Betulinic acid (ALS-357) is a pentacyclic lupane-type triterpene derivative of betulin (isolated from the bark of Betula alba, the common white birch) which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as a more recently discovered potential as an anticancer agent, by inhibition of topoisomerase.

In LNCaP cell cultures of athymic nude mice, Betulinic acid inhibits the growth of prostate cancer cells and tumors (xenografts). This inhibitory effect is partly due to the downregulation of protease-dependent Sp1/3/4 and several SP-regulated genes.

As an anti-melanoma agent, Betulinic acid inhibits the activity of aminopeptidase N (IC50: 7.3 μM). It exhibits anti-HIV properties by blocking HIV replication in H9 lymphocytes (EC50: 1.4 μM) and inhibiting the growth of uninfected H9 cells (IC50: 13 μM). Moreover, Betulinic acid shows potential as an anti-cancer candidate, suppressing the activity of eukaryotic topoisomerase I (IC50: 5 μM).

Topoisomerase I-DNA interaction: Annealed 25-mer duplex of oligonucleotide-1 and oligonicleotide-2 is incubated with 25 or 50 units of rat liver topoisomerase I at 8 °C for 15 min in the presence or absence of betulinic acid in binding buffer. After incubation the reaction mixtures are electrophoresed in 7% non-denaturing polyacrylamide gel at 4 °C in 0.167 × TBE buffer and DNA bands are stained with ethidium bromid