.  Rational approach to drug designstructural analogy with known active agentshas been used in our research A pharmacophore model has been created assuming the central part of verapamil as the linker and methoxyphenyl groups as essential features for the pharmacophore A. Krauze

2.Inhibition of multidrug resistance by inhibition of drug efflux pumps
Modulation of multidrug resistance in tumor cells may be used to improve cancer chemotherapy. Synthesis of multidrug resistance nodulators (P-glycoprotein, MDR associated protein BCRP1, breast cancer resistance protein MRP1) on the basis of partially hydrogenated pyridines and related polycyclic heterocycles has been designed and performed.
The calcium channel blocker verapamil is the most investigated and often used as a reference compound but, unfortunately, cardiotoxicity is observed in combination with actual anticancer drugs Outer (periferal) parts of verapamil were (partially) preserved, but inner part -linker -was exchanged to "privileged" system -dihydropyridine.
DHPs 5a-d were prepared by one-pot reaction of ethyl 2arylmethylidenacetoacetate 1 with 2cyanothio-acetamide (2) in the presence of equimolar amount of piperidine (3) as base in ethanol followed by subsequent alkylation of the resultant thiolate with substituted 2bromoacetophenone 4 ( pathway A). In turn, DHPs 5e,f were prepared in 73-89% yields by treatment of the thiolate 6 with substituted 2-bromoacetophenone 4 (pathway B).
DHP 5a at 20 μm concentration displays high P-gp inhibition activity, the activity of DHPs 5c is comparable, DHPs 5b,d are slightly less active than verapamil. Compounds 5a-d have low Ca 2+. antagonist activity. MDR modulating activity and calculated logP values of tested compounds.
Especially compound 6r Recent 90 page review article by Stefan and Wiese contains large quantity of small molecule inhibitors of multidrug resistance-associated protein-1: derivatives of different heterocycles. This article pays special attention to just discussed compoundsderivatives of thienopyridine and especially to compound 6rthe best known pleiotropical active on all three important proteins of the ABC cassette. 3.Improvement of efficacy of cancer radiotherapy -by radioprotectors to prevent damage of normal tissues.
Ionizing radiation is used in diagnostics, cancer-related therapy, has industrial applications. Exposure to ionizing radiation includes induction of cellular death, genetic mutations, carcinogenesis [1], acute skin and mucosal tissues damage Nowadays stereotactic approach is used in cancer clinics quite often (that is, focusing of radiation energy from several radiation sources); nevertheless, radiation damage of normal tissues is still noticed, radiation dermatitis; radiation induced oral mucositis, radiation-induced xerostomia take place [2]). Chemical radioprotectors are promising strategy. Late effects of radiation such as radiation induced cancer could compromise the quality of life of cancer patients. Unfortunately usually radioprotectors are highly toxic. [

Acute skin and mucosal toxicities and pharmaceutical interventions
Ionizing radiation is not only a problem for cancer patients, but also a public health concern due to the potential for a nuclear and/or radiological event, e.g. bioterrorism and nuclear attack [5].
Amifostine is recommended for the prevention of mucositis at radiotherapy associated with head and neck malignancies or esophagitis associated with non-small-cell lung cancer [3,4].
Amifostine has to be administered intravenously (slow infusions!) or subcutaneosly. It causes hypotension. Paliformin -(a recombinant form of keratinocyte growth factor) is administered intravenously. So more convenient, low toxic and effective radioprotectors are advisable.
Diethone was studied comparing with radioprotective substances, as cystamine, eugenol, methyluracil. Diethone had the best results. Therapeutic activity of dietone ointment: it is better than methyluracil ointment. Time of recovery is shorter, regeneration is more intense. Dietone (diethone) has very low toxicity, its LD 50 > 20,000 mg/kg (mice). It does not possess embriotoxic activity, but it has antimutagenic properties. It belongs to new class of antioxidants -1,4-dihydropyridines; it inhibits auto-oxidation of polyunsaturated systems, e.g.,β-carotene, vitamin A, polyunsaturated lipids, it has synergy with vitamin E. . Several compounds of the class of heteroaryl dihydropyrimidine (or HAP), such as BAY 41-4109, are capable of suppressing hepatitis B virus replication by blocking the proper self-assembly of capsids: capsid proteins associate in wrong manner by different kinetics. In collaboration with the Latvian Biomedical Research and Study Centre we synthesized and studied novel heteroaryldihydropyrimidine (HAP ) derivatives, which revealed different type of activities on hepatitis B capsid protein assembling comparing to BAY 41-4109. Compounds 1b and 1c showed a dose dependent effects on hepatitis B core aggregation, inducing formation of increased size aggregates. Standard compound BAY 41-4109 is quite different: it induces dose dependent decrement of the relative quantity of assembled capsids (similar to compounds 1a and 1d). These studies are related to the protein-protein interaction field, which is new, fast developing approach. Bakail M., Ochsenbein F. Targeting protein-protein interactions, a wide open field for drug design. C.R. Chimie ,2016,19, 19-27.