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Target therapies based on BRAF and MEK inhibitors (MAPKi) have changed the therapeutic landscape for metastatic melanoma patients bearing mutations in the BRAF kinase. However, the emergence of drug resistance imposes the necessity to conceive novel therapeutic strategies capable to achieve a more durable disease control. In the last years, retrotransposons laying in human genome have been shown to undergo activation during tumorigenesis, where they contribute to genomic instability. Their activation can be efficiently controlled with reverse transcriptase inhibitors (RTIs) frequently used in the treatment of AIDS. These drugs have demonstrated anti-proliferative effects in several cancer models, including also metastatic melanoma. However, to our knowledge no previous study investigated the capability of RTIs to mitigate drug resistance to target therapy in BRAF-mutant melanomas. In this short report we show that the non-nucleoside RTI, SPV122 in combination with MAPKi strongly inhibits BRAF-mutant melanoma cell growth, induces apoptosis, and delays the emergence of resistance to target therapy in vitro. Mechanistically, this combination strongly induces DNA double-strand breaks, mitochondrial membrane depolarization and increased ROS levels. Our results shed further light on the molecular activity of RTI in melanoma and pave the way to their use as a novel therapeutic option to improve the efficacy of target therapy. Video Abstract.

Emerging data indicate that the reverse transcriptase (RT) protein encoded by LINE-1 transposable elements is a promising cancer target. Nonnucleoside RT inhibitors, e.g. efavirenz (EFV) and SPV122.2, reduce proliferation and promote differentiation of cancer cells, concomitant with a global reprogramming of the transcription profile. Both inhibitors have therapeutic anticancer efficacy in animal models. Here we have sought to clarify the mechanisms of RT inhibitors in cancer cells. We report that exposure of PC3 metastatic prostate carcinoma cells to both RT inhibitors results in decreased proliferation, and concomitantly induces genome damage. This is associated with rearrangements of the nuclear architecture, particularly at peripheral chromatin, disruption of the nuclear lamina, and budding of micronuclei. These changes are reversible upon discontinuation of the RT-inhibitory treatment, with reconsititution of the lamina and resumption of the cancer cell original features. The use of pharmacological autophagy inhibitors proves that autophagy is largely responsible for the antiproliferative effect of RT inhibitors. These alterations are not induced in non-cancer cell lines exposed to RT inhibitors. These data provide novel insight in the molecular pathways targeted by RT inhibitors in cancer cells., Competing Interests: Declaration of competing interest Authors declare no competing financial interests., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A series of 5-alkyl-2-(alkylthio)-6-(1-(2,6-difluorophenyl)propyl)-3,4-dihydropyrimidin-4(3H)-one derivatives (3a-h) belonging to the F(2)-DABOs class of non-nucleoside HIV-1 reverse transcriptase inhibitors (NNRTIs) are endowed with a strong antiproliferative effect and induce cytodifferentiation in A375 melanoma cells. Among tested compounds, the most potent is 3g (SPV122), which also induces apoptosis in a cell-density-dependent manner and antagonizes tumor growth in animal models. All these effects are similar or even more pronounced than those previously reported for other nucleoside or non-nucleoside inhibitors of reverse transcriptase or by functional knockout of the reverse-transcriptase-encoding long interspersed element 1 by RNA interference (RNAi). Taken together with our previously reported results, these data further confirm our idea that cellular alterations induced by NNRTIs are a consequence of the inhibition of the endogenous reverse transcriptase in A375 cells and support the potential of NNRTIs as valuable agents in cancer therapy., (© 2011 American Chemical Society)

Following the disclosure of dihydro-alkoxy-, dihydro-alkylthio-, and dihydro-alkylamino-benzyl-oxopyrimidines (DABOs, S-DABOs, and NH-DABOs) as potent and selective anti-HIV-1 agents belonging to the non-nucleoside reverse transcriptase inhibitor (NNRTI) class, we report here the synthesis and biological evaluation of a novel series of DABOs bearing a N,N-disubstituted amino group or a cyclic amine at the pyrimidine-C2 position, a hydrogen atom or a small alkyl group at C5 and/or at the benzylic position, and the favorable 2,6-difluorobenzyl moiety at the C6 position (F2-N,N-DABOs). The new compounds were highly active up to the subnanomolar level against both wt HIV-1 and the Y181C mutant and at the submicromolar to nanomolar range against the K103N and Y188L mutant strains. Such derivatives were more potent than S-DABOs, NH-DABOs, and nevirapine and efavirenz were chosen as reference drugs. The higher inhibitor adaptability to the HIV-1 RT non-nucleoside binding site (NNBS) may account for the higher inhibitory effect exerted by the new molecules against the mutated RTs.

