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surprising since this compound, a pentacyclic triterepenoid, is structurally different to the
other three abietane diterpenoids.
The criteria followed by the CSIR states that compounds with TGI > 50µg/mL are
regarded as being inactive, TGI ranging between 15µg/mL and 50µg/mL are weakly
active whilst TGI values between 6.25µg/mL and 15µg/mL are indicative of compounds
which are moderately active. Any compound having a TGI value of less that 6.25µg/mL
for at least two of the three cell lines, is considered to be potent (Fouche et al., 2008).
According to these criteria, compounds I to III are weakly active towards the melanoma
cell line (44.71 µg/mL (I), 42.18µg/mL (II) and 44.64µg/mL (III)) while the TGI values
obtained for the breast (51.20µg/mL, 52.72µg/mL and 81.22µg/mL, respectively) and
renal (49.10µg/mL, 55.84µg/mL and 53.99µg/mL, respectively) cell lines were only
slightly above 50µg/mL suggesting that these compounds could also be regarded as
weakly active anticancer agents against these cell lines (Table 28). Since I to III are
regarded as weakly active, slight chemical modifications to the structure may enhance it’s
anticancer activity. The chemical modifications could not be carried out in this work
since the samples isolated were insufficient for chemical derivatisation.
The standard used in the three cell pre-screening method was Etoposide having TGI
values of >100µg/mL, 36.20µg/mL and 27.00µg/mL for breast (MCF-7), melanoma
(UACC-62) and renal (TK-10) human cell lines, respectively. In comparison to the
standard, compounds I to III were proven to be less active with regard to the renal and
melanoma cell lines. Compounds II and III displayed TGI values of 55.84µg/mL and
53.99ug/mL respectively for the renal cell line. These values are twice that of etoposide
having a TGI value of 27.00µg/mL against the same cell line. Compounds I to III were
found to be more active against the breast cell line than the control with compounds I and
II having TGI values measuring half at most of that of etoposide with values of
51.20µg/mL and 52.72µg/mL, respectively.
Compounds I to III inhibited the growth of the melanoma cell line (UACC-62) more than
the other two cell lines having GI50 values ranging between 12.05µg/mL and 13.53µg/mL
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