This invention provides a novel potent α/β and β/α hybrid peptides, containing tBu-β3,3-Acec and β2,2- Acec, which inhibit the cancer cell lines including HCT-116, MCF-7, MIA-PACA and A549. Among all the hybrid peptides, P-12 was the most potent against colon cancer with an IC50 value of 3.3 pM±0.27. Furthermore, P-12 effectively triggered the potential of mitochondrial membrane and decrease the formation of Reactive oxygen species (ROS). The percentage inhibition of tumor growth in HCT-116 was 51% in the 5FU treated group, whereas it was around 77% in the P-12 treated groups. Moreover, no significant loss in body weight and substantial difference in serum biochemical parameters was observed in the P-12 treated group compared to the control except for glucose and triglycerides.