*Cytotoxic Activity of Secondary Metabolite Compounds from Myanmar Medicinal Plants DOI: http://dx.doi.org/10.5772/intechopen.105153*

(IC50 0.35 μM) [19]. In a cytotoxic study by Sommit et al., natural labdanes (labda-7,12(E),14-triene-17-al and 17-hydroxylabda-7,12(E)14-triene) and their modified derivatives (15-hydroxylabda-7,13(*E*)diene-17,12-olide, labda-7,13(E)-diene-17,12 olide, 12,17-dihydroxylabda-7,13(*E*)-diene) were found to have non-specific moderate cytotoxicity against BT474, CHAGO, HEP-G2, KATO-3, and SW620 [20]. The ethyl acetate extract of *C. oblongifolius* was found to be cytotoxic toward the A549 lung cancer cell line [55]. In 2020, Poofery et al. studied the cytotoxic activity of ethyl acetate extract from *Bridelia ovata* and *Croton oblongifolius*. They reported that both extracts possessed anticancer properties in breast cancer cells and induce apoptosis in these cells

#### **Figure 2.**

*Cytotoxic compounds from* Croton oblongifolius.

via a mitochondrial pathway and oxidative stress [56]. In addition, Chaichantipyuth and coworkers isolated eight new labdane-type diterpenoids and a clerodane from the stem bark of *C. oblongifolius*. They examined the cytotoxic capability of specific compounds and semisynthesis products against human tumor cell lines (KATO-3, BT474, CHAGO, HEPG-2, and SW620) in vitro MTT assay. Among which isolates, ent-3-oxomanoyl oxide, ent-1,2-dehydro-3-oxomanoyl oxide, ent-3α-hydroxymanoyl oxide, nidorellol, and ent-6α,7β,8α,-trihydroxylabda-13(16),14-diene showed strong cytotoxic activity (<1 μg/mL) against KATO-3, moderated activity against BT474, and undifferentiated against CHAGO, HEPG-2, and SW620. Similarly, hardwickiic acid had a substantial effect (<1 μg/mL) on BT474, while semisynthesis products (*ent*-3βhydroxymanoyl oxide and *ent*-3β-hydroxy-1,2-dehydromanoyl oxide) had a modest effect in all cell lines. The remaining isolates were inert [57]. The authors found, two new cleistanthane-type diterpenoids, 3-hydroxycleistantha-13(17),15-diene and 3,4-seco-cleistantha-4(18),13(17),15-triene-3-oic acid, have cytotoxic activity against various human tumor cell lines. Both were isolated from the stem bark of *C. oblongifolius*. 3-hydroxycleistantha-13(17),15-diene showed nonspecific strong cytotoxic activity (KATO-3; IC50 value 6.0 μg/mL, BT474; IC50 value 6.1 μg/mL, HEP-G2; IC50 value 0.5 μg/mL, CHAGO; IC50 value 5.5 μg/mL) and 3,4-seco-cleistantha-4(18),13(17),15 triene-3-oic acid showed weak activity (KATO-3; IC50 value 9.6 μg/mL, BT474; IC50 value 10 μg/mL, HEP-G2; IC50 value 8.6 μg/mL) [58]. In another study, Nasimalun A has a cytotoxic effect on the MOLT-3 cell line with an IC50 value of 26.44 μg/mL [59]. The chemical structures of some cytotoxic compounds are shown in **Figure 2**.
