**Light-Mediated Transformation of Renieramycins and Semisynthesis of 4***-* **-Pyridinecarbonyl-Substituted Renieramycin-Type Derivatives as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells**

**Suwimon Sinsook 1,2, Koonchira Buaban 1,3, Iksen Iksen 4, Korrakod Petsri 4,5, Bhurichaya Innets 4,5, Chaisak Chansriniyom 1,3, Khanit Suwanborirux 1,3, Masashi Yokoya 6, Naoki Saito 6, Varisa Pongrakhananon 4,7, Pithi Chanvorachote 4,5 and Supakarn Chamni 1,3,\***


**Abstract:** The semisynthesis of renieramycin-type derivatives was achieved under mild and facile conditions by attaching a 1,3-dioxole-bridged phenolic moiety onto ring A of the renieramycin structure and adding a 4- -pyridinecarbonyl ester substituent at its C-5 or C-22 position. These were accomplished through a light-induced intramolecular photoredox reaction using blue light (4 W) and Steglich esterification, respectively. Renieramycin M (**4**), a bis-tetrahydroisoquinolinequinone compound isolated from the Thai blue sponge (*Xestospongia* sp.), served as the starting material. The cytotoxicity of the 10 natural and semisynthesized renieramycins against non-small-cell lung cancer (NSCLC) cell lines was evaluated. The 5-*O*-(4- -pyridinecarbonyl) renieramycin T (**11**) compound exhibited high cytotoxicity with half-maximal inhibitory concentration (IC50) values of 35.27 ± 1.09 and 34.77 ± 2.19 nM against H290 and H460 cells, respectively. Notably, the potency of compound **11** was 2-fold more than that of renieramycin T (**7**) and equal to those of **4** and doxorubicin. Interestingly, the renieramycin-type derivatives with a hydroxyl group at C-5 and C-22 exhibited weak cytotoxicity. In silico molecular docking and dynamics studies confirmed that the mitogen-activated proteins, kinase 1 and 3 (MAPK1 and MAPK3), are suitable targets for **11**. Thus, the structure–cytotoxicity study of renieramycins was extended to facilitate the development of potential anticancer agents for NSCLC cells.

**Keywords:** *Xestospongia* sp.; cytotoxicity; renieramycins; semisynthesis; light-induced intramolecular photoredox reaction; non-small-cell lung cancer; bis-tetrahydroisoquinoline; molecular docking; molecular dynamics

**Citation:** Sinsook, S.; Buaban, K.; Iksen, I.; Petsri, K.; Innets, B.; Chansriniyom, C.; Suwanborirux, K.; Yokoya, M.; Saito, N.; Pongrakhananon, V.; et al. Light-Mediated Transformation of Renieramycins and Semisynthesis of 4- -Pyridinecarbonyl-Substituted Renieramycin-Type Derivatives as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells. *Mar. Drugs* **2023**, *21*, 400. https:// doi.org/10.3390/md21070400

Academic Editors: Barbara De Filippis, Alessandra Ammazzalorso and Marialuigia Fantacuzzi

Received: 24 June 2023 Revised: 9 July 2023 Accepted: 10 July 2023 Published: 13 July 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

Renieramycins, bis-tetrahydroisoquinolinequinone marine alkaloids, along with ecteinascidins and jorunnamycins, have been reported to exhibit significant anticancer activity (Figure 1) [1,2]. Trabectedin (also known as ecteinascidin 743, **1**), which was isolated from the Caribbean tunicate (*Ecteinascidia turbinate*), was approved by the United States Food and Drug Administration in 2015 for the treatment of advanced soft tissue sarcoma and ovarian carcinoma [3–5]. Lurbinectedin (PM01183, **2**), a bis-tetrahydroisoquinoline analog of **1**, was approved for the second-line treatment of metastatic small-cell lung cancer in 2020 [6,7]. Compounds **1** and **2** are chemotherapeutic drugs that covalently bind specifically to the N2 position of guanine in the DNA minor groove, leading to double-strand breaks and apoptosis in cancer cells [3,6].