Two 2,6-difluoro-DABO derivatives (MC 1047, 1, and MC 1220, 2, respectively) were tested against endogenous, nontelomeric reverse transcriptase (endo-RT) in human differentiating cell systems to investigate their antiproliferative and cytodifferentiating activity. The two compounds significantly reduced cell proliferation and facilitated the morphological differentiation of cells. These results propose F(2)-DABOs as useful tools in preventive and/or curative therapy to counteract the loss of differentiation in dedifferentiating pathologies and as antiproliferative drugs in tumor therapy.

2-Alkylamino-6-[1-(2,6-difluorophenyl)alkyl]-3,4-dihydro-5-alkylpyrimidin-4(3H)-ones (F(2)-NH-DABOs) 4, 5 belonging to the dihydro-alkoxy-benzyl-oxopyrimidine (DABO) family and bearing different alkyl- and arylamino side chains at the C(2)-position of the pyrimidine ring were designed as active against wild type (wt) human immunodeficiency virus type 1 (HIV-1) and some relevant HIV-1 mutants. Biological evaluation indicated the importance of the further anchor point of compounds 4, 5 into the non-nucleoside binding site (NNBS): newly synthesized compounds were highly active against both wild type and the Y181C HIV-1 strains. In anti-wt HIV-1 assay the potency of amino derivatives did not depend on the size or shape of the C(2)-amino side chain, but it associated with the presence of one or two methyl groups (one at the pyrimidine C(5)-position and the other at the benzylic carbon), being thymine, alpha-methyluracil or alpha-methylthymine derivatives almost equally active in reducing wt HIV-1-induced cytopathogenicity in MT-4 cells. Against the Y181C mutant strain, 2,6-difluorobenzyl-alpha-methylthymine derivatives 4d, 5h'-n' showed the highest potency and selectivity among tested compounds, both a properly sized C(2)-NH side chain and the presence of two methyl groups (at C(5) and benzylic positions) being crucial for high antiviral action.

Dihydro-alkoxy-benzyl-oxopyrimidines (DABOs) are a family of potent NNRTIs developed in the past decade. Attempts to improve their potency and selectivity led to thio-DABOs (S-DABOs), DATNOs, and difluoro-thio-DABOs (F(2)-S-DABOs). More recently, we reported the synthesis and molecular modeling studies of a novel conformationally constrained subtype of the S-DABO series characterized by the presence of substituents on the methylene linkage connecting the pyrimidine ring to the aryl moiety (Mai, A., et al. J. Med. Chem. 2001, 44, 2544-2554). Now we report the computer-aided design, synthesis, and biological evaluation of four new DABO prototypes (5-alkyl-2-cyclopentylamino-6-[1-(2,6-difluorophenyl)alkyl]-3,4-dihydropyrimidin-4(3H)-ones, F(2)-NH-DABOs) in which the sulfur atom of the related F(2)-S-DABOs is replaced by an amino group. For these studies, we used as a reference model the cocrystallized MKC-442/RT complex. Docking studies with Autodock of the newly designed F(2)-NH-DABOs on the ligand-derived RT confirmed the findings previously described for the F(2)-S-DABOs. The F(2)-NH-DABO binding mode resembles that reported for F(2)-S-DABOs, with the difference that the NH moiety at the C-2 position represents a new anchor site for ligand/enzyme complexation. The predicted inhibition constant (K(i)) values by the internal scoring function of Autodock, and the predicted IC(50) values by the application of a VALIDATE II/HIV-RT model strongly suggested the synthesis of the designed amino-DABOs. F(2)-NH-DABOs were shown to be highly active in both anti-RT and anti-HIV biological assays with IC(50) and EC(50) comparable with that of the reference compound MKC-442. Interestingly, 2-cyclopentylamino-6-[1-(2,6-difluorophenyl)ethyl]-3,4-dihydro-5-methyl pyrimidin-4(3H)-one (9d) was active against the Y181C HIV-1 mutant strain at submicromolar concentration, with a resistance value similar to that of efavirenz, the last FDA-approved NNRTI for AIDS therapy, and 2-fold lower than that of its 2-cyclopentylthio counterpart 8d. The introduction in 9d of a new anchor point (pyrimidine C-2 NH group), with the formation of a new hydrogen bond with Lys101, could compensate for the lack of positive hydrophobic ligand/NNBP interactions due to the Tyr181 to Cys181 mutation.

