**5. Cyclic bisdesmosides**

Cyclic bisdesmosides, new compounds analogous to cucurbitacins, share the tetracyclic triterpenoid core but contain carbohydrates to form a bicycle (**Figure 6**). These compounds were isolated from *Actinostemma lobatum* MAXIM and *Bolbostemma paniculatum* (Maxim) Franquet.

Two new cyclic bisdesmosides elucidated as lobatoside L (**36′**) and lobatoside M (**37′**) and four known cyclic bisdesmosides (**38′–41′**) were isolated from *A. lobatum*  Maxim. The inhibitory effects of these six compounds on human cancer cell growth (including the esophageal squamous carcinoma cell line ECA109, lung cancer cell line A549, and gastric cancer cell line MGC-803) were determined using the MTT assay. The six compounds exhibited cytotoxicity against all the cell lines tested, and compounds (**36′**, **38′**, and **40′**) showed significant activity in a dose-dependent manner against all the cell lines. The IC50 values for compounds (**36′** and **40′**) against ECA-109 cells were 8.25 and 3.71 μM, respectively. The rest of the results are shown in **Table 2** [34].

Tubeimoside I (**42′**) isolated from *B. paniculatum* (Maxim) Franquet exhibited cytotoxic activity against HepG2 human cancer cells. The IC50 values at different times of exposure (24, 48, and 72 h) were 15.5, 11.7, and 9.2 μM, respectively. This compound induced shrinkage, nuclear condensation, fragmentation, and cell cycle arrest in phase G2/M. The inhibition of growth in this case is mediated by a cascade of apoptosis [35].

*Cytotoxic and Antitumoral Activities of Compounds Isolated from Cucurbitaceae Plants DOI: http://dx.doi.org/10.5772/intechopen.82213* 

#### **Figure 6.**

*Cyclic bisdesmosides structure.* 


#### **Table 2.**

*Cytotoxic activities of cyclic bisdesmosides* **36′***–***41'***.* 