**Figure 1.** Structures of the bis-tetrahydroisoquinoline alkaloids as anticancer drugs and promising drug leads.

Renieramycins are isolated from marine sponges, such as genera*Reniera* [8,9],*Cribrochalina* [10], and *Xestospongia* [11,12], and they possess a pentacyclic bis-tetrahydroisoquinolinequinone moiety as the core scaffold (Figure 1). Several renieramycins containing an angelate ester at the C-22 position display potent bioactivities, including antimicrobial [8], antileishmanial [13], and anticancer [11,12,14,15] activities. Interestingly, renieramycins M (**4**) and N (**5**) have been successfully isolated in the gram scale of the Thai blue sponge (*Xestospongia* sp.) [11]. Renieramycins M, N, and O (**4**–**6**) have been demonstrated to exhibit potent cytotoxicity against colon (HCT116) and lung carcinoma (QG56) [11,12]. Additionally, compound **4** has been reported to display strong cytotoxicity against various human cancer cell lines, including colon (DLD1), lung (NCI-H460), pancreatic adenocarcinoma (AsPC1), and ductal breast epithelial (T47D) cells [11,12,14]. Renieramycins T (**7**) and U (**8**), renieramycin– ecteinascidin hybrid marine natural alkaloids containing a 1,3-dioxole ring that is similar to the left-side carbon framework of trabectedin, exhibit strong in vitro anticancer activity against non-small-cell lung cancer (NSCLC) cells [14]. Furthermore, the cytotoxicity mechanisms of the renieramycin–ecteinascidin hybrid derivatives against NSCLC cells have been revealed. Compound **7** was discovered to enhance apoptosis induction via the degradation of the myeloid cell leukemia 1 (Mcl-1) protein in NSCLC [16,17]. Further, it suppressed mouse melanoma (B16F10) cell metastasis and migration through the downregulation of

NF-E2-related factor 2 [18]. Moreover, the 5-*O*-ester derivatives of **7**, which possess acetyl and *N*-Boc-L-alaninoyl substituents, induced apoptosis and suppressed cancer stem cell markers via protein kinase B (AKT) inhibition in NSCLC cells [19,20].

According to the structure–activity relationship (SAR) study, nitrogen-containing heterocyclic ester substituents, particularly 4- -pyridinecarbonyl ester derivatives, as side chains on the renieramycin framework have a remarkable effect on the cytotoxicity of renieramycin against various cancer cells (Figure 2). The 22-*O*-(4- -pyridinecarbonyl) jorunnamycin A compound (**9**) exhibited significantly better cytotoxicity than jorunnamycin A (**3**), its parent compound, against human colon (HCT116), breast (MDA-MB-435), and NSCLC (H292 and H460) cell lines [21,22]. Furthermore, hydroquinone 5-*O*-(4- -pyridinecarbonyl) renieramycin M (**10**) was prepared from **4** by a two-step process, including hydrogenation and Steglich esterification. The resulting derivative (**10**) exhibited cytotoxicity against the highly metastatic H292 and H460 NSCLC cell lines at inhibitory concentration (IC50) values in the nanomolar range [15].

22-*O*-(4'-pyridinecarbonyl) jorunnamycin A (**9**)

hydroquinone 5-*O*-(4'-pyridinecarbonyl) renieramycin M (**10**)

Me

22-*O*-(4'-pyridinecarbonyl) renieramycin T (**12**) 5-*O*-(4'-pyridinecarbonyl) renieramycin T (**11**)

**Figure 2.** Semisynthetic derivatives of the renieramycin-type derivatives containing a 4- pyridinecarbonyl ester substituent.

Regarding the continuous structure–cytotoxicity relationship study of the renieramycintype derivatives, the semisynthesis of the renieramycin–ecteinascidin hybrid derivatives of natural bis-tetrahydroisoquinolinequinones (**4**–**6**) was conducted via a facile, light-induced intramolecular photoredox reaction to transform quinone ring A into the 1,3-dioxolebridged phenolic moiety. The mild photoredox reaction enables the selective one-step modification of the methoxy-substituted quinone unit located on ring A of renieramycins, resulting in the formation of 5-hydroxy-tetrahydroisoquinol-1,3-dioxoles with excellent yields [23]. This transformation yields a series of renieramycin–ecteinascidin derivatives that closely resemble the structure of ring A found in Trabectedin and Lurbinectedin, well-known tetrahydroisoquinoline-based chemotherapeutic drugs. Next, a series of 4- -pyridinecarbonyl esters for the renieramycin-type derivatives were prepared by mild and selective Steglich esterification. The new 4- -pyridinecarbonyl esters, **11** and **12**, were obtained (Figure 2). The in vitro cytotoxicity of the compounds against human H292 and H460 NSCLC cell lines was evaluated using the 3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, the in silico prediction of the target genes and molecular pathways associated with the activity of the compounds

was achieved by virtual network pharmacology study, including molecular docking and molecular dynamics studies.