5-Alkyl-2-(alkylthio)-6-(2,6-difluorobenzyl)-3,4-dihydropyrimidin-4(3H)-ones (S-DABOs, 2) have been recently described as a new class of human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) active at nanomolar concentrations (Mai, A. et al. J. Med. Chem. 1999, 42, 619-627). In pursuing our lead optimization efforts, we designed novel conformationally restricted S-DABOs, 3, featuring a methyl at the benzylic carbon (Y = Me) and at the pyrimidine 5-position (R = Me). Conformational analyses and docking simulations suggested that the presence of both methyls would significantly reduce conformational flexibility without compromising, in the R enantiomers, the capability of fitting into the RT non-nucleoside binding pocket. To develop structure-activity relationships, we prepared several congeners of type 3 belonging to the thymine (R = Me) and uracil (R = H) series, featuring various 2-alkylthio side chains (X = Me, i-Pr, n-Bu, i-Bu, s-Bu, c-pentyl, and c-hexyl) and aryl moieties different from the 2,6-difluorophenyl (Ar = phenyl, 2,6-dichlorophenyl, 1-naphthyl). Moreover, alpha-ethyl derivatives (Y = Et) were included in the synthetic project in addition to alpha-methyl derivatives (Y = Me). All of the new compounds were evaluated for their cytotoxicity and anti-HIV-1 activity in MT-4 cells, and some of them were assayed against highly purified recombinant wild-type HIV-1 RT using homopolymeric template primers. The results were expressed as CC(50) (cytotoxicity), EC(50) (anti-HIV-1 activity), SI (selectivity, given by the CC(50)/EC(50) ratio), and IC(50) (RT inhibitory activity) values. In the 2,6-difluorobenzylthymine (R = Me) series, methylation of the benzylic carbon improved anti-HIV-1 and RT inhibitory activities together with selectivity. Compound 3w (Ar = 2,6-F(2)-Ph, R = Y = Me, X = c-pentyl) turned out the most potent and selective among the S-DABOs reported to date (CC(50) > 200 microM, EC(50) = 6 nM, IC(50) = 5 nM, and SI > 33 333). Assays performed on the pure enantiomer (+)-3w, much more active than (-)-3w, yielded the following results: CC(50) > 200 microM, EC(50) = 2 nM, IC(50) = 8 nM, and SI > 100 000, under conditions wherein MKC-442 was less active and selective (CC(50) > 200 microM, EC(50) = 30 nM, IC(50) = 40 nM, SI > 6666). The 2,6-difluorophenylethylthymines (R = Me) were generally endowed with higher potency compared with the uracil counterparts (R = H). In the 2,6-difluorophenyl series the best and the least performant 2-alkylthio side chains were the 2-c-pentylthio and the 2-methylthio, respectively. When the methyl at the benzylic carbon was replaced by an ethyl, activity was retained or decreased slightly, thus suggesting that the dimensions of the cavity within the RT hosting this substituent would not be compatible with groups larger than ethyl. Aryl moieties different from the 2,6-difluorophenyl (phenyl, 1-naphthyl, 2,6-dichlorophenyl) were generally detrimental to activity, consistent with a favorable electronic effect exerted by the 2,6-fluorines on a putative charge-transfer interaction between the aromatic moieties of the inhibitor and Tyr188.

