Table 2 (a) and (b) show the percentage A549/H1299 cell viability with different concentrations of herbal extracts.

Table 3 shows the IC50 values derived from the dose-response curves plotted for the six herbs and the two cell lines.

Figures 1 (a), (b), (c), (d), (e) and (f) are the survival curves obtained from the experimental results, with percentage cell viability against the extract concentrations of the six herbs.

Overall, there is a general decreasing cell viability values as concentration of the herbal extract increases. This shows that most of the TCM herbs tested in this study do exhibit anti-cancer properties. In cases such as in figure 1(f) of Prunella vulgaris, it is possible that the herb extract is only effective against cancer cell growth at low concentrations below (mg/mL). Some herbs may also fail to exhibit a decreasing trend because they might not be effective against the A549 cell line or the H1299 cell line. For example, in figure 1(b), Scutellaria barbata exhibited a decreasing trend for A549 but not H1299 because it is not effective against the H1299 cancer strain.
Based on the IC50 readings for the A549 cell line, the MeOH extract of Hedyotis diffusa was the most effective inhibitor of cell proliferation, at 9.872 mg/ml, while Curcumae longa was the least effective, at 207.2 mg/ml (Table 3). For the H1299 cell line, the MeOH extract of Scutellaria barbata was the most effective inhibitor of cell proliferation, at 59.43 mg/ml, while Smilax glabra had the least effective anti-cancer activity, at 253.4 mg/ml. American National Cancer Institute (NCI) states that the criteria of cytotoxic activity for plant extracts is an IC50 < 30 μg/ml [19]. However, none of the six extracts tested had IC50 values corresponding to the stated criteria.

 The MeOH extract of Hedyotis diffusa was the most effective inhibitor of cancer cell proliferation in the A549 cell line. Numerous studies, both in vitro and in vivo, have demonstrated the ability of Hedyotis diffusa to effectively suppress cancer cell replication. Results hence back up existing knowledge.

 The MeOH extract of Scutellaria barbata displayed the greatest cytotoxicity against the H1299 cell line. Known to target specific metabolic pathways in cancer cells, as shown by a study by Klawitter et. al [13], and possessing the ability to cause DNA fragmentation, loss of plasma membrane asymmetry, collapse of mitochondrial membrane potential and other potent effects, as shown by Lee TK et. al [22], inhibition of cancer cell proliferation by Scutellaria barbata can be attributed to its precise specificity and high cytotoxicity.

Curcumae longa, the herbal extract which displayed the least anti-proliferative effects on the A549 cell line, is known for a wide range of medicinal abilities, such as relieving chronic depression, decreasing blood lipid levels, reducing inflammation, and treating liver disorders [14]. Therefore, it is possible that Curcumae longa lacks the required specificity to target human lung cancer cells, thus generating results which do not fit the criteria for cytotoxic activity (IC50 < 30μg/ml).

Smilax glabra displays cytotoxic activity primarily against liver cancer cells, and is also used in a variety of treatments for liver diseases. This may mean that Smilax glabra, which displayed the least effects on the H1299 cell line, may be more specific towards liver cells and possibly less cytotoxic towards lung cancer cell lines.