The present invention pertains to acridone and acridine compounds of formula (I), wherein either: (a) K is ═O, L is —H, alpha is a single bond, beta is a double bond, gamma is a single bond (acridones); or, (b) K is a 9-substituent, L is absent, alpha is a double bond, beta is a single bond, gamma is a double bond (acridines); and wherein: J1 is a 2- or 3-substituent; J2 is a 6- or 7-substituent; J1 and J2 are each independently a group of the formula —NHCO(CH2)nNR1R2, wherein: n is an integer from 1 to 5; and, R1 and R2 are independently hydrogen, C1-7alkyl, C3-20heterocyclyl, or C5-20aryl, or R1 and R2, taken together with the nitrogen atom to which they are attached, form a heterocyclic ring having from 3 to 8 ring atoms; and wherein, when K is a 9-substituent, K is a group of the formula —N(RN)Q, wherein: RN is an amino substituent and is hydrogen, C1-7alkyl, C3-20heterocyclyl, or C5-20aryl; and, Q is C1-7alkyl, C3-20heterocyclyl, or C5-20aryl, and is optionally substituted; and pharmaceutically acceptable salts, esters, amides, solvates, hydrates and protected forms thereof. The present invention also pertains to pharmaceutical compositions comprising such compounds, and the use of such compounds and compositions, both in vitro and in vivo, to inhibit telomerase, to regulate cell proliferation, and in the treatment of proliferative conditions, such as cancer.