rac-2-Cyclopentylthio-6-[1-(2,6-difluorophenyl)ethyl]-3,4-dihydro-5-methylpyrimidin-4(3H)-one (MC-1047) is a potent inhibitor of HIV-1 multiplication in acutely infected cells. MC-1047 racemate has been resolved by chiral HPLC using, as chiral stationary phase (CSP), a commercially available (R,R)-Whelk-01 column. The optical purity and the circular dichroism (CD) of the two resolved enantiomers were determined and their biological activities tested in in vitro assays. Molecular modeling inspection of the binding of (R) and (S) enantiomers to the non-nucleoside binding site (NNBS) of reverse transcriptase (RT) using the defined model of F(2)-S-DABO/RT complex indicates the (R) enantiomer as the more active isomer., (Copyright 2001 Wiley-Liss, Inc.)

Several 5-alkyl, 5-alkenyl, 5-iso-alkyl, 5-halo, 5-aminomethyl and 5-carboxy derivatives of S-DABOs (dihydro-alkyl (or cyclo-alkyl)thio-benzyloxopyrimidines), DATNOs (dihydro-alkylthionaphthylmethyl-oxopyrimidines) and F2-S-DABOs (dihydro-alkyl (or cyclo-alkyl)thio-2,6-difluorobenzyl-oxopyrimidines) have been prepared and tested as anti-HIV-1 agents. S-DABO derivatives bearing at C-6 position monosubstituted phenylmethyl or heteroarylmethyl units have also been synthesized. 2-Alkylthio-3,4-dihydropyrimidin-4(3H)-one derivatives of F2-S-DABO series bearing small alkyl groups at C-5 proved to be potent inhibitors of HIV-1 replication in vitro with selectivity indexes ranging from 250 to >2,500.

Molecular modeling analysis of compounds belonging to the recently published series of dihydro-alkoxy-benzyl-oxopyrimidines (DABOs), such as S-DABOs and DATNOs, gave support to the design of new 2, 6-disubstituted benzyl-DABO derivatives as highly potent and specific inhibitors of the HIV-1 reverse transcriptase (RT). To follow up on the novel DABO derivatives, we decided to investigate the effect of electron-withdrawing substituents in the benzyl unit of the S-DABO skeleton versus their anti-HIV-1 activity. Such chemical modifications impacted the inhibitory activity, especially when two halogen units were introduced at positions 2 and 6 in the phenyl portion of the benzyl group bound to C-6 of the pyrimidine ring. Various 5-alkyl-2-(alkyl(or cycloalkyl)thio)-6-(2, 6-dichloro(or 2,6-difluoro)phenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones were then synthesized and tested as anti-HIV-1 agents in both cell-based and enzyme (recombinant reverse transcriptase, rRT) assays. Among the various mono- and disubstituted phenyl derivatives, the most potent were those containing a 6-(2,6-difluorophenylmethyl) substituent (F-DABOs), which showed EC50's ranging between 40 and 90 nM and selectivity indexes up to >/=5000. An excellent correlation was found between EC50 and IC50 values which confirmed that these compounds act as inhibitors of the HIV-1 RT. The structure-activity relationships of the newly synthesized pyrimidinones are presented herein.

Novel compounds related to 2-(cyclohexylthio)-3,4-dihydro-5-methyl-6-(3-methylbenzyl)-4-ox opyrimidine (3c, MC 639) have been synthesized and tested as inhibitors of human immunodeficiency virus type-1 (HIV-1). Reaction of thiourea with ethyl arylmethylacetoacetates furnished 5-alkyl-6-(arylmethyl)-3,4-dihydro-2-mercapto-4-oxopyrimidines which were then alkylated at the sulfur atom to afford the required 2-alkylthio or 2-cycloalkylthio derivatives (S-DABOs). Chemical modifications at N-3, C-4, and C-6 of the pyrimidine ring were attempted with the aim of improving antiretroviral activity. In particular, replacement of the benzyl group with the 1-naphthylmethyl moiety enhanced the activity of S-DABOs, whereas N-3 alkylation and C=O transformation into C=S at position 4 of the pyrimidine ring led to compounds devoid of anti-HIV-1 activity. Lower activity was generally observed when 1-naphthylmethyl was replaced by the isomeric 2-naphthylmethyl moiety. The most active compounds showed activity in the low micromolar range with EC50 values comparable to that of nevirapine.