Polyketides are a large group of secondary metabolites that have notable variety in their structure and function. Polyketides exhibit a wide range of bioactivities such as antibacterial, antifungal, anticancer, antiviral, immune-suppressing, anti-cholesterol, and anti-inflammatory activity. Naturally, they are found in bacteria, fungi, plants, protists, insects, mollusks, and sponges. Streptomyces is a genus of Gram-positive bacteria that has a filamentous form like fungi. This genus is best known as one of the polyketides producers. Some examples of polyketides produced by Streptomyces are rapamycin, oleandomycin, actinorhodin, daunorubicin, and caprazamycin. Biosynthesis of polyketides involves a group of enzyme activities called polyketide synthases (PKSs). There are three types of PKSs (type I, type II, and type III) in Streptomyces responsible for producing polyketides. This paper focuses on the biosynthesis of polyketides in Streptomyces with three structurally-different types of PKSs.

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Objective: Breast cancer is a malignant disease of women most often found after cervical cancer in Indonesia. Increased levels of free radicals can cause DNA damage, which could lead to malignancy; this can play role in breast cancer etiopathogenesis. The present research was conducted to determine the activity of catechins as antioxidants and their potential efficacy in inhibiting breast cancer malignancy. Methods: The research was done by examining the antioxidant and free radical scavenging activity including 1,1-diphenyl-2-picryl-hydrazyl (DPPH), the value of superoxide dismutase (SOD), and assays in breast cancer cell lines (T47D, MCF7). The cytotoxic potency was determined by the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4sulfophenyl)-2H-tetrazolium) assay. Results: The highest DPPH scavenging activity is presented by (-)-epigallocatechin (EGC) and the lowest by gallo catechins (GC). The highest SOD value were reached with EGC at 500 µg/ml, followed by (-)-epicatechin gallate (ECG) at 125 µg/ml, and GC at 31.25 µg/ml concentrations. The highest cytotoxic activity in T47D cell line for 24 and 48 h incubation was exhibited by (-)gallocatechin gallate (GCG). The greatest cytotoxic activity in MCF7 cell line for 24 h was presented by (-)-epigallocatechin gallate (EGCG), and for 48 h incubation by (+)-catechin (C). Conclusion: Catechins have high antioxidant activities proven by both DPPH scavenging and SOD activities. They possess higher anticancer action on T47D than on MCF7 cell line.