To reduce the toxicity and increase the anticancer efficacy of ATO, a peptide-linked arsenic compound (PhAs-LHP, where LHP is a peptide that possesses a penetrating motif (RLRR) that promotes uptake by a macropinocytotic pathway that is upregulated in KRAS-transformed cells) was synthesized, and its effect was tested on pancreatic cancer growth in vitro and in vivo and compared to the effects of the analogous non-peptide-linked arsenic compounds PAO and ATO. The gene discussed is KRAS; the disease is pancreatic neoplasm